Preparation and characterization of nanocrystalline porous TiO 2/WO3 composite thin films

TiO2 materials possessing not only photocatalytic but also electrochromic properties have attracted many research and development interests. Though WO3 exhibits excellent electrochromic properties, the much higher cost and water-sensitivity of WO3 as compared with the TiO2 may restrict the practical application of WO3 materials. In the present study, the feasibility of preparing nanocrystalline porous TiO2/WO3 composite thin films was investigated. Precursors of sols TiO2 and/or WO3 and polystyrene microspheres were used to prepare nanocrystalline pure TiO2, WO 3, and composite TiO2/WO3 thin films by spin coating. The spin-coated thin films were amorphous and, after heat treating at a temperature of 500°C, nanocrystalline TiO2, TiO 2/WO3, and WO3 thin films with or without pores were prepared successfully. The heat-treated thin films were colorless and coloration-bleaching phenomena can be observed during cyclic voltammetry tests. The heat-treated thin films exhibited good reversible electrochromic behavior while the porous TiO2/WO3 composite film exhibited improved electrochromic properties.