Unveiling the plasmonic electron origin: dual vacancies synergy in an S-scheme Cu(7)S(4)@ZnIn(2)S(4) heterojunction boosting hot electron flow for photothermal H(2) evolution.

The integration of plasmonic nanomaterials integrated with semiconductors broadens light absorption spectrum and excites abundant hot electrons via localized surface plasmon resonance (LSPR), offering a promising route to enhance photocatalytic hydrogen evolution. However, their underlying governing mechanisms remain largely unexplored. Herein, guided by theoretical calculations and simulations, an S-scheme CuS@ZnInS heterojunction incorporating Cu and S double vacancies was constructed. The as-synthesized CuS@ZnInS achieves a high hydrogen evolution rate of 47.41 mmol·g·h under photothermal conditions and a quantum efficiency of 52.6% at 500 nm. Finite-difference time-domain (FDTD) simulations and density functional theory (DFT) calculations demonstrate that the core-shell structure formed between sulfur vacancy-rich ZnInS and solid CuS enhances the local electromagnetic field, while the dual copper‑sulfur vacancies modulate the work function and reduce the H* adsorption barrier, respectively. Both in-situ irradiated X-ray photoelectron spectroscopy (ISIXPS) and femtosecond transient absorption spectroscopy (fs-TAS) confirmed that the vacancies and the S-scheme heterojunction synergistically promote efficient charge transfer at the interface. This work elucidates the origin of LSPR in copper-deficient semiconductors and provides a defect-interface coupling strategy for designing broad-spectrum, high-performance photocatalysts.