Fabrication of Porous LSCF-SDC Carbonates Composite Cathode for Solid Oxide Fuel Cell (SOFC) Applications

Composite cathodes made of perovskite La0.6Sr0.4Co0.2Fe0.8O3 (LSCF) and SDC carbonates (SDC-(Li/Na)(2)CO3) were investigated in relation to their structure, morphology, thermal expansion coefficient and porosity. As a first step, the LSCF powder was prepared by sol-gel technique. This was followed by the preparation of the LSCF-SDC carbonates composite cathode by mixing the LSCF with SDC-(Li/Na)(2)CO3 electrolyte via solid state reaction in various compositions, i.e. 30, 40 and 50 wt.%, namely 70LSCF-30SDC7030, 60LSCF-40SDC7030 and 50LSCF-50SDC7030, respectively. The powder mixtures were then calcined at 680 C. The resultant powder was fine with surface area of about 3.39-7.42 m(2)/g and particle size of 0.56-0.66 mu m. The powder consists of two distinct phases, i.e. LSCF and SDC-(Li/Na)(2)CO3 as confirmed with x-ray diffraction. The microstructures were observed under scanning electron microscopy (SEM). Increasing the amount of the SDC-(Li/Na)2CO3 electrolyte in the composite cathode was found to bring the thermal expansion of the cathode closer to that of the electrolyte. The cathode pellets were later compacted at different pressures (27, 32 and 37 MPa) and sintered at 600 degrees C. The optimum porosity (20.99-24.98%) was achieved for samples with SDC-(Li/Na)(2)CO3 content of 30-50% sintered at 600 degrees C and cold pressed at 37 MPa.