Optical, electrochemical and structural properties of long-term cycled tungsten oxide films prepared by sol-gel

A peroxopolytungstic acid sol has been employed for preparing tungsten oxide (WO3) films by sol-gel dip-coating technique. Three-electrode cells with 0.5 mol/L H2SO4 electrolyte were fabricated using the prepared WO3 films as active working electrode. Optical, electrochemical and structural properties of the films as a function of coloration-bleaching cycle were characterized by ultraviolet-visible spectrophotometer, cyclic voltammetry (CV), X-ray diffraction (XRD), scanning electron microscopy (SEM). The films showed a stable behavior of reversible and reproducible electrochemical switching up to 1000 coloration-bleaching cycles. XRD peaks were found for the films being cycled more than 2000, and the irregular cracks, uniform nano-particles and novel nano-blades were observed on the long-term cycled film surface by SEM. The degradation of the electrochromic behavior is due to the film change to loose and crystallization after the long-term cycling. (c) 2007 Elsevier B.V. All rights reserved.