Molecular Dynamics Simulations of Hydrogen Adsorption in Finite and Infinite Bundles ofSingle Walled Carbon Nanotubes

Molecular dynamics simulations have been used to systematically study hydrogen storage in single walled carbon nanotubes of various diameters and chiralities using a recently developed curvature-dependent force field. Several fundamental issues related to the effects of nanotube size, chirality and the thickness of nanotube bundles have been examined. A novel methodology for the analysis of effective average adsorption energy and storage capacity was developed. Our simulation results suggest strong dependence of H

2

adsorption energies on the nanotube diameter but less dependence on the chirality. Substantial lattice expansion upon H

2

adsorption was found. The average adsorption energy increases with the lowering of nanotube diameter (higher curvature) and decreases with higher H

2

loading. The calculated H

2

vibrational power spectra and radial distribution functions indicate a strong attractive interaction between H

2

and nanotube walls. The calculated diffusion coefficients are much higher than what has been reported for H

2

in microporous materials such as zeolites, indicating that diffusivity does not present problem for adsorption energy and effective capacity hydrogen storage in carbon nanotubes. We show that adsorption energy and effective storage capacity can be defined in a distance-dependent manner, providing a more comprehensive understanding of adsorption behavior