WO2009106620A1

WO2009106620A1 - 5- or 7-layer membrane electrode assembly (mea) and production thereof by hot pressing in the presence of solvent vapor

Info

Publication number: WO2009106620A1
Application number: PCT/EP2009/052381
Authority: WO
Inventors: Oemer Uensal; Sigmar Braeuninger; Thomas Haag
Original assignee: Basf Se
Priority date: 2008-02-29
Filing date: 2009-02-27
Publication date: 2009-09-03

Abstract

The invention relates to a method for producing a membrane electrode assembly comprising at least one polymer electrolyte membrane, at least one electrode layer and at least one gas diffusion layer by compressing at least one polymer electrolyte membrane and at least one gas diffusion electrode or of at least one catalyst-coated polymer electrolyte membrane and at least one gas diffusion layer in the presence of a solvent, the at least one solvent being applied from the exterior in liquid form or in the form of vapor prior to and/or during compression of the at least one polymer electrolyte membrane, to the at least one gas diffusion electrode and/or to the at leas tone gas diffusion layer. The invention further relates to a membrane electrode assembly which is produced by said method and to a fuel cell which contains said membrane electrode assembly.

Description

5- or 7-layer membrane electrode assembly (MEA) and its production by hot pressing in the presence of solvent vapor

description

The present invention relates to a method for producing a membrane-electrode assembly comprising at least one polymer electrolyte membrane, at least one electrode layer and at least one gas diffusion layer by compressing at least one polymer electrolyte membrane and at least one gas diffusion electrode or at least one catalyst-coated polymer electrolyte membrane and at least one gas diffusion layer in the presence of a solvent, wherein the at least one solvent in liquid form or in vapor form is externally applied to the at least one polymer electrolyte membrane to which at least one gas diffusion electrode and / or to the at least one gas diffusion layer is extruded; Electrode unit manufactured by this method, and a fuel cell containing such a membrane-electrode unit.

Fuel cells are energy converters that convert chemical energy into electrical energy. In a fuel cell, the principle of electrolysis is reversed. In this case, a fuel, such as hydrogen, and an oxidizing agent, such as oxygen, locally separated from each other at two electrodes in electrical power, water and heat are converted. The structure of the various fuel cells known to those skilled in principle is the same. They generally consist of two electrodes, an anode and a cathode, where the reactions take place, and an electrolyte between the two electrodes. In the case of a polymer electrolyte membrane fuel cell (PEM fuel cell), the electrolyte used is a polymer membrane which conducts ions, in particular H ⁺ ions. The electrolyte has three functions. It establishes the ionic contact, prevents the electronic contact and also ensures the separation of the gases supplied to the electrodes. The electrodes are usually supplied with gases, which are reacted in the context of a redox reaction. The purpose of the electrodes is to supply the gases, for example hydrogen or methanol and oxygen or air, to remove reaction products such as water or CO ₂ , catalytically convert the starting materials and remove or supply electrodes. The conversion of chemical to electrical energy takes place at the three phase boundary of catalytically active centers, for example platinum, ionic conductors, for example ion exchange polymers, electron conductors, for example graphite, and gases, for example hydrogen and oxygen. Methods of making membrane-electrode assemblies are already known in the art.

SS Kocha et al., Handbook of Fuel Cells, Vol. 3, Chapter 43, pages 538 to 565 of open-label methods of making membrane-electrode assemblies (MEA). By way of example, MEAs comprising a polymer electrolyte membrane which is provided on both sides with in each case one electrode layer and in which a respective gas distribution layer is present on both electrode layers are obtained by compressing the corresponding layers under pressure and at elevated temperature. The pressure is about 5000 to 15000 kPa, and the temperature is about 120 to 160 ⁰ C. To avoid unwanted drying of the polymer electrolyte membrane, this is according to SS Kocha et al. stored in water prior to compression so that it accumulates in the membrane. During hot pressing, the water stored in the membrane evaporates so that the membrane does not dry out completely.

