U.S. patent application number 10/685179 was filed with the patent office on 2004-05-13 for polymer composition, membrane containing said composition, method for the production and uses thereof.
Invention is credited to Baurmeister, Jochen, Frank, Georg, Knauf, Rudiger, Pawlik, Jurgen, Soczka-Guth, Thomas.
Application Number | 20040091762 10/685179 |
Document ID | / |
Family ID | 7887108 |
Filed Date | 2004-05-13 |
United States Patent
Application |
20040091762 |
Kind Code |
A1 |
Soczka-Guth, Thomas ; et
al. |
May 13, 2004 |
Polymer composition, membrane containing said composition, method
for the production and uses thereof
Abstract
The composition described comprises 30 to 99.5% by weight of a
sulfonated aromatic polyether ketone which has an ion-exchange
capacity of from 1.3 to 4.0 meq (--SO.sub.3H)/g of polymer, and
from 0.5 to 70% by weight of a polybenzimidazole. This composition
can, as can a sulfonated polyether ketone of PEK type, be processed
to give membranes, preferably used in fuel cells.
Inventors: |
Soczka-Guth, Thomas;
(Hofheim, DE) ; Frank, Georg; (Tubingen, DE)
; Baurmeister, Jochen; (Eckernforde, DE) ; Pawlik,
Jurgen; (Frankfurt, DE) ; Knauf, Rudiger;
(Aull, DE) |
Correspondence
Address: |
CONNOLLY BOVE LODGE & HUTZ, LLP
P O BOX 2207
WILMINGTON
DE
19899
US
|
Family ID: |
7887108 |
Appl. No.: |
10/685179 |
Filed: |
October 14, 2003 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
10685179 |
Oct 14, 2003 |
|
|
|
09831338 |
Oct 22, 2001 |
|
|
|
6632847 |
|
|
|
|
09831338 |
Oct 22, 2001 |
|
|
|
PCT/EP99/08084 |
Oct 26, 1999 |
|
|
|
Current U.S.
Class: |
429/413 ;
252/62.2; 429/493; 429/506; 429/535; 521/27 |
Current CPC
Class: |
Y02P 70/50 20151101;
H01M 8/1044 20130101; H01M 8/1027 20130101; H01M 8/103 20130101;
H01M 8/1086 20130101; Y02E 60/50 20130101; H01M 8/1025 20130101;
H01M 8/1081 20130101; H01M 8/1069 20130101 |
Class at
Publication: |
429/033 ;
521/027; 252/062.2 |
International
Class: |
H01M 008/10; C08J
005/22; H01G 009/025 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 9, 1998 |
DE |
198 51 498.0 |
Claims
What is claimed is:
1. A composition comprising from 30 to 99.5% by weight of a
sulfonated aromatic polyether ketone which has an ion-exchange
capacity of from 1.3 to 4.0 meq (--SO.sub.3H)/g of polymer, and
from 0.5 to 70% by weight of a polybenzimidazole.
2. A composition as claimed in claim 1, wherein the sulfonated
polyether ketone has the repeat unit of formula I
--[Ar.sup.1--O--Ar.sup.2--CO]-- (I), where Ar.sup.1 and Ar.sup.2,
independently of one another, are bivalent, aromatic or
heteroaromatic radicals, unsubstituted or substituted with one or
more monovalent organic groups inert under usage conditions, and
where at least a portion of the radicals Ar.sup.1 and Ar.sup.2 have
substitution by radicals of the formula --(SO.sub.3).sub.wM, where
M is a metal cation of valency w, an ammonium cation or in
particular hydrogen, and w is an integer, in particular 1 or 2.
3. A composition as claimed in claim 2, wherein Ar.sup.1 and
Ar.sup.2 are naphthylene or in particular phenylene.
4. A composition as claimed in claim 2, wherein Ar.sup.1 and
Ar.sup.2 have substitution by from one to four amino, alcohol,
ether, alkyl, aryl, sulfonyl, phosphonyl, carbonyl, nitro or
carboxylic acid groups, and/or the nitrogen atoms of the
polybenzimidazole have substitution by these groups.
5. A composition as claimed in claim 1, wherein the sulfonated
polyether ketone has an ion-exchange capacity of from 1.6 to 2.9
meq (--SO.sub.3H)/g of polymer.
6. A composition as claimed in claim 1, wherein the
polybenzimidazole has repeat structural units of the formula II
2where Ar" is a tetravalent aromatic radical, Ar' is a bivalent
aromatic radical and R is hydrogen or an inert monovalent organic
radical.
