成果報告書詳細
管理番号20090000000607
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 マルチ銅酵素を基軸とする新規カソード触媒の研究開発
公開日2010/3/2
報告書年度2008 - 2008
委託先名国立大学法人京都大学
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 (1)内容 燃料電池の新規な白金代替酸素還元触媒の創生を目指し、酸素の完全4電子還元反応を実現できる触媒としてマルチ銅オキシダーゼ(MCO)に焦点をあて、その探索・改変・構造解析・機能解析・反応機構解析・電極反応解析を行い、得られた研究成果を基に、バイオカソードを試作することを目的とした。
英文要約Multi-copper oxidases (MCOs) catalyze 4-electron reduction of dioxygen (O2) to water with suitable electron donors and can be utilized as cathode catalysts of (bio)fuel cells. The significant benefit of MCO as a cathode catalyst is that the reaction does not produce any reactive oxygen species such as superoxide radical and hydrogen peroxide (and then hydroxyl radical). This works are concerned with search and screening, mutation, structural analysis, functional analysis, mechanistic analysis and electro reaction analysis of MCO. All these aspects will give some important suggestions for the development of novel artificial cathode catalysts for O2 reduction. In this work, (1) YfiH protein as a MCO homolog has been expressed on Escherichia coli ME5305 with vector pCA/yfiH. The protein expressed shows strong MCO activity in the presence of 10 mM CuSO4 with syringaldazine as an electron donor. (2) Type I (T1) site has been found to be an electron accepting site from electrodes. The axial amino acid governs the redox potential strongly. The T1 potential is in order of Phe > Leu = Met > Gln. Mutation of Asp439 hydrogen-bonded to the axial His443 in CueO by Ala causes a positive shift of the T1 potential by 50 mV. (3) Mutation of Cys500 coordinated to T1 Cu in CueO, and that of Asp112 and Glu506 hydrogen-bonded to T2/3 cluster have yielded oxygen-reduction intermediates I and II. Characterization of the intermediates seems to be very important to understand the mechanism of MCO-catalyzed O2 reduction. (4) The electron transfer from electrode to MCO is independent of reaction path and is explained by a long-range electron transfer model. Surface functional groups also have a significance role in the electron transfer kinetics from electrode to MCO. The order is COOH(COO-) >> OH >> SO3-- CH3 > NH3+(NH2). (5) Carbon cryogels with mesoporous in the range from few nm to few ten nm in raidus have been successfully prepared. The catalytic current depends on the radius and then it has been found to be very important to tune the radius for each enzyme. (6) Air-breath type cathode has been fabricated. Teflon is found to be suitable as a binder and the optimized mixing ratio of the binder to Ketjen Black was 2:3. The maximum current density of above 20 mA cm-2 has been realized for the first time in the world.
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