WO2003069708A2

WO2003069708A2 - Electrolyte membrane comprising a diffusion barrier, membrane electrode units containing said membranes, method for the production thereof and specific uses of the same

Info

Publication number: WO2003069708A2
Application number: PCT/EP2003/000169
Authority: WO
Inventors: Volker Hennige; Christian Hying; Gerhard HÖRPEL
Original assignee: Creavis Gesellschaft Für Technologie Und Innovation Mbh
Priority date: 2002-02-13
Filing date: 2003-01-10
Publication date: 2003-08-21
Also published as: WO2003069708A3; DE10205852A1; AU2003205588A1; TW200304245A

Abstract

The invention relates to a proton conducting membrane, to a method for the production thereof and to the use of the same. The inventive membrane represents a novel class of proton conducting membranes, which can be used, in particular, in fuel cells. The disadvantage associated with conventional proton conducting membranes, which are based on a porous, flexible ceramic membrane, as disclosed in PCT/EP98/05939, said membrane being infiltrated by a proton conducting material, which is subsequently hardened, is that the electrolyte is washed out of membranes of this type by water or methanol. The inventive membranes comprise a coating that is insoluble in water and methanol as the diffusion barrier, said coating preventing the electrolyte from being washed out by the water or methanol. Said electrolyte membranes can be configured in a flexible manner and can be used without problems as the membrane in a fuel cell.

Description

Electrolyte membrane with diffusion barrier, these comprehensive membrane electrode units, manufacturing processes and special uses

The present invention relates to special proton-conductive, flexible electrolyte membranes for a fuel cell that have an outer proton-conductive coating that is insoluble in water and methanol on both sides, to methods for producing these electrolyte membranes, and to a flexible membrane electrode assembly for a fuel cell that comprises an electrolyte membrane according to the invention. The present invention further relates to special intermediates in the manufacture of the membrane electrode assembly and special uses of the electrolyte membrane and membrane electrode assembly.

Fuel cells contain electrolyte membranes which, on the one hand, ensure the proton exchange between the half-cell reactions and, on the other hand, prevent a short circuit between the half-cell reactions.

So-called membrane electrode units (MEAs), which consist of an ion-conducting electrolyte membrane and the optionally catalytically active electrodes (anode and cathode) applied to it, are conventionally used in fuel cells.

Electrolyte membranes made from organic polymers which are modified with acidic groups, such as Nation® (DuPont, EP 0 956 604), sulfonated polyether ketones (Höchst, EP 0 574 791), are known from the prior art as proton-exchanging membranes (PEMs) for fuel cells. , sulfonated hydrocarbons (Dais, EP 1 049 724) or the phosphoric acid-containing polybenzimidazole membranes (Celanese, WO 99/04445).

However, organic polymers have the disadvantage that the conductivity depends on the water content of the membranes. Therefore, these membranes must be swollen in water before use in the fuel cell and although water is constantly being formed on the cathode, additional water must be added from the outside during operation of the membrane to prevent drying out or a decrease in proton conductivity. Typically, organic polymer membranes in a fuel cell must both and operated on the cathode side in an atmosphere saturated with water vapor.

At elevated operating temperatures, electrolyte membranes made of organic polymers cannot be used, because at temperatures of more than about 100 ° C the water content in the membrane at atmospheric pressure can no longer be guaranteed. The use of such membranes in a reformate or direct methanol fuel cell is therefore generally not possible. In addition, the polymer membranes show a too high permeability for methanol when used in a direct methanol fuel cell. The so-called cross-over of methanol on the cathode side means that only low power densities can be achieved in the direct methanol fuel cell.

Therefore, conventional organic polymer membranes for use in a reformate or direct methanol fuel cell are not practical in spite of the high proton conductivity.

Inorganic proton conductors are e.g. B. from "Proton Conductors", P. Colomban, Cambridge University Press, 1992 known. However, for the purposes of a fuel cell, proton-conductive zirconium phosphates known from EP 0 838 258 show conductivities which are too low. On the other hand, in the case of defect perovskites, a usable proton conductivity is only achieved at temperatures which are above the operating temperatures of a fuel cell that occur in practice. Known proton-conducting MHSO ₄ salts are readily soluble in water and are therefore only of limited use for fuel cell applications in which water is formed in the fuel cell reaction (WO 00/45447).

Known inorganic proton-conducting materials can also not be produced in the form of thin membrane foils, which are required to provide a low total resistance of the cell. Low sheet resistances and high power densities of a fuel cell for technical applications in automobile construction are therefore not possible with the known materials.

WO 99/62620 proposes an ion-conducting, permeable composite material as well its use as an electrolyte membrane of an MEA in a fuel cell. The electrolyte membrane from the prior art consists of a metal network which is coated with a porous ceramic material to which a proton-conducting material has been applied. This electrolyte membrane has a proton conductivity superior to an organic Nafion membrane at temperatures of more than 80 ° C. However, the prior art does not contain an embodiment of a fuel cell in which such an electrolyte membrane was used.

It has now been found that the electrolyte membrane known from WO 99/62620 has serious disadvantages with regard to the usability of an MEA containing this electrolyte membrane in practice and with regard to the production process which is required for the provision of such MEAs. Due to these disadvantages, the MEA known from WO 99/62620 is unsuitable for use in a fuel cell in practice. It has been shown that the known electrolyte membranes have good proton conductivity at elevated temperatures, but that, under practical conditions of use, short circuits occur in a fuel cell that render the electrolyte membranes unusable. The use of glass supports is not excluded, but due to the low acid stability of glasses, long-term stability under the strongly acidic conditions in a fuel cell is problematic, especially with regard to long-term stability with a required service life of more than 5000 hours in a fuel cell on board a vehicle , Furthermore, the electrolyte membranes known from WO 99/62620 are problematic with regard to the adhesion of the ceramic material to the metal carrier, so that the ceramic layer has to be expected to detach from the metal network in the event of long standing times.

Against this background, the applicant has developed membranes which have no metal support (DE 100 61 920, DE 101 15 927, DE 101 15 928). Although these membranes are excellent proton-conducting materials, in practice it has been shown that the use of these membranes in the fuel cell leads to a significant loss in the power density of the cell over time. The reason for this is the gradual "bleeding" of the electrolyte. Although the known membranes are only operated at low humidities, the bleeding is inevitable, because in the fuel cell on the cathode there is always water. This water leaches out of the electrolyte and a drop in the pH value can be observed in downstream gas scrubbers. As the electrolyte bleeds out, the conductivity of the membrane and thus the performance of the cell decrease.

In particular, the use of such membranes in direct methanol fuel cells, in which a liquid water / methanol mixture is added as the fuel on the anode side, is not possible.

In the above-mentioned applications (DE 100 61 920, DE 101 15 927, DE 101 15 928), sulfonic and phosphonic acids which are immobilized are also used as proton-conducting materials. Because of the proton conductivity required for use in fuel cells, the largest possible ratio of acid groups to network formers is required in these applications. These insufficiently immobilized acids are washed out during operation of the fuel cell due to the insufficient fixation in the material. The mineral acids also mentioned in these applications are not chemically bound to the inorganic network at all. Proton-conducting membranes made from them lose power much faster in the fuel cell than the silylsulfonic or phosphonic acids due to the loss of electrolytes.

The aim of the present invention is now to optimize the existing proton-conducting membranes so that they withstand the requirements in the fuel cell. In particular, the use of proton-conducting membranes in direct methanol fuel cells, in which a liquid water / methanol mixture is added as fuel on the anode side, is to be made possible.

It was therefore an object of the present invention to provide membranes which are suitable for use in fuel cells in practice and in particular (i) have a high proton conductivity with significantly reduced atmospheric humidity compared to polymer membranes, (ii) enables a low overall resistance of a membrane electrode assembly,

(iii) has mechanical properties, such as tensile strength and flexibility, which are suitable for use under extreme conditions, such as occur during the operation of a vehicle, are suitable, (iv) elevated operating temperatures of more than 80 ° C tolerated, (v) regardless of the proton-conductive material, can be produced in membrane thicknesses that are at least as thin as those that can be achieved with conventional nafϊon membranes,

(vi) short circuits and especially in a direct methanol fuel cell cross-over

Avoids problems, (vii) is easy to manufacture, and (viii) avoids electrolyte bleeding.

It has surprisingly been found that this object can be achieved by applying a very thin coating with a proton-conducting material, which acts as a diffusion barrier and is not soluble in water and methanol, to an electrolyte membrane. Since this layer can be made very thin, the proton conductivity of the membrane itself is only slightly influenced, although the coating has a significantly lower proton conductivity than the actual membrane.

The present invention therefore relates to the reaction components of the fuel cell reaction, impermeable, proton-conductive, electrolyte membranes for a fuel cell, comprising a material-permeable composite material made of a support which comprises perforated, non-conductive, glass or ceramic, the composite material being permeated with a proton-conductive material which is suitable selectively conduct protons through the membrane, which are characterized in that the electrolyte membranes have an outer proton-conductive coating on at least one side, which is insoluble in water and methanol.

The present invention also relates to a method for producing an electrolyte membrane according to the invention, which is characterized in that it comprises the following steps:

(a) Infiltration of a permeable composite material from a flexible, perforated, non-conductive, glass or ceramic carrier with a first Mixture containing

(al) an immobilizable hydroxysilylalkyl acid of sulfur or phosphorus or a salt thereof; or (a2) a Bronsted acid and / or an immobilizable hydroxysilylalkyl acid of sulfur or phosphorus or a salt thereof and a sol which is a precursor for

Comprises oxides of aluminum, silicon, titanium, zirconium, and / or phosphorus, (b) solidifying the mixture infiltrating the composite in order to create a material penetrating the composite, preferably a gel, which is capable of selectively guiding protons through the membrane, so that a proton-conducting membrane is obtained and

(c) subsequently applying a second mixture to at least one side of the electrolyte membrane obtained and solidifying it to form a proton-conducting coating which is insoluble in water and methanol, and an electrolyte membrane produced by this process.

The present invention also relates to a preferably flexible membrane electrode unit for a fuel cell, with an electrically conductive anode and cathode layer, each on opposite sides of a proton-conductive electrolyte membrane for a fuel cell, which is impermeable to the reaction components of the fuel cell reaction, in particular according to one of claims 1 to 30, are provided, the electrolyte membrane comprising a permeable composite material which is permeated with a proton-conductive material which is suitable for selectively guiding protons through the membrane, and which on at least one side, preferably on all sides, particularly preferably on two sides outer proton conductive coating as a diffusion barrier, which is insoluble in water and methanol and wherein the anode layer and the cathode layer are porous and each have a catalyst for the anode and cath ode reaction, a proton conductive component and optionally a catalyst support.

The present invention also relates to a method for producing a membrane electrode unit according to the invention, the method comprising the following steps: (A) Provision of a proton-conductive, flexible electrolyte membrane which is impermeable to the reaction components of the fuel cell reaction, for a fuel cell, in particular an electrolyte membrane according to the invention, the electrolyte membrane having a permeable composite material made of a flexible, breakthrough, non-conductive, glass or ceramic carrier, wherein the

Composite material is interspersed with a proton-conductive material which is suitable for selectively guiding protons through the membrane, and wherein the electrolyte membrane has an outer proton-conductive coating as a diffusion barrier on at least one side, preferably all sides, (B) provision in each case a means for producing an anode layer and a cathode layer, the means in each case comprising: (B1) a condensable component which, after the condensation of the electrode layer

Gives proton conductivity, (B2) a catalyst which catalyzes the anode reaction or the cathode reaction, or a precursor compound of the catalyst,

(B3) optionally a carrier and (B4) optionally a pore former, (C) applying the agents from stage (B) to one side of the electrolyte membrane from stage (A) to form a coating, (D) creating a firm bond between the Coatings and the electrolyte membrane to form a porous, proton-conductive anode layer or cathode layer, wherein the formation of the anode layer and the cathode layer can take place simultaneously or in succession.

The present invention also relates to the use of an electrolyte membrane according to the invention or a membrane electrode assembly according to the invention in a fuel cell or for producing a fuel cell or a fuel cell stack.

Consequently, the present invention relates to fuel cells with an electrolyte membrane according to the invention, fuel cells with a membrane electrode unit according to the invention and mobile or stationary systems with a membrane electrode unit, a fuel cell or a fuel cell stack containing an electrolyte membrane according to the invention or a membrane electrode unit according to the invention.

It has been found that the practical usability of an electrolyte membrane known from the prior art is related to the fact that the electrolyte is leached out of the membrane, in particular by water and / or methanol. The membranes according to the invention have the advantage that they have coatings which are insoluble in water and / or methanol as so-called diffusion barriers which prevent the electrolyte from leaching out. Despite these coatings, the membranes according to the invention are very flexible and can be made very thin.

It has also been found that, surprisingly, an electrolyte membrane which is useful in practice and in particular insensitive to short circuits and cross-over problems can be provided if a non-conductive support comprising glass and / or ceramic is selected as the material for the membrane support.

The electrolyte membrane of the present invention has the advantage that it does not have to be swelled in water to achieve useful conductivity. It is therefore much easier to combine the electrodes and the electrolyte membrane to form a membrane electrode assembly. In particular, it is not necessary to provide a swollen membrane with an electrode layer, as is necessary in the case of a Nafion membrane, in order to prevent the electrode layer from tearing during swelling. Also by the choice of special non-conductive material as a carrier z. B. a solid adhesion of a porous ceramic material to the carrier is possible by choosing an all-ceramic carrier. In a special embodiment, by using only a single ceramic material, phase boundaries between different materials in the composite material according to the invention can be avoided. It is thus possible to provide a composite material in which problems, for example due to different coefficients of thermal expansion of different materials, cannot occur. This enables a stable MEA to be manufactured that can withstand high mechanical loads. Due to the good stability and conductivity, the electrolyte membrane according to the invention can be used in a reformate or direct methanol fuel cell, which has a long service life and a long service life Have power densities even at low water partial pressures and high temperatures.

