Oxygen dissociation at close-packed Pt terraces, Pt steps, and
Ag-covered Pt steps studied with density functional theory

Oxygen dissociation at close-packed Pt terraces, Pt steps, and Ag-covered Pt steps studied with density functional theory
=========================================================================================================================

by Z. Sljivancanin and B. Hammer.

Surf. Sci. **515**, 235-244 (2002).

Abstract
--------

Using density functional theory we have characterized O$\_{2}$
dissociation on flat and stepped Pt(111) surfaces. The reactivity of the
steps is significantly higher than that of the flat terraces. Inclusion
of Ag monatomic chains along the Pt steps modifies the reactivity of the
Pt steps towards that of the flat Pt terraces. Our investigations reveal
the reaction energetics and the geometries for the molecular precursor
states (MPS), transition states (TS) and final states of the
dissociating oxygen. Both the MPS and TS geometries on stepped Pt
involve oxygen species at the top of the step with no oxygen atoms
diffusing onto the lower terrace. We further find that the Ag chains
mainly modify the adsorption and reaction bond strengths while they
leave the MPS and TS geometries essentially unchanged. The high
reactivity of the Pt steps is explained in terms of the coordinative
unsaturation of the Pt step atoms which cause a highlying valence
$5d$-electron system.