Journal Article Estimation of the Inherent Kinetic Parameters for Oxygen Reduction over a Pt-Free Cathode Catalyst by Resolving the Quasi-Four-Electron Reduction

難波江, 裕太  ,  Nabae, Yuta

120 ( No. 39 )  , pp.22515 - 22525 , 2016-09 , American Chemical Society
Understanding the kinetics of the oxygen reduction reaction (ORR) for fuel cell applications is quite important but difficult because the four-electron pathway is often overestimated by including a quasi-four-electron pathway that consists of the formation and reduction of H2O2. To solve this problem, here we demonstrate a novel analysis method with experimental data over a Pt-free Fe/N/C cathode catalyst. In this study, H2O2 voltammetry was conducted separately to evaluate the rate constant of the H2O2 reduction more accurately, and the obtained data were combinatorally analyzed with those from the ORR experiments. First, mathematical modification of the conventional Damjanovic approach was performed, and then the effect of the catalyst loading density was carefully studied by utilizing a novel reaction model with consideration of the quasi-four-electron pathway to avoid overestimation of the four-electron pathway kinetic parameters. In the most overestimated case, the percentages contribution of four-electron pathway over the Fe/N/C catalyst was estimated as 85% with the conventional Damjanovic model, while that from the newly proposed model is 51%. This method will be applicable for many other cathode catalysts and will facilitate understanding the nature of the ORR.

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