Biomedical Engineering Reference
In-Depth Information
gravimetric and volumetric hydrogen gas adsorption capacities up
to 20 wt% and declared the validity of such carbon nanomaterials
not only for hydrogen storage, but also for natural gas and oxygen
storage, expanding therefore the application fields. However, a
confirmation of this level of gases adsorption on similar adsorbents
has not been given by other researchers. In partial contradictions
with the data of [50] are also the results reported in Ref. [35], where
the hydrogen adsorption was increased of about five times by milling
crystalline fullerene up to an amorphous state. Semi-empirical
analysis of hydrogen sorption on various types of fullerenes is
presented in Ref. [51]. Here the mechanisms of interaction of
hydrogen molecules and atoms with the structure of fullerene have
been considered in great details. By the way, the same authors have
performed a similar work by investigating physical and chemical
nitrogen sorption on fullerene structures [52].
A significantly larger number of active researches have been
performed on hydrogen adsorption by carbon nanotubes [13, 14,
53]. The carbon nanotubes are chemically stable, have greater
specific adsorption surface, insignificant weight, and are relatively
inexpensive. These properties make carbon nanotubes an ideal
material for storage of hydrogen. Already in one of the first works
on hydrogen sorption on single-walled nanotubes (SWCNT) the
possibility to achieve a hydrogen sorption level up to 5-10 wt%
has been shown [54]. It is obvious, that to achieve such results not
only superficial adsorption, but also volumetric filling of internal
micropores, taking into account gas liquefaction in micropores by
processes of capillary condensation, should be involved. The sorption
value also depends on diameter of the used nanotubes samples or of
the special fibers, made on their basis.
Note that for the highest possible density of the sorbent, the
complete filling of nanotube cavities by capillary condensation
would correspond to a mass density of liquid hydrogen equal to
~0.07 g/sm
3
. And the minimal sorption capability of the hydrogen
adsorbents necessary for practical applications is equal to 6 wt%.
It is necessary to note that the number of published papers on
hydrogen sorption by single-walled and multi-walled nanotubes
samples and various types of nanotube-based structures is so
large, that their detailed analysis is rather difficult. Therefore, we
shall mention only the most relevant points evidenced in these
works that give valuable suggestions for the implementation of
