U.S. patent application number 15/307142 was filed with the patent office on 2017-02-16 for hydrogen storage element for a hydrogen store.
The applicant listed for this patent is GKN Sinter Metals Engineering GmbH. Invention is credited to Antonio CASELLAS, Klaus DOLLMEIER, Eberhard ERNST, Rene LINDENAU, Anastasia OZKAN, Lars WIMBERT.
Application Number | 20170044011 15/307142 |
Document ID | / |
Family ID | 53055037 |
Filed Date | 2017-02-16 |
United States Patent
Application |
20170044011 |
Kind Code |
A1 |
CASELLAS; Antonio ; et
al. |
February 16, 2017 |
Hydrogen Storage Element for a Hydrogen Store
Abstract
The hydrogen storage element for a hydrogen store comprises a
pressed article having a hydrogen-storing first material and having
a thermally conductive second material, wherein the second material
is in thermal contact with the hydrogen-storing first material and
has, in some regions, a different three-dimensional distribution
within the pressed article.
Inventors: |
CASELLAS; Antonio;
(Siegburg, DE) ; DOLLMEIER; Klaus; (Westhausen,
DE) ; ERNST; Eberhard; (Eichenzell, DE) ;
LINDENAU; Rene; (Radevormwald, DE) ; OZKAN;
Anastasia; (Witten, DE) ; WIMBERT; Lars;
(Schwelm, DE) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
GKN Sinter Metals Engineering GmbH |
Radevormwald |
|
DE |
|
|
Family ID: |
53055037 |
Appl. No.: |
15/307142 |
Filed: |
May 4, 2015 |
PCT Filed: |
May 4, 2015 |
PCT NO: |
PCT/EP2015/059706 |
371 Date: |
October 27, 2016 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
Y02E 60/325 20130101;
C01B 3/0031 20130101; Y02E 60/327 20130101; C01B 3/0021 20130101;
Y02E 60/32 20130101; C09K 5/14 20130101; C01B 3/0084 20130101; C01B
3/0078 20130101 |
International
Class: |
C01B 3/00 20060101
C01B003/00; C09K 5/14 20060101 C09K005/14 |
Foreign Application Data
Date |
Code |
Application Number |
May 5, 2014 |
DE |
10 2014 006 372.0 |
Claims
1. A hydrogen storage element for a hydrogen storage means
comprising: a compact comprising a first material having hydrogen
storage capacity and comprising a heat-conducting second material,
wherein the second material is in thermal contact with the first
material having hydrogen storage capacity and has, in some regions,
a different three-dimensional distribution within the compact.
2. The hydrogen storage element as claimed in claim 1, wherein the
three-dimensional distribution of the second material has repeating
sections and each section has three-dimensional distributions.
3. The hydrogen storage element as claimed in claim 1, wherein the
heat-conducting second material takes the form of a layer, film or
ribbon.
4. The hydrogen storage element as claimed in claim 3, wherein the
layer, film and/or ribbon is arranged primarily in a plane of
extension of any shape, with subregions of the layer, film and/or
ribbon having one or more alignments differing from this plane of
extension.
5. The hydrogen storage element as claimed in claim 3, wherein the
layer, film and/or ribbon has a helical or screw form and is
embedded into the first material having hydrogen storage
capacity.
6. The hydrogen storage element as claimed in claim 1, wherein the
heat-conducting second material takes the form of a free-flowing
material and/or of a bed in the compact prior to pressing
thereof.
7. The hydrogen storage element as claimed in claim 6, wherein the
heat-conducting second material has an additive which prevents
alloy formation of the heat-conducting second material with the
first material having hydrogen storage capacity.
8. The hydrogen storage element as claimed in claim 7, wherein the
heat-conducting second material comprises aluminum or an aluminum
alloy, in that the first material having hydrogen storage capacity
comprises magnesium or a magnesium alloy, and in that the additive
comprises graphite, expandable graphite and/or naturally expanded
graphite which separates the aluminum or the aluminum alloy from
the magnesium or magnesium alloy.
9. The hydrogen storage element as claimed in claim 7, wherein the
additive is arranged as a separating layer between the first
material having hydrogen storage capacity and the heat-conducting
second material.
10. The hydrogen storage element as claimed in claim 1, wherein the
heat-conducting second material is permeable to at least hydrogen,
preferably with horizontal alignment of lenticular graphite
particles on filling, such that it is possible to utilize
conduction of heat in the direction of a hexagonal lattice
structure of a graphite structure.
11. The hydrogen storage element as claimed in claim 1, wherein the
heat-conducting second material is permeable to a fluid, especially
a liquid- and/or gas-comprising heat carrier flow for removal of
heat in the course of hydrogenation and for supply of heat in the
course of dehydrogenation of the first material having hydrogen
storage capacity.
12. The hydrogen storage element as claimed in claim 1, wherein the
compact comprises a third material having heat carrier transport
capacity, which is permeable to a fluid, especially a liquid-
and/or gas-comprising heat carrier flow for removal of heat in the
course of hydrogenation and for supply of heat in the course of
dehydrogenation of the first material having hydrogen storage
capacity, and in that the third material having heat carrier
transport capacity is arranged adjacent to the first material
having hydrogen storage capacity and/or to the heat-conducting
second material of the compact therein.
13. The hydrogen storage element as claimed in claim 11, wherein
the third material having heat carrier transport capacity and/or
the heat-conducting second material is porous and/or has open
and/or closed cells.
14. The hydrogen storage element as claimed in claim 1, wherein the
first material having hydrogen storage capacity comprises a polymer
as binder for hydrogenatable material of the first material having
hydrogen storage capacity.
Description
[0001] The present patent application claims the priority of German
patent application 10 2014 006 372.0, the content of which is
hereby incorporated by reference into the subject matter of the
present patent application.
[0002] The present invention relates to a hydrogen storage means
comprising a hydrogen-permeable structure and to a process for
producing a layer structure.
