U.S. patent application number 13/734993 was filed with the patent office on 2013-05-16 for polymer electrolyte membrane with functionalized nanoparticles.
This patent application is currently assigned to Elcomax Membranes GmbH. The applicant listed for this patent is Elcomax Membranes GmbH, Lanxess Deutschland GmbH, Rhein Chemie Rheinau GmbH. Invention is credited to Thomas Fruh, Oliver Gronwald, Ulrich Mahr, Dieter Melzner, Werner Obrecht, Annette Reiche, Torsten Ziser.
Application Number | 20130122399 13/734993 |
Document ID | / |
Family ID | 39511097 |
Filed Date | 2013-05-16 |
United States Patent
Application |
20130122399 |
Kind Code |
A1 |
Reiche; Annette ; et
al. |
May 16, 2013 |
POLYMER ELECTROLYTE MEMBRANE WITH FUNCTIONALIZED NANOPARTICLES
Abstract
The present invention relates to a polymer electrolyte membrane
for fuel cells, comprising a polymer matrix of at least one basic
polymer and one or more doping agents, wherein particles containing
ionogenic groups and having a mean particle diameter in the
nanometer range are embedded in the polymer matrix and the
particles containing ionogenic groups are distributed homogeneously
in the polymer matrix in a concentration of less than 50% relative
to the weight of the polymer matrix, as well as to the production
and use of same, especially in high-temperature fuel cells.
Inventors: |
Reiche; Annette; (Cottingen,
DE) ; Melzner; Dieter; (Gottingen, DE) ; Mahr;
Ulrich; (Gottingen, DE) ; Gronwald; Oliver;
(Gottingen, DE) ; Obrecht; Werner; (Moers, DE)
; Fruh; Thomas; (Mutterstadt, DE) ; Ziser;
Torsten; (Birkenau, DE) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Elcomax Membranes GmbH;
Lanxess Deutschland GmbH;
Rhein Chemie Rheinau GmbH; |
Munchen |
|
DE
US
US |
|
|
Assignee: |
Elcomax Membranes GmbH
Munchen
DE
Rhein Chemie Rheinau GmbH
Lanxess Deutschland GmbH
|
Family ID: |
39511097 |
Appl. No.: |
13/734993 |
Filed: |
January 6, 2013 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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12555021 |
Sep 8, 2009 |
8367231 |
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13734993 |
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PCT/EP2008/001803 |
Mar 6, 2008 |
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12555021 |
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Current U.S.
Class: |
429/493 ;
429/492 |
Current CPC
Class: |
Y02P 70/50 20151101;
H01M 8/1048 20130101; H01M 8/103 20130101; H01M 8/1027 20130101;
Y02E 60/50 20130101; H01M 8/1023 20130101; H01M 8/1046 20130101;
H01M 8/1069 20130101; H01M 8/1081 20130101; H01M 8/1088 20130101;
H01M 8/1032 20130101 |
Class at
Publication: |
429/493 ;
429/492 |
International
Class: |
H01M 8/10 20060101
H01M008/10 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 8, 2007 |
DE |
10 2007 011 424.0 |
Claims
1. A method for production of a polymer electrolyte membrane for
high temperature fuel cells in a temperature range up to
approximately 200.degree. C., the polymer electrolyte membrane
comprising a polymer matrix, wherein the polymer matrix comprises
at least one basic polymer, one or more doping agents, and
particles containing ionogenic groups and having a mean particle
diameter in the nanometer range, wherein said particles are
embedded in the polymer matrix and are distributed homogeneously in
the polymer matrix in a concentration of less than 50% relative to
the weight of the polymer matrix, the method comprising: (a)
producing a membrane casting solution, at least comprising a
solvent, at least one matrix-forming basic polymer and particles
containing ionogenic groups, (b) casting the membrane casting
solution in the form of a membrane and (c) removing the
solvent.
2. A method according to claim 1, wherein the membrane is doped
after step c) with at least one doping agent in a further step
d).
3. A method according to claim 2, wherein the doping agent with
which the membrane is doped in step d) is selected from the group
comprising phosphoric acid, phosphoric acid derivatives, phosphonic
acid, phosphonic acid derivatives, sulfuric acid, sulfuric acid
derivatives, sulfonic acid, sulfonic acid derivatives or a
combination of two or more thereof.
4. A method according to claim 3, wherein solvent is selected from
the group comprising N-methylpyrrolidone (NMP), dimethylformamide
(DMF), dimethyl sulfoxide (DMSO), dimethylacetamide (DMAc) and any
desired mixtures thereof.
5. A method according to claim 3, wherein removal of the solvent is
achieved by heating the cast membrane casting solution and/or by
applying a vacuum.
Description
[0001] This application is a division of U.S. application Ser. No.
12/555,021, filed Sep. 8, 2009, which is a continuation application
of International Application No. PCT/EP2008/001803, filed on Mar.
6, 2008, now pending, which claims priority to German Patent
Application No. 10 2007 011 424.0, filed on Mar. 8, 2007, the
entire contents of each of which are incorporated herein by
reference.
[0002] The present invention relates to a polymer electrolyte
membrane for fuel cells, comprising a polymer matrix of at least
one basic polymer and one or more doping agents, wherein particles
containing ionogenic groups and having a mean particle diameter in
the nanometer range are embedded in the polymer matrix and the
particles containing ionogenic groups are distributed homogeneously
in the polymer matrix in a concentration of less than 50% relative
to the weight of the polymer matrix, as well as to the production
and use of same, especially in high-temperature fuel cells.
[0003] Polymer electrolyte membranes, for example of the Nafion
type, which are based on polymers containing perfluorinated
sulfonic acid groups, are known in the prior art. Because charge
transport in these membranes is contingent on the presence of
water, however, the operating range of corresponding polymer
electrolyte membrane fuel cells is limited to a maximum of
100.degree. C. In order to achieve a higher operating temperature,
membranes provided with inorganic particles have been proposed for
fuel cells (see DE 19919988 A1, DE 10205849 A1, WO 03/063266 A2 and
WO 03/081691 A2). Membranes using another kind of particles for
fuel cells have not been known heretofore.
[0004] DE 102004009396 A1 describes membranes for fuel cells with
improved electrical, mechanical and thermal properties in fuel-cell
operation. These membranes are composed of a polymer, particularly
preferably a plastic, a natural substance, silicone or rubber, and
of a proton-conducting substance. However, such membranes do not
exhibit any industrially significant conductivities at room
temperature and have poor mechanical stability.
[0005] The object of the present invention is therefore to provide
a polymer membrane for fuel cells that is designed to have improved
conductivity at room temperature and high long-term stability in
fuel-cell operation. Another object is a polymer membrane for fuel
cells that is designed to operate efficiently for a long time at a
high operating temperature in fuel cells and to have high proton
conductivity, without losing substantial amounts of the components
responsible for proton conduction during operation in a fuel
cell.
[0006] This technical object is achieved by provision of the
embodiments characterized in the claims.
[0007] In particular, according to the present invention, there is
provided a polymer electrolyte membrane for fuel cells comprising a
polymer matrix of at least one basic polymer and one or more doping
agents, wherein particles containing ionogenic groups and having a
mean particle diameter in the nanometer range are embedded in the
polymer matrix and the particles containing ionogenic groups are
distributed homogeneously in the polymer matrix in a concentration
of less than 50% relative to the weight of the polymer matrix.
[0008] In the inventive polymer electrolyte membrane, the particles
containing ionogenic groups are distributed homogeneously in the
polymer matrix in a concentration of less than 50% relative to the
weight of the polymer matrix. Thereby it is ensured that the
particles present in the matrix and containing ionogenic groups are
substantially not in contact with one another and are surrounded by
matrix-forming polymer. According to a preferred embodiment of the
inventive polymer electrolyte membrane, the particles containing
ionogenic groups are distributed homogeneously in the polymer
matrix in a concentration of less than 40%, particularly preferably
10 to 30%, relative to the weight of the polymer matrix.
[0009] According to the present invention, particles containing
ionogenic groups are to be understood in particular as oligomeric
and/or polymeric particles, which may but do not necessarily have
to exhibit a solid phase boundary with the surrounding polymer
matrix. A substantial property of the particles containing
ionogenic groups is especially that they are not lost from the
polymer matrix or polymer electrolyte membrane in the manner, for
example, of low molecular weight proton-conducting components.
Suitable particles containing ionogenic groups are in particular
all organic particles composed mainly of one or more organic
polymer(s) and/or oligomer(s). In principle, the polymers or
oligomers suitable for the organic particles containing ionogenic
groups are not subject to any substantial restriction.
Nevertheless, it is preferred that the particles containing
ionogenic groups are composed mainly of a rubber-like polymer or
oligomer or of a non-rubber-like polymer or oligomer, preferably a
thermoplastic polymer or oligomer. The particles containing
ionogenic groups may be of oligomeric and/or polymeric nature.
[0010] As an example, the particles containing ionogenic groups may
be composed mainly of base monomers having at least one
polymerizable or copolymerizable group, preferably at least two and
particularly preferably two to four polymerizable or
copolymerizable groups, especially C.dbd.C double bonds.
[0011] Examples of suitable base monomers, which preferably contain
one to four polymerizable or copolymerizable group(s), are
butadiene, styrene, acrylonitrile, isoprene, esters of acrylic and
methacrylic acid, tetrafluoroethylene, vinylidene fluoride,
hexafluoropropene, 2-chlorobutadiene, 2,3-dichlorobutadiene,
double-bond-containing carboxylic acids, such as acrylic acid,
methacrylic acid, maleic acid or itaconic acid,
double-bond-containing sulfonic acids, double-bond-containing
phosphonic acids, double-bond-containing hydroxy compounds, such as
hydroxyethyl methacrylate, hydroxyethyl acrylate or hydroxybutyl
methacrylate, amine-functionalized (meth)acrylates,
diisopropenylbenzene, divinylbenzene, divinyl ether, divinyl
sulfone, diallyl phthalate, triallyl cyanurate, triallyl
isocyanurate, 1,2-polybutadiene, N,N'-m-phenylene maleimide,
2,4-toluoylenebis(maleimide) and/or triallyl trimellitate. Base
monomers with two to four polymerizable or copolymerizable groups
are chosen in particular when efficient cross-linking is desired.
