Fabrication Ba0.5Sr0.5Co0.8Fe0.2O3−δ(BSCF)/Ce0.9Gd0.1O2−δ(GDC) and La0.6Ba0.4Co0.2Fe0.8O3−δ(LBCF)/Ce0.9Gd0.1O2−δ(GDC) Composite Cathodes for Intermediate Temperature Solid Oxide Fuel Cells

The potential candidates for IT-SOFCs cathode materials, Ba 0.5 Sr 0.5 Co 0.8 Fe 0.2 O 3-δ (BSCF) and La 0.6 Ba 0.4 Co 0.2 Fe 0.8 O 3-δ (LBCF) powders, were synthesized by a EDTA-citrate combined method from Sr(NO₃)2, Ba(NO₃)₂, La(NO₃)₃ㆍ6H₂O, Co(NO₃)₂ㆍ6H₂O, Fe(NO₃)₃ ㆍ9H₂O, citric acid and EDTA-NH₃. The cathode performance of symmetrical electrochemical cells consisting of BSCF-GDC or LBCF-GDC composite electrodes and a GDC electrolyte was investigated using by AC impedance spectroscopy at the temperature range of 500 to 700℃. It was found that a single phase perovskite could be successfully synthesized when the precursor is heated at 850℃ for 2 h. Due to thermal expansion mismatch between BSCF and GDC, the composite cathodes with lower GDC content than 45 wt% were peeled off from the GDC electrolyte and their electrode polarization resistance was estimated to be high. The thermal expansion coefficient of BSCF-GDC composites was decreased with increasing the GDC content and the electrode peeling off did not occur in BSCF-45 and 55 wt% GDC composites. BSCF-45 wt% GDC composite electrode showed the lowest area specific resistances (ASR) of 0.15 and 0.04 Ωㆍ㎠ at 600 and 700℃, respectively. On the other hand, LBCF-GDC composite cathodes showed higher ASR than the BSCF-45 and 55 wt% GDC and their cathode performance were decreased with the GDC content.