KR20130038826A - Improved polymer membranes, processes for production thereof and use thereof - Google Patents

Abstract

The present invention relates to improved polymer membranes, methods for their preparation and their use.

Description

IMPROVED POLYMER MEMBRANES, PROCESSES FOR PRODUCTION THEREOF AND USE THEREOF}

The present invention relates to improved polymer membranes, methods for their preparation and their use in electrochemical reactors such as fuel cells.

Its use in polymer membranes and fuel cells is already known. In membrane electrode assemblies (MEA) based on polyazole membranes, such as polybenzimidazole (PBI), doping the polymer with phosphoric acid achieves the required proton conductivity. Doping with phosphoric acid lowers the mechanical stability of the polymer. At the same time, a high acid content is advantageous for ionic conductivity. In particular, membranes prepared by the sol-gel process consist of a high proportion of phosphoric acid and a low proportion of PBI polymer. This causes a membrane flow under the action of pressure and temperature. In fuel cells, this flow is prevented by using hard gaskets compressed to a predetermined thickness. Between the gasket is not present the actual rather than the membrane, for example to the so-called sub-gasket composed of a polyimide ^(Kapton?) FEP- coating is present, which provides an airtight seal between the above connection of the gas diffusion membrane. WO 92/22096 A2 discloses the use of gasket materials, for example, which do not consist of actual membrane polymers. WO 2008/014964 A2 describes membranes with reinforcing elements. The connection of the membrane to the subgasket can be a weak point, at which point defects can occur during MEA fabrication and leakage can occur during battery operation.

WO 2004/066428 A2 describes a fuel cell with a phosphoric acid-doped PBI membrane, wherein the PBI membrane is used in an acid free form, and the active region is doped with phosphoric acid during assembly through the acid-impregnated electrode, The region is in an undoped state. DE 10 2004 028 141 A1 describes PBI membranes which have low or no doping in the gasket region and are heavily doped with phosphoric acid in the active region.

Disadvantages of a system comprising a subgasket are that defects easily occur during their manufacture and their long-term stability is unsatisfactory. This is because the subgasket material may detach or break from the membrane depending on the operating time. Even during MEA manufacturing, shear may cause premature damage to the membrane because the membrane is squeezed in areas overlapping the subgasket. Often, manufacturing steps are complicated and difficulties in automation can exist. A further disadvantage is that subsequent doping of the PBI membrane generates less acid than the membrane made by the solgel process. This adversely affects conductivity and long term stability (small acid reservoirs).

It is an object of the present invention to provide an improved membrane which can increase the reinforcement in the gasket region when introduced into the frame.

FIELD OF THE INVENTION The present invention relates to an ion conductive membrane having a layer S and based on polymer PM, wherein the layer S is applied to the membrane in an imaged manner and attached onto the membrane, and is based on a powder of polymer PP. .

The layer S together with the membrane is particularly suitable as a gasket edge in the MEA and provides mechanical reinforcement. Membranes are particularly suitable for use in electrochemical reactors, in particular fuel cells.

The layer S is particularly suitable as the gasket edge with the gasket body in the MEA. Reinforcement (force) means that the amount of polymer in the reinforced region increases compared to the unreinforced region. Thus the membrane does not flow under the action of pressure and temperature in the reinforced region used as the gasket edge.

The polymers PM and PP of the membrane and the powder may be the same or different.

The powder PP is preferably in paste form. "Imagewise" is interpreted to mean that the application is not done over the entire area of the membrane, but only in a controlled manner in a particular area.

In a preferred embodiment, the membrane is doped with an acid, in particular phosphoric acid. Particularly preferred polymer membranes are based on polybenzimidazole (PBI).

In a preferred embodiment, both the polymer membrane and the powder comprise or consist of polybenzimidazole, the polymer membrane being especially doped with phosphoric acid.

The powder used to prepare layer S preferably comprises the following as a substantial component:

a) polymer PP, in particular polybenzimidazole (PBI),

b) flexible component B), in particular polytetrafluoroethylene powder (PTFE), and

c) dispersant C), in particular sulfonated polytetrafluoroethylene, eg Nafion in the form of an aqueous dispersion ^? polymer.