It is also possible to control the water balance of the new membrane electrode units by adjusting the hydrophobicity / hydrophilicity of the membrane and electrodes. The effect of capillary condensation can also be exploited through the targeted creation of nanopores in the membrane. Flooding of the electrodes by product water or drying out of the membrane at a higher operating temperature or current density can thus be avoided. Furthermore, it is possible to manufacture the electrolyte membranes of the present invention in a membrane thickness regardless of the proton conductive material, which is of the same order of magnitude as that which can be achieved with conventional Nafion membranes. This allows the conductivity and the sheet resistance to be controlled via the membrane thickness in a range which is described for Nafion membranes, but it is now possible to choose from a large number of proton-conductive materials. The decoupling according to the invention of the choice of the proton-conductive material from the achievable layer thickness to create electrolyte membranes for fuel cells with the desired conductivities and surface resistances is unprecedented in the prior art and enables access to tailor-made electrolyte membranes.

The membranes of the invention are gas-tight or impermeable to the reaction components in a fuel cell, such as. B. hydrogen, oxygen, air and / or methanol. For the purposes of the present invention, gas-tight or impermeable to the reaction components is understood to mean that less than 50 liters of hydrogen and less than 25 liters of oxygen per day, bar and square meter pass through the membranes according to the invention and that the membrane's permeability to methanol is significantly less than with commercially available Nafion membranes, which are usually also referred to as impermeable.

The membranes according to the invention, their manufacture and their use are described below by way of example, without the invention being restricted to these embodiments. The proton-conductive electrolyte membrane for a fuel cell, which is impermeable to the reaction components of the fuel cell reaction, comprises a permeable composite material made of a perforated, non-conductive, glass or ceramic carrier, the composite material being permeated with a proton-conductive material which is suitable for selectively protons Conducting the membrane is characterized in that it has an outer proton-conductive coating on at least one side, which is insoluble in water and / or methanol. The membrane according to the invention preferably has the coating on all sides, which usually have contact with the anodes and cathodes, or with the starting materials and / or the secondary products (water) in the fuel cell, the so-called functional sides. Since the electrolyte membrane usually has two functional sides, the electrolyte membrane according to the invention has an outer proton-conductive coating on both sides as a diffusion barrier, which is insoluble in water and methanol. The electrolyte membrane according to the invention can also be flexible. In this embodiment of the electrolyte membrane according to the invention, the permeable composite material must also be flexible.

The electrolyte membrane preferably has an immobilized hydroxysilylalkyl acid of sulfur or phosphorus as the proton-conductive material, and optionally an oxide of aluminum, silicon, titanium, zirconium and / or phosphorus as a network former, and / or a Bronsted acid and an oxide of aluminum, silicon, titanium, zirconium , and / or phosphorus as a network former.

The inventive, for the reaction components of the fuel cell reaction impermeable, proton conductive electrolyte membrane for a fuel cell is, for. B. available through

(a) Infiltration of a permeable composite material comprising a perforated, non-conductive support comprising glass or ceramic and a porous ceramic material with a first mixture

(al) an immobilizable hydroxysilylalkyl acid of sulfur or phosphorus or a salt thereof; or

(a2) a Bronsted acid and / or an immobilizable hydroxysilylalkyl acid of sulfur or phosphorus or a salt thereof and a sol which is a precursor for Includes oxides of aluminum, silicon, titanium, zirconium, and / or phosphorus, (b) solidifying the composite infiltrating mixture to create a composite penetrating material capable of selectively guiding protons through the membrane, and (c) then Applying a second mixture to at least one side of the electrolyte membrane obtained and solidifying it to form a proton-conducting coating which is insoluble in water and methanol. Again, a membrane according to the invention produced in this way has the coating on all sides, which are usually in contact with the anodes and cathodes, or with the starting materials and / or the secondary products (water) in the fuel cell, the so-called

Function pages on.

The proton conductive material of an electrolyte membrane according to the invention preferably comprises a Bronsted acid, an immobilized hydroxysilylalkyl acid of sulfur or phosphorus or a salt thereof. These components give the electrolyte membrane the necessary proton conductivity. The proton-conductive material can optionally contain an oxide of aluminum, silicon, titanium, zirconium and / or phosphorus as a network former. Such an oxide is essential when using a _^ Brönsted acid in order to obtain a stable gel which has elastic and plastic properties. In the event that an immobilized hydroxysilylalkyl acid of sulfur or phosphorus or a salt thereof is present, the additional oxide can be dispensed with, since an SiO ₂ network can form in which the acidic groups via the three remaining OH groups of the Hydroxysilylalkyl acid are condensed. The network can also contain other network-forming oxides such as SiO ₂ , Al ₂ O ₃ , ZrO, or TiO ₂ .

The Bronsted acid can e.g. B. sulfuric acid, phosphoric acid, perchloric acid, nitric acid, hydrochloric acid, sulfurous acid, phosphorous acid and esters thereof and / or a monomeric or polymeric organic acid.

As the hydroxysilylalkyl acid of sulfur or phosphorus, the proton-conducting material in the electrolyte membrane according to the invention preferably has an organosilicon compound of the general formulas [{(RO) _y (R ² ) _z } _a Si {R ¹ -SO ₃ -} _a ] _x M ^{x +} (I) or

[(RO) _y (R ² ) _z Si {R ¹ -O _b -P (O _c R ³ ) O ₂ -} _a ] χM ^{x +} (π), where R ^{1 represents} a linear or branched alkyl or alkylene group with 1 to 12

C atoms, a cycloalkyl group with 5 to 8 C atoms or a unit of the general

formulas

or

where n, m each represents an integer from 0 to 6,

M represents H, NH ₄ or a metal, x = 1 to 4, y = 1 to 3, z = 0 to 2 and a = 1 to 3, with the proviso that y + z = 4 - a, b, c = 0 or 1,

R, R ^{2 are the} same or different and represent methyl, ethyl, propyl, butyl or H and R ^{3 represents} M or a methyl, ethyl, propyl or butyl radical.

The proton-conducting material (gel) in the electrolyte membrane according to the invention particularly preferably has trihydroxysilylpropylsulfonic acid, trihydroxysilylpropylmethylphosphonic acid or dihydroxysilylpropylsulfonedioic acid as hydroxysilylalkyl acid of sulfur or phosphorus. The hydroxysilylalkyl acid of sulfur or phosphorus is preferred with a hydrolyzed compound of phosphorus or a hydrolyzed nitrate, oxynitrate, chloride, oxychloride, carbonate, alcoholate, acetate, acetylacetonate of a metal or semimetal or a hydrolyzed compound obtained from diethylphosphite (DEP), diethylethylphosphonate ( DEEP), titanium propylate, titanium ethylate, tetraethyl orthosilicate (TEOS) or tetramethyl orthosilicate (TMOS), zirconium nitrate, zirconium oxynitrate, zirconium propylate, zirconium acetate, zirconium acetylacetonate, phosphoric acid methyl ester or immobilized with precipitated silica.

It can be advantageous if the proton-conductive material (gel) has ceramic particles from at least one oxide selected from the series Al ₂ O ₃ , SiO ₂ , ZrO ₂ or TiO ₂ . The proportion of ceramic particles which make no contribution to proton conductivity in the gel is preferably less than 40 percent by volume, particularly preferably less than 30 percent by volume and very particularly preferably less than 10 percent by volume. It can be advantageous if the ceramic particles have one or more particle size fractions with particle sizes in the range from 10 to 100 nm and / or from 100 to 1000 nm. Particle fractions with particle sizes of 50 nm to 500 nm are particularly preferred, such as. B. Aerosil 200, Aerosil Ox50 or Aerosil VP 25 (each Degussa AG), or very fine-scaled particles, the z. B. be used directly as a suspension, such as. B. Levasil200E (Bayer AG). However, it should be noted here that the particles used are significantly smaller than the smallest pore diameter of the composite material serving as the carrier. The average particle diameter is typically less than 1/2, preferably less than 1/5 and very particularly preferably less than 1/10 of the average pore diameter of the composite material used.

It can be advantageous if the proton-conducting material (gel) has further proton-conducting substances. Preferred proton-conducting substances are e.g. For example, selected from the titanium phosphates, Titanphosphonaten, Titansulfoarylphosphonate, zirconium phosphates, Zirkoniumphosphonaten, Zirkoniumsulfoarylphosphonate, iso- and heteropoly acids, preferably tungstophosphoric acid or silicotungstic acid, or nano-crystalline metal oxides and Al ₂ O ₃ - ZrO ₂ -, TiO ₂ - or SiO ₂ powder are preferred. These can again (if necessary) in combination with the network formers mentioned Form proton-conducting material (gel). In the case of the phosphates or phosphonates, the Zr-OP or Ti-OP groups are immobilized via a ZrO ₂ or TiO ₂ network.

The electrolyte membrane can have a wide variety of known composite materials as a permeable composite material, in particular ceramic composite materials or composite materials that have a carrier made of ceramic or glass, as they are known for. B. have already been described as microfiltration membranes, such. B. in WO 99/15262.

In addition to the carrier, the composite material can also have a porous ceramic material. According to mercury porosimetry, this porous ceramic material preferably has a porosity of 10% to 60%, preferably of 20% to 50%. This results in porosities for the composite material infiltrated with this ceramic material of up to 45%, typically from 30 to 35%. It can be advantageous if the porous ceramic material has pores with an average diameter of at least 20 nm, preferably of at least 100 nm, very particularly preferably more than 250 nm. The porous ceramic material can in particular be an oxide of one of the elements titanium, zirconium, aluminum and / or silicon.

The carrier must be stable under the operating conditions in a fuel cell. The carrier must therefore be stable with respect to the protons which are passed through the membrane, the proton-conducting material with which the composite material is penetrated and the ceramic material with which the carrier is contacted.

The carrier comprising glass and / or ceramic preferably has fibers or filaments made of glass and / or ceramic. The electrolyte membrane according to the invention particularly preferably has a carrier which comprises fibers and / or filaments with a diameter of 0.5 to 150 μm, preferably 0.5 to 20 μm, and / or threads with a diameter of 5 to 150 μm, preferably 20 up to 70 μm. The carrier can e.g. B. a fabric or a nonwoven. The carrier is preferably a fabric with a mesh size of 5 to 500 μm, preferably 10 to 200 μm, or a nonwoven with a thickness of 5 to 100 μm and preferably 10 to 30 μm. In the event that the carrier is a woven fabric, in particular a glass woven fabric, it is preferably a woven fabric made of 11-Tex yarns with 5-50 warp or weft threads and in particular 20-28 warp and 28-36 weft threads , 5,5-Tex yarns with 10-50 warp or weft threads are particularly preferred, and 20-28 warp and 28-36 weft threads are preferred.

In the case of a ceramic carrier, the ceramic is preferably a ceramic fleece or a ceramic fabric made of refractory ceramic fibers with a predominantly polycrystalline microstructure. A ceramic fleece is preferred over a ceramic fabric because it has a higher porosity and no mesh. If the carrier has ceramic, it is preferably a material which has a proportion greater than 50% by weight of aluminum oxide, silicon carbide, silicon nitride or a zirconium oxide. The carrier preferably has fibers or filaments made of aluminum oxide, which have a ratio of 0 to 30% silicon oxide / aluminum oxide. Fibers containing alumina are preferred. The ceramic from which the carrier is produced preferably has a melting / softening point of greater than 1400 ° C., particularly preferably greater than 1550 ° C.

A carrier comprising glass preferably has glass, in particular ECR, S or (with restriction) also E glass. In addition to the glass, the carrier can also have other components. In particular, the glass substrate as components oxidic coatings, such as. B. A1 ₂ 0 ₃ , SiO ₂ , TiO ₂ or ZrO ₂ coatings of the glass. The oxidic coatings are particularly preferred for types of glass that have low acid stability, such as. B. E-glass. The weight ratio of oxide coating to glass in the carrier is preferably less than 15 to 85, preferably less than 10 to 90 and very particularly preferably less than 5 to 95. In order to achieve good protection of the glass fabric, very dense oxide films must be formed. This can be achieved by using particle-free, polymeric sols based on the corresponding hydrolyzable compounds of Al, Zr, Ti or Si.

An aluminosilicate glass is particularly preferred. The glass preferably contains at least 50% by weight SiO ₂ and optionally at least 5% by weight Al ₂ O ₃ , preferably at least 60% by weight SiO ₂ and optionally at least 10% by weight A1 ₂ 0 ₃ . In the event that the glass contains less than 60% by weight of SiO ₂ , the chemical resistance of the glass is likely to be too low and the carrier will be destroyed under the operating conditions. In the event that less than 10% by weight of Al ₂ O _{3 is present} in the glass, the softening point of the glass may be too low and the industrial manufacture of the membranes according to the invention may therefore become very difficult.

Further elements which can be present in an aluminosilicate glass, silicate glass or borosilicate glass are alkali metals, such as lithium, sodium, potassium, rubidium or cesium, alkaline earth metals, such as magnesium, calcium, strontium or barium and lead, zinc, titanium, arsenic, antimony, Zirconium, iron, lanthanum, cerium, cadmium, or halogens, such as fluorine or chlorine.

A preferred glass composition for a support is as follows: from 64 to 66% by weight SiO ₂ , from 24 to 25% by weight Al ₂ O ₃ , from 9 to 12% by weight MgO and less than 0.2% by weight. -% CaO, Na ₂ O, K ₂ O and / or Fe ₂ O ₃ .

