An interpretation of small values of the transfer coefficient at conducting polymers

Abstract

The electrochemical oxidation of electronically conducting polymers has shown values of the anodic transfer coefficient close to zero at the Tafel equation, rather than 0.5. This experimental result is interpreted in this report as a difference between the ionic conductance in the reactant in the neutral state and the electric conductance in the product in the polaron state. Since the electric conductance generates a lower electric field for the charged activated complex than the ionic conductance in the reaction coordinate, it compels the activated complex to move less toward the reactant than toward the product. The asymmetry of the activation potential hill makes the anodic transfer coefficient small. This concept is demonstrated by use of the Langevin equation for the activated complex at the activation energy hill. The transfer coefficient is expressed in terms of the thermal fluctuation of the conductance, and the current density. The Tafel plot shows a convex deviation from a straight line, and depends on applied potential, as is consistent with experimental results.