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

Sr-doped LaMnO3 (LSM) is a promising oxygen reduction reaction electrocatalyst in solid oxide fuel cells and other electrochemical devices. The presence of CO₂ and H₂O has been reported to promote the oxygen dissociation reaction on LSM surfaces. Here, we investigate the coadsorption mechanism of O₂ with H₂O or CO₂ by combining first-principles calculations of the (0 0 1) surface containing 25–100% Sr with thermodynamic adsorption models. The molecules were found to chemisorb by formation of charged oxygen, hydroxide, and carbonate species, and the adsorption energies were exothermic up to monolayer coverage. Low concentrations of H₂O or CO₂ do not compete with O₂ for adsorption sites under relevant conditions. However, their presence contributes to the total amount of oxygen-containing species. The increased coverage of oxygen species provides a quantitative explanation for the reported enhancement in oxygen dissociation kinetics in the presence of H₂O/CO₂. This study thereby provides insights into oxygen exchange mechanisms on LSM surfaces.