V. Mehta et al., Journal of Power Sources 1 14 (2003), pages 32 to 53 also disclose methods of making MEAs. These are obtained, for example, by combining a membrane and a gas diffusion electrode by hot pressing. According to this document, the membrane is previously heated in a solution of hydrogen peroxide in water, rinsed with water, treated with dilute sulfuric acid and treated repeatedly in boiling water to remove organic or metallic residues.

US 5,871,860 discloses a method of making membrane-electrode assemblies. For this purpose, a gas diffusion layer of plastic-coated paper is coated with a paste containing a catalytically active material. This gas diffusion electrode is then brought together with a membrane and compressed at elevated pressure and elevated temperature.

EP 1 369 948 A1 discloses a process for producing membrane-electrode assemblies using adhesives. To this end, the three components consisting of a polymer electrolyte membrane provided with electrode layers on both sides and two gas diffusion layers are laminated to a five-layer MEA using an adhesive selected from thermoplastic and thermosetting polymer compositions.

The known methods for the production of membrane-electron units have

Disadvantages. In hot pressing, the water necessary for the proton conduction is evaporated from the electrode and out of the membrane. As a result, membrane Electrode units an activation step, which, depending on the ionomer, can be very time consuming. In addition, the decrease of the water content in the electrode and the membrane in many sulfonated ionomers increases the gas transition temperature. As a result, significantly higher temperatures have to be used during the compression process in order to achieve intimate bonding, which in turn places a high thermal load on the materials used. If no intimate bond is achieved during pressing, this has the consequence that the resistance increases, and the performance of the resulting fuel cell is greatly reduced. The incompletely assembled MEAs also tend to delaminate membranes and electrodes in the long-term test, as contact at the boundary layer is not permanent. When joining the layers present in a membrane-electrode assembly by gluing an additional layer is applied, which usually leads to a decrease in electrical conductivity and / or deterioration of the mass transport through the layers due to their lack of conductivity. A method in which a water-saturated membrane is hot-pressed has a drawback that water or water vapor expanding during the compression process prevents the layers to be pressed from intimately bonding. Furthermore, a further process step is necessary to ensure that the membrane is completely loaded with water.

The object of the present application is therefore to provide a process for producing a membrane-electrode assembly which does not have the disadvantages of the prior art processes. In particular, a method is to be provided in which a membrane-electrode assembly is obtained which has a sufficient and above all uniform adhesion of the individual layers to one another. It should be introduced into the MEA no interfering during later operation of the fuel cell components. Furthermore, according to the method of the invention, the MEA is to be present in a form which makes it possible for this MEA to be operated directly after installation in corresponding devices of a fuel cell, i. H. Time-consuming and costly activation steps should be eliminated as far as possible.

These objects are achieved by a method for producing a membrane-electrode assembly comprising at least one polymer electrolyte membrane, at least one electrode layer and at least one gas diffusion layer by compressing at least one polymer electrolyte membrane and at least one gas diffusion electrode or at least one catalyst-coated polymer electrolyte membrane and at least one Gas diffusion layer in the presence of a solvent, wherein the at least one solvent in liquid form or in vapor form before and / or during the compression of externally to the less at least one polymer electrolyte membrane to which at least one gas diffusion electrode and / or the at least one gas diffusion layer is applied.

The core of a PEM fuel cell is a polymer electrolyte membrane coated on both sides with a catalyst (cate / ysf-coated membrane, CCM) or a membrane electrode assembly (membrane-electrode-assemby, MEA). In this context, a bilayer catalyst-coated polymer electrolyte membrane (CCM) is understood as meaning a three-layer, catalyst-coated polymer electrolyte membrane comprising an outer anode catalyst layer on one side of the membrane, the central membrane layer and an outer cathode catalyst layer on the opposite side of the membrane layer from the anode catalyst layer covers. The membrane layer consists of proton-conducting polymer materials, which are referred to below as ionomers. The catalyst layers contain catalytically active components which catalytically support the respective reaction at the anode or cathode, for example oxidation of hydrogen, reduction of oxygen. The catalytically active components used are preferably platinum group metals of the Periodic Table of the Elements.

