Long-term stability of the oxygen exchange properties of (La,Sr)1 − z(Co,Fe)O3 − δ in dry and wet atmospheres

The long-term degradation of the surface oxygen exchange kinetics of the IT-SOFC cathode material La0.58Sr0.4Co0.2Fe0.8O3 − δ (LSCF) is investigated in dry and wet O2–Ar atmospheres at 600–700 °C. Conductivity relaxation measurements indicate high chemical surface exchange coefficients (kchem) in dry O2–Ar atmosphere at 600–800 °C with Ea(kchem) ∼ 200 kJ mol− 1. However, during 1 kh an exponential decrease of kchem is observed at 600 °C in dry atmosphere. After switching to a H2O-containing atmosphere a further step-wise decrease of kchem by a factor of 2 occurs, followed by an approximately linear long-term degradation with a rate of ∼ 10% kh− 1. At 700 °C a pronounced decrease of the surface exchange coefficient by 2 orders of magnitude is found after switching from dry to wet atmospheres. Post-test XPS analysis indicates that the deterioration of the catalytic activity of LSCF originates in significant changes of the surface cation composition (especially Sr enrichment) and silicon poisoning.