"Flexibilizing" is more specifically interpreted to mean that the gasket edge thus produced is not broken and the polymer particles do not desorb when bent at a 90 ° radius.

Preferred flexible component B) corresponds in principle to all fluoropolymers, in particular FEP (fluorinated polyethylenepropylene), PVDF (polyvinylidene fluoride) and PFA (perfluoroalkoxy compound).

Dispersant C is an additive that optimizes and stabilizes the mixing of the components of the powder. Preferred dispersants are for example as follows:

Alcohol alkoxylates, for example Degressal ^? SD 23;

Naphthalenesulfonic acid condensates, in particular its sodium salt, for example Tamol ^? NN890;

Guerbet alcohol ethoxylate, for example Lutensol ^? XP50;

Acetylene glycol based products such as Dynol ^? 604;

Acetylenediol based nonionic gemini surfactants such as Surfynol ^? 104;

High molecular weight block copolymers with pigment-affinity groups, for example Byk ^? 190-193;

Organically modified polymers with pigment-affinity groups such as Tego ^? 750 W / 760 W;

Siloxane containing gemini surfactants such as Tego ^? Twin 4000;

Silica-containing, silicon-free, organic polymers such as Tego ^? Foamex 830; And

Occasionally fluorosurfactants, such as Zonyl ^? , which are present in a blend with alcohols such as isopropyl alcohol and water ^. FSA.

The powders used for layer S are preferably used in the form of dispersions or free-flowing pastes, preferably dispersions having a viscosity measured at a temperature of 20 ° C. in the range from 1 to 10 000 mPas, in particular from 10 to 1000 mPas Used in the form of water or free-flowing paste.

Solids present in the dispersion of the powder for use according to the invention are preferably as follows:

a) 30 to 50 parts by weight of polymer PP

b) 30 to 50 parts by weight of the flexible component B)

c) 5 to 15 parts by weight of dispersant C).

Also preferably,

d) 10 to 20 parts by weight of a wettability improving agent, preferably alcohols, in particular n-propanol.

Also preferably 20 to 60 parts by weight, in particular 35 to 45 parts by weight of water, are present.

Such powder is preferably

1. Grinding the polymer PP to a particle diameter of preferably less than 60 μm

2. Dispersing the powder obtained in step 1 together with the flexible component B and the dispersant C in the liquid phase, preferably in the aqueous or alcohol phase and optionally adjusting it to the desired viscosity

Is prepared by.

The invention further relates to a process for producing the membrane of the invention, comprising applying a powder of polymer PP to a substrate (eg a carrier film) and then compressing it into an acid-doped membrane. In one preferred embodiment, the application of the powder on the membrane is in the form of a lamination transfer process, in particular a continuous process. Such lamination transfer processes are described, for example, in Electrochimica Acta, Vol. 40, No. 3, pp. 355-363, 1995 and in J. Appl. Electrochemistry 22 (1992) 1. Lamination transfer processes are also known as "decal" processes. Compressing the powder results in at least a portion of the powder penetrating into and reinforcing the membrane.

The polymer membranes of the present invention are suitable for many electrochemical reactors, in particular fuel cell applications. The present invention therefore also provides a membrane electrode assembly (MEA) for a fuel cell, comprising at least:

I. Polymeric membranes of the invention with gasket edge S,

II. Gasket body, where

III. The membrane around the layer S is buried in the gasket body and compressed.

In one preferred embodiment, the gasket body is based on an elastomer according to DE 10 2004 028 141 A1. In a further preferred embodiment, the inelastic spacer is embedded in the gasket body composed of elastomer and prevents excessive compression of the gasket body without affecting the elastic properties of the gasket body. For example, an element or shim made of a more rigid metal, plastic or carbon may be used as compared to the elastomer.

The invention further relates to an electrochemical reactor, in particular a fuel cell, comprising at least one membrane of the invention.