The membrane-electrode unit (MEA) comprises, in addition to a catalyst-coated polymer electrolyte membrane (CCM) on both sides, at least one gas diffusion layer (GDL). The gas diffusion layers serve to supply gas to the catalyst layers and to divert the cell current. A three-layered MEA contains a membrane coated on one side with a cathode catalyst layer and on the other side with an anode catalyst layer (CCM). A five-layer MEA corresponds to a three-layer MEA in which a gas diffusion layer is applied to each of the catalyst layers. On the one hand, a five-layer MEA can be obtained by providing a CCM on each side with one GDL each. Second, a five-layered MEA can be obtained by providing a respective membrane on each side with a gas diffusion electrode (GDE) containing a gas diffusion layer and an electrode layer containing the corresponding catalyst. A seven-layer MEA is a five-layer MEA in which two gas diffusion layers each have a layer of sealing material applied.

In a PEM fuel cell, the membrane electrode assembly (MEA) is typically inserted between two gas distribution plates. The gas distribution plates serve as current collectors and as distributors for the reaction fluid streams, for example hydrogen, oxygen or a liquid fuel, for example formic acid. In order to achieve the distribution of the reaction fluid flows to the electrochemically active area of the membrane-electrode unit, those of the membrane electrodes are usually Unit facing surfaces of the gas diffusion layers with channels or wells with open side.

According to the invention, it is possible to produce an MEA by compressing in a first variant at least one polymer electrolyte membrane and at least one gas diffusion electrode (GDE) or, in a second variant, at least one catalyst-coated polymer electrolyte membrane (CCM) and at least one gas diffusion layer ( GDL) are compressed. The two variants differ from each other only in which of the at least two layers to be connected to one another the electrode layer is applied. In the first variant, the electrode layer containing the catalytically active material is applied to the gas diffusion layer, in the second variant the at least one electrode layer containing the catalytically active material is located on the polymer electrolyte membrane.

In a preferred embodiment, the process according to the invention is used to produce a membrane-electrode assembly comprising a polymer electrolyte membrane (CCM) coated on both sides with catalyst, which is provided on both sides with a respective gas diffusion layer. Furthermore, the method according to the invention can preferably be used to produce a five-layered membrane-electrode assembly comprising a membrane and two gas diffusion electrodes. Furthermore, the method according to the invention can preferably be used in the production of a seven-layer membrane-electrode assembly comprising a membrane, two gas diffusion electrodes and two sealing layers or a polymer electrolyte membrane (CCM) coated on both sides with catalyst, two gas diffusion layers and two sealing layers ,

The polymer electrolyte membrane used according to the invention is constructed in a preferred embodiment of an ionomer having acidic properties. However, it is also possible that the membrane also contains non-acidic ionomers. The ionomers which can be used in the process according to the invention are known from the prior art and disclosed, for example, in WO-A 03/054991. Preferably, at least one ionomer is used which has sulfonic acid, carboxylic acid and / or phosphonic acid groups and their salts. Suitable ionomers containing sulfonic acid, carboxylic acid and / or phosphonic acid groups are likewise known to the person skilled in the art. Sulfonic acid, carboxylic acid and / or phosphonic acid groups are to be understood as meaning groups of the formulas -SO ₃ X, -COOX and -PO ₃ X ₂ , where XH, NH ₄ ⁺ , NH ₃ R ₁ ⁺ , NH ₂ R ' ₃ ⁺ , NHR ' ₃ ⁺ , NR ₄ ⁺ , Na ⁺ , K ⁺ or Li ⁺ , and R is any radical, preferably an alkyl radical, which may optionally have one or more further radicals which can give off protons under conditions commonly encountered for fuel cells.

