Nano/Microporous Materials: Hydrogen-Storage
Materials
David J. Collins and Hong-Cai Zhou
Miami University, Oxford, OH, USA
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5
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8
9
Introduction
General Considerations
Carbon Materials
Inorganic Materials
Hybrid Organic – Inorganic Materials
Conclusions
Related Articles
Abbreviations and Acronyms
References
1 INTRODUCTION
The hydrogen-fuel-cell-powered vehicle offers the
prospect of a clean, efficient, and renewable energy future.
Besides the fuel cell itself, another barrier exists, however,
on the road to the fuel-cell vehicle: namely, the problem of
storing optimum amounts of hydrogen on board. To maintain a
typical driving range of 400 – 500 km, it is estimated that about
5 kg of hydrogen would be needed.1 Hydrogen, unfortunately,
has a density of only 0.09 g l−1 at room temperature and
atmospheric pressure. It is this extremely low density that
leads to the difficulty of onboard hydrogen storage.
Either of the currently available storage technologies,
high-pressure compression or liquefaction of hydrogen, would
be difficult to implement in a typical small personal vehicle.
Compression of 5 kg of hydrogen to a reasonable volume (a
standard 45-l automotive fuel tank) would require dangerously
high pressures, in excess of 1000 bar, and the tank itself
would, by necessity, be quite heavy to withstand the
pressure. Liquefaction requires extreme cooling (to 21 K)
and efficient insulation; the hydrogen volume required would
still be slightly larger than current automobile fuel tanks
(before inclusion of the necessary insulation and refrigeration
machinery).
Hydrogen adsorption on porous materials is one
of the alternative methods under consideration for onboard
fuel storage for automotive applications. The US Department
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6
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of Energy target for hydrogen-storage systems for 2010 is
6.0 wt% (60 g H2 /kg of storage system) and 45 g hydrogen/l;
the 2015 target is 9.0 wt% and 81 g l−1 .2 Ideally, this
storage would be at near-ambient temperatures (within the
range of simple refrigeration) and reasonable pressures (less
than 100 atm). In addition to improved tank technology,
the bulk of research currently focuses on tank additives,
which must store a greater volume of hydrogen than
could be compressed into the space occupied by the
additive itself to be advantageous. Proposed hydrogen-storage
materials include chemical hydrides and metal hydrides,
which chemically bind hydrogen, and porous adsorbents,
which can hold hydrogen by physisorption via van der Waals
forces. It is these nanoporous adsorbents and their hydrogenadsorption properties and prospects that are the focus of this
article.
2 GENERAL CONSIDERATIONS
Microporous materials are defined as materials with
a regular organic or inorganic framework supporting a
regular porous structure, with pore sizes between 0.2 and
2.0 nm (2 – 20 Å).3 Such materials include organic materials
such as activated carbons (ACs) and carbon nanotubes,
inorganic materials such as zeolites and other silicates, and
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This article is © 2009 John Wiley & Sons, Ltd.
This article was published in the Encyclopedia of Inorganic Chemistry in 2009 by John Wiley & Sons, Ltd.
DOI: 10.1002/0470862106.ia379
NANOMATERIALS: INORGANIC AND BIOINORGANIC PERSPECTIVES
3.0
3.0
2.5
2.5
Hydrogen adsorption (wt %)
Hydrogen adsorption (wt %)
2
2.0
1.5
1.0
AC
SWCNT
MOF
Cyanometalate
Zeolite
0.5
1.5
1.0
AC
SWCNT
MOF
Cyanometalate
Zeolite
0.5
0.0
0.0
0
(a)
2.0
1000
2000
3000
Surface area
4000
(m2
5000
6000
g−1)
0.0
(b)
0.5
1.0
Micropore volume
1.5
(cm3
2.0
g−1)
Figure 1 H2 adsorption at 1 atm and 77 K for activated carbons (AC), single-walled carbon nanotubes (SWCNT), metal – organic frameworks
(MOF), cyanometalates, and zeolites, as related to (a) specific surface area and (b) micropore volume. (Data from References 4 – 6 (activated
carbons), 7 (zeolites and activated carbons), 8 (MOFs), 9 – 11 (cyanometalates), and 12 (SWCNTs))
hybrid materials such as metal – organic frameworks (MOFs).
