Investigation of Nd _0.6Sr _0.4Co _1-yM _yO _3-δ (M = Fe and Mn) as cathode materials for intermediate temperature solid oxide fuel cells

Nd _0.6Sr _0.4Co _1-yM _yO _3-δ (M = Fe and Mn) perovskite oxides have been investigated as cathodes for intermediate temperature solid oxide fuel cells (SOFC) with La _0.8Sr _0.2Ga _0.8Mg _0.2O _2.8 electrolyte. The crystal chemistry, electrical conductivity, thermal expansion behavior, and electrochemical performance of the cathodes are presented. The oxygen non-stoichiometry and electrical conductivity decrease with increasing Fe and Mn contents. Both the Fe- and Mn-doped systems exhibit a metal to semiconductor transition at y ≈ 0.2, but the Mn-doped system exhibits higher activation energy than the Fe-doped system. The thermal expansion coefficient (TEC) decreases with increasing Fe and Mn contents due to a suppression of the low-spin to high-spin transition associated with the Co ³⁺ ions and a stronger M-O bonding. The electrocatalytic activity decreases with increasing Fe and Mn contents, but the decrease is rapid with the Mn-doped system due to a faster decrease in the oxide ion and electronic conductivities.