The carrier must be stable both in the course of the production of the electrolyte membrane and under the operating conditions in a fuel cell. Therefore, the glass for the carrier is preferably stable against protons which are passed through the membrane and against the proton-conducting material with which the membrane is permeated. It is therefore particularly preferred if the glass does not contain any acid leachable cations. On the other hand, leachable cations can be present in the glass if the stability of the support does not suffer, if cations are replaced by protons, for example if the glass is suitable for forming a gel layer on the surface which protects the glass support from further attack by the acid ,

It is also possible to use a glass, quartz or quartz glass which has a stability under operating conditions which is not sufficient for practical use (in particular an insufficient acid stability). In this case, the surface of the carrier can be coated with a material that gives the carrier the necessary stability. An acid-resistant coating made of e.g. B. SiO ₂ , α-Al ₂ O ₃ , ZrO ₂ or TiO ₂ can, for example, after a sol-gel process can be provided. A glass fabric (softening point:> 800 ° C.) with the following chemical composition is then available as the material: from 52 to 56% by weight SiO ₂ , from 12 to 16% by weight Al ₂ O ₃ , from 5 to 10 % By weight B ₂ O ₃ , from 16 to 25% by weight CaO, from 0 to 5% by weight MgO, less than 2% by weight Na ₂ O + K ₂ O, less than 1.5% by weight % TiO ₂ and less than 1% by weight Fe ₂ O ₃

The glass from which the carrier is produced preferably has a softening point of greater than 700 ° C., particularly preferably greater than 800 and very particularly preferably greater than 1000 ° C. Preferred carriers have glasses whose weight loss in 10% HC1 after 24 hours is preferably less than 4% by weight and after 168 hours less than 5.5% by weight.

The electrolyte membrane itself is preferably stable at at least 80 ° C, preferably at least 120 ° C, and most preferably at least 140 ° C.

The electrolyte membrane according to the invention preferably has a composite material which has a thickness in the range from 5 to 150 μm, when using a fabric preferably a thickness from 10 to 80 μm, very particularly preferably from 10 to 50 μm, and preferably when using a nonwoven from 5 to 50 μm, very particularly preferably from 10 to 30 μm.

The diffusion barrier has at least one polymeric and / or organic and / or inorganic proton conductor. As a polymeric proton conductor, the diffusion barrier preferably has a proton conductor selected from Nation, sulfonated or phosphonated polyphenylsulfones, polyimides, polyoxazoles, polytriazoles, polybenzimidazoles, polyether ether ketones (PEEK) or polyether ketones (PEK). As the inorganic proton conductor, the diffusion barrier preferably has an inorganic proton conductor selected from sulfonic or phosphonic acids (such as, for example, hydroxysilylalkyl acids from phosphorus or Sulfur), zirconium or titanium phosphates, sulfoaryl phosphonates or phosphonates, or mixtures thereof. These inorganic proton conductors can also contain other oxides, e.g. B. of AI, Zr, Ti or Si, included as a network former. The diffusion barrier can also have a composite material made of polymeric and inorganic proton conductors. Such composite materials can e.g. B. Solidified solutions from Nafion with precipitated silica (Levasil®), tetraethoxysilane (Dynasilan A ®, TEOS) or with sols based on Al ₂ O ₃ , SiO ₂ , TiO ₂ or ZrO ₂ . The combination of organic proton conductors with immobilized inorganic sulfonic and phosphonic acids is also possible. The use of composite materials has the advantage that the adhesive strength of the protective layer on the membrane is better than that of the pure (hydrophobic) proton-conducting polymer.

From the range of polymeric proton conductors in particular, however, it is also possible to use all materials which do not form thin films, or which form only very poorly, and which therefore separate as self-supporting membranes.

The diffusion barrier, which is insoluble in water and methanol and which is preferably also not permeable to methanol, prevents bleeding of the electrolyte membrane. This results in a higher long-term performance compared to membranes that show bleeding of the electrolyte.

In addition to the proton-conducting materials, the diffusion barrier can have materials that have no proton-conducting properties. Such materials can in particular be oxides of aluminum, zirconium, silicon and / or titanium.

The electrolyte membrane according to the invention preferably has, as a coating which is insoluble in water and / or methanol, a proton-conducting coating (diffusion barrier) which has a thickness of less than 5 μm, preferably from 10 to 1000 nm and very particularly preferably from 100 to 500 nm ,

As already described, the electrolyte membrane according to the invention can be designed to be flexible. The electrolyte membrane is preferably flexible and preferably tolerates a bending radius of down to 100 m, in particular down to 20 mm and entirely particularly preferably from down to 5 mm.

At room temperature and at a relative atmospheric humidity of 35%, the electrolyte membrane according to the invention preferably has a conductivity of at least 2 mS / cm, preferably of at least 10 mS / cm, very particularly preferably of at least 15 mS / cm.

The production of the electrolyte membranes according to the invention is described below. The method according to the invention for producing an electrolyte membrane according to the invention is characterized in that the method comprises the following steps:

(a) providing an electrolyte membrane and

(b) applying a mixture which has at least one proton-conducting material to at least one side of the electrolyte membrane obtained and

(c) Solidifying this into a proton-conducting coating that is insoluble in water and methanol.

It goes without saying that steps (b) and (c) are not restricted to only one side of an electrolyte membrane, but depending on the intended use of the electrolyte membrane, the mixture from step (b) can be applied and solidified on several sides of the electrolyte membrane. Electrolyte membranes preferably have two functional sides, which is why the mixture is applied and solidified on these two sides. The mixture can be applied and solidified simultaneously or in succession.

The mixture according to the invention from step (b) can be applied by printing, pressing, pressing, rolling, knife coating, spreading, dipping, spraying or pouring the mixture onto the electrolyte membrane.

The mixture from step (b) can be applied repeatedly and, if appropriate, a drying step, preferably at an elevated temperature in a range from 50 to 200 ° C., can take place between the repeated application. The mixture from step (b) is preferably solidified by heating to a temperature of 50 to 300 ° C., preferably 50 to 200 ° C., very particularly preferably 80 to 150 ° C. The heating can be done with heated air, hot air, infrared radiation or microwave radiation. In a further embodiment, the solidification of the second mixture can be achieved by contacting the second mixture with a preheated electrolyte membrane and thus solidifying immediately after contacting.

The mixture from step (b) preferably has an organic and / or inorganic proton conductor. The mixture from step (b) can have, inter alia, a polymeric proton conductor selected from Nafion®, sulfonated or phosphonated polyphenylsulfones, polyimides, polyoxazoles, polytriazoles, polybenzimidazoles, polyether ether ketones (PEEK) or polyether ketones (PEK) and / or an inorganic proton conductor from sulfonic or phosphonic acids (such as, for example, hydroxysilylalkyl acids from sulfur or phosphorus) or their salts, zirconium or titanium phosphates, phosphonates or sulfoaryl phosphonates or mixtures thereof. A prerequisite for use as a proton-conducting material is the insolubility of the materials or material combinations in water or methanol. The mixture can also have a composite material made of polymeric and organic and / or inorganic proton conductors. In addition, these mixtures can additionally contain typical solvents such as water or alcohols.

It can be advantageous if the mixture from step (b) has a material which has no proton-conducting properties. Such a material can e.g. B. can be selected from the oxides of aluminum, zirconium, silicon and / or titanium, precipitated silica, tetraethoxysilane or sols or precursor compounds of Al O ₃ , SiO ₂ , TiO ₂ or ZrO ₂ .

As electrolyte membranes, all proton-conductive electrolyte membranes for a fuel cell, which are impermeable to the reaction components of the fuel cell reaction, comprising a permeable composite material made of a broken, non-conductive, glass and / or ceramic carrier, the composite material being permeated with a proton-conductive material that is suitable is used to selectively conduct protons through the membrane. It can be beneficial if flexible proton-conducting electrolyte membranes are used.

Electrolyte membranes are preferably used in the method according to the invention, which can be provided by the following steps: (al) infiltration of a permeable composite material from a perforated, non-conductive, glass and / or ceramic carrier with (al.l) a mixture containing one immobilizable hydroxysilylalkyl acid from

Sulfur or phosphorus or a salt thereof; or (al.2) a mixture containing a Bronsted acid and / or an immobilizable hydroxysilylalkyl acid of sulfur or phosphorus or a salt thereof and a sol which comprises a precursor for oxides of aluminum, silicon, titanium, zirconium and / or phosphorus and (a2) Solidification of the mixture infiltrating the composite in order to create a material penetrating the composite which is suitable for selectively guiding protons through the membrane, so that a proton-conducting membrane is obtained.

As in the mixture according to (al.2) Brönsted acid z. B. sulfuric acid, phosphoric acid, perchloric acid, nitric acid, hydrochloric acid, sulfurous acid, phosphorous acid and esters thereof and / or a monomeric or polymeric organic acid. Preferred organic acids are immobilizable sulfonic and / or phosphonic acids. The oxides of Al, Zr, Ti and Si can be used as additional network formers.

Organosilicon compounds of the general formulas are preferably used as the hydroxysilylalkyl acid of sulfur or phosphorus in the mixture according to (al.l)

[{(RO) _y (R ² ) _z } _a Si {R ¹ -SO ₃ -} _a ] _x M ^{x +} (I) or

[(RO) _y (R ² ) _z Si {R ¹ -O _b -P (O _c R ³ ) O ₂ -} _a ] _x M ^{x +} (II), where R ^{1 is} a linear or branched alkyl or Alkylene group with 1 to 12 carbon atoms, a cycloalkyl group with 5 to 8 carbon atoms or a unit of the general

formulas

or

, where n, m each represents an integer from 0 to 6, M represents H, NH ₄ or a metal, x = 1 to 4, y = 1 to 3, z = 0 to 2 and a = 1 to 3 mean, with the proviso that y + z = 4 - a, b, c = 0 or l,

R, R ^{2 are the} same or different and stand for methyl, ethyl, propyl, butyl or H and

R ^{3 represents} M or a methyl, ethyl, propyl or butyl radical.

Trihydroxysilylpropylsulfonic acid, trihydroxysilylpropylmethylphosphonic acid or dihydroxysilylpropylsulfonedioic acid are particularly preferably used as hydroxysilylalkyl acid of sulfur or phosphorus in the mixture.

The hydroxysilylalkyl acid of sulfur or phosphorus is preferably with a hydrolyzed compound of phosphorus or a hydrolyzed nitrate, oxynitrate, chloride, oxychloride, carbonate, alcoholate, acetate, acetylacetonate of a metal or semimetal or a hydrolyzed compound obtained from diethylphosphite (DEP), diethylethylphosphonate ( DEEP), titanium propylate, titanium ethylate, tetraethyl orthosilicate (TEOS) or tetra methyl orthosilicate (TMOS), zirconium nitrate, zirconium oxynitrate, zirconium propylate, zirconium acetate, circomum acetylacetonate, phosphoric acid methyl ester or immobilized with precipitated silica. It can be advantageous if the mixture according to (al.l) and / or (al.2) further proton-conducting substances selected from the group of iso- or heteropolyacids, such as, for example, tungsten phosphoric acid or silicon-tungstic acid, zeolites, mordenites, aluminosilicates, Aluminum oxides, zirconium, titanium, or cerium phosphates, phosphonates or sulfoaryl phosphonates, antimonic acids, phosphorus oxides, sulfuric acid, perchloric acid or salts thereof and / or crystalline metal oxides, where A1 ₂ 0 ₃ -, ZrO ₂ -, TiO ₂ - or Si0 ₂ Powder are preferred.

The sol from step (al.2) is preferably obtainable by (al.2-1) hydrolysis of a hydrolyzable compound, preferably in a mixture of water and alcohol, to give a hydrolyzate, the hydrolyzable compound being selected from hydrolyzable alcoholates, acetates , Acetylacetonates, nitrates, oxynitrates, chlorides, oxychlorides, carbonates, of aluminum, silicon, titanium, zirconium, and / or phosphorus or esters, preferably methyl esters, ethyl esters and / or propyl esters of phosphoric acid or phosphorous acid and (al .2-2 ) Peptizing the hydrolyzate to a sol.

The infiltration according to step (a1) can be carried out by printing, pressing on, pressing in, rolling up, knife coating, spreading on, dipping, spraying or pouring the mixture of (al.l) or (al.2) onto the permeable composite material. The solidification in step (a2) is preferably carried out by heating to a temperature of 50 to 300 ° C, preferably 50 to 200 ° C, most preferably 80 to 150 ° C. In a preferred embodiment, the infiltration of the permeable composite material takes place continuously. It may be advantageous to preheat the composite material for infiltration.

It can be advantageous if the infiltration is carried out repeatedly with the mixture according to step (al.l) or (al.2) and, if appropriate, a drying step, preferably at an elevated temperature in a range from 50 to 200 ° C., between the repeated Infiltration takes place. Repeated infiltration can leave gaps, e.g. B. arise from shrinkage processes during solidification, so that a suitable electrolyte membrane is obtained.

The electrolyte membranes according to the present invention can have a special composite material which is known in general form and for another application from PCT / EP98 / 05939. This composite can be infiltrated with a proton-conducting material or a precursor thereof, whereupon the membrane is dried, solidified and, if appropriate, modified in a suitable manner, so that an impermeable, proton-conducting and flexible membrane is obtained. To produce the composite material, the support containing a glass or ceramic is first transferred according to PCT / EP98 / 05939 into a mechanically and thermally stable, permeable ceramic basic membrane which is neither electrically nor ionically conductive. Then this porous, electrically insulating basic membrane is penetrated with the proton-conducting material.

In this production of the composite material, a flexible, perforated support comprising glass and / or ceramic is contacted or infiltrated with a suspension which contains a precursor for the porous ceramic material. As a preliminary stage for the porous

Ceramic material comes at least one inorganic component from a compound of a metal, a semi-metal or a mixed metal with one of the elements of the 3rd to 7th

Main group in question, which can be applied as a suspension to the carrier and preferably solidified by heating. Contacting or infiltrating can be done by

Printing, pressing, pressing, rolling, knife coating, spreading, dipping, spraying or pouring.

If a ceramic or glass fleece or woven fabric is used as the carrier, the carrier can be treated with a sol before the porous ceramic material is applied. The sol preferably contains precursor compounds of the oxides of aluminum, titanium, zirconium or silicon. By solidifying the sol, the fibers of the ceramic fleece or glass fleece are glued, thereby improving the mechanical stability of the fleece. In addition, the acid resistance of glass fabrics or nonwovens is increased by a coating applied in this way.

