ELECTROCHEMICAL CHARACTERIZATION OF LSM/YSZ COMPOSITE CATHODE IN ANODE-SUPPORTED SOFC CONFIGURATION

Sr-doped LaMnO3 (LSM) and yttria stabilized zirconia (YSZ) composites are widely studied as cathodic materials for high temperature solid oxide fuel cells. The oxygen reduction (O.R.) mechanism of these electrodes is still uncertain. In previous works we suggested the existence of a "critical" temperature for the activation of the entire composite cathode volume close to 750°C and the presence of transport limitations. In this study the behaviour of the system is investigated in anode-supported cell with the aim to individuate and characterize the cathodic contribution from the overall impedance response, varying the partial pressure of the reactant gases. The LSM/YSZ composite cathode is screen printed on a Ni/YSZ cermet anode- supported half-cell with yttria stabilized zirconia (8YSZ) electrolyte. The cell is analyzed by Electrochemical Impedance Spectroscopy in different fuel and oxygen partial pressure conditions in the temperature range between 650 and 850°C. A procedure for the interpretation of the possible kinetic mechanism controlling the O.R. process is presented and discussed. The results confirm that between 700 and 800°C the rate determining step of the oxygen reduction reaction changes.