Surface and interface behaviors of (La0.8Sr0.2)xMnO3 air electrode for solid oxide cells

Abstract

In solid oxide cell operation, the stoichiometry of the air electrode is an important factor for its interaction with electrolyte and interconnect and long-term cell performance. In this study, tri-layer samples of yttria stabilized zirconia (YSZ)/(La0.8Sr0.2)xMnO3 (LSM)/AISI 441 stainless steel are made and thermally treated in dry air atmosphere at 800°C for 500h. The air electrode composition is varied by changing the x value in (La0.8Sr0.2)xMnO3 from 0.95 to 1.05 (LSM95, LSM100, and LSM105). The LSM composition segregation, YSZ/LSM/AISI 441 interfacial interaction, and the reaction of volatile chromium species with the LSM surface are characterized by scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), and X-ray diffraction (XRD). Surface segregation of Sr and La are detected for all the LSM samples. Cr deposition is found across the LSM surface. For the LSM95 sample, Sr-containing compound leads to a high Cr content at the YSZ/LSM interface. For the LSM105 sample, on the other hand, the enrichment of La at the YSZ/LSM interface hinders the Cr deposition, leading to a very low Cr content. The mechanisms of LSM elemental surface segregation and Cr deposition are discussed.