7. A composition as claimed in claim 6, wherein Ar" is
1,2,4,5-phenylene or 3,4,3',4'-biphenylene, Ar' is 1,3- or
1,4-phenylene and R is hydrogen.
8. A composition as claimed in claim 2, wherein the proportion of
the polybenzimidazole is selected depending on the degree of
sulfonation of the sulfonated polyether ketone according to formula
III below: percent by weight of
polybenzimidazole=9.4x-12.4.+-.(9.4x-12.4).times.0.5 (III), where x
is the ion-exchange capacity of the sulfonated polyether ketone in
meq (--SO.sub.3H)/g of polymer.
9. A composition as claimed in claim 1, wherein the type and amount
of the polybenzimidazole and of the sulfonated polyether ketone are
selected in such a way as to permit preparation of a solution in
N-methylpyrrolidone with a viscosity of from 500 to 5000 mPas
(measured at 80.degree. C. in a solution of the polymer in NMP
using a Couette rotary viscometer).
10. A sulfonated aromatic polyether ketone of PEK type which has an
ion-exchange capacity of from 1.3 to 4.0 meq (--SO.sub.3H)/g of
polymer.
11. A membrane comprising the polyether ketone as claimed in claim
10 or the composition as claimed in claim 1.
12. A membrane as claimed in claim 11, which has a thickness of at
least 5 .mu.m, in particular of at least 30 .mu.m.
13. A membrane as claimed in claim 11, which has an
ion-conductivity, mesured in contact with liquid water at room
temperature with the aid of 4-pole impedance spectroscopy at a
phase angle .vertline..theta..vertline- .<1.degree., of not less
than 50 mS/cm.
14. A membrane as claimed in claim 11, which remains mechanically
stable after treatment for 72 hours in boiling water at 100.degree.
C.
15. A membrane as claimed in claim 11, which has a modulus of
elasticity (determined as gradient of the tangent at 1.2 MPa) in
the dry state of at least 600 MPa at 23.degree. C. and 50% relative
humidity.
16. A membrane as claimed in claim 11, which has a modulus of
elasticity (determined as gradient of the tangent at 1.2 MPa) in
water at 60.degree. C. of at least 90 MPa, and an ultimate
elongation of more than 200%.
17. A membrane as claimed in claim 11, which has a residual solvent
content of less than 0.5% by weight.
18. A membrane as claimed in claim 11, which has a
proton-conductivity of more than 50 mS/cm in contact with water at
room temperature.
19. A process for producing the membrane as claimed in claim 11,
which comprises a) preparing a solution comprising from 30 to 99.5%
by weight of a salt of a sulfonated polyether ketone and from 0.5
to 70% by weight of a polybenzimidazole or of the PEK-type
sulfonated polyether ketone by dissolving the polymer(s) in a
suitable organic solvent, in particular dimethyl sulfoxide,
N,N-dimethylformamide, N,N-dimethylacetamide or
N-methyl-2-pyrrolidone, and b) shaping this solution by processes
known per se, such as casting, doctoring, spraying or centrifugal
processes, to give a membrane.
20. The process for producing a membrane as claimed in claim 19,
wherein, after the membrane has been produced, it is freed from
residual solvent and, as appropriate, from other water-soluble
impurities present by washing in water or in a dilute acid of from
0.1 to 20% strength, for example nitric acid, sulfuric acid or
phosphoric acid.
21. The process for producing a membrane as claimed in claim 19,
wherein the membrane is dried by heating until the residual content
of solvent is less than 0.5% by weight.
22. The process for producing a membrane as claimed in claim 19,
wherein the solution comprising from 30 to 99.5% by weight of the
salt of the sulfonated polyether ketone and from 0.5 to 70% by
weight of the polybenzimidazole is introduced into an absorbent web
and the solvent is then removed by evaporation.
23. The use of the membrane as claimed in claim 11 for application
in fuel cells, in particular for application in direct methanol
fuel cells.
24. The use of the membrane as claimed in claim 11 for application
in high-performance capacitors.
25. The use of the membrane as claimed in claim 11 for application
in electrodialysis or in ultrafiltration.
Description
DESCRIPTION
[0001] The present invention relates to a polymer composition which
is suitable in particular for producing membranes, and also to the
use of these membranes in fuel cells, in high-performance
capacitors, in dialysis equipment and in ultrafiltration.
[0002] Fuel cells are electrochemical energy converters which
feature in particular a high level of efficiency. Among the various
types of fuel cells, polymer electrolyte fuel cells (PEM
hereinafter) feature high power density and a low weight to power
ratio.
