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

Abstract

Ca-doped La₂NiO_4+δ is synthesized via the nitrate–citrate route. The effects of Ca substitution for La on the sinterability, lattice structure and electrical properties of La₂NiO_4+δ are investigated. Ca-doping is unfavorable for the densification process of La_2−xCa_xNiO_4+δ 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 La_2−xCa_xNiO_4+δ. 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 La₂NiO_4+δ material at high temperatures and renders the material a good thermal cycleability. La_1.7Ca_0.3NiO_4+δ exhibits an excellent chemical compatibility with CGO electrolyte. La_2−xCa_xNiO_4+δ is a promising cathode alternative for solid oxide fuel cells.