S-vacancy defect engineering in CdS via hydrothermal acidification: Enhanced photocatalytic hydrogen evolution

Amidst the continuously growing global energy demand and increasingly severe environmental challenges, hydrogen energy has emerged as a promising clean alternative and is expected to play a critical role in the future energy landscape. Photocatalytic water splitting represents a transformative technology in the field of solar-to-hydrogen conversion. Driven by abundant sunlight and using water as the feedstock, it directly decomposes water into clean and renewable hydrogen gas with the assistance of photocatalysts. Among various photocatalysts, cadmium sulfide (CdS) has attracted considerable attention as a visible-light-responsive semiconductor with great potential for photocatalytic hydrogen evolution. Nevertheless, the practical deployment of CdS is still hindered by two major limitations: rapid recombination of photogenerated charge carriers and inherent photochemical instability. In this work, sulfur vacancy-modified CdS (S v -CdS) was synthesized via a hydrothermal acidification method. The introduction of sulfur vacancies enables precise modulation of the electronic properties of CdS, resulting in a narrower bandgap (decreased from 2.77 eV to 2.08 eV) and a broader range of light absorption (extended from 474 nm to 599 nm). Furthermore, it significantly promotes the separation and mobility of photogenerated charge carriers. As a result, the S v -CdS catalyst exhibits substantially enhanced photocatalytic hydrogen production activity. As a result, the Sv-CdS catalyst shows much stronger photocatalytic hydrogen evolution activity with lactic acid acting as the sacrificial agent. Under visible light irradiation (λ ≥ 420 nm), the best-performing sulfur-deficient sample, S v -CdS-3, reaches a hydrogen evolution rate of 688.79 μmol g −1  h −1 , approximately 125 times higher than that of unmodified CdS (5.50 μmol g −1  h −1 ).