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Sources of performance degradation in thin film La0.6Sr0.4FeO3 air electrodes

2020    Demirkal, Emrah; Ozdemir, Okan; Arslan, Leyla Colakerol; Buyukaksoy, Aligul

Origins of long-term oxygen reduction activity degradation at 700 degrees C in polymeric precursor-derived La0.6Sr0.4FeO3 (LSF) thin film cathodes were investigated. Electrochemical impedance spectroscopy measurements revealed that the LSF thin films pre-calcined at 900 degrees C (LSF-900) exhibited much faster electrochemical activity loss than did LSF pre-calcined at 700 degrees C (LSF-700). As similar losses in surface area were determined upon scanning electron microscopy image analyses of samples, microstructure evolution was excluded as a possible reason for the difference in degradation rates. Upon X-ray diffraction analyses and comparison of results with literature, it was suggested that small amounts of Ruddlesden-Popper type (La, Sr)(2)FeO4 (214) phases were present throughout the 100 hour exposure of both LSF-700 and LSF-900 to 700 degrees C, thus not affecting the long-term performance degradation rates. X-ray photoelectron spectroscopy analyses revealed that the ratio of surface-bound Sr to the lattice-bound one increased significantly in LSF-900, suggesting electrochemically inactive SrO/Sr(OH)(2)/SrCO3 rich layer formation and thus contributing to fast activity loss. Overall, it was established that microstructural evolution was not the sole source of degradation in LSF-based cathodes. Since LSF thin films deposited by a solution precursor onto YSZ electrolytes constitute a model structure, the results obtained in the present study can also provide useful information on the degradation of LSF-YSZ composite cathodes prepared by LSF infiltration into YSZ scaffolds.