INABA MINORU
Faculty of Science and Engineering Department of Molecular Chemistry and Biochemistry
Professor
Last Updated :2020/02/29

Researcher Profile and Settings

Profile and Settings

  • Profile

    Professor Minoru Inaba received his B. Sc. from Faculty of Engineering, Kyoto University in 1984, and his M. Sc. in 1986 and Dr. Eng. in 1995 from Graduate School of Engineering, Kyoto University. He has worked on electrochemical energy conversion systems at Kyoto University (1992-2002) and at Doshisha University (2002-present). He has worked as the leader of a NEDO PEFC research project on platinum catalysts in FY2008-2019, and served as the chairperson of The Committee of Battery Technology, The Electrochemical Society of Japan (2015-18). His research interests are fundamental aspects in polymer electrolyte fuel cells, solid oxide fuel cells, and lithium-ion batteries. He has authored over 200 peer-reviewed papers, 60 review articles, 25 book chapters, and 20 patents.

Research Areas

  • Manufacturing technology (mechanical, electrical/electronic, chemical engineering)/Electronic devices and equipment
  • Nanotechnology/Materials/Inorganic compounds/materials chemistry

Research History

  • 1984-1994 Electrolysis using solid polymer electrolyte/electrode composites
  • 1986-1992 Development of electroceremics
  • 1992- In situ observation of the reactions at electrode/electrolyte interfaces in rechargeable lithium batteries
  • 1992- Studies on oxygen reduction reaction in polymer electrolyte fuel cells
  • 1993- Studies on low-temperature solid oxide fuel cells
  • 2001-2007 Durability of polymer electrolyte fuel cells
  • 2002- Electrode Materials for Next-Generation Lithium Ion Batteries
  • 2008- Development of Highly Active and Durable Platinum Core-Shell Catalysts

Academic & Professional Experience

  • Professor, Graduate School of Science and Engineering, Doshisha University, 2012/04 - Today
  • Professor, Graduate School of Engineering, Doshisha University, 2010/04 - 2012/03
  • New Energy and Industrial Technology Development Organization, 2008 - 2009
  • Graduate School of Engineering, Department of Energy and Hydrocarbon Chemistry, Kyoto University, 1998 - 2002
  • Graduate School of Engineering, Department of Energy and Hydrocarbon Chemistry, Kyoto University, 1996 - 1998
  • School of Industrial Chemistry, Faculty of Engineering, Kyoto University, 1992 - 1996
  • Graduate School of Science, Rikkyo University, 2011
  • Faculty of Engineering, Department of Applied Chemistry, University of Yamanashi, 2010
  • Graduate School of Engineering, Nagaoka University of Technology, 2009
  • Graduate School of Engineering, Kyoto University, 2002

Education

  • Kyoto University, 1986
  • Kyoto University, Graduate School, Division of Engineering, 1986
  • Kyoto University, Faculty of Engineering, 1984
  • Kyoto University, Faculty of Engineering, 1984

Academic Degrees

  • Doctor of Engineering, Kyoto University
  • Master of Engineering, Kyoto University