Furthermore, the particles containing ionogenic groups may be
composed mainly of acrylates and/or methacrylates of preferably
polyhydric, particularly preferably dihydric to tetrahydric
alcohols, such as ethylene glycol, 1,2-propanediol, butanediol,
hexanediol, polyethylene glycol with 2 to 20, preferably 2 to 8
oxyethylene units, neopentyl glycol, bisphenol A, glycerol,
trimethylolpropane, pentaerythritol or sorbitol with unsaturated
polyesters of aliphatic dials and polyols, and maleic acid, fumaric
acid and/or itaconic acid or mixtures thereof.
[0012] Examples of suitable base monomers are in particular the
following compounds:
[0013] Vinylcarbazole, N-vinyl-1-pyrrolidone, N-allylurea,
N-allylthiourea, secondary amino-(meth)-acrylic acid esters, such
as 2-tert-butylaminoethyl methacrylate, 2-tert-butylaminoethyl
methacrylamide, dimethylaminopropyl methacrylamide,
2-dimethylaminoethyl methacrylate, vinylimidazole, such as
1-vinylimidazole, vinylpyridine, such as 2-vinylpyridine and
4-vinylpyridine, acrylamide, 2-acrylamidoglycolic acid,
2-acrylamido-2-methyl-1-propanesulfonic acid, acrylic acid
[2-(((butylamino)-(carbonyl)oxyl)ethyl ester], acrylic acid
2-(diethylamino)ethyl ester, acrylic acid 2-(dimethylamino)ethyl
ester, acrylic acid 3-(dimethylamino)propyl ester, acrylic acid
isopropylamide, acrylic acid phenylamide, acrylic acid
3-sulfopropyl ester potassium salt, methacrylic acid amide,
methacrylic acid 2-aminoethyl ester hydrochloride, methacrylic acid
2-(tert-butylamino)ethyl ester, methacrylic acid
2-(dimethylamino)methyl ester, methacrylic acid
3-(dimethylamino)propylamide, methacrylic acid isopropylamide,
methacrylic acid 3-sulfopropyl ester potassium salt,
3-vinylaniline, 4-vinylaniline, N-vinylcaprolactam,
N-vinylformamide, 1-vinyl-2-pyrrolidone, 5-vinyluracil.
[0014] According to a preferred embodiment, the particles
containing ionogenic groups have ionogenic groups on the surface or
in the entire particles. Furthermore, it is also possible to use
functional groups that can be transformed to ionogenic groups,
preferably acid groups, after a chemical reaction, such as a
deprotection reaction, a hydrolysis, an addition reaction or a
substitution reaction.
[0015] The ionogenic groups can be introduced, especially at the
surface of the particles, by making reagents that are reactive in
particular with C.dbd.C double bonds react chemically with reactive
groups present at the surface of a cross-linked or pre-cross-linked
polymer or oligomer particle. Examples of reagents that can be
reacted with reactive groups present at the surface of a
cross-linked or pre-cross-linked particle, especially with C.dbd.C
double bonds, are aldehydes, hydroxy compounds, carboxyl compounds,
nitrile compounds, sulfur compounds, such as compounds with
mercapto, dithiocarbamate, polysulfide, xanthogenate,
thiobenorthiazole and/or dithiophosphonic acid groups, unsaturated
carboxylic acids or dicarboxylic acids, unsaturated sulfonic acids,
unsaturated phosphonic acids, N,N'-m-phenylenediamine, acrylic
acid, methacrylic acid, hydroxyethyl methacrylate, hydroxyethyl
acrylate, hydroxybutyl methacrylate, acrylamide, methacrylamide,
amine-functionalized (meth)acrylates, such as acrylonitrile,
acrolein, N-vinyl-2-pyrrolidone, N-allylurea and N-allylthiourea,
and derivatives and mixtures thereof.
[0016] Preferably the particles containing ionogenic groups are
functionalized at the surface or in the entire particles by
ionogenic groups, particularly preferably by covalently bonded acid
groups, such as acid groups of monobasic or polybasic acids, acid
groups of polybasic acids being particularly preferred. The acid
groups bonded covalently at the surface or in the entire particles
are preferably carboxylic acid, sulfonic acid, phosphonic acid
and/or phosphoric acid groups with one or more acid group(s).
However, it is also possible to use other acid groups with similar
acidity or functional groups that can be transformed to acid
groups. According to a particularly preferred embodiment, the
ionogenic groups are selected from one or more of the following
functional groups: --COOH, --SO.sub.3H, --OSO.sub.3H,
--P(O)(OH).sub.2, --O--P(OH).sub.2 and --O--P(O)(OH).sub.2 and/or
salts thereof and/or derivatives thereof, especially partial esters
thereof. The salts represent the conjugate bases to the acid
functional groups, or in other words --COO.sup.-, --SO.sub.3.sup.-,
--OSO.sub.3.sup.-, --P(O).sub.2(OH).sup.- or --P(O).sub.3.sup.3-,
--O--P(O).sub.2.sup.2- and --OP(O).sub.2(OH).sup.- or
--OP(O).sub.3.sup.2- in the form of their metal salts, preferably
alkali metal or ammonium salts.
[0017] Consequently, the particles containing ionogenic groups may
have ionogenic groups at the surface of the particles and form a
core-shell type of structure or may contain ionogenic groups in
substantially the entire particle, in which case they are
functionalized almost homogeneously or throughout.
[0018] The ionogenic groups described in the foregoing may be
introduced at the surface or in the entire particle by different
methods.
[0019] However, it is preferable to form particles containing
ionogenic groups by copolymerization of at least one of the
foregoing base monomers in the presence of at least one monomer
having ionogenic groups, preferably acid groups. By this method,
which may also be referred to as a one-stage method, it is possible
to obtain particles containing not only oligomeric but also
polymeric ionogenic groups. Copolymerization in a homogeneous
phase, such as in solution or in bulk, is particularly suitable for
formation of particles containing oligomeric ionogenic groups with
the foregoing ionogenic groups in the entire particle. In the case
of copolymerization by emulsion polymerization, for example, or in
other words by using an emulsion of a monomer or monomer mixture in
water, for example, it is possible to produce in particular
particles containing polymeric ionogenic groups, wherein the
ionogenic groups are localized preferably on the microgel surface.
However, it is also possible to assemble an oligomeric or polymeric
particle by starting from a base monomer having suitable ionogenic
groups, preferably add groups or groups that can be transformed to
acid groups. For example, it is conceivable, in order to create
protein-conducting properties in particular, firstly to obtain an
oligomeric or polymeric particle by cross-linking a base monomer
containing groups that can be transformed to acid groups, and only
thereafter to form the desired ionogenic groups at the surface of
the particle by chemical modification, for example by a
deprotection reaction, a hydrolysis, an addition reaction or a
substitution reaction.
[0020] Furthermore, it is preferable firstly to cross-link at least
one of the foregoing base monomers in such a way that an oligomer,
prepolymer or polymer particle is formed, and thereafter to graft
at least one monomer having ionogenic groups, preferably acid
groups, onto the surface of this particle, in order to form a
structure of the core-shell type. According to this procedure,
which corresponds to a two-stage method, particles containing
oligomeric or polymeric ionogenic groups can be produced wherein
the ionogenic groups are present substantially only on the surface
or in a zone near the surface. The procedure in a homogeneous
phase, for example in solution or in bulk, is suitable in
particular for the formation of particles containing oligomeric
ionogenic groups, and the procedure of emulsion polymerization is
suitable in particular for the production of particles containing
polymeric ionogenic groups. In this connection it is preferable
that grafting of a monomer with ionogenic groups achieves a high
degree of coverage with the ionogenic groups on the surface of the
particle. Preferably the surface of the particle containing
ionogenic groups is functionalized almost quantitatively with
ionogenic groups, preferably acid groups, which means that
substantially every reactive group present on the surface of a
cross-linked or pre-cross-linked particle has reacted with a
monomer having ionogenic groups.
[0021] According to a preferred embodiment, the monomers having
ionogenic groups are monomers having acid groups, such as
(meth)acrylic acid, maleic acid, vinylsulfonic acid,
vinylphosphonic acid and/or styrenesulfonic acid, as well as
derivatives and mixtures thereof. According to a particularly
preferred embodiment, the ionogenic groups are selected from one or
more of the following functional groups: --COON, --SO.sub.3H,
--OSO.sub.3H, --P(O)(OH).sub.2, --O--P(OH).sub.2 and
--O--P(O)(OH).sub.2 and/or salts thereof and/or derivatives
thereof, especially partial esters thereof. The salts represent the
conjugate bases to the acid functional groups, or in other words
--COO.sup.-, --SO.sub.3.sup.-, --OSO.sub.3.sup.-,
--P(O).sub.2(OH).sup.- or --P(O).sub.3.sup.3-,
--O--P(O).sub.2.sup.2- and --OP(O).sub.2(OH).sup.- or
--OP(O).sub.3.sup.2- in the form of their metal salts, preferably
alkali metal or aluminum salts.
[0022] According to a preferred embodiment, the particles
containing ionogenic groups are organic polymers and/or oligomers
produced from at least polystyrene and vinylsulfonic acid.
[0023] The formation of the particles containing ionogenic groups
by polymerization or copolymerization is achieved by standard
methods, for example thermal, photochemical or radical methods, if
necessary with addition of a radical starter of the peroxide type
or azo type. Suitable radical starters of the peroxide type or azo
type are known to those skilled in the pertinent art and can be
selected as appropriate.
[0024] In principle, the particle size of the particles containing
ionogenic groups is not subjected to any substantial restriction,
as long as it falls within the nanometer range. The particles
containing ionogenic groups preferably have a mean particle
diameter in a range of 5 nm to 500 nm, a range of 20 nm to 400 nm
being particularly preferred and a range of 30 nm to 300 nm being
most particularly preferred.
