Rotating ring-disk electrode theory and method to correct quasi-four-electron oxygen reduction over Fe/N/C and N/C cathode catalysts

Abstract

Understanding the mechanism of the oxygen reduction reaction over nonprecious metal catalysts is important for green and sustainable electrochemical energy conversion. This article presents our recent progress in kinetic studies using rotating ring-disk electrodes. We have established a mathematically and experimentally modified rotating ring-disk electrode approach to calculate the corresponding kinetic rate constants of the 4-e reduction of O 2 to H 2 O ( k 1 ), the 2-e reduction of O 2 to H 2 O 2 ( k 2 ), and the 2-e reduction of H 2 O 2 to H 2 O ( k 3 ). Furthermore, the overestimation of the 4-e reduction process, which derives from the (2 + 2)-e pathway in the catalyst layer matrix, was corrected by studying the effect of catalyst loading density. The established method has been successfully applied to the oxygen reduction reaction over Fe/N/C and N/C catalysts in acidic and alkaline media.