Atomic Hydrogen Storage in Carbon Nanotubes Promoted by Metal Catalysts

Abstract

Atomic hydrogen storage by carbon nanotubes (CNTs) at atmospheric pressure is studied using Pd and La catalysts for dissociation of H 2 into atomic hydrogen and formation of defects on CNT surfaces, respectively. The defect sites on CNTs as adsorption sites of atomic hydrogen are prepared by oxidation pretreatment using a La catalyst. Pd catalysts are then deposited on CNT surfaces for dissociation of H 2 into atomic hydrogen, which then spills over to the defect sites. In the best case, 1.0 wt % hydrogen is stored in the defective CNT with Pd particles at 1 atm and 573 K. The hydrogen desorption in temperature programmed desorption (TPD) experiments started at 700-900 K, which agreed with the annealing temperatures of CNTs prior to hydrogen storage. Also, the amount of hydrogen stored in CNTs decreased with increasing annealing temperature. These results are ascribed to the crystallization of the defective structure of CNT into graphitic structure. The activation energies of 46.6, 87.3, and 129.8 kJ/mol derived from the desorption peaks of hydrogen in the defective CNT with Pd particles vary from 46.6 to 129.8 kJ/mol, depending on the annealing temperatures at 523, 623, and 773 K, respectively. The difference in the activation energies is probably due to the energies required for the recrystallization of the defect sites into the graphite structure.

Effects of acid treatment duration and sulfuric acid molarity on purification of multi-walled carbon nanotubes

“…1, the pristine MWCNTs have the lowest onset and offset temperatures among the other samples. Yoo et al reported the rate of catalyst role in the starting of MWCNT oxidation at lower temperature [22]. Also, Chen et al reported that the oxidation stability of carbon nanotubes is influenced by defect sites in graphite and nanotube diameters [21].…”

Is Spillover Relevant for Hydrogen Adsorption and Storage in Porous Carbons Doped with Palladium Nanoparticles?

“…However, a number of experiments indicate that doping porous carbon materials (nanotubes, nanofibers, nanoporous carbons) with metallic clusters or nanoparticles could provide a strategy to increase the hydrogen uptake. [18][19][20][21][22][23][24][25][26] The metals mostly used in those investigations are alkali metals 18,19 and some transition metals like vanadium, palladium, and platinum. [22][23][24][25][26][27] To explain the observed enhancement of the hydrogen adsorption, a mechanism of spillover 28,29 has generally been assumed.…”

Possibilities of atomic hydrogen storage by carbon nanotubes or graphite materials

“…Our methodology here of the hydrogen storage is to adsorb atomic hydrogen at the defect sites of CNTs after dissociation of H 2 by Pd catalyst particles attached to the CNTs [15][16][17]. La catalysts have been doped to CNTs in order to introduce the defect sites [17], which catalyze oxidation of CNTs by O 2 .…”

“…La catalysts have been doped to CNTs in order to introduce the defect sites [17], which catalyze oxidation of CNTs by O 2 . We have used thick MWCNT for the atomic hydrogen storage, because the defect density on the wall of MWCNTs is expected to be much more than that on SWCNTs or thin CNTs and because MWCNTs can be obtained at low cost by catalytic decomposition of hydrocarbons as a mass production.…”