Multilayer electrolyte membrane

Translation of description of equivalent WO 03092090 A2

Multilayer electrolyte membrane

description

The present invention relates to a proton-conducting multi-layered

Electrolyte membrane, a process for their preparation and a fuel cell containing such a membrane.

A fuel cell usually comprises an electrolyte and two electrodes separated by the electrolyte. In the case of a fuel cell is one of the two

Electrodes, a fuel such as hydrogen gas, and the other electrode, an oxidizing agent such as oxygen gas is supplied and thereby the chemical energy of the fuel oxidation is converted into electrical energy.

The electrolyte is permeable to hydrogen ions, ie permeable protons, but not to reactive gases such as hydrogen gas and oxygen gas.

A fuel cell generally comprises a plurality of individual cells called MEE^'s (membrane electrode assembly), which each contain an electrolyte and two electrodes separated by the electrolyte.

As the electrolyte for the fuel cell are solids such as polymer electrolyte membranes or liquids such as phosphoric acid. Recently, polymer electrolyte membranes have attracted as electrolytes for fuel cells attention. In principle, one can distinguish between 2 categories of polymer membranes.

The first category encompasses cation-exchange membranes comprising a polymer framework containing covalently bound acid groups, preferably sulfonic acid. The sulfonic acid group is release of a hydrogen in an anion, and therefore conducts protons. The mobility of the

Proton and thus the proton conductivity is linked directly to the water content. The membrane dries out, for example, resulted in a high temperature, so the conductivity of the membrane and consequently the performance of the fuel cell drops drastically. The operating temperatures of fuel cells containing such cation is thus limited to the boiling point of water. So we used as materials for polymer electrolyte membranes for example, perfluorosulfonic. The perfluorosulfonic acid polymer (such as Nation) generally comprises a perfluorinated hydrocarbon on, such as a copolymer of tetrafluoroethylene and trifluorovinyl, and attached thereto Side chain with a sulfonic acid as a side chain having a sulfonic acid group bound to a perfluoroalkylene.

The moistening of the fuels constitutes a major technical challenge for the use of polymer electrolyte membrane fuel cell (PEMFC), in which are conventional, sulfonated membranes such as Nafion used.

The second category, polymer electrolyte membranes have been developed with complexes of basic polymers and strong acids. Thus W096 / 13872 and the corresponding US-PS 5,525,436 describes a process for preparing a proton-conducting polymer electrolyte membranes, in which a basic polymer such as polybenzimidazole, with a strong acid, such as phosphoric acid, sulfuric acid, etc., treated.

Such a fuel cell in which such a polymer electrolyte membrane is used has the advantage that it can be operated without humidification and at temperatures of 100 ° C or above.

In J. Electrochem. Soc, vol 142, no. 7, 1995, pp L121-L123 describes the doping of a polybenzimidazole in phosphoric acid.

to achieve the required proton conductivity - - used mineral acid (usually concentrated phosphoric acid) used either after molding, or alternatively the basic polymer membrane directly from polyphosphoric as described in German Patent Application No. 10117686.4, No. In the known prior art basic polymer membranes which is.. 10144815.5 and no.

10117687.2 prepared. The polymer acts as a support for the electrolyte consisting of the highly concentrated phosphoric acid or polyphosphoric acid. The polymer membrane fulfills further essential functions, in particular they must have a high mechanical stability and serve as separator for the two fuels mentioned.

Major advantages of such a phosphoric acid doped membrane is the fact that this system can be operated at temperatures above 100 ° C without otherwise necessary moistening of the fuels. This is the ability of phosphoric acid protons without additional water by means of the so-called. Grotthus to transport mechanism (K.-D. Kreuer, Chem. Mater. 1996, 8, 610-641).

The possibility of operation at temperatures above 100 ° C in further advantages for the fuel cell system arise. On the one hand, the sensitivity Pt catalyst to gaseous impurities, in particular CO, is greatly reduced. CO is formed as by-product in the reforming of the hydrogen-rich gas from carbon-containing compounds, such as natural gas, methanol or gasoline, or as an intermediate in the direct oxidation of methanol. Typically, the CO content of the fuel at temperatures must

<100 ° C be less than 100 ppm. However, 10000 ppm or more of CO can be tolerated (NJ Bjerrum et. al. Journal of Applied Electrochemistry, 2001.31, 773-779) at temperatures in the range 150-200 °. This leads to significant simplifications of the upstream reforming process and thus to cost reductions for the overall fuel cell system.

A great advantage of fuel cells is the fact that during the electrochemical reaction, the energy of the fuel is directly converted into electrical energy and heat. As reaction product is produced at the cathode water. As a by-product during the electrochemical reaction thus heat is generated. For applications in which only the current for driving electric motors will be used, such as for automotive applications, the heat must be dissipated to avoid overheating of the system. Additional energy-consuming equipment are then necessary for cooling, which reduces the overall electrical efficiency of the fuel cell. For stationary applications such as centralized or decentralized generation of electricity and heat, heat can be used efficiently by existing technologies, such as heat exchangers. To increase the efficiency, high temperatures are desired. If the operating temperature above 100 ° C and is the temperature difference between the ambient temperature and the

Operating large, so it is possible the fuel cell system more efficiently to cool or to use small cooling surfaces and dispense with additional equipment compared to fuel cells that need to be operated on the basis of membrane humidification at below 100 ° C.

In addition to these advantages, such a system to two distinct disadvantages. Phosphoric acid present as an electrolyte which is not permanently bound by ionic interactions to the basic polymer and can be washed out by water. Water is formed as described above in the electrochemical reaction at the cathode. If the operating temperature above 100 ° C as the water for the most part is discharged as steam through the gas diffusion electrode and the acid loss is very low. However, if the operating temperature below 100 ° C, such as startup and shutdown of the cell or in part load operation when a high current yield is sought, so the condensed water formed and may lead to increased leaching of the electrolyte, highly concentrated phosphoric acid.

This can in the above described mode of operation of the fuel cell lead to a continuous loss of conductivity and cell performance, which can reduce the lifetime of the fuel cell.

Another drawback of fuel cells, in which the phosphoric acid acts as the electrolyte, the inhibition of the reduction reaction at the cathode is characterized by a high overvoltage. This results in a low open-circuit potential and relatively low power.

Furthermore (DMFC), the known doped with phosphoric acid membranes can not be used in the so-called direct methanol fuel cell. Such cells are of particular interest, as a methanol-water mixture is used as fuel. If a known membrane based on

used phosphoric acid, the fuel cell fails after quite a short time.

The present invention therefore has the object of providing a polymer electrolyte membrane, wherein the washing of the

Mineral acid is reduced or prevented, and in addition a reduced overvoltage, especially at the cathode comprises. In particular, as to the operating temperature of <0 ° C can be extended up to 200 ° C.

Moreover, it was an object of the present invention a membrane for

Make available, which also has in operation a low permeability to the various fuels, such as hydrogen or methanol, said membrane should also have a low oxygen permeability.

the object of the invention, by a multi-layer membrane system of a doped with mineral acid polymer electrolyte membrane which is at least one side coated with a mineral acid for the barrier layer is achieved. In this configuration, doped with mineral acid membrane essential functions fulfilled as a separator for the fuel and ensuring the mechanical stability. The barrier layer is intended to prevent the loss of the mineral acid and reducing the overvoltage at the cathode.

A polymer electrolyte membrane of the invention has a very low Methanol permeability and is particularly suitable for use in a DMFC. Long-term operation of a fuel cell using a variety of fuels such as hydrogen, natural gas, gasoline, methanol or biomass is possible. Here, the membranes permit a particularly high activity of these fuels. Due to the high temperatures, the methanol oxidation can occur with high activity.

