EP1664166A2

EP1664166A2 - Proton-conducting polymer membrane coated with a catalyst layer, said polymer membrane comprising phosphonic acid polymers, membrane/electrode unit and the use thereof in fuel cells

Info

Publication number: EP1664166A2
Application number: EP04764850A
Authority: EP
Inventors: Jörg BELACK; Isabel Kundler; Thomas Schmidt; Oemer Uensal; Joachim Kiefer; Christoph Padberg; Mathias Weber
Original assignee: Pemeas GmbH
Current assignee: BASF Fuel Cell Research GmbH
Priority date: 2003-09-04
Filing date: 2004-09-04
Publication date: 2006-06-07
Also published as: WO2005023914A3; WO2005023914A2; DE10340928A1; JP2007504333A

Abstract

The invention relates to a polymer membrane that is coated with a catalyst layer, said polymer membrane comprising phosphonic acid polymers. Said polymers are obtainable by polymerization of phosphonic acid monomers. The invention is characterized in that the catalyst layer comprises phosphonic acid ionomers, said ionomers being obtainable by polymerization of phosphonic acid monomers.

Description

description

Proton-conducting polymer membrane coated with a catalyst layer and containing polymers comprising phosphonic acid groups, membrane electrode assembly and their use in fuel cells

The present invention relates to a proton-conducting polymer electrolyte membrane coated with a catalyst layer and containing phosphonic acid groups, comprising polymers, membrane electrode units and their use in fuel cells.

In today's polymer electrolyte (PE) fuel cells, mainly sulfonic acid-modified polymers are used (e.g. Nafion from DuPont). Due to the water content-dependent conductivity mechanism of these membranes, fuel cells equipped with them can only be operated at temperatures from 80 ° C to 100 ° C. This membrane dries out at higher temperatures, so that the resistance of the membrane increases sharply and the fuel cell can no longer supply electrical energy.

Furthermore, polymer electrolyte membranes with complexes, for example of basic polymers and strong acids, have been developed. For example, WO96 / 13872 and the corresponding US Pat. No. 5,525,436 describe a process for producing a proton-conducting polymer electrolyte membrane, in which a basic polymer, such as

Polybenzimidazole, is treated with a strong acid such as phosphoric acid, sulfuric acid, etc.

In J. Electrochem. SOG, volume 142, No. 7, 1995, p. L121-L123 the doping of a

Polybenzimidazole described in phosphoric acid.

In the basic polymer membranes known in the prior art, the mineral acid (usually concentrated phosphoric acid) used to achieve the required proton conductivity is usually added after the shaping of the polyazole film. The polymer serves as a carrier for the electrolyte consisting of the highly concentrated phosphoric acid. The polymer membrane fulfills further essential functions, in particular it must have high mechanical stability and serve as a separator for the two fuels mentioned at the beginning.

Significant advantages of such a membrane doped with phosphoric acid is the fact that a fuel cell in which such a polymer electrolyte membrane is used can be operated at temperatures above 100 ° C. without the fuels otherwise having to be moistened. This is due to the property of phosphoric acid

To be able to transport protons without additional water using the so-called Grotthus mechanism (K.-D. Kreuer, Chem. Mater. 1996, 8, 610-641). The possibility of operating at temperatures above 100 ° C results in further advantages for the fuel cell system. On the one hand, the sensitivity of the Pt catalyst to gas impurities, especially CO, is greatly reduced. CO arises as a by-product in the reforming of the hydrogen-rich gas from carbon-containing compounds, such as natural gas, methanol or gasoline, or as

Intermediate product in the direct oxidation of methanol. Typically, the CO content of the fuel must be less than 100 ppm at temperatures <100 ° C. At temperatures in the range of 150-200 °, however, 10,000 ppm CO or more can also be tolerated (N.J. Bjerrum et. Al. Journal of Applied Electrochemistry, 2001, 31, 773-779). This leads to significant simplifications of the upstream reforming process and thus to cost reductions for the entire fuel cell system.

The performance of a membrane electrode assembly produced with such membranes is described in WO 01/18894 A2. In a 5 cm ² cell at a gas flow of 160 ml / min and a pressure of 1 atm for pure hydrogen and at a gas flow of 200 ml / min and a pressure of 1 atm for pure oxygen. However, the use of pure oxygen, such a high overpressure and such high stochiometries is technically uninteresting. The performances with such phosphoric acid doped polyazole membranes

Uses of pure hydrogen and pure oxygen are also described in Electrochimica Acta, Volume 41, 1996, 193-197. With a platinum loading of 0.5 mg / cm ² at the anode and 2 mg / cm ² at the cathode, when using humidified fuel gases with pure hydrogen and pure oxygen and a pressure of 1 atm for each fuel gas, a current density of less than 0 , 2 A / cm ^{2 achieved} at a voltage of 0.6 V. If air is used instead of oxygen, this value drops to less than 0.1 A / cm ² .

A great advantage of fuel cells is the fact that in the electrochemical reaction the energy of the fuel is directly converted into electrical energy and heat

■ is converted. Water forms as a reaction product on the cathode. Heat is therefore a by-product of the electrochemical reaction. For applications in which only the electricity is used to drive electric motors, such as for automotive applications, or as a versatile replacement for battery systems, part of the heat generated during the reaction must be dissipated to prevent the system from overheating. Additional energy-consuming devices are then required for cooling, which further reduce the overall electrical efficiency of the fuel cell system. For stationary applications such as the central or decentralized generation of electricity and heat, the heat can be used efficiently using existing technologies such as heat exchangers. High temperatures are aimed at to increase efficiency. If the operating temperature is above 100 ° C and the temperature difference between the ambient temperature and the operating temperature is large, this becomes possible to cool the fuel cell system more efficiently or to use small cooling surfaces and to dispense with additional devices compared to fuel cells, which have to be operated at below 100 ° C due to the membrane humidification.

In addition to these advantages, such a fuel line system also has disadvantages.

The durability of membranes doped with phosphoric acid is relatively limited. Here, the service life is significantly reduced, in particular by operating the fuel cell below 100 ° C., for example at 80 ° C. In this context, however, it should be noted that when the fuel cell is started up and shut down, the cell must be operated at these temperatures.

Furthermore, the production of membranes doped with phosphoric acid is relatively expensive, since a polymer is usually first formed, which is then cast into a film using a solvent. After the film has dried, it is doped with an acid in a last step. So have the previously known

Polymer membranes have a high content of dimethylacetamide (DMAc), which cannot be completely removed using known drying methods.

In addition, the performance, for example the conductivity of known membranes, is still to be improved. ^'" -'

Furthermore, the durability of known high-temperature membranes with high conductivity is still to be improved.

In addition, a very large amount of catalytically active substances are used to arrive at a membrane electrode assembly.

The present invention is therefore based on the object of providing a novel polymer electrolyte membrane which achieves the objects set out above. In particular, a membrane according to the invention should be able to be produced inexpensively and simply.

Moreover, it was an object of the present invention ^'to provide Polymerelektroiytmembranen which show a high efficiency, in particular high conductivity over a wide temperature range. Here, the

Conductivity, especially at high temperatures, can be achieved without additional humidification. The membrane should be suitable for further processing into a membrane-electrode unit, which can deliver particularly high power densities. In addition, a membrane electrode unit obtainable via the membrane according to the invention should have a particularly high durability, in particular a long service life with high power densities. Furthermore, it was therefore an object of the present invention to provide a membrane which can be converted to a membrane electrode unit which has high performance even with a very low content of catalytically active substances, such as platinum, ruthenium or palladium having.

Another object of the invention was to provide a membrane which can be pressed to form a membrane-electrode unit and the fuel cell can be operated with low stoichiometries, with low gas flow and / or with low excess pressure and high power density.

Furthermore, it should be possible to extend the operating temperature from <80 ° C to 200 ° C without reducing the life of the fuel cell very much.

These objects are achieved by a proton-conducting polymer membrane comprising polyazoles coated with a catalyst layer and having all the features of claim 1.

The present invention relates to a proton-conducting polymer membrane coated with a catalyst layer, the polymer membrane containing polymers comprising phosphonic acid groups which can be obtained by polymerizing monomers comprising phosphonic acid groups, characterized in that the catalyst layer contains phosphonic acid groups comprising monomers which can be obtained by polymerizing phosphonic acid groups are.