Published Papers

  • Oxygen-content dependence of cycle performance and morphology changes in amorphous-SiOx thin-film negative electrodes for lithium-ion batteries
    Masakazu Haruta, Takayuki Doi, Minoru Inaba
    © 2019 The Electrochemical Society. The silicon - oxygen binary system (SiOx) is a promising candidate as a negative electrode for next-generation lithium-ion batteries. Thin SiOx films of different oxygen contents were prepared by magnetron sputtering. Although almost all Si atoms in SiOx at low oxygen contents (x = 0.21 and 0.48) contributed to the reversible alloying/dealloying reactions, an irreversible fraction of Si in SiOx at high oxygen contents (x = 1.09 and 1.78) increased owing to the formation of Li4SiO4. In return for the decrease of reversible capacity, the capacity retention of heavily O-doped SiOx films improved owing to the buffer effect of Li4SiO4 matrix against volume changes. The addition of vinylene carbonate (VC) to the electrolyte further improved the cyclability of the SiOx films, especially those of higher oxygen contents. For the pure-Si film, a sponge-like porous structure appeared after cycling owing to repeated crack formation and inhomogeneous volume changes, and resulted in massive electrode swelling. The morphology change with cycling was suppressed by the presence of Li4SiO4 matrix and a homogeneous solid electrolyte interphase derived from VC, resulting in a superior cycle performance of the heavily O-doped SiOx negative electrodes., Journal of the Electrochemical Society, Journal of the Electrochemical Society, 166(2)A258 - A263, 2019, 研究論文(学術雑誌)
  • Improved cycle performance of LiNi0.8Co0.1Mn0.1O2 positive electrode material in highly concentrated LiBF4/DMC
    Ziyang Cao, Michihiro Hashinokuchi, Takayuki Doi, Minoru Inaba
    © 2019 The Electrochemical Society. Charge/discharge characteristics of nickel-rich LiNi0.8Co0.1Mn0.1O2 cathode was investigated in highly concentrated lithium tetrafluroborate (LiBF4)/dimethylcarbonate (DMC) electrolytes with better electrochemical stability against oxidation. Raman spectra indicated that almost all DMC solvent molecules coordinated Li+ ions, and BF4− anions were likely to form aggregates (AGGs) with Li+ ions and DMC in the nearly saturated 8.67 mol kg−1 electrolyte. A LiNi0.8Co0.1Mn0.1O2|Li half-cell using the nearly saturated 8.67 mol kg−1 LiBF4/DMC showed a good cycle performance up to 50 cycles at C/10 rate with a capacity retention of 93.3%. Furthermore, cross-sectional SEM images and EDX mappings revealed that the highly concentrated electrolyte effectively suppressed not only oxidative decomposition of electrolyte solution on the particle surface, but also the particle fracture caused by crack propagation., Journal of the Electrochemical Society, Journal of the Electrochemical Society, 166(2)A82 - A88, 2019, 研究論文(学術雑誌)
  • Improvement of Cycleability and Rate-Capability of LiNi0.5Co0.2Mn0.3O2 Cathode Materials Coated with Lithium Boron Oxide by an Antisolvent Precipitation Method
    Satoshi Hashigami, Kei Yoshimi, Yukihiro Kato, Hiroyuki Yoshida, Toru Inagaki, Masakazu Haruta, Michihiro Hashinokuchi, Takayuki Doi, Minoru Inaba
    © 2019 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim LiNi0.5Co0.2Mn0.3O2 (NCM) particles coated with lithium boron oxide were prepared by an antisolvent precipitation method. In the antisolvent precipitation method, ethanol was used to strip off the hydrated water coordinated with lithium ions and borate ions. By the antisolvent precipitation method, the NCM particles were coated with a uniform layer of LiBO2. The capacity fading on cycling was successfully suppressed for the lithium boron oxide-coated samples. In addition, the rate capability was also improved by the coating. The lithium boron oxide coating effectively suppressed the increase of the electrode impedance associated with the electrolyte decomposition. Crack formation in the secondary particles after charge-discharge cycling was greatly inhibited for lithium boron oxide-coated NCM. It was demonstrated that the lithium boron oxide coating layer suppressed the side reactions not only on the particle surface, but also in the intergranular cracks by inhibiting the penetration of the electrolyte solution., ChemistrySelect, ChemistrySelect, 4(29)8676 - 8681, 2019, 研究論文(学術雑誌)
  • Communication-enhancement of structural stability of LiNi0.5Co0.2Mn0.3O2 cathode particles against high-voltage cycling by lithium silicate addition
    Yukihiro Kato, Michihiro Hashinokuchi, Satoshi Hashigami, Kei Yoshimi, Hiroyuki Yoshida, Toru Inagaki, Masakazu Haruta, Takayuki Doi, Minoru Inaba
    © 2019 The Electrochemical Society. Lithium silicate was incorporated within Ni0.5CoZMn0.3(OH)2 precursor particles via an anti-solvent precipitation method to prepare lithium silicate-added LiNi0.5Co0.2Mn0.3O2 (NCM) particles. Lithium silicate was found at the grain boundaries in the NCM secondary particles, which significantly improved the capacity retention in high voltage operation (3.0 4.6 V). Cross-sectional SEM images revealed that cracks were seriously formed inside the lithium silicate-free NCM particles after cycling, while crack formation was remarkably inhibited for lithium silicate-added NCM. These results suggested that lithium silicate at the grain boundaries strengthened the interfacial-adhesion between primary particles, resulting in the improved cycling stability., Journal of the Electrochemical Society, Journal of the Electrochemical Society, 166(6)A941 - A943, 2019, 研究論文(学術雑誌)
  • Influence of lithium silicate coating on retarding crack formation in LiNi0.5Co0.2Mn0.3O2 cathode particles
    Satoshi Hashigami, Yukihiro Kato, Kei Yoshimi, Hiroyuki Yoshida, Toru Inagaki, Michihiro Hashinokuchi, Takayuki Doi, Minoru Inaba
    © 2018 Elsevier Ltd LiNi0.5Co0.2Mn0.3O2 particles coated with lithium silicate were prepared via a precipitation method and their charge and discharge properties were investigated. The capacity retention and coulombic efficiency of the 0.5 wt% lithium silicate-coated LiNi0.5Co0.2Mn0.3O2 was improved at a high cut-off voltage of 4.6 V. Cross-sectional scanning electron microscope images revealed that extensive cracks were formed within the uncoated LiNi0.5Co0.2Mn0.3O2 particle along the grain boundaries after the charge and discharge cycling, while the crack generation was significantly inhibited for the coated particles. From cross-sectional transmission electron microscope analysis, it was shown that Si-rich regions were concentrated not only on the surface, but also at the grain boundaries even at a depth of 400 nm from the surface of the lithium silicate-coated sample. These results suggested that the Si-rich regions inhibited the crack formation and prevented the intrusion and the decomposition of the electrolyte solution within the particles. Consequently, lithium silicate coating is an effective way for improving the charge and discharge characteristics of LiNi0.5Co0.2Mn0.3O2., Electrochimica Acta, Electrochimica Acta, 291304 - 310, 20 Nov. 2018
  • Artificial lithium fluoride surface coating on silicon negative electrodes for the inhibition of electrolyte decomposition in lithium-ion batteries: visualization of a solid electrolyte interphase using in situ AFM
    Masakazu Haruta, Yuki Kijima, Ryuya Hioki, Takayuki Doi, Minoru Inaba
    © The Royal Society of Chemistry. The solid electrolyte interphase (SEI), which is a surface layer formed on the negative electrode, plays an important role in inhibiting the reductive decomposition of the electrolyte solution in a lithium-ion battery. However, it has not been understood well which components are important for the SEI to prevent the electrolyte decomposition. Lithium fluoride (LiF), as an artificial SEI, was formed on an amorphous-Si thin film by physical vapor deposition. Changes in the surface morphology of the Si electrode with potential sweeping were investigated using in situ atomic force microscopy (AFM). Although large amounts of non-uniform surface deposits that originate from electrolyte decomposition emerged on the bare Si-film electrode during the first lithiation process, few surface deposits were observed on the LiF-coated Si-film electrode even after two cycles in an ethylene carbonate-based electrolyte solution without additives. It is clear that LiF is a required SEI component that inhibits electrolyte decomposition on Si negative electrodes., Nanoscale, Nanoscale, 1017257 - 17264, 28 Sep. 2018
  • Enhancement of anode activity and stability by Cr addition at Ni/Sm-doped CeO2cermet anodes in NH3-fueled solid oxide fuel cells
    Michihiro Hashinokuchi, Mengjia Zhang, Takayuki Doi, Minoru Inaba
    © 2018 Chromium was added to nickel/Sm2O3-doped ceria (Ni/SDC) cermets by a CrCl3impregnation method, and the activity of the resulting Ni-Cr/SDC cermets was evaluated as anodes in ammonia-fueled solid oxide fuel cells (SOFCs) in the temperature range of 773 to 1173 K. It has been revealed that the addition of Cr was effective for the catalytic activity for NH3reforming, followed by hydrogen oxidation. The optimum amount of Cr was 3 at.% of the total metal in the Ni-Cr/SDC cermets. In addition, we demonstrated the improved stability of the Ni97-Cr3/SDC cermets in NH3atmosphere at 873 K. The addition of Cr suppressed the agglomeration of Ni, and promoted the anode durability. XRD analysis suggested the formation of a nitride CrN during operation in the Ni97–Cr3/SDC anode, and the role of the nitride was discussed in detail., Solid State Ionics, Solid State Ionics, 319180 - 185, 01 Jun. 2018, English, 研究論文(学術雑誌)
  • Solvation-controlled ester-based concentrated electrolyte solutions for high-voltage lithium-ion batteries
    Takayuki Doi, Michihiro Hashinokuchi, Minoru Inaba
    © 2018 Elsevier B.V. Highly concentrated electrolyte solutions exhibit high stability against oxidation, and hence have a high potential for the high voltage operation of lithium-ion batteries (LIBs). However, they are highly viscous and very costly due to an extensive use of lithium salts. These problems were solved by diluting the highly concentrated electrolyte solutions with a diluent that has a low donor number, a high miscibility, and a high stability against oxidation. The resultant electrolyte solutions suppressed the degradation of 5 V-class LiNi0.5Mn1.5O4positive-electrodes upon repeated charge/discharge cycling, and extended the reversible capacity of LiNi0.5Co0.2Mn0.3O2electrodes to ca. 200 mAh g−1by charging to a high voltage of 4.6 V., Current Opinion in Electrochemistry, Current Opinion in Electrochemistry, 949 - 55, 01 Jun. 2018, English
  • Morphology changes and long-term cycling durability of Si flake powder negative electrode for lithium-ion batteries
    Masakazu Haruta, Ryuya Hioki, Takashi Moriyasu, Akira Tomita, Toshio Takenaka, Takayuki Doi, Minoru Inaba
    © 2018 Elsevier Ltd Silicon flake powder (Si LeafPowder®, Si-LP) with the thickness and lateral dimension of 100 nm and 3–5 μm, respectively, demonstrated superior cycle performance as a negative electrode in lithium-ion batteries. A multi-folded layered structure with many voids was spontaneously formed in Si-LP composite electrodes by morphology changes of Si-LP sheets in repeated charge and discharge cycles. The multi-folded layered structure accommodated volumetric changes of the Si active material and prevented exfoliation of the active material from the current collector, which led to the superior long-term cyclability of the Si-LP electrode. The main factor for capacity fading in long-term cycling was a gradual loss of conduction pathways between Si-LP sheets due to the accumulation of electrolyte reduction products in the electrode. The film-forming additives, vinylene carbonate and fluoroethylene carbonate, effectively suppressed the electrolyte decomposition and remarkably improved the cycle performance of the Si-LP electrode., Electrochimica Acta, Electrochimica Acta, 26794 - 101, 20 Mar. 2018, English, 研究論文(学術雑誌)
  • Enhancement of Oxygen Reduction Reaction Activity of Pd Core-Pt Shell Structured Catalyst on a Potential Cycling Accelerated Durability Test
    Naoya Aoki, Hideo Inoue, Takashi Okawa, Takashi Okawa, Yuta Ikehata, Yuta Ikehata, Akira Shirai, Akira Shirai, Hideo Daimon, Takayuki Doi, Yuki Orikasa, Yuki Orikasa, Yoshiharu Uchimoto, Hiroshi Jinnai, Shin Inamoto, Yuji Otsuka, Minoru Inaba
    © 2017, Springer Science+Business Media, LLC. Carbon-supported Pd core-Pt shell structured catalyst (Pt/Pd/C) was synthesized by a modified Cu under potential deposition/Pt displacement method without any precise potential control. The specific activity for oxygen reduction reaction (ORR) of the Pt/Pd/C catalyst increased by 5-fold after an accelerated durability test (ADT; rectangular wave potential cycling of 0.6 V (3 s)–1.0 V (3 s) performed in Ar-saturated 0.1 M HClO4at 80 °C for 10,000 cycles), which enhanced ORR mass activity of the catalyst by 1.4-fold although its electrochemical surface area significantly decreased. TEM observation showed that the morphology of the catalyst particles changed into a spherical shape and the mean diameter decreased after the ADT. TEM-EDX compositional analysis revealed that the Pd core preferentially dissolved out and that the Pt shell was rearranged and thickened with the ADT. CV measurement using Bi3+probe implied that the Pt(111) facet was partially formed on the Pt shell after the ADT. Furthermore, EXAFS analysis showed that the Pt–Pt bond distance of the Pt shell was shortened after the ADT. It was considered that the drastic enhancement in the ORR-specific activity of the catalyst after the ADT arises from the decrease in number of lowly coordinated surface Pt atoms, partially formed Pt(111) facet on the catalyst surface, and properly induced compressive strain in the Pt shell via the rearrangement of the Pt shell assisted by the preferential dissolution of the Pd core during the ADT. [Figure not available: see fulltext.]., Electrocatalysis, Electrocatalysis, 9125 - 138, 01 Mar. 2018, English, 研究論文(学術雑誌)
  • Fluoroalkyl ether-diluted dimethyl carbonate-based electrolyte solutions for high-voltage operation of LiNi 0.5 Co 0.2 Mn 0.3 O 2 electrodes in lithium ion batteries
    Takayuki Doi, Ryo Matsumoto, Ziyang Cao, Masakazu Haruta, Michihiro Hashinokuchi, Minoru Inaba
    © 2018 The Royal Society of Chemistry. The energy density of lithium-ion batteries can be increased by improving the battery voltage and/or specific capacity. However, conventional electrolyte solutions decompose oxidatively at high voltages. The stability against oxidation of electrolyte solutions could be enhanced by increasing the concentration of lithium salts. The nearly saturated 8.67 mol kg -1 LiBF 4 /dimethyl carbonate (DMC) electrolyte solution enabled high-voltage operation of LiNi 0.5 Co 0.2 Mn 0.3 O 2 positive-electrodes at 4.6 V, and extended the discharge capacity to ca. 200 mA h g -1 . BF 4- anions, as well as DMC solvents, were stabilized at the high concentration. To reduce the viscosity and Li concentration without losing the high stability against oxidation toward practical use, the highly concentrated electrolyte solution was diluted with fluorinated co-solvents having a low donor ability. Raman spectroscopy revealed that the solvation structure of LiBF 4 /DMC was maintained after dilution with a specific fluoroalkyl ether. The resultant low-viscosity and -concentration electrolyte solution was highly stable against oxidation at the LiNi 0.5 Co 0.2 Mn 0.3 O 2 electrodes as long as the DMC/LiBF 4 molar ratio was kept low. The charge/discharge performance was much better than that for a conventional 1 M LiPF 6 /ethylene carbonate-based electrolyte solution and the energy density far exceeded that of 5 V class LiNi 0.5 Mn 1.5 O 4 electrodes., Sustainable Energy and Fuels, Sustainable Energy and Fuels, 21197 - 1205, 01 Jan. 2018
  • Durability improvement of Pd core-Pt shell structured catalyst by porous SiO2 coating
    Naoya Aoki, Hideo Inoue, Hisashi Kawasaki, Hideo Daimon, Takayuki Doi, Minoru Inaba
    © 2018 The Electrochemical Society. Porous SiO2 coating was investigated to suppress agglomeration of catalyst nanoparticles (NPs) and mitigate ECSA decay of carbon supported Pd core-Pt shell structured catalyst (Pt/Pd/C), which is a promising cathode catalyst for polymer electrolyte fuel cells because of its high Pt utilization and enhanced oxygen reduction reaction (ORR) activity. SiO2 coating was formed onto the catalyst via a sol-gel route using 3-aminopropyltriethoxysilane (APTES) or 3-mercaptopropyltrimethoxysilane (MPTES) as a seed molecule prior to hydrolysis of tetraethoxysilane (TEOS). When APTES with an amino functional group (-NH2) was used as the seed, SiO2 was coated not only onto catalyst nanoparticles (NPs), but also onto carbon support. On the contrary, SiO2 was selectively coated onto catalyst NPs when MPTES with a thiol functional group (-SH) was used as the seed. Cyclic voltammetry experiments revealed that -SH functional group much strongly adsorbed onto Pt and Pd surfaces than -NH2 functional group did. SiO2 coating formed by the MPTES seed well suppressed NPs' agglomeration and mitigated ECSA decay with less loading of SiO2 coating, improving durability and ORR mass activity of Pt/Pd/C catalyst even after accelerated durability test performed at 80°C., Journal of the Electrochemical Society, Journal of the Electrochemical Society, 165, 01 Jan. 2018
  • Pre-film formation and cycle performance of silicon-flake-powder negative electrode in a solvate ionic liquid for silicon-sulfur rechargeable batteries
    Haruta Masakazu, Takashi Moriyasu, Akira Tomita, Toshio Takenaka, Takayuki Doi, Minoru Inaba
    © 2018 The Electrochemical Society. In developing silicon-sulfur batteries with a high energy density, the cycle performance of a Si-flake-powder (Si LeafPowder, Si-LP) negative electrode in a solvate ionic liquid of lithium salt-glyme equimolar complex electrolyte were improved by stable pre-film formation on the Si-LP. The pre-film was formed by pre-cycling in a fluoroethylene carbonate-based electrolyte prior to cycle tests in the glyme-based electrolyte. The capacity retention of the pre-cycled Si-LP electrode in the glyme-based electrolyte improved remarkably. Surface deposition originating from decomposition products of the electrolyte decreased by formation of the pre-film. The pre-film consisted of fine LiF grains and organo-fluorine compounds, the combination of which is important for inhibiting decomposition of the glyme-based electrolyte on Si negative electrodes., Journal of the Electrochemical Society, Journal of the Electrochemical Society, 165A1874 - A1879, 01 Jan. 2018, English, 研究論文(学術雑誌)
  • Low-Viscosity γ-Butyrolactone-Based Concentrated Electrolyte Solutions for LiNi0.5Mn1.5O4Positive Electrodes in Lithium-Ion Batteries
    Takayuki Doi, Yusuke Shimizu, Michihiro Hashinokuchi, Minoru Inaba
    © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim Highly concentrated electrolyte solution with a low viscosity and high stability against oxidation was obtained by using a single solvent system of LiBF4/γ-butyrolactone (GBL). Although up to 4.65 mol kg−1LiBF4could be dissolved in GBL at room temperature, 3.87 mol kg−1LiBF4/GBL was a reasonable compromise to attain a low viscosity (52.1 mPa s) and a low GBL/Li molar ratio (3.00). Sodium carboxymethylcellulose and poly(acrylic acid) were used as binders for the spinel LiNi0.5Mn1.5O4positive electrode and the graphite negative electrode, respectively, to suppress the swelling of conventional poly(vinylidene fluoride)-based binder. The charge and discharge performances of the LiNi0.5Mn1.5O4positive electrode and the graphite negative electrode were improved by using 3.87 mol kg−1LiBF4/GBL, as compared with concentrated propylene carbonate-based electrolyte solution., ChemElectroChem, ChemElectroChem, 42398 - 2403, 01 Sep. 2017, English, 研究論文(学術雑誌)
  • Electrochemical and Chemical Treatment Methods for Enhancement of Oxygen Reduction Reaction Activity of Pt Shell-Pd Core Structured Catalyst
    Naoya Aoki, Hideo Inoue, Akira Shirai, Shunya Higuchi, Yuki Matsui, Hideo Daimon, Takayuki Doi, Minoru Inaba
    © 2017 Elsevier Ltd Based on the accelerated durability test protocol (ADT, rectangular wave, 1.0 V (3 s)-0.6 V (3 s), 10,000 cycles, at 80 °C), a high activation protocol (HAP) was developed as an electrochemical treatment method using rectangular wave potential cycling for a carbon supported Pt shell-Pd core structured catalyst (Pt/Pd/C), which mitigated the decay of electrochemical surface area (ECSA) and enhanced the mass activity for oxygen reduction reaction (ORR). It was found that a longer holding time and a less cycle number (300 s and 30 cycles) compared with those used for the ADT protocol (3 s and 10,000 cycles) effectively suppressed the ECSA decay and enhanced the ORR mass activity. A potential in the range of 0.2 to 0.6 V was suitable as the lower limit potential of the HAP protocol for the ORR activity enhancement when the upper limit potential was fixed at 1.0 V. Furthermore, H2-O2and Cu-O2chemical treatment methods, which chemically realize the HAP performed on GC electrode, were developed, where the equilibrium potentials of Cu/Cu2+, hydrogen and oxygen were utilized for surface oxidation and reduction of Pd and Pt. Both methods mitigated the ECSA decay and enhanced the ORR mass activity, and the Cu-O2chemical treatment method gave a higher mass activity. These chemical treatment methods are useful for mass-production of highly active Pt core-shell structured catalyst., Electrochimica Acta, Electrochimica Acta, 244146 - 153, 01 Aug. 2017, English, 研究論文(学術雑誌)
  • Effect of infiltrated transition metals in Ni/Sm-doped CeO2cermet anode in direct NH3-fueled SOFCs
    M. Zhang, M. Hashinokuchi, R. Yokochi, T. Doi, M. Inaba
    © The Electrochemical Society. The activity of transition metals (Cr and V) infiltrated Ni/Smdoped ceria (SDC) cermet anodes for NH3oxidation was investigated at 973 to 1173 K. The 3 at.% addition of Cr and V with respect to the total metal composition improved the anode activity for NH3oxidation. The relationship between the anode activity of the Ni-based binary anode and the metal-nitrogen binding energy of the added transition metal, which is a key to realize the highly active anode for direct NH3-fueled SOFCs, is discussed., ECS Transactions, ECS Transactions, 781517 - 1522, 30 May 2017, English, 研究論文(国際会議プロシーディングス)
  • Enhanced activity and stability of Ni-based binary anode in direct NH3-fueled SOFCs
    M. Hashinokuchi, M. Zhang, R. Yokochi, T. Doi, M. Inaba
    © The Electrochemical Society. The activity and stability of Ni-based binary alloy anodes for direct ammonia-fueled SOFCs were investigated in the temperature range of 823 to 973 K. It was found that the activities of Ni40-Fe60and Ni97-Mo3/SDC anodes for ammonia oxidation were higher than Ni/SDC anode at temperature of 823 to 973 K. In addition, the Ni40-Fe60and Ni97-Mo3/SDC anodes exhibited higher stability in a heat cycle test between 873 and 973 K in ammonia atmosphere than the Ni/SDC anode. It was found that the change in the shape of the metal catalysts induced by the heat cycle was suppressed in the Ni40-Fe60and Ni97-Mo3/SDC anodes., ECS Transactions, ECS Transactions, 781495 - 1500, 30 May 2017, English, 研究論文(国際会議プロシーディングス)
  • Temperature effects on SEI formation and cyclability of Si nanoflake powder anode in the presence of SEI-forming additives
    Masakazu Haruta, Takashi Okubo, Yuta Masuo, Shuhei Yoshida, Akira Tomita, Toshio Takenaka, Takayuki Doi, Minoru Inaba
    © 2016 Elsevier Ltd Silicon nanoflake powder (Si LeafPowder®, Si-LP) used as an anode material for lithium-ion batteries has demonstrated superior cycle performance at 30 °C in an ethylene-carbonate-based electrolyte solution because its characteristic thin-film-based structure resists pulverization. However, capacity fading was accelerated at 60 °C owing to enhanced decomposition of the electrolyte solution and growth of a solid electrolyte interface (SEI), which leads to loss of the electronic contact between Si-LP particles. The SEI-forming additives vinylene carbonate (VC), fluoroethylene carbonate (FEC), and difluoroethylene carbonate improved the capacity retention and Coulombic efficiency at 30 °C. Although VC is the most effective additive at 60 °C, the discharge capacity was decreased dramatically at −5 °C owing to poor ionic and electronic conductivity of the SEI layer formed from the VC-added electrolyte solution. The added FEC produced better performance in a wide temperature range of −5 to 60 °C because the SEI layer formed in the FEC-added electrolyte solution had higher ionic and electronic conductivity than that formed from VC, even at −5 °C. To obtain Si anodes with high discharge capacity and long cycle life, an appropriate choice of SEI-forming additive taking into account the operating temperature is important., Electrochimica Acta, Electrochimica Acta, 224186 - 193, 10 Jan. 2017, English, 研究論文(学術雑誌)
  • AdsorbedWater on Nano-Silicon Powder and Its Effects on Charge and Discharge Characteristics as Anode in Lithium-Ion Batteries
    Shuhei Yoshida, Shuhei Yoshida, Yuta Masuo, Daisuke Shibata, Masakazu Haruta, Takayuki Doi, Minoru Inaba
    © The Author(s) 2016. Published by ECS. The amounts of adsorbed water on several kinds of carbon and silicon materials including Si nano-flake powder (Si LeafPowder, Si-LP) were determined at 250?C. It was found that nano-sized Si materials adsorb a large amount of water even after being dried at 120?C because of the hydrophilicity of the surface and the high specific surface area. The adsorbedwater on Si-LP can be removed, but not completely, after drying at a 180°C. The charge and discharge characteristics of Si-LP, especially the initial irreversible capacity and the coulombic efficiencies upon repeated cycling, were significantly improved by removal of the adsorbed water at 180?C. The 180°C-dried sample also suppressed gas evolution during the initial charging and discharging cycle. From the results of gas analysis, it was found that gases evolved from the Si-LP electrodes were mainly H2and CO2. From the results of charge and discharge tests and gas analysis, the effect of the adsorbed water on the irreversible decomposition of the electrolyte solution was discussed., Journal of the Electrochemical Society, Journal of the Electrochemical Society, 164A6084 - A6087, 01 Jan. 2017, English, 研究論文(国際会議プロシーディングス)
  • Suppression of Mn–Ion-Dissolution of LiNi0.5Mn1.5O4Electrodes in a Highly Concentrated Electrolyte Solution at Elevated Temperatures
    Takayuki Doi, Yusuke Shimizu, Ryo Matsumoto, Michihiro Hashinokuchi, Minoru Inaba
    © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim Mn-based active materials, such as LiMn2O4, are widely used for positive electrodes in lithium ion batteries, and spinel LiNi0.5Mn1.5O4is drawing much attention to realize 5-V class batteries. However, the oxidative decomposition of electrolyte solution at high voltages and Mn-dissolution of LiNi0.5Mn1.5O4are serious problems to be solved. These two drawbacks are more marked at elevated temperatures, and should be caused by free solvent molecules in electrolyte solution. In this study, highly concentrated electrolyte solution, which contains few free solvent molecules, was investigated to solve the problems. LiNi0.5Mn1.5O4electrodes worked at 50oC in nearly saturated 7.25 mol kg−1LiBF4/ propylene carbonate (PC) electrolyte solution, whereas not in the nearly saturated 4.30 mol kg−1LiPF6/PC. In addition, Mn-ion dissolution from LiNi0.5Mn1.5O4was significantly suppressed in highly concentrated electrolyte solutions, and correlated to the fraction of free PC molecules in them., ChemistrySelect, ChemistrySelect, 28824 - 8827, 01 Jan. 2017, English, 研究論文(学術雑誌)
  • High rate charge and discharge characteristics of graphite/SiOxcomposite electrodes
    Shuhei Yoshida, Shuhei Yoshida, Takashi Okubo, Yuta Masuo, Yasuyuki Oba, Daisuke Shibata, Masakazu Haruta, Takayuki Doi, Minoru Inaba
    © The Electrochemical Society of Japan, All rights reserved. Charge and discharge properties of a graphite/SiOxcomposite electrode were studied over a wide range of charge/ discharge rates (1/20 to 5C) for use in automotive applications. The graphite/SiOx(90/10 by weight) composite electrode gave a high reversible capacity (453mAh·g-1), and showed a good capacity retention at a low rate of 1/ 20 C. However, the capacity decreased significantly on cycling at a high rate of 2C. From the analysis of the charging and discharging processes, it was found that the charging reaction occurs predominantly at SiOxparticles initially at higher potentials and then proceeds at graphite particles at lower potentials to be fully charged. This tendency was also supported by a dependence of the activation energy of the charge transfer reaction on the state of charge (SOC) estimated by ac impedance analysis. Because the composite electrode contains only 10% SiOx, the current was excessively concentrated to the SiOxparticles at the initial state when charged at high rates. This caused crack formation in SiOxparticles, and the resulting contact loss between particles was considered as the reason for the observed poor cycleability at 2C., Electrochemistry, Electrochemistry, 85403 - 408, 01 Jan. 2017, English, 研究論文(学術雑誌)
  • Silicon nano-flake powder as an anode for the next generation lithium-ion batteries: Current status and challenges
    Minoru Inaba, Masakazu Haruta, Morihiro Saito, Takayuki Doi
    © The Electrochemical Society of Japan, All rights reserved. Silicon is electrochemically alloyed and de-alloyed with Li at potentials close to Li+/Li and is widely recognized as the most promising candidate for the anode of LIBs with a high energy density (250-300Whkg-1) in the next generation. The most serious issue of Si anode is poor capacity retention owing to large volume changes during charging and discharging. We developed Si LeafPowder® with a nano-flake structure to overcome the poor capacity retention. However Si anodes still have some problems such as large irreversible capacity, ceaseless electrolyte decomposition, swelling of the electrode, etc. for use in high-energy density LIBs in the next generation. In this article, these problems and the challenges to mitigate them are overviewed based on our resent data obtained by Si nano-flakes (Si LeafPowder®)., Electrochemistry, Electrochemistry, 85623 - 629, 01 Jan. 2017, English, 研究論文(学術雑誌)
  • Dilution of highly concentrated libf4/propylene carbonate electrolyte solution with fluoroalkyl ethers for 5-V LiNi0.5Mn1.5O4positive electrodes
    Takayuki Doi, Yusuke Shimizu, Michihiro Hashinokuchi, Minoru Inaba
    © The Author(s) 2017. Published by ECS. Various kinds of fluoroalkyl ethers were investigated as diluents to reduce the high viscosity of highly concentrated LiBF4/PC electrolyte solutions. 1,1,2,2-Tetrafluoroethyl 2,2,3,3-Tetrafluoropropyl ether (HFE) was the most suitable diluent because of a high solubility of LiBF4. 2.50 mol kg-1 LiBF4/PC+HFE (2:1 by volume) was a reasonable compromise to attain a low viscosity (51.7 mPa s) and a low PC/Li molar ratio (2.39). Raman spectroscopy revealed that the fraction of free PC molecules in 2.50 mol kg-1 LiBF4/PC+HFE (2:1) was much smaller than 2.50 mol kg-1 LiBF4/PC (PC/Li molar ratio = 4.00), and that the interactions of HFE with Li+ cations and BF4 -Anions were very weak. LiNi0.5Mn1.5O4positive electrodes showed high charge/discharge performance with low irreversible capacities in 2.50 mol kg-1 LiBF4/PC+HFE (2:1), which showed that the highly concentrated LiBF4/PC system can be diluted with HFE without losing the high stability against oxidation., Journal of the Electrochemical Society, Journal of the Electrochemical Society, 164A6412 - A6416, 01 Jan. 2017, English, 研究論文(国際会議プロシーディングス)
  • Suppression of manganese-ion dissolution by sio2aerosol addition from spray pyrolyzed li2mno3-limn1/3ni1/3co1/3o2
    Satoshi Hashigami, Satoshi Hashigami, Masayuki Kawanishi, Kei Yoshimi, Satoshi Ujiie, Toru Inagaki, Michihiro Hashinokuchi, Takayuki Doi, Minoru Inaba
    © The Electrochemical Society of Japan, All rights reserved. Layered Li2MnO3-LiMn1/3Ni1/3Co1/3O2solid-solution cathode materials modified with SiO2were prepared by spra pyrolysis and their charge-discharge properties were investigated. Both the capacity and voltage fades of SiO2modified Li2MnO3-LiMn1/3Ni1/3Co1/3O2during charge/discharge cycling were suppressed compared with that of th unmodified sample. It was found that the addition of SiO2suppressed the dissolution of manganese ions at 60° from the results of inductively coupled plasma (ICP) emission spectroscopy. X-ray diffraction (XRD) data indicate that weak reflections corresponding to Li2SiO3appeared as the SiO2content increases to 5wt%. Scanning electro microscope (SEM) studies showed that the microstructure of the particles was significantly changed by SiO addition. As indicated by transmission electron microscope (TEM) analysis, Si-rich regions were seen on th Li2MnO3-LiMn1/3Ni1/3Co1/3O2primary particles. The suppression of Mn ions and the improved charge and discharg properties were correlated with the microstructural changes., Electrochemistry, Electrochemistry, 84842 - 847, 01 Nov. 2016, English, 研究論文(学術雑誌)
  • Si/li2s battery with solvate ionic liquid electrolyte
    Zhe Li, Yutaro Kamei, Masakazu Haruta, Toshio Takenaka, Akira Tomita, Takayuki Doi, Shiguo Zhang, Kaoru Dokko, Minoru Inaba, Masayoshi Watanabe
    © The Electrochemical Society of Japan, All rights reserved. A lithium-sulfur cell was developed, consisting of a Si nanoflake negative electrode, a Li2S/graphene positiv electrode, and a non-flammable solvate ionic liquid electrolyte. This cell configuration allows us to avoid the use o Li metal electrode and the concomitant dendritic deposition of Li metal at the negative electrode during charging thereby rendering the cell operation highly safe and stable. The solvate ionic liquid electrolyte solution wa composed of tetraglyme, lithium bis(trifluoromethanesulfonyl)amide, and a hydrofluoroether. The solubility o lithium polysulfide (reaction intermediate of the positive electrode) is very low, resulting in high Coulombi efficiency of discharge/charge and long cycle life of the Si/Li2S cell., Electrochemistry, Electrochemistry, 84887 - 890, 01 Nov. 2016, English, 研究論文(学術雑誌)
  • In situ Scanning Electron Microscopy of Silicon Anode Reactions in Lithium-Ion Batteries during Charge/Discharge Processes
    Chih Yao Chen, Teruki Sano, Tetsuya Tsuda, Koichi Ui, Yoshifumi Oshima, Masaki Yamagata, Masashi Ishikawa, Masakazu Haruta, Takayuki Doi, Minoru Inaba, Susumu Kuwabata
    © The Author(s) 2016. A comprehensive understanding of the charge/discharge behaviour of high-capacity anode active materials, e.g., Si and Li, is essential for the design and development of next-generation high-performance Li-based batteries. Here, we demonstrate the in situ scanning electron microscopy (in situ SEM) of Si anodes in a configuration analogous to actual lithium-ion batteries (LIBs) with an ionic liquid (IL) that is expected to be a functional LIB electrolyte in the future. We discovered that variations in the morphology of Si active materials during charge/discharge processes is strongly dependent on their size and shape. Even the diffusion of atomic Li into Si materials can be visualized using a back-scattering electron imaging technique. The electrode reactions were successfully recorded as video clips. This in situ SEM technique can simultaneously provide useful data on, for example, morphological variations and elemental distributions, as well as electrochemical data., Scientific Reports, Scientific Reports, 6, 26 Oct. 2016, English, 研究論文(学術雑誌)
  • Concentrated LiPF6/PC electrolyte solutions for 5-V LiNi0.5Mn1.5O4positive electrode in lithium-ion batteries
    Takayuki Doi, Rin Masuhara, Michihiro Hashinokuchi, Yusuke Shimizu, Minoru Inaba
    © 2016 Elsevier Ltd Charge and discharge properties of spinel LiNi0.5Mn1.5O4positive electrodes were investigated using propylene carbonate (PC)-based concentrated electrolyte solutions in the range of 0.83 (ca. 1 mol dm−3) to 4.45 (nearly saturated) mol kg−1. The solvation state of PC in the concentrated electrolyte solution was studied by Raman spectroscopy. The HOMO energy of PC in Li+(PC)nwas evaluated by first-principle calculation to assess the oxidative stability of PC molecules solvating lithium ion. Charge and discharge measurements revealed that the irreversible capacity due to solvent decomposition decreased with increasing the concentration of LiPF6, while discharge capacity increased. In addition, cycle performance of LiNi0.5Mn1.5O4positive electrodes was remarkably improved by the use of graphitized Ketjenblack as a conductive additive., Electrochimica Acta, Electrochimica Acta, 209219 - 224, 10 Aug. 2016, English, 研究論文(学術雑誌)
  • Enhancement of anode activity at Ni/Sm-doped CeO2cermet anodes by Mo addition in NH3-fueled solid oxide fuel cells
    Michihiro Hashinokuchi, Ryuji Yokochi, Wataru Akimoto, Takayuki Doi, Minoru Inaba, Junichiro Kugai
    © 2015 Elsevier B.V. All rights reserved. Molybdenum was added to nickel/Sm2O3-doped ceria (Ni/SDC) cermets by a MoCl5impregnation method, and the activity of the resulting Ni-Mo/SDC cermets was evaluated as anodes in ammonia-fueled solid oxide fuel cells (SOFCs) in the temperature range of 973-1173 K. It has been revealed that the addition of Mo improved remarkably the catalytic activity for NH3reforming and enhanced the cell performance. The Ni-Mo/SDC anode with a Mo content of ~ 3 atomic % of the total metal showed the highest catalytic activity for NH3reforming. XRD analysis of a NiO-MoO3powder mixture annealed in NH3revealed the formation of a nitride NixMo1-xN during operation of Ni-Mo/SDC anodes, and the role of the nitride in NH3reforming was discussed in detail., Solid State Ionics, Solid State Ionics, 285222 - 226, 01 Feb. 2016, English, 研究論文(学術雑誌)
  • Synthesis of SiO2-modified Li2MnO3-LiMn1/3Ni1/3Co1/3O2by spray pyrolysis with acid addition as cathode materials for lithium ion batteries
    Satoshi Hashigami, Satoshi Hashigami, Kei Yoshimi, Masayuki Kawanishi, Satoshi Ujiie, Toru Inagaki, Michihiro Hashinokuchi, Takayuki Doi, Minoru Inaba
    © The Electrochemical Society. SiO2-modified Li2MnO3-LiMn1/3Ni1/3Co1/3O2cathode materials for lithium ion batteries were synthesized by a spray pyrolysis technique using starting solutions containing citric acid and boric acid. SEM images showed that most of the particles using citric acid had spherical shapes and thin shell structures. Some particles were collapsed when the amount of citric acid was large. The specific surface area of the particles prepared from the citric acid-added solution was higher than that without citric acid. The addition of boric acid decreased the specific surface area of the material by acting as a sintering agent. The charge and discharge capacities for the synthesized materials were investigated and it was found that the addition of citric acid, which gave a higher specific surface area, enhanced the rate capability., ECS Transactions, ECS Transactions, 7311 - 17, 01 Jan. 2016, English, 研究論文(国際会議プロシーディングス)
  • LiBF4-Based concentrated electrolyte solutions for suppression of electrolyte decomposition and rapid lithium-ion transfer at LiNi0.5Mn1.5O4/electrolyte interface
    Takayuki Doi, Yusuke Shimizu, Michihiro Hashinokuchi, Minoru Inaba
    © 2016 The Electrochemical Society. Charge and discharge properties of spinel LiNi0.5Mn1.5O4positive electrodes were investigated using concentrated LiBF4/propylene carbonate (PC) electrolyte solutions in the range of 0.833 (ca. 1 mol dm-3) to 7.25 (nearly saturated) mol kg-1. The irreversible decomposition of electrolyte solution was effectively suppressed with an increase in concentration. In addition, the polarization in charge/discharge reactions remained small in the nearly saturated 7.25 mol kg-1LiBF4/PC even though the viscosity was very high and the ionic conductivity was low. The rate capability was higher than that obtained with nearly saturated 4.3 mol kg-1LiPF6/PC. The structure, viscosity, and ionic conductivity of the concentrated LiBF4/PC were investigated. Based on the experimental results, the rapid charge/discharge reactions at LiNi0.5Mn1.5O4electrodes were discussed., Journal of the Electrochemical Society, Journal of the Electrochemical Society, 163A2211 - A2215, 01 Jan. 2016, English, 研究論文(学術雑誌)
  • Analysis of the Ionic Conduction Behavior in a Few of Room Temperature Molten Fluorides
    Akimasa Tasaka, Akimasa Tasaka, Hidemi Inoue, Tomohiro Isogai, Takaaki Nakai, Saito Morihiro, Saito Morihiro, Minoru Inaba, Minoru Inaba
    © 2015 Elsevier Ltd. All rights reserved. The average self-diffusion coefficients of cations and anions increased with increasing the HF-concentration and temperature in (CH<inf>3</inf>)<inf>3</inf>N·mHF, (CH<inf>3</inf>)<inf>4</inf>NF·mHF, (C<inf>2</inf>H<inf>5</inf>)<inf>3</inf>N·mHF, and (C<inf>2</inf>H<inf>5</inf>)<inf>4</inf>NF·mHF melts. The behavior of the self-diffusion coefficients of cations and anions in every melt is in good agreement with an increase in ionic conductivity and a decrease in viscosity. The transference number of (FH)<inf>n</inf>F<sup>-</sup> anions estimated from the values of self-diffusion coefficients for each ion in every melt was almost constant and their values were around 0.6 in the (CH<inf>3</inf>)<inf>3</inf>N·mHF melt and around 0.7 in the (CH<inf>3</inf>)<inf>4</inf>NF·mHF, the (C<inf>2</inf>H<inf>5</inf>)<inf>3</inf>N·mHF, and the (C<inf>2</inf>H<inf>5</inf>)<inf>4</inf>NF·mHF melts. The value of theoretical conductivity (σ<inf>NMR</inf>) obtained from the average self-diffusion coefficients of cations and anions by using Nernst-Einstein equation was higher than the value of experimental ionic conductivity (σ). Therefore, it is concluded that the diffusion of (FH)<inf>n</inf>F<sup>-</sup> anions is faster than that of each cation in every melt and that a part of both cation and anion in each melt may associate by interaction between both ions., Electrochimica Acta, Electrochimica Acta, 174721 - 727, 26 Jun. 2015, English, 研究論文(学術雑誌)
  • Effects of nitride formation on anode catalytic activity in ammonia-fueled SOFCs
    Ryuji Yokochi, Michihiro Hashinokuchi, Takayuki Doi, Minoru Inaba
    © The Electrochemical Society. Four kinds of anodes, Ni-Mo(3%)/, Ni-W(3%)/, Ni-Ta(3%)/ and Ni-Nb(3%)/Sm<inf>0.2</inf>Ce<inf>0.8</inf>O<inf>2</inf> (SDC) were prepared by impregnating Mo, W, Ta and Nb precursor solutions into pre-sintered Ni/SDC cermets. Their anode performance was evaluated in ammonia-fueled SOFCs at 973-1173 K to clarify the correlation between nitride formation and anode activity. The addition of Mo, W and Ta enhanced the anode activity for NH<inf>3</inf> oxidation, but Nb did not. Under the operation conditions (i.e. at 973-1173 K in NH<inf>3</inf>), MoO<inf>3</inf>, WO<inf>3</inf> and Ta<inf>2</inf>O<inf>5</inf> reacted with NH<inf>3</inf> to form nitrides (Mo<inf>2</inf>N, W<inf>2</inf>N and TaON), but Nb<inf>2</inf>O<inf>5</inf> did not. These results suggest that the easiness of the nitride formation is closely related to the high activity anode for NH<inf>3</inf> oxidation., ECS Transactions, ECS Transactions, 682745 - 2750, 01 Jan. 2015, English, 研究論文(国際会議プロシーディングス)
  • Development of highly active and durable platinum core-shell catalysts forpolymer electrolyte fuel cells
    Minoru Inaba, Hideo Daimon
    © 2015, Japan Petroleum Institute. All rights reserved. Polymer electrolyte fuel cells (PEFCs) are clean and highly efficient energy sources without emission of global warming CO<inf>2</inf> gas, and have been developed as electric power sources in fuel cell vehicles (FCVs). One of the most important issues in the development of PEFCs is currently a drastic reduction of Pt usage by an improvement in the activity for oxygen reduction reaction at the Pt cathode catalyst. To improve the activity of the Pt catalyst, we have so far developed core-shell catalysts using Pt monolayer shell covered on Au or Pd core materials. In this review article, a novel preparation method for Pt monolayer formation on non-Pt core nanoparticles that is suitable for mass production of the core-shell catalysts, and the results on the activity and durability of the resulting core-shell catalysts are overviewed. The potentials and difficulties of the core-shell catalysts for use in practical FCVs are discussed., Journal of the Japan Petroleum Institute, Journal of the Japan Petroleum Institute, 5855 - 63, 01 Jan. 2015, English
