WO3 powder can be used to prepare an electrochromic device in form of a tungsten trioxide electrochromic film. The reason why the obtained device has the electrochromic effect is that the tungsten trioxide nano film has the surface effect.
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It is reported that the electrochromic effect was first observed on alkali-halogen crystals. Light absorption was observed when a voltage was applied to the two electrodes fabricated on the alkali halide crystal and heated to about 700°C, which is known as the phenomenon of F color absorption. The electrons injected from the dot-shaped negative electrode are trapped in the anion vacancies (forming the F-center). Depending on the electrical neutrality and current continuity requirements, the anion vacancies near the positive electrode will move toward the cathode. That is, there is a net mass transport of anions to the positive electrode, and a halogen is released at the positive electrode. If the polarity of the external voltage is reversed, the center of the hole is generated accompanying the release of the alkali metal at the negative electrode, and the light absorption disappears.
