Abstract:

The oxygen reduction reaction (ORR) is a complex process. This is particularly the case for carbon-supported electrocatalysts in alkaline electrolytes, because carbon can catalyze the ORR via a two-electron transfer to generate hydroperoxide (HO₂^-), which subsequently undergoes either chemical decomposition to generate O₂ and OH^- (HODR) or electrochemical reduction to OH^- (HORR). In this study, we elucidated the ORR pathway on a series of carbon-supported manganese oxides, which have been extensively studied as electrocatalysts in alkaline electrolytes. A comparison of the turnover frequencies of the HODR and HORR showed that although an apparent four-electron transfer process was identified when the HO₂^- yield was measured using the rotating ring disk electrode technique, the real ORR pathway involved a two-electron transfer process to generate HO₂^-, with subsequent chemical decomposition of HO₂^-. These results will help us to understand the intrinsic catalytic behavior of carbon-supported transition-metal oxides for the ORR in alkaline electrolytes.

Key words: Oxygen reduction reaction pathway, Alkaline electrolyte, Carbon-supported electrocatalyst, Manganese oxide