Size-Dependent Atomic and Electronic Structures of Small-Sized Nin (n=2-10) Clusters Supported on the Anatase TiO2(101) Surface: A Density Functional Theory Study

The atomic and electronic structures of small-sized Nin (n = 2-10) clusters supported on the anatase TiO2(101) surface [denoted as A(101)] are systematically investigated by an extensive evolutionary structural search and density functional theory calculations. The predicted low-energy structures show that 3D geometries are more favored for most supported Nin clusters. Thermodynamic stability analysis indicates that the cluster-substrate interaction plays a critical role in stabilizing the Nin/A(101) system. Ni4/A(101), Ni6/A(101), and Ni8/A(101) are more stable compared to their neighbors and may be easily formed experimentally. Electrons transfer from the supported Nin clusters to the TiO2 substrate and mostly accumulate at the Ti5c sites just below the Nin cluster. These extra electrons may easily transfer to other surface sites, enhancing the reactivity of the TiO2 surface, and can also transfer back to the Nin cluster, providing additional active sites besides the metallic Ni atoms. Moreover, the introduction of Nin clusters can enhance the visible light response of the system. The results of this work indicate that Nin/TiO2 systems are promising high-performance photocatalysts or electrocatalysts for efficient N2 reduction reactions and NH3 synthesis.