AC impedance analysis of polypyrrole films

A preliminary study is presented on the AC impedance properties of polypyrrole covered platinum electrodes in contact with an aqueous electrolyte containing an electroactive species (K ferricyanide). AC impedance data have been measured over the frequency range 0.003 Hz – 100 kHz. A suitable circuit model to fit the data requires five resistive and five capacitative elements. Compared with a bare platinum electrode in contact with the same electrolyte solution, the polypyrrole covered electrode shows lower impedances in both real and imaginary parts over a wide range of frequencies. This is reflected in both lower values for the resistive circuit elements and higher values for the capacitative elements. The polypyrrole is clearly capable of charge storage, and in addition might be acting as a catalytic surface for the heterogeneous charge transfer reaction between the electrode and the electroactive species in solution.