These materials exhibit type I gas-adsorption isotherms.
For materials with this pore size, the potential fields of
attraction between pore walls and adsorbate molecules
overlap, increasing the attractive force acting on the adsorbate
and, in turn, increasing adsorption. In some cases, the
adsorbate molecules may pack nearly as closely as in the
bulk liquid. However, for some adsorbate gases, the pores
and passages may be small enough to render some portions
of the interior volume inaccessible; obviously, this is more
a problem for larger adsorbate molecules than for small
molecules such as hydrogen.3 Microporous materials typically
have an internal surface area on the order of tens to thousands
of square meters per gram. The internal surface area of a
microporous material is relatively easy to measure using the
Brunauer – Emmett – Teller (BET) method; however, surface
area does not necessarily correlate well with hydrogen uptake,
as shown in Figure 1(a). A better (although, still rough)
correlation is found when the hydrogen uptake is compared to
the micropore volume, as shown in Figure 1(b).
Other important parameters in a practical hydrogenstorage application include the kinetics and thermodynamics
of recharging and release. Of primary consideration is
the heat of formation (for species that bind hydrogen
chemically) or heat of adsorption (for physisorbents), Hf
or Hads . The large Hf of chemisorbents, from 50 to
over 200 kJ mol−1 , necessitates operation considerably above
ambient temperature to drive hydrogen release. In contrast,
physisorbents interact with adsorbed hydrogen weakly,
with Hads typically considerably less than 10 kJ mol−1 ;
significant adsorption of hydrogen can only occur at cryogenic
temperatures. For the binding of hydrogen on a homogeneous
surface, Bhatia and Meyers have calculated the optimum
Hads at room temperature and 30 atm pressure to be
∼15 kJ mol−1 .13
3 CARBON MATERIALS
3.1 Activated Carbons
Charcoal has been known as an effective adsorbent
of gases since the late eighteenth century. Since then, much
improvement has been made both in the synthesis and
understanding of AC materials. In a typical ‘‘top-down’’
synthesis, solid organic materials such as coal, cellulosic
materials (wood, coconut shells, etc.), or polymeric materials,
are pyrolyzed in the absence of oxygen to prepare a charcoal,
which is then activated either thermally or chemically to create
surface functionalization. A ‘‘bottom-up’’ synthetic route can
also be used, in which a template, such as porous silica or
microporous zeolite, is suffused with a gaseous or liquid
organic precursor, which is then carbonized. The template is
then etched away, leaving a porous carbon black, which can
then be activated as above.14
Generally speaking, the hydrogen uptake of ACs is
directly related to the specific surface area and micropore
volume of the material. The theoretical maximum surface
area for carbon adsorbents, ∼2630 m2 g−1 , is derived from
consideration of an infinite single graphene sheet. As
the typical AC studied has a specific surface area of
500 – 1500 m2 g−1 , the overall uptake is generally limited to
less than 4.5 wt% at 77 K.15 It is also difficult to synthesize
an AC material with small pore sizes and minimal pore-size
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This article is © 2009 John Wiley & Sons, Ltd.
This article was published in the Encyclopedia of Inorganic Chemistry in 2009 by John Wiley & Sons, Ltd.
DOI: 10.1002/0470862106.ia379
HYDROGEN-STORAGE MATERIALS
variation. Conventional thermal processing typically results
in 50% or more of pore volume as macropores (greater than
40 Å),16 a wide distribution of pore sizes, and a fraction of
carbon atoms that are inaccessible (i.e., not part of a surface).
The synthesis of nanostructured (templated) carbon materials
is one way of surmounting this problem.
