Mixed Ionic-Electronic Conduction of a Conducting Polymer Film. ac Impedance Study of Polypyrrole.

Polypyrrole (PPy) films were studied by ac impedance spectroscopy both in a free-standing membrane and in a modified electrode arrangement. The experimental results were analyzed by comparison with previously derived kinetic models, allowing to obtain, through a non-linear least-squares fitting procedure, both transport (diffusion coefficients and concentration of ion-and electron-exchanging sites) and interfacial parameters (charge transfer resistances and double layer capacitances). PPy film thickness, nature and concentration of the electrolytes and duration of the immersion were varied in a systematic way. The transport properties were found to depend on both anions and cations contained in the electrolyte and to be independent of polymer film thickness.