The present invention is therefore a multilayer electrolyte membrane comprising A. one with one or more mineral acids doped planar material, wherein

B. at least one barrier layer comprising at least one of the two faces of said under A. material covered.

The sheet materials according to A. be both basic polymers, mixtures of basic polymers with other polymers, chemically inert

Carrier, preferably ceramic materials, in particular silicon carbide (SiC) as described in US-A-4,017,664 and US-A-4,695,518, are used. These materials are capable of transporting protons after Grotthus mechanism.

As a sheet material, a temperature-stable and chemically inert carrier may be used which is filled for obtaining the proton conductivity with phosphoric acid. As support materials, for example, ceramic materials such as silicon carbide SiC (US Patent 4,017,664 and US Patent No. 4,695,518) or inorganic glasses are suitable. This support may for example be a fabric or a fleece. Further, also be constructed from porous materials of the support.

As a chemically inert carrier, porous organic polymers can be used having an open pore structure. The open pore volume amounts to more than 30% preferably more than 50% and very particularly preferably more than 70%. The glass transition temperature of the organic base polymer of such membranes is higher than the operating temperature of the fuel cell and is preferably at least 150 ° C, preferably at least 160 ° C and most preferably at least 180 ° C. Such membranes find use as

Separation membranes for ultrafiltration, gas separation, pervaporation, nanofiltration, microfiltration or hemodialysis.

Methods for making such membranes are described in HP Hentze, M. Antonietti "Porous polymers and resins" in F. Schuth "Handbook of Porous Solids" p. 1964- 2013 described.

As a chemically inert carrier, organic foams can be produced. These foams can be prepared by the synthesis of the organic

Polymers gases such as C0₂ are released or volatile liquids. A process for preparing organic foams are described in D. Klempner, KC Frisch "Handbook of Polymeric Foams and Foam Technology" and FA Shutov Advances in Polymer Science Volume 73/74, 1985, pages 63-123. As pore formers can also supercritical CO₂ be used.

A particularly more appropriate carrier is a phase separation membrane of polybenzimidazole which can be prepared as described in US 5091087 US 4693824 or US 4666996 or. By cross-linking by the method described in US 4634530, the chemical stability of these membranes against phosphoric acid or polyphosphoric acid can be further improved.

As support materials, expanded polymeric films such as expanded Teflon can furthermore be employed. A process for producing proton-conducting membranes by filling such expanded perfluorinated membrane are described in US 5547551st

As support materials, highly porous thermosets can also be used, which were prepared by chemically induced phase separation. In this method is added to a mixture of several more capable of crosslinking monomers a slightly volatile solvent. In the crosslinking of this solvent is insoluble and forms a heterogeneous polymer. By

Evaporation of the solvent results in a chemically inert, porous thermoset, which can be subsequently impregnated with phosphoric acid or polyphosphoric acid.

A particularly suitable carrier may be made of inorganic materials, for example made of glass or materials that comprise at least one compound of a metal, a semimetal or a misch metal or phosphorous with at least one element of the 3rd to 7th main group. Particularly preferably, the material on at least one oxide of the elements Zr, Ti, AI or Si. The support can be an electrically insulating material, such. B.

Minerals, glasses, plastics, ceramics or natural substances exist. Preferably, the carrier has special woven fabrics, nonwovens or porous materials from high-temperature and high-acid-resistant quartz or glass. The glass preferably contains at least one compound from the group Si0₂, Al₂0₃ or MgO. In a further variant of the base fabric, nonwovens or porous materials from AI₂O₃-, ZrO₂-, Ti0₂-, Si₃N₄Or SiC ceramic. In order to keep the total resistance of the electrolyte membrane small, but has this carrier preferably has a very large porosity and a low thickness of less than 1000 microns, preferably less than 500 microns and most preferably less than 200 .mu.m. Preferably

Carrier is used having woven fibers of glass or quartz, wherein the tissue preferably consist of 11-Tex yarns having 5-50 warp and weft yarns, and preferably 20-28 28-36 warp and weft threads. Very preferably 5,5-Tex yarns having 10-50 warp and weft threads and preferably 20-28 warp and 28 -36 wefts used.

As set forth above support made of woven fabrics, nonwovens or porous materials can be used. Porous materials can are known in particular based on organic or inorganic foams.

Preferred carriers are permeable without barrier for mineral acids. This property can be demonstrated by the examples set out in the attempt to effect blocking. According to a particular aspect of the present invention, at least 5% of a subject present in the flat structure mineral acid is released within 1 hour, if the sheet-like material a large excess of water (at least 100-fold amount, based on the weight of the film) is exposed to the a temperature of 80 ° C.

Depending on the application, the flat structure in accordance with step A) may be stable at high temperatures. High thermal stability means that the carrier at a

Temperature of at least 150 ° C, preferably at least 200 ° C and particularly preferably at least 250 ° C is stable. Stable means that the essential characteristics of the carrier be maintained. Thus, there occurs no change in the mechanical properties or the chemical composition of a upon exposure of the sheet material for at least 1 hour.

The carrier is generally chemically inert. Chemically inert, that a doped with a mineral acid sheet material is resistant. Resistant means that the material is not decomposed by the acid. Thus, the material exhibits after 100 hours of at least 95% of the mechanical properties, having the material at the start of the measurement. This applies, for example, the E-modulus and microhardness.

As with mineral acid doped basic polymer membrane come almost all known polymer membranes in which the protons without additional water, for example by means of so-called Grotthuss mechanism, transported.

is used as basic polymer in the sense of the present invention, a basic

Polymer having at least one nitrogen atom in a repeating unit.

The repeating unit in the basic polymer preferably contains an aromatic ring having at least one nitrogen atom. The aromatic

Ring is preferably a five- or six-membered ring having one to three nitrogen atoms, which may be fused to another ring, in particular another aromatic ring.

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 (XVI II) and / or (XIX) and / or (XX) and / or (XX!) and / or (XXI I)

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Ar are identical or different and are each a tetravalent aromatic or heteroaromatic group which may be mono- or polynuclear, Ar¹ are identical or different and are each a divalent aromatic or heteroaromatic group which may be mono- or polynuclear, Ar² are the same or different and are a divalent or trivalent aromatic or heteroaromatic group which may be mono- or polynuclear, Ar³ are identical or different and are each a trivalent aromatic or heteroaromatic group which may be mononuclear or polynuclear,

Ar⁴ are identical or different and are each a trivalent aromatic or heteroaromatic group which may be mono- or polynuclear, Ar⁵ are identical or different and are each a tetravalent aromatic or heteroaromatic group which may be mono- or polynuclear, Ar⁶ are identical or different and are each a divalent aromatic or heteroaromatic group which may be mono- or polynuclear, Ar⁷ are identical or different and are each a divalent aromatic or heteroaromatic group which may be mono- or polynuclear, Ar^8th are identical or different and are each a trivalent aromatic or heteroaromatic group which may be mononuclear or polynuclear,

Ar⁹ are identical or different and are each a divalent or trivalent or tetravalent aromatic or heteroaromatic group which may be mono- or polynuclear, Ar¹⁰ are identical or different and, for a two- or trivalent aromatic or heteroaromatic group which may be mononuclear or polynuclear,

Ar¹¹ are identical or different and are each a divalent aromatic or heteroaromatic group which may be mono- or polynuclear, X is the same or different and is oxygen, sulfur or

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

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

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

According to the invention preferred aromatic or heteroaromatic groups derived from benzene, naphthalene, biphenyl, diphenyl ether, diphenylmethane, diphenyldimethylmethane, bisphenone, diphenyl sulfone, thiophene, furan, pyrrole, thiazole, oxazole, imidazole, isothiazole, isoxazole, pyrazole, 1,3,4-oxadiazole , 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-triazol, 1, 2,4-oxadiazole, 1,2,4-thiadiazole, 1, 2,4-triazole, 1,2,3-triazole, 1, 2,3,4-tetrazol, 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, Chinoiin, 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, anthracene, benzopyrrole, Benzooxathiadiazol,

Benzooxadiazol, benzopyridine, benzopyrazine, Benzopyrazidin, benzopyrimidine, benzotriazine, indolizine, Pyridopyridin, imidazopyrimidine, Pyrazinopyrimidin, carbazole, Aciridin, phenazine, benzoquinoline, phenoxazine, phenothiazine, acridizine, benzopteridine, phenanthroline and phenanthrene from which can be optionally substituted.