According to the invention, polymer powder PP, in particular powdery polybenzimidazole (particle size, preferably <60 μm) is applied to both sides of the membrane in the gasket area and then under the action of pressure and temperature (eg At 140 ° C., 3 minutes, 3000 N / cm 2), in particular within a temperature range of 50 to 200 ° C., preferably 70 to 160 ° C., over 0.5 to 10 minutes, in particular 1 to 5 minutes, generally 500 to 6000 Reinforcement of the membrane can be achieved by compression under a pressure of preferably 1000 to 4000, in particular 2500 to 3500 N / cm 2. The applied PBI powder absorbs some of the acid from the membrane, substantially penetrates into and binds to the membrane. This increases the polymer content in the membrane preferably from 5 to 10% by weight to 50 to 90% by weight. This reinforced membrane no longer free flows even at high pressures and temperatures. However, it is flexible enough. A further advantage compared to the use of subgaskets of other materials is that the transfer from the active, eg phosphate-doped, membrane surface to the reinforced gasket region binds to the same material, ie the membrane This does not end there but rather continues to the gasket area in reinforced form.

The uniform thickness of layer S by powder application is preferably achieved by a screen printing process. Using a mixture of polytetrafluoroethylene (PTFE) powder, PBI powder and sulfonated tetrafluoroethylene polymer as the dispersing additive, the weight ratio of dispersing additive to PBI is preferably 0.9: 1.1 to 1.1: 0.9, It has been found that printable pastes can be prepared. Such paste may be printed directly onto the membrane oxidized with phosphoric acid, surface dried and then hot pressed. This achieves membrane reinforcement. The advantage is that PTFE is introduced between the PBI particles. After hot compression, the reinforcing layer has a uniform thickness, is flat and gas-tight.

In a preferred application process, the above-mentioned pastes, in particular pastes consisting of PBI, PTFE and sulfonated tetrafluoroethylene powders, are applied by screen printing in the form of gaskets to carrier substrates composed of, for example, polyether sulfone (PES) films. . The paste is partially dried. The PBI membrane oxidized with phosphoric acid is then compressed between two of these coated substrates (the gasket frame covering each other). This leads to lamination transfer from the carrier film to the PBI membrane. Compression is advantageously carried out for 1 minute at 80 ° C. and a pressure of 3000 N / cm 2.

The edge reinforced PBI membrane is later assembled with the gas diffusion electrode to produce the MEA. This is done in such a way that the electrodes with reinforced membrane edges overlap approximately 1-2 mm. This achieves the effect that the compressive stress at the edge of the electrode depends on the reinforcement.

Suitable polymer PMs and PPs for the purpose of the present invention for the production of polymer electrolyte membranes are known per se. All proton conductive materials are suitable. Preference is given to using membranes comprising acids which can be covalently bonded to the polymer. In addition, the flat material may be doped with an acid to form a suitable membrane. It is also possible to use gels, in particular polymer gels, as membranes, in which case for the purposes of the invention, particularly suitable polymer membranes are described, for example, in DE 102 464 61.

Such membranes are obtained, in particular, by swelling a flat material, for example a polymer film, with a liquid comprising an acid containing compound or by preparing a mixture of polymer and acid containing compound and then molding and solidifying a flat object to form a membrane. Can lose.

Suitable polymers for this purpose include polyolefins such as poly (chloroprene), polyacetylene, polyphenylene, poly (p-xylylene), polyarylmethylene, polystyrene, polymethylstyrene, polyvinyl alcohol, polyvinyl acetate, polyvinyl Ether, polyvinyl amine, poly (N-vinylacetamide), polyvinylimidazole, polyvinylcarbazole, polyvinylpyrrolidone, polyvinylpyridine, polyvinyl chloride, polyvinylidene chloride, polytetrafluoroethylene (PTFE), polyhexafluoropropylene, copolymers of PTFE and hexafluoropropylene, copolymers of PTFE and perfluoropropyl vinyl ether, copolymers of PTFE and trifluoronitromethane, PTFE and carboalkoxyperfluoro Copolymers of roalkoxy vinyl ether, polychlorotrifluoroethylene, polyvinyl fluoride, polyvinylidene fluoride, polyacrol A, polyacrylamide, polyacrylonitrile, policy cyano acrylate, polymethacrylic imide, cycloolefin copolymer, cycloolefin copolymer formed from a particular play norbornene;

