Oxygen functionalization of carbon quantum dots enables efficient acidic hydrogen peroxide electrosynthesis

The electrocatalytic synthesis of hydrogen peroxide (H₂O₂) using carbon-based materials is currently constrained by limited activity levels that fall short of industrially relevant production rates, particularly in acidic electrolytes, as well as a lack of atomic-level understanding of the active motifs. Herein, we utilize well-defined zero-dimensional carbon quantum dots (CQDs) with delicately engineered edge-site oxygen functional groups to elucidate the nature of sp³-hybridized carbon active sites and the promotional effects of aldehyde (-CHO), hydroxyl (-OH), and carboxyl (-COOH) groups in promoting acidic O₂-to-H₂O₂ conversion. Moreover, Ampere-level current densities are successfully achieved by integrating these CQDs into a solid-state electrolyte electrolyzer, resulting in a H₂O₂ Faradaic efficiency of up to 99.03% and a production rate of up to 3.0 μmol s^-1 cm^-2 with optimized ionic conduction over CQDs-CHO. Theoretical modeling and calculations reveal that the reconfiguration of carbon edge sites upon functionalization can alter the adsorption behavior of oxygenated intermediates in the 2e^- oxygen reduction pathway. Additionally, the combined experimental and theoretical findings underscore the crucial role of electron-withdrawing functional groups in facilitating charge transfer kinetics, thereby enhancing the efficiency of H₂O₂ electrosynthesis.