The identification of defects and their roles in photocatalytic production of hydrogen peroxide (H2O2) with carbon nitride (CN) is a challenging but important task. Here, a simple route was employed to generate defects in CN by tuning the ratio of the two synthesis precursors: acetylacetone (AcAc) and urea. In this way, a set of modified CNs (AxCN) with dual defects (C doping and surface −OH modification) were successfully fabricated. The one with an AcAc-to-urea ratio (x) of 0.05 showed a photocatalytic H2O2 production rate of 3.6 mmol·g–1·h–1, which was greater than most of the reported CNs. Moreover, the selectivity of H2O2 production was increased from 60% (CN) to 85% (A0.05CN). On the basis of density functional theory and the first-principles calculation, the high performance of A0.05CN was attributed to the synergistic roles of the dual defects in oxygen reduction reactions. The C doping enhanced the anchoring of dioxygen, while the −OH group facilitated the diffusion of charge carriers. The finding here provides an insight into the defect engineering for green generation of H2O2.

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