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(211) surface. The results are compared with those on the flat Cu(111) 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(211) surface vs. -4.3 eV at its preferred site on the relaxed Cu(111) surface, and the binding energy of the molecular oxygen precursor is increased from similar to-0.6 to similar to-1.0 eV. Several possible O-2 dissociation paths at the edge of the Cu(211) 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(111). However, compared to Cu(111) the paths on Cu(211) are stabilized in their entirety by the step by similar to0.5 eV in terms of initial state, transition state, and final state energies. The dissociation of O-2 precursors at the foot of the step is close to being barrier-less. Because of the small dissociation barrier on Cu(111), the effect of steps on O-2 dissociation is nevertheless not expected to be as pronounced as in other gas/metal systems. (C) 2003 Elsevier B.V. All rights reserved.