Study on Ba_(0.5)Sr_(0.5)Co_(0.8)Fe_(0.2)O_(3-delta)-Sm_(0.5)Sr_(0.5)CoO_(3-delta) composite cathode materials for IT-SOFCs

摘要

Ba_(0.5)Sr_(0.5)Co_(0.8)Fe_(0.2)O_(3-delta)-Sm_(0.5)Sr_(0.5)CoO_(3-delta) (BSCF-xSSC, x=0-40wt percent) composite cathodes supported on Sm_(0.2)Ce_(0.8)O_(1.9) (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 percent 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 percent, e.g., the polarization resistance value of BSCF-30wt percent SSC was only 0.71 OMEGA cm~2 at 550 deg C, about one seventh of that BSCF at 550 deg C.