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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 O2 evolution
from aqueous solution of sacrificial reagent AgNO3 under visible-light irradiation (λ > 420nm) and H2 evolution from
aqueous solution of sacrificial reagent CH3OH under near visible-light irradiation (λ > 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.
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