Simulation Studies on Hydrogen Sorption and Its Thermodynamics in Covalently Linked Carbon Nanotube Scaffold

Carbon nanotubes are potential hydrogen storage materials because of their large surface area and high sorbate-surface interaction energy due to the curvature effect. However, single walled carbon nanotubes bundle up tightly, so most of their surface areas become inaccessible for adsorption. As a solution, spacer molecules can be used to hold the tubes at a distance from each other in a scaffolded structure. Here, using grand canonical Monte Carlo simulation, we show that scaffolds can achieve high sorption capacity. We analyze the sorption capacity of (6, 6), (9, 9), (12, 12), (15, 15), (18, 18), and (21, 0) tube scaffolds with linker distances along the c-axis ranging from 8.14 to 24.4 angstrom, as a function of tube diameter and spacer density, for various temperatures and pressures. In order to explore additional avenues to further improve the sorption capacity, we studied surface functionalized and Li+ ion decorated nanotube scaffolds. We also report the thermodynamics of sorption based on isosteric heat.