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

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 (Vs) to regulate d orbitals and thereby optimize H-Ads/Des in NiCo2S4-modified CdSe photocatalysts (Vs-NiCo2S4/CdSe). Experimental results and theoretical calculations demonstrate that the S vacancies in Vs-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 Vs-NiCo2S4/CdSe. Ultimately, Vs-NiCo2S4/CdSe with an appropriate amount of Vs 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.