The surface oxidation of a Au@NiO core-shell catalyst is the key to its catalytic activity. In this density functional theory (DFT) study, we explain why the Au core promotes the oxidation of the NiO shell. The Au@NiO catalyst is represented by a slab model in which NiO(001) layers are placed on Au(001) substrates (NiO/Au). Ni vacancy and oxygen adsorption are examined as the surface oxidized state. Spin density analysis, as well as differential charge density analysis, shows that the oxidation of NiO/Au depletes the electrons in the Au—O antibonding orbitals at the interface, instead of creating holes in NiO. Thus, the highly-oxidized state of the NiO shell is stabilized by its interaction with the Au core.
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