Tailoring Charge Dynamics via Cu-Doped TiO₂/g-C₃N₄ S-Scheme Composites for Solar Hydrogen Evolution

Copper (Cu) doping modifies the band structure of TiO₂ by slightly narrowing the bandgap and shifting the Fermi level, while creating localized states that serve as temporary electron reservoirs to suppress carriers rapid recombination. On this basis, a ternary heterojunction Cu-TiO₂/g-C₃N₄ (Cu-CT) was constructed by anchoring Cu-TiO₂ onto g-C₃N₄ nanosheets. The synergistic interaction between Cu-doping and the S-scheme interfacial configuration generates an internal electric field that promotes vectorial carrier migration, enabling electrons in the conduction band of Cu-TiO₂ and holes in the valence band of g-C₃N₄. This spatial separation preserves strong redox potentials and markedly suppresses recombination. Consequently, Cu-CT achieves a hydrogen evolution rate of 10.21 mmol g^-1 h^-1, more than twenty times higher than pristine TiO₂. In-situ XPS, KPFM, and DFT analyses collectively validate the S-scheme charge-transfer pathway and highlight the synergistic role of Cu doping with heterojunction engineering, providing mechanistic insights to the rational design of advanced ternary photocatalysts for efficient solar-driven hydrogen production.