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Scientific Report 2007-2009
Condensed matter physics and biophysics
C39. Nanomaterials for alternative energies. Solid-state hydrogen
storage
Hydrogen is attracting renewed interest as an energy
carrier, due to the necessity of finding ecological energy
media which may decrease the environmental pollution
from fossil fuels. Hydrogen storage represents a nodal
point for the development of a hydrogen economy. Of
the three possible ways to store hydrogen, i.e. as high
pressure gas, as a liquid (≃20 K at atmospheric pressure),
or as hydrides in solids, the latter one appears
as the most promising, due to the high mass and volume
density and safety. The development of hydrogen
storage media is currently considered as the most technologically
challenging way for achieving a hydrogen-based
economy. There are many compounds with promising
hydrogen absorption capacities which, however, display
serious drawbacks, like lack of reversibility, slow kinetics
or deterioration with proceeding cycling. There is currently
general agreement that adopting only traditional
materials and methods will not lead to the achievement
of the strict requirements necessary for the solid state
hydrogen storage. At present, a considerable part of the
international research efforts is devoted to the study of
solid state hydrogen storage materials finely dispersed on
artificial nanoporous supports. This approach is considered
promising, since the use of thin layers of hydrogen
absorbing compounds is expected to avoid sample compacting
and to increase the surface to volume ratio to
very high values. However the real interest in the dispersion
of nanoparticles into nanoscaffolds resides in the
possibility of obtaining a compound with better storage
properties than the starting bulk material.
of the most promising compounds, ammonia borane
(NH 3 BH 3 ), finely dispersed in the channels of mesoporous
silica does not undergo the structural phase transition
present in the bulk, thus providing a clear indication
that the basic physical properties of this material
are strongly modified by such assembling on a nanoscale.
The occurrence of different electronic and lattice interactions
in nanostructured scaffolded hydrogen storage systems
could provide an alternative approach to modify
the thermodynamic features of bulk materials to obtain
enhanced dehydrogenation properties and to accomplish
reversibility. Finally anelastic spectroscopy has been
proven to be a powerful tool, complementary to NMR
and neutron scattering, in the study of the hydrogen dynamics.
This information is highly demanded, because
the hydrogenation/dehydrogenation of storage materials
resides on the possibility for hydrogen atoms to perform
short or long range diffusion processes. Anelastic spectroscopy
investigations conducted in alanates allowed us
to propose a model for the dehydrogenation process.
The extension of the studies in ammonia borane lead
us to identify the rotational and torsional dynamics of H
atoms and to derive their activation energies [2]. Moreover,
we used the measurements of the dynamic elastic
modulus, which is very sensitive to the occurrence of
phase transformations, to characterize the nature and
the kinetics of the phase transition in NH 3 BH 3 [3].
E/E
0 . 3
0 . 2
0 . 1
0 . 0
3
1
1 M C M - 4 1
2 N H 3 B H 3 b u l k p o w d e r
3 N H 3 B H 3 : M C M - 4 1 ( 1 : 2 )
heat exchange (W/g)
- 0 . 1
- 0 . 2
1 . 2
0 . 8
0 . 4
0 . 0
- 0 . 4
- 0 . 8
1
2
- 1 . 2
1 8 0 2 0 0 2 2 0 2 4 0 2 6 0 2 8 0
T ( K )
2
3
Figure 1: Effect on the Young modulus of the confinement
of ammonia borane into mesoporous silica, MCM-41 [2].
An important task of the research conducted in our
Laboratory is the understanding of the basic mechanisms
of the hydrogenation/dehydrogenation process and the
changes induced by the nanoconfinement. A combined
study performed by anelastic spectroscopy and differential
scanning calorimetry allowed us to show that one
Figure 2: Schematic representation of the rotational and
torsional dynamics of the NH 3 BH 3 molecule with the corresponding
energy profile [3].
References
1. O. Palumbo et al., Int. J. Hydr. En. 33, 3107 (2008).
2. A. Paolone et al., J. Phys. Chem C 113, 5872 (2009).
3. A. Paolone et al., J. Phys. Chem C 113, 10319 (2009).
Authors
R. Cantelli, A. Paolone 3 , O. Palumbo 3 , P. Rispoli
Sapienza Università di Roma 92 Dipartimento di Fisica