Grafting mechanism of electrochromic PAA-WO3 composite 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 micro-Raman spectra for the bleached and colored PAA-WO3 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, the authors can confirm that the electrochromism of the nanocrystalline tungsten oxide is dominated by the grafting process, i.e., the surface modification of single bondWVI double-bond O bonds into single bondWV double-bond O(1-δ)+emdash Mδ+ (M = H, Li) ones