Enhanced one dimensional mobility of oxygen on strained LaCoO3(001) surface

Abstract

Mechanisms by which lattice strain alters the oxygen reduction reaction (ORR) kinetics are important to understand in order to increase the ORR activity of solid oxide fuel cell cathodes. Here we assess the mechanistic and quantitative effects of strain on oxygen diffusion on the LaCoO₃(LCO)(001) surface using density functional theory calculations. Planar tensile strain is found to reduce the migration barrier of oxygen vacancy anisotropically on the LCO(001) surface, inducing an enhanced mobility along the [10] direction and a suppressed mobility along the [110] direction. The increase of space around Co that the oxygen (vacancy) traverses with a curved path is the cause of the enhanced mobility along the [10]. The increasing octahedral distortions with planar tensile strain inhibit the migration of oxygen vacancy along the [110] direction. Furthermore, the mobility of the adsorbed oxygen atom is suppressed with increasing strain due to its stronger adsorption on the surface. On the basis of rate theory estimates, the significantly lower energy barrier for oxygen vacancy diffusion is expected to dominate the other degrading factors and actually accelerate the ORR kinetics on LCO(001) up to 3% strain. The insights obtained here are useful for designing strategies to control the desired anisotropic and uni-directional oxygen transport along strained hetero-interfaces.