  • Cycle performances of si-flake-powder anodes in lithium salt-tetraglyme complex electrolytes
    Masakazu Haruta, Yuta Masuo, Takashi Moriyasu, Akira Tomita, Chihiro Sakakibara, Akika Kamei, Masato Hirota, Toshio Takenaka, Takayuki Doi, Minoru Inaba
    © The Electrochemical Society of Japan, All rights reserved. Charge and discharge properties of amorphous Si nano-flake powder (Si Leaf Powder, Si-LP) in lithium bis(trifluoromethanesulfonyl)amide-tetraglyme complex electrolyte, [Li(G4)][TFSA], were investigated for use as an anode in silicon-sulfur battery. Though a high reversible capacity (2,300-2,700mAhg?1) was obtained initially in [Li(G4)][TFSA], the overpotential gradually increased upon cycling. The increase in overpotential was reduced by dilution with 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether. The addition of fluoroethylene carbonate (FEC) further reduced the overpotential and improved cycleability. Electrochemical impedance spectroscopy analysis revealed that the observed improvements in charge and discharge characteristics are due to the formation of solid electrolyte interface layer with a high ionic-conductivity in the presence of FEC., Electrochemistry, Electrochemistry, 83837 - 839, 01 Jan. 2015, English, 研究論文(国際会議プロシーディングス)
  • Li pre-doping of amorphous silicon electrode in li-naphthalene complex solutions
    Shuhei Yoshida, Shuhei Yoshida, Yuta Masuo, Daisuke Shibata, Masakazu Haruta, Takayuki Doi, Minoru Inaba
    © The Electrochemical Society of Japan, All rights reserved. To compensate a large initial irreversible capacity (Qirr) of silicon electrode, a novel Li pre-doping technique using Linaphthalene complex/tetrahydrofuran solutions was developed. Li was successfully doped to amorphous silicon nano-flake particles, and the doping level of Li was easily controlled by adjusting naphthalene concentration. A large Qirrof the pristine electrode (1200mAhg?1) was almost completely compensated after pre-doped in 0.1 moldm?3 Li-naphthalene solution for 1 h. In addition, no harmful effects of pre-doping on cycleability were observed., Electrochemistry, Electrochemistry, 83843 - 845, 01 Jan. 2015, English, 研究論文(国際会議プロシーディングス)
  • Preparation and charge/discharge characteristics of carbon-modified ramsdellite TiO2as a high potential anode
    Ryotaro Kanazawa, Masakazu Haruta, Takayuki Doi, Minoru Inaba
    © The Electrochemical Society of Japan, All rights reserved. Carbon-modified ramsdellite titanium dioxide, TiO2(R), was prepared without using metallic Ti powder, and its charge and discharge properties was investigated as an anode of lithium ion batteries. Carbon sources (citric acid and multi-walled carbon nanotubes) were added in the calcination process to obtain a LiTi2O4precursor. The carbon addition was indispensable to obtain stoichiometric LiTi2O4 as a precursor and the resulting Li+-free TiO2(R). The carbon-modified TiO2(R) had a round shape and a smaller particle size of 0.5-1.5?m. The discharge capacity and rate-capability were improved by carbon modification due to an enhancement of the electronic conductivity and a reduction of the lithium-ion diffusion path., Electrochemistry, Electrochemistry, 83867 - 869, 01 Jan. 2015, English, 研究論文(国際会議プロシーディングス)
  • Mechanism and activity of Ni-based (Ni-M: M = Fe, Mo, W, Ta) cermet anodes for ammonia oxidation in SOFCs
    M. Hashinokuchi, R. Yokochi, W. Akimoto, T. Doi, M. Inaba, J. Kugai
    © The Electrochemical Society. We investigated the activity for Ni-based (Ni-M: M = Mo, W and Ta) anodes for ammonia oxidation in SOFCs. It was found that Mo was the most effective additive for the anode cermets in this study. It was found that the activity for ammonia oxidation at Ni-Mo anode was determined by a balance between ammonia adsorption and nitrogen desorption, and synergetic effects of Ni and Mo improved the anode activity for NH<inf>3</inf> oxidation., ECS Transactions, ECS Transactions, 682739 - 2744, 01 Jan. 2015, English, 研究論文(国際会議プロシーディングス)
  • Effects of Li pre-doping on charge/discharge properties of Si thin flakes as a negative electrode for Li-ion batteries
    Takashi Okubo, Morihiro Saito, Chihiro Yodoya, Akika Kamei, Masato Hirota, Toshio Takenaka, Toyoki Okumura, Akimasa Tasaka, Minoru Inaba
    To compensate the large irreversible capacity (Qirr), lithium was pre-doped to Si thin flakes (Si Leaf Powder® (Si-LP), thickness: 100 nm) for different times, and its effects on the charge/discharge characteristics such as reversible capacity, cycleability, and rate-capability were investigated in detail. The charge/discharge test results showed that a large initial Qirrof ca. 2300 mAh g- 1for the Si-LP can be completely compensated by Li pre-doping, and a high capacity (> 2500 mAh g- 1) was obtained for pre-doped Si-LPs. The pre-doping did not cause any harmful effects on cycleability as long as lithium was uniformly pre-doped. The addition of vinylene carbonate to the electrolyte solution in the pre-doping and in the test cell greatly improved the cycleability, and a high discharge capacity of ca. 2300 mAh g- 1was kept after 40 cycles. © 2013 Elsevier B.V., Solid State Ionics, Solid State Ionics, 26239 - 42, 01 Sep. 2014, English, 研究論文(学術雑誌)
  • Effects of Temperature and Boron Concentration of a Boron-Doped Diamond (BDD) Electrode on NF3Current Efficiency, and Stability of BDD Electrode in Molten NH4F·2HF
    A. Tasaka, A. Tasaka, Y. Iida, T. Shiono, M. Uno, Y. Nishiki, T. Furuta, M. Saito, M. Inaba, M. Inaba
    © 2014 John Wiley & Sons, Ltd. The current efficiency for NF3formation was independent of the current density in the range of 200-1000mAcm-2. The average values of NF3current efficiencies on a boron-doped diamond (BDD) anode with a boron concentration of 2500ppm were 32.3% at 80°C, 63.3% at 100°C, and 59.7% at 120°C. The best current efficiencies for NF3formation on the BDD anode with boron concentrations of 2500, 5000, and 7500ppm were obtained at 100°C and those were 63.3, 73.3, and 56.2%, respectively. Although an anode effect occurred on BDD electrodes whose surface was partly covered with the spiculate structure, which had boron concentrations higher than 7500ppm, it did not take place on BDD electrodes whose surface was covered with the diamond structure, even if the BDD electrode had a boron concentration of 8000ppm., Molten Salts Chemistry and Technology, Molten Salts Chemistry and Technology, 9781118448731123 - 131, 23 Jun. 2014, English
  • Electrolytic Synthesis of (CF3)3N from a Room Temperature Molten Salt of (CH3)3N·mHF with BDD Electrode
    A. Tasaka, A. Tasaka, K. Ikeda, N. Osawa, M. Saito, M. Uno, Y. Nishki, T. Furuta, M. Inaba, M. Inaba
    © 2014 John Wiley & Sons, Ltd. The electrolytic synthesis of (CF3)3N using a BDD anode from the room temperature molten salt of (CH3)3N·mHF (m=3.0, 4.0, and 5.0) and mixed melts of (CH3)3N · 5.0HF and CsF · 2.3HF were investigated. When the (CH3)3N·mHF (m=3.0, 4.0, and 5.0) melts without CsF were electrolyzed using a BDD anode, the yield of (CF3)3N was low and the main product was a partially fluorinated amine such as (CF3)2CHF2N. In the mixed melt of (CH3)3N·5.0HF+70wt% CsF · 2.3HF, the yield of (CF3)3N became higher in comparison with that obtained in electrolysis of the (CH3)3N · 5.0HF melt. This may be caused by an increase in the viscosity due to an increase in the electrostatic interaction between species such as HF, anion, a partially fluorinated tertiary ammonium cation, and a partially fluorinated compound by adding CsF · 2.3HF to a (CH3)3N·5.0HF melt, resulting in an increase in retention time of partially fluorinated tertiary amines with polarity in the mixed melt., Molten Salts Chemistry and Technology, Molten Salts Chemistry and Technology, 9781118448731351 - 358, 23 Jun. 2014, English
  • Ni-Fe/Sm-doped CeO2anode for ammonia-fueled solid oxide fuel cells
    Wataru Akimoto, Tadashi Fujimoto, Morihiro Saito, Minoru Inaba, Hiroyuki Yoshida, Toru Inagaki
    Anode cermets using various transition metals (Ni, Co, and Fe) and Ce0.8Sm0.2O2 - σ(SDC) were prepared and their catalytic activity for ammonia oxidation in solid oxide fuel cells (SOFCs) was investigated. Ni/SDC showed a high activity for hydrogen, but not for ammonia. Co/SDC showed a poor activity for both hydrogen and ammonia. Fe/SDC has the highest activity for ammonia oxidation in the temperature range of 973 to 1173 K. Moreover, it was found that Ni-Fe alloy/SDC anodes showed improved performance for ammonia oxidation. Ni40-Fe60/SDC anode showed the highest catalytic activity for NH3oxidation, and therefore is promising for ammonia-fueled SOFCs. © 2013 Elsevier B.V. All rights reserved., Solid State Ionics, Solid State Ionics, 2561 - 4, 01 Mar. 2014, English, 研究論文(学術雑誌)
  • Effect of surface fluorination on the charge/discharge properties of high potential negative electrode TiO2(B) for LIBs
    Morihiro Saito, Yoshiyuki Nakano, Mikihiro Takagi, Takuma Maekawa, Akimasa Tasaka, Minoru Inaba, Hitoshi Takebayashi, Yoshio Shodai
    Surface fluorination of TiO2(B) powder was conducted by pure F2 gas at room temperature for 1 h and the effect on the charge/discharge properties was examined as a negative electrode of Li-ion batteries (LIBs). X-ray diffraction (XRD) pattern was not changed before and after the surface fluorination though the peak intensities became weaker than that of the pristine sample, indicating the etching of the surface of SF-TiO2(B) power. This was supported by scanning electron microscopy (SEM) observation. However, X-ray photoelectron spectroscopy (XPS) analysis clearly revealed that F atoms exist on the surface of TiO2(B) particles and probably were covalently bonded with Ti atoms near the surface. From the charge/discharge tests at a C/6 rate, the SF-TiO2(B) exhibited a higher 1st discharge (203 mAh g-1) than the pristine sample (181 mAh g-1) with a good cycleability. Impedance analysis revealed that both resistances of solid electrolyte interphase (SEI) film and charge transfer at the SEI/active material interface were reduced by surface fluorination, implying the improvement of SEI film and permeability of the electrolyte solution to the interphase. The rate capability was improved by the surface fluorination up to 1C rate, at which the SF-TiO2(B) exhibited a high discharge capacity of around 150 mAh g-1. © (2014) Trans Tech Publications, Switzerland., Key Engineering Materials, Key Engineering Materials, 582127 - 130, 01 Jan. 2014
  • Oxygen reduction catalytic activity of hollandite-type manganese oxides
    Takuya Kenko, Tatsuya Takakuwa, Morihiro Saito, Hideo Daimon, Akimasa Tasaka, Minoru Inaba, Yoshihiro Kadoma, Naoaki Kumagai, Hidenobu Shiroishi, Takeo Hatai, Jun Kuwano
    Hollandite-type Mn oxides were synthesized by a co-precipitation (CP) and a hydrothermal (HT) method as the cathode catalysts for anion-exchange membrane fuel cells (AEMFCs), and their oxygen reduction reaction (ORR) activities and AEMFC single cell performances were evaluated. In this study, we prepared two kinds of hollandite oxides K0.14MnO2·0.12H 2O(KMO-CP) and K0.12MnO2·0.06H 2O(KMO-HT) and their partially Co-substituted ones K 0.11(Mn0.88 Co0.12)O2· 0.16H2O(KMC0.12-CP) and K0.11(Mn 0.88Co0.12)O2· 0.08H 2O(KMC0.12-HT), and examined the ORR activities with a rotating ring-disk electrode (RRDE) in 0.1 M KOH at 50°C. All the samples showed high onset potentials of ORR, ca. 0.9 V vs. reversible hydrogen electrode (RHE), and relatively high ORR currents at 0.75 V and high efficiencies for 4-electron reduction (EFF4) of around 90% were obtained for the HT samples owing to higher crystallinity and higher specific surface area than those of the CP ones. The AEMFC single cells prepared with KMO-HT and KMC 0.12-HT cathode catalysts were operated stably and exhibited the maximum power densities of ca. 49 and 42 mW cm-2, respectively, which were comparable to that of the single cell using a conventional 50 wt% Ag/C catalyst. © (2013) Trans Tech Publications., Key Engineering Materials, Key Engineering Materials, 566253 - 257, 11 Sep. 2013
  • Controllable growth orientation of Ag2O and Cu2O films by electrocrystallization from aqueous solutions
    Tsutomu Shinagawa, Yuya Ida, Kotaro Mizuno, Seiji Watase, Mitsuru Watanabe, Minoru Inaba, Akimasa Tasaka, Masanobu Izaki
    We demonstrate that Ag2O and Cu2O polycrystal films with a cubic cuprite structure can be grown on F:SnO2 substrates with controllable crystal orientation between 111 and 100 directions by galvanostatic electrocrystallization from aqueous electrolytes. The Ag 2O and Cu2O films have been electrodeposited at different applied current densities determined by linear-sweep voltammetry (LSV) measurements, and their crystal structure and morphology were characterized with X-ray diffraction (XRD) and field emission scanning electron microscopy (FESEM). The XRD results show the preferred growth orientation changed from 111 to 100 with increasing and decreasing current density for Ag2O and Cu2O, respectively. The surface morphology, especially for the Cu2O films, was also changed from a three-sided pyramidal shape to a four-sided pyramidal shape corresponding to the orientation. We also give a reasonable explanation for the observed trend in the growth orientation by considering the formation rate of AgOH and CuOH; higher and lower rates appear to yield 111 and 100 preferred orientation, respectively. © 2012 American Chemical Society., Crystal Growth and Design, Crystal Growth and Design, 1352 - 58, 02 Jan. 2013, English, 研究論文(学術雑誌)
  • The mechanism of ammonia oxidation at Ni-Fe-SDC anode in ammonia-fueled SOFCs
    Wataru Akimoto, Morihiro Saito, Minoru Inaba, Hiroyuki Yoshida, Toru Inagaki
    The mechanism for ammonia oxidation at Ni-Fe alloy/Sm-doped ceria (SDC) anode cermet was investigated under SOFC operating conditions in the temperature range of 973 to 1173 K. OCV and AC impedance analysis revealed that ammonia is directly oxidized at Ni-Fe/SDC anode, especially at lower temperatures. It was also found that the activity is determined by a balance between ammonia adsorption and nitrogen desorption on the catalyst, and the synergy effects of Ni and Fe improved the activity of Ni-Fe alloy catalysts for ammonia oxidation. © The Electrochemical Society., ECS Transactions, ECS Transactions, 571639 - 1645, 01 Jan. 2013
  • Improvement of tap density of TiO2(B) powder as high potential negative electrode for lithium ion batteries
    Morihiro Saito, Yoshiyuki Nakano, Mikihiro Takagi, Naoki Honda, Akimasa Tasaka, Minoru Inaba
    To improve the tap density of TiO2(B) as a high potential negative electrode for lithium-ion batteries, the particle size and the shape of the TiO2(B) were controlled by a new synthetic method using large-size Nbdoped rutile TiO2as a starting material. The Nb-doped TiO2(B) particles, Ti0.93Nb0.07O2(B) and Ti0.90Nb0.10O2(B), were much smaller (diameter: ca. 100 nm, length: ca. 800 nm) than the conventional TiO2(B) prepared using fine anatase TiO2particles as a starting material, and were agglomerated to form secondary particles with a diameter of 3-30 mm. The tap densities of Ti0.93Nb0.07O2(B) and Ti0.90Nb0.10O2(B) were successibly high (0.77 and 0.66 g cm-3, respectively), which were ca. 2-fold higher than that of the conventional TiO2(B) (0.30 g cm-3). As a result, the discharge capacity per electrode volume was significantly improved for both Nb-doped samples without sacrificing the cycleability. Non-doped TiO2(B) was prepared from large-size rutile TiO2by a similar method, but it deteriorated upon cycling, accompanied by the formation of the anatase phase. It was shown that Nb-doping not only improves the discharge capacity per electrode volume, but also effectively stabilizes the TiO2(B) crystal structure of the small particles. © 2013 Elsevier B.V. All rights reserved., Journal of Power Sources, Journal of Power Sources, 24450 - 55, 01 Jan. 2013, English, 研究論文(学術雑誌)
  • Synthesis and electrochemical properties of carbon-coated Li 2FeP2O7 for li-ion batteries
    Morihiro Saito, Sosuke Yano, Takuma Maekawa, Akimasa Tasaka, Minoru Inaba
    Carbon-coated Li2FeP2O7 (Li 2FeP2O7-C) and Mg-doped Li2FeP 2O7-C were successfully synthesized with pitch as a carbon source and Mg(C2O4)-H2O as a Mg source, and the charge/discharge properties were compared with that of bare Li 2FeP2O7. A thin carbon layer (ca. 5 nm in thickness) was coated on Li2FeP2O7 powder after heat-treatment. Li2FeP2O7-C and Mgdoped Li2FeP2O7-C exhibited high discharge capacities of 97 and 104 mAh g-1, respectively, at C/10 rate, implying a great improvement from that of bare Li2FeP2O7 (69 mAh g-1). The cycleability and rate-capability were also improved by carboncoating and Mg doping. Mg-doped Li2FeP2O7-C kept a high discharge capacity of 88 mAh g-1 even at 1 C rate. AC impedance analysis revealed that Mg-addition suppresses excess electrolyte decomposition on the surface of Li2FeP2O7 and reduces the resistance of SEI. © The Electrochemical Society., ECS Transactions, ECS Transactions, 50251 - 259, 01 Dec. 2012, English, 研究論文(国際会議プロシーディングス)
  • Improvement of tap density of TiO2(B) powder as high potential negative electrode
    Yoshiyuki Nakano, Kanji Masuda, Mikihiro Takagi, Morihiro Saito, Akimasa Tasaka, Minoru Inaba
    The shape and size of TiO2(B) particles were controlled by ballmilling K2Ti4O9, H2Ti4O9 and TiO2(B) powders to improve the tap density of TiO2(B). It was found that only K2Ti4O9 endured the ball-milling process and provided a fine TiO2(B) powder after the ion-exchange and dehydration processes. In contrast, ball-milling of H2Ti4O9 and TiO2(B) powders resulted in a formation of a large amount of the rutile and anatase phase, respectively. In addition, a reduction of the spinning rate to 600 rpm suppressed the formation of the minor impurity of the anatase phase in the TiO2(B) sample prepared from the milled K2Ti4O9 powder. The resulting TiO2(B) (M1-600) powder exhibited a high tap density of 0.71 g cm-3 and a high electrode density of 1.25 g cm-3, which were 2.37 and 1.29 times, respectively, higher than those of the pristine TiO2(B). In charge/discharge tests, M1-600 exhibited a discharge of 213.1 mAh g-1, which is higher than that of the pristine TiO2(B), with a good cycleability. It gave a discharge capacity of 80.1 mAh g-1 even at a high rate of 10 C. © The Electrochemical Society., ECS Transactions, ECS Transactions, 50261 - 269, 01 Dec. 2012, English, 研究論文(国際会議プロシーディングス)
  • Improvement of cycleability for Li-Si alloy anodes using Si thin flakes for Li-ion batteries
    Tomoyuki Yamada, Morihiro Saito, Chihiro Yodoya, Akika Kamei, Masato Hirota, Toshio Takenaka, Akimasa Tasaka, Minora Inaba
    Pure Si thin flakes (Si Leaf Powder® (Si-LP)) of different thicknesses (50, 100, 200, 300 and 400 nm) were prepared, and their charge/discharge properties were investigated as anode materials for lithium ion batteries (LIBs). Thickness of the thin Si-LP (100 nm) changed reversibly during charging and discharging, while the expanded thickness upon charging was kept after fully discharged for the thick one (300 nm), indicating insufficient Li de-alloying at C/6 rate. The slower kinetics for the thicker Si-LPs was also confirmed by examination of the open circuit potential (OCP) and the rate capability. These suggested that Li atoms diffused easily within the thinner Si-LPs and the uniform Li distribution suppressed the physical stress due to the Li alloying and de-alloying, resulting a good cycleability. In addition, addition of vinylene carbonate (VC) in electrolyte reduced charge transfer resistance of the Li alloying/de-alloying reaction and much more improved the cycleability of Si-LPs. ©The Electrochemical Society., ECS Transactions, ECS Transactions, 4127 - 35, 01 Dec. 2012, English, 研究論文(国際会議プロシーディングス)
  • Electrolytic production of (CF3)3N from room-temperature molten fluoride of (CH3)3N · 3HF using LaNiO3coated Ni sheet anode
    N. Osawa, M. Saito, M. Inaba, A. Tasaka
    The LaNiO3coated Ni sheet anodes prepared by sol-gel coating method was developed to improve the Ni sheet anode for electrolytic synthesis of perfluorotrimethylamine, (CF3)3N, using the (CH3)3N·3HF melt as the electrolyte. The LaNiO3films may give the electric conductivity to the Ni sheet anode during electrolysis of the (CH3)3N·3HF melt. (CF3)3N was successfully obtained at a ratio of about 62 and 55% together with other partially fluorinated gaseous products. ©The Electrochemical Society., ECS Transactions, ECS Transactions, 4161 - 67, 01 Dec. 2012, English, 研究論文(国際会議プロシーディングス)
  • Influence of Li diffusion distance on the negative electrode properties of Si thin flakes for Li secondary batteries
    Morihiro Saito, Tomoyuki Yamada, Chihiro Yodoya, Akika Kamei, Masato Hirota, Toshio Takenaka, Akimasa Tasaka, Minoru Inaba
    Pure Si thin flakes (Si Leaf Powder® (Si-LP)) of different thicknesses (50, 100, 200, 300 and 400 nm) were prepared, and their charge/discharge properties were investigated as negative electrode materials for lithium ion batteries (LIBs). High reversible capacity (2200-2500 mAh g - 1) and good capacity retention were obtained for thinner Si-LPs (50-200 nm), while thicker samples (300 and 400 nm) exhibited rapid capacity fade upon cycling at C/6. For the thinner flakes, agglomeration and large cracks were confirmed on the composite electrodes, but no pulverization of the flakes was observed. These data suggested that Li atoms diffused easily within the thinner Si-LPs and the uniformity of Li distribution suppressed the localized physical stress that caused by alloying and de-alloying. In addition, the addition of vinylene carbonate (VC) in the electrolyte was found to be quite effective for improving not only the cycleability, but also the rate-capability. The best performance was obtained for Si-LP (100 nm), which exhibited a superior cycleability (ca. 2300 mAh g - 1 at C/6 after 50 cycles) and a high rate capability (ca. 1400 mAh g - 1 at 12 C rate). © 2011 Elsevier B.V., Solid State Ionics, Solid State Ionics, 225506 - 509, 04 Oct. 2012
  • Carbon coating of Si thin flakes and negative electrode properties in lithium-ion batteries
    Takashi Okubo, Tomoyuki Yamada, Morihiro Saito, Chihiro Yodoya, Akika Kamei, Masato Hirota, Toshio Takenaka, Akimasa Tasaka, Minoru Inaba
    To reduce the high irreversible capacity (Qirr) of Si thin flake (Si-LP) negative electrode, carbon-coated Si-LPs were prepared using citric acid as a precursor and their charge/discharge properties were investigated as negative electrodes in lithium-ion batteries. The carbon-coated powder was homogeneously coated with a thin carbon layer (8-10 and 6-8 nm in thickness for Si-LPs heat-treated at 600 and 700°C, respectively, 14wt% for each). The irreversible capacity Qirr was successfully reduced to about a half (ca. 1100 mAhg-1) of that of the pristine Si-LP (2336 mAhg -1), though the cycleability was slightly deteriorated. The cycleability of Si-LP@Cs was significantly improved by the addition of 10 wt% VC in the electrolyte solution. Si-LP@C(700°C) kept high discharge capacities over 2000 mAhg-1 even after 50 cycles with a reduced Qirr of ca. 1300 mAhg-1 compared with the pristine Si-LP (ca. 2450 mAhg-1). © The Electrochemical Society of Japan., Electrochemistry, Electrochemistry, 80720 - 724, 01 Oct. 2012
  • Improvement of the reversible capacity of TiO 2(B) high potential negative electrode
    Morihiro Saito, Yosuke Murota, Mikihiro Takagi, Makoto Tajima, Takayuki Asao, Hidemi Inoue, Akimasa Tasaka, Minoru Inaba
    To improve the reversible capacity of TiO 2(B) negative electrode close to the theoretical one, some preparation and experimental conditions such as the precursor (Na 2Ti 3O 7, K 2Ti 4O 9 and Cs 2Ti 5O 11), the co-solvent in ethylene carbonate-based electrolyte solutions, and homogeneity of the composite electrode were optimized. TiO 2(B) powder samples were successfully prepared from K 2Ti 4O 9 and Cs 2Ti 5O 11 precursors, but not from Na 2Ti 3O 7. The sample prepared from Cs 2Ti 5O 11 gave a higher discharge capacity (185.5 mAh g -1) than that prepared from K 2Ti 4O 9 (156.6 mAh g -1). The reversible capacity of TiO 2(B) was significantly influenced by the kind of co-solvent in the electrolyte solutions. The presence of dimethyl carbonate (DMC) as a co-solvent drastically improved the capacity, and the highest discharge capacity of 235.3 mAh g -1 was obtained in 1 M LiPF 6 dissolved EC+DMC (1:2 by volume). Furthermore, improvement of the homogeneity of the composite electrode by premixing the TiO 2(B) and Ketjen Black conductor was effective to improve the discharge capacity. The optimized electrode gave an initial discharge capacity of 314.4 mAh g -1, which reached 93.9% of the theoretical capacity (335 mAh g -1). It also exhibited a good cycleability (287.9 mAh g -1 after 50 cycles) and a high rate capability (118.5 mAh g -1 at 10 C rate). © 2011 The Electrochemical Society., Journal of the Electrochemical Society, Journal of the Electrochemical Society, 159, 29 Feb. 2012
  • Si thin platelets as high-capacity negative electrode for Li-ion batteries
    Morihiro Saito, Kenta Nakai, Tomoyuki Yamada, Toshio Takenaka, Makoto Hirota, Akika Kamei, Akimasa Tasaka, Minoru Inaba
    Pure Si platelets and Ni or Cu layer-laminated Si platelets with difference thickness were prepared, and their charge/discharge properties were examined in 1 M LiClO 4 /EC + DEC (1:1 by volume) as alternative negative electrode materials to graphite for Li-ion batteries. The shape of thin platelets and lamination with Ni layer are significantly effective to improve the cycleability in Li-Si alloy system by relieving the stress during the alloying/de-alloying processes, reinforcing the mechanical strength and reducing the Li + ion diffusion length. Moreover, the first irreversible capacity is minimized by reduction of the amount of Ketjen Black (KB) in the composite electrode because of electrolyte decomposition on the surface of KB. Consequently, the Si/Ni/Si-LP30 (30/30/30 nm) composite electrode with 5 wt% KB also exhibits over 700 mAh g -1 even after 50 cycles in 1 M LiPF 6 /EC + DEC (1:1). © 2011 Elsevier B.V. All rights reserved., Journal of Power Sources, Journal of Power Sources, 1966637 - 6643, 15 Aug. 2011
  • Analysis of cationic structure in some room-temperature molten fluorides and dependence of their ionic conductivity and viscosity on hydrofluoric acid concentration
    Tomohiro Isogai, Takaaki Nakai, Hidemi Inoue, Kenta Nakanishi, Shinji Kohara, Morihiro Saito, Minoru Inaba, Minoru Inaba, Akimasa Tasaka, Akimasa Tasaka
    To understand the ionic and nonionic species in (CH3)4NF·mHF, (CH3)3N·mHF, (C2H5)4NF·mHF, and (C2H5)3N·mHF melts, the structures of these melts were investigated by infrared spectroscopy, NMR, and high-energy X-ray diffraction. Infrared spectra revealed that three kinds of fluorohydrogenate anions, (FH)nF-(n = 1, 2, and 3), and molecular hydrofluoric acid (HF) are present in every melt. Ionic conductivity and viscosity of these melts were measured and correlated with their cationic structure. The ionic conductivity of the R4N+-systems was higher than that of corresponding R3NH+-systems because a strong N-H⋯F(HF)ninteraction prevents the motion of R3NH+cations in the R3N·mHF melts. (CH3)4N+and (CH3)3NH+cations gave higher ionic conductivity than (C2H5)4N+and (C2H5)3NH+cations, respectively, because the ionic radii of former cations were smaller than those of latter. It was concluded that these effects on ionic conductivity can be explained by the cationic structure and the concentration of molecular HF in the melts. © 2011 American Chemical Society., Journal of Physical Chemistry B, Journal of Physical Chemistry B, 1159593 - 9603, 11 Aug. 2011, English, 研究論文(学術雑誌)
  • Performances of metal fluoride added carbon anodes with pre-electrolysis for electrolytic synthesis of NF3
    Tomohiro Isogai, Tomohiro Isogai, Kazuhiro Hirooka, Tetsuro Tojo, Hitoshi Takebayashi, Morihiro Saito, Minoru Inaba, Minoru Inaba, Akimasa Tasaka, Akimasa Tasaka
    Metal fluoride added carbon anodes treated by pre-electrolysis were investigated for electrolytic production of nitrogen trifluoride (NF3) in molten NH4F·KF·4HF at 100 °C. The conditions for pre-electrolysis were first optimized using a graphite sheet anode as a model anode. The formation of fluorine-graphite intercalation compounds (fluorine-GICs) with semi-covalent C-F bonds, (CxF)n, on the MgF2and CaF2added carbon anode surface was accelerated by pre-electrolysis at potentials less than 4.0 V. Critical current densities (CCD) on the MgF2added carbon anodes pre-electrolyzed under various conditions were determined, and the highest CCD was 290 mA cm-2obtained for that pre-electrolyzed at 3.5 V for 500 C cm-2. This anode was successfully used in the electrolysis at 100 mA cm-2for 290 h and the maximum NF3current efficiency was 55%. From these results, it was concluded that the metal fluoride added carbon anode treated by pre-electrolysis has a high potential for electrolytic production of NF3at higher current density. © 2010 Elsevier Ltd., Electrochimica Acta, Electrochimica Acta, 564425 - 4432, 30 Apr. 2011, English, 研究論文(学術雑誌)
  • New molten salt systems for high temperature molten salt batteries: Ternary and quaternary molten salt systems based on LiF-LiCl, LiF-LiBr, and LiCl-LiBr
    Syozo Fujiwara, Minoru Inaba, Akimasa Tasaka
    Using a new simulative technique developed by us, we systematically investigated new ternary or quaternary molten salt systems, which are based on LiF-LiCl, LiF-LiBr, and LiCl-LiBr binary systems, for use as electrolytes in thermal batteries, and evaluated their ionic conductivities and melting points experimentally. It was confirmed experimentally that LiF-LiBr-KF (melting point: 425 °C, ionic conductivity at 500 °C: 2.52 S cm-1), LiCl-LiBr-KF (405 °C, 2.56 S cm-1), LiCl-LiBr-NaF-KF (425 °C, 3.11 S cm-1), LiCl-LiBr-NaCl-KCl (420 °C, 2.73 S cm -1), and LiCl-LiBr-NaBr-KBr (420 °C, 2.76 S cm-1) meet our targets for both melting point (350-430 °C) and ionic conductivity (2.0 S cm-1 and higher at 500 °C). A single cell using the newly developed LiCl-LiBr-NaCl-KCl molten salt as an electrolyte was prepared, and the DC-IR of the cell decreased by 20% than that of a single cell using the conventional LiCl-KCl molten salt. It was therefore concluded that the use of new quaternary molten salt systems can improve the discharge rate-capability in practical battery applications because of their high ionic conductivities. © 2011 Published by Elsevier B.V., Journal of Power Sources, Journal of Power Sources, 1964012 - 4018, 15 Apr. 2011
  • Effect of CsF-concentration on electrolytic conductivity, viscosity and anodic reaction of nickel electrode in (CH3)3N-CsF-HF system at room temperature
    Akimasa Tasaka, Kenta Nakanishi, Noriaki Masuda, Takaaki Nakai, Koji Ikeda, Kunitaka Momota, Morihiro Saito, Minoru Inaba
    In order to increase the formation ratio of perfluorotrimethylamine, (CF3)3N, to overall anode gas in electrolytic production using Ni anode, mixed melts of (CH3)3N·mHF + CsF·2.3HF were used as electrolytes at room temperature. The ionic conductivity of the mixed melts decreased with an increase in the CsF concentration, whereas the viscosity of the mixed melts increased with increasing the CsF concentration. AC impedance and XRD analysis revealed that the presence of CsNi2F6 in the oxidized layer formed on the Ni anode after electrolysis. The gas evolved at the Ni anode was composed of (CF3)3N, (CF3)2CHF2N, CF3(CHF2)2N, (CHF2)3N, CF4, NF3, CHF3, C2HF5, and C2F6. The best ratio of (CF3)3N to the overall anode gas (52.11%) was obtained in the electrolyte of (CH 3)3N·5.0HF + 50 wt% CsF·2.3HF mixed melt at 20 mA cm-2. © 2011 Elsevier Ltd. All rights reserved., Electrochimica Acta, Electrochimica Acta, 564335 - 4343, 15 Apr. 2011
  • In situ scanning probe microscopy of interfacial phenomena in batteries
    Minoru Inaba, Soon Ki Jeong, Zempachi Ogumi
    Scanning probe microscopy (SPM) is a type of microscopy that generates images of surfaces using a probe that scans the specimen. The most important point is to use an SPM unit in an inert atmosphere where water and oxygen are strictly removed, because most of the active materials and their battery reactions are significantly affected. The authors recommend that the SPM unit be placed in an argon glove box with water and oxygen content less than 1 ppm. The cell for in situ SPM measurements is simple, and can be constructed with a commercially available highly purified electrolyte solution and lithium foil as counter and reference electrodes. Metals such as Sn and Si make alloys with lithium metal, and hence are expected as high capacity negative electrodes because their theoretical capacities are much higher than graphite. SPM will be used for the analysis of a variety of battery materials and interfacial reactions by many researchers in the near future., Electrochemical Society Interface, Electrochemical Society Interface, 2055 - 59, 01 Jan. 2011
  • Determination of surface compositions of Pt-Ru alloy thin films using Cu stripping voltammetry
    Hirohisa Yamada, Toru Ikeda, Daisuke Shimoda, Akimasa Tasaka, Minoru Inaba
    Pure Pt, Pure Ru, and Pt-Ru alloy thin films of different compositions (Ru:Pt = 0.5-2.0) were prepared by magnetron sputtering. These thin films were characterized by Cu stripping voltammetry at different deposition potentials. Furthermore, we developed a novel technique to determine the surface Ru/Pt ratio of Pt-Ru alloys using Cu stripping voltammetry. The Ru/Pt ratios calculated from Cu stripping data agreed well with those measured by EDX in the Ru/Pt range of 0.6 to 2.0., Electrochemistry, Electrochemistry, 79357 - 360, 01 Jan. 2011
  • Effects of carbon dioxide on the performance of anion-exchange membrane fuel cells
    Minoru Inaba, Yu Matsui, Morihiro Saito, Akimasa Tasaka, Kenji Fukuta, Shin Watanabe, Hiroyuki Yanagi
    The effects of CO2 on the performance of an anion-exchange membrane fuel cell were investigated using a three-electrode single cell equipped with a reference electrode. Though the membrane resistance decreased at high current densities in the presence of CO2 via the self-purging mechanism, the cell voltage was significantly lower than that for pure O 2 especially at low current densities even at a very low CO 2 concentration of 100 ppm. The overpotential at the cathode was hardly changed by the presence of CO2, while that at the anode significantly increased in the presence of CO2. It was concluded that carbonate/bicarbonate ions accumulated at the anode during operation, and reduces the ionic conductivity and the pH in the anode catalyst layer, which results in a high overpotential at the anode., Electrochemistry, Electrochemistry, 79322 - 325, 01 Jan. 2011
  • New molten salt systems for high-temperature molten salt batteries: LiF-LiCl-LiBr-based quaternary systems
    Syozo Fujiwara, Minoru Inaba, Akimasa Tasaka
    To develop novel multi-component molten salt systems more effectively, we developed a simulative technique using the CALPHAD (Calculation of Phase Diagram and Thermodynamics) method to estimate the ionic conductivity and the melting point. The validity of this new simulative technique was confirmed by comparing the simulated ionic conductivities and melting points of typical high-temperature molten salts, such as LiF-LiCl-LiBr, LiF-LiBr-KBr, LiCl-LiBr-KBr, and LiCl-LiBr-LiI, with those reported data in the literature or experimentally obtained. This simulative technique was used to develop new quaternary molten salt systems for use as electrolytes in high-temperature molten salt batteries (called thermal batteries). The targets of the ionic conductivity and the melting point were set at 2.0 S cm-1 and higher at 500 °C, and in the range of 350-430 °C, respectively, to replace the LiCl-KCl system (1.85 S cm-1 at 500 °C) within the conventional design of the heat generation system for thermal batteries. Using the simulative method, six kinds of novel quaternary systems, LiF-LiCl-LiBr-MX (M = Na and K; X = F, Cl, and Br), which contain neither environmentally instable anions such as iodides nor expensive cations such as Rb+ and Cs+, were proposed. Experimental results showed that the LiF-LiCl-LiBr-0.10NaX (X = Cl and Br) and LiF-LiCl-LiBr-0.10KX (X = F, Cl, and Br) systems meet our targets of both the ionic conductivity and the melting point. © 2010 Elsevier B.V., Journal of Power Sources, Journal of Power Sources, 1957691 - 7700, 15 Nov. 2010
  • Simultaneous measurement of the effective ionic conductivity and effective electronic conductivity in a porous electrode film impregnated with electrolyte
    Zyun Siroma, Jumpei Hagiwara, Kazuaki Yasuda, Minoru Inaba, Akimasa Tasaka
    A new method for the simultaneous measurement of the effective ionic conductivity and effective electronic conductivity in a porous sheet consisting of an electronic conductor and an ionic conductor (electrolyte) is proposed. In this method, two potentiostats and a voltage source are used, and these instruments are connected to the sample via two terminals made of the electronic conductor and two terminals made of the ionic conductor. The underlying principle of this technique does not include any assumption about charge-transfer resistance at the ionic conductor/electronic conductor interface, since the measurement is designed to let the potential difference at the interface be the OCP value at each point throughout the sample. The validity of this method was confirmed by measuring a pseudo-catalyst layer for a proton-exchange membrane fuel cell (PEMFC). The results revealed that the effective ionic and electronic conductivity depends on the relative humidity. © 2010 Elsevier B.V. All rights reserved., Journal of Electroanalytical Chemistry, Journal of Electroanalytical Chemistry, 64892 - 97, 01 Oct. 2010, English, 研究論文(学術雑誌)
  • Shape-Controlled Platinum Nanoparticles of Different Sizes and Their Electrochemical Properties
    Koichi Matsuzawa, Tomoko Fukushima, Minoru Inaba
    Platinum (Pt) nanoparticles with controlled shapes and sizes were prepared from a solution of K 2PtCl 4 in the presence of polyacrylic acid (PAA) as a capping reagent. The effect of temperature, pH, and PAA concentration on the shape, size, and stability of the nanoparticles were investigated. Cubic Pt nanoparticles of different sizes in the range of 4. 4-14 nm and cuboctahedral nanoparticles of an average size of 14 nm were obtained. The cubic and cuboctahedral Pt nanoparticles showed strong features of Pt {1 0 0} faces and Pt {1 0 0} and Pt {1 1 1} faces, respectively, on their cyclic voltammograms under argon atmosphere, respectively. Rotating ring disk electrode measurements in O 2-saturated H 2SO 4 solution revealed that the catalytic activity for oxygen reduction reaction (ORR) of cubic Pt nanoparticles (average size 10 nm) was higher than that of cuboctahedral Pt nanoparticles (average size 14 nm). The activity for ORR of both cubic and cuboctahedral Pt nanoparticles decreased slightly after polycrystallization by repeated potential cycling in the range of 0. 05 to 1. 4 V. © 2010 Springer., Electrocatalysis, Electrocatalysis, 1169 - 177, 08 Sep. 2010
  • Shape-controlled silicon particles for high-capacity negative electrode of Li-ion batteries
    Kenta Nakai, Ikuro Tsuchioka, Morihiro Saito, Akimasa Tasaka, Toshio Takenaka, Masato Hirota, Akika Kamei, Minoru Inaba
    Pure Si platelets (Si-LP, thickness: 100 nm) and Ni layer-laminated Si platelets with different thicknesses (Si/Ni/SiLP50 (50/50/50 nm) and Si/Ni/Si-LP30 (30/30/30 nm)) were prepared by a vapor deposition method, and their charge/discharge properties were investigated as alternative negative electrode materials to graphite for lithiumion batteries. The shape of thin platelet effectively relieved the stress during the alloying and de-alloying processes, and improved the charge/discharge cycleability as compared with a commercially available Si powder. In particular, the laminated platelet samples showed very good cycleability, probably because of a shorter diffusion length of Li+ ions in the Si layers and an improved mechanical strength by the presence of the Ni layer., Electrochemistry, Electrochemistry, 78438 - 441, 01 Jan. 2010
  • Irreversible capacity and lithium-ion insertion/extraction kinetics of a high potential negative electrode TiO2(B)
    Yosuke Murota, Yasuyuki Oba, Mikihiro Takagi, Takayuki Asao, Morihiro Saito, Akimasa Tasaka, Minoru Inaba
    Li+ion insertion/extraction properties of TiO2(B) powder, which was prepared from a K2Ti4O9precursor by ionexchange and dehydration, was investigated as a high-potential negative electrode. The irreversible capacity greatly decreased from 124 mAh g-1to ca. 40 mAh g-1when the lower potential limit was raised from 1.0 V to E ≥ 1.2 V, which indicated that the irreversible capacity mainly originated from surface reactions, such as solvent decomposition, at E ≤ 12 V in the first cycle. In galvanostatic intermittent titration tests, large polarization was observed at the beginning and the end of charging. This clearly indicated that a slow process is involved in the insertion reaction at the beginning and the end of charging, which causes solvent decomposition at potentials lower than 1.4 V. The reversible capacity was greatly improved to 246 and 276 mAh g-1at an elevated temperature of 60°C and at a lower rate of C/60, respectively. The TiO2(B) sample contained ca. 14 wt% of the anatase phase as an impurity, and a reduction of the anatase phase was found to be effective for an increase in reversible capacity at moderate charge/discharge rates., Electrochemistry, Electrochemistry, 78431 - 434, 01 Jan. 2010, English, 研究論文(国際会議プロシーディングス)
  • Rechargeable batteries as innovative energy storage devices
    Minoru Inaba
    Electrochemistry, Electrochemistry, 78318 , 01 Jan. 2010, English
  • Durability of electrocatalysts in polymer electrolyte fuel cells
    Minoru Inaba
    Durability of electrocatalysts in polymer electrolyte fuel cells has been a major critical issue for commercialization of electric vehicles and stationary cogeneration systems. Though various methods mitigation have been proposed and the durability of fuel cell stacks has been greatly improved, further improvement of durability is needed for use in automotive applications. Here degradation phenomena of electrocatalysts for the cathode and the anode in PEFCs are reviewed and the mechanisms for degradation are discussed. ©The Electrochemical Society., ECS Transactions, ECS Transactions, 25573 - 581, 01 Dec. 2009, English, 研究論文(国際会議プロシーディングス)
  • Chemical degradation of perfluorinated sulfonic acid membranes
    Minoru Inaba
    Chemical degradation of perfluorinated sulfonic acid (PFSA) membranes during operation is a serious problem to be overcome before commercialization of electric vehicles and stationary cogeneration systems based on polymer electrolyte fuel cells. In this chapter, the mechanism for peroxide/radical formation, which works as an active species for membrane degradation, in the cell is comprehensively introduced, including recent findings. Accelerated testing methodology and the chemistry of PFSA membrane degradation are also outlined to improve the durability of PFSA membranes in polymer electrolyte fuel cells. © 2009 Springer New York., Polymer Electrolyte Fuel Cell Durability, Polymer Electrolyte Fuel Cell Durability, 57 - 69, 01 Dec. 2009, English
  • Polymer electrolyte fuel cell durability
    Felix N. Büchi, Thomas J. Schmidt, Minoru Inaba
    A major part of the competitiveness gap of polymer electrolyte fuel cell (PEFC) technology in automotive and stationary co-generation applications is due lack of durability. This book analyzes the relevant degradation processes in PEFC on the level of components, cells and stacks, and applications. Prominent authors from the PEFC field describe and analyze in 23 chapters the relevant degradation mechanisms and mitigation strategies. © Springer Science+Business Media, LLC 2009. All rights reserved., Polymer Electrolyte Fuel Cell Durability, Polymer Electrolyte Fuel Cell Durability, 1 - 507, 01 Dec. 2009, English
  • New iodide-based molten salt systems for high temperature molten salt batteries
    Syozo Fujiwara, Fumio Kato, Syouichiro Watanabe, Minoru Inaba, Akimasa Tasaka