Polymers having a CO bond in the main chain, such as polyacetal, polyoxymethylene, polyether, polypropylene oxide, polyepichlorohydrin, polytetrahydrofuran, polyphenylene oxide, polyether ketone, polyester, Especially polyhydroxyacetic acid, polyethylene terephthalate, polybutylene terephthalate, polyhydroxybenzoate, polyhydroxypropionic acid, polypivalolactone, polycaprolactone, polymalonic acid, polycarbonate; Polymers having a C-S bond in the main chain, such as polysulfide ether, polyphenylene sulfide, polysulfone, polyether sulfone;

Polymers having CN bonds in the main chain, for example polyimines, polyisocyanides, polyetherimines, polyetherimides, polyanilines, polyaramids, polyamides, polyhydrazides, polyurethanes, polyimides, polyazoles, polyazole ethers Ketones, polyazines;

Liquid-crystalline polymers, in particular thermoplastics, liquid crystalline polyesters such as Vectra ^™ , and

Inorganic polymers such as polysilane, polycarbosilane, polysiloxane, polysilic acid, polysilicate, silicone, polyphosphazene and polythiazyl.

Basic polymers are preferred, especially in the case of membranes comprising acids or doped with acids. Useful basic polymer membranes of this type include virtually all known polymer membranes through which protons can be transported. Preference is given to acids which can carry protons without additional water, for example by the so-called Grutthuss mechanism.

The basic polymer used in the present invention is preferably a basic polymer having at least one nitrogen, oxygen or sulfur atom, preferably at least one nitrogen atom in the repeating unit. Further preferred are basic polymers comprising at least one heteroaryl group.

In a preferred embodiment, the repeating unit in the basic polymer comprises an aromatic ring having at least one nitrogen atom. The aromatic ring is preferably a five or six membered ring having 1-3 nitrogen atoms, which can be fused with another ring, in particular another aromatic ring.

In certain embodiments of the invention, a high thermal stability polymer is used which comprises one or more nitrogen, oxygen and / or sulfur atoms in one repeat unit or in different repeat units.

Polymers of high thermal stability in the present invention are polymers that can be operated for a long time as polymer electrolytes in fuel cells at temperatures of 120 ° C. or higher. "Over a long time" means that the membrane of the present invention has a performance (WO 01 /) for at least 100 hours, preferably at least 500 hours, at least 80 ° C, preferably at least 120 ° C, more preferably at least 160 ° C. Measurable by the method described in 18894 A2).

In the present invention, the aforementioned polymers can be used individually or as a mixture (blend). Particular preference is given to blends comprising polyazoles and / or polysulfones. Preferred blend components are polymers modified with polyether sulfones, polyether ketones and sulfonic acid groups, which are described in German patent applications DE 100 522 42 and DE 102 464 61.

Furthermore, polymer blends particularly useful for the purposes of the present invention are polymer blends (so-called acid-base polymer blends) comprising at least one basic polymer and at least one acidic polymer, preferably in a weight ratio of 1:99 to 99: 1. Confirmed. Particularly suitable acidic polymers in this respect include polymers having sulfonic acid groups and / or phosphoric acid groups. Very particularly suitable acid-base polymer blends according to the invention are described in detail in publication EP1073690 A1, for example.

Particularly preferred groups of basic polymers are polyazole groups. Polyazole-based basic polymers are formulas (I) and / or (II) and / or (III) and / or (IV) and / or (V) and / or (VI) and / or (VII) and / or (VIII). ) And / or (IX) and / or (X) and / or (XI) and / or (XII) and / or (XIII) and / or (XIV) and / or (XV) and / or (XVI) and And / or azole repeat units of (XVII) and / or (XVIII) and / or (XIX) and / or (XX) and / or (XXI) and / or (XXII):

In the above formula

Ar is a tetravalent aromatic or heteroaromatic group, which may be the same or different and each may be monocyclic or polycyclic,

Ar ¹ is the same or different and each is a divalent aromatic or heteroaromatic group which may be monocyclic or polycyclic,

Ar ² is the same or different and each is a divalent or trivalent aromatic or heteroaromatic group which may be monocyclic or polycyclic,

Ar ³ is the same or different and each is a trivalent aromatic or heteroaromatic group which may be monocyclic or polycyclic,

Ar ⁴ is the same or different and each is a trivalent aromatic or heteroaromatic group which may be monocyclic or polycyclic,

