Tungsten oxide electrochromic films are widely used in modern society, and therefore improve the application of tungsten trioxide for widely plays an important role. And to improve the tungsten trioxide electrochromic the key point is to short the ions diffusion and transport time in the material. In addition to using the sol-gel method and magnetron sputtering method, with further research there are many methods for produce tungsten trioxide eletrochromic which has greatly improved. Such as using hot filament chemical vapor deposition method produce electrochromic films. Nano crystalline of tungsten trioxide films annealed at 300 ℃ air, the film primarily monoclinic crystal. Crystalline tungsten trioxide compared with conventional amorphous then performance are more stable in a sulfuric acid solution H + cycle and the usage rate can up to 3000 times. And nano tungsten trioxide films have a greater surface area, so the coloring of it will better than conventional amorphous oxide film. And using hydrothermal synthesis method can produce controlled morphology of tungsten trioxide nano particles, and then based on this using drop-casting method to produce tungsten trioxide films. Tungsten trioxide film in the lithium ion electrolyte compare with sulfuric acid solution the H+ will smaller than Li, higher power density, faster response times and greater coloration efficiency.

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In inorganic electrochromic material there are most of the transition metal oxide and its derivatives. In inorganic electrochromic material which can be divided into different type which is according to the different coloring process such as reduction status coloring staining material, oxidation status staining material and oxidation/reduction status all staining. Tungsten trioxide is reduction status staining material. At present, there are many inorganic electrochromic material, such as tungsten trioxide (WO₃), nickel oxide (NiO_x) and Prussian blue (PB). And WO₃ is the most studied and the most mature one electrochromic material. WO₃ is perovskite structure which is made of WO₆ octahedron. W atoms occupy the cube apex. O atoms occupy the position of each cube. When the center position vacant the valence states of W is +6, then WO₃ films are transparent. When the cation fills the center position, oxidation status of W will reduce to form a mixed valence compound W^V and W^VI, and WO₃ film is blue. Although the mechanism of color changing of film is not clear yet, but double injection model was accepted by most scholars. That mean the color of tungsten trioxide films change is due to hydrogen ions and electrons injected simultaneously to film material. WO₃ electrochromic reaction can be represented by the following chemical equation: WO3 + xe^- + xH ⁺ ← → HxWO₃.

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Tungsten trioxide electrochromic response time is based on the ion/electron diffusion and transport speed on the internal material. Due to the size of the ion is much larger than electrons, thus transportation and diffusion of ions is the slowest part during the whole reaction process. Therefore, to improve the tungsten oxide electrochromic response time is the key to shorten the ion diffusion and transport time in the material. Limit ion injection / withdrawal rate has two main factors: First, the ion diffusion coefficient. Second are the ion diffusion pathways. With further research, at present, to enhance rapid response time of WO3 films, mainly change the microstructure of WO3 film. For example, using sol - gel method to produce WO3 • H2O, because the (WO4) 2- surrounded by water molecules so it will cause reactive ion (H +, Li +) are more likely to spread, thus greatly reducing the reaction time. According to double injection / extraction mode, thereby increasing the surface area of ​​the film can be improved electrochromic properties. And using magnetron sputtering method to produce ZnO thin films which is a base material produce where it is on the ITO conductive glass. And then produce ZnO nano rods. Finally using pulsed laser deposition method let WO3 particles deposited on the surface of the nanorods. Tests show that the stability of tungsten oxide film and the corresponding rate has been greatly improved.

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At the early time, after studied electrochromism of tungsten trioxide researchers found that the films color change due to the hydrogen ions and electrons are simultaneously injected to it.  Besides the chemical reaction process is reversible. However, It also led many scholars believe that tungsten trioxide gasochromic also cause by the hydrogen ions and electrons injected. But after study found that double-injection model of gaschromic is more complicate than electrochromic’s. In the double injection model of gasochromic, the coloring process is by dissociate H2 into H atoms or H ⁺ which is absorbed to catalytic Pt particle surface, H atom transfer from the metal particle surface to the surface of the tungsten trioxide film, and then injected into the tungsten trioxide film. Then make the color of the film change. The bleaching process also adsorbed O₂ which is on the catalyst surface, then transfer to WO₃ film surface, forming a strong chemical activity of O atom or O^2-, so that it can attract out H ⁺ which is exist in film, and with H ⁺ to form H₂O molecules. Therefore H₂O released from the film causing discoloration of the film. From this we can see that fade and coloring is an irreversible chemical reaction process.

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