Effects of Fluorination and Molybdenum Codoping on Monoclinic BiVO₄ Photocatalyst by HSE Calculations

Monoclinic phase bismuth vanadate (BiVO₄) is one of the most promising photoelectrochemical materials used in water-splitting photoelectrochemical cells. It could be even better if its band gap and charge transport characteristics were optimized. Although codoping of BiVO₄ has proven to be an effective strategy, its effects are remarkably poorly understood. Using the Heyd-Scuseria-Ernzerhof (HSE) hybrid functional, we estimate the formation energy, electronic properties, and photocatalytic activities of F and Mo codoped BiVO₄. We find that Mo atoms prefer to replace V atoms, whereas F atoms prefer to replace O atoms (F_OMo_V-doped BiVO₄) under oxygen-poor conditions according to calculated formation energies. BiVO₄ doped with F_OMo_V is found to be shallow-level doped, occurring with some continuum states above the conduction band edge, which is advantageous for photochemical catalysis. Moreover, F_OMo_V-doped BiVO₄ shows absorption stronger than that of pure BiVO₄ in the visible spectrum. Based on the band-edge calculation, BiVO₄ doped with F_OMo_V still retains a high oxidizing capacity. It has been shown that F_OMo_V-doped BiVO₄ exhibits a very high photocatalytic activity under visible light.