EP1537164A1

EP1537164A1 - Method for the production of proton-conducting polymer membranes, improved polymer membranes, and the use thereof in fuel cells

Info

Publication number: EP1537164A1
Application number: EP03794874A
Authority: EP
Inventors: Joachim Kiefer; Oemer Uensal; Gordon Calundann; Ursula Leister; Kilian Brehl; Edmund Thiemer; Melanie Schlegel
Original assignee: Pemeas GmbH
Current assignee: BASF Fuel Cell Research GmbH
Priority date: 2002-08-29
Filing date: 2003-08-14
Publication date: 2005-06-08
Also published as: US7883818B2; CN1678662A; JP2005537384A; WO2004024796A1; US20060127705A1; KR20050043921A; CA2496589A1; CN1309762C; KR101010180B1

Abstract

The invention relates to proton-conducting polymer membranes containing polyazole. Said polymer membranes are obtained by means of a method which comprises the steps of A) producing a mixture comprising polyphosphoric acid, at least one polyazole, and/or at least one or several compounds that are suitable for forming polyazoles when subjected to thermal treatment according to step B), B) heating the mixture obtained in step A) to temperatures of up to 400 DEG C under an inert gas atmosphere, C) applying a layer of the mixture obtained in step A) and/or B) to a carrier, D) treating the membrane formed in step C) until said membrane is self-supporting, the treatment being done by means of a hydrolysis liquid that contains phosphorus oxyacids and/or sulfur oxyacids.

Description

description

Process for the production of proton-conducting polymer membranes, improved polymer membranes and their use in fuel cells

The present invention relates to processes for the production of proton-conducting polymer membranes and improved polymer membranes which, owing to their outstanding chemical and thermal properties, can be used in a variety of ways and are particularly suitable as a polymer electrolyte membrane (PEM) in so-called PEM fuel cells.

Proton-conducting polymer membranes with good properties are known. For example, the publications DE No. 10117686.4 and DE No. 10117687.2 describe membranes which have a high phosphoric acid content. These membranes are obtained by solidifying a soft layer containing polyphosphoric acid into a membrane comprising phosphoric acid. The solidification is achieved by the hydrolysis of polyphosphoric acid to phosphoric acid.

In general, hydrolysis can be accomplished by atmospheric humidity. The disadvantage here, however, is that the moisture content can fluctuate. As a result, the hydrolysis proceeds unevenly, as a result of which no consistent product quality can be achieved. If the air humidity is very low, phase separation can occur.

According to the above publications, the hydrolysis can also take place under air-conditioned conditions. However, it is problematic that the hydrolysis proceeds very slowly in order to achieve a high acidity. It should be borne in mind that a climate chamber is quite expensive.

In addition, the hydrolysis starts on one side from a surface, the hydrolysis starting selectively. However, it is advisable to hydrolyze the membrane until a homogeneous membrane is formed, since otherwise the membrane is relatively unstable, so that it can be damaged when detached from an inert carrier.

In addition, it was found that a fairly short hydrolysis leads to a membrane with a high phosphoric acid content, but this membrane has a rather low mechanical stability. If the hydrolysis is carried out for longer, the mechanical stability increases, but the phosphoric acid content decreases.

The present invention is therefore based on the object of providing methods for producing polymer electrolyte membranes which achieve the objects set out above. In particular, the method should enable inexpensive production of polymer electrolyte membranes with high, constant product quality. In addition, it was therefore an object of the present invention to provide polymer electrolyte membranes which, in relation to their performance, have high mechanical stability. Furthermore, the membranes should have a high performance, in particular a high conductivity over a wide temperature range.

These problems are solved by a process for the production of proton-conducting polymer membranes with all the features of claim 1. With regard to the polymer membranes, claim 18 provides a solution to the underlying problem.

The present invention accordingly relates to a proton-conducting polymer membrane comprising polyazole blends obtainable by a process comprising the steps

A) preparation of a mixture comprising polyphosphoric acid, at least one polyazole and / or at least one or more compounds which are suitable for the formation of polyazoles under the action of heat in accordance with step B),

B) heating the mixture obtainable according to step A) under inert gas to temperatures up to 400 ° C.,

C) applying a layer using the mixture according to step A) and / or B) on a support,

D) Treatment of the membrane formed in step C), characterized in that the membrane is treated with a hydrolysis liquid which comprises oxygen acids of phosphorus and / or oxygen acids of sulfur.

According to the present invention, the membrane can be passed directly into a hydrolysis liquid which has, for example, a predetermined concentration of phosphoric acid. This enables automated production of high-performance membranes. By varying the Acid concentration allows you to adjust the hydrolysis rate and membrane properties (H ₃ PO ₄ content, conductivity) in a targeted manner. Here phase separation, which can occur during hydrolysis in an environment with low air humidity, can be essentially ruled out.

The hydrolysis time of the membrane can also be significantly reduced by increasing the temperature. These advantages enable the membranes to be manufactured in a more controlled manner, so that a particularly high quality is achieved.

The method according to the invention in particular enables membranes to be obtained which have a high mechanical stability at a very high acid concentration.

In addition, the membranes obtained by the present process can be stored for a relatively long time particularly simply by welding in an acid-stable film, for example a polyethylene or polypropylene film.

A membrane according to the invention exhibits a high conductivity over a wide temperature range, which is also achieved without additional moistening. Here, a membrane according to the invention has a relatively high mechanical stability.

Furthermore, these membranes have a surprisingly long service life.

The composition produced according to step B) comprises polyazoles. These polymers can already be added in step A). Furthermore, these polymers can also be obtained from the monomers, oligomers and / or prepolymers on which the polymer is based during the heating according to step B).

Polymers based on polyazole contain recurring azole units of the general formula (I) and / or (II) and / or (III) and / or (IV) and / or (V) and / or (VI) and / or (VII) and / or (VIII) and / or (IX) and / or (X) and / or (XI) and / or (XII) and / or (XIII) and / or (XIV) and / or (XV) and / or (XVI) and / or (XVI) and / or (XVII) and / or (XVIII) and / or (XIX) and / or (XX) and / or (XXI) and / or (XXil)

(III)

N-N

(V)

- -Ar ⁶ - ^ -Ar ⁶ - ^ X

(XIV)

(Xvm;

N ^ N

wherein

Ar are the same or different and for a tetra-bonded aromatic or heteroaromatic group, which can be mono- or polynuclear, Ar ^{1 are the} same or different and for a divalent aromatic or heteroaromatic group, which can be mono- or polynuclear, Ar ^{2 are the} same or different Ar ^{3 are the} same or different for a two or three-membered aromatic or heteroaromatic group, which may be mono- or polynuclear, and for a tridentic aromatic or heteroaromatic group, which may be single or polynuclear, Ar ^{4 are the} same or different and for a three-membered aromatic or heteroaromatic group which may be mono- or polynuclear, Ar ^{5 are the} same or different and for a tetra-aromatic or heteroaromatic group which may be mono- or polynuclear, Ar ^{6 are the} same or different and for a divalent aromatic or heteroaromatic group, which can be mononuclear or polynuclear, Ar ⁷ identical or ve are different and for a divalent aromatic or heteroaromatic group, which can be mono- or polynuclear, Ar ^{8 are the} same or different and for a trivalent aromatic or heteroaromatic group, which can be mono- or polynuclear, Ar ^{9 are the} same or different and for a bi- or tri- or tetra-bonded aromatic or heteroaromatic group, which may be mono- or polynuclear, Ar ^{10 are the} same or different and, for a di- or tri-bonded aromatic or heteroaromatic group, which may be mono- or polynuclear, Ar ^{11 is the} same or are different and for a divalent aromatic or heteroaromatic group, which can be mono- or polynuclear, X is the same or different and for oxygen, sulfur or one

Amino group which has a hydrogen atom, a group having 1-20 carbon atoms, preferably a branched or unbranched

Alkyl or alkoxy group, or an aryl group as further radical R carries the same or different for hydrogen, an alkyl group and an aromatic

Group stands with the proviso that R in formula XX is a divalent group and n, m is an integer greater than or equal to 10, preferably greater than or equal to 100. Aromatic or heteroaromatic groups preferred according to the invention are derived from benzene, naphthalene, biphenyl, diphenyl ether, diphenylmethane, diphenyldimethylmethane, bisphenone, diphenylsulfone, thiophene, furan, pyrrole, thiazole, oxazole, imidazole, isothiazole, isoxazole-pyrazole, pyrazole , 2.5- Diphenyl-1, 3,4-oxadiazole, 1, 3,4-thiadiazole, 1, 3,4-triazole, 2,5-diphenyl-1,3,4-triazole, 1, 2,5-triphenyl-1, 3,4-triazole, 1, 2,4-oxadiazole, 1, 2,4-thiadiazole, 1, 2,4-triazole, 1, 2,3-triazole, 1, 2,3,4-tetrazole, benzo [ b] thiophene, benzo [b] furan, indole, benzo [c] thiophene, benzo [c] furan, isoindole, benzoxazole, benzothiazole, benzimidazole, benzisoxazole, benzisothiazole, benzopyrazole, benzothiadiazole, benzotriazole, dibenzofuran, carbazole, dibenzothiophen Bipyridine, pyrazine, pyrazole, pyrimidine, pyridazine, 1, 3,5-triazine, 1, 2,4-triazine, 1, 2,4,5-triazine, tetrazine, quinoline, isoquinoline, quinoxaline, quinazoline, cinnoline, 1, 8-naphthyridine, 1, 5-naphthyridine, 1, 6-naphthyridine, 1, 7-naphthyridine, phthalazine, pyridopyrimidine, purine, pteridine or quinolizine, 4H-quinolizine, diphenyl ether, anthracene, benzopyrrole, benzooxathiadiazole, benzooxadidinol, benzooxadidinol, benzooxadidinol, benzooxadidinol, benzooxadidinol, benzooxadidinol, benzooxadidinol, benzooxadidinol, benzooxadidinzole, Benzopyrazidine, benzopyrimidine, benzotriazine, indolizine, pyridopyridine, imidazopyrimidine, pyrazinopyrimidine, carba zol, aciridine, phenazine, benzoquinoline, phenoxazine, phenothiazine, acridizine, benzopteridine, phenanthroline and phenanthrene, which can optionally also be substituted.

