A Water‐Splitting System with a Cobalt (II,III) Oxide Co‐Catalyst‐Loaded Bismuth Vanadate Photoanode Along with an Organo‐Photocathode

In the water‐splitting reaction, the oxidation of water to O 2 is considered to be a kinetically demanding process, so that a co‐catalyst has been usually applied to promote water oxidation. This work demonstrates that, when loading mixed‐valence cobalt (II,III) oxide (Co 3 O 4 ) dispersed in a Nafion membrane (Nf) on a nanoporous bismuth vanadate (BiVO 4 ) photoanode (i. e., BiVO 4 /Nf[Co 3 O 4 ]), stable and efficient water oxidation occurred. In particular, it is noteworthy that the BiVO 4 /Nf[Co 3 O 4 ] photoanode exhibited stable performance even in an acidic medium (pH=2). In the present system consisting of a BiVO 4 /Nf[Co 3 O 4 ] photoanode along with an organo‐photocathode, the stoichiometric formation of O 2 and H 2 successfully occurred by applying just 0.1 V between the photoelectrodes (cf. maximum efficiency, ca. 0.2 %), which was superior to the prototype comprising BiVO 4 and Pt counter electrode. The Co 3 O 4 loading can effectively suppress the collapse of the nanostructured BiVO 4 upon photocorrosion, resulting in the stable and kinetically efficient consumption of holes in BiVO 4 .