Carbon materials have a low affinity for the
dihydrogen molecule. Between two ideal infinite parallel
sheets of graphite with the appropriate spacing, the enthalpy
of adsorption of dihydrogen has been calculated to be
∼10 kJ mol−1 ;17 actual materials have measured adsorption
enthalpies considerably lower than this, with typical values
3 – 5 kJ mol−1 . The overall potential for AC as a practical
fuel tank adsorbent was investigated by Hynek et al. in
1997.18 Results of this study indicated that (of the sorbents
studied at the time) none were more than marginally able
to increase the volumetric density of hydrogen in a realistic
compressed-hydrogen storage system. Furthermore, at liquidnitrogen temperatures, none could provide better storage than
an unaugmented cryogenic pressure cylinder.
More recently, research has continued toward more
highly structured carbon materials,2 with the intention of
increasing their affinity for hydrogen by reducing pore
size and modifying pore shape; uptakes of ∼5 wt% have
been reported at 77 K for these materials.6,15 Of particular
interest are nanostructured carbon materials with regular,
well-defined pore shapes — especially ‘‘slitpores’’ with widths
approximately twice the diameter of the hydrogen molecule.
Grand canonical Monte Carlo (GCMC) simulations indicate
that an optimal material with such pores could store up to
5.5 wt% hydrogen at 77 K.19 Another class of carbon materials,
carbon aerogels, has also been shown to have very high surface
area (>3000 m2 g−1 ) and adsorbs up to 5.3 wt% H2 at 77 K
and 40 bar.20
3.2 Carbon Nanotubes
Carbon nanotubes, and specifically single-walled
carbon nanotubes (SWCNTs), are seemingly ideal material for
the storage of hydrogen: such tubes contain internal pores of
well-controlled size and distribution, and could conceivably
be arrayed in a close-packed solid with minimization of
macropore volume. Hydrogen would be adsorbed both into the
interior of the nanotube and into the interstitial spaces between
tubes. However, the production of nanotubes often results
in soot with a very small fraction of SWCNTs; moreover,
SWCNTs are often closed or capped, with the interior volume
inaccessible, and a significant fraction of metal catalyst is also
often present as an impurity. (See Inorganic Semiconductor
Nanomaterials for High-Performance Flexible Electronics;
Carbon Nanotubes and Nanocomposites for Electrical and
Thermal Applications; Carbon Nanotubes, Single-Walled:
Functionalization by Intercalation.)
Early reports on hydrogen adsorption by SWCNTs
indicated that high-density condensation of hydrogen was
3
possible, with hydrogen adsorption in the range of 5 – 10 wt%
at 77 K, and reported Hads of nearly 20 kJ mol−1 .21 Since
this initial report, controversy has ensued over whether these
values were misstated or miscalculated; a majority of the
hydrogen adsorption may have arisen from metal impurities,
either residual from synthesis or from the sonication used to
break open closed tubes. At present, the general consensus,
based on work with pure, nearly metal-free nanotubes and on
simulation, indicates that unmodified SWCNTs do not make
good candidates for a hydrogen-storage material. The seeming
success of early, metal-contaminated nanotubes, however,
indicates that carbon SWCNTs modified or doped with metals
or alloys in a controlled manner to make metal – carbon
hybrid nanotube materials may yet be worthy of continued
investigation.2 Simulation and preliminary investigation also
indicates that novel arrangements22 and doping23 or surface
modification24,25 of SWCNTs may yet yield higher H2
adsorption values as well.
4 INORGANIC MATERIALS
4.1 Zeolites, Aluminates, and Silicates
The utility of zeolite materials as sorbents and
catalysts are well-known; however, it has only been in the
last 10 years that the hydrogen-storage properties of zeolites
have been intensively investigated. In 2001, Nijkamp et al.
performed a survey of the hydrogen-adsorption properties
of various carbon-based and silicate-based materials at
low temperatures.7 Many of the commercially available
materials investigated were mesoporous, with pore sizes
considerably larger than 20 Å; these materials, as a group,
have relatively low surface areas and generally low hydrogen
adsorption at 77 K and 1 bar. Those zeolitic materials
with a large micropore volume were found to have the
larger hydrogen-adsorption values, as seen in Figure 1. (See
Nano/Microporous Materials: Hydrothermal Synthesis of
Zeolites.)
