The adsorption and dissociation of O2 molecular precursors on Cu: the effect of steps

The adsorption and dissociation of dioxygen on Cu steps are studied using periodic self-consistent density functional theory (PW91-GGA) calculations. Cu steps are modeled with a Cu(2 1 1) surface. The results are compared with those on the flat Cu(1 1 1) surface. The adsorption of both atomic and molecular oxygen is enhanced on the stepped surface: the binding energy of atomic oxygen is −4.5 eV at its preferred site on the relaxed Cu(2 1 1) surface vs. −4.3 eV at its preferred site on the relaxed Cu(1 1 1) surface, and the binding energy of the molecular oxygen precursor is increased from ∼−0.6 to ∼−1.0 eV. Several possible O₂ dissociation paths at the edge of the Cu(2 1 1) step have been investigated. The activation energies range from 0.09 to 0.24 eV, comparable to a minimum activation energy of 0.20 eV found on Cu(1 1 1). However, compared to Cu(1 1 1) the paths on Cu(2 1 1) are stabilized in their entirety by the step by ∼0.5 eV in terms of initial state, transition state, and final state energies. The dissociation of O₂ precursors at the foot of the step is close to being barrier-less. Because of the small dissociation barrier on Cu(1 1 1), the effect of steps on O₂ dissociation is nevertheless not expected to be as pronounced as in other gas/metal systems.