[0003] It is known that hydrogen is stored in cylindrical vessels
into which sheets of a metal hydride/graphite composite material
are inserted. These sheets must have high radial thermal
conductivity in order to remove the heat that arises in the course
of hydrogenation--exothermic intercalation. In the course of
dehydrogenation, this heat has to be supplied again--endothermic
operation. Since metals are good conductors of heat, but their
hydrides are extremely poor conductors of heat, it is necessary to
install them such that heat flow through a second material is
assured. For this purpose, the metal or the metal hydride is mixed
with graphite, for example, in which case the graphite assumes the
function of heat conduction. This mixture is pressed, for example,
axially to give cylinders or sheets or blocks or slabs, and
inserted into a vessel, especially a tank. For this purpose, a
mixture of expanded graphite having very low density is mixed with
the hydrogenatable metal or the metal hydride, such that the
expanded graphite becomes aligned transverse/at right angles to the
pressing direction through the axial pressing. This gives rise to
high thermal conductivity transverse to pressing direction.
[0004] EP-A-1 348 527, EP-A-2 221 131, EP-A-1 407 877 and
JP-A-60162702 disclose processes and apparatuses for production of
components using shaping molds, in which powders of at least two
different compositions are introduced into a shaping mold or into a
cavity of a shaping mold. Further processes of this kind are known,
for example, in DE-B-10 2009 005 859, DE-A-10 2010 015 016, DE-T-60
2004 005 070 and WO-A-2013/036982.
[0005] Further hydrogen storage means approaches and constructions
are known from DE-A-10 2011 103 490, DE-T-600 30 221, U.S. Pat. No.
6,318,453, US-A-2011/0142752 and US-A-2006/0030483.
[0006] It is an object of this invention to provide a material
structure in which conduction of heat is assured, especially for
prevention of overheating or excessive cooling in the course of
dehydrogenation with accompanying loss of function of the hydrogen
storage means.
[0007] This object is achieved by the invention by proposing a
hydrogen storage element for a hydrogen storage means having the
features of claim 1. Advantageous features, configurations and
developments will be apparent from the description which follows,
the figures and also the dependent claims, without restriction of
individual features from a configuration thereto. Instead, one or
more features from one configuration can be combined with one or
more features of another configuration to give further
configurations of the invention. More particularly, the respective
independent and dependent claims can also each be combined with one
another. Nor should the wording of the independent claim be
regarded as a restriction of the subject matter claimed. One or
more features of the claim wording can therefore be exchanged or
else omitted, but may additionally also be added on. It is also
possible to use features cited with reference to a specific working
example in generalized form as well, or likewise to use them in
other working examples, especially applications.
[0008] According to the invention, the hydrogen storage element
comprises a heat-conducting material in thermal contact with the
first material having hydrogen storage capacity. In this case,
these two materials intermesh, meaning that they do not take the
form of mere layers alongside one another. The heat-conducting
second material projects into the first material having hydrogen
storage capacity in subregions, i.e. has different
three-dimensional distribution in this respect within the hydrogen
storage element. This three-dimensional distribution may itself in
turn have regular repeating structures, but this need not
necessarily be the case. For example, it is conceivable that the
second material is a film or ribbon which projects out of the plane
or the film or ribbon in sections. By virtue of the inventive
three-dimensional distribution of the heat-conducting second
material, there is thus an increase in its surface area in thermal
contact with the hydrogen-storing first material, which leads for
good removal of heat in the course of hydrogenating and supply of
heat in the course of dehydrogenating.
[0009] The heat-conducting second material thus extends within the
compact both in the X and Y directions, i.e. in the direction of
the second material, and in the Z direction, i.e. in the direction
of the succession of several layers of first and second
material.
[0010] Different three-dimensional distributions of the second
material are particularly advantageous when it has a helical form.
The second material in helical or spiral form effectively permeates
the compact and is thus in thermal contact with the first material
having hydrogen storage capacity over a large surface area
contact.
[0011] In a further variant of the invention, a hydrogen storage
means is proposed, having a hydrogen-permeable structure,
preferably a porous structure, which is present as a compressed
component in the hydrogen storage means and serves for flow of a
hydrogenous gas.
[0012] The invention especially relates to a layered structure of
hydrogen storage means, especially metal hydride storage means
having graphite laminas of good thermal conductivity, such that the
graphite can remove the large amounts of heat in the hydrogenation
of the hydrogen storage means and supply them in the
dehydrogenation. One of the layers of the layered structure has
mainly at least one of the following functions: primary hydrogen
storage, primary heat conduction and/or primary gas conduction. The
functions of "primary hydrogen storage", "primary heat conduction"
and/or "primary gas conduction" are understood to mean that the
respective layer fulfills at least one of these functions as a main
object in one region of the composite material compact. For
instance, it is possible that a layer is utilized primarily for
hydrogen storage, but is simultaneously also capable of providing
at least a certain thermal conductivity. It may be the case here
that at least one other layer is present which assumes the primary
task of heat conduction, which means that the majority of the
amount of heat is dissipated from the compressed material composite
via this layer. In this case, it is on the other hand possible to
utilize the primarily gas-conducting layer, through which, for
example, the hydrogen can be passed into the material composite or
else, for example, conducted out of it. In this case, the flowing
fluid can also entrain heat.
[0013] The term "hydrogen storage means" describes a reservoir
vessel in which hydrogen can be stored by means of hydrogen-storing
elements or components which for the most part remain intrinsically
dimensionally stable and are in the form, for example, of sheets,
blocks, tablets or pellets. This can be done using conventional
methods of saving and storage of hydrogen, for example compressed
gas storage, such as storage in pressure vessels by compression
with compressors, or liquefied gas storage, such as storage in
liquefied form by cooling and compression. Further alternative
forms of storage of hydrogen are based on solids or liquids, for
example metal hydride storage means, such as storage as a chemical
compound between hydrogen and a metal or an alloy, or adsorption
storage, such as adsorptive storage of hydrogen in highly porous
materials. In addition, for storage and transport of hydrogen,
there are also possible hydrogen storage means which temporarily
bind the hydrogen to organic substances, giving rise to liquid
compounds that can be stored at ambient pressure, called
"chemically bound hydrogen".
[0014] "Element" and "component" each refer to a component of any
geometry having hydrogen storage capacity, for example in sheet,
cylinder, block or slab form or the like. One or more prefabricated
hydrogen storage components of this kind are positioned in the
(pressure) vessel of a hydrogen storage means.
[0015] The term "layers" means that preferably one material, but
also two or more material laminas, are in an arrangement and these
material laminas can be delimited from their direct environment.
