Research On Hydrogen Storage Performance Of Li-doped γ-Graphdiyne Based On First Principles

Hydrogen energy,has become one of the most promising sustainable energy sources to replace fossil fuels in the 21st century.However,the storage of hydrogen energy is the key to the development of hydrogen energy,so it is very important to explore high density storage materials.γ-Graphdiyne has excellent ion shuttle performance,which makes it have broad application prospects in energy storage and gas adsorption fields.However,due to the limitations of the current preparation process,the actual preparation of γ-graphdiyne inevitably has various defects,which influence the gas adsorption properties.In this paper,the intrinsic and vacancy defects of γ-graphdiyne and its Li doping of hydrogen adsorption process as the research object,with the hydrogen storage density as the key index,using first-principles calculation method to study the hydrogen storage performance of γgraphdiyne.This provides the necessary theoretical basis for the application and performance potimization.The main research contents of this paper are as follows:1.The models of γ-GDY at different highly symmetric sites(B1,B2,B3,B4,H1,H2,T1,T2 and T3)were established,and the adsorption characteristics were calculated by CASTEP software.The results show that the optimal site is located at H2.At this site,the adsorption energy is-0.0786eV,and the lowest adsorption height is 2.816(?).The adsorption process ofγ-GDY with different concentrations of hydrogen molecules was analyzed.The results showed that the band structure did not change significantly,and there was no obvious impurity energy level.The adsorption process was simple physical adsorption.The maximum mass hydrogen storage density of the H4NC96 system is 7.69%,and the volume hydrogen storage density is 2.24×104kg/m3.The storage performance of it only reaches the target set by the U.S.Department of Energy in 2015.2.The model of Lix-GDY was established,and the hydrogen storage performance of Li at different γ-GDY doping sites(T1,T2,T3,H1,H2 and A)was studied.The calculation results show that the optimal site is H2,where the adsorption energy is-2.657eV and the adsorption height is 0.084(?).When the Lix-GDY system is doped with Li of different concentrations,the soft agglomeration of the Li3-GDY system occurs.The adsorption energy of the Li2GDY system is higher,the adsorption height is reasonable,and the doping performance is the best.The hydrogen storage performance of Li2-GDY at different hydrogen molecular concentration was analyzed.The adsorption energy is-0.2264eV at a steady-state,which meets the requirement of hydrogen storage.At this time,the mass and volume hydrogen storage density of Li2H56-CDY system are 13.02%and 5.22×104kg/m3.3.The model of γ-VGDY adsorption on hydrogen molecules with different concentrations was established to analyze the hydrogen storage performance of the defective materials.The results show that the adsorption process is an endothermic reaction when 1-3 hydrogen molecules are adsorbed,and there is no charge exchange between atoms.The adsorption process is an exothermic reaction when 4-7 hydrogen molecules are adsorbed,and the charge transfer occurs.When γ-VGDY adsorbed 6 molecules,the adsorption energy is-0.1679eV,and the average adsorption energy is-0.1305eV.The adsorption energy and average adsorption energy are both the largest,and the system adsorption effect is the best.4.The Lix-VGDY models of Li-doped vacancy defect γ-VGDY were established to analyze the effect of doping concentration on hydrogen storage performance.The results show that with the increase of Li doping concentration,the steady-state energy and adsorption energy decrease,and the adsorption height increases.There is no agglomeration phenomenon during doping.The performance of γ-VGDY doped Li is better than the γ-GDY.The model Li2H2NVGDY under different hydrogen concentrations was analyzed to study its hydrogen storage performance.The results show that the adsorption effect is better when 28 hydrogen molecules are stored.At this time,the intermolecular force is acted by Van Der Waals force and chemical bond.The hydrogen storage adsorption effect is stronger than the γ-GDY.The maximum hydrogen storage capacity model Li2H56-VCDY has steady-state adsorption energy of-0.2088eV.The mass hydrogen storage density and volume hydrogen storage density are 14.66%and 5.22×104kg/m3.Therefore,the Li-VGDY system can significantly improve the hydrogen storage performance of γ-GDY materials.