Adsorption and desorption behavior of titanium-decorated polycrystalline graphene toward hydrogen storage: a molecular dynamics study

Abstract

The hydrogen adsorption and desorption capacity of polycrystalline graphene sheets (PGs) with and without titanium (Ti) decoration is investigated using molecular dynamics simulations. Interatomic interactions of PGs are modeled using Tersoff potential, and the remainder of interactions are calculated via Lennard‒Jones potential. The effect of grain size and Ti concentration on the mechanical properties and hydrogen adsorption capacity of PGs is studied. The presence of grain boundaries in PGs reduces their mechanical properties, while the decoration of Ti adatoms does not significantly alter the mechanical properties of PGs. PGs showed a ~ 57% increase in the gravimetric density of H2 at 300 K and 50 bar compared to the pristine graphene sheet. At 100 bar pressure, PGs with 1% Ti concentration achieved a gravimetric density of 9.9 wt.% and 3.2 wt.% at 77 and 300 K, respectively. In Ti-decorated PGs, the desorption curve follows the same path at 300 K as the adsorption curve with increasing Ti concentration, and the desorption curve diverges from the adsorption curve after 1.5% Ti concentration at 77 K. The potential use of the isosteric enthalpy of adsorption to determine the adsorbent’s capability for adsorbing H2 molecules is also discussed.