Fabrication of a porous ZnRh₂O₄ photocathode for photoelectrochemical water splitting under visible light irradiation and a significant effect of surface modification by ZnO necking treatment

A porous ZnRh₂O₄ electrode was fabricated by an electrophoretic deposition method on a fluorine-doped tin oxide substrate, and photoelectrochemical water splitting under visible light irradiation (λ > 420 nm) was performed. The porous ZnRh₂O₄ electrode exhibited a cathodic photocurrent under visible light irradiation and an extremely positive onset potential at +1.2 V vs. reversible hydrogen electrode (RHE) in aqueous Na₂SO₄ solution. ZnO necking treatment, by which effective contact between ZnRh₂O₄ particles is formed, afforded a significant increase in the photocurrent. The incident photon to current efficiencies (IPCEs) of the ZnRh₂O₄ and ZnO/ZnRh₂O₄ photocathodes were calculated to be ca. 8% and ca. 13% at 400 nm, respectively, at 0 V vs. RHE in aqueous Na₂SO₄ solution. H₂ evolution under visible light (λ > 420 nm) was demonstrated using the ZnRh₂O₄ and ZnO/ZnRh₂O₄ photocathodes combined with a Pt electrode under an applied bias (0 V vs. RHE).