Electrochemical impedance characterization of polyaniline-coated graphite electrodes for electrochemical capacitors - effects of film coverage/thickness and anions

The electrochemical impedance spectroscopic (EIS) responses of polyaniline (PANI)-coated graphite electrodes are governed by the process occurring at the PANI \ electrolyte interface and the bulk faradaic redox transitions within the conducting polymer in the high-frequency and low-frequency regions, respectively. The redox transitions between the different oxidation structures of PANI cause the polymer to behave as a pseudocapacitor, especially at potentials greater than or equal to 200 mV. A combination of the respective equivalent circuits for the electrode completely coated with a PANI film and for a bare graphite substrate successfully represents the EIS spectra of the electrodes with partial coverage of the polymer. A comparison of the EIS and chronopotentiometric results reveals that the effects of the anions on the electrochemical behavior of PANI are more obviously illustrated by the EIS method. (C) 2001 Elsevier Science B.V. All rights reserved.