Gasochromic refers to the material after exposing to certain gases, the reversible chemical reaction will make the material produce a color effect on the absorption of a specific wavelength of light. Research on gasochromism is relatively less than electrochromism. Gasochromic device has simple structure, less influential factors, are all solid material, a wider range of optical adjustment, easy-to-large-scale production, no external voltage, can run without energy consumption which make the WO3 gasochromic film, especially Research associated with complex WO3 films will gradually become the focus of our attention.
Gasochromism of pure WO3 thin film is not ideal, usually there should be a noble metal film layer deposited on the surface of thin film to improve its gasochromic property. Au-doped thin film has fine gas sensitivity for H2S, Ag-doped WO3 thin film can improve gas sensitivity for SO2, Au-doped thin film can improve gas sensitivity for NH3.
In the study of WO3 electrochromic thin film of hydrogen performance, usually deposit a Pd or Pt layer on surface of the film of WO3 thin film to improve the sensitivity and selectivity toward H2. Add catalyst or other metal oxides to WO3 thin film material can control the grain size of thin film crystalline, provide gas-sensitive reaction centers, but the film gas sensing response mechanism is very complex, understanding for this mechanism is not mature, the existing theories are mainly followed the electrochromic mechanism.
Currently, report of using gasochromic effects of WO3 films to prepare related devices is unusual, using a variety of deposition methods on a glass substrate covered with a layer of amorphous WO3 particles, and made with gas electrochromic window, its structure is shown as below. Results of the tests show that electrochromic window coloring and fading fastly, and after repeating several times of gas sensing test, discoloration performance of the device remains stable. Finally in 2004 successfully developed a standard commercial WO3 gas electrochromic window.
In addition to being used in smart window, WO3 film is also applied as hydrogen gas sensors. In recent years, the development of optical fiber sensors based on WO3 gasochromic effect has made some progress, such sensors belong to the optical sensor, with more excellent performance, great research value, but it’s difficult to achieve mass production, the package sensing system requires the use of expensive optical devices, the cost is relatively high, and therefore it is not widely used.