Theoretical Study On Two-dimensional Topological Materials And Its Catalytic Activities

With the successful stripping of graphene,two-dimensional(2D)materials have gradually been a research hotspot in the fields of material science and condensed matter physics.Compared to three-dimensional materials,2D materials have the lower dimension,which brings in novel physical properties,and has important application in reducing the size of electronic components and integrated circuits.Graphene is a hexagonal honeycomb structure composed of carbon atoms,whose electronic structure near the Fermi energy has a linear energymomentum dispersion relationship which is called Dirac cone.Due to the existence of the Dirac cone in the electronic structure,graphene has many excellent properties,such as high carrier mobility,giant magnetoresistance,and so on.Up to now,a large number of 2D Dirac materials have been predicted theoretically or discovered experimentally.In addition,Weyl semimetals and DNL semimetals have similar electronic structure,which are collectively referred to as topological semimetals.As another topological materials,topological insulators have different characteristics and physical properties from topological semimetals.The novel physical properties,such as the quantum spin Hall effect and the quantum anomalous Hall effect,occurring on the topological insulators are closely related to the topological band gap at the Fermi energy,in which the lossless conduction of electrons on the boundary makes them valuable for the applications in high-speed and low-power electronic devices.With the continuous discovery of topological materials,the application fields of topological materials have gradually expanded.In recent years,topological catalysis emerges as a hot topic.The research of catalysts focuses on solving the problems of energy shortage and environmental pollution.Traditional catalysts have evolved many designing methods such as nanometerization,alloying,dimensionality reduction,and monatomization based on the geometry and non-topological electronic structure of materials.Topological catalysis,on the other hand,takes a new approach by using the boundary states of topological insulators that conduct high speed electrons as electron pools,which play an important role in regulating the adsorption energy of molecules through the gain and loss of electrons,thereby designing topological catalysts with high catalytic performance.Based on the first principle calculation,combining with tight-binding models,in this thesis,we theoretically predicts 2D CxNyOz materials with topological semimetallic properties,and regulates quantum anomalous Hall states through doping magnetic atoms,adding new members to the topological material family.In addition,we take 2D magnetic topological insulator FeS as an example,to reveal the role of topological electronic states in improving the catalytic performance of oxygen evolution reaction(OER),which broaden the application field of topological materials,providing a new idea for the design of new catalysts.The main research contents and results are as follows:(1)Based on the first-principle calculations,we theoretically predict three GNMs materials with topological semimetallic properties(C10N3,C9N4,and C10O3),enriching the topological semimetallic family,and providing an idea for continuing to search for two-dimensional topological semimetallic materials.These three GNMs materials are composed of honeycomb lattice and kagome lattice.The coupling between the two lattices contributes to the topological semimetals.Combined with the tight-binding model,the rationality of this conclusion is verified,by using a Hamiltonian of the two sub-lattices,which are Honeycomb lattice and Kagome lattice.In addition,the doping of the magnetic atom Re regulates the quantum anomalous Hall state at the Fermi energy and 0.78 eV below the Fermi energy in the C10N3,which enriches the topological properties of the CxNyOz material family.(2)This thesis focuses on the catalytic performance of topological materials and finds that two-dimensional magnetic topological insulator FeS has an excellent OER catalytic performance.Based on the first-principles calculations,selecting iron atoms located on the boundary as the catalytic sites,we predict an extremely low overpotential of 0.42 eV,which is superior to most non-noble metal catalytic materials.Considering that FeS belongs to a strongly correlated system,the spin-orbit coupling effect is expected to be closely related to the magnitude of the U value.The larger the U value,the stronger the spin orbit coupling effect,and the more prominent the topological properties.By changing the U value of iron,it is found that the catalytic performance of FeS is directly proportional to the U value,further indicating that topological boundary states play a positive role in improving the catalytic performance of OER.These theoretical results are expected to open up the application fields of topological materials and provide new ideas for the design of efficient catalysts.