SWCNTs and Carbon foams

In chapters 3 and 4 the H2 storage capacities of hypothetical and experimentally synthesised[82] materials have been discussed. A comparison between ``frozen'' and C60 separated graphene layers have shown comparable gravimetric storage capacities (4.3 and 3.2). The spacer molecules, however, reduce the active volume (the space with only attractive potential) which can be used to store hydrogen. This is compensated by the narrower pores and the sequent increase of the hydrogen density. Therefore, it is suggested that further tuning of the materials is possible.

Another class of aromatic carbon nanostructures with potential applicability to store H$_2$ and which have been heavily discussed in the literature are carbon nanotubes (CNTs).[29,30] An attractive potential is found both on the inner and the outer surfaces of the nanotubes. Due to the concave interior, a rather strong physisorption, reaching more than 25 kJ$\,$mol$^{-1}$[53], is found inside CNTs with selected diameters. Despite the controversial results for their storage capacities[11,24,25,26,27], nanotubes remain still valuable and simple model structures due to their well-defined porosity. Unlike the slit pores, they provide additional information about the interaction of H$_2$ with bent graphene surfaces.

In this chapter the storage abilities of a series of nanotubes and their bundles will be discussed in context of their geometrical parameters. Moreover, the storage capabilities of proposed hypothetical carbon structures, as carbon foams will be assessed.