Accelerated Water Oxidation Kinetics Induced by Oxygen Vacancies in the BiVO₄/C₃N₄ S-Scheme Heterojunction for Enhanced Photocatalytic CO₂ Reduction

The solar-driven photocatalytic reduction of CO₂ into fuels using a C₃N₄-based photocatalyst has shown great application potential in addressing challenges related to energy and CO₂ emission. However, this process suffers from severe charge recombination and sluggish H₂O oxidation kinetics, resulting in low efficiency. In this study, a 2D/2D S-scheme heterojunction by combining oxygen vacancy-rich BiVO₄ nanoflakes with C₃N₄ nanosheets (denoted as O_v-BVO/CN) was fabricated to mitigate the aforementioned issues, where BiVO₄ serves as a water oxidation booster and C₃N₄ serves as the CO₂ reduction center. By leveraging the synergistic effects of a lamellar morphology and an S-scheme charge-transfer pathway, the O_v-BVO/CN heterojunction achieves efficient charge separation while maintaining maximized redox capabilities. Moreover, theoretical calculations demonstrated that the O_v on the surface of BiVO₄ reverses the rate-limiting step in H₂O oxidation while reducing its energy barrier, thereby accelerating reaction kinetics. The optimized O_v-BVO/CN S-scheme heterojunction demonstrates remarkably improved photocatalytic evolution rates for CO (13.8 μmol g^-1 h^-1) and CH₄ (5.9 μmol g^-1 h^-1), which are approximately 3.8 and 3.5 times higher than those of CN nanosheets under visible-light irradiation, respectively. This work highlights the design and fabrication of highly efficient heterostructure photocatalysts for CO₂ photoreduction.