**2. Graphene based materials**

Graphene, a 2D carbon allotrope that is positioned in a sp<sup>2</sup> -bonded aromatic structure, has attracted a lot of attention for hydrogen storage application due to its low weight, cost and ability to be synthesized in large quantities [5]. This two dimensional material configuration is formed by covalent bonds that are distributed on the hexagonal honeycomb lattice [6]. Apart from this, graphene has intriguing properties which have made them applicable in these fields: energy storage, sensors, electrodes, field effect devices, nanocomposites and solar cells [6].

The large surface area of graphene (2630 g<sup>2</sup> m�<sup>1</sup> ) is tremendously beneficial for hydrogen storage. The interaction of graphene systems is based on instantaneous dipole–dipole induced forces because hydrogen is a non-polar molar [7]. A number of theoretical studies have been undertaken to explain the adsorption of hydrogen on the surface of graphene material and give more information on the pathway experimentalist need to take [7]. These studies have shown that the spatial distribution of adsorbed hydrogen on the surface of graphene is delocalized and that molecular hydrogen exhibits unrestricted lateral movement [7].