For example, it is possible for different materials to be poured in
successively in loose form, such that adjacent layers are in direct
contact with one another. In a preferred configuration, the
hydrogenatable layer is arranged directly adjacent to a thermally
conductive layer, such that the heat that arises on absorption of
hydrogen and/or release of hydrogen can be released from the
hydrogenatable material directly to the adjacent layer.
[0016] One of the layers may, for example, be produced by spray
application. An example of a suitable method for this purpose is
one known in other sectors by the term "wet powder spraying". In
the context of the disclosure is made by way of example to the
article "Wet powder spraying--a process for the production of
coatings" by A. Ruder, H. P. Buchkremer, H. Jansen, W. Mallener, D.
Stover published in "Surface and Coatings Technology", volume 53,
issue 1, Jul. 24, 1992, pages 71-74. WO-A-2008 006 796, on the
other hand, reveals how a material can be processed. In that case,
however, there has been no use of any hydrogenatable material, let
alone any production of a hydrogen storage means or a layer
therefor. In principle, however, this document shows how spray
application can be enabled. Likewise cited therein are other
methods of layer formation as well. As well as spraying, it is
alternatively possible to employ deposition of an electrochemical
nature in order to obtain desired layer formation. Layer formation
is also possible, for example, by means of screenprinting.
[0017] The contents of the publications and literature sources
cited above and any still to be cited below are hereby incorporated
by reference in the subject matter of the present patent
application.
[0018] In a further method by which a layer can be formed,
preferably surface-coated fibers are combined to form bundles.
These bundles are, for example, stretched and then cut in order to
obtain, for example, a layer comprising short fibers. The surface
coating is preferably hydrogen-permeable. If the material of the
fibers is hydrogen-storing, the coating can especially form
protection against oxidation.
[0019] Preferably, a hydrogen storage means is provided, comprising
a first material and a second material at separate locations from
one another, each of which form separate layers adjacent to one
another, preferably abutting one another, the first material
comprising a primarily hydrogen-storing material and the second
material being a primarily heat-conducting material, with the
primarily heat-conducting material extending preferably from the
interior of the hydrogen storage element outward.
[0020] In a development of the hydrogen storage means, a gradient
is formed between the first and second layers, along which a
transition from the first to the second layer is accomplished via a
change in the respective material content (density content) of the
first and second materials.
[0021] A gradient can be brought about, for example, by moving a
bar, in the case of several bars by means of a comb, or generally
by means of a contact element having a different geometry, in the
materials of the first and second layers, when they are yet to be
further processed, for example yet to be laid down with compression
together. Through the controlled gradient formation, it is
especially possible to be able to provide a large heat transfer
area between the first and second materials.
[0022] A further configuration of the hydrogen storage means has
components in the form of a core-shell structure, in which the core
comprises a first material and the shell comprises a different
second material, the first material and/or the second material
comprising a hydrogen-storing material, the components preferably
being selected from the group comprising powders, granules, flakes,
fibers and/or other geometries.
[0023] It is further preferable when the hydrogen storage element
comprises the second material of the shell in the form of a polymer
configured so as to be at least hydrogen-permeable.
[0024] It may also be the case that the hydrogen storage component
has a structure in which the core comprises a primarily
heat-conducting material and the shell a primarily hydrogen-storing
material.
[0025] In a development, the core comprises a primarily
hydrogen-storing material and the shell a primarily heat-conducting
material, the heat-conducting material being
hydrogen-permeable.
[0026] Preferably, the hydrogen-storing material has a
hydrogen-permeable coating which prevents oxidation of the
hydrogen-storing material, the coating preferably being
hydrogen-storing. This coating can alternatively be used to prevent
oxidation or else additionally serve for coherence, i.e. for
mechanical bonding of the hydrogenatable material present, for
example, in particulate form.
[0027] Through the use of at least one polymer, the matrix can
impart good optical, mechanical, thermal and/or chemical properties
to the material. For example, the hydrogen storage means, by virtue
of the polymer, may have good thermal stability, resistance to the
surrounding medium (oxidation resistance, corrosion resistance),
good conductivity, good hydrogen absorption and storage capacity or
other properties, for example mechanical strength, which would
otherwise not be possible without the polymer. It is also possible
to use polymers which, for example, do not enable storage of
hydrogen but do enable high expansion, for example polyamide or
polyvinyl acetates.
[0028] According to the invention, the polymer may be a homopolymer
or a copolymer. Copolymers are polymers composed of two or more
different types of monomer unit. Copolymers consisting of three
different monomers are called terpolymers. According to the
invention, the polymer, for example, may also comprise a
terpolymer.
[0029] Preferably, the polymer (homopolymer) has a monomer unit
which, as well as carbon and hydrogen, preferably additionally
includes at least one heteroatom selected from sulfur, oxygen,
nitrogen and phosphorus, such that the polymer obtained, in
contrast to polyethylene, for example, is not entirely nonpolar. It
is also possible for at least one halogen atom selected from
chlorine, bromine, fluorine, iodine and astatine to be present.
Preferably, the polymer is a copolymer and/or a terpolymer in which
at least one monomer unit, in addition to carbon and hydrogen,
additionally includes at least one heteroatom selected from sulfur,
oxygen, nitrogen and phosphorus and/or at least one halogen atom
selected from chlorine, bromine, fluorine, iodine and astatine is
present. It is also possible that two or more monomer units have a
corresponding heteroatom and/or halogen atom.
[0030] The polymer preferably has adhesive properties with respect
to the hydrogen storage material. This means that it adheres well
to the hydrogen storage material itself and hence forms a matrix
having stable adhesion to the hydrogen storage material even under
stresses as occur during the storage of hydrogen.
[0031] The adhesive properties of the polymer enable stable
penetration of the material into a hydrogen storage means and the
positioning of the material at a defined point in the hydrogen
storage means over a maximum period of time, i.e. over several
cycles of hydrogen storage and hydrogen release. A cycle describes
the operation of a single hydrogenation and subsequent
dehydrogenation. The hydrogen storage material should preferably be
stable over at least 500 cycles, especially over at least 1000
cycles, in order to be able to use the material economically.
"Stable" in the context of the present invention means that the
amount of hydrogen which can be stored and the rate at which the
hydrogen is stored, even after 500 or 1000 cycles, corresponds
essentially to the values at the start of use of the hydrogen
storage means.
