Strain and support effects on phase transition and surface reactivity of ultrathin ZnO films: DFT insights

Strain and support effects play a crucial role in heterogeneous catalysis, which has been intensively studied over metal-based catalysts. In contrast, there is little discussion about the two effects in oxide systems. In this work, using an ultrathin ZnO film as an example, we investigate strain and support effects on the structure and surface reactivity of oxide catalysts through density functional theory calculations. Our results suggest that tensile strain increases the surface reactivity of ZnO films as indicated by enhanced CO and NH3 adsorptions and compressive strain renders an early phase transition from an inert graphene-like phase to a more reactive wurtzite-like phase. The support (Au, Pt, and Ru) can promote the phase transition and surface reactivity concurrently, which exhibits a larger effect on the reactivity than the strain. The support effect can be ascribed to the increasing rumple and polarization of ZnO films through the strong ZnO–substrate interaction, which enhances the surface reactivity. The insight helps us to develop advanced oxide-based catalysts through the strain and/or substrate engineering.