Unveiling the role of S site in nitrogen-rich carbon nitride for photoactivation of molecular oxygen into hydrogen peroxide

A metal-free sulfur-doped nitrogen-rich carbon nitride (S-C 3 N 5 ) photocatalyst was constructed to promote directional photogenerated charge migration for enhanced hydrogen peroxide (H 2 O 2 ) production and explored the potential for environmental remediation. Physicochemical properties of S-C 3 N 5 such as the surface morphologies, photoresponse characteristics, and charge separation efficiencies were thoroughly analyzed, meanwhile the performance of H 2 O 2 production was evaluated and its reaction pathway was demonstrated through electrochemical characterization and theoretical simulation calculation. Under simulated sunlight, S‑C 3 N 5 achieves a H 2 O 2 photosynthesis rate of 2784 μmol g -1  h -1 with a 95% selectivity toward 2e - oxygen reduction reaction (ORR), compare with C 3 N 5 . This high performance originates from the introduced S sites, which act as strong electron donors and localized active centers that facilitate O 2 adsorption and activation via an indirect 2e⁻ ORR pathway. This work clarifies the critical role of metal-free heteroatom doping in regulating charge behavior and offers a design strategy for efficient molecular‑oxygen activation in photocatalysis.