Synergistic band and electronic engineering in cyano-oxygen co-functionalized carbon nitride for efficient photocatalytic H₂O₂ synthesis

Photocatalytic hydrogen peroxide (H₂O₂) synthesis via the two-electron oxygen reduction reaction (2e− ORR) offers a sustainable alternative to industrial methods. However, conventional carbon nitride photocatalysts suffer from rapid charge recombination, limited visible-light utilization, and insufficient 2e− ORR selectivity. Herein, we report a novel precursor-molten salt synergistic strategy. Using the oxygen-containing precursor itself, the spontaneous oxygen doping of the carbon nitride skeleton was initiated by a one-step heat-induced condensation process, and the O-doped cyano-functionalized carbon nitride (MCN-N15) was further synthesized by molten salt-assisted synthesis. Under visible light, MCN-N15 achieves an exceptional H₂O₂ production rate of 950.14 μmol·g⁻¹·h⁻¹ in ethanol. O-doping induces n → π* electronic transitions, broadening the visible-light absorption range. Simultaneously, the introduced cyano groups (–C≡N) facilitate charge separation and enhance 2e− ORR selectivity. Crucially, this approach not only realizes the self-doping of O, but also mitigates the conduction band downshifting typically caused by conventional molten salts, yielding a more negative conduction band potential (E_CB = –0.84 V vs. NHE) that provides a strong thermodynamic driving force for 2e− ORR. The results of density functional theory calculations show that the synergistic modification strategy of oxygen doping and cyano modification effectively reduces the Gibbs free energy change (ΔG) of the rate-determining step (* + O₂ → *O₂) and promotes the formation of intermediate *OOH, thereby significantly improving the selectivity and reaction rate of H₂O₂ synthesis. The synergistic modification optimizes the electronic and band structure of carbon nitride, providing a novel “energy band engineering-surface functionalization” co-regulation strategy for designing efficient photocatalytic H₂O₂ generation systems.

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