Preparação e caracterização eletroquímica de filmes finos de WO3 em substrato flexível.

Abstract

The present work consists in the study of thin films of tungsten oxide (WO3) on flexible substrate for application as working electrode in a flexible electrochromic devices. The oxide was prepared by the sol-gel process, where the sol was obtained from the reaction between metallic tungsten, hydrogen peroxide, acetic acid and finally dissolved in ethanol. The films were prepared by the dip-coating technique on a flexible substrate of polyethylene terephthalate (PET) coated with an electronic conductor formed by indium trioxide with gold and silver (In2O3:Au:Ag, resistance ≤ 10Ω). A systematic study was carried out to obtain films with homogeneity and desired electrochemical properties. The deposited films, after ten minutes of hydrolysis in air with controlled humidity (max. 40%), were submitted to the heat treatment of 100°C for one hour. A systematic study was carried out to evaluate the influence of the deposition velocity on the electrochemical characteristics of the films using the techniques of Cyclic Voltammetry (VC), Chronoamperometry (CA) and Chronocoulometry (CC). The results obtained allowed to select the deposited film at 60mm.min-1 as the best due to its high storage capacity in the ion insertion processes, reaching -32.86mC.cm-2 with a total time of 60s of application of the potentials, in addition to excellent kinetic response requiring only 22s to color and 7s to discolor. Comparison of charge densities after 2,100 and 200 charge/discharge cycles indicate good film stability. The optical characterization (UV-vis) shows that the films when polarized acquire intense blue coloration and return to the initial state when depolarized, with a variation of 32% transmittance. In order to study the structural properties, X-Ray Diffraction (XRD) techniques, X-ray Dispersive Energy Spectroscopy (EDS), Scanning Electron Microscopy (SEM) and Infrared Spectroscopy with Fourier (FTIR). To study the morphology of the films were made measurements of scanning electron microscopy (SEM) and atomic force microscopy (AFM). Thermal characterization was also performed through Thermogravimetric Analysis (TG) and Differential Scanning Calorimetry and DSC. Thus, the results indicate that WO3 films can be applied as a working electrode in flexible electrochromic devices.