A membrane according to the invention exhibits a high conductivity over a wide temperature range, which is also achieved without additional moistening. Furthermore, a membrane according to the invention can be produced simply and inexpensively. Large quantities of expensive solvents such as dimethylacetamide can thus be dispensed with.

Furthermore, these membranes have a surprisingly long service life. Furthermore, a fuel cell that is equipped with a membrane according to the invention can also be operated at low temperatures, for example at 80 ° C., without the service life of the fuel cell being greatly reduced thereby.

In addition, the membrane can be further processed into a membrane electrode unit, which can deliver particularly high currents. A membrane electrode unit obtained in this way has a particularly high durability, in particular a long service life at high currents. Furthermore, the membrane of the present invention can be transferred to a membrane electrode assembly which has high performance even with a very low content of catalytically active substances, such as platinum, ruthenium or palladium.

The polymer membrane according to the invention has polymers comprising phosphonic acid groups which are obtainable by polymerizing monomers comprising phosphonic acid groups.

Such polymer membranes can be obtained, inter alia, by a method comprising the steps

A) Preparation of a composition comprising monomers comprising phosphonic acid groups,

B) applying a layer using the composition according to step A) on a support,

C) polymerization of the monomers comprising phosphonic acid groups present in the sheet-like structure obtainable according to step B),

D) applying at least one catalyst layer to the membrane formed in step B) and / or in step C).

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 have a slight steric hindrance to the

Lead 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 used in step A) is preferably a compound of the formula ^ - R- (PO ₃ Z ₂ ) _x

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

Z independently of one another denotes hydrogen, C1-C15-alkyl group, C1-C15-alkoxy group, ethyleneoxy group or C5-C20-aryl or heteroaryl group, where the above radicals in turn can be substituted by 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 _x (Z ₂ O ₃ P> -R- - _R - ₍ po ₃ Z ₂ ) _χ wherein R is 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, where the above radicals can in turn 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, where the above radicals can in turn be substituted with halogen, -OH, -CN, and x is an integer 1, 2, 3, 4, 5, 6, 7, 8, 9 or 10 and / or of 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 means, where the above radicals can in turn be substituted with halogen, -OH, COOZ, -CN, NZ ₂ R is 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, where the above radicals can in turn be substituted with halogen, -OH, COOZ, -CN, NZ ₂ , Z independently of one another denotes hydrogen, C1-C15-alkyl group, C1-C15-alkoxy group, ethyleneoxy group or C5-C20-aryl or heteroaryl group, where the above radicals in turn can be substituted by 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 that 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 vinyl phosphonic 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 furthermore 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. To this

Derivatives include in particular the salts, the esters, the amides and the halides of the monomers comprising phosphonic acid groups.

The composition produced in step A) preferably comprises at least 20% by weight, in particular at least 30% by weight and particularly preferably at least 50

% By weight, based on the total weight of the composition, of monomers comprising phosphonic acid groups.

The composition produced in step A) can additionally contain further organic and / or inorganic solvents. The organic solvents include in particular polar aprotic solvents such as dimethyl sulfoxide (DMSO), esters such as ethyl acetate and polar protic solvents such as alcohols such as ethanol, propanol, isopropanol and / or butanol. The inorganic solvents include in particular water, phosphoric acid and polyphosphoric acid.

These can have a positive impact on processability. In particular, the solubility of polymers which are formed, for example, in step B) can be improved by adding the organic solvent. The content of monomers comprising phosphonic acid groups in such solutions is generally at least 5% by weight, preferably at least 10% by weight, particularly preferably between 10 and 97% by weight.

%. According to a particular aspect of the present invention, ionomeric compositions comprising monomers comprising sulfonic acid groups can be used to prepare the polymers and / or phosphonic acid groups comprising phosphonic acid groups.

Monomers comprising sulfonic acid groups are known in the art. These are compounds which 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 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 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 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 is independently hydrogen, C1-C15-alkyl group, C1-C15-alkoxy group, ethyleneoxy group or C5-C20-aryl or heteroaryl group, where the above radicals can in turn be substituted by halogen, -OH, -CN, and x is a whole Number 1, 2, 3, 4, 5, 6, 7, 8, 9 or 10 means y an integer 1, 2, 3, 4, 5, 6, 7, 8, 9 or 10 and / or of the formula wherein

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 being halogen, -OH, COOZ, -CN, NZ ₂ can be substituted,

Z independently of one another denotes hydrogen, C1-C15-alkyl group, C1-C15-alkoxy group, ethyleneoxy group or C5-C20-aryl or heteroaryl group, where the above radicals in turn can be substituted by 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, where the above radicals in turn can be substituted with halogen, -OH, COOZ, -CN, NZ ₂ R is 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, where the above radicals can in turn 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, where the above radicals may in turn be substituted with halogen, -OH, -CN, and x denotes an integer 1, 2, 3, 4, 5, 6, 7, 8, 9 or 10.

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, the

Have sulfonic acid groups, such as, for example, 2-suifonomethyl-acrylic acid, 2-sulfonomethyl (methacrylic! Acid, 2-sulfonomethyl-acrylic acid amide and 2-suifonomethyl-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.

According to a particular aspect of the present invention, the weight ratio of monomers comprising sulfonic acid groups to monomers comprising phosphonic acid groups can be in the range from 100: 1 to 1: 100, preferably 10: 1 to 1:10 and particularly preferably 2: 1 to 1: 2.

In a further embodiment of the invention, the.

Polymer membranes capable of crosslinking are used. These monomers can be added to the composition according to step A). In addition, the monomers capable of crosslinking can also be applied to the flat structure according to step C).

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

Dimethylacrylates, Trimethylycrylate, Tetramethylacrylate of the formula

Diacrylates, triacrylates, tetraacrylates of the formula

wherein

R is a C1-C15-alkyl group, C5-C20-aryl or heteroaryl group, NR ^' , -S0 ₂ , PR ^' , Si (R ^' ) ₂ , 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 crosslinkers 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, trimethylolpropane trimethacrylate, epoxy acrylates, 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 Monomers comprising phosphonic acid groups can be used.

The polymeric membranes of the present invention can be used in addition to

Polymers comprising phosphonic acid groups include further polymers (B) which are not obtainable by polymerizing monomers comprising phosphonic acid groups.

For this purpose, for example, a further polymer (B) can be added to the composition produced in step A). This polymer (B) can be dissolved, dispersed or suspended, among other things.

The preferred polymers (B) include, inter alia, polyolefins, such as poly (chloroprene), polyacetylene, polyphenylene, poly (p-xylylene), polyarylmethylene, polystyrene, polymethylstyrene, polyvinyl alcohol, polyvinyl acetate, polyvinyl ether, polyvinylamine, poly (N-vinyl acetamide), Polyvinyl imidazole, polyvinyl carbazole, polyvinyl pyrrolidone, polyvinyl pyridine, polyvinyl chloride, polyvinylidene chloride, polytetrafluoroethylene, polyvinyl difluoride, polyhexafluoropropylene, polyethylene tetrafluoroethylene, copolymers of PTFE with Hexafluoropropylene, with perfluoropropyl vinyl ether, with trifluoronitrosomethane, with carbalkoxy perfluoroalkoxy vinyl ether, polychlorotrifluoroethylene, polyvinyl fluoride, polyvinylidene fluoride, polyacrolein, polyacrylamide, polyacrylonitrile, polycyanacrylates, polymethacrylimide, especially cycloolefinic copolymers, cycloolefinic copolymers Polymers with CO bonds in the main chain, for example

Polyacetal, polyoxymethylene, polyether, polypropylene oxide, polyepichlorohydrin, polytetrahydrofuran, polyphenylene oxide, polyether ketone, polyether ether ketone, polyether ketone ketone, polyether ether ketone ketone, polyether ketone ether ketone, polyester, in particular polyhydroxyacetic acid, polyethylene terephthalate, polybutylene hydroxypropionic acid, polybutylene terephthalate, polybutylene hydroxypropionate,

Polypivalolactone, polycaprolactone, furan resins, phenol aryl resins, polymalonic acid, polycarbonate;

Polymeric C-S bonds in the main chain, for example polysulfide ether, polyphenylene sulfide, polyether sulfone, polysulfone, polyether ether sulfone, polyaryl ether sulfone, polyphenylene sulfone, polyphenylene sulfide sulfone, poly (phenyl sulfide-1,4-phenylene;

Polymeric CN bonds in the main chain, for example polyimines, polyisocyanides, polyetherimine, polyetherimides, poly (trifluoromethyl bis (phthalimide) phenyl, polyaniline, polyaramides, polyamides, polyhydrazides, polyurethanes, polyimides, polyazoles, polyazole ether ketone, polyureas, polyazines; Liquid crystalline polymers, especially Vectra as well

Inorganic polymers, for example polysilanes, polycarbosilanes, polysiloxanes, polysilicic acid, polysilicates, silicones, polyphosphazenes and polythiazyl. These polymers can be used individually or as a mixture of two, three or more polymers.

