Oxygen-rich g-C3N4 quantum dot engineered graphene cathode enabling highly selective 2e− oxygen reduction reaction in a value-added reaction assisted Zn–air battery

Abstract

The electrochemical two-electron oxygen reduction reaction (2e⁻ ORR) offers a sustainable and energy-efficient alternative to the conventional anthraquinone process for hydrogen peroxide (H₂O₂) production. While metal-free carbon-based electrocatalysts have shown promise, optimizing their active sites for the selective 2e⁻ ORR remains a critical challenge. Given their nitrogen and oxygen-rich species, graphitic carbon nitride quantum dots (CNQDs) hold promise for promoting selective 2e⁻ ORR. Herein, we report the rational design of oxygen-rich CNQDs decorated on graphene frameworks (CNQDs/Gr), enabling the precise tailoring of active sites to promote the 2e⁻ ORR pathway. The rich C–O–C moieties within CNQDs effectively address the oxygen-deficient sites in Gr, serving as key active sites for selective 2e⁻ ORR for H₂O₂ generation. Furthermore, the interaction between the C atoms in Gr and neighboring N atoms in CNQDs facilitates π–π stacking, which stabilizes the *OOH intermediate and thus promotes selective H₂O₂ formation. These synergistic effects result in CNQDs/Gr with outstanding H₂O₂ selectivity of 96.5% at 0.6 V vs. RHE in 0.1 M KOH, far exceeding that of pristine Gr (∼60%). Furthermore, the CNQDs/Gr demonstrates outstanding performance in a value-added reaction assisted Zn–air battery (VAR-ZAB), achieving an impressive capacity of 768.58 mA h g⁻¹ with a high H₂O₂ production rate of 136 mmol g⁻¹ h⁻¹. This work presents a novel design strategy for metal-free carbon electrocatalysts, providing new insights into green H₂O₂ electrosynthesis.