The suspension with which the carrier is contacted preferably contains an inorganic one Component and a metal oxide sol, a semi-metal oxide sol or a mixed metal oxide sol or a mixture of these sols. Such a preferred suspension can be prepared by suspending an inorganic component in one of these brines.

Commercial brines such as titanium nitrate sol, zirconium nitrate sol or silica sol can be used. However, the sols can also be obtained by hydrolysis of a metal compound, semimetal compound or mixed metal compound in a medium such as water, alcohol or an acid. The compound to be hydrolyzed is preferably a metal nitrate, a metal chloride, a metal carbonate, a metal alcoholate compound or a semimetal alcoholate compound, particularly preferably at least one metal alcoholate compound, a metal nitrate, a metal chloride, a metal carbonate or at least one semimetal alcoholate compound selected from the compounds of the elements Ti , Zr, AI, Si, Sn, Ce and Y, such as. B. titanium alcoholates, (eg titanium isopropylate), silicon alcoholates, zirconium alcoholates, or a metal nitrate (eg zirconium nitrate), hydrolyzed. It may be advantageous to carry out the hydrolysis with at least half the molar ratio of water, based on the hydrolyzable group of the hydrolyzable compound. The hydrolyzed compound can be peptized with an acid, preferably with a 10 to 60% acid, preferably with a mineral acid selected from sulfuric acid, hydrochloric acid, perchloric acid, phosphoric acid and nitric acid or a mixture of these acids.

An inorganic component with a grain size of 1 to 10,000 nm can be suspended in the sol. An inorganic component which has a compound selected from metal compounds, semimetal compounds, mixed metal compounds and mixed metal compounds with at least one of the elements of the 3rd to 7th main group, or at least a mixture of these compounds, is preferably suspended. Particular preference is given to at least one inorganic component which comprises at least one compound from the oxides of the subgroup elements or from the elements of the 3rd to 5th main group, preferably oxides, selected from the oxides of the elements Y, Ti, Zr, Ce, Al, Si, or Sn, such as B. Y ₂ O ₃ , ZrO ₂ , SiO ₂ , Al ₂ O ₃ , suspended. The inorganic component can also have aluminosilicates, zeolites and other microporous mixed oxides.

The mass fraction of the suspended component is preferably 0.1 to 500 times the hydrolyzed compound used.

Cracks in the composite material can be avoided by a suitable choice of the grain size of the suspended compounds depending on the size of the pores, holes or interstices of the carrier, but also by a suitable choice of the layer thickness of the composite material and the proportionate ratio of sol / solvent / metal oxide.

When using a mesh fabric with a mesh size of z. B. 100 microns can preferably be used to increase the freedom from cracks, which has a suspended compound with a grain size of at least 0.7 microns. In general, the ratio of grain size to mesh or pore size should be from 1: 1000 to 1:10. The composite material can preferably have a thickness of 5 to 1000 μm, particularly preferably from 10 to 70 μm and very particularly preferably from 10 to 30 μm. The suspension of sol and compounds to be suspended preferably has a ratio of sol to compounds to be suspended from 1: 1000 to 1000: 1, preferably from 1: 100 to 100: 1 parts by weight.

After contacting the carrier, the suspension can be solidified by heating the composite of suspension and carrier to 50 to 1000 ° C. In a particular embodiment, the composite is exposed to a temperature of 50 to 100 ° C. for 10 seconds to 1 hour, preferably 10 seconds to 10 minutes. In a further particular embodiment, the composite is exposed to a temperature of 100 to 800 ° C. for 5 seconds to 10 minutes, preferably 5 seconds to 5 minutes, particularly preferably for 5 seconds to 1 minute. The composite can be heated with heated air, hot air, infrared radiation or microwaves. In a further embodiment, the suspension can be solidified by contacting the suspension with a preheated carrier and thus solidifying immediately after contacting.

In a further particular embodiment, the carrier is unrolled from a roll at a speed of 1 m h to 1 m / s, onto an apparatus which the suspension with

Carrier contacted and then to another apparatus that solidifies the

Suspension made possible by heating. The composite material thus produced is placed on a second roll rolled up. In this way it is possible to manufacture the composite material continuously.

By treating a carrier with a suspension or a sol several times, it is possible to use those carriers whose pore or mesh size is used to produce a composite material with a specific pore size

Composite material with the required pore size is not suitable. This can e.g. B. be the case when a composite material with a pore size of 250 nm using a

Carrier with a mesh size of over 250 microns to be produced. To obtain such a composite, it may be advantageous to first place at least one on the carrier

Bring suspension that is suitable to treat carriers with a mesh size of 250 microns, and solidify this suspension after application. The composite material obtained in this way can now be used as a carrier with a lower mesh or

Pore size can be used. A further suspension can be applied to this carrier, which has a compound with a grain size of 0.5 μm.

The insensitivity to cracks in composite materials with large mesh or pore widths can also be improved by applying suspensions to the carrier which have at least two suspended compounds. Compounds to be suspended are preferably used which have a particle size ratio of 1: 1 to 1:20, particularly preferably 1: 1.5 to 1: 2.5. The weight fraction of the grain size fraction with the smaller grain size should not exceed a proportion of at most 50%, preferably 20% and very particularly preferably 10%, of the total weight of the grain size fraction used.

This invention also relates to a membrane electrode assembly which contains a proton-conducting membrane according to the invention. Such a membrane electrode unit according to the invention is described below. The preferably flexible membrane electrode assembly for a fuel cell comprises an anode layer and a cathode layer, each of which is provided on opposite sides of a proton-conductive, preferably flexible electrolyte membrane for a fuel cell, which is impermeable to the reaction components of the fuel cell reaction, the Electrolyte membrane comprises a permeable composite material made of a flexible, perforated, electrically non-conductive, glass or ceramic support, the composite material being permeated with a proton conductive material which is suitable for selectively guiding protons through the membrane and which has an outer surface on at least one side proton-conductive coating as a diffusion barrier, which is insoluble in water and methanol and wherein the anode layer and the cathode layer are porous and each include a catalyst for the anode and cathode reaction, a proton conductive component and optionally a catalyst support. It can be advantageous if the membrane electrode unit according to the invention has an electrolyte membrane which not only has a diffusion barrier on one side, but on several sides.

It can be advantageous if the membrane electrode assembly according to the invention has a permeable composite material which has a flexible, openwork, non-conductive support based on glass or ceramic and which has a porous ceramic coating, a ceramic coating or no coating.

The proton-conductive component of the anode and / or cathode layer and / or the proton-conductive material of the composite material preferably comprises (i) an immobilized hydroxysilylalkyl acid of sulfur or phosphorus or a salt thereof and optionally an oxide of aluminum, silicon, titanium, zirconium and / or Phosphorus as a network former, and / or (ii) a Bronsted acid and an oxide of aluminum, silicon, titanium, zirconium, and / or

Phosphorus as a network former and optionally (iii) further proton-conducting substances, preferably titanium phosphates, titanium phosphonates, zirconium phosphates, zirconium phosphonates, iso- and heteropolyacids, preferably

Tungsten phosphoric acid or silicon tungsten acid or nanocrystalline metal oxides, with Al ₂ O ₃ , ZrO ₂ , TiO ₂ or SiO ₂ powder being preferred.

In a preferred embodiment, the hydroxysilylalkyl acid of sulfur or phosphorus or a salt thereof is an organosilicon compound of the general formulas

[{(RO) _y (R ² ) _z } _a Si {R ¹ -SO ₃ ^" } _a ] _x M ^{x +} (I) or

[(RO) _y (R ² ) _z Si {R ¹ -O _b -P (O _c R ³ ) O ₂ ^" } _a ] _x M ^{x +} (II)

where R ^{1 is} a linear or branched alkyl or alkylene group having 1 to 12 carbon atoms, a cycloalkyl group having 5 to 8 carbon atoms or a unit of the general formulas

or

where n, m each represents an integer from 0 to 6,

M represents H, NH or a metal, x = 1 to 4, y = 1 to 3, z = 0 to 2 and a = 1 to 3, with the proviso that y + z = 4 - a, b , c = 0 or 1,

R ^{3 represents} M or a methyl, ethyl, propyl or butyl radical.

The hydroxysilylalkyl acid of sulfur or phosphorus is preferred

Trihydroxysilylpropylsulfonic acid, trihydroxysilylpropylmethylphosphonic acid or

Dihydroxysilylpropylsulfondisäure. The hydroxysilylalkyl acid of sulfur or phosphorus or a salt thereof with a hydrolyzed compound of phosphorus or a hydrolyzed nitrate, oxynitrate, chloride, oxychloride, carbonate, alcoholate, acetate, is preferably

Acetylacetonate of a metal or semi-metal immobilized. In another preferred Embodiment, the Hydroxysilylalkylsäure of sulfur or of phosphorus or a salt thereof with a hydrolyzed compound obtained from titanium propylate, titanium ethoxide, tetraethylorthosilicate (TEOS) or tetramethyl orthosilicate (TMOS), zirconium nitrate, zirconium oxynitrate, zirconium propoxide, zirconium acetate, Zirkomumacetylacetonat, Phosphorsäuremethylester, diethyl phthalate (DEP) or immobilized on diethyl ethyl phosphonate (DEEP).

The membrane electrode assembly according to the invention can preferably be operated in a fuel cell at a temperature of at least 80 ° C, preferably at least 100 ° C, and very particularly preferably at at least 120 ° C. The membrane electrode assembly according to the invention preferably tolerates a bending radius of down to 100 m, in particular down to 20 mm, very particularly preferably down to 5 mm.

In a special embodiment of the membrane electrode unit according to the invention, the proton-conductive components of the anode layer and cathode layer and the proton-conductive material of the electrolyte membrane have the same composition. However, it is also possible that the compositions are different. It is also possible that only the anode layer and the cathode layer have the same composition or that the anode layer and the cathode layer have different catalysts. In a preferred embodiment, the catalyst support is electrically conductive in the anode layer and in the cathode layer.

To produce the membrane electrode assembly, an electrolyte membrane is coated with the optionally catalytically active electrode material by a suitable method.

The electrolyte membrane can be provided with the electrode in various ways. The manner and the sequence in which the electrically conductive material, catalyst, electrolyte and possibly further additives are applied to the membrane are at the discretion of the person skilled in the art. It is only necessary to ensure that the interface gas space / catalyst (electrode) / electrolyte is formed. In a special case, the electrically conductive material as a catalyst carrier is dispensed with, in this case the electrically conductive catalyst directly removes the electrons from the membrane electrode assembly.

The membrane electrode unit according to the invention is preferably produced by a method which comprises the following steps,

(A) Provision of a proton-conductive, preferably flexible electrolyte membrane, preferably flexible according to the invention for the reaction components of the fuel cell reaction, for a fuel cell, the electrolyte membrane having a permeable composite material made of a preferably flexible, perforated, non-conductive, glass or ceramic carrier, the composite material is permeated with a proton-conductive material which is suitable for selectively guiding protons through the membrane and wherein the electrolyte membrane has an outer proton-conductive coating on at least one side as a diffusion barrier, which is insoluble in water and methanol,

(B) Provision of an agent for producing an anode layer and a cathode layer, the agent each comprising:

(B1) a condensable component that occurs after the condensation of the electrode layer

Gives proton conductivity, (B2) a catalyst which catalyzes the anode reaction or the cathode reaction, or a precursor compound of the catalyst, (B3) optionally a carrier and (B4) optionally a pore former,

(C) applying the agents from stage (B) to one side of the electrolyte membrane from stage (A) to form a coating,

(D) Creation of a firm bond between the coatings and the electrolyte membrane to form a porous, proton-conductive anode layer or cathode layer, wherein the formation of the anode layer and the cathode layer can take place simultaneously or in succession.

The application of the agent in step (C) can, for. B. by printing, pressing, pressing, rolling, knife coating, spreading, dipping, spraying or pouring. The agent according to step (B) for producing an anode layer or a cathode layer is preferably a suspension and can e.g. B. can be obtained by:

(51) Preparation of a sol comprising a hydroxysilylalkyl acid of sulfur or phosphorus or its salt and optionally a hydroxysilylalkyl acid of sulfur or phosphorus or its

Salt-immobilizing hydrolyzable compound of phosphorus or a hydrolyzable nitrate, oxynitrate, chloride, oxychloride, carbonate, alcoholate, acetate, acetylacetonate of a metal or semimetal, preferably methylphosphate, diethylphosphite (DEP), diethylethylphosphonate (DEEP), titanium propylate, titanium ethylate silicate, titanium ethylate silicate TEOS) or

Tetramethyl orthosilicate (TMOS), zirconium nitrate, zirconium oxynitrate,

Zirconium propylate, zirconium acetate or circomum acetylacetonate,

(52) Dispersing the catalyst and optionally the catalyst support and pore former in the sol from (SI).

Likewise, the agent according to step (B) for producing an anode layer or a cathode layer can be a suspension which is obtainable from

(Hl) hydrolysis of a hydrolyzable compound to a hydrolyzate, the hydrolyzable compound being selected from a hydrolyzable compound of phosphorus or hydrolyzable nitrates, oxynitrates, chlorides, oxychlorides, carbonates, alcoholates, acetates, acetylacetonates of a metal or semimetal, preferably aluminum alcoholates, vanadium alcoholates, titanium propylate, titanium ethylate, zirconium nitrate, zirconium oxynitrate, zirconium propylate, zirconium acetate or zirconium acetylacetonate, or

Metal acids of aluminum, silicon, titanium, vanadium, antimony, tin, lead, chromium, tungsten, molybdenum, manganese, preference being given to tungsten phosphoric acid and silicon tungstic acid, (H2) peptizing the hydrolyzate with an acid to give a dispersion, (H3) mixing the dispersion with a nanocrystalline proton-conducting metal oxide, preferably Al ₂ O ₃ , ZrO ₂ , TiO ₂ or SiO ₂ powder, (H4) dispersing the catalyst and, if appropriate, the support and pore former. It can be advantageous if the means for producing an anode layer and a cathode layer are printed in step (C) and for creating a firm bond between the coatings and the electrolyte membrane, with the formation of a porous, proton-conductive anode layer or cathode layer in step (D) at a temperature from 50 to 300 ° C, preferably 50 to 200 ° C, most preferably 80 to 150 ° C.