The substitution pattern of Ar¹, Ar⁴, Ar⁶, Ar⁷, Ar^8th, Ar⁹, Ar¹⁰, Ar¹¹ any, in the case of phenylene for example, Ar¹, Ar⁴, Ar⁶, Ar⁷, Ar^8th, Ar⁹, Ar¹⁰, Ar¹¹ ortho-, meta- and para-phenylene. Particularly preferred groups are derived from benzene and biphenylene, which may also be substituted, from.

Preferred alkyl groups are lower alkyl groups having 1 to 4 carbon atoms, such as, for example, 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 may be substituted.

Preferred substituents are halogen atoms such., Fluorine, amino groups, hydroxy groups or lower alkyl groups such as. For example, methyl or ethyl groups.

Polyazoles with repeating units of formula (I) in which the radicals X within a recurring unit are identical.

The Polyazoles may in principle also have different recurring units which differ, for example, in their radical X..

Preferably, however, it has only identical radicals X in a recurring unit.

Further preferred polyazole polymers are polyimidazoles, polybenzthiazoles, Polybenzoxazoles, polyoxadiazoles, Polyquinoxalines, polythiadiazoles, poly (pyridines), poly (pyrimidines), and poly (tetraazapyrenes).

In a further embodiment of the present invention, the polymer comprising recurring azole units is a copolymer or a blend containing at least two units of the formula (I) to (XXII), which differ from each other. The polymers can be block copolymers (diblock, triblock), random copolymers, periodic copolymers and / or alternating polymers.

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

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

In the present invention, polymers containing recurring benzimidazole units are preferred. Some examples of extremely advantageous

Polymers containing recurring benzimidazole units are represented by the following formulas:

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wherein n and m is an integer greater than or equal to 10, preferably greater than or equal 100th

Further preferred polyazole polymers are polyimidazoles, Polybenzimidazoletherketon, polybenzthiazoles, polybenzoxazoles, polytriazoles, polyoxadiazoles, polythiadiazoles, polypyrazoles, Polyquinoxalines, poly (pyridines), poly (pyrimidines), and poly (tetraazapyrenes).

Preferred Polyazoles are characterized by a high molecular weight. This is especially true for the polybenzimidazoles. Measured as intrinsic viscosity, this is in the range of 0.3 to 10 dl / g, preferably 1 to 5 dl / g.

Particular preference is Celazole. Celanese. The properties of the polymer film and polymer membrane can be described 10129458.1 be improved by screening the starting polymer, as described in German Patent Application No...

The polymer film used for doping based on basic polymers may comprise further additions of fillers and / or auxiliaries. In addition, the polymer film can have further modifications, for example by cross-linking as described in German patent application no. 10110752.8 or in WO 00/44816. In a preferred embodiment, used for doping the polymer film of a basic polymer and at least one blend component additionally contains a crosslinking agent as described in German Patent Application Nos. 10140147.7. An important advantage of such a system is the fact that higher degrees of doping and thus higher conductivity with sufficient mechanical stability of the membrane can be achieved.

In addition to the above basic polymers can also be used a blend with another polymer of one or more basic polymers. The blend component essentially has the task of improving the mechanical properties and reduce the material cost. A preferred blend component polyether as described in German patent application no. 10052242.4 is described.

Among the preferred polymers which can be used as Blenkomponente, include polyolefins, such as poly (cloropren), polyacetylene, polyphenylene, poly (p-xylylene), Polyarylmethylen, Polyarmethylen, polystyrene, polymethylstyrene, polyvinyl alcohol, polyvinyl acetate, polyvinyl ether, polyvinyl amine, poly (N-vinylacetamide), polyvinyl imidazole, polyvinyl carbazole, polyvinyl pyrrolidone, polyvinyl pyridine, polyvinyl chloride, polyvinylidene chloride, polytetrafluoroethylene,

Polyhexafluoropropylene, copolymers of PTFE with hexafluoropropylene, with perfluoropropyl, with Trifluoronitrosomethan with Sulfonylfluoridvinylether with carbalkoxy perfluoroalkoxy, polychlorotrifluoroethylene, polyvinylidene fluoride, polyacroleine, polyacrylamide, polyacrylonitrile, polycyanoacrylates, Polymethacrylimide, Cycloolefinic copolymers, in particular of norbornene;

Polymers with C-O bonds in the backbone, for example polyacetal, polyoxymethylene, polyether, polypropylene, polyepichlorohydrin, polytetrahydrofuran, polyphenylene oxide, polyether, polyester, especially Polyhydroxyessigsäure, polyethylene terephthalate, polybutylene terephthalate, Polyhydroxybenzoat, polylactic acid, polypivalolactone, polycaprolactone,

Polymalonsäure, polycarbonate;

Polymers having C-S bonds in the backbone, for example polysulfide, polyphenylene sulfide, polyether sulfone; Polymeric C-S bonds in the main chain, for example Polyimines, polyisocyanides, polyaniline, polyamides, polyhydrazides

Polyurethanes, polyimides, Polyazoles, polyazines; Liquid crystalline polymers, in particular Vectra and

Inorganic polymers, for example polysilanes, polycarbosilanes, polysiloxanes, polysilicic acid, polysilicates, silicones, polyphosphazenes and polythiazyl.

For use in fuel cells with a continuous use temperature above 100 ° C., such blend polymers are preferred which have a glass transition temperature or Vicat softening temperature VST / A / 50 of at least 100 ° C, preferably at least 150 ° C and very particularly preferably have at least 180 ° C.

Here are polysulphones with a Vicat softening temperature VST / A / 50 of

180 ° C preferably to 230 ° C.

The preferred polymers include polysulphones, in particular polysulphone having

Aromatic groups in the main chain. In a particular aspect of the present invention, preferred polysulphones and polyethersulfones a melt volume rate MVR 300 / 21.6 less than or equal 40 cm³/ 10 min, especially less than or equal to 30 cm³/ 10 min and particularly preferably less than or equal to 20 cm³/ 10 min measured according to ISO 1133 on.

To further improve the performance characteristics, the sheet material fillers, in particular proton-conducting fillers, exhibit.

Non-limiting examples of proton-conducting fillers are

Sulfates such as: CsHSO₄, Fe (SO₄)₂, (NH₄)₃H (SO₄)₂, LiHSO₄, NaHS0₄, KHSO₄.

RbSO_4l LiN₂H₅SO₄, NH₄HSO₄, Phosphates such as Zr₃(PO₄)₄, Zr (HPO₄)₂, HZR₂(PO₄)₃, UO₂PO₄.3H₂O, H_8thU0₂PO₄.

Ce (HPO₄)₂, Ti (HPO₄)₂, KH₂PO₄, Close₂PO₄, LiH₂P0₄, NH₄H₂P0₄, CsH₂PO₄, CaHPO₄, MgHPO₄, HSBP₂0_8th, HSb₃P₂0₁₄, H₅Sb₅P₂θ₂O,

Polyacid as H₃PW₁₂O₄₀.nH₂θ (n = 21-29), H₃SiW₁₂0₄o.nH₂O (n = 21-29), H_xW0₃, HSbWO₆, H₃PMo₁₂O₄₀, H₂Sb₄On, HTaWO₆, HNbO₃, HTiNbO₅, HTiTaO₅, HSbTeO₆, H₅Ti₄O₉, HSBO₃, H₂MoO₄ Selenite and Arsenide as (NH₄)₃H (SeO)₂, UO₂AsO, (NH₄)₃H (SeO₄)₂, KH₂AsO₄, Cs₃H (SeO₄)₂, Rb₃H (SeO₄)₂.

