Analytical Impedance Model for Electrochemically Driven Conducting Polymer Devices

Abstract

An analytical model is presented to describe the electrochemical impedance of conducting polymer based devices. The analytical expression of the impedance is obtained from a two dimensional finite transmission line equivalent circuit. The model relates impedance to cell geometry, electrolyte conductivity, polymer ionic and electronic conductivities and capacitance. These parameters were measured for a hexafluorophosphate (PF 6 -) doped polypyrrole material (the conducting polymer used in this study) and entered to the model to predict its impedance as a function of frequency. The model is unique in representing the two dimensional charging of the polymer, namely ionic mass transport through the thickness of the polymer structure and electronic resistance along its length. Close agreement is observed between impedance spectroscopy results and model prections of the charging of a polypyrrole film electrically connected at one end. This provides a means of modeling the electrochemical charging of conducting polymers and electrochemical double layer capacitor electrodes having significant ionic and electronic conductivities.