The method according to the invention for producing the membrane electrode unit according to the invention is preferably carried out in such a way that the steps (M1) apply the agent for producing an anode layer or cathode layer to a support membrane, preferably made of polytetrafluoroethylene, (M2) drying the coating obtained under (M1),

(M3) pressing the dried coating onto the electrolyte membrane at a temperature of 20 to 300 ° C, preferably 50 to 200 ° C, very particularly preferably 80 to 150 ° C,

(M4) Removing the support membrane, in particular by mechanical detachment, chemical

Dissolving or pyrolizing or (Nl) applying the agent for producing an anode layer or cathode layer to a support membrane, preferably made of carbon paper or an electrically conductive fleece or fabric,

(N2) drying the coating obtained under (Nl) to produce a coated

Support membrane, (N3) pressing the coated support membrane onto the electrolyte membrane at a temperature of from room temperature to 300 ° C., preferably 50 to 200 ° C., very particularly preferably 80 to 150 ° C.

The method is preferably also carried out in such a way that in step (B) the agent is provided in each case when providing an agent for producing an anode layer and a cathode layer

(i) comprises a catalyst metal salt, preferably hexachloroplatinic acid

(ii) after application of the agents by step (C) the catalyst metal salt into one Catalyst which catalyzes the anode reaction or the cathode reaction is reduced, (iii) in step (D) an open-pore gas diffusion electrode, preferably an open-pore carbon paper, is pressed onto the catalyst or glued to the catalyst with an electrically conductive adhesive.

Preferably, the application of the agent for producing an anode layer or cathode layer is carried out repeatedly and optionally a drying step takes place, preferably at an elevated temperature in a range from 50 to 200 ° C., between the repeated application of the application.

It can be advantageous if the method according to the invention is carried out in such a way that the agent for producing an anode layer or cathode layer is applied to a flexible electrolyte membrane or flexible support membrane rolled off a first roll. The agent for producing an anode layer or cathode layer is particularly preferably applied continuously. It can be advantageous if the agent for producing an anode layer or cathode layer is applied to a heated electrolyte or support membrane, so that the cathode or anode layer is rapidly solidified. In general, it is preferred to solidify in step (D) to create a firm bond between the coatings and the electrolyte membrane to a temperature of 50 to 300 ° C., preferably 50 to 200 ° C., very particularly preferably 80 to 150 ° C. heat. The heating can take place by means of heated air, hot air, infrared radiation or microwave radiation.

In a special embodiment, the catalytically active (gas diffusion) electrodes are built up on the electrolyte membrane to produce the membrane electrode unit. For this purpose, an ink is produced from a soot catalyst powder and at least one proton-conducting material. The ink can also contain other additives that improve the properties of the membrane electrode assembly. The carbon black can also be replaced by other electrically conductive materials (such as metal powder, metal oxide powder, carbon, coal). In a special embodiment, a metal or semi-metal oxide powder (such as Aerosil) is used as the catalyst carrier instead of soot. used. This ink is then applied to the membrane, for example by screen printing, knife coating, spraying on, rolling on or by dipping.

The ink can contain any proton-conducting materials that are also used to infiltrate the composite. The ink can thus contain an acid or its salt, which is immobilized by a chemical reaction in the course of a solidification process after the ink has been applied to the membrane. So this acid can e.g. B. simple Bronsted acid, such as sulfuric or phosphoric acid, or a silylsulfonic or silylphosphonic acid. As materials that support the solidification of the acid, for. B. Al ₂ O ₃ , SiO ₂ , ZrO ₂ , TiO ₂ are used, which are also added via molecular precursors of the ink.

In contrast to the proton-conductive material of the composite material, which must be impermeable to the reaction components of the fuel cell reaction, both the cathode and the anode must have a large porosity so that the reaction gases, such as hydrogen and oxygen, are brought to the interface between the catalyst and the electrolyte without inhibiting mass transfer can. This porosity can be influenced, for example, by using metal oxide particles with a suitable particle size and by organic pore formers in the ink or by a suitable solvent content in the ink.

In a very special embodiment of the method according to the invention for producing the membrane electrode unit according to the invention, the agent in step (B) or the special ink just described comprises: (TI) a condensable component which, after the condensation of an anode layer or a cathode layer of a membrane electrode unit of a fuel cell, has proton conductivity gives selected from

(I) hydrolyzable compound of phosphorus or hydrolyzable nitrates,

Oxynitrates, chlorides, oxychlorides, carbonates, alcoholates, acetates, acetylacetonates of a metal or semimetal, preferably aluminum alcoholates, vanadium alcoholates, titanium propylate, titanium ethylate, zirconium nitrate,

Zirconium oxynitrate, zirconium propylate, zirconium acetate or zirconium acetylacetonate, or metal acids of aluminum, titanium, vanadium, antimony, tin, lead, chromium, tungsten, molybdenum, manganese, with tungsten phosphoric acid being preferred, and / or (II) an immobilizable hydroxysilylalkyl acid of sulfur or phosphorus or a

Salt thereof and, if appropriate, a hydrolyzable compound of phosphorus or a hydrolyzable nitrate immobilizing the hydroxysilylalkyl acid of sulfur or phosphorus or its salt, oxynitrate, chloride, oxychloride, carbonate, alcoholate, acetate, acetylacetonate of a metal or semimetal, preferably diethylphosphonate (DEP), diethylethylphosphonate (DEEP)

Phosphoric acid methyl ester, titanium propylate, titanium ethylate, tetraethyl orthosilicate (TEOS) or tetramethyl orthosilicate (TMOS), zirconium nitrate, zirconium oxynitrate, zirconium propylate, zirconium acetate or circomum acetylacetonate. (T2) a catalyst which catalyzes the anode reaction or the cathode reaction in a fuel cell, or a precursor compound of the catalyst, preferably selected from a platinum metal, preferably platinum, palladium and / or ruthenium or an alloy which contains at least one of these metals (T3 ) optionally a catalyst support, which is preferably electrically conductive and is preferably selected from carbon black, graphite, carbon, carbon, activated carbon or metal oxides, and

(T4) optionally a pore former, preferably selected from an organic and / or inorganic substance, which decomposes at a temperature between 50 and 300 ° C and preferably between 100 and 200 ° C, particularly preferably ammonium carbonate or ammonium bicarbonate, and (T5) optionally additives to improve foam behavior, viscosity and adhesion.

The ink can also be used to increase the proton conductivity, nanoscale oxides such. B. of aluminum, titanium, zirconium or silicon, or zirconium or titanium phosphates, - sulfoaryl phosphonates or phosphonates.

In a further embodiment, a prefabricated gas distributor, which Gas diffusion electrode, consisting of an electrically conductive material (e.g. a porous carbon fleece) containing catalyst and electrolyte, can be applied directly to the membrane. In the simplest case, the gas distributor and membrane are fixed using a pressing process. For this it is necessary that the membrane or gas distributor have thermoplastic properties at the pressing temperature. The gas distributor can also be fixed on the membrane by an adhesive. This adhesive must have ion-conducting properties and can in principle consist of the material classes already mentioned. For example, a metal oxide sol that additionally contains a hydroxysilyl acid can be used as the adhesive. Finally, the gas distributor can also be applied "in situ" in the last stage of membrane or gas diffusion electrode production. At this stage, the proton-conducting material in the gas distributor or in the membrane has not yet hardened and can be used as an adhesive. The gluing process takes place in both cases by gelling the sol with subsequent drying / solidification.

However, it is also possible to deposit the catalyst directly on the membrane and to provide it with an open-pore gas diffusion electrode (such as an open-pore carbon paper). For this, e.g. B. a metal salt or an acid applied to the surface and reduced to metal in a second step. For example, platinum can be applied via hexachloroplatinic acid and reduced to metal. In the last step, the lead electrode is fixed using a pressing process or an electrically conductive adhesive. The solution containing the metal precursor may additionally contain a compound that is already proton-conductive or at least ion-conductive at the end of the manufacturing process. Suitable ionic materials are the ionic substances mentioned above.

With all embodiments of the method according to the invention, a membrane electrode unit according to the invention is available which can be used in a fuel cell, in particular in a direct methanol fuel cell or a reformate fuel cell.

The electrolyte membrane according to the invention and the membrane electrode assembly according to the invention can be used in particular for producing a fuel cell or a fuel cell stack, the fuel cell in particular being a direct Is a methanol fuel cell or a reformate fuel cell used in a vehicle.

Fuel cells with an electrolyte membrane according to the invention or fuel cells with a membrane electrode unit according to the invention are particularly preferred objects of the present invention.

Mobile or stationary systems with a membrane electrode unit according to the invention or with a fuel cell or a fuel cell stack containing an electrolyte membrane according to the invention or a membrane electrode unit according to the invention can be accessed with the aid of the objects mentioned. Such mobile or stationary systems can e.g. B. vehicles, especially cars, or a home energy system.

The invention is explained in more detail below with the aid of examples, without the invention being restricted to these exemplary embodiments.

Production Example 1 Production of suspensions

Production Example 1.1 120 g of titanium tetra-isopropylate are stirred with 140 g of deionized ice with vigorous stirring until the precipitate formed is finely divided. After adding 100 g of 25% hydrochloric acid, the mixture is stirred until the phase becomes clear. 280 g of aluminum oxide of the type CT300OSG from Alcoa, Ludwigshafen, are then added and the mixture is stirred for several days until the aggregates have dissolved. This suspension can then be used to manufacture a composite or as a precursor for a proton conductive material.

Production example 1.2

80 g of titanium tefraisopropylate are hydrolyzed with 20 g of water and the resulting precipitate is peptized with 120 g of nitric acid (25%). This solution will last until

Are stirred clear and after adding 40 g of titanium dioxide from Degussa (P25) until

Dissolve the agglomerates stirred. This suspension can then be used to produce a Composite or used as a precursor for a proton conductive material.

Production example 1.3

50 g of titanium tetraethoxylate were hydrolyzed with 270 g of water and peptized with 30 g of nitric acid (25%). 100 g of ethanol and 350 g of CT 2000 SG from Alcoa were then added and stirred. This suspension can then be used to manufacture a composite or as a precursor for a proton conductive material.

Production Example 1.4 120 g of titanium tetra-isopropylate are stirred with 140 g of deionized ice with vigorous stirring until the precipitate formed is finely divided. After addition of 100 g of 25% nitric acid, the mixture is stirred until the phase becomes clear and 280 g of aluminum oxide of the type CT300OSG from Alcoa, Ludwigshafen, are added and the mixture is stirred for several days until the aggregates have dissolved. This suspension can then be used to manufacture a composite or as a precursor for a proton conductive material.

Production example 1.5

70 g of tetraethoxysilane are hydrolyzed with 20 g of water and the resulting precipitate is peptized with 120 g of nitric acid (25%). This solution is stirred until it becomes clear and, after adding 40 g of amorphous silica or amorphous silicon dioxide from Degussa, the solution is stirred until the agglomerates have dissolved. This suspension can then be used to manufacture a composite or as a precursor for a proton conductive material.

Production example 1.6

20 g of zirconium tetraisopropylate are hydrolyzed with 15 g of water and the resulting precipitate is peptized with 30 g of nitric acid (25%). After the precipitate has completely dissolved, 10 g of VP 25 zirconium dioxide from Degussa are added until the agglomerates are completely dissolved. This suspension can then be used to manufacture a composite or as a precursor for a proton conductive material. Production example 1.7

120 g of zirconium tetraisopropylate are stirred with 140 g of deionized ice with vigorous stirring until the precipitate formed is finely divided. After addition of 100 g of 25% hydrochloric acid, the mixture is stirred until the phase becomes clear and 280 g of α-aluminum oxide of the type CT3000SG from AlCoA, Ludwigshafen, were added and the mixture was stirred for several days until the aggregates dissolved. This suspension can then be used to manufacture a composite or as a precursor for a proton conductive material.

Production Example 1.8 280 g of aluminum oxide CT3000SG (company AlCoA) were stirred with 150 g of water. For stabilization, 1 g of concentrated hydrochloric acid is added to this suspension. The slip is stirred with a magnetic stirrer for at least 24, then 10 g of zirconium nifrate sol (30% from MEL Chemicals) are added. This suspension can then be used to manufacture a composite or as a precursor for a proton conductive material.

Production example 2 Production of the composite materials

Production example 2.1

A ceramic fleece with a thickness of approximately 10 μm made of Al ₂ θ ₃ fibers is treated with a zirconium nifrate sol containing 30% by weight of Zrθ ₂ and annealed at 200 ° C. in order to bond the ceramic fibers. A suspension according to Example 1.4 is knife-coated onto the treated ceramic fleece and dried within 10 seconds by blowing with hot air which had a temperature of 550 ° C. A flat composite material was obtained which can be used as a composite material with a pore size of 0.2 to 0.4 mm. The composite material can be bent to a radius of 5 mm without the composite material being destroyed. The composite material can be used to produce an electrolyte membrane according to the invention.

Production Example 2.2 A suspension according to Production Example 1.2 was applied to a composite material as described in Example 2.1 by rolling up with a layer thickness of 5 mm. The suspension was solidified again by blowing the composite with hot air at 550 ° C for about 5 seconds. A composite material was obtained which had a pore size of 30-60 nm and is suitable for producing an electrolyte membrane according to the invention.

Production example 2.3

The suspension produced according to production example 1.3 is applied in a thin layer

Ceramic fleece applied and solidified at 550 ° C within 5 seconds. The received one

Composite material can be used to produce a composite membrane according to the invention.