Ar ⁵ is the same or different and each is a tetravalent aromatic or heteroaromatic group which may be monocyclic or polycyclic,

Ar ⁶ is the same or different and each is a divalent aromatic or heteroaromatic group which may be monocyclic or polycyclic,

Ar ⁷ is the same or different and each is a divalent aromatic or heteroaromatic group which may be monocyclic or polycyclic,

Ar ⁸ is the same or different and each is a trivalent aromatic or heteroaromatic group which may be monocyclic or polycyclic,

Ar ⁹ is a divalent, trivalent or tetravalent aromatic or heteroaromatic group which may be the same or different and each may be monocyclic or polycyclic,

Ar ¹⁰ is the same or different and each is a divalent or trivalent aromatic or heteroaromatic group which may be monocyclic or polycyclic,

Ar ¹¹ is the same or different and each is a divalent aromatic or heteroaromatic group which may be monocyclic or polycyclic,

X is the same or different and is an amino group having a hydrogen atom, a group having 1-20 carbon atoms, preferably a branched or unbranched alkyl or alkoxy group, or an aryl group as oxygen, sulfur or an additional radical,

R is the same or different and is a hydrogen, an alkyl group or an aromatic group and is an alkyl group or an aromatic group in formula (XX) provided that R in formula (XX) is not hydrogen,

n and m are each an integer of 10 or more, preferably an integer of 100 or more.

Preferred aromatic or heteroaromatic groups are benzene, naphthalene, biphenyl, diphenyl ether, diphenylmethane, diphenyldimethylmethane, bisphenone, diphenylsulphone, quinoline, pyridine, bipyridine, pyridazine, pyrimidine, pyrazine, benzone Photo, triazine, tetrazine, pyrrole, pyrazole, anthracene, benzopyrrole, benzotriazole, benzooxadiadiazole, benzooxadiazole, benzopyridine, benzopyrazine, benzopyrazidine, benzopyrimidine, benzopyrazine , Benzotriazine, indolizine, quinolysine, pyridopyridine, imidazopyrimidine, pyrazinopyrimidine, carbazole, acridine, phenazine, benzoquinoline, phenoxazine, phenothiazine, acridizin Derived from benzopteridine, phenanthroline and phenanthrene, which may optionally be substituted.

The substitution pattern of Ar ¹ , Ar ⁴ , Ar ⁶ , Ar ⁷ , Ar ⁸ , Ar ⁹ , Ar ^lO , Ar ¹¹ is as desired; In the case of phenylene, for example, Ar ¹ , Ar ⁴ , Ar ⁶ , Ar ⁷ , Ar ⁸ , Ar ⁹ , Ar ^lO , Ar ¹¹ may be ortho-, meta- and para-phenylene. Particularly preferred groups are derived from benzene and biphenylene, which may optionally be substituted.

Preferred alkyl groups are short-chain alkyl groups having 1-4 carbon atoms, for example methyl, ethyl, n- or i-propyl and t-butyl groups.

Preferred aromatic groups are phenyl or naphthyl groups. Alkyl and aromatic groups may be substituted.

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

Preference is given to polyazoles in which the X radicals have the same repeat units of formula (I) in one repeat unit.

The polyazoles may in principle have different repeating units different from one another, for example in the X radical. However, it preferably has only the same X radical in one repeating unit.

Further preferred polyazole polymers are polyimidazole, polybenzothiazole, polybenzoxazole, polyoxadiazole, polyquinoxaline, polythiadiazole, poly (pyridine), poly (pyrimidine), poly (tetraazaprene) ) And polybenzoxazines.

In a further embodiment of the invention, the polymer comprising azole repeat units is a copolymer or blend comprising two or more units different from one another in formulas (I) to (XXII). The polymer may be in the form of block copolymers (diblock, triblock), random copolymers, periodic copolymers and / or alternating polymers.

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

The number of azole repeat units in the polymer is preferably an integer of at least 10. Particularly preferred polymers comprise at least 100 azole repeat units.

In the present invention, polymers containing benzimidazole repeat units are preferred. Some examples of very suitable polymers comprising benzimidazole repeat units are represented by the following formula:

N and m are each an integer of 10 or more, preferably an integer of 100 or more.