    Novel multi-component molten salt systems containing iodides, LiF-LiBr-LiI, LiF-NaBr-LiI, and LiF-LiCl-LiBr-LiI, were investigated for use as electrolytes in high temperature molten salt batteries to improve the discharge rate-capability. The iodide-based molten salts showed higher ionic conductivity (∼3 S cm-1at 500 °C) than conventional LiCl-KCl, and had low enough melting points (below 400 °C) that can be used in practical high temperature molten salt batteries. The iodide-based salts showed instability at temperatures higher than 280 °C in dried air. The decomposition mechanism of iodide-based molten salts was discussed, and it was found that elimination of oxygen from the environment is effective to stabilize the iodide-based molten salts at high temperatures. © 2009 Elsevier B.V. All rights reserved., Journal of Power Sources, Journal of Power Sources, 1941180 - 1183, 01 Dec. 2009, English, 研究論文(学術雑誌)
  • Effects of type of reactor, crystallinity of SiC, and N F3gas pressure on etching rate and smoothness of SiC surface using N F3gas plasma
    A. Tasaka, H. Yamada, T. Nonoyama, T. Kanatani, Y. Kotaka, T. Tojo, M. Inaba
    Polycrystalline β-SiC and single-crystalline 4H-SiC surfaces were etched by reactive ion etching (RIE) using N F3gas plasma. A smooth surface was obtained on the polycrystalline SiC after RIE at N F3gas pressures of 2 and 10 Pa for 10 min, and neither spikes nor pillars were formed on it. On the other hand, some pillars were formed on the single-crystalline SiC surface by RIE at N F3gas pressures of 2 and 10 Pa. Though the absence of carbon-rich regions and Si O;xon the outermost surface before etching was confirmed by x-ray photoelectron spectroscopy and Raman analysis, x-ray diffraction analysis revealed that graphite crystallites were present in the single-crystalline SiC bulk. It was concluded that the graphite crystallites acted as masks and the pillars grew up from the graphite crystallites in the single crystalline SiC during RIE. © 2009 American Vacuum Society., Journal of Vacuum Science and Technology A: Vacuum, Surfaces and Films, Journal of Vacuum Science and Technology A: Vacuum, Surfaces and Films, 271369 - 1376, 16 Nov. 2009, English, 研究論文(学術雑誌)
  • Preparation of core/shell and hollow nanostructures of cerium oxide by electrodeposition on a polystyrene sphere template
    Ippei Yamaguchi, Mitsuru Watanabe, Tsutomu Shinagawa, Masaya Chigane, Minoru Inaba, Akimasa Tasaka, Masanobu Izaki
    Core/shell nanostructures of polystyrene (PS)/CeO 2 have been prepared on conductive glass substrates by using a novel electrochemical route consisting of (i) the electrophoretic deposition of a PS sphere monolayer on the substrate and (ii) the following potentiostatic electrodeposition of CeO 2 on the PS sphere template in Ce(NO 3) 3 aqueous solutions. The structural morphologies of the deposit changed drastically depending on the Ce(NO 3) 3 concentration; i.e., spherical and needlelike shells were deposited. The deposit was formed only on the PS sphere surface because of an interaction between cationic cerium species and a sulfate group that was immobilized on the PS sphere surface. The spherical shell layer was assigned as CeO 2, and the needlelike shells were composed of Ce(OH) 3 needles formed on the CeO 2 layer surface, indicating that the deposit species changes from CeO 2 to Ce(OH) 3 during electrodeposition only in a 1 mM Ce 3+ solution. Deposition of Ce(OH) 3 would begin when electrogenerated hydrogen peroxide was consumed by decomposition under reductive conditions and could no longer oxidize Ce 3+ ions. The corresponding CeO 2 hollow shells were obtained by thermal elimination of the PS sphere core and transformation of Ce(OH) 3 into CeO 2 while keeping their original shapes. © 2009 American Chemical Society., ACS Applied Materials and Interfaces, ACS Applied Materials and Interfaces, 11070 - 1075, 27 May 2009
  • TiO2(B) as a promising high potential negative electrode for large-size lithium-ion batteries
    Minoru Inaba, Yasuyuki Oba, Fumiharu Niina, Yosuke Murota, Yasuyuki Ogino, Akimasa Tasaka, Ken Hirota
    Needle-like TiO2(B) powder was obtained from K2Ti4O9 precursor by ion exchange to protons, followed by dehydration. The charge and discharge characteristics of the TiO2(B) powder were investigated as a high potential negative electrode in lithium-ion batteries. It had a high discharge capacity of 200-250 mAh g-1 at around 1.6 V vs. Li/Li+, which was comparable with that of TiO2(B) nanowires and nanotubes prepared via a hydrothermal reaction in alkaline solution. It showed very good cycleability, and gave a discharge capacity of 170 mAh g-1 even in the 650th cycle. It also had a high rate capability, and gave a discharge capacity of 106 mAh g-1 even at 10 °C. In most of ethylene carbonate-based solutions, the TiO2(B) powder exhibited good charge and discharge characteristics. However, it showed a poor compatibility with LiBF4, propylene carbonate, and γ-butyrolactone. The TiO2(B) powder showed good cycle performance in the presence of a non-flammable additive, trimethyl phosphate, up to 20 vol.%, and a high tolerance to water up to 1000 ppm. It was also found that inexpensive Al foil can be used as a current collector of the TiO2(B) powder instead of Cu foil without sacrificing the performance. © 2008 Elsevier B.V. All rights reserved., Journal of Power Sources, Journal of Power Sources, 189580 - 584, 01 Apr. 2009
  • Electronic structures of partially fluorinated lithium manganese spinel oxides and their electrochemical properties
    Keisuke Matsumoto, Tomokazu Fukutsuka, Toyoki Okumura, Yoshiharu Uchimoto, Koji Amezawa, Minoru Inaba, Akimasa Tasaka
    Partially fluorinated lithium manganese spinel oxides (LiMn1.8Li0.1Ni0.1O4-xFx) were prepared by solid-state reaction. Relationship between the electronic structures of LiMn1.8Li0.1Ni0.1O4-xFx and their electrochemical properties were investigated. X-ray absorption near-edge structure (XANES) of Mn K-edge showed that the absorption edge shifted to lower energy with increasing F- content, which indicated decrease of the Mn average oxidation state. Discharge capacity at first cycle was increased by decrease of the Mn average oxidation state with increasing F- content. © 2008 Elsevier B.V. All rights reserved., Journal of Power Sources, Journal of Power Sources, 189599 - 601, 01 Apr. 2009, English, 研究論文(学術雑誌)
  • Carbon surface oxidation by short-term ozone treatment for modeling long-term degradation of fuel cell cathodes
    Jun Maruyama, Masatoshi Umemura, Minoru Inaba, Akimasa Tasaka, Ikuo Abe
    In regard to degradation phenomena in a polymer electrolyte fuel cell (PEFC), there is little information on voltage loss due to the excess accumulation of liquid water blocking pores for the gas supply in the cathode (flooding) observed in a long-term operation over 5000-10,000 h. In this study, modeling of this degradation phenomenon was attempted using ozone treatment of the cathode catalyst layer (CL). The hydrophilicity of the layer was increased by the treatment, which was attributed to oxidation of the carbon surface of the catalyst (Pt-loaded carbon black, PtC) exposed to the gas phase in the CL. The flooding was observed at the PEFC with the cathode CL formed using 10 wt % PtC and treated with ozone for 10 h, and the extent of the flooding was enlarged by the ozone treatment of 15 h. The flooding was caused by the 5 h ozone treatment when the Pt content was 20 or 50 wt %. These results indicated that modeling of the long-term degradation was achieved by the short-term ozone treatment, and that the excessive hydrophilicity of the carbon surface of PtC was one of the highly potent candidates for causes of the degradation. © 2009 The Electrochemical Society., Journal of the Electrochemical Society, Journal of the Electrochemical Society, 156, 09 Feb. 2009
  • Ionic conductivity and viscosity of low temperature molten fluorides containing HF
    Tomohiro Isogai, Takaaki Nakai, Kenta Nakanishi, Minoru Inaba, Akimasa Tasaka
    The effects of HF content on the ionic conductivity and the viscosity of low temperature molten fluorides, (CH3)4NF-·mHF, (CH3)3N-·mHF, KF-·mHF HF, and NH 4F-·mHF melts, were investigated. The ionic conductivity of the (CH3)3N-·mHF and (CH3) 4NF-·mHF melts increased, whereas their viscosity decreased with increasing the m value. The ionic conductivity and the viscosity of the (CH3)3N-·mHF melts were lower and higher, respectively, than those of the (CH3)4NF-·mHF melts at a given m value and a given temperature. The activation energy for ionic migration decreased with increasing the m value in both systems. Similar effects of the m value on the conductivity and viscosity were obtained for the KF-·mHF and NH4F-·mHF melts. The KF-·mHF melts exhibited lower conductivity and higher viscosity than the NH 4F-·mHF melts at a given m value and a given temperature. It was concluded that these effects of the HF content can be explained in terms of the concentration change of molecular HF and the resulting change in electrostatic cation-anion interactions., Electrochemistry, Electrochemistry, 77713 - 720, 01 Jan. 2009
  • Effects of temperature and relative humidity on Oxygen permeation in nation® and sulfonated poly(arylene ether sulfone)
    Y. Takamura, E. Nakashima, H. Yamada, A. Tasaka, M. Inaba
    Oxygen permeation in Nafion®117 and sulfonated poly(arylene ether sulfone) (BPSH-50) were investigated at different temperatures and relative humidities by a potential step method using a Pt microelectrode. The diffusion coefficient increased, while the solubility decreased with an increased in temperature and relative humidity for both samples. Consequently, the permeability increased with an increased in temperature and relative humidity for both samples. The permeability in BPSH-50 was approximately four times lower than that in Nafion®117, due to a smaller diffusion coefficient and a lower solubility in BPSH-50 than those in Nafion®l 17. Mass transport of oxygen in these membranes was correlated with microstructural changes of the membranes. © The Electrochemical Society., ECS Transactions, ECS Transactions, 16881 - 889, 01 Dec. 2008, English, 研究論文(国際会議プロシーディングス)
  • Electrolysis of (CF3)4NF· 5HF melt with boron-doped diamond anode
    Makoto Shizuno, Kenta Nakanishi, Minoru Inaba, Masaharu Uno, Yoshinori Nishiki, Tsuneto Furuta, Akimasa Tasaka
    Since a boron-doped diamond (BDD) electrode is able to be used as an anode in the (CH3)4NF·mHF melt, the performance of BDD anode for electrolytic production of perfluorotrimethylamine [(CF 3)3N] was investigated in the melt of (CH 3)4NF·5.0HF by galvanostatic electrolysis at 20, 40, 60 and 100 mA·cnf-2. The anode gas was analyzed quantatively by gas chromatography-mass spectroscopy. Also, the surface of BDD electrode before and after electrolysis was analyzed by XRD and Raman spectroscopy and was observed by SEM. The ratios of (CF3) 3N and (CF3)2CHF2N to overall anode gas increased with increasing the current density. This fact suggests that electrolytic fluorination may be promoted at higher current density. From the results of surface analyses, it is concluded that the electrolytic production of (CF3)3N from (CH3)4NF·5.0HF melt using a BDD anode is an appropriate process because the BDD film on the carbon substrate has a good electric conductivity during electrolysis. ©The Electrochemical Society., ECS Transactions, ECS Transactions, 161 - 6, 01 Dec. 2008, English, 研究論文(国際会議プロシーディングス)
  • Effect of electrolyte composition and anode material on current efficiency for NF3 formation in electrolytic synthesis using diamond anode
    Akira Nishida, Atsushi Kobayashi, Hiroyuki Omori, Minora Inaba, Masaharu Uno, Yoshinori Nishiki, Tsuneto Furatab, Akimasa Tasaka
    The current efficiency for NF3 formation was investigated using a Boron-Doped diamond (BDD) anode in the NH4F·mHF melts. The current efficiency for NF3 formation depended on both the current density and the NH4F-concentration in the melt and it trended to decrease at the higher current density. Its maximum value on the BDD anode in a NH4F·2.0HF melt was 72.4% at 40 mA cm-2 and that in a NH4F·1.7HF melt was 46.2% at 100 mA cm-2. Addition of nickel fluoride to the NH4F·mHF melt was effective for increasing the current efficiency for NF3 formation. This is because Ni2+ ion may be oxidized on the BDD anode to form highly oxidized nickel compounds such as NiF3 and/or Ni2F 5 on the anode and NiF63- and/or NiF 62- ions in the melt, which are strong fluorinating agents. The maximum current efficiency for NF3 formation on the BDD anode in a NH4F·2.0HF melt having nickel ion was 61.9% even at the current density of 1000 mA cm-2. ©The Electrochemical Society., ECS Transactions, ECS Transactions, 16469 - 477, 01 Dec. 2008, English, 研究論文(国際会議プロシーディングス)
  • Effect of CsF-concentration on electrolytic conductivity, viscosity and anodic reaction of nickel electrode in (CH3)3N-CsF-HF system at room temperature
    Akimasa Tasaka, Akimasa Tasaka, Kenta Nakanishi, Noriaki Masuda, Takaaki Nakai, Kunitaka Momota, Minora Inaba, Minora Inaba
    In order to improve the current efficiency for perfluorotrimethylamine, (CF3)3N, formation using Ni anode, mixed melts of (CH 3)3N·mHF + CsF·2.3HF were used as electrolytes at room temperature. The ionic conductivity of the mixed melts decreased with an increase in CsF concentration, whereas the viscosity of the mixed melts increased with increasing CsF concentration. XRD analysis revealed the presence of CsNi2F6 in the oxidized layer formed on the Ni anode after electrolysis. The gas evolved at the Ni anode was composed of (CF 3)3N, (CF3)2CHF2N, CF3(CHF2)2N, (CHF2)3N, CF4, NF3, CHF3, C2HF5, and C2F6. The best ratio of (CF3)3N to the total anode gas (52.11%) was obtained in the electrolyte of (CH 3)3N·5.0HF + 50 wt.% CsF·2.3HF mixed melt at 20 mA cm-2. ©The Electrochemical Society., ECS Transactions, ECS Transactions, 16517 - 527, 01 Dec. 2008, English, 研究論文(国際会議プロシーディングス)
  • Electrochemical AFM study of LiMn2O4thin film electrodes exposed to elevated temperatures
    Takayuki Doi, Minoru Inaba, Hiroshi Tsuchiya, Soon Ki Jeong, Yasutoshi Iriyama, Takeshi Abe, Zempachi Ogumi
    Surface morphology changes of LiMn2O4thin film positive electrodes in lithium-ion batteries after repeated potential cycling or storage at elevated temperatures were observed by in situ atomic force microscopy (AFM) to elucidate the origin of capacity fading of LiMn2O4. After repeated potential cycling in the overall potential range from 3.50 to 4.30 V at elevated temperatures, the entire thin film surface was covered with small round-shaped particles accompanied by capacity fading of the electrode, while no significant changes were observed at 25 °C. The discharge capacity decreased more significantly when cycled in the lower potential range (3.81-4.07 V) than when cycled in the higher potential range (4.04-4.30 V). After storage at elevated temperatures at a depth of discharge (DOD) of 75%, which is located in the lower potential range, similar surface morphology changes were observed. In addition, discharge capacity markedly decreased, and the crystallinity of the LiMn2O4thin film was lowered after storage. Hence, the observed changes in morphology at elevated temperatures are closely related to capacity fading of the LiMn2O4thin film. The loss of crystallinity was caused by the formation of small particles on the LiMn2O4surface, which would be accelerated on the LiMn2O4surface in contact with an electrolyte solution through some kind of dissolution/precipitation reaction. © 2008 Elsevier B.V. All rights reserved., Journal of Power Sources, Journal of Power Sources, 180539 - 545, 15 May 2008, English, 研究論文(学術雑誌)
  • Zinc oxide nano-cauliflower array with room temperature ultraviolet light emission
    Masanobu Izaki, Mitsuru Watanabe, Hiroki Aritomo, Ippei Yamaguchi, Shunsuke Asahina, Tsutomu Shinagawa, Masaya Chigane, Minora Inaba, Akimasa Tasaka
    A novel geometry of a ZnO nanocauliflower array has been fabricated by an electrochemical route of the electrophoresis deposition of anionic polystyrene spheres on a conductive glass substrate followed by the electrodeposition of ZnO in aqueous solutions. The structural and optical characteristics were investigated by using X-ray diffraction, field-emission scanning electron microscopy, and photoluminescence spectrum measurements. The ZnO nanocauliflower was constructed of a polystyrene sphere core and a shell of ZnO hexagonal columns radially grown from the sphere surface. The ZnO nanocauliflower array possessed a high quality that emits ultraviolet light at a photon energy of 3.3 eV at room temperature due to the recombination of bound excitons. © 2008 American Chemical Society., Crystal Growth and Design, Crystal Growth and Design, 81418 - 1421, 01 Apr. 2008
  • Impacts of air bleeding on membrane degradation in polymer electrolyte fuel cells
    Minoru Inaba, Masashi Sugishita, Junpei Wada, Koichi Matsuzawa, Hirohisa Yamada, Akimasa Tasaka
    A long-term accelerated test (4600 h) of a 25 cm2 single cell with excess air bleeding (5%) was carried out to investigate the effects of air bleeding on membrane degradation in polymer electrolyte fuel cells. The rate of membrane degradation was negligibly low (fluoride-ion release rate = 1.3 × 10-10 mol cm-2 h-1 in average) up to 2000 h. However, membrane degradation rate was gradually increased after 2000 h. The CO tolerance of the anode gradually dropped, which indicated that the anode catalyst was deteriorated during the test. The results of the rotating ring-disk electrode measurements revealed that deterioration of Pt-Ru/C catalyst by potential cycling greatly enhances H2O2 formation in oxygen reduction reaction in the anode potential range (∼0 V). Furthermore, membrane degradation rate of the MEA increased after the anode catalyst was forced to be deteriorated by potential cycling. It was concluded that excess air bleeding deteriorated the anode catalyst, which greatly enhanced H2O2 formation upon air bleeding and resulted in the increased membrane degradation rate after 2000 h. © 2007 Elsevier B.V. All rights reserved., Journal of Power Sources, Journal of Power Sources, 178699 - 705, 01 Apr. 2008
  • Direct electrodeposition of 1.46 eV bandgap silver(I) oxide semiconductor films by electrogenerated acid
    Yuya Ida, Seiji Watase, Tsutomu Shinagawa, Mitsuru Watanabe, Masaya Chigane, Minoru Inaba, Akimasa Tasaka, Masanobu Izaki
    A direct electrodeposition of 1.46 eV bandgap Silver(I) oxide semiconductor AgO2 films by oxides synthesis induced electrogenerated acid was reported. The thermodynamically stable region of dissolving silver(I) species is expanded to the alkaline region by forming ammonia silver complex ion. The application of constant current density of 10.0 mA cm-1 anodically to a F:SnO2-coated glass substrate results in the evolution of O 2gas accompanied by the formation of dark-gray deposit on the substrate. Surface and cross-sectional images of the AgO2 electrodeposited are seen to be continuous and well-faceted over the entire substrate. The anodic electrodeposition of AgO2 from the ammonical electrolyte are explained by the deposition mechanism of bulk of solution and vicinity of electrode., Chemistry of Materials, Chemistry of Materials, 201254 - 1256, 26 Feb. 2008
  • Interfacial reactions between graphite electrodes and propylene carbonate-based solutions: Electrolyte-concentration dependence of electrochemical lithium intercalation reaction
    Soon Ki Jeong, Minoru Inaba, Yasutoshi Iriyama, Takeshi Abe, Zempachi Ogumi
    This study examines the electrochemical reactions occurring at graphite negative electrodes of lithium-ion batteries in a propylene carbonate (PC) electrolyte that contains different concentrations of lithium salts such as, LiClO4, LiPF6 or LiN(SO2C2F5)2. The electrode reactions are significantly affected by the electrolyte concentration. In concentrated solutions, lithium ions are reversibly intercalated within the graphite to form stage 1 lithium-graphite intercalation compounds (Li-GICs), regardless of the lithium salt used. On the other hand, electrolyte decomposition and exfoliation of the graphene layers occur continuously in the low-concentration range. In situ analysis with atomic force microscopy reveals that a thin film (thickness of ∼8 nm) forms on the graphite surface in a concentrated solution, e.g., 3.27 mol kg-1 LiN(SO2C2F5)2/PC, after the first potential cycle between 2.9 and 0 V versus Li+/Li. There is no evidence of the co-intercalation of solvent molecules in the concentrated solution. © 2007., Journal of Power Sources, Journal of Power Sources, 175540 - 546, 03 Jan. 2008
  • Electrochemical STM observation of Li1+x Mn2-x O4 thin films prepared by pulsed laser deposition
    Takayuki Doi, Minoru Inaba, Yasutoshi Iriyama, Takeshi Abe, Zempachi Ogumi
    Spinel Li1+x Mn2-x O4 (x=0.01 and 0.03) thin films were prepared by pulsed laser deposition (PLD). The LiMn ratio of Li1+x Mn2-x O4 thin films were controlled by the energy fluence of the laser beam in the PLD method. Changes in surface morphology of the thin films after potential cycling in different potential ranges were observed in 1 mol dm-3 LiClO4 /propylene carbonate by electrochemical scanning tunnel microscopy (STM). The discharge capacities of the nearly stoichiometric Li1.01 Mn1.99 O4 electrode faded rapidly upon charge/discharge cycling in a higher potential region (4.04-4.25 V). After repeated cycling in the higher potential region, smaller round-shaped particles of around 100 nm in diameter were newly formed on the electrode, and the entire surface was covered with them. These small particles were likely to be newly formed from the electrolyte solution through dissolution/precipitation reactions. Capacity-fading with repeated cycling was suppressed for the lithium-ion excess Li1.03 Mn1.97 O4 thin film electrode compared to Li1.01 Mn1.99 O4. In addition, no small, round-shaped particles appeared on Li1.03 Mn1.97 O4 even after the 75th cycle. Based on these results, it was concluded that the observed changes in morphology in the higher potential region are closely related to the observed capacity-fading of the nearly stoichiometric Li1.01 Mn1.99 O4. © 2007 The Electrochemical Society., Journal of the Electrochemical Society, Journal of the Electrochemical Society, 155, 01 Jan. 2008
  • Preparation of lithium manganese oxide fine particles by spray pyrolysis and their electrochemical properties
    Y. Iriyama, Y. Tachibana, R. Sasasoka, N. Kuwata, T. Abe, M. Inaba, A. Tasaka, K. Kikuchi, J. Kawamura, Z. Ogumi
    Highly crystalline nano-sized lithium manganese oxide particles were fabricated by spray pyrolysis. The resultant particles had well-developed facet planes in a transmission electron microscopy (TEM) image and electron diffraction pattern from a single particle also showed clear diffraction spots, indicating that the prepared particles were highly crystalline. The mean crystallite size estimated from X-ray diffraction peaks was ca. 18 nm, which was in good agreement with the diameter of the particles observed in the TEM image. These particles were gathered on platinum mesh and their electrochemical properties were investigated. The mean crystallite size increased with an increase in annealing temperature, which influenced the electrochemical lithium insertion/extraction properties of the particles. In particular, samples annealed at 773 K showed different kinds of lithium extraction/insertion properties in the cyclic voltammogram (CV), and only a couple of broad redox peaks were observed at around 0.8 V (versus Ag/AgCl) between 0.4 and 1.0 V. It is suggested that lithium distribute randomly in the sample annealed at 773 K sample due to the effects of grain boundaries, which resulted in different kinds of phase transition reactions. © 2007 Elsevier B.V. All rights reserved., Journal of Power Sources, Journal of Power Sources, 1741057 - 1062, 06 Dec. 2007
  • Stability of Pt-Ru/C catalysts: Effect of Ru content
    H. Yamada, D. Shimoda, K. Matsuzawa, K. Matsuzawa, A. Tasaka, M. Inaba
    Stability of four kinds of commercially available Pt-Ru/C (Pt:Ru = 1:1 for Samples A1, B1, and C1, and Pt:Ru = 1:2 for Sample B2) anode catalysts was investigated in 0.5 M H2SO4 by potential cycling. When the upper limit was set at potentials higher than 0.4 V, all Pt-Ru(1:1)/C samples were unstable and Ru concentration on the surface decreased during potential cycling tests. The degradation rate increased with increasing the upper potential limit. On the other hand, Samples A1 and B1 showed different tendencies in stability in the potential range of 0.05 to 0.2 V, depending on the crystallinity and the surface state (e.g. the presence of RuOx). Sample B2 (Pt:Ru = 1:2) had a higher stability than Sample B1 (Pt:Ru = 1:1) at high potentials > 0.4 V. On the contrary, the former had an inferior stability in the potential range of 0.05 to 0.2 V. © The Electrochemical Society., ECS Transactions, ECS Transactions, 11325 - 334, 01 Dec. 2007, English, 研究論文(国際会議プロシーディングス)
  • Measurment and thermodynamic analysis of NiF2/Ni electrode potential in a dehydrated melt of NH4F·2HF
    Akimasa Tasaka, Eiki Morimoto, Atsuhisa Mimoto, Akitoshi Inoue, Minoro Inaba
    A Ni reference electrode was prepared and its potential was also determined in a NH4F·2HF melt at 100°C The value of potential on the Ni electrode was unstable for 30 days. On the other hand, potentials on Ni electrodes treated with anodic oxidation at 10 mA/cm2for 3 days and thermal fluorination with NF3under 1 atm at 300°C for 1 hour became stable after shorter time. The former was 0.075 V and the latter was 0.072 V against hydrogen evolution potential (V vs. H2). The value of potential was almost the same in every measurement. SEM observation and XPS analysis revealed that both pre-treated Ni electrodes were covered with the dense layer composed of NiF2with a small amount of nickel oxide and/or nickel oxyfluoride. The potential of the NiF2/Ni electrode at 100°C calculated from the thermodynamic data is -0.178 V vs. H2. This value of potential was different from the observed one. On the other hand, the potential of the NiO/Ni electrode calculated from thermodynamic data is 0.164 V vs. H2. AS the observed value of potential on the Ni electrode is between both potentials of the NiF2/Ni and the NiO/Ni electrodes, its potential may be determined by nickel oxyfluoride, NiOxFy, in the surface layer of the Ni electrode. Therefore, it is concluded that a Ni electrode covered with the oxidized layer mainly composed of NiF2is useful as a reference electrode for electrochemical measurement and electrolytic production of NF3using a nickel anode. copyright The Electrochemical Society., ECS Transactions, ECS Transactions, 3529 - 542, 01 Dec. 2007, English, 研究論文(国際会議プロシーディングス)
  • Stability and thermodynamic analysis of Pt and Ni Ox Fy Ni reference electrodes in a dehydrated melt of NH4F-2HF
    Akimasa Tasaka, Eiki Morimoto, Atsuhisa Mimoto, Akitoshi Inoue, Minoru Inaba
    The stability of platinum and nickel (bare and fluorinated) electrodes was investigated for use as contamination-free reference electrodes in electrolytic production of N F3 using Ni as an anode in N H4 F2HF melt. Though the platinum reference electrode showed stable potentials, thermodynamic analysis revealed that it is inappropriate as a reference electrode in long-term electrolysis using nickel anode because the potential depends on the concentration ratio of Ni3+ Ni2+. The stability of the bare nickel electrode was poor; however, an anodically and a thermally fluorinated nickel electrode showed excellent stability at 0.073±0.001 V at 373 K with good reproducibility. It is therefore concluded that the fluorinated nickel electrodes are useful as reference electrodes for electrolytic production of N F3 using Ni as an anode in the N H4 F2HF melt. The equilibrium potential (0.073±0.001 V) obtained experimentally did not agree with the theoretically calculated potentials of Ni F2 Ni (-0.178 V) nor NiONi (0.164 V) at 373 K, and it was speculated that the potential might be determined by nickel oxyfluoride, Ni Ox Fy, formed on the surface of nickel electrode. © 2007 The Electrochemical Society., Journal of the Electrochemical Society, Journal of the Electrochemical Society, 154, 05 Oct. 2007
  • Scientific aspects of polymer electrolyte fuel cell durability and degradation
    Rod Borup, Jeremy Meyers, Bryan Pivovar, Yu Seung Kim, Rangachary Mukundan, Nancy Garland, Deborah Myers, Mahlon Wilson, Fernando Garzon, David Wood, Piotr Zelenay, Karren More, Ken Stroh, Tom Zawodzinski, James Boncella, James E. McGrath, Minoru Inaba, Kenji Miyatake, Michio Hori, Kenichiro Ota, Zempachi Ogumi, Seizo Miyata, Atsushi Nishikata, Zyun Siroma, Yoshiharu Uchimoto, Kazuaki Yasuda, Ken Ichi Kimijima, Norio Iwashita
    This review article discusses one of the major remaining barriers to commercialization of fuel cells, namely durability. The correlation of durability with cost cannot be overlooked in developing fuel cell systems, as the two are interrelated in materials. In this review, we present some of the targets for PEM fuel cell systems as set by the U.S. DOE (Department of Energy) and Japanese NEDO (New Energy & Industrial Technology Development Organization). We discuss durability testing and effects that operating conditions have on fuel cell durability. Then we cover the internal component durability of fuel cells, considering the polymer-electrolyte membrane, the electrocatalyst and electrocatalyst support, and the gas diffusion media. As PEM fuel cell technology has advanced in terms of performance and cost, more emphasis has recently been put on durability, which is hopefully one of the final steps on the road to commercialization. © 2007 American Chemical Society., Chemical Reviews, Chemical Reviews, 1073904 - 3951, 01 Oct. 2007
  • Stability of platinum particles on a carbon substrate investigated by atomic force microscopy and scanning electron microscopy
    Zyun Siroma, Kenta Ishii, Kazuaki Yasuda, Minoru Inaba, Akimasa Tasaka
    To investigate the stability of platinum particles, a flat carbon substrate coated with platinum nano-particles was made as a model of PEMFC cathode catalyst. Changes of the platinum particles caused by potential retention in acid solution were observed by FE-SEM. Stability of the carbon substrate without platinum was also observed by AFM. The position of the AFM and FE-SEM observation before and after each potential retention was identical so that morphological change could be traced like in situ experiments. Behaviors of each particle, i.e. disappearance, migration and aggregation, was observed after potential retentions. Statistical analysis of the images revealed that small platinum particles on the model electrode decreased in number, especially at high potentials and under an oxygen atmosphere. © 2007 Elsevier B.V. All rights reserved., Journal of Power Sources, Journal of Power Sources, 171524 - 529, 27 Sep. 2007
  • Electrochemically constructed p-Cu2O/n-ZnO heterojunction diode for photovoltaic device
    Masanobu Izaki, Tsutomu Shinagawa, Ko Taro Mizuno, Yuya Ida, Minoru Inaba, Akimasa Tasaka
    Polycrystalline n-ZnO/p-Cu2O heterojunctions have been fabricated by low-temperature eletrodepositions of ZnO and Cu2O layers in aqueous solutions. The condition for forming the Cu2O layer significantly reflected the electrical rectification characteristic and the photovoltaic performance, and the heterojunction fabricated under optimized conditions showed an excellent electrical rectification characteristic and a photovoltaic performance of 1.28% in conversion efficiency under an AM 1.5 illumination. © 2007 IOP Publishing Ltd., Journal of Physics D: Applied Physics, Journal of Physics D: Applied Physics, 403326 - 3329, 07 Jun. 2007, English, 研究論文(学術雑誌)
  • Effect of oxygen concentration on the spike formation during reactive ion etching of SiC using the mixed gas plasma of N F3 and O2
    A. Tasaka, E. Watanabe, T. Kai, W. Shimizu, T. Kanatani, M. Inaba, T. Tojo, M. Tanaka, T. Abe, Z. Ogumi
    Reactive ion etching (RIE) of poly- Β-SiC was investigated in the N F3 O2 mixture gas plasma. The addition of 10% oxygen concentration to the N F3 plasma increased the etching rate to ∼80 nmmin at a total pressure of 10 Pa and 997 nmmin at a total pressure of 20 Pa. The ratio of increase in etching rate against that in the pure N F3 plasma was ∼43%. RIE for longer than 30 min in the 90% N F3 and 10% O2 mixture gas plasma gave a much smoother surface than that etched in the pure N F3 plasma. However, the further addition of O2 decreased the etching rate. Optical-emission spectra indicated the presence of an oxygen radical, in addition to fluorine radical and molecular nitrogen cations, in the N F3 O2 mixture gas plasma. X-ray photoemission spectroscopy analysis of the etched samples revealed that the Si O2 layer was formed on the surface at the higher O2 concentration. The role of oxygen in the N F3 O2 mixture gas plasma was elucidated. Scanning electron microscopy observation revealed that many thornlike substances, i.e., spikes, were formed on the SiC surface during RIE at the total pressure of 10 Pa. Images of the cross section of spike formed during RIE at the total pressure of 2 Pa also indicated that the sputtered aluminum particle from a mask may be preferentially deposited on the top of carbon-rich island formed on the SiC surface and act as a micromask together with carbon on the carbon-rich island to form a thornlike spike. An etching model of the SiC surface and the mechanism on formation and growth of the spike on the SiC surface in the N F3 O2 mixture gas plasma are proposed. © 2007 American Vacuum Society., Journal of Vacuum Science and Technology A: Vacuum, Surfaces and Films, Journal of Vacuum Science and Technology A: Vacuum, Surfaces and Films, 25391 - 400, 21 May 2007
  • Meniscus formation and hydrogen oxidation on partially immersed Pt-carbon electrode
    Taro Kinumoto, Yoshiharu Uchimoto, Xiaoming Xiao, Katsumi Katakura, Kenji Kikuchi, Yasutoshi Iriyama, Takeshi Abe, Minoru Inaba, Zempachi Ogumi
    Meniscus formation and hydrogen oxidation on partially immersed Nafion® coated and uncoated electrodes were investigated as a model of the reaction sites in polymer electrolyte fuel cells. Hydrogen oxidation current was measured at 0.4 V with raising the electrode, and simultaneously the optical microscope observation was carried out. The intrinsic meniscus developed from the boundary between Nafion®-coated (Pt-loaded) and the uncoated parts. A liquid thin film, which would have sub-micron order thickness, was observed above the intrinsic meniscus on the uncoated electrode under hydrogen atmosphere after development of the intrinsic meniscus was terminated. At the same time, hydrogen oxidation current was further increased. Therefore, the liquid thin film behaved as an effective supermeniscus on the uncoated electrode. On Nafion®-coated electrode, hydrogen oxidation current was small in the intrinsic meniscus region; however, it became larger with an increase in the exposed area of Nafion®-coated part to the gas phase. This fact showed that hydrogen oxidation reaction occurred mainly in the exposed Nafion®-coated part. The current distribution in the supermeniscus region was discussed, and it was found that the effective area is controlled by the ohmic drop in the Nafion® coating., Electrochemistry, Electrochemistry, 75248 - 257, 01 Jan. 2007
  • Membrane degradation in polymer electrolyte fuel cells under low humidification conditions
    Minoru Inaba, Hirohisa Yamada, Ryota Umebayashi, Masashi Sugishita, Akimasa Tasaka
    A durability test of a PEFC single cell using perfluorinated ionomer membrane as an electrolyte was carried out at 80 °C under low humidification. The observed voltage drop under low humidification was mostly reversible up to 5200 h. However, hydrogen crossover increased with time and fluoride-ion was continuously detected in drain water, which indicated that membrane degradation proceeded steadily during the test under low humidification. Fluoride-ion release rate decreased with increasing current density, which suggested that hydrogen peroxide was formed at the anode catalyst layer upon direct combustion of hydrogen with crossover oxygen. Drain water analysis revealed that large amounts of sulfate ions and Fe(II or III) ions were released in addition to fluoride ions when the cell was temporarily operated under full humidification. From this fact, it was concluded that accumulation of impurities and hydrogen peroxide under low humidification is a reason why low humidification enhances membrane degradation., Electrochemistry, Electrochemistry, 75207 - 212, 01 Jan. 2007
  • Electrochemical corrosion of carbon materials in an aqueous acid solution
    Zyun Siroma, Masatoshi Tanaka, Kazuaki Yasuda, Kazumi Tanimoto, Minoru Inaba, Akimasa Tasaka
    In this fundamental study on corrosion of the carbon catalyst support in a PEMFC cathode, corrosion rates of electrodes made of carbon powder were investigated by measuring CO2 generation. The corrosion rate was affected by not only the retention potential but also by the presence of dissolved oxygen in the electrolyte. The corrosion rate showed two stages; initial corrosion was observed for several hours, and was followed by steady-state corrosion. Even in this latter stage, change to a lower potential induced a peak in the corrosion rate that exceeded the previous steady value just after the potential was restored. Corrosion was also accelerated by platinum catalyst., Electrochemistry, Electrochemistry, 75258 - 260, 01 Jan. 2007
  • Controlled growth and shape formation of platinum nanoparticles and their electrochemical properties
    Minoru Inaba, Miwa Ando, Aoi Hatanaka, Akihiro Nomoto, Koichi Matsuzawa, Akimasa Tasaka, Taro Kinumoto, Yasutoshi Iriyama, Zempachi Ogumi
    Cubic Pt nanoparticles were prepared from a solution of K2PtCl4 containing sodium polyacrylate as a capping reagent. The effects of the Pt/polymer molar ratio, the average molecular weight (Mw) of the polymer, and reaction temperature on the shape and size were investigated. When the polymer of Mw = 5100 was added at a molar ratio of Pt/polymer = 1/12, cubic platinum nanoparticles of an average size of 10.3 nm were predominantly formed (ca. 50% in number) at 25 °C. The electron diffraction pattern of the cubic nanoparticles revealed that they are single crystals with Pt {1 0 0} faces on the surface. The cubic nanoparticles were electrochemically active, and showed strong features of Pt {1 0 0} faces on cyclic voltammogram under argon atmosphere. After repeated potential cycling in the range 0.05-1.4 V, the features of Pt {1 0 0} were gradually lost, and changed to those of polycrystalline Pt. Rotating ring disk electrode measurements in O2-saturated H2SO4 solution revealed that the cubic nanoparticles had a high catalytic activity for oxygen reduction reaction (ORR). After polycrystallization by repeated potential cycling, the activity for ORR and hydrogen peroxide formation decreased slightly, which were attributed to the surface structural change from Pt {1 0 0} to polycrystalline. © 2006 Elsevier Ltd. All rights reserved., Electrochimica Acta, Electrochimica Acta, 521632 - 1638, 01 Dec. 2006
  • Anodic behavior of each component in a few nickel-metal composites and effect of added metal in composites on electrolytic production of NF3
    Sojiro Kon, Atsuhisa Mimoto, Atsuhisa Mimoto, Tsuyoshi Maeda, Minoru Inaba, Akimasa Tasaka, Akimasa Tasaka
    The nickel-metal composites such as Ni-Co, Ni-Mn, Ni-Ag, and Ni-Si were prepared by Hot Isostatic Pressing (HIP). The ratios of each metal in the mixture were 5 and 10 mol%. These materials were employed as the anode for electrolytic production of NF3. The current efficiencies for NF3formation on the Ni-Co, the Ni-Mn, the Ni-Ag, and the Ni-Si composite anodes were 42-38%, 52-40%, 52-47%, and 41%, respectively, and were small compared with those on the Ni sheet and the HIPed Ni anodes. On the other hand, the current losses caused by anodic dissolution (Qa/Qt) of the Ni-Co, the Ni-Mn, the Ni-Ag, and the Ni-Si composites were 7.95-4.42%, 6.40-7.02%, 5.60-6.30%, and 0.18%, respectively. Those of the Ni-Co, the Ni-Mn, and the Ni-Ag were large compared with those of the Ni anodes, whereas that of the Ni-Si composite was small compared with those of the Ni anodes. Therefore, it is concluded that only Si may prevent effectively the Ni-based composite from anodic dissolution., Proceedings - Electrochemical Society, Proceedings - Electrochemical Society, PV 2004-24528 - 536, 01 Dec. 2006
  • Measurement and thermodynamic analysis of reference electrode potentials in a few fluoride melts containing HF
    Atsuhisa Mimoto, Atsuhisa Mimoto, Tatsuo Miyazaki, Kazuchika Takao, Jumpei Yamashita, Shingo Nagamine, Minoru Inaba, Akimasa Tasaka, Akimasa Tasaka
    Potential on a copper reference electrode was measured at 100°C in each dehydrated melt of a KF·2HF, a NH4F·KF·4HF, and a NH4F·2HF against hydrogen evolution potential on a Pt rod by voltammetry with a sweep rate of 5 to 10 mV/s. Its value on a fresh copper reference electrode was unstable for first 30 days, whereas those on the anodically oxidized and the thermally fluorinated copper reference electrodes became stable for the shorter time. The stable value of potential on the thermally fluorinated copper reference electrode in a KF·2HF melt was 0.402 ± 0.003 V vs. H2. On the other hand, the theoretical value of potential calculated from thermodynamic data was 0.388 V. It has a little difference from observed value of it, and it may be caused by coexistence of CuF with CuF2 on the surface of a copper reference electrode. Although the theoretical potential on a Ni/NiF2 reference electrode was -0.248 V, the observed potential on a nickel reference electrode in a KF·2HF melt at 100°C was 0.096 ± 0.010 V vs. H2. It was different from the calculated potential of a Ni/NiF2 electrode. From these results, it is concluded that a new type of a copper electrode designated as Cu/CuF2-x (0<x<1) is useful as a reference electrode in the fluoride melts containing HF., Proceedings - Electrochemical Society, Proceedings - Electrochemical Society, PV 2004-24448 - 457, 01 Dec. 2006
  • Development of anode for electrolysis of (CH3)4NF-HF room-temperature molten fluoride
    Kazuki Onoda, Yoshio Shodai, Minoru Inaba, Akimasa Tasaka, Akimasa Tasaka
    The sol-gel LiNiO2 coated Ni and the sol-gel LaNiO3 coated Ni sheet anodes were developed to improve the Ni sheet anode for electrolytic synthesis of perfluorotrimethylamine, (CF3) 3N, using the (CH3)4NF-4HF melt as the electrolyte. The LiNiO2 and the LaNiO3 films may give the electric conductivity to the Ni sheet anode during electrolysis of the (CH 3)4NF-4HF melt. (CF3)3N was successfully obtained at a ratio of about 25% together with other partially fluorinated gaseous products., Proceedings - Electrochemical Society, Proceedings - Electrochemical Society, PV 2004-24537 - 546, 01 Dec. 2006
  • Photochemical construction of photovoltaic device composed of p-copper(I) oxide and n-zinc oxide
    Masanobu Izaki, Ko Taro Mizuno, Tsutomu Shinagawa, Minoru Inaba, Akimasa Tasaka
    The photochemical deposition of a p-type semiconducting copper(I) oxide (Cu 2O) layer by irradiating visible light in an aqueous solution containing a lactic acid and copper sulfate hydrate is presented. The p-Cu 2O layer was photochemically stacked on a chemically deposited n-type semiconducting ZnO layer/quartz glass substrate, and the photovoltaic device was constructed by forming a Au top electrode using a sputtering technique. The Au/p-Cu 2O/n-ZnO photovoltaic device showed an electrical rectification and the performance of 46 mV in open-circuit voltage (V∝) and 75 μA cm -2 in short-circuit current density (J sc) under an Air Mass 1.5 illumination. © 2006 The Electrochemical Society. All rights reserved., Journal of the Electrochemical Society, Journal of the Electrochemical Society, 153, 24 Oct. 2006
  • Measurement and thermodynamic analysis of M/MF n (M = Cu and Fe) electrode potentials in a few fluoride melts containing HF
    Atsuhisa Mimoto, Atsuhisa Mimoto, Tatsuo Miyazaki, Jumpei Yamashita, Shingo Nagamine, Minoru Inaba, Minoru Inaba, Akimasa Tasaka, Akimasa Tasaka, Akimasa Tasaka