Preferred ionomers are, for. B. sulfonic acid-containing polymers selected from the group consisting of perfluorinated sulfonated hydrocarbons such as Nafion ^® by EI Dupont, sulfonated aromatic polymers such as sulfonated polyaryl aryl ether ketones such as polyetheretherketones (sPEEK), sulfonated polyether ketones (sPEK), sulfonated polyether ketone ketones (sPEKK), sulfonated Polyetheretherke- clay ketones (sPEEKK), sulfonated polyether ketone ether ketone ketone (sPEKEKK), sulfonated polyarylene ether sulfones, sulfonated polybenzobisbenzazoles, sulfonated polybenzothiazoles, sulfonated polybenzimidazoles, sulfonated polyamides, sulfonated polyetherimides, sulfonated polyphenylene oxides, eg. As poly-2,6-dimethyl-1, 4-phenylene oxides, sulfonated polyphenylene sulfides, sulfonated phenol-formaldehyde resins (linear or branched), sulfonated polystyrenes (linear or branched), sulfonated polyphenylenes and other sulfonated aromatic polymers. The sulfonated aromatic polymers may be partially or completely fluorinated.

Further suitable sulfonated polymers include polyvinylsulfonic acids, copolymers composed of acrylonitrile and 2-acrylamido-2-methyl-1-propanesulfonic acids, acrylonitrile and vinylsulfonic acids, acrylonitrile and styrenesulfonic acids, acrylonitrile and methacryloxyethoxyoxypropanesulfonic acids, acrylonitrile and methacryloxyethyleneoxytetrafluoroethylene sulfonic acids, etc. The polymers can again be partially or completely fluorinated. Other groups of suitable sulfonated polymers include sulfonated polyphosphazenes such as poly (sulfophenoxy) phosphazenes or poly (sulfoethoxy) phosphazenes. The polyphosphazene polymers may be partially or fully fluorinated. Sulfonated polyphenylsiloxanes and copolymers thereof, poly (sulfoalkoxy) phosphazenes, poly (sulfotetrafluoroethoxypropoxy) siloxanes are also suitable.

Examples of suitable carboxylic acid group-containing polymers include polyacrylic acid, polymethacrylic acid and any copolymers thereof. Suitable polymers are, for. B. copolymers with vinylimidazole or acrylonitrile. The polymers may in turn be partially or fully fluorinated.

Suitable polymers containing phosphonic acid groups are, for. Polyvinylphosphonic acid, polybenzimidazole phosphonic acid, phosphonated polyphenylene oxides, e.g. B. poly-2,6-dimethyl-phenylene oxides, etc. The polymers may be partially or fully fluorinated.

Besides cation-conducting (acidic) polymers, anion-conducting (basic) polymers are also conceivable, although the proportion of acidic ionomers must predominate. These carry, for example, tertiary amine groups or quaternary ammonium groups. Examples of such polymers are disclosed in US-A 6,183,914; JP-A 11273695 and Slade et al., J. Mater. Chem. 13 (2003), 712-721.

Furthermore, acid-base blends are suitable as ionomers, as described, for. In WO 99/54389 and WO 00/09588. These are generally polymer blends comprising a sulfonic acid group-containing polymer and a polymer having primary, secondary or tertiary amino groups as disclosed in WO 99/54389 or polymer blends prepared by blending polymers containing basic groups in side chain containing polymers containing sulfonate, phosphonate or carboxylate groups (acid or salt form). Suitable polymers containing sulfonate, phosphonate or carboxylate groups are mentioned above (see sulfonic acid, polymers containing carboxylic acid or phosphonic acid groups). Polymers containing basic groups in the side chain are those polymers obtained by side-chain modification of organometallic-deprotonatable engineering-aryl backbone polymers with arylene-containing nitrogen-basic groups, tertiary basic nitrogen groups, for example, tertiary amine or basic Nitrogen-containing heterocyclic aromatic compounds such as pyridine, pyrimidine, triazine, imidazole, pyrazole, triazole, thiazole, oxazole, etc., containing aromatic ketones and aldehydes are attached to the metalated polymer. In this case, the resulting as an intermediate metal alkoxide can be either protonated in a further step with water or etherified with haloalkanes (W00 / 09588).