The substitution pattern of Ar ¹ , Ar ⁴ , Ar ⁶ , Ar ⁷ , Ar ⁸ , Ar ⁹ , Ar ¹⁰ , Ar ^{11 is} arbitrary, in the case of phenylene, for example, Ar ¹ , Ar ⁴ , Ar ⁶ , Ar ⁷ , Ar ⁸ , Ar ⁹ , Ar ¹⁰ , Ar ^{11 are} ortho-, meta- and para-phenyien. Particularly preferred groups derive from benzene and biphenyls, which may also be substituted.

Preferred alkyl groups are short-chain alkyl groups with 1 to 4 carbon atoms, such as. B. methyl, ethyl, n- or i-propyl and t-butyl groups.

Preferred aromatic groups are phenyl or naphthyl groups. The alkyl groups and the aromatic groups can be substituted.

Preferred substituents are halogen atoms such as. B. fluorine, amino groups, hydroxyl groups or short-chain alkyl groups such as. B. methyl or ethyl groups.

Preference is given to polyazoles having repeating units of the formula (I) in which the radicals X are the same within a repeating unit.

In principle, the polyazoles can also have different recurring units which differ, for example, in their X radical. However, it preferably has only the same X radicals in a recurring unit.

Further preferred polyazole polymers are polyimidazoles, polybenzimidazole ether ketone, polybenzothiazoles, polybenzoxazoles, polyoxadiazoles, Polyquinoxalines, polythiadiazoles poly (pyridines), poly (pyrimidines), and poly (tetrazapyrenes).

In a further embodiment of the present invention, the polymer containing recurring azole units is a copolymer or a blend which contains at least two units of the formulas (I) to (XXII) which differ from one another. The polymers can be present as block copolymers (diblock, triblock), statistical copolymers, periodic copolymers and / or alternating polymers.

In a particularly preferred embodiment of the present invention, the polymer containing recurring azole units is a polyazole which contains only units of the formula (I) and / or (II).

The number of repeating azole units in the polymer is preferably an integer greater than or equal to 10. Particularly preferred polymers contain at least 100 repeating azole units.

In the context of the present invention, polymers containing recurring benzimidazole units are preferred. Some examples of the extremely useful polymers containing recurring benzimidazole units are represented by the following formulas:

H

where n and m is an integer greater than or equal to 10, preferably greater than or equal to 100.

The polyazoles used in step A), but especially the polybenzimidazoles, are distinguished by a high molecular weight. Measured as intrinsic viscosity, this is preferably in the range from 0.3 to 10 dl / g, in particular 1 to 5 dl / g. Furthermore, the polyazoles can also be prepared in step B) by heating. For this purpose, one or more compounds can be added to the mixture in step A) which are suitable for the formation of polyazoles under the action of heat in step B).

Mixtures are suitable for this purpose which comprise one or more aromatic and / or heteroaromatic tetra-amino compounds and one or more aromatic and / or heteroaromatic carboxylic acids or their derivatives which comprise at least two acid groups per carboxylic acid monomer. Furthermore, one or more aromatic and / or heteroaromatic diaminocarboxylic acids can be used for the production of polyazoles.

The aromatic and heteroaromatic tetra-amino compounds include, inter alia, 3,3 ', 4,4'-tetraaminobiphenyl, 2,3,5,6-tetraaminopyridine, 1, 2,4,5-tetraaminobenzene, 3,3', 4,4'-tetraaminodiphenyl sulfone, 3,3 ', 4,4'-tetraaminodiphenyl ether, 3,3', 4,4'-tetraaminobenzophenone, 3,3 ', 4,4'-tetraaminodiphenylmethane and 3,3', 4, 4'-tetraaminodiphenyldimethylmethane and their salts, in particular their mono-, di-, tri- and tetrahydrochloride derivatives. Of these, 3,3 ', 4,4'-tetraaminobiphenyl, 2,3,5,6-tetraaminopyridine and 1,2,4,5-tetraaminobenzene are particularly preferred.

Mixture A) may further comprise aromatic and / or heteroaromatic carboxylic acids. These are dicarboxylic acids and tricarboxylic acids and tetracarboxylic acids or their esters or their anhydrides or their acid halides, in particular their acid halides and / or acid bromides. The aromatic dicarboxylic acids are preferably isophthalic acid, terephthalic acid, phthalic acid, 5-hydroxyisophthalic acid, 4-hydroxyisophthalic acid, 2-hydroxyterephthalic acid, 5-aminoisophthalic acid, 5-N, N-dimethylaminoisophthalic acid, 5-N, N-diethylaminoisinoamino - Dihydroxy terephthalic acid, 2,6-dihydroxyisophthalic acid, 4,6-dihydroxyisophthalic acid, 2,3-dihydroxyphthalic acid, 2,4-dihydroxyphthalic acid. 3,4-dihydroxyphthalic acid, 3-fluorophthalic acid, 5-fluoroisophthalic acid, 2-fluoroterphthalic acid, tetrafluorophthalic acid, tetrafluoroisophthalic acid, tetrafluoroterephthalic acid, 1, 4-naphthalenedicarboxylic acid, 1, 5-naphthalenedicarboxylic acid, 2,6-naphthalenediconic acid, 1, 8-dihydroxynaphthalene-3,6-dicarboxylic acid, diphenyl ether-4,4'-dicarboxylic acid, benzophenone-4,4'-dicarboxylic acid, diphenyl sulfone-4,4'-dicarboxylic acid, biphenyl-4,4'-dicarboxylic acid, 4- Trifluoromethylphthalic acid, 2,2-bis (4-carboxyphenyl) hexafluoropropane, 4,4'-stilbenedicarboxylic acid, 4- Carboxycinnamic acid, or their C1-C20 alkyl esters or C5-C12 aryl esters, or their acid anhydrides or their acid chlorides.

In the case of aromatic tricarboxylic acids or their C1-C20-alkyl esters or C5-C12-

Aryl esters or their acid anhydrides or their acid chlorides are preferably 1,3,5-benzene-tricarboxylic acid (Trimesic acid), 1,2,4-benzene-tricarboxylic acid (Trimellitic acid),

(2-carboxyphenyl) iminodiacetic acid, 3,5,3'-biphenyltricarboxylic acid, 3,5,4'-

Biphenyltricarboxylic.

The aromatic tetracarboxylic acids or their C1-C20 alkyl esters or C5-C12 aryl esters or their acid anhydrides or their acid chlorides are preferably 3,5,3 ', 5'-biphenyltetracarboxylic acid, 1, 2.4 , 5-benzenetetracarboxylic acid, benzophenonetetracarboxylic acid, 3,3 ', 4,4'-biphenyltetracarboxylic acid, 2, 2', 3,3'-biphenyltetracarboxylic acid, 1, 2,5,6-naphthalenetetracarboxylic acid, 1, 4,5,8-naphthalenetetracarboxylic acid ,

The heteroaromatic carboxylic acids are heteroaromatic dicarboxylic acids and tricarboxylic acids and tetracarboxylic acids or their esters or their anhydrides. Heteroaromatic carboxylic acids are understood to mean aromatic systems which contain at least one nitrogen, oxygen, sulfur or phosphorus atom in the aromatic system. It is preferably pyridine-2,5-dicarboxylic acid, pyridine-3,5-dicarboxylic acid, pyridine-2,6-dicarboxylic acid, pyridine-2,4-dicarboxylic acid, 4-phenyl-2,5-pyridinedicarboxylic acid, 3.5 -PyrazoIdicarboxylic acid, 2,6 - Pyrimidinedicarboxylic acid, 2,5-Pyrazinedicarboxylic acid, 2,4,6-Pyridinetricarboxylic acid, Benzimidazole-5,6-dicarboxylic acid. As well as their C1-C20 alkyl esters or C5-C12 aryl esters, or their acid anhydrides or their acid chlorides.

The content of tricarboxylic acid or tetracarboxylic acids (based on the dicarboxylic acid used) is between 0 and 30 mol%, preferably 0.1 and 20 mol%, in particular 0.5 and 10 mol%.

Mixture A) can also contain aromatic and heteroaromatic diaminocarboxylic acids. These include diaminobenzoic acid, 4-phenoxycarbonyl-3, '4'-diaminodiphenyl ether and their mono- and dihydrochloride derivatives.

