KR20050018679A - Grafted polymer electrolyte membrane, method for the production thereof, and application thereof in fuel cells - Google Patents

Abstract

The present invention relates to proton conductive polymer electrolyte membranes based on polyvinylphosphonic acid / polyvinylsulfonic acid polymers, which, due to their excellent chemical and thermal properties, can be used for various purposes. Membranes of the invention are particularly suitable as polymer electrolyte membranes (PEMs) in PEM fuel cells.

Description

Grafted Polymer Electrolyte Membranes, Methods of Making the Same, and Uses thereof in Fuel Cells {GRAFTED POLYMER ELECTROLYTE MEMBRANE, METHOD FOR THE PRODUCTION THEREOF, AND APPLICATION THEREOF IN FUEL CELLS}

FIELD OF THE INVENTION The present invention relates to proton conductive polymer electrolyte membranes based on organic polymers grafted with vinylphosphonic acid and / or vinylsulfonic acid after pretreatment by radiation treatment, which, thanks to their excellent chemical and thermal properties, It can be used as a polymer electrolyte membrane (PEM) in a PEM fuel cell.

The fuel cell generally includes an electrolyte and two electrodes separated by an electrolyte. In the case of a fuel cell, one of the two electrodes is provided with a fuel, such as a hydrogen gas or a methanol / water mixture, the other electrode is provided with an oxidant such as oxygen gas or air, and in this way chemical energy from the fuel oxidation It is converted directly into electrical energy. Oxidation reactions form protons and electrons.

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

Fuel cells generally comprise several single cells, so-called membrane-electrode units (MEUs), each comprising an electrolyte and two electrodes separated by an electrolyte.

The electrodes used in fuel cells are solids such as polymer electrolyte membranes or liquids such as phosphoric acid. In recent years, polymer electrolyte membranes have attracted attention as electrolytes for fuel cells. In principle, it can be divided into two categories of polymer membranes.

The first category includes cation exchange membranes comprising a polymer backbone containing covalently bonded acid groups, preferably sulfonic acid groups. Sulphonic acid groups release hydrogen ions and are converted to anions, thus conducting protons. The proton mobility and hence the proton conductivity is directly related to the water content. Because of the very good miscibility of methanol and water, the cation exchange membrane has high methanol permeability and is therefore not suitable for use in direct current methanol fuel cells. When the membrane is dried, for example, as a result of high temperatures, the membrane's conductivity and thus the power of the fuel cell drops dramatically. Therefore, the operating temperature of the fuel cell including the cation exchange membrane is limited to the boiling point of water. The humidification of the membrane represents a major technical challenge for the use of conventional sulfonated membranes, such as polymer electrolyte membrane fuel cells (PEMFC) with Nafion.

The material used for the polymer electrolyte membrane is, for example, a perfluorosulfonic acid polymer. Perfluorosulfonic acid polymers (such as Nafion) generally have perfluorinated hydrocarbon backbones, such as copolymers of tetrafluoroethylene and trifluorovinyl, and side chains containing sulfonic acid groups, such as perfluoroalkyl, bound to the backbone It has a side chain which has a sulfonic acid group couple | bonded with a len group.

The cation exchange membrane is preferably an organic polymer having covalently bonded acid groups, in particular sulfonic acids. Methods of sulfonation of polymers are described in F. Kucera et al., Polymer Engineering and Science 1988, Vol. 38, no. 5, 783-792.

Next, the most important type of cation exchange membrane that achieves commercial importance for use in fuel cells is described.

The most important representative is the perfluorosulfonic acid polymer Nafion from DuPont. (US-A-3692569). As described in US-A-4453991, the polymer can be used as an ionomer after it is in solution. Cation exchange membranes are also obtained by filling a porous support material with the ionomer. As the support material, expanded Teflon is preferred (US-A-5635041).

In addition, methods for synthesizing membranes from similar perfluorinated polymers containing sulfonic acid groups have been developed by Dow Chemical, Asahi Glass or 3M Innovative Properties (US-A-6268532, WO 2001/44314, WO 2001/094437).

