Mechanism for enhanced oxygen reduction kinetics at the (La,Sr)CoO3−δ/(La,Sr)2CoO4+δ hetero-interface

Abstract

The recently reported fast oxygen reduction kinetics at the interface of (La,Sr)CoO_3−δ (LSC₁₁₃) and (La,Sr)₂CoO_4+δ (LSC₂₁₄) phases opened up new questions for the potential role of dissimilar interfaces in advanced cathodes for solid oxide fuel cells (SOFCs). Using first-principles based calculations in the framework of density functional theory, we quantitatively probed the possible mechanisms that govern the oxygen reduction activity enhancement at this hetero-interface as a model system. Our findings show that both the strongly anisotropic oxygen incorporation kinetics on the LSC₂₁₄ and the lattice strain in the vicinity of the interface are important contributors to such enhancement. The LSC₂₁₄(100) surface exposed to the ambient at the LSC₁₁₃/LSC₂₁₄ interface facilitates oxygen incorporation because the oxygen molecules very favorably adsorb onto it compared to the LSC₂₁₄(001) and LSC₁₁₃(001) surfaces, providing a large source term for oxygen incorporation. Lattice strain field present near the hetero-interface accelerates oxygen incorporation kinetics especially on the LSC₁₁₃(001) surface. At 500 °C, 4 × 10² times faster oxygen incorporation kinetics are predicted in the vicinity of the LSC₁₁₃/LSC₂₁₄ hetero-interface with 50% Sr-doped LSC₂₁₄ compared to that on the single phase LSC₁₁₃(001) surface. Contributions from both the anisotropy and the local strain effects are of comparable magnitude. The insights obtained in this work suggest that hetero-structures, which have a large area of (100) surfaces and smaller thickness in the [001] direction of the Ruddlesden–Popper phases, and larger tensile strain near the interface would be promising for high-performance cathodes.