Zeolites typically have lower surface areas
(<500 m2 g−1 ), smaller micropore fractions, and more than
double the framework mass density of ACs (vide supra) and
MOFs (vide infra). These factors alone make it improbable
that zeolitic materials will become a long-term choice for
onboard hydrogen-storage solutions. However, as ubiquitous,
highly regular, and designable materials, zeolites will likely
remain a simple test bed for new methods in gas-adsorption
investigation.
4.2 Inorganic Nanotubes
A variety of inorganic nanotubes have been
examined for hydrogen-adsorption properties: boron nitride,
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This article is © 2009 John Wiley & Sons, Ltd.
This article was published in the Encyclopedia of Inorganic Chemistry in 2009 by John Wiley & Sons, Ltd.
DOI: 10.1002/0470862106.ia379
4
NANOMATERIALS: INORGANIC AND BIOINORGANIC PERSPECTIVES
molybdenum sulfide, nickel oxide, titanium sulfide, and
titanium oxide.26,27 Of all these, the most extensively studied
has been boron nitride nanotubes, which are isoelectronic
and isostructural to carbon nanotubes. Computational studies
indicate that the hydrogen molecule should interact more
strongly with the B – N dipole than with the carbon atoms
found in SWCNTs, thus increasing both Hads and ultimate
adsorption capacity when compared with carbon nanotubes
of the same surface area.28 Experimentation has shown that
hydrogen adsorption at room temperature by collapsed boron
nitride nanotubes is at least comparable to SWCNTs, with
4.2 wt% adsorbed at 10 MPa.26 (See Inorganic Nanocrystals:
Patterning and Assembling.)
5 HYBRID ORGANIC–INORGANIC MATERIALS
5.1 Metal–Organic Frameworks
Metal – organic frameworks (also known as coordination polymers or coordination networks) are constructed of
metal atoms or small metal-containing clusters connected by
multidentate organic ligands (typically carboxylates) via coordination bonds.8,29,30 MOFs possess highly ordered crystalline
structures, with channels and pores of uniform size and shape.
High-quality single-crystal X-ray data are generally not difficult to generate, thus simplifying the determination of pore
size and micropore volume. These pores and channels often
contain guest species introduced during the synthesis; these
guests can often be removed under vacuum and/or elevated
temperature. In some cases, removal of these guests leads to
collapse of the framework; however, many MOFs retain a
permanent porosity, and guest molecules, such as hydrogen or
nitrogen molecules, can be reintroduced into the network.
By varying the choice of metal ion and the
coordination mode and shape of the organic linker, a
variety of topologies and structures can be produced. One
relatively simple modification, a lengthening of the organic
linker, has been shown to produce identical topologies with
increasing pore sizes. This versatile ability to ‘‘tune’’ the
MOF composition and functionality to match a particular
application has proven to be quite powerful, as MOFs have
been proposed for a number of practical applications, including
separations and gas storage. In 2003, Yaghi et al. reported the
first measurements of hydrogen adsorption on an MOF;31 since
then, the hydrogen-adsorption properties of at least 60 MOFs
have been measured.8 Attempts to harness the versatility of
MOF design have taken two directions in the search for ideal
hydrogen-storage materials: increasing the specific surface
area and/or pore volume, and increasing the interaction energy
between the framework and the hydrogen molecule.
MOFs have been reported with surface areas in
excess of 4000 m2 g−1 , and with micropore volumes greater
than 1 cm3 g−1 , both values higher than any reported for AC
or zeolite. Some of these high-surface-area materials have
been found to have a maximum hydrogen uptake at 77 K
of over 6 wt% at pressures less than 80 atm.8,29 However,
these materials still have uptakes at room temperature of less
than 0.5 wt% — clearly, high surfaces area and large porosities
are insufficient to achieve high-capacity ambient-temperature
storage.