The polyazoles used, in particular polybenzimidazoles, are excellent for high molecular weight. When measured as an intrinsic viscosity it is at least 0.2 dl / g, preferably 0.8 to 10 dl / g, in particular 1 to 10 dl / g.

Preferred polybenzimidazoles are sold under the trade name Celazole? Commercially available

Preferred polymers also include polysulfones, in particular polysulfones having aromatic and / or heteroaromatic groups in the main chain. In certain embodiments of the present invention, preferred polysulfones and polyether sulfones have a melt volume velocity MVR 300 / 21.6 of 40 cm 3/10 min or less, in particular 30 cm 3/10 min or less, more preferably 20 cm 3, as measured according to ISO 1133. / 10 min or less. Preference is given to polysulfones having a Vcat softening point VST / A / 50 of 180 to 230 ° C. In another preferred embodiment of the invention, the number average molecular weight of the polysulfone is greater than 30 000 g / mol.

Polysulfone-based polymers include in particular polymers having repeating units having linking sulfone groups corresponding to the formulas A, B, C, D, E, F and / or G:

Wherein the R radicals are the same or different and each is independently an aromatic or heteroaromatic group, wherein these radicals are described in detail above. These include especially 1,2-phenylene, 1,3-phenylene, 1,4-phenylene, 4,4'-biphenyl, pyridine, quinoline, naphthalene, phenanthrene.

Preferred polysulfones in the present invention include homopolymers and copolymers, for example random copolymers. Particularly preferred polysulfones comprise repeating units of formula H to N:

The above polysulfone is to brand ^names? Victrex 200 P ^,? Victrex 720 P ^,? Ultrason E ^,? Ultrason S ^,? Mindel ^,? Radel A ^,? Radel R ^,? Victrex HTA ^,? Astrel and ^? Commercially available as Udel.

Also particularly preferred are polyether ketones, polyether ketone ketones, polyether ether ketones, polyether ether ketone ketones and polyaryl ketones. Such high performance polymers are known per se and are under the trade name Victrex? PEEK ^{TM ,?} Hostatec ^,? Commercially available under Kadel.

To prepare the polymer film, the polymer, preferably polyazole, can be dissolved in a further step in a polar aprotic solvent, for example dimethylacetamide (DMAc), and the film can be obtained by conventional processes. In order to remove the solvent residue, the film thus obtained can be treated with a washing liquid as in German patent application DE 101 098 29. The removal of solvent residues from polyazole films as described in the German patent application surprisingly improves the mechanical properties of the film. These properties include, in particular, the modulus of elasticity of the film, elongation at break and fracture toughness.

The polymer film can also have further modifications, for example by crosslinking, as described in German patent application DE 101 107 52 or WO 00/44816. In a preferred embodiment, the polymer film consisting of the basic polymer and at least one blend component additionally comprises a crosslinking agent as described in German patent application DE 101401 47.

The thickness of the polyazole film can vary in a wide range. The thickness of the polyazole film prior to doping with an acid is preferably in the range of 5 μm to 2000 μm, more preferably in the range of 10 μm to 1000 μm, particularly preferably in the range of 20 μm to 1000 μm, which is limited It is not to be interpreted as intended.

In order to achieve proton conductivity, such films are doped with acids. Acids in this respect include all known Lewis and Bronsted acids, preferably inorganic Lewis and Bronsted acids.

It is also possible to use polyacids, in particular isopoly and heteropoly acids, and mixtures of different acids. In the present invention, heteropolyacids refer to inorganic polyacids having two or more different central atoms of metals (preferably Cr, Mo, V, W) and nonmetals (preferably As, I, P, Se, Si, Te). They form, in part, mixed anhydrides from polybasic oxygen acids, each of which is weak. This includes 12-molybdate phosphoric acid and 12-tungstophosphoric acid.

Degree of doping can be used to promote the conductivity of the polyazole film. Increasing the concentration of the dopant until the maximum value is obtained increases the conductivity.

According to the invention, the degree of doping is described as moles of acid per mole of polymer repeating units. In the present invention, the preferred doping degree is 3 to 80, suitably 5 to 60, in particular 12 to 60.

