Computational Screening of La2NiO4+δ Cathodes with Ni Site Doping for Solid Oxide Fuel Cells

Doping on the crystal structure is a common strategy to modify electronic conductivity, ion conductivity, and thermal stability. In this work, a series of transition metal elements (Fe, Co, Cu, Ru, Rh, Pd, Os, Ir, and Pt) doped at the Ni site of La2NiO4+δ compounds as cathode materials of solid oxide fuel cells (SOFCs) are explored based on first-principles calculations, through which the determinant factors for interstitial oxygen formations and migrations are discussed at an atomistic level. The interstitial oxygen formation and migration energies for doped La2NiO4 are largely reduced in contrast to the pristine La2NiO4+δ, which is explained by charge density distributions, charge density gradients, and Bader charge differences. In addition, based on a negative correlation between formation energy and migration barrier, the promising cathode materials for SOFCs were screened out between the doped systems. The Fe-doped structures of x = 0.25, Ru-doped structures of x = 0.25 and x = 0.375, Rh-doped structures of x = 0.50, and Pd-doped structures of x = 0.375 and x = 0.50 are screened out with interstitial oxygen formation energy less than -3 eV and migration barrier less than 1.1 eV. In addition, DOS analysis indicates that doping to La2NiO4+δ also facilitates the electron conductions. Our work provides a theoretical guideline for the optimization and design of La2NiO4+δ-based cathode materials by doping.