Ionic transport in polyaniline film electrodes: an impedance study

Thin polyaniline films on platinum were studied in aqueous acid solutions (HCl, HF, HBF4) at potentials corresponding to the first redox process and the conducting reversibly oxidized polymer state. Diffusional processes observed in impedance spectra were examined for electrolyte solutions characterized by different conductivities and doping anions, and for different thicknesses of the polymer film. Ionic migration and diffusion in the thin film polyaniline electrode were seen for the oxidized and reduced polyaniline respectively. Estimated values of diffusion coefficients are of the order of 10−9 cm2 s−1. A mechanistic—kinetic scheme for the ionic ejection/injection accompanying the redox process is discussed. A preferred route for the reduction process in hydrofluoric acid is postulated. Differences in solvation, basicity and steric properties are invoked to explain differences among the systems studied.