Mixtures of at least 2 different aromatic carboxylic acids are preferred in step A). Mixtures are particularly preferred used, which contain not only aromatic carboxylic acids but also heteroaromatic carboxylic acids. The mixing ratio of aromatic carboxylic acids to heteroaromatic carboxylic acids is between 1:99 and 99: 1, preferably 1:50 to 50: 1.

These mixtures are in particular mixtures of N-heteroaromatic dicarboxylic acids and aromatic dicarboxylic acids. Non-limiting examples of dicarboxylic acids are isophthalic acid, terephthalic acid, phthalic acid, 2,5-dihydroxyterephthalic acid, 2,6-dihydroxyisophthalic acid, 4,6-dihydroxyisophthalic acid, 2,3-dihydroxyphthalic acid, 2,4-dihydroxyphthalic acid. 3,4-dihydroxyphthalic acid, 1,4-naphthalenedicarboxylic acid, 1,5-naphthalenedicarboxylic acid, 2,6-naphthalenedicarboxylic acid, 2,7-naphthalenedicarboxylic acid, diphenic acid, 1,8-dihydroxynaphthalene-3,6-dicarboxylic acid, diphenyl ether-4,4 ' -dicarboxylic acid, benzophenone-4,4'-dicarboxylic acid, diphenylsulfone-4,4'-dicarboxylic acid, biphenyl-4,4'-dicarboxylic acid, 4-trifluoromethylphthalic acid, pyridine-2,5-dicarboxylic acid, pyridine-3,5-dicarboxylic acid, Pyridine-2,6-dicarboxylic acid, pyridine-2,4-dicarboxylic acid, 4-phenyl-2,5-pyridinedicarboxylic acid, 3,5-pyrazole dicarboxylic acid, 2,6-pyrimidine dicarboxylic acid, 2,5-pyrazine dicarboxylic acid.

If the highest possible molecular weight is to be achieved, the molar ratio of carboxylic acid groups to amino groups in the reaction of tetraamino compounds with one or more aromatic carboxylic acids or their esters, which contain at least two acid groups per carboxylic acid monomer, is preferably close of 1: 2.

The mixture produced in step A) preferably comprises at least 0.5% by weight, in particular 1 to 30% by weight and particularly preferably 2 to 15% by weight, of monomers for the production of polyazoles.

If the mixture according to step A) also contains tricarboxylic acids or tetracarboxylic acid, branching / crosslinking of the polymer formed is achieved in this way. This contributes to the improvement of the mechanical property.

According to a further aspect of the present invention, the mixture prepared in step A) comprises compounds which, under the action of heat in step B), are suitable for the formation of polyazoles, these compounds by reaction of one or more aromatic and / or heteroaromatic tetraamino -Compounds with one or more aromatic and / or heteroaromatic carboxylic acids or their derivatives, which contain at least two acid groups per carboxylic acid monomer, or of one or more aromatic and / or heteroaromatic diaminocarboxylic acids in the melt at temperatures of up to 400 ° C, in particular up to 350 ° C, preferably up to 280 ° C are available. The compounds to be used to prepare these prepolymers have been set out above.

The polyphosphoric acid used in step A) is a commercially available polyphosphoric acid such as is available, for example, from Riedel-de Haen. The polyphosphoric acids H _n + ₂ PnO _{3n +} ι (n> 1) usually have a content calculated as P ₂ Os (acidimeth) of at least 83%. Instead of a solution of the monomers, a dispersion / suspension can also be produced.

According to a particular aspect of the present invention, at least one further polymer which is not a polyazole can be added to the composition produced in step A) and / or step B) (polymer (B)). This polymer can be dissolved, dispersed or suspended, among other things.

The weight ratio of polyazole to polymer (B) can be in particular in the range from 0.1 to 50, preferably from 0.2 to 20, particularly preferably from 1 to 10. If the polyazole is only formed in step B), the weight ratio can be calculated from the weight of the monomers to form the polyazole, the compounds released during the condensation, for example water, having to be taken into account.

The preferred polymers include polyolefins, such as poly (chloroprene), polyacetylene, polyphenylene, poly (p-xylylene), polyarylmethylene, polyarmethylene, polystyrene, polymethylstyrene, polyvinyl alcohol, polyvinyl acetate, polyvinyl ether, polyvinylamine, poly (N-vinyl acetamide), polyvinyl imidazole , polyvinylcarbazole, polyvinylpyrrolidone, polyvinylpyridine, polyvinyl chloride, polyvinylidene chloride, polytetrafluoroethylene, polyhexafluoropropylene, copolymers of PTFE with hexafluoropropylene, perfluoropropyl vinyl ether with with Trifluoronitrosomethan with Sulfonylfluoridvinylether, perfluoroalkoxy vinyl ethers with carbalkoxy, polychlorotrifluoroethylene, Poiyvinylfluorid, polyvinylidene fluoride, polyacrolein, polyacrylamide, polyacrylonitrile, polycyanoacrylates, polymethacrylimide , Cycloolefinic copolymers, in particular from norbornene; Polymers with CO bonds in the main chain, for example polyacetal, polyoxymethylene, polyether, polypropylene oxide, polyepichlorohydrin, polytetrahydrofuran, polyphenylene oxide, polyether ketone, polyester, in particular Polyhydroxyacetic acid, polyethylene terephthalate, polybutylene terephthalate,

Polyhydroxybenzoate, polyhydroxypropionic acid, polypivalolactone, polycaprolactone,

Polymalonic acid, polycarbonate;

Polymeric C-S bonds in the main chain, for example polysulfide ether,

Polyphenylene sulfide, polyether sulfone;

Polymeric C-N bonds in the main chain, for example

Polyimines, polyisocyanides, polyetherimine, polyaniline, polyamides, polyhydrazides,

Polyurethanes, polyimides, polyazoles, polyazines;

Liquid crystalline polymers, especially Vectra as well

Inorganic polymers, for example polysilanes, polycarbosilanes, polysiloxanes,

Polysilicic acid, polysilicates, silicones, polyphosphazenes and polythiazyl.

According to step B), the mixture obtained in step A) is heated to a temperature of up to 400 ° C., in particular up to 350 ° C., preferably up to 280 ° C., in particular 100 ° C. to 250 ° C. and particularly preferably in the range from 180 ° C to 250 ° C heated. An inert gas, for example nitrogen or a noble gas, such as neon, argon, is used here. Depending on the starting material, this step either serves to dissolve or disperse the polyazoles, or to form polyazoles from monomers or polymeric precursors of the poiyazoie.

In a variant of the method, the heating according to step B) can take place after the formation of a flat structure according to step C).

The mixture produced in step A) and / or step B) may additionally contain organic solvents. These can have a positive impact on processability. For example, the rheology of the solution can be improved so that it can be extruded or squeegee more easily.

To further improve the application properties, fillers, in particular proton-conducting fillers, and additional acids can also be added to the membrane. The addition can take place, for example, in step A), step B) and / or step C). Furthermore, these additives, if they are in liquid form, can also be added after the polymerization in step D). Furthermore, these additives can be added to the hydrolysis liquid.

Non-limiting examples of proton-conducting fillers are sulfates such as: CsHSO ₄ , Fe (SO ₄ ) ₂ , (NH ₄ ) ₃ H (SO ₄ ) ₂ , LiHSO ₄ , NaHS0 ₄ , KHSO ₄ , RbSO ₄ , LiN ₂ H ₅ SO ₄ , NH ₄ HSO ₄ , Phosphates such as Zr ₃ (PO ₄ ) ₄ , Zr (HPO ₄ ) ₂ , HZr ₂ (PO ₄ ) ₃ , UO ₂ PO ₄ .3H ₂ O, H ₈ UO ₂ PO ₄ ,

Ce (HPO ₄ ) ₂ , Ti (HPO ₄ ) ₂ , KH ₂ PO ₄ , NaH ₂ PO ₄ , LiH ₂ PO ₄ , NH ₄ H ₂ PO ₄ ,

CsH ₂ PO ₄ , CaHPO ₄ , MgHPO ₄ , HSbP ₂ O ₈ , HSb ₃ P ₂ O ₁₄ , H ₅ Sb ₅ P2θ ₂ o, polyacid such as H ₃ PW ₁₂ O ₄₀ .nH ₂ O (n = 21-29) , H ₃ SiW ₁₂ O ₄₀ .nH ₂ O (n = 21-29), H _x WO ₃ ,

HSbWO ₆ , H ₃ PMo ₁₂ O ₄₀ , H ₂ Sb ₄ On, HTaWO ₆ , HNbO ₃ , HTiNbO ₅ ,

HTiTaO ₅ , HSbTeO ₆ , H ₅ Ti ₄ O ₉ , HSbO ₃ , H ₂ MoO ₄ selenites and arsenides such as (NH ₄ ) ₃ H (SeO ₄ ) ₂ , UO ₂ AsO ₄ , (NH ₄ ) ₃ H (SeO ₄ ) ₂ , KH ₂ AsO ₄ ,

Cs ₃ H (SeO ₄ ) ₂ , Rb ₃ H (SeO ₄ ) ₂ , oxides such as Al ₂ O ₃ , Sb ₂ O ₅ , ThO ₂ , SnO ₂ , ZrO ₂ , MoO ₃

Silicates such as zeolites, zeolites (NH ₄ +), layered silicates, framework silicates, H-natrolites,

H-mordenite, NH ₄ -analine, NH ₄ -sodalite, NH ₄ -galate, H-

Montmohllonite acids such as HCIO, SbF ₅ fillers such as carbides, especially SiC, Si ₃ N, fibers, especially glass fibers,

Glass powders and / or polymer fibers, preferably based on

Polyazole.

