Water splitting property of Gd_1-xBi_xVO₄ powder photocatalysts and their thin film photoelectrodes

New water splitting solid solution photocatalysts with the composition of Gd_1-xBi_xVO₄ (x = 0, 0.3, 0.5, 0.7, 0.8, 0.9, 0.95, 1.0) were synthesized by a solid-state reaction. Gd_0.3Bi _0.7VO₄ was found as novel photocatalyst with both O ₂ evolution from aqueous solution of sacrificial reagent AgNO ₃ under visible-light irradiation (λ > 420nm) and H ₂ evolution from aqueous solution of sacrificial reagent CH ₃OH under near visible-light irradiation (λ > 380nm). The obtained solid solutions such as GdVO₄, Gd_0.7Bi _0.3VO₄, Gd_0.5Bi_0.5VO₄, and Gd_0.3Bi_0.7VO₄ crystallized in zircon-tetragonal crystal structures, while Gd_0.05Bi _0.95VO₄ and BiVO₄ crystallized in scheelite-monoclinic structures. The diffuse reflectance spectra of the solid solutions shift monotonically to a long wavelength as the ratio of Bi ions to Gd ions increases in the solid solution. The structure and water splitting activity were discussed in relation to the solid solution compositions and photophysical properties. Furthermore, new thin film photoelectrodes of Gd _0.7Bi_0.3VO₄ and BiVO₄ for solar hydrogen production were prepared by metal organic decomposition (MOD) method and polymerized complex (PC) method. The photoelectrodes were characterized by using Grazing Incidence X-ray Analysis (GIXA), SEM, cyclic voltammetry (CV) and IPCE measurement. Finally, solar energy conversion efficiency for water splitting (STH efficiency) was measured. Best STH efficiencies of BiVO ₄ and Gd_0.3Bi_0.7VO₄ thin film photoelectrodes were 0.05% at the applied potential of 0.9 V and 0.025% at the applied potential of 0.5 V vs NHE, respectively.