  Graphynes are 2D porous structures deriving from graphene featuring
triangular and regularly distributed subnanometer pores, which may be exploited
to host small gaseous species. First principles adsorption energies of
molecular hydrogen (H2) on graphene, graphdiyne and graphtriyne molecular
prototypes are obtained at the MP2C level of theory. First, a single layer is
investigated and it is found that graphynes are more suited than graphene for
H2 physical adsorption since they provide larger binding energies at
equilibrium distances much closer to the 2D plane. In particular, for
graphtriyne a flat minimum located right in the geometric center of the pore is
identified. A novel graphite composed of graphtriyne stacked sheets is then
proposed and an estimation of its 3D arrangement is obtained at the DFT level
of theory. In contrast to pristine graphite this new carbon material allow both
H2 intercalation and out-of-plane diffusion by exploiting the larger volume
provided by its nanopores. Related H2 binding energies for intercalation and
in-pore adsorption are around 0.1 eV and they could lead to high storage
capacities. The proposed carbon-based layered material could represent a safer
and potentially cheaper alternative for hydrogen on-board storage than
conventional solutions based on cryogenic liquefaction and/or high compression.
