Carbon Doping Regulates Charge Transfer Paths via a Type-II to S-Scheme Transformation to Improve Photocatalytic...

Designing S-scheme heterojunctions with enhanced interfacial interaction is an effective strategy for promoting the separation of photocarriers while maintaining strong photoredox capabilities. However, precisely tailoring the interfacial charge transport pathways between two contacted semiconductors remains a significant challenge due to the similar band alignment in type-II and S-scheme heterostructures. Herein, we report a facile and low-cost carbon doping strategy to smartly tune the charge transfer pathway via a type-II to S-scheme transformation for efficient photocatalytic H₂ evolution and H₂O₂ synthesis. Density functional theory calculations combined with in situ XPS studies demonstrate that the Fermi level of MoO₂ shifts from being higher than that of C₃N₄ to being lower after carbon doping, which drives the inversion of the internal electric field (IEF) direction between MoO₂ and C₃N₄, thus enabling a transition from type-II MoO₂/C₃N₄ heterojunctions to S-scheme C-MoO₂/C₃N₄ heterojunctions. As a result, the optimal S-scheme C-MoO₂/C₃N₄ heterojunctions exhibit a high H₂ evolution rate of 16.2 mmol g^-1 h^-1 and a H₂O₂ production rate of 877 μmol g^-1 h^-1, notably surpassing those of the original C₃N₄ and type-II MoO₂/C₃N₄ heterojunctions. This work provides valuable insights into the fabrication of C₃N₄ heterostructures and the control of electron migration pathways, thereby creating new possibilities for photocatalysis and optoelectronics applications.