Electron polarons in the subsurface layer of Mo/W-doped BiVO surfaces.

Monoclinic BiVO has been regarded as a promising photocatalyst for water splitting in recent years. In this research, the effects of Mo/W dopants near the surfaces of BiVO on electron transport are investigated using first-principles calculations. We demonstrate that the additional electron introduced by Mo/W either in the bulk or near the surfaces forms a self-trapped small polaron. The polaron prefers to be localized on the transition metal ions in the subsurface layer when Mo/W is doped in the vicinity of the surfaces. The localized positions of polarons can be rationalized by the d-orbital energy levels of the transition metals and the variation of electrostatic potential. The concentrated electron polarons in the subsurface layer of BiVO surfaces can build fast lanes for electron migration and mitigate the electron-hole recombination process, which underlines the importance of dopants near the surfaces as compared with those in the bulk.