Particularly preferred dopants are sulfuric acid and phosphoric acid, or compounds which release these acids, for example compounds which release acids upon hydrolysis. Very particularly preferred dopant is phosphoric acid (H ₃ P0 ₄ ). In this respect, high concentrations of acid are generally used. In certain embodiments of the invention, the concentration of phosphoric acid is at least 50% by weight, in particular at least 80% by weight, based on the weight of the dopant.

In a preferred embodiment, the membrane of the present invention is fiber reinforced as described in WO 2008/014964 A2, page 17 line 39 to page 21 line 33 line.

The membrane of the present invention can be produced in a manner known per se, as described in page 21 ff of WO 2008/014964 A2.

The membrane electrode assembly of the present invention comprises at least one membrane of the present invention having a gasket edge S of the present invention and at least two electrochemically active electrodes (anode and cathode) separated from each other by such a membrane. The electrode is known per se and can promote the oxidation of hydrogen and / or one or more reformates and the reduction of oxygen. This property can be obtained by coating the electrode with platinum or a platinum alloy. The term "electrode" means that the material is electrically conductive. Such electrodes are known and described, for example, in US 4,191,618, US 4,212,714 and US 4,333,805.

The catalyst layer is generally not self-supporting but rather typically is applied to the gas diffusion layer and / or the membrane. In this case, part of the catalyst layer can penetrate into the gas diffusion layer and / or the membrane, for example, which forms a transition layer. As a result, the catalyst layer may be interpreted as part of the gas diffusion layer.

According to the invention, the surface of the polymer electrolyte membrane is (partially or fully, in each case preferably, partly) such that the first electrode covers the front face of the polymer electrolyte membrane and the second electrode covers the back face of the polymer electrolyte membrane. Covering only the electrode). In this aspect, the front and back sides of the polymer electrolyte membrane refer to the side facing and away from the observer of the polymer electrolyte membrane, respectively, the observation being the first electrode (front), preferably the second electrode (rear) at the cathode, Preferably proceeds in the direction of the anode.

In order to make the membrane electrode assembly of the present invention, the various components of the membrane electrode assembly are placed on top of each other and joined to each other by pressure and temperature, typically in the range of 10 to 300 ° C., in particular in the range of 20 to 200 ° C. The lamination is carried out at a temperature and at a pressure of 1 to 1000 bar, in particular at a pressure of 3 to 300 bar.

Since the performance of a single fuel cell is often too low for many applications, it is desirable in the present invention to produce a fuel cell (fuel cell stack) by combining a plurality of single fuel cells by a separator. In this case, the separator should seal between the gas space of the cathode and the anode, and the gas space of the cathode and the gas space of the anode from outside (and possibly intersect with additional gasket material). For this purpose, the separator is preferably placed sealingly onto the membrane electrode assembly. The sealing action can be further improved by compressing the composite consisting of separator and membrane electrode assembly.

The separators preferably each have one or more gas channels for the reaction gas, which are advantageously arranged on the side facing the electrode. The gas channel should allow for the distribution of the reactant fluid.

In particular, it has been found that the membrane electrode assembly of the present invention is excellent for a marked improvement in terms of mechanical stability and strength, and thus can be used in the manufacture of fuel cell stacks with particularly stable performance. At the same time, in the resulting fuel cell stack, the typical performance deviations are no longer observed today, and the characteristics, reliability and reproducibility never seen have been achieved.

Electrochemical performance is not affected by edge reinforcement,

Reinforced edges are more stable than unreinforced membranes in accelerated ex situ storage tests,

The reinforced membrane does not flow under gasket compression conditions,

The battery has been found to be airtight (for technical purposes).

Example

Edge reinforced MEAs of the present invention were prepared as follows:

Specific Example

1. Preparation of printing paste

Initially, the beaker was filled with 10 g of 10% sulfonated tetrafluoroethylene polymer (Nafion ^? ) Aqueous solution. At room temperature, 2 g of n-propanol were added while stirring with a magnetic stirrer and the mixture was stirred for an additional 5 minutes. Thereafter, 5 g of the selected PBI powder (250 mesh) was metered in and the mixture was stirred for an additional 5 minutes. Then 5 g of Teflon powder (average particle diameter 1 μm) was added. The mixture was stirred for an additional 30 minutes at room temperature. The paste then had a viscosity of approximately 1000 mPas.

