ION CONDUCTIVE MEMBRANE FOR ELECTROCHEMICAL APPLICATION

MEMBRANE CONDUCTRICE D'IONS POUR APPLICATION ELECTROCHIMIQUE

English Abstract

An ion conductive membrane for electrochemical applications is provided for forming the membrane on the basis of a polyimide or copolyimide polymer, which contains in its structure heterocyclic groups, particularly in the form of imidazole-, pyridin or pyrimidin groups. The electrochemical applications include particularly the use of such membranes in fuel cells.

French Abstract

L'invention concerne une membrane conductrice d'ions destinée à des applications électrochimiques pour former la membrane sur la base d'un polymère polyimide ou copolyimide,qui contient dans sa structure des groupes hétérocycliques, particulièrement sous la forme de groupes d'imidazole-, pyridine ou pyrimidine. Les applications électrochimiques comprennent particulièrement l'utilisation de telles membranes dans les piles à combustible.

Claims

What is claimed is:
1. Use of an ion conductive membrane for electrochemical applications, the ion
conductive membrane having a base of an aromatic polyimide or copolyimide
polymer
containing units which may be the same or different units, having the general
formula I;
<IMG>
wherein residue B represents at least one aromatic heterocycle having the
general formula II:
<IMG>
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R represents H, a phenyl residue, a phosphoric acid group or at least one
chain containing a
phosphoric acid group and
A represents one of the following groups containing at least one napthalene
unit having the
general formula III:
<IMG>
and forms rings with 6 atoms with the adjacent imide groups.
2. Use of the membrane according to claim 1, wherein said polymer is made up
of
recurring units having the general formula I.
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3. A use according to claim 1, wherein the membrane is obtained by reacting at
least
one diamine, diaminopyridine or diaminopyrimidine, with at least one of
bis(napthalene-
acidanhydride), or a diacid-diakylyester or dialcylchloride-diakylester
derivative of the
dianhydrides.
4. A use according to claim 3, wherein the diamine is at least one of
4,5-di(3-aminophenyl)imidazole or 5-(2-benzimidazole)-1,3-phenylendiamine.
5. A use according to claim 1, wherein said polymer is modified by introducing
a
phosphoric acid group, and the membrane is doped with an acid or an organic
modifier.
6. A use according to claim 1, wherein said membrane is produced by casting a
solution of one of the polyimide or the copolyimide polymer.
7. The use of the membrane as defined in claim 1 for installation in a fuel
cell.
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Description

