Analysis of Adsorption Effects on a Metal-Nitrogen-Carbon Catalyst Using a Rotating Ring-Disk Study

A steady-state, rotating ring disk study of the oxygen reduction reaction (ORR) was conducted in acid environment using a pyrolyzed metal/nitrogen/carbon (MNC) electrocatalyst. Analysis of peroxide generation indicates that ORR proceeds both via a direct four-electron pathway to water at high potentials and an indirect peroxide pathway at low potentials. Above 0.6 V vs RHE, the direct four-electron pathway to water without a desorbing intermediate dominates oxygen reduction because peroxide generation is inhibited due to site availability. In contrast, at potentials below 0.6 V, oxygen reduction begins to shift to the indirect peroxide pathway due to fast kinetics and higher site availability. The net peroxide generation remains relatively low over the entire range due to reduction of peroxide to water.