Chemical stability of La0.6Sr0.4CoO3− δ in oxygen permeation applications under exposure to N2 and CO2

Phase stability and chemical reactivity of (La0.6Sr0.4)0.99CoO3− δ (LSC64) was tested in oxidative (pO2 = 0.21 atm) and slightly reducing conditions (pO2 ~ 10− 5 atm), as well as in carbon dioxide (pO2 ~ 10− 4 atm) to evaluate the material performance for oxygen separation technologies. Thin film LSC64 oxygen separation membranes (20–30 μm) were manufactured and electrochemical performance was evaluated at a range of temperatures with either nitrogen or CO2 purged on the permeate side of the membrane. Material stability was also investigated by high temperature X-ray diffraction, TGA and conductivity measurements in air, N2 and CO2. Under mild reduction LSC64 partly decomposes to a K2NiF4-type phase (i.e. (La,Sr)2CoO4), and Co-oxide, and under high pCO2 forms SrCO3. The latter is found to impair membrane performance. Electrical properties and oxygen permeation (jO2) in thin membranes depend on the thermal and chemical history of the samples. A flux of 4–6 Nml min− 1 cm− 2 in the temperature range of 800–900 °C was demonstrated for optimized membranes and conditions.

► La0.4Sr0.6CoO3 decomposes in N2 and CO2 with formation of (La,Sr)2CoO4 and SrCO3.
► (La,Sr)2CoO4 Ruddlesden–Popper phase can exist as a metastable phase at low T.
► Thin film membranes (30 μm) of La0.4Sr0.6CoO3 have been manufactured.
► The oxygen flux through thin film membranes decays in CO2 at 800 °C.
► Oxygen flux values of 4–6 Nml min− 1 cm− 2 at 900 °C have been obtained.