Grafting Mechanism of Electrochromic PAA–WO3Composite Film

Abstract A micro-Raman spectroscopic study has been carried out to investigate the electrochromic process in a porous and nanocrystalline tungsten oxide film. The film was prepared by dipping the tin-doped indium oxide glass into an aqueous mixture solution of PAA (polyacrylic acid) and WO 3 –NH 4 OH. After heating at low temperature, around 100°C, the film was treated in 1 N HCl in order to achieve polycondensation, where the ammonium ion was replaced with a proton. In the micro-Raman spectra for the bleached and colored PAA–WO 3 films, it was evident that the coloration accompanies a peak reduction at ∼960 cm −1 and a peak enhancement at ∼810 cm −1 . Based upon the present Raman observation, we can confirm that the electrochromism of the nanocrystalline tungsten oxide is dominated by the grafting process, i.e., the surface modification of –W VI =O bonds into –W V =O (1− δ )+ — M δ + ( M =H, Li) ones.