Résumé
There are many theoretical attempts to propose a porous system which would store hydrogen at the minimum requirements fixed by DOE for mobile applications. One of the potentially promising groups of materials are porous structures based on carbon. However, the heat of hydrogen physisorption in such materials is low, in the range of about 4-8 kJ/mol. As a consequence, the total amount of hydrogen adsorbed at P=100 bar do not, and cannot exceed 2 wt% at room temperature and about 12 wt% at 77 K. To get better storage capacity, the adsorbing surfaces must be modified, either by substitution of some atoms in the all-carbon skeleton by other elements, or by doping/intercalation with other species. Here we analyze the variation of interaction energy between a molecule of hydrogen and graphene-based sorbents prepared as hypothetical modifications of the graphene layer. In particular, we show that partial substitution of carbons (for example, by boron) modifies both the symmetry of the energy landscape and strength of hydrogen physisorption. The effect of substituent extends over several sites of graphene lattice making the surface more heterogeneous. The consequences of such substitution on the hydrogen uptake will be discussed.