Oxides such as Al₂0₃, Sb₂O₅, ThO₂, SnO₂, ZrO₂, MoO₃

Silicates such as zeolites, zeolites (NH +), sheet silicates, framework silicates, H-natrolites, H-mordenites, NH₄-Analcine, NH₄-Sodalite, NH -Gallate, H- Montmorillonite acids such hci0₄, SbF₅

Fillers such as carbides, in particular SiC, Si₃N₄, Fibers, in particular glass fibers, glass powders and / or polymer fibers, preferably based on polyazoles.

These additives can in the proton-conducting polymer membrane in usual

contain amounts, but the positive properties such as high conductivity, long service life and high mechanical stability of the membrane by adding excessive amounts of additives should not be impaired too much. Generally, the membrane comprises more than 80 wt .-%, preferably at most 50 wt .-% and particularly preferably at most 20 wt .-% of additives.

To prepare the polymer film, the polymer components are first as in the above-cited applications, for example DE no. 10110752.8 or

WO 00/44816, dissolved or suspended described and then used to produce the polymer films. Furthermore, the polymer films according to EN no. 10052237.8 can be produced continuously.

Alternatively, the film formation in accordance with the Japanese in the application

No. Hei 10-125560 described occur.

Here, the solution is poured into a cylinder having a cylindrical inner surface, and then the cylinder is rotated. At the same time is allowed to evaporate the solvent by the centrifugal force caused by the rotation; wherein on the inner surface of the barrel forms a cylindrical polymer film having a substantially uniform thickness.

With this process, the basic polymer can be formed with a uniform matrix.

This method described in Japanese Patent Application Hei 10-125560 is also part of the present description.

Subsequently, the solvent is removed. This can slow the specialist well-known methods to happen, for example, by drying.

Subsequently, the film of basic polymer or polymer blend with a strong acid, preferably a mineral acid impregnated, or doped, can be treated with the film as described in the German patent application Nos. 10109829.4 before. This variant is advantageous to interactions of the residual solvent exclude the barrier layer.

For this purpose, the film is immersed in a basic polymer or polymer blend in a strong acid, so that the film is impregnated with the strong acid and the proton-conducting membrane. For this purpose, the basic polymer is usually immersed in a highly concentrated strong acid at a temperature of at least 35 ° C over a period of several minutes to several hours.

The strong acid used mineral acid, especially phosphoric acid and / or sulfuric acid.

In the context of the present specification is meant by "phosphoric acid" polyphosphoric acid (H_n+ 2Pn0₃n + ι (n&gt; 1) usually have a content calculated as P₂O₅ (Acidimetrically) of at least 83%), phosphorous acid (H₃PO₃)

Orthophosphoric acid (H₃PO₄), Pyrophosphoric (H₄P₂O), triphosphoric (H₅P₃O₁₀) And metaphosphoric. The phosphoric acid, particularly orthophosphoric acid, preferably having a concentration of at least 80 percent by weight, more preferably a concentration of at least 85 weight percent, even more preferably a concentration of at least 87

Weight percent, and most preferably a concentration of at least 89 percent by weight. The reason for this is the fact that the basic polymer can be impregnated with an increasing concentration of the strong acid having a larger number of strong acid molecules.

The obtained polymer electrolyte membrane, namely the complex of the basic polymer and the strong acid is proton-conducting. After the doping, the degree of doping is expressed as moles of acid per repeat unit greater than 6, preferably greater than 8 and most preferably greater than 9th

Instead of the produced by classical methods polymer membranes based on basic polymers can also use the polyazole polymer membranes such as in the German Patent Application Nos. 10117686.4, 10144815.5, 10117687.2 describes, used. Such provided with at least one barrier layer, polymer electrolyte membranes are also

Object of the present invention.

Accordingly, sheet materials of the invention can be obtained by a process comprising the steps of i) preparing a mixture comprising

Polyphosphoric acid, at least a polyazole and / or at least one or more compounds which are suitable under the action of heat in step ii) to form polyazole, ii) heating the mixture obtainable according to step i) under inert gas

Temperatures of up to 400 ° C, iii) applying a layer using the mixture according to step i) and / or ii) on a support, iv) treating the membrane formed in step iii). For this purpose, the mixture from step i) one or more compounds can be added, which are suitable under the action of heat in accordance with step ii) to form polyazole.

For this purpose mixtures are suitable for the one or more aromatic and / or heteroaromatic tetraamino compounds and one or more aromatic and / or heteroaromatic carboxylic acids or their derivatives, comprising at least two acid groups per carboxylic acid monomer. Furthermore, one or more aromatic and / or heteroaromatic diamino to

Preparation polyazole be used.

The aromatic and heteroaromatic tetraamino compounds include 3,3 ', 4,4'-tetraaminobiphenyl, 2,3,5,6-tetraaminopyridine, 1, 2,4,5-tetraaminobenzene, 3,3', 4,4'-Tetraaminodiphenylsulfon, 3,3 ', 4,4^!-

Tetraaminodiphenyl, 3,3 ', 4,4'-tetraaminobenzophenone, 3,3', 4,4' tetraaminodiphenylmethane and 3,3 ', 4,4'-tetraaminodiphenyldimethylmethane as well as their salts, especially their mono-, di-, tri- - and tetrahydrochloride derivatives. Of these, 2,3,5,6-tetraaminopyridine and 1, 2,4,5-tetraaminobenzene are 3,3 ', 4,4'-tetraaminobiphenyl, particularly preferred.

Further, the mixture A) include aromatic and / or heteroaromatic carboxylic acids. These are dicarboxylic acids and tricarboxylic acids and tetracarboxylic acids or their esters or their anhydrides or their acid halides, especially acid halides thereof, and / or

Bromides. Preferably, the aromatic dicarboxylic acids to terephthalic acid, phthalic acid, 5-hydroxyisophthalic, 4- hydroxyisophthalic, 2-hydroxyterephthalic, 5-aminoisophthalic, 5-NN Dimethylaminoisophthalsäure, 5-N, N-Diethylaminoisophthalsäure, 2,5-dihydroxyterephthalic , 2,6-Dihydroxyisophthalsäure, 4,6-

Dihydroxyisophthalsäure, 2,3-Dihydroxyphthalsäure, 2,4-Dihydroxyphthalsäure. 3,4 Dihydroxyphthalsäure, 3-Fluorophthalsäure, 5-Fluoroisophthalsäure, 2- Fluoroterphthalsäure, Tetrafluorophthalsäure, Tetrafluoroisophthalsäure, Tetrafluoroterephthalsäure, 1, 4-naphthalenedicarboxylic acid, 1, 5- naphthalene dicarboxylic acid, 2,6-naphthalenedicarboxylic acid, 2,7-

Naphthalenedicarboxylic acid, diphenic acid, 1, 8-dihydroxynaphthalene-3,6-dicarboxylic acid, DiphenyIether-4,4'-dicarboxylic acid, benzophenone-4,4'-dicarboxylic acid, diphenyl sulfone 4,4'-dicarboxylic acid, biphenyl-4,4'- dicarboxylic acid, 4-Trifluoromethylphthalsäure, 2,2-bis (4-carboxyphenyl) hexafluoropropane, 4,4'-stilbenedicarboxylic acid, 4- Carboxycinnamic, or their C1-C20-alkyl esters or C5-C12 aryl esters or their acid anhydrides or their acid chlorides.

