報告書番号

U93058

タイトル（和文）

生体物質を模擬した燃料電池用電極触媒の開発２－酸素還元におけるボルフィリン鉄錯体の触媒活性の評価－

タイトル（英文）

DEVELOPMENT OF CATALYST FOR FUEL CELLS BY MIMICKING BIOMATERIALS. -EVALUATION OF CATALYTIC ACTIVITY OF PORPHYRIN IRON COMPLEXES FOR REDUCTION OF MOLECULAR OXYGEN-

概要 （図表や脚注は「報告書全文」に掲載しております）

２種類の両親媒性ボルフィリン鉄錯体、ｍｕ－オキソ錯体及び塩素イオン錯体を合成した。これらを電極触媒として用いると、酸素還元の過電圧が減少した。また、塩素イオン錯体で修飾したグラッシーカーボン（ＧＣ）電極により酸素還元を行ったところ、電位が－０．３Ｖ付近のときには３％程度の直接４電子還元が、－０．４Ｖ以下の電位では２電子還元で生成した過酸化水素をさらに２電子還元する間接４電子還元がおきており、－０．７Ｖでは約４２％の電流が４電子還元に関与していた。さらに、塩素イオン錯体で修飾したＧＣ電極をアルゴンガス下で８００度で加熱処理することで酸素還元反応が安定化することが示された。しかし、効率の良い酸素の４電子還元には高い過電圧が必要であり、安定化に伴い酸素還元活性が低下することから、現段階では実用的にはまだ不十分な触媒であった。

概要 （英文）

WE DEVELOPED A CATALYST FOR AN ELCTRODE FOR THE HYDROGEN-OXYGEN FUEL CELL BY MIMICKING A BIO-MATERIAL. TWO AMHIPHILIC PORPHYRIN IRON COMPLEXES, MU-OXO COMPLEX AND CL COMPLEX, WERE SYNTHESIZED. GLASSY CARBON (GC) ELECTRODES MODIFIED BY THE MU-OXO COMPLEX OR THE CL COMPLEX WERE MADE TO INVESTIGATE THE CATALYTIC ACTIVITY OF THE REDUCTION OF MOLECULAR OXYGEN. BOTH COMPLEXES CATALYZED THE REDUCTION OFMOLECULAR OXYGEN. PEAK POTENTIALS CAUSED BY REDUCTION OF MOLECULAR OXYGEN ON THE ELECTRODES SHIFTED POSITIVELY BY ABOUT 260 MV RATHER THAN THE REDUCTION POTENTIAL ON A BARE GC ELECTRODE. WHEN THE MECHANISM OF THEREDUCTION OF MOLECULAR OXYGEN WAS INVESTIGATED USING A ROTATING RING-DISK ELECTRODE (RRDE), IT WAS FOUND THAT THE DIRECT CONVERSION OF MOLECULAR OXYGEN TO WATER BY A GC ELECTRODE MODIFIED BY CL COMPLEX WAS 3% OF THE CURRENT AT AN APPLIED POTENTIAL OF ABOUT -0.3 V VS. AG/AGCL. BELOW -0.4 V, THE RATIO OF THE FOUR-ELECTRON REDUCTION INCREASED WITH DECREASED APPLIED POTENTIAL. AT -0/7 V, THE RATIO REACHED 42%. HOWEVER, THE MODIFIED ELECTRODES HAVE LOW STABILITY. THE CATALYTIC ACTIVITY OF THE CL COMPLEX MODIFIED ELECTRODE WAS STABILIZED BY TREATING THE ELECTRODE AT 800.C FOR 1 HOUR UNDER AR. THE REDUCTION OF MOLECULAR OXYGEN WAS A TWO-ELECTRON MECHANISM. IT WAS CONCLUDED THAT THESE ELECTRODES CANNOT BE APPLIED TO AN ACTUAL FUEL CELL BECAUSE THY HAVE LOW STABILITY AND THE HEAT-TREATED MODIFIED ELECTRODE HAS LOW ACTIVITY. FURTHER INVESTIGATION ISNEEDED TO STABILIZE THE REDUCTION ACTIVITY BY MOLECULAR DESIGN.

報告者

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