A Full-Spectrum ZnS Photocatalyst with Gradient Distribution of Atomic Copper Dopants and Concomitant Sulfur Vacancies for Highly Efficient Hydrogen Evolution

A rarely discussed phenomenon in the realm of photocatalytic materials involves the presence of gradient distributed dopants and defects from the interior to the surface. This intriguing characteristic has been successfully achieved in the case of ZnS through the incorporation of atomic monovalent copper ions (Cu⁺) and concurrent sulfur vacancies (V_s), resulting in a photocatalyst denoted as G-CZS_1-x. Through the cooperative action of these atomic Cu dopants and Vs, G-CZS_1-x significantly extends its photoabsorption range to encompass the full spectrum (200-2100 nm), which improves the solar utilization ability. This alteration enhances the efficiency of charge separation and optimizes Δ(H*) (free energy of hydrogen adsorption) to approach 0 eV for the hydrogen evolution reaction (HER). It is noteworthy that both surface-exposed atomic Cu and V_s act as active sites for photocatalysis. G-CZS_1-x exhibits a significant H₂ evolution rate of 1.01 mmol h^-1 in the absence of a cocatalyst. This performance exceeds the majority of previously reported photocatalysts, exhibiting approximately 25-fold as ZnS, and 5-fold as H-CZS_1-x with homogeneous distribution of equal content Cu dopants and Vs. In contrast to G-CZS_1-x, the H adsorption on Cu sites for H-CZS_1-x (ΔG(H*) = -1.22 eV) is excessively strong to inhibit the H₂ release, and the charge separation efficiency for H-CZS_1-x is relatively sluggish, revealing the positive role of a gradient distribution model of dopants and defects on activity enhancement. This work highlights the synergy of atomic dopants and defects in advancing photoactivity, as well as the significant benefit of the controllable distribution model of dopants and defects for photocatalysis.