Biomedical Engineering Reference
In-Depth Information
Therefore, it is important to emphasize that to achieve the
system-level targets, the gravimetric and volumetric capacities of the
storage material should be considerably higher than the established
system-level improvements. In addition to weight, volume and cost,
there are also several important DOE targets defined by vehicular
requirements, such as hydrogen charging and discharging rates,
durability, safety, and operability over temperatures and pressures.
At present, the hydrogen on-board storage is realized mainly by
the use of rather expensive composite vessels with molecular gaseous
hydrogen under pressure of about 70-80 MPa. Obviously, these
systems are not suitable in terms of costs and safety requirements
[1-3].
For the last 10 years various storage strategies and technologies
have been proposed and tested, but to date none of the approaches
have fulfilled all of the DOE requirements and targets for either
transportation or utility use. As concluded in a paper on the DOE
National Hydrogen Storage Project [1], DOE agrees with the National
Academies' recent recommendation [2] that new concepts and
ideas should be elicited, because success in overcoming the major
drawbacks that are blocking the on-board storage is crucial for the
future of fuel cells in transportation systems. The development of
hydrogen-fueled vehicles and portable electronics will require new
materials, and especially, nanomaterials that can store large amount
of hydrogen at ambient temperature and at relatively low pressures
(not higher than 15 MPa) providing safety, small volume, low weight,
and fast kinetics for recharging.
During the last decade graphite, carbon nanotubes, and nano-
fibers have been both theoretically and experimentally investigated
as potential adsorbent structures (cf. reviews in Refs. [4, 5]). Even
though some reports claim very high storage capacity, such findings
have not been supported by the majority of investigators. However,
recently hydrogen storage in nanostructured carbon has attracted
renewed interest because of new developments in nanotechnology
research and to the significant advantage in terms of light weight
and of reasonably inexpensiveness of such materials.
According to a physical-chemical analysis [5], the most
appropriate technology for efficient hydrogen storage, that would
satisfy the majority of DOE requirements [1], could be hydrogen
multilayer intercalation in various carbonaceous nanostructures
(Fig. 2.1). These structures would have physical and chemical
