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. Cost-effective carbon is inherently selective for O2-to-H2O2 conversion, yet challenged by insufficient activity and unclear active site identification. Here, the authors report surface-engineered carbon quantum dots that elucidate the active motifs and achieve high-rate H2O2 electrosynthesis.