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 Mo(6+), W(6+) and Sn(4+)-doped BiVO(4) were studied systematically. The results suggested that Mo(6+) or W(6+)-doped BiVO(4) had a much higher photocurrent while the photocurrent of Sn(4+)-doped BiVO(4) did not change obviously. Raman and XPS were used to identify the doping sites in the BiVO(4) 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 SnO(2) segregation on the surface of the Sn(4+)-doped BiVO(4) thin film, which was the main reason for the poor performance of Sn-doped BiVO(4). The higher formation energy of Sn(4+) 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.