[0032] More particularly, "stable" means that the hydrogenatable
material is kept at least roughly at the position within the
hydrogen storage means where it was originally introduced into the
storage means. "Stable" should especially be understood to the
effect that no separation effects occur during the cycles, where
finer particles separate and are removed from coarser
particles.
[0033] The hydrogen storage material of the present invention is
especially a low-temperature hydrogen storage material. In the
course of hydrogen storage, which is an exothermic process,
temperatures of up to 150.degree. C. therefore occur. A polymer
which is used for the matrix of a corresponding hydrogen storage
material therefore has to be stable at these temperatures. A
preferred polymer therefore does not break down up to a temperature
of 180.degree. C., especially up to a temperature of 165.degree.
C., especially up to 145.degree. C.
[0034] More particularly, the polymer is a polymer having a melting
point of 100.degree. C. or more, especially of 105.degree. C. or
more, but less than 150.degree. C., especially of less than
140.degree. C., particularly of 135.degree. C. or less. Preferably,
the density of the polymer, determined according to ISO 1183 at
20.degree. C., is 0.7 g/cm.sup.3 or more, especially 0.8 g/cm.sup.3
or more, preferably 0.9 g/cm.sup.3 or more, but not more than 1.3
g/cm.sup.3, preferably not more than 1.25 g/cm.sup.3, especially
1.20 g/cm.sup.3 or less. The tensile strength according to ISO 527
is preferably in the range from 10 MPa to 100 MPa, especially in
the range from 15 MPa to 90 MPa, more preferably in the range from
15 MPa to 80 MPa. The tensile modulus of elasticity according to
ISO 527 is preferably in the range from 50 MPa to 5000 MPa,
especially in the range from 55 MPa to 4500 MPa, more preferably in
the range from 60 MPa to 4000 MPa. It has been found that,
surprisingly, polymers having these mechanical properties are
particularly stable and have good processibility. More
particularly, they enable stable coherence between the matrix and
the hydrogenatable material embedded therein, such that the
hydrogenatable material remains at the same position within the
hydrogen storage means over several cycles. This enables a long
lifetime of the hydrogen storage means.
[0035] More preferably, in the context of the present invention,
the polymer is selected from EVA, PMMA, EEAMA and mixtures of these
polymers.
[0036] EVA (ethyl vinyl acetate) refers to a group of copolymers of
ethylene and vinyl acetate having a proportion of vinyl acetate in
the range from 2% by weight to 50% by weight. Lower proportions of
vinyl acetate lead to the formation of rigid films, whereas higher
proportions lead to greater adhesiveness of the polymer. Typical
EVAs are solid at room temperature and have tensile elongation of
up to 750%. In addition, EVAs are resistant to stress cracking. EVA
has the following general formula (I):
##STR00001##
[0037] EVA in the context of the present invention preferably has a
density of 0.9 g/cm.sup.3 to 1.0 g/cm.sup.3 (according to ISO
1183). Yield stress according to ISO 527 is especially 4 to 12 MPa,
preferably in the range from 5 MPa to 10 MPa, particularly 5 to 8
MPa. Especially suitable are those EVAs which have tensile
strengths (according to ISO 527) of more than 12 MPa, especially
more than 15 MPa, and less than 50 MPa, especially less than 40
MPa, particularly 25 MPa or less. Elongation at break (according to
ISO 527) is especially >30% or >35%, particularly >40% or
45%, preferably >50%. The tensile modulus of elasticity is
preferably in the range from 35 MPa to 120 MPa, particularly from
40 MPa to 100 MPa, preferably from 45 MPa to 90 MPa, especially
from 50 MPa to 80 MPa. Suitable EVAs are sold, for example, by
Axalta Coating Systems LLC under the Coathylene.RTM. CB 3547 trade
name.
[0038] Polymethylmethacrylate (PMMA) is a synthetic transparent
thermoplastic polymer having the following general structural
formula (II):
##STR00002##
[0039] The glass transition temperature, depending on the molar
mass, is about 45.degree. C. to 130.degree. C. The softening
temperature is preferably 80.degree. C. to 120.degree. C.,
especially 90.degree. C. to 110.degree. C. The thermoplastic
copolymer is notable for its resistance to weathering, light and UV
radiation.
[0040] PMMA in the context of the present invention preferably has
a density of 0.9 to 1.5 g/cm.sup.3 (according to ISO 1183),
especially of 1.0 g/cm.sup.3 to 1.25 g/cm.sup.3. Especially
suitable are those PMMAs which have tensile strength (according to
ISO 527) of more than 30 MPa, preferably of more than 40 MPa,
especially more than 50 MPa, and less than 90 MPa, especially less
than 85 MPa, particularly of 80 MPa or less. Elongation at break
(according to ISO 527) is especially <10%, particularly <8%,
preferably <5%. The tensile modulus of elasticity is preferably
in the range from 900 MPa to 5000 MPa, preferably from 1200 to 4500
MPa, especially from 2000 MPa to 4000 MPa. Suitable PMMAs are sold,
for example, by Ter Hell Plastics GmbH, Bochum, Germany, under the
trade name of 7M Plexiglas.RTM. pellets.
[0041] EEAMA is a terpolymer formed from ethylene, acrylic ester
and maleic acid anhydride monomer units. EEAMA has a melting point
of about 102.degree. C., depending on the molar mass. It preferably
has a relative density at 20.degree. C. (DIN 53217/ISO 2811) of 1.0
g/cm.sup.3 or less and 0.85 g/cm.sup.3 or more. Suitable EEAMAs are
sold, for example, under the Coathylene.RTM. TB3580 trade name by
Axalta Coating Systems LLC.
[0042] Preferably, the composite material comprises essentially the
hydrogen storage material and the matrix. The proportion by weight
of the matrix based on the total weight of the composite material
is preferably 10% by weight or less, especially 8% by weight or
less, more preferably 5% by weight or less, and is preferably at
least 1% by weight and especially at least 2% by weight to 3% by
weight. It is desirable to minimize the proportion by weight of the
matrix. Even though the matrix is capable of storing hydrogen, the
hydrogen storage capacity is not as significant as that of the
hydrogen storage material itself. However, the matrix is needed in
order firstly to keep any oxidation of the hydrogen storage
material that occurs at a low level or prevent it entirely and to
assure coherence between the particles of the material.
