Hybrid density functional study on band structure engineering of ZnS(110) surface by anion-cation codoping for overall water splitting

Zinc sulfide (ZnS) is known as a promising photocatalyst for hydrogen production through water splitting, but it suffers from limited photoreaction efficiency under solar light due to the large band gap. In the present study, we carry out a systematic study on band structure engineering of Ru-, C-, N-, and F-monodoped and (Ru + C)-, (Ru + N)-, and (Ru + F)-codoped ZnS(110) surfaces by performing extensive hybrid density functional theory calculations. The theoretical results clearly reveal that although the monodoping of Ru or nonmetal atoms can reduce the band gap of the ZnS(110) surface to some extent, the appearance of some unoccupied located states are unfavorable for water redox reactions. In contrast, the anion-cation codoped ZnS(110) surfaces, especially in the case of (Ru + C), not only have a substantially reduced band gap without creating unwanted impurity states, with enhanced optical absorption in the visible spectral range, but also have appropriate band edge positions aligning well with water redox potentials. Remarkably, the photogenerated electrons and holes of the (Ru + C)-codoped ZnS(110) surface have adequate driving forces to trigger both hydrogen reduction and water oxidation half-reactions. Furthermore, the (Ru + C) codoping pair greatly reduces the formation energy of Ru monodoping, thus enhances the thermodynamic solubility. These findings demonstrate that (Ru + C)-codoped ZnS(110) surfaces are a potential candidate for overall water splitting under solar light irradiation.