    The potentials of copper and iron reference electrodes were measured in dehydrated melts of KF·2HF, NH 4F·KF·4HF, and NH 4F·2HF against the hydrogen evolution potential on Pt. The potential of a fresh copper reference electrode was unstable for the initial 30 days and then became constant, whereas those of an anodically oxidized and a thermally fluorinated copper reference electrode became stable in a shorter time. The potential of the thermally fluorinated copper reference electrode obtained experimentally in the KF·2HF melt was 0.402 ± 0.003 vs H 2 at 373 K, and the values for the three kinds of copper electrodes were close to one another. Theoretical electrode potentials calculated from thermodynamic data were 0.458 V for CuF 2/Cu and 0.307 V for CuF/Cu against HF/H 2. Because the observed potentials on the copper electrodes existed between these values, it may be caused by coexistence of CuF and CuF 2 on the surface. These copper electrodes, which should be denoted as CuF 2 + CuF/Cu or CuF x(1 < x < 2)/Cu, are useful as reference electrodes for electrochemical measurements in fluoride melts containing HF. The observed potentials of the fresh iron and the thermally fluorinated iron electrodes in the KF·2HF melt at 373 K were -0.1.47 ± 0.004 and -0.195 ± 0.003 V vs H 2, respectively, and were not in agreement with each other. Both iron electrodes after immersion in the melt were covered with the film composed of FeF 3 and FeF 2; however, the theoretical potentials [E(FeF 3/Fe) 373 = -0.355 V and E(FeF 2/Fe) 373 = -0.434 V vs E(HF/H 2) 373] were fairly lower than the experimentally observed values. These results suggested that the potential of iron electrodes was determined by other minor species on the surface and therefore, they cannot be used as reference electrodes in fluoride melts containing HF. © 2006 The Electrochemical Society. All rights reserved., Journal of the Electrochemical Society, Journal of the Electrochemical Society, 153D149 - D154, 24 Oct. 2006, English, 研究論文(学術雑誌)
  • Durability of perfluorinated ionomer membrane against hydrogen peroxide
    Taro Kinumoto, Minoru Inaba, Yoko Nakayama, Kazuhito Ogata, Ryota Umebayashi, Akimasa Tasaka, Yasutoshi Iriyama, Takeshi Abe, Zempachi Ogumi
    The durability of perfluorinated ionomer membrane, Nafion® 117, with various counter ions against hydrogen peroxide was investigated as a degradation factor of polymer electrolyte fuel cells (PEFC). After protonated Nafion membrane was tested in 30% H2O2 solution at 80 °C, small amounts of fluoride ion and sulfate ion, which are derived from the C{single bond}F bonds and the sulfonic acid groups, respectively, of the membrane, were detected in the solution. This fact indicated a potential vulnerability of the electrolyte membrane to H2O2 formed in the cell. The durability of Nafion with alkali and alkaline earth metal ions as counter ions were similar to that of protonated Nafion, and hence these cations do not have any specific effects on membrane degradation. In contrast, the presence of ferrous and cupric ions as counter ions significantly enhanced the decomposition rate of Nafion. This is due to the formation of strongly nucleophilic radicals such as hydroxy and hydroperoxy radicals upon decomposition of H2O2 at these catalyst ions. The results of FT-IR and 19F NMR measurements of deteriorated Fe2+-Nafion membrane revealed that both the main and side chains are decomposed at similar rates by radical attack, most probably because the decomposition proceeds through radical de-polymerization (so-called un-zippering mechanism). © 2005 Elsevier B.V. All rights reserved., Journal of Power Sources, Journal of Power Sources, 1581222 - 1228, 25 Aug. 2006
  • Gas crossover and membrane degradation in polymer electrolyte fuel cells
    Minoru Inaba, Taro Kinumoto, Masayuki Kiriake, Ryota Umebayashi, Akimasa Tasaka, Zempachi Ogumi
    Hydrogen gas crossover measurements and durability tests of a single cell under open-circuit conditions were carried out to investigate membrane degradation in polymer electrolyte fuel cells (PEFCs). The limiting current density for hydrogen crossover was approximately 0.8 mA cm-2 at 80 °C under atmospheric pressure, and gas crossover increased with an increase in cell temperature, humidity and hydrogen gas pressure. Under open-circuit conditions, the perfluorinated ionomer electrolyte membrane deteriorated significantly although no net electrochemical reactions took place at the cathode and anode. The mechanism for membrane degradation was discussed in terms of heat generation and hydrogen peroxide formation upon gas crossover and the resulting catalytic combustion, and it was concluded that the latter is the primary reason, in which hydrogen peroxide is most probably formed by gas crossover of oxygen and the resulting catalytic combustion at the anode side. In addition, it was inferred that reactive oxygen radicals (HO{radical dot} and HO2{radical dot}) were formed in the presence of minor impurities such as Fe2+ and Cu2+ ions, which could accelerate the membrane degradation. © 2006 Elsevier Ltd. All rights reserved., Electrochimica Acta, Electrochimica Acta, 515746 - 5753, 15 Aug. 2006
  • Porous metal tubular support for solid oxide fuel cell design
    Atsushi Mineshige, Atsushi Mineshige, Koji Fukushima, Sachio Okada, Takeyuki Kikuchi, Masafumi Kobune, Tetsuo Yazawa, Kenji Kikuchi, Minoru Inaba, Minoru Inaba, Zempachi Ogumi, Zempachi Ogumi
    A porous nickel tubular support of 1 mm diam was successfully created by heat-treating a commercial nickel tube. The resulting tube contained uniform pores, whose diameters ranged from 0.5 to 2.5 μm, depending on treatment temperature. The porous metal tube obtained is a promising candidate for support materials for microfuel cells or gas separation membranes because it has the necessary gas permeability and mechanical strength. It was also confirmed that a solid oxide fuel cell design employing the porous nickel tube as a supporting anode could be operated. © 2006 The Electrochemical Society., Electrochemical and Solid-State Letters, Electrochemical and Solid-State Letters, 9A427 - A429, 03 Aug. 2006, English, 研究論文(学術雑誌)
  • Anodic behavior of LiF-impregnated carbon and surface analysis of pristine carbon (FE-5) electrode polarized at various potentials in dehydrated melts of NH4F·KF-·mHF (m = 3 and 4)
    Akimasa Tasaka, Akimasa Tasaka, Masako Yamanaka, Eiki Morimoto, Shingo Nagamine, Atsuhisa Mimoto, Atsuhisa Mimoto, Tsuyoshi Fujikawa, Masaaki Abe, Atsushi Kobayashi, Hitoshi Takebayashi, Tetsuro Tojo, Minoru Inaba
    or electrolytic production of NF3in a dehydrated melt of NH4F·KF·4HF at 100° C, impregnation of LiF into the pores of carbon FE-5 anode enhanced the formation of fluorine-graphite intercalation compounds (GICs) having semi-covalent C-F bonds, (CxF)n, on the surface. The addition of LiF to a NH4F·KF·3HF melt also enhanced the formation of the GICs on a graphite sheet anode, and suppresses the occurrence of the anode effect. The minimum stage number of GICs formed on the graphite sheet anode in the NH4F·KF-3HF melt without LiF decreased in an increase in the charge passed during galvanostatic electrolysis at 10 mA cm-2. However, graphite fluoride, (CF)n, with covalent C-F bonds was formed on the outermost surface after 2500 C cm-2were passed without LiF. On the other hand, the addition of LiF to the melt further enhanced the formation of GICs with low stages (e.g. stage 3), and no graphite fluoride was formed up to 5000 C cm-2. It was found that pre-electrolysis at potentials lower than 3 V is effective for obtaining GICs with semi-covalent bonds. The critical current density after treated by pre-electrolysis of 500 C cm-2at 2.3 V, followed by further 500 C cm-2at 4.0 V, increased to 120 mA cm-2. © J. New. Mat. Electrochem. Systems., Journal of New Materials for Electrochemical Systems, Journal of New Materials for Electrochemical Systems, 9297 - 303, 01 Jul. 2006
  • Vapor-phase deposition for dense CeO2film growth on porous substrates
    Atsushi Mineshige, Atsushi Mineshige, Minoru Inaba, Minoru Inaba, Shinji Nakanishi, Shinji Nakanishi, Masafumi Kobune, Tetsuo Yazawa, Kenji Kikuchi, Zempachi Ogumi, Zempachi Ogumi
    Pure and Sm-doped CeO2 thin films were deposited on porous substrates by vapor-phase deposition, which is similar to the well-known electrochemical vapor deposition (EVD). By supplying metal chlorides (M Cl3, M; Ce and Sm) vapor and oxygen to a disk-shaped porous substrate from opposite directions, a dense oxide film was grown on the chloride side of the substrate with high homogeneity. The films deposited are suitable for the electrolytes in the ceria-based intermediate temperature solid oxide fuel cells (SOFCs). The growth kinetics of these films was also discussed along with an observed growth rate and theoretical analysis based on oxygen flux and oxygen potential gradient over the film and the substrate. It was found that the film growth was governed by rates of each competitive process: diffusion of oxygen molecules through substrate pores, oxygen reduction (O2 →2 O2-) at the film/substrate interface, and transport of electrochemical species (O2- and e-) through the growing dense film. © 2006 The Electrochemical Society., Journal of the Electrochemical Society, Journal of the Electrochemical Society, 153A975 - A981, 16 May 2006, English, 研究論文(学術雑誌)
  • Stability of Pt-catalyzed highly oriented pyrolytic graphite against hydrogen peroxide in acid solution
    Taro Kinumoto, Kenji Takai, Yasutoshi Iriyama, Takeshi Abe, Minoru Inaba, Zempachi Ogumi
    Aiming at clarifying the effects of hydrogen peroxide on the degradation of Pt/C catalyst in polymer electrolyte fuel cells (PEFCs), a model electrode for the Pt/C catalyst was prepared by electrodeposition of Pt on highly oriented pyrolytic graphite (HOPG) and its durability against hydrogen peroxide investigated. After storage in acidic 1.0 mol dm-3 H 2O2 solution at room temperature, many scars were formed by oxidative etching of HOPG and Pt-particle catalysts aggregated on the surface. In contrast, no surface change was observed without hydrogen peroxide. These results showed that hydrogen peroxide significantly deteriorates the Pt/HOPG electrode, and the active surface area of the Pt particles, which was determined by cyclic voltammetry, was reduced after immersion in the H 2O2 solution. The influence of applied potential was also investigated, and the deterioration of the electrode was accelerated at potentials both more positive and negative than open-circuit potential (ca. 0.8 V). Moreover, similar degradation phenomenon was observed when the potential was set at 0.1 V, at which a large amount of H2O2 is formed in oxygen reduction, in O2-saturated H2O2-free acid solution for 5 days. © 2005 The Electrochemical Society. All rights reserved., Journal of the Electrochemical Society, Journal of the Electrochemical Society, 153, 10 Apr. 2006
  • Preparation of lanthanum nickel oxide-coated Ni sheet anodes and their application to electrolytic production of (CF3)3N in (CH3)4NF·4.0HF melt
    Yoshio Shodai, Minoru Inaba, Kazuki Onoda, Akimasa Tasaka
    A new process for electrolytic production of a perfluorinated compound, (CF3)3N, using lanthanum nickel oxide-coated Ni sheet anode in the (CH3)4NF·4.0HF melt at room temperature, was developed. Thin films of the lanthanum nickel oxides were prepared on Ni sheets by sol-gel coating method using polyvinlylpyrrolidone (PVP). The main components of the thin films were La2O3, LaNiO3, and La2NiO4at 500, 750 and 1000°C, respectively. The anode performance in the (CH3)4NF·4.0HF melt depends greatly on the main component of the thin film, and the LaNiO3-coated Ni sheet anode gives the best anode performance. The potential of LaNiO3-coated Ni sheet anode remains constant at 5.9 V during electrolysis at 20 mA·cm-2in the ((CH3)4NF·4.0HF melt for 100 h. This is because LaNiO3and NiF3and/or Ni2F5, the latter of which was formed during electrolysis, in the film give a high electronic conductivity to the surface film during electrolysis. The maximum mole fraction of (CF3)3N (21.4%) was obtained at 20 mA·cm-2in (CH3)4NF·4.0HF melt using the LaNiO3-coated Ni sheet., Journal of Rare Earths, Journal of Rare Earths, 241 - 8, 01 Jan. 2006, English, 研究論文(学術雑誌)
  • Hydrogen peroxide formation as a degradation factor of polymer electrolyte fuel cells
    M. Inaba, H. Yamada, J. Tokunaga, K. Matsuzawa, A. Hatanaka, A. Tasaka
    20wt.% Pt/C catalyst was loaded at different densities (0.28-56.7 μgcarboncm-2) on glassy carbon (GC) disk electrode, and the effect of its agglomeration on hydrogen peroxide formation in oxygen reduction reaction (ORR) was investigated by the rotating ring-disk electrode technique. The formation of H2O2was enhanced with a reduction in agglomeration of Pt/C. Even in the operating potential range of PEFC cathodes (0.6-0.8 V), 20% of hydrogen peroxide was formed on Pt/C loaded at densities lower than 1.41 μgcarboncm-2on GC. These results revealed that series 2-electron reduction pathway, which is negligible on clean bulk Pt surface, exists on Pt nanoparticles supported on carbon. A large amount of H2O2formation was observed on Pt nanoparticles deposited not only on GC, but also on Au, which indicated that H2O2formation is not specific to Pt nanoparticles on carbon support. copyright The Electrochemical Society., ECS Transactions, ECS Transactions, 1315 - 322, 01 Dec. 2005, English, 研究論文(国際会議プロシーディングス)
  • Preparation of LiNiO 2-coated Ni sheet anodes and their application to electrolytic production of (CF 3) 3N in (CH 3) 4NF·4.0HF melt
    Yoshio Shodai, Akihiro Miyasaka, Kazuki Onoda, Hiroyuki Takei, Minoru Inaba, Akimasa Tasaka, Akimasa Tasaka
    LiNiO 2-coated Ni sheet modes were prepared by a sol-gel coating method and an atmospheric plasma-spraying technique, and were used in electrolytic production of (CF 3) 3N in a room-temperature molten fluoride (CH 3) 4NF·4.0HF. Li xNi 2-xO 2 thin films of x = 0.6-0.8 were successfully formed on Ni sheets by the sol-gel coating methods. The LiNiO 2 film prepared by atmospheric plasma-spraying technique had nearly the stoichiometric composition (x ≈ 1). These LiNiO 2-coated Ni sheet anodes gave lower anode potentials than pure Ni anode during electrolysis, because the presence of the LiNiO 2 layer suppressed the formation of NiF 2 insulation layer and the electronic conductivity of the former was much higher than that of the latter. The maximum mole fraction of (CF 3) 3N of 33% in the anode gas was obtained in electrolysis using the plasma-sprayed LiNiO 2-coated Ni sheet anode at 20 mA cm -2 in the (CH 3) 4NF·4.0HF melt. The anodic potential under the above conditions was 4.13 V after electrolysis for 100 h, which was the lowest of all experiments. Consequently, stoichiometric LiNiO 2-coated Ni sheet was the most preferable anode material for the electrolytic (CF 3) 3N synthesis in the (CH 3) 4NF·4.0HF melt. © 2005 The Electrochemical Society. All rights reserved., Journal of the Electrochemical Society, Journal of the Electrochemical Society, 152D220 - D226, 01 Dec. 2005, English, 研究論文(学術雑誌)
  • Suppression of an alkyl dicarbonate formation in li-ion cells
    Takeshi Sasaki, Takeshi Abe, Takeshi Abe, Yasutoshi Iriyama, Yasutoshi Iriyama, Minoru Inaba, Minoru Inaba, Minoru Inaba, Zempachi Ogumi, Zempachi Ogumi
    Two methods were developed to suppress the formation of alkyl dicarbonate in Li-ion cells. One is the addition of vinylene carbonate (VC), which is vulnerable to nucleophilic attack, into the electrolyte to trap alkoxide anions that promote an alkyl dicarbonate formation. The addition of VC into the electrolyte of practical graphite/LiCoO2prismatic cells effectively suppressed an alkyl dicarbonate formation and gave better cycle and power performance. The other method is a surface treatment of graphite to reduce the concentration of phenolic groups that were directly bonded to the graphite edge plane. The mild burn-off treatment successfully decreased the oxygen concentration on graphite surface and effectively suppressed an alkyl dicarbonate formation in the electrolyte. However, the irreversible capacity increased significantly, which was considered to be due to a change in the surface morphology of graphite by the burn-off treatment. © 2005 The Electrochemical Society. All rights reserved., Journal of the Electrochemical Society, Journal of the Electrochemical Society, 152A2046 - A2050, 11 Nov. 2005, English, 研究論文(学術雑誌)
  • Effect of an alkyl bicarbonate on Li-ion cell performance
    Takeshi Sasaki, Soon Ki Jeong, Takeshi Abe, Takeshi Abe, Yasutoshi Iriyama, Yasutoshi Iriyama, Minoru Inaba, Minoru Inaba, Zempachi Ogumi
    The effect of an alkyl dicarbonate, diethyl 2,5-dioxahexane dicarboxylate (DEDOHC, C2H5OCO2C2H4OCO2C2H5), which is formed by an ester exchange reaction in a mix solvent system of ethylene carbonate (EC) and diethyl carbonate (DEC), on the performance of graphite/LiCoO2lithium-ion cells was investigated. In the presence of 10 vol % DEDOHC in 1 M LiClO4/EC + DEC(1:1 v/v), discharge capacity decreased, in particular at a high charge/discharge rate. Capacity retention at a high charge/discharge rate also decreased during repeated charge and discharge cycles. These deteriorations in performance were attributed to an increase in cell impedance and deficiency of mobile lithium ion, which is caused by continuous consumption of lithium ion on graphite negative electrode. The results of half-cell tests revealed that the addition of DEDOHC causes serious degradation for the graphite half-cell. From ac impedance measurements it was found that surface film resistance on graphite electrode was fourfold higher in the solution containing DEDOHC, whereas charge-transfer resistance scarcely changed. Atomic force microscopy observation revealed the formation of dense and highly adhesive surface precipitate layer on graphite electrode in the presence of DEDOHC. Consequently, it was concluded that the increase in cell impedance, which leads to deterioration of charge and discharge performance, is mainly due to the increase in the resistance of the surface film formed from the reduction of DEDOHC on the graphite negative electrode. © 2005 The Electrochemical Society. All rights reserved., Journal of the Electrochemical Society, Journal of the Electrochemical Society, 152A1963 - A1968, 11 Nov. 2005, English, 研究論文(学術雑誌)
  • Imaging of highly oriented pyrolytic graphite corrosion accelerated by Pt particles
    Zyun Siroma, Kenta Ishii, Kazuaki Yasuda, Yoshinori Miyazaki, Minoru Inaba, Akimasa Tasaka
    Carbon corrosion that is presumed to occur at the proton exchange membrane fuel cell (PEMFC) cathode was visualized by atomic force microscopy (AFM) and field emission-scanning electron microscopy (FE-SEM) observations using a fundamental model electrode. Platinum nanoparticles were deposited on a highly oriented pyrolytic graphite (HOPG) substrate as a model cathode catalyst, and its stability in an acid solution at a fixed potential was investigated. The formation of blisters on the surface of the model electrode was observed by AFM after it was kept at 1.0 V vs. RHE, especially at and around the Pt particles. FE-SEM observations using a backscattered electron detector revealed that Pt particles remained unchanged at their original positions after the formation of blisters. © 2005 Elsevier B.V. All rights reserved., Electrochemistry Communications, Electrochemistry Communications, 71153 - 1156, 01 Nov. 2005
  • Formation mechanism of alkyl dicarbonates in Li-ion cells
    Takeshi Sasaki, Takeshi Abe, Yasutoshi Iriyama, Minoru Inaba, Zempachi Ogumi
    The mechanism for the formation of alkyl dicarbonates in Li-ion cells was investigated. Alkyl dicarbonates are formed in graphite half-cells at 1.5 V versus Li/Li+ or lower, and its concentration increased with lowering charging voltage. The results of the storage tests of solvents and electrolyte solutions in the presence of various kinds of lithium salts suggested that lithium alkoxides, which are formed by reductive decomposition of solvents, are the most probable active species for alkyl dicarbonate formation. The formation reaction proceeds through two-step nucleophilic reactions initiated by lithium alkoxides. At the first step, alkoxide anion attacks alkyl carbonate to generate an active nucleophile intermediate, which further attacks another alkyl carbonate to form alkyl dicarbonate at the second step. © 2005 Elsevier B.V. All rights reserved., Journal of Power Sources, Journal of Power Sources, 150208 - 215, 04 Oct. 2005
  • Irreversible capacity of electrodeposited Sn thin film anode
    Minoru Inaba, Takeshi Uno, Akimasa Tasaka
    Tin thin film anodes for lithium-ion cells were prepared by electroplating and morphology changes of the surface during alloying and de-alloying were investigated by in situ AFM to understand the origin of large irreversible capacity on Li-Sn alloy anodes. The results of cyclic voltammetry (CV) revealed that an irreversible reduction peak, which is assigned to solvent decomposition, was observed in the range 1.0-1.4 V not in the first cycle, but in the second cycle and later. AFM observation during CV revealed that surface roughening by alloying and de-alloying occurred significantly in the first and second cycles. This surface roughening destroyed existing surface film and brought about a large area of active surface, and therefore is the reason for the appearance of large irreversible capacities in the second and third cycles in constant current charge and discharge tests. © 2005 Elsevier B.V. All rights reserved., Journal of Power Sources, Journal of Power Sources, 146473 - 477, 26 Aug. 2005
  • Electrochemical properties of LiFePO4 thin films prepared by pulsed laser deposition
    Chihiro Yada, Yasutoshi Iriyama, Soon Ki Jeong, Takeshi Abe, Minoru Inaba, Zempachi Ogumi
    Lithium iron phosphate (LiFePO4) thin film electrodes were prepared by pulsed laser deposition (PLD). The thin films were annealed at various temperatures under argon gas flow and the influence of annealing temperature on their electrochemical performance was studied. The thin films annealed at 773 and 873 K exhibited a couple of redox peaks at 3.4 V (versus Li/Li+) that are characteristics of the electrochemical lithium insertion/extraction of LiFePO4. Atomic force microscopy (AFM) observation revealed that the film annealed at 773 K (773 K-film) consisted of small grains with 50 nm in thickness, and the grain size increased with an increase of annealing temperature. Because of its small-sized grains, the 773 K-film showed high rate capability and the discharge capacity at 10 μA maintained 65% of that at 25 nA. However, the discharge capacity of the 773 K-film was ca. 10% smaller than that of the film annealed at 873 K, indicating that annealing at 773 K is slightly insufficient to obtain well-crystallized LiFePO4. From these results, it was concluded that a point of optimization between high rate capability and capacity would be found between 773 and 873 K. © 2005 Elsevier B.V. All rights reserved., Journal of Power Sources, Journal of Power Sources, 146559 - 564, 26 Aug. 2005
  • Electrolytic synthesis of perfluorotrimethylamine with CaF2 added carbon and original carbon anodes
    Akimasa Tasaka, Akimasa Tasaka, Akihiro Miyasaka, Yoshio Shodai, Atsuhisa Mimoto, Atsuhisa Mimoto, Jumpei Yamashita, Tatsuo Miyazaki, Kazuki Onoda, Hitoshi Takebayashl, Tetsuro Tojo, Kunitaka Momota, Minoru Inaba
    The new carbon electrodes containing alkali and/or alkali earth metal fluorides such as LiF-CaF2 and CaF2 were developed to prevent the occurrence of anode effect in electrochemical fluorination and were used as the anode for electrolytic synthesis of perfluorotrimethylamine, (CF3)3N, from mixed melt of (CH3) 4NF·5HF and KF·2HF at 100°C. The ratio of (CF 3)3N to the overall anode gas increased with increasing the concentration of (CH3)4NF and decreasing the current density, and the best value of 61.7% was obtained in electrolysis of the mixed melt of (CH3)4NF·5HF (40 mol %) and KF-2HF (60 mol%) at 20 mA cm-2 with the 4 wt% CaF2 added carbon anode. Also, the best value of its ratio in electrolysis at the same current density with the ordinary carbon anode (FE-5) was obtained in the mixed melt of (CH3)4NF-5HF (30 mol%) and KF-2HF (70 mol%) and was 81.4%. XPS analysis revealed that the surface of anode after electrolysis was mainly covered with the layer of the C-F intercalation compounds having the semi-covalent and ionic bonds. However, the new carbon anode was broken down in the mixed melt of (CH3)4NF·5HF (50 mol%) and KF-2HF (50 mol%) during electrolysis at 40 mA cm-2. From these results, it is concluded that the alkali and/or alkali earth metal fluoride added carbons as well as the carbon (FE-5) is available as the anode for electrolytic production of (CF3)3N from the mixed melt having the molar fraction of KF higher than 0.143., Electrochemistry, Electrochemistry, 73661 - 667, 01 Aug. 2005
  • Anodic behavior of nickel-based alloys in the electrolytic production of NF3
    Atsuhisa Mimoto, Atsuhisa Mimoto, Sojiro Kon, Tsuyoshi Maeda, Takuya Motomura, Kengo Nishimura, Minoru Inaba, Akimasa Tasaka, Akimasa Tasaka
    The Ni-based alloys, such as Ni-Co, Ni-Mn, Ni-Ag, Ni-Cu, Ni-Al and Ni-Si, prepared by hot isostatic pressing (HIP) at 1000°C under 2 × 108Pa for 2 h were employed as the anodes for electrolytic production of NF3. The current efficiencies for NF3formation were 42-38, 52-40, 52-47, 63-62, 50 and 41% for Ni-Co, Ni-Mn, Ni-Ag, Ni-Cu, Ni-Al and Ni-Si alloys, respectively. The current efficiencies only on Ni-Cu alloys with Cu concentrations lower than 10 mol% were almost the same as those on Ni sheet and HIPed Ni anodes, whereas those on the other alloys used in this study were smaller compared with those on both Ni anodes. On the other hand, the current losses caused by anodic dissolution of Ni-Co, Ni-Mn, Ni-Ag, Ni-Cu, Ni-Al and Ni-Si alloy electrodes were 7.95-4.42, 6.40-7.02, 5.60-6.30, 3.34-6.33, 5.10 and 0.18%, respectively. The anode consumptions of Ni-5 mol% Cu and Ni-5 mol% Si alloys were almost the same or smaller compared with those of Ni sheet and HIPed Ni electrodes, though those of other alloys used were large compared with those of both Ni anodes. Consequently, addition of Cu to the nickel matrix is available for a cheaper cost of anode with keeping a same current efficiency as that on the Ni anode and addition of Si to the nickel matrix is effective for decreasing anode consumption largely. A Ni sheet electrode containing a trace of impurities, such as Co, Mn, Ag and Al, is also favorable as the anode for electrolytic production of NF3., Journal of Fluorine Chemistry, Journal of Fluorine Chemistry, 1261101 - 1110, 01 Jul. 2005, English, 研究論文(学術雑誌)
  • Structural and electrical characterizations of electrodeposited p-type semiconductor Cu2O films
    Kotaro Mizuno, Masanobu Izaki, Kuniaki Murase, Tsutomu Shinagawa, Masaya Chigane, Minora Inaba, Akimasa Tasaka, Yasuhiro Awakura
    The p-type semiconductor cuprous oxide (Cu2O) film has been of considerable interest as a component of solar cells and photodiodes due to its bandgap energy of 2.1 eV and high optical absorption coefficient. We prepared Cu2O films on a conductive substrate by electrodeposition at 318 K from an aqueous solution containing copper sulfate and lactic acid. The structural and electrical characterizations of the resulting films were examined by X-ray diffraction. X-ray photoelectron spectroscopy, and X-ray absorption measurements, and the Hall effect measurement, respectively. The resistivity varied from 2.7 × 104 to 3.3 × 106 Ω cm, while the carrier density was from 1012 to 1014 cm -3 and the mobility from 0.4 to 1.8 cm2 V-1 s-1, depending on the preparation conditions, i.e., solution pH and deposition potential. The carrier density was sensitive to the atomic ratio of Cu to O in the films and the mobility to the grain size. © 2005 The Electrochemical Society. All rights reserved., Journal of the Electrochemical Society, Journal of the Electrochemical Society, 152C179 - C182, 20 May 2005, English, 研究論文(学術雑誌)
  • Effects of mixed conduction on the open-circuit voltage of intermediate-temperature SOFCs based on Sm-doped ceria electrolytes
    Toshiaki Matsui, Takuya Kosaka, Minoru Inaba, Atsushi Mineshige, Zempachi Ogumi
    The effects of mixed conduction on the open-circuit voltage of intermediate-temperature solid oxide fuel cells (SOFCs) based on SDC20 were studied in the temperature range of 723-973 K. Though the measured OCVs of a test cell using high activity electrodes agreed well with theoretical values calculated using the conductivity data at 973 K, they deviated from the theoretical ones at lower temperatures. The OCV was dependent on electrode activity and electrolyte thickness, and it was concluded that overpotential at the electrode/electrolyte interfaces affected the OCV because of internal short circuit. The ionic transference number of SDC 20 that is free from the effect of overpotential was obtained using a method derived by Liu et al. SDC20 exhibited high ionic transference number with suppressed electronic conduction at low temperatures with highly humidified fuel. These results indicate that the electronic conduction of SDC20 can be suppressed at intermediate temperatures with high humidification of fuel, which agreed well with the results from the theoretical consideration of the conductivity data. © 2004 Elsevier B.V. All rights reserved., Solid State Ionics, Solid State Ionics, 176663 - 668, 28 Feb. 2005
  • Electrochemical properties of ceria-based oxides for use in intermediate-temperature SOFCs
    Toshiaki Matsui, Minoru Inaba, Atsushi Mineshige, Zempachi Ogumi
    The electrochemical properties of Ce0.8Sm0.2O 1.9-δ (SDC20) at intermediate temperature (673-1073 K) were studied. The dependence of total conductivity on the partial pressure of oxygen [P(O2)] showed that Ce4+ was partially reduced to Ce 3+, and electronic conduction was seen at a low P(O2) region at each temperature. This result suggested that it was difficult to avoid introducing electronic conduction even at 673 K. However, under open circuit and operating conditions, simulations revealed that it was possible to suppress electronic conduction by reducing the operating temperature and using high fuel humidification, resulting in a high P(O2). Furthermore, the maximum efficiency increased with a decrease in temperature and an increase in P(O2) on fuel side although the maximum power density decreased. For the cell with 10-μm-thick electrolyte and reversible electrodes, the total efficiency at 673-873 K showed almost the same value of 0.61 under the typical operating condition of 0.72 V when H2 humidified at 293 K and air was used as fuel and oxidant, respectively. © 2004 Elsevier B.V. All rights reserved., Solid State Ionics, Solid State Ionics, 176647 - 654, 28 Feb. 2005
  • Hydrogen peroxide formation as a degradation factor of polymer electrolyte fuel cells
    Minoru Inaba, Hirohisa Yamada, Junko Tokunaga, Masayuki Kiriake, Akimasa Tasaka, Taro Kinumoto, Zempachi Ogumi
    Durability is one of the most important issues in commercialization of PEFCs. Hydrogen peroxide formation, which is formed electrochemically or chemically during operation, is one of the potential deteriorating factors of PEFCs. We have focused on hydrogen peroxide as a degradation factor of PEFC stacks, and have investigated durability of the electrolyte membrane used in MEAs against hydrogen peroxide and the mechanism for hydrogen peroxide formation at Pt/C catalysts. We have also studied the degradation of MEAs by operating a single cell under accelerated operating conditions. In this report, recent results on these topics are summarized., Proceedings - Electrochemical Society, Proceedings - Electrochemical Society, PV 2004-21370 - 379, 01 Dec. 2004
  • AFM study on SEI growth on graphite negative electrode at elevated temperatures
    Minoru Inaba, Hanako Tomiyasu, Akimasa Tasaka, Soon Ki Jeong, Zempachi Ogumi
    Morphology changes of the surface of highly oriented pyrolytic graphite (HOPG) electrode during cycling and storage at elevated temperatures were observed by in situ AFM to envisage the SEI growth and its stability. AFM observation of the SEI layer revealed that two important facts on the stability of the SEI at elevated temperatures: (i) dissolution and agglomeration of the SEI layer at the discharged state, and (ii) serious SEI growth at the charged state. These phenomena well explained the results of the charge and discharge tests. It was also shown that the addition of vinylene carbonate greatly improves the stability of the SEI at an elevated temperature., Proceedings - Electrochemical Society, Proceedings - Electrochemical Society, PV 2003-2811 - 19, 01 Dec. 2004
  • Preparation of dense electrolyte layer using dissociated oxygen electrochemical vapor deposition technique
    Atsushi Mineshige, Koji Fukushima, Kazuhiro Tsukada, Masafumi Kobune, Tetsuo Yazawa, Kenji Kikuchi, Minoru Inaba, Zempachi Ogumi
    A dense layer of yttria-stabilized zirconia (YSZ) was deposited on a porous substrate by a modified type of electrochemical vapor deposition (EVD) technique, making use of dissociated oxygen from nickel oxide in the porous substrate as an oxygen source for the reaction. As the oxygen-supplying substrates, NiO-ceria porous pellets containing some depressions on the deposited face were used to fabricate modified planar-type SOFC based on the rough anode of Ni-ceria. The dissociated oxygen electrochemical vapor deposition (DOEVD) technique was very suitable for fabrication of this type of cell. © 2004 Elsevier B.V. All rights reserved., Solid State Ionics, Solid State Ionics, 175483 - 485, 30 Nov. 2004
  • Preparation of LiFePO4thin films by pulsed laser deposition and their electrochemical properties
    Yasutoshi Iriyama, Misuzu Yokoyama, Chihiro Yada, Soon Ki Jeong, Soon Ki Jeong, Izumi Yamada, Takeshi Abe, Minoru Inaba, Zempachi Ogumi
    Olivine structured LiFePO4thin films were prepared by pulsed laser deposition and their electrochemical properties were investigated by cyclic voltammetry (CV) and charge-discharge tests. The resultant films exhibited only a couple of anodic and cathodic peaks at ∼3.4 V, which is characteristic of olivine LiFePO4, on CV between 2.0 and 5.0 V (vs. Li/Li+). The discharge capacity estimated from the CV obtained at 100 mVs-1maintained 69% of that obtained at 1 mVs-1. This high rate capability is probably due to the film being so thin that the intrinsically poor electronic conductivity of LiFePO4was not of importance. © 2004 The Electrochemical Society. All rights reserved., Electrochemical and Solid-State Letters, Electrochemical and Solid-State Letters, 7A340 - A342, 22 Nov. 2004, English, 研究論文(学術雑誌)
  • Electrolysis of mixed melt of (CH3)4NF· mHF + x wt.% CsF·2.0HF with nickel anode
    Yoshio Shodai, Minoru Inaba, Kunitaka Momota, Tomotaka Kimura, Akimasa Tasaka
    A new process for electrolytic synthesis of a perfluorinated compound using mixed melts of (CH3)4NF·4.0HF + xwt.% CsF·2.0HF as electrolytes and Ni sheet anode at room temperature was developed. The addition of CsF·2.0HF reduced the overvoltage of the Ni anode. The surface film on the anode formed in the presence of CsF·2.0HF consisted of inorganic compounds of NiF2, CsNi2F6, and an organic compound of (CH3)4NF. The presence of CsNi2F6, which is a highly oxidized nickel compound, gave a high electronic conductivity to the film and decreased the anode overvoltage. The gas evolved on the anode was composed of (CF3)3N and CF4as main products with small amounts of NF3, C2F6, CHF3, C2HF5, CF3N(CF2H)2, and (CF3)2NCHF2. The addition of 20wt.% CsF·2.0HF gave the highest ratio of (CF3)3N of 40.5% when the electrolysis was carried out at 5mAcm-2at room temperature. © 2004 Elsevier Ltd. All rights reserved., Electrochimica Acta, Electrochimica Acta, 492131 - 2137, 30 May 2004, English, 研究論文(学術雑誌)
  • Anionic species (FH)xF-in room-temperature molten fluorides (CH3)4NF·mHF
    Yoshio Shodai, Shinji Kohara, Yasuo Ohishi, Minoru Inaba, Akimasa Tasaka
    Ionic and nonionic species in (CH3)4NF·mHF melts (m = 3.0-5.0) were investigated by1H NMR, IR spectroscopy, Raman spectroscopy, and high-energy X-ray diffraction measurements. Three types of anions, (FH)F-, (FH)2F-, and (FH)3F-, were identified in these melts. The(FH)2F-anion was thermodynamically the most stable of the complex anions in the (CH3)4NF·mHF (3.0 ≤ m ≤ 5.0), and its concentration was the highest. (FH)xF-anions with x = 4 and 5 were not present at room temperature though the presence of (FH)xF-(x = 1-5) has been known in the solid-state crystals. In the (CH3)4NF·mHF melts with m = 3.0 - 5.0, the number of HF combined with F-is three or less, and excess HF exists as molecular HF., Journal of Physical Chemistry A, Journal of Physical Chemistry A, 1081127 - 1132, 19 Feb. 2004, English, 研究論文(学術雑誌)
  • Atomic Force Microscopy Study on the Stability of a Surface Film Formed on a Graphite Negative Electrode at Elevated Temperatures
    Minoru Inaba, Hanako Tomiyasu, Akimasa Tasaka, Soon Ki Jeong, Soon Ki Jeong, Zempachi Ogumi
    The stability at elevated temperatures of a solid electrolyte interphase (SEI) formed on a graphite negative electrode in lithium ion batteries was investigated by storage tests and in situ atomic force microscopy (AFM) observation. When the fully discharged graphite electrode was stored at elevated temperatures, the irreversible capacity in the following cycle increased remarkably. On the other hand, when the electrode was stored at the fully charged state at elevated temperatures, it was severely selfdischarged during storage. AFM observation of the SEI layer formed on a model electrode of highly oriented pyrolytic graphite revealed two important facts on the stability of the SEI at elevated temperatures: (i) dissolution and agglomeration of the SEI layer at the discharged state and (ii) serious SEI growth at the charged state. These phenomena well explain the results of the charge and discharge tests. It was also shown that the addition of vinylene carbonate greatly improves the stability of the SEI at elevated temperatures, and gives good charge and discharge performance after storage., Langmuir, Langmuir, 201348 - 1355, 17 Feb. 2004, English, 研究論文(学術雑誌)
  • Proton conductivity of (NH4)2TiP4O13-based material for intermediate temperature fuel cells
    Toshiaki Matsui, Shinya Takeshita, Yasutoshi Iriyama, Takeshi Abe, Minoru Inaba, Zempachi Ogumi
    A new proton-conductive electrolyte of (NH4)2TiP4O13was synthesized for intermediate temperature fuel cells. Structure of the resultant electrolyte was studied by X-ray diffraction and its ionic conductivities was obtained from AC impedance spectroscopy. Partial decomposition of (NH4)2TiP4O13occurred by annealing at 300°C under a dry argon atmosphere, resulting in the formation of TiP2O7, and after annealing its proton conductivity was evaluated to be about 5 mS cm-1at 300°C under the same dry argon atmosphere. Electrolyte of (NH4)2SiP4O13was prepared for comparison. In contrast to (NH4)2TiP4O13, it is stable under a dry Ar atmosphere at 300°C, and its proton conductivity was 0.6 mS cm-1. These results indicate that partial decomposition of (NH4)2TiP4O13to TiP2O7should be responsible for high proton conductivity. © 2003 Elsevier B.V. All rights reserved., Electrochemistry Communications, Electrochemistry Communications, 6180 - 182, 01 Jan. 2004, English, 研究論文(学術雑誌)
  • Study on the decomposition mechanism of alkyl carbonate on lithium metal by pyrolysis-gas chromatography-mass spectroscopy
    Ryo Mogi, Minoru Inaba, Yasutoshi Iriyama, Takeshi Abe, Zempachi Ogumi
    The surface films formed on deposited lithium in electrolyte solutions based on ethylene carbonate (EC), diethyl carbonate (DEC), and dimethyl carbonate (DMC) were analyzed by pyrolysis-gas chromatography-mass spectroscopy (Py-GC-MS). In 1M LiClO4/EC, the main component of the surface film was easily hydrolyzed to give ethylene glycol after exposure to air, and hence was considered to have a chemical structure of ROCH2CH2OR′, of which -OR and -OR′ are -OLi or -OCO2Li. Ethylene oxide, acetaldehyde, and 1,4-dioxane were detected in decomposition products, and they were considered to have been formed by pyrolysis of ROCH2CH2OR′ in the pyrolyzer. The presence of ethanol in decomposition products confirmed that ring cleavage at the CH2-O bonds of EC occurs by one electron reduction. In addition, the presence of methanol implied the cleavage of the C-C bond of EC upon reduction. From the surface films formed in 1 M LiClO4/DEC and /DMC, ethanol and methanol, respectively, were detected, which suggested that corresponding lithium alkoxides and/or lithium alkyl carbonates were the main components. In 1M LiClO4/EC + DEC (1:1), EC dominantly decomposed to form the surface film. The surface film formed in 1M LiPF6/EC + DEC (1:1) contained a much smaller amount of organic compounds. © 2003 Elsevier Science B.V. All rights reserved., Journal of Power Sources, Journal of Power Sources, 119-121597 - 603, 01 Jun. 2003
  • AFM study of surface film formation on a composite graphite electrode in lithium-ion batteries
    Soon Ki Jeong, Soon Ki Jeong, Minoru Inaba, Yasutoshi Iriyama, Takeshi Abe, Zempachi Ogumi
    An in situ electrochemical atomic force microscopy (AFM) observation of a composite graphite electrode surface was performed in 1 mol dm-3LiClO4dissolved in a mixture of ethylene carbonate (EC)+diethyl carbonate (DEC), and propylene carbonate (PC) to show the applicability of scanning probe microscopy (SPM) to studies using composite graphite electrodes. In EC + DEC, three kinds of morphological changes (curling, swelling, and exfoliation) in the vicinity of the particle edges were observed in the potential range of 0.8-1.4 V versus Li+/Li. These morphological changes were caused by the intercalation of solvated lithium ions and their subsequent decomposition between graphene layers. On the other hand, vigorous exfoliation and rupturing of graphene layers of the graphite particles were observed at 0.9 V in PC. In addition, deterioration by the formation of holes in the composite graphite electrode was observed in PC, which is attributable to gas evolution upon decomposition of PC molecules. © 2003 Elsevier Science B.V. All rights reserved., Journal of Power Sources, Journal of Power Sources, 119-121555 - 560, 01 Jun. 2003, English, 研究論文(国際会議プロシーディングス)
  • Density functional theory calculation on the effect of local structure of doped ceria on ionic conductivity
    Hiroyuki Yoshida, Toru Inagaki, Kazuhiro Miura, Minoru Inaba, Zempachi Ogumi
    The oxide ionic conductivity of doped ceria was investigated from the viewpoint of local structure using first principles density functional theory (DFT) calculation. Singly doped ceria (DC) with Y, La, and Sm dopants (YDC, LDC, and SDC, respectively) and doubly doped ceria with equal amounts of Y and La dopants (CLY) were used as model lattices. The results obtained for doubly doped ceria (CLY) indicated that the energy difference variation with movement of oxide ion is mostly affected by the nearest neighbor cation arrangement of the moving oxide ion. For singly doped ceria, the order of the energy differences (ΔE) at the saddle points was estimated to be LDC>SDC>YDC, which is not completely consistent with the order of the activation energy obtained experimentally (LDC>YDC>SDC). The lowest ionic conductivity of LDC was reproduced by the DFT calculations, which was considered to be mainly brought about by the effect of the local cation arrangements of moving oxide ions. On the other hand, the order of ΔE's between YDC and SDC was reversed, which suggested that the effect of lattice deformation plays an important role in determining the ionic conductivity. © 2003 Elsevier Science B.V. All rights reserved., Solid State Ionics, Solid State Ionics, 160109 - 116, 01 May 2003
  • Correlation between cointercalation of solvents and electrochemical intercalation of lithium into graphite in propylene carbonate solution
    Takeshi Abe, Naoki Kawabata, Yasuo Mizutani, Minoru Inaba, Zempachi Ogumi
    Correlation of solvent cointercalation and electrochemical intercalation of Li into graphite was studied. Cointercalation of dimethylsulfoxide (DMSO), 2-methyltetrahydrofuran (2-MeTHF), dimethoxymethane (DMM), diethoxymethane (DEM), 1,2-diethoxyethane (DEE) and 1,2-dibutoxyethane (DBE) into graphite with Li was investigated by the solution method to find out that DMSO, DMM, DEM, and DEE can cointercalate into graphite with Li and that 2-MeTHF and DBE cannot. By using the functional density theory, steric hindrance of solvated lithium ion was found to be predominant for cointercalation. Electrochemical Li intercalation into graphite was studied in propylene carbonate (PC) solution containing 1 mol dm-3 LiClO4 in the presence of various amounts of the above solvents. By the addition of DMSO in the PC electrolyte, solvent decomposition at around 1.0 V (vs. Li/Li+) was thoroughly suppressed, and electrochemical intercalation of Li took place. Suppression of the solvent decomposition was dependent on the amount of DMSO. This is because competing cointercalation of DMSO suppressed the cointercalation of PC which causes the exfoliation of graphite, leading to the formation of the stable solid electrolyte interface. Suppression of cointercalation of PC was also observed by the addition of DMM, DEM, and DEE in a limited condition. Addition of 2-MeTHF and DBE into the PC electrolyte is not available for electrochemical intercalation of lithium. These results show that cointercalation plays an important role for electrochemical intercalation of lithium into graphite., Journal of the Electrochemical Society, Journal of the Electrochemical Society, 150A257 - A261, 01 Mar. 2003, English, 研究論文(学術雑誌)
