THE INFLUENCE OF POROSITY AND THE NATURE OF THE CHARGE STORAGE CAPACITANCE ON THE IMPEDANCE BEHAVIOR OF ELECTROPOLYMERIZED POLYANILINE FILMS

Impedance spectra of electropolymerized polyaniline films were analyse d by the theory of the impedance of macrohomogeneous porous electrodes . Specific ohmic and charge transfer resistivities were calculated, an d their potential and pH dependence is discussed in terms of structura l changes of the polymer during redox and protonation processes. Furth ermore 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 o f a compact polymer film are avoided. Another not well understood elec trochemical phenomenon of conducting polymers is the apparently capaci tive current plateau in the cyclic voltammogram and the large series a c capacitance. It will be demonstrated that this supposed 'capacitive' behaviour is related to continuous faradaic charge transfer at potent ials beyond the first oxidation wave in the cyclic voltammogram. (C) 1 998 Elsevier Science S.A.