Production examples 2.4 to 2.8

The suspensions of preparation examples 1.4 to 1.8 are each applied to a glass fabric support. The carrier has a chemical composition of 64 to 66% by weight SiO ₂ , 24 to 25% by weight A1 ₂ 0 ₃ and 9 to 12% by weight MgO. The fabric is made of 11-Tex yarn with 24 warps and 32 wefts. The coated fabric is dried by blowing with air at a temperature of 450-550 ° C for a few seconds. The composite material obtained can be used to produce a composite membrane according to the invention.

Example 1: Production of an electrolyte membrane by treating a composite material with silanes

An inorganic, permeable composite material, which was produced by applying a thin layer of the suspension from preparation example 1.1 on a ceramic carrier according to preparation example 2.1, was immersed in a solution which consisted of the following components: 5% Degussa silane 285 (a propylsulfonic acid triethoxysilane), 20% deionized (VE) water in 75% ethanol. The solution had to be stirred at room temperature for 1 h before use.

After the supernatant solution was drained, the composite was dried at 80 to 150 ° C to provide an electrolyte membrane of the present invention. Example 2 Production of an Electrolyte Membrane

20 g of aluminum alcoholate and 17 g of vanadium alcoholate were hydrolyzed with 20 g of water and the resulting precipitate was peptized with 120 g of nitric acid (25%). This solution was stirred until it became clear and, after addition of 40 g of titanium dioxide from Degussa (P25), stirring was continued until all agglomerates had dissolved. After the pH had been adjusted to about 6, the suspension was knife-coated onto a composite material prepared according to production example 2.1 and dried in order to create a proton-conducting electrolyte membrane equipped with negative fixed charges.

Examples 3 and 4 Production of an Electrolyte Membrane with Zeolites

10 g of methyltriethoxisilane, 30 g of tetraethylorthosilicate and 10 g of aluminum trichloride were hydrolyzed with 50 g of water in 100 g of ethanol. 190 g of zeolite USY (CBV 600 from Zeolyst) were then added. The mixture was stirred until all the agglomerates had dissolved and then the suspension was coated on the one hand on a composite material prepared according to preparation example 2.1 and on the other hand on a composite material prepared according to preparation example 2.2 and solidified by heat treatment at 600 ° C. in order to create a proton-conducting electrolyte membrane ,

Example 5: Production of an electrolyte membrane

10 ml of anhydrous trihydroxysilylpropylsulfonic acid, 30 ml of ethanol and 5 ml of water are mixed by stirring. 40 ml of TEOS (tetraethyl orthosilicate) are slowly added dropwise to this mixture with stirring. For condensation, this sol is stirred in a closed vessel for 24 h. The composite material from production example 2.3 is immersed in this sol for 15 minutes. The sol is then allowed to gel in the impregnated membrane for 60 minutes in air and dry. The membrane filled with the gel is dried at a temperature of 150 ° C. for 60 minutes, so that the gel solidifies and becomes water-insoluble. In this way a dense membrane is obtained which has a proton conductivity at room temperature and normal ambient air of approx. 2 • 10 ^"3 S / cm.

Example 6 Production of an Electrolyte Membrane

An additional 25 g of tungsten phosphoric acid are dissolved in 50 ml of the sol from Example 5. In The composite material from production example 2.1 is immersed in this sol for 15 minutes. Then proceed as in Example 5.

Example 7: Production of an electrolyte membrane 100 ml of titanium isopropylate is added dropwise to 1200 ml of water with vigorous stirring. The resulting precipitate is aged for 1 h and then mixed with 8.5 ml of concentrated nitric acid and peptized at the boiling point for 24 h. 50 g of tungsten phosphoric acid are dissolved in 25 ml of this sol. A further 25 ml of trihydroxysilylpropylsulfonic acid are added to this solution and the mixture is stirred for one hour at room temperature. The composite material from production example 2.1 is then immersed in this sol for 15 minutes. The membrane is then dried and solidified by a temperature treatment at 150 ° C. and converted into the proton-conducting form.

EXAMPLE 8 Production of an Electrolyte Membrane Sodium trihydroxysilylmethylphosphonate dissolved in a little water is diluted with ethanol. The same amount of TEOS is added to this solution and stirring is continued briefly. The composite material from production example 2.1 is immersed in this sol for 15 minutes. The membrane is then dried and solidified by a temperature treatment at 250 ° C. and converted into the proton-conducting form by an acid treatment.

EXAMPLE 9 Production of an Electrolyte Membrane by Immobilizing a Bronsted Acid A TEOS solution consisting of TEOS: ethanol: H ₂ O: HCl = 1: 8: 4: 0.05 mol is precondensed for 24 h. Then give 20 vol% conc. HClO ₄ (70%) to the sol and after briefly stirring by knife coating it with a base membrane, which was produced according to Preparation Example 2.3. Following the infiltration, the membrane is solidified at RT and dried. The conductivity of the membrane at room temperature and approx. 35% r. F. is approx. 20 mS / cm.

EXAMPLE 10 Production of an Electrolyte Membrane by Immobilizing a Bronsted Acid An electrolyte membrane was produced as in Example 9, with H ₂ SO ₄ (98% strength) being added to the sol instead of HClO ₄ as acid. Under the same measuring conditions (room temperature and approx. 35% rh), the conductivity is approx. 23 mS / cm after a thermal treatment of 100 ° C (1 h).

EXAMPLE 11 Production of an Electrolyte Membrane by Immobilizing a Bronsted Acid A TEOS sol consisting of TEOS (11 ml), diethyl phosphite (19 ml), ethanol (11 ml) and H ₃ PO ₄ (10 ml) is precondensed for one hour and then with it a base membrane, which was produced according to the preparation example 2.8, infiltrated by doctor blade. The membrane is dried at 150 ° C for 1 h. The conductivity of the membrane at room temperature and approx. 35% relative humidity (RH) is around. 2.9 mS / cm.

EXAMPLE 12 Production of an Electrolyte Membrane by Immobilizing a Bronsted Acid 100 ml of titanium isopropoxide are dropped into 1200 ml of water with vigorous stirring. The resulting precipitate is aged for 1 h and then concentrated with 8.5 ml. HN0 _{3 was} added and peptized at the boiling point for 24 h. 10 ml of H ₂ SO ₄ (98%) are added to 100 ml of this sol. After coating the base membrane according to Production Example 2.3 with such a sol and solidifying at temperatures of up to approximately 150 ° C., the proton-conducting membrane is obtained.

Example 13: Preparation of a cPEM based on a mineral acid

8 g of a 20% solution of precipitated silica (Levasil®) are mixed with 1 g of diethyl phosphite, 1 g of H ₂ SO ₄ and 1 g of ethanol. After 1 h, 5% by weight of Aerosil200 is added to the sol and the suspension is homogenized for a further 30 min. In a continuous rolling process, an S-glass fabric is coated with it and the membrane is dried at 100 ° C.

Example 14 Preparation of a cPEM based on a mineral acid

8 g of a 20% solution of precipitated silica (Levasil®) are mixed with 1 g of diethyl phosphite, 1 g of H ₂ SO ₄ and 1 g of ethanol. After stirring briefly, an MF membrane (according to preparation example 2.8) is infiltrated with this sol using a doctor blade and the cPEM is dried at 100.degree. This membrane has a conductivity of 50 mS / cm at 45% RH and 110 mS / cm at 85% RH

Example 15: Continuous production of a cPEM based on a mineral acid 200 g of a 20% solution of precipitated silica (Levasil®) are mixed with 25 g diethyl phosphite, 25 g H ₂ SO ₄ and 38 g ethanol. After stirring for two hours using a magnetic stirrer, an MF membrane (according to Production Example 2.8) is infiltrated from the front using a roller application and dried at 120 ° C. using this sol. The belt speed is about 10 m / h. For better infiltration, this membrane is coated on the back in a second step with the same sol under otherwise the same conditions. This membrane has a conductivity of 68 mS / cm at 85% RH and 23 mS / cm at 33% RH.

Example 16 Coating with pure Nafion

A membrane according to Example 13 is coated with a 5% Nafion® solution in a continuous rolling process and dried at 100 ° C. The conductivity of the entire membrane decreases somewhat, but the membrane is suitable for the DMFC.

Example 17 Coating with Nafion / TEOS

10 ml of Dynasil A ® are added to 10 ml of 5% Nafion® solution with vigorous stirring and the mixture is stirred until only a clear phase is present. A membrane according to Example 14 is coated with this solution in a continuous rolling process and coated 100 ° C dried.

Example 18 Coating with Nafion / TEOS / Ethanol

90 ml of Dynasil A ® dissolved in 90 ml of ethanol are added to 90 ml of 5% Nafion® solution with vigorous stirring and stirring is continued for a short time. A membrane according to Example 15 is successively coated on both sides with this solution in a continuous rolling process (belt speed of 8 m / h) and dried at 100.degree. Compared to the membrane without diffusion barrier, the conductivity decreases somewhat to 44 mS / cm at 84% RH and 17 mS / cm at 42% RH.

Example 19 Coating with Trihydroxisilylpropylsulfonic Acid / Levasil 10 g of a 30% trihydroxisilylpropylsulfonic acid are dissolved in 50 g Levasil200®. A membrane according to Example 13 is coated with this solution in a continuous rolling process and dried at 100.degree. Example 20 Coating with trihydroxysilylpropylsulfonic acid / TEOS

10 g of a 30% trihydroxysilylpropylsulfonic acid are dissolved in 80 g of ethanol. A few drops of HC1 and then 30 ml of Dynasilan A ® are added to this solution, with vigorous stirring, and the solution is stirred for a further 24 hours. A membrane according to Example 15 is coated with this solution in a continuous rolling process and dried at 100.degree.

Example 21 Coating with zirconium phosphate

A membrane produced according to Example 14 is first coated with a thin layer of zirconium propylate using a doctor blade. The alcoholate is hydrolyzed in the presence of air humidity. The freshly precipitated zirconium hydroxide / oxide is then reacted with H ₃ PO ₄ and the membrane is briefly dried at 200 ° C. in order to solidify the zirconium phosphate formed. This thin layer is then insoluble in water and prevents the electrolyte from bleeding out.

Example 22: Preparation of an anode ink

10 ml of anhydrous trihydroxysilylpropylsulfonic acid, 60 ml of ethanol and 5 ml of water are mixed by stirring. 40 ml of TEOS (tetraethyl orthosilicate) are slowly added dropwise to this mixture with stirring. The catalyst known from DE 197 21 437 and DE 198 16 622 is dispersed in this sol so that a degree of catalyst coverage of approximately 0.2 mg / cm 2 or 0.5 mg / cm can be achieved in the electrode.

Example 23: Preparation of an anode ink

100 ml of titanium isopropoxide are dropped into 1200 ml of water with vigorous stirring. The resulting precipitate is aged for 1 h and then concentrated with 8.5 ml. HNO _{3 was} added and peptized at the boil for 24 h. 50 g of tungsten phosphoric acid are dissolved in 50 ml of this sol and the catalyst is then dispersed therein as described in Example 22.

Example 24: Preparation of an anode ink 20 g of aluminum alcoholate and 17 g of vanadium alcoholate are hydrolyzed with 20 g of water and the resulting precipitate is peptized with 120 g of nitric acid (25%). This solution is stirred until clear and after adding 40 g of titanium dioxide from Degussa (P25) is stirred until all agglomerates have dissolved. After the pH has been adjusted to about 6, the catalyst is dispersed therein as described in Example 22.

Example 25: Preparation of a cathode ink

10 ml of anhydrous trihydroxysilylpropylsulfonic acid, 60 ml of ethanol and 5 ml of water are mixed by stirring. 20 ml of TEOS (tetraethyl orthosilicate) and 20 ml of methyltriethoxysilane are slowly added dropwise to this mixture with stirring. The catalyst used in DE 196 11 510 or the one used in DE 198 12 592 is dispersed in this sol, so that a Pt coverage of about 0.15 mg / cm ² or 0.25 mg / cm ² can be achieved in the electrode ,

Example 26: Preparation of a cathode ink

20 g of methyltriethoxysilane, 20 g of tetraethyl orthosilicate and 10 g of aluminum trichloride are hydrolyzed with 50 g of water in 200 g of ethanol. 190 g of zeolite USY (CBV 600 from Zeolyst) are then added. The mixture is stirred until all agglomerates have dissolved and then the catalyst is dispersed therein, as described in Example 25.

Example 27: Preparation of a membrane electrode assembly

A membrane according to Example 18 is first screen-printed with the ink according to Example 23 by screen printing. This side serves as an anode in the later membrane electrode assembly. The printed membrane is dried at a temperature of 150 ° C. In addition to the escape of the solvent, the silylpropylsulfonic acid is also immobilized.

In the second step, the membrane on the back, which will later serve as the cathode, is printed with the ink from Example 25. Even now the printed membrane is again dried at a temperature of 150 ° C., whereby the solvent escapes and at the same time the silylpropylsulfonic acid is immobilized. Since the cathode is hydrophobic, the product water can easily escape when the membrane electrode unit is operated in the fuel cell. This membrane electrode assembly can be installed in a direct methanol fuel cell or a reformate fuel cell.

Example 28: Preparation of a membrane electrode assembly To produce the electrodes, both the anode ink according to Example 23 and the cathode ink according to Example 26 are each applied to an electrically conductive carbon paper. A heat treatment at a temperature of 150 ° C removes the solvent and immobilizes the proton-conductive component. These two gas diffusion electrodes are pressed with a proton-conductive membrane according to Example 20 to form a membrane electrode unit, which can then be installed in the fuel cell.

Example 29: Production of a fuel cell To produce the MEA, the electrodes are first manufactured. For this, a ceramic fleece is coated with a carbon black / platinum mixture (40%). These electrodes are pressed onto the electrolyte membrane according to Example 18. The pressure is applied via a graphitic gas distributor plate, which also serves for electrical contacting. Pure hydrogen is used on the anode side and pure oxygen is used on the cathode side. Both gases are moistened via water vapor saturators (so-called "bubblers").