  • Study of the decomposition of propylene carbonate on lithium metal surface by pyrolysis - Gas chromatography - Mass spectroscopy
    Ryo Mogi, Ryo Mogi, Minoru Inaba, Minoru Inaba, Yasutoshi Iriyama, Takeshi Abe, Zempachi Ogumi
    The compositions of surface films formed on lithium metal in different propylene carbonate (PC)-based solutions and the decomposition processes in the surface film formation were investigated by pyrolysis-gas chromatography-mass spectroscopy (Py-GC-MS). It was found that the main component in the surface film formed in 1 mol dm-3(M) LiClO4/PC has a chemical structure of ROCH(CH3)CH2OR′, of which -OR and -OR′ can be -OLi or -OCO2Li. A general scheme for reactions that took place on the lithium electrode in 1 M LiClO4/PC and in the pyrolyzer was elucidated from the results by Py-GC-MS analysis. In 1 M LiClO4/PC containing 5 wt% fluoroethylene carbonate (FEC) as an additive, FEC was dominantly reduced to form an active species, Li+-OCO2̇, which further reacted with a PC molecule to form the same main component, ROCH(CH3)CH2OR′. This mechanism suggested that the same active species also might be formed from PC even in the absence of FEC. Another possible route was suggested, in which decomposition of PC is initiated by a nucleophilic attack of an alkoxide. The chemical composition of surface film was greatly affected by the kind of lithium salts. Decomposition products of lithium bis(perfluoroethylsulfonyl)-imide (LiBETI) were detected from the surface film formed in 1 M LiBETI/PC. In contrast, the surface film formed in 1 M LiPF6/PC consisted mainly of inorganic compounds with a much smaller amount of organic compounds., Langmuir, Langmuir, 19814 - 821, 04 Feb. 2003, English, 研究論文(学術雑誌)
  • Electrochemical intercalation of lithium ion within graphite from propylene carbonate solutions
    Soon Ki Jeong, Soon Ki Jeong, Minoru Inaba, Yasutoshi Iriyama, Takeshi Abe, Zempachi Ogumi
    Electrochemical lithium intercalation within graphite was investigated in propylene carbonate (PC) containing different concentrations, 0.82 and 2.72 mol dm-3, of bis(perfluoroethylsulfonyl)imide, LiN(SO2C2F5)2. Lithium ion was reversibly intercalated into and deintercalated from graphite in the latter concentrated solution in spite of the use of pure PC as a solvent, whereas ceaseless solvent decomposition and intensive exfoliation of graphene layers occurred in the former solution. X-ray diffraction analysis revealed that a stage I graphite intercalation compound was formed after being fully charged in the 2.72 mol dm-3 solution. The results of Raman analysis indicated that no free PC molecules are present in the concentrated solution, which suggested that the ion/solvent interactions would be an important factor that determines the ability of stable surface film formation in PC-based solutions., Electrochemical and Solid-State Letters, Electrochemical and Solid-State Letters, 6A13 - A15, 01 Jan. 2003, English, 研究論文(学術雑誌)
  • Lithium ion transfer at carbon thin film electrode/electrolyte interface
    Takeshi Abe, Shigeki Yamate, Yasutoshi Iriyama, Minoru Inaba, Zempachi Ogumi, Tomokazu Fukutsuka
    Lithium ion transfer at an interface between carbonaceous thin film electrode prepared by plasma-assisted chemical vapor deposition and electrolyte was studied by AC impedance spectroscopy. In Nyquist plots, semi-circles assigned as charge (Li+) transfer resistance were observed. The charge transfer resistance was dependent on the electrode potentials. Activation energy for the lithium ion transfer through the interface between electrode and electrolyte was also evaluated., Molecular Crystals and Liquid Crystals Science and Technology Section A: Molecular Crystals and Liquid Crystals, Molecular Crystals and Liquid Crystals Science and Technology Section A: Molecular Crystals and Liquid Crystals, 388, 01 Dec. 2002
  • Oxygen chemical potential and mixed conduction in doped ceria under influence of oxygen partial pressure gradient
    Atsushi Mineshige, Tadashi Yasui, Noriyuki Ohmura, Masafumi Kobune, Satoshi Fujii, Minoru Inaba, Zempachi Ogumi
    The procedure to evaluate an oxygen chemical potential in Sm2O3-doped ceria, Ce0.8Sm0.2O2-δ (SDC), was developed using Raman spectroscopy. The oxygen chemical potentials of any positions in the SDC samples placed between fuel and air at 1273 K could be determined throughout the entire range of P(O2) by using relative areas and intensities of their Raman spectra. Using this method, P(O2) variation in the SDC disc-shaped sample of 4 mm in thickness and 15 mm in diameter was determined by evaluating P(O2) between fuel- and air-side faces, and along the radius inside the pellet under the open-circuit conditions of SOFCs. In addition, the variation of total (ionic and electronic) conduction in the sample under the influence of P(O2) gradient was discussed. © 2002 Elsevier Science B.V. All rights reserved., Solid State Ionics, Solid State Ionics, 152-153493 - 498, 01 Dec. 2002
  • Effects of some organic additives on lithium deposition in propylene carbonate
    Ryo Mogi, Minoru Inaba, Soon Ki Jeong, Yasutoshi Iriyama, Takeshi Abe, Zempachi Ogumi
    The effects of some film-forming organic additives, fluoroethylene carbonate (FEC), vinylene carbonate (VC), and ethylene sulfite (ES), on lithium deposition and dissolution were investigated in 1 M LiClO4 dissolved in propylene carbonate (PC) as a base solution. When 5 wt % FEC was added, the cycling efficiency was improved. On the contrary, addition of 5 wt% VC or ES significantly lowered the cycling efficiency. The surface morphology of lithium deposited in each electrolyte solution was observed by in situ atomic force microscopy (AFM). In PC + FEC, the surface was covered with a uniform and closely packed layer of particle-like deposits of about 100-150 nm diam. The surface film seemed to be more solid in PC + VC, and inhomogeneous in PC + ES. From ac impedance measurements, it was revealed that the surface film formed in PC + FEC has a lower resistance than that in the additive-free solution, whereas that formed in PC + VC or PC + ES has a higher resistance. Large volume changes during lithium deposition and dissolution require that the surface film should be elastic (or soft) and be self-repairable when being damaged. In addition, a nonuniform current distribution is liable to cause dendrite formation, which requires that the surface film should be uniform and its resistance should be as low as possible. PC + FEC gave a surface film that satisfies all these requirements, and therefore only FEC was effective as an additive for deposition and dissolution of lithium metal., Journal of the Electrochemical Society, Journal of the Electrochemical Society, 149, 01 Dec. 2002
  • Surface modification of carbonaceous thin films by NF3plasma and their effects on electrochemical properties
    Tomokazu Fukutsuka, Yoshiaki Matsuo, Yosohiro Sugie, Takeshi Abe, Minoru Inaba, Zempachi Ogumi
    Carbonaceous thin films were prepared by plasma-assisted chemical vapor deposition. Surface of resultant films were treated by NF3plasma at room temperature. From Roman spectra, crystallinity of sample remained almost unchanged by the surface treatment. The reduction current at 0.6V vs. Li/Li+in the cyclic voltammograms at the 1st cycle decreased with increasing the flow rate of NF3. This result indicates that fluorine atoms bonded to carbon atoms play an important role in decreasing the side reaction at the 1st reduction process., Molecular Crystals and Liquid Crystals Science and Technology Section A: Molecular Crystals and Liquid Crystals, Molecular Crystals and Liquid Crystals Science and Technology Section A: Molecular Crystals and Liquid Crystals, 388[531]/117 - [536]/122, 01 Dec. 2002, English, 研究論文(国際会議プロシーディングス)
  • Plasma etching of SiC surface using NF3
    A. Tasaka, K. Takahashi, K. Tanaka, K. Shimizu, K. Mori, S. Tada, W. Shimizu, T. Abe, M. Inaba, Z. Ogumi, T. Tojo
    The RIE process for the βSiC was developed and it had a high etching rate of 87 nm/min. However, it was restricted by the conditions such as rf power of 100 W and NF3pressure ranging from 0.5 to 1 Pa. The surface of the SiC has many spikes under other conditions. The repetitive alternating treatment for the surface of SiC with DFE using NF3and Ar plasma sputtering enabled to obtain the smooth surface without Si3N4formation on it., Journal of Vacuum Science and Technology A: Vacuum, Surfaces and Films, Journal of Vacuum Science and Technology A: Vacuum, Surfaces and Films, 201254 - 1260, 01 Jul. 2002, English, 研究論文(学術雑誌)
  • Surface film formation on nickel electrodes in a propylene carbonate solution at elevated temperatures
    Ryo Mogi, Minoru Inaba, Yasutoshi Iriyama, Takeshi Abe, Zempachi Ogumi
    The effect of temperature on surface film formation on nickel electrode was studied in 1 mol dm-3 bis(perfluoroethylsulfonyl)imide dissolved in propylene carbonate by atomic force microscopy (AFM) and ac impedance spectroscopy. Cyclic voltammetry measurements revealed that electrolyte decomposition reactions are accelerated at elevated temperatures, especially at 60 and 80 °C. In situ AFM measurements showed that the film formation is fast and the resulting surface film is thicker at 80 °C than at room temperature. Furthermore, it was confirmed by ac impedance measurements that the resistance of surface film was very low at elevated temperatures. These results were discussed in relation to superior cycling characteristics of lithium deposition and dissolution at the elevated temperatures. © 2002 Elsevier Science B.V. All rights reserved., Journal of Power Sources, Journal of Power Sources, 108163 - 173, 01 Jun. 2002
  • Surface film formation on a graphite negative electrode in lithium-ion batteries: AFM study on the effects of co-solvents in ethylene carbonate-based solutions
    Soon Ki Jeong, Minoru Inaba, Yasutoshi Iriyama, Takeshi Abe, Zempachi Ogumi
    In situ AFM observation of the basal plane of highly oriented pyrolytic graphite (HOPG) was performed before and after cyclic voltammetry in 1 mol dm-3LiClO4dissolved in ethylene carbonate (EC), EC+diethyl carbonate (DEC), and EC+dimethyl carbonate (DMC) to clarify the effects of co-solvents in EC-based solutions on surface film formation on graphite negative electrodes in lithium-ion cells. In each solution, surface film formation involved the following two different processes: (i) intercalation of solvated lithium ions and their decomposition beneath the surface; and (ii) direct decomposition of solvent molecules on the basal plane to form a precipitate layer. The most remarkable difference among these solvent systems was that solvent co-intercalation took place more extensively in EC+DEC than in EC+DMC or EC. Raman analysis of ion-solvent interactions revealed that a lithium ion is solvated by three EC molecules and one DEC molecule in EC+DEC, whereas it is solvated exclusively by EC in EC+DMC and in EC, which suggested that the presence of linear alkyl carbonates in the solvation shell of lithium ion enhance the degree of solvent co-intercalation that occurs in the initial stage of the surface film formation. © 2002 Elsevier Science Ltd. All rights reserved., Electrochimica Acta, Electrochimica Acta, 471975 - 1982, 07 May 2002, English, 研究論文(学術雑誌)
  • Synthesis of highly graphitized carbonaceous thin films by plasma assisted chemical vapor deposition and their electrochemical properties in propylene carbonate solution
    Takeshi Abe, Kazuhisa Takeda, Tomokazu Fukutsuka, Yasutoshi Iriyama, Minoru Inaba, Zempachi Ogumi
    Carbonaceous thin film electrode was prepared by plasma assisted chemical vapor deposition. The films were very flat and pin-hole free with c-axis orientation. X-ray diffraction and Raman spectroscopy revealed that the bulk of the film was highly graphitized but the surface of the film was less crystallized, indicating that the surface modified graphitized thin film electrode was obtained by a single process. Electrochemical properties of this film were studied in electrolyte of propylene carbonate (PC) containing 1 mol dm-3 LiClO4 by cyclic voltammetry. The first cycle of voltammogram showed reduction current observed at 1.0-0.5 V (vs. Li/Li+), but the reduction current at those potentials completely disappeared over the second cycle. Large reduction and oxidation currents were observed near 0 V (vs. Li/Li+), and in addition, the peak splitting was observed for oxidation peaks near 0 V. These electrochemical properties are quite similar to that of graphite electrode used in Li-ion batteries. © 2002 Elsevier Science B.V. All rights reserved., Electrochemistry Communications, Electrochemistry Communications, 4310 - 313, 18 Apr. 2002
  • In situ atomic force microscopy study on lithium deposition on nickel substrates at elevated temperatures
    Ryo Mogi, Minoru Inaba, Yasutoshi Iriyama, Takeshi Abe, Zempachi Ogumi
    The effects of temperature on lithium deposition and dissolution on Ni substrate were investigated in 1 mol dm-3 solutions of lithium bis(perfluoroethylsulfonyl)imide [LiN(C2F5SO2)2] and lithium trifluoromethanesulfonate (LiCF3SO3) dissolved in propylene carbonate. The cyclability for lithium deposition and dissolution was greatly improved at elevated temperatures of 60 and 80°C. The surface morphologies of lithium deposited on Ni substrates at different temperatures were observed by in situ atomic force microscopy (AFM). The surface film formed at room temperature and 40°C was inhomogeneous, and large masses of deposits appeared after prolonged deposition (0.3 C cm-2). In contrast, closely packed, uniform surface film consisting of particle-like deposits of 100-200 nm diam was formed at 60 and 80°C, and no significant morphology changes were observed after prolonged deposition and even after dissolution. It was concluded that the uniformity and self-reparability of the surface film, and an enhanced surface diffusion of lithium atoms suppressed dendritic deposition and improved the cycling characteristics at the elevated temperatures., Journal of the Electrochemical Society, Journal of the Electrochemical Society, 149, 01 Apr. 2002
  • Creation of nanospaces by intercalation of alkali metals into graphite in organic solutions
    Y. Mizutani, T. Abe, M. Inaba, Z. Ogumi
    Co-intercalation of alkali metals (Li, Na, K, Rb and Cs) with various organic solvents has been utilized for introducing nanospaces in graphite. The co-intercalation has been conducted by a solution method. Resultant products were studied by X-ray diffraction. For solvents of cyclic ethers, co-intercalation is likely to occur for heavy alkali metals of Rb and Cs. For linear ethers with one oxygen atom, binary graphite intercalation compounds (GICs) were mainly obtained, irrespective of alkali metal species. For linear ethers with two oxygen atoms, light alkali metal, in particular, Li tends to give ternary Li-solvent-GICs. From these results, it is concluded that co-intercalation is mainly influenced by the interaction between alkali metals and solvents and by the size of solvated alkali metals. © 2001 Elsevier Science B.V. All rights reserved., Synthetic Metals, Synthetic Metals, 125153 - 159, 01 Jan. 2002, English, 研究論文(学術雑誌)
  • Surface film formation on a graphite negative electrode in lithium-ion batteries: Atomic force microscopy study on the effects of film-forming additives in propylene carbonate solutions
    Soon Ki Jeong, Minoru Inaba, Ryo Mogi, Yasutoshi Iriyama, Takeshi Abe, Zempachi Ogumi
    In situ electrochemical atomic force microscopy (AFM) observation of the basal plane of highly oriented pyrolytic graphite (HOPG) was performed during cyclic voltammetry in 1 M LiClO4/propylene carbonate (PC) containing 3 wt % vinylene carbonate (VC), fiuoroethylene carbonate (FEC), and ethylene sulfite (ES) in order to clarify the roles of these additives in the formation of a protective surface film on a graphite negative electrode in lithium-ion batteries. Particle-like precipitates appeared on the HOPG surface at the potentials 1.35, 1.15, and 1.05 V versus Li+/Li in PC + VC, PC + FEC, and PC + ES, respectively, and covered the whole surface at lower potentials. No evidence for cointercalation of solvent molecules was observed in the presence of each additive. It was concluded that the layer of the precipitates functions as a protective surface film, which suppresses cointercalation of PC molecules as well as direct solvent decomposition on the surface of the graphite negative electrode., Langmuir, Langmuir, 178281 - 8286, 25 Dec. 2001
  • Effect of co-intercalated organic solvents in graphite on electrochemical Li intercalation
    T. Abe, Y. Mizutani, N. Kawabata, M. Inaba, Z. Ogumi
    Electrochemical properties of graphite in propylene carbonate based electrolytes containing various organic solvents have been studied by cyclic voltammetry and charge-discharge measurements. Good correlation between solvent co-intercalation and electrochemical lithium intercalation into graphite was found. Effect of co-intercalated organic solvents in graphite on electrochemical Li intercalation was discussed. © 2001 Elsevier Science B.V. All rights reserved., Synthetic Metals, Synthetic Metals, 125249 - 253, 20 Nov. 2001
  • Up-to-date development of lithium-ion batteries in Japan
    Minoru Inaba, Zempachi Ogumi
    In 1991, Japan first marketed small-sized secondary lithium-ion batteries (LIBs). This paper reviews up-to-date development of LIBs, focusing mainly on the situation in Japan. The materials, constructions, and performance of the latest commercially available LIBs, including lithium polymer batteries, are described. Furthermore, the recent trends in the development of battery materials for LIBs as well as those of large-scale LIBS are discussed., IEEE Electrical Insulation Magazine, IEEE Electrical Insulation Magazine, 176 - 20, 01 Nov. 2001
  • Electrochemical Properties of Carbonaceous Thin Films Prepared by Plasma Chemical Vapor Deposition
    Tomokazu Fukutsuka, Takeshi Abe, Minoru Inaba, Zempachi Ogumi
    Carbonaceous thin films were prepared from acetylene and argon by plasma-assisted chemical vapor deposition (plasma CVD). The carbonaceous thin films were characterized mainly by scanning electron microscope (SEM) and Raman spectroscopy. Then their electrochemical properties were studied by cyclic voltammetry, charge-discharge measurements, and linear sweep voltammetry. From the SEM image carbonaceous thin films appeared flat and pinhole free. Crystallinity of carbonaceous thin films are affected by the applied rf power from Raman spectra. The difference of the applied rf power also affected the results of cyclic voltammetry and charge-discharge measurements. The lithium ion storage mechanism of carbonaceous thin film is discussed from the results of electrochemical measurements. © 2001 The Electrochemical Society. All rights reserved., Journal of the Electrochemical Society, Journal of the Electrochemical Society, 148, 01 Nov. 2001
  • Surface Film Formation on Graphite Negative Electrode in Lithium-Ion Batteries: AFM Study in an Ethylene Carbonate-Based Solution
    Soon Ki Jeong, Minoru Inaba, Takeshi Abe, Zempachi Ogumi
    In situ atomic force microscopic (AFM) observation of the basal plane of highly oriented pyrolytic graphite was performed during cyclic voltammetry at a slow scan rate of 0.5 mV s-1 in 1 mol dm-3 LiClO4 dissolved in a mixture of ethylene carbonate and diethyl carbonate. In the potential range 1.0-0.8 V, atomically flat areas of 1 or 2 nm height (hill-like structures) and large swellings of 15-20 nm height (blisters) appeared on the surface. These two features were formed by the intercalation of solvated lithium ions and their decomposition beneath the surface, respectively, and may have a role in suppressing further solvent cointercalation. At potentials more negative than 0.65 V, particle-like precipitates appeared on the basal plane surface. After the first cycle, the thickness of the precipitate layer was 40 nm, and increased to 70 nm after the second cycle. The precipitates were considered to be mainly organic compounds that are formed by the decomposition of solvent molecules, and they have an important role in suppressing further solvent decomposition on the basal plane. © 2001 The Electrochemical Society. [DOI: 10.1149/1.1387981] All rights reserved., Journal of the Electrochemical Society, Journal of the Electrochemical Society, 148A989 - A993, 01 Sep. 2001, English, 研究論文(学術雑誌)
  • In situ atomic force microscopy observation of lithium deposition at an elevated temperature
    Ryo Mogi, Minoru Inaba, Takeshi Abe, Zempachi Ogumi
    Lithium deposition was carried out on a Ni substrate in a 1 M solution of lithium bis(perfluoroethylsulfonyl)imide (LiBETI) dissolved in propylene carbonate(PC) at room temperature and at an elevated temperature of 80°C. The morphologies of lithium deposits were compared using in situ atomic force microscopy. The cycling efficiency for lithium deposition and dissolution at 80°C was higher than that at room temperature in 1 M LiBETI/PC. Large masses of deposits were observed after lithium deposition at room temperature. However, the surface of lithium deposited at 80°C was smooth and uniform throughout lithium deposition and dissolution. It was shown that temperature is one of the important factors that affect the cycling efficiency. © 2001 Elsevier Science B.V., Journal of Power Sources, Journal of Power Sources, 97-98265 - 268, 01 Jul. 2001
  • Effects of the molecular structure of fluorinated additives on the kinetics of cathodic oxygen reduction
    Jun Maruyama, Minoru Inaba, Tohru Morita, Zempachi Ogumi
    The kinetics of oxygen reduction at a gold electrode was studied in 0.5 M sulfuric acid, in which different kinds of straight-chain [CF3(CF2)2CH2OH, CF3CF2CH2OH, and CF3CH2OH] and branched [(CF3)2CHOH] fluorinated alcohols were added. The adsorbed layers of the fluorinated alcohols were used as models of the fluorocarbon phase of the perfluorinated polymer electrolyte in gas-diffusion electrodes in proton-exchange membrane fuel cells. A rotating ring-disk electrode was used to determine kinetic parameters for O2reduction and to detect intermediate H2O2formation. The kinetics of oxygen reduction were strongly dependent on the molecular structure of fluorinated additives. The addition of the straight-chain fluorinated alcohols enhanced the kinetic current density while addition of the branched alcohol did not. The linear C3fluorinated alcohol, CF3CF2CH2OH, gave the maximum enhancement effect. Oxygen is reduced predominantly via the two-electron series path in the range of 0.4 to 0.0 V at Au, on which no effect of fluorinated additives was observed. The rate constant for intermediate H2O2reduction, k3, was negligible in the range 0.40-0.25 V, whereas it increased with decreasing EDin the range 0.25-0.0 V. In the lower potential range, k3decreased with an increase in the concentration of fluorinated alcohol and this decreasing tendency was greatly dependent on the molecular structure of the fluorinated alcohol. © 2001 Elsevier Science B.V., Journal of Electroanalytical Chemistry, Journal of Electroanalytical Chemistry, 504208 - 216, 18 May 2001, English, 研究論文(学術雑誌)
  • Structure and electrochemical behaviors of LixCoO2(x > 1) treated under high oxygen pressure
    N. Imanishi, M. Fujii, A. Hirano, Y. Takeda, M. Inaba, Z. Ogumi
    The electrochemical behavior of LixCoO2(x > 1.0) and its high pressure oxygen-treated samples were examined as cathode of lithium ion battery. LixCoO2was prepared at nominal compositions of Li/Co = 1.02, 1.05, 1.10, 1.15, 1.20, 1.25, and 1.30. The practical compositions and cobalt valences were analyzed by ICP and iodometric titration technique. X-ray diffraction patterns show that the lattice gradually contracts with increasing Li/Co ratio. The lattice contraction stops at Li/Co = 1.15, which corresponds to the solid solution limit. The high oxygen pressure treatment reduced the number of oxygen defects and enlarged the interlayer distance. The electrochemical behavior of oxygen-treated samples show better cycling efficiency and less irreversible capacities. The reversible capacities show clear dependence on Li/Co ratio that the highest capacity of 140 mA h g-1was obtained when Li/Co = 1.10 and beyond that value it decreased linearly with Li/Co ratio. © 2001 Elsevier Science B.V., Solid State Ionics, Solid State Ionics, 14045 - 53, 01 Mar. 2001, English, 研究論文(学術雑誌)
  • Preparation of c-axis oriented thin films of LiCoO2by pulsed laser deposition and their electrochemical properties
    Yasutoshi Iriyama, Minoru Inaba, Takeshi Abe, Zempachi Ogumi
    Thin films of LiCoO2with a preferred c-axis orientation were prepared by pulsed laser deposition. Thin films deposited for 1-2 h had a preferred c-axis orientation, but films deposited for 3 h and longer lost the preferred orientation. The textures of these films were investigated in detail by transmission electron microscopy and selected area electron diffraction. The electrochemical properties of these films were compared by cyclic voltammetry and alternating current impedance spectroscopy. In the cyclic voltammograms of the c-axis oriented films, the anodic and cathodic peaks corresponding to the first-order phase transition at around 3.9 V were sharp and their peak separation was small due to their thin and uniform texture. However, their smooth surface and texture of the aligned (0 0 3) planes gave a larger charge-transfer resistance and a smaller apparent diffusion coefficient in the direction normal to the substrate, respectively, which resulted in poor utilizations (approximately 50%) of the active material. The reactivity in the single-phase region at potentials more positive than 4.0 V was lower than that of randomly oriented films., Journal of Power Sources, Journal of Power Sources, 94175 - 182, 01 Mar. 2001, English, 研究論文(学術雑誌)
  • Pyrolysis/gas chromatography/mass spectroscopy analysis of the surface film formed on graphite negative electrode
    Zempachi Ogumi, Atsushi Sano, Minoru Inaba, Takeshi Abe
    The chemical constituents of the protective surface film formed on graphite negative electrode in ethylene carbonate (EC)-based electrolyte solutions were analyzed by pyrolysis/gas chromatography/mass spectroscopy (Pyro/GC/MS). Oligomers that consist of oxyethylene units, such as ethylene glycol, di(ethylene glycol), and tri(ethylene glycol) methyl ester, were detected. These oligomers were formed by reductive decomposition of EC, and their presence suggested that the surface film contained polymer-like substances that have repeated oxyethylene units. © 2001 Elsevier Science B.V., Journal of Power Sources, Journal of Power Sources, 97156 - 158, 01 Jan. 2001, English, 研究論文(学術雑誌)
  • High capacity technology of nickel-metal hydride batteries
    Zempachi Ogumi, Soon Ki Jeong, Minoru Inaba, Takeshi Abe
    The nickel-Metal hydride battery has been recognized as an important power source for various cordless appliances since its commercialization in 1990. Therefore, demands for capabilities of the batteries have been increasing. A key technology to meet these demands is improvement of the electrode materials. This work is focused on improving composition and microstructure of the bulk and surface states of hydrogen-absorbing alloys used as the negative electrode material and the composition of the nickel hydroxide and additives used for the positive electrode., Macromolecular Symposia, Macromolecular Symposia, 156203 - 211, 21 Dec. 2000
  • Oxygen chemical potential variation in ceria-based solid oxide fuel cells determined by Raman spectroscopy
    Atsushi Mineshige, Toshiya Taji, Yasunori Muroi, Masafumi Kobune, Satoshi Fujii, Naoya Nishi, Minoru Inaba, Zempachi Ogumi
    The profile of oxygen chemical potential in 20 mol% Sm-doped ceria Ce0.8Sm0.2O2-δ (SDC) at 1273 K under the open-circuit conditions of solid oxide fuel cells was determined using Raman spectroscopy. SDC pellets were annealed in various atmospheres, and a peak intensity of a Raman band of SDC in the range 540-600 cm-1, which has been assigned to a band that originates in the oxygen vacancies, increased with decreasing oxygen partial pressure [P(O2)] upon annealing. A clear relationship between the peak area of the oxygen-vacancy band and P(O2) upon annealing was obtained. This relationship was used to determine the profile of oxygen partial pressure, P(O2), in SDC located between fuel and air. The experimental profile was in good agreement with that obtained theoretically. The profile revealed that most part of SDC was mixed conductive and only a thin layer adjacent to the air side remained purely ionic conductive under the open-circuit conditions of SOFCs., Solid State Ionics, Solid State Ionics, 135481 - 485, 01 Nov. 2000
  • Calorimetric study on the hysteresis in the charge-discharge profiles of mesocarbon microbeads heat-treated at low temperatures
    Minoru Inaba, Masato Fujikawa, Takeshi Abe, Zempachi Ogumi
    Thermal behavior during charge and discharge of mesocarbon microbeads (MCMB) heat-treated at 700, 1000, and 1800 °C was investigated by calorimetry to clarify the origin of the hysteresis in the voltage profiles of the former two kinds of MCMB. MCMB heat-treated at 700 and 1000 °C exhibited large exotherms over voltage plateaus at cell voltages close to 0 V during lithium insertion and at about 1 V during lithium extraction, which cannot be explained by polarization or entropy change. The large generation of heat indicated that some exothermic chemical reactions are associated with insertion/extraction reactions in the plateau regions in both directions. The anomalous thermal behaviors over the plateau regions were successfully explained by an energy diagram proposed by Zheng et al. in which lithium insertion is followed by a chemical reaction that has an activation energy barrier., Journal of the Electrochemical Society, Journal of the Electrochemical Society, 1474008 - 4012, 01 Nov. 2000
  • Transmission electron microscopy (TEM) analysis of two-phase reaction in electrochemical lithium insertion within α-MoO3
    Yasutoshi Iriyama, Takeshi Abe, Minoru Inaba, Zempachi Ogumi
    The mechanism of a phase transition in electrochemical lithium insertion into α-MoO3was investigated by transmission electron microscopy (TEM) and X-ray diffraction (XRD). α-MoO3was deposited on a special Au micro grid for TEM observation by pulsed laser ablation. The phase transition ranged from x = 0 to 0.25 in LixMoO3upon electrochemical lithium insertion into α-MoO3. In this two-phase coexistence region, the XRD (020) line of the lithium inserted phase (Li0.25MoO3) grew at the expense of the (020) line of the pristine α-MoO3as lithium ions were inserted. However, the intensity of the lithium-inserted phase was much weaker than expected in the initial stage of the phase transition. TEM observation revealed that lithium ions were inserted randomly into some preferred crystallites of α-MoO3to form a disordered phase in the initial stage, which explained the presence of the induction period upon the growth of the lithium inserted phase., Solid State Ionics, Solid State Ionics, 13595 - 100, 01 Nov. 2000, English, 研究論文(学術雑誌)
  • Electrical Property, Crystal Structure and Oxygen Nonstoichiometry of La1-xSrxCo0.2Fe0.8O 3-δ
    Atsushi Mineshige, Junko Izutsu, Maiko Nakamura, Kengo Nigaki, Masafumi Kobune, Satoshi Fujii, Minoru Inaba, Zempachi Ogumi, Takeshi Yao
    Electrical conductivity of mixed conducting perovskite-type oxide, La1-xSrxCo0.2Fe0.8O 3-δ (LSCF, 0.4≤x≤0.7) was determined as functions of Sr-content (x), temperature (T) and oxygen partial pressure [P(O2)]. Crystal structure and oxygen nonstoichiometry (δ) of LSCF was evaluated and correlated with its electrical property. The electrical conductivity (σ) in LSCF was greatly affected by oxygen nonstoichiometry and B-O-B angle (B; B-site elements) in the crystal., Electrochemistry, Electrochemistry, 68515 - 518, 01 Jun. 2000
  • Raman scattering study of acceptor-acceptor-type graphite bi-intercalation compounds
    Takeshi Abe, Minoru Inaba, Zempachi Ogumi, Yasukazu Yokota, Yasuo Mizutani
    Stages 4 and 5 (Formula presented)-graphite intercalation compounds (GIC’s) were prepared by a two-bulb method, and were used as host materials for the synthesis of graphite bi-intercalation compounds (GBC’s), where the bi-intercalated species were ICl, IBr, and (Formula presented) Various types of GBC’s were obtained by changing the reaction temperatures, and the layer sequences were clarified by x-ray diffraction. Lattice dynamics of the resultant GBC’s was investigated by Raman spectroscopy. Since the layer sequence of GBC’s from a stage 4 (Formula presented) with one bi-intercalated layer is (Formula presented) where (Formula presented) and (I) denote the (Formula presented) graphite, (Formula presented) and bi-intercalated layers, respectively, and all graphene layers are adjacent to an intercalate layer. The GBC’s give only one Raman-active (Formula presented) mode frequency in the Raman spectra although the intercalates are different. GBC’s from stage 5 (Formula presented) with one bi-intercalated layer give the stacking sequence of (Formula presented) Since two types of graphene layers, interior (Formula presented) and bounding (Formula presented) layers exist, two peaks identified as Raman-active (Formula presented) and (Formula presented) mode frequencies appear in Raman spectra. Both frequencies were affected by the bi-intercalated species. From the (Formula presented) frequencies, the degree of electron affinities of the bi-intercalated layers was evaluated to be in the order of (Formula presented) For the GBC’s with two bi-intercalated layers, their layer sequences were determined to be (Formula presented) or (Formula presented) In this case, only bounding layers of graphite exist. However, two peaks were observed in the Raman spectra. The difference of the Raman-active (Formula presented) mode frequencies was due to the intercalate coupling effect. © 2000 The American Physical Society., Physical Review B - Condensed Matter and Materials Physics, Physical Review B - Condensed Matter and Materials Physics, 6111344 - 11347, 01 Jan. 2000
  • Electrochemical intercalation of Li into carbon thin films prepared by plasma CVD
    Tomokazu Fukutsuka, Takeshi Abe, Minoru Inaba, Zempachi Ogumi
    Carbonaceous thin films were prepared from acetylene and argon by plasma CVD. The carbon thin films were characterized by Raman spectroscopy and then their electrochemical properties were studied by cyclic voltammetry and charge-discharge measurements. Crystallinity of the films prepared at 90W was much higher than that at 10W. The difference of the applied RF power also effected on the results of cyclic voltammetry and charge-discharge measurements. Correlation of applied RF power and the electrochemical properties of carbon thin films was discussed., Molecular Crystals and Liquid Crystals Science and Technology Section A: Molecular Crystals and Liquid Crystals, Molecular Crystals and Liquid Crystals Science and Technology Section A: Molecular Crystals and Liquid Crystals, 340517 - 522, 01 Jan. 2000
  • Surface film formation on graphite negative electrodes in rechargeable lithium batteries
    Zempachi Ogumi, Soon Ki Jeong, Minoru Inaba, Takeshi Abe
    The choice of solvent is quite important to obtain good protecting surface film on graphite negative electrodes in rechargeable lithium batteries. A subtle difference of the molecular structure of solvent greatly affects the easiness of surface film formation. In order to understand the solvent effects and to elucidate the mechanism of surface film formation, morphology changes of the basal plane of highly oriented pyrolytic graphite were studied using electrochemical scanning tunneling microscopy (EC-STM). In this article, our recent results of EC-STM observation in different solvent systems are reviewed., Macromolecular Symposia, Macromolecular Symposia, 156195 - 202, 01 Jan. 2000
  • Nucleation and phase-boundary movement upon stage transformation in lithium-graphite intercalation compounds
    Atsushi Funabiki, Minoru Inaba, Takeshi Abe, Zempachi Ogumi
    Nucleation and phase-boundary movement upon stage transformation in lithium-graphite intercalation compounds were investigated by potential-step chronoamperometry and alternating current impedance spectroscopy. Highly oriented pyrolytic graphite was used as a host graphite material. The current response obtained by potential step was strongly dependent on the kind and direction of stage transformation. A current hump due to the nucleation and nuclear growth of a new stage was observed during the stage transformations from dilute stage 1 to stage 4 and from stage 2 to stage 1 upon lithium intercalation, and from stage 4 to dilute stage 1 upon deintercalation. The rate-determining steps for nucleation and for phase-boundary movement were discussed in the stage transformation between dilute stage 1 and stage 4. It was shown that the nucleation rate was controlled by the reaction at the graphite/electrolyte interface in both directions. The rate of the phase-boundary movement was affected greatly by the diffusivity of lithium ions in a growing phase; that is, it was controlled mainly by the diffusion in stage 4 in the direction from dilute stage 1 to stage 4, whereas by the interfacial reaction in the reverse direction., Electrochimica Acta, Electrochimica Acta, 45865 - 871, 01 Dec. 1999
  • STM Study of Well-Defined Graphite/Electrolyte Interface Polarized in Propylene Carbonate Solution Containing 12-Crown-4
    Minoru Inaba, Yutaka Kawatate, Atsushi Funabiki, Soon Ki Jeong, Takeshi Abe, Zempachi Ogumi
    Surface morphology change of highly oriented pyrolytic graphite was investigated in 1 M (M = mol dm-3) LiClO4 dissolved in propylene carbonate (PC) and PC - 0.5 M 12-crown-4 using electrochemical scanning tunneling microscopy to elucidate the mechanism of passive film formation on graphite electrode in rechargeable lithium batteries. In PC, vigorous exfoliation of graphite layers was observed after potential cycling down to 0 V vs. Li/Li+. Such exfoliation was greatly suppressed by 12-crown-4 addition. The original step structure was nearly maintained, but swellings of graphite surface appeared after potential cycling. From these results, the role of 12-crown-4 in passive film formation was discussed., Electrochemistry, Electrochemistry, 671153 - 1155, 01 Dec. 1999
  • Effect of fluorinated alcohol on the kinetics of cathodic oxygen reduction at gold electrodes
    Jun Maruyama, Minoru Inaba, Zempachi Ogumi
    The kinetics of oxygen reduction at Au was studied in 0.5 M H2SO4, in which a fluorinated alcohol, 2,2,3,3,3-pentafluoro-1-propanol (CF3CF2CH2OH) was added as a model of the fluorocarbon phase of Nafion in the electrodes of proton-exchange membrane fuel cells (PEMFCs). A rotating ring-disk electrode technique was used to detect intermediate H2O2 formation and to determine kinetic parameters for O2 reduction. Kinetic parameters such as the kinetic current, Tafel slope, the ratio of the direct four-electron reduction to the series two-electron reduction, and the rate constant for reduction of intermediate H2O2 were determined. The kinetic current increased with an increase in the concentration of CF3CF2CH2OH up to 1 × 10-2 M, and then decreased with further addition. The rate constant for the reduction of intermediate H2O2 decreased monotonously by the addition of CF3CF2CH2OH over the whole concentration range tested. The increase in kinetic current was attributed to a higher concentration of O2 in the adsorption layer of CF3CF2CH2OH, while the decreases in kinetic current above 1 × 10-2 M and in the rate constant were attributed to a decrease in the number of the reaction sites on Au surface., Electrochimica Acta, Electrochimica Acta, 45415 - 422, 15 Oct. 1999
  • STM study on graphite/electrolyte interface in lithium-ion batteries: solid electrolyte interface formation in trifluoropropylene carbonate solution
    Minoru Inaba, Yutaka Kawatate, Atsushi Funabiki, Soon Ki Jeong, Takeshi Abe, Zempachi Ogumi
    Lithium intercalation within graphite was studied in an electrolyte system, 1 M LiClO4 dissolved in trifluoropropylene carbonate (TFPC). Lithium was intercalated within graphite in TFPC. The reversible capacity obtained (275 mAh g-1) was smaller than that in ethylene carbonate-based solutions while the irreversible capacity was larger (335 mAh g-1). The morphology change of the basal plane of highly oriented pyrolytic graphite (HOPG) was observed by electrochemical scanning tunneling microscopy (STM) to obtain information about passivating film (solid electrolyte interface, SEI) formation in this solvent system. The exfoliation of graphite layers was observed at 1.1 and 1.0 V vs. Li+/Li, and then swelling of graphite layers appeared along step edges at 0.5 V. The feature observed at 0.5 V was considered as SEI itself in this solvent system., Electrochimica Acta, Electrochimica Acta, 4599 - 105, 30 Sep. 1999
  • Stage transformation of lithium-graphite intercalation compounds caused by electrochemical lithium intercalation
    Atsushi Funabiki, Minoru Inaba, Takeshi Abe, Zempachi Ogumi
    The kinetics of the stage transformation of lithium-graphite intercalation compounds from dilute stage 1 to stage 4 were studied using potential-step chronoamperometry and alternating current impedance spectroscopy. Highly oriented pyrolytic graphite was used as a host material. The current-transient curve showed a current hump, suggesting that the stage transformation was initiated by the nucleation and growth of stage 4. The phase-boundary movement was discussed quantitatively using a simple geometric model. The phase boundary progressed in proportion to time during the initial stage. The rate constant was inversely proportional to the product of the interfacial resistance and the geometric edge-plane area, indicating that the phase-boundary movement was determined by the rate of the reaction at the graphite/electrolyte interface. In the following stage, the phase boundary advanced in proportion to the square root of time. The parabolic rate constant obtained experimentally was in satisfactory agreement with that calculated using Wagner's classical model which describes the diffusion within two phases separated by a phase boundary. These results indicated that the phase-boundary movement was initially determined by the rate of the interfacial electrochemical reaction and was controlled thereafter by a diffusion process., Journal of the Electrochemical Society, Journal of the Electrochemical Society, 1462443 - 2448, 01 Jul. 1999
  • Metal-Insulator Transition and Crystal Structure of La1-xSrxCoO3as Functions of Sr-Content, Temperature, and Oxygen Partial Pressure
    Atsushi Mineshige, Masafumi Kobune, Satoshi Fujii, Zempachi Ogumi, Minoru Inaba, Takeshi Yao, Kenji Kikuchi
    Electrical properties of La1-xSrxCoO3(LSC) change with variations in Sr content, temperature, and oxygen partial pressure. With a change in each variable, LSC showed metal-insulator transition (MIT). The changes in electrical properties of LSC were correlated here with those of its crystal structure. The variations of crystallographic parameters such as the length ofa-axis, the rhombohedral angle, the Co-O distance, and the Co-O-Co angle (θ) were precisely determined by powder X-ray Rietveld analysis. Of these, the variation ofθdescribed most consistently the variation of conduction state, metallic or insulating, of LSC. The Co-O-Co angle increased whenever the conduction state changed from insulating to metallic by changing each variable, Sr content, temperature, and oxygen partial pressure. In addition, MIT took place at a critical Co-O-Co angle of ca. 165° in each case. It was concluded that the transition from insulator to metal is caused by the closing of the charge transfer band gap, induced by broadening of the electronic bandwidths of the Co-3dand O-2pbands with an expansion of the Co-O-Co angle. © 1999 Academic Press., Journal of Solid State Chemistry, Journal of Solid State Chemistry, 142374 - 381, 01 Feb. 1999, English, 研究論文(学術雑誌)
