Abstract: The electrochromic and auto-bleatching processes at the WO₃anodic oxide film in 0. 5 mol/L H₂SO₄solution were studied by cyclic voltammetry, A. C. impedance technique and photocur-rent spectrbscopy. The coloration mechanism consists of hydrogen adsorption on the WO₃film surface and the transport of Hatoms in the WO₃lattice. The bleatching process involves at least. transport of interstitial Hatoms and hydrogen desdrption at the WOS film surface, resulting in interstitial H⁺ions; then extration of H⁺droven by the external electric field. The auto-bleatching is arised from hydroxy-lation due to both partial interstitial Hatoms and the trace amount of water contained in the film.

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