An effect of Ag(i)-substitution at Cu sites in CuGaS2 on photocatalytic and photoelectrochemical properties for solar hydrogen evolution

Abstract

We investigated an effect of Ag(I)-substitution at the Cu sites in CuGaS₂ with a chalcopyrite structure on physicochemical, photocatalytic and photoelectrochemical properties. Cu_1−xAg_xGaS₂ (x = 0–0.8) solid solutions possessed 2.34–2.35 eV of band gaps. Ru-loaded Cu_1−xAg_xGaS₂ (x = 0–1.0) powders showed photocatalytic activity for hydrogen evolution from an aqueous solution containing SO₃²⁻ and S²⁻ as electron donors under simulated sunlight irradiation. The photocatalytic activity of CuGaS₂ (x = 0) was improved, when excess Ga₂S₃ was added in a starting material for the preparation to give a single phase of a chalcopyrite structure. Cu_1−xAg_xGaS₂ (x = 0.1–1.0) showed higher activity than the CuGaS₂ (x = 0), when prepared with the optimum excess Ga₂S₃. Cu_1−xAg_xGaS₂ (x = 0–0.8) electrodes gave cathodic photocurrents under visible light irradiation, indicating that they possessed p-type characters. Cu_0.8Ag_0.2GaS₂ gave the largest cathodic photocurrent and possessed the most positive onset potential of the cathodic photocurrent among the Cu_1−xAg_xGaS₂ (x = 0–0.8) electrodes. Loading a Ru cocatalyst increased the cathodic photocurrent. Solar water splitting proceeded without an external bias using a photoelectrochemical cell consisting of the Ru-loaded Cu_0.8Ag_0.2GaS₂ photocathode and a CoO-loaded BiVO₄ photoanode. Thus, the photocatalytic and photoelectrochemical performances of CuGaS₂ were improved by Ag(I)-substitution at the Cu sites.