  • Functionally gradient polymer electrolyte prepared by plasma polymerization
    Zempachi Ogumi, Takeshi Abe, Satomi Nakamura, Minoru Inaba
    Functionally gradient polymer electrolytes were prepared from 2-[2-(2-ethoxyethoxy)ethoxy]ethoxydimethylvinylsilane (EDVS) containing 10 wt% LiCF3SO3 by a plasma polymerization technique from liquid phase. The polymer electrolytes were characterized by FT-IR, X-ray photoelectron spectroscopy, and the ionic conductivity measurements. From the IR spectra of EDVS plasma polymer electrolytes, the characteristic peaks for olefin groups disappeared but the spectra were similar to that of EDVS monomer, indicating that the polymerization occurs mainly by a chain propagation. The ionic conductivity increased from surface to bulk of the plasma polymer, that is, functionally gradient polymer electrolytes were prepared., Solid State Ionics, Solid State Ionics, 121289 - 293, 01 Jan. 1999
  • Development of a carbon-based lithium microbattery
    K. Kinoshita, X. Song, J. Kim, M. Inaba
    A conceptual design for a carbon-based rechargeable Li microbattery and the progress in fabricating the electrode microstructures are described in this paper. The microstructures are produced from photoresists that are typically used by the semiconductor industry. The photoresist is spin coated on a silicon wafer, 'patterned' by photolithography and then heated in an inert environment to form carbon microstructures (< 50-micron dimension) which serve as the electrodes. Progress in fabricating the electrode microstructures, lithiation of the carbon negative electrode and electropolymerization of the polypyrrole positive electrode will be discussed. © 1999 Elsevier Science S.A. All rights reserved., Journal of Power Sources, Journal of Power Sources, 81-82170 - 175, 01 Jan. 1999
  • Influence of defects on the phase-boundary movement in a stage transformation of lithium-graphite intercalation compounds
    Atsushi Funabiki, Minoru Inaba, Takeshi Abe, Zempachi Ogumi
    The influence of defects on the phase-boundary movement in the stage transformation from random stage (dilute stage 1) to stage 4 of lithium-graphite intercalation compounds was investigated using highly oriented pyrolytic graphite (HOPG). Potential-step chronoamperometry and in situ optical microscopy coupled with micro Raman spectroscopy were used to clarify macroscopic and microscopic influence of defects. Potential-step chronoamperometry confirmed that the diffusion-limited rate of the phase-boundary movement in the bulk of HOPG was independent of the crystallinity of the samples. This result indicates that defects have macroscopically no appreciable influence on the phase-boundary movement. In situ optical microscopy on the basal plane of HOPG revealed that the nucleation and growth of the stage-4 phase took place quite inhomogeneously in the initial stage. The rate of the phase-boundary movement in the surface region of HOPG was roughly evaluated to be in the range of 5 to 10 μm min-1. The phase-boundary movement was seriously retarded by cracks formed on the basal plane during the stage transformation., Carbon, Carbon, 371591 - 1598, 01 Jan. 1999, English, 研究論文(学術雑誌)
  • Electrochemical STM observation of LiMn2O4thin films prepared by pulsed laser deposition
    Minoru Inaba, Takayuki Doi, Yasutoshi Iriyama, Takeshi Abe, Zempachi Ogumi
    Spinel LiMn2O4thin films were prepared by pulsed laser deposition. The surface morphology change of the film with potential cycling between 3.5 and 4.25 V was observed in 1 M LiClO4/PC by electrochemical scanning tunneling microscopy. After cycling, small round-shaped particles of 120-250 nm in diameter appeared on the surface. The number of the newly formed particles increased with repeated cycling while the size decreased. The observed morphology change suggested that the small particle were formed from the solution through a kind of dissolution/precipitation reactions. © 1999 Elsevier Science S.A. All rights reserved., Journal of Power Sources, Journal of Power Sources, 81-82554 - 557, 01 Jan. 1999, English, 研究論文(学術雑誌)
  • In situ raman and STM techniques for studies on rechargeable lithium batteries
    Minoru Inaba, Zempachi Ogumi
    Electrochemistry, Electrochemistry, 66986 - 991, 01 Dec. 1998
  • In situ Raman and STM techniques for studies on rechargeable lithium batteries
    Minoru Inaba, Zempachi Ogumi
    Denki Kagaku, Denki Kagaku, 66986 - 991, 01 Dec. 1998
  • Rotating ring-disk electrode study on the cathodic oxygen reduction at Nafion®-coated gold electrodes
    Jun Maruyama, Minoru Inaba, Zempachi Ogumi
    The influence of Nafion® films on the kinetics of cathodic oxygen reduction was investigated using Nafion®-coated gold electrodes. A rotating ring-disk electrode (RRDE) technique was used to determine kinetic parameters for O2reduction and to detect intermediate H2O2formation. Kinetic parameters such as the kinetic current, Tafel slope, potential dependence of the ratio of the direct 4-electron reduction to the series 2-electron reduction were determined and compared with those obtained at bare Au in 0.5 M H2SO4. The kinetic data showed no clear evidence of the enhancement effects of Nafion®-coating on the cathodic O2reduction at Au. This suggested that the Au surface has less affinity for the hydrophobic region of Nafion®, in which a high O2solubility is expected. © 1998 Elsevier Science S.A. All rights reserved., Journal of Electroanalytical Chemistry, Journal of Electroanalytical Chemistry, 458175 - 182, 30 Oct. 1998, English, 研究論文(学術雑誌)
  • Electroreduction of 2-cyclohexen-1-one on metal-solid polymer electrolyte composite electrodes
    Akira Kunugi, Masaru Fujioka, Mikito Yasuzawa, Minoru Inaba, Zempachi Ogumi
    The effects of the electrode material on electro reduction of 2-cyclohexen-1-one were examined using various metal-solid polymer electrolyte electrodes, i.e., unmodified, Bi-modified and Zn-modified Pt- and Au-Nafion, Bi-Selemion and Zn-modified Au-Selemion electrodes. A mixture of monomeric products such as cyclohexanone 2 and 2-cyclohexen-1-ol 3, and/or dimeric products such as the diketone 4, the hydroxyketone 5 and the glycol 6 were produced, the main products being largely dependent on electrolytic conditions. For example, modification of Pt-Nafion electrode with bismuth or zinc gave 2 selectively at high current efficiency. Modification of Au-Nafion electrode with bismuth was effective in giving dimeric products, whereas with Bi,Pt-Nafion and Zn,Pt- and Zn,Au-Nafion electrodes, only monomeric products were obtained. The use of Bi-Selemion and Zn,Au-Selemion electrodes gave preferentially dimeric products. © 1998 Elsevier Science Ltd. All rights reserved., Electrochimica Acta, Electrochimica Acta, 44653 - 657, 30 Sep. 1998
  • Preparation of ceria thin films and microtubes by vapor-phase deposition using NiO as oxygen source
    Minoru Inaba, Atsushi Mineshige, Shinji Nakanishi, Isao Nishimura, Akimasa Tasaka, Kenji Kikuchi, Zempachi Ogumi
    A modified version of electrochemical vapor deposition (EVD) using NiO as an oxygen source was applied to the fabrication of CeO2 thin films and microtubes. Cerium trichloride was used as a metal source, and NiO pellets and surface-oxidized Ni wires of 125 μm diameter as substrates for deposition. Thin films of cubic CeO2 were formed on both substrates by the vapor-phase reaction at 900 and 950°C. Furthermore, ceria microtubes of 130 μm diameter were obtained by soaking the ceria-coated Ni wires in hydrochloric acid. © 1998 Elsevier Science S.A. All rights reserved., Thin Solid Films, Thin Solid Films, 32318 - 22, 22 Jun. 1998
  • Influence of Nafion® film on the kinetics of anodic hydrogen oxidation
    Jun Maruyama, Minoru Inaba, Katsumi Katakura, Zempachi Ogumi, Zen Ichiro Takehara
    The influence of Nafion® film on the kinetics of anodic oxidation of hydrogen was investigated on Nafion®-coated platinum electrodes. Hydrodynamic voltammetry was used to obtain the kinetic current for the H2oxidation reaction, and the exchange current densities at bare and Nafion®-coated Pt rotating disk electrodes were determined using the modified Koutecky-Levich equations. The exchange current density at Nafion®-coated Pt was higher by 20% than that at bare Pt in 0.1 M HClO4. The enhancement in exchange current density was attributed to a higher H2solubility in recast Nafion® than in the solution. The hydrogen solubility in recast Nafion® determined by potential step chronoamperometry (PSCA) was 1.4 × 10-6mol cm-3, which was 1.8 times higher than that in the solution (0.78 × 10-6mol cm-3). The difference in H2solubility determined by potential step chronoamperometry was larger than that estimated from the difference in exchange current density. The discrepancy was explained by the peculiar multiphase-structure of Nafion®, where H2solubility in the electrochemically inactive fluorocarbon region is higher than that in the ionic cluster region. © 1998 Elsevier Science S.A. All rights reserved., Journal of Electroanalytical Chemistry, Journal of Electroanalytical Chemistry, 447201 - 209, 30 Apr. 1998, English, 研究論文(学術雑誌)
  • Electrochemical Lithium Intercalation within Carbonaceous Materials: Intercalation Processes, Surface Film Formation, and Lithium Diffusion
    Zempachi Ogumi, Minoru Inaba
    Electrochemical lithium intercalation within carbonaceous materials has attracted much attention for use to produce anodes in rechargeable lithium batteries. Although small-size rechargeable lithium cells using carbon anodes have been already commercialized, there still remain a lot of problems to be solved. Furthermore, recent global environmental issues require carbon anodes with high energy densities for use in electric energy storage and electric vehicles in the near future. This review article covers recent topics of the lithium intercalation, focusing on three fundamental aspects: intercalation processes, surface film formation, and lithium diffusion within carbons., Bulletin of the Chemical Society of Japan, Bulletin of the Chemical Society of Japan, 71521 - 534, 01 Jan. 1998
  • Impedance study on the electrochemical lithium intercalation into natural graphite powder
    Atsushi Funabiki, Minoru Inaba, Zempachi Ogumi, Shin Ichi Yuasa, Junhiko Otsuji, Akimasa Tasaka
    Electrochemical lithium intercalation into natural graphite powder of different sizes was studied by alternating current impedance spectroscopy. Impedance spectra at various potentials were fitted with a modified Randles equivalent circuit including a pseudocapacitance to express the observed finite diffusional behavior. The variations of electrochemical parameters with electrode potential, such as the charge-transfer resistance, the pseudocapacitance, the Warburg prefactor, and, finally, the chemical diffusion coefficient of lithium ion within graphite, were evaluated and discussed. It was shown that the charge-transfer reaction takes place on the whole surface of graphite particles, whereas lithium ion is intercalated from the edge plane and diffuses to the interior. The kinetics of the charge-transfer reaction was independent of the structure of the host. In contrast, the diffusivity of lithium ion within graphite was strongly dependent on the host structure, and the dependence was explained in terms of differences in in-plane and stacking order of lithium-graphite intercalation compounds formed by the intercalation., Journal of the Electrochemical Society, Journal of the Electrochemical Society, 145172 - 178, 01 Jan. 1998, English, 研究論文(学術雑誌)
  • Growth rate of yttria-stabilized zirconia thin films formed by electrochemical vapour-deposition using NiO as an oxygen source: II. Effect of the porosity of NiO substrate
    Minoru Inaba, Atsushi Mineshige, Tomoyuki Maeda, Shinji Nakanishi, Tsutomu Ioroi, Tadayoshi Takahashi, Akimasa Tasaka, Kenji Kikuchi, Zempachi Ogumi
    Yttria-stabilized zirconia (YSZ) thin films were formed at 1000°C by a modified electrochemical vapour-deposition (EVD) using NiO as an oxygen source, and ZrCl4and YCl3as metal sources. Growth rate kinetics were examined using NiO pellet substrates with different pore structures. The thickness of YSZ film increased linearly with deposition time, and the growth rate increased with increasing the porosity of the substrate. The pore size as well as the porosity affected the growth rate. In addition, the observed growth rate was much slower than the theoretical one assuming that the electrochemical transportation of the charged species across the growing film is rate limiting. From these results, it was concluded that the rate-determining step is not the bulk electrochemical transport, but the mass transport of dissociated oxygen in the substrate pore., Solid State Ionics, Solid State Ionics, 104303 - 310, 11 Dec. 1997
  • Intercalation of lithium into natural graphite flakes and heat-treated polyimide films in ether-type solvents by chemical method
    T. Abe, Y. Mizutani, T. Tabuchi, K. Ikeda, M. Asano, T. Harada, M. Inaba, Z. Ogumi
    X-ray diffraction and Raman spectroscopy have been used to study the intercalation of Li into natural graphite flakes and heat-treated polyimide films (HTT = 1800-3000 °C) by chemical method in various ether-type solvents. Here, naphthalene was used as a dissolving agent for Li, and the solvents were tetrahydrofuran (THF), 2-methyltetrahydrofuran (MeTHF), 2,5-dimethyltetrahydrofuran (diMeTHF), 1,2-dimethoxyethane (DME), 1,2-diethoxyethane (DEE), 1-methoxypropane (MP), 1-methoxybutane (MB) and diethyl ether (Et2O). First, to elucidate the effects of the solvents, natural graphite flakes were used as a host material. By use of THF, DME and DEE, co-intercalation of Li and these solvents occurred to form ternary Li-solvent graphite intercalation compounds (GICs), but binary Li-GICs without solvents were obtained in MeTHF, diMeTHF, MP, MB and Et2O solvents. These results were confirmed by (00l) X-ray diffraction patterns. Second, co-intercalation of Li and THF into the heat-treated polyimide films was studied mainly by use of the Raman scattering results. As a result, co-intercalation of Li and THF occurred to form Li-THF-GIC for highly graphitized polyimide films heat-treated above 2400 °C, while only Li was found to be intercalated into the less graphitized films heat-treated below 2100 °C. © 1997 Published by Elsevier Science S.A., Journal of Power Sources, Journal of Power Sources, 68216 - 220, 01 Jan. 1997
  • Electrochemical scanning tunneling microscopy analysis of the surface reactions on graphite basal plane in ethylene carbonate-based solvents and propylene carbonate
    Minoru Inaba, Zyun Siroma, Yutaka Kawatate, Atsushi Funabiki, Zempachi Ogumi
    In order to elucidate the mechanism of surface film formation on graphite negative electrodes of rechargeable lithium-ion batteries, topographical changes of the basal plane of a highly oriented pyrolytic graphite were observed in a few electrolyte solutions under polarization by electrochemical scanning tunneling microscopy. In 1 M LiClO4/ethylene carbonate (EC)+diethyl carbonate, a hill-like structure of ∼ 1 nm height appeared on the surface of highly oriented pyrolytic graphite at 0.95 V versus Li/Li+, and then changed at 0.75 V to irregular shaped blister-like features with a maximum height of ∼ 20 nm. In 1 M LiClO4/EC+dimethoxyethane, hemispherical blisters of ∼ 20 nm height appeared at 0.90 V. These morphology changes, hill and blister formation, were attributed to the intercalation of solvated Li+ ions into graphite interlayers and to the accumulation of its decomposed products, respectively. On the other hand, only rapid exfoliation and rupturing of graphite layers were observed in 1 M LiClO4/propylene carbonate (PC), which was considered to be responsible for ceaseless solvent decomposition when graphite electrodes are charged in PC-based solutions. From the observed topographical changes, it was concluded that the intercalation of solvated Li+ ions is a necessary step for stable surface film formation on graphite. © 1997 Elsevier Science S.A., Journal of Power Sources, Journal of Power Sources, 68221 - 226, 01 Jan. 1997
  • A.c. impedance analysis of electrochemical lithium intercalation into highly oriented pyrolytic graphite
    Atsushi Funabiki, Minoru Inaba, Zempachi Ogumi
    Electrochemical lithium intercalation into graphite was studied by cyclic voltammetry and a.c. impedance spectroscopy. Highly oriented pyrolytic graphite was used as a model graphite material to distinguish the difference in electrochemical behavior between the basal and the edge planes at graphite. A comparison between cyclic voltammograms of the basal plane and the whole surface of highly oriented pyrolytic graphite revealed that electrochemical lithium intercalation proceeds predominantly at the edge plane/electrolyte interface. The charge-transfer resistance changed continuously with electrode potential, and no significant change was observed at stage transition potentials (210, 120, and 90 mV versus Li/Li+). From the variations of the Warburg impedance of samples of different sizes, it was concluded that lithium diffuses from the edge plane to the interior in the direction parallel to the basal plane and that its diffusivity changes with the stage structure of the bulk lithium-graphite intercalation compound. © 1997 Elsevier Science S.A., Journal of Power Sources, Journal of Power Sources, 68227 - 231, 01 Jan. 1997
  • Graphite intercalation compounds prepared in solutions of alkali metals in 2-methyltetrahydrofuran and 2, 5-dimethyltetrahydrofuran
    Y. Mizutani, T. Abe, K. Ikeda, E. Ihara, M. Asano, T. Harada, M. Inaba, Z. Ogumi
    The intercalation of alkali metals (Li, K, Rb and Cs) into natural graphite flakes in the solutions of 2-methyltetrahydrofuran (MeTHF) and 2, 5-dimethyltetrahydrofuran (diMeTHF) containing naphthalene has been studied by X-ray diffraction (XRD), where naphthalene is used as a dissolving agent for alkali metals. When MeTHF is used as a solvent, binary Li-and K-graphite intercalation compounds (GICs) have been obtained, in contrast to the case of Rb and Cs, where both binary alkali metal GICs and ternary alkali metal-MeTHF-GICs are obtained. Using diMeTHF instead of MeTHF, a selective preparation of binary GICs for all the alkali metals has been established. Copyright © 1997 Elsevier Science Ltd., Carbon, Carbon, 3561 - 65, 01 Jan. 1997, English, 研究論文(学術雑誌)
  • Raman study of layered rock-salt LiCoO2and its electrochemical lithium deintercalation
    Minoru Inaba, Yasutoshi Iriyama, Zempachi Ogumi, Yasufumi Todzuka, Akimasa Tasaka
    Unpolarized and polarized Raman spectra (200-800 cm-1) of LiCoO2with a layered rock-salt structure were measured. The Raman-active lattice modes of LiCoO2were assigned by polarized Raman measurements of a c-axis oriented thin film. The variation of the Raman spectra of Li1-xCoO2powder prepared by electrochemical lithium deintercalation was investigated, and the spectral changes were well correlated with the structural changes determined by x-ray diffraction except that peak splitting by the distortion in the monoclinic phase was not observed. The observed line broadening of the second hexagonal phase and the monoclinic phase indicated that the lithium ions remaining in the lattice after deintercalation randomly occupy the available sites on the lithium planes in the lattice the layered rock-salt structure. © 1997 John Wiley & Sons, Ltd., Journal of Raman Spectroscopy, Journal of Raman Spectroscopy, 28613 - 617, 01 Jan. 1997, English, 研究論文(学術雑誌)
  • Hydrogen oxidation on partially immersed Nafion®-coated electrodes
    Minoru Inaba, Masaharu Uno, Jun Maruyama, Akimasa Tasaka, Katsumi Katakura, Zempachi Ogumi
    The mass transport of hydrogen on partially immersed Nafion®-coated electrodes (Nafion®|Pt|highly oriented pyrolytic graphite) was investigated as a model of the three-phase region of the gas-diffusion electrodes in proton-exchange membrane fuel cells. On raising the electrode from a position at which the Nafion® coating was fully immersed in the electrolyte solution (h = 0mm), the dependence of the H2oxidation current on h was similar to that reported for a partially immersed flat platinum electrode. In contrast, on raising from a partially immersed position (h = 3mm), the current was independent of h, and higher than that when raising from h = 0mm at a given Nafion® thickness. When raising from h = 3 mm, the Nafion® coating above the intrinsic meniscus was not covered with a thin liquid electrolyte film, but functioned solely as a supermeniscus. This made hydrogen diffusion easier, resulting in the observed higher current. From the above results, useful implications for the design of gas-diffusion electrodes in PEMFCs are demonstrated., Journal of Electroanalytical Chemistry, Journal of Electroanalytical Chemistry, 417105 - 111, 07 Nov. 1996, English, 研究論文(学術雑誌)
  • Crystal structure and metal-insulator transition of La1-xSrxCoO3
    Atsushi Mineshige, Minoru Inaba, Takeshi Yao, Zempachi Ogumi, Kenji Kikuchi, Masaya Kawase
    Crystal structure of perovskite La1-xSrxCoO3(0.0 ≤ x ≤ 0.7) was precisely determined by powder X-ray Rietveld analysis, and its correlation with the electrical properties was discussed. The space group was assigned to rhombohedral R3̄c in the range 0.0 ≤ x ≤ 0.5 and to cubic Pm3m in the range 0.55 ≤ x ≤ 0.7. At x ∼ 0.25 the Co-O distance and Co-O-Co angle of this system showed an abrupt decrease and increase with increasing x, respectively, and the conductivity behavior changed from semiconducting to metallic. The abrupt changes in crystal structure were attributed to a change in the band structure at the transition from semiconducting to metallic, that is, an increase in the overlap between the valence band and doped hole sates. © 1996 Academic Press, Inc., Journal of Solid State Chemistry, Journal of Solid State Chemistry, 121423 - 429, 01 Feb. 1996, English, 研究論文(学術雑誌)
  • Preparation of functionally gradient fluorocarbon polymer films by plasma polymerization of NF3and propylene
    Akimasa Tasaka, Akiko Komura, Yoshiharu Uchimoto, Minoru Inaba, Zempachi Ogumi
    Fluorocarbon polymer films were prepared by plasma polymerization using nitrogen trifluoride (NF3) and propylene as starting materials. To improve their adhesiveness to substrates, a novel functionally gradient film in which the content of fluorine decreased continuously from the surface to the interior was prepared by changing source gas composition during deposition. This film had a smooth and pinhole-free surface, and had a high contact angle (110°) for water drop. In addition, it showed good adhesion to a glass substrate. © 1996 John Wiley & Sons, Inc., Journal of Polymer Science, Part A: Polymer Chemistry, Journal of Polymer Science, Part A: Polymer Chemistry, 34193 - 198, 30 Jan. 1996, English, 研究論文(学術雑誌)
  • Preparation of hollow YSZ fibre by electrochemical vapour deposition
    Atsushi Mineshinge, Minoru Inaba, Zempachi Ogumi, Tadayoshi Takahashi, Tomoo Kawagoe, Akimasa Tasaka, Kenji Kikuchi
    Yttria-stabilized zirconia (YSZ) thin films were prepared on NiO pellets by a vapour-phase reaction using ZrCl4 and YCl3 as metal sources and the NiO substrate as an oxygen source for the reaction. The film obtained was cubic YSZ, and its Y2O3 content was approx. 8 mol%. The effect of the sintering temperature of NiO substrates was examined. A surface-oxidized nickel wire was then used as a substrate, and a cubic YSZ layer was coated over the wire. The substrate (nickel and nickel oxide) was dissolved in aqueous hydrochloric acid, and a hollow YSZ fibre of approx. 100 μm diameter was obtained., Solid State Ionics, Solid State Ionics, 86-881251 - 1254, 01 Jan. 1996
  • Preparation of alkali metal graphite intercalation compounds in organic solvents
    Yasuo Mizutani, Eiji Ihara, Takeshi Abe, Mitsuru Asano, Toshio Harada, Zempachi Ogumi, Minoru Inaba
    Binary alkali metal graphite intercalation compounds (GICs) and ternary alkali metal organic solvent GICs have been prepared from natural graphite flakes in ether-type solvents containing alkali metals. Here, phenanthrene is used as a dissolving reagent for alkali metals. The stage structures of GICs prepared from five alkali metals; Li, Na, K, Rb and Cs, and four solvents; tetrahydrofuran (THF), 2-methyltetrahydrofuran (MeTHF), 2,5-dimethyltetrahydrofuran (diMeTHF), 1,2-dimethoxyethane (DME) and 1-methoxybutane (MB) are studied by X-ray diffraction. When the THF and DME solvents are used, ternary alkali metal organic solvent GICs are obtained, irrespective of the type of alkali metal. In contrast, binary alkali metal GICs are formed for some limited combinations of alkali metals and organic solvents such as MeTHF, diMeTHF and MB. In the case of MeTHF, the intercalation of Li, Na and K into graphite takes place without the solvent to form binary alkali metal GICs, but Rb intercalates into graphite both with and without the solvent to form ternary and binary GICs, and furthermore only ternary GIC is formed with Cs. In diMeTHF, binary GICs with Li and Cs and ternary GICs with K and Rb are formed. Binary GICs with Li and K are synthesized in MB., Journal of Physics and Chemistry of Solids, Journal of Physics and Chemistry of Solids, 57799 - 803, 01 Jan. 1996
  • X-ray diffraction and Raman scattering studies of FeCl3-SbCl5-graphite bi-intercalation compounds
    Takeshi Abe, Yasukazu Yokota, Yasuo Mizutani, Mitsuru Asano, Toshio Harada, Minoru Inaba, Zempachi Ogumi
    X-ray diffraction (XRD) and Raman spectroscopy have been used for the study of the bi-intercalation of SbCl5into a stage 5 FeCl3-graphite intercalation compound (GIC). The stage 5 FeCl3-GIC is prepared by an ordinary two-bulb method with the temperature of graphite at 788 K and that of FeCl3at 573 K. The FeCl3-SbCl5-graphite bi-intercalation compound (GBC) with one SbCl5layer is obtained when the temperature of the stage 5 FeCl3-GIC is held at 443 K and the temperature of SbCl5at 373 K in the two-zone system. The stacking sequence of the GBC is found to be an admixture of G(FeCl3)GG(SbCl5)GGG(FeCl3)G and G(FeCl3)GGG(SbCl5)GG(FeCl3)G by XRD, where G, (FeCl3), and (SbCl5) are the graphite, FeCl3, and SbCl5layers, respectively. The Raman spectrum of the GBC shows two peaks associated with the E(2)i2gand E(2)b2gmodes at 1588 cm-1and 1610 cm-1, respectively. For the temperatures of stage 5 FeCl3-GIC at 443 K and SbCl5at 403 K in the two-zone system, the FeCl3-SbCl5-GBC with two SbCl5layers is obtained. The stacking sequence of the GBC is determined to be an admixture of G(FeCl3)GG(SbCl5)GG(SbCl5)G(FeCl3)G and G(FeCl3)G(SbCl5)GG(SbCl5)GG(FeCl3)G. In the Raman spectrum of this GBC, two peaks associated with the E(2)b2gmode are observed at 1616 and 1624 cm-1., Journal of Materials Research, Journal of Materials Research, 113039 - 3044, 01 Jan. 1996, English, 研究論文(学術雑誌)
  • In situ roman study of electrochemical lithium insertion into mesocarbon microbeads heat-treated at various temperatures
    Minoru Inaba, Hiroyuki Yoshida, Zempachi Ogumi, Zempachi Ogumi
    In situ Raman spectra were measured to elucidate the electrochemical lithium insertion mechanism of mesocarbon microbeads (MCMBs) heat-treated at 700 to 2800°C. The spectral changes of the Raman E2g2band of MCMBs heat-treated at 2800°C showed that the lithium insertion mechanism into the microbeads is similar to that into graphite via the formation of staged graphite intercalation compounds, although a clear phase transition from dilute stage 1 to stage 4 was not observed. For MCMBs heat-treated at 1800 and 1000°C the E2g2band shifted downward and upward upon charging and discharging, respectively. No discontinuous change suggesting the formation of staged phases was observed, which indicated that lithium is inserted randomly between graphene layers without the formation of staged phases. The charge and discharge profile of MCMBs heat-treated at 700°C showed a large hysteresis. A potential plateau appeared at about 1 V on the discharge curve, which led to a high capacity of 710 mAh/g. In the case of MCMBs heat-treated at 700°C, the peak wave number of the E2g2band did not shift at all in the whole potential range during charging and discharging. It was considered that the plateau region of MCMBs heat-treated at 700°C giving the high discharge capacity originates not from lithium species inserted between organized graphene layers, but from lithium doped into regions without organized graphitic structure., Journal of the Electrochemical Society, Journal of the Electrochemical Society, 1432572 - 2578, 01 Jan. 1996, English, 研究論文(学術雑誌)
  • Raman spectroscopic analysis of electrochemical behavior of propylviologen in Nafion
    Minoru Inaba, Yumi Osa, Zempachi Ogumi
    The electrochemical and Raman spectroscopic characteristics of propylviologen incorporated into Nafion® film coated on a silver electrode were studied. The results were compared with those on silver in solutions containing Triton X-100, cetyltrimethylammonium bromide (CTAB) and sodium dodecyl sulfate (SDS) micelles. Propylviologen incorporated into Nafion® showed unusual electrochemical and Raman spectroscopic behavior. The half-wave potential for the second step was shifted in the negative direction with respect to that in an aqueous solution, and only a small amount of the doubly reduced form was detected by Raman spectroscopy. Similar behavior was observed in the anionic SDS micellar solution. On the basis of the observed similarity, the residence sites of propylviologen in Nafion® were discussed. © 1995., Journal of Electroanalytical Chemistry, Journal of Electroanalytical Chemistry, 38391 - 98, 21 Feb. 1995, English, 研究論文(学術雑誌)
  • In Situ Raman Study on Electrochemical Li Intercalation into Graphite
    Minoru Inaba, Hiroyuki Yoshida, Zempachi Ogumi
    Electrochemical lithium intercalation into highly oriented pyrolytic graphite and natural graphite powder was investigated using in situ Raman spectroscopy. Three plateaus were observed on the charging curve for both samples. From the Raman spectral changes the first plateau was assigned to a phase transition from dilute stage 1 to stage 4, the second from a stage 2 phase to another stage 2 phase, and the third from stage 2 to stage 1, which are in good agreement with Dahn’s results by in situ x-ray diffraction. The spectral changes associated with the phase transitions occurred reversibly during a charge and discharge cycle. It was shown from the Raman spectral changes of the HOPG electrode that the electrode potential during the electrochemical intercalation is determined by the surface stage of graphite intercalation compounds. © 1994, The Electrochemical Society, Inc. All rights reserved., Journal of the Electrochemical Society, Journal of the Electrochemical Society, 14220 - 26, 01 Jan. 1995
  • Preparation of Yttria‐Stabilized Zirconia Microtube by Electrochemical Vapor Deposition
    Atsushi Mineshige, Minoru Inaba, Zempachi Ogumi, Tadayoshi Takahashi, Tomoo Kawagoe, Akimasa Tasaka, Kenji Kikuchi
    A microtube of yttria‐stabilized zirconia of ca. 100 μm diameter was prepared. An yttria‐stabilized zironia film was formed over a surface‐oxidized nickel wire with a diameter of 10 μm by electrochemical vapor deposition using zirconium tetrachloride and yttrium trichloride as metal sources, and nickel oxide as an oxygen source for the reaction. The YSZ‐coated wire was then immersed in aqueous 11.5 mol.L‐1 hydrochloric acid to dissolve the nickel and nickel oxide, and a microtube of 80 mol? yttria‐stabilized zirconia with a cubic crystal structure was obtained. The surface of the microtube was rough, but was pinhole‐free, from SEM observation. The thickness of the zirconia layer was about 3 μm. Copyright © 1995, Wiley Blackwell. All rights reserved, Journal of the American Ceramic Society, Journal of the American Ceramic Society, 783157 - 3159, 01 Jan. 1995
  • Debye-Waller factors of FeCl3- and ICl-graphite intercalation compounds
    Takeshi Abe, Yasuo Mizutani, Naoki Shinoda, Eiji Ihara, Mitsuru Asano, Toshio Harada, Minoru Inaba, Zempachi Ogumi
    Stage 2 and 3 FeCl3-graphite intercalation compounds (GICs) and stage 1-3 ICl-GICs are prepared by a two-bulb method. The stage structures of the GICs are studied by X-ray diffraction, and the GICs are characterized by the full width at half maximum of the (00l) diffraction peaks. The effective Debye-Waller (DW) factors of the well crystallized FeCl3-GICs and ICl-GICs along the c-axis are determined from the structure parameters, with which the minimum crystallographic R factor is obtained. The effective DW factors are found to decrease with increasing the stage number of the FeCl3-GICs and ICl-GICs. The DW factors of the constituent atoms, carbon, iron, and chlorine, in the FeCl3-GICs and those of carbon, iodine, and chlorine in the ICl-GICs are also determined. © 1995., Carbon, Carbon, 331789 - 1793, 01 Jan. 1995, English, 研究論文(学術雑誌)
  • Electrotransportation of Aniline Through a Perfluorosulfonate Ion-Exchange Membrane
    Minoru Inaba, Koji Toyama, Zempachi Ogumi, Zen Ichiro Takehara, Katsumi Katakura
    Transport phenomena of aniline through Na+-, K+-, and Cs+-form of a perfluorosulfonate ion-exchange membrane, Nafion® 117, under a flow of dc current, electro transportation, were investigated. In each form, an increase in transport number of aniliniumcation was observed in the current density range from 0.3 to 1.3 mA cm-2. The transport number of the anilinium cation in Cs+-form was larger than that expected from the concentration and diffusion coefficient of the anilinium cation in Cs+-form Nafion. These aniline transport phenomena may be attributable to a structural change of Nafion or a decrease in hydrophobic interaction between the anilinium cation and Nafion caused by the flow of dc current. © 1994, The Electrochemical Society, Inc. All rights reserved., Journal of the Electrochemical Society, Journal of the Electrochemical Society, 1411827 - 1831, 01 Jan. 1994
  • Application of the Solid Polymer Electrolyte Method to Organic Electrochemistry: XVII. Indirect Electrochemical Debromination Using Viologens as Microscopic Phase-Transfer Mediators
    Minoru Inaba, Zempachi Ogumi, Zen Ichiro Takehara
    Solid polymer electrolyte (SPE®) composite electrodes using a perfluorinated ion-exchange membrane (Nation®), which is known to be microscopically separated into hydrophilic and hydrophobic domains, were prepared. Various IV, lV‘-dialkyl-4-4’-bipyridinium salts (viologens) were incorporated in the SPE composite electrodes as phase transfer mediators. Electrochemical debromination of meso-l,2-dibromo-l,2-diphenylethane was carried out on the SPE composite electrodes. The results were compared with those obtained in an emulsion system consisting of water and dichloromethane. Of the viologen compounds tested, propyl viologen was the most effective mediator for the SPE composite electrode, while octyl viologen dibromide was the most effective mediator in the emulsion system. The active species for the debromination in the emulsion system was shown to be a doubly reduced neutral form of viologen that was generated by the disproportionation of cation radicals. The disproportionation constant, Kd, of octyl viologen cation radical in a two-phase system consisting of water and dichloromethane was estimated to be 809. The reaction mechanism on the SPE composite electrode was discussed, and it was considered that the active species was generated by disproportionation at the microscopically heterogeneous interface between the hydrophilic and hydrophobic domains of the Nafion. © 1994, The Electrochemical Society, Inc. All rights reserved., Journal of the Electrochemical Society, Journal of the Electrochemical Society, 1412579 - 2586, 01 Jan. 1994
  • Application of the Solid Polymer Electrolyte Method to Organic Electrochemistry XV. Influence of the Multiphase Structure of Nafion on Electroreduction of Substituted Aromatic Nitro Compounds on Cu, Pt-Nafion
    Minoru Inaba, James T. Hinatsu, Zempachi Ogumi, Zen Ichiro Takehara
    The influence of Nafion® and its multiphase structure on reactant selectivity in the electroreduction of aromatic nitro compounds on a solid polymer electrolyte composite electrode was investigated. Equimolar solutions of p -nitrotoluene and p-nitrophenol and equimolar solutions of o- and p -nitrotoluene were subjected to electroreduction on Cu, Pt-Nafion. The reactant selectivities, that is, the relative ease with which the reactants are reduced to the corresponding amino compounds, were compared with those on a conventional Cu electrode. Para -nitrotoluene was electroreduced preferentially in both equimolar solutions tested. Enhanced selectivity was observed with Cu, Pt-Nafion relative to the Cu electrode. The enhanced selectivity with Cu, Pt-Nafion was explained in terms of hydrophilic/hydrophobic interactions between the reactants and Nafion, which has a multiphase structure consisting of the polytetrafluoroethylene backbone, ionic clusters, and an interfacial region hydrophobic amorphous region). © 1993, The Electrochemical Society, Inc. All rights reserved., Journal of the Electrochemical Society, Journal of the Electrochemical Society, 140706 - 711, 01 Jan. 1993, English, 研究論文(学術雑誌)
  • Oxygen permeation through perfluorinated carboxylate ion exchange membranes
    Minoru Inaba, Minoru Inaba, Tohru Kuroe, Tohru Kuroe, Zempachi Ogumi, Zempachi Ogumi, Zen Ichiro Takehara, Zen Ichiro Takehara, Katsumi Katakura, Katsumi Katakura, Sachio Ichikawa, Sachio Ichikawa, Yoshifumi Yamamoto, Yoshifumi Yamamoto
    Permeation of oxygen through perfluorinated carboxylate membranes (Flemion®) of different counterions and equivalent weights (EW = 700 and 800) was investigated. Solubilities and diffusion coefficients of oxygen in the membranes were determined by an electrochemical monitoring technique using solid polymer electrolyte composite electrodes. The solubilities were close to the values in perfluorocarbon media rather than to the value in water. The solubility decreased with increasing water content of the membranes. The diffusion coefficient in 700 EW membranes increased with increasing water content, while that in 800 EW membranes decreased slightly. On the basis of these results, the diffusion path of oxygen through the membranes was discussed in terms of morphological properties of perfluorinated ion exchange membranes. © 1993., Electrochimica Acta, Electrochimica Acta, 381727 - 1731, 01 Jan. 1993, English, 研究論文(学術雑誌)
  • Application of the Solid Polymer Electrolyte Method to Organic Electrochemistry: XIV. Effects of Solvents on the Electroreduction of Nitrobenzene on Cu, Pt-Nafion
    Minoru Inaba, Zempachi Ogumi, Zen ichiro Takehara
    The effects of solvents on the electroreduction of nitrobenzene on Cu, Pt-Nafion were investigated. The presence of a sufficient amount of a cosolvent in the catholyte or in the anolyte facilitated the reduction of nitrobenzene to aniline. Without a sufficient amount of a cosolvent, the mass transfer of nitrobenzene to the active sites on the cathode was suppressed, and hydrogen evolution became significant. The solubility parameter value, δmix, of the catholyte is an important index for predicting the effectiveness of mass transfer of nitrobenzene to the active sites of the solid polymer electrolyte composite electrode. When an aqueous solution was used as the anolyte, catholytes with δmix >11 cal-1/2 cm-3/2 were effective for aniline production by the electroreduction of nitrobenzene on Cu, Pt-Nafion. © 1993, The Electrochemical Society, Inc. All rights reserved., Journal of the Electrochemical Society, Journal of the Electrochemical Society, 14019 - 22, 01 Jan. 1993, English, 研究論文(学術雑誌)
  • Infrared sensing properties of positive temperature coefficient thermistors with large temperature coefficients of resistivity
    Minoru Inaba, Masaru Miyayama, Hiroaki Yanagida
    Infrared (IR) detecting elements were prepared using positive temperature coefficient (PTC) thermistors with large temperature coefficients of resistivity (α). Their compositions were denoted as Ba1-xSrxNb0.003Ti0.997O3+ 1 mol % TiO2+ 0.07 mol %MnO (x=0, 0.2), and their temperature coefficients of resistivity were 78 and 50% K-1, respectively. Their IR sensing properties were measured under the self-regulating heating conditions, and were compared with those of a detector with small α (18 % K-1). It was shown that large α was effective for controlling the element temperature by self-regulating heating and for improving sensitivity. The responsivity, Rvof the element with x=0.2 was 980 VW-1, and was as large as those of pyroelectric detectors. Expressions which normalize the sensitivity and the thermal time constant were derived. From these expressions, criteria for improving some IR sensing properties were obtained. © 1992 Chapman & Hall., Journal of Materials Science, Journal of Materials Science, 27127 - 132, 01 Jan. 1992, English, 研究論文(学術雑誌)
  • Infrared sensing properties of positive temperature coefficient thermistors with large temperature coefficients of resistivity
    Minoru Inaba, Masaru Miyayama, Hiroaki Yanagida
    Infrared (IR) detecting elements were prepared using positive temperature coefficient (PTC) thermistors with large temperature coefficients of resistivity (α). Their compositions were denoted as Ba1-xSrxNb0.003Ti0.997O3+ 1 mol % TiO2+ 0.07 mol %MnO (x=0, 0.2), and their temperature coefficients of resistivity were 78 and 50% K-1, respectively. Their IR sensing properties were measured under the self-regulating heating conditions, and were compared with those of a detector with small α (18 % K-1). It was shown that large α was effective for controlling the element temperature by self-regulating heating and for improving sensitivity. The responsivity, Rvof the element with x=0.2 was 980 VW-1, and was as large as those of pyroelectric detectors. Expressions which normalize the sensitivity and the thermal time constant were derived. From these expressions, criteria for improving some IR sensing properties were obtained. © 1992 Chapman & Hall., Journal of Materials Science, Journal of Materials Science, 27127 - 132, 01 Jan. 1992, English, 研究論文(学術雑誌)
  • Infrared sensing properties of BaTiO3PTC thermistor
    Minoru Inaba, Masaru Miyayama, Hiroaki Yanagida
    Properties of an infrared (IR) detector using a positive temperature coefficient (PTC) thermistor, Ba0.997La0.003TiO3+ 2 mol% SiO2+ 0.07 mol% MnO, operated under the self-regulating heating conditions were investigated. The temperature coefficient of resistance was 18% K-1, and the Curie point was 122°C. It was shown that a PTC thermistor can detect IR radiation from a 600 K blackbody furnace under the self-regulating conditions. However, the response and the thermal time constant were greatly affected by the variation in the ambient temperatures (15°-124°C) and the applied voltage(1-100 V). Theoretical expressions for the response and the thermal time constant were discussed, and the calculated results were consistent with the experimental ones., Nippon Seramikkusu Kyokai Gakujutsu Ronbunshi/Journal of the Ceramic Society of Japan, Nippon Seramikkusu Kyokai Gakujutsu Ronbunshi/Journal of the Ceramic Society of Japan, 971250 - 1255, 01 Dec. 1989
  • Application of the SPE method to organic electrochemistry-VII. The reduction of nitrobenzene on a modified Pt-nafion
    Zempachi Ogumi, Minoru Inaba, Shin ichi Ohashi, Masaaki Uchida, Zen ichiro Takehara
    SPE composite electrodes prepared by deposition of platinum on Nafion, Pt-Nafions, were modified by electrochemical deposition of nickel and copper. The modified electrodes were applied to the reduction of nitrobenzene. The modification was very effective for aniline formation and suppressed side reactions such as hydrogen evolution. On Cu, Pt-Nafion the Bamberger's rearrangement was inhibited and no p-aminophenol was obtained. The inhibition was caused by Nafion which coated the active site on Cu, Pt-Nafion. It was suggested that SPE composite electrodes behaved in the same manner as polymer coated electrodes. The active site for charge transfer reaction was concluded to be at an interior surface of the metal layer bound to Nafion. © 1988., Electrochimica Acta, Electrochimica Acta, 33365 - 369, 01 Jan. 1988, English, 研究論文(学術雑誌)