Polymers which contain at least one nitrogen atom, oxygen atom and / or sulfur atom in a repeating unit are particularly preferred. Particularly preferred are polymers which contain at least one aromatic ring with at least one nitrogen, oxygen and / or sulfur heteroatom per repeating unit. Polymers based on polyazoles are particularly preferred within this group. These basic polyazole polymers contain at least one aromatic ring with at least one nitrogen heteroatom per repeat unit.

The aromatic ring is preferably a five- or six-membered ring with one to three nitrogen atoms, which can be fused to another ring, in particular another aromatic ring.

Polyazoles are particularly preferred here. Polymers based on polyazole generally 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 (XXII) ^X VAr - (I) NX n

(III)

wherein

Ar are the same or different and are the same or different for a tetra-aromatic or heteroaromatic group which may be mononuclear or polynuclear, Ar ^{1 are the} same or different and for a divalent aromatic or heteroaromatic group which may be mononuclear or polynuclear,

Ar ^{2 are the} same or different and for a two or three-membered aromatic or heteroaromatic group which can be mono- or polynuclear, Ar ^{3 are the} same or different and for a three-membered aromatic or heteroaromatic group which can be mono- or polynuclear, Ar ⁴ are the same or different and for a three-membered aromatic or heteroaromatic group which can be mono- or polynuclear, Ar ^{5 are the} same or different and for a tetra-aromatic or heteroaromatic group which can 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 are identical or different and represent a divalent aromatic or heteroaromatic group, which may be mono- or polynuclear, Ar ⁸ are identical or different and represent a trivalent aromatic or heteroaromatic group, which may be mono- or polynuclear, Ar ⁹ are identical or are different and are the same or different for a two- or three- or four-membered aromatic or heteroaromatic group, which can be mono- or polynuclear, and Ar ^{10 are the} same or different and for a di- or tri-bonded aromatic or heteroaromatic group, which can be mono- or polynuclear , Ar ^{11 are the} same or different and are for a double-bonded aromatic or heteroaromatic group which can be mononuclear or polynuclear,

X is identical or different and for oxygen, sulfur or an 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 a further radical, R is identical or different for hydrogen , an alkyl group and an aromatic group are identical or different to hydrogen, an alkyl group and an aromatic group are provided 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 is.

Preferred aromatic or heteroaromatic groups are derived from benzene, naphthalene, biphenyl, diphenyl ether, diphenyl methane, diphenyldimethyl methane, bisphenone, diphenyl sulfone, thiophene, furan, pyrrole, thiazole, oxazole, imidazole, isothiazole, isoxazole, pyrazole, 1, 3,4-pyrazole, 1, 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, dibenzothiophene, carbazole, pyridine, 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, Benzooxathiadiazol, Benzooxadiazol, benzopyridine, benzopyrazine, Benzopyrazidin, benzopyrimidine, benzotriazine, indolizine, pyridopyridine, imidazopyrimidine, Pyrazinopyrimidin, carbazole, Aciridin, phenazine, benzoquinoline, phenoxazine, phenothiazine, acridizine, benzopteridine, phenanthroline and phenanthrene, from which optionally also be substituted can.

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-phenylene. Particularly preferred groups are derived from benzene and biphenylene, 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, polybenzthiazoles, 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:

0

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

Further preferred polyazole polymers are polyimidazoles, polybenzimidazole ether ketone, polybenzthiazoles, polybenzoxazoles, polytriazoles, polyoxadiazoles, polythiadiazoles, polypyrazoles, polyquinoxalines, poly (pyridines), poly (pyrimidines), and poly (tetrazapyrenes). Preferred polyazoles are distinguished by a high molecular weight. This applies in particular to the polybenzimidazoles. Measured as intrinsic viscosity, this is preferably at least 0.2 dl / g, preferably 0.7 to 10 dl / g, in particular 0.8 to 5 dl / g.

Celazole from Celanese is particularly preferred. The properties of the polymer film and

Polymer membranes can be improved by sieving the starting polymer as described in German Patent Application No. 10129458.1.

In addition, polymers with aromatic sulfonic acid groups can be used as polymer (B). Aromatic sulfonic acid groups are groups in which the

Sulfonic acid group (-S0 ₃ H) is covalently bound to an aromatic or heteroaromatic group. The aromatic group may be part of the backbone of the polymer or part of a side group, with polymers having aromatic groups in the main chain being preferred. The sulfonic acid groups can often also be used in the form of the salts. Furthermore, it is also possible to use derivatives, for example esters, in particular methyl or ethyl esters, or halides of the sulfonic acids which are converted into the sulfonic acid during operation of the membrane.

The polymers modified with sulfonic acid groups preferably have a sulfonic acid group content in the range from 0.5 to 3 meq / g, preferably 0.5 to 2.5. This value is determined via the so-called ion exchange capacity (IEC).

To measure the IEC, the sulfonic acid groups are converted into the free acid. For this purpose, the polymer is treated with acid in a known manner, excess acid being removed by washing. The sulfonated polymer is first treated in boiling water for 2 hours. Excess water is then dabbed off and the sample is dried for 15 hours at 160 ° C. in a vacuum drying cabinet at p <1 mbar. Then the dry weight of the membrane is determined. The polymer dried in this way is then dissolved in DMSO at 80 ° C. for 1 hour. The solution is then titrated with 0.1 M NaOH. The ion exchange capacity (IEC) is then calculated from the consumption of the acid up to the equivalent point and the dry weight.

Polymers with sulfonic acid groups covalently bonded to aromatic groups are known in the art. For example, polymers with aromatic sulfonic acid groups can be produced by sulfonating polymers. Process for the sulfonation of

Polymers are described in F. Kucera et. al. Polymer Engineering and Science 1988, Vol. 38, No 5, 783-792. The sulfonation conditions can be selected so that a low degree of sulfonation is produced (DE-A-19959289).

With regard to polymers with aromatic sulfonic acid groups, their aromatic radicals

Part of the side group, in particular reference is made to polystyrene derivatives. So describes the publication US-A-6110616 copolymers of butadiene and styrene and their subsequent sulfonation for use in fuel cells.

Furthermore, such polymers can also be obtained by polyreactions of monomers which comprise acid groups. Perfluorinated polymers such as in

US-A-5422411 described by copolymerization of trifluorostyrene and sulfonyl-modified trifuorostyrene.

According to a particular aspect of the present invention, high-temperature stable thermoplastics are used which are bound to aromatic groups

Have sulfonic acid groups. In general, such polymers have aromatic groups in the main chain. Thus, sulfonated polyether ketones (DE-A-4219077, WO96 / 01177), sulfonated polysulfones (J. Membr. Sei. 83 (1993) p.211) or sulfonated polyphenylene sulfide (DE-A-19527435) are preferred.

The polymers set out above with sulfonic acid groups bonded to aromatics can be used individually or as a mixture, with particular preference being given to mixtures which have polymers with aromatics in the main chain.

The preferred polymers include polysulfones, especially polysulfones with aromatics in the main chain. Have According to a particular aspect of the present invention, preferred polysulfones and polyether sulfones have a melt volume rate MVR 300/21, 6 is less than or equal to 40 cm ^3/10 min, especially less than or equal to 30 cm ^3/10 min and particularly preferably less than or equal to 20 cm ³ / 10 min measured according to ISO 1133.

