Simultaneously Tuning Charge Separation and Oxygen Reduction Pathway on Graphitic Carbon Nitride by Polyethylenimine for Boosted Photocatalytic Hydrogen Peroxide Production

The synthesis of hydrogen peroxide (H₂O₂) from H₂O and O₂ by metal-free photocatalysts (e.g., graphitic carbon nitride, C₃N₄) is a potentially promising approach to generate H₂O₂. However, the photocatalytic H₂O₂ generation activity of the pristine C₃N₄ in pure H₂O is poor due to unpropitious rapid charge recombination and unfavorable selectivity. Herein, we report a facile method to boost the photocatalytic H₂O₂ production by grafting cationic polyethylenimine (PEI) molecules onto C₃N₄. Experimental results and density functional theory (DFT) calculations demonstrate PEI can tune the local electronic environment of C₃N₄. The unique intermolecular electronic interaction in PEI/C₃N₄ not only improves the electron–hole separation but also promotes the two-electron O₂ reduction to H₂O₂ via the sequential two-step single-electron reduction route. With the synergy of improved charge separation and high selectivity of two-electron O₂ reduction, PEI/C₃N₄ exhibits an unexpectedly high H₂O₂ generation activity of 208.1 μmol g^–1 h^–1, which is 25-fold higher than that of pristine C₃N₄. This study establishes a paradigm of tuning the electronic property of C₃N₄ via functional molecules for boosted photocatalysis activity and selectivity.