First Principles Study of H₂and CH₄Physisorption on Carbon Nanotubes

Methane Adsorption on Aggregates of Fullerenes: Site‐Selective Storage Capacities and Adsorption Energies

“…In its optimal configuration, CH 4 resides 6.57 Å away from the center of the fullerene in the so-called “face” geometry. This structure was discussed for carbon nanotubes by Akai and Saito 42. They reported a maximum adsorption energy of 90 meV on the outside of the tube over a nanotube-hexagon and 96 meV on graphene.…”

“…Although hydrogen is the primary candidate for fuel cells or internal combustion engines, CH 4 is also of interest because of its low toxicity and dominance in natural gas 1, 34. Room-temperature storage on graphitic nanostructures appears more feasible for CH 4 because the physisorption energies for CH 4 are twice as large as for hydrogen; numerous experimental and theoretical investigations of CH 4 and other small hydrocarbon molecules adsorbed on graphite,35–39 graphene,40 nanotubes,9, 10, 12, 37, 39, 41, 42 and layers of C 60 19 have been reported.…”

Methane Adsorption on Graphitic Nanostructures: Every Molecule Counts

“…3,12 Weak corrugation arises from the atomistic structure of graphite or graphene; over curved convex surfaces, the adsorption energy decreases, whereas the strength of the corrugation increases. 13,14 Bundles of nanotubes 14−19 and layers of fullerenes 20,21 offer additional, stronger adsorption sites. However, experiments involving nanotubes are hampered by their heterogeneity, the presence of impurities including metal catalysts used for tube synthesis, and the presence of uncapped tubes; these factors make it difficult to determine the nature, storage capacities, and energies of adsorption sites.…”

“…They offer the same types of adsorption sites as bundles of nanotubes, namely, groove sites between adjacent tubes, and registered exterior sites. 14−16,19,24 For C 60 trimers and beyond, they also offer dimple sites that are characteristic of close-packed layers of C 60 . 20 We determine the adsorption capacity in the various sites by direct weighing, that is, by mass spectrometry.…”

“…14 The bond strength of the CH 4 –CH 4 dimer is an order of magnitude weaker (10.8 meV). Thus, the [(C 60 ) m (CH 4 ) n ] + system is dominated by the [C 60 –C 60 ] + interaction (413 meV with the PBE1PBE functional without counterpoise) and the CH 4 –substrate interaction.…”