LnBaCo[sub 2]O[sub 5+δ] Oxides as Cathodes for Intermediate-Temperature Solid Oxide Fuel Cells

(, Sm, Gd, and Y) oxides with a cation ordered perovskite structure have been investigated as cathode materials for intermediate-temperature solid oxide fuel cells (SOFCs). The oxygen content , thermal expansion coefficient (TEC), and electrical conductivity (metallic) decrease with decreasing size of the ions from to Y. While the decrease in TEC is due to the decreasing ionicity of the Ln–O bond, the decrease in electrical conductivity is due to the increasing oxide ion vacancies and a bending of the O–Co–O bonds. The power density of single-cell SOFCs fabricated with the cathodes, electrolyte, and cermet anode decrease with decreasing size of the ions, partly due to a decreasing electrical conductivity. The cathodes with an intermediate lanthanide ion such as offer a trade-off between catalytic activity and TEC.