Morphology control of one-dimensional heterojunctions for highly efficient photoanodes used for solar water splitting

In a dual bandgap system such as WO3/BiVO4, the morphology of each component should be controlled by understanding its properties, in particular with respect to the charge flow in the system. For WO3/BiVO4 photoanodes, a porous BiVO4 film allows contact of an electrolyte to the bottom layer with enhanced surface area, thereby promoting the oxidation reaction, while one-dimensional (1-D) WO3 nanorods, directly grown on F-doped tin oxide, are advantageous for transporting electrons to the back contact. The morphology of the BiVO4 film covered by 1-D WO3 nanorods varies with the addition of organic additives such as ethylcellulose in the metal precursor solution. The cross-sectional images from scanning electron microscopy show that 1-D WO3 nanorods is coated with the BiVO4 layer, which forms a porous top layer that can effectively absorb visible light and enhance charge transfer resulting in enhanced photocurrents. We report on the highest photocurrent at a potential of 1.23 V versus a reversible hydrogen electrode (RHE) by means of a 1-D WO3/BiVO4/Co-Pi photoanode. The strategies for constructing such kind of heterojunctions are well applicable to other dual bandgap photoanodes.