Electrochemical impedance studies on oxidative degradation, overoxidative degradation, deactivation and reactivation of conducting polymers

Electrochemical impedance spectroscopy (EIS) measurements in a wide frequency range were used to study the oxidative degradation, overoxidative degradation, deactivation and reactivation phenomena in polythiophene (PT) films on Pt electrode doped from aqueous solution of lithium trifluoromethanesulphonate (LiTFMS). The different parameters as electrolyte resistance, double layer capacitance, pore resistance, fractal dimensions, internal capacitance and charge resistance were derived. In addition, they furnish information about the different phenomena that can occur in the polymer film during the doping process. SEM observation of PT films provided strong evidence of the close relationship between the polarization potential, deactivation, reactivation and their morphology, also in good agreement with ac impedance results interpretation. The results are interpreted on the basis of models developed for intercalation electrodes in relation to the geometry and morphology of the polymer electrode. The deactivated PT films could reactivate by polarizing at a highly positive potential. The mechanisms of degradation, deactivation and reactivation are also discussed.