In3+-doped BiVO4 photoanodes with passivated surface states for photoelectrochemical water oxidation

Abstract

BiVO₄ is a promising photoanode material for photoelectrochemical water splitting, but its actual activity is hindered by the high energy surface states. Here, we report that In³⁺ can be used as a dopant to substitute the partial sites of Bi³⁺ in BiVO₄ for modifying the surface states and improving the water oxidation activity of a BiVO₄ nanoflake film. Among the In³⁺-doped BiVO₄ film photoanodes, the 7% In³⁺-doped BiVO₄ film shows optimal photoelectrochemical water oxidation activity. At 1.23 V vs. RHE, the 7% In³⁺-doped BiVO₄ photoanode exhibits a photocurrent density of 1.56 mA cm⁻² in 0.1 M Na₂SO₄, which is over 200% greater than that of the undoped BiVO₄ photoanode. In³⁺-doping did not change the morphology, phase and band gap of BiVO₄ obviously, but resulted in a positive shift of the flat band position and higher surface charge separation efficiency for water oxidation. Density functional theory calculations indicate that the surface energy of BiVO₄ decreased after In³⁺-doping that involved more unsaturated electrons of the Bi atom in the Bi–O bonds, thus reducing the amount of exposed unsaturated Bi atoms and broken Bi–O bonds. Therefore, the enhanced water oxidation activity on the In³⁺-doped BiVO₄ photoanode can be ascribed to In³⁺-doping that passivated the surface states of BiVO₄ and thus inhibited the surface charge recombination.