Storage of hydrogen in single-walled carbon nanotube bundles with optimized parameters: Effect of external surfaces

We theoretically predict that the discharging gravimetric storage capacity of hydrogen in a diamond-shaped bundle of single-walled carbon nanotubes (SWNTs) with optimized parameters reaches 2.5 wt% at temperature T=300K and pressure p=12.1MPa, where the discharge pressure is set to 0.1 MPa. The external surfaces of SWNTs under the optimized parameters play an important role on hydrogen storage. It leads to an improvement of around four times in hydrogen uptake, compared to that without optimized parameters. Indeed, the exohedral capacity caused by the external surface is twofold larger than the endohedral capacity. Moreover, we find that gravimetric and volumetric capacities of hydrogen in the diamond-shaped bundle of SWNTs at T=105K and p=13.2MPa achieve 7.4 wt% and 62.2kg/m3, respectively. Both of them exceed the targets of 6.5 wt% and 62kg/m3, issued by department of energy (DOE, USA) for hydrogen fuel cell powered vehicles.