The second strategy, the design of MOFs with
increased binding interactions with the dihydrogen molecule
(increased Hads ), has been pursued in several directions.
The first, and perhaps simplest, approach is to reduce the size
of the pores to more closely match the size of the hydrogen
molecule. This has been achieved by the use of smaller
ligands, or more commonly, by generating interpenetrated
structures, in which two or more identical frameworks are
physically entangled.32 The effect of interpenetration is to
subdivide large pores into several smaller ones, with each
pore bounded by only part of the whole organic linker.
Interpenetration also results in an increase in specific surface
area despite a decrease in overall micropore volume. An
elegant experiment by Ma et al. demonstrated a 41% increase
in surface area and a 133% increase in volumetric hydrogen
uptake by an interpenetrated MOF over the identical MOF in
a noninterpenetrated form.33 GCMC studies on the IRMOF
series indicate that interpenetration allows the hydrogen
molecule to interact with the phenyl-containing central portion
of multiple ligands, and that the potential overlap should
increase Hads .34 As with carbon adsorbents, pore shape
has been found to be an important factor: recent research
indicates that MOFs composed of cuboctahedra based on the
isophthalate motif contain networks with pores and windows
of optimal dimensions for hydrogen storage.35
Another method to increase Hads is by increasing
the number of higher-energy hydrogen-adsorption sites within
the network. Such sites can be either ligand-based or associated with the metal center. The most successful ligand-based
strategy has been to increase the aromaticity of the central part
of the linker molecule: the incorporation of naphthalene rather
than a benzene ring at the center of the organic linker has
been shown to increase hydrogen uptake in the IRMOF series
by nearly 1 wt% at 77 K and 1 atm.36 Additional ligand-based
strategies include the use of electron donors as substituents
on the central phenyl ring of the ligand, and the use of heterocyclic ligands to induce dipole moments within the linker.
In both cases, computational results on small models indicate
that such linkers should have a higher affinity for the hydrogen
molecule; however, such gains have been difficult to realize
in practice.37–39
Just as the active center of hemoglobin possesses a
coordinatively unsaturated iron atom that captures and releases
gas molecules, such unsaturated or entatic metal sites have
been proposed to act as sites of higher hydrogen affinity
in MOFs. In many cases, metal atoms in as-synthesized
MOFs coordinate one or more solvent or water molecules in
addition to forming bonds with the linking ligand; often, these
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DOI: 10.1002/0470862106.ia379
HYDROGEN-STORAGE MATERIALS
solvent molecules can be removed without destroying the
framework by heating the MOF under vacuum. Once these
coordinated solvent molecules are removed, the metal ion is
left coordinatively unsaturated; computational studies indicate
that such sites should have a high affinity for hydrogen
molecules.40,41 Such unsaturated metal centers (UMCs) have
been shown to be among the first sites occupied by adsorbed
hydrogen molecules. One such example is the coppercontaining MOF known as HKUST-1, or Cu3 (btc)2 (btc =
1,3,5-benzenetricarboxylate). Bordiga et al. have shown that,
in this MOF, the removal of axial aqua ligands from dicopper
paddlewheels within the MOF, dubbed ‘‘thermal activation’’,
produces coordinatively unsaturated copper atoms, and that
these copper UMCs are accessible to adsorbed gases (in this
case, CO).42 After activation, HKUST-1 can adsorb up to
3.6 wt% hydrogen at 10 bar and 77 K. Neutron diffraction
of D2 -loaded HKUST-1 revealed D2 molecules associated
with the unsaturated copper sites, as shown in Figure 2; the
D2 · · ·Cu distances indicate significant interaction.
A second example of an MOF with unsaturated
metal sites and the ability to adsorb significant amounts of
hydrogen is Mn3 [(Mn4 Cl)3 (btt)3 (CH3 OH)10 ]2 (btt = 1,3,5benzenetristetrazolate), as reported by Long et al. Upon
thermal activation, at 90 bar of hydrogen pressure, this MOF
adsorbs 6.9 wt% hydrogen at 77 K and 1.4 wt% at 298 K.
