DFT-Based Cu(111)∥Cu2O(111) Model for Copper Metal Covered by Ultrathin Copper Oxide: Structure, Electronic Properties, and Reactivity

In many applications, metallic copper can be covered by an ultrathin native or a passive oxide film depending on the redox conditions of the interface formed with the environment, which governs its surface properties. In the present work, we constructed and optimized through quantum chemical density functional theory (DFT) calculations a model of this Cu(111)parallel to Cu2O(111) stoichiometric oxide supported in parallel epitaxy on a Cu(111) substrate. Energetic analysis of the metal-oxide interface shows the stable formation of the interface between the oxide film and metal substrate. The Cu2O(111) film binds to the Cu(111) surface via the unsaturated oxygen atoms bonded to copper metal atoms in top, bridge, and hollow sites. Structural analysis of the Cu2O(111) film surface shows reconstruction with modifications of the distances between the unsaturated and the saturated copper atoms. The surface interlayer relaxation is inward for Cu(111)parallel to Cu2O(111), whereas it is outward for the nonsupported Cu2O(111) oxide and converges to that of bulk oxide with increasing the Cu2O(111) thickness. The electronic work function is not significantly modified with respect to the Cu(111) electronic work function, whatever the oxide thickness. The hydration of the surface is energetically favorable, and water molecular adsorption is favored over dissociative adsorption. Water molecules chemisorb on top over unsaturated copper atoms. The hydroxylation of the surface shows two adsorption modes of the OH groups on top over unsaturated Cu atoms and on a bridge site between unsaturated and saturated Cu atoms.