According to a particular aspect of the present invention, the weight ratio of polymer with monomers covalently bonded to aromatic groups to monomers comprising phosphonic acid groups can be in the range from 0.1 to 50, preferably from 0.2 to 20, particularly preferably from 1 to 10.

According to a particular aspect of the present invention, preferred proton-conducting polymer membranes are obtainable by a process comprising the steps I) swelling a polymer film with a liquid which contains monomers comprising phosphonic acid groups, II) polymerizing at least part of the monomers comprising phosphonic acid groups, which in step I) in the polymer film was introduced and III) applying at least one catalyst layer to the membrane formed in step II).

Swelling means an increase in weight of the film of at least 3% by weight.

The swelling is preferably at least 5%, particularly preferably at least 10%. Determination of the swelling Q is determined gravimetrically from the mass of the film before swelling m ₀ and the mass of the film after the polymerization according to step B), m ₂ . Q = (m ₂ -m ₀ ) / m ₀ x 100

The swelling is preferably carried out at a temperature above 0 ° C., in particular between room temperature (20 ° C.) and 180 ° C. in a liquid which preferably contains at least 5% by weight of monomers comprising phosphonic acid groups. Furthermore, the swelling can also be carried out at elevated pressure. The limits result from economic considerations and technical possibilities.

The polymer film used for swelling generally has a thickness in the range from 5 to 3000 μm, preferably 10 to 1500 μm and particularly preferably 20 to 500 μm. The production of such films from polymers is generally known, some of which are commercially available.

The liquid containing monomers comprising phosphonic acid groups can be a solution, wherein the liquid can also contain suspended and / or dispersed constituents. The viscosity of the liquid which contains monomers comprising phosphonic acid groups can be in wide ranges, with the addition of solvents or an increase in temperature in order to adjust the viscosity.

The dynamic viscosity is preferably in the range from 0.1 to 10000 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 composition produced in step A) or the liquid used in step I) may additionally contain further organic and / or inorganic solvents. The organic solvents include in particular polar aprotic solvents such as dimethyl sulfoxide (DMSO), esters such as ethyl acetate and polar protic solvents such as alcohols such as ethanol, propanol, isopropanol and / or butanol. The inorganic solvents include in particular water, phosphoric acid and polyphosphoric acid. 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. Such substances preferably have an intrinsic conductivity at 100 ° C. of at least 10 ⁶ S / cm, in particular 10 ⁵ S / cm. The addition can take place, for example, in step A) and / or step B) or step I) If these additives are in liquid form, these additives can also be added after the polymerization in step C) or step II). Non-limiting examples of proton-conducting fillers are

Sulfates such as: CsHS0 ₄ , Fe (S0 ₄ ) ₂ , (NH ₄ ) ₃ H (S0 ₄ ) ₂ , LiHS0 ₄ , NaHS0 ₄ , KHS0 ₄ , RbS0 ₄ , LiN ₂ H ₅ S0 ₄ , NH ₄ HS0 ₄ , phosphates like Zr ₃ (P0 ₄ ) ₄ , Zr (HP0 ₄ ) ₂ , HZr ₂ (P0 ₄ ) ₃ , U0 ₂ P0 ₄ .3H ₂ 0, H ₈ U0 ₂ P0 ₄ , Ce (HP0 ₄ ) ₂ , Ti (HP0 ₄ ) ₂ , KH ₂ P0 ₄ , NaH ₂ P0 ₄ , LiH ₂ P0 ₄ , NH ₄ H ₂ PÖ ₄ , CsH ₂ P0 ₄ , CaHP0 ₄ , MgHP0 ₄ , HSbP ₂ 0 ₈ , HSb ₃ P ₂ 0 ₁₄ , H ₅ Sb ₅ P ₂ O ₂₀ , polyacids such as H ₃ PW ₁₂ O ₄₀ .nH ₂ O (n = 21-29), H ₃ SiW ₁₂ 0 ₄ o.nH ₂ 0 (n = 21-29), H _x W0 ₃ , HSbW0 ₆ , H ₃ PMo ₁₂ O ₄₀ , H ₂ Sb ₄ 0n, HTaW0 ₆ , HNb0 ₃ , HTiNb0 ₅ , HTiTa0 ₅ , HSbTe0 ₆ , H ₅ Ti ₄ 0 ₉ , HSb0 ₃ , H ₂ Mo0 ₄ Selenite and Arsenite as (NH ₄ ) ₃ H (Se0 ₄ ) ₂ , U0 ₂ As0 ₄ , (NH ₄ ) ₃ H (Se0 ₄ ) ₂ , KH ₂ As0 ₄ , Cs ₃ H (Se0 ₄ ) ₂ , Rb ₃ H (Se0 ₄ ) ₂ , phosphides ZrP, TiP, HfP

Oxides such as Al ₂ 0 ₃ , Sb ₂ 0 ₅ , Th0 ₂ , Sn0 ₂ , Zr0 ₂ , Mo0 ₃

Silicates such as zeolites, zeolites (NH +), layered silicates, framework silicates, H-natrolites, H-mordenites, NH ₄ -analyses, NH ₄ -sodalites, NH ₄ -galates, H-montmorillonites

Acids such as HCI0 ₄ , SbF ₅

Fillers such as carbides, in particular SiC, Si ₃ N, fibers, in particular glass fibers, glass powders and / or polymer fibers, preferably based on polyazoles.

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 polymerization in step C) or step II) comprises at most 80% by weight, preferably at most 50% by weight and particularly preferably at most 20

% By weight 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, near the cathode increase

Oxygen solubility and diffusion and to reduce the adsorption of the electrolyte on the catalyst surface. (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 cell. Razaq, M .; Razaq, A;

Yeager, E .; DesMarteau, Darryl D .; Singh, S. Case Cent Electrochem. Be., Case West. Reserve Univ., Cleveland, OH, USA. J. Electrochem. Soc. (1989), 136 (2), 385-90.) Non-limiting examples of perfluorinated sulfonic acid additives are: trifluomethanesulfonic acid, potassium trifluoromethanesulfonate, sodium trifluoromethanesulfonate, lithium trifluoromethanesulfonate, ammonium trifluoromethanesulfonate,

Potassium perfluorohexane sulfonate, sodium perfluorohexane sulfonate, lithium perfluorohexane sulfonate, ammonium perfluorohexane sulfonate, Perfluorohexane sulfonic acid, potassium nonafluorobutane sulfonate, sodium nonafluorobutane sulfonate, lithium nonafluorobutane sulfonate, ammonium nonafluorobutane sulfonate, cesiu nonafluorobutane sulfonate, triethylammonium perfluorohexasulfonate and perflurosulfoimide.

The formation of the flat structure according to step B) takes place 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 supports include, in particular, films made from polyethylene terephthalate (PET), polytetrafluoroethylene (PTFE), polyhexafluoropropylene,

Copolymers of PTFE with hexafluoropropylene, polyimides, polyphenylene sulfides (PPS) and polypropylene (PP).

The thickness of the flat structure according to step B) 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 500 μm.

The polymerization of the monomers comprising phosphonic acid groups in step C) or step II) is preferably carried out 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 composition after the composition has been heated in accordance with step A). Furthermore, a starter solution to the after

Step B) obtained flat structures are applied. This can be done by means of measures known per se (e.g. spraying, dipping, etc.) which are known from the prior art. If the membrane is made by swelling, a starter solution can be added to the liquid. This can also be applied to the flat structure after swelling.

Suitable radical formers include azo compounds, peroxy compounds, persulfate compounds or azoamidines. Non-limiting examples include dibenzoyl peroxide, dicumyl peroxide, cumene hydroperoxide, diisopropyl peroxydicarbonate, bis (4-t-butylcyclohexyl) peroxydicarbonate, Dikaliumpersulfat, ammonium peroxydisulfate, 2,2'-azobis (2-methylpropionitrile) (AIBN), 2,2 ^'azobis- (isobuttersäureamidin ) hydrochloride, benzpinacol, dibenzyl derivatives, methyl ethylene ketone peroxide, 1, 1-azobiscyclohexane carbonitrile, methyl ethyl ketone peroxide, acetylacetone peroxide, dilauryl peroxide, didecanoyl peroxide, tert-butyl per-2-ethylhexanoate, ketone peroxide, methyl isobutyl ketone peroxy, oxybenzyl peryl peroxy, oxyperyl peroxyl, oxybenzyl peryl peroxide, cyclo , 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, and also the radical formers available from DuPont under the name © Vazo, for example ®Vazo V50 and ®Vazo WS.

