Hydrogen adsorption on a single-walled carbon nanotube material: a comparative study of three different adsorption techniques (original) (raw)

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.

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.

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.

Physisorption of hydrogen in single-walled carbon nanotubes

Carbon, 2003

The interaction of hydrogen with single-walled carbon nanotubes (SWNTs) was analysed. A SWNT sample was exposed to D or H at a pressure of 2 MPa for 1 h at 298 or 873 K. The desorption spectra were measured by thermal desorption 2 2 spectroscopy (TDS). A main reversible desorption site was observed throughout the range 77 to 320 K. The activation energy of this peak at about 90 K was calculated assuming first-order desorption. This corresponds to physisorption on the surface of the SWNTs (19.261.2 kJ / mol). A desorption peak was also found for multi-walled carbon nanotubes (MWNTs), and also for graphite samples. The hydrogen desorption spectrum showed other small shoulders, but only for the SWNT sample. They are assumed to originate from hydrogen physisorbed at sites on the internal surface of the tubes and on various other forms of carbon in the sample. The nanosized metallic particles (Co:Ni) used for nanotube growth did not play any role in the physisorption of molecular hydrogen on the SWNT sample. Therefore, it is concluded that the desorption of hydrogen from nanotubes is related to the specific surface area of the sample. 

Hydrogen adsorption on N-decorated single wall carbon nanotubes

Physics Letters A, 2009

Using density functional theory and molecular dynamics we found that N-decorated single walled (8, 0) carbon nanotubes are potential high capacity hydrogen storage media. This system could store up to 6.0 wt% hydrogen at 300 K and ambient pressure, with average adsorption energy of −80 meV/(H 2 ). Nitrogen coverage was C 8 N.

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.

Role of surface chemistry in hydrogen adsorption in single-wall carbon nanotubes

Chemical Physics Letters, 2003

A combination of tight-binding molecular dynamics and grand-canonical-ensemble Monte Carlo is used to model adsorption of molecular hydrogen in chemically modified matrices of single-wall carbon nanotubes. We study the effects of chemical modification of the nanotube surface by including different coverages of chemisorbed atomic hydrogen and surface oxidation by removing islands of missing carbon atoms with H-saturated bonds. Chemisorbed hydrogen reduces the gas storage capabilities of carbon nanotubes, while the opening of cavities by oxidation tends to increase the mass of stored hydrogen gas in terms of both gravimetric and volumetric 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.

Hydrogen sorption properties of arc generated single-wall carbon nanotubes

Journal of Alloys and Compounds, 2003

Studies regarding the possible use of single-wall carbon nanotubes (SWNTs) as a hydrogen storage material have attracted considerable interest in the last years. However, a large discrepancy in the results reported by different scientific groups is evident, and many of the recent studies do not confirm superior H adsorbing properties of SWNTs compared to more conventional carbon materials. Nevertheless, 2 synthesis of SWNTs with different diameters and a development of techniques for purification and opening can contribute to the improvement of their H storage efficiency. In the present work, SWNTs were produced by arc evaporation of graphite electrodes with the use of two different catalysts, 3Co / Ni and YNi . A three-step purification technique allowed enrichment of the samples with SWNTs 2 reaching a level of purity exceeding 75%. In carefully performed sorption experiments on purified samples, reversible storage capacity of 2.4 wt.% H was observed at cryogenic temperatures below 2150 8C and at a pressure of 25 bar H . Thermal desorption studies revealed 2 2 the presence of weakly bonded physisorbed hydrogen (90%) and chemically bonded hydrogen (10%). The latter was released at temperatures above 450 8C as a result of breaking of the covalent C-H bonds. 

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