Fabrication of a Core–Shell-Type Photocatalyst via Photodeposition of Group IV and V Transition Metal Oxyhydroxides: An Effective Surface Modification Method for Overall Water Splitting

Abstract

The design of optimal surface structures for photocatalysts is a key to efficient overall water splitting into H₂ and O₂. A unique surface modification method was devised for a photocatalyst to effectively promote overall water splitting. Photodeposition of amorphous oxyhydroxides of group IV and V transition metals (Ti, Nb, Ta) over a semiconductor photocatalyst from corresponding water-soluble metal peroxide complexes was examined. In this method, amorphous oxyhydroxide covered the whole surface of the photocatalyst particles, creating a core–shell structure. The water splitting behavior of the novel core–shell-type photocatalyst in relation to the permeation behavior of the coating layer was investigated in detail. Overall water splitting proceeded successfully after the photodeposition, owing to the prevention of the reverse reaction. The photodeposited oxyhydroxide layers were found to function as molecular sieves, selectively filtering reactant and product molecules. By exploiting the selective permeability of the coating layer, redox reactions on the photocatalyst surface could be suitably controlled, which resulted in successful overall water splitting.