Discovery of Overcoating Metal Oxides on Photoelectrode for Water Splitting by Automated Screening.

We applied an automated semiconductor synthesis and screen system to discover overcoating film materials and optimize coating conditions on the BiVO4/WO3 composite photoelectrode to enhance stability and photocurrent. Thirteen metallic elements for overcoating oxides were examined with various coating amounts. The stability of the BiVO4/WO3 photoelectrode in a highly concentrated carbonate electrolyte aqueous solution was significantly improved by overcoating with Ta2O5 film, which was amorphous and porous when calcined at 550 °C. The photocurrent for the water oxidation reaction was only minimally inhibited by the presence of the Ta2O5 film on the BiVO4/WO3 photoelectrode.