[0003] Conventional fuel cells generally operate using membranes
based on fluorine-containing polymers, for example using the
material Nafion.RTM..
[0004] For the commercialization of fuel cell technology, in
particular for relatively large-scale applications, it is necessary
to reduce the production costs of the materials used without
thereby having to accept sacrifice of performance compared with the
materials conventionally used.
[0005] Proton-conducting membranes based on sulfonated polyether
ketones are known, for example from a report article by A. Steck in
Proc. 1.sup.st Inter. Symp. on New Materials for Fuel Cell Systems,
Montreal 1995, pp. 74 or from an article by C. A. Linkous et al. in
Int. J. Hydrogen Energy, Vol. 23, No. 7, pp. 525-9 (1998).
WO-A-96/29359 and WO-A-96/29360 describe polymer electrolytes made
from sulfonated aromatic polyether ketones, and the production of
membranes from these materials.
[0006] EP-A-0152161 describes polyether ketones (PEK hereinafter)
composed predominantly of the repeat unit --O--Ar--CO--Ar--, and
molded structures produced therefrom.
[0007] Sulfonated, strictly alternating polyether ketones with the
repeat unit --O--Ar--CO--Ar-- are described in J. Polym. Sci.: Vol.
23, 2205-2222, 1985. The structure of the polyether ketones here is
a result of electrophilic attack, and not nucleophilic attack as
described in EP-A-0152161. The polymers were sulfonated by sulfur
trioxide using triethyl phosphate in dichloroethane. Another
sulfonation method used in this literature reference is
chlorosulfonation using chlorosulfonic acid. However, in this
method, depending on the degree of sulfonation, molecular-weight
degradation is also observed. The amidation of the acid chloride
follows on. A possible application sector given for polymers of
this type is use as ion exchanger or as salt remover. Use in fuel
cells is not described. Property profiles which suggest use in fuel
cells are also absent.
[0008] EP-A-0688824 mentions membranes also for use in
electrochemical cells and made from homogeneous polymer alloys
based on sulfonated aromatic polyether ketones and polyether
sulfones and a third, hydrophilic polymer.
[0009] WO-A-98/07164 has disclosed mixtures made from
high-molecular-weight acids (sulfonated polyether ketones, for
example) and high-molecular-weight bases (polybenzimidazoles, for
example). However, there is no indication here of the combinations
of properties required to permit operation in fuel cells. The
invention described in this document is also directed toward a
water-free conductivity mechanism brought about by acid/base
interaction, and therefore permitting use of these materials at
temperatures above 100.degree. C. and at atmospheric pressure.
[0010] The application of polybenzimidazoles in the fuel cell has
previously been described by Savinell et al. in J. Electrochemical
Soc., 141, 1994, pp. L46-L48. Mixtures of different polymers with
polybenzimidazoles are also known, e.g. from U.S. Pat. No.
5,290,884.
[0011] The suitability of nonfluorinated aromatic polymers, a class
which includes aromatic polyether ketones, for use in fuel cells is
questioned in the literature (A. Steck, Proc. 1.sup.st Inter. Symp.
on New Materials for Fuel Cell Systems, Montreal 1995, pp 74).
[0012] Modifying the properties of polymeric materials by admixing
other components is a well known process. However, the property
profile of polymer mixtures is difficult to predict. It is doubtful
that there is any theory which reflects the complex nature of
polymer-polymer interactions (Macromolecules, Vol. 16, 1983, pp.
753-7).
[0013] The invention provides compositions from which
high-performance membranes can be produced using cost-effective
materials. The novel compositions moreover provide a material whose
performance exceeds that of the standard fluorinated materials
conventionally used. The novel compositions also provide a material
from which membranes with good mechanical properties, and also
excellent proton conductivity, can be produced.
[0014] This combination of properties was not to be expected and
does not arise with other polymer mixtures. For example, with
compositions made from sulfonated polyether ketone and polyether
sulfone it is found that addition of even small amounts of
polyether sulfone leads to a marked fall-off of proton conductivity
of the membranes made from this material.
[0015] The present invention provides compositions comprising from
30 to 99.5% by weight of a sulfonated aromatic polyether ketone
which has an ion-exchange capacity of from 1.3 to 4.0 meq
(--SO.sub.3H)/g of polymer and from 0.5 to 70% by weight of a
polybenzimidazole.
[0016] The ion-exchange capacity (hereinafter also "IEC") is
determined by elemental analysis of the washed and dried polymer
via determination of the ratio of carbon to sulfur (C/S
quotient).
