Carbon nanofibers , hydrogen storage

The prineiple appheation of a carbon nanofiber hydrogen storage medium is in a fuel tank for an integrated on-board fuel cell system with a polymer electrolyte membrane (PEM) fuel eell stack at its core and a hydrogen supply stored as adsorbed hydrogen in a pressurized tank containing carbon nanofibers. 

Carbon nanofibers consist of near-submicroscopic tubes of carbon atoms. They outclass almost all other known materials in their ability to absorb hydrogen molecules. With carbon nanofibers, for example, a volume of 36,000 liters of hydrogen can be reduced to a mere 35 liters. Carbon nanofibers are a recent discovery, however, and much research is still required to confirm their applicability to hydrogen storage and to develop the technology. 

Hydrogen interaction with the carbon nanostructural materials (nanotubes, nanofibers, fullerenes C60 and C70 has been intensively studied over the last years. A developed surface of nanotubes and nanofibers induced a considerable applied interest aimed at hydrogen storage and reduced consumption of organic fuel in modem industry. For the academic studies, of interest is the nature of the hydrogen interaction with the carbon nanomaterials. 

D.J. Browning et al., Studies into the storage of hydrogen in carbon nanofibers Proposal of a possible reaction mechanism. Nano Lett. 2, 201 (2002)... 

The obtained carbon nanofibers were used for the synthesis of composite materials MgH2-CNF, whose hydrogen storage characteristics were thoroughly studied. 

The investigation of hydrogen sorption properties of the MgH2-CNF composites, obtained by mechanochemical treatment of mixtures of the components, testifies about availability of use of carbon nanofibers for creation of hydrogen storage composite materials. 

Hydrogen-storage characteristics of samples of four types were studied as synthesized MgH2(l), MgH2 after mechanical activation, m/a (2) MgH2-graphite (3) and MgH2-carbon nanofibers (CNF) both after mechanical activation. 

Simonyan, V.V. and Johnson, J.K. (2002). Hydrogen storage in carbon nanotubes and graphitic nanofibers.Alloys Compd., 330, 659-65. 

On the other hand, also carbon nanofibers based on stacked graphite layers seem show appreciable gravimetric storage capacity at room temperature and at moderate pressure (about 120 bar) [133], but other experimental results obtained on similar nano-materials appear contradictory [134], and the hydrogen storage mechanism is still far to be understood. 

Very low hydrogen uptake values for carbon nanofibers are reported by both a Canadian group [23] and by Hirscher et al [24]. They obtained at around 11 MPa, respectively 0.7 and 0.1 wt%. Ritschel et al. [25] and Tibbetts et al. [26] confirm with their measurements insignificant or very low hydrogen storage capacity for GNFs. 

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