Hydrogen storage in engineered carbon nanospaces

Abstract

It is shown how appropriately engineered nanoporous carbons provide materials for reversible hydrogen storage, based on physisorption, with exceptional storage capacities (∼80 g H 2 /kg carbon, ∼50 g H 2 /liter carbon, at 50 bar and 77 K). Nanopores generate high storage capacities (a) by having high surface area to volume ratios, and (b) by hosting deep potential wells through overlapping substrate potentials from opposite pore walls, giving rise to a binding energy nearly twice the binding energy in wide pores. Experimental case studies are presented with surface areas as high as 3100 m 2 g −1 , in which 40% of all surface sites reside in pores of width ∼0.7 nm and binding energy ∼9 kJ mol −1 , and 60% of sites in pores of width >1.0 nm and binding energy ∼5 kJ mol −1 . The findings, including the prevalence of just two distinct binding energies, are in excellent agreement with results from molecular dynamics simulations. It is also shown, from statistical mechanical models, that one can experimentally distinguish between the situation in which molecules do (mobile adsorption) and do not (localized adsorption) move parallel to the surface, how such lateral dynamics affects the hydrogen storage capacity, and how the two situations are controlled by the vibrational frequencies of adsorbed hydrogen molecules parallel and perpendicular to the surface: in the samples presented, adsorption is mobile at 293 K, and localized at 77 K. These findings make a strong case for it being possible to significantly increase hydrogen storage capacities in nanoporous carbons by suitable engineering of the nanopore space.

Enhanced hydrogen adsorption in boron substituted carbon nanospaces

“…However, the low heat of hydrogen physisorption on carbons ͑4-8 kJ/mol͒ results in low storage capacities at room temperature ͑ϳ0.02 kg H 2 / kg system at P = 100 bar͒. 5,6 The challenge is, thus, to find ways to increase the interaction of hydrogen and a carbon substrate.Boron-doped carbons are widely conjectured to be the suitable materials for hydrogen storage. It is believed that boron doping raises the binding energy to levels that would enable room temperature storage at moderate ͑Ͻ100 bar͒ pressures.…”

“…However, the low heat of hydrogen physisorption on carbons ͑4-8 kJ/mol͒ results in low storage capacities at room temperature ͑ϳ0.02 kg H 2 / kg system at P = 100 bar͒. 5,6 The challenge is, thus, to find ways to increase the interaction of hydrogen and a carbon substrate.…”

“…The development of a suitable material for reversible storage of hydrogen still remains a "grand challenge," 1,2 in particular for vehicular applications. 1 Although some materials are potentially attractive, even the most promising candidates, nanoporous activated carbons, [3][4][5][6] have yet to meet the U.S. Department of Energy ͑DOE͒ 2010 targets ͑0.045 kg H 2 / kg system, 28 kg H 2 / m 3 system at room temperature for light-duty vehicles 7 ͒. Recent achievement in engineering carbons nanospaces resulted in preparation of very high surface area materials ͑Ͼ3000 m 2 / g͒ performing exceedingly well at cryogenic temperature ͑ϳ0.1 kg H 2 / kg system at P = 100 bar 6,8 ͒.…”

Hydrogen storage property of laser induced Pd-nanoparticle decorated multi-walled carbon nanotubes

“…Such additional steps of nanotube decoration are not only inefficient but also increase the overall production cost. 39,50,51 Despite the pristine CNTs have unique properties to serve as hydrogen storage materials, however this property is enhanced by the combination of CNTs with the selective nanostructures and compounds. 30 Among the metal nanoparticles anchored to CNTs, the Pd decorated one has found attractive interest mainly due to its a Phys.…”

Boundary effect on the adsorption properties of H2 on charged MgCaHb complex

“…One of the most important reasons is the relatively low energy of adsorption of hydrogen about 4-9 kJ/mol [4][5][6][7][8][9], especially in most carbon materials (such as activated carbons, graphene, or carbon nanotubes). Additionally, using first-principles calculations, the binding energy of a H 2 on a flat graphene is 5.0-6.5 kJ/mol, depending on the adsorption site with respect to graphene structure and with an equilibrium distance of 2.68-2.91 Å [6,10].…”