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.