Photoelectrochemical properties of Fe2O3-Nb2O5 films prepared by sol-gel method.

Fe2O3-Nb2O5 coating films of various Nb/(Fe + Nb) mole ratios were prepared on nesa silica glass substrates from Fe(NO3)3.9H2O - NbCl5 - CH3(CH2)2CH2OH - CH3COOH solutions by the sol-gel method. The photoanodic properties were studied in a three-electrode cell with an aqueous buffer solution of pH = 7 as the supporting electrolyte. The crystalline phases identified were alpha-Fe2O3 (Nb/(Fe + Nb) = 0), alpha-Fe2O3 + FeNbO4 (Nb/(Fe + Nb) = 0.25), FeNbO4 (Nb/(Fe + Nb) = 0.5), FeNbO4 + Nb2O5 (Nb/(Fe + Nb) = 0.75), and Nb2O5 (Nb/(Fe + Nb) = 1). When the Nb/(Fe + Nb) mole ratio increased from 0 to 0.25, the crystalline phases changed from alpha-Fe2O3 to alpha-Fe2O3 + FeNbO4, the photoanodic current under white light illumination increased, and the photoanodic current under monochromatized light illumination increased in both visible and ultraviolet regions. When the Nb/(Fe + Nb) ratio increased over 0.25, the crystalline phases changed to FeNbO4, FeNbO4 + Nb2O5, or Nb2O5, and the photoanodic current decreased. The sample consisting of alpha-Fe2O3 and FeNbO4 (Nb/(Fe + Nb) = 0.25) exhibited photoresponse extending to 600 nm and an IPCE of 18% at a wavelength of 325 nm.