Hydrogen storage in Na-decorated H4,4,4-graphyne: A density functional theory and Monte Carlo study

To find appropriate hydrogen storage materials, Na-decorated H4,4,4-graphyne has been investigated by combing a density functional theory (DFT) and grand canonical Monte Carlo simulations (GCMC). From DFT, we find that the most priority adsorption site for Na atom is the acetylenic ring center of the H4,4,4-graphyne. The Na atoms are adsorbed on two sides of the acetylenic ring named 4Na-decorated H4,4,4-graphyne, with the average binding energy of 2.33 eV. With H2 molecules are introduced into the surface of 4Na-decorated H4,4,4-graphyne continuously, it is found that up to 9 H2 molecules are adsorbed around each Na atom and the adsorbed H2 molecules are split into two layers with the average hydrogen adsorption energy of 0.12 eV/H2, corresponding to a huge gravimetric density of 16.03 wt%. From GCMC simulations, the gravimetric H2 uptake of Na-decorated H4,4,4-graphyne reaches to the maximum value of 16.97 wt% at 77 K and 100 bar which echoes the results attained by DFT. So, our findings suggest that the Na-decorated H4,4,4-graphyne can be a high-capacity hydrogen storage medium.