Brief Experimental Overview

A lot of recent experiments are trying to investigate the hydrogen storage in SWNTs. First, in 1997, Dillon et al. reported that SWNTs could store hydrogen [4]. Using temperature-programmed desorption spectroscopy they showed that hydrogen would condense inside SWNTs under conditions that do not induce adsorption within a standard mesoporous activated carbon.

Two years later Liu et al. found out that this storage can take place in room temperature [5]. They used SWNTs of 1.85 nm diameter, synthesized by a semicontinuous hydrogen arc discharge method, and found a storage capacity of 4.2 wt% at room temperature and under modestly high pressure; 78.3% of the adsorbed hydrogen can be released under ambient pressure and room temperature.

The same year Chen et al. reported that alkali-doped carbon nanotubes possess high hydrogen uptake [9]. They investigated lithium and potassium doped carbon nanotubes and found hydrogen absorption of 14 to 20 wt% between 400 °C and room temperature. These values are higher than those of metal hydride and cryoadsorption systems. The stored hydrogen could be released at higher temperatures and the sorption-adsorption cycle can be repeated with minor loss of the storage capacity.

After that a lot of experimental work has been performed trying to investigate the hydrogen adsorption in SWNTs and to improve the storage capacity of the tubes by doping them

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Encyclopedia of Nanoscience and Nanotechnology Edited by H. S. Nalwa Volume 4: Pages (1-11)

[13-20]. Nevertheless the experiments on hydrogen storage in nanotube samples have been controversial as reported by the recent review of Ding et al. [8].

Concerning the electronic properties of the nanotubes, Collins et al. reported that they are extremely sensitive to the chemical environment [10]. The exposure to atmospheric air or oxygen dramatically influences the nanotubes' electrical resistance, thermoelectric power, and density of states, as determined by transport measurements and scanning tunneling microscopy [10]. The most interesting observation of Collins et al. is that these electronic parameters can be reversibly tuned by a surprisingly small concentration of adsorbed gases.

Periodic Boundary

Quantum Mechanics Molecular Mechanics

Periodic Boundary

Conditions

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