COMPARISON OF THE AC-IMPEDANCE OF CONDUCTING POLYMER-FILMS STUDIED ASELECTRODE-SUPPORTED AND FREESTANDING MEMBRANES

The ac impedance response of a symmetrically bathed membrane consistin g of a conducting polymer is modeled. The model is an extension of a r ecent one proposed for a conducting polymer film contacting an electro nic and an ionic conductor on its two faces (modified electrode geomet ry) and takes into account both diffusion-migration of ionic and elect ronic charge carriers inside the film and charge-transfer across metal /polymer and polymer/electrolyte interfaces. The membrane impedance is calculated for various combinations of parameters in order to stress the effect of diffusion coefficients, charge-transfer resistance, and double layer capacitance at the interfaces. The impedance responses in the modified electrode and membrane geometries are compared. It is th us shown how some ambiguities in the attribution of certain features o f the impedance of modified electrodes to either the polymer/electrode or polymer/electrolyte interfaces may be eliminated by this compariso n.