Additional perfluorinated cation exchange membranes may be prepared as described in US-A-5422411 by copolymerization of trifluorostyrene with sulfonyl modified trifluorostyrene. A composite membrane comprising an ionomer-filled porous support material, in particular expanded Teflon, composed of the sulfonyl-modified trifluorostyrene copolymer is described in US Pat. No. 5,834,523.

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

In addition to the membranes, an additional series of non-fluorinated membranes have been developed which are prepared by sulfonation of high temperature stable thermoplastics. Thus, sulfonated polyether ketones (DE-A-4219077, WO-96 / 01177), sulfonated polysulfones (J. Membr. Sci. 83 (1993) p.211) or sulfonated polyphenylene sulfides (DE A membrane consisting of -A-19527435 is known. Ionomers made from sulfonated polyether ketones are described in WO 00/15691.

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

To further improve the membrane properties, cation exchange membranes known in the art can be mixed with high temperature stable polymers. Sulfonated polyether ketones and a) polysulfones (DE-A-4422158), b) aromatic polyamides (DE-A-42445264) or c) polybenzimidazoles (DE-A-19851498). The preparation and properties of cation exchange membranes are known.

The membrane can also be obtained by the method in which the polymer is grafted. For this purpose, a previously irradiated polymer film comprising a fluorinated or partially fluorinated polymer, as described in EP-A-667983 or DE-A-19844645, can be grafted with styrene, preferably have. Alternatively, fluorinated aromatic monomers such as trifluorostyrene can be used as the graft component (WO 2001/58576). The side chain is then sulfonated in the subsequent sulfonation reaction. Chlorosulfonic acid or oleum is used as the sulfonating agent. In JP 2001/302721, a styrene-graft film is reacted with 2-ketopentafluoropropanesulfonic acid, whereby a membrane having a proton conductivity of 0.32 S / cm in a humidified state is obtained. The crosslinking reaction can also be carried out simultaneously with the grafting reaction, in which the mechanical properties and fuel permeability can be altered. As the crosslinking agent, it is possible to use, for example, divinylbenzene and / or triallyl cyanurate described in EP-A-667983, or 1,4-butanediol diacrylate described in JP 2001/216837.

The method of making such radiation-grafted and sulfonated membranes is very complex and includes many steps as follows: i) preparation of a polymer film; ii) irradiation of the polymer film preferably under inert gas and low temperature (≦ 60 ° C.) storage; iii) grafting reaction under nitrogen in a solution of suitable monomers and solvents; iv) extraction of the solvent; v) drying of the grafted film; vi) sulfonation reactions in the presence of highly reactive reagents and chlorinated hydrocarbons such as chlorosulfonic acid in tetrachloroethane; vii) repeated washings to remove excess solvent and sulfonation reagents; viii) reaction with diluted alkali, such as aqueous potassium hydroxide solution, for conversion to salt form; ix) repeated washings to remove excess alkali; x) reaction with dilute acids, such as hydrochloric acid; xi) final wash to remove excess acid.

A disadvantage of the cation exchange membrane is that the membrane must be humidified, the operating temperature is limited to 100 ° C., and the membrane has high permeability to methanol. The cause of this drawback is the conductive mechanism of the membrane, where the transport of protons is associated with the transport of water molecules. This is called the "vehicle mechanism" (K.-D. Kreuer, Chem. Mater. 1996, 8, 610-641).

One possible way to increase the operating temperature is to operate the cell fuel system under superatmospheric pressure to increase the boiling point of water. However, the method has a number of disadvantages, which have been found to make the fuel cell system more complicated, less efficient, and that there is an increase in weight instead of a desired decrease in weight. In addition, an increase in pressure can result in high mechanical stress on thin polymer membranes, which can render the membranes inoperable and cause the system to stop operating.

The second category developed includes polymer electrolyte membranes comprising complexes of basic polymers and strong acids that can be manipulated without humidification. Thus, WO 96/13872 and the corresponding US-A-5525436 disclose a process for producing proton conductive polymer electrolyte membranes, wherein the basic polymers such as polybenzimidazole are treated with strong acids such as phosphoric acid, sulfuric acid and the like.

