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

Copper (Cu) doping modifies the band structure of TiO 2 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-TiO 2 /g-C 3 N 4 (Cu-CT) was constructed by anchoring Cu-TiO 2 onto g-C 3 N 4 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-TiO 2 and holes in the valence band of g-C 3 N 4 . 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 TiO 2 . 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. A ternary Cu-TiO 2 /g-C 3 N 4 heterojunction was constructed, where Cu doping tunes the band structure and introduces electronic states that cooperate with Z-scheme charge transfer. The internal electric field enables efficient electron–hole separation while retaining strong redox potential, resulting in a hydrogen evolution rate of 10.21 mmol g -1 h -1 , over twentyfold higher than pristine TiO 2 . • Synergistic Cu doping and Z-scheme engineering enable effective charge separation while retaining strong redox potentials. • Cu-TiO 2 /g-C 3 N 4 heterojunction achieves a hydrogen evolution rate of 10.21 mmol g -1 h -1 , over twentyfold higher than pristine TiO 2 . • In situ XPS, KPFM, and DFT analyses reveal the cooperative role of Cu dopant states and interfacial electric field in directing carrier dynamics.