| With the continuous development of society and economy,green,clean,pollution-free and low-loss energy sources have gradually become the focus of worldwide attention.When the world's first energy crisis occurred,the hydrogen economy portrayed the future of hydrogen replacing oil as the main energy source supporting the global economy.The efficient and safe storage and use of hydrogen has become a key research topic.Single-layer twodimensional hexagonal boron nitride(2D h-BN)is very similar to graphene in structure and properties.It is a single-layer two-dimensional nanostructure arranged in a honeycomb lattice.It can be used as a carrier for catalysis and oxidation,Hydrogenation and other reactions.Due to the extremely small size of hydrogen molecules,there will be some interaction with the surface of the two-dimensional material,thereby achieving the effect of hydrogen storage.This topic uses the generalized gradient approximation in density functional theory to approximate the geometric structure,electronic properties,and intrinsic properties of 2D h-BN systems doped with intrinsic 2D h-BN and transition metal atoms(TM = V,Cr,Mn,Fe,Co).The energy band,state density and formation energy can be calculated and studied.On this basis,different amounts of H atoms were adsorbed on the intrinsic 2D h-BN and the doped system surface respectively,and the adsorption energy of the doped system was calculated to obtain the most stable configuration.The specific research contents are as follows:(1)Intrinsic 2D h-BN and its hydrogen storage performanceBased on the density functional theory(DFT)plane wave pseudopotential method,the CASTEP module is used to perform structural optimization and electronic property calculations on 2D h-BN,and perform single atom adsorption on the surface to obtain the most stable adsorption position for boron.Increasing the number of adsorbed hydrogen atoms showed that the adsorption energy gradually decreased.The research results show that when the number of H atoms adsorbed is larger,the adsorption energy is lower and the adsorption system is more stable.When 6 H atoms were adsorbed,the adsorption energy was 2.136 e V,which shows that intrinsic 2D h-BN is a promising two-dimensional nano hydrogen storage material,and the surface can also achieve single-sided high-density hydrogen storage.(2)Electronic structure analysis of 2D h-BN doped with transition atoms Adsorption of single transition atoms(TM = V,Cr,Mn,Fe,Co)on the surface of intrinsic 2D h-BN,the Grimme diffusion correction method in the exchange correlation potential is used in the calculation,and the electron spin is considered,Occupied states are introduced into the h-BN energy gap,resulting in a significant reduction in the energy gap of the system after adsorption,the 3d orbital electrons of the transition atoms will hybridize with the 2p orbital electrons of the N atom,and the hybridization of electrons will also make the system magnetic.The formation energy of Cr atom doping system is the largest,and the formation energy of Co atom doping system is the smallest,which is-0.258 e V and-0.724 e V,respectively.Therefore,when the adsorption density is the same,and different transition atoms are doped,the Co atom doping system is the most stable.(3)Study the adsorption characteristics of the doping system for a single H atom The calculation of the adsorption agglomeration state,electronic structure,electron transfer,and adsorption energy of a single H atom on the surface of 2D h-BN.The layout number,charge density,etc.can be seen that after each single doping system adsorbs a single H atom,an electron cloud intersects between the H atom and the transition atom and generates polarization in the direction.The BN-Fe-1h system and the BN-Co-1h In the system,the bond length between the transition atom and the H atom is relatively reduced,and the adsorption energy is calculated to be relatively lower in the BN-Fe-1h system and the BNFe-1h system,which are-0.53434 e V,-0.50478 e V.The lower the adsorption energy,the more stable the adsorption system.Therefore,the most stable are the BN-Fe-1h system and the BN-Co-1h system.(4)Study the adsorption characteristics of doping system for multiple H atoms The CASTEP software package based on the plane wave pseudopotential method was used to systematically study the stability of the adsorption of multiple H atoms on the surface of five transition atom doping systems.The calculation results show that: compared with the intrinsic 2D h-BN adsorption of multiple H atoms,the adsorption energy of multiple H atoms adsorbed by each doping system generally decreases,and the energy of adsorption of multiple H atoms by the BN-Co system is calculated by the calculation of the adsorption energy It is relatively the lowest and most stable.When 6 H atoms are adsorbed,the adsorption energy is-0.415 e V.Therefore,it is concluded that the most suitable adsorption system when adsorbing multiple H atoms is the BN-Co doping system.This research can provide a research direction for hydrogen storage in two-dimensional materials and provide a theoretical basis for experiments. |
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