The heteroaromatic carboxylic acids is heteroaromatic dicarboxylic acids and tricarboxylic acids and tetracarboxylic acids or their esters or their anhydrides. As heteroaromatic carboxylic acids are aromatic systems in which contain at least one nitrogen, oxygen, sulfur or phosphorus atom in the aromatic. Preferably is pyridine-2,5-dicarboxylic acid, pyridine-3,5-dicarboxylic acid, pyridine-2,6-dicarboxylic acid, pyridine-2,4-dicarboxylic acid, 4-phenyl-2,5-pyridinedicarboxylic acid, 3,5 -Pyrazoldicarbonsäure, 2.6 -

Pyrimidindicarbonsäure, 2,5-pyrazinedicarboxylic acid, 2,4,6-pyridinetricarboxylic acid, benzimidazole-5,6-dicarboxylic acid. As well as their C1-C20-alkyl esters or C5-C12 aryl esters or their acid anhydrides or their acid chlorides.

Further, the mixture i) aromatic and heteroaromatic

Diamino included. These include among others diaminobenzoic, 4-phenoxycarbonyl-3, '4'-diaminodiphenyl and the mono- and dihydrochloride.

The mixture prepared in step i) preferably comprises at least

0.5 wt .-%, particularly 1 to 30 wt .-% and particularly preferably 2 to 15 wt .-% of monomers for the preparation of polyazoles.

According to a further aspect of the present invention, the mixture prepared in step A) comprises compounds which are covered by the action of heat

Step B) are suitable for the formation of polyazoles, said compounds by reacting one or more aromatic and / or heteroaromatic tetraamino compounds with one or more aromatic and / or heteroaromatic carboxylic acids or derivatives thereof which per at least two acid groups carboxylic acid monomer contain, or of one or more aromatic and / or heteroaromatic diaminocarboxylic acids in the melt at temperatures of up to 400 ° C, especially up to 350 ° C, preferably up to 280 ° C are available. The selected for the preparation of these prepolymers compounds have been described above.

Furthermore, monomers are used which comprise covalently bound acid groups for the preparation of polyazoles. These include aromatic and heteroaromatic dicarboxylic acids or derivatives thereof, the have at least one phosphonic acid, such as 2,5-dicarboxyphenylphosphonic, 2,3-dicarboxyphenylphosphonic 3,4- and 3,5-dicarboxyphenylphosphonic dicarboxyphenylphosphonic; aromatic and heteroaromatic dicarboxylic acids or derivatives thereof, which have at least one sulfonic acid, in particular 2,5-

Dicarboxyphenylsulphonic acid, 2,3-dicarboxyphenylsulphonic acid 3,4-dicarboxyphenylsulphonic acid and 3,5-dicarboxyphenylsulphonic acid; aromatic and heteroaromatic diamino comprising at least one phosphonic acid, for example, 2,3-diamino-5- carboxyphenylphosphonsäure, 2,3-Diamino-6-carboxyphenylphosphonsäure and

3,4-diamino-6-carboxyphenylphosphonsäure; aromatic and heteroaromatic diaminocarboxylic acids, comprising at least one sulfonic acid group, for example, 2,3-diamino-5-carboxyphenylsulfonsäure, 2,3-diamino-6- carboxyphenylsulfonsäure and 3,4-diamino-6-carboxyphenylsulfonsäure.

A polyazole membrane produced in accordance with the procedure set forth above may contain detailed above optional components. These include in particular blend polymers and fillers. Blend polymers can od in accordance with step i) and / are present it dissolved mixing step ii) obtained, inter alia, dispersed or suspended. Here, the weight ratio of polyazole to

Polymer (B) is preferably in the range from 0.1 to 50, preferably from 0.2 to 20, more preferably from 1 to 10, without this constituting a restriction. If the polyazole is formed only in step ii), the weight ratio can be obtained by calculation from the weight of the monomers to form the polyazole, the released during condensation

Compounds, for example water to be considered.

To further improve the performance properties of the membrane additionally fillers, in particular proton-conducting fillers, and additional acids can be added. The addition may be, for example, in step i)

Step ii) and / or step iii) take place. Furthermore, these additives, when they are present in liquid form, also be added after the polymerization according to step iv). These additives have been previously described.

The polyphosphoric acid used in step i) is a commercial polyphosphoric acid as this example from Riedel-de Haen text. The polyphosphoric H_{n + 2}Pn0_3nown + ι (n&gt; 1) usually have an assay calculated as P₂0₅ (Acidimetrically) of at least 83%. Instead of a solution of the monomers can also be a dispersion / suspension is produced. The mixture obtained in step i) according to step ii) to a temperature of up to 400 ° C, in particular 350 ° C, preferably up to 280 ° C, in particular 100 ° C to 250 ° C and particularly preferably in the range of 200 ° C. to 250.degree. Here, an inert gas, for example nitrogen or a noble gas, such as neon, argon, is used.

The mixture prepared in step i) and / or step ii) may additionally contain organic solvent. This may affect the workability positive. For example, the rheology of the solution can be improved so that they can be more easily extruded or lolled.

The formation of the sheet-like structure according to step iii) is carried out by means of measures known per se (pouring, spraying, knife coating, extrusion) which are known from the prior art for polymer film production. As carriers are all under the

Conditions suitable referred to as inert carriers. These supports include in particular polyethylene terephthalate (PET), polytetrafluoroethylene (PTFE), polyhexafluoropropylene, copolymers of PTFE with hexafluoropropylene, polyimides, polyphenylene sulfides (PPS), and polypropylene (PP). Furthermore, the formation of the membrane directly on a

Barrier provided electrode done.

The thickness of the sheet-like structure according to step iii) is preferably 10-4000 .mu.m, preferably 15-3500 .mu.m, in particular 20-3000 .mu.m, more preferably between 30 and 1500μm and most preferably between 50 and about 1200 microns.

The treatment of the membrane in step iv) is carried out in particular at temperatures in the range of 0 ° C and 150 ° C, preferably at temperatures between 10 ° C and 120 ° C, in particular between room temperature (20 ° C) and 90 ° C, in the presence from

Moisture or water and / or steam. The treatment is preferably carried out under normal pressure, but can also take place under the action of pressure. It is important that the treatment is done in the presence of sufficient moisture whereby the polyphosphoric acid present by partial hydrolysis to form low molecular weight polyphosphoric acid and / or

Phosphoric acid to solidify the membrane contributes.

The partial hydrolysis of the polyphosphoric acid in step iv) leads to strengthening of the membrane and to a decrease in the layer thickness and training a membrane. The solidified membrane generally has a thickness from 15 to 3000 microns, preferably 20 and 2000 .mu.m, in particular 20 to 1500 microns.

The upper temperature limit of the treatment according to step iv) is generally

150 ° C. With extremely short action of moisture, for example from overheated steam, this steam can also be hotter than 150 ° C. Essential for the upper temperature limit is the duration of the treatment.

The partial hydrolysis (step iv) may also carried out in chambers at the defined moisture action, the hydrolysis can be specifically controlled. The humidity of the temperature or saturation of the contacting environment, for example gases such as air, nitrogen, carbon dioxide or other suitable gases, or steam can be specifically adjusted. The duration of treatment depends on the parameters selected above.

Furthermore, the treatment time of the thickness of the membrane is dependent.

In general, the treatment time ranges from a few seconds to minutes, for example under the action of superheated steam, or up to whole days, for example, in air at room temperature and low relative humidity is. Preferably, the treatment time is between 10 seconds and 300 hours, in particular 1 minute to 200 hours.

If the partial hydrolysis at room temperature (20 ° C) with ambient air having a relative humidity of 40-80%, the treatment time between 1 and 200 hours.

The membrane obtained in step iv) can be made self-supporting, ie it can be detached from the support without any damage and then optionally further processed.

The treatment according to step iv) results in a cure of the coating. If the membrane is formed directly on the electrode, the treatment in step D) is carried out until the coating has sufficient hardness to a

Membrane-electrode assembly are pressed can. Sufficient hardness is given when a membrane treated accordingly is self-supporting. In many cases, however, a lower hardness. The DIN 50539 (microhardness measurement) certain hardness is generally at least 1 mN / mm², Preferably at least 5 mN / mm² and most preferably at least 50 mN / mm²Without this constituting a restriction.