[0043] It is preferable that the matrix is a polymer having low
crystallinity. The crystallinity of the polymer can considerably
alter the properties of a material. The properties of a
semicrystalline material are determined both by the crystalline and
the amorphous regions of the polymer. As a result, there is a
certain relationship with composite materials, which are likewise
formed from two or more substances. For example, the expansion
capacity of the matrix decreases with increasing density.
[0044] The matrix may also take the form of prepregs. Prepreg is
the English abbreviation of "preimpregnated fibers". Prepregs are
semifinished textile products preimpregnated with a polymer, which
are cured thermally and under pressure for production of
components. Suitable polymers are those having a highly viscous but
unpolymerized thermoset polymer matrix. The polymers preferred
according to the present invention may also take the form of a
prepreg.
[0045] The fibers present in the prepreg may be present as a pure
unidirectional layer, as a fabric or scrim. The prepregs may, in
accordance with the invention, also be comminuted and be processed
as flakes or shavings together with the hydrogenatable material to
give a composite material.
[0046] In one version of the present invention, the polymer may
take the form of a liquid which is contacted with the
hydrogenatable material. One meaning of "liquid" here is that the
polymer is melted. However, the invention also encompasses
dissolution of the polymer in a suitable solvent, in which case the
solvent is removed again after production of the composite
material, for example by evaporation. However, it is also possible
that the polymer takes the form of pellets which are mixed with the
hydrogenatable material. As a result of the compaction of the
composite material, the polymer softens, so as to form the matrix
into which the hydrogenatable material is embedded. If the polymer
is used in the form of particles, i.e. of pellets, these preferably
have an x.sub.50 particle size (volume-based particle size) in the
range from 30 .mu.m to 60 .mu.m, especially 40 .mu.m to 45 .mu.m.
The x.sub.90 particle size is especially 90 .mu.m or less,
preferably 80 .mu.m or less.
[0047] The hydrogenatable material can absorb the hydrogen and, if
required, release it again. In a preferred embodiment, the material
comprises particulate materials in any 3-dimensional configuration,
such as particles, pellets, fibers, preferably cut fibers, flakes
and/or other geometries. More particularly, the material may also
take the form of sheets or powder. In this case, the material does
not necessarily have a homogeneous configuration. Instead, the
configuration may be regular or irregular. Particles in the context
of the present invention are, for example, virtually spherical
particles, and likewise particles having an irregular, angular
outward shape. The surface may be smooth, but it is also possible
that the surface of the material is rough and/or has unevenness
and/or depressions and/or elevations. According to the invention, a
hydrogen storage means may comprise the material in just one
specific 3-dimensional configuration, such that all particles of
the material have the same spatial extent. However, it is also
possible that a hydrogen storage means comprises the material in
different configurations/geometries. By virtue of a multitude of
different geometries or configurations of the material, the
material can be used in a multitude of different hydrogen storage
means.
[0048] Preferably, the material comprises hollow bodies, for
example particles having one or more cavities and/or having a
hollow shape, for example a hollow fiber or an extrusion body with
a hollow channel. The term "hollow fiber" describes a cylindrical
fiber having one or more continuous cavities in cross section.
Through the use of a hollow fiber, it is possible to combine a
plurality of hollow fibers to give a hollow fiber membrane, by
means of which absorption and/or release of the hydrogen from the
material can be facilitated because of the high porosity.
[0049] Preferably, the hydrogenatable material has a bimodal size
distribution. In this way, a higher bulk density and hence a higher
density of the hydrogenatable material in the hydrogen storage
means can be enabled, which increases the hydrogen storage
capacity, i.e. the amount of hydrogen which can be stored in the
storage means.
[0050] According to the invention, the hydrogenatable material may
comprise, preferably consist of, at least one hydrogenatable metal
and/or at least one hydrogenatable metal alloy.
[0051] Other hydrogenatable materials used may be: [0052] alkaline
earth metal and alkali metal alanates, [0053] alkaline earth metal
and alkali metal borohydrides, [0054] metal-organic frameworks
(MOFs) and/or [0055] clathrates, and, of course, respective
combinations of the respective materials.
[0056] According to the invention, the material may also include
non-hydrogenatable metals or metal alloys.
[0057] According to the invention, the hydrogenatable material may
comprise a low-temperature hydride and/or a high-temperature
hydride. The term "hydride" refers to the hydrogenatable material,
irrespective of whether it is in the hydrogenated form or the
non-hydrogenated form. Low-temperature hydrides store hydrogen
preferably within a temperature range between -55.degree. C. and
180.degree. C., especially between -20.degree. C. and 150.degree.
C., particularly between 0.degree. C. and 140.degree. C.
High-temperature hydrides store hydrogen preferably within a
temperature range of 280.degree. C. upward, especially 300.degree.
C. upward. At the temperatures mentioned, the hydrides cannot just
store hydrogen but can also release it, i.e. are able to function
within these temperature ranges.
[0058] Where `hydrides` are described in this context, this is
understood to mean the hydrogenatable material in its hydrogenated
form and also in its non-hydrogenated form. According to the
invention, in the production of hydrogen storage means, it is
possible to use hydrogenatable materials in their hydrogenated or
non-hydrogenated form.
[0059] With regard to hydrides and their properties, reference is
made in the context of the disclosure to tables 1 to 4 in S.
Sakietuna et al., International Journal of Energy, 32 (2007), p.
1121-1140.
[0060] Hydrogen storage (hydrogenation) can be effected at room
temperature. Hydrogenation is an exothermic reaction. The heat of
reaction that arises can be removed. By contrast, for the
dehydrogenation, energy has to be supplied to the hydride in the
form of heat. Dehydrogenation is an endothermic reaction.
[0061] For example, it may be the case that a low-temperature
hydride is used together with a high-temperature hydride. For
instance, in one configuration, it may be the case that, for
example, the low-temperature hydride and the high temperature
hydride are provided in a mixture in a layer of a second region. It
is also possible for these each to be arranged separately in
different layers or regions, especially also in different second
regions. For example, it may be the case that a first region is
arranged between these second regions. In a further configuration,
a first region has a mixture of low- and high-temperature hydride
distributed in the matrix. It is also possible that different first
regions include either a low-temperature hydride or a
high-temperature hydride.
