Electrochemical investigations of electronically conductive polymers: Part VI. Mechanism of the redox reactions for the electronically conductive form of polypyrrol

Abstract

A small amplitude current-step method has been developed to study redox reactions of polypyrrole at high doping levels (equilibrium potentials between 0.1 and 0.6 V vs. SCE). The polymer is an electronic conductor in this potential window. It has been proven rigorously that both the oxidation and reduction processes of polypyrrole films are purely capacitive in this potential region. The effect of external electrolyte concentration on the film resistance and capacitance was studied. The results suggest that the film ionic conductivity is determined by the concentration of excess free electrolyte inside the film. Charge balancing anions do not contribute to the ionic conductivity. It was also found that the morphology of polypyrrole films is uniform throughout the film thickness. Finally, we present here a simple heuristic model for redox reactions of conductive polymers.