Physisorption of hydrogen in single-walled carbon nanotubes (original) (raw)
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Hydrogen Adsorption in Several Types of Carbon Nanotubes
Journal of Nanoscience and Nanotechnology, 2009
In this work, we aim to study the hydrogen adsorption in several kinds of carbon nanotubes grown under different process conditions and to correlate the findings with the morphological microstructure and physical properties of these materials. The growth conditions and the behaviour with respect to hydrogen interaction of various carbon nanotubes are discussed, to establish microstructure-process-property relationships. In particular, we have analyzed several types of carbon nanotubes, namely one single-walled and five multi-walled having different tube diameter (due to different deposition techniques and conditions), different defectiveness and submitted to different surface treatments. To better understand the differences among the various samples, they have been investigated using field emission scanning electron microscopy and high resolution transmission electron microscopy for the morphological and structural characteristics, thermo-gravimetric analysis for the sample purity and Brunauer-Emmett-Teller analysis for the surface area. The experimental measurements on the ability of the different types of carbon nanotubes to adsorb and/or releasing hydrogen have been performed at 77 K with a volumetric Sievert analytical tool. Our findings clearly demonstrate a direct correlation between the exposed surface area and adsorbed hydrogen capacity, which confirms their linear relationship observed previously. For instance, singlewalled nanotubes with surface area density of ∼800 m 2 /g have showed hydrogen storage of approximately 1.7 wt% at a pressure of 35 atm. Adsorption process seems to be perfectly reversible. The adsorption values have been compared with a simple model, in order to evaluate the potentialities for carbon-based nanomaterials in future hydrogen storage applications.
Hydrogen adsorption studies on single wall carbon nanotubes
Carbon, 2004
Hydrogen adsorption data on as-grown and heat-treated single walled carbon nanotubes (SWNTs) obtained by a volumetric procedure using a Quantachrome Autosorb-1 equipment are presented. The amounts of hydrogen adsorbed at atmospheric pressure reach approximately 0.01 wt.% at 298 K and 1 wt.% at 77 K. The isosteric heat of adsorption has been calculated for both samples from H 2 equilibrium adsorption data at three temperatures, having initial values of 7.42 and 7.75 kJ mol À1 . Studies in porous structure by N 2 adsorption and density measurements in helium pycnometer are reported.
Nanotechnology, 2004
Hydrogen adsorption measurements on mixed carbon material containing single-walled carbon nanotubes (SWNTs) obtained by the electric-arc method were carried out by three different techniques: a volumetric system, a gravimetric system and an electrochemical method. The found H 2 gas adsorption capacity (volumetric and gravimetric) is very low, around 0.01 wt% at room temperature and pressure, increasing to 0.1 wt% at 20 bar. Electrochemical measurements show a slightly higher capacity (0.1-0.3 wt%) than volumetric and gravimetric data. The results obtained by the three different techniques are compatible within each other and they are also in good agreement with other previously reported data from different researchers.
Enhanced hydrogen adsorption on single-wall carbon nanotubes by sample reduction
Materials Science and Engineering B, 2004
The effect of the reduction of single-wall carbon nanotubes (SWNTs) samples on the hydrogen adsorption is reported. Hydrogen adsorption isotherms have been performed at 77 K and until 300 Torr of hydrogen pressure on raw and modified SWNTs material produced by arc-discharge using Ni/Y as catalyst at different atomic percentages. The hydrogen adsorption isotherms of the samples after hydrogen reduction at 350 • C show around 40% of higher hydrogen adsorption than those of the unreduced material. This fact suggests hydrogen dissociation by the reduced metal nanoparticles and subsequent spillover to the SWNTs. The maximum hydrogen adsorption is low, around 3 wt.%, and higher pressures and temperatures at which spillover effect from metals to carbon surfaces has been probed have to be tested with carbon nanostructures. The samples have been characterized by ICPS and Raman Spectroscopy and the porous structure by using standard BET methods from nitrogen adsorption isotherms at 77 K.
Hydrogen sorption by carbon nanotubes and other carbon nanostructures
Journal of Alloys and Compounds, 2002
We have analyzed the hydrogen storage capability of a set of carbon samples including a variety of carbon nanotubes, in the gas phase and in the electrolyte as well. The nanotube samples synthesized in our laboratory by pyrolysis of acetylene are of the multi-wall type. The hydrogen sorption properties of our synthesized nanotubes were compared with the properties of commercially available nanotubes and high surface area graphite as well. The nanotube samples and the high surface area graphite as well absorb hydrogen up to 5.5 mass% at cryogenic temperatures (77 K). However, at room temperatures this value drops to¯0.6 mass%. The electrochemical experiments on the carbon samples showed a maximum discharge capacity of 2.0 mass% at room temperature (298 K). The hydrogen tends to covalently bind to carbon when the absorption takes place at elevated temperatures (.573 K). Therefore, hydrocarbons desorbed from the sample were analyzed by means of temperature programmed desorption measurements. We conclude that the adsorption of hydrogen on nanotubes is a surface phenomenon and is similar to the adsorption of hydrogen on high surface area graphite.
