Hydrogen sorption by carbon nanotubes and other carbon nanostructures (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.
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 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 storage in carbon nanotubes and related materials
Journal of Materials Chemistry, 2003
Adsorption of hydrogen at 300 K has been investigated on well-characterized samples of carbon nanotubes, besides carbon fibres by taking care to avoid many of the pitfalls generally encountered in such measurements. The nanotube samples include single-and multi-walled nanotubes prepared by different methods, as well as aligned bundles of multi-walled nanotubes. The effect of acid treatment of the nanotubes has been examined. A maximum adsorption of ca. 3.7 wt% is found with aligned multi-walled nanotubes. Electrochemical hydrogen storage measurements have also been carried out on the nanotube samples and the results are similar to those found by gas adsorption measurements.
Hydrogen sorption by carbon nanomaterials
Russian Microelectronics, 2011
Hydrogen sorption by carbon nanomaterials has been investigated at a temperature of 298K and pressure of 10 MPa by single and multiwalled nanotubes, graphitic nanofibers, and split graphite. The mea surement error is calculated for the presented method. The obtained results are analyzed on the base of the physical-chemical foundation of sorption.
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
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.
Hydrogen adsorption in carbon nanostructures: comparison of nanotubes, fibers, and coals
2003
Single-walled carbon nanotubes (SWNT) were reported to have record high hydrogen storage capacities at room temperature, indicating an interaction between hydrogen and carbon matrix that is stronger than known before. Here we present a study of the interaction of hydrogen with activated charcoal, carbon nanofibers, and SWNT that disproves these earlier reports. The hydrogen storage capacity of these materials correlates with the surface area of the material, the activated charcoal having the largest. The SWNT appear to have a relatively low accessible surface area due to bundling of the tubes; the hydrogen does not enter the voids between the tubes in the bundles. Pressure ± temperature curves were used to estimate the interaction potential, which was found to be 580 AE 60 K. Hydrogen gas was adsorbed in amounts up to 2 wt % only at low temperatures. Molecular rotations observed with neutron scattering indicate that molecular hydrogen is present, and no significant difference was found between the hydrogen molecules adsorbed in the different investigated materials. Results from density functional calculations show molecular hydrogen bonding to an aromatic CÀC bond that is present in the materials investigated. The claims of high storage capacities of SWNT related to their characteristic morphology are unjustified.