Effects of native defects and Cerium impurity on monoclinic BiVO4 photocatalyst by PBE+U calculations
In this article, we report periodic density functional theory (DFT) investigation on the formation of the native defects and Cerium doping in monoclinic BiVO4 (m-BiVO4) and their effect on the electronic structures, using the Perdew-Burke-Ernzerhof functionals corrected for on-site Coulombic interactions (PBE + U). From the point defect formation energies and transition levels, the Bivac (Bi vacancy), Vvac (V vacancy), Oint (O interstitial) and CeV (Ce doping on V site) defects in m-BiVO4 are identified as shallow acceptors. For Ce doping in m-BiVO4, substitution of Bi by Ce is energetically favorable in the single positively charged state (Ce_Bi_1+ ) under Bi/V-poor conditions, while substitution of V by Ce is in the single negatively charged state (Ce_V_1- ) under O-rich conditions. The calculated electronic structures suggest that Ce_Bi_1+ degrades the activity by an unoccupied deep level in the gap region, mainly composed of Ce 4f orbitals, which makes this defect as the photogenerated electron-hole recombination center, in good agreement with experimental results. For Ce_V_1- , no localized state exists within the calculated band gap. Its formation energy is all sensitive to the chemical potentials and Fermi energy, suggesting that the Bi/V-poor and O-rich conditions are desirable to eliminate the deep-level states and to improve photocatalysis. Our results provide insights into how to enhance the photocatalytic activity of m-BiVO4 for energy and environmental applications through rational design of defect controlled synthesis conditions.