Synergistic N _2C and NH _<i>x</i> Vacancies in 2D g-C ₃ N ₄ Optimize the Oxygen Reduction Pathway for Efficient H ₂ O ₂ Photosynthesis

The photocatalytic two-electron oxygen reduction reaction (2e– ORR) for hydrogen peroxide (H2O2) production is a green and promising route, yet the development of efficient photocatalysts remains challenging. While defect-engineered graphitic carbon nitride (g-C3N4) has shown potential, the specific roles of defect sites in the interfacial reaction mechanism for the 2e– ORR are still unclear. Herein, we report a two-dimensional g-C3N4 rich in nitrogen vacancies (2D-NvCN) via thermal exfoliation and an argon etching strategy. The optimized 2D-NvCN catalyst, featuring concurrently introduced N2C and NHx vacancies, exhibits a remarkable H2O2 generation rate under visible light, which is 13.3 times higher than that of its pristine counterpart. Crucially, combined experimental characterization and theoretical calculations elucidate the distinct and synergistic roles of these vacancies: the N2C sites serve as primary centers for O2 adsorption and activation, effectively suppressing the formation of undesired reactive oxygen species (·O2–, 1O2), while the NHx vacancies significantly modulate the electronic structure, enhancing charge separation efficiency. This synergy optimizes the 2e– ORR pathway, providing fundamental insights into the rational design of high-performance catalytic materials via defect engineering for energy conversion and environmental remediation.