These additives can be contained in the proton-conducting polymer membrane in customary amounts, but the positive properties, such as high conductivity, long service life and high mechanical stability of the membrane, should not be adversely affected by the addition of excessive amounts of additives. In general, the membrane after the treatment in step D) comprises at most 80% by weight, preferably at most 50% by weight and particularly preferably at most 20% by weight of additives.

Furthermore, this membrane can also contain perfluorinated sulfonic acid additives (preferably 0.1-20% by weight, preferably 0.2-15% by weight, very preferably 0.2-10% by weight). These additives improve performance, increase proximity to the cathode to increase oxygen solubility and diffusion, and decrease the adsorption of phosphoric acid and phosphate to platinum. (Electrolyte additives for phosphoric acid fuel cells. Gang, Xiao; Hjuler, HA; Olsen, C; Berg, RW; Bjerrum, NJ. Chem. Dep. A, Tech. Univ. Denmark, Lyngby, Den. J. Electrochem. Soc . (1993), 140 (4), 896-902 and Perfluorosulfonimide as an additive in phosphoric acid fuel celi. Razaq, M .; Razaq, A .; Yeager, E .; DesMarteau, Darryl D .; Singh, S. Gase Cent. Electrochem. Sei., Gase West. Reserve Univ., Cleveland, OH, USA. J. Electrochem. Soc. (1989), 136 (2), 385-90.) Non-limiting examples of persulfonated additives are: trifluomethanesulfonic acid, Potassium trifluoromethanesulfonate, sodium trifluoromethanesulfonate, lithium trifluoromethanesulfonate, Ammoniumtrifluormethansulfonat, Kaliumperfluorohexansulfonat, Natriumperfluorohexansulfonat perfluorohexanesulphonate, lithium, ammonium perfluorohexanesulphonate, perfluorohexanesulphonic acid, Kaliumnonafluorbutänsulfonat, Natriumnonafluorbutansuifonat, Lithiumnonafluorbutansulfonat, Ammoniumnonafluorbutansulfonat, Cäsiumnonafluorbutansulfonat, Triethylammoniumperfluorohexasulfonat, Perflurosulfoimide and Nafion.

The flat structure according to step C) is formed by means of measures known per se (casting, spraying, knife coating, extrusion) which are known from the prior art for polymer film production. Suitable carriers are all carriers which are inert under the conditions. These carriers include, in particular, films made from polyethylene terephthalate (PET), polytetrafluoroethylene (PTFE), polyhexafluoropropylene, copolymers of PTFE with hexafluoropropylene, polyimides, polyphenylene sulfides (PPS) and polypropylene (PP).

To adjust the viscosity, the solution can optionally be mixed with an easily evaporable organic solvent. As a result, the viscosity can be adjusted to the desired value and the formation of the membrane can be facilitated.

The thickness of the flat structure according to step C) is preferably between 10 and 4000 μm, preferably between 15 and 3500 μm, in particular between 20 and 3000 μm, particularly preferably between 30 and 1500 μm and, very particularly preferably between 50 and 1200 μm.

The treatment of the membrane in step D) is carried out in particular at temperatures in the range from 0 ° C. and 150 ° C., preferably at temperatures between 10 ° C. and 120 ° C., in particular between room temperature (20 ° C.) and 90 ° C. Hydrolysis liquid, which comprises water and at least one oxygen acid of phosphorus and / or sulfur. The treatment is preferably carried out under normal pressure, but can also be carried out under the action of pressure.

The hydrolysis liquid can be a solution, wherein the liquid can also contain suspended and / or dispersed constituents. The viscosity of the hydrolysis liquid can be in a wide range, and solvents can be added or the temperature increased to adjust the viscosity. The dynamic viscosity is preferably in the range from 0.1 to 10,000 mPa * s, in particular 0.2 to 2000 mPa * s, these values being able to be measured, for example, in accordance with DIN 53015.

The treatment according to step D) can be carried out using any known method. For example, the membrane obtained in step C) can be immersed in a liquid bath. Furthermore, the hydrolysis liquid can be sprayed onto the membrane. Furthermore, the hydrolysis liquid can be poured over the membrane. The latter methods have the advantage that the concentration of acid in the hydrolysis liquid remains constant during the hydrolysis. However, the first method is often less expensive to implement.

The oxygen acids of phosphorus and / or sulfur include in particular phosphinic acid, phosphonic acid, phosphoric acid, hypodiphosphonic acid, hypodiphosphoric acid, oligophosphoric acids, sulfurous acid, disulfurous acid and / or sulfuric acid. These acids can be used individually or as a mixture.

Furthermore, the oxygen acids of phosphorus and / or sulfur include radically polymerizable monomers which comprise phosphonic acid and / or sulfonic acid groups

Monomers comprising phosphonic acid groups are known in the art. These are compounds which have at least one carbon-carbon double bond and at least one phosphonic acid group. The two carbon atoms which form the carbon-carbon double bond preferably have at least two, preferably 3, bonds to groups which lead to a slight steric hindrance of the double bond. These groups include hydrogen atoms and halogen atoms, especially fluorine atoms. In the context of the present invention, the polymer comprising phosphonic acid groups results from the polymerization product which is obtained by polymerizing the monomer comprising phosphonic acid groups alone or with further monomers and / or crosslinking agents.

The monomer comprising phosphonic acid groups can comprise one, two, three or more carbon-carbon double bonds. Furthermore, the monomer comprising phosphonic acid groups may contain one, two, three or more phosphonic acid groups. In general, the monomer comprising phosphonic acid groups contains 2 to 20, preferably 2 to 10, carbon atoms.

The monomer comprising phosphonic acid groups is preferably a compound of the formula

^ - R— (PO ₃ Z ₂ ) _X

wherein

R represents a bond, a divalent C1-C15 alkylene group, divalent C1-C15 alkyleneoxy group, for example ethyleneoxy group or divalent C5-C20 aryl or heteroaryl group, the above radicals in turn being halogen, -OH, COOZ, -CN, NZ ₂ can be substituted,

Z independently of one another hydrogen, C1-C15-alkyl group, C1-C15-

Alkoxy group, ethyleneoxy group or C5-C20-aryl or heteroaryl group, it being possible for the above radicals in turn to be substituted with halogen, -OH, -CN, and x is an integer 1, 2, 3, 4, 5, 6, 7, 8 , 9 or 10 y is an integer 1, 2, 3, 4, 5, 6, 7, 8, 9 or 10 and / or the formula

_x (Z ₂ O ₃ P) - R- -R-_ _(P o ₃ Z ₂ ) _x where

Z independently of one another hydrogen, C1-C15-alkyl group, C1-C15-

Alkoxy group, ethyleneoxy group or C5-C20-aryl or heteroaryl group, it being possible for the above radicals in turn to be substituted with halogen, -OH, -CN, and x is an integer 1, 2, 3, 4, 5, 6, 7, 8 , 9 or 10 means and / or the formula

R- (P0 ₃ Z ₂ ) _x

= <

A wherein

A represents a group of the formulas COOR ² , CN, CONR ² ₂ , OR ² and / or R ² , wherein R ^{2 is} hydrogen, a C1-C15-alkyl group, C1-C15-alkoxy group, ethyleneoxy group or C5-C20-aryl or heteroaryl group, the above radicals in turn being substituted by halogen, -OH, COOZ, -CN, NZ ₂ R denotes a bond, a divalent C1-C15-alkylene group, divalent C1-C15-alkyleneoxy group, for example ethyleneoxy group or divalent C5-C20-aryl or heteroaryl group ^" , the above radicals in turn having halogen, -OH, COOZ, -CN, NZ ₂ can be substituted, Z independently of one another hydrogen, C1-C15-alkyl group, C1-C15-

Alkoxy group, ethyleneoxy group or C5-C20-aryl or heteroaryl group, it being possible for the above radicals in turn to be substituted with halogen, -OH, -CN, and x is an integer 1, 2, 3, 4, 5, 6, 7, 8 , 9 or 10 means. ^''

The preferred monomers comprising phosphonic acid groups include alkenes which have phosphonic acid groups, such as ethenephosphonic acid, propenephosphonic acid, butenephosphonic acid; Acrylic acid and / or methacrylic acid compounds which have phosphonic acid groups, such as 2-phosphonomethyl-acrylic acid, 2-phosphonomethyl-methacrylic acid, 2-phosphonomethyl-acrylic acid amide and 2-phosphonomethyl-methacrylic acid amide.

Commercial vinylphosphonic acid (ethenephosphonic acid), as is available, for example, from Aldrich or Clariant GmbH, is particularly preferably used. A preferred vinylphosphonic acid has a purity of more than 70%, in particular 90% and particularly preferably more than 97% purity.

The monomers comprising phosphonic acid groups can also be used in the form of derivatives which can subsequently be converted into the acid, the conversion to the acid also being able to take place in the polymerized state. These derivatives include in particular the salts, the esters, the amides and the halides of the monomers comprising phosphonic acid groups.

