PH Effect on Electrochemistry of Nitrogen-Doped Carbon Catalyst for Oxygen Reduction Reaction

Abstract

In this work, the effect of pH on a nitrogen-doped ordered mesoporous carbon catalyst for the oxygen reduction reaction (ORR) is extensively investigated. Electrochemical methods, including cyclic voltammetry (CV), rotating ring-disk electrode (RRDE), and cathodic stripping voltammetry, are applied to investigate the electrochemical behavior in electrolyte solutions of different pHs (0–2, 7, 12–14). The CV result reveals that nitrogen-doped carbon has a variety of enriched reversible redox couples on the surface, and the pH has a significant effect. Whether these redox couples are electrochemically active or inactive to the ORR depends on the electrolyte used. In acid media, an oxygen molecule directly interacts with the redox couple, and its reduction proceeds by the surface-confined redox-mediation mechanism, yielding water as the product. Similarly, the first electron transfer in alkaline media is achieved by the surface-confined redox-mediation mechanism at the higher potentials. With decreasing poten...