Unravelling unsaturated edge S in amorphous NiSx for boosting photocatalytic H2 evolution of metastable phase CdS confined inside hydrophilic beads

The unsaturated edge S in the cocatalyst plays an important role in the enrichment of both protons and electrons during the photocatalytic hydrogen evolution process. However, a mild and simple strategy for effectively exposing edge S is still a significant challenge. Herein, amorphous nickel sulfide (NiSx) as an efficient cocatalyst was decorated on the cubic phase CdS surface, which were confined growth inside hydrophilic chitosan hydrogel beads (CHB@CdS-NiSx) for efficient and durable photocatalytic H2 evolution. The optimal CHB@CdS-0.02NiSx achieved a photocatalytic activity of 11.88 mmol/h/g and displayed ultra-long stability of 60 h. NiSx could effectively accelerate the electron migration from CdS to NiSx in composite photocatalyst and provide abundant unsaturated edge active S as H2-evolution sites. Further density functional theory (DFT) calculation revealed that NiSx lowered activation energy for H2O dissociation to boost the local proton concentration, thereby facilitating the activity of H2 evolution. This study highlights the significance of amorphization strategy for consciously modulating edge sulfur of transition metal sulfide cocatalysts to improve the photocatalytic performance.