Furthermore, radical formers can also be used which form radicals when irradiated. The preferred compounds include D D-diethoxyacetophenone (DEAP, Upjon Corp), n-butylbenzoin ether (®Trigonal-14, AKZO) and 2,2-dimethoxy-2-phenylacetophenone (© Igacure 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 monomers comprising phosphonic acid groups) is added

Free radical generator added. 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.492-51 1;

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 is irradiated with a radiation dose in the range from 1 to 300 kGy, preferably from 3 to 250 kGy and very particularly preferably from 20 to 200 kGy.

The polymerization of the monomers comprising phosphonic acid groups in step C) or step II) 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 done under pressure. The polymerization leads to a solidification of the flat structure, this solidification by Micro hardness measurement can be followed. 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 embodiment of the present invention, the

Membranes have a high mechanical stability. This size results from the hardness of the membrane, which is determined by means of microhardness measurement according to 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 0.01 N / mm ² , preferably at least 0.1 N / mm ² and very particularly preferably at least 1 N / 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 C _HU 0.003 / 20/5 under these conditions is less than 20%, preferably less than 10% and very particularly preferably less than 5%. The module determined by means of microhardness measurement is YHU at least 0.5 MPa, in particular at least 5 MPa and very particularly preferably at least 10 MPa, without this being intended to impose a restriction.

The hardness of the membrane relates both to a surface which has no catalyst layer and to a side which has a catalyst layer.

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 repeat units, in particular at least 50 repeat units, very particularly preferably at least 100 repeat 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 polymers comprising phosphonic acid groups contained in the membrane preferably have a broad molecular weight distribution. The polymers comprising phosphonic acid groups can have a polydispersity M _w / M _n in the range from 1 to 20, particularly preferably from 3 to 10. The water content of the proton-conducting membrane is preferably at most 15% by weight, particularly preferably at most 10% by weight and very particularly preferably at most 5% by weight.

In this context it can be assumed that the conductivity of the membrane can be based on the Grotthus mechanism, which means that the system does not require additional moistening. Accordingly, preferred membranes comprise portions of polymers comprising low molecular weight phosphonic acid groups. For example, the proportion of polymers comprising phosphonic acid groups with a degree of polymerization in the range from 2 to 20 can preferably be at least 10% by weight, particularly preferably at least 20% by weight, based on the weight of the polymers comprising phosphonic acid groups.

The polymerization in step C) or step II) can lead to a decrease in the layer thickness. The thickness of the self-supporting membrane is preferably between 15 and 1000 μm, preferably between 20 and 500 μm, in particular between 30 and 250 μm.

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

Following the polymerization in step C) or step II), the membrane can be crosslinked thermally, photochemically, chemically and / or electrochemically on the surface. This hardening of the membrane surface additionally improves the properties of the membrane.

According to a particular aspect, 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 thermal crosslinking is preferably carried out in the presence of oxygen. 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 this resulting in a

Restriction should take place.

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) and / or UV light. Another method is radiation with β, γ and / or electron beams. The radiation dose is preferably between 5 and 250 kGy, in particular 10 to 200 kGy. Irradiation can take place in air or under inert gas. This improves the performance properties of the membrane, in particular its durability. Depending on the desired degree of crosslinking, the duration of the crosslinking reaction can be in a wide range. In general, this reaction 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.

According to a particular embodiment of the present invention, the membrane comprises at least 3% by weight, preferably at least 5% by weight and particularly preferably at least 7% by weight of phosphorus, based on the total weight of the membrane, after elemental analysis. The proportion of phosphorus can be determined using an elementary analysis. For this purpose, the membrane is dried at 110 ° C. for 3 hours in a vacuum (1 mbar).

The polymers comprising phosphonic acid groups preferably have a phosphonic acid group content of at least 5 meq / g, particularly preferably at least 10 meq / g. This value is determined via the so-called ion exchange capacity (IEC).

To measure the IEC, the phosphonic acid groups are converted into the free acid, the measurement being carried out before polymerization of the monomers comprising phosphonic acid groups. The sample is then titrated with 0.1 M NaOH. The ion exchange capacity then becomes from the consumption of the acid to the equivalent point and the dry weight

^' (IEC) calculated.

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 1 mS / cm, preferably at least 2 mS / cm, in particular at least 5 mS / cm, preferably measured without humidification.

Furthermore, the membranes show a high temperature even at 70 ° C

Conductivity. The conductivity depends, among other things, on the sulfonic acid group content of the membrane. The higher this proportion, the better the conductivity at low temperatures. Here, a membrane according to the invention can be moistened at low temperatures. For this purpose, for example, the compound used as an energy source, for example hydrogen, can be provided with a proportion of water. In many cases, however, the water formed by the reaction is sufficient to achieve humidification.

The specific conductivity is determined 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 composed of a simple model parallel arrangement of an ohmic resistor and a capacitance evaluated. 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.

The passage current density when operating with 0.5 M methanol solution and 90 ° C. in a so-called liquid direct methanol fuel cell is preferably less than 100 mA cm ² , in particular less than 70 mA / cm ^2, particularly preferably less than 50 mA / cm ² and entirely particularly preferably less than 10 mA cm ² . The passage current density when operating with a 2 M methanol solution and 160 ° C. in a so-called gaseous direct methanol fuel cell is preferably less than 100 mA cm ² , in particular less than 50 mA / cm ^2, very particularly preferably less than 10 mA / cm ² .

To determine the cross-over current density, the amount of carbon dioxide released at the cathode is measured by means of a CO ₂ sensor. From the value of the C0 ₂ amount thus obtained, as from P. Zelenay, SC Thomas, S. Gottesfeld in S. Gottesfeld, TF filler "Proton Conducting Membrane Fuel Cells II" ECS Proc. Vol. 98-27 p. 300 -308, the passage current density is calculated.

Furthermore, a polymer membrane according to the invention has one or two catalyst layers which are electrochemically active. The term “electrochemically active” denotes that the catalyst layer or layers are able to catalyze the oxidation of fuels, for example H ₂ , methanol, ethanol, and the reduction of 0 ₂ .

The catalyst layer or layers contain or contain catalytically active substances. These include platinum group precious metals, i.e. Pt, Pd, Ir, Rh, Os, Ru, or also the precious metals Au and Ag. Furthermore, alloys of all of the aforementioned metals can also be used. Furthermore, at least one catalyst layer may contain alloys of the platinum group elements with base metals such as Fe, Co, Ni, Cr, Mn, Zr, Ti, Ga, V etc. In addition, the oxides of the aforementioned noble metals and / or non-noble metals can also be used.

The catalytically active particles, which comprise the substances mentioned above, can be used as metal powder, so-called black noble metal, in particular platinum and / or platinum alloys. Such particles generally have a size in the range from 5 nm to 200 nm, preferably in the range from 7 nm to 100 nm.

In addition, the metals can also be used on a carrier material. This carrier preferably comprises carbon, which in particular in the form of carbon black, Graphite or graphitized carbon black can be used. Furthermore, electrically conductive metal oxides, such as SnO _x , TiO _x , or phosphates, such as FePO _x , NbP0 _x , Zr _y (PO _x ) _z , can also be used as carrier material. The indices x, y and z denote the oxygen or metal content of the individual compounds, which can be in a known range since the transition metals differ

Can assume oxidation levels.

The content of these supported metal particles, based on the total weight of the metal support compound, is generally in the range from 1 to 80% by weight, preferably 5 to 60% by weight and particularly preferably 10 to 50% by weight. % without any limitation. The particle size of the carrier, in particular the size of the carbon particles, is preferably in the range from 20 to 100 nm, in particular 30 to 60 nm. The size of the metal particles located thereon is preferably in the range from 1 to 20 nm, in particular 1 to 10 nm and particularly preferably 2 to 6 nm.

The sizes of the different particles represent mean values and can be determined using transmission electron microscopy or powder X-ray diffractometry.

