Theoretical Study Of Electron Spin-polarization And Catalytic Characteristics In Two-dimensional Nickel-based Materials

In 2004,Geim,Novoselov,and others first obtained atomically thin single-crystal carbon films,known as graphene,through mechanical exfoliation,and explored its extraordinary transport properties,leading to the revival of two-dimensional（2D）materials and opening a new era for the exploration of their novel properties.Geometrically,2D materials have a sheet-like shape with a thickness of a single or a few atomic layers and a lateral dimension ranging from hundreds of nanometers to tens of micrometers.Therefore,the unique structural features of 2D materials endow them with various unconventional physical,chemical,optical,electronic,and magnetic properties different from those of bulk,zero-dimensional,and one-dimensional materials.Research has shown that 2D materials have been demonstrated to be one of the most promising candidate materials among numerous potential applications,such as electronics,optoelectronics,catalysis,energy storage,solar cells,biomedical,sensors,and environment,and their number is increasing year by year.Introducing electron spin polarization into 2D materials is an important research hotspot for exploring multifunctional effects of new functional materials.Compared with 2D inorganic materials,2D organic nanomaterials are not only easy to synthesize but also easy to process on a large area.More importantly,the multifunctional materials（devices）based on 2D organic nanomaterials have good flexibility,excellent mechanical properties,and rich electrical,magnetic,optical,and catalytic properties.In addition,the functional materials（devices）based on electron spin can significantly improve the processing speed and storage density of information,as well as the charge transfer and dissolution ability of catalytic reactions,and have advantages such as non-volatility and low energy consumption.Therefore,to meet the specific performance requirements of multifunctional nanomaterials（devices）,it is particularly important to regulate the electron spin polarization of nanomaterials.In this paper,two-dimensional organic nickel metal-organic frameworks and inorganic nickel compounds are studied using quantum mechanical first-principles calculation methods to systematically simulate the topological electronic states related to spin-orbit coupling and electron spin polarization based on d orbitals in the materials.The main research results include the following aspects:1)Theoretical proofThe Ni₂（TCNQ）₂lattice is the first lattice to realize multi-spin polarized Dirac materials in a 2D Cairo pentagonal lattice.Studies have shown that the Ni₂（TCNQ）₂ lattice has a linear spin-polarized ground state,with magnetic moments arranged in a ferromagnetic manner,and a Curie temperature as high as 127 K.In addition,stress can manipulate the cone bands near the Fermi level,exhibiting quadruple-degenerate electronic states at a critical tensile strain of about 2.35%,with energy dispersion consistent with the 2D Cairo pentagonal lattice.Spin-orbit coupling can induce a bandgap at the A cone,making the crystal exhibit topologically nontrivial electronic states with a nonzero Chern number and nanoscale boundary states.These research results expand the scope of research on 2D Dirac materials and topological lattices,providing a theoretical basis for the realization of fully spin-polarized and massless spintronics in the 2D Cairo pentagonal Ni₂（TCNQ）₂ crystal.2)Research shows that revealing the precise physical mechanisms of the interaction between adsorbate components and reaction sites in multiphase catalysis is crucial for predicting and designing efficient catalysts.The unique geometric configurations and magnetic properties of the metal-organic framework composed of the organic ligand tetracyanoquinodimethane（TCNQ）and 3d transition metal elements（Cr,Mn,Fe,Co,and Ni）largely promote its hydrogen evolution reaction.Regulated by the electronegativity of its transition metal,the most stable adsorption position of the metal-organic framework shifts from C1 to C2.For the single-molecule magnet（Cr-Fe）,the Gibbs free energy of the metal adsorption site is controlled by the charge and magnetic moment changes of neighboring metal atoms,which show a linear relationship.For non-single-molecule magnets（Co,Ni）,their optimal active site is located at C3 due to the influence of charge transfer.These research results provide new ideas and insights for exploring the role of spin selection in chemical reactions.3)Research indicates.Through the study of the electronic properties,stability,and magnetic changes of the new inorganic nickel compound NiClO monolayer,we found that the band structure of NiClO monolayer has Dirac points with both spin up and spin down,indicating its potential research value.By applying external strain to the NiClO monolayer,we discovered a magnetic phase transition from a ferromagnetic state to an antiferromagnetic state at a strain coefficient of around 18%.Additionally,both high and low wrinkled states of NiClO exhibit negative Poisson’s ratio,indicating predictable excellent performance.These research findings provide a theoretical basis for the laboratory preparation of NiClO monolayer.In summary,a deep investigation of the spin polarization and catalytic properties of nickel-based organic and inorganic 2D materials has provided theoretical support for their applications in spintronics and catalysis,and target materials for designing multifunctional nanodevices.Additionally,this paper explores the experimental exfoliation and preparation processes of novel 2D materials,providing design ideas and theoretical foundations for subsequent experimental synthesis and device fabrication.The aim is to guide experimental progress through theoretical predictions and adjust theoretical design ideas based on experimental advances.