Comparative example:

A fuel cell was made as described in Example 29, except that a conventional Nafion® 117 membrane was used as the MEA. It was found that when a Nafion membrane was used, the proton conductivity dropped drastically at a relative humidity of less than 100%, and the surface resistance increased significantly, so that the fuel cell could no longer be operated. On the other hand, a membrane according to the invention can also be operated at a relative atmospheric humidity which was a maximum of 50% on the anode side and 0 to a maximum of 50% on the cathode side without the function of the fuel cell being significantly impaired.

Claims

Claims:

1. For the reaction components of the fuel cell reaction impermeable, proton-conductive, electrolyte membrane for a fuel cell, comprising a permeable composite material made of a perforated, non-conductive, glass or ceramic carrier, wherein the composite material is permeated with a proton-conductive material which is suitable, selectively by protons to conduct the membrane, characterized in that the electrolyte membrane has on at least one side an outer proton-conductive coating as a diffusion barrier, which is insoluble in water and methanol.

2. For the reaction components of the fuel cell reaction impermeable, proton-conductive, flexible electrolyte membrane for a fuel cell, available from

(a) infiltration of a permeable composite material from a flexible, perforated, non-conductive, glass or ceramic carrier with a first mixture, comprising:

(al) an immobilizable hydroxysilylalkyl acid of sulfur or phosphorus or a salt thereof; or (a2) a Bronsted acid and / or an immobilizable hydroxysilylalkyl acid of sulfur or phosphorus or a salt thereof and a sol which comprises a precursor for oxides of aluminum, silicon, titanium, zirconium and / or phosphorus and

(b) solidifying the first mixture infiltrating the composite to create a material penetrating the composite that is capable of selectively guiding protons through the membrane and

(c) subsequently applying a second mixture to at least one side of the electrolyte membrane obtained and solidifying it to form a proton-conducting coating as a diffusion barrier which is insoluble in water and methanol.

3. Electrolyte membrane according to claim 1 or 2, characterized in that the electrolyte membrane has an outer proton-conductive coating on both sides as a diffusion barrier, which is insoluble in water and methanol.

4. Electrolyte membrane according to one of claims 1 to 3, characterized in that the proton conductive material which gives the membrane proton conductivity inside,

(i) an immobilized hydroxysilylalkyl acid of sulfur or phosphorus and optionally an oxide of aluminum, silicon, titanium, zirconium and / or phosphorus as a network former, and / or (ii) a Bronsted acid and an oxide of aluminum, silicon, titanium, zirconium, and / or includes phosphorus as a network former.

5. Electrolyte membrane according to claim 2 or 4, characterized in that the Bronsted acid comprises sulfuric acid, phosphoric acid, perchloric acid, nitric acid, hydrochloric acid, sulfurous acid, phosphorous acid and esters thereof and / or a monomeric or polymeric organic acid.

6. Electrolyte membrane according to claim 2, 4 or 5, characterized in that the hydroxysilylalkyl acid of sulfur or phosphorus or a salt thereof is an organosilicon compound of the general formulas

[{(RO) _y (R ² ) _z } _a Si {R ¹ -S0 ₃ ^" } _a ] _x M ^{x +} (I) or [(RO) _y (R ² ) _z Si {R ¹ -O _b -P (O _c R ³ ) O ₂ -} _a ] _x M ^{x +} (II)

is, where R ^{1 is} a linear or branched alkyl or alkylene group having 1 to 12 carbon atoms, a cycloalkyl group having 5 to 8 carbon atoms or a unit of the general

formulas

or

where n, m each represents an integer from 0 to 6,

7. The electrolyte membrane according to claim 6, wherein the hydroxysilylalkyl acid of sulfur or phosphorus is trihydroxysilylpropylsulfonic acid, trihydroxysilylpropylmethylphosphonic acid or dihydroxysilylpropylsulfonedioic acid.

8. Electrolyte membrane according to one of claims 6 or 7, characterized in that the hydroxysilylalkyl acid of sulfur or phosphorus or a salt thereof with a hydrolyzed compound of phosphorus or a hydrolyzed nitrate, oxynitrate, chloride, oxychloride, carbonate, alcoholate, acetate, acetylacetonate one Metal or semi-metal or with a hydrolyzed compound obtained from diethyl phosphite (DEP), diethyl ethyl phosphonate (DEEP), titanium propylate, titanium ethylate, tetraethyl orthosilicate (TEOS) or tetramethyl orthosilicate (TMOS), zirconium nitrate, zirconium oxynitrate, zirconium propylate, zirconium acetate or zirconium acetylacetonate or phosphoric acid methyl ester.

9. Electrolyte membrane according to one of claims 1 to 8, characterized in that the composite material has porous ceramic material.

10. Electrolyte membrane according to claim 9, characterized in that the composite material comprising a porous ceramic material has a porosity of

20 to 60%, preferably from 25 to 50% and very particularly preferably from 30 to

35%.

11. Electrolyte membrane according to one of claims 9 or 10, characterized in that the porous ceramic material has pores with an average diameter of at least 20 nm, preferably of at least 100 nm, very particularly preferably more than 250 nm.

12. Electrolyte membrane according to one of claims 1 to 11, characterized in that the carrier is flexible.

13. Electrolyte membrane according to one of claims 1 to 12, characterized in that the carrier has fibers or filaments.

14. Electrolyte membrane according to claim 13, characterized in that the carrier fibers and / or filaments with a diameter of 0.5 to 150 microns, preferably 0.5 to 20 μm, and / or threads with a diameter of 5 to 150 μm, preferably 10 to 70 μm.

15. Electrolyte membrane according to claim 13 or 14, characterized in that the carrier comprises a fabric or a nonwoven.

16. Electrolyte membrane according to claim 15, characterized in that the carrier is a fabric with a mesh size of 5 to 500 microns, preferably 10 to 200 microns, or that the carrier is a nonwoven with a thickness of 5 to 100 microns and preferably of 10 is up to 30 μm.

17. Electrolyte membrane according to one of claims 1 to 16, characterized in that the carrier has a ceramic which has a proportion of aluminum oxide, silicon carbide, silicon nitride or a zirconium oxide of greater than 50% by weight.

18. Electrolyte membrane according to one of claims 1 to 16, characterized in that the carrier has an aluminosilicate glass which has at least 60% by weight SiÜ2 and at least 10% by weight Al ₂ O ₃ .

19. Electrolyte membrane according to claim 18, characterized in that the carrier has a glass which from 64 to 66 wt .-% SiO ₂ , from 24 to 25 wt .-% Al ₂ O ₃ , from 9 to 12 wt .-% MgO and less than 0.2 wt .-% CaO, Na ₂ O, K ₂ O and / or Fe ₂ O ₃ .

20. Electrolyte membrane according to one of claims 1 to 19, characterized in that the carrier has fibers or filaments made of aluminum oxide, which have a ratio of 0 to 30% silicon oxide / aluminum oxide.

21. Electrolyte membrane according to one of claims 1 to 20, characterized in that the composite material has a thickness in the range of 5 to 150 microns, when using a fabric preferably 10 to 80 microns, very particularly preferably 10 to 50 microns, and when using a fleece preferably 5 to 50 microns, most preferably 10 to 30 microns.

22. Electrolyte membrane according to one of claims 1 to 21, characterized in that it is stable at at least 80 ° C, preferably at least 100 ° C, and very particularly preferably at at least 120 ° C.

23. Electrolyte membrane according to one of claims 1 to 22, characterized in that the diffusion barrier has a polymeric and / or organic and / or inorganic proton conductor.

24. The electrolyte membrane according to claim 23, characterized in that the diffusion barrier has a polymeric proton conductor selected from Nafion®, sulfonated or phosphonated polyphenyl sulfones, polyimides, polyoxazoles, polytriazoles, polybenzimidazoles, polyether ether ketones (PEEK) or polyether ketones (PEK).

25. Electrolyte membrane according to claim 23 or 24, characterized in that the diffusion barrier comprises an inorganic proton conductor, selected from sulfonic or phosphonic acids, zirconium or titanium phosphates, sulfoaryl phosphonates or phosphonates, or mixtures thereof.

26. Electrolyte membrane according to one of claims 23 to 25, characterized in that the diffusion barrier is a composite material made of polymeric and inorganic

Has proton conductors.

27. Electrolyte membrane according to one of claims 1 to 26, characterized in that the diffusion barrier has at least one material which has no proton-conducting properties.

28. Electrolyte membrane according to claim 27, characterized in that the diffusion barrier has at least one oxide of aluminum, zirconium, silicon and / or titanium.

29. Electrolyte membrane according to one of claims 1 to 28, characterized in that the diffusion barrier has a thickness of less than 5 microns, preferably from 10 to

1000 nm.

30. Electrolyte membrane according to one of claims 1 to 29, characterized in that the electrolyte membrane is flexible and tolerates a bending radius of down to 100 m, preferably from down to 20 mm, very particularly preferably from down to 5 mm without damage.

31. Electrolyte membrane according to one of claims 1 to 30, which at room temperature and at a relative humidity of max. 45% a conductivity of at least

2 mS / cm, preferably at least 10 mS / cm, most preferably 17 mS / cm.

32. A method for producing an electrolyte membrane according to one of claims 1 to 31, characterized in that the method comprises the following steps: (a) providing an electrolyte membrane and (b) applying a mixture which has at least one proton-conducting material to at least one side of the obtained electrolyte membrane and (c) solidifying it into a proton-conducting coating which is insoluble in water and methanol.

33. The method according to claim 32, characterized in that the mixture from step (b) is applied to both sides of the electrolyte membrane.

34. The method according to claim 32 or 33, characterized in that the mixture from step (b) has an organic and / or inorganic proton conductor.

35. The method according to any one of claims 32 to 34, characterized in that the mixture from step (b) is a polymeric proton conductor selected from Nafion®, sulfonated or phosphonated polyphenylsulfones, polyimides, polyoxazoles, polytriazoles, polybenzimidazoles, polyether ether ketones (PEEK) or has polyether ketones (PEK).

36. The method according to any one of claims 32 or 35, characterized in that the mixture from step (b) is an inorganic proton conductor selected from

Has sulfonic or phosphonic acids or their salts, zirconium or titanium phosphates, phosphonates or sulfoaryl phosphonates or mixtures thereof.

37. The method according to any one of claims 32 to 36, characterized in that the mixture from step (b) comprises a composite material made of polymeric and organic and / or inorganic proton conductors.

38. The method according to any one of claims 32 to 37, characterized in that the mixture from step (b) has at least one material which has no proton-conducting properties, selected from the oxides of aluminum, zirconium, silicon and / or titanium, precipitated silica , Tefraethoxysilane, brine

Basis of TiO ₂ or ZrÜ2.

39. The method according to any one of claims 32 to 38, characterized in that the application of the mixture from step (b) by printing, pressing,

Pressing, rolling, knife coating, spreading, dipping, spraying or pouring the mixture onto the electrolyte membrane takes place.

40. The method according to any one of claims 32 to 39, wherein the application of the mixture from step (b) is carried out repeatedly and optionally a drying step, preferably at an elevated temperature in a range from 50 to 200 ° C., is carried out between the repeated applications.

41. The method according to any one of claims 32 to 40, wherein the solidification of the mixture from step (b) by heating to a temperature of 50 to 300 ° C, preferably 50 to

200 ° C, very particularly preferably 80 to 150 ° C.

42. The method according to at least one of claims 32 to 41, characterized in that the provision of an electrolyte membrane (a) comprises the following steps:

(al) Infiltration of a permeable composite material from a perforated, non-conductive, glass or ceramic carrier with (al .1) a mixture containing an immobilizable hydroxysilylalkyl acid of

Sulfur or phosphorus or a salt thereof; or (al.2) a mixture comprising a Bronsted acid and / or an immobilizable hydroxysilylalkyl acid of sulfur or phosphorus or a salt thereof and a sol which is a precursor for oxides of aluminum,

Silicon, titanium, zirconium, and / or phosphorus comprises and (a2) solidification of the mixture infiltrating the composite to create a material penetrating the composite, which is capable of selectively guiding protons through the membrane, so that a proton-conducting membrane is obtained

43. The method according to claim 42, characterized in that the sol from step (al .2) is obtainable by (al.2-1) hydrolysis of a hydrolyzable compound, preferably in a mixture of water and alcohol, to give a hydrolyzate, the hydrolyzable compound is selected from hydrolyzable alcoholates, acetates, acetylacetonates, nitrates, oxynitrates, chlorides, oxychlorides, carbonates, aluminum, silicon, titanium, zirconium, and / or phosphorus or esters, preferably methyl esters, ethyl esters and / or propyl esters of phosphoric acid or phosphorous acid, and (al .2-2) peptizing the hydrolyzate to a sol.

44. The method according to at least one of claims 32 to 43, characterized in that the mixture according to (al.l) or (al.2) further proton-conducting substances, preferably titanium phosphates, titanium phosphonates, zirconium phosphates, zirconium phosphonates, iso- and heteropolyacids, preferably tungsten phosphoric acid or silicon tungstic acid, nanocrystalline and / or crystalline metal oxides, with Al ₂ O ₃ , ZrO ₂ , Ti0 ₂ or SiO ₂ powder being preferred.

45. The method according to any one of claims 32 to 44, wherein the infiltration according to step (al) by printing, pressing, pressing, rolling up, knife coating, spreading on, dipping, spraying or pouring the mixture of (al.l) or (al.2) onto the permeable composite material.

46. The method according to any one of claims 32 to 45, wherein the infiltration with the mixture according to step (al.l) or (al.2) is carried out repeatedly and optionally a drying step, preferably at an elevated temperature in a range from 50 to 200 ° C, between repeated infiltration.

47. The method according to any one of claims 32 to 46, wherein the solidification according to step (a2) is carried out by heating to a temperature of 50 to 300 ° C, preferably 50 to 200 ° C, very particularly preferably 80 to 150 ° C.

