Multi-scale Simulation Study On Hydrogen Storage Performance Of Three Graphyne Materials

With the acceleration of industrialization,the consumption of fossil fuels has also accelerated dramatically.Energy shortages and environmental pollution are becoming more and more serious.The development of clean and pollution-free new energy has become the general trend.Hydrogen is a renewable and clean energy with high combustion calorific value,which has received wide attention from all walks of life.Finding a suitable carrier material for hydrogen storage is a major problem facing this field.In recent years,the use of porous nanomaterials for hydrogen storage has attracted more and more attention from researchers.Among them,graphyne is a new type of two-dimensional carbon-based material with excellent characteristics of traditional non-metallic two-dimensional materials,such as large specific surface area Features such as light weight.At the same time,compared with graphene,the hydrogen storage capacity of graphyne is more prominent.In this paper,through the combination of first-principles and Monte Carlo simulation,the hydrogen storage processes and principles of three graphene materials:H_4,4,4-graphyne,T_4,4,4-graphyne,and Triphenylene-graphdiyne are thoroughly explored.The main work in the paper is as follows:?1?The study found that the best adsorption site of Na atoms on the surface of H_4,4,4-graphyne is located above the center of the alkyne ring,and finally the H_4,4,4-graphyne structure was modified by 4 Na atoms to apply to hydrogen storage,the average binding energy of Na atom is greater than its own cohesive energy,indicating that it can be adsorbed on the surface of the material without agglomeration.Through charge density difference analysis,it can be seen that a charge transfer occurs between the metal Na and H_4,4,4-graphyne,thereby forming a local electrostatic field,so that the metal Na can be distributed discretely on the surface of the material.Then,based on the first-principle principle,hydrogen molecules are added one by one until saturation,and the calculated molecular hydrogen binding energy is 0.17 e V/H₂,and the mass ratio is 9.59 wt%.At the same time,based on the giant regular Monte Carlo simulation?GCMC?,hydrogen storage simulations at different temperatures and pressures were performed,and the mass ratio of hydrogen storage was 16.97 wt%?77K,100bar?.The hydrogen storage trends studied by the two methods are consistent,and hydrogen molecules have obvious delamination on the surface of the material.?2?In order to obtain a high hydrogen storage capacity,the hydrogen storage performance of Li and Na co-decorated T_4,4,4-graphyne was studied by first-principles calculations.The adsorption positions and order of metal atoms and H₂molecules were analyzed in detail.In the hydrogen adsorption structure,Li atoms and Na atoms are located on both sides of the hexagonal rings and acetylenic rings contained in T_4,4,4-graphyne.It can be seen that the electric field caused by charge transfer enhances the storage of hydrogen through the difference in charge density.In addition,molecular dynamics simulations have proven that the hydrogen storage structure is thermodynamically stable at room temperature.At the same time,we also verified the hydrogen storage capacity of the material through GCMC.Our results show that Li and Na co-decorated T_4,4,4-graphyne is a promising practical hydrogen storage material.?3?B atom modification can significantly improve adsorption of metal atoms,thereby enhancing the structure's hydrogen storage capacity.Therefore,based on the triphenylene-graphdiyne?Tp G?material,we modified the surface of the original Tp G and B atom-doped Tp G structures with Li and Ca atoms,respectively.In addition to the Ca-modified original Tp G structure,the other three structures have good storage Hydrogen potential.B atom modification can significantly improve the structure's adsorption of metal atoms,thereby enhancing the structure's hydrogen storage capacity.