Experimental probes of the molecular hydrogen–carbon nanotube interaction

Pradhan, Bhabendra K.; Суманасекера, Гамини; Adu, Kofi W.; Romero, Hugo; Williams, Keith A.; Eklund, P. C.

doi:10.1016/s0921-4526(02)00994-8

Cited by 71 publications

(53 citation statements)

References 16 publications

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“…3. This result is consistent with many experiments, which reported that SWNTs have a certain hydrogen storage capacity at low temperature, [13][14][15] but have very low hydrogen uptake capacity at room temperature. [8][9][10][11][12] For H 2 molecules adsorbed on defected SWNTs, the situation is very different.…”

Section: B Adsorption Energies and Electron Density Contours Around supporting

confidence: 93%

“…2. The collision energy, 0.01 eV, is equivalent to the average translational kinetic energy of a particle system at a thermal equilibrium temperature of ϳ77 K. The high sticking coefficient in this case is consistent with the experimental results, [13][14][15][16] which showed that hydrogen uptake under cryogenic operating conditions were more favorable than at an ambient temperature. The second feature shown in Fig.…”

Section: A Hydrogen Molecules Adsorption On and Desorption From Swntssupporting

confidence: 87%

“…14,16,[37][38][39][40][41] Recently, Pradhan et al reported the experimental isosteric heat ϳ125± 5 meV for H 2 molecules adsorbed on SWNTs. 14,15 Since the isosteric heat of adsorption is very close to the adsorption ͑binding͒ energy at low temperature, we can compare their result with our theoretical result. It seems that the adsorption energy given by our empirical calculation agrees quite well with their result.…”

Section: B Adsorption Energies and Electron Density Contours Around mentioning

confidence: 99%

“…Hydrogen adsorption capacity more than 8 wt % in purified crystalline ropes of SWNTs was observed at ϳ128 atm and at 80 K. 13 A storage capacity of more than 6 wt % at T = 77 K and pressure 1 -2 atm for hydrogen physisorbed on heavily processed ropes of SWNTs was also reported. 14,15 Open tipped MWNTs were found to adsorb about 6.46 wt % of hydrogen at 77 K and at a pressure of ϳ12 MPa. 16 However, recent measurements on pretreated large MWNT samples ͑ϳ85 g͒ showed that the maximum releasable H 2 adsorbed at 77 K was 2.27 wt %.…”

Section: Introductionmentioning

confidence: 99%

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Enhancement of hydrogen physisorption on single-walled carbon nanotubes resulting from defects created by carbon bombardment

et al. 2005

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The defect effect on hydrogen adsorption on single-walled carbon nanotubes ͑SWNTs͒ has been studied by using extensive molecular dynamics simulations and density functional theory ͑DFT͒ calculations. It indicates that the defects created on the exterior wall of the SWNTs by bombarding the tube wall with carbon atoms and C 2 dimers at a collision energy of 20 eV can enhance the hydrogen adsorption potential of the SWNTs substantially. The average adsorption energy for a H 2 molecule adsorbed on the exterior wall of a defected ͑10,10͒ SWNT is ϳ150 meV, while that for a H 2 molecule adsorbed on the exterior wall of a perfect ͑10,10͒ SWNT is ϳ104 meV. The H 2 sticking coefficient is very sensitive to temperature, and has a maximum value around 70 to 90 K. The electron density contours, the local density of states, and the electron transfers obtained from the DFT calculations clearly indicate that the H 2 molecules are all physisorbed on the SWNTs. At temperatures above 200 K, most of the H 2 molecules adsorbed on the perfect SWNT are soon desorbed, but the H 2 molecules can still remain on the defected SWNTs at 300 K. The detailed processes of H 2 molecules adsorbing on and desorbing from the ͑10,10͒ SWNTs are demonstrated.