2. Screen printing of paste onto carrier film

The paste is then in the form of an edge of the gasket UltrasonS ^? Printed on (BASF) film. The screen size used was 32 × 120 W PW. The paste was dried at room temperature under air. The height of the dried printed layer was approximately 65 μm.

3. Fabrication of Edge Reinforced Membrane by Lamination Transfer

Two of the films coated with printing paste were arranged to cover the top and bottom of the CeltecP membrane using a tool. Lamination transfer to the membrane was performed by hot press at 80 ° C. and 3000 N / cm 2 over 1 minute. The printing paste partially penetrated into the membrane, the PBI powder absorbed acid, and the edge region of the membrane was reinforced accordingly. Lamination transfer took place only when the tool applied pressure. Thus, the actual reinforcement region could be fixed by the tool geometry. The membrane thus obtained had a thickness of 150 μm in the reinforced gasket area. The unreinforced active region had a thickness of 400 μm.

4. Preparation of MEA from Edge Reinforced Membrane

Two gas diffusion electrodes (anode and cathode) were positioned to cover the membrane using a positioning and pressing tool. The gas diffusion electrodes overlapped approximately 1-2 mm with the reinforced edges. The outer region of the reinforced membrane edge remained uncovered. The MEA thickness was 1100 μm in the uncompressed state. Compression was carried out at 140 ° C. for 30 seconds with a predetermined thickness (determined by the spacers). The pressure was chosen such that the MEA was completely compressed to the height of the shim (500 μm). This deformed the MEA plastically and elastically. The elastic element allows the MEA to regain thickness after the pressure is released. This thickness was approximately 900 μm. The thickness of the reinforced membrane edge was 125 μm.

5. Fuel Cell Test

The MEA thus prepared was fired in an oven at 160 ° C. for 30 minutes to prepare a fuel cell. There was no difference in current / voltage characteristics in performance compared to standard MEA. 1 shows the corresponding properties, which were recorded under the following conditions:

T: 160 ℃

Supply gas: hydrogen, air

Properties named as 1) were recorded as standard MEAs, and properties named as 2) were recorded as inventive MEAs.

The membranes of the present invention have been found to exhibit high stability and good gasket properties even in continuous manufacturing processes.

Claims (13)

An ion conductive membrane having a layer S and based on polymer PM, wherein the layer S is applied to the membrane in an imagewise manner, attached to the membrane, and is based on a powder of polymer PP. The ion conductive membrane of claim 1, wherein said layer S is suitable as a gasket edge with the membrane and provides mechanical reinforcement. The ionically conductive membrane of claim 2, wherein the polymer content at the gasket edge comprising the membrane and layer S is higher than outside the gasket edge. The ion conductive membrane according to any one of claims 1 to 3, wherein the polymer PM used as the base for the membrane is the same as the polymer PP of the powder. The ionically conductive membrane of claim 1, wherein the powder is at least partially present on the membrane surface as well as on the membrane itself. The ion conductive membrane according to any one of claims 1 to 5, wherein the polymer PP and / or PM is based on polybenzimidazole (PBI). As a powder for use in the membrane according to claim 1
a) polymer PP, in particular polybenzimidazole, in particular in an amount of from 30 to 50 parts by weight, based on powder
b) flexible components, in particular polytetrafluoroethylene powder, and
c) powders comprising substantially a dispersant, in particular sulfonated polytetrafluoroethylene. A method of making a membrane according to any one of claims 1 to 6, comprising applying a powder of polymer PP to the membrane film and compressing it. The method of claim 8, wherein the membrane film is acid doped. The method of claim 8, wherein the powder is applied in the form of a dispersion or paste. The method of claim 10, wherein the paste or dispersion of the powder has a viscosity of 1 to 1000 mPas. At least
I. Polymeric membrane according to any one of claims 1 to 6,
II. Gasket body
Lt; / RTI &gt;
III. The membrane electrode assembly (MEA) for fuel cell, wherein the membrane around the layer S is embedded and compressed in the gasket body. An electrochemical reactor comprising at least one membrane electrode assembly according to claim 12.

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