Misc

  • Analysis of the ionic conduction behavior in some room temperature molten fluorides
    H. Inoue, T. Isogai, T. Nakai, M. Saito, M. Inaba, A. Tasaka
    The self-diffusion coefficients of cations and anions increased with increasing the HF-concentration and temperature in (CH3) 3N·mHF and (CH3)4NF·mHF melts. Behavior of the self-diffusion coefficients of cation and anion in every melt is good agreement with an increase in ionic conductivity and a decrease in viscosity (1). The transference number of (FH)nF- anions estimated from the values of self-diffusion coefficients for each ion in every melt was almost constant and their values were around 0.6 and 0.7 in the (CH3)3N·mHF and the (CH3) 4NF·mHF melts, respectively. Therefore, it is concluded that the diffusion of (FH)nF- anions is faster than that of each cation in these melts. ©The Electrochemical Society., ECS Transactions, ECS Transactions, 417 - 12, 01 Dec. 2012
  • Effect of addition of alkali metal fluoride to a molten NH4F-HF system on current efficiency for NF3 formation and nickel anode consumption
    Tomoyuki Shiono, Yuki Iida, Hiroyuki Omori, Morihiro Saito, Minoru Inaba, Akimasa Tasaka
    The current efficiency for NF3 formation and the current loss caused by Ni dissolution were investigated in electrolysis of the NH 4F·2HF melts with and without alkali metal fluorides such as CsF, KF, and LiF. The addition of CsF to the melt was most effective for increasing the NF3 current efficiency. In contrast, the addition of KF to the melt decreased the current efficiency for NF3 formation and increased the current loss caused by Ni dissolution. The SEM observation and XRD analysis revealed that the oxidized layer formed on nickel in the melt containing LiF or CsF was composed of NiF2 with highly oxidized nickel fluoride. On the other hand, the oxidized layer in the melt containing KF was composed of only KNiF3, and was very brittle. Therefore, it is concluded that KF is detrimental to the nickel anode and highly oxidized nickel fluoride may relate to the NF3 current efficiency. ©The Electrochemical Society., ECS Transactions, ECS Transactions, 4169 - 74, 01 Dec. 2012
  • Development of highly active and durable Pt core-shell catalysts for polymer electrolyte fuel cells
    Minoru Inaba, Hideo Daimon
    Reducing the Pt usage by improving the activity of Pt catalysts for oxygen reduction reaction is important for the cost reduction of polymer electrolyte fuel cells. Core-shell catalysts, in which Pt monolayer is deposited on different metal core nanoparticles, are one of the key techniques to improve the mass activity of Pt. We are developing highly active and durable Pt ML core-shell catalysts, especially focusing on Au cores, which have highly electrochemical stability. Here we overview our research results on the core/shell catalysts prepared by the Cu-UPD method, the new method for Pt monolayer formation on Au cores, and the improvement of the stability of Au core nanoparticles. © The Electrochemical Society., ECS Transactions, ECS Transactions, 5065 - 73, 01 Dec. 2012
  • Improvement of electrochemical properties of a high potential negative electrode TiO 2(B)
    Mikihiro Takagi, Yosuke Murota, Makoto Tajima, Takayuki Asao, Morihiro Saito, Akimasa Tasaka, Minoru Inaba
    To improve the practical capacity of TiO 2(B), optimization of precursor (K 2Ti 4O 9 and Cs 2Ti 5O 11), solvent (EC+DEC, EC+DMC and EC+DMC) in electrolyte and homogeneity (mixing with a mortar or wet-ball milling machine) of Ketjen Black (KB) as conductive agent was conducted. Use of Cs 2Ti 5O 11 precursor reduced the content of TiO 2 anatase as an impurity in the obtained TiO 2(B). Choice of DMC solvent with the highest dielectric constant (3.1) and the lowest viscosity (0.59 cP) and improvement of the homogeneity of KB conductive agent enhanced the Li + ion and electron conductivities in the electrode. As a result, the optimized TiO 2(B) electrode exhibited a high discharge capacity of 314.4 mAh g -1 in 1 M LiPF 6/EC+DMC(1:2), which corresponds to ca. 93.9% of the theoretical capacity of TiO 2(B), 335 mAh g -1. Moreover, a high rate capability of 118.5 mAh g -1 even at 10 C was also achieved. ©The Electrochemical Society., ECS Transactions, ECS Transactions, 3357 - 66, 01 Dec. 2011
  • Development of oxygen reduction electrocatalysts based on manganese oxides for AEMFCs
    T. Takakuwa, M. Akiyoshi, T. Kenko, M. Saito, H. Daimon, A. Tasaka, M. Inaba, H. Shiroishi, T. Hatai, J. Kuwano
    Perovskite and Mn oxide nanosheet-based electrocatalysts were synthesized as the cathode of anion-exchange membrane fuel cells (AEMFCs), and their oxygen reduction reaction (ORR) activities and AMFC performances were evaluated. Perovskite La 0.6Sr 0.4MnO 3 (LS 0.4M/KB) loaded on Ketjen Black exhibited the highest ORR activity (onset potential: ca. 0.9 V vs. reversible hydrogen electrode (RHE) and efficiency for 4-electron reduction of O 2: > 90%), and achieved a maximum power density of ca. 92 mW cm -2. © 2011 ECS - The Electrochemical Society., ECS Transactions, ECS Transactions, 412185 - 2192, 01 Dec. 2011
  • Oxygen reduction reaction activity of shape controlled Pt catalysts
    Akihide Toge, Takashi Yokono, Morihiro Saito, Hideo Daimon, Akimasa Tasaka, Minora Inaba
    In order to clarify the effect of surface atomic structure on oxygen reduction reaction (ORR) activity for Pt/C catalysts, cubic and cuboctahedral Pt nanoparticles (NPs) colloidal solutions were prepared from K 2PtCl 4 solutions using sodium polyacrylate (PAA) as a capping reagent, and furthermore the shape-controlled Pt NPs were deposited on a Ketjen Black support. The cubic and cuboctahedral Pt/C catalysts (Pt cubic/C and Pt cuboctahedral/C) gave characteristic H 2 absorption/desorption peaks in the CV curves attributed to their crystal facets. The Pt cuboctahedral/C having the (100) and (111) faces showed higher ORR activity than a commercially available polycrystalline Pt/C and the Pt cubic/C composed of mainly (100) facet. © 2011 ECS - The Electrochemical Society., ECS Transactions, ECS Transactions, 412283 - 2288, 01 Dec. 2011
  • Analysis of cationic structure in some room temperature molten fluorides and dependence of their ionic conductivity and viscosity on HF-concentration
    Akimasa Tasaka, Takaaki Nakai, Hidemi Inoue, Kenta Nakanishi, Tomohiro Isogai, Shinji Kohara, Morihiro Saito, Minoru Inaba
    To understand the ionic and non-ionic species in (CH3) 4NF·mHF, (CH3)3N·mHF, (C 2H5)4NF·mHF, and (C2H 5)3N·mHF melts, the structures of these melts were investigated by infrared spectroscopy, NMR and high-energy X-ray diffraction. IR spectra revealed that the complex fluoride anions such as (HF) nF- (n = 1, 2, 3) and molecular HF are present in all melts. Ionic conductivity and viscosity of these melts were measured and correlated with their cationic structure. The ionic conductivity of the R 4N+-systems was higher than those of corresponding R 3NH+-systems. (CH3)4N+ and (CH3)3NH+ cation gave higher ionic conductivity than (C2H5)4N+ and (C2H5)3NH+ cation, respectively. It was concluded that these effects on ionic conductivity can be explained by the cationic structure and the concentration of molecular HF in the melts. ©The Electrochemical Society., ECS Transactions, ECS Transactions, 33627 - 639, 01 Dec. 2010
  • Effect of core size on activity and durability of Pt core-shell catalysts for PEFCs
    Minoru Inaba, Hiroyuki Ito, Hiroaki Tuji, Teturo Wada, Michiko Banno, Hirohisa Yamad, Morihiro Saito, Akimasa Tasaka
    Pt/Au/C and Pt/Pd/C core-shell catalysts were prepared from Au/C and Pd/C cores with different core sizes using under potential deposition (UPD) of Cu, and the activity for oxygen reduction reaction and durability of the Pt/Au/C and Pt/Pd/C catalysts were investigated. Pt/Au/C and Pt/Pd/C core-shell catalysts showed higher mass activities than a commercially available Pt2.8nm/C catalyst, and hence they are promising for reducing the Pt usage in PEFCS. In potential cycling durability tests between 0.6-1.0 V, opposite effects of core size on were observed for Pt/Au/C and Pt/Pd/C. For Pt/Au/C, smaller cores gave high durability, whereas for Pt/Pd/C, larger cores gave high durability comparable with the Pt2.8nm/C. ©The Electrochemical Society., ECS Transactions, ECS Transactions, 33231 - 238, 01 Dec. 2010
  • Influence of carbon dioxide on the performance of anion-exchange membrane fuel cells
    Yu Matsui, Morihiro Saito, Akimasa Tasaka, Minora Inaba
    The influence of CO2 in the oxidant gas on the cell performance of anion-exchange membrane fuel cells was investigated using a three-electrode single cell with a reversible hydrogen electrode (RHE). The overpotential of the cathode was hardly changed by the presence of CO2, while the overpotential of the anode increased after the introduction of CO2 at the cathode. The high anode overpotential was caused by a high CO 32- concentration in the anode catalyst layer, even when most of the CO32- ions in the electrolyte membrane are purged during operation through the self-purging mechanism. ©The Electrochemical Society., ECS Transactions, ECS Transactions, 25105 - 110, 01 Dec. 2010
  • Negative electrode properties of Sn and Si leaf Powder® for Li-ion batteries
    Morihiro Saito, Kenta Nakai, Makoto Hagiwara, Aikimasa Tasaka, Toshio Takenaka, Masato Hirota, Akika Kamei, Minoru Inaba
    Two kinds of metal thin platelets (Leaf Powder®, Oike Co., Ltd.) based on Sn and Si were prepared, and their charge/discharge properties were investigated as alternative negative electrode materials to graphite for Li-ion batteries. One was simple metal platelets (M-LP, thickness: 100 nm) and the other was laminated platelets with an inactive Ni layer (M/Ni/M-LP, thickness: 30/30/30 nm). For both Sn and Si platelets, the shape of thin platelets effectively relieved the stress by volume expansion and shrinkage during the alloying and de-alloying processes, and improved their charge/discharge cycleabilities. Particularly, the Si platelets suppressed their agglomeration and pulverization, and much more remained the shapes than the Sn platelets. The lamination with the inactive Ni layer further improved the cycleability, though the specific capacity decreased by its presence. The alloying and de-alloying reaction with Li+ ion was substantially smooth, which was due to a decrease in the diffusion distance of Li+ ion by using the thin platelets. As a result, the Si/Ni/Si-LP exhibited a good capability over ca. 400 mAh g-1 up to 3C rate. ©The Electrochemical Society., ECS Transactions, ECS Transactions, 25101 - 108, 01 Dec. 2010
  • ZnO nano-cauliflower array dye-sensitized solar cells
    Ippei Yamaguchi, Mitsuru Watanabe, Tsutomu Shinagawa, Masaya Chigane, Minoru Inaba, Akimasa Tasaka, Masanobu Izaki
    Zinc oxide (ZnO) nano-cauliflower arrays with high-aspect-ratio hexagonal ZnO nanopillars have been prepared by using a polystyrene (PS) sphere template and an electrodeposition technique in zinc nitrate aqueous solutions. The ZnO electrodeposition is a two-step process, which is composed of electrodepositon (i) in a higher Zn(NO3)2 concentration and (ii) in a lower concentration. The structural and optical characteristics were investigated by using a field-emission scanning electron microscope and spectrofluorometer. The ZnO nano-cauliflower array is so high-quality that it emits ultraviolet light with a phton energy of 3.2 eV at room temperature due to the recombination of bound exitons. Dye-sensitized solar cells using the ZnO nano-cauliflower array as a transparent electrode have been fabricated and an energy conversion efficiency of 0.15% was obtained. ©The Electrochemical Society., ECS Transactions, ECS Transactions, 163 - 10, 23 Nov. 2009
  • Secondary Batteries - Lithium Rechargeable Systems - Lithium-Ion | Negative Electrodes: Graphite
    M. Inaba
    © 2009 Elsevier B.V. All rights reserved. Graphite has been used as a negative electrode in most of the commercially available rechargeable lithium-ion cells. Lithium ions are intercalated within graphite on charging and deintercalated on discharging at extremely negative potentials of about -3 V against the standard hydrogen electrode. Many of the advantages of lithium-ion cells, such as high voltage and high energy density, are realized not by positive electrode, but by graphite negative electrode. The electrochemical intercalation reactions at graphite negative electrode consist of various processes such as surface reactions, interfacial charge transfer reactions, and lithium diffusion inside the host. Each of the elementary processes plays a vital role and greatly affects the charge and discharge characteristics of graphite negative electrodes. In this article, fundamental aspects of graphite negative electrodes are reviewed, focusing on (1) charge and discharge characteristics of graphite and other carbonaceous materials, (2) solvent decomposition and surface film formation, and (3) diffusion of lithium ions in graphite., Encyclopedia of Electrochemical Power Sources, Encyclopedia of Electrochemical Power Sources, 198 - 208, 01 Jan. 2009
  • Preparation of cubic platinum nanoparticles of different sizes and their electrochemical properties
    K. Matsuzawa, T. Fukushima, H. Yamada, M. Inaba
    Pt nanoparticles with controlled shapes and sizes would be useful for fundamental researches on the catalytic activity for oxygen reduction reaction. In the present study, cubic R nanoparticles were prepared from a solution of K2RCl4 in the presence of polyacrylic acid (PAA) as a capping reagent. The effect of temperature, pH, and PAA concentration on the shape, size, and stability of the nanoparticles were investigated, and cubic R nanoparticles of different sizes in the range of 4.4-10 nm were obtained. The cubic nanoparticles showed strong features of R {1 0 0} faces on their cyclic voltammogram under argon atmosphere. Rotating ring disk electrode measurements in O2-saturated H2SO4 solution revealed that the cubic nanoparticles have a high catalytic activity for ORR. © The Electrochemical Society., ECS Transactions, ECS Transactions, 11181 - 189, 01 Dec. 2007
  • Effect of dichromate added to the electrolyte on reduction of hypochlorite ion on SS400 cathode
    Toshikazu Hayashida, Ayako Tagawa, Satoshi Hatano, Atsushi Kuniyone, Masatsugu Morimitsu, Minoru Inaba, Akimasa Tasaka
    Kinetic study of ClO- reduction on the cathode has been carried out in catholytes composed of 80 g/l-NaCl, 1.0 wt%-NaClO and x g/l-dichromate (x = 0, 3.0, and 5.0) at temperatures such as 30, 40, and 50°C by galvanostatic method. The rate constant of reduction of ClO- (k 2) on the SS400 steel cathode was sharply decreased in the dichromate concentration of 5.0 g//l at every temperature. And the activation energy of ClO- reduction (E(k2)) was increased in the dichromate concentration of 5.0 g/l. SEM observation and XPS analysis revealed that a thin layer of chromium trihydroxide was formed on the cathode surface after electrolysis. From these results, it is considered that reduction of ClO - was suppressed by addition of dichromate and that the formed Cr(OH)3 layer may prevent ClO- from reduction on the cathode. copyright The Electrochemical Society., ECS Transactions, ECS Transactions, 323 - 28, 01 Dec. 2007
  • Diagnostics of cathode flooding in a segmented pemfc with local reference electrodes
    Z. Siroma, J. Takahashi, K. Yasuda, K. Tanimoto, M. Inaba, A. Tasaka
    A fourfold-segmented PEMFC with four reference electrodes was created to measure current distribution, local polarization of the anode and cathode, and local impedance. When sufficient amounts of fully humidified gases were fed to the anode and cathode, cathode flooding was observed. When the feeding of the anode gas was reduced, reaction downstream of the anode was hindered, which seemed to be caused by anode flooding, instead of starvation due to consumption of the gas. copyright The Electrochemical Society., ECS Transactions, ECS Transactions, 31041 - 1047, 01 Dec. 2006