S-vacancy-mediated efficient Z-scheme photocatalytic H ₂ generation on an ultrathin nanosheet-based 2D/2D tight heterojunction

Visible-light-driven Z-scheme photocatalysts integrated with two-dimensional (2D) ultrathin semiconductor nanosheets (NSs) are promising for efficient solar fuel production; however, enhancing Z-scheme photocatalysis via controllable vacancy modulation is still underdeveloped to date. Herein, a sulfur vacancy (SV)-engineered CdS ultrathin NS/MoSe₂ few-layered NS 2D/2D heterojunction with tight Mo-S bond linkages was constructed, whose Z-scheme charge-transfer pathway was revealed through in situ light-irradiated X-ray photoelectron spectroscopy, surface photovoltage spectroscopy, and radical production analysis. Notably, density functional theory calculations revealed that SV could serve as the active site for H₂ production. Moreover, by modulating the SV content to broaden the Fermi level gap of the components, the Z-scheme charge transport efficiency of the CdS-MoSe₂ heterojunction increased, affording a visible-light (λ > 400 nm) photocatalytic H₂ evolution activity as high as 47.52 mmol g⁻¹ h⁻¹ (apparent quantum yield of 22.9% at 400 nm), which is approximately 12.2- and 7.1-fold higher than that of CdS and 3 wt% Pt-loaded CdS, respectively. The results of this study provide useful insights for boosting photocatalytic capability via vacancy-engineering-reinforced Z-scheme charge transfer.