[0017] For the purposes of this invention, aromatic polyether
ketones are any polymer which has structural units --Ar--O-- and
--Ar--CO--, where Ar is an aromatic radical. These structural units
may have been linked to one another in a variety of ways,
particularly in the para position. Following widely used
terminology the first unit is termed "E" (ether) and the second
unit "K" (ketone). Depending on the sequence of the ether units and
ketone units, a distinction can be made between, for example, PEK,
PEEK, PEKK and PEEKK types. All of these types of polymer are
included in the term polyether ketones for the purposes of this
invention. The sulfonated aromatic polyether ketones used according
to the invention may be any desired polymers, for example PEEK,
PEKK, PEEKK or in particular PEK, as long as they have the
ion-exchange capacity defined above.
[0018] Particular preference is given to compositions in which the
sulfonated polyether ketone has the repeat unit of formula I
--[Ar.sup.1--O--Ar.sup.2--CO]-- (I),
[0019] where Ar.sup.1 and Ar.sup.2, independently of one another,
are bivalent aromatic radicals, unsubstituted or substituted by one
or more monovalent organic groups inert under usage conditions, and
where at least a portion of the radicals Ar.sup.1 and Ar.sup.2 have
substitution by radicals of the formula --(SO.sub.3).sub.wM, where
M is a metal cation of valency w, an ammonium cation or in
particular hydrogen, and w is an integer, in particular 1 or 2. M
is preferably a cation of an alkali metal or of an alkaline earth
metal.
[0020] If any radicals are bivalent aromatic radicals, these are
mono- or polynuclear aromatic hydrocarbon radicals or
heterocyclic-aromatic radicals which may be mononuclear or
polynuclear. In the case of heterocyclic-aromatic radicals, these
have in particular one or two oxygen, nitrogen or sulfur atoms in
the aromatic radical.
[0021] Polynuclear aromatic radicals may have been fused with one
another or bonded via C--C bonds or via bridging groups, such as
--O--, --S--, --CO--, --SO.sub.2-- or --C.sub.nH.sub.2n--, where n
is an integer from 1 to 10.
[0022] In the case of the bivalent aromatic radicals, the location
of the valence bonds may be in the para position or in a comparable
coaxial or parallel position or in the meta position or in a
comparable angled position relative to one another.
[0023] The valence bonds which are in a coaxial or parallel
position relative to one another point in opposite directions. An
example of coaxial bonds which point in opposite directions is
given by the bonds in 4,4'-biphenylene. An example of parallel
bonds which point in opposite directions is given by the bonds in
1,5- or 2,6-naphthalene, while the 1,8-naphthalene bonds are
parallel and point in the same direction.
[0024] Examples of preferred bivalent aromatic radicals Ar.sup.1
and Ar.sup.2, the location of whose valence bonds is in the para
position or in a comparable coaxial or parallel position relative
to one another, are given by the mononuclear aromatic radicals with
free valences in the para position relative to one another, in
particular 1,4-phenylene, or fused binuclear aromatic radicals with
parallel bonds which point in opposite directions, in particular
1,4-, 1,5- and 2,6-naphthylene, or binuclear aromatic radicals
linked via a C--C bond and having coaxial bonds which point in
opposite directions, in particular 4,4'-biphenylene.
[0025] The valence bonds which are in the meta position or a
comparable angled position relative to one another are arranged at
an angle.
[0026] Examples of preferred bivalent aromatic radicals Ar.sup.1
and Ar.sup.2, the location of whose valence bonds is in the
metaposition or in a comparable angled position relative to one
another, are given by mononuclear aromatic radicals with free
valences in the metaposition relative to one another, in particular
1,3-phenylene, or fused binuclear aromatic radicals with bonds
which point at an angle relative to one another, in particular 1,6-
and 2,7-naphthylene, or binuclear aromatic radicals linked via a
C--C bond and having bonds which point at an angle relative to one
another, in particular 3,4'-biphenylene.
[0027] Preferred radicals Ar.sup.1 and Ar.sup.2 are 1,3-phenylene
or in particular 1,4-phenylene.
[0028] The aromatic radicals of the polymers used according to the
invention may have substitution by inert groups. For the purposes
of the present invention, these are substituents which do not
adversely affect the application under consideration.
[0029] Examples of substituents of this type are alkyl, alkoxy,
aryl, amino, alcohol, ether, sulfonyl, phosphonyl, acyl, nitro,
carboxylic acid, carboxylic ester or carboxamide groups, or
halogen.
[0030] For the purposes of the present invention, alkyl groups are
branched or preferably straight-chain alkyl radicals, for example
alkyl having from one to six carbon atoms, in particular
methyl.
