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

Sulfur vacancies modulate d‑orbitals to tune the adsorption‑desorption equilibrium of hydrogen intermediates. • A noble‑metal‑free V s ‑NiCo 2 S 4 /CdSe heterojunction is fabricated for efficient photocatalytic H 2 evolution. • Schottky heterojunction formation and its photocarrier‑separation mechanism are deeply explored. Achieving the adsorption and desorption equilibrium of H species (H-Ads/Des) is crucial for accelerating hydrogen evolution kinetics in photocatalytic H 2 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 NiCo 2 S 4 -modified CdSe photocatalysts (V s -NiCo 2 S 4 /CdSe). Experimental results and theoretical calculations demonstrate that the S vacancies in V s -NiCo 2 S 4 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 -NiCo 2 S 4 /CdSe. Ultimately, V s -NiCo 2 S 4 /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. Download: Download high-res image (124KB) Download: Download full-size image