The Thermodynamic Stability, Electronic and Photocatalytic Properties of the ZnWO4(100) Surface as Predicted by Screened Hybrid Density Functional Theory.

Abstract

Zinc tungstate (ZnWO4) is an outstanding photocatalyst for water splitting and organic contaminant degradation under visible light irradiation. Surface termination stabilities are significant for understanding the photochemical oxidation and reactions on the ZnWO4 surface. Based on density functional theory, we calculated the thermodynamic stability of possible surface terminations for ZnWO4(100). The surface stability phase diagrams show that the Zn2O4-Zn8W6O28, W2O4-Zn8W10O36, and Zn2-Zn8W6O24 terminations of ZnWO4(100) can be stabilized under certain thermodynamic equilibrium conditions. The electronic structures for these three possible stability surface terminations are calculated based on the Heyd–Scuseria–Ernzerhof (HSE06) hybrid functional to give dependable theoretical band gap values. It is found that the surface states of W2O4-Zn8W10O36 termination are in the band gap, which shows a delocalized performance. The calculated absorption coefficients of W2O4-Zn8W10O36 termination show stronger absorption than bulk ZnWO4 in the visible-light region. The band edge calculation shows that the valence band maximum and conduction band minimum of the W2O4-Zn8W10O36 termination can fulfill the hydrogen evolution reaction and oxygen evolution reaction requirements at the same time. Furthermore, work functions are extraordinarily distinct for various surface terminations. This result suggests that the ZnWO4-based direct Z-scheme heterostructure can be controlled by obtaining the thermodynamically preferred surface termination under suitable conditions. Our results can predict ZnWO4(100) surface structures and properties under the entire range of accessible environmental conditions.