The catalytically active particles set out above can generally be obtained commercially.

Furthermore, this catalyst layer comprises ionomers comprising phosphonic acid groups, which can be obtained by polymerizing monomers comprising phosphonic acid groups.

The monomers comprising phosphonic acid groups have been set out above so that reference is made to them. Ethenephosphonic acid, propenephosphonic acid, butenephosphonic acid are preferred; Acrylic acid and / or methacrylic acid compounds that 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 are used to prepare the ionomers to be used according to the invention. ,

Commercial vinylphosphonic acid (ethenephosphonic acid), such 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.

Furthermore, for the preparation of the ionomeric sulfonic acid groups can include

Monomers are used. According to a particular aspect of the present invention, monomers comprising phosphonic acid groups and monomers comprising sulfonic acid groups are used in the preparation of the ionomeric mixtures in which the weight ratio of monomers comprising phosphonic acid groups to monomers comprising sulfonic acid groups is in the range from 100: 1 to 1: 100, preferably 10: 1 to 1:10 and particularly preferably 2: 1 to 1: 2

The ionomer preferably has a molecular weight in the range from 300 to 100,000 g / mol, preferably from 500 to 50,000 g / mol. This value can be determined via GPC.

According to a particular aspect of the present invention, the ionomer can have a polydispersity M _w / M _n in the range from 1 to 20, particularly preferably from 3 to 10.

In addition, commercially available polyvinylphosphonic acids can also be used as ionomers. These are available from Polysciences Inc., among others.

According to a particular embodiment of the present invention, the ionomers can have a particularly uniform distribution in the catalyst layer. This uniform distribution can in particular be achieved in that the ionomer is brought into contact with the catalytically active substances before the catalyst layer is applied to the polymer membrane.

The uniform distribution of the ionomer in the catalyst layer can be determined, for example, by EDX. The scatter within the catalyst layer is at most 10%, preferably 5% and particularly preferably 1%.

The proportion of ionomer in the catalyst layer is preferably in the range from 1 to 60% by weight, particularly preferably in the range from 10 to 50% by weight.

According to elemental analysis, the proportion of phosphorus in the

Catalyst layer at least 0.3% by weight, in particular at least 3 and particularly preferably at least 7% by weight. According to a particular aspect of the present invention, the proportion of phosphorus in the catalyst layer is in the range from 3% by weight to 15% by weight.

Various methods can be used to apply at least one catalyst layer. For example, in step C) a support can be used which is provided with a coating containing a catalyst in order to provide the layer formed in step C) with a catalyst layer.

The membrane can be provided with a catalyst layer on one or both sides. If the membrane is only provided with a catalyst layer on one side, then the opposite side of the membrane are pressed with an electrode which has a catalyst layer. If both sides of the membrane are to be provided with a catalyst layer, the following methods can also be used in combination in order to achieve an optimal result.

According to the invention, the catalyst layer can be applied by a method in which a catalyst suspension is used. Powders comprising the catalyst can also be used.

In addition to the catalytically active substance and the ionomer comprising phosphonic acid groups, the catalyst suspension can contain conventional additives. These include fluoropolymers such as Polytetrafluoroethylene (PTFE), thickeners, especially water-soluble polymers such as e.g. Cellulose derivatives, polyvinyl alcohol, polyethylene glycol, and surface-active substances.

The surface-active substances include in particular ionic surfactants, for example fatty acid salts, in particular sodium laurate, potassium oleate; and alkyl sulfonic acids, alkyl sulfonic acid salts, in particular sodium perfluorohexane sulfonate, lithium perfluorohexane sulfonate, ammonium perfluorohexane sulfonate, perfluorohexane sulfonic acid, potassium nonafluorobutane sulfonate, as well as nonionic surfactants, especially ethoxylated fatty alcohols and polyethylene glycols.

Furthermore, the catalyst suspension can comprise liquid constituents at room temperature. These include organic solvents, which can be polar or non-polar, phosphoric acid, polyphosphoric acid and / or water. The

The catalyst suspension preferably contains 1 to 99% by weight, in particular 10 to 80% by weight, of liquid constituents.

The polar, organic solvents include in particular alcohols, such as ethanol, propanol, isopropanol and / or butanol.

The organic, non-polar solvent include known thin as Dünnschichtverdünner 8470 DuPont, which comprises turpentine oils ^•.

Particularly preferred additives are fluoropolymers, in particular tetrafluoroethylene polymers. According to a particular embodiment of the present invention, the catalyst suspension can contain 0 to 60% fluoropolymer based on the weight of the catalyst material, preferably 1 to 50%. The weight ratio of fluoropolymer to catalyst material, comprising at least one noble metal and optionally one or more support materials, can be greater than 0.1, this ratio preferably being in the range from 0.2 to 0.6 The catalyst suspension can be applied to the membrane using customary methods. Depending on the viscosity of the suspension, which can also be in paste form, various methods are known with which the suspension can be applied. Processes are suitable for coating films, fabrics, textiles and / or papers, in particular spray processes and printing processes, such as, for example

Stencil and screen printing processes, inkjet processes, roller application, in particular anilox rollers, slot nozzle application and doctor blades. The particular process and the viscosity of the catalyst suspension depend on the hardness of the membrane.

The viscosity can be determined by the solids content, in particular the proportion of catalytically active

Particles, and the proportion of additives can be influenced. The viscosity to be set depends on the method of application of the catalyst suspension, the optimum values and their determination being familiar to the person skilled in the art.

Depending on the hardness of the membrane, an improvement in the binding of catalyst and

Membrane done by heating and / or pressing. In addition, the bond between the membrane and the catalyst increases as a result of a previously described surface crosslinking treatment which can be carried out thermally, photochemically, chemically and / or electrochemically.

According to a particular aspect of the present invention, the catalyst layer is applied using a powder process. Here, a catalyst powder is used, which may contain additional additives, which have been set out above by way of example.

To apply the catalyst powder, spray processes and

Screening processes are used. In the spraying process, the powder mixture is sprayed onto the membrane using a nozzle, for example a slot nozzle. In general, the membrane provided with a catalyst layer is then heated in order to improve the connection between the catalyst and membrane. The heating can take place, for example, using a hot roller. Such methods and devices for applying the powder are described, inter alia, in DE 195 09 748, DE 195 09 749 and DE 197 57 492.

In the sieving process, the catalyst powder is applied to the membrane with a vibrating sieve. A device for applying a catalyst powder to a membrane is described in WO 00/26982. After the catalyst powder has been applied, the binding of the catalyst and membrane can be improved by heating. Here, the membrane provided with at least one catalyst layer can be heated to a temperature in the range from 50 to 200 ° C., in particular 100 to 180 ° C.

In addition, the catalyst layer can be applied by a method in which a coating containing a catalyst is applied to a support and then transfers the coating on the support containing a catalyst to a membrane. Such a method is described by way of example in WO 92/15121.

The support provided with a catalyst coating can be produced, for example, by producing a previously described catalyst suspension. This catalyst suspension is then applied to a carrier film, for example made of polytetrafluoroethylene. After the suspension has been applied, the volatile constituents are removed.

The coating containing a catalyst can be transferred, inter alia, by hot pressing. For this purpose, the composite comprising a catalyst layer and a membrane, as well as a carrier film, is heated to a temperature in the range from 50 ° C. to 200 ° C. and pressed at a pressure of 0.1 to 5 MPa. In general, a few seconds are sufficient to connect the catalyst layer to the membrane. This time is preferably in the range from 1 second to 5 minutes, in particular 5 seconds to 1 minute.

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 membrane provided with at least one catalyst layer comprises 0.1 to 10.0 mg / cm ² , preferably 0.2 to 6.0 mg / cm ² and particularly preferably 0.2 to 2 mg / cm ^{2 of} the catalytically active metal, for example Pt. These values can be determined by elemental analysis of a flat sample. If the membrane is provided with two opposite catalyst layers, the above-mentioned values of the metal basis weight per catalyst layer apply.

^■ In a particular aspect of the present invention, one side of a membrane has a higher metal content than the opposite side of the membrane. The metal content on one side is preferably at least twice as high as the metal content on the opposite side.

Following the treatment according to step C) and / or step D), the membrane can still be crosslinked by the action of 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 reaction 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.

