Monoclinic BiVO _(4) 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 _(4) 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 _(4) 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.
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