Enhanced photocatalytic H2 evolution: optimized atomic hydrogen desorption via free-electron transfer in sulfur-rich MoWS2+x on vacancy-engineered CdS crystals†

Abstract

The hydrogen evolution capacity of MoS₂ is impeded by its intrinsically highly electronegative sulfur sites, which firmly bind absorbed atomic H through S–H_ads bonds and subsequently diminish H₂ release. Designing effective surface-active sites to optimize atomic hydrogen activation and desorption for the hydrogen evolution reaction (HER) in water, while also expanding near-infrared (NIR) light responsiveness, remains a significant challenge. We have developed complexes of sulfur vacancy (S_v) enriched CdS_v capped with W-modified MoS_2+x (MoWS_2+x) through an in situ substitution approach, followed by a photoreduction reaction. The bimetallic MoWS_2+x cocatalyst not only increases the density of unsaturated coordinating S active sites but also attenuates the strength of the S–H_ads bond. The optimized MoWS_2+x/CdS_v hybrid shows synergistic improvement of atomic H activation and desorption for the solar-driven HER, achieving the highest recorded H₂-evolution rate of 9166.13 μmol g⁻¹ h⁻¹ under visible light (λ ≥ 420 nm), which marks a substantial improvement (greater than 750%), and an apparent quantum yield of 19.13%. Remarkably, the target photocatalyst, which is abundant in sulfur vacancies within its CdS_v component, also achieves H₂ production driven by NIR light beyond 780 nm, with a H₂ evolution rate of 1326.82 μmol g⁻¹ h⁻¹. Comprehensive experimental and theoretical investigations corroborate that the existence of unsaturated coordinated S sites mitigates the strength of S–H_ads bonds, resulting in the high driving force of H₂ bubble release from water and long-lived active charge carriers. In this paper, we constructed visible light and NIR-active photocatalysts successfully for hydrogen production, highlighting the synergetic effects within this unique system. Additionally, the photo-behaviors of charge carriers have been investigated by ultra-fast spectroscopic techniques to gain a deeper understanding of the interfacial charge transfer kinetics. This study provides valuable insights into the development and optimization of photocatalysts that are responsive to both NIR and visible light, paving the way for more efficient solar-driven applications.