On the faradaic and non-faradaic mechanisms of electrochemical processes in conducting polymers and some other reversible systems with solid-phase reagents

The electrochemical peculiarities of classical redox systems with solid-state reagents (non-soluble quinones, intercalation compounds of graphite) as well as polyaniline-type conducting polymers have been considered. The conducting polymers show a significant non-faradaic component of the electrochemical mechanism. The essential differences of faradaic and non-faradaic systems in equilibrium behavior, trends of galvanostatic charge-discharge curves and cyclic voltammograms have been shown, and criteria for the identification of these mechanisms are proposed. Our investigations of the current-producing mechanism for the polyaniline electrode have shown that at least within a narrower range of potentials DeltaE(n) from 0.30-0.40 to 0.80-0.90 V versus SHE (depending on pH value) the 'capacitor' model of ion electrosorption/desorption in well conducting emeraldine salt phase is more preferable. Nevertheless, such a model should take into account the transport of both anions and protons (cations in a general case). Besides the possibilities of redox processes at the limits and beyond this range of potentials DeltaE(n) should be taken into account. At the same time, these processes can lead to the fast formation of thin passive layers of new poorly conducting phases (leucoemeraldine salt, leucoemeraldine base, etc.) near the current collector. The formation of such phases, even in a small amount, rapidly inhibits and discontinues the electrochemical process. (C) 2001 Elsevier Science Ltd. All rights reserved.