Electrical and microstructural aging of porous lanthanum. Strontium manganite/yttria-doped cubic zirconia electrodes

The formation of insulating phases at the interface between cathode and electrolyte materials during solid oxide fuel cell (SOFC) operation leads to deleterious effects on SOFC properties. We report in situ impedance spectroscopy measurements of the degradation process of porous La0.65Sr0.35MnO3/Zr0.84Y0.16O1.92 electrodes submitted to annealing temperatures above normal SOFC operating temperature, which is around 1173 K, simulating longterm SOFC operation. To measure the remaining effects after high-temperature annealing, impedance diagrams were plotted during the entire heating process up to the annealing temperatures, and during the complete cooling process. These diagrams were also plotted during the aging periods to follow the overall degradation. It was possible to detect and quantify electrical and electrochemical degradations, which are related to the formation of insulating phases at the electrode/electrolyte interface. Samples were annealed for about 200 h in air at temperatures between 1373 and 1673 K. Scanning electron microscopy and energy-dispersive X-ray spectrometry were also used to detect microstructural changes at the electrode.