Thermodynamic stability and structure of copper oxide surfaces: A first-principles investigation

To obtain insight into the structure and surface stoichiometry of copper-based catalysts in commercially important chemical reactions such as the oxygen-assisted water-gas shift reaction, we perform density-functional theory calculations to investigate the relative stability of low-index copper oxide surfaces. By employing the technique of ``ab initio atomistic thermodynamics,'' we identify low-energy surface structures that are most stable under realistic catalytic conditions are found to exhibit a metallic character. Three surfaces are shown to have notably lower surface free energies compared to the others considered and could be catalytically relevant; in particular, under oxygen-rich conditions, they are the Cu₂O(110):CuO surface, which is terminated with both Cu and O surface atoms, and the Cu₂O(111)-CuCUS surface, which contains a surface (coordinatively unsaturated) Cu vacancy, while for the oxygen-lean conditions, the Cu₂O(111) surface with a surface interstitial Cu atom is found to be energetically most favorable, highlighting the importance of defects at the surface.