The above-mentioned ionomers may be further crosslinked. Suitable crosslinking reagents are, for. B. epoxide as the decanols commercially available ^®. Suitable solvents in which the crosslinking can be carried out can be chosen inter alia as a function of the crosslinking reagent and the ionomers used. Suitable among others are aprotic solvents such as DMAc (N, N-dimethylacetamide), DMF (dimethylformamide), NMP (N-methylpyrrolidone) or mixtures thereof. Suitable crosslinking processes are known to the person skilled in the art.

Particularly preferred ionomers are the aforementioned sulfonic acid group-containing polymers. Particularly preferred are perfluorinated sulfonated hydrocarbons, such as Nafion ^®, sulfonated aromatic polyether ether ketones (sPEEK), sulfonated polyether ether (SPES), sulfonated polyether imides, sulfonated Polybenzi- midazole, sulfonated polyether sulfones, and mixtures of said polymers. Particularly preferred perfluorinated sulfonated hydrocarbons, such as Nafion ^® and sulfonated polyether ether ketones (sPEEK). It is also possible to use copolymers. which contain blocks of the abovementioned polymers, preferably polymers containing sulfonic acid groups. An example of such a block copolymer is sPEEK-PAMD.

The polymers mentioned can be used alone or in mixtures, so-called blends, with other ionomers. Particularly preferred are blends of sPEEK, for example with polyethersulfone (PES), polyvinylidene difluoride (PVdF) and / or polysulfone. These preferred blend partners are present in a proportion of less than 20% by weight, preferably less than 15% by weight, more preferably less than 10% by weight, in each case based on the blend.

The degree of functionalization of the ionomers containing sulfonic acid, carboxylic acid and / or phosphonic acid groups is generally from 0.1 to 100%, more preferably from 30 to 70%, particularly preferably from 40 to 60%.

Sulfonated polyetheretherketones used with particular preference have degrees of sulfonation of from 0 to 100%, more preferably from 0.1 to 100%, even more preferably from 30 to 70%, particularly preferably from 40 to 60%. In this context, a sulfonation of 100% or a functionalization of 100% means that each repeat unit of the polymer contains a functional group, in particular a sulfonic acid group.

In the process according to the invention, the polymer electrolyte membrane used preferably has a thickness of from 10 to 200 .mu.m, preferably from 15 to 100 .mu.m, particularly preferably from 20 to 70 .mu.m.

The anode and cathode catalyst layer in the membrane-electrode assembly to be produced according to the invention contain at least one catalytically active component which catalytically supports, for example, the oxidation of hydrogen or the reduction of oxygen. The catalyst layers may also contain a plurality of catalytically active substances with different functions. In addition, the respective catalyst layer may contain a functionalized polymer (ionomer) or a non-functionalized polymer.

Furthermore, preferably an electron conductor in the catalyst layers is used inter alia for conducting the electric current flowing in the fuel cell reaction and as a carrier material for the catalytically active substances.

The catalyst layers preferably comprise as catalytically active components at least one element from the 3rd to 14th group of the Periodic Table of the Elements (PSE), more preferably from the 8th to 14th group of the PSE. The cathode catalyst layer preferably contains, as the catalytically active component, at least one element selected from the group consisting of platinum, cobalt, iron, chromium, manganese, copper, vanadium, ruthenium, palladium, nickel, molybdenum, tin, zinc, gold, silver, rhodium , Iridium, tungsten and mixtures thereof, more preferably platinum. It is also possible to use the polyoxymetalates known to the person skilled in the art.

The anode catalyst layer preferably contains, as the catalytically active component, at least one element selected from the group consisting of cobalt, iron, chromium, manganese, copper, vanadium, ruthenium, palladium, nickel, molybdenum, tin, zinc, gold, rhodium, iridium, tungsten and mixtures of these, more preferably platinum in combination with ruthenium. It is also possible to use the polyoxymetalates known to the person skilled in the art.

