The non-metallic character of conducting polymers and the mechanism of electron exchange with redox electrolytes

The electrochemical reduction of EU(3+) Fe(CN)(6)(3-) and RU(NH3)(6)(3+) is studied on electrodes coated with ''conducting polymers'' of the polypyrrole type. Theoretical considerations along with the experimental findings lead to a consistent picture of the electronic state of the conducting polymer acting as mediator for electron transfer between the metal electrode and the redox electrolyte. As the applied electrode potential is changed, the polymer assumes a new equilibrium state characterized by a new value of the chemical potential of electrons, i.e., the ratio between tbe concentrations of oxidized and reduced polymer sites varied. On the other hand, tire electrical potential of the polymer phase is shown to remain largely unchanged, as long as the polymer phase and the electrolyte contain a reasonably large concentration of ions. The solvated conducting polymers are therefore concluded to be better described as special redox polymers than as metals. The consequences of this fact for understanding the mechanism of electron exchange between liquid redox electrolytes and tire conducting polymers are discussed.