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Theoretical limits of the hydrogen adsorption in carbon nanospaces are modeled using Monte Carlo simulations. A detailed analysis of storage capacity of slit pores has been performed as a function of the pore size, gas pressure (up to 100 bars) and temperature of adsorption (77 and 298 K). The H-2-slit wall interaction has been modeled assuming energies of adsorption ranging from 4.5 kJ/mol (pure graphene surface) to 15 kJ/mol (hypothetical chemically modified graphene). The quantum nature of H-2 has been incorporated in the calculations using the Feynman-Hibbs approach. it has been shown that in a hypothetical chemically modified porous carbon, with energy of adsorption of 15 kJ/mol or higher and pore size between 0.8 and 1.1 nm, the gravimetric and volumetric storage capacity can achieve targets required for practical applications. The relation between the energy of adsorption and the effective delivery has been discussed. (C) 2009 Elsevier Ltd. All rights reserved.

We present and discuss the results of explicit - hydrogen Molecular Dynamics computer simulations of tetracosane (C24 H50 ) bi- layers deposited on a graphite substrate in the temperature range 100 K ≤ T ≤ 450 K. Both layers exhibit strong coupling between the internal molecular degrees of freedom and bulk behavior but because of the different boundary conditions between layers, they exhibit dis- tinctly different dynamics and phase transition signatures. Structural, thermodynamic and bond - orientational distributions and parameters are utilized in understanding the solid, intermediate and liquid phases presented in and phase transitions presented by the system.

We present results of molecular dynamics computer simulations of hexane (C6H14 or C6) and pentane (C5H12 or C5) adlayers physisorbed onto a graphite substrate, for various submonolayer coverages. The hexane and pentane molecules incorporate explicit hydrogens and the graphite is modelled as a six-layer all-atom structure. Even though C6 and C5 have different structures at monolayer completion, both systems generally behave similarly in the submonolayer regime and results are in reasonable agreement with experiment for both systems. Specifically, there are four distinct topological regimes involving empty space: at densities closest to full coverage, there are large domains with individual vacancies, then with decreasing density, large vacancy patches appear first, followed by the formation of connected networks of smaller domains with multiple orientations that ultimately separate into individual patches. The energetics and melting behaviour of all systems are readily understood within the framework of the topology presented at various densities.

Heterogeneity is an ubiquitous aspect of adsorption, often modifying substantially the observed behavior of the adsorbate-adsorbent system. In this paper, the influence of heterogeneity is explicitly analyzed for the case of the adsorption of molecular hydrogen onto nanoporous carbon. Grand Canonical Monte Carlo simulations were used to study the mechanism of adsorption in models of the adsorbate that include both energetic and structural modifications of graphene-based slit pores. In particular, a partial substitution of carbons by boron modifies both the symmetry of the energy landscape and strength of hydrogen physisorption; which results in considerable increases of the amount of adsorbed gas without major modification of the mechanism of adsorption. Additional heterogeneity arises from structural modifications of the adsorbent by neutron irradiation of boron-doped samples, where the boron fission products generate additional surface area for adsorption. Simulations of adsorption in such pores show that hydrogen uptake is strongly dependent on the chemical nature of the modified pore walls.

Nanoporous carbon offers promise for reversible storage of hydrogen. In this paper we discuss the influence of various parameters (energy of adsorption, H-2-H-2 interaction, pore geometry, chemical substitution of carbon by boron atom or Li+, quantum effects) on the adsorption capacity. The limits for these parameters have been explored using extensive grand canonical Monte Carlo simulations. We show that multilayer structures of hydrogen can be stabilized at low temperatures in pores larger than 1 nm. Furthermore, chemical substitution of carbon atoms by boron leads to increased adsorption. We also discuss how the mechanism of adsorption changes when the adsorption surface area is increased by drilling holes in graphene sheets. (C) 2010 Elsevier B.V. All rights reserved.