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.