Mechanisms of H₂O and CO₂ Formation from Surface Oxygen Reduction on Co(0001)

Surface O removal by H and CO on Co(0001) has been studied using periodic density functional method (revised Perdew–Burke–Ernzerhof ; RPBE) and ab initio atomistic thermodynamics. On the basis of the quantitative agreement in the H₂O formation barrier between experiment (1.34 ± 0.07 eV) and theory (1.32 eV), H₂O formation undergoes a consecutive hydrogenation process [O + 2H → OH + H → H₂O], while the barrier of H₂O formation from OH disproportionation [2OH → H₂O + O] is much lower (0.72 eV). The computed desorption temperatures of H₂ and H₂O under ultrahigh vacuum conditions agree perfectly with the experiment. Surface O removal by CO has a high barrier (1.41 eV) and is strongly endothermic (0.94 eV). Precovered O and OH species do not significantly affect the barriers of H₂O and CO₂ formation. All of these results indicate that the present RPBE method and the larger surface model are more suitable for studying cobalt systems