The monomers comprising phosphonic acid groups can also be introduced onto and into the membrane after the hydrolysis. This can be done by means of measures known per se (for example spraying, dipping, etc.) which are known from the prior art. According to a particular aspect of the present invention, the ratio of the weight of the sum of phosphoric acid, polyphosphoric acid and the hydrolysis products of polyphosphoric acid to the weight of the radically polymerizable monomers, for example the monomers comprising phosphonic acid groups, is preferably greater than or equal to 1: 2, in particular greater than or equal to 1: 1. and particularly preferably greater than or equal to 2: 1.

The ratio of the weight of the sum of phosphoric acid, polyphosphoric acid and the hydrolysis products of polyphosphoric acid to the weight of the radically polymerizable monomers is preferably in the range from 1000: 1 to 3: 1, in particular 100: 1 to 5: 1 and particularly preferably 50: 1 to 10 :1.

This ratio can easily be determined by conventional methods, in which the phosphoric acid, polyphosphoric acid and their hydrolysis products can be washed out of the membrane in many cases. The weight of the polyphosphoric acid and its hydrolysis products can be related to the phosphoric acid after complete hydrolysis. This generally also applies to the radically polymerizable monomers.

Monomers comprising sulfonic acid groups are known in the art. These are connections that _. have at least one carbon-carbon double bond and at least one sulfonic acid group. The two carbon atoms which form the carbon-carbon double bond preferably have at least two, preferably 3, bonds to groups which have little inhibition _. the double bond. These groups include hydrogen atoms and halogen atoms, especially fluorine atoms. In the context of the present invention, the polymer comprising sulfonic acid groups results from the polymerization product which is obtained by polymerization of the monomer comprising sulfonic acid groups alone or with further monomers and / or crosslinking agents.

The monomer comprising sulfonic acid groups can comprise one, two, three or more carbon-carbon double bonds. Furthermore, the monomer comprising sulfonic acid groups may contain one, two, three or more sulfonic acid groups.

In general, the monomer comprising sulfonic acid groups contains 2 to 20, preferably 2 to 10, carbon atoms. The monomer comprising sulfonic acid groups is preferably a compound of the formula

wherein

Z independently of one another hydrogen, C1-C15-alkyl group, C1-C15-

Alkoxy group, ethyleneoxy group or C5-C20-aryl or heteroaryl group, it being possible for the above radicals in turn to be substituted with halogen, -OH, -CN, and x is an integer 1, 2, 3, 4, 5, 6, 7, 8 , 9 or 10 y means an integer 1, 2, 3, 4, 5, 6, 7, 8, 9 or 10

and / or the formula

wherein

Z independently of one another hydrogen, C1-C15-alkyl group, C1-C15-

Alkoxy group, ethyleneoxy group or C5-C20-aryl or heteroaryl group, it being possible for the above radicals in turn to be substituted with halogen, -OH, -CN, and x is an integer 1, 2, 3, 4, 5, 6, 7, 8 , 9 or 10 means

and / or the formula

R- (S0 ₃ Z) _x

A wherein

A represents a group of the formulas COOR ² , CN, CONR ² ₂ , OR ² and / or R ² , wherein R ^{2 is} hydrogen, a C1-C15-alkyl group, C1-C15-alkoxy group, ethyleneoxy group or C5-C20-aryl or heteroaryl group means the above radicals in turn can be substituted with halogen, -OH, COOZ, -CN, NZ ₂

Z independently of one another hydrogen, C1-C15-alkyl group, C1-C15-

Alkoxy group, ethyleneoxy group or C5-C20-aryl or heteroaryl group, it being possible for the above radicals in turn to be substituted with halogen, -OH, -CN, and x is an integer 1, 2, 3, 4, 5, 6, 7, 8 , 9 or 10 means.

The preferred monomers comprising sulfonic acid groups include alkenes which have sulfonic acid groups, such as ethene sulfonic acid, propene sulfonic acid, butene sulfonic acid; Acrylic acid and / or methacrylic acid compounds that have sulfonic acid groups, such as 2-sulfonomethyl-acrylic acid, 2-sulfonomethyl-methacrylic acid, 2-sulfonomethyl-acrylic acid amide and 2-sulfonomethyl-methacrylic acid amide.

Commercial vinyl sulfonic acid (ethene sulfonic acid), as is available, for example, from Aldrich or Clariant GmbH, is particularly preferably used. A preferred vinyl sulfonic acid has a purity of more than 70%, in particular 90% and particularly preferably more than 97% purity.

The monomers comprising sulfonic acid groups can also be used in the form of derivatives which can subsequently be converted into the acid, the conversion to the acid also being able to take place in the polymerized state. These derivatives include in particular the salts, the esters, the amides and the halides of the monomers comprising sulfonic acid groups.

The monomers comprising sulfonic acid groups can also be introduced onto and into the membrane after the hydrolysis. This can be done by means of measures known per se (e.g. spraying, dipping, etc.) which are known from the prior art.

In a further embodiment of the invention, monomers capable of crosslinking can be used. These monomers can be added to the hydrolysis liquid. In addition, the monomers capable of crosslinking can also be applied to the membrane obtained after the hydrolysis. The monomers capable of crosslinking are, in particular, compounds which have at least 2 carbon-carbon double bonds. Dienes, trienes, tetraenes, dimethylacrylates, trimethylacrylates, tetramethylacrylates, diacrylates, triacrylates, tetraacrylates are preferred.

Dienes, trienes and tetraenes of the formula are particularly preferred

Dimethyl acrylates, trimethyl acrylates, tetramethyl acrylates of the formula

Diacrylates, triacrylates, tetraacrylates of the form!

wherein

R is a C1-C15-alkyl group, C5-C20-aryl or heteroaryl group, NR ^' , -SO ₂ ,

PR ^' , Si (R ^' ) ₂ means, where the above radicals can in turn be substituted, R 'independently of one another hydrogen, a C1-C15-alkyl group, C1-C15-

Alkoxy group, C5-C20 aryl or heteroaryl group and n is at least 2.

The substituents of the above radical R are preferably halogen, hydroxyl, carboxy, carboxyl, carboxyl esters, nitriles, amines, silyl, siloxane radicals.

Particularly preferred crosslinking agents are allyl methacrylate, ethylene glycol dimethacrylate, diethylene glycol dimethacrylate, triethylene glycol dimethacrylate, tetra- and polyethylene glycol dimethacrylate, 1,3-butanediol dimethacrylate, glycerol dimethacrylate, diurethane dimethacrylate, trimethylpropane trimethacrylate, for example Ebacryl, N ', N-methylenebisacrylamide, carbinol, butadiene, isoprene, chloroprene, divinylbenzene and / or bisphenol-A-dimethylacrylate. These compounds are commercially available, for example, from Sartomer Company Exton, Pennsylvania under the designations CN-120, CN104 and CN-980.

The use of crosslinking agents is optional, these compounds usually being in the range between 0.05 to 30% by weight, preferably 0.1 to 20% by weight, particularly preferably 1 and 10% by weight, based on the weight of the Membrane, can be used.

The crosslinking monomers can be introduced onto and into the membrane after the hydrolysis. This can be done by means of measures known per se (e.g. spraying, dipping, etc.) which are known from the prior art.

According to a particular aspect of the present invention, the monomers comprising phosphonic acid and / or sulfonic acid groups or the crosslinking monomers can be polymerized, the polymerization preferably taking place by free radicals. The radical formation can take place thermally, photochemically, chemically and / or electrochemically.

For example, a starter solution which contains at least one substance capable of forming radicals can be added to the hydrolysis liquid. Furthermore, a starter solution can be applied to the membrane after the hydrolysis. This can be done by means of measures known per se (e.g. spraying, dipping, etc.) which are known from the prior art.

Suitable radical formers include azo compounds, peroxy compounds, persulfate compounds or azoamidines. Non-limiting examples are dibenzoyl peroxide, dicumyl peroxide, cumene hydroperoxide, diisopropyl, bis (4-t-butylcyclohexyl) peroxydicarbonate, Dikaliumpersulfat, ammonium peroxydisulfate, ^2,2'-azobis (2-methylpropionitri!) (AIBN), 2,2'-azobis- ( isobutyric acid amidine) hydrochloride, benzpinacol, dibenzyl derivatives, methyl ethylene ketone peroxide, 1, 1-azobiscyclohexane carbonitrile, methyl ethyl ketone peroxide, acetylacetone peroxide, dilauryiperoxide, didecanoyl peroxide, tert.-butylper-2-ethylhexanoate, ketone peroxide, methyl peroxidyloxybenzyl peroxybenzyl peroxybenzyl peroxybenzoyl peroxide, methyl peroxidyloxybenzone 2,5-bis (2-ethylhexanoyl-peroxy) -2,5-dimethylhexane, tert-butylperoxy-2-ethylhexanoate, tert-butylperoxy-3,5,5-trimethylhexanoate, tert-butylperoxyisobutyrate, tert-butylperoxyacetate, dicumyl peroxide, 1,1-bis (tert-butylperoxy) cyclohexane, 1,1-bis (tert-butylperoxy) 3,3,5-trimethylcyclohexane, cumyl hydroperoxide, tert-butyl hydroperoxide, bis (4-tert-butylcyclohexyl) peroxydicarbonate, as well as the radical formers available from DuPont under the name ®Vazo, for example ®Vazo V50 and © Vazo WS.

