Electron and ion transport in polypyrrole/polystyrenesulfonate composite films

Abstract

The impedance response of polypyrrole/polystyrenesulfonate composite films has been studied under three different experimental arrangements: solution ∣ film ∣ solution, metal ∣ film ∣ metal, and metal ∣ film ∣ solution. The impedance data for the composite films have been analyzed on the basis of the diffusion-migration transport of both hole and cation. This treatment explains satisfactorily the observed changes in charge-transfer resistance, film resistance, low-frequency capacitance, and the width of the Warburg region with the oxidation level and thickness of the polymer. The growth of the Warburg region with reduction of the polymer is compatible with the corresponding change in the film’s electronic resistance, while it is opposite to that in the film's ionic resistance. This result suggests that the transference number of holes is much less than that of cations at low oxidation levels although the diffusion coefficient of holes is larger than that of cations. A uniform conductor model gives a good description of the charge-transport behavior of the composite films.