Studies on Electrode Processes of Stabilized Zirconia Cell System by Complex Impedance Method

Abstract

Abstract Three kinds of materials, Pt, Ag, and La0.5Sr0.5CoO3, were applied to stabilized zirconia as electrodes and the electrode behavior was investigated by means of the complex impedance method. The impedance arc due to the electrode/stabilized zirconia interface was always depressed semi-circles. Impedance behavior was strongly dependent on the electrode materials. Assuming that the impedance arc could be interpreted by a parallel R-C circuit, the interface resistance Ri and the interface capacitance Ci were determined. The apparent activation energy determined from the slope of the plots of logRi vs. 1/T was nearly the same for the same electrode material. (Ag electrode: 92 kJ/mol and Pt electrode: 201 kJ/mol). The oxygen pressure dependence of Ci and Ri was also investigated. Although Ci was virtually independent of the oxygen partial pressure PO2, Ri was proportional to PO2−2⁄3 for Ag electrodes and PO2−1⁄4 for Pt electrodes. The rate-determining step was supposed to be the dissociation of oxygen molecules into atoms for Ag electrodes, and the dissociation of oxygen molecules or one of the subsequent steps for Pt electrodes.