Electrochemical impedance spectroscopy of oxidized poly(3,4-ethylenedioxythiophene) film electrodes in aqueous solutions

The electrochemical properties of oxidized (p-doped) poly(3,4-ethylenedioxy thiophene) (PEDOT) film electrodes in aqueous solutions were investigated b y electrochemical impedance spectroscopy (EIS). PEDOT was electrochemically deposited on platinum from aqueous solutions containing 0.01 M 3,3-ethylen edioxythiophene (EDOT) and 0.1 M supporting electrolyte: KCl, NaCl or poly( sodium 4-styrenesulfonate) (NaPSS). Impedance spectra were obtained for Pt/ PEDOT electrodes at de potentials where PEDOT is in the oxidized (p-doped) state. Electrodes with PEDOT films of different thickness, containing diffe rent doping ions, were investigated in contact with different aqueous suppo rting electrolyte solutions. The EIS data were fitted to an equivalent elec trical circuit in order to characterize the electrochemical properties of t he Pt/PEDOT film electrodes. Best fits to the experimental impedance data w ere obtained for an equivalent circuit where the total bulk (redox) capacit ance of the polymer film is composed of the diffusional pseudocapacitance i n series with a second bulk capacitance. The results imply that the PEDOT f ilm contains an excess of supporting electrolyte, which facilitates ion dif fusion and gives rise to a large diffusional pseudocapacitance. (C) 2000 El sevier Science S.A. All rights reserved.