ELECTROCHEMICAL CHARACTERISTICS OF POLYTHIOPHENE FILM ELECTRODES IN ACETONITRILE SOLUTION

The effect of electrode potential and film thickness on the kinetic parameters of the oxidation process of polythiophene (PT) was investigated by an a.c. impedance method and conductivity measurements. The conductivity of a PT film increased with its oxidation and reached a limiting value at higher potentials than 0.8 V despite a rise in oxidation state of PT. The oxidation of the PT film lowered the activation energy of electric conduction, which suggested the broadening of a polaron band. An increase in the oxidized form of thiophene unit brings about the decrease in charge transfer resistance at the polymer electrode in the lower potential range than the half-wave potential of PT. Both the redox capacitance of the polymer and d.c. resistance associated with the diffusion of a charge carrier indicated the dependence on the potential and film thickness which was expected from a finite diffusion model. A large capacitance of the order of 1-30 mF cm-2 in the oxidized state is explained in terms of the charge saturation effect due to the finite thickness and porous nature of the polymer film.