A hollow core-shell TiO₂/NiCo₂S₄ Z-Scheme heterojunction photocatalyst for efficient hydrogen evolution

Constructing heterojunctions have received significant attention in photocatalysis because of their efficient separation of photogenerated carriers and improving light utilization efficiency. Bimetallic sulfides (e.g. NiCo₂S₄) are applied in electrocatalysis and supercapacitors that can be coupled with TiO₂ to form a heterojunction. Owing to the staggered energy band arrangement between TiO₂ and NiCo₂S₄, the establishing of a Z-scheme heterojunction between them is expected to enhance the carrier separation efficiency and reduce the sulfide photo-corrosion. However, the application of NiCo₂S₄ in photocatalysis and studies on the mechanism of the TiO₂/NiCo₂S₄ Z-scheme heterojunction have seldom been reported. In this work, we obtained a hollow core-shell TiO₂/NiCo₂S₄ Z-scheme photocatalyst through a solvothermal method for photocatalytic hydrogen evolution (PHE). The PHE rate of the optimized TiO₂/NiCo₂S₄-0.3 is 8.55 mmol g⁻¹ h⁻¹, approximately 34 times higher than pure TiO₂, 94 times higher than pure NiCo₂S₄. The remarkable photocatalytic activity can be ascribed to the hollow structure and the in-situ constructed Z-scheme heterojunction. The photogenerated charge transfer mechanism is revealed by hydroxyl radical trapping experiments and electron paramagnetic resonance (EPR) characterization. The in-situ construction of the Z-scheme heterojunction not only enhances the efficiency of separating the photogenerated carriers but also reduces the photo-corrosion of NiCo₂S₄. This study proposes an effective strategy for the design of TiO₂-based Z-scheme heterojunctions and the application of NiCo₂S₄ in photocatalysis.