Formation energy and photoelectrochemical properties of BiVO4 after doping at Bi3+ or V5+ sites with higher valence metal ions

Photoelectrochemical water splitting is an attractive method to produce H-2 fuel from solar energy and water. Ion doping with higher valence states was used widely to enhance the photocurrent of an n-type oxide semiconductor. In this study, the different doping sites and the photoelectrochemical properties of Mo6+, W6+ and Sn4+-doped BiVO4 were studied systematically. The results suggested that Mo6+ or W6+-doped BiVO4 had a much higher photocurrent while the photocurrent of Sn4+-doped BiVO4 did not change obviously. Raman and XPS were used to identify the doping sites in the BiVO4 crystal lattice. It was found that Mo or W substituted V sites but Sn did not substitute Bi sites. Results of theoretical calculation indicated that a higher formation energy and lower solubility of impurity ions led to serious SnO2 segregation on the surface of the Sn4+-doped BiVO4 thin film, which was the main reason for the poor performance of Sn-doped BiVO4. The higher formation energy of Sn4+ came from the large mismatch of ion radius and different outer shell electron distribution. These results can offer guidance in choosing suitable doping ions for other semiconductor photoelectrodes.