Possible areas of application of the polymer membranes according to the invention include. among others the 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. For more information on

Membrane electrode units are referred to the technical literature, in particular to the patents US-A-4,191, 618, US-A-4,212,714 and US-A-4,333,805. The disclosure contained in the above-mentioned references [US-A-4,191, 618, US-A-4,212,714 and US-A-4,333,805] with regard to the construction and manufacture of membrane-electrode assemblies, as well as the electrodes, gas diffusion layers and

Catalysts are also part of the description.

To produce a membrane-electrode unit, the membrane according to the invention can be connected to a gas diffusion layer. If the membrane is provided with a catalyst layer on both sides, the gas diffusion layer does not have to be before the pressing

Have catalyst. However, gas diffusion layers provided with a catalytically active layer can also be used. The gas diffusion layer 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 fabric and / or flat structures which have been made conductive by adding carbon black.

The gas diffusion layers are connected to the membrane provided with at least one catalyst layer by pressing the individual components under conventional methods

Conditions. Generally at a temperature in the range of 10 to 300 ° C, laminated in particular from 20 ° C. to 200 ° and with a pressure in the range from 1 to 1000 bar, in particular from 3 to 300 bar.

Furthermore, the membrane can also be connected to the catalyst layer by using a gas diffusion layer provided with a catalyst layer. Here, a membrane-electrode unit can be formed from a membrane without a catalyst layer and two gas diffusion layers provided with a catalyst layer.

A membrane electrode assembly according to the invention shows a surprisingly high one

Power density. According to a particular embodiment, preferred membrane electrode units have a current density of at least 0.05 A / cm ² , preferably 0.1 A / cm ² , particularly preferably 0.2 A / cm ² . This current density is reached in operation with pure hydrogen at the anode and air (approx. 20 vol.% Oxygen, approx. 80 vol.% Nitrogen) at the cathode at normal pressure (absolute 1013 mbar, with open cell outlet) and 0.6V Cell voltage measured. Particularly high temperatures in the range of 150-200 ° C., preferably 160-180 ° C., in particular 170 ° C., can be used here. Furthermore, the MEE according to the invention can also be operated in the temperature range below 100 ° C., preferably from 50-90 ° C., in particular at 80 ° C. At these temperatures, the MEE shows a current density of at least 0.02 A / cm ² , preferably of at least 0.03 A / cm ² and particularly preferably of 0.05 Acm ² measured at a voltage of 0.6 V below that otherwise mentioned conditions mentioned.

The aforementioned power densities can also be achieved with a low stoichiometry of the fuel gas. According to a particular aspect of the present invention, the stoichiometry is less than or equal to 2, preferably less than or equal to 1.5, very particularly preferably less than or equal to 1.2. The oxygen stoichiometry is less than or equal to 3, preferably less than or equal to 2.5 and particularly preferably less than or equal to 2.

Example 1 :

Example 1 shows a polarization curve of a membrane-electrode assembly consisting of a membrane containing phosphonic acid and two electrodes. This example serves as a reference example for Examples 2 and 3. The production of the individual components is described in the following: Membrane: A film made of high molecular weight polybenzimidazole, which consists of a PBI-DMAc

Solution prepared according to DE 10052237.8 and by selecting suitable polymer granules according to DE 10129458.1 is first washed as described in DE10110752.8 at 45 ° C for 30 min. Excess water is then dabbed off from the PBI film pretreated in this way with a paper towel. This undoped PBI film is then poured into a solution consisting of 1 part by weight of water and 10 parts by weight

Vinylphosphonic acid (97%) available from Clariant at 70 ° C. for 2 hours. Then the increase in thickness and the increase in area are determined. Then the membrane treated with electron radiation and a radiation dose of 50-80 kGy. The content of vinylphosphonic acid on the membrane thus obtained is calculated as n (VPA) / n (PBI) by titration.

Electrodes: Commercial PTFE-bonded electrodes, each with a Pt content of 1 mg / cm ^2, are used as anode and cathode, a carbon-supported Pt catalyst (30% Pt on Vulcan XC72) being used in the catalyst layer. Both electrodes contain no ionomer.

Manufacture of the membrane electrode unit: The electrodes are placed on one side of the membrane and pressed at a temperature in the range of 100-180 ° C.

Polarization measurement: The measurement is carried out in a single fuel cell (50cm ² active area) at a temperature of 160 ° C with hydrogen (24.1 L / h) as anode gas and air as cathode gas (99.3 L / h). The reaction gases are not humidified. Due to the non-ionomer-containing electrodes and the associated poor utilization of the catalyst, the cell power achieved at 0.6 V is only approx. 12 mW / cm ² .

Example 2: Example 2 shows three polarization curves of a membrane electrode unit, consisting of a membrane containing phosphonic acid and two electrodes. The manufacture of the individual components is described below:

Membrane: See description in example 1.

Electrodes: Commercial PTFE-bonded electrodes, each with a Pt content of 1 mg / cm ^2, are used as anode and cathode, a carbon-supported Pt catalyst (30% Pt on Vulcan XC72) being used in the catalyst layer. A solution of 5% vinylphosphonic acid in ethanol is sprayed onto the respective catalyst layer of the electrodes at 150 ° C. up to a vinylphosphonic acid loading of 0.5 mg / cm ² . The electrodes are then dried at 100 ° C.

Polarization measurement: The measurement is carried out in a single fuel cell (50 cm ² active area) with hydrogen (24.1 L / h) as anode gas and air as cathode gas (99.3 L / h). The reaction gases are not humidified. Curve A in Example 2 shows a polarization curve at 1.60 ° C. The fuel cell was then cooled to 80 ° C. and curve B was recorded after 24 hours. The fuel cell was then heated again to 160 ° C. and curve C was recorded after another 24 hours. Example 2 shows a significant line improvement compared to Example 1, ie at 160 ° C and 0.6 V. achieves an output of 130 mW / cm ² . At 80 ° C and 0.6 V, a cell output of 36 mW / cm ^{2 is} achieved. Due to the good binding of the ionomer in the catalyst layer, example 2 makes it clear that the membrane electrode unit produced in this way is stable to the temperature cycle. This property can be seen by comparing curves A and C.

Example 3:

Example 3 shows three polarization curves of a membrane-electrode unit, consisting of a membrane containing phosphonic acid and two electrodes. The manufacture of the individual components is described below:

Membrane: See description in example 1.

Electrodes: Commercial PTFE-bonded electrodes, each with a Pt content of 1 mg / cm ^2, are used as anode and cathode, a carbon-supported Pt catalyst (30% Pt on Vulcan XC72) being used in the catalyst layer. A solution of polyvinyl phosphonic acid, 1-propanol and water (weight ratio 1: 4: 2) is applied to the respective catalyst layer of the electrodes at room temperature with a brush. The polyvinyl phosphonic acid (PVPA) content of the catalyst layers is 2.4 mg / cm ^{2 in} each case. The electrodes are then dried at 100 ° C.

The polyvinyl sulfonic acid is produced by radical polymerization using an azo initiator.

A defined amount of vinylphosphonic acid monomer, preferred manufacturer Clariant (purity min. 90%) in a semi-open system with the addition of 1% wt of an azo initiator, preferably 2,2-azobis (isobutyric acid amidine) dihydrochloride from the manufacturer

Aldrich, reacted with warming. The mixture is first heated to a temperature of 60 ° C. for 30 minutes and then to a temperature of 80 ° C. for a further 30 minutes. After this time, the reaction should be completed, which is indicated by the absence of bubbles. The molecular weight of the PVPA produced by radical polymerization was determined using a standard purchased, preferably PVPA from the company

PSS (Mainz, Germany), (polyvinylsulfonic acid, Mw = 20,000 g / mol according to the manufacturer's specification) and gel permeation chromatography with an element of water and acetonitrile with the addition of NaN0 ₃ . The intensities measured for individual elution volumes are evaluated using a pull line based on Pullulan. The system used consists of a pump from Bischoff, a column from PSS

(Mainz) of the Suprema 100 type (pore sizes 1e3 to 3e3) and an infrared detector Shrodex RI-71. Measurements were made at a column temperature of T = 35 ° C, a sample concentration of c = 3.5 mg / l (injection volume 100μl) at a flow of 1 ml / min. The molecular weight of the commercial PVPA was determined in this way to Mw = 33100 g / mol (Mn = 22550g / mol) and the PVPA produced by free-radical polymerization to Mw = 26600 g / mol (Mn = 16800g / mol). Manufacture of the membrane-electrode unit: The electrodes are placed on one side of the membrane and pressed at a temperature in the range of 100 - 2180 ° C.

