Thermodynamic and kinetic aspects of charge transfer inside conducting polymer films

A new variant of the theory of charging processes for electroactive polymer films on electrode surfaces was recently developed for conducting polymers containing cation-radicals (polarons) of identical sizes. Compared with the previously proposed models, the new approach explicitly takes into account the polaron charge delocalization over several monomer units of a polymer chain. Although the obtained theoretical predictions appeared to be in a qualitative agreement with experimental results, it has not been explored earlier whether the developed approach is consistent with thermodynamic principles. With that in mind, we complete the previously derived expressions for fluxes of charged quasi-particles and then treat them within the framework of the non-equilibrium thermodynamics. As a result, it has been established in the limit of the quasi-reversible character of charging/discharging processes that such a treatment allows one to achieve complete accordance of these expressions with thermodynamic requirements. This confirms validity of the previous predictions and, at the same time, creates premises for treating the electrochemical properties of more complicated systems than those considered in this paper. In parallel to these general conclusions, we have calculated quasi-equilibrium voltammetry curves of electrodes modified with polymer films containing polaron and bipolaron charge carriers of equal sizes. A primary comparison of such calculated curves with experimental ones confirms their qualitative agreement.