In a further preferred embodiment, the at least one catalytically active material is applied to a suitable catalyst support. Suitable catalyst supports are known to the person skilled in the art, for example carbon black, graphite, carbon nanotubes or graphitized carbon black. A particularly preferred catalyst support is graphitized carbon black, wherein the content of at least one catalytically active metal is preferably from 20 to 80% by weight, based on the sum of the amounts of catalytically active metal and catalyst support.

The application of the catalyst layer to the polymer electrolyte membrane for producing a polymer electrolyte membrane (CCM) coated on at least one side or to a gas diffusion layer for producing a gas diffusion electrode (GDE) can be carried out by methods known to the person skilled in the art, for example by applying a so-called catalyst ink containing at least one catalytic catalyst active component-containing solution or dispersion. The catalyst ink, which is optionally paste-like, can be applied according to the invention by methods known to the person skilled in the art, for example printing, screen printing, spraying, knife coating or rolling. Subsequently, the catalyst layer can be dried. Suitable drying methods are, for example, hot-air drying, infrared drying, microwave drying, plasma methods or combinations of these methods.

The membrane-electrode assembly preferably includes one or two gas diffusion layers, one of which is disposed on the anode catalyst layer and the other on the cathode catalyst layer. The gas diffusion layer can serve as a mechanical support for the electrode and ensures a good distribution of the respective gas over the catalyst layer and for the discharge of the electrons. A gas dif- Fusion layer is needed in particular for fuel cells, which are operated with hydrogen on the one hand and oxygen or air on the other hand.

Suitable materials contained in the gas diffusion layer are known to those skilled in the art and described in V. Mehta et al., Journal of Power Sources 114 (2203), pages 32 to 53, for example carbon nonwoven, carbon paper or the like called carbon wovens, ie woven carbon fibers. These materials may optionally comprise a thin microporous layer of carbon and Teflon. Teflon serves as a binder and / or for hydrophobization.

By means of the method according to the invention, the individual layers which are present in a 5-layer MEA can be connected to one another. In this case, it is possible according to the invention that initially two layers are joined together, and the third remaining layer is applied after complete bonding of these two layers. For example, it is possible for a polymer electrolyte membrane, which is provided on one or both sides with one or two electrode layers, to be connected to a gas diffusion layer by the method according to the invention. It is also possible according to the invention for a gas distributor electrode to be connected to a polymer electrolyte membrane by the method according to the invention.

In a preferred embodiment of the process of the present invention, in one step, a 5-layered MEA is prepared by bonding either of two gas diffusion electrodes and a polymer electrolyte membrane, or a catalyst coated polymer electrolyte membrane and two gas diffusion layers, each with the polymer electrolyte membrane in the middle has on both sides of electrode layers, and each of the two electrode layers each followed by a gas diffusion layer.

The inventive method is carried out in a preferred embodiment so that at least one solvent in liquid form before and / or during the compression of externally on the at least one polymer electrolyte membrane is applied to the at least one gas diffusion electrode and / or on the at least one gas diffusion layer, and the layers to be joined are pressed together.

In a particularly preferred embodiment, the at least one solvent is applied externally to the at least one gas diffusion electrode. This can be done by any method known to the person skilled in the art, for example spraying, application of tissue or nonwoven impregnated with the at least one solvent and combinations of these methods. Suitable fabrics or nonwovens are the person skilled in the art and, for example, made of natural or synthetic fibers, for. For example, natural fabrics such as cotton, cellulose, such as filter paper, fabric made of synthetic polymers such as polyamides, polyesters or combinations thereof. It is also possible according to the invention for the at least one solvent to be applied by means of openings provided in the press to the layers to be pressed against one another during the pressing.

Methods and devices for spraying the at least one solvent are known to the person skilled in the art, for example by means of a spray gun or by airbrush etc. In a preferred embodiment, the at least one solvent is sprayed on prior to compression.

In a preferred embodiment of the method according to the invention, the solvent is applied externally to the at least one gas diffusion electrode before and / or during the compression by applying a tissue, preferably filter paper, which is impregnated with the solvent to the gas diffusion electrode. In a particularly preferred embodiment, the impregnated tissue remains on the gas diffusion electrode during compression.