[0025] When the particles containing ionogenic groups are of
polymeric nature, they may exhibit a solid phase boundary with the
surrounding polymer matrix. However, it is also possible that they
do not exhibit any solid phase boundary with the surrounding
polymer matrix. The particle size of such polymers, which may also
be referred to as microgels, lies preferably in a range of
approximately 40 nm to approximately 200 nm. These particles
containing ionogenic groups are preferably produced by emulsion
polymerization.
[0026] Emulsion polymerization within the meaning of the present
invention is to be understood in particular as a method known in
itself, wherein water is used as the reaction medium, in which the
monomers used are polymerized in the presence of emulsifiers and
radical-forming substances to form aqueous polymer latices (see,
among other references, Rompp Lexicon of Chemistry, Volume 2,
10.sup.th Edition 1997; P. A. Lovell, M. S. El-Aasser, Emulsion
Polymerization and Emulsion Polymers, John Wiley & Sons, ISBN:
0471967467; H. Gerrens, Fortschr. Hochpolym. Forsch. 1, 234
(1959)). In contrast to suspension or dispersion polymerization,
emulsion polymerization usually yields finer particles, thus
permitting a smaller particle spacing in a matrix. The finer
particles, with their small mean diameter, are smaller than the
critical defect size, and so they subject the matrix containing
them to only slight mechanical impairments while having a
corresponding degree of dispersion.
[0027] The choice of monomers is used to adjust the glass
transition temperature and the glass transition interval of the
polymer particles. The glass transition temperature (Tg) and the
glass transition interval (.DELTA.Tg) of the microgels or of the
substantially spherical polymer particles are determined by
differential scanning calorimetry (DSC), preferably as described
hereinafter. For this purpose, two cooling/heating cycles are
performed for the determination of Tg and .DELTA.Tg. Tg and
.DELTA.Tg are determined in the second heating cycle. For the
determinations, approximately 10-12 mg of the selected microgel is
placed in a DSC sample holder (standard aluminum pan) of
Perkin-Elmer. The first DSC cycle is performed by cooling the
sample first with liquid nitrogen to -100.degree. C. and then
heating to +150.degree. C. at a rate of 20K/min. The second DSC
cycle is begun by cooling the sample immediately, as soon as a
sample temperature of +150.degree. C. has been reached. Cooling is
achieved by rapid cooling with liquid nitrogen. In the second
heating cycle, the sample is heated to +150.degree. C. once again,
as in the first cycle. The heating rate in the second cycle is
again 20K/min. Tg and .DELTA.Tg are determined graphically on the
DSC curve of the second heating operation. For this purpose, three
lines are fitted to the DSC curve. The first line is constructed
along the curve part of the DSC curve below Tg, the second line is
constructed along the curve branch with inflection point passing
through Tg, and the third line is constructed along the curve
branch of the DSC curve above Tg. In this way three lines with two
points of intersection are obtained. Each of the two points of
intersection represents a characteristic temperature. The glass
transition temperature Tg is obtained as the mean value of these
two temperatures, and the glass transition interval .DELTA.Tg is
obtained from the difference between the two temperatures.
[0028] Rubber-like polymer particles exhibit a glass temperature of
generally lower than 23.degree. C. Thermoplastic polymer particles
generally have a glass transition temperature higher than
23.degree. C.
[0029] For the polymer particles used according to the invention,
the glass transition interval is preferably broader than 5.degree.
C., preferably broader than 10.degree. C.
[0030] Rubber-like polymer particles are preferably particles based
on conjugated dienes, such as butadiene, isoprene,
2-chlorobutadiene and 2,3-dichlorobutadiene, as well as ethene,
esters of acrylic and methacrylic acid, vinyl acetate, styrene or
derivatives thereof, acrylonitrile, acrylamides, methacrylamides,
tetrafluoroethylene, vinylidene fluoride, hexafluoropropene,
double-bond-containing hydroxy compounds, such as hydroxyethyl
methacrylate, hydroxyethyl acrylate, hydroxypropyl acrylate,
hydroxybutyl methacrylate, acrolein or combinations thereof.
[0031] Preferred monomers or monomer combinations include:
butadiene, isoprene, acrylonitrile, styrene, .alpha.-methylstyrene,
chloroprene, 2,3-dichlorobutadiene, butyl acrylate, 2-ethylhexyl
acrylate, hydroxyethyl methacrylate, tetrafluoroethylene,
vinylidene fluoride and hexafluoropropene.
[0032] Here, "based on" means that preferably more than 60 wt % of
the polymer particles consists of the cited monomers, preferably
more than 70 wt % and more preferably more than 90 wt %.
[0033] The polymer particles may be cross-linked or
non-cross-linked. Cross-linked polymer particles are also referred
to as microgels or substantially spherical polymer particles. In
particular, the polymer particles may be particles based on
homopolymers or statistical copolymers. The terms homopolymers and
statistical copolymers are known to those skilled in the art and,
for example, are explained in Vollmert, Polymer Chemistry, Springer
Verlag 1973.
[0034] As the polymer base of the rubber-like, cross-linked or
non-cross-linked particles containing ionogenic groups there can be
used in particular: [0035] BR: polybutadiene, [0036] ABR:
butadiene/acrylic acid C.sub.1-4-alkyl ester copolymers, [0037] IR:
polyisoprene, [0038] SBR: statistical styrene-butadiene copolymers
with styrene contents of 1-60, preferably 5-50 weight percent,
[0039] FKM: fluoro rubber, [0040] ACM: acrylate rubber, [0041] NBR:
polybutadiene-acrylonitrile copolymers with acrylonitrile contents
of 5-60, preferably 10-60 weight percent, [0042] CR:
polychloroprene, [0043] EAM: ethylene/acrylate copolymers, [0044]
EVM: ethylene/vinyl acetate copolymers.
[0045] Inventive, non-rubber-like, especially thermoplastic polymer
particles expediently have a glass transition temperature Tg higher
than 23.degree. C. For the thermoplastic polymer particles, the
glass transition interval is preferably broader than 5.degree. C.
(where Tg or the glass transition interval is determined as
described hereinabove). Non-rubber-like, especially thermoplastic
polymer particles are preferably particles based on methacrylates,
especially methyl methacrylate, styrene or styrene derivatives,
such as .alpha.-methylstyrene, para-methylstyrene, acrylonitrile,
methacrylonitrile, vinylcarbazole or combinations thereof. Here,
"based on" means that preferably more than 60 wt % of the polymer
particles consists of the cited monomers, preferably more than 70
wt % and more preferably more than 90 wt %.
[0046] More preferred thermoplastic polymer particles are particles
based on methacrylates, especially methyl methacrylate, styrene,
.alpha.-methylstyrene and acrylonitrile.
[0047] The polymer particles preferably have an approximately
spherical geometry.
[0048] The polymer particles used according to the invention
preferably have a mean particle diameter in the range of 5 nm to
500 nm, particularly preferably of 20 nm to 400 nm, most preferably
of 30 nm to 300 nm. The mean particle diameter is determined by
means of ultracentrifugation with the aqueous latex of the polymer
particles from the emulsion polymerization. The method yields a
mean value for the particle diameter that allows for the possible
presence of agglomerates (H. G. Muller (1996) Colloid Polymer
Science 267; 1113-1116 as well as W. Scholtan, H. Lange (1972)
Kolloid-Z and Z Polymere 250: 782). Ultracentrifugation has the
advantage that the entire particle-size distribution is
characterized and different mean values such as number-average mean
and weight-average mean can be calculated from the distribution
curve.
[0049] The mean diameter data used according to the invention
relate to the weight-average mean.
[0050] Hereinafter diameter parameters such as d.sub.10, d.sub.50
and d.sub.80 will be used. These parameters mean that 10, 50 and 80
wt % respectively of the particles have a diameter smaller than the
corresponding numerical value in "nm".
[0051] The determination of diameter by means of dynamic light
scattering leads in a first approximation to comparable mean
particle diameters. It is also performed on the latex. Lasers
operating at 633 nm (red) and 532 nm (green) are commonly used. In
contrast to ultracentrifugation, dynamic light scattering yields
not the entire particle-size distribution but instead a mean value
in which large particles are weighted disproportionately.
[0052] The polymer particles used according to the invention
preferably have a weight-average mean particle diameter in the
range of 5 nm to 500 nm, preferably of 20 nm to 400 nm,
particularly preferably of 30 nm to 300 nm.
[0053] The inventive particles containing ionogenic groups can be
produced by emulsion polymerization, in which case the particle
size is adjusted within a wide diameter range by variation of the
starting materials, such as emulsifier concentration, initiator
concentration, liquor ratio of organic to aqueous phase, ratio of
hydrophilic to hydrophobic monomers, amount of cross-linking
monomers, polymerization temperature, etc.
[0054] After the polymerization, the latices can be treated by
vacuum distillation or by treatment with superheated steam, in
order to separate volatile components, especially unreacted
monomers.
[0055] The polymer particles produced in this way can be further
processed, for example by evaporation, by electrolyte coagulation,
by co-coagulation with a further latex polymer, by
freeze-coagulation (see U.S. Pat. No. 2,187,146) or by spray
drying.
[0056] In a preferred embodiment, the particles containing
ionogenic groups and produced by emulsion polymerization are at
least partly cross-linked.
[0057] Cross-linking of the particles containing ionogenic groups
and produced by emulsion polymerization is achieved preferably by
the addition of polyfunctional monomers during polymerization, such
as by the addition of compounds having at least two, preferably 2
to 4 copolymerizable C.dbd.C double bonds, such as
diisopropenylbenzene, divinylbenzene, divinyl ether,
divinylsulfone, diallyl phthalate, triallyl cyanurate, triallyl
isocyanurate, 1,2-polybutadiene, N,N'-m-phenylene maleimide,
2,4-tolulenebis(maleimide), triallyl trimellitate, acrylates and
methacrylates of polyhydric, preferably dihydric to tetrahydric
C.sub.2-10 alcohols, such as ethylene glycol, 1,2-propanediol,
butanediol, hexanediol, polyethylene glycol having 2 to 20,
preferably 2 to 8 oxyethylene units, neopentyl glycol, bisphenol A,
glycerol, trimethylolpropane, pentaerythritol, sorbitol as well as
unsaturated polyesters from aliphatic diols and polyols and maleic
acid, fumaric acid and/or itaconic acid.