On the degree of hydrolysis, ie the time, temperature and ambient humidity, the concentration and the amount of phosphoric acid and thus the conductivity of the polymer membrane according to the invention adjustable. According to the invention, the concentration of phosphoric acid is reported as mole of acid per mole of repeating unit of the polymer. In the present invention, a concentration (mol of phosphoric acid per repeating unit of the formula (III), ie polybenzimidazole) between 10 and 80, especially between 12 and 60, are preferred. Such high degrees of doping (concentrations) are very difficult or impossible to obtain by doping polyazoles with commercially available ortho-phosphoric acid.

The thickness of the barrier layer of a multilayer inventive

Polymer electrolyte membrane is generally not critical as long as these layers have a sufficient barrier effect against mineral acids. The blocking action can be found on the washed out by water quantity of mineral acid. In a particular aspect of the present invention occurs within an hour, more than 10%, preferably at most 5% of the mineral acid in the aqueous phase. These values ​​relate to the weight of mineral acid or of the weight of the sheet-like material with the mineral acid, whereby for calculating the value of each of the surface is taken into consideration, which is in contact with water.

According to a particular embodiment of the present invention, the thickness of the barrier layer is less than 10 microns, preferably 1 to 8 microns and more preferably 2 to 6 microns. An advantage of such barrier layers is their relatively low resistance.

Proper another embodiment of the present invention, the thickness of the barrier layer is at least 10 microns, preferably, the thickness in the range of 10 .mu.m to 30 .mu.m. An advantage of such barrier layers is their particularly high barrier effect and their stability.

The thickness of the barrier layer can be measured by scanning electron microscopy (SEM). This results in the thickness of the barrier layer over the average of the thickness, which is obtained via the ratio of length to area of ​​the barrier layer. In the barrier layer according to the invention is preferably a cation exchange material. This cation exchange material allows the transport of protons but not of anions such as phosphate anions. For better adhesion can at the interface between

Polymer electrolyte membrane and cation exchange also block copolymers of these components consisting of the polymer electrolyte membrane and the cation exchange membrane.

This barrier layer may take the form of a separate sheet, preferably self-supporting, connected to the doped polymer membrane and the doped polymer blend membrane (laminated) be.

Furthermore, the barrier layer can be done also by applying a layer on the doped membrane and / or the electrode. For example, use a

Mixture comprising a cation exchange material or a precursor material are applied to the membrane and / or the electrode. Suitable methods include casting, spraying, knife coating and / or extrusion.

The barrier layer may further have a gradient. For example, to vary the concentration of acid groups. Such gradient can for example the (energy X-ray diffraction (EDX), spatially resolved Raman spectroscopy and space-resolved infrared spectroscopy to measure.

In a variant of the present invention may - in so far as present, the cation exchange material in the form of a self-supporting film - this as a separate foil in an MEA between the doped polymer electrolyte membrane and the catalyst layer or the electrode to be installed (on both sides).

It has been found that it is advantageous if the barrier layer is on the cathode side of the polymer electrolyte membrane, because the surge is significantly reduced. However, apart from this embodiment, the barrier layer may be applied on both sides.

As stated above, the cation exchange material subject to any significant restriction. Preferably those materials which are cation exchange capacity less than 0.9 meq / g, in particular less than 0.8 meq / g. The cation exchange capacity is in accordance with a particular aspect of the present invention is at least 0.1 meq / g, more preferably 0.2 meq / g, without this constituting a restriction. Preferably, such materials are their Flächenquellung in water at 80 ° C of less than 20%, in particular less than 10%. Preferred materials which are

Conductivity at 80 ° C in moistened state is less than 0.06 S / cm, in particular less than 0.05 S / cm.

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

At high current density and temperatures above 100 ° C the moistening of this thin layer by the product water produced at the cathode takes place. When using hydrogen-rich reformate gas existing in the reformate moisture for humidification of the barrier layer is sufficient. Thus, the system does not require additional humidification at temperatures above 100 ° C and high electrical performance. However, sometimes it may be necessary to

Fuels at the start or at low temperatures or at low current densities to moisturize addition. Preferably, the force applied to the cathode side barrier layer is thicker than the barrier layer located on the anode side.

The barrier layer preferably includes a cation exchange material. Here, in principle be used all cation exchange materials which can be processed into membranes. These are preferably organic polymers having covalently bound acid groups. Particularly suitable acid groups include carboxylic acid, sulfonic and

Phosphonic acid groups, sulfonic acid groups in particular polymers are preferred. Process for sulfonating polymers are described in F. Kucera et. al. Polymer Engineering and Science1988, Vol. 38, No. 5, 783-792 described. The cation exchange materials are preferably used as barrier layers can not be used alone as the cation-exchange membranes in fuel cells, in general, because their proton conductivity and swelling is too low and the mechanical stability due to the low thickness can not be ensured. The cation described in the prior art, however, were specifically developed with a high ion exchange capacity, high swelling, high proton conductivity and sufficient thickness to ensure a sole use as a polymer electrolyte membrane in an MEU.

The most important types of cation exchange membranes are listed that have become commercially important in fuel cells for use.

The most important representative is the perfluorosulfonic Nation^® (US-A-3692569). This polymer can be described as brought into solution are then used as ionomer in US-A-4453991 and. Cation can also be obtained by filling a porous support material with such an ionomer. As support material is given to expanded Teflon preferred (US Patent No. 5,635,041). Another perfluorinated cation can as described in US-A-

5422411 described are prepared by copolymerization of trifluorostyrene and sulfonyl trifluorostyrene. Composite membranes consisting of a porous support material, in particular expanded Teflon, filled with ionomers consisting of such sulfonyl Trifluorostyrol- copolymers are described in US Pat 5,834,523th

US-A-6110616 describes copolymers of butadiene and styrene and their subsequent sulfonation for the preparation of cation exchange membranes for fuel cells.

Another class of partially fluorinated cation can by

Radiation grafting and subsequent sulfonation are produced. In this case, a grafting reaction is preferably carried out with styrene as DE-A-19844645 described in a previously irradiated polymer film in EP-A-667 983 or. In a subsequent sulfonation is then carried out the sulfonation of the side chains. Simultaneously with the grafting can also be a cross-linking thus carried out and the mechanical properties are altered.

In addition to the above membranes, a further class of non-fluorinated membranes by sulfonation of high temperature-stable thermoplastics has been developed. Thus, membranes made from sulfonated polyether ketones (DE-A-4219077, WO96 / 01177), sulfonated polysulfone (J. Membr. Sci. 83 (1993) p.211) or sulfonated polyphenylene sulfide (DE-A-19527435) is known. Ionomers prepared from sulfonated polyether ketones are described in WO 00/15691.

Furthermore, acid-base blend membranes are known, which are described in DE-A-19817374 or WO 01/18894 prepared by mixing sulfonated polymers and basic polymers.

To adjust the ion exchange capacity for optimum retention acid, a known from the prior art cation-exchange membrane with a polymer that comprises no or only a small amount of acid groups, are mixed. Suitable polymers have been set forth as a blending component above, where high-temperature stable polymers are particularly preferred. The preparation and properties of cation exchange membranes comprising sulphonated PEK and a) polysulfones (DE-A-4,422,158), b) aromatic polyamides (DE-A-42445264) or c) polybenzimidazole (DE-A-19851498) are described. Alternatively, the sulfonation can be selected so that a low sulphonation develops (DE-A-19959289).

In addition to the mentioned in the prior art cation based on organic polymers, the cation exchange material may also consisting of organic-inorganic composite materials. Such composite materials can preferably be prepared by the sol-gel method. while mixtures of metal alkoxides are particularly connects siloxanes as starting compounds. These mixtures are distinguished by a high purity of the starting materials and a low viscosity. This liquid precursor mixtures can be applied to very thin and evenly covering layers on a substrate by means of known technologies such as spraying or spin coating. By hydrolysis and condensation of

Precursor mixtures can be generated on the surface of then-resistant films. To adjust the proton conductivity, the organic radicals of the alkoxides acidic groups, in particular sulfonic acid group.

