The influence of porosity and the nature of the charge storage capacitance on the impedance behaviour of electropolymerized polyaniline films

Impedance spectra of electropolymerized polyaniline films were analysed by the theory of the impedance of macrohomogeneous porous electrodes. Specific ohmic and charge transfer resistivities were calculated, and their potential and pH dependence is discussed in terms of structural changes of the polymer during redox and protonation processes. Furthermore it is shown that a correct understanding of the high frequency limit of the impedance is achieved only if the porosity is implemented and thus the discrepancies inherent in the inappropriate assumption of a compact polymer film are avoided. Another not well understood electrochemical phenomenon of conducting polymers is the apparently capacitive current plateau in the cyclic voltammogram and the large series ac capacitance. It will be demonstrated that this supposed 'capacitive' behaviour is related to continuous faradaic charge transfer at potentials beyond the first oxidation wave in the cyclic voltammogram. (C) 1998 Elsevier Science S.A.