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Journal of the Electrochemical Society, Vol.156, No.1, B188-B196, 2009
Spinel and Perovskite Protection Layers Between Crofer22APU and La0.8Sr0.2FeO3 Cathode Materials for SOFC Interconnects
The interaction of the metallic interconnects with the cathode and the resulting time-dependent resistance of these material combinations is a major problem in solid oxide fuel cells (SOFCs). In this study, different conductive oxide coatings were used as protective layers to improve surface stability and electrical performance, as well as to mitigate or prevent chromium poisoning of the cells. Dense layers were obtained on the steel by electron-beam physical vapor deposition, by screen printing and by electroplating. The degradation of the interface between the coated Crofer22APU alloy and the La0.8Sr0.2FeO3 (LSF) cathode was studied by resistance measurements in air at 800 degrees C up to 1000 h and analyzed by scanning electron microscopy, energy-dispersive X-ray analysis, X-ray diffraction, and secondary ion mass spectrometry after exposure. La0.6Sr0.4FeO3 measured the lowest resistance between the tested coatings. The highest resistance was found for CeO2, which also showed low protection against SrCrO4 formation. Y2O3 exhibited the lowest resistance increase; however, this coating was not protective enough to prevent the formation of SrCrO4, especially during cyclic operation. Among the Mn-Co-Fe spinel compositions tested, the lowest resistivity values and the highest Cr retention were obtained with the MnCo1.9Fe0.1O4 spinel.
Keywords:electrical resistivity;electrochemical electrodes;electron beam deposition;electroplating;protective coatings;scanning electron microscopy;secondary ion mass spectra;solid oxide fuel cells;vapour deposited coatings;X-ray chemical analysis;X-ray diffraction