Preparação e caracterização de filmes finos de NiO e NiO:V2O5 para aplicação eletrocrômica

Abstract

In this dissertation is reported the preparation and characterization of nickel oxide thin films and vanadium doped nickel oxide films, aiming as a possible application as a counter electrode in an electrochromic devices. The addition of vanadium as doping agent aims to improve the electrochemical, structural and morphological performance of the films. The precursor solutions were prepared by the sol-gel process using the nickel acetate salt and the solvent 2-methoxyethanol, for the doped films different percentages (5, 10 and 15 mol%) of vanadium oxytripropoxide were added. Subsequently they were deposited on an ITO-coated glass substrate, by spin-coating technique. In the next step, the films were conducted to a thermal treatment at 300°C, which resulted in the formation of a dense film. A systematic study was carried out to evaluate the number of layers and the concentration of dopant. The results showed that the film with 5 layers had better responses. Thus, films with 5 layers and different percentages of dopant were prepared and characterized by electrochemical technique, such as cyclic voltammetry, chronoamperometry, chronoucoulometry and electrochemical impedance spectroscopy. In order to study structural properties x-ray diffraction and x-ray dispersive were done. The morphology of the films were realized by scanning electron microscopy and atomic force microscopy techniques. The analyzes indicate that the addition of 10% dopant promotes significant improvements in the electrochemical performance of films, increasing the charge density and the kinetics of the intercalation processes. Further improves the cyclic process reversibility and the homogeneity of the films conserving the crystalline structure of the host matrix. Optical characterization shows that films are highly transparent when depolarized and acquire intense brown coloration when polarized, being that the addition of 10% of vanadium promotes greater variation of transmittance between the colored and discolored states. Thus, the results indicate that NiO: 10% V2O5 films can be used as counter electrodes in an electrochromic devices.