Effects of native defects and cerium impurity on the monoclinic BiVO₄ photocatalyst obtained <i>via</i> PBE+<i>U</i> calculations

Abstract

In this article, we report a 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 Bi_vac (Bi vacancy), V_vac (V vacancy), O_int (O interstitial) and Ce_V (Ce doping on V site) defects in m-BiVO₄ are identified as shallow acceptors. For Ce doping in m-BiVO₄, the substitution of Bi by Ce is energetically favorable in the single positively charged state (Ce) under Bi/V-poor conditions, while the substitution of V by Ce is in the single negatively charged state (Ce) under O-rich conditions. The calculated electronic structures suggest that Ce 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 the experimental results. For Ce, no localized state exists within the calculated band gap. Its formation energy is 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 improve photocatalysis. Our results provide insights into enhancing the photocatalytic activity of m-BiVO₄ for energy and environmental applications through the rational design of defect-controlled synthesis conditions.