Environmental Engineering Reference
In-Depth Information
In another study, ultrahigh surface area carbons (3000-3500 m
2
·g
−1
) have
been obtained via chemical activation of polypyrrole with KOH and the
carbon materials exhibit large pore volumes (up to similar to 2.6 cm
3
·g
−1
)
and possess two pore systems: one of pores in the micropore range (similar
to 1.2 nm) and the other in the small mesopore range (2.2-3.4 nm) [29].
Tuning of the carbon textural properties through the control of the activation
parameters (temperature and amount of KOH) led to the generation of acti-
vated carbon that exhibits excellent hydrogen storage capacity of up to
7.03 wt% at −196°C and 20 bar, which is the highest ever reported for one-
step ACs and among the best for any porous material. The gravimetric
hydrogen uptake of the carbons translates to a very attractive volumetric
density of up to 37 g H
2
·L
−1
at 20 bar. These carbons exhibit excellent gravi-
metric and volumetric capacity due to the fact that their high porosity is not
at the detriment of packing density.
In a very recent study, the effect of Pd nanoparticle doping of AC on
hydrogen storage capacity has been studied [30]. Three ACs with an apparent
surface area ranging from 2450 to 3200 m
2
/g were doped with Pd nanopar-
ticles at different levels within the range 1.3-10.0 wt%, and their excess
hydrogen storage capacities were measured at 77 and 298 K at pressures up
to 8 MPa. The hydrogen storage properties depend linearly on Pd content
when hydrogen storage is carried out at 298 K and at pressures up to 1 MPa.
At higher pressures, hydrogen storage depends on microporous volume so
Pd addition does not bring capacity enhancement. Hydrogen storage at 77 K
fundamentally depends on the specific micropore volume and consequently,
Pd doping decreases hydrogen storage capacities by decreasing the specific
micropore volume available for physisorption.
Other carbon-related but not pure carbon-based nanomaterals for hydro-
gen storage include pristine and modified polymers or composite structures
involving organic polymers and metal-doped polymers [17, 31-33]. Some
of these materials show improved hydrogen storage capacity compared with
pristine carbon nanostructures.
7.1.2 Other Nanostructures and Microstructures
Some noncarbon-based nanostructures and microstructures have also been
investigated for hydrogen storage, for example, glass capillary arrays [34-
36], hollow glass microspheres [37, 38], and zeolites [39-43]. Glass capillary
arrays have been developed as systems for safe infusion, storage, and con-
trolled release of hydrogen gas, with storage pressures up to 1200 bar [36].
This technology enables the storage of a significantly higher amount of
hydrogen than other approaches, and the main determinant in this storage
technology is the pressure resistance of glass capillaries.
