Study on Ba0.5Sr0.5Co0.8Fe0.2O3-δ-Sm0.5Sr0.5CoO3-δ composite cathode materials for IT-SOFCs

Ba0.5Sr0.5Co0.8Fe0.2O3-delta-xSm0.5Sr0.5CoO3-delta (BSCF-xSSC, x = 0-40 wt%) composite cathodes supported on Sm0.2Ce0.8O1.9 (SDC) electrolyte were studied for applications in IT-SOFCs. X-ray diffraction patterns showed obvious solid-state reactions between BSCF and SSC. However, the composite materials exhibited higher conductivity than that of pure BSCF, e.g., around 176 S cm-1 at 500 deg C for the x = 30 wt% composite, which was nearly seven times higher than that of BSCF. The thermal expansion coefficients of the BSCF-SSC were between (18.0 and 21.9) X 10-6 K-1 from 30 to 800 deg C, which was slightly higher than that of BSCF. In addition, electrochemical impedance spectra exhibited the better performance of BSCF-SSC composite cathodes than pure BSCF. The results of the polarization resistance indicated that the optimum content of SSC in the composite cathodes was about 30 wt%, e.g., the polarization resistance value of BSCF-30 wt%SSC was only 0.71 Omega cm2 at 550 deg C, about one seventh of that BSCF at 550 deg C.