Trends in Adhesion Energies of Gold on MgO(100), Rutile TiO2(110), and CeO2(111) Surfaces: A Comparative DFT Study

The adhesion of gold on three oxide surfaces (magnesia, titania, and ceria) is studied by means of dispersion-corrected DFT+U calculations, considering in a systematic approach an isolated Au atom, Au-20 clusters, and periodic extended interfaces to model large nanoparticles. The results show that for a Au-1 monomer the adhesion energy on the three oxides is similar: 0.83 eV (TiO2), 0.99 eV (CeO2), and 1.09 eV (MgO). The picture is more complex for nanoclusters and extended interfaces, where morphological factors largely determine the binding capability of these oxides toward Au. For Au-20, the adhesion on rutile TiO2 is smaller and dominated by long-range dispersion contributions, while the better match between Au atoms and surface oxygen anions leads to a larger binding on magnesia and ceria. Overall, a CeO2 > MgO > TiO2 trend is observed. For the extended interfaces, the trend is CeO2 approximate to MgO > TiO2. Notice that the adhesion energies of a 20-atom cluster are 2-3 times larger than those of the extended interfaces because of (a) the structural flexibility of nanoclusters and (b) the presence of several undercoordinated Au atoms at the cluster border in contact with the oxide surface. While for monomers dispersion contributions are of the order of 20% of the total adsorption energy, for clusters and nanoparticles they represent an important and sometimes dominant contribution to the adhesion energy. The picture is radically altered if the oxide supports are not perfectly stoichiometric. The presence of oxygen vacancies enhances the gold adhesion energy, an effect that may render a direct comparison of DFT results with experimental estimates of adhesion energies more complex due to the difficulty to fully control defects concentration at the oxide surfaces