KINETICS AND MECHANISM OF CHARGE-TRANSFER REACTIONS BETWEEN CONDUCTING POLYMERS AND REDOX IONS IN ELECTROLYTES

Charge-transfer reactions of selected ionic redox couples were studied on rotating glassy carbon electrodes covered with conducting-polymers of different membrane properties: poly-N-methylpyrrole as the anion exchanger or poly-N-methylpyrrole with immobilized poly(4-styrenesulfonate) ions as the cation exchanging matrix. The electrochemical and spectroscopic (EDAX) results obtained with the redox systems: Fe(CN)(6)(3-/4-), Ru(NH3)(6)(3+/2+), Eu3+/Eu2+, Co(en)(3)(3+/2+) and Fe(C2O4)(3)(3-/4-) pointed to reactions proceeding at the polymer-solution interface. The data were analysed on the basis of a model in which the charge transfer was regarded as a redox reaction between polymeric sites in the film and the redox species in the solution. The rate of electron transfer was found to be: (i) proportional to the concentration of the oxidized or reduced polymeric sites; (ii) dependent to some extent on the Donnan potential prevailing at the interface; and (iii) correlated with the thermodynamic driving force of the reaction between the polymer and redox species.