Degradation Mechanism in La0.8Sr0.2CoO3 as Contact Layer on the Solid Oxide Electrolysis Cell Anode

Detailed chemical and structural analyses are presented for the degradation mechanism of La0.8Sr0.2CoO3 (LSC) as the contact layer of solid oxide electrolysis cell (SOEC) anodes. SOEC stack cells, which were operated in the presence of Cr-containing interconnects, and reference half-cells, which were tested with Pt interconnects, were investigated. The as-prepared surface chemistry of LSC showed a spatially uniform A-site (La and Sr) enrichment. Undesirable secondary phases of Cr2O3, LaCrO3, La2CrO6, and Co3O4 were identified in the contact layer of the SOEC stack cells, which had significantly reduced electrochemical performance after long-term testing. Auger electron spectroscopy and analytical transmission electron microscopy showed the presence of Cr throughout the layer cross section on the surface and in the bulk, respectively, with significant variations in the local chemistry at the micro- to nanoscale. Particularly, a long-range transport of Sr and Co cations out of the LSC phase to the top of the contact layer was evident. However, when tested with electrolytic potential and current without a Cr environment, the LSC contact layer composition remained stable. The dissociation of the LSC in the SOEC stack cells can be, most probably, driven by the La-Cr-O related thermodynamics under the electrolytic potential and oxygen pressure at the anode.