Abstract
This study investigates the absorption of hydrogen molecules between graphite layers
using both first principles calculations and classical grand canonical Monte Carlo
simulations. While a recent theoretical study showed that graphite layers have high
storage capacity at room temperature, previous simulation results on hydrogen-graphite
systems showed otherwise. Our first-principles calculations suggest that it is possible to
store hydrogen molecules between the graphene layers if the energetically unfavorable
initial absorption stage could be overcome. The barrier to the initial absorption originates
from the large lattice strain required for H2 absorption: small amounts of initial
absorption cause an interlayer expansion of more than 60%. To determine if significant
storage is indeed possible at finite temperature (and pressure), we performed grand
canonical Monte Carlo H2-absorption simulations with variable graphite interlayer
spacing. Using two different potentials for the H2-C interaction, we found low H2 mass
uptake at room temperature and moderate pressures (e.g., close to 2 wt-% at 298 K and 5
2
MPa.). Our results suggest that a graphite pore width or interlayer spacing around 6 �
has the optimum absorption capacity.
PACS numbers: 68.43.-h, 81.05.Uw, 82.20.Wt, 83.10.-y