Density-functional theory study of the initial oxygen incorporation in Pd(111)

TL;DR

This study uses density-functional theory to analyze how oxygen initially incorporates into Pd(111), revealing that sub-surface oxygen acts as a metastable precursor to surface oxide formation, with mechanisms consistent across late 4d transition metals.

Contribution

It provides an atomic-scale understanding of initial oxygen incorporation and the formation of surface oxides on Pd(111), highlighting the role of sub-surface oxygen as a precursor.

Findings

Oxygen incorporation begins at similar coverage as surface oxide formation.

Sub-surface oxygen acts as a metastable precursor in oxidation.

Formation of O-TM-O trilayers is key to oxide stabilization.

Abstract

Pd(111) has recently been shown to exhibit a propensity to form a sub-nanometer thin surface oxide film already well before a full monolayer coverage of adsorbed O atoms is reached on the surface. Aiming at an atomic-scale understanding of this finding, we study the initial oxygen incorporation into the Pd(111) surface using density-functional theory. We find that oxygen incorporation into the sub-surface region starts at essentially the same coverage as formation of the surface oxide. This implies that the role of sub-surface oxygen should be considered as that of a metastable precursor in the oxidation process of the surface. The mechanisms found to play a role towards the ensuing stabilization of an ordered oxidic structure with a mixed on-surface/sub-surface site occupation follow a clear trend over the late 4d transition metal series, as seen by comparing our data to previously published studies concerned with oxide formation at the basal surface of Ru, Rh and Ag. The formation of a linearly aligned O-TM-O trilayered structure (TM = Ru, Rh, Pd, Ag), together with an efficient coupling to the underlying substrate seem to be key ingredients in this respect.