Revealing the electron transfer mechanism of defective carbon nitride during photocatalytic H₂O₂ production

Photosynthesis is a promising method for H₂O₂ production, but its application in pure water is limited by slow oxidation kinetics and rapid photocarrier recombination of photocatalysts. Herein, a novel defective carbon nitride photocatalyst (D-C_3−xN₄) containing the C vacancies and the frustrated Lewis pairs (B and N of cyano group) is designed for H₂O₂ photosynthesis, and the role of C vacancies on the electron transfer mechanism during photocatalysis is systematically investigated. The D-C_3−xN₄ exhibits a H₂O₂ production rate of 140.1 μmol·g⁻¹·h⁻¹ in pure water, which is 87.6 times that of C₃N₄. Such superior performance for H₂O₂ photosynthesis is found to arise from the C vacancies and frustrated Lewis pairs (FLPs). The C vacancies have strong electron-trapping ability, which greatly enhances the separation of photocarriers. The C vacancies can also effectively reduce O₂ to ^*OOH via a proton-coupled process, which significantly accelerates the O₂ reduction kinetics. Meanwhile, the FLPs show an outstanding catalytic activity for H₂O oxidation. This study not only provides a new structure for highly active photocatalysts, but also deepens the understanding of the electron transfer mechanism of photocatalysts with trapped sites.