Ab initio thermodynamic investigation of monolayer stability of multicomponent metal oxides: M_xO_y/ZnO(0001) and M_xO_y/TiO₂(110) (M = Pd, Ru, Ni, Pt, Au, Zn)

Multicomponent metal oxide catalysts can offer a tunable redox capacity and chemical reactivity. These materials are used in fuel cells, in gas sensors, and as heterogeneous catalysts. The large number of possible combinations of different mixed-metal oxides and their metastability make the experimental discovery of such systems very inefficient. Herein, we develop an ab initio thermodynamic framework using density functional theory to accelerate this discovery process by predicting stable monolayer metal oxides that can be subjected to further computational study or experimental investigation. As an example of the application of this framework, we present our stability analysis of ZnO(0001)-Zn terminated and rutile TiO₂(110) surfaces with epitaxial M_xO_y (M = Pd, Ru, Ni, Pt, Au, Zn) monolayers. Metastability is predicted relative to segregated particle structures of varying radii. We predict that NiO can form a metastable monolayer with the same stoichiometry as the support, ZnO(0001). A PdO and RuO₂ monolayer on ZnO(0001) are potentially stable. A monolayer of RuO₂ on TiO₂(110) is stable relative to segregated RuO₂ particles of 2 nm radius or less. However, RuO₂ shows a high preference for growing as 2D multilayer islands. Predicted stable monolayers are also found stable against subsurface segregation in the host oxide.