[0058] Cross-linking of the polymer particles containing ionogenic
groups may be achieved directly during emulsion polymerization,
such as by copolymerization with cross-linking multifunctional
compounds or by subsequent cross-linking as described hereinafter.
Direct cross-linking during emulsion polymerization is preferred.
Preferred multifunctional comonomers are compounds having at least
two, preferably 2 to 4 copolymerizable C.dbd.C double bonds, such
as diisopropenylbenzene, divinylbenzene, divinyl ether,
divinylsulfone, diallyl phthalate, triallyl cyanurate, triallyl
isocyanurate, 1,2-polybutadiene, N,N'-m-phenylene maleimide,
2,4-tolulenebis(maleimide) and/or triallyl trimellitate. Other
compounds that come into consideration are the acrylates and
methacrylates of polyhydric, preferably dihydric to tetrahydric
C.sub.2-10 alcohols, such as ethylene glycol, 1,2-propanediol,
butanediol, hexanediol, polyethylene glycol having 2 to 20,
preferably 2 to 8 oxyethylene units, neopentyl glycol, bisphenol A,
glycerol, trimethylolpropane, pentaerythritol, sorbitol with
unsaturated polyesters of aliphatic diols and polyols as well as
maleic acid, fumaric acid and/or itaconic acid.
[0059] Cross-linking during emulsion polymerization may also take
place by prolonging the polymerization up to high conversions or,
in the monomer-feed method, by polymerization with high internal
conversions. Another possibility also consists in performing the
emulsion polymerization in the absence of regulators.
[0060] For cross-linking of the non-cross-linked or weakly
cross-linked polymer particles following emulsion polymerization,
it is best to use the latices that are obtained during emulsion
polymerization.
[0061] Examples of suitable cross-linking chemicals are organic
peroxides, such as dicumyl peroxide, t-butyl cumyl peroxide,
bis(t-butylperoxyisopropyl)benzene, di-t-butyl peroxide,
2,5-dimethylhexane-2,5-dihydroperoxide,
2,5-dimethylhexyne-3,2,5-dihydroperoxide, dibenzoyl peroxide,
bis-(2,4-dichlorobenzoyl) peroxide, t-butyl perbenzoate as well as
organic azo compounds, such as azobisisobutyronitrile and
azobiscyclohexanenitrile as well as dimercapto and polymercapto
compounds, such as dimercaptoethane, 1,6-dimercaptohexane,
1,3,5-trimercaptotriazine and mercapto-terminated polysulfide
rubbers, such as mercapto-terminated reaction products of
bis-chloroethyl formal with sodium polysulfide.
[0062] The optimal temperature for performing post-cross-linking
naturally depends on the reactivity of the cross-linking agent, and
it may range from temperatures such as room temperature to
approximately 180.degree. C., if necessary at elevated pressure (in
this regard see Houben-Weyl, Methods of Organic Chemistry, 4.sup.th
Edition, Volume 14/2, page 848). Particularly preferred
cross-linking agents are peroxides.
[0063] Cross-linking of rubbers containing C.dbd.C double bonds to
microgels may also be achieved in dispersion or emulsion with
simultaneous, partial or if necessary complete hydrogenation of the
C.dbd.C double bond, as described in U.S. Pat. No. 5,302,696 or
U.S. Pat. No. 5,442,009 or if necessary other hydrogenating agents,
such as organometal hydride complexes.
[0064] If necessary, particle growth by agglomeration may be
performed before, during or after post-cross-linking.
[0065] The polymer particles containing cross-linked ionogenic
groups and used according to the invention expediently have
toluene-insoluble fractions (gel content) at 23.degree. C. of at
least approximately 70 wt %, more preferably at least approximately
80 wt %, even more preferably at least approximately 90 wt %. This
toluene-insoluble fraction is determined in toluene at 23.degree..
For this purpose, 250 mg of the polymer particles is swollen for 24
hours with shaking in 25 mL toluene at 23.degree. C. After
centrifugation at 20000 rpm, the insoluble fraction is separated
and dried. The gel content is obtained from the quotient of the
dried residue and the initial weight and is reported in weight
percent.
[0066] The polymer particles containing cross-linked ionogenic
groups and used according to the invention further expediently have
a swelling index in toluene at 23.degree. C. of less than
approximately 80, more preferably of less than 60, even more
preferably of less than 40. Thus the swelling indices (Qi) of the
polymer particles may lie particularly preferably between 1-15 and
1-10. The swelling index is calculated from the weight of the
solvent-containing polymer particles swollen in toluene for 24
hours at 23.degree. C. (after centrifugation at 20000 rpm) and the
weight of the dried polymer particles:
Qi=wet weight of the polymer particles/dry weight of the polymer
particles.
[0067] To determine the swelling index, 250 mg of the polymer
particles is allowed to swell for 24 hours with shaking in 25 mL
toluene. The gel is centrifuged off and weighed, then dried to
constant weight at 70.degree. C. and weighed once again.
[0068] The polymer particles containing ionogenic groups and used
according to the invention contain ionogenic groups that are ionic
or are capable of forming ionic groups. In this way they are
capable of being proton-donating and/or proton-accepting.
[0069] According to a preferred embodiment, the ionogenic groups
are acid groups. According to a particularly preferred embodiment,
the ionogenic groups are selected from one or more of the following
functional groups: --COON, --SO.sub.3H, --OSO.sub.3H,
--P(O)(OH).sub.2, --O--P(OH).sub.2 and --O--P(O)(OH).sub.2 and/or
salts thereof and/or derivatives thereof, especially partial esters
thereof. The salts represent the conjugate bases to the acid
functional groups, or in other words --COO.sup.-, --SO.sub.3.sup.-,
--OSO.sub.3.sup.-, --P(O).sub.2(OH).sup.- or --P(O).sub.3.sup.3-,
--O--P(O).sub.2.sup.2- and --OP(O).sub.2(OH).sup.- or
--OP(O).sub.3.sup.2- in the form of their metal salts, preferably
alkali metal or ammonium salts.
[0070] According to the invention, particularly preferred ionogenic
groups within the meaning of the invention are selected from
--SO.sub.3H, --PO(OH).sub.2, --O--P(O)(OH).sub.2 and/or salts
thereof and/or derivatives thereof, especially partial esters
thereof.
[0071] Depending on the production technique, the ionogenic groups
may be located on the surface and/or not on the surface.
[0072] The ionogenic groups may be introduced into the polymer
particles by incorporation of functionalized monomers during
polymerization and/or by modification after polymerization.
[0073] As examples, functionalized monomers are selected from the
group consisting of: acrylic acid, methacrylic acid, vinylbenzoic
acid, itaconic acid, maleic acid, fumaric acid, crotonic acid,
vinylsulfonic acid, styrenesulfonic acid, monomers containing
phosphonic acid or phosphoric acid groups and having polymerizable
C.dbd.C double bonds, such as vinylphosphonic acid,
2-phosphonomethylacrylic acid and 2-phosphonomethylacrylic acid
amide, phosphonic acid or phosphoric acid esters of
hydroxyfunctional monomers having polymerizable C.dbd.C double
bonds or salts or derivatives thereof.
[0074] Phosphoric acid esters of hydroxyfunctional monomers having
polymerizable C.dbd.C double bonds preferably have the following
formulas (I) or (II) of the following methacrylate compounds:
##STR00001##
in which R is a divalent organic group, especially such as
C.sub.1-10 alkylene. Preferably R is a C.sub.2-4 alkylene group (or
in other words a C.sub.2-4 alkandiyl group), such as an ethylene or
an n-propylene group. Salts of these compounds are also usable,
especially such as alkali metal salts, preferably the sodium salt
or ammonium salts. The corresponding acrylates are also usable.
Furthermore, partial esters with other saturated or unsaturated
carboxylic acids of these compounds may be used. According to the
invention, the term partial ester includes both the case that some
of the acid hydroxyl groups of the ionogenic group are partly
esterified and the case in which some of the hydroxyl groups in the
polymer particles are esterified while others are not
esterified.
[0075] The proportion of the functional monomers incorporated by
polymerization and containing ionogenic groups is preferably 0.1 to
100 wt %, more preferably 0.2 to 99.5 wt % relative to the total
amount of monomers. This means that homopolymers of these monomers
containing ionogenic groups may also be used. For example, at least
10 wt %, at least 20 wt % or at least 30 wt % of these monomers may
be present.
[0076] As an example, the ionogenic groups --OSO.sub.3H and
--OP(O)(OH).sub.2 may also be introduced into the polymer particles
by reaction of hydroxyl-modified polymer particles (such as
obtained by incorporation of hydroxyalkyl (meth)acrylates by
polymerization) or by addition of sulfuric or phosphoric acid to
epoxy-containing (for example, glycidyl methacrylate-containing)
polymer particles with sulfuric acid or phosphoric acid, by
addition of sulfuric acid or phosphoric acid to
double-bond-containing polymer particles, by decomposition of
persulfates or perphosphates in the presence of
double-bond-containing polymer particles, as well as by
transesterification after polymerization. Furthermore, the
--SO.sub.3H and --P(O)(OH).sub.2 groups may also be introduced by
sulfonation or phosphonation of aromatic vinyl polymers.
[0077] Furthermore, ionogenic groups may also be produced by
reaction of hydroxyl-modified polymer particles with
correspondingly functionalized epoxides.
