Redox Reactions of H ₂ O ₂ and Their Interaction with the Oxygen Reduction Reaction at the Au(100) Electrode

In electrochemical energy devices, multiple parallel reactions commonly occur, yet deconvoluting their individual contributions to the total current and disentangling their mutual influences remains a major challenge. This significantly hinders the elucidation of structure–activity relationships and the optimization of reaction conditions. Using the Au(100) single-crystal electrode as a model system, this work leverages conventional rotating disk electrode voltammetry, atmosphere comparison, and subtraction analysis to systematically investigate the interaction between H2O2 redox (HPOOR/HPORR) and the oxygen reduction reaction (ORR) in both acidic and alkaline media. Our results reveal that in alkaline solution, at E < 0.7 VRHE, OHad generated from H2O2 reduction activates O2 and significantly promotes the ORR; at E > 0.95 VRHE, local enrichment of HO2– produced by the ORR, together with hydrogen-bonding assistance from OHad, markedly enhances the HPOOR. In acidic solution, the HPOOR exhibits fast kinetics, while the HPORR requires a large overpotential; this highly asymmetric kinetics locks the mixed potential near the HPOOR equilibrium potential (∼0.78 VRHE). In alkaline media, it shifts to ca. 0.95 V; the difference in mixed potential between acidic and alkaline media arises from the fact that in alkaline media, Au(100) can form a highly active (1 × 1) surface structure under O2, enabling an efficient four-electron ORR from ∼1.0 VRHE. Based on these bidirectional promotion/inhibition mechanisms, reaction conditions can be rationally optimized: at low potentials, utilize H2O2 to boost the ORR; at high potentials, exploit the O2-promoted HPOOR to remove the undesired byproduct H2O2. This study provides new insights into the dynamic evolution of intermediates in complex electrocatalytic systems and offers strategies for reaction condition optimization.