Optimizing the Electronic Structure of ZnS via Cobalt Surface Doping for Promoted Photocatalytic Hydrogen Production

Developing highly efficient semiconductor photocatalysts for H₂ evolution is intriguing, but their efficiency is subjected to the following three critical issues: limited light absorption, low carrier separation efficiency, and sluggish H₂ evolution kinetics. Element surface doping is a feasible strategy to synchronously break through the above limitations. In this study, we prepared a series of Co-surface-doped ZnS photocatalysts to systematically investigate the effects of Co surface doping on photocatalytic activity and electronic structure. The implantation of Co results in the emergence of the impurity level above the valence band (VB) and the upshifted conduction band (CB) and enhances its visible light absorption. Co gradient doping inhibits the combination and facilitates the migration of carriers. S atoms are proven to be reactive active sites for photocatalytic H₂ evolution over both ZnS and Co-doped ZnS. Co doping alters the surface electronic structure and decreases the absolute value for the hydrogen binding free energy (ΔG_H) of the adsorbed hydrogen atom on the catalyst. As a consequence, Co-surface-doped ZnS shows boosted photocatalytic H₂ evolution activity relative to the undoped material. This work provides insights into the mechanistic understanding of the surface element doping modification strategy to developing efficient photocatalysts.