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.