Solar‐Water‐Splitting BiVO 4 Thin‐Film Photoanodes Prepared By Using a Sol–Gel Dip‐Coating Technique

A facile and low cost method to construct a bismuth vanadate thin film photoanode was implemented with the aim of integrating it in a tandem dual water splitting photoelectrochemical cell. Multilayer semi‐transparent thin films of BiVO 4 were fabricated by a sol–gel process and deposited by dip‐coating onto transparent conducting oxide substrates with intermediate annealing treatment between layers and final calcination at a low temperature of 450 °C in air. The effect of the intermediate annealing temperature has a great impact on the porosity, and therefore density, of thin layers of BiVO 4 when fabricated by sol–gel dip‐coating methods; thus, for optimal activity, the annealing temperature should be kept at 400 °C for thinner layers and 450 °C for thicker layers. The annealing temperature has a direct effect on the size of the crystallites which determines the microstructural density and porosity. In contrast, the final calcination temperature must be 450 °C in order to achieve good electrochemical performances. Optimized BiVO 4 photoanodes exhibit a photocurrent of up to 2.1 mA cm −2 with an average Faradic efficiency of 85 % for oxygen evolution in neutral pH potassium phosphate buffer at 1.23 V vs. RHE under 350 mW cm −2 light irradiation.