Hydrogen Storage Structure Design And Physical Adsorption Performance Study Of Low Dimensional Porous Carbon Materials Naphthylene And Coronene

The environmental pollution and frequent occurrence of extreme weather on account of the excessive use of fossil fuels are becoming more and more serious.Under the background,the hydrogen energy emerges from great deal energy sources with its respective characteristics,and is regarded as the clean energy with the greatest potential in today’s energy structure.In this paper,density functional theory and Monte Carlo method are selected to predict the hydrogen storage capacity of two porous carbon materials,naphthylene and coronene.And we attempt three methods that element doping,light alkali metal modification and superalkali molecular surface adsorption to improve the storage properties which the process and mechanism are deeply explored:（1）Based on the first principles,the optimal adsorption positions of light alkali metal Li and K atoms on the surface of n naphthylene were calculated.The energy indicated that the metal Li and K atoms would not form clusters,and then the naphthylene structure modified stably by four Li atoms at the nine-membered ring and two K atoms at the twelve-membered ring were constructed.By calculating and analyzing the differential charge,it can be found that there is an obvious charge transfer between alkali metal atoms and naphthylene,forming a potential difference,which makes alkali metal atoms stably adsorbed on the surface of naphthalene.Then hydrogen molecules were gradually added to the system until the space was saturated.The adsorption performance of K atom modified naphthalene is poor,the mass ratio is only 4.4wt%.The Li atom-modified naphthalene can adsorb up to 24 hydrogen,the adsorption energy is 0.16 e V,and the mass ratio is as high as11.07 wt%,which meets the application standards of vehicle hydrogen storage materials set by the Department of Energy.（2）Boron-doping can improve the bonding energy between metal atoms and the base material,so as to improve the system’s hydrogen storage capacity.The second work of this article is using Li-decoration after boron-doping to modulate the coronene surface.The calculated data showed that the binding energy between Li atom and coronene increased significantly compared with the original coronene which coincides with the apparent electron transfer around the boron atom.Furthermore,density functional theory and Grand Canonical Monte Carlo method were used to simulate the maximum hydrogen storage performance of boron-doped and Li-modified coronene,and its thermal stability at room temperature was verified by molecular dynamics.（3）The hydrogen storage capacity of coronene modified by the superalkali molecule NLi₄ was calculated.Because of its spatial configuration that the Li atoms repel each other,the NLi₄ molecule maintains the system stability,and can support more sites for the adsorption of hydrogen,which theoretically can greatly improve the hydrogen storage capacity of the material.In this paper,the unilateral and bilateral adsorption behaviors of NLi₄ on the surface of coronene were calculated.The data show that the system can adsorb up to 18 hydrogen molecules,with a mass ratio of 8.64wt%.The results show that NLi₄ modified coronene can be a preferable candidate for hydrogen storage.