J. Electrochem. Soc., Volume. 142, No. 7, 1995, p. L121-L123 describes doping of polybenzimidazoles in phosphoric acid.

In the case of basic polymer membranes known in the art, the inorganic acids (generally concentrated phosphoric acid) used to achieve the required proton conductivity are introduced after molding, or alternatively, the basic polymer membranes are prepared in German patent applications 10117686.4, 10144815.5 and 10117687.2. As described, it is prepared directly from polyphosphoric acid. Here, the polymer acts as a support for the electrolyte consisting of very concentrated phosphoric acid or polyphosphoric acid. Here, the polymer membrane achieves a further important function, in particular, should have high mechanical stability and act as a separator for the two fuels mentioned at the outset.

One possible method for producing radiation-grafted membranes for operation at temperatures in excess of 100 ° C. is described in JP 2001-213987 (Toyota). To this end, the partially fluorinated polymer film of polyethylene-tetrafluoroethylene or polyvinyl difluoride is investigated and subsequently reacted with a basic monomer such as vinylpyridine. As a result of incorporation of the graft side chains of polyvinylpyridine, these radiation-grafted materials exhibit phosphoric acid and high swelling. Proton-conducting membranes having a conductivity of 0.1 S / cm at 180 ° C. without humidification are prepared by doping with phosphoric acid.

JP 2000/331693 describes the preparation of anion exchange membranes by radiation grafting. Here, the graft reaction is carried out using a vinylbenzyltrimethylammonium salt or a quaternary salt of vinylpyridine or vinylimidazole. However, such anion exchange membranes are not suitable for use in fuel cells.

An important advantage of the membrane doped with phosphoric acid or polyphosphoric acid is the fact that the fuel cell in which the polymer electrolyte membrane is used can be operated at temperatures in excess of 100 ° C. in other cases without the need for humidification of the fuel cell. This is due to the so-called Grotthus mechanism (K.-D. Kreuer, Chem. Mater. 1996, 8, 610-641), the ability of phosphoric acid to transport protons without additional water.

Maneuverability at temperatures above 100 ° C. provides additional advantages for fuel cell systems. First, the sensitivity of the Pt catalyst to impurities in the gas, in particular CO, is significantly reduced. CO is produced as a by-product in the refining of a hydrogen-rich gas comprising carbon-containing compounds such as natural gas, methanol or gasoline, or as an intermediate in the direct oxidation of methanol. Typically, the CO content of the fuel should be less than 100 ppm at temperatures below 100 ° C. However, in the temperature range of 150-200 ° C., more than 10,000 ppm CO can be tolerated (N. J. Bjerrum et al., Journal of Applied Electrochemistry, 2001, 31, 773-779). This leads to a significant simplification of the preceding refining process and consequently reduced costs throughout the fuel cell system.

The main advantage of a fuel cell is the fact that the energy of the fuel is converted directly into electrical energy and heat during the electrochemical reaction. Water is formed as a reaction product at the cathode. Thus, heat is generated as a byproduct in the electrochemical reaction. In applications where only power is used to drive the electric motor, for example in automotive applications or as a replacement for battery systems in various applications, heat must be removed to prevent overheating of the system. In addition, an additional energy consuming device is then required for cooling, which further reduces the overall electrical efficiency of the fuel cell. For static applications, such as intensive or decentralized generation of power and heat, heat can be efficiently utilized by available techniques such as heat exchangers. In order to increase the efficiency, high temperatures are sought here. If the operating temperature exceeds 100 ° C and the temperature difference between the room temperature and the operating temperature is large, additional devices are removed and the fuel cell system more efficiently compared to the fuel cell that has to be operated below 100 ° C due to the humidification of the membrane. It is possible to cool or use a small cooling area.

In addition to the above advantages, the fuel cell system has a critical disadvantage. Phosphoric acid or polyphosphoric acid is present as an electrolyte that is not permanently bound to the basic polymer by ionic interactions and can be washed off by water. As described above, water is formed at the cathode during the electrochemical reaction. If the operating temperature exceeds 100 ° C., most of the water escapes to the vapor through the gas diffusion electrode and the acid loss is very low. However, if the operating temperature is less than 100 ° C., for example, during operation at partial load to drive or short circuit the cell or obtain high current efficiency, the water formed condenses to increase the electrolyte, i.e. high concentration of phosphoric acid or polyphosphoric acid. Can lead to a complete removal of the wash. During this operation of the fuel cell, this can lead to continuous degradation of conductivity and cell performance, which can reduce the life of the fuel cell.

