Síntese e degradação eletroquímica de filmes finos de polianilina caracterizados por espectroscopia de impedância eletroquímica e utilização de modelos de circuitos equivalentes

Abstract

After considerable advances in synthesizing polymers with conductive properties, technological advances for this huge application market have been gaining more and more strength as their characterization begins to be represented not only chemically, but with physical models of equivalent circuits that can relate the properties presented in practice, with which it is possible to measure in theory. Cyclic voltammetry is another very useful characterization technique in the development of studies on conductive polymers, revealing the redox transitions of the material, as well as electrochemical impedance spectroscopy that allows us to understand in a frequency range the information related to the transport resistance of charge of these polymeric films. The present work aimed to use the tools mentioned above to obtain a theoretical equivalent circuit model that could represent the electrochemical phenomena characteristic of polyaniline formed as a thin film on the surface of a platinum disc electrode under different deposition conditions (0.1 or 0.5M of H2S04, with or without LED flashlight lighting) and evaluate the impacts caused by the electrochemical degradation of this film. For polymerization and degradation, an electrochemical cell with three electrodes was used, the working electrode being the platinum disk with an area of 0.2cm2 that had a potential of 0.8V applied constantly in the solution containing 0.1M of aniline. and different concentrations of sulfuric acid mentioned above. The characterization and degradation took place in the same electrochemical cell only in the presence of H2S04, initially being performed cyclic voltammetry and then the anodic polarization of 0.75V and cathodic of -0.2V, potential applied for 5 minutes and 15 minutes respectively, this process was repeated 6 times totaling 120 minutes of degradation. The results achieved with the chronocoulometric and chronoamperometric growth showed better resistance to degradation for the films with the highest amount of dopant ions and exposed to lighting at the time of polymerization. By linking the EIE and the equivalent circuits, it was possible to determine that the behavior of the film had better overlap for the R RC RC equivalent circuit, with this circuit and through the Nyquist diagrams it was possible to calculate the load transfer resistances, with emphasis on the greater degradation suffered by the samples that did not have illumination and less degradation for samples that were illuminated. With the peak current data of each sample, it was possible to determine the degradation rate of the films that occurred in Pseudo 1st Order, with the film with the lowest degradation rate being that of sample 3.