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Section: B Adsorption Energies and Electron Density Contours Around supporting

confidence: 93%

Section: A Hydrogen Molecules Adsorption On and Desorption From Swntssupporting

confidence: 87%

Section: B Adsorption Energies and Electron Density Contours Around mentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Enhancement of hydrogen physisorption on single-walled carbon nanotubes resulting from defects created by carbon bombardment

et al. 2005

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“…Optimization of the size and shape of the pores yields some improvement 5,6 but the hydrogen storage capacity of these materials remains too low for practical application. The main difficulty arises from the small adsortion energy [7][8][9][10] , below 100 meV, of hydrogen to the pore walls.…”

Section: Introductionmentioning

confidence: 99%

Competition between molecular and dissociative adsorption of hydrogen on palladium clusters deposited on defective graphene

et al. 2015

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The contribution of Pd doping to enhance the hydrogen storage capacity of porous carbon materials is investigated. Using the Density Functional Formalism, we have studied the competition between the molecular adsorption and the dissociative chemisorption of H 2 on Pd clusters anchored on graphene vacancies. The molecular adsorption of H 2 takes place with energies in the range of 0.7 -0.3 eV for adsorption of one to six hydrogen molecules. Six molecules saturate the cluster, and additional hydrogen could only be adsorbed, with much smaller adsorption energies, at farther distances from the cluster. The dissociative chemisorption is the preferred adsorption channel from one to three hydrogen molecules, with adsorption energies in the range of 1.2 -0.6 eV. After the first three molecules are dissociatively quemisorbed, three additional hydrogen molecules can be adsorbed * Corresponding Author: E-mail: maria.lopez@fta.uva.es 1 non-dissociatively onto the Pd cluster with adsorption energies of 0.5 eV. The desorption of Pd-H complexes is prevented in all cases because the Pd clusters are firmly anchored to graphene vacancies. Our results are very promising and show that Pd clusters anchored on graphene vacancies retain their capacity to adsorb hydrogen and completely prevent the desorption of Pd-H complexes that would spoil the hydrogen releasing step of the cycle.

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Physisorption in Porous Materials

Hirscher¹,

Panella²

2010

Handbook of Hydrogen Storage

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Physisorption or physical adsorption is the mechanism by which hydrogen is stored in the molecular form, that is, without dissociating, on the surface of a solid material. Responsible for the molecular adsorption of H 2 are weak dispersive forces, called van der Waals forces, between the gas molecules and the atoms on the surface of the solid. These intermolecular forces derive from the interaction between temporary dipoles which are formed due to the fluctuations in the charge distribution in molecules and atoms. The combination of attractive van der Waals forces and short range repulsive interactions between a gas molecule and an atom on the surface of the adsorbent results in a potential energy curve which can be well described by the Lennard-Jones Eq. (2.1).where e is the depth of the energy well, r i the distance between an H 2 molecule and a generic atom i on the surface and s the value of r i for which the potential is zero [1]. The minimum of the potential curve occurs at a distance from the surface which is approximately the sum of the van der Waals radii of the adsorbent atom and the adsorbate molecule. For microporous materials (r pore < 1 nm) [2] where the pore dimensions are comparable to the diameter of the adsorbate molecules this interaction potential is also influenced by the pore shape and the pore dimensions. Adsorption is an exothermic process, that is, heat is released during the adsorption of gas molecules on a surface. Owing to the low polarizability of the H 2 molecule this type of interaction is very weak and leads to low values of the heat of adsorption, typically in the range of 1-10 kJ mol À1 [3]. Compared to chemisorption which involves a change in the chemical nature of the H 2 molecule by, for example, dissociation, physisorption has approximately a ten times smaller heat of adsorption. Chemical hydrides and complex hydrides, which store hydrogen chemically, both have the disadvantage of producing an excessive amount of heat during fast Handbook of Hydrogen Storage. Edited by Michael Hirscher

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Experimental probes of the molecular hydrogen–carbon nanotube interaction

Cited by 71 publications

References 16 publications

Enhancement of hydrogen physisorption on single-walled carbon nanotubes resulting from defects created by carbon bombardment

Enhancement of hydrogen physisorption on single-walled carbon nanotubes resulting from defects created by carbon bombardment

Competition between molecular and dissociative adsorption of hydrogen on palladium clusters deposited on defective graphene

Physisorption in Porous Materials

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