成果報告書詳細
管理番号20090000000624
タイトル*平成20年度中間年報 固体高分子形燃料電池実用化戦略的技術開発 次世代技術開発 形態制御複合金属酸化物系カソード触媒の研究開発
公開日2010/3/13
報告書年度2008 - 2008
委託先名国立大学法人信州大学
プロジェクト番号P05011
部署名燃料電池・水素技術開発部 燃料電池グループ
和文要約以下本編抜粋:1.研究開発の内容及び成果等 本研究は「高活性・高耐久性・安全・安価」の条件を満たす、白金を用いない導電性金属酸化物カソード触媒を開発することを目的としている。平成20年度に得られた主な成果は次の3点である。(1)酸化チタン、酸化タンタル、酸化ジルコン及びそれらの複合酸化物被覆電極を塗布熱分解法にて作製し、酸性水溶液中での酸素還元活性を調べたところ、その多くが高い酸素還元活性を示すことを見出した。(2)金属酸化物触媒被覆カソードを用いたPEFC燃料電池の発電試験に成功し、触媒層に炭素材料を一切使用しないカソードが機能し得ることを実証した。
英文要約Title: Strategic Development of PEFC Technologies for Practical Application/Development of Technology for Next-generaton Fuel Cells/ Development of Ordered Oxide Electrocatalysts for Oxygen Reduction (FY2005-FY2009) FY2008 Annual Report
Various kinds of less-expensive cathode catalysts for polymer electrolyte fuel cells have so far been proposed; such as carbides, nitrides, oxynitrides, silicides, sulfides, bronzes, thermally decomposed metal complexes, and so on. However, those candidate electrocatalysts have many problems to be overcome; such as overpotential, stability and catalytic activity compared to those of platinum catalyst. We have started this research project focusing oxide cathode catalysts. Many single and binary oxide electrodes have been prepared on titanium rods or plates by a dip-coating method with alcoholic solutions of each metal complexes. The catalytic activity of these oxide-coated electrocatalysts for the electrochemical reduction of oxygen (ORR) was evaluated by a single sweep voltammetry in an aqueous electrolyte of 0.5 M H2SO4 or 0.1 M HClO4 at 60°C. Since these test electrodes were not rotated during the measurement, the threshould electrode potential for the reduction of oxygen, E(ORR), was used for the comparison of the catalytic activity of these oxide electrodes. The E(ORR) of the oxide coated electrodes TiO2/Ti, Ta2O5/Ti, ZrO2/Ti, Ti-Ta-O/Ti and Ti-Zr-O/Ti electrodes were 0.91 V, 0.82 V, 0.81 V, 0.90 and 0.86 V (vs RHE), respectively. The open circuit potential (OCV) of a polymer electrolyte fuel cell using an IrO2 cathode dip-coated over a porous titanium substrate and a platinum/carbon black anode under pure oxygen and hydrogen gases, respectively, both at 1 atmosphere, was 0.89 V, and the power density was 40 mW cm-2 at 80°C. Thus, the carbon-free oxide cathode has been proved to work under a usual condition. In order to develop a supporting material for any less-conductive oxide particle catalysts, activated carbons showing ORR activity was examined. Activated carbon prepared from silk fibroin, which is free of contaminating metal elements, showed a high catalytic activity for the ORR. The activated carbon had a very high OCV of 0.91 V (vs RHE) in oxygen saturated 0.5 M sulfuric acid at 60°C. The ORR on the activated carbon proceeded by a four-electron process in the high-electrode-potential region; this gradualy decreased to a 3.5-electron reaction below about 0.6 V (vs. RHE). Only about 1 % of nitrogen atoms (mostly quaternary) remained in the activated carbon by heat treatment at up to 1200 °C are responsible for the high catalytic activity. The OCV of a polymer electrolyte fuel cell using the activated carbon as the cathode and a platinum/carbon black anode under pure oxygen and hydrogen gases, respectively, both at 1 atmosphere, was 0.95 V at 27°C.
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