Isotopic and spin selectivity of<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msub><mml:mrow><mml:mi mathvariant="normal">H</mml:mi></mml:mrow><mml:mrow><mml:mn>2</mml:mn></mml:mrow></mml:msub></mml:mrow></mml:math>adsorbed in bundles of carbon nanotubes

Trasca, R. A.; Kostov, Milen K.; Cole, Milton W.

doi:10.1103/physrevb.67.035410

Cited by 40 publications

(46 citation statements)

References 49 publications

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“…Although the thermodynamic behavior of the free H 2 gas in the 200-to 300-K temperature range is essentially classical, this is no longer true in the presence of soft external potentials. Quantum behavior of hydrogen adsorbed in narrow pores manifests itself in the quantum sieving effects (21), which persist up to 300 K (22). Inclusion of the quantum effects in the free energy is a nontrivial computational problem.…”

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confidence: 99%

Graphene nanostructures as tunable storage media for molecular hydrogen

Patchkovskii

Tse

Yurchenko

et al. 2005

Proc. Natl. Acad. Sci. U.S.A.

597

409

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Many methods have been proposed for efficient storage of molecular hydrogen for fuel cell applications. However, despite intense research efforts, the twin U.S. Department of Energy goals of 6.5% mass ratio and 62 kg͞m 3 volume density has not been achieved either experimentally or via theoretical simulations on reversible model systems. Carbon-based materials, such as carbon nanotubes, have always been regarded as the most attractive physisorption substrates for the storage of hydrogen. Theoretical studies on various model graphitic systems, however, failed to reach the elusive goal. Here, we show that insufficiently accurate carbon-H 2 interaction potentials, together with the neglect and incomplete treatment of the quantum effects in previous theoretical investigations, led to misleading conclusions for the absorption capacity. A proper account of the contribution of quantum effects to the free energy and the equilibrium constant for hydrogen adsorption suggest that the U.S. Department of Energy specification can be approached in a graphite-based physisorption system. The theoretical prediction can be realized by optimizing the structures of nano-graphite platelets (graphene), which are lightweight, cheap, chemically inert, and environmentally benign. equilibrium constants ͉ hydrogen storage ͉ quantum effects A recent report on hydrogen clathrate hydrate (1) shows that under high pressure, molecular hydrogen can be trapped in the clathrate cavities reaching a mass ratio close to that defined by the U.S. Department of Energy (DOE) (2). However, the hydrogen clathrate is only stable under high pressure or at very low temperature. Simple sterical considerations suggest that the use of a ''help gas'' to stabilize the clathrate hydrate under less severe thermodynamic conditions would lead to the deterioration of the hydrogen storage mass ratio and may not be viable for mobile applications. On the other hand, there have also been numerous experimental studies on the binding capacity of molecular hydrogen with graphitic substrates (3, 4). At technologically viable conditions, reliably reproducible results are still far from the DOE goal (3, 4). In the attempt to understand and improve the storage capacity of graphitic materials, calculations have been made on many models. Some of the calculations were based on empirical interaction potentials (5-9), and the others used potentials derived from quantum mechanical calculations (10-16). The role of quantum behavior of molecular hydrogen at low temperatures has also been investigated (6,8,(17)(18)(19). Unfortunately, the binding capacity for hydrogen at near-ambient conditions has not been calculated, including the quantum effects and accurate, ab initio-based interaction potentials. To date, there has not been a reliable theoretical study indicating that the DOE goal of 6.5% mass ratio can or cannot be achieved in pure graphitic materials.The interaction of nonpolar H 2 molecules with physisorption substrates in graphitic system is mainly the London dispersion. Accurate...

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mentioning

confidence: 99%

Graphene nanostructures as tunable storage media for molecular hydrogen

Patchkovskii

Tse

Yurchenko

et al. 2005

Proc. Natl. Acad. Sci. U.S.A.