Moreover, known membranes doped with phosphoric acid cannot be used in so-called direct current methanol fuel cells (DMFCs). However, the cells are of particular interest because the methanol / water mixture is used as fuel. If a known membrane based on phosphoric acid is used, the fuel cell is broken after a relatively short time.

Accordingly, it is an object of the present invention to provide a novel polymer electrolyte membrane in which the washing away of the electrolyte is prevented. In this way, in particular, the operating temperature should be able to extend in the range of more than 0 ° C to 200 ° C. Fuel cells comprising the polymer electrolyte membrane according to the invention should be suitable for operation using pure hydrogen and a plurality of carbon containing fuels, in particular natural gas, gasoline, methanol and biomass.

In addition, the preparation of the membranes according to the invention should be inexpensive and simple. It is therefore a further object of the present invention to produce polymer electrolyte membranes which also exhibit high performance, in particular high conductivity.

In addition, it is an object to provide a polymer electrolyte membrane having high mechanical stability, especially high elastic modulus, high tensile strength, low creep and high fracture toughness.

Furthermore, it is an object of the present invention to provide membranes having low permeability even during operation for various fuels such as hydrogen or methanol. This membrane also exhibits low oxygen permeability.

A further object of the present invention is to reduce and simplify the number of process steps in the film production according to the invention by radiation grafting, so that the steps can also be carried out on an industrial scale.

This object is achieved by the modification of industrial polymer based powders, which process radiation and subsequent treatment with monomers comprising vinylphosphonic acid and / or vinylsulfonic acid, and their subsequent polymerization and graft polymer electrolyte membranes or ionomers. Resulting in molding into a polyvinylphosphonic acid / polyvinylsulfonic acid polymer covalently bound to the polymer backbone.

Due to the concentration of the polyvinylphosphonic acid / polyvinylsulfonic acid polymer, its high chain flexibility and the high acidity of the polyvinylphosphonic acid, the conductivity is based on the Grotthus mechanism, so the system needs additional humidification at temperatures above the boiling point of water. Do not Conversely, with adequate humidification due to the presence of polyvinylsulfonic acid, satisfactory conductivity of the system is observed at temperatures below the boiling point of water.

The polymerizable polyvinylphosphonic acid / polyvinylsulfonic acid, which can also be crosslinked by a reactive group, is covalently bound to the polymer chain as a result of the grafting reaction and washed by water by-products formed or by aqueous fuel in the case of DMFC It is not removed. The polymer electrolyte membrane according to the invention has very low methanol permeability and is particularly suitable for use in DMFC. Thus, long term sustainable operation of fuel cells using many fuels such as hydrogen, natural gas, gasoline, methanol or biomass is possible. Here, the membrane enables particularly high activity of the fuel. Because of the high temperatures, methanol oxidation can occur with high activity. In certain embodiments, these membranes are suitable for operation in gaseous DMFCs, in particular in the temperature range of 100 to 200 ° C.

The operability at temperatures above 100 ° C. results in a large decrease in the sensitivity of the Pt catalyst to impurities in the gas, in particular CO. CO is formed as a byproduct in the refining of carbon-containing compounds, for example hydrogen-rich gas comprising natural gas, methanol or gasoline, or as an intermediate in the direct oxidation of methanol. The CO content of the fuel can be in excess of 5000 ppm, typically at temperatures above 120 ° C., without a sharp decrease in the catalytic activity of the Pt catalyst. However, at temperatures in the range from 150 to 200 ° C., more than 10000 ppm of CO can also be tolerated (N. J. Bjerrum et al. Journal of Applied Electrochemistry, 2001, 31, 773-779). This results in a significant simplification of the upper refining process, thus leading to a reduction in the overall cost of the fuel cell system.

The membranes according to the invention exhibit high conductivity, which is also achieved without further humidification over a wide temperature range. Furthermore, the fuel cell equipped with the membrane according to the present invention can be operated even at low temperatures, for example below 80 ° C., by which the life of the fuel cell is not significantly reduced.

