Characterization of Nd_1-xSr_xCoO_3-δ (0 ≤ x ≤ 0.5) cathode materials for intermediate temperature SOFCs

The crystal chemistry, thermal expansion behavior, electrical conductivity, chemical compatibility, and electrochemical performance in intermediate temperature solid oxide fuel cells (SOFCs) of Nd_1-xISr _xCoO_3-δ (0 ≤ x ≤ 0.5) perovskite oxides have been investigated. The samples crystallize in an orthorhombic structure, and the lattice volume increases with increasing Sr content, x. The thermal expansion coefficient decreases with x, reaches a minimum at x = 0.3, and then increases. The electrical conductivity increases with x, and the system exhibits a semiconductor-to-metal transition at around x = 0.3. The electrocatalytic activity and power density increase with increasing x, reaches a maximum around x = 0.4, and then decreases due to an interfacial reaction of the x = 0.5 sample with the electrolyte. The x = 0.4 sample shows a maximum power density value of 0.24 W/cm² at 800°C in single cells fabricated with the La _0.8Sr_0.2Ga_0.8Mg_0.2O_2.8 electrolyte and Ni-Ce_0.1Gd_0.1O_1.95 cermet anode.