Polarization measurement: The measurement is carried out in a single fuel cell (50 cm ² active area) with hydrogen (24.1 L / h) as anode gas and air as cathode gas (99.3 L / h). The

Reaction gases are not humidified. Curve D in Example 3 shows a polarization curve at 160 ° C. The fuel cell was then cooled to 80 ° C. and curve E was recorded after 24 hours. The fuel cell was then heated again to 160 ° C. and curve F was recorded after another 24 hours. Example 3 shows a significant line improvement in comparison to example 1, that is to say a power of 120 mW / cm ^{2 is} achieved at 160 ° C. and 0.6 V. At 80 ° C and 0.6 V, a cell output of 36 mW / cm ^{2 is} achieved. Due to the good binding of the ionomer in the catalyst layer, example 3 makes it clear that the membrane electrode unit produced in this way is stable in the temperature cycle. This property can be seen by comparing curves D and F.

Claims

claims:

1. Proton-conducting polymer membrane coated with a catalyst layer, the polymer membrane containing polymers comprising phosphonic acid groups which can be obtained by polymerizing monomers comprising phosphonic acid groups, characterized in that the catalyst layer contains phosphonic acid groups comprising ionomers which are obtainable by polymerizing monomers comprising phosphonic acid groups.

2. Polymer membrane according to claim 1, characterized in that the membrane contains at least 7 wt .-% polymers comprising phosphonic acid groups.

3. Polymer membrane according to claim 1 or 2, characterized in that at least one catalyst layer comprises at least 3 wt .-% phosphorus.

4. Polymer membrane according to one of the preceding claims, characterized in that for the preparation of the polymers comprising phosphonic acid groups and / or ionomers comprising phosphonic acid groups, a monomer of the formula comprising phosphonic acid groups

+ - R— (P0 ₃ Z ₂ ) _x ^ where

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 being halogen, -OH, COOZ, -CN, NZ ₂ may be substituted, Z is independently hydrogen, C1-C15-alkyl group, C1-C15-alkoxy group, ethyleneoxy group or C5-C20-aryl or heteroaryl group, where the above radicals may in turn 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

wherein

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 denotes hydrogen, C1-C15-alkyl group, C1-C15-alkoxy group, ethyleneoxy group or C5-C20-aryl or heteroaryl group, where the above radicals in turn can be substituted by halogen, -OH, -CN, and x is an integer 1, 2, 3, 4, 5, 6, 7, 8, 9 or 10 and / or of the formula R- (P0 ₃ Z ₂ ) _x = <A. wherein

A represents a group of the formulas COOR2, CN, CONR22, OR2 and / or R2, in which R2 denotes hydrogen, a C1-C15-alkyl group, C1-C15-alkoxy group, ethyleneoxy group or C5-C20-aryl or heteroaryl group, the above radicals in turn may be substituted with halogen, -OH, COOZ, -CN, NZ2 R is 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, where the above radicals may in turn be substituted by halogen, -OH, COOZ, -CN, NZ, Z independently of one another is hydrogen, C1-C15-alkyl group, C1-C15-alkoxy group, ethyleneoxy group or C5-C20-aryl or heteroaryl group, where the the above radicals may in turn be substituted with halogen, -OH, -CN, and x is an integer 1, 2, 3, 4, 5, 6, 7, 8, 9 or 10, are used.

5. Polymer membrane according to one of the preceding claims, characterized in that for the preparation of the polymers comprising phosphonic acid groups and / or ionomers comprising phosphonic acid groups, a monomer of the formula comprising sulfonic acid groups wherein

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 being halogen, -OH, COOZ, -CN, NZ ₂ may be substituted, Z is independently hydrogen, 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, -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 wherein

Z independently of one another denotes hydrogen, C1-C15-alkyl group, C1-C15-alkoxy group, ethyleneoxy group or C5-C20-aryl or heteroaryl group, where the above radicals in turn can be substituted by halogen, -OH, -CN, and x is an integer 1, 2, 3, 4, 5, 6, 7, 8, 9 or 10 and / or of the formula R- (see above 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, where the above radicals in turn can be substituted with halogen, -OH, COOZ, -CN, NZ ₂ R is 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, where the above radicals can in turn be substituted with halogen, -OH, COOZ, -CN, NZ ₂ ,

Z independently of one another denotes hydrogen, C1-C15-alkyl group, C1-C15-alkoxy group, ethyleneoxy group or C5-C20-aryl or heteroaryl group, where the above radicals in turn can be substituted by halogen, -OH, -CN, and x is an integer 1, 2, 3, 4, 5, 6, 7, 8, 9 or 10 means can be used.

6. Polymer membrane according to one of the preceding claims, characterized in that the ionomer has a molecular weight in the range from 300 to 100,000 g / mol.

7. Polymer membrane according to one of the preceding claims, characterized in that the ionomer has a polydispersity M _w / M _n in the range from 3 to 10.

8. Polymer membrane according to one of the preceding claims, characterized in that the membrane comprises at least one polymer (B) which is different from the polymer comprising phosphonic acid groups.

9. Polymer membrane according to one of the preceding claims, characterized in that the polymers comprising phosphonic acid groups are crosslinked thermally, photochemically, chemically and / or electrochemically.

10. The polymer membrane according to claim 9, characterized in that crosslinking monomers are used to produce the polymers comprising phosphonic acid groups.

11. Polymer membrane according to one of the preceding claims, characterized in that the polymer membrane has a thickness in the range of 20 and 4000 microns.

12. Polymer membrane according to claim 8, characterized in that the catalyst layer has a thickness in the range of 1-1000μm.

13. The polymer membrane according to claim 12, characterized in that the catalyst layer comprises a catalyst, the active particles of which have a size in the range of 1-200 nm.

14. Polymer membrane according to one of the preceding claims, characterized in that the polymer membrane comprises 0.1-10 mg / cm ^{2 of} a catalytically active substance.

15. The polymer membrane according to claim 14, characterized in that the catalytically active substance comprises particles comprising platinum, palladium, gold, rhodium, iridium and / or

Contain ruthenium.

16. The polymer membrane according to claim 15, characterized in that the catalyst comprises particles containing carbon.

17. A method for producing a polymer membrane according to any one of claims 1 to 16, comprising the steps A) producing a composition comprising monomers comprising phosphonic acid groups, B) applying a layer using the composition according to Step A) on a support, C) polymerizing the in the flat structure obtainable according to step B) existing monomers comprising phosphonic acid groups, D) applying at least one catalyst layer to the membrane formed in step B) and / or in step C).

18. A method for producing a polymer membrane according to any one of claims 1 to 16, comprising the steps I) swelling a polymer film with a liquid containing monomers comprising phosphonic acid groups, II) polymerizing at least a portion of the monomers comprising phosphonic acid groups in step I) in the polymer film was introduced and III) applying at least one catalyst layer to the membrane formed in step II).

19. The method according to claim 17 or 18, characterized in that the

Catalyst layer is applied using a powder process.

20. The method according to claim 17 or 18, characterized in that the catalyst layer is applied by a method in which a catalyst suspension is used.

21. The method according to any one of claims 20, characterized in that the catalyst suspension contains at least one organic, non-polar solvent.

22. The method according to any one of claims 19 to 21, characterized in that in

Step D) the catalyst layer is applied by a process in which a coating containing a catalyst is applied to a support and then the coating containing a catalyst on the support is transferred to the membrane.

23. The method according to claim 22, characterized in that the transfer of the coating containing a catalyst is carried out by hot pressing.

24. The method according to claim 17 or 18, characterized in that the catalyst layer applied to the membrane is connected to a gas diffusion layer.

25. membrane electrode assembly containing at least one membrane according to one or more of claims 1 to 16.

26. Fuel cell containing one or more membrane electrode units according to

Claim 25.