Phenomenological description of dark redox reactions at electrodes covered with conducting polymer films. Part I. Mechanism and kinetics of ferrocene oxidation at polythiophene

A thermodynamic analysis of the potential distribution in an equilibrium galvanic circuit with a conducting polymer film electrode permeable for anions has been carried out. The distribution of the total potential difference between two interfaces (metal/polymer and polymer/electrolyte solution) and, hence, the dependence of the concentrations of all charged redox forms on the potential E are determined by the type of charged form that prevails in the polymer film (of polaron or bipolaron type, in particular). On the basis of these relationships, some phenomenological equations have been obtained for the charge-transfer rates of the bulk solution redox species. The conclusion on the dependence of the mechanism and kinetics of dark redox reactions on the concentration of free charge carriers in the polymer is supported by our experimental data on ferrocene oxidation at polythiophene electrodes in acetonitrile.