AC Impedance Characterization of Highly Resistive Media Using Four-Electrode Electrochemical Cells

Abstract

Electrochemical impedance spectroscopy (EIS) was employed for characterization studies of highly resistive non-aqueous media using four-electrode cells with solid state reference electrodes. The influence of internal resistance of the impedance analyzer, the media's temperature and conductivity, shielding of the cables, and the electrochemical cell geometry and configuration on the impedance results were investigated. The most accurate EIS measurements can be made in the 2-electrode cells with active shields where a single arc at high frequencies and a complicated low frequency interfacial impedance feature were observed. When 4-electrode cells were employed, the relative impedances of the sample and the analyzer, geometry and positioning of voltage electrodes, and capacitive coupling between the signal lines introduced two types of impedance measurement artifacts. A capacitive-resistive low frequency load was interpreted as a measurement artifact originating from the voltage electrodes' geometry and positioning. The medium frequency artifact combining resistive, capacitive and inductive features is intrinsic to the experimental setup resulting in a voltage divider effect.