The Precursorgemische may also functional organic groups include a cross-linking of the layer formed, and thus bring about a further reduction in the permeability of the mineral acid and the fuels. The crosslinking can be effected both thermally and by irradiation (e-, UN IR, ΝIR) or by means of a starter after the film formation. The manufacture of such a composite material is described for example in Electrochimica Acta Volume 37, 1992, pages 1615-1618. Furthermore, such composite materials from GW Scherer, CJ Brinker, sol-gel Science, Academic Press, Boston, 1990, known.

A group of preferred compounds is represented by formula (A) represented

(RO)_y(R¹)_zMX_a (A) wherein y is 1, 2 or 3, preferably 3, z is 0 or 1, preferably 0, and a is 1 or 2, preferably 1, and

R and R¹ is independently hydrogen, a linear or branched alkyl, alkenyl, cycloalkyl or cycloalkenyl radical having from 1 to 20, preferably 1 to 8 carbon atoms, or an aromatic or heteroaromatic group having 5 to 20 carbon atoms, M is an element selected from Si, Zr, Ti , preferably Si and

X is independently a linear or branched alkylene or cycloalkylene group having from 1 to 20, preferably 1 to 8 carbon atoms, or an aromatic or heteroaromatic group having 5 to 20 carbon atoms, having at least one sulfonic or phosphonic acid, represent.

The radicals R, R¹ and X can further substituents, in particular halogens such as fluorine atoms have. Preferably, the group X represents a radical of the formula Ph-SO₃H, CnH₂n-Sθ₃H, C_nF_2n-SO₃Represent H, where Ph is phenyl and n is an integer from 1 represents to 20th Preferably, the group R represents a radical of the formula C_nH_2n+ Ι represents with n = 1 to. 3

Preferred compounds are particularly hydroxysilyl, the known per se and are described for example in DE 100 61 920, EP 0771 589, EP 0765 897 and EP 0582879.

Preferred hydroxysilyl can be represented by the formulas B or C

[(RO)_y(R²)_zSi {R -SO₃-}_a] χM^{x +} (B)

[(RO)_y(R²)_zSi {R¹-O_b-P (O_cR₃0₂-}_a]_xM^{x +} (C) wherein M is a H⁺ a NH₄⁺ or a metal cation having a valency of x equals 1 to 4 indicating in which y = 1-3, z = 0 to 2 and a = 1 to 3, with the proviso that y + z = 4 - a, in the b and c = 0 or 1, R and R² are identical or different and Methyl, ethyl, propyl, butyl or H, respectively, and in which R³ equal to M or a methyl, ethyl, propyl, butyl radical, and wherein R¹ a linear or branched alkyl or alkylene group having 1 to 12 C

Atoms, a cycloalkyl group having 5 to 8 C-atoms or a unit of the general formulas

<img id="imgf000036_0001" he="44" wi="122" file="imgf000036_0001.tif" img-format="tif" img-content="drawing" orientation="portrait" inline="no" /> indicating in which n or m is a number from 0 to 6th

Preferred hydroxysilyl or their precursors (derivatives) are Trihydroxysilylethylsulfonsäure, Trihydroxysilylphenylsulfonsäure, trihydroxysilylpropylsulfonic, Trihydroxysilylpropylmethylphosphonsäure, or

Dihydroxysilylpropylsulfondisäure or salts thereof.

The structure of the cation exchange material, by appropriate choice of tri (network formers), di- (chain-) and Monohydroxysilylsäure (chain link) and can be adjusted precisely by enclosing further Solbildner. Suitable

Solbildner are z. B. the hydrolyzed precursor of SiO₂, AI₂O₃, P₂O₅, Ti0₂ or ZrO₂, The compounds preferably used include tetramethoxysilane, tetraethoxysilane, triethoxy, Trimethoxyvinylsilane, Triethoxypropenylsilan and Trimethoxypropenylsilan.

As substrates for the deposition of the barrier layer, optionally, a film of the basic polymer, a mineral acid doped polymer electrolyte membrane or a surface coated with noble metal catalyst electrode can be used.

In a variant of the invention the barrier layer is deposited on an electrode.

According to a particular aspect of the present invention, the material from which the barrier layer is produced, chemically compatible with the planar doped with at least one mineral acid material so that a good adhesion of the

Barrier layer is obtained on the sheet material. When using a polyazole especially organic cation exchanger are used accordingly, on which the Polyazoles set to have a high liability. These include in particular sulfonated polysulfones, polyether ketones, and other polymers which have aromatic groups in the main chain. When using inorganic materials, a high adhesion to the organic or inorganic carriers by selecting suitable functional groups can be obtained.

When using inorganic sheet materials are accordingly preferably the detailed above inorganic layers, which can be obtained for example by hydrolysis of hydroxysilyl used.

The multilayer electrolyte membranes of the invention show, taking into account the barrier layer an excellent conductivity and

Performance.

The proton conductivity of the electrolyte membranes is preferred laminated at temperatures of 120 ° C, preferably at least 0.1 S / cm, in particular at least 0.11 S / cm, more preferably at least 0.12 S / cm.

This conductivity is achieved even at temperatures of 80 ° C.

Here, a membrane of the invention can be moistened at low temperatures. For this example, the used as a power source connection, for example hydrogen, are provided with a proportion of water. In many cases, however, the water formed by the reaction in order to achieve wetting.

The specific conductivity is measured by means of impedance spectroscopy in a 4-pole arrangement in potentiostatic mode and using platinum electrodes

(Wire, 0.25 mm diameter). The distance between the current-collecting electrodes is 2 cm. The spectrum obtained is with a simple model consisting of a parallel arrangement of an ohmic^'rule resistance and a capacitor evaluated. The sample cross-section of the phosphoric acid doped membrane is measured immediately prior to sample mounting. To measure the temperature dependence, the measurement cell is placed in an oven to the desired temperature and controlled via a positioned in the immediate vicinity of the sample of Pt-100 resistance thermometer. After reaching the temperature, the sample will be before the start of measurement 10 minutes this Temperature maintained.

The polymer membrane of the invention has improved material properties compared to the previously known doped polymer membranes. Due to the low methanol permeability, the multi-layer membranes can be used in particular in direct methanol fuel cells.

The crossover current density in operation with 0.5 M methanol solution and 90 ° C in a liquid direct methanol fuel cell is preferably less than 100 mA / cm², In particular less than 70 mA / cm² more preferably less than 50 mA / cm² and most preferably less than 10 mA cm², The crossover current density in operation with a 2 M methanol solution and 160 ° C. in a gaseous direct methanol fuel cell is preferably less than 100 mA / cm², In particular less than 50 mA / cm² most preferably less than 10 mA / cm²,

To determine the crossover current density (cross over current density), the amount of carbon dioxide that is released at the cathode, by means of a CO₂Sensor measured. From the resulting value of the C0₂Quantity is, as described by P. Zelenay, SC Thomas, S. Gottesfeld in S. Gottesfeld, TF filler "Proton Conducting

Membrane Fuel Cells II "ECS Proc. Vol. 98-27 S. 300-308 describes calculates the crossover current density.

The invention further relates to the preferred use of the multilayer electrolyte membrane of the invention or of the coated

Electrode in a membrane electrode assembly (MEA) for a fuel cell.

The MEA contains at least one multilayer electrolyte membrane according to the invention and two electrodes between which the multilayer electrolyte membrane is sandwiched.

The electrodes each have a catalytically active layer and a gas diffusion layer for supplying a reaction gas to the catalytically active layer. The gas diffusion layer is porous, so that the reactive gas can pass.

