Study of H2 physical adsorption in single-walled carbon nanotube array

Abstract

The potential energies of a single H2 inside and outside an armchair single-walled carbon nanotube (SWCNT) are calculated by the electronic density functional theory (DFT), and influences of the SWCNT tube diameter on the potential energy minimum and equilibrium position are studied. Hydrogen storage capacity of the armchair SWCNTs in the rhombic arrays is estimated by using grand canonical Monte Carlo (GCMC) simulations in a pressure range from 10 to 100 bar and at temperatures of 77 K, 150 K, 220 K, 298 K, and 318 K, respectively; influences of the SWCNT diameter and VDW distance on the hydrogen storage capacity, and the isosteric heats of the H2-armchair SWCNTs arrays at several discrete temperatures and pressures are also investigated. The present main discoveries include (i) variation pattern of the H2 adsorption saturation pressure with the tube diameter and temperature; (ii) existence of extremum of the hydrogen storage capacity as a function of the VDW distance and tube diameter; (iii) diametrically opposite change of H2 storage capacity with the tube diameter in different pressure domains; (iv) layered distribution of the H2 adsorbed inside the tube. A theoretical mode is suggested to explain self-consistently all of these discoveries by combining the potential field information with the arguments of liquid state theories, and further verified by snapshots of representative configuration. The present discoveries, particularly, the theoretical mode explaining them, may serve to provide some guidance in improving the hydrogen storage capacity by doping the CNT and optimization of parameters.