This high uptake capacity can be attributed to exposed
Mn2+ sites within the network, which interact strongly with
H2 molecules, with a Hads of over 10 kJ mol−1 .44 The
association of H2 molecules with the manganese UMC is
(a)
(b)
D2(3)
D2(1)
(c)
(d)
,
D2(4)
D2(2),
D2(5)
D2(6)
(e)
Figure 2 D2 adsorption sites in HKUST-1, as identified by neutron
powder diffraction, numbered in order of occupation with increased
loading, shown along [001] (a), [111] (b), D2 associated with the
axial Cu(II) paddlewheel UMC (c), within the 5 Å pore (d), and
within the 9 Å pore (e). (Reprinted with permission from Peterson
et al.43  2006 American Chemical Society)
5
IV
C
N
III
I
Mn
Cl
II
Figure 3 D2 adsorption sites in Mn(btt), as identified by neutron
powder diffraction. (Reprinted with permission from Dincǎ et al.44
 2006 American Chemical Society)
evident via neutron powder diffraction studies, as shown
in Figure 3. Incorporation of the nitrogen-rich btt ligand may
also contribute to high hydrogen adsorption, as other nitrogenheterocycle-based ligands in MOFs have been shown to lead
to heats of adsorption in excess of 8 kJ mol−1 .38,45
As a class, MOFs hold exceptional promise as
hydrogen-storage materials. These highly ordered materials,
with a high degree of porosity and tunable pore size and
framework-adsorbent interaction, make them ideal candidates
for further exploration. Reported Hads for hydrogen in MOFs
range from 6 to 12 kJ mol−1 ,8,35 with rapid improvements
reported as techniques of rational design are more widely
applied to these novel materials. As more carefully tuned
networks and compounds are generated, it is entirely
conceivable that these values will increase even further,
bringing MOFs into the 15 – 20 kJ mol−1 range deemed ideal.
5.2 Cyanometalates
A material class closely related to MOFs is the
Prussian-blue-type solids, or mixed-oxidation-state transitionmetal cyanides. (See Nano/Microporous Materials: Transition Metal Cyanides.) These form cubic networks of the form
M[M (CN)6 ], composed of [M (CN)6 ]n− octahedra linked
via octahedral nitrogen-coordinated Mn+ cations. These networks have vacancies in a fraction of the hexacyanometalate
sites to preserve charge balance, varying from 25% in Prussian blue, Fe4 [Fe(CN)6 ]3 , to 50% in M2 [M (CN)6 ] species.
Guest molecules occupy not only the voids within the cubic
framework but also the vacancy sites.
A number of such compounds have been synthesized, and BET surface areas and hydrogen adsorption
Encyclopedia of Inorganic Chemistry, Online © 2006–2009 John Wiley & Sons, Ltd.
This article is © 2009 John Wiley & Sons, Ltd.
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DOI: 10.1002/0470862106.ia379
6
NANOMATERIALS: INORGANIC AND BIOINORGANIC PERSPECTIVES
Figure 4 Hydrogen-adsorption sites within Cu3 [Co(CN)6 ]2 , as
determined by difference Fourier analysis of neutron diffraction
of H2 -loaded material. (Reprinted with permission from Hartman
et al.46  2006 American Chemical Society)
measured.9 Typical surface areas for these compounds are
500 – 900 m2 g−1 ; hydrogen adsorption at 77 K and 1 atm
ranges from 0.5 – 1.5 wt%. Hads for hydrogen in these
compounds has been measured to be 6 – 8 kJ mol−1 , and maximum hydrogen capacities at 77 K and high pressure have been
estimated to be ∼2 wt%. Neutron diffraction shows that hydrogen is adsorbed both within the interstitial pores and in the
framework vacancies, as shown in Figure 4;46 although these
vacancies are UMCs, they are not the primary contributors to
the hydrogen capacity of these compounds.9 Work by Long
et al. continues, with the goal of incorporating electron-rich
metal centers with higher affinity for the hydrogen molecule
into these networks.
