Structural, thermal and electrochemical properties of layered perovskite SmBaCo 2O 5+ d, a potential cathode material for intermediate-temperature solid oxide fuel cells

The synthesis, conductivity properties, area specific resistance (ASR) and thermal expansion behaviour of the layered perovskite SmBaCo ₂O _{5+ d} (SBCO) are investigated for use as a cathode material for intermediate-temperature solid oxide fuel cells (IT-SOFCs). The SBCO is prepared and shows the expected orthorhombic pattern. The electrical conductivity of SBCO exhibits a metal-insulator transition at about 200 °C. The maximum conductivity is 570 S cm ^-1 at 200 °C and its value is higher than 170 S cm ^-1 over the whole temperature range investigated. Under variable oxygen partial pressure SBCO is found to be a p-type conductor. The ASR of a composite cathode (50 wt% SBCO and 50 wt% Ce _0.9Gd _0.1O _{2- d}, SBCO:50) on a Ce _0.9Gd _0.1O _{2- d} (CGO91) electrolyte is 0.05 Ω cm ² at 700 °C. An abrupt increase in thermal expansion is observed in the vicinity of 320 °C and is ascribed to the generation of oxygen vacancies. The coefficients of thermal expansion (CTE) of SBCO is 19.7 and 20.0 × 10 ^-6 K ^-1 at 600 and 700 °C, respectively. By contrast, CTE values for SBCO:50 are 12.3, 12.5 and 12.7 × 10 ^-6 K ^-1 at 500, 600 and 700 °C, that is, very similar to the value of the CGO91 electrolyte.