Characterization of Ba _0.5Sr _0.5M _1-xFe _xO _3-δ (M = Co and Cu) perovskite oxide cathode materials for intermediate temperature solid oxide fuel cells

Ba _0.5Sr _0.5Co _1-xFe _xO _3-δ (x = 0.2, 0.6, and 0.8) and Ba _0.5Sr _0.5Cu _1-xFe _xO _3-δ (x = 0.6 and 0.8) perovskite oxides have been investigated as cathode materials for intermediate temperature solid oxide fuel cells. All the samples synthesized by a citrate-EDTA complexing method were single-phase cubic perovskite solid solutions. Then, the thermal expansion coefficient, electrical conductivities, the oxygen vacancy concentrations, the polarization resistances (R _p), and the power densities were measured. An increase in the Co content resulted in a decrease in the polarization resistance, the electrical conductivities at low temperatures, and the inflection point of the thermal expansion coefficient, but it led to an increase in the electrical conductivities at high temperatures, the oxygen vacancy concentrations, and the maximum power densities. The Cu-based system has similar behavior to the Co-based system; yet, in terms of the electrical conductivities, high Cu content gave a better result than low content for the entire range of temperatures.