[0031] For the purposes of the present invention, alkoxy groups are
branched or preferably straight-chain alkoxy radicals, for example
alkoxy radicals having from one to six carbon atoms, in particular
methoxy.
[0032] For the purposes of the present invention, amino groups are
radicals of the formula --NH.sub.2, --NHR.sup.1 or
--NR.sup.1R.sup.2, where R.sup.1 and R.sup.2 independently of one
another, are alkyl radicals or aryl radicals, preferably
methyl.
[0033] For the purposes of the present invention, alcohol groups
are radicals of the formula --OH.
[0034] For the purposes of the present invention, ether groups are
radicals of the formula R.sup.1--O--, where R.sup.1 is as defined
above.
[0035] For the purposes of the present invention, sulfonyl groups
are radicals of the formula --SO.sub.2R.sup.1, where R.sup.1 is as
defined above.
[0036] For the purposes of the present invention, phosphonyl groups
are radicals of the formula --P(OR.sup.3).sub.3, where the radicals
R.sup.3, independently of one another, are hydrogen, alkyl or
aryl.
[0037] For the purposes of the present invention, acyl groups are
radicals of the formula --CO--R.sup.3, where R.sup.3 is as defined
above.
[0038] For the purposes of the present invention, carboxylic acid
groups are radicals of the formula --COOH.
[0039] For the purposes of the present invention, carboxylic ester
groups are radicals of the formula --COOR.sup.1, where R.sup.1 is
as defined above.
[0040] For the purposes of the present invention, carboxamide
groups are radicals of the formula --CONH.sub.2, --CONHR.sup.1 or
--CONR.sup.1R.sup.2, where R.sup.1 and R.sup.2 are as defined
above.
[0041] If any radicals are halogen, these are fluorine or bromine,
for example, or in particular chlorine.
[0042] Preference is given to compositions in which Ar.sup.1 and
Ar.sup.2 are naphthylene or in particular phenylene.
[0043] Preference is given to compositions in which Ar.sup.1 and
Ar.sup.2 have substitution by from one to four amino, alcohol,
ether, alkyl, aryl, sulfonyl, phosphonyl, acyl, nitro, carboxylic
acid, carboxylic ester and/or carboxamide groups, and/or in which
the nitrogen atoms of the polybenzimidazole have substitution by
these groups.
[0044] Particular preference is given to compositions in which the
sulfonated polyether ketone has an ion-exchange capacity of from
1.6 to 2.9 meq (--SO.sub.3H)/g of polymer.
[0045] For the purposes of the present invention,
polybenzimidazoles are any polymer which has repeat structural
units of the formula II 1
[0046] where Ar" is a tetravalent aromatic radical, Ar' is a
bivalent aromatic radical and R is hydrogen or an inert monovalent
organic radical.
[0047] The bivalent aromatic radicals Ar' may, as for Ar.sup.1 and
A.sup.2, be mono- or polynuclear aromatic hydrocarbon radicals or
heterocyclic-aromatic radicals, which may be mono- or polynuclear.
The location of the valence bonds in Ar' may be in the para
position or in a comparable coaxial or parallel position or in the
meta position or in a comparable angled position with respect to
one another. Examples of radicals Ar' have already been given above
when describing the radicals Ar.
[0048] Preferred radicals Ar' are 1,3-phenylene and in particular
1,4-phenylene.
[0049] The tetravalent aromatic radicals Ar" may likewise be mono-
or polynuclear aromatic hydrocarbon radicals or
heterocyclic-aromatic radicals, which may be mono- or polynuclear.
The valence bonds in Ar" are in each case in a pair arrangement, to
allow the two imidazole rings to form.
[0050] Preferably, the location of the two valence bonds is in each
case in the ortho position with respect to one another, and in turn
the location of these pairs is in opposite positions on the
aromatic ring or on the ring system.
[0051] Examples of preferred radicals Ar" are 1,2,4,5-phenylene and
3,4,3',4'-biphenylene.
[0052] Other polybenzimidazoles and preferred radicals Ar" and Ar'
are described in U.S. Pat. No. 5,290,884, the Description of which
is incorporated into the present Description.
[0053] The aromatic radicals Ar' and/or Ar" of the
polybenzimidazoles used according to the invention may have
substitution by inert groups. For the purposes of the present
invention, these are substituents which do not adversely affect the
application under consideration. Examples of these have been listed
above for the sulfonated polyether ketones.
[0054] Particular preference is given to a polybenzimidazole of the
formula II, in which Ar is 1,2,4,5-phenylene or
3,4,3',4'-biphenylene, Ar' is 1,3- or 1,4-phenylene and R is
hydrogen.
