The Cationic Enhancement Effect on the Two-Electron Oxygen Reduction Reaction in Acidic Conditions at Carbon-Based Cathodes

Hydrogen peroxide (H2O2) is a green oxidant, widely used in industry. To turn its synthesis green, research focused on the development of efficient catalysts for the two-electron oxygen reduction reaction (2e-ORR) to produce H2O2 from water and molecular oxygen. Despite recent progress, electrolyte effects of the electrochemical H2O2 production have remained little understood. We report a significant effect of alkali metal cations (AMCs) on the electrocatalytic H2O2 production on carbon catalysts in acidic environments. The presence of AMCs at the electrified carbon interface shift the half wave potential of the 2e-ORR from -0.48 V to -0.22 VRHE. This cationic induced enhancement effect exhibits a uniquely sensitive on/off switching behaviour depending on the voltammetric protocol. Voltammetric and direct in situ X-ray photoemission spectroscopic evidence is presented that supports a controlling role of the potential of zero charge (PZC) of the catalytic enhancement. Depending whether the electrode potential is kept cathodic or even just briefly reaches values anodic of the PZC, AMCs accumulate at the electrified interface and enhance the 2e-ORR or get repelled away from it, respectively. Density functional theory calculations associate the enhancement by the stabilization of the *OOH key intermediate. Based on this finding, we developed a refined reaction mechanism for the H2O2 production in presence of AMCs.