Hydrogen adsorption and storage in carbon nanotubes
Synthetic Metals, 2000
A comprehensive studies on hydrogen adsorption and storage in carbon nanotubes CNTs have been done both experimentally and theoretically. Hydrogen atoms have been stored electrochemically in CNTs. We find that hydrogens exist as a form of H molecule in an 2 empty space inside CNTs, which was confirmed by Raman spectra. Several adsorption sites inron CNTs are observed during the discharging process. We perform density-functional-based tight-binding calculations to search for adsorption sites and predict maximum hydrogen storage capacity. Our calculations show that the storage capacity of hydrogen, limited by the repulsive forces between H 2 molecules inside nanotubes, increases linearly with tube diameters in single-walled nanotubes, whereas this value is independent of tube . 3 . diameters in multi-walled nanotubes. We predict that H storage capacity in 10,10 nanotubes can exceed 14 wt.% 160 kg H rm . 2
Hydrogen adsorption/desorption in functionalized single-walled carbon nanotubes
The adsorption and desorption of hydrogen in SWCNTs functionalized with borane is investigated experimentally. The SWCNTs are functionalized with borane (BH 3 ) using LiBH 4 as the precursor. The functionalized samples are hydrogenated and storage capacities of 3.2 wt.% and 3.8 wt.% are achieved at 50°C. Desorption of hydrogen is carried out by thermal annealing. Experimental evidences are provided by FTIR, CHNS and TG/TDS techniques. From the results it is confirmed that the designed hy drogen storage system is suitable for vehicular fuel cells.
H2 adsorption on multiwalled carbon nanotubes at low temperatures and low pressures
Physical Review Special Topics - Accelerators and Beams, 2008
We present an experimental study on H 2 adsorption on multiwalled carbon nanotubes (MWCNTs) at low temperatures (12-30 K) and low pressures (2 Â 10 À5 Torr) using the temperature programmed desorption technique. Our results show that the molecular hydrogen uptake increases nearly exponentially from 6 Â 10 À9 wt: % at 24.5 K to 2 Â 10 À7 wt: % at 12.5 K and that the desorption kinetics is of the first order. Comparative measurements indicate that MWCNTs have an adsorption capacity about two orders higher than that of activated carbon (charcoal) making them a possible candidate as hydrogen cryosorber for eventual applications in accelerators and synchrotrons.
First-Principle Study of Hydrogen Adsorption on Na-Coated Carbon Nanotubes
2011 International Conference on Nanoscience, Technology and Societal Implications, 2011
We investigate the hydrogen adsorption capacity of Na-coated carbon nanotube using first-principles plane wave method. A single Na atom always occupies the hollow site of a hexagonal carbon ring in all, with a nearly uniform Na-C bond length of 2.5 A. Semiconducting zigzag nanotubes, (8,0) show stronger binding energies of the Na atom of -2.1 eV. The single Na atom can further adsorb up to six hydrogen molecules with a relatively constant binding energy of -0.26 eV/H 2 . Mulliken population analysis shows that positively charged Na atoms with 0.82e charge transfer to nearest carbon atoms which polarizes the CNT leading to local dipole moments. This chargeinduced dipole interaction is responsible for the higher hydrogen uptake of Na-coated CNT. We also investigate the clustering of Na atoms to find out the maximum weight percentage adsorption of H 2 molecules. At high Na coverage, we show that Na-coated CNTs can adsorb 9.2 wt % hydrogen. Our analysis shows that, although indeed Na-coated CNT present potential material for the hydrogen storage, care should be taken to avoid Na atoms clustering on support material, to achieve higher hydrogen capacity.
Adsorption of Atomic Hydrogen on Single-Walled Carbon Nanotubes
The Journal of Physical Chemistry B, 2005
We have investigated atomic and electronic structures of hydrogen-chemisorbed single-walled carbon nanotubes (SWCNTs) by density functional calculations. We have searched for relative stability of various hydrogen adsorption geometries with coverage. The hydrogenated SWCNTs are stable with coverage of H/C, θ g 0.3. The circular cross sections of nanotubes are transformed to polygonal shapes with different symmetries upon hydrogen adsorption. We find that the band gap in carbon nanotubes can be engineered by varying hydrogen coverage, independent of the metallicity of carbon nanotubes. This is explained by the degree of sp 3 hybridization.