Environmental Engineering Reference
In-Depth Information
Figure 28.6
Atomic structures of Ti-hydroxyl complexes attached to CNTs. The left figure is the cross-sectional view and the right figure
is the oblique view. reprinted with permission from ref. [101]. © Elsevier.
hydrogen storage technologies have been reported by yürüm et al. [95]. Among all porous materials, metal-organic frameworks
are the best candidates for h
2
adsorption, since they consist of light atoms, they are highly porous, and their pore dimensions
can be tailored by chemical engineering [96]. The most recent achievements in developing novel microporous silicon-based
structures, aluminosilicates, and related materials have been described by Azzouz [97].
The transformation from the physisorption state to the chemisorption state of h
2
molecules in nanostructured carbon
materials as applied to a fullerene C
20
and a B-doped fullerene C
19
B system was investigated by Tian et al. [98] using different
density function methods. The convenient carbon-based adsorbent material could form the basis of technologically viable
hydrogen storage systems is CNTs. recent applications of CNTs in hydrogen production and storage were examined by
Oriňáková and Oriňák [38]. The investigation of the structure and hydrogen storage behavior of Ca-decorated graphene
shows that Ca dimers act as nucleation positions of hydrogen adsorption [99]. The hydrogen storage capacity via the spillover
mechanism in Ca-adsorbed graphene depends on the Ca content and could approach 7.7 wt%. Theoretical analysis [100]
shows that the magnesium-decorated boron fullerene B
80
has a high hydrogen storage capacity storing up to 96 h
2
molecules
with an ideal hydrogen uptake of 14.2%. This suggests a possible method of engineering new structures for high-capacity
hydrogen storage materials with the reversible adsorption and desorption of hydrogen molecules. Various forms of storage
materials, which are obtained by modifying well-known nanomaterials using Ti-functional group complexes, were investi-
gated by lee et al. [101]. As calculations show, Ti-decorated 2-mercaptoethyl sulfide, hydroxylfunctionalized polyethylene,
and CNTs can store h
2
molecules with a gravimetric density of 8.8, 11.5, and 5.5 wt%, respectively. The atomic structure of
Ti-hydroxyl complexes attached to CNTs is shown in Figure 28.6.
28.7
CoNClusioN
Nanotechnology occupies an important place in the production and investigation of new functional materials for applications in
fuel cell vehicles. One of the most important challenges for ultimate commercialization of the fuel cell technology is the
preparation of active, robust, and low-cost catalysts on the base of nanomaterials, such as Pt or multimetallic nanoparticles,
nonprecious-metal chalcogenides, organometallic compounds, surface-modified CNTs, and graphene. The performance and
durability of fuel cells seriously depend on catalyst support materials. recent studies show that catalyst nanoparticles supported
on nanostructured carbon materials (carbon nanofibers, nanotubes, and graphene) display higher electrocatalytic activity than
those supported on traditional ones.
Nanostructured materials are also used in the development of cheaper and more efficient membranes for fuel cells (nanocomposite
membranes with the addition of nanocrystalline ceramic oxides or functionalized graphene oxide nanosheets to the commercial
Nafion material, nanocomposites prepared on the base of multiwalled CNTs, etc.). Some recent investigations show advantages of
track-etched membranes in fuel cell applications such as no need to wet the membrane, larger proton conductivity, and resistance to
extreme conditions.
Although hydrogen is widely recognized as a promising energy carrier for the transportation sector, widespread adoption of
hydrogen and fuel cell technologies depends critically on the ability to store hydrogen at adequate densities. Solid-state storage
is potentially the most convenient and safest method from a technological point of view, because this storage technology supposes
the presence of near-ambient temperatures and pressures. This category of storage media includes a group of mg-based
nanostructured hydrides, novel microporous silicon-based structures, and different nanostructured carbon materials.