In addition, radical formers can also be used which form free radicals when irradiated. The preferred compounds include, among others, α-diethoxyacetophenone (DEAP, Upjon Corp), n-butylbenzoin ether (®Trigonal-14, AKZO) and 2,2-dimethoxy-2-phenylacetophenone (®lgacure 651) and 1-benzoylcyclohexanol (® Igacure 184), bis (2,4,6-trimethylbenzoyl) phenylphosphine oxide (®lrgacure 819) and 1- [4- (2-hydroxyethoxy) phenyl] -2-hydroxy-2-phenylpropan-1-one (®lrgacure 2959 ), each from Ciba Geigy Corp. are commercially available.

Usually between 0.0001 and 5% by weight, in particular 0.01 to 3% by weight (based on the weight of the free-radically polymerizable monomers; monomers comprising phosphonic acid and / or sulfonic acid groups or the crosslinking monomers) are added to free-radical formers , The amount of radical generator can be varied depending on the desired degree of polymerization.

The polymerization can also be carried out by exposure to IR or NIR (IR = InfraRot, ie light with a wavelength of more than 700 nm; NIR = Near IR, ie light with a wavelength in the range from approx. 700 to 2000 nm or an energy in the range of approx. 0.6 to 1.75 eV).

The polymerization can also be carried out by exposure to UV light with a wavelength of less than 400 nm. This polymerization method is known per se and is described, for example, in Hans Joerg Elias, Macromolecular Chemistry, δ.auflage, Volume 1, p.492-511; D.R. Arnold, N.C. Baird, J.R. Bolton, J.C. D. Brand, P.W. M Jacobs, P.de Mayo, W.R. Ware, Photochemistry-An Introduction, Academic Press, New York and M.K. Mishra, Radical Photopolymerization of Vinyl Monomers, J. Macromol. Sci.-Revs. Macromol. Chem. Phys. C22 (1982-1983) 409.

The polymerization can also be achieved by the action of β, γ and / or electron beams. According to a particular embodiment of the present invention, a membrane with a radiation dose in the range of Irradiated from 1 to 300 kGy, preferably from 3 to 200 kGy and very particularly preferably from 20 to 100 kGy.

The polymerization of the monomers comprising phosphonic acid and / or sulfonic acid groups or of the crosslinking monomers is preferably carried out at temperatures above room temperature (20 ° C.) and below 200 ° C., in particular at temperatures between 40 ° C. and 150 ° C., particularly preferably between 50 ° C and 120 ° C. The polymerization is preferably carried out under normal pressure, but can also be carried out under the action of pressure. The polymerization leads to a solidification of the flat structure, this solidification being able to be followed by microhardness measurement. The increase in hardness due to the polymerization is preferably at least 20%, based on the hardness of the sheet-like structure obtained in step B).

According to a particular aspect of the present invention, the molar ratio of the molar sum of phosphoric acid, polyphosphoric acid and the hydrolysis products of polyphosphoric acid to the number of moles of the phosphonic acid groups and / or sulfonic acid groups in the polymers obtainable by polymerizing phosphonic acid groups and / or monomers comprising sulfonic acid groups, preferably greater than or equal to 1: 2, in particular greater than or equal to 1: 1. and particularly preferably greater than or equal to 2: 1.

The molar ratio of the molar sum of phosphoric acid, polyphosphoric acid and the hydrolysis products of polyphosphoric acid to the number of moles of the phosphonic acid groups and / or sulfonic acid groups in the monomers comprising monomers comprising phosphonic acid groups and / or monomers comprising sulfonic acid groups is preferably in the range from 1000: 1 to 3: 1, in particular 100: 1 to 5: 1 and particularly preferably 50: 1 to 10: 1.

The molar ratio can be determined using conventional methods. Spectroscopic methods, for example NMR spectroscopy, can be used for this purpose. It should be borne in mind here that the phosphonic acid groups are in the formal oxidation state 3 and the phosphorus in phosphoric acid, polyphosphoric acid or hydrolysis products thereof in the oxidation state 5.

Depending on the desired degree of polymerization, the flat structure which is obtained after the polymerization is a self-supporting membrane. The degree of polymerization is preferably at least 2, in particular at least 5, particularly preferably at least 30 repetition units, in particular at least 50 repetition units, very particularly preferably at least 100 repetition units. This degree of polymerization is determined by the number average molecular weight M _n , which can be determined by GPC methods. Because of the problems of isolating the polymers comprising phosphonic acid groups contained in the membrane without degradation, this value is determined on the basis of a sample which is carried out by polymerizing monomers comprising phosphonic acid groups without addition of polymer. The proportion by weight of monomers comprising phosphonic acid groups and of radical initiators is kept constant in comparison with the ratios of the manufacture of the membrane. The conversion achieved in a comparative polymerization is preferably greater than or equal to 20%, in particular greater than or equal to 40% and particularly preferably greater than or equal to 75%, based on the monomers comprising phosphonic acid groups used.

The hydrolysis liquid comprises water, and the concentration of the water is generally not particularly critical. According to a particular aspect of the present invention, the hydrolysis liquid comprises 5 to 80% by weight, preferably 8 to 70% by weight and particularly preferably 10 to 50% by weight of water. The amount of water that is formally contained in the oxygen acids is not taken into account in the water content of the hydrolysis liquid.

Of the aforementioned acids, phosphoric acid and / or sulfuric acid are particularly preferred, these acids comprising in particular 5 to 70% by weight, preferably 10 to 60% by weight and particularly preferably 15 to 50% by weight of water.

The partial hydrolysis of the polyphosphoric acid in step D) leads to a solidification of the membrane and to a decrease in the layer thickness and formation of a membrane. The solidified membrane generally has a thickness of between 15 and 3000 μm, preferably 20 and 2000 μm, in particular between 20 and 1000 μm, the membrane being self-supporting.

The upper temperature limit of the treatment in step D) is generally 150 ° C. With an extremely short exposure, the hydrolysis liquid can also be hotter than 150 ° C. The duration of the treatment is essential for the upper temperature limit. According to a special aspect of the present invention, the membrane is cooled to room temperature in the hydrolysis liquid. The duration of treatment can be in a wide range, the duration depending in particular on the water concentration of the hydrolysis liquid. Furthermore, the treatment time depends on the thickness of the membrane.

As a rule, the duration of treatment is between 10 seconds and 20 hours, in particular 1 minute to 10 hours.

The membrane obtained in step D) can be self-supporting, i.e. it can be detached from the carrier without damage and then, if necessary, processed or stored directly.

About the degree of hydrolysis, i.e. the duration, temperature and hydrolysis liquid, the concentration of phosphoric acid and thus the conductivity of the polymer membrane according to the invention can be adjusted. According to the invention, the concentration of phosphoric acid is given as mole of acid per mole of repeating unit of the polymer. In the context of the present invention, a concentration (mol of phosphoric acid based on a repeating unit of the formula (III), i.e. polybenzimidazo!) Between 10 and 100, in particular between 12 and 95, is preferred. Such high degrees of doping (concentrations) are very difficult or even impossible to obtain by doping polyazoles with commercially available orthophosphoric acid.

Following the treatment in step D), the membrane can still be crosslinked by exposure to heat in the presence of oxygen. This hardening of the membrane additionally improves the properties of the membrane. For this purpose, the membrane can be heated to a temperature of at least 150 ° C., preferably at least 200 ° C. and particularly preferably at least 250 ° C. The oxygen concentration in this process step is usually in the range from 5 to 50% by volume, preferably 10 to 40% by volume, without any intention that this should impose a restriction.

The crosslinking can also be effected by the action of IR or NIR (IR = InfraRot, ie light with a wavelength of more than 700 nm; NIR = Near IR, ie light with a wavelength in the range from approx. 700 to 2000 nm or an energy in the range of approx. 0.6 to 1.75 eV). Another method is radiation with β-rays. The radiation dose is between 5 and 200 kGy.

Depending on the desired degree of crosslinking, the duration of the crosslinking reaction can be in a wide range. In general, this response time is in the range from 1 second to 10 hours, preferably 1 minute to 1 hour, without this being intended to impose any restriction.

The polymer membrane according to the invention has improved material properties compared to the previously known doped polymer membranes. In particular, they perform better than known doped polymer membranes. This is due in particular to an improved proton conductivity. At temperatures of 120 ° C., this is at least 0.1 S / cm, preferably at least 0.11 S / cm, in particular at least 0.12 S / cm.

The. specific conductivity is measured by means of impedance spectroscopy in a 4-pole arrangement in potentiostatic mode and using platinum electrodes (wire, 0.25 mm diameter). The distance between the current-consuming electrodes is 2 cm. The spectrum obtained is evaluated using a simple model consisting of a parallel arrangement of an ^ohmic resistance and a capacitor. The sample cross-section of the phosphoric acid-doped membrane is measured immediately before the sample assembly. To measure the temperature dependency, the measuring cell is brought to the desired temperature in an oven and controlled via a Pt-100 thermocouple positioned in the immediate vicinity of the sample. After reaching the temperature, the sample is kept at this temperature for 10 minutes before starting the measurement.

