Surface Reduction in Monoclinic BiVO4 for Photocatalytic Applications

Bismuth vanadate (BiVO4, short BVO) is a promising photoelectrochemically active candidate for water splitting used for hydrogen generation. Compared to TiO2, i.e. the most widely used and investigated photocatalyst, BVO uses visible instead of ultraviolet light for its photoelectrochmical activity. Amongst the three polymorphs of BVO, the monoclinic clinobisvanite BVO (m-BVO) phase exhibits the highest photocatalytical activity. This is due to both, the favorable band gap energy of ~2.4 eV and the valence band position, which is suitable for driving water oxidation under irradiation. Despite the fact that the conduction band is reported to be too low relative to the proton reduction potential for hydrogen evolution [1], the water splitting reaction can be promoted by simultaneously using a hydrogen evolution catalyst, such as a nobleor transition-metal catalyst [2]. Apart from the low charge carrier mobility of m-BVO [3], which can be improved by using various dopants [2,4], another crucial point, which affects m-BVO’s photocatalytic activity, concerns oxygen vacancies. These vacancies, which have been recognized to play a key role in the photocatalytic performance of m-BVO, are the dominant intrinsic defects in m-BFO [5] and might act as harmful photogenerated carrier traps [6]. However, little is known about the concentration and the distribution of oxygen vacancies in m-BVO.