Synergistic Multiple Charge Carrier Transfer Pathways for High-Efficiency Visible-Light-Driven Hydrogen Evolution

The construction of step-scheme (S-scheme) heterojunctions by integrating single-component semiconductors with strategic cocatalyst loading facilitates enhanced charge transfer, improving visible-light-driven photocatalytic hydrogen evolution efficiency. In this work, In₂O₃/CdS/NiSe₂ and In₂O₃/NiSe₂/CdS heterostructures are synthesized through sequential deposition of CdS and NiSe₂ onto In₂O₃ nanosheets with different loading orders. Combined analysis using in situ irradiated X-ray photoelectron spectroscopy and electron paramagnetic resonance (EPR) confirms the S-scheme charge transfer pathway in both In₂O₃/CdS and In₂O₃/NiSe₂/CdS systems. The results show that the In₂O₃/CdS/NiSe₂ heterostructure exhibits three charge transfer pathways, while In₂O₃/NiSe₂/CdS possesses only one. Charge density difference analysis and photoelectrochemical measurements indicate that, compared to In₂O₃/NiSe₂/CdS, the multiple charge transfer pathways in In₂O₃/CdS/NiSe₂ significantly enhance photoinduced electron migration efficiency. According to Gibbs free energy calculations, Ni in In₂O₃/CdS/NiSe₂ resides at the outermost layer and exhibits the weakest hydrogen adsorption free energy, enabling it to serve as an additional active site that facilitates hydrogen desorption and enhances hydrogen evolution activity. Owing to these synergistic effects, the In₂O₃/0.8CdS/NiSe₂-5 photocatalyst achieves a hydrogen evolution rate of 16,797.1 µmol g^-1 under visible light-nearly four times higher than that of In₂O₃/NiSe₂-5/0.8CdS (3,902.4 µmol g^-1). This study offers theoretical and practical guidance for designing ternary heterojunctions with efficient multiple charge transfer pathways.