Impact of SO2 on the Oxygen Exchange Kinetics of the Promising SOFC/SOEC Air Electrode Material La0.8Ca0.2FeO3-δ

The mass and charge transport properties of La0.8Ca0.2FeO3-delta (LCF82) were determined at 600-800 degrees C and pO(2) = 0.1 bar. The electronic conductivity is in the range of 112 S cm(-1) at 700 degrees C. The chemical surface exchange coefficient (k(chem)) and the chemical diffusion coefficient of oxygen (D-chem) were measured. LCF82 shows exceptionally fast oxygen exchange kinetics in pure O-2-Ar at 700 degrees C. Long-term measurements at 700 degrees C in pure O-2-Ar showed an excellent stability of the kinetic parameters during 1000 h. However, when 2 ppm of sulfur dioxide were added, k(chem) decreased by a factor of 40 within the first 24 h. After further 1000 h, the total decrease in k(chem) amounted to two orders of magnitude. Post-test analyses of LCF82 were performed by SEM-EDXS, XPS, and STEM. Ca-enrichment and La-/Fe-depletion of the LCF82 surface occurred during the first 1000 h without SO2. At the surface of the sample exposed to 2 ppm SO2 for additional 1000 h, CaSO4 crystals with diameters of 1-2 mu m and an underlying layer of Fe2O3 (thickness approx. 300-450 nm) were found. Remarkably, LCF82 shows faster oxygen exchange kinetics than La0.6Sr0.4CoO3-delta even in the degraded state. Therefore, LCF82 is suggested as a promising material for SOFC and SOEC air electrodes. (C) The Author(s) 2017. Published by ECS. This is an open access article distributed under the terms of the Creative Commons Attribution Non-Commercial No Derivatives 4.0 License (CC BY-NC-ND, http://creativecommons.org/licenses/by-nc-nd/4.0/), which permits non-commercial reuse, distribution, and reproduction in any medium, provided the original work is not changed in any way and is properly cited. For permission for commercial reuse, please email: oa@electrochem.org. All rights reserved.