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 (LSC 113) and (La,Sr) 2CoO 4+δ (LSC 214) 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 LSC 214 and the lattice strain in the vicinity of the interface are important contributors to such enhancement. The LSC 214(100) surface exposed to the ambient at the LSC 113/LSC 214 interface facilitates oxygen incorporation because the oxygen molecules very favorably adsorb onto it compared to the LSC 214(001) and LSC 113(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 LSC 113(001) surface. At 500°C, 4 × 10 2 times faster oxygen incorporation kinetics are predicted in the vicinity of the LSC 113/LSC 214 hetero-interface with 50% Sr-doped LSC 214 compared to that on the single phase LSC 113(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. © 2012 The Royal Society of Chemistry.