Fabrication and characterisation of La0.8Sr0.2MnO3/metal interfaces for application in SOFCs

Fabrication and characterisation of La0.8Sr0.2MnO3 (LSMO)/metal interfaces are important for the application of LSMO as the cathode and the metal as the interconnector in solid oxide fuel cells (SOFCs). Interfaces between LSMO and either Fecralloy, or Cr–5Fe–Y2O3, or Pt metal were fabricated by using screen printing, followed by sintering at 1200°C in different atmospheres. The microstructures of these LSMO/metal interfaces were examined using scanning electron microscopy (SEM) coupled with energy dispersive spectroscopy (EDS) and X-ray diffraction analysis. The electrical properties were characterised using impedance spectroscopy. The LSMO/Fecralloy interface fabricated in air shows a high electrical resistance (about 105 Ω cm2 at 800°C) due to the formation of an interlayer consisting of alumina and the mixed oxide M2O3·nAl2O3 at the interface during the fabrication process. When the interface was fabricated at 1200°C in argon or vacuum, a thicker interfacial layer was formed compared with that formed in air. In addition, the La0.8Sr0.2MnO3 decomposed into (La0.8Sr0.2)2MnO4+λ, (La, Sr)2O3 and MnO. Annealing of the specimen at 1200°C for 5 h in air can partially reverse the decomposition. The interface resistance of the annealed sample across the interface is one order of magnitude lower than that of an interface fabricated in air. A thick Cr2O3 layer was found at the LSMO/Cr–5Fe–Y2O3 interface fabricated in air and a spinel phase (Mn, Cr)3O4 formed a network surrounding LSMO grains due to the reaction between LSMO phase and CrO3 vapour released from the Cr2O3 layer during the fabrication. The electrical resistances of both phases are high at room temperature, but become significantly lower at 400°C. They can be negligible above 500°C. However the evaporation of CrO3 increases the resistivity of the LSMO layer. No reaction or oxidation interlayer was found between LSMO and Pt metal producing an interface resistance of 0.52 Ω cm2 at room temperature.