The electrochemical impedance of a free-standing polypyrrole membrane

Electrochemical impedance measurements of polypyrrole in 0.1 M KCl were carried out on film electrodes in asymmetrical configuration (metal-film-solution) and on free standing membranes in symmetrical configuration (solution-film-solution) in a two-compartment electrochemical cell with two Pt counter electrodes and two Ag/AgCl (sat. KCl) reference electrodes. Films of 7.5-20 mu m thickness were deposited on a micro-porous gold sputtered polycarbonate foil as support by electropolymerisation from aqueous solution of 0.07-0.1 M pyrrole monomer and 0.1 M KCI. The impedance of the membrane was measured as function of the film thickness and the redox potential. The data were analysed with a theory of a macroscopically homogeneous porous membrane, previously developed for a porous layer coating on a metal electrode and here extended for heterogeneous charge transfer between better conducting (stronger oxidised) regions and less conducting regions within the film. (C) 1998 Elsevier Science Ltd. All rights reserved.