Mechanistic Insights into Surfactant-Modulated Electrode–Electrolyte Interface for Steering H2O2 Electrosynthesis

Electrocatalytic reactions taking place at the electrified electrode–electrolyte interface involve processes of proton-coupled electron transfer. Interfacial protons are delivered to the electrode surface via a H₂O-dominated hydrogen-bond network. Less efforts are made to regulate the interfacial proton transfer from the perspective of interfacial hydrogen-bond network. Here, we present quaternary ammonium salt cationic surfactants as electrolyte additives for enhancing the H₂O₂ selectivity of the oxygen reduction reaction (ORR). Through in situ vibrational spectroscopy and molecular dynamics calculation, it is revealed that the surfactants are irreversibly adsorbed on the electrode surface in response to a given bias potential range, leading to the weakening of the interfacial hydrogen-bond network. This decreases interfacial proton transfer kinetics, particularly at high bias potentials, thus suppressing the 4-electron ORR pathway and achieving a highly selective 2-electron pathway toward H₂O₂. These results highlight the opportunity for steering H₂O-involved electrochemical reactions via modulating the interfacial hydrogen-bond network.