Effects of M-Doping and Oxygen Vacancy on the Electronic and Photocatalytic Water-Splitting Properties of α-BiNbO₄ (M = Mo, W)

Based on the first-principles density-functional theory, formation energies, transition energy levels of M (M = Mo, W) doped α-BiNbO₄ systems are studied. The calculation results show that the donor defects form easily under Bi-rich condition. Of these, the W_int (W interstitial) and Mo_int (Mo interstitial) are the two main defects that lead to n-type conductivity. Then, the electronic structures of M-mono-doped and M/O_vac (O vacancy)-codoped α-BiNbO₄ were investigated. Our results show that the band gap of W_int/O_vac-codoped α-BiNbO₄ is reduced by 0.43 eV, and the conduction band minimum and valence band maximum are reduced by 0.20 and 0.23 eV, respectively, compared to pure α-BiNbO₄, with less driving force required for the redox reaction process and then an increased redox rate. The α-BiNbO₄ with W_int+O_vac defects with n-type conductivity has good photocatalytic activity in water splitting.