[0055] Particular preference is given to compositions in which the
proportion of the polybenzimidazole is selected depending on the
degree of sulfonation of the sulfonated polyether ketone. It has
been found that there is an ideal mixing ratio of sulfonated
polyether ketone to polybenzimidazole, depending on the
ion-exchange capacity of the polyether ketone used. Membranes
produced from polymer mixtures of this type have an ideal
combination of properties comprising modulus of elasticity at
80.degree. C. in water, swelling behavior at 80.degree. C. and
proton conductivity.
[0056] For sulfonated PEK types of the formula I it has been found
that the proportion of the polybenzimidazole should preferably be
selected depending on the degree of sulfonation of the sulfonated
polyether ketone according to formula III below:
percent by weight of
polybenzimidazole=9.43x-12.4.+-.(9.4x-12.4).times.0.5 (III).
[0057] x here is the ion-exchange capacity of the sulfonated
polyether ketone in meq (--SO.sub.3H)/g of polymer.
[0058] The molecular weight of the polymers used in the novel
compositions must be sufficient to allow polymer solutions to form
from which moldings, preferably membranes, can be constructed.
[0059] The sulfonated polyether ketones preferably have molar
masses (number-average) in the range from 45,000 to 70,000 g/mol,
determined by gel permeation chromatography in NMP using salts with
polystyrene calibration.
[0060] The polybenzimidazoles preferably have an intrinsic
viscosity in the range from 0.8 to 1.2, measured at 25.degree.
C.
[0061] The novel compositions are particularly suitable for
producing membranes with excellent performance characteristics.
[0062] The invention also provides membranes comprising the
compositions defined above.
[0063] The novel membranes usually have a thickness of at least 5
.mu.m, preferably more than 10 .mu.m, particularly preferably from
10 to 100 .mu.m. For applications in the fuel cell the thickness of
the membranes is generally at least 30 .mu.m, and for applications
as a dielectric in capacitors the thickness of the membranes is
generally at least 5 .mu.m.
[0064] It is preferable to use polymer solutions with different
viscosities, depending on the desired thickness of the membrane.
For membranes of thickness of from 5 to 50 .mu.m it is preferable
to use polymer solutions with a viscosity of from 500 to 2000 mPas
(measured at 80.degree. C. on a solution of the polymers in the
relevant solvent). For membranes of from 10 to 100 .mu.m thickness
it is preferable to use polymer solutions with a viscosity of from
1500 to 5000 mPas (measured at 80.degree. C. on a solution of the
polymers in the relevant solvent).
[0065] The resultant membranes were tested mainly with respect to
their mechanical stability in the dry state and in the wet state,
their proton conductivity and their performance in the fuel
cell.
[0066] It has been found that the novel membranes feature excellent
electrical properties. These include an ion conductivity of not
less than 50 mS/cm (measured in contact with liquid water at room
temperature with the aid of 4-pole impedance spectroscopy at a
phase angle .vertline..theta..vertline.<1.degree.).
[0067] Proton conductivity in the range from 120 to 200 mS/cm at
80.degree. C. (measured by impedance spectroscopy using the 4-pole
method in pure water) has been found, together with excellent
mechanical properties.
[0068] The novel membranes feature excellent mechanical properties.
These include a modulus of elasticity of at least 600 MPa in the
dry state at 23.degree. C. and 50% relative humidity, a modulus of
elasticity of at least 90 MPa in water at 60.degree. C., a modulus
of elasticity of at least 50 MPa in water at 80.degree. C. and an
ultimate elongation of more than 200%. The moduli of elasticity
here were in each case determined as a gradient of the tangent at
1.2 MPa.
[0069] It has been found, therefore, that there is an increase in
mechanical stability. For example, the modulus of elasticity
determined in water (gradient of the tangent at 1.2 MPa) rises to a
value of 350 N/mm.sup.2 at 80.degree. C. In contrast to this, the
modulus of elasticity determined for pure materials was only from 4
to 5 N/mm.sup.2. It is highly surprising that results of this type
have not been found with mixtures using PES and PEEK (IEC 1.54
mmol/g of polymer).
[0070] The novel membranes also feature excellent resistance to
boiling water. For example, it has been found that novel membranes
based on sulfonated PEK remain mechanically stable after 72 hours
of treatment in boiling water at 100.degree. C.
[0071] The novel membrane preferably has a residual content of
solvent of less than 0.5% by weight.
