Water splitting property of Gd1-xBixVO4 powder photocatalysts and their thin film photoelectrodes

New water splitting solid solution photocatalysts with the composition of Gd1-xBixVO4 (x = 0, 0.3, 0.5, 0.7, 0.8, 0.9, 0.95, 1.0) were synthesized by a solid-state reaction. Gd0.3Bi0.7VO4 was found as novel photocatalyst with both O-2 evolution from aqueous solution of sacrificial reagent AgNO3 under visible-light irradiation (lambda > 420nm) and H-2 evolution from aqueous solution of sacrificial reagent CH3OH under near visible-light irradiation (lambda > 380nm). The obtained solid solutions such as GdVO4, Gd0.7Bi0.3VO4, Gd0.5Bi0.5VO4, and Gd0.3Bi0.7VO4 crystallized in zircon-tetragonal crystal structures, while Gd0.05Bi0.95VO4 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 Gd0.7Bi0.3VO4 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 BiVO4 and Gd0.3Bi0.7VO4 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.