Proton insertion into thin films of amorphous WO3: kinetics study

✍ Scribed by O. Bohnke; B. Vuillemin

• Publisher: Elsevier Science
• Year: 1992
• Tongue: English
• Weight: 318 KB
• Volume: 13
• Category: Article
• ISSN: 0921-5107
• DOI: 10.1016/0921-5107(92)90172-6

✦ Synopsis

Thin films of electrochromic materials may greatly contribute to understanding the mechanism of cation insertion into mixed conductors. In this paper, we present the results of electrochemical and optical in-situ measurements during proton insertion performed on thin films of tungsten trioxide deposited by vacuum evaporation onto conductive substrates. The measurements clearly show that the electrochemical insertion of protons and electrons into the oxide, i.e. the current density, is limited by a resistance and not, as generally believed, by the charge transfer reaction at the electrode-electrolyte interface. The coloration of the oxide is limited by the ionic diffusion of the inserted cation into the host matrix. From these experimental results, we propose a model to explain the electrocoloration of tungsten oxide. This model involves simultaneous diffusion and chemical reaction. A finite difference method has been used to solve the differential equations and to obtain the diffusion coefficient of the species diffusing into the oxide.