[0072] It has been found that membranes made from sulfonated PEEK
with an IEC of at least 1.5 meq (--SO.sub.3H)/g of polymer (based
on Victrex 450 PF) are stable for only from about 2 to 3 hours in
boiling water. Surprisingly, membranes made from sulfonated
polyether ketones, e.g. based on Victrex PEK and having a
comparable IEC, are stable for more than 50 h in boiling water. The
invention therefore also provides a polyether ketone of PEK type
which has an ion-exchange capacity of from 1.3 to 4.0 meq
(--SO.sub.3H)/g of polymer, and also a membrane produced
therefrom.
[0073] It has also been found that the polyether ketone polymer
backbone structure, which is electron-deficient due to the absence
of --O--Ar--O-- units, appears to be particularly suitable for
fuel-cell applications.
[0074] Sulfonated polyether ketones having the repeat unit
--O--Ar--CO--Ar-- can currently be produced on an industrial scale
up to an IEC of about 4.0 meq (--SO.sub.3H)/g of polymer.
[0075] It has been found that membranes made from highly sulfonated
polymers of this type or membranes made from compositions
comprising highly sulfonated polymers of this type and
polybenzimidazoles are particularly useful for fuel cells with
little or no humidification and also for so-called super-caps, i.e.
capacitors with extremely high capacitance. The membrane may also
be used in electrodialysis or in ultrafiltration. The invention
also provides the use of the membranes for these applications.
[0076] The invention further provides a process for producing the
membranes described above. The process comprises
[0077] a) preparing a solution comprising from 30 to 99.5% by
weight of a salt of a sulfonated polyether ketone and from 0.5 to
70% by weight of a polybenzimidazole by dissolving the two polymers
in a suitable organic solvent, in particular dimethyl sulfoxide,
N,N-dimethylformamide, N,N-dimethylacetamide or
N-methyl-2-pyrrolidone, and
[0078] b) shaping this solution by processes known per se, such as
casting, doctoring, spraying or centrifugal processes, to give a
membrane.
[0079] Mixtures of polybenzimidazoles and sulfonated polyether
ketones tend to gel spontaneously as a result of the acid-base
interaction which takes place, and it is therefore difficult or
impossible to process them further to give sheet-like structures,
such as membranes. This also applies at elevated temperature.
[0080] A homogeneous solution of sulfonated polyether ketones and
polybenzimidazoles can be prepared by using polybenzimidazole and
the salts, preferably the Li, Na, K or ammonium salts, of the
sulfonic acids in dry organic solvents, preferably DMSO, DMF, DMAC
or NMP. The resultant solution of the blend can be applied to a
support and dried at temperatures up to 160.degree. C.
[0081] Despite the diversion described via the salts of the
sulfonic acid, the production technology described is of great
interest, since it allows production of membranes having the
combined properties of high proton conductivity and high modulus of
elasticity at 80.degree. C. in water, and also low swelling.
[0082] Phase-inversion membranes for use in ultrafiltration are
usually produced by introducing the solution of the polymer or of
the polymer mixture (e.g. sulfonated PEK/PBI in NMP or in DMAC) and
precipitating in a non-solvent (e.g. water).
[0083] The membrane is usually converted into the acid form of the
sulfonic acid by conditioning using a dilute acid, preferably a
dilute mineral acid, such as an acid of from 0.1 to 20% strength
(sulfuric acid, phosphoric acid or nitric acid). At the same time,
ionic (salts) and organic (solvent residues) impurities are removed
by this treatment.
[0084] Another way is to convert the ammonium form of the membrane
into the acid form by thermal cleavage of the ammonium group
(liberating NH.sub.3).
[0085] If desired, the membrane obtained from the pretreatment
described above may then be washed with water.
[0086] The membrane may be then be dried by heating, until, for
example, the residual content of solvent is less than 0.5% by
weight.
[0087] Another preferred version of the novel process provides the
production of a membrane in which the solution comprising from 30
to 99.5% by weight of the salt of the sulfonated polyether ketone
and from 0.5 to 70% by weight of the polybenzimidazole is
introduced into an absorbent web, and the solvent is then removed
by evaporation.
[0088] The novel membranes may be further processed wet or dry.
[0089] The examples below illustrate the invention without limiting
the same.
EXAMPLE 1
[0090] The values for proton conductivity of mixtures using
sulfonated PEK and PBI were determined. The PEK had an IEC of 2.12
meq (--SO.sub.3H)/g of polymer. Proton conductivity was measured
using a 4-pole arrangement. The electrode material used was
platinum. During the measurement, temperature-controlled
demineralized water flowed across the membrane. The thickness and
width of the membrane were determined in the wet state at room
temperature after the treatment with 10% strength nitric acid at
40.degree. C. and washing with demineralized water at room
temperature.
