Bismuth based ternary oxide such as BiVO₄, Bi₂WO₆ and Bi₂MoO₆ have been reported to oxidise water into oxygen under visible light. These materials have sufficient absorption within the solar spectrum (UV and visible region) and stability against photocorrosion. The hybridized valence band of these ternary oxides made them active towards water oxidation. In this presentation, we investigate the performance of these bismuth based ternary oxides in photoelectrochemical water oxidation. A few aspects will be discussed to highlight the differences when they were employed in photocatalytic water splitting or through photoelectrochemical means. It is generally acknowledged that surface area and crystallinity of photocatalysts are critical factors regulating performances in powder type suspension reactions. When they were made into thin film, quality of the contact between bismuth based ternary oxides and the charge collecting substrate becomes another crucial factor.

BiVO₄, Bi₂WO₆ and Bi₂MoO₆ thin films are synthesised in this work. BiVO₄ with controlled exposed facet is engineered to study the dynamic of charge interactions between their respective facets. It is revealed that a balance of charge transfer and charge trapping are occurring to govern the overall performance of BiVO₄. From that point of view, specific interface is engineered to boost the higher charge transfer efficiency, for example, by using graphene as electron mediator. Bi₂WO₆ and Bi₂MoO₆ thin films are synthesised by a direct conversion of anodised WO₃ and MoO₃ films. The adhesion of the resultant Bi₂WO₆ and Bi₂MoO₆ on the substrate is highly stable. With the control of synthesis parameter, a concentration gradient can be introduced to form the composite of Bi₂WO₆/WO₃ and Bi₂MoO₆/MoO₃ with desired composition. With the favourable band alignment in this composite material, an improved photoelectrochemical performance is observed.