IMPEDANCE SPECTROSCOPY ANALYSIS OF LA-1-XSRXMNO3-YTTRIA-STABILIZED ZIRCONIA ELECTRODE-KINETICS

The impedance of the La1-xSrxMnO3-Yttria-stabilized zirconia oxygen el ectrode has been analyzed as a function of the overpotential, temperat ure and oxygen partial pressure. At equilibrium, the impedance diagram is characterized by a large capacitive effect, approximately constant , and a resistance varying with the oxygen partial pressure as P-O2(-1 /2). The resistance activation energy is 1.8 eV in air. Under low anod ic and cathodic overpotentials, the observed behavior is similar to th at of metallic electrodes. This could be related to a limiting oxygen adsorption process in the triple contact zone. Under large anodic pola rization, inductive effects set in at low frequencies with a significa nt decrease of the electrode resistance. Under large cathodic polariza tion, the onset of the electrocatalytic process due to the creation of oxygen vacancies in the electrode material is observed, as already re ported. The impedance diagrams suggest a limiting diffusion process wh ich is assumed to be the oxygen transport in the electrode material. A numerical calculation provides an estimate for the corresponding diff usion coefficient and the volume of the electrode material involved in the process.