Nanostructured polyethylene glycol-titanium oxide composites as solvent-free viscous electrolytes for electrochromic devices

Composites of polyethylene glycol (PEG) and titanium oxide compounds have been prepared by sol-gel method using different molar ratio between PEG and titanium isopropoxide. Transmission electron microscope (TEM) images and UV-vis absorption spectra of these composites indicate that titanium oxide particles or clusters were formed inside the composite materials and their maximum sizes were between 1.8 and 7 nm for PEG:Ti molar ratio changing from 24:1 to 4:1. Fourier Transform Infrared spectroscopy analysis of the same PEG-Ti composites suggests the presence of tetragonal titanium oxide compounds and its association with ether oxygen atoms of PEG molecules. As lithium iodide salt was added into PEG-Ti composites, iodide ions were oxidized into iodine and tri-iodides and, at the same time, titanium oxide compounds should be reduced. Color change speeds of tungsten oxide thin films were significantly improved when PEG-Ti-Lil composites were used as electrolytes compared to salt-in-polymer one (PEG-Lil); the bleaching time of tungsten oxide was reduced from 22 to 2.5 s under +1.0 V polarization, and the coloring time under -1.5 V lowered from 16 to 2.2 s. The transfer of negative charges from smaller iodide ions onto longer or crosslinked PEG-Ti macromolecules could be the origin of faster lithium ion transport/insertion speeds in PEG-Ti composite electrolyte based electrochromic devices. (C) 2011 Elsevier B.V. All rights reserved.