Gases Do Not Adsorb on the Interstitial Channels of Closed-Ended Single-Walled Carbon Nanotube Bundles

Single-walled carbon nanotubes (SWNT) were reported to have record high hydrogen storage capacities at room temperature, indicating an interaction between hydrogen and carbon matrix that is stronger than known before. Here we present a study of the interaction of hydrogen with activated charcoal, carbon nanofibers, and SWNT that disproves these earlier reports. The hydrogen storage capacity of these materials correlates with the surface area of the material, the activated charcoal having the largest. The SWNT appear to have a relatively low accessible surface area due to bundling of the tubes; the hydrogen does not enter the voids between the tubes in the bundles. Pressure ± temperature curves were used to estimate the interaction potential, which was found to be 580 AE 60 K. Hydrogen gas was adsorbed in amounts up to 2 wt % only at low temperatures. Molecular rotations observed with neutron scattering indicate that molecular hydrogen is present, and no significant difference was found between the hydrogen molecules adsorbed in the different investigated materials. Results from density functional calculations show molecular hydrogen bonding to an aromatic CÀC bond that is present in the materials investigated. The claims of high storage capacities of SWNT related to their characteristic morphology are unjustified.

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“…[29] On our sample we found that the X-ray diffraction pattern showed a peak at a momentum transfer of 0.536 ä…”

Section: Discussion Ins Resultsmentioning

confidence: 94%

Hydrogen Adsorption in Carbon Nanostructures: Comparison of Nanotubes, Fibers, and Coals

Schimmel¹,

Kearley²,

Nijkamp³

et al. 2003

Chemistry A European J

182

107

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“…The opposite limit, R approaching zero, is here called "lineland", a 1d limit. Matter in lineland has been explored for many years as an abstract problem [7] and has recently received particular attention in connection with the possible realization of 1d phases within interstitial channels or external surface grooves on nanotube bundles [2,8,9,10,11,12,13,14,15,16]. A logical question addressed in this paper is whether the properties of matter in "cylinderland" evolves smoothly (or even monotonically) between these limits as the value of R is varied.…”

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confidence: 99%

Enhanced cohesion of matter on a cylindrical surface

et al. 2003

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We evaluate the cohesive energies E b of four systems in which particles move on a cylindrical surface, at fixed distance R from the axis. We find quite nonuniversal dependences of E b on R. For the Coulomb binding problem, E b is a monotonically decreasing function of R. For three problems involving Lennard-Jones interactions, the behavior is nonmonotonic; E b is larger at R = ∞ than at R=0; the maximum binding corresponds to R ∼ 0.7 σ (the hard core parameter). Consequences of the enhanced binding are discussed.

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“…Each adsorption isotherm exhibits two inclined steps, which is consistent with previous findings on gas adsorption on SWCNTs. 6,7,[13][14][15][16] In the case of formation of successive condensed monolayer on the same adsorption sites (Kr adsorption on exfoliated graphite for example [17][18][19] ) the step heights are identical because each adsorbed layer corresponds to condensation of the same adsorbate amount. On the other hand, in our case, we clearly observe that the heights of the first and second steps are not equal.…”

Section: Gas Adsorption Studiesmentioning

confidence: 99%