Investigation of the electronic properties and morphology of conducting polymer electrodes for engineering applications

Abstract

DISCLAIMERT h i s report was prepared as an account of work sponsored by an agency of the United States Government Neither the United States Government nor any agency thereof, nor any of their employees, make any warranty, express or implied, or assumes any legal liability or responn'bility for the accuracy, completeness, or usefulness of any information, appa- AbstractIn this project experiments were conducted to evaluate the performance of the conducting polymer polyaniline (PAni) and poly-3-(4-fluorophenyI)-thiophene (PFPT) as the active material in electrochemical capacitors. Using scanning electron microscopy and cyclic voltammetry, the morphology and charge/discharge characteristics of the as-grown polymers were studied under different electrochemical conditions. When electropolymerized at high current densities in aqueous acid solution, PAni exhibits a morphology consisting of a network of interwoven fibrils. It was shown that layers of this P h i network can be electropolymerized onto a thin-planar metal substrate resulting in a decrease in cathodic and anodic peak separations, improving charge/discharge reversibility. A continuous P h i network will make possible a decreases in the total weight of the electrodes with respect to those electrodes grown onto a fibrous carbon substrate of high surface area and high porosity. The effect of different growth electrolytes on the charge/discharge process was also characterized. Hydrochloric acid electrolyte provided an optimum polymer deposition, with respect to morphology and capacitive performance.PFPT films were grown from a solution in a non-aqueous solution. High growth current densities affected the performance of PFPT polymer films in a positive manner. A growth rate of 20 mA/cm2 not only provided an increase in charge storage, but in the amount of polymer deposited when compared to equivalent amounts deposited at 1 mA/cm2. The morphology of the deposited conducting polymer is shown to be one of the most important characteristics in the attempt to achieve an ideal electrochemical capacitor electrode. The polymer morphology directly affects the charge/discharge process because of the strong interaction between ionic conductivity in the electrolyte and the electronic conductivity of the polymer.Cyclic-dependent degradation of the PFPT films was observed. Further research is required to define the controlling mechanism@) of electrolyte/electrode degradation.