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 O₂ 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 (Co₃O₄) dispersed in a Nafion membrane (Nf) on a nanoporous bismuth vanadate (BiVO₄) photoanode (i. e., BiVO₄/Nf[Co₃O₄]), stable and efficient water oxidation occurred. In particular, it is noteworthy that the BiVO₄/Nf[Co₃O₄] photoanode exhibited stable performance even in an acidic medium (pH=2). In the present system consisting of a BiVO₄/Nf[Co₃O₄] photoanode along with an organo-photocathode, the stoichiometric formation of O₂ and H₂ successfully occurred by applying just 0.1 V between the photoelectrodes (cf. maximum efficiency, ca. 0.2 %), which was superior to the prototype comprising BiVO₄ and Pt counter electrode. The Co₃O₄ loading can effectively suppress the collapse of the nanostructured BiVO₄ upon photocorrosion, resulting in the stable and kinetically efficient consumption of holes in BiVO₄.