Re-visiting the O/Cu(111) system -- When metastable surface oxides could become an issue!

TL;DR

This study investigates the metastability and potential catalytic relevance of the '8'-structure oxide phase on Cu(111), revealing its comparable stability to other oxide structures and its possible role as a reactive phase in catalytic processes.

Contribution

The paper demonstrates through computational methods that the '8'-structure is metastable and likely to be a reactive phase during catalytic reactions on Cu(111).

Findings

The '8'-structure oxide phase is metastable and competitively populated.

The atomic configuration resembles Cu₂O(110), a known active facet.

If formed, the '8'-structure could be a reactive catalytic phase.

Abstract

Surface oxidation processes are crucial for the functionality of Cu-based catalytic systems used for methanol synthesis, partial oxidation of methanol or the water-gas shift reaction. We assess the stability and population of the "8"-structure, a $|\begin{smallmatrix} 3&2\\ -1&2 \end{smallmatrix}|$ oxide phase, on the Cu(111) surface. This structure has been observed in x-ray photoelectron spectroscopy and low-energy electron diffraction experiments as a Cu(111) surface reconstruction that can be induced by a hyperthermal oxygen molecular beam. Using density-functional theory calculations in combination with \textit{ab initio} atomistic thermodynamics and Boltzmann statistical mechanics, we find that the proposed oxide superstructure is indeed metastable and that the population of the "8"-structure is competitive with the known "29" and "44" oxide film structures on Cu(111). We show that the configuration of O and Cu atoms in the first and second layers of the "8"-structure closely resembles the arrangement of atoms in the first two layers of Cu$_2$O(110), where the atoms in the "8"-structure are more constricted. Cu$_2$O(110) has been suggested in the literature as the most active low index facet for reactions such as water splitting under light illumination. If the "8"-structure were to form during a catalytic process, it is therefore likely to be one of the reactive phases.