[0078] Besides the cited ionogenic groups, further functional
groups for control of the properties may be introduced in
particular into the surface of the polymer particles, such as by
chemical reaction of the already cross-linked polymer particles
with chemicals having reactivity toward C.dbd.C double bonds. These
reactive chemicals are in particular compounds with which polar
groups such as aldehyde, hydroxyl, carboxyl, nitrile, etc., as well
as sulfur-containing groups, such as mercapto, dithiocarbamate,
polysulfide, xanthogenate and/or dithiophosphoric acid groups
and/or unsaturated dicarboxylic acid groups may be chemically
bonded to the polymer particles. The goal of modification is in
particular to improve the compatibility with a matrix polymer or a
matrix-forming polymer material, into which the proton-conducting
polymer particles can be incorporated, for example in order to
achieve good compatibility during production as well as good
coupling.
[0079] Particularly preferred methods of modification are grafting
of the polymer particles with functional monomers as well as
reaction with low molecular weight agents. In this way the
ionogenic, proton-donating or proton-accepting monomers may also be
incorporated into the polymer particles if necessary.
[0080] The starting point for grafting of the polymer particles
with functional monomers is expediently the aqueous microgel
dispersion, which is reacted with polar monomers such as
vinylsulfonic acid, styrenesulfonic acid, acrylic acid, methacrylic
acid, itaconic acid, hydroxyethyl (meth)acrylate (in the present
Application, the term "(meth)acrylate" includes both methacrylate
and acrylate), hydroxypropyl (meth)acrylate, hydroxybutyl
(meth)acrylate, acrylonitrile, acrylamide, methacrylamide,
acrolein, monomers containing phosphonic acid or phosphoric acid
groups and having polymerizable C.dbd.C double bonds, such as
vinylphosphonic acid, 2-phosphonomethylacrylic acid and
2-phosphonomethylacrylic acid amide, phosphonic acid or phosphoric
acid esters of hydroxyfunctional monomers having polymerizable
C.dbd.C double bonds or salts or derivatives thereof, especially
such as partial esters thereof, under the conditions of radical
emulsion polymerization. In this way polymer particles having
core-shell morphology are obtained. It is desirable that the
monomer used in the modification step be grafted as quantitatively
as possible onto the unmodified polymer particles or microgel.
Expediently, the functional monomers are added before complete
cross-linking of the microgels. Modification of
double-bond-containing polymer particles, for example by
ozonolysis, is also an option.
[0081] In a preferred embodiment, the polymer particles, especially
the microgels, are modified by hydroxyl groups, especially also at
the surface thereof. The hydroxyl group content of the polymer
particles, especially of the microgels, is determined according to
DIN 53240, as the hydroxyl number in units of mg KOH/g polymer, by
reaction with acetic anhydride and titration of the liberated
acetic acid with KOH. The hydroxyl number of the polymer particles,
especially of the microgels, preferably lies between 0.1 and 100,
more preferably between 0.5 and 50 mg KOH/g polymer.
[0082] The amount of modification agent used is contingent on its
effectiveness and on the requirements applicable to the individual
case, and it lies in the range of 0.05 to 30 weight percent
relative to the total amount of polymer particles and especially
microgel used. A value of 0.5 to 10 weight percent relative to the
total amount of polymer particles, especially microgel, is
particularly preferred.
[0083] The modification reactions may be performed at temperatures
of 0 to 180.degree. C., preferably 20 to 95.degree. C., if
necessary under a pressure of 1 to 30 bar. The modifications may be
carried out on rubber microgels in bulk or in the form of a
dispersion thereof, in which case inert organic solvents or even
water may be used as the reaction medium. Particularly preferably,
the modification is performed in an aqueous dispersion of the
cross-linked rubber.
[0084] Within the polymer matrixes, such as in the form of
membranes, especially polymer electrolyte membranes for fuel cells,
the particles containing ionogenic groups and used according to the
invention may be present in a proportion of matrix polymer to
particles containing ionogenic groups equal to 1:99 to 99:1,
preferably 10:90 to 90:10, particularly preferably 20:80 to 80:20.
The amount of the particles containing ionogenic groups and used
according to the invention depends on the desired properties of the
membrane, such as the proton conductivity of the membranes.
[0085] According to a preferred embodiment, the present invention
relates to a polymer electrolyte membrane for fuel cells,
comprising a polymer matrix, in which particles containing
ionogenic groups are embedded, which particles have a mean particle
diameter in the range of 5 nm to 500 nm (determined by means of
ultracentrifugation as explained in the foregoing), which are
produced by emulsion polymerization and which contain ionogenic
groups selected from the group consisting of: --SO.sub.3H,
--OSO.sub.3H, --P(O)(OH).sub.2, --O--P(OH).sub.2 and
--O--P(O)(OH).sub.2 and/or salts thereof and/or derivatives
thereof. The preferred groups are --SO.sub.3H, --OSO.sub.3H,
--P(O)(OH).sub.2, --O--P(O)(OH).sub.2 and/or salts thereof and/or
derivatives thereof, especially esters, such as partial esters.
[0086] The proportion of the said ionogenic groups in the polymer
particles containing ionogenic groups preferably lies in the range
of 0.1 to 95 wt %, more preferably 1 to 90 wt %, relative to the
total amount of polymer particles.
[0087] Suitable salts of the polymer particles include metal or
ammonium salts, especially alkali metal salts, alkaline earth
salts, etc.
[0088] Suitable derivatives of the polymer particles include in
particular esters and partial esters of the cited ionogenic
groups.
[0089] When the particles containing ionogenic groups are of
oligomeric nature, they preferably do not have a solid phase
boundary with the surrounding matrix. The particle size of such
oligomers, which may also be referred to as star oligomers, is
preferably in a range of approximately 2 nm to approximately 10 nm.
These oligomeric particles containing ionogenic groups are
preferably produced by polymerization or copolymerization in
solution or in bulk.
[0090] Regardless of whether the particles containing ionogenic
groups are of polymeric or oligomeric nature, the ionogenic groups,
especially acid groups, may be present either at the surface, or in
other words in the form of a core-shell structure, or in the entire
particles.
[0091] The particles containing ionogenic groups preferably have a
substantially spherical shape (microgel) or a substantially
star-like shape, but do not necessarily have to have a solid phase
boundary with the surrounding polymer matrix. Thus it is also
possible for the particles containing ionogenic groups to have a
shape different from a substantially spherical shape or a
substantially star-like shape. According to a preferred embodiment,
the particles containing ionogenic groups are solid particles,
which preferably have a particle size in the nanometer range.
[0092] The type of production of the particles containing ionogenic
groups is not subject to any particular restriction. For example,
the particles containing ionogenic groups may be produced by
polymerization or copolymerization in solution or in bulk, by
emulsion polymerization or by suspension polymerization. However,
the particles containing ionogenic groups are preferably produced
by emulsion polymerization, especially when polymer particles
containing ionogenic groups are desired.
[0093] The polymer matrix comprises at least one basic polymer. If
necessary, standard processing aids may be embedded in the polymer
matrix. Furthermore, at least one non-basic polymer may also be
included in the polymer matrix, for example to influence the
thermal or mechanical properties if so desired.
[0094] Suitable doping agents for the inventive polymer electrolyte
membrane containing the polymer matrix are known to those skilled
in the art. Examples are phosphoric acid, phosphoric acid
derivatives, phosphonic acid, phosphonic acid derivatives, sulfuric
acid, sulfuric acid derivatives, sulfonic acid or sulfonic acid
derivatives. Further preferred doping agents are the reaction
product of an at least dibasic, inorganic acid with an organic
compound, wherein the reaction product contains an unreacted acid
group. The degree of doping is preferably between 60 and 95%,
particularly preferably between 65 and 90%, relative to the weight
of the undoped polymer matrix.
[0095] Standard additives used in membranes for fuel cells may be
used as processing aids. A person skilled in the pertinent art will
be capable of selecting suitable processing aids.
[0096] The basic polymers are preferably selected from the group
comprising polybenzimidazole, polypyridine, polypyrimidine,
polyimidazoles, polybenzthiazoles, polybenzoxazoles,
polyoxadiazoles, polyquinoxalines, polythiadiazoles,
poly(tetrazapyrenes) or a combination of two or more thereof,
polybenzimidazole being particularly preferred. Furthermore,
however, other polymers may also be incorporated in the polymer
matrix in order to modify the mechanical or thermal properties.
[0097] The inventive polymer electrolyte membrane provides
excellent proton conductivity in the presence of water, but even in
the anhydrous condition it has industrially relevant
conductivity.
[0098] According to a preferred embodiment, the inventive polymer
electrolyte membrane has a conductivity of at least 2.5 S/m at a
temperature of 25.degree. C., although a conductivity of at least
3.1 S/m at a temperature of 25.degree. C. is particularly
preferred.
[0099] Furthermore, there is provided a method for production of a
polymer electrolyte membrane for fuel cells, especially according
to the present invention and the preferred embodiments described
here, which method comprises the following steps: [0100] (a)
producing a membrane casting solution, at least comprising a
solvent, a matrix-forming basic polymer and particles containing
ionogenic groups, as described in the foregoing, [0101] (b) casting
the membrane casting solution in the form of a membrane, and [0102]
(c) removing the solvent.
[0103] According to the invention, the particles containing
ionogenic groups are dispersed in step a) in a solution of the
matrix-forming basic polymer. Optimal dispersion or homogenization
of the particles containing ionogenic groups in a solution of the
basic polymer is possible particularly preferably in accordance
with WO 2005033186 A1 and WO 2005030843 A1, and it ensures that,
according to the invention, the particles containing ionogenic
groups do not touch one another in the polymer matrix after step
c).
[0104] In a further step d), the membrane may be doped with at
least one doping agent after step c).
[0105] The solvent is not subject to any substantial restriction,
as long as the matrix-forming basic polymer and/or the particles
containing ionogenic groups can be dissolved or suitably dispersed
so as to form the desired membrane. However, the solvent is
preferably selected from the group comprising N-methylpyrrolidone
(NMP), dimethylformamide (DMF), dimethyl sulfoxide (DMSO),
dimethylacetamide (DMAc) and mixtures thereof.
