Orbital-tailoring strategy via defect engineering in NiCo₂S₄/CdSe heterojunction for enhanced photocatalytic hydrogen...

Achieving the adsorption and desorption equilibrium of H species (H-Ads/Des) is crucial for accelerating hydrogen evolution kinetics in photocatalytic H₂ production. However, the precise manipulation of H-Ads/Des behavior remains a critical bottleneck. Herein, we propose a strategy that uses S vacancies (V_s) to regulate d orbitals and thereby optimize H-Ads/Des in NiCo₂S₄-modified CdSe photocatalysts (V_s-NiCo₂S₄/CdSe). Experimental results and theoretical calculations demonstrate that the S vacancies in V_s-NiCo₂S₄ modulate the Co 3d orbitals. Specifically, as the S-vacancy concentration increases, the Co d band gradually broadens and its center shifts away from the Fermi level, enabling precise control over H-Ads/Des kinetics on V_s-NiCo₂S₄/CdSe. Ultimately, V_s-NiCo₂S₄/CdSe with an appropriate amount of V_s exhibits a remarkable photocatalytic hydrogen evolution rate of 8387.92 μmol·g^-1·h^-1. This work elucidates how defect engineering regulates H-Ads/Des dynamics and provides insights into the design of highly efficient heterojunction photocatalysts.