Thermodynamic, electronic and structural properties of Cu/CeO $_2$2 surfaces and interfaces from first-principles DFT+U calculations

Abstract

The thermodynamic, structural and electronic properties of Cu-CeO(2) (ceria) surfaces and interfaces are investigated by means of density functional theory (DFT+U) calculations. We focus on model systems consisting of Cu atoms (i) supported by stoichiometric and reduced CeO(2) (111) surfaces, (ii) dispersed as substitutional solid solution at the same surface, as well as on (iii) the extended Cu(111)/CeO(2)(111) interface. Extensive charge reorganization at the metal-oxide contact is predicted for ceria-supported Cu adatoms and nanoparticles, leading to Cu oxidation, ceria reduction, and interfacial Ce(3+) ions. The calculated thermodynamics predict that Cu adatoms on stoichiometric surfaces are more stable than on O vacancies of reduced surfaces at all temperatures and pressures relevant for catalytic applications, even in extremely reducing chemical environments. This suggests that supported Cu nanoparticles do not nucleate at surface O vacancies of the oxide, at variance with many other metal/ceria systems. In oxidizing conditions, the solid solutions are shown to be more stable than the supported systems. Substitutional Cu ions form characteristic CuO(4) units. These promote an easy and reversible O release without the reduction of Ce ions. The study of the extended CeO(2)(111)/Cu(111) interface predicts the full reduction of the interfacial ceria trilayer. Cu nanoparticles supported by ceria are proposed to lie above a subsurface layer of Ce(3+) ions that extends up to the perimeter of the metal-oxide interface.

Distinct Physicochemical Properties of the First Ceria Monolayer on Cu(111)

“…The interface between the stoichiometric thin ceria film and a copper surface displays a charge transfer from the metal to the oxide, yielding electron localization and reduction of all the interfacial Ce ions to Ce 3+ . This interfacial effect, observed also in the case of thicker ceria films, 42 is clearly displayed by the spin polarization of the cerium atoms (see spin density in Figure 4) and by the charge population analysis of the Cu atoms reported in Table 3. Creating an oxygen vacancy in the bulk or at surfaces of ceria is usually accompanied by the localization of two excess electrons at two Ce 4+ ions, leading to their reduction to Ce 3+ .…”

Energetics of Cu Adsorption and Adhesion onto Reduced CeO2(111) Surfaces by Calorimetry

“…37,38 There are more vacancies where this can occur on the more reduced CeO 1.8 (111) surface. On the CeO 1.95 (111), this still occurs at step edges only, but the opposite effect occurs to a greater extent at the stoichiometric sites on both steps and terraces.…”

Interface-level thermodynamic stability diagram for in situ internal oxidation of Ag(SnO2)p composites

“…To face such challenges, first-principles based calculations have emerged as an indispensable tool for interface analyses in recent years. Specific application examples include Ni/Al 2 O 3 [5][6][7][8][9][10], Cu/Al 2 O 3 [10][11][12][13], Ag/ Al 2 O 3 [14,15], Ag/MgO [16], Ag/ZnO [17], and Cu/CeO 2 [18].…”