CA 02412415 2009-03-03
NI 150
ION CONDUCTIVE MEMBRANE FOR ELECTROCHEMICAL APPLICATION
BACKGROUND OF TBE IlWENTION
The invention relates to an ion-conductive membrane for electrochemical
applications having a base of an aromatic polyimide- and co-polyimide polymer
and its use.
Fuel cells are presently the subject of intense development work since they
are
promising alternatives for energy conversion. For mobile applications, the so-
called poly-
electrolyte membrane fuel cell (PEFC) has been found to be particularly
suitable, see F.R.
Kalhammer, P. R. Prokopius, V.P. Roan, G.E. Voecks, Status and Prospects of
Fuel Cells
as Automobile Engines, State of California Air Research Board, 1998. An
essential
criterion for bringing this technology to the market is the availability of
suitable membranes
with high proton conductivity, a low fuel, or respectively, energy carrier
permeability
(hydrogen or methanol) and a high chemical stability. Such membranes however
must also
be relatively inexpensive.
For fuel cells, so far, so called Nafion membranes which are fluorinated
membranes from DuPont or similar, membranes from Dow and Asahi have been
commercially available and have been widely used. (0. Savadogo, J. New
Materials for
Electrochemical Systems 1 (1998) 47).
An essential disadvantage of these Nafion membranes however is their price.
Therefore various non-fluorinated membranes have been tested in the last
years. Most of
them are based on sulfonated polymers and copolymers. Membranes of sulfonated
polysulfon, sulfonated polyether ketone, sulfonated polyphosphene and
sulfonated
polyarnides are descnbed in various publications, see Q Guo, P.N. Pintauro, H.
Tang, S.
O'Connor, Sulfonated and cross-linked polyphosphazene-based proton exchange
membranes, J. Membrane Sci. 154 (1999) 175, E. Vallejo, G. Pourcelli, C.
Gavach, R.
Mercier and M. Pineri, Sulfonated polyimides as proton conductor exchange
membranes.
Physicochemical properties and separation H+1Mz+ by electrodialysis comparison
with a
perfluorosulfonic membrane, J. Membrane Sci. 160 (1999) 127; S. Faure, M.
Pineri, P.
Aldebert, R. Mercier, B. Sillion, US 6 245 881 B1.
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CA 02412415 2009-03-03
A further disadvantage of the Nafion membranes resides in the loss of proton
conductivity at temperatures above 100 C, because of the removal of water.
However,
operation at 100 - 150 C would be advantageous in order to reduce the
poisoning of the
catalyst by CO. A polymer which is believed to be usable in this temperature
range is
polybenzimidazole, which is usually doped with phosphoric acid (R. F.
Savinell, M. H.
Litt, Protein conducting polymers prepared by direct acid casting, US-A-5 716
727).
Polybenzimidazole (PBI) has also been modified by sulfonizing in order to
increase
the conductivity below 100 C (D. J. Jones and J. Roziere, Recent advances in
the
functionalisation of polybenzimidazole and polyether ketone for fuel
applications, J.
Membrane Sci. 185 (2001) 41). The basic character of the imidazole groups
plays in this
case an essential role in the transport of protons in PBI membranes and in
their good
performance above 100 C.
Also sulfonated polyimides have already been examined for use in fuel cells
(C.
Genies, R. Mercier, B. Sillion, N. Cornet, G. Gebel, M. Pineri; Soluble
sulfonated
napthalenic polyimides as materials for proton exchange membranes, Polymer 42
(2001)
359-373; C. Genies, R. Mercier, B. Sillion, R. Petiaud, N. Comet, G. Gebel, M.
Pineri.
Stability study of sulfonated phtalic and naphtalenic polyimide structures in
aqueous
medium. Polymer 42(2001) 5097 - 5105). The possibilities for synthesis are
very flexible
and a multitude of structures can be obtained. However, the membranes examined
so far
are inadequate in many respects.
It is the object of the present invention to provide an improved membrane,
which
can be used for electrochemical applications, particularly in connection with
fuel cells.
SUMMARY OF THE INVENTION
An ion conductive membrane for electrochemical applications is provided for
forming the membrane having a base of a polyimide or copolyimide polymer,
which contains
in its structure heterocyclic groups, particularly in the form of imidazole-,
pyridine or
pyrimidine groups. The electrochemical applications include particularly the
use of such
membranes in fuel cells.
The polyimide or, respectively, copolyimide polymers include units which may
be
same or different but which correspond to the following general formula.
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CA 02412415 2009-03-03
. N A ---- s --- m
