Cu₃MS₄ (M=V, Nb, Ta) and its Solid Solutions with Sulvanite Structure for Photocatalytic and Photoelectrochemical H₂ Evolution under Visible-Light Irradiation

Solid solutions with of Cu₃VS₄ with either Cu₃NbS₄ or Cu₃TaS₄ (Cu₃Nb_1−xV_xS₄ or Cu₃Ta_1−xV_xS₄) were prepared by a solid-state reaction and adopted a sulvanite structure. Their band gaps were 1.6–1.7 eV corresponding to the absorption of a wide range of visible light. Ru cocatalyst-loaded Cu₃MS₄ (M=V, Nb, Ta), Cu₃Nb_1−xV_xS₄, and Cu₃Ta_1−xV_xS₄ showed photocatalytic activities for sacrificial H₂ evolution under visible-light irradiation. Most solid solutions showed better activities than the single-component Cu₃MS₄ (M=V, Nb, Ta). Cu₃MS₄ (M=V, Nb), Cu₃Nb_1−xV_xS₄, and Cu₃Ta_1−xV_xS₄ also functioned as photoelectrodes and gave cathodic photocurrents under visible-light irradiation, indicating a p-type semiconductor character. Cu₃Nb_0.9V_0.1S₄ showed the best photocatalytic and photoelectrochemical performances. When Ru-loaded Cu₃Nb_0.9V_0.1S₄ was used as a photocathode with a CoO_x-loaded BiVO₄ photoanode, photoelectrochemical water splitting proceeded under simulated sunlight irradiation without an external bias.