Water splitting property of Gd 1-x Bi x VO 4 powder photocatalysts and their thin film photoelectrodes

Abstract

New water splitting solid solution photocatalysts with the composition of Gd 1-x Bi x VO 4 (x = 0, 0.3, 0.5, 0.7, 0.8, 0.9, 0.95, 1.0) were synthesized by a solid-state reaction. Gd 0.3 Bi 0.7 VO 4 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 3 OH under near visible-light irradiation (λ > 380nm). The obtained solid solutions such as GdVO 4 , Gd 0.7 Bi 0.3 VO 4 , Gd 0.5 Bi 0.5 VO 4 , and Gd 0.3 Bi 0.7 VO 4 crystallized in zircon-tetragonal crystal structures, while Gd 0.05 Bi 0.95 VO 4 and BiVO 4 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 0.7 Bi 0.3 VO 4 and BiVO 4 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 0.3 Bi 0.7 VO 4 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.