Formation energy and photoelectrochemical properties of BiVO4after doping at Bi3+or V5+sites with higher valence metal ions

Photoelectrochemical water splitting is an attractive method to produce H2 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.