Reversible aging behavior of La0.8Sr0.2MnO3 electrodes at open circuit

Abstract

La0.8Sr0.2MnO3 (LSM) electrodes on yttria-stabilized zirconia (YSZ) electrolytes were characterized at open circuit by impedance spectroscopy. An initial irreversible change in the polarization resistance is observed for cells aged with no prior current activation. After the initial break-in, the polarization resistance rises with time at 700 °C and decays at 800 °C, reversibly, over repeated temperature cycles. The initial irreversible break-in and subsequent reversible cycling behavior suggests multiple processes happening within the time and temperatures measured. The authors propose that these processes are (1) changes in the wetting behavior of the LSM on the YSZ and (2) the reversible segregation/desegregation of cations within LSM. Between 700 °C and 800 °C, there is a transition temperature at which the segregation behavior of cations to the cathode surface changes. These measurable changes in the impedance behavior of LSM indicate that cation segregation, while considered by some to be part of the cathode activation process, may be dictated by thermodynamic factors, and thus not strictly dependent on the passage of current through the cathode.