According to a special embodiment of the present invention, the membranes have high mechanical stability. This size results from the hardness of the membrane, which is determined by means of microhardness measurement in accordance with DIN 50539. For this purpose, the membrane is successively loaded with a Vickers diamond within 20 s up to a force of 3 mN and the depth of penetration is determined. Accordingly, the hardness at room temperature is at least 5 mN / mm ² , preferably at least 50 mN / mm ² and very particularly preferably at least 200 mN / mm ² , without any intention that this should impose a restriction. The force is then kept constant at 3 mN for 5 s and the creep is calculated from the penetration depth. In preferred membranes, the creep CHU 0.003 / 20/5 under these conditions is less than 30%, preferably less than 15% and very particularly preferably less than 5%. The module determined by means of microhardness measurement is YHU at least 0.1 MPa, in particular at least 2 MPa and very particularly preferably at least 5 MPa, without this being intended to impose a restriction. In comparison to known polyazole membranes, which are obtained according to the applications DE No. 10117686.4 and DE No. 10117687.2, the membranes obtained by the process according to the invention have particularly good mechanical properties. The fracture toughness is surprisingly high with a high phosphoric acid content.

Thus, new polymer electrolyte membranes are made available which have a phosphoric acid concentration of at least 85% by weight with a fracture toughness of at least 30 kJ / m ² , in particular 50 kJ / m ² and particularly preferably 100 kJ / m ² .

Furthermore, preferred polymer electrolyte membranes have a high elongation at break of at least 60%, in particular at least 80% and particularly preferably at least 100% at a phosphoric acid concentration of at least 85% by weight.

Particularly powerful new polymer electrolyte membranes are obtained according to the invention which, at a phosphoric acid concentration of at least 95% by weight, have a fracture toughness of at least 10 kJ / m ² , in particular 20 kJ / m ² and particularly preferably 30 kJ / m ² .

The elongation at break / stress (fracture toughness) can be measured on strip-shaped samples with a width of 15 mm and a length of 120 mm on the Zwick Z010. The tensile test can be carried out at a temperature of 25 ° C with an expansion rate of 50 mm / min.

Possible areas of application of the polymer membranes according to the invention include use in fuel cells, in electrolysis, in capacitors and in battery systems.

The present invention also relates to a membrane electrode unit which has at least one polymer membrane according to the invention. The membrane electrode unit has a high performance even with a low content of catalytically active substances, such as platinum, ruthenium or palladium. For this purpose, gas diffusion layers provided with a catalytically active layer can be used.

Gas diffusion diffusion generally shows electron conductivity. Flat, electrically conductive and acid-resistant structures are usually used for this. These include, for example, carbon fiber papers, graphitized carbon fiber papers, carbon fiber fabrics, graphitized carbon fiber fabrics and / or flat structures which have been made conductive by adding carbon black.

The catalytically active layer contains a catalytically active substance. These include noble metals, in particular platinum, palladium, rhodium, iridium and / or ruthenium. These substances can also be used with one another in the form of alloys. Furthermore, these substances can also be used in alloys with base metals, such as Cr, Zr, Ni, Co and / or Ti. In addition, the oxides of the aforementioned noble metals and / or base metals can also be used. According to a particular aspect of the present invention, the catalytically active compounds are used in the form of particles which preferably have a size in the range from 1 to 1000 nm, in particular 10 to 200 nm and preferably 20 to 100 nm.

Furthermore, the catalytically active layer can contain conventional additives. These include fluoropolymers such as Polytetrafluoroethylene (PTFE) and surface-active substances.

According to a particular embodiment of the present invention, the weight ratio of fluoropolymer to catalyst material, comprising at least one noble metal and optionally one or more support materials, is greater than 0.1, this ratio preferably being in the range from 0.2 to 0.6.

According to a particular embodiment of the present invention, the catalyst layer has a thickness in the range from 1 to 1000 μm, in particular from 5 to 500, preferably from 10 to 300 μm. This value represents an average value that can be determined by measuring the layer thickness in the cross section of images that can be obtained with a scanning electron microscope (SEM).

According to a particular embodiment of the present invention, the noble metal content of the catalyst layer is 0.1 to 10.0 mg / cm ² , preferably 0.3 to 6.0 mg / cm ² and particularly preferably 0.3 to 3.0 mg / cm ² , These values can be determined by elemental analysis of a flat sample.

For more information on membrane electrode assemblies, see the

Technical literature, in particular on patent applications WO 01/18894 A2,

DE 195 09 748, DE 195 09 749, WO 00/26982, WO 92/15121 and DE 197 57492 directed. The disclosure contained in the above-mentioned references with regard to the construction and manufacture of membrane electrode assemblies, as well as the electrodes, gas diffusion layers and catalysts to be selected, is also part of the description.

In a further variant, a catalytically active layer can be applied to the membrane according to the invention and this can be connected to a gas diffusion layer.

The present invention also relates to a membrane electrode unit which contains at least one polymer membrane according to the invention, optionally in combination with a further polymer membrane based on polyazoles or a polymer blend membrane.

In a further variant, a catalytically active layer can be applied to the membrane according to the invention and this can be connected to a gas diffusion layer. For this purpose, a membrane is formed in accordance with steps A) to D) and the catalyst is applied. These structures are also the subject of the present invention.

In addition, the membrane according to steps A) to D) can also be formed on a support or a support film which already has the catalyst. After removing the carrier or the carrier film, the catalyst is on the membrane according to the invention. These structures are also the subject of the present invention.

The present invention likewise relates to a membrane-electrode unit which has at least one coated electrode and / or at least one polymer membrane according to the invention in combination with a further polymer membrane based on polyazoles or a polymer blend membrane containing at least one polymer based on polyazoles.

Examples 1-5

A poly (2,2 '- (p-phenylene) -5,5'-bibenzimidazole-co-poly ((6-6'-bibenzimidazole-2,2'-dyl) -2,5- pyridine) solution in PPA prepared as follows.

5.283 g of 2,5-pyridinedicarboxylic acid (125 mmol), 15.575 g of terephthalic acid (375 mmol), 26.785 g of TAB (0.5 mol) and 468 g of PPA were placed in a 500 ml three-necked flask submitted. The reaction suspension was heated to 120 ° C for 2 h then to 150 ° C for 4 h, then to 190 ° C for 6 h then to 220 ° C for 20 ° C. The reaction solution was then diluted at 220 ° C. with 600 g of 85% H ₃ PO, and then stirred at 240 ° C. for 6 hours.

A small part of the solution was precipitated with water. The precipitated resin was filtered, washed three times with H ₂ O, neutralized with ammonium hydroxide, then washed with H ₂ O and dried at 100 ° C. for 24 hours at 0.001 bar. The inherent viscosity ηj _{no was} measured from a 0.2 g / dL polymer solution in 100 ml of 96% H ₂ SO ₄ . ηj _no = 3.2 dL / g at 30 ° C

The highly viscous solution was knife-coated at 200 ° C. with a preheated doctor blade on a polyethylene terephthalate film (PET film) with a 500 μm thick membrane. In each case one piece of membrane with the size 20x30 cm was placed in 11 H ₃ PO ₄ with the following concentration.

Example 1: 40% H ₃ PO ₄ Example 2: 50% H ₃ PO ₄ Example 3: 60% H ₃ PO ₄ Example 4: 70% H ₃ PO ₄ Example 5: 80% H ₃ PO ₄

Then the membranes were hydrolyzed for 15 minutes, 30 minutes, 1 hour, 2 hours, 4 hours, 6 hours, and 20 hours at RT in these hydrolysis baths. The membranes were then titrated with 0.1 N NaOH to determine the acid number per repeat unit. Results of the hydrolysis are shown in Table 1 below.

Examples 6-8

The highly viscous solution was knife-coated at 160 ° C. using a preheated doctor blade on a PET film with a thickness of 500 μm. One piece of membrane with the size 20x30 cm was hydrolyzed in 11 H ₃ P0 with the following concentration and time.

Comparison 1: hydrolyzed with air humidity, 24 hours at room temperature

Example 6 in 50% H ₃ PO ₄ 20 min. Example 7 in 60% H ₃ PO ₄ 1 h. Example 8 in 70% H ₃ PO ₄ 2 h

The membranes were titrated with 0.1 N NaOH to determine the acid number per repeat unit. The titration results are summarized in Table 2 below.

Table 2

The material properties were determined with tensile strain measurement and compared with Comparative Example 1 (Table 3). The elongation at break / stress (fracture toughness) is measured on strip-shaped samples with a width of 15 mm and a length of 120 mm on the Zwick Z010. The tensile test is carried out at a temperature of 25 ° C with an expansion rate of 50 mm / min.

Table 3:

50 cm ² MEAs (membrane electrode assembly) were then produced from these membranes and measured with H ₂ / air. The values (resting potential (OCV); mV at 0.2 A / cm ² ; mV at 0.6 A / cm ² at 160 ° and 0 bar) are compared with sample 0 below in Table 4. Table 4:

The resting potential is directly linked to the permeability of the membrane to the fuel. The higher this permeability, the lower the resting potential. A high resting potential therefore means a low hydrogen permeability (see Handbook of Fuel Cells Fundamentals, Technology and Application, Editors: W. Vielstich; A. Lamm, H.A. Gasteiger).

