The Electrochromic Process at WO 3 Electrodes Prepared by Vacuum Evaporation and Anodic Oxidation of W

Abstract

The kinetics of the electrochromic process and the stability with different electrodes (evaporated film, electrodes obtained by anodic oxidation of W, polycrystalline, and single crystal) were studied. Cyclic voltammetry and chronoamperometry, together with optical absorption measurements in the electrochromic region were carried out. Impedance measurements at different frequencies of the (aq) interface were also made to compare the evaporated film and anodic oxide electrodes. These measurements showed that the electrochromic reaction at the anodic film was much faster than that at the evaporated film electrode (by about two to three orders of magnitude). This difference in the reaction rates reflects the difference in the rate of diffusion of H+ in the films. Infrared spectroscopic measurements of the films were carried out to obtain information about the water content of the films. The differences in the kinetic behavior of the electrochromic process at the two electrodes were attributed to differences in porosity and water content of these two films. The stability of the film toward dissolution in aqueous solution was also shown to depend on the quantity of water in the film. In addition electrochemical behavior in the electrochromic region was studied in several other systems, including systems which contain as the electrolyte but with nonaqueous solvents and systems which contain Li+, replacing H+, in nonaqueous solvents. The solvent and the cation both affect the kinetics of the electrochromic process and the stability of the amorphous films. The electrochromic process at single crystal and polycrystalline was also studied and compared to the behavior of the amorphous film electrodes.