Microscopic Electrode Processes in the Four-Electron Oxygen Reduction on Highly Active Carbon-Based Electrocatalysts

Abstract

Nitridated carbon (NC) catalysts have attracted considerable interest as promising Pt-free alternatives to standard Pt/C catalysts in the oxygen reduction reaction (ORR). Aiming at a better understanding of the microscopic reaction mechanism and of the nature of the reaction-limiting step, we have investigated the ORR kinetics and in particular the kinetic isotope effects (KIEs) therein for three different NC catalysts with different nitrogen contents. The measurements were performed using ordinary and deuterated water electrolytes, under both alkaline and acidic solutions. From an analysis of the ORR kinetics on the most active NC-I catalyst, including the kH/kD ratio and the transfer coefficients, and from density functional theory (DFT) based computations, we derive that the initial proton-coupled electron transfer (PCET), whose process is to form OOH* from O2*, acts as the potential-determining step (PDS) under acidic conditions and the initial electron transfer, whose process is to form (O2•–)* from ...