In a further particularly preferred embodiment of the method according to the invention, the solvent is applied externally to the at least one gas diffusion electrode before and / or during the compression, by being sprayed onto the at least one gas diffusion electrode.

In general, any solvent which is externally applied in the process of the invention during compression may be any solvent known to those skilled in the art as suitable for use in the preparation of membrane-electrode assemblies. Examples of suitable solvents are selected from the group consisting of water, mono- and polyhydric alcohols, nitrogen-containing polar solvents, glycols, glycol ether alcohols, glycol ethers and mixtures thereof. Particularly suitable are, for example, water, propylene glycol, dipropylene glycol, glycerol, ethylene glycol, hexylene glycol, dimethylacetamide (DMAc), N-methylpyrrolidone (NMP), n-propanol and mixtures thereof.

Due to the presence of the at least one solvent during compression, the polymer electrolyte membrane, the gas diffusion layers and / or the gas diffusion electrodes do not dry out, ie the so accessible MEA is immediately ready for use in a fuel cell after production. Therefore, no time-consuming activation of the fuel cell after its production has to be performed. Furthermore, by applying at least one solvent achieved a particularly good cohesion of the individual layers before and / or during compression.

In the method according to the invention, the compression can generally be carried out at any pressure suitable for achieving sufficient and lasting adhesion between the layers. In a preferred embodiment of the process according to the invention, the compression is carried out at a pressure of 0.1 to 40 bar, particularly preferably 0.2 to 20 bar, very particularly preferably 0.25 to 10 bar, in each case overpressure.

In the process of the invention, compression may generally be carried out at any temperature suitable for achieving sufficient and sustained adhesion between the layers. In a preferred embodiment of the process according to the invention, the compression is carried out at a temperature of from room temperature, ie 25 ^° C., to 150 ^° C., particularly preferably 50 to 120 ^° C., very particularly preferably 50 to 100 ^° C.

The compression of the corresponding layers can be carried out by methods known to those skilled in the art, for example by hot pressing, hot pressing and / or lamination. Suitable devices are known in the art. The compression is generally performed for a time sufficient to achieve sufficient and sustained adhesion between the individual layers, for example 15 to 600 seconds, preferably 30 to 600 seconds. The duration of the compression depends on the nature of the layers which are compressed and can easily be determined by the person skilled in the art.

The membrane electrode assembly produced by the method according to the invention is characterized by a particularly high adhesion between the individual layers. Furthermore, a membrane-electrode unit produced according to the invention exhibits a particularly high power, for example greater than 50 mW / cm ² , preferably greater than 80 mW / cm ² , particularly preferably greater than 120 mW / cm ² . An upper limit of power is, for example, less than 200 mW / cm ^2, preferably less than 150 mW / cm ^2, measured at 0.3 A / cm ^3.

Therefore, the present invention also relates to a membrane-electrode assembly obtainable by the method according to the invention.

The membrane electrode assembly produced according to the invention can be used in a fuel cell because of its advantageous features. The inventive examples and comparative examples describe the present invention in more detail without limiting it.

Examples:

Example 1: Preparation of the Anodentinte

Two parts by weight of Nafion ^® ionomer in H ₂ O (10 wt .-% strength) (EW1 100, Fa. DuPont) and a weight rope dimethylacetamide (DMAc) were introduced into a glass bottle and stirred with the magnetic stirrer. Then, one part by weight of catalyst (PtRu / C, Pt: 42 wt .-%, Ru: 32 wt .-%) weighed and slowly added to the mixture with stirring. The mixture is stirred for about 5 to 10 minutes at room temperature with the magnetic stirrer. The sample is then treated with ultrasound until the value of the registered energy is 0.015 KWh. This value refers to a batch size of 20 g.