[0062] Preferably, the hydrogenatable material comprises a metal
selected from magnesium, titanium, iron, nickel, manganese, nickel,
lanthanum, zirconium, vanadium, chromium, or a mixture of two or
more of these metals. The hydrogenatable material may also include
a metal alloy comprising at least one of the metals mentioned.
[0063] More preferably, the hydrogenatable material (hydrogen
storage material) comprises at least one metal alloy capable of
storing hydrogen and releasing it again at a temperature of
150.degree. C. or less, especially within a temperature range from
-20.degree. C. to 140.degree. C., especially from 0.degree. C. to
100.degree. C. The at least one metal alloy here is preferably
selected from an alloy of the AB.sub.5 type, the AB type and/or the
AB.sub.2 type. A and B here each denote different metals, where A
and/or B are especially selected from the group comprising
magnesium, titanium, iron, nickel, manganese, nickel, lanthanum,
zirconium, vanadium and chromium. The indices represent the
stoichiometric ratio of the metals in the particular alloy.
According to the invention, the alloys here may be doped with
extraneous atoms. According to the invention, the doping level may
be up to 50 atom %, especially up to 40 atom % or up to 35 atom %,
preferably up to 30 atom % or up to 25 atom %, particularly up to
20 atom % or up to 15 atom %, preferably up to 10 atom % or up to 5
atom %, of A and/or B. The doping can be effected, for example,
with magnesium, titanium, iron, nickel, manganese, nickel,
lanthanum or other lanthanides, zirconium, vanadium and/or
chromium. The doping can be effected here with one or more
different extraneous atoms. Alloys of the AB.sub.5 type are readily
activatable, meaning that the conditions needed for activation are
similar to those in the operation of the hydrogen storage means.
They additionally have a higher ductility than alloys of the AB or
AB.sub.2 type. Alloys of the AB.sub.2 or of the AB type, by
contrast, have higher mechanical stability and hardness compared to
alloys of the AB.sub.5 type. Mention may be made here by way of
example of FeTi as an alloy of the AB type, TiMn.sub.2 as an alloy
of the AB.sub.2 type and LaNi.sub.5 as an alloy of the AB.sub.5
type.
[0064] More preferably, the hydrogenatable material (hydrogen
storage material) comprises a mixture of at least two
hydrogenatable alloys, at least one alloy being of the AB.sub.5
type and the second alloy being an alloy of the AB type and/or the
AB.sub.2 type. The proportion of the alloy of the AB.sub.5 type is
especially 1% by weight to 50% by weight, especially 2% by weight
of 40% to weight, more preferably 5% by weight to 30% by weight and
particularly 5% by weight to 20% by weight, based on the total
weight of the hydrogenatable material.
[0065] The hydrogenatable material (hydrogen storage material) is
preferably in particulate form (particles).
[0066] The particles especially have a particle size x.sub.50 of 20
.mu.m to 700 .mu.m, preferably of 25 .mu.m to 500 .mu.m,
particularly of 30 .mu.m to 400 .mu.m, especially 50 .mu.m to 300
.mu.m. x.sub.50 means that 50% of the particles have a median
particle size equal to or less than the value mentioned. The
particle size was determined by means of laser diffraction, but can
also be effected by sieve analysis, for example. The median
particle size in the present case is the particle size based on
weight, the particle size based on volume being the same in the
present case. What is reported here is the particle size of the
hydrogenatable material before it is subjected to hydrogenation for
the first time. During the storage of hydrogen, stresses occur
within the material, which can lead to a reduction in the x.sub.50
particle size over several cycles.
[0067] Preferably, the hydrogenatable material is incorporated in
the matrix to such a firm degree that it decreases in size on
storage of hydrogen. Preference is therefore given to using, as
hydrogenatable material, particulate material which breaks up while
the matrix remains at least predominantly undestroyed. This result
is surprising, since it was expected that the matrix would if
anything tend to break up on expansion as a result of the increase
in volume of the hydrogenatable material during the storage of
hydrogen when there is high expansion because of the increase in
volume. It is assumed at present that the outside forces acting on
the particles, as a result of the binding within the matrix, when
the volume increases, lead to breakup together with the stresses
within the particles resulting from the increase in volume. Breakup
of the particles was discovered particularly clearly on
incorporation into polymer material in the matrix. The matrix
composed of polymer material was capable of keeping the particles
broken up in this way in a stable fixed position as well.
[0068] Tests have incidentally shown that, in the case of
utilization of a binder, especially of an adhesive binder in the
matrix for fixing of these particles, particularly good fixed
positioning within the matrix is enabled. A binder content may
preferably be between 2% by volume and 3% by volume of the matrix
volume.
[0069] Preferably, there is a change in the particle size because
of breakup of the particles resulting from the storage of hydrogen
by a factor of 0.6, more preferably by a factor of 0.4, based on
the x.sub.50 particle size at the start and after 100 storage
operations.
[0070] For example, it may be the case that a low-temperature
hydride is used together with a high-temperature hydride. For
instance, in one embodiment of the invention, it may be the case
that, for example, the low-temperature hydride and the
high-temperature hydride are provided in a mixture in a layer of a
second region of the hydrogen storage element. These may also be
arranged separately in different layers, especially also in
different regions, of one and the same layer of the hydrogen
storage element. For example, it may be the case that another
region is arranged between these elements. In a further
configuration, a region comprises a mixture of low- and
high-temperature hydride distributed in a matrix. It is also
possible that different regions of the element comprise either a
low-temperature hydride or a high-temperature hydride.
[0071] In a further configuration of the invention, the hydrogen
storage means has a high-temperature hydride vessel and a
low-temperature vessel. The high-temperature hydrides may generate
temperatures of more than 350.degree. C., which have to be
dissipated. This heat is released very rapidly and can be utilized,
for example, for heating of a component thermally associated with
the hydrogen storage element. High-temperature hydrides utilized
may, for example, be metal powders based on titanium. The
low-temperature hydride, by contrast, assumes temperatures within a
range preferably between -55.degree. C. and 155.degree. C.,
especially preferably within a temperature range between 80.degree.