[0106] Removal of the solvent is achieved by standard means,
although removal by heating the cast membrane casting solution
and/or by applying a vacuum is preferred.
[0107] Furthermore, there is provided the use, in fuel cells,
preferably in high-temperature fuel cells in a temperature range up
to approximately 200.degree. C., of the polymer electrolyte
membrane defined in the foregoing or of the polymer electrolyte
membrane obtainable according to the foregoing method.
[0108] The inventive polymer electrolyte membrane may provide
excellent proton conductivity for a long time in fuel cells, such
as high-temperature fuel cells in a temperature range up to
approximately 200.degree. C.
[0109] The following examples are presented in order to explain the
present invention in more detail, without limiting the scope of
protection of the subject matter claimed in the present
invention.
BRIEF DESCRIPTION OF FIGURES
[0110] FIG. 1 illustrates DMA measurements related to Example 8
described below.
[0111] FIG. 2 illustrates the development of voltage versus time at
the 0.5 A/cm2 operating point and summarizes the performance
parameters achieved with dry gases as described in Example 11
below.
EXAMPLES
Example 1
Examples of Production of Microgels or of Substantially Spherical
Polymer Particles Containing Ionogenic Groups
[0112] The production of microgels that may be used as particles
containing ionogenic groups for production of the inventive polymer
electrolyte membranes for fuel cells will be described
hereinafter.
[0113] The microgels are produced by emulsion polymerization. The
monomer combinations as well as the main formulation components
used for production of the microgels are summarized in Tables 1)
and 2). All formulation components are relative to 100 parts by
weight of the monomer mixture.
[0114] The experiments in which Mersolat.RTM. H95 of Lanxess
Deutschland GmbH was used as emulsifier are summarized in Table 1).
Mersolat.RTM. H95 is the sodium salt of a mixture of long-chain
(C16-C18) alkylsulfonates.
[0115] The experiments in which a mixture of disproportionated
resinic acid (Dresinate.RTM. 731/70% of Abieta) and fatty acid
(Edenor.RTM. HTiCT N of Oleo Chemicals/12% in water) was used as
emulsifier are summarized in Table 2). In these experiments, 0.6
parts by weight of potassium hydroxide was also added (Table 2)).
The mixture of resinic and fatty acid was formally neutralized in a
ratio of 150% by the amount of potassium hydroxide.
[0116] The following monomers were used for production of the
microgels listed in Tables 1) and 2):
[0117] Styrene (98%) of KMF Labor Chemie Handels GmbH
[0118] Butadiene (99%, destabilized) of Lanxess Deutschland
GmbH
[0119] Trimethylolpropane trimethacrylate (90%) of Aldrich; Product
number: 24684-0 (abbreviation: TMPTMA)
[0120] Hydroxyethyl methacrylate (96%) of Acros; Product number:
156330010 (abbreviation: HEMA)
[0121] Na vinylsulfonate; 30% aqueous solution of Fluka; Product
number: 95061 (abbreviation: NaVS)
[0122] Na styrenesulfonate (90%) of Fluka; Product number: 94904
(abbreviation: NaSS)
[0123] Vinylphosphonic acid (95%) of Fluka; Product number: 95014
(abbreviation: H.sub.2VP)
[0124] 2-(Methacryloyloxy)ethyl phosphate of Aldrich; Product
number: 463337 (abbreviation: H.sub.2MOOEP)
TABLE-US-00001 TABLE 1 Microgel formulations on the basis of
Mersolat .RTM. H95 emulsifier Mersolat .RTM. Water Styrene
Butadiene TMPTMA NaVS Na.sub.2VP.sup.1) NaSS H.sub.2MOOEP.sup.2)
H95.sup.3) amount.sup.4) Microgel [parts by [parts by [parts by
[parts by [parts by [parts by [parts by [parts by [parts by
designation weight] weight] weight] weight] weight] weight] weight]
weight] weight] OBR 1290-2 88.5 -- 1.5 10 -- -- -- 0.7 400 OBR
1290-4 88.5 -- 1.5 10 -- -- -- 4.0 400 OBR 1293-1 84 -- 6 10 -- --
-- 2.5 400 OBR 1291-1 84 -- 6 10 -- -- -- 1.5 400 OBR 1297-1 88.5
-- 1.5 -- 10 -- -- 2.5 400 OBR 1294-1 93.5 -- 1.5 -- -- 5 -- 2.5
400 OBR 1361-B -- 84 6 10 -- -- -- 2.5 400 OBR 1438-1 86.9 -- 5 --
-- -- 8.1 2.5 400 .sup.1)Na.sub.2VP was obtained from H.sub.2VP by
neutralization in situ with 2 equivalents of NaOH. The weight value
is relative to the sodium salt of vinylphosphonic acid (Na.sub.2VP)
.sup.2)The weight value of 2-(methacryloyloxy)ethyl phosphate is
relative to the free acid (H.sub.2MOOEP); before initiation of the
polymerization, H.sub.2MOOEP was neutralized by addition of 2
equivalents of KOH, so that the corresponding dipotassium salt
(K.sub.2MOOEP) was present in the reaction mixture .sup.3)The
amount value is relative to the total amount of Mersolat .RTM. H95
in the reaction mixture .sup.4)The amount value is relative to the
total amount of water in the reaction mixture
TABLE-US-00002 TABLE 2 Microgel formulations on the basis of a
resinic acid/fatty acid emulsifier system Dresinate .RTM. Edenor
Total water Styrene Butadiene TMPTMA HEMA 731* HTiCT N* KOH amount
Microgel [parts by [parts by [parts by [parts by [parts by [parts
by [parts by [parts by designation weight] weight] weight] weight]
weight] weight] weight] weight] OBR 1435-4 91 -- 1.5 7.5 4.0 1.0
0.6 230 OBR 1327 B 67 22.5 3 7.5 4.0 1.0 0.6 400 OBR 1330 I 81.5
11.5 4 3.0 4.0 1.0 0.6 400 *Amount value for 100% material
Dresinate .RTM.: disproportionated resinic acid (Dresinate .RTM.
731/70% of Abieta) Edenor .RTM. HTiCT N: disproportionated fatty
acid of Oleo Chemicals (12% in water)
[0125] The products OBR 1290-2, OBR 1290-4, OBR 1293-1, OBR 1291-1,
OBR 1297-1, OBR 1294-1 and OBR 1438-1 (Table 1)) were produced in a
6-liter glass reactor with stirring system, whereas the products
OBR 1361-B, OBR 1435-4, OBR 1327 B and OBR 1330 I (Table 1) and
Table 2)) were produced in a 20-liter steel autoclave with stirring
system.
[0126] For each emulsion polymerization reaction in the glass
reactor, 3.93 kg water was introduced and purged with a stream of
nitrogen. Part of the total Mersolat amount was added to the water
pool and dissolved. The following amounts were added to the water
and dissolved; for the production of OBR 1290-2, 5.3 g
Mersolat.RTM. H95; for OBR 1291-1, 13.7 g Mersolat.RTM. H95; for
OBR 1293-1, OBR 1297-1, OBR 1294-1, OBR 1361-B and OBR 1438-1, 24.2
g Mersolat.RTM. H95; and for OBR 1290-4, 40.0 g Mersolat.RTM. H95.
Then 1000 g of the monomer mixtures listed in Table 1) were
introduced together with 0.08 g 4-methoxyphenol (Arcos Organics,
Article No. 126001000, 99%) into the reaction vessel. After the
reaction mixture had been heated to 30-40.degree. C., a freshly
produced 4% aqueous premix solution was added. This premix solution
consisted of:
0.169 g ethylenediaminetetraacetic acid (Fluka, Article number
03620), 0.135 g iron(II) sulfate.7H.sub.2O (Riedel de Haen, Article
number 12354), (calculated without water of crystallization) 0.347
g Rongalit C, Na formaldehyde sulfoxylate 2-hydrate
(Merck-Schuchardt, Article number 8.06455) (calculated without
water of crystallization) as well as 0.524 g trisodium
phosphate.12H.sub.2O (Acros, Article number 206520010) (calculated
without water of crystallization).
[0127] For activation of the polymerization, an activator solution
of 0.56 g p-menthanehydroperoxide (Trigonox.RTM. NT 50 of
Akzo-Degussa) in 50 g water and the remaining amount of
Mersolat.RTM. H95 (2.1 g) was prepared.
[0128] Half of the aqueous activator solution was introduced into
the reaction vessel 5 minutes after addition of the premix
solution. Hereby the polymerization reaction was started. After a
reaction time of 2.5 hours, the reaction temperature was raised to
40-50.degree. C. After one further hour, the second half of the
aqueous activator solution was added. Once a polymerization
conversion of >90% had been reached (usually: 95%-100%), the
polymerization was stopped by addition of an aqueous solution of
2.35 g diethylhydroxylamine (DEHA, Aldrich, Article number
03620).
[0129] OBR 1361-B, OBR 1327 B and OBR 1330 I were produced by an
analogous procedure in a 20-liter autoclave with stirring system.
In each case, 3.5 kg of the monomer mixture and a total water
amount of 14 kg were used. Thereafter the experiments were
performed in a manner analogous to that of the experiments carried
out in the glass reactor.
[0130] After the polymerization reactions were stopped, unreacted
monomers and volatile components were removed from the latex by
stripping with steam.
[0131] The latices of Tables 1) and 2) were filtered then mixed
with stabilizer, coagulated and dried as in Example 2 of U.S. Pat.
No. 6,399,706.
[0132] The gels were characterized both in the latex condition by
means of ultracentrifugation (UZ) and dynamic light scattering
(DLS) relative to their particle diameter, and in the solid
condition relative to solubility in toluene (gel content, swelling
index/QI) and by means of DSC (glass transition temperature/Tg and
width of the Tg interval).
[0133] Characteristic data of the microgels described in Tables 1)
and 2) are compiled in Table 3).
