The widespread use of methane as fuel in for vehicular application is still braked by the lack of sorbent that will allow highly efficient, reversible storage at room temperature and moderate pressures at one hand, and fulfill the safety requirements on the other. One of the ways to dill with the safety problems (in particular, easy leak detection) is to add methane with highly odorant gases, e.g. thiols (mercaptans). Here we present computer simulations of methane-methylmercaptan and methane-ethylmercaptan mixtures adsorption on single graphene surface and in graphene-based slit pores. Two models of the methane and thiols molecules (within rigid molecule approximation) are compared: all-atom and the united-atom model. The empirical potentials come from ??? and CHARMM2 force fields. Methane is modeled in two-phase system, (the gas phase is in equilibrium with the adsorbed phase) using molecular dynamics (MD) technique are used. The simulations have been carried out in the temperature range between 150 and 300 K, where no molecular dissociation occurs, and in large range of pressures, up to the saturation pressure of methane. We will focus our study on the analysis of thiols’ trajectories during the adsorption-desorption cycle of methane and the reversibility of their adsorption in the presence of methane.

Carbon-based materials, due to their low cost and weight, have long been considered as suitable phy-sisorption substrates for the reversible storage of hydrogen. In fact, carbons can be engineered to achieve exceptional storage capacities: the ALL-CRAFT1 nanoporous carbon achieves (at T = 80 K, P = 100 bar) gravimetric excess adsorption of 0.073  0.003 kg H2/kg carbon, gravimetric storage capacity of 0.106  0.005 kg H2/kg carbon (including the gas in pore spaces), and volumetric storage capacity of 0.040  0.002 kg H2/l carbon. The nanopores generage high storage capacity by: (i) having a very high surface area (~2,600 m2/g carbon); (ii) by generating a high H2-wall interaction potential; and (iii) by allowing multi-layer adsorption of H2 (at cryogenic temperatures). In this presentation we will show how the experimental characteristics of the ALL-CRAFT1 carbon correlate to the observed H2 storage properties, with help from basic theoretical considerations and computational simulations of the adsorption process (Grand Canonical Monte Carlo). The ALL-CRAFT carbon is composed of a large variety of pore sizes (pore-size distributions from sub-critical N2 adsorption analyzed via quenched solid-state density functional theory, corroborated via small-angle X-ray scattering, SAXS). This generates substantial heterogeneity in the adsorption potentials. Hydrogen adsorption isotherms can be readily simulated (GCMC) at low pressures (< 30 bar) by a two-binding energies (~9 kJ and ~5 kJ/mol), corresponding to narrow (< 1 nm) and wide pores. The H2 adsorption in our samples has two further characteristics that we explain: (i) exceptional low-temperature H2 storage (in excess of the usual Chahine’s rule), and (ii) absence of an excess adsorption peak (for 0 < P < 100 bar). By performing extensive computer simulations that take into account the sample’s pore-size distributions we are able to explain these characteristics in terms of a weak multi-layer adsorption and the existence of lower binding-energy regions. Finally we will discuss the influence of these significant sources of heterogeneity on the adsorption-desorption cycle, in particular in terms of the amount of stored H2 that is deliverable via an isothermal pressure sweep.

Czysty porowaty węgiel adsorbuje wodór w ilościach niewystarczających dla praktycznych zastosowań ( mniej niż 8% masy w temperaturze azotowej i mniej niż 1.5% w temperaturze pokojowej) [1]. Mała adsorbcja jest głównie konsekwencją słabej energii fizysorbcji wodoru na węglu (~5 kJ/mol). Ograniczona powierzchnia dostępna dla adsorbcji, wynikająca ze struktury adsorbenta, jest dodatkowym parametrem ograniczajacym adsorbcję. Jednym ze sposobów zwiększenia adsorpcji porowatych węgli jest ich modyfikacja albo poprzez kontrolę kształtu i wielkości porów, albo poprzez domieszkowanie lub substytucję atomów węgla innymi pierwiastkami. W niniejszej pracy przedyskutujemy teoretyczne granice adsorbcji wodoru w nanoporach zbudowanych z płaszczyzn grafitowych. Omówiony zostanie wpływ skończonych rozmiarów i geometrii porów na parametry adsorpcji (Rys.1). Przeanalizowane zostaną niektóre perspektywy zwiększenia adsorbcji poprzez modyfikację ścian adsorbenta, strukturalną (np. hole drilling) lub chemiczną (podstawienie części atomów węgla borem). Ta ostania prowadzi do lokalnej deformacji zarówno struktury grafitu, jak i energetycznej struktury adsorbentu i jest aktualnie intensywnie badana zarówno eksperymentalnie jak i numerycznie. Całość przedstawionych rezultatów jest wynikiem eksperymentów numerycznych (symulacje Monte Carlo w wielkim układzie kanonicznym) i zostanie przedyskutowana w porównaniu z najnowszymi wynikami eksperymentalnymi.

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.

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