Charging process in electron conducting polymers: dimerization model

Theory of the charging and discharging process in electron-conducting polym er films at an electrode surface has been presented. It is based on the con cept of two coexisting subsystems at the polymer matrix, 'usual' sites P wh ich can exchange with the electrode by the electronic charge in a quasi-rev ersible manner, and sites D where intermolecular bonds between neighboring polymer molecules can be formed. The charging and discharging of the latter subsystem may be realized along different reaction pathways, e.g. via the bond formation after the generation of two cation radicals within such site D in the course of the anodic scan while the bond dissociation may take pl ace via a partially discharged state of the intermolecular bond. This diffe rence leads to a hysteresis in cyclic voltammograms, first of all to a sign ificant mutual shift of the anodic and cathodic peaks of the current origin ated from the redox transformations of D sites. An important feature of the P sites extracted from experimental CV data is their broad energetic inhom ogeneity (dispersion of their redox potentials) responsible for plateaus of the current observed at high charging levels in both directions of the pot ential scan. Several approaches to the numerical integration of the kinetic equations for the sites' states have been analyzed, and qualitative predic tions of the theoretical model have been illustrated. (C) 2001 Elsevier Sci ence Ltd. All rights reserved.