Enhanced Electrochemical Properties of Non-stoichiometric Layered Perovskites, Sm_1-xBaCo₂O_5+d, for IT-SOFC Cathodes

In this study, electrochemical properties of layered perovskites having non-stoichiometric compositions (Sm_1-xBaCo₂O_5+d, x = 0, 0. 01, 0.02, 0.03, 0.04, 0.05, 0.10, and 0.15) were analyzed for the direct application of cathode materials for Intermediate Temperature-operating Solid Oxide Fuel Cells (IT-SOFC). From the Sm_1-xBaCo₂O_5+d oxide systems calcined at 1,100°C for 8 h, single phase (SmBaCo₂O_5+d, SBCO_1) was maintained only in the case of the x = 0 composition. In the compositions of x = 0.05-0.10, BaCoO_2.6 was mixed with the pattern of SBCO. In addition, in the composition of x = 0.15, it was confirmed that BaCoO_2.6 and CoO phases coexisted with SBCO. In the compositions of Sm_1-xBaCo₂O_5+d, the overall Area Specific Resistance (ASR) values decreased as the removal amount of Sm increased from x = 0-0.10; then, the values increased for compositions from x = 0.15. For example, the ASRs of SBCO_1, Sm_0.95BaCo₂O_5+d (SBCO_0.95), Sm_0.90BaCo₂O_5+d (SBCO_0.90), and Sm_0.85BaCo₂O_5+d (SBCO_0.85) measured at 600°C were 0.301, 0.147, 0.119, and 0.179 Ω cm², respectively. In particular, SBCO_0.90 was found to have an excellent ASR property of about 0.035 Ω cm² at 700°C. Typical properties of the metal-insulator transition (MIT) electrical conductivity were shown in all measured compositions. The temperature at which MIT occurred increased as the non-stoichiometric composition increased.