A density functional theory study on the adsorption of CO and O ₂ on Cu-terminated Cu ₂O (111) surface

The adsorptions of CO and O ₂ molecules individually on the stoichiometric Cu-terminated Cu ₂O (111) surface are investigated by first-principles calculations on the basis of the density functional theory. The calculated results indicate that the CO molecule preferably coordinates to the Cu ₂ site through its C atom with an adsorption energy of -1.69 eV, whereas the O ₂ molecule is most stably adsorbed in a tilt type with one O atom coordinating to the Cu ₂ site and the other O atom coordinating to the Cu ₁ site, and has an adsorption energy of -1.97 eV. From the analysis of density of states, it is observed that Cu 3d transfers electrons to 2π orbital of the CO molecule and the highest occupied 5σ orbital of the CO molecule transfers electrons to the substrate. The sharp band of Cu 4s is delocalized when compared to that before the CO molecule adsorption, and overlaps substantially with bands of the adsorbed CO molecule. There is a broadening of the 2π orbital of the O ₂ molecule because of its overlapping with the Cu 3d orbital, indicating that strong 3d-2π interactions are involved in the chemisorption of the O ₂ molecule on the surface.