| Hydrogen energy has attracted widespread attention for the advantages of efficient, clean; environmental protection and renewable etc. However, it also has the characteristics of inflammable and explosive. In order to utilize the hydrogen energy safely, it is necessary to develop and use hydrogen sensors which have steady performance and high sensitivity. Besides, preparing the hydrogen sensitive material with outstanding performance is the key to develop hydrogen sensors.Tungsten trioxide (WO3) is an important gas sensing material, it is sensitive to hydrogen when doped with the noble metal Pd or Pt, and presently, the research of WO3 is very popular. In this article, different types of WO3-based hydrogen sensitive materials were prepared with several methods, then the structure and morphology of these materials were investigated, and the hydrogen sensing properties of the samples were in-situ analyzed by UV-Vis spectrophotometer. The results were compared, and the hydrogen sensitive mechanism of WO3 thin film was discussed. The main content and research results in this thesis can be summarized as follows:(1)WO3-based hydrogen sensitive films were prepared with magnetron sputtering and sol-gel methods, and then the samples were characterized by XRD and SEM, the results showed that the WO3 and Pd/WO3 films prepared with magnetron sputtering method were amorphous before heat treatment. And after heat treatment at 400℃, the films transformed into crystalline structure. Additionally, the surface of the sputtered films was smooth, flat and compact. The WO3 and Pt/WO3 films prepared with sol-gel method were crystalline after heat treatment, their surface roughness was a little large, and both of them had loose and porous structure.(2) Part of the WO3 and Pd/WO3 films were transformed into crystalline by heat treatment, then the hydrogen sensing properties of the WO3 and Pd/WO3 films were in-situ analyzed by UV-Vis spectrophotometer. It was found that, the pure WO3 films almost didn't respond to H2 at room temperature, while the Pd/WO3 double-layer thin films all showed good sensitivity to H2, and the gas sensing properties of the double-layer thin films in amorphous were better than the films in crystalline. Furthermore, the thickness of the film had an effect on the gas sensing properties, and the amorphous Pd(30 nm)/WO3(110 nm) film showed the best hydrogen sensing properties in all sputted films, the change in it's relative transmittance was about 52.4% at the wavelength of 500 nm after the hydrogen was injected.(3) The hydrogen sensing properties of the WO3 and Pt/WO3 films prepared with sol-gel method were in-situ analyzed by UV-Vis spectrophotometer. It was found that, the films prepared with sol-gel method were both sensitive to H2 at room temperature, and after 4% hydrogen was injected, the change in the relative transmittance of the Pt/WO3 film was about 36.6% at the wavelength of 500 nm and about 57.1% at the wavelength-of 750 nm. Besides, when the hydrogen concentration is in the range of 1%～4%, the response to hydrogen of the Pt/WO3 film was linear with the hydrogen concentration.(4) The hydrogen sensitive mechanism of WO3 thin film is discussed. The gasochromic phenomenon of WO3 film should be related to the electrons hopping between W6+ and W5+. The significance of doping in WO3 thin films was illustrated and the theoretical optimum dopant content in WO3 thin films prepared with different methods was given. |
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