C. and 140.degree. C. A low-temperature hydride is, for example,
Ti.sub.0.8Zr.sub.0.2CrMn or
Ti.sub.0.98Zr.sub.0.02V.sub.0.43Cr.sub.0.05Mn.sub.1.2. One
configuration envisages transfer of hydrogen from the
high-temperature hydride container to the low-temperature hydride
container and vice versa, and storage therein in each case. By way
of example, and forming part of the disclosure of the present
patent application, reference is made for this purpose to DE-C 36
39 545.
[0072] In addition, for example, it is possible to utilize, as a
matrix, a carbon matrix into which the low-temperature hydride is
inserted. For example, the University of Utrecht thesis entitled
"Carbon matrix confined sodium alanate for reversible hydrogen
storage" by J. Gao, retrievable under
http://dspace.library.uu.nl/handle/1874/256764, reveals how the
hydrogenatable material to be used and the matrix can be matched to
one another, such that it is possible to operate a hydrogen storage
element at relatively low temperatures as well. With regard to
hydrides and their properties, reference is made to tables 1 to 4
in B. Sakietuna et al., International Journal of Energy, 32 (2007),
p. 1121-1140. Both publications/literature references are hereby
incorporated by reference into the disclosure of the present patent
application.
[0073] In addition, it is proposed that the expanded graphite be
very substantially replaced by using a specific filling technique
to introduce layers of hydrogen-storing material, preferably a
hydride, and a heat-conducting material such as graphite into a
shaping mold in order then to give, compressed together, a sandwich
structure in which the graphite again assumes the task of heat
conduction. For this purpose, it is possible, for example, to
utilize a heat-conducting metal powder and/or normal natural
graphite, the lenticular particles of which are preferably aligned
horizontally on filling, such that it is possible to efficiently
utilize the good conduction of heat in the direction of the
hexagonal lattice structure. Alternatively, it is possible to use
films or film pieces composed of rolled expanded graphite or flakes
of this material or else graphite fabric. At the same time, laminas
of materials that remain porous can be introduced in between as
gas-guiding layers and compressed as well.
[0074] More particularly, it is possible to introduce at least the
first and second materials together but separately from one another
the cavity of a shaping mold, to fill this simultaneously, with
relative movement between the cavity and the first and second
materials to be fed in. In this way, it is possible to produce
different patterns, for example wavy layers, helical geometries and
screw geometries.
[0075] Further filling of a cavity is effected, for example, into a
press cavity having a lower ram and an upper ram.
[0076] For example, filling of the cavity may be undertaken layer
by layer, in which case, for example, every new or every second or
every third new layer is followed by immediate compaction by means
of the upper and lower rams. This allows a particularly close
association of, for example, the primarily heat-conducting material
and the primarily hydrogen-storing material.
[0077] In a further concept of the invention, a process for
producing a hydrogen storage element, preferably a hydrogen storage
element as described above, is proposed, wherein separate layers of
a hydrogen-storing material and a heat-conducting material are
introduced into a press mold and these are compressed together to
generate a sandwich structure, the heat-conducting material, on use
of the sandwich structure as hydrogen storage element, assuming the
task of conducting heat, preferably in a direction transverse to
the direction of succession of the layers of the hydrogen storage
element.
[0078] In one configuration of the process of the invention, a
metal powder and/or normal natural graphite is/are utilized as
heat-conducting material, in which case, on utilization of normal
natural graphite, the lenticular particles thereof are preferably
aligned horizontally in the course of filling, such that conduction
of heat in the direction of a hexagonal lattice structure of the
graphite structure can be utilized.
[0079] In a further configuration of the process of the invention,
alternatively or additionally, one or more films composed of rolled
expanded graphite, flakes of a rolled expanded graphite and/or a
graphite fabric may be introduced into the sandwich structure as
heat-conducting material.
[0080] It may also be the case that one of more layers of a
material that remains porous are introduced into the sandwich
structure as gas-guiding layers and compressed as well.
[0081] It is likewise possible, in a development of the invention,
that two or more sandwich structures are pressed separately from
one another and then arranged in a common vessel.
[0082] Preferably, the layers are compacted by means of a press,
for example a rotary press or a revolving press. The principle of a
rotary press is known, for example, from DE-B-10 2010 005 780, and
also from DE-B-10 2005 019 132.
[0083] The apparatuses presented in each case can also be utilized
for the production of layers of a hydrogen storage means.
[0084] Preferably, the first and second layers are compressed
together and form the sandwich structure. The compression can be
effected, for example, with the aid of an upper ram and a lower ram
by pressure. In addition, the compression can be effected via
isostatic pressing. The isostatic press method is based on the
physical law that pressure in liquids and gases propagates
uniformly in all directions and generates forces on the areas
subjected thereto, the sizes of which are directly proportional to
these areas. The materials to be compressed can be introduced, for
example, into the pressure vessel of a pressing system, for
example, in a rubber mold. The pressure that acts on the rubber
mold on all sides via the liquid in the pressure vessel compresses
the enclosed materials (at least the first and second layers) in a
uniform manner. It is also possible to insert a preform comprising
at least the first and second layers into the isostatic press, for
example into a liquid. By applying high pressures, preferably
within a range from 500 to 6000 bar, the sandwich structure can be
produced. The high pressures in isostatic pressing permit, for
example, the creation of new material properties in the composite
material.
[0085] It may additionally be the case that, alternatively or
additionally, one or more films composed of a rolled expanded
graphite, flakes of a rolled expanded graphite and/or a graphite
fabric are introduced as heat-conducting material into the sandwich
structure.
[0086] In a further configuration, one or more laminas of a
material that remains porous are introduced into the sandwich
structure as gas-guiding layers and compressed as well. Preferably,
two or more sandwich structures are pressed separately from one
another and then arranged in a common vessel.
[0087] Further advantageous configurations and also features are
apparent from the figures which follow and the corresponding
description. The individual features that are apparent from the
figures and the description are merely illustrative and not
restricted to the particular configuration. Instead, one or more
features from one or more figures can be combined with other
features from the above description to give further configurations.
Therefore, the features are specified not in a restrictive manner
but merely by way of example. The figures show:
[0088] FIG. 1 a schematic view of a section of a hydrogen storage
means having alternating layers,
[0089] FIG. 2 a schematic view of a section of another hydrogen
storage means or another portion of the hydrogen storage means
according to FIG. 1 with a schematic representation of another
layer arrangement having a non-planar 3-D form, and
[0090] FIG. 3 a first and second layer shown in schematic form,
having a gradient.