Claims

claims

1. A method for producing proton-conducting polymer membranes comprising the steps

B) heating the mixture obtainable according to step A) under inert gas to temperatures of up to 400 ° C.,

D) Treatment of the membrane formed in step C), characterized in that the treatment of the membrane is carried out with a hydrolysis liquid which comprises oxygen acids of phosphorus and / or oxygen acids of sulfur.

2. The method according to claim 1, characterized in that the mixture prepared in step A) comprises compounds which, under the action of heat according to step B), are suitable for the formation of polyazoles, these compounds comprising one or more aromatic and / or heteroaromatic tetrahedra. Amino compounds and one or more aromatic and / or heteroaromatic carboxylic acids or their derivatives, which comprise at least two acid groups per carboxylic acid monomer, and / or one or more aromatic and / or heteroaromatic diaminocarboxylic acids.

3. The method according to claim 1, characterized in that the mixture prepared in step A) comprises compounds which are suitable under the action of heat according to step B) for the formation of polyazoles, these compounds by reaction of one or more aromatic and / or heteroaromatic tetra-amino compounds with one or more aromatic and / or heteroaromatic carboxylic acids or their derivatives, which contain at least two acid groups per carboxylic acid monomer, or one or more aromatic and / or heteroaromatic diaminocarboxylic acids in the melt at temperatures of up to 400 ° C are available.

4. The method according to claim 2 or 3, characterized in that the compounds suitable for the formation of polyazoles as aromatic and / or heteroaromatic tetra-amino compound comprise compounds which are selected from the group consisting of 3,3 ', 4,4'- tetraaminobiphenyl,

^• 2,3,5,6-tetraaminopyridine and / or 1, 2,4,5-tetraaminobenzene.

5. The method according to claim 2, 3 or 4, characterized in that the compounds suitable for the formation of polyazoles as aromatic and / or heteroaromatic carboxylic acids or their derivatives, which contain at least two acid groups per carboxylic acid monomer, comprise compounds which are selected from the Group consisting of isophthalic acid, terephthalic acid, phthalic acid, 5-hydroxyisophthalic acid, 4-hydroxyisophthalic acid, 2-hydroxyterephthalic acid, 5-aminoisophthalic acid, 5N, N-dimethylaminoisophthalic acid, 5-N, N-diethylaminoisophthalic acid, 2,5-dihydroxy-2,5-dihydroxyter -Dihydroxyisophthalic acid, 2,3-dihydroxyisophthalic acid, 2,3-dihydroxyphthalic acid, 2,4-dihydroxyphthalic acid. 3,4-dihydroxyphthalic acid, 3-fluorophthalic acid, 5-fluoroisophthalic acid, 2-fluoroterphthalic acid, tetrafluorophthalic acid, tetrafluoroisophthalic acid, tetrafiuoroterephthalic acid, 1, 4-naphthalenedicarboxylic acid, 1, 5-naphthalenedicarboxylic acid, 2,6-naphthalenedioic acid, diphthalic acid, 2,6-naphthalenedioic acid, 1,8-dihydroxynaphthalene-3,6-dicarboxylic acid, diphenyl ether-4,4'-dicarboxylic acid, benzophenone-4,4'-dicarboxylic acid, diphenyl sulfone-4,4'-dicarboxylic acid, biphenyl-4,4'-dicarboxylic acid, 4- Trifluoromethylphthalic acid, 2,2-bis (4-carboxyphenyl) hexafluoropropane, 4,4'-stilbenedicarboxylic acid, 4-carboxycinnamic acid, or their C1-C20-alkyl esters or C5-C12-aryl esters, or their acid anhydrides or their acid chlorides ,

6. The method according to claim 2, 3, 4 or 5, characterized in that the compounds suitable for the formation of polyazoles aromatic tricarboxylic acids, their C1-C20 alkyl esters or C5-C12 aryl esters or their acid anhydrides or their acid halides or Tetracarboxylic acids, their C1-C20 alkyl esters or C5-C12 aryl esters, or their acid anhydrides or their acid halides.

7. The method according to claim 6, characterized in that the aromatic tricarboxylic acids comprise compounds selected from the group consisting of 1,3,5-benzenetricarboxylic acid (trimesic acid); 2,4,5-benzenetricarboxylic acid (trimellitic acid); (2-carboxyphenyl) iminodiacetic acid, 3,5,3'-biphenyltricarboxylic acid; 3,5,4'-biphenyltricarboxylic acid, 2,4,6-pyridine tricarboxylic acid, benzene-1, 2,4,5-tetracarboxylic acids; Naphthaiine-1, 4,5,8-tetracarboxylic acids, 3,5,3 ', 5'-biphenyl-tetracarboxylic acids, benzophenonetetracarboxylic acid, 3,3', 4,4'-biphenyltetracarboxylic acid, 2,2 ', 3,3'- Biphenyltetracarboxylic acid, 1, 2,5,6-naphthalenetetracarboxylic acid and / or 1, 4,5,8-naphthalenetetracarboxylic acid.

8. The method according to claim 6 or 7, characterized in that the content of tricarboxylic acid and / or tetracarboxylic acids between 0 and 30 mol%, preferably 0.1 and 20 mol%, in particular 0.5 and 10 mol%, based on dicarboxylic acid used.

9. The method according to one or more of claims 2 to 8, characterized in that the compounds suitable for the formation of polyazoles comprise heteroaromatic dicarboxylic acids, tricarboxylic acids and / or tetracarboxylic acids which contain at least one nitrogen, oxygen, sulfur or phosphorus atom in the aromatic system.

10. The method according to claim 9, characterized in that pyridine-2,5-dicarboxylic acid, pyridine-3,5-dicarboxylic acid, pyridine-2,6-dicarboxylic acid, pyridine-2,4-dicarboxylic acid, 4-phenyl-2,5 -pyridine dicarboxylic acid, 3,5-pyrazole dicarboxylic acid, 2,6-pyrimidine dicarboxylic acid, 2,5-pyrazine dicarboxylic acid, 2,4,6-pyridine dicarboxylic acid, benzimidazole-5,6-dicarboxylic acid, and their C1-C20-alkyl ester or C5-C12 Aryl esters, or their acid anhydrides or their acid chlorides are used.

11. The method according to claim 2 or 3, characterized in that the compounds suitable for the formation of polyazoles include diaminobenzoic acid and / or its mono- and dihydrochloride derivatives.

12. The method according to any one of the preceding claims, characterized

■ characterized in that the composition obtainable in step A) and / or step B) is added at least one further polymer (polymer B) which is not polyazole, the weight ratio of polyazole to polymer B being in the range from 0.1 to 50 lies.

13. The method according to any one of the preceding claims, characterized in that the heating according to step B) takes place after the formation of a flat structure according to step C)

14. The method according to any one of the preceding claims, characterized in that the treatment according to step D) takes place at temperatures in the range from 0 ° C and 150 ° C.

15. The method according to any one of the preceding claims, characterized in that the hydrolysis liquid comprises water in a concentration of 5 to 80 wt .-%.

16. The method according to any one of the preceding claims, characterized in that phosphoric acid is used as the hydrolysis liquid, which comprises 10 to 60 wt .-% water.

17. The method according to any one of the preceding claims, characterized in that the hydrolysis liquid comprises phosphinic acid, phosphonic acid, phosphoric acid, hypodiphosphonic acid, hypodiphosphoric acid, oligophosphoric acids, sulfurous acid, disulfurous acid and / or sulfuric acid.

18. The method according to any one of the preceding claims, characterized in that the hydrolysis liquid comprises radically polymerizable monomers with phosphonic acid and / or sulfonic acid groups.

19. The method according to any one of the preceding claims, characterized in that the hydrolysis liquid comprises radically polymerizable crosslinking monomers.

20. The method according to any one of the preceding claims, characterized in that after the hydrolysis, radically polymerizable, crosslinking monomers are applied to the membrane.

21. The method according to any one of claims 18 to 20, characterized in that the free-radically polymerizable monomers are polymerized after the hydrolysis.

22. Proton-conducting polymer membrane obtainable by a process of claims 1 to 21, characterized in that the membrane has a phosphoric acid concentration of at least 85% by weight with a breaking stress of at least 30 kJ / m ² .

23. Proton-conducting polymer membrane obtainable by a process of claims 1 to 21, characterized in that the membrane has a phosphoric acid concentration of at least 95% by weight with a breaking stress of at least 10 kJ / m ² .

24. Proton-conducting polymer membrane comprising phosphoric acid, at least one polyazole and at least one free-radically polymerizable monomer, which comprises phosphonic acid and / or sulfonic acid groups, characterized in that the ratio of the weight of the sum of phosphoric acid, polyphosphoric acid and the hydrolysis products of polyphosphoric acid to the weight of the free-radically polymerizable Monomers is greater than or equal to 1: 2.

25. Proton-conducting polymer membrane according to claim 20, characterized in that the ratio of the weight of the sum of phosphoric acid, polyphosphoric acid and the hydrolysis products of polyphosphoric acid to the weight of the radically polymerizable monomers is from 100: 1 to 5: 1.

26. Proton-conducting polymer membrane according to claim 24 or 25, obtainable by polymerizing the radically polymerizable monomers.

27. Membrane-electrode unit containing at least one polymer membrane according to one of claims 24 to 26.

28. Fuel cell containing one or more membrane electrode assemblies according to claim 27.