MODELING THE IMPEDANCE PROPERTIES OF ELECTRODES COATED WITH ELECTROACTIVE POLYMER-FILMS

The response of a metal/electroactive polymer film/solution system to a low-amplitude variation of electrode polarization is analysed, takin g account of both the electrodiffusion transport of electronic and ion ic species in the bulk film and non-equilibrium heterogeneous charge t ransfer, namely electrons at the metal-film boundary and ions at the f ilm-solution boundary. Exact analytical solutions are obtained for con centration and electric field profiles inside the film, interfacial po tential drops, and complex impedance. Their dependence on frequency an d the ratio of diffusion coefficients, D(e) and D(i), are analysed. Fo r unequal values, D(e) not-equal D(i), the electric field inside the f ilm is shown to be nonuniform and the instantaneous concentration prof ile is non-symmetrical with respect to the middle-plane of the film. T he impedance of the system contains (in addition to the interfacial ch arging and solution contributions) a frequency-independent resistivity due to ohmic potential drops in the bulk film and at both interfaces as well as distributed capacitive and resistive elements.