Résumé
Nanoporous carbons are one of potentially promising groups of materials for hydrogen storage by adsorption. Recent achievements in engineering activated carbons' architecture resulted in preparation of materials with surface area exceeding 3,000 m2/g and showing high storage capacity at cryogenic temperature (~10 wt% at 77 K and P = 100 bar). However, the heat of hydrogen physisorption in such materials is low, in the range of ~ 4-8 kJ/mol, which limits the total amount of hydrogen adsorbed at at room temperature to ~2 wt% (at P = 100 bar). To improve the sorption characteristics 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 present coupled ab initio calculations and Monte Carlo simulations showing that partial substitution of carbon atoms in nanoporous matrix with boron results in significant increases of the adsorption energy (up to 10-13.5 kJ/mol) and storage capacity (~ 5 wt. % at 298 K, P = 100 bar), even if the substitution ratio is low (5-10%). Although substitution introduces both energetic and structural heterogeneity of the adsorbing surface, at room temperature the delivery rate over adsorption-desorption cycle is high, ~ 97 %. We analyze whether the location of boron atoms in nanoporous structure (substitution within the graphene plane or intercalation between two adjacent planes) and randomness of its distribution modify the mechanism of adsorption and storage parameters. In particular the heterogeneity of energy landscape is discussed in a context of optimization of system delivery.