Atomistic modelling of hydrogen storage on monolayer polycrystalline graphene

Abstract

Hydrogen as a fuel is a good replacement for fossil fuel. The main problem lies in the efficient and safe storage system for hydrogen, various studies have been performed to unravel the potential of carbon-based material for hydrogen storage. In our study, the adsorption of molecular hydrogen on a monolayer pristine and polycrystalline graphene is studied using molecular dynamic simulation (MDS). Peripheral density profile and potential energy distribution (PED) are observed to calculate the gravimetric density. The Lennard-Jones (LJ) potential describes the interaction between graphene and hydrogen molecules, and interatomic interactions of the graphene sheets are modeled using Tersoff potentials. The effect of pressure and temperature was observed on the adsorption energy and gravimetric density for hydrogen storage. The effect of grain boundaries in graphene sheet on hydrogen adsorption capacity was evaluated. The adsorption capacity was calculated at various temperatures and pressure for pristine as well as polycrystalline graphene using two different approaches. At a pressure of 2MPa and temperature 77K the weight percent of hydrogen adsorption was found to be 5.54 % for pristine and 5.984% for polycrystalline graphene using Potential energy approach and 6.452% for pristine graphene and 7.093 % for polycrystalline graphene using Peripheral density profile approach. The results obtained revealed that graphene is a promising member for hydrogen storage and the modification in graphene such as graphene containing grain boundary enhances the adsorption capacity. The polycrystalline graphene was found to have 8-10% more gravimetric hydrogen adsorption capacity. The Specific surface area (SSA) of graphene with different dopants was calculated and it was observed that with doping of metals the SSA value increases.