[0091] The test equipment used was a Zahner IM 5d adapted for
measurement in a 4-pole arrangement.
[0092] The table below gives the conductivity values determined for
membranes made from various novel compositions.
1 5% PBI 6% PBI 7.5% PBI 10% PBI 20% PBI Temperature in PEKT2 in
PEKT2 in PEKT2 in PEKT2 in PEKT2 (.degree. C.) Cond. (S/cm) Cond.
(S/cm) Cond. (S/cm) Cond. (S/cm) Cond. (S/cm) 23 0.056282855
0.032303263 0.020937892 0.013605442 0.003425338 30 0.06373923
0.037894398 0.025139398 0.016196955 0.004068961 40 0.075557805
0.045612115 0.030444042 0.019729946 0.004964972 50 0.090157708
0.053875319 0.035936192 0.023627396 0.005839962 60 0.120093433
0.072562358 0.043677182 0.028423626 0.00668619 70 0.165000165
0.104427736 0.065316573 0.03554655 0.007445129 80 0.212844755
0.153029799 0.094613645 0.044791579 0.008032903 80 0.21159084
0.162716718 0.101837142 0.047391961 0.007758072 70 0.193606813
0.146548329 0.0927432 0.046527588 0.006821236 60 0.178111123
0.131412736 0.082758164 0.037013218 0.006063031 50 0.159793228
0.073186886 0.033942891 0.005317593 40 0.143398472 0.101506097
0.063428635 0.028582862 0.004400614 30 0.12434795 0.053606943
0.023420644 0.00363643 25 0.116734811 0.077666133 0.046482549
0.02159594 0.003248673
EXAMPLE 2
Preparation of the Blends Taking the Example of the Membrane Used
in 1.
[0093] The ground sulfonated polymer was introduced into an excess
of 1-molar aqueous sodium hydroxide solution and heated to a
temperature of from 40 to 80.degree. C. The sodium salt of the
polymersulfonate was isolated via a suction filter and compressed
to remove excess aqueous sodium hydroxide solution. Finally, the
polymer was washed until neutral and dried to constant weight.
[0094] The dried powder was used to prepare a solution of from 15
to 20% strength in NMP with the aid of a toothed-wheel stirrer. The
clear solution was mixed with the corresponding amount of a 15%
strength solution of PBI in DMAc (prepared as in EP-A-816,415) and
stirred with a toothed-disk stirrer for at least 1 h.
[0095] After filtration via a deep-bed PET filter with an average
pore width of 0.7 .mu.m at 80.degree. C. the solution was applied
to a glass plate by doctoring, and dried overnight in a
circulating-air drying cabinet at temperatures of from 80 to
140.degree. C.
[0096] After drying, the film was separated from the glass plate
and the sodium salt removed by treating with 1-molar sulfuric acid
at 40.degree. C. The membranes were washed with demineralized water
until neutral and dried.
EXAMPLE 3
Sulfonation of PEK
[0097] 3.49 kg of 98% strength sulfuric acid were charged to a
double-walled reaction vessel which could be heated. Using stirring
by a toothed disk, 400 g of Victrex PEK were introduced as rapidly
as possible into the solution. The temperature was increased to
50.degree. C. As soon as a clear, red solution had been obtained,
2.40 kg of oleum (20% of free SO.sub.3) were added. As soon as the
desired degree of sulfonation had been achieved (after about 1-2
hours in the case of an IEC of 2.12 meq (--SO.sub.3H)/g of polymer)
the solution was cooled to 20.degree. C. and the polymer
precipitated in distilled water.
[0098] The polymer was filtered off with suction, washed until
neutral (test using BaCl.sub.2 solution) and dried in a
circulating-air drying cabinet at from 60 to 120.degree. C.
EXAMPLE 4
Mechanical Data for the Membranes Produced as in Example 3
[0099]
2 Modulus of Content Modulus of elasticity at IEC of elasticity,
23.degree. C., Ultimate 60.degree. C., Ultimate of PBI 50% rel.
humidity elongation water* elongation PEK [%] [MPa] [%] [MPa] [%]
2.12 0 695 121 7 200 2.12 5 1140 72 536 284 2.12 7.5 725 30 158 288
2.12 10 646 28 195 300 2.12 12.5 1445 111 124 370 2.12 17.5 636 26
110 231 2.12 20 1058 40 100 235 *measured in water, modulus of
elasticity in water determined as gradient of the tangent at 1.2
MPa
* * * * *