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Posted: March 20, 2007
Fullerenes as hydrogen storage
(Nanowerk News) Hydrogen is considered to be one of the promising power sources in the future. But hydrogen has to be obtained, stored, transported. Various devices – hydrogen accumulators - are used now for hydrogen storage. Their design is being constantly improved, but so far devices have not been created that would contain hydrogen sufficient for wide commercial application. In the accumulators used nowadays, the hydrogen content does not exceed five to six percent of the weight. In the industry, hydrogen is now stored in the compressed gaseous state, in liquefied state, in the form of hydrides or metal-hydride systems, and in zeolites.
As nanotechnologies developed, the researchers proceeded to investigations of carbonic nanoelements – nanotubes, nanofibers, nanocones, which possess unique properties to absorb various gases. The hydrogen quantity in such systems depends on adsorptive properties of nanostructures, pressure and environmental temperature. Their main advantage is the ability to store hydrogen at low pressure. Although this did to come to application yet, the researchers are carrying out theoretical study. In general, they came to studying nanotubes’ properties. It has turned out that they are theoretically capable to accumulate five to ten percent of hydrogen at the temperature of 77 Kelvin degrees - the boiling temperature of nitrogen.
The researchers from the Institute of Applied Mechanics, Ural Branch of Russian Academy of Sciences, believe that absorbing properties of fullerenes and other nanostructures that include fullerenes have not been fully investigated. Therefore, they set a problem: to study the influence of thermodynamic parameters – pressure and temperature – on the process of molecular hydrogen absorption by such nanosystems. With the help of molecular dynamics methods, they performed numerical analysis of processes of hydrogen absorption by the C20, C60, C80, C180, C240, C540 fullerenes and the C46, C167, C505 carbonic clusters at various pressures and temperatures. The researchers managed not only to determine the influence of these thermodynamic parameters on the fullerenes’ hydrogen absorption ability but also to discover the parameters at which hydrogen can be stably stored in these nanoobjects.
“The quantity of hydrogen absorbed at the temperature of 60 Kelvin degrees and the pressure of ten megapascals achieves the 13.61 percent, and at the temperature of liquid nitrogen boiling - 77 Kelvin degrees - and the pressure of ten megapascals it reaches 6.6 percent”, say the authors of the research. Utilization of carbonic clusters the resemble fullerenes in shape is highly promising, the researchers state, as clusters’ internal surface opens for absorption, which is not the case with fullerenes.