| La2NiO4+δ(LN) and La0.6Sr0.4Co0.2Fe0.8O3-δ (LSCF) are current candidate materials for cathodes of intermediate temperatures solid oxide fuel cells (SOFC) because of their electronic-ionic conducting properties. In this work, (100-x)wt.% LN-xwt.% LSCF (x=10-60) composite cathodes have been designed and prepared with the LN and LSCF as the two components. The effects of sintering temperature and composition on the structure, chemical stability, mixed conducting properties and thermal expansion behaviors of the composite cathodes have been investigated from the viewpoint of seeking for the preferred compositions with both the desired electrical conducting and thermal expansion properties.The chemical compatibility between the LN and LSCF at high temperatures has been investigated. X-ray diffraction (XRD) analysis was employed to examine the phase structure of the composites after annealing at 1450℃. The results indicated that the XRD peaks of the composites can be assigned to those of the two end members, respectively. No significant solid state reaction product was detected between the two components during the annealing, demonstrating an acceptable chemical compatibility for the LN and LSCF.The effects of sintering temperature and composition on the mixed conducting and thermal expansion properties of the composite cathodes have been investigated. The preferred sintering temperatures have been ascertained for the composites in terms of the electrical conductivity data. The composition with x=60 presented the highest electrical conductivity when sintering at 1400℃, while the other compositions showed a preferred sintering temperature of 1450℃. It has been found that increasing the relative content of LSCF resulted in a rise of electrical conductivity, a decrease of ionic conductivity and an increase of thermal expansion coefficient (TEC).The preferred composition was determined to be 70wt.% LN-30wt.% LSCF with respect to both the electric conductivity and TEC data. The composition exhibited electrical conductivities above 100 S·cm-1 in the temperature range of 600℃-800℃and a TEC of 14.4×10-6K-1 averaged between 100℃-730℃. |
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