Accordingly, the present invention provides a proton conductive electrolyte membrane obtainable by a method comprising the following steps:

A. irradiating the polymer to generate free radicals,

B. preparing a mixture of the polymer irradiated in step A) with a vinyl containing phosphonic acid monomer and / or a vinyl containing sulfonic acid monomer,

C. polymerizing the vinyl containing phosphonic acid and / or vinyl containing sulfonic acid monomers introduced in step B),

D. casting a sheet-like structure comprising the polymer obtained according to step C),

E. Drying the sheet-like structure to form a freestanding film.

The polymer used in step A) is preferably at least one polymer having a solubility of at least 1% by weight, preferably at least 3% by weight, in the phosphonic acid and / or vinyl containing sulfonic acid monomers, the solubility depending on the temperature. However, the mixture used to form the sheet-like structure can also be obtained at a wide range of temperatures, so that only the minimum solubility desired is achieved. The lower limit of the temperature is given by the melting point of the liquid present in the mixture, and the upper limit of the temperature is generally imposed by the decomposition temperature of the components or polymers of the mixture. In general, the mixture is prepared in the temperature range of 0 ° C to 250 ° C, preferably 10 ° C to 200 ° C. In addition, superatmospheric pressure can be used for dissolution, the limitation imposed by technical considerations. Particular preference is given to using a polymer having a solubility of at least 1% by weight in phosphonic acid and / or vinyl containing sulfonic acid monomers at 160 ° C. and 1 bar in step A).

Preferred polymers are in particular polyolefins such as poly (chloroprene), polyacetylene, polyphenylene, poly (p-xylene), polyarylmethylene, polystyrene, polymethylstyrene, polyvinylalcohol, polyvinylacetate, polyvinylether, poly Vinylamine, poly (N-vinylacetamide), polyvinylimidazole, polyvinylcarbazole, polyvinylpyrrolidone, polyvinylpyridine, polyvinylchloride, polyvinylidenechloride, polytetrafluoroethylene, polyvinyl Air with difluoride, polyhexafluoropropylene, polyethylene-tetrafluoroethylene, PTFE and hexafluoropropylene, perfluoropropylvinylether, trifluoronitrosomethane, carvalkoxyperfluoroalkoxyvinylether Coalesce, polychlorotrifluoroethylene, polyvinylfluoride, polyvinylidene fluoride, polyacrolein, poly Methacrylamide, polyacrylonitrile, policy cyano acrylate, polymethacrylic imide, cycloolefin-based copolymers, particularly those of the norbornane-derived norbornene; Polymers having a CO bond in the main chain such as polyacetal, polyoxymethylene, polyether, polypropylene oxide, polyepichlorohydrin, polytetrahydrofuran, polyphenyleneoxide, polyetherketone, polyetheretherketone, poly Ether ketone ketones, polyether ether ketone ketones, polyether ketone ether ketone ketones, polyesters, in particular polyhydroxyacetic acid, polyethylene terephthalate, polybutylene terephthalate, polyhydroxybenzoate, polyhydroxypropionic acid, polypropionic acid, Polypivalolactone, polycaprolactone, furan resin, phenol-aryl resin, polymalonic acid, polycarbonate; Polymers having CS bonds in the main chain, such as polysulfide ether, polyphenylene sulfide, polyether sulfone, polysulfone, polyether ether sulfone, polyarylether sulfone, polyphenylene sulfone, polyphenylene sulfide sulfone, poly (phenyl Sulfide-1,4-phenylene); Polymers having CN bonds in the main chain, such as polyimines, polyisocyanides, polyetherimines, polyetherimides, poly (trifluoromethylbis (phthalimido) phenyl), polyaniline, polyaramides, polyamides, polyhydra Zide, polyurethane, polyimide, polyazole, polyazole ether ketone, polyurea, polyazine; Liquid crystal polymers, in particular Vectra and inorganic polymers such as polysilanes, polycarbosilanes, polysiloxanes, polysilicic acids, polysilicates, silicones, polyphosphazenes and polythiazyls.

