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

Electrochemical impedance spectroscopy (EIS) measurements in a wide frequen cy range were used to study the oxidative degradation, overoxidative degrad ation, deactivation and reactivation phenomena in polythiophene (PT) films on Pt electrode doped from aqueous solution of lithium trifluoromethanesulp honate (LiTFMS). The different parameters as electrolyte resistance, double layer capacitance, pore resistance, fractal dimensions, internal capacitan ce and charge resistance were derived. In addition, they furnish informatio n about the different phenomena that can occur in the polymer film during t he doping process. SEM observation of PT films provided strong evidence of the close relationship between the polarization potential, deactivation, re activation and their morphology, also in good agreement with ac impedance r esults interpretation. The results are interpreted on the basis of models d eveloped for intercalation electrodes in relation to the geometry and morph ology of the polymer electrode. The deactivated PT films could reactivate b y polarizing at a highly positive potential. The mechanisms of degradation, deactivation and reactivation are also discussed. (C) 1999 Elsevier Scienc e S.A. All rights reserved.