Fabrication of bowl-like porous WO3 film by colloidal crystal template-assisted electrodeposition method

Large scale of bowl-like porous WO3 film was successfully fabricated by electrodeposition into two-dimensional (2D) polystyrene (PS) colloidal crystal template. The technological process involved the following steps: colloidal crystal template preparation, potentiostatic electrodeposition of WO3 into the template, and template removal. 1.5 μm PS spheres were used to prepare the 2D colloidal crystal template by means of spinning on indium-tin-oxide (ITO) glass. A two-electrode cell was used for electrodeposition, in which the anode was graphite and the cathode was PS-coated ITO glass. The electrodeposition solution consisted of 25 mM Na2WO4 and 30 % H2O2 acidified at pH 1.2. Via electrodeposition, the interstitial space of the densely packed PS colloidal crystal template was filled with WO3. Bowl-like porous WO3 film was obtained after the removal of the PS colloidal crystal template by a thermal treatment at 475 °C. Scanning electron microscopic, X-ray diffraction spectra and transmission electron microscopy were performed to analyze and compare bowl-like porous WO3 film with dense WO3 film. The homogeneous area of the obtained film was 25 × 15 mm2. The template-assisted electrodeposition method was simple and low-cost that can be completed within 30 min.