Oxygen Adsorption on Au–Ni(111) Surface Alloys

Abstract

Molecular O[subscript 2] dissociates upon interaction with a Ni(111) surface, as the spatial and energetic overlap between the Ni 3d electrons and the O[subscript 2] antibonding orbitals is quite favorable. On a Au–Ni(111) surface alloy where the extent of this overlap is greatly reduced, exposure to O[subscript 2] results in adsorption of molecular O[subscript 2] characterized by three peroxo- or superoxo-like vibrational bands centered at 743, 856, and 957 cm[superscript –1] as observed by high resolution electron energy loss spectroscopy. These bands correspond to the stretch vibrational mode of O[subscript 2] at respective adsorption sites of type pseudo-3-fold fcc/hcp, degenerate-pseudo-2-fold fcc/hcp and bridge, and pseudo-3-fold bridge. These unusual chemical environments are brought about by surface alloying, rather than the presence of Au clusters on Ni, and are further stabilized by a dramatic reconstruction of the top two surface layers, as explained with an idealized surface alloy model in conjunction with electronic structure considerations. The ability to adjust the relative populations of the different oxygen cohorts by varying the Au content suggests the utility of surface alloy motifs for engineering applications.