TABLE-US-00003 TABLE 3 Characteristic data of the microgels (from
Tables 1) and 2)) Diameter parameters Gel Microgel d.sub.10
d.sub.50 d.sub.80 d.sub.DLS content Swelling Tg .DELTA.Tg
designation [nm] [nm] [nm] [nm] [wt %] index [.degree. C.]
[.degree. C.] OBR 1290-2 154.9 195.8 240.2 -- 99.9 5.9 112 6.4 OBR
1290-4 -- -- -- 35 82.5 9.8 111 7.6 OBR 1293-1 27.5 39.2 47.2 --
99.9 8.2 124.5 12.2 OBR 1291-1 -- -- -- 155 99.1 4.0 120 14.2 OBR
1297-1 -- -- -- 171 100.0 6.5 112 6.0 OBR 1294-1 63.1 78.7 88.1 --
99.6 9.2 112 8.0 OBR 1361-B -- -- -- 137 95.6 5.1 -78 10.4 OBR
1435-4 -- -- -- 48.3 93.1 9.4 103.5 9.8 OBR 1327 B 30.7 40.3 46.1
-- 94.2 6.4 36 21.8 OBR 1330 I 35.1 47.6 53.3 -- 91.2 11.3 62 20
OBR 1438-1 -- -- 250 99.9 5.4 116 15.6 Meaning of symbols in Table
3): d.sub.10, d.sub.50 and d.sub.80: The particle diameter was
determined on the stopped and steam-stripped latex by means of
ultracentrifugation (W. Scholtan, H. Lange, "Determination of the
Particle Size Distribution of Latices with the Ultracentrifuge",
Kolloid-Zeitschrift and Zeitschrift fur Polymere (1972) Volume 250,
No. 8). The latices have a characteristic particle size
distribution, which is described by the diameter parameters
d.sub.10, d.sub.50 and d.sub.80. These diameter parameters mean
that respectively 10 wt % (d.sub.10), 50 wt % (d.sub.50) and 80 wt
% (d.sub.80) of the particles have a diameter smaller than the
indicated numerical value. The particle size of the microgels in
the latex and in the solid products isolated from the latex and as
used in the inventive compositions are practically identical.
d.sub.dls: particle diameter determined on the latex by means of
dynamic light scattering (DLS). A Zetasizer .RTM. Nano Instrument
(model number: Nano ZS) of Malvern Instruments Ltd.,
Worcestershire, England was used for the determination. A mean
particle diameter is obtained by means of dynamic light scattering.
Tg: glass transition temperature .DELTA.Tg: width of the Tg
interval
[0134] The DSC-2 instrument of Perkin-Elmer was used to determine
Tg and .DELTA.Tg. In the first measurement cycle, the sample is
quickly cooled to -130.degree. C. with liquid nitrogen then heated
to 150.degree. C. at a heating rate of 20 K/min. In the second
measurement cycle, it is again cooled to -130.degree. C. then
heated at 20 K/min. Tg and .DELTA.Tg are determined in the second
measurement cycle.
[0135] The microgels are characterized by the insoluble fraction
and by the degree of swelling of the insoluble fraction. The
insoluble fraction and the degree of swelling are determined in
toluene. For this purpose, 250 mg of the microgel particles is
swollen for 24 hours with shaking in 25 mL toluene at 23.degree. C.
After centrifugation at 20,000 rpm, the insoluble fraction is
separated and dried. The gel content is obtained from the quotient
of the weight of the residue dried to constant weight at 70.degree.
C. and the initial weight and is reported in weight percent.
QI: Swelling index is defined as the wet weight of the microgel
divided by the dry weight of the microgel.
[0136] The swelling index is calculated from the weight of the
solvent-containing microgel (MG.sub.wet) swollen in toluene at
23.degree. C. for 24 hours (after centrifugation at 20,000 rpm) and
the weight of the dry microgel (MG.sub.dry).
QI=MG.sub.wet/MG.sub.dry
[0137] The gel content is calculated as the percentage of the
toluene-insoluble microgel (MG.sub.dry) relative to the initial
weight of microgel (250 mg):
Gel content [ % ] = 100 .times. MG dry 250 ##EQU00001##
Example 2
Microgel Dispersion for Production of Polymer Membranes for Fuel
Cells
[0138] Various acid-group-containing microgels are dispersed in a
solution of 16 wt % polybenzimidazole (PBI, product of Sartorius
AG) and 84 wt % dimethylacetamide (DMAc, 99%, Aldrich) (Table 4),
PBI solution (16%)).
[0139] The composition of the dispersion is given in Table 4):
TABLE-US-00004 TABLE 4 Composition of the dispersion of microgel,
PBI and solvent Material Wt % Formulation in g PBI solution (16%)
33.33 200 DMAc 54.17 325 Microgel 12.5 75 (OBR 1294-1, OBR 1297-1
or OBR 1290-4 according to Table 5)) Total 100 600
[0140] The following starting materials in the indicated
proportions by weight were used for production of the microgels OBR
1294-1, OBR 1297-1 and 1290-4 listed in Tables 5) and 6). The
microgels were produced as described in the foregoing in Example
1.
TABLE-US-00005 TABLE 5 Formulations for production of the microgels
OBR 1294-1 and OBR 1297-1, OBR 1290-4 Microgel Styrene TMPTMA NaSS
NaVS Na.sub.2VP OBR [wt %] [wt %] [wt %] [wt %] [wt %] 1294-1 93.5
1.5 5 -- -- 1297-1 88.5 1.5 -- -- 10 1290-4 88.5 1.5 -- 10 --
Explanations: Styrene (98%) of KMF Labor Handels GmbH, TMPTMA:
Trimethylolpropane trimethacrylate (90%) of Aldrich; Product
number: 24684-0, NaSS: Na styrenesulfonate (90%) of Fluka; Product
number: 94094, NaVS: Na vinylsulfonate; 30% aqueous solution of
Fluka; Product number: 95061, Na.sub.2VP: Sodium salt of
vinylphosphonic acid H.sub.2VP (95%) of Fluka; Product number:
95014. Na.sub.2VP is obtained from H.sub.2VP by neutralization in
situ with 2 equivalents of NaOH.
[0141] The characteristic data of the gels are summarized in Table
6).
TABLE-US-00006 TABLE 6 Properties of OBR 1284-1, OBR 1297-1 and OBR
1290-4 Analytical data Sulfuric or Gel content/ Width of phosphoric
acid Microgel T.sub.g/.degree. C. wt % QI .DELTA.T.sub.g/.degree.
C. content/% OBR 1294-1 112 99.6 9.2 8.0 0.70% S OBR 1297-1 112 100
6.5 6.0 0.24% P OBR 1290-4 111 82.5 9.8 7.6 0.30% S Explanations:
T.sub.g = glass transition temperature QI = swelling index
[0142] The inventive microgel dispersions according to Table 4)
were produced by adding 75 g (corresponding to 12.5 wt % according
to Table 4)) of microgel to 200 g of 16 percent by weight of PBI
solution while stirring by means of a propeller stirrer. Part of
the 325 g of dimethylacetamide according to Table 4) was also added
if needed for the viscosity of the propeller stirring process.
[0143] Thereafter the remaining amount of the 325 g of
dimethylacetamide was added. The mixture was allowed to stand for
24 h at room temperature and then further processed with a
high-pressure homogenizer (type APV 1000 or APV 2000 of APV
Deutschland GmbH (invensys)). The mixture according to Table 4) was
introduced into the homogenizer at room temperature and passed
through the homogenizer six times at 900 to 1000 bar. Up to 5 bar
was needed for transport of the mixture through the homogenizer.
The processing temperature was between 40.degree. C. and 70.degree.
C.
Example 3
Production of a Membrane Casting Solution with Microgel 1297-1
[0144] 50 g of a dispersion of microgel 1297-1, PBI and
dimethylacetamide according to Table 4) were introduced into 310 g
of a 19.1 percent by weight PBI solution in DMAc with stirring. The
PBI solid content in the solution was lowered to 15 percent by
weight by addition of 55 g of dimethylacetamide (DMAc). The
solution was intimately mixed for 0.5 to 1 h at room temperature by
means of a PTFE half-moon stirring shaft. Thereafter it was
degassed for 1 h at room temperature and 30 mbar. Table 7) lists
the compositions of the alternative casting solutions used for
membrane production.
TABLE-US-00007 TABLE 7 Casting solution components for membrane
production Amount of Amount of PBI solid Amount of Microgel
microgel PBI solution content in optionally added type dispersion
in DMAc DMAc solution DMAc 1290-4 50 g 300 g 19.2% 60 g 1297-1 50 g
310 g 19.1% 55 g 1297-1 150 g 250 g 19.1% -- 1297-1 150 g 150 g
19.1% -- 1294-1 40 g 280 g 16.8% 30 g 1294-1 65 g 220 g 16.8% 6 g
1294-1 120 g 260 g 16.8% -- 1294-1 140 g 160 g 16.8% --
[0145] Table 8) lists the physical properties of the casting
solutions produced according to Example 3 and Table 7):
TABLE-US-00008 TABLE 8 Physical properties of the casting solutions
Viscosity Microgel (room Thickness Microgel type proportion*
temperature) PBI content of wet layer 1290-4 10% 3300 mPas 15.0%
300 .mu.m 1297-1 10% 5000 mPas 15.0% 300 .mu.m 1297-1 30% 7900 mPas
14.0% 300 .mu.m 1297-1 50% 6800 mPas 12.5% 300 .mu.m 1294-1 10%
10400 mPas 14.5% 340 .mu.m 1294-1 20% 13800 mPas 14.5% 340 .mu.m
1294-1 30% 13400 mPas 14.0% 340 .mu.m 1294-1 50% 10800 mPas 12.6%
340 .mu.m *Microgel content in wt % relative to the
polybenzimidazole content in % according to Table 8). For a PBI
content of 15%, a microgel proportion of 10% corresponds to a
proportion by weight of 1.5% microgel in the casting solution.
