We present systematic molecular dynamics simulation studies of hydrogen storage in single walled carbon nanotubes of various diameters and chiralities using a recently developed curvature-dependent force field. Our main objective is to address the following fundamental issues: 1. For a given H 2 loading and nanotube type, what is the H 2 distribution in the nanotube bundle? 2. For a given nanotube type, what is the maximal loading (H 2 coverage)? 3. What is the diameter range and chirality for which H 2 adsorption is most energetically favorable? 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 a problem for hydrogen storage in carbon nanotubes.

Using calculations from first principles, we found that water can dissociate over defective sites in graphene or nanotubes following many possible reaction pathways, some of which have activation barriers lower than half the value for the dissociation of bulk water. This reduction is caused by spin selection rules that allow the system to remain on the same spin surface throughout the reaction.

A general force field methodology is developed for description of molecular interactions in carbon-based materials. The method makes use of existing parameters of potential functions developed for sp(2) and sp(3) carbons and allows accurate representation of molecular forces in curved carbon environment. The potential parameters are explicitly curvature and site dependent. The proposed force field approach was used in molecular dynamics (MD) simulations for hydrogen adsorption in single-walled carbon nanotubes (SWNTs). The results reveal significant nanotube deformations and the calculated energies of adsorption are comparable to the reported experimental heat of adsorption for H2 in SWNTs.