CHARACTERIZATION OF CHARGE-TRANSFER AND CHARGE-TRANSPORT IN POLYPYRROLE FILM ELECTRODES

The a.c. response of polypyrrole film electrodes in 0.2 M KNO3 was investigated at different applied potentials and film thicknesses. The results of impedance analysis on the basis of the Randles equivalent circuit indicated that the electron exchange between a metal and the polymer controlled the rate of charge-transfer process at the film electrode. Accordingly, the oxidation of the polymer proceeds from the back of the film to its surface. The resistance due to electric migration in the film strongly depended on the concentration of the supporting electrolyte; this dependence suggests that the migration is ionic. This effect may be due to a change in the solvent swelling of the polymer. The oxidation of the polymer brought about each decrease in the charge-transfer resistance at a metal-polymer interface and the limiting resistance associated with the diffusion of charge carriers. The low-frequency pseudocapacitance of the polymer increased with increasing oxidation level and film thickness, which was expected from a finite diffusion model.