Example 4
Production of Inventive Polymer Membranes with Polymer Particles
Containing Ionogenic Groups
[0146] By means of a pilot-plant drawing machine, the casting
solutions produced according to Example 3 and Table 7) were applied
in layer thicknesses of between 300 and 340 .mu.m on a polyester
film, and were then dried at 65.degree. C. The membrane was
stripped from the backing film and then post-dried for 4 h at
250.degree. C. A polymer membrane devoid of any microgels as
precursors for particles containing ionogenic groups was produced
as a comparison example by the same method.
Example 5
Tensile Stress Measurements
[0147] The mechanical stability of the polymer membranes was
evaluated by tensile stress measurements. Membrane samples having a
length of 10 cm and a width of 2 cm were clamped in a Z 2.5
measuring machine of Zwick GmbH & Co. and subjected at room
temperature to a tensile stress test at a rate of 5 mm/min. An
undoped polymer membrane (10% OBR 1294-1*) produced according to
Example 4 had a modulus of elasticity of approximately 4700
N/mm.sup.2 and higher. In contrast to the pure PBI polymer membrane
without polymer particles containing ionogenic groups, it tore at
tensile stresses of 125 N/mm.sup.2 and an elongation of 4 to 5%.
The results are summarized in Table 9).
TABLE-US-00009 TABLE 9 Tensile stress measurements on polymer
membranes Max. Modulus of tensile strength Elongation elasticity
PBI without microgel 142 N/mm.sup.2 5% 5500 N/mm.sup.2 10% OBR
1294-1* 125 N/mm.sup.2 5% 4700 N/mm.sup.2 20% OBR 1294-1* 117
N/mm.sup.2 4% 4700 N/mm.sup.2 30% OBR 1294-1* 113 N/mm.sup.2 4%
4700 N/mm.sup.2 50% OBR 1294-1* 65 N/mm.sup.2 2% 4000 N/mm.sup.2
*Microgel content in wt % relative to the polybenzimidazole content
in % according to Table 8)
Example 6
Doping with Phosphoric Acid
[0148] To evaluate the uptake capacity for the doping agent,
membrane samples measuring 11.8 cm.times.13.5 cm were placed in 85
percent by weight phosphoric acid at 130.degree. C. for 30 minutes.
The adhering phosphoric acid was then wiped off and the weight gain
was determined gravimetrically according to the following formula
(see Table 10).
(Doped weight-starting weight)/doped weight.times.100=degree of
doping [%]
Example 7
Measurement of the Proton Conductivity
[0149] To evaluate the proton conductivity, doped and undoped
polymer membranes were cut into pieces measuring 4.5 cm.times.2 cm
and the mean thickness was determined by measurement at three
points at least, after which they were mounted in a measuring cell.
The measuring cell was composed of four electrodes, and the
resistance was determined by means of impedance spectroscopy at
room temperature with exclusion of atmospheric humidity. Compared
with a pure PBI membrane devoid of polymer particles containing
ionogenic groups, inventive polymer membranes had a conductivity of
2.5 S/m at room temperature after doping. In the undoped condition,
polymer membranes having different contents of polymer particles
containing ionogenic groups exhibit only very low proton
conductivity.
TABLE-US-00010 TABLE 10 Conductivity measurement with phosphoric
acid-doped membranes Degree of doping with Polymer membrane
H.sub.3PO.sub.4 .sigma. (room temperature) Pure PBI 81 wt % 3.2 S/m
Pure PBI undoped (0 wt %) <10.sup.-6 S/m 10% OBR 1290-4* 87 wt %
4.0 S/m 10% OBR 1297-1* 86 wt % 4.4 S/m 10% OBR 1297-1* undoped (0
wt %) 4 .times. 10.sup.-4 S/m 30% OBR 1297-1* 86 wt % 3.5 S/m 30%
OBR 1297-1* undoped (0 wt %) 3 .times. 10.sup.-4 S/m 50% OBR
1297-1* 89 wt % 3.6 S/m 50% OBR 1297-1* undoped (0 wt %) 2 .times.
10.sup.-4 S/m 10% OBR 1294-1* 82 wt % 3.7 S/m 20% OBR 1294-1* 84 wt
% 3.9 S/m 30% OBR 1294-1* 79 wt % 3.1 S/m 50% OBR 1294-1* 78 wt %
2.6 S/m *Microgel content in wt % relative to the PBI content in %
according to Table 8)
Example 8
Measurement of the Dynamic Mechanical Properties
[0150] Dynamic mechanical analyses (DMA) on undoped membranes were
carried out with a DMA 242 C of the Netsch Geratebau Co. The
measurements were made in tension mode with the following
measurement parameters: temperature range -50 to 480.degree. C.,
heating rate 3 K/min, frequency 1 Hz, proportionality factor 1.1,
maximum dynamic force 7.1 N, additional static preload 0 N,
amplitude 40 .mu.m. The glass transition temperature was determined
on the basis of the maxima of the tan .delta. curves. Table 11) and
FIG. 1 present the results of the measurements.
[0151] Microgel OBR-1297-1 was used as precursor for production of
polymer particles containing ionogenic groups in PBI polymer.
[0152] The glass transition temperature determined for pure PBI
devoid of polymer particles containing ionogenic groups was
420.degree. C. At this temperature, the free volume within the
polymer reached a value that caused large parts of the polymer
chains to have mobility and allowed the material properties of the
polymer to change from the hard glass condition to the rubber
condition. The presence of polymer particles containing ionogenic
groups in weight proportions of 10 and 30 percent by weight in the
PBI matrix led to lowering of the glass transition temperature to
340 or 295.degree. C. due to the plasticizing effect of the polymer
particles. In contrast, a proportion of higher than 50 percent by
weight of polymer particles did not lead to any further lowering of
the glass transition temperature for the PBI matrix polymer,
although at 50 percent by weight a pronounced glass transition of
the material from polymer particles containing ionogenic groups was
evident at a temperature of 89.degree. C. A possible interpretation
of this phenomenon is that the percolation limit of the polymer
particles containing ionogenic groups is exceeded when the
proportion is higher than 50 percent by weight, and so a continuous
phase of mutually touching polymer particles forms, whereas when
the proportion of polymer particles containing ionogenic groups is
lower than 50 percent by weight (especially lower than 40 wt %),
these particles are embedded in the PBI matrix in a condition
isolated from one another.
TABLE-US-00011 TABLE 11 DMA measurements on inventive polymer
membranes Polymer particles containing Polymer ionogenic groups PBI
matrix membrane T.sub.g [.degree. C.] T.sub.g [.degree. C.] Only
PBI -- 420.degree. C. 10% OBR 1297-1* -- 340.degree. C. 30% OBR
1297-1* -- 295.degree. C. 50% OBR 1297-1* 89.degree. C. 295.degree.
C. *Microgel content in wt % relative to the polybenzimidazole
content in % according to Table 8)
Example 9
Production of a Fuel Cell
[0153] The membranes produced according to Example 4 were cut into
square pieces measuring 104 cm.sup.2 and combined with commercially
available ELAT electrodes of the E-TEK Co., each loaded with 2.0
mg/cm.sup.2 Pt, measuring 50 cm.sup.2 and impregnated with 0.68 g
phosphoric acid. The membrane-electrode sandwich was pressed
between plane-parallel plates for 4 h at 160.degree. C. and 50 bar
to form membrane-electrode units. The membrane-electrode units
obtained in this way were mounted in a standard arrangement in the
test fuel cell of Fuel Cell Technologies, Inc. and sealed with a
contact pressure of 15 bar.
Example 10
Determination of the Performance Parameters of the Fuel Cells
[0154] The cells according to Example 9 were connected to a
standard commercial fuel-cell test bench FCATS Advanced Screener of
Hydrogenics Inc. and tested in operating condition at 160.degree.
C. and 3 bar (absolute). Table 12) summarizes the performance
parameters achieved with dry gases.
TABLE-US-00012 TABLE 12 Performance parameters P at 0.6 V
[W/cm.sup.2]/ H.sub.2/air gas H.sub.2 permeation (U.sub.0 [V]) at
160.degree. C., flow, mL/ in 3 bar min (STP) air/nitrogen Pure PBI
0.28 W/cm.sup.2 (0.79 V) 914/2900 3000/3000 ppm 10% OBR 1294-1 0.24
W/cm.sup.2 (0.98 V) 783/2486 0/0 ppm 0% OBR 1294-1 0.31 W/cm.sup.2
(1.02 V) 783/2486 0/0 ppm 0.30 W/cm.sup.2 (1.03 V) 914/2900 30% OBR
1294-1 0.34 W/cm.sup.2 (1.01 V) 914/2900 0/0 ppm 50% OBR 1294-1
0.29 W/cm.sup.2 (1.00 V) 783/2486 10/3000 ppm 10% OBR 1290-1 0.36
W/cm.sup.2 (1.05 V) 1044/3314 0/0 ppm Explanations: P at 0.6 V:
power at a voltage of 0.6 volt U.sub.0: open-circuit voltage
without collection of current
Example 11
Determination of the Long-Term Stability of the Fuel Cells
[0155] The cell according to Example 9, equipped with a polymer
electrolyte membrane containing polymer particles based on OBR
1290-4 (10% relative to the PBI matrix), was connected to a
standard commercial fuel-cell test bench FCATS Advanced Screener of
Hydrogenics Inc. and tested in operating condition at 160.degree.
C. and 3 bar absolute. FIG. 2 illustrates the development of
voltage versus time at the 0.5 A/cm.sup.2 operating point and
summarizes the performance parameters achieved with dry gases. Dry
gases having a gas flow of 261 mL/min (at STP) for hydrogen and a
gas flow of 829 mL/min (at STP) for air were used. Over an
operating time of 1100 h, a membrane-electrode unit based on
microgel OBR 1290-4 exhibited a voltage drop of 48 .mu.V/h. A
membrane-electrode unit based on pure PBI, wherein the polymer
electrolyte membrane was devoid of polymer particles containing
ionogenic groups, exhibited an open-circuit voltage of 0.8 V under
currentless condition from the very beginning of operation and
therefore was not suitable for long-term operation.
* * * * *