Role of Adsorbate Coverage on the Oxygen DissociationRate on Sr-Doped LaMnO 3 Surfaces in the Presence of H 2 O and CO 2
2020
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.
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