Molecular dynamics study on the enhancement in hydrogen storage capacity for different types of graphynes through a modification by a joint Na (sodium)-decoration and B (boron)-doping technique

Graphynes are potential hydrogen storage materials due to their unique acetylene bond structure (C-C equivalent to C-C), and can be classified into alpha-GY, beta-GY, gamma-GY, sigma-GY, GDY, etc., according to the proportion of their involved acetylene bonds. To enhance their hydrogen storage capacities, four typical graphynes (alpha-GY, beta-GY, delta-GY, and GDY) were modified by a joint Na-decoration and B-doping technique in this research, and the hydrogen adsorption processes of these modified graphynes were investigated by molecular dynamics simulation to clarify the effects of the structure modification on their hydrogen storage capacities. The results showed that the hydrogen storage capacities of the modified graphynes are larger than those of non-modified graphynes, and that the joint Na-decorated and B-doped alpha-GY obtains the largest hydrogen storage capacity of 9.41 wt%. The mechanism of the enhancement of hydrogen storage by the joint Na-decoration and B-doping was found to be that the Na-decoration and B-doping strengthen the adsorption energy between acetylene bonds and hydrogen atoms. Since the modified alpha-GY has satisfactory hydrogen storage capacity, far exceeding the target set by the U.S. Department of Energy (DOE) in 2020 for portable hydrogen storage system, it can be expected to be a potential hydrogen storage material in the future.