Tailoring interfacial proton-coupled electron transfer via electrolyte engineering for high-selectivity H2O2 production

The targeted modulation of electric double layer through electrolyte design has emerged as a transformative strategy for controlling electrochemical reaction pathways. While the oxygen reduction reaction (ORR) represents a paradigmatic example where electrolyte effects are pronounced, the atomic-scale mechanisms underlying electrolyte-mediated regulation of interfacial microenvironments remain incompletely understood. Here, we elucidate how acetonitrile (ACN) additive tailors the alkaline ORR pathway toward selective H₂O₂ electrosynthesis on carbon catalysts. Through integrated molecular dynamics simulations, in situ spectroscopy, and electrochemical impedance analysis, we demonstrate that ACN optimizes the three-phase interface to enhance ORR activity, and restructures interfacial water environments by displacing water in cationic solvation-shell and disrupting H-bonding continuity of water molecules. These synergistic effects effectively mitigate interfacial proton/electron flooding while optimizing proton-coupled electron transfer kinetics, resulting in dramatically enhanced H₂O₂ selectivity (90%) compared to the unmodified KOH system (60%). By establishing the structure-activity relationship of electrolyte composition with interfacial microenvironment and reaction pathway, this work provides a novel strategy for sustainable H₂O₂ electrosynthesis.