[0091] FIG. 1 shows a schematic view of a detail of a layer stack
of a hydrogen storage means 1 having a plurality of cylindrically
repeating layer sequences composed of one or more hydrogen storage
components. For example, a first layer 2, a second layer 3 and a
third layer 4 are each arranged in an alternating manner. As shown
in this example, the first layer 2 comprises, for example, a
heat-storing material, the second layer 3 a heat-removing material
and the third layer 4 a gas-permeable material as gas-guiding
layer. Compression, especially isostatic compression, makes it
possible for there to be very intimate contact between the
heat-conducting layer and the hydrogen-storing layer.
[0092] FIG. 2 shows a detail 5 of another or an identical hydrogen
storage means with a schematic representation of another layer
arrangement which is non-planar. As elucidated above, for example,
a material may be supplied in such a way that a relative movement
between cavity and material supply is executed. In this way, as
shown, a helical layer is generated in a surrounding support layer.
It is also possible to generate other geometries along an axis of
the cavity. The helical layer has heat-conducting and/or
gas-conducting properties. For production of a helical structure or
another structure, preference is given to using an apparatus and a
process as disclosed, for example, by DE 10 2014 006 374, to which
reference is made in the context of the disclosure.
[0093] FIG. 3 shows a detail from a compressed sandwich structure 6
with a first layer 7 and a second layer 8. Between the first layer
7 and second layer 8, a groove 9 has been drawn with the aid of a
body pulled through the two layers, which has led to formation of a
gradient 10 in the sandwich structure. The gradient formation is
indicated by the finer shading. Subsequent compression of these two
layers prior to new supply of further layer-forming material
results in particularly intensive "safeguarding" of the gradient in
the sandwich structure.
[0094] The invention and various configurations of the invention
will be apparent from the groups of features specified hereinafter,
it being possible to combine individual features from one group
with individual features from the other groups and/or with features
of other embodiments and configurations disclosed in the above
description of the invention (additions and omissions). [0095] 1. A
hydrogen storage means having a hydrogen-permeable structure,
preferably a porous structure, which is present as a component in
the hydrogen storage means and serves for flow of a hydrogenous
gas. [0096] 2. The hydrogen storage means, preferably according to
point 1, characterized in that it comprises a first material and a
second material at separate locations from one another, each of
which form separate layers adjacent to one another, preferably
abutting one another, the first material comprising a primarily
hydrogen-storing material and the second material being a primarily
heat-conducting material, with the primarily heat-conducting
material extending preferably from the interior of the hydrogen
storage means to an exterior of the hydrogen storage means. [0097]
3. The hydrogen storage means according to point 1 or 2,
characterized in that a gradient is formed between the first and
second layers, along which a transition from the first to the
second layer is accomplished via a change in the respective
material content of the first and second materials. [0098] 4. The
hydrogen storage means preferably according to point 1, 2 or 3,
characterized in that the hydrogen storage means has components in
the form of a core-shell structure, in which the core comprises a
first material and the shell comprises a different second material,
the first material and/or the second material comprising a
hydrogen-storing material, the components preferably being selected
from the group comprising powders, granules, flakes, fibers and/or
other geometries. [0099] 5. The hydrogen storage means according to
point 4, characterized in that the second material of the shell
comprises a polymer configured so as to be at least
hydrogen-permeable. [0100] 6. The hydrogen storage means according
to point 4 or 5, characterized in that the core comprises a
primarily heat-conducting material and the shell a primarily
hydrogen-storing material. [0101] 7. The hydrogen storage means
according to point 3, characterized in that the core comprises a
primarily hydrogen-storing material and the shell a primarily
heat-conducting material, the heat-conducting material being
hydrogen-permeable. [0102] 8. The hydrogen storage means according
to any of the preceding points, characterized in that
hydrogen-storing material has a hydrogen-permeable coating which
prevents oxidation of the hydrogen-storing material, the coating
preferably being hydrogen-storing. [0103] 9. A process for
producing a hydrogen storage means, preferably a hydrogen storage
means according to any of the preceding points, wherein separate
layers comprising hydrogen-storing material and heat-conducting
material are introduced into a press mold and these are compressed
together to generate a sandwich structure, the heat-conducting
material, on use of the sandwich structure as hydrogen storage
means, assuming the task of conducting heat, preferably in the
directions of expansion of the heat-conducting layer of the
hydrogen storage means. [0104] 10. The process according to point
9, characterized in that a metal powder and/or normal natural
graphite is utilized as heat-conducting material, wherein, in the
case of utilization of normal natural graphite, the lenticular
particles thereof are preferably aligned horizontally on filling,
such that it is possible to efficiently utilize conduction of heat
in the direction of a hexagonal lattice structure of the graphite
structure. [0105] 11. The process according to point 9 or 10,
characterized in that, alternatively or additionally, one or more
films composed of a rolled expanded graphite, flakes of a rolled
expanded graphite and/or a graphite fabric are introduced into the
sandwich structure as heat-conducting material. [0106] 12. The
process according to any of the preceding points, characterized in
that one or more layers of a material that remains porous can be
introduced into the sandwich structure as gas-guiding layers and
compressed as well. [0107] 13. The process according to any of the
preceding points, characterized in that two or more sandwich
structures are pressed separately from one another and then
arranged in a common vessel. [0108] 14. The process according to
any of the preceding points, characterized in that the layers are
compacted by means of a rotary compression or a revolving press.
[0109] 15. The process according to any of the preceding points,
characterized in that the layers are compressed isostatically.
[0110] 16. The process according to any of the preceding points,
characterized in that at least one low-temperature hydride and/or a
high-temperature hydride is used for the hydrogen-storing
material.
LIST OF REFERENCE NUMERALS
[0110] [0111] 1 hydrogen storage element [0112] 2 first layer of
the hydrogen storage element [0113] 3 second layer of the hydrogen
storage element [0114] 4 third layer of the hydrogen storage
element [0115] 5 section of a hydrogen storage means [0116] 6
sandwich structure [0117] 7 first layer of the sandwich structure
[0118] 8 second layer of the sandwich structure [0119] 9 groove
[0120] 10 gradient formation in the sandwich structure
* * * * *
References