A second type of cyanometalate, the metal
nitroprusside, is of similar composition, with formula
M[M (CN)5 (NO)]. Two such compounds have been synthesized by Bockrath et al.; the surface areas are 500 – 650 m2 g−1 ,
with micropore volumes of ∼0.3 cm3 g−1 . Each compound
adsorbs ∼1.6 wt% hydrogen at 77 K and 1 atm, with heat of
adsorption at low coverage of ∼7.5 kJ mol−1 .11 For these compounds, the network is characterized by vacancies in the M2+
sites due to the inability of NO to act as a bridging ligand;
as in Prussian blue analogs, these vacancies are associated
with UMCs. The similarity between these compounds and
Prussian blue analogs in Hads indicates that similar adsorption environments exist in these two classes of closely related
compounds.
some approaching, under high pressure, the 6.0 wt% goal of
the US Department of Energy. None of these physisorbents,
however, is able to adsorb more than 1.5 wt% at near-ambient
temperatures. Those materials with micropores (less than
20 Å) prove to be more able to take up larger amounts
of hydrogen than those with mesopores. Several types of
templated ACs, modified carbon nanotubes, and hybrid
organic – inorganic materials hold promise for increasing
room-temperature storage amounts, as each can be tuned via
additives, surface modifications, or composition to increase the
amount of interaction between the adsorbent and the hydrogen
molecule, as measured by Hads . Considerably higher heats
of adsorption, between 15 and 20 kJ mol−1 , will be necessary
to vault nanoporous physisorbents to the ‘‘top choice’’ for the
solution to the onboard hydrogen-storage problem. Research
into each of these classes of novel materials is poised to
continue to make leaps forward, both in hydrogen uptake and
in understanding of the mechanisms and factors necessary to
meet the hydrogen-storage goals of the next decade.
7 RELATED ARTICLES
Carbon Nanotubes and Nanocomposites for Electrical and Thermal Applications; Carbon Nanotubes,
Single-Walled: Functionalization by Intercalation; Inorganic
Nanocrystals: Patterning and Assembling; Inorganic Nanotubes; Inorganic Semiconductor Nanomaterials for HighPerformance Flexible Electronics; Nano/Microporous Materials: Hydrothermal Synthesis of Zeolites; Nano/Microporous
Materials: Transition Metal Cyanides.
8 ABBREVIATIONS AND ACRONYMS
ACs = activated carbons; BET = Brunauer – Emmett – Teller; btc = 1,3,5-benzenetricarboxylate; btt = 1,3,5benzenetristetrazolate; GCMC = Grand canonical Monte
Carlo; MOFs = metal – organic frameworks; SWCNTs =
single-walled carbon nanotubes; UMCs = unsaturated metal
centers.
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6 CONCLUSIONS
A variety of nanoporous materials have been shown
to adsorb at least limited amounts of hydrogen at 77 K, with
2. U.S. Department of Energy, Hydrogen, Fuel Cells & Infrastructure Technologies Program Multi-Year Research,
Development and Demonstration Plan, 2007; http://www1.eere.
energy.gov/hydrogenandfuelcells/mypp.
Encyclopedia of Inorganic Chemistry, Online © 2006–2009 John Wiley & Sons, Ltd.
This article is © 2009 John Wiley & Sons, Ltd.
This article was published in the Encyclopedia of Inorganic Chemistry in 2009 by John Wiley & Sons, Ltd.
DOI: 10.1002/0470862106.ia379
HYDROGEN-STORAGE MATERIALS
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Encyclopedia of Inorganic Chemistry, Online © 2006–2009 John Wiley & Sons, Ltd.
This article is © 2009 John Wiley & Sons, Ltd.
This article was published in the Encyclopedia of Inorganic Chemistry in 2009 by John Wiley & Sons, Ltd.
DOI: 10.1002/0470862106.ia379