Oxygen exchange kinetics of La0.6Sr0.4CoO3-δ affected by changes of the surface composition due to chromium and silicon poisoning

In dry atmosphere with 10% O2 high values of kchem = 1 × 10− 3 cm s− 1 and Dchem = 2 × 10− 5 cm2 s− 1 were found. A stable performance was observed during 1300 h without or with the presence of Cr- and Si-impurities. However, a significant decrease in kchem and Dchem occurred when the atmosphere was humidified (30-60% relative humidity). XPS depth profiles showed Sr-enrichment and Co-depletion of the surface already during 1300 h in dry atmosphere. After the treatment in humidified atmospheres for additional 2100 h significant amounts of Cr and Si contaminations were found. SEM and STEM showed crystallites of SrCrO4 and La-silicate on the surface. SrCrO4 and Co3O4 were also found at the grain boundaries in the near-surface region. It can be concluded that the observed decrease in the oxygen exchange kinetics is closely related to significant changes of the surface composition as a result of Cr and Si poisoning which leads to the decomposition of the oxygen exchange-active LSC phase into inactive secondary phases.