Example 2: Preparation of the cathode ink

One part by weight of catalyst (Pt / C Pt: 70 wt .-%), two weight parts Nafion ^® and three parts by weight water are weighed into a glass bottle. Afterwards Fox- Mahlperlen (1-1, 2mm) are added to the batch and shaken well by hand. The weight of the grinding beads corresponds to half of the total batch. The ink is dispersed for 60 minutes on the Kugelschüttelmischer (Skandex) at level 3. The ink is separated from the grinding beads by sieving. Then, five parts by weight of n-propanol (based on the amount after filtration) are added with stirring and the batch is stirred on a magnetic stirrer for 10 min. At 500 rpm. touched.

Example 3 Production of Gas Diffusion Electrodes (GDE) and Membrane Electrode Assembly (MEA)

The gas diffusion electrode (GDE) is produced from the anode side to H2315 (Freudenberg) with the anode ink from Example 1 and from the cathode side to H2315 1X11 CX45 (from Freudenberg) with the cathode ink from Example 2, in each case by screen printing.

Example 4:

A sPEEK membrane (SG = 43%), which was previously activated in 0.5M HNO ₃ at 55 ° C. for two hours and then dried at room temperature, is mixed with 0.05 ml of dimethylacetamide (DMAc) on the anode and cathode side. sprayed. Subsequently the membrane having anode and cathode GDE from Example 3 using a spacer around 5% at 100 ⁰ C is pressed for 5 minutes.

Example 5:

After activating a sPEEK membrane (SG = 43%) in 0.5M HNO ₃ at 55 ⁰ C for two hours, this is then dried at room temperature, and bottom and cathode side GDEs from Example 3 at 95 ⁰ C with 20 kN over 10 Minutes pressed. For this purpose, wet, water-saturated filter papers are placed on the gas diffusion layers at the top and bottom during hot pressing.

Comparative Example:

A sPEEK membrane (SG = 43%), which at 55 ⁰ C for two hours has been the dried activated and then at room temperature before in 0.5M HNO _3, with anode and cathode GDE from Example 3 at 120 ⁰ C with 20 kN / 25 cm ² , corresponding to 0.8 kN / cm ² , 10 minutes dry pressed.

All samples are tested at 70 ^° C., 1 M MeOH, anode stoichiometry 3 (at least 49 ml / h), cathode stoichiometry 3 (at least 130 ml / min air). The adhesion of the electrodes and performance of the samples at 0.3 A / cm ² are compared in Table 1.

Table 1: Performance of the samples at 0.3 A / cm ²

Claims

claims

A process for producing a membrane-electrode assembly comprising at least one polymer electrolyte membrane, at least one electrode layer and at least one gas diffusion layer by compressing at least one polymer electrolyte membrane and at least one gas diffusion electrode or at least one catalyst-coated polymer electrolyte membrane and at least one gas diffusion layer in the presence of a solvent; characterized in that the at least one solvent in liquid form or in vapor form before and / or during the compression of externally on the at least one polymer electrolyte membrane, is applied to the at least one gas diffusion electrode and / or on the at least one gas diffusion layer.

2. The method according to claim 1, characterized in that the membrane electrode unit comprises a polymer electrolyte membrane, which is provided on both sides, each with a gas diffusion electrode.

3. The method according to any one of claims 1 or 2, characterized in that the compression is carried out at a temperature of from room temperature to 150 ⁰ C.

4. The method according to any one of claims 1 to 3, characterized in that the compression is carried out at a pressure of 0.1 to 40 bar.

5. The method according to any one of claims 1 to 4, characterized in that the solvent is applied before and / or during the compression of externally on the at least one gas diffusion electrode by being sprayed onto the at least one gas diffusion electrode.

6. The method according to any one of claims 1 to 5, characterized in that the solvent is applied before and / or during the compression of externally on the at least one gas diffusion electrode by a tissue, which is impregnated with the solvent, on the gas diffusion electrode is brought.

7. The method according to any one of claims 1 to 6, characterized in that the solvent is selected from the group consisting of water, monohydric and polyhydric alcohols, nitrogen-containing polar solvents, glycols, glycol ether, glycol ethers and mixtures thereof.

8. Membrane electrode unit, producible by the method according to one of claims 1 to 7.

9. A fuel cell containing a membrane-electrode assembly according to claim 8.