Characterization of layered perovskite oxides NdBa_(1-x)Sr_xCo)2O_(5+δ) (x = 0 and 0.5) as cathode materials for IT-SOFC

摘要

The crystal structure, thermal expansion, and electrochemical properties of the layered perovskite series NdBa_(1-x)Sr_xCo)2O_(5+δ) (x = 0 and 0.5) were investigated to study the effects of substituting Sr for Ba on a layered perovskite oxide. A tetragonal layered perovskite structure was observed in NdBaCo_2O_(5+δ) (NBCO), and a tetragonal structure was also observed in NdBa_(0.5)Sr_(0.5)Co_2O_(5+δ) (NBSCO) when Sr was substituted into NBCO. The thermal expansion coefficients (TECs) of NBSCO and NBCO were both bigger than 22 × 10~(-6) K~(-1) at 530 ℃. However, the TEC values for 50 wt% of NBSCO and 50 wt% of Ce_(0.9)Gd_(0.1)O_(2-δ) (CGO91) (NBSCO:50) were 13.2 × 10~(-6) K~(-1) at 600 ℃ and 13.7 × 10~(-6) K~(-1) at 700 ℃; for 50 wt% of NBCO and 50 wt% of CGO91 (NBCO:50) they were 12.4 × 10~(-6) K~(-1) at 600 ℃ and 12.5 × 10~(-6) K~(-1) at 700 ℃. The cathode polarizations (Rp) of NBSCO and NBCO on a CGO91 electrolyte were observed to be 0.25 and 0.11 Ocm~2, respectively, at 700 ℃. The Rps of composite cathodes in NBSCO:50 and NBCO:50 were 0.061 and 0.038 Ωcm~2, respectively, at 700 ℃.