Factors in the metal doping of BiVO₄ for improved photoelectrocatalytic activity as studied by scanning electrochemical microscopy and first-principles density-functional calculation

Metal doping of the metal oxide photoelectrocatalyst, BiVO₄, dramatically increases its activity for water oxidation. Scanning electrochemical microscopy (SECM) was used to screen various dopants for their photoelectrochemical performance and to optimize the used dopant material concentrations with this photocatalyst. For example, adding Mo to W-doped BiVO₄ enhanced the performance. The photocatalytic activity was examined on larger electrodes by means of photoelectrochemical and electrochemical measurements. The developed photoelectrocatalyst, W- and Mo-doped BiVO₄, shows a photocurrent for water oxidation that is more than 10 times higher than undoped BiVO₄. Factors that affect performance are discussed, and enhanced separation of excited electron-hole pairs by doping onto the semiconductor is suggested by first-principles density-functional theory (DFT) calculations. Distortion of the crystal structure of monoclinic scheelite-like BiVO₄ by addition of W and Mo doping predicted by DFT is also revealed by X-ray diffraction and Rietveld refinement analysis. The results indicate that the consecutive doping of W and Mo into the metal oxide photocatalyst introduces improved electron-hole separation without a significant change of the band gap or the material's optical properties.