First-principles investigation of novel direct-Z ZnS/ZrS2 heterojunction: Electronic properties and photocatalytic potential

The potential of ZnS/ZrS₂ heterojunction as a high-efficiency photocatalyst is studied by first-principles calculations in this work. The calculated results show that the ZnS/ZrS₂ heterojunction processes a 1.64 eV narrow direct band gap to enhance visible light absorption and a favorable staggered band alignment conducive to efficient charge separation. The internal electric field between ZnS and ZrS₂ blocks the transfer channels of carriers which confines electrons in ZnS layer and holes in ZrS₂ layer to facilitate redox reaction. Thus, the overall water splitting can be achieved in Z-scheme. The catalytic activity of redox reaction on the surface of ZnS/ZrS₂ heterojunction is demonstrated through the analysis of Gibbs free energy. The probable adsorption site for the OER and HER process is the top-site of Zr atom and S atom, respectively. The 1.78 and 2.43 eV external potential endows the heterojunction with the conducive to the HER and OER, respectively. The catalytic efficiency is guaranteed by a 29.64% STH efficiency. Notably, 32.58% efficiency can be achieved, due to compressive strain induced band gap reduction and visible-light optical absorption enhancement. These findings suggest that the ZnS/ZrS₂​ heterojunction has great potential as a photocatalytic material.