A Coupled Charge Transfer–Structural Distortion Model for Memory Effects in Conducting Polymer Electrochemistry

This article presents a simple electrochemical model to elucidate the anomalous electrochemical responses which were recently observed for a series of poly(3-alkylthiophenes) (P3ATs), some of which have been long observed for many other conducting polymers (CPs). Using original experimental data with literature evidence, we develop a simple model, which reconciles several long-standing peculiarities in the CPs’ responses. The model accounts for oxidation-driven distortion of the film matrix and allows for describing the mechanism underlying the so-called memory effect and the time-dependent evolution of charge-transfer resistance in the reduced state of the conducting polymer. It further resolves the origin of the characteristic nonmonotonic current transients (exhibiting peaks) during large-step anodic chronoamperometry and rationalizes the absence of such features during polymer reduction. Additionally, the pronounced asymmetry between anodic and cathodic voltammetric branches is explained, including the fact that the cathodic branch remains largely insensitive to moderate changes in the potential scan rate and film thickness, whereas the anodic branch is strongly affected. The model clarifies the known deviation of the anodic kinetics from Butler–Volmer behavior, including a superlinear increase of peak current with the potential scan rate. In addition to that, the developed model includes the possibility to describe the charge–discharge hysteresis─a fundamental feature that many conducting polymers possess. We believe this comprehensive analysis provides a fundamental basis for interpreting the electrochemical properties of conducting polymer systems, offering insights that will be valuable for the scientific community and for the development of novel types of smart materials.