Hydrogen incorporation in gasochromic coloration of sol–gel WO3 thin films

In the present work, nanostructured WO3 films were prepared by the sol–gel spin coating method. The as-prepared films were annealed at different temperatures and their structures were characterized by field-emission scanning electron microscopy and X-ray diffraction. A layer of platinum (Pt) was then sputtered onto the surface of WO3 films. The gasochromic properties of the prepared Pt/WO3 thin films were examined by use of optical transmittance under alternate exposures to various H2–N2 gas mixture and air. The results indicated that the sol–gel derived WO3 films with amorphous structure exhibited excellent gasochromic performance with good coloration change and fast response rate under ambient condition. The coloration kinetics was well fitted by exponential equation, indicating the coloration was a surface reaction-controlled process. A new model based on double-injection concept is proposed. According to the model, it is found that the hydrogen insertion coefficient (x) in the gasochromic colored tungsten bronze state (HxWO3) of the studied sol–gel WO3 films is about 0.29, which is similar to the reported gasochromic and electrochromic studies.