Grafting Mechanism of Electrochromic PAA–WO3Composite Film

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 WO3–NH4OH. 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 microRaman spectra for the bleached and colored PAA–WO3films, it was evident that the coloration accompanies a peak reduction at ~960 cm-1and 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 –WVI=O bonds into –WV=O(1-)+––M+(M=H, Li) ones.