Role of Adsorbate Coverage on the Oxygen Dissociation Rate on Sr-Doped LaMnO3 Surfaces in the Presence of H2O and CO2

Sr-dopedLaMnO3 (LSM) is a promising oxygen reductionreaction electrocatalyst in solid oxide fuel cells and other electrochemicaldevices. The presence of CO2 and H2O has beenreported to promote the oxygen dissociation reaction on LSM surfaces.Here, we investigate the coadsorption mechanism of O2 withH2O or CO2 by combining first-principles calculationsof the (0 0 1) surface containing 25–100% Sr with thermodynamicadsorption models. The molecules were found to chemisorb by formationof charged oxygen, hydroxide, and carbonate species, and the adsorptionenergies were exothermic up to monolayer coverage. Low concentrationsof H2O or CO2 do not compete with O2 for adsorption sites under relevant conditions. However, their presencecontributes to the total amount of oxygen-containing species. Theincreased coverage of oxygen species provides a quantitative explanationfor the reported enhancement in oxygen dissociation kinetics in thepresence of H2O/CO2. This study thereby providesinsights into oxygen exchange mechanisms on LSM surfaces.