Light-Induced Efficient Hydrogen Peroxide Production Mediated by an Integrated Catalytic Microenvironment on Carbon Quantum Dots

Proton-coupled electron transfer (PCET) has emerged as a promising strategy for boosting hydrogen peroxide (H₂O₂) production through the two-electron oxygen reduction reaction (ORR). To achieve efficient H₂O₂ production, a specific C═N–NH–C═O structure was engineered on CQDs through Schiff-base addition reaction, creating an ideal catalytic microenvironment within the molecule via the integration of a proton donor and oxygen adsorption site. Benefiting from that, the obtained benzohydrazide-modified CQDs (BD-CQDs) exhibited a H₂O₂ production efficiency of 1562 μmol g^–1 h^–1 even without an external oxygen supply and electron donor, nearly three times that of the pristine CQDs. Mechanism investigation verified that oxygen adsorption shifted from a side-on type to an end-on type after modification, and the O═O bond was stretched on the C═O adjacent to −NH–, improving H₂O₂ selectivity to 92.5%. Identification of active sites revealed that −NH– provided sustainable proton flux for PCET, while the C═N bridge boosted the charge separation and transfer. Owing to the spatial proximity within the integrated catalytic microenvironment, the proton transfer energy barrier was significantly decreased, thermodynamically favoring H₂O₂ production. BD-CQDs retained an efficiency of over 88% after five successive cycles or in an ionic environment, highlighting their practical application potential in photocatalytic energy conversion.