Theoretical investigation of the effect of graphite interlayer spacing on hydrogen absorption

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