Y0
In this general formula I, the residue B represents at least one, possibly
substituted,
aromatic heterocycle of the following generat formula II
NYNH
R 20
N
Here, the residue R represents a hydrogen atom, a phenyl residue, a phosphoric
acid
group or at least one chain containing a phosphoric acid group.
The group A in the general formula I repre.sents one of the following, at
least one
naphthalene unit containing, groups of the general formula III:
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CA 02412415 2002-11-20
.~
lo
/
Fo f
s
CF3
The group A forms with the neighboring imide groups (see the general formula
I)
rings with 6 atoms.
Preferably, the polymers, of which the membranes according to the invention
consist, comprise recurring units of the general formula I.
The polymers used for the manufacture of the membrane according to the
invention
are provided preferably by a direct conversion of diamines (particularly 4,5-
di(3-
aminophenyl)imidazole and 5-(2-benzimidazole)-1.3-phenylenedianine, diamino-
pyridines
and/or diaminopyrimidines with naphthaline - 1, 4, 5, 8 tetracarbonic acid
dianhydride
(NTCDA) , or bis(napthaline acid anhydrides) as well as the diacid-
dialkylester- or
dialcylchloride-dialkylester derivatives of these dianhydrides.
The polymer may further be modified by the introduction of other groups, such
as
acids generally and particular phosphoric acid groups which, among others, can
increase
the photon conductivity. The membranes are manufactured preferably by casting
the
solution of the polymers. It is also possible to modify the membranes with
acids or other
organic substances, for example, with phosphates in order to improve the
conductivity.
The invention will be explained below in greater detail on the basis of
examples
which represent preferred embodiments.
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CA 02412415 2002-11-20
Example 1:
A 250 ml three-necked flask provided with a mechanical stirrer, an inlet for
an inert
gas (argon) and a Dean-Stark system with a cooler and a dry tube at its tip,
was charged
with 0.4365 g (4 mmol) 2.6-diaminopyridine, 1.601 g (8 mmol) bis-(4-
aminophenyl)-ether,
3.2182 g (12 mmol) napthalene-1,4, 5,8 tetra carbonic acid dianhydride, 7.82 g
(64 mmol
benzoic acid and 45 g m-kresol. This mixture (dark red solution) was heated in
a
thermostatically controlled silicon oil bath for 8 hours at 80 C and for 24
hours at 190 C
while being stirred. Then lOg m kresol were added and the reaction mixture was
cooled to
t o room temperature and poured into ethylacetate: The light brown precipitate
was filtered
out, washed with ethylacetate and then with ethanol and was dried in a vacuum
at 80 C.
Example 2:
Into a 100 ml three-necked flask provided with a mechanical stirrer an inlet
for an
inert gas (argon) and a dry tube, 0.1882 g (1 mmol) 2.4-diaminobenzene
sulfonic acid and
0.17 ml (1.2 mmol) dry, triethylamin were introduced and stirred at room
temperature for
several minutes. Then 0.1091 g (1 mmol) 2,6-diaminopyriden, 0.2007g (1 mmol)
bis-(4-
aminophenyl)-ether, 0.80454 g (3 mmol) napthalene 1,4,5,8 tetra carbonic acid
dianhydride
and 18 g benzoic acid were added. This mixture was heated in a
thermostatcially controlled
silicone oil bath to 140 C. After the melting of the benzoic acid, the stirrer
was activated.
The temperature was increased to 160 C and the mixture was stirred at this
temperature
overnight. After cooling to room temperature, acetone was added to the mixture
in order to
dissolve benzoic acid and to remove it subsequently. The light brown residue
was filtered
out, washed with acetone and dried in a vacuum at 70 C.
Example 3:
1.7941 g(8mmol)5-(2-benzimidazole)-1,3-phenylendiamine, 0.8001 g (4mmol) bis-
(4-aminophenyl)-ether, 3.2182g (12 mmol) napthalene-1,4,5,8-tetracarbonic acid
dianhydride, 2.56 g (21 mmol) benzoic acid and 45 g m-kresol were filled into
a 250 ml
three-necked flasks. This mixture was heated in a silicon oil bath - while
being stirred - to
80 C for 4 h and for 20 h to 190 C. Then lOg m-kresol were added and the
mixture was
cooled to room temperature and poured into ethyl acetate. The precipitate was
filtered out,
washed with ethyl acetate and then with ethanol and dried in a vacuum at 80 C.
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CA 02412415 2002-11-20
For the manufacture of the membranes according to the invention, a solution of
the
polymers as prepared in the example 1 to 3 is prepared. The membranes are
manufactured
in a well-known manner from this solution by casting.
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