First principles modeling of oxygen adsorption on LaMnO3 (001) surface

We present and discuss the results of ab initio DFT plane-wave supercell calculations of the atomic and molecular oxygen adsorption and diffusion on the LaMnO3 (001) surface which serves as a model material for a cathode of solid oxide fuel cells. The dissociative adsorption of O2 molecules from the gas phase is energetically favorable on surface Mn ions even on a defect-free surface. The surface migration energy for adsorbed O ions is found to be quite high, 1.6 eV. We predict that the adsorbed O atoms could penetrate into electrode first plane when much more mobile surface oxygen vacancies (migration energy of 0.69 eV) approach the O ions strongly bound to the surface Mn ions. Ab initio thermodynamics predicts that at typical SOFC operation temperatures (~1200 K) the MnO2 (001) surface with adsorbed O atoms is the most stable in a very wide range of oxygen gas pressures (above 10^2 atm).