597

409

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“…The heat capacity of 4 He adsorbed on c-SWNT bundles was investigated at temperatures below 6 K [6,33]. It was observed [6] that the heat capacity of the adsorbed helium exhibited the behavior of 1D and 2D structures depending on the technique of sample preparation (laser evaporation or arc discharge).…”

Section: Introductionmentioning

confidence: 99%

“…It was observed [6] that the heat capacity of the adsorbed helium exhibited the behavior of 1D and 2D structures depending on the technique of sample preparation (laser evaporation or arc discharge). Structures of 4 He adsorbates in the grooves and at the OS of c-SWNT bundles were studied by the neutron diffraction method [18]. At low coverage, the 4 He atoms formed a 1D single line lattice along the grooves.…”

Section: Introductionmentioning

confidence: 99%

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Heat Capacity of 1D Chains of Atom/Molecule Adsorbates in the Grooves of c-SWNT Bundles

Sumarokov

Bagatskii

Barabashko

2014

Springer Proceedings in Physics

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Since the discovery of carbon nanotubes in 1991 [1], investigations of the physical properties of these novel materials have been rated as a fundamentally important trend in physics of condensed matter [2,3]. Of special interest is the study of properties of low-dimensional systems [4][5][6][7][8][9]. The unique structure of bundles of single-walled carbon nanotubes (SWNTs) permits obtaining quasi-one-dimensional (1D), 2D, and 3D structures formed by adsorbates [5,10]. Technologically, most of the nanotubes in the prepared bundles have closed ends unless special steps are taken to open them. Figure 15.1 demonstrates the possible sites of adsorption of a relatively small admixture atoms or molecules in a bundle of closed SWNTs (c-SWNTs): interstitial channels (IC), grooves (G) at the outer surface, and the outer surface (OS). These positions differ in geometrical size and energy of adsorbate binding to c-SWNT bundles [11]. At low adsorbate concentrations, quasi-1D chains of admixture atoms/molecules are formed in the IC-and G-sites. One or several layers of atoms/molecules adsorbed at the OS of the c-SWNT bundle form quasi-2D or quasi-3D systems. The 1D, 2D, and 3D systems have different properties at low temperatures [12][13][14][15][16][17][18][19]. Physical properties (adsorption, thermal, and structural) of simple gas admixtures deposited in c-SWNT bundles were investigated in experimental and theoretical works [5, 6, 9-11, 15, 20-39].The heat capacity of 4 He adsorbed on c-SWNT bundles was investigated at temperatures below 6 K [6,33]. It was observed [6] that the heat capacity of the adsorbed helium exhibited the behavior of 1D and 2D structures depending on the technique of sample preparation (laser evaporation or arc discharge). Structures of 4 He adsorbates in the grooves and at the OS of c-SWNT bundles were studied by the neutron diffraction method [18]. At low coverage, the 4 He atoms formed a 1D single line lattice along the grooves. As the concentration of the adsorbed helium atoms increased,

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“…Much recent research has been devoted to hydrogen within nanotubes bundles, partly due to the exciting prospects of technologies related to hydrogen storage and isotope separation [25,26,27,28,29]. The vast majority of the theoretical research to date (including that of our group) has assumed a monodisperse distribution of tubes.…”

Section: Introductionmentioning

confidence: 99%

Bose-Einstein condensation of helium and hydrogen inside bundles of carbon nanotubes

et al. 2004

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Helium atoms or hydrogen molecules are believed to be strongly bound within the interstitial channels (between three carbon nanotubes) within a bundle of many nanotubes. The effects on adsorption of a nonuniform distribution of tubes are evaluated. The energy of a single particle state is the sum of a discrete transverse energy E t (that depends on the radii of neighboring tubes) and a quasicontinuous energy E z of relatively free motion parallel to the axis of the tubes. At low temperature, the particles occupy the lowest energy states, the focus of this study. The transverse energy attains a global minimum value (E t = E min ) for radii near R min = 9.95Å for H 2 and 8.48A for 4 He. The density of states N (E) near the lowest energy is found to vary linearly above this threshold value, i.e. N (E) is proportional to (E − E min ). As a result, there occurs a Bose-Einstein condensation of the molecules into the channel with the lowest transverse energy. The transition is characterized approximately as that of a four dimensional gas, neglecting the interactions between the adsorbed particles. The phenomenon is observable, in principle, from a singular heat capacity.The existence of this transition depends on the sample having a relatively broad distribution of radii values that include some near R min .

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Isotopic and spin selectivity ofH2adsorbed in bundles of carbon nanotubes

Cited by 40 publications

References 49 publications

Graphene nanostructures as tunable storage media for molecular hydrogen

Graphene nanostructures as tunable storage media for molecular hydrogen

Heat Capacity of 1D Chains of Atom/Molecule Adsorbates in the Grooves of c-SWNT Bundles

Bose-Einstein condensation of helium and hydrogen inside bundles of carbon nanotubes

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