Abstract: Electrochromic and auto-bleaching processes at the WO₃ anodic film in 0.5 mol/L H₂SO₄ solution were investigated by cyclic voltammetry, a. c. impedance technique and photocurrent spectrometry. The colouration mechanism consists of hydrogen adsorption on the WO₃ surface and the transport of Hatoms in the WO₃ lattice. The bleaching process involves at least two steps: transport of interstitial Hatoms and hydrogen desorption on the Wsurface, resulting in interstitial H⁺ ions; then extration of the H⁺ ions driven by the external electric field. The auto-bleaching arises from the hydroxylation due to both partial interstitial Hatoms and a little of water contained in the film.

Key words: Electrochromism, Tungsten trioxide film, Tungsten electrode, Anodic oxide film