Post-test analysis of silicon poisoning and phase decomposition in the SOFC cathode material La0.58Sr0.4Co0.2Fe0.8O3 − δ by transmission electron microscopy

A degraded sample of the solid oxide fuel cell cathode material La0.58Sr0.4Co0.2Fe0.8O3 − δ (LSCF) is investigated by analytical transmission electron microscopy (TEM) with energy dispersive X-ray spectroscopy (EDXS) and electron energy loss spectroscopy (EELS). In the present study TEM is applied in order to analyse the relevant surface-near regions of an LSCF sample which was pre-treated for 1000 h in a dry O2–Ar atmosphere and an additional 1000 h in a humidified atmosphere in the vicinity of a silicon source. The results show that Si contamination occurs in an approximately 20 nm thick layer (with local variations from 4 to 35 nm) at the surface of the degraded LSCF sample. In addition, TEM gives evidence of isolated nanocrystals of SrSO4 with diameters in the range of 200–500 nm. A local decomposition of the perovskite phase is found within depths of 500–600 nm from the surface. The decomposition products are ternary oxides which contain either Sr–La–O or Co–Fe–O.

► TEM investigations of degraded La0.58Sr0.4Co0.2Fe0.8O3 − δ (LSCF) ► Degradation due to 20 nm thick Si surface layer ► Formation of SrSO4 crystals at the LSCF surface ► Decomposition of perovskite phase at the LSCF surface ► High relevance for application of LSCF as SOFC cathode in ambient air