48. Membrane electrode unit for a fuel cell, with an electrically conductive anode and cathode layer, each on opposite sides for one

Reaction components of the fuel cell reaction impermeable, proton-conductive, electrolyte membrane for a fuel cell, in particular according to one of claims 1 to 31, are provided, wherein the electrolyte membrane comprises a permeable composite material which is permeated with a proton-conductive material which is suitable for selectively protons through the membrane conduct, and which has on at least one side an outer proton-conductive coating as a diffusion barrier, which is insoluble in water and methanol and wherein the anode layer and the cathode layer are porous and each have a catalyst for the anode and cathode reaction, a proton-conductive component and optionally a catalyst support include.

49. Membrane electrode unit according to claim 48, wherein the proton-conductive component of the anode and / or cathode layer and / or the proton-conductive material of the electrolyte membrane each comprises

(i) an immobilized hydroxysilylalkyl acid of sulfur or phosphorus or a salt thereof and optionally an oxide of aluminum, silicon, titanium, zirconium and / or phosphorus as a network former, and / or (ii) a Bronsted acid and an oxide of aluminum, silicon, titanium Zirconium and / or phosphorus as a network former and optionally (iii) further proton-conducting substances, preferably titanium phosphates, titanium phosphonates, zirconium phosphates, zirconium phosphonates, iso- and heteropoly acids, preferably tungsten phosphoric acid or silicon tungstic acid or nanocrystalline metal oxides, where AI ₂ O ₃ -, Zrθ ₂ -, Ti0 ₂ - or SiO ₂ powder are preferred.

50. Membrane electrode unit according to claim 49, wherein the hydroxysilylalkyl acid of sulfur or phosphorus or a salt thereof is an organosilicon compound of the general formulas [{(ROMR ^ SH ^ -SO J.M ^ (I) or

[(RO) _y (R ² ) _z Si {R ¹ -O _b -P (O _c R ³ ) O ₂ ^' } _a ] _x M ^{x +} (II), where R ^{1 is} a linear or branched alkyl or Alkylene group with 1 to 12 carbon atoms, a cycloalkyl group with 5 to 8 carbon atoms or a unit of the general formulas

or

where n, m is an integer from 0 to 6, M is H, NH ₄ or a metal, x = 1 to 4, y = 1 to 3, z = 0 to 2 and a = 1 to 3, with the proviso that y + z = 4 - a, b, c = O or 1,

51. Membrane electrode unit according to claim 50, wherein the hydroxysilylalkyl acid of sulfur or phosphorus is trihydroxysilylpropylsulfonic acid, trihydroxysilylpropylmethylphosphonic acid or dihydroxysilylpropylsulfonedioic acid.

52. Membrane electrode unit according to one of claims 49 to 51, characterized in that the hydroxysilylalkyl acid of sulfur or phosphorus or a salt thereof with a hydrolyzed compound of phosphorus or a hydrolyzed nitrate, oxynitrate, chloride, oxychloride, carbonate, alcoholate, acetate, acetylacetonate one Metal or semimetal or with a hydrolyzed compound obtained from diethyl phosphite (DEP), diethyl ethyl phosphonate (DEEP), titanium propylate, titanium ethylate, tetraethyl orthosilicate (TEOS) or tetramethyl orthosilicate (TMOS), zirconium nitrate, zirconium oxynitrate,

Zirconium propylate, zirconium acetate or zirconium acetylacetonate or methyl phosphorate is immobilized.

53. Membrane electrode unit according to one of claims 48 to 52, which can be operated at a temperature of at least 80 ° C, preferably at least 100 ° C, and very particularly preferably at least 120 ° C.

54. Membrane electrode unit according to one of claims 48 to 53, wherein the permeable composite material, a flexible, openwork, non-conductive

Carrier based on glass or ceramic, which has a porous ceramic coating, a ceramic coating or no coating.

55. Membrane electrode unit according to one of claims 48 to 54, which tolerates a bending radius of at least 100 m, preferably of at least 20 mm, very particularly preferably of at least 5 mm.

56. Membrane electrode unit according to one of claims 48 to 55, wherein the proton-conductive component of the anode layer and / or the cathode layer and / or the proton-conductive material of the electrolyte membrane have the same or different composition.

57. Membrane electrode unit according to one of claims 48 to 56, wherein the anode layer and the cathode layer have different catalysts.

58. Membrane electrode unit according to one of claims 48 to 57, wherein the catalyst support in the anode layer and in the cathode layer is electrically conductive.

59. A method for producing a membrane electrode unit according to one of claims 48 to 58, the method comprising the following steps,

(A) Provision of a proton-conductive, flexible electrolyte membrane which is impermeable to the reaction components of the fuel cell reaction, for a fuel cell, in particular according to one of claims 1 to 31, the electrolyte membrane comprising a permeable composite material comprising a flexible, openwork, non-conductive, glass or ceramic Carrier, wherein the composite material is interspersed with a proton-conductive material which is suitable for selectively guiding protons through the membrane and which has an outer proton-conductive coating on at least one side as a diffusion barrier which is insoluble in water and methanol,

(B1) a condensable component which gives proton conductivity after the electrode layer has condensed,

(B2) a catalyst which catalyzes the anode reaction or the cathode reaction, or a precursor compound of the catalyst, (B3) optionally a carrier and (B4) optionally a pore former, (C) applying the agents from stage (B) to one side of the electrolyte membrane from stage (A) to form a coating, (D) creating a firm bond between the Coatings and the

Electrolyte membrane with the formation of a porous, proton-conductive anode layer or cathode layer, it being possible for the anode layer and the cathode layer to be formed simultaneously or in succession.

60. The method of claim 59, wherein the application of the agent in step (C) is carried out by printing, pressing on, pressing in, rolling up, knife coating, spreading on, dipping, spraying or pouring on.

61. The method according to any one of claims 59 or 60, wherein the agent according to step (B) for producing an anode layer or a cathode layer is a suspension which is obtainable by

(51) Preparation of a sol comprising a hydroxysilylalkyl acid of sulfur or phosphorus or its salt and optionally a hydrolysable compound of phosphorus immobilizing the hydroxysilylalkyl acid of sulfur or phosphorus or its salt or a hydrolyzable nitrate, oxynitrate, chloride, oxychloride, carbonate, alcoholate , Acetate, acetylacetonate of a metal or semimetal, preferably methyl phosphate, diethyl phosphite (DEP), diethyl ethyl phosphonate (DEEP), titanium propylate, titanium ethylate, tetraethyl orthosilicate (TEOS) or tetramethyl orthosilicate (TMOS), zirconium nifrate, zirconium oxynomate acylate nitrate

62. The method according to any one of claims 59 to 61, wherein the agent according to step (B) for producing an anode layer or a cathode layer is a suspension which is available through

(Hl) hydrolysis of a hydrolyzable compound to a hydrolyzate, the hydrolyzable compound being selected from a hydrolyzable compound of phosphorus or hydrolyzable nitrates, oxynitrates, chlorides, oxychlorides, carbonates,

Alcoholates, acetates, acetylacetonates of a metal or semimetal, preferably aluminum alcoholates, vanadium alcoholates, titanium propylate,

Titanium ethylate, zirconium nitrate, zirconium oxynitrate, zirconium propylate,

Zirconium acetate or circomum acetylacetonate, or metallic acids of aluminum, silicon, titanium, vanadium, antimony, tin,

Lead, chromium, tungsten, molybdenum, manganese, with tungsten phosphoric acid and silicon tungstic acid being preferred, (H2) peptizing the hydrolyzate with an acid to form a dispersion, (H3) mixing the dispersion with a nanocrystalline proton-conducting metal oxide, preferably Al ₂ O ₃ -, ZrO ₂ , TiO ₂ or SiO ₂ powder,

(H4) dispersing the catalyst and optionally the carrier and pore former.

63. The method according to any one of claims 59 to 62, wherein the means for producing an anode layer and a cathode layer are printed in step (C) and for creating a firm bond between the coatings and the

Electrolyte membrane with the formation of a porous, proton-conductive anode layer or cathode layer in step (D) to a temperature of 50 to 300 ° C, preferably 50 to 200 ° C, most preferably 80 to 150 ° C is heated.

64. The method according to any one of claims 59 to 62, characterized by (Ml) applying the agent for producing an anode layer or cathode layer to a support membrane, preferably made of polytretrafluoroethylene, (M2) drying the coating obtained under (Ml), (M3) pressing on the dried coating on the electrolyte membrane at a

Temperature of 20 to 300 ° C, preferably 50 to 200 ° C, very particularly preferably 80 to 150 ° C, (M4) removing the support membrane, in particular by mechanical detachment, chemical dissolution, or pyrolyzing or characterized by (Nl) applying the agent for producing an anode layer or cathode layer to a support membrane, preferably made of carbon paper or an electrically conductive fleece or fabric, (N2) drying the coating obtained under (Nl) for producing a coated support membrane, (N3) pressing the coated support membrane onto the electrolyte membrane at a temperature from room temperature to 300 ° C., preferably 50 to 200 ° C., very particularly preferably 80 to 150 ° C.

65. The method according to any one of claims 59 to 64, wherein in step (B) in each the provision of a means for producing an anode layer and a cathode layer, the means

(iv) a catalyst metal salt, preferably hexachloroplatinic acid, comprises (v) after the application of the agents by step (C) the catalyst metal salt into one

Catalyst which catalyzes the anode reaction or the cathode reaction is reduced (vi) in step (D) an open-pore gas diffusion electrode, preferably an open-pore one

Carbon paper, pressed onto the catalyst or glued to the catalyst with an electrically conductive adhesive.

66. The method according to any one of claims 59 to 65, wherein the application of the agent for producing an anode layer or cathode layer is carried out repeatedly and optionally a drying step, preferably at an elevated temperature in a range of 50 to 200 ° C, between the repeated implementation of the Applying.

67. The method according to any one of claims 59 to 66, wherein the application of the means for producing an anode layer or cathode layer takes place on a flexible electrolyte membrane or flexible support membrane rolled off a first roll.

68. The method according to any one of claims 59 to 67, wherein the application of the means for producing an anode layer or cathode layer is carried out continuously.

69. The method according to any one of claims 59 to 68, wherein the application of the means for producing an anode layer or cathode layer on a heated electrolyte or

Support membrane is made.

70. The method according to any one of claims 59 to 69, wherein in step (D) to create a firm bond between the coatings and the electrolyte membrane to a temperature of 50 to 300 ° C, preferably 50 to 200 ° C, most preferably 80 to 150 ° C is heated.

71. The method according to claim 70, wherein heating is carried out by means of air, hot air, infrared radiation or microwave radiation.

72. The method according to any one of claims 59 to 71, wherein the agent in step (B) comprises: (TI) a condensable component which, after the condensation of an anode layer or a cathode layer, imparts proton conductivity to a fuel cell of a membrane cell unit selected from (I) hydrolyzable compounds of phosphorus or hydrolyzable nitrates,

Oxynitrates, chlorides, oxychlorides, carbonates, alcoholates, acetates, acetylacetonates of a metal or semimetal, preferably aluminum alcoholates, vanadium alcoholates, titanium propylate, titanium ethylate, zirconium nitrate, zirconium oxynitrate, zirconium propylate, zirconium acetate or zirconium metal or titanium acetic acid, desiccantum or acetylacetanoacetate, desiccum or acetic acid

Vanadium, antimony, tin, lead, chromium, tungsten, molybdenum, manganese, with tungsten phosphoric acid being preferred, and / or (II) an immobilizable hydroxysilylalkyl acid of sulfur or phosphorus or a salt thereof and optionally one of the hydroxysilylalkyl acid

Sulfur or phosphorus or their salt immobilizing hydrolyzable compound of phosphorus or a hydrolyzable nitrate, oxynitrate, Chloride, oxychloride, carbonate, alcoholate, acetate, acetylacetonate of a metal or semimetal, preferably diethyl phosphonate (DEP), diethyl ethyl phosphonate (DEEP), Phosphorsäuremethylester, titanium propylate, titanium ethoxide, tetraethylorthosilicate (TEOS) or tetramethyl orthosilicate (TMOS), Zirkoniumnifrat, zirconium oxynitrate, zirconium propoxide, zirconium acetate or

Zirkomumacetylacetonat. (T2) a catalyst which catalyzes the anode reaction or the cathode reaction in a fuel cell, or a precursor compound of the catalyst selected from a platinum metal, in particular platinum, palladium and / or ruthenium or an alloy of platinum metals, and optionally one

Cocatalyst, wherein the cocatalyst is a transition metal complex of phthalocyanine or substituted phthalocyanines, (T3) optionally a catalyst support which is electrically conductive and is preferably selected from carbon black, graphite, carbon, carbon, activated carbon or metal oxides, and

(T4) optionally a pore former selected from an organic and / or inorganic substance which decomposes at a temperature between 50 and 300 ° C and preferably between 100 and 200 ° C, and (T5) optionally additives to improve foam behavior, Viscosity and adhesion.

73. Use of an electrolyte membrane according to one of claims 1 to 31 in a fuel cell.

74. Use according to claim 73, wherein the fuel cell is a direct methanol fuel cell or a reformate fuel cell.

75. Use of an electrolyte membrane according to one of claims 1 to 31 for producing a membrane electrode unit, a fuel cell or a fuel cell stack.

76. Use of a membrane electrode unit according to one of claims 48 to 58 in a fuel cell.

77. Use according to claim 76, wherein the fuel cell is a direct methanol fuel cell or a reformate fuel cell.

78. Fuel cell with an electrolyte membrane according to one of claims 1 to 31.

79. A fuel cell with a membrane electrode unit according to one of claims 48 to 58.

80. Mobile or stationary system with a membrane electrode unit, a fuel cell or a fuel cell stack, containing an electrolyte membrane according to one of claims 1 to 31 or a membrane electrode unit according to one of claims 48 to 58.

81. Vehicle, which is a mobile system according to claim 80.

82. Building energy system, which is a stationary system according to claim 80.