An investigation on the role of W doping in BiVO4 photoanodes used for solar water splitting

Abstract

n-Type doping has been widely employed to enhance the performance of a photoanode in a photoelectrochemical cell used for water splitting. However, little is known about how doping affects the catalytic activity during surface catalysis. Herein, we took BiVO₄ as an example to investigate the effect of doping on surface catalysis from both experimental and theoretical perspectives. To enable an impartial comparison, we have prepared planar BiVO₄ thin films with and without W doping. It was found that W doping had no obvious effect on the morphology, crystallinity, and light absorption of the film; however, the photocurrent was significantly enhanced upon W doping. This enhancement is contributed by two important factors: better charge separation efficiency and improved surface charge transfer efficiency. Electrochemical analysis reveals that W doping lowers the surface charge transfer resistance and forms active surface states, facilitating charge transfer. Theoretical analysis shows that W doping activates the V atoms to be reactive sites. Moreover, the adsorption energies and distance between adsorption species (OH_ads, O_ads, and OOH_ads) involved in the water splitting process become more favorable for surface charge transfer. The current study provides an insight into the roles of W doping in BiVO₄, especially during surface catalysis.