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Enhancement in Kinetics of the Oxygen Reduction Reaction on a Nitrogen-Doped Carbon Catalyst by Introduction of Iron via Electrochemical Methods

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journal contribution
posted on 19.05.2015 by Jiajia Wu, Da Zhang, Hideharu Niwa, Yoshihisa Harada, Masaharu Oshima, Hironori Ofuchi, Yuta Nabae, Takeyoshi Okajima, Takeo Ohsaka
The iron (Fe) electrodeposition–electrochemical dissolution has been employed on nitrogen-doped carbon material (P-PI) prepared via multi-step pyrolysis of a polyimide precursor to achieve the introduction of Fe species, and its influence on the oxygen reduction reaction (ORR) is investigated by cyclic and rotating ring-disk electrode voltammetry in 0.5 M H2SO4. After the electrochemical treatment, the overpotential and H2O2 production percentage of ORR on the P-PI are decreased and the number of electrons transferred is increased in the meanwhile. In combination with the results of X-ray absorption fine structure spectra, the presence of Fe–Nx sites (Fe ions coordinated by nitrogen) is believed to be responsible for the improved ORR performance. Further kinetic analysis indicates that a two-electron reduction of O2 is predominant on the untreated P-PI with coexistence of a direct four-electron transformation of O2 to H2O, while the introduction of Fe species leads to a larger increase in the rate constant for the four-electron reduction than that for the two-electron process, being in good agreement with the view that Fe–Nx sites are active for four-electron ORR.