Abstract

Electrochromic tungsten oxide nanostructures were prepared from tungsten oxide nanoparticles for the first time by the filtration and transfer technique. This novel and facile method for film preparation presents many advantages that include the possibility to obtain nanoparticle films with various porosities and compositions. The films obtained in the present work exhibited indeed porous structures and were generally composed of a mixture of nanoparticles. When the amount of the nanoparticles in the suspensions increased, we observed thicker films with higher coverage densities. Films prepared at room temperature exhibited very good electrochromic properties. It was found that annealing at 500oC increases the film stability and life time. Using cyclic voltammetry, fast diffusion behaviour (D of the order of 10-6 cm2s-1) for proton insertion/extraction has been observed. Moreover, fast switching response time (less than a second) during the bleaching process due to the rapid decay of the anodic current during chronoamperometry was also noted. The coloration efficiency for such devices was about 20 cm2C-1. The coloration of the films is associated with the number of color centers and depends on the number of inserted charges. However, we have shown that good optical reversibility does not necessarily need fast electrochemical kinetics. Finally, the effect of high applied potentials on the films was investigated, followed by an analysis of the electronic properties of the films.