Hydrogen Adsorption Of Graphene Based On Grand Canonical Monte Carlo Statistical Method

In recent years,the surging consumption of fossil fuels and other non-renewable energy sources has not only caused human energy crisis,but also led to a more serious ecological disaster.Therefore,more and more attention is paid to the development and research of clean and renewable energy,such as hydrogen energy.Hydrogen storage is the focus of this topic,which is the key link from hydrogen energy preparation to hydrogen energy application.Therefore,it is of great significance to find suitable hydrogen storage technology and materials to improve hydrogen storage capacity and availability for reducing hydrogen transportation cost and promoting the range of hydrogen energy use.From the perspective of combining statistics and physics,this thesis applied the Grand Canonical Monte Carlo method combined with first principles and other related theories to study the hydrogen storage properties of pha-graphene and C68-graphyne materials.The main research contents are as follows:(1)Based on the statistical method,the appropriate molecular force field was found and the exact force field parameters were calculated for the selected materials.Through the Grand canonical Monte Carlo simulation,the mass density of hydrogen storage pha-graphene was studied under different metal densities,temperature and pressure.The results show that the optimal adsorption location of lithium atoms is above the center of the seven-membered ring of the pha-graphene structure,whose binding energy is greater than the cohesive energy of lithium atoms(1.63 e V),and lithium metal atoms are dispersed on both sides of the pha-graphene material structure without forming metal clusters.In order to more accurately study the hydrogen storage performance of the lithium modified pha-graphene material structure,based on the first principles,the force field parameters of hydrogen molecules at different positions on the surface of the lithium modified pha-graphene material were fitted,and the giant canonical Monte Carlo statistical method was used to simulate the hydrogen adsorption.The research found that,Under the conditions of 77 K and 100 bar,the maximum hydrogen storage mass ratio of 4Li modified pha-graphene was 15.88wt%,and the effects of different metal adsorption densities on hydrogen storage properties were considered.Finally,the stability of the structure was proved by molecular dynamics simulation.(2)The hydrogen storage mass density of lithium metal modified C68-graphyne with and without boron doping was investigated by Grand Canonical Monte Carlo simulations at different temperatures and pressures varying from 0 to 100 bar.To accurately investigate the hydrogen storage properties of C68-graphyne with and without boron doping,the force field parameters of hydrogen molecules at different locations on the surface of lithium-modified C68-graphyne with and without boron doping were fitted separately based on the first-nature principle,and the fitted results showed that the fitted curves were in full agreement with the DFT calculations.Using the modified force field to perform GCMC simulations,the study shows that the resultant hydrogen storage performance of C68-graphyne with boron doping is higher at different temperatures,further validating the boron doping modification means to improve the hydrogen storage capacity of the 2D material.(3)The hydrogen storage performance of 68-graphyne was studied based on density functional theory.The results showed that 3Li modified 68-graphyne could adsorb 12 hydrogen molecules,and its maximum hydrogen storage mass ratio reached 7.26 wt %,and the average adsorption energy of each hydrogen molecule was 0.16 e V.In summary(2)and(3),the mass ratio of hydrogen storage obtained by the Grand Canonical Monte Carlo statistical method is in strict match with the results obtained from the first-principles calculation,and meets the 2025 hydrogen energy application standards of the United States Department of Energy.At the same time,the thermal stability of Limodified C68-graphyne structure was verified based on ab initio molecular dynamics,indicating that C68-graphyne material is expected to be a candidate for hydrogen storage materials.