Preparation and electrical properties of Ca-doped La2NiO4+delta cathode materials for IT-SOFC

Ca-doped La2NiO4+delta is synthesized via the nitrate-citrate route. The effects of Ca substitution for La on the sinterability, lattice structure and electrical properties of La2NiO4+delta are investigated. Ca-doping is unfavorable for the densification process of La2-xCaxNiO4+delta materials. The introduction of Ca leads to the elongation of the La-O(2) bond length, which provides more space for the migration of oxygen ion in La2O2 rock salt layers. The substitution of Ca increases remarkably the electronic conductivity of La2-xCaxNiO4+delta. With increasing Ca-doping level, both the excess oxygen concentration and the activation energy of oxygen ion migration decrease, resulting in an optimization where a highest ionic conductivity is presented. Ca-doping is charge compensated by the oxidation of Ni2+ to Ni3+ and the desorption of excess oxygen. The substitution of Ca enhances the structural stability of La2NiO4+delta material at high temperatures and renders the material a good thermal cycleability. La1.7Ca0.3NiO4+delta exhibits an excellent chemical compatibility with CGO electrolyte. La2-xCaxNiO4+delta is a promising cathode alternative for solid oxide fuel cells.