Photocathodes prepared using p-type semiconductor photocatalyst powders of copper gallium selenides (CGSe) were investigated for visible-light-driven photoelectrochemical water splitting. The CGSe powders were prepared by solid-state reaction of selenide precursors with various Ga/Cu ratios. The CGSe photoelectrodes prepared by the particle transfer method showed cathodic photocurrent in an alkaline electrolyte. Pt modification was conducted for all the photoelectrodes by photoassisted electrodeposition. CGSe particles with a Ga/Cu ratio of 2, consisting of the CuGa3Se5 phase and an intermediate phase between CuGaSe2 and CuGa3Se 5, yielded the largest cathodic photocurrent. By surface modification with a CdS semiconductor layer, the photocurrent density and onset potential clearly increased, indicating enhancement of charge separation caused by the formed p-n junction with appropriate band alignment at solid-liquid interfaces. A multilayer structure on the particles was confirmed to be beneficial for enhancing the photocurrent, as in the case of thin-film photoelectrodes. A Pt/CdS/CGSe electrode (Ga/Cu = 2) was demonstrated to work as a photocathode contributing stoichiometric hydrogen evolution from water for 16 h under visible light irradiation.
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