Early Stages of Cu(111) Surface Oxidation: Substrate-Mediated Many-Body O–Cu–O Interactions Promote Facile Barrierless Terrace Oxidation

Copper is an important catalyst in industrial oxidation reactions. Although many theoretical studies assume the Cu catalyst to be in metallic form, it is well established that the copper surface readily oxidizes under ambient conditions, forming a passivating oxide layer. Experimental investigations spanning two decades have shown that in addition to the anticipated step-oxide formation, oxide can directly form at the Cu(111) terrace. The atomistically resolved mechanism for direct oxidation at flat terraces remains unknown. To address this gap, we demonstrate using density functional theory (DFT) calculations that subsurface oxide formation proceeds through a concerted move involving a cluster of adsorbed O atoms in particular arrangements. The O adatoms in these arrangements induce localized surface restructuring and act as pincers by extracting a copper atom from the surface layer. This process creates open channels that allow another O atom to readily move into the subsurface layer. The subsurface oxide formation is barrierless, suggesting that the Cu oxide surface is highly dynamic. We show that terrace oxidation is highly probable at O coverages >0.25 ML. These insights provide a foundation for developing more accurate dynamic computational models for copper catalysis.