The inventive multilayer electrolyte membrane can be used as the electrolyte membrane in electrochemical processes. In addition, one can, the electrolyte membrane as well as a precursor for a MEA with one or two catalytically active layers can be produced. Furthermore, one can prepare the MEA also by fixing the gas diffusion layer on the precursor.

Another object of the present invention is a fuel cell system with a plurality of different MEUs of which contain at least one novel multi-layer membrane.

An inventive membrane-electrode assembly exhibits a surprisingly high power density. According to a particular embodiment, preferred membrane-electrode assemblies, a current density of at least 0.1 A / cm², Preferably 0.2 Acm², More preferably 0.3 A / cm², This current density is in the operation with pure hydrogen at the anode and air (about 20 vol .-% oxygen, 80 vol .-% of nitrogen) at the cathode at atmospheric pressure (1013 mbar absolute, with open cell output) and 0.6V a cell voltage. In this case, particularly high temperatures in the range of 150-200 ° C, preferably 160-180 ° C, are used in particular of 170 ° C.

The power densities mentioned above can be achieved on both sides, even at low stoichiometry of the fuel gases. In 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 second

Examples 1 to 6

Producing cation:

For the preparation of cation exchange membranes following stock solutions were prepared. a) 10 wt% PES (Ultrason E 7020 P) in NMP b) 17 wt% Spek (sulfonation geräkelt mixed together 50.3%) in NMP solutions were as shown in Table 1 given conditions and with the squeegee frame (50 microns). Subsequently, the films were dried in an oven at 120 ° C 11h. The thickness of the films produced are 20-25 microns. The polymers used for the preparation of the membrane are set forth in Table 1 Table 1

<img id="imgf000040_0001" he="54" wi="162" file="imgf000040_0001.tif" img-format="tif" img-content="table" orientation="portrait" inline="yes" />

The specific conductivity is measured by means of impedance spectroscopy in a 4-pole arrangement in potentiostatic mode and using platinum electrodes (wire, 0.25 mm diameter). The distance between the current-collecting electrodes is 2 cm. The spectrum obtained is evaluated using a simple model consisting of a parallel arrangement of an ohmic resistance and a capacitor. The specimen cross section of sulfonated PEK membranes and sulphonated PEK blend membranes is measured by swelling in water at 80 ° C for 1 h prior to sample mounting. To measure the temperature dependence and to moisten the measuring cell is flushed with tempered water. the cell is held for 30 minutes at 80 ° C and then started the conductivity measurement Before the test. The cooling takes place at 1 K / min. Before the start of each new measurement, then 10 minutes is kept at the desired temperature.

In Table 2, the result of the conductivity measurements of sulfonated PEK membranes and sulfonated PEK blend membranes is shown.

Table 2: Conductivity values ​​of sulfonated PEK membranes and sulphonated PEK blend membranes (proportion of PES blend component in weight percent) for use as a barrier for phosphoric

<img id="imgf000040_0002" he="55" wi="139" file="imgf000040_0002.tif" img-format="tif" img-content="table" orientation="portrait" inline="yes" /> The conductivity and barrier effect of the cation exchange membrane for phosphoric depend heavily on the content of acid groups expressed by the so-called. Ion exchange capacity (IEC).

To measure the IEC the sulfonated polymer or sulfonated blend membrane is first treated 2 hours in boiling water. Subsequently, excess water is dabbed off and the sample dried for 15 hours at 160 ° C in a vacuum drying cabinet at p &lt;1 mbar. Then, the dry weight of the membrane is determined. The dried polymer is then dissolved in DMSO at 80 ° C for 1h. The solution is then titrated with 0.1 M NaOH. The ion exchange capacity (IEC) is then calculated from the consumption of acid to reach the equivalence point and the dry weight.

To determine the swelling behavior, the sulfonated membranes or

swollen blend membranes for 2 hours at 80 ° C and the area increase.

Table 3 shows the ion exchange capacity of sulfonated PEK membrane (0% PES) and blend membranes of sulphonated PEK and different contents of PES are shown.

Table 3: ion exchange capacity and swelling at 80 ° C of sulfonated PEK membrane (0% PES) and blend membranes from sulfonated PEK and various levels of PES

T = 80 ° C

IEC (meg / g) Swelling (%)

Example 1 2.06 156

Example 2 1.71 124.6

Example 3 1, 34 61, 6

Example 4 1.03 41 7

Example 5 0.8 8.6

Example 6 0.59 2

To measure the blocking effect of the cation on the example of phosphoric acid doped membranes The procedure is as follows: First, a cation exchange membrane is punched out with a diameter of 7 cm in the dry state. This membrane is then immersed in 300 ml of water and the pH change is measured as a function of time. These membranes can lead to a drop in pH due to residues of free acid in the sulfonation reaction due to the chosen material. Since each membrane contains different amounts of acid groups, this blank value must be measured for each membrane.

Subsequently, such a membrane is again clamped in the measurement apparatus and placed on a membrane doped with acid. To dope a PB1 film with an initial thickness of 50 microns is placed at room temperature in 85% phosphoric acid for at least 72 hours. Of these acid-doped membrane a piece is punched with a diameter of 3 cm and placed directly on the cation. The sandwich thus formed is then placed in a 300 ml water-filled beaker, and the change in pH for 15 hours at room temperature (20 ° C). A schematic structure of the measuring device is shown in FIG. 1 The result thus obtained is shown graphically in FIG. 2

The negative values ​​in Figure 3 after correction of the blank value can be explained by the loss of acid from. the cation exchange membrane (blank) is even greater than the passage of phosphoric acid by the cation exchange membrane.

4 shows the measurement of the amount of acid which has permeated through the barrier layer, and which has been retained by the barrier layer, clearly confirm.

The results demonstrate that the use of cation exchange materials as a barrier layer results in a surprisingly significant reduction in the release of mineral acid.

From the results obtained shows that, surprisingly, have preferred inventive cation in moistened state at 80 ° C, a conductivity &lt;0.06 S / cm, in particular &lt;0.05 S / cm.

Preferred cation-exchange membranes according to the invention have a value of IEC of less than 0.9 meq / g. The swelling of preferred cation exchange membranes is less than 20% at 80 ° C. Surprise was found that the use of according to the invention ie, with a barrier layer provided membrane having an ion exchange capacity of less than 0.9 meq / g and a swelling in water of less than 10% at 80 ° C leads to a particularly significant reduction of the phosphoric passage and the acid concentration is not within 15 hours via 0.0005 mol / l increases.

Step Example 7

Preparation of an ultrathin cation exchange membrane as a barrier layer on the membrane surface: Preparation PBI film:

From a 15 wt% strength polybenzimidazole (PBI) solution in DMAc was a 50 .mu.m

geräkelt thick film and dried in an oven at 120 ° C 12h.

Preparation of spray solution:

There was a 10 wt% solution of PES (Ultrason E 7020) and spotting (sulfonation 50.3%) prepared in DMAc, wherein the weight ratio of

PES was to spotting 60:40. coating:

For coating a glass plate was placed on a hot plate and heated to 150 ° C. After reaching the temperature of PBI film was placed on the glass plate. Once the film plan refers to the glass plate, was a

Metal mask placed. The spray solution was sprayed several times by means of an airbrush on the film surface. The solvent was evaporated between each spraying. Thereafter, the metal mask of the sprayed area was removed, cut. The coating thickness was 4-5 microns.

The coated polyazole is clamped shown with the coated side up as shown in Figure 1 and then immersed in a filled with 100 ml of water beaker. In this configuration, the bottom is in contact with water, while 0.5 ml of phosphoric acid is applied to the opposite side.

The change in pH was observed over a period of 50 hours. For comparison, a polyazole was subjected to the same test without a barrier layer.

The results obtained are shown in Figure 5, wherein the effectiveness of the thin barrier layer is visible.