Salt Solution Concentration Effects on the Electrochemical Impedance Spectroscopy of Poly(3,4-ethylenedioxythiophene) (PEDOT)

Poly(3,4-ethylenedioxythiophene) (PEDOT) has become a widely used modifier for biomedical electrodes because of its ability to significantly decrease the impedance at low frequencies (below 1 kHz). However, in past studies the role of the solution concentration (ionic conductivity) on the electrochemical impedance behavior has not been well established. Here we describe the electrochemical impedance spectroscopy of the conjugated polymer (PEDOT) using standard screen-printed electrodes and various standard salt (NaCl) solutions with known conductivities from 1.0E-2 S/cm to 3.1E-6 S/cm. Changing the conductivity of the salt solution used for impedance measurements had a dramatic influence on the experimentally obtained spectra. An equivalent circuit consisting of a constant phase element in series with a parallel resistor and second constant phase element was used to match and describe these systems. Our results make it possible to better elucidate the influence of electrode, solution, and polymer coating on the resulting impedance response.