CO2 Adsorption on Cu2O(111): A DFT+U and DFT-D Study

Adsorption of CO2 on the Cu2O(111) surface is investigated using density functional theory + U with and without dispersion corrections. A number of adsorbate geometries are considered on four different surface terminations that include the bulk-terminated surface and surfaces with oxygen and/or copper vacancies. CO2 is found to adsorb most strongly as a tilted linear molecule coordinated to an unsaturated surface cation. Surface vacancies allow for bent adsorbate configurations to be accessed but they are all less stable than the linear adsorbate. Bader analysis confirms that adsorption of bent CO2 is accompanied by charge transfer from the surface to the molecule, whereas minimal charge transfer occurs in linear physisorption. We show that surface oxygen vacancies have a small impact on adsorption free energies, while surface copper vacancies result in a significant reduction of CO2 adsorption. Including dispersion corrections increases the stability of adsorbed CO2, but adsorption is mostly endoergic at 298.15 K and 1 atm. Our findings reveal that adsorption of CO2 on cuprous oxide is contingent on the presence of copper cations at the surface. Thus, this surface's chemistry is dominated by Lewis acidity, in contrast to other oxide surfaces where oxygen anions may act as Lewis bases to form carbonates. The suppression of carbonate formation is important, as it confirms that this surface may be useful for CO2 reduction to fuels.