Indirect contribution of transition metal towards oxygen reduction reaction activity in iron phthalocyanine-based carbon catalysts for polymer electrolyte fuel cells

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• 作者：Masaki Kobayashi^a ; ^b ; ^{mkoba@sr.t.u-tokyo.ac.jp} ; Hideharu Niwa^a ; Makoto Saito^a ; Yoshihisa Harada^a ; ^b ; Masaharu Oshima^a ; ^b ; Hironori Ofuchi^c ; Kiyoyuki Terakura^d ; Takashi Ikeda^e ; Yuka Koshigoe^f ; Jun-ichi Ozaki^f ; Seizo Miyata^g
• 关键词：Polymer electrolyte fuel cell ; Cathode catalyst ; Carbon-based catalyst ; Iron phthalocyanine ; X-ray absorption fine structure
• 刊名：Electrochimica Acta
• 出版年：2012
• 期刊代码：30_00134686
• 类别：ch
• 出版时间：15 July, 2012
• 卷：74
• 期：Complete
• 页码：254-259
• 文件大小：892 K

摘要

The electronic structure of the residual metal atoms in Fe phthalocyanine (FePc)-based carbon catalysts, prepared by pyrolyzing a mixture of FePc and phenolic resin polymer at 800 掳C, before and after acid washing have been investigated using X-ray absorption fine structure (XAFS) spectroscopy to clarify the role of Fe in the oxygen reduction reaction (ORR) activity. The Fe K X-ray emission intensity suggests that the acid washing process reduces 36%of the total amount of residual Fe in the FePc-based catalysts. The decomposition analyses for the XAFS spectra reveal that the composition ratio of each Fe component is unaltered by the acid washing, indicating that the residual Fe components were removed by the acid washing irrespective of their chemical states. Because the oxygen reduction potential was approximately unchanged by the acid washing, the residual Fe itself does not seem to contribute directly to the ORR activity of the samples. The residual Fe is composed mainly of metallic Fe components (Fe metal and iron carbide Fe₃C), which can act as a catalyst to accelerate the growth of the sp² carbon network during pyrolysis. The results imply that light elements such as C and N are components of the ORR active sites in the FePc-based carbon catalysts pyrolyzed at high temperatures where the metal-N₄ structures in the macrocycles are mostly decomposed.