Electrochemical switching of conducting polymers: A variable resistance transmission line model

We present a model to explain some anomalous properties that have been observed in the electrochemical switching of conducting polymers, including: moving phase fronts on charging from the reduced, insulating state; residual charge in the polymer after complete reduction; and, the sharp anodic peak and flattened cathodic peak observed in cyclic voltammograms. The electrochemistry is modeled as an RC transmission line, typical of a distributed capacitor network, with the addition that the oxidation state dependence of the polymer’s electronic conductivity is explicitly included. The transient charges and currents during potentiostatic steps and linear sweeps are solved using the method of finite differences in the time domain, and results compare well with experiment in experimental geometries where electron transport is rate limiting. The model can also be generalized to other geometries provided that variation in the other physical parameters with oxidation state can be determined.