According to certain aspects of the invention, preference is given to using polymers containing one or more fluorine, nitrogen, oxygen and / or sulfur atoms in one repeating unit or in another repeating unit.

In certain embodiments, preference is given to using high temperature stable polymers. For the purposes of the present invention, polymers are stable at high temperatures when they can be used continuously for a long time as polymer electrolytes in fuel cells at temperatures above 120 ° C. "Long-lasting" means that the membrane according to the invention can be measured according to the method described in WO 01/18894 A2, at a temperature of at least 120 ° C, preferably at least 160 ° C, without a performance drop of more than 50% relative to the initial performance. It means that it can be operated for at least an hour, preferably at least 500 hours.

The polymer used in step A) is preferably a polymer having a Vicat softening point VST / A / 50 or glass transition temperature of at least 100 ° C., preferably at least 150 ° C., very particularly preferably at least 180 ° C.

Particular preference is given to polymers having at least one nitrogen atom in the repeating unit. Particular preference is given to polymers having at least one aromatic ring containing at least one nitrogen heteroatom per repeat unit. Of these, polyazole based polymers are particularly preferred. These basic polyazole polymers have one or more aromatic rings containing one or more nitrogen heteroatoms per repeat unit.

The aromatic ring is preferably a 5- or 6-membered ring containing 1 to 3 nitrogen atoms, which can be fused with other rings, in particular with other aromatic rings.

Polyazole based polymers may be of the formula I and / or II and / or IIII 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 Repeating azole units of XII and / or XIII and / or XIV and / or XV and / or XVI and / or XVII and / or XVIII and / or XIX and / or XX and / or XXI and / or XXII:

(In the meal,

The radicals Ar are the same or different and each is a tetravalent aromatic or heteroaromatic group which may be monocyclic or polycyclic;

The radicals Ar ¹ are the same or different and each is a divalent aromatic or heteroaromatic group which may be monocyclic or polycyclic;

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

The radicals Ar ³ are the same or different and are each a trivalent aromatic or heteroaromatic group which may be monocyclic or polycyclic;

The radicals Ar ⁴ are the same or different and are each a trivalent aromatic or heteroaromatic group which may be monocyclic or polycyclic;

The radicals Ar ⁵ are the same or different and are tetravalent aromatic or heteroaromatic groups, which may each be monocyclic or polycyclic;

The radicals Ar ⁶ are the same or different and each is a divalent aromatic or heteroaromatic group which may be monocyclic or polycyclic;

The radicals Ar ⁷ are the same or different and each is a divalent aromatic or heteroaromatic group which may be monocyclic or polycyclic;

The radicals Ar ⁸ are the same or different and are each a trivalent aromatic or heteroaromatic group which may be monocyclic or polycyclic;

The radicals Ar ⁹ are the same or different and are a divalent or trivalent or tetravalent aromatic or heteroaromatic group which may be monocyclic or polycyclic, respectively;

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

The radicals Ar ¹¹ are the same or different and each is a divalent aromatic or heteroaromatic group which may be monocyclic or polycyclic;

The radicals X are the same or different and each is an oxygen, sulfur or amino group, which has, as further radicals, one hydrogen atom, a group having 1 to 20 carbon atoms, preferably a branched or unbranched alkyl or alkoxy group or an aryl group;

The radicals R are the same or different and are each hydrogen, an alkyl group or an aromatic group; And

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

Preferred aromatic or heteroaromatic groups according to the invention are benzene, naphthalene, biphenyl, diphenylether, diphenylmethane, diphenyldimethylmethane, bisphenol, diphenylsulfone, thiophene, furan, pyrrole, thia Sol, oxazole, imidazole, isothiazole, isoxazole, pyrazole, 1,3,4-oxadiazole, 2,5-diphenyl-1,3,4-oxadiazole, 1,3,4 -Thiadiazole, 1,3,4-triazole, 2,5-diphenyl-1,3,4-triazole, 1,2,5-triphenyl-1,3,4-triazole, 1, 2,4-oxadiazole, 1,2,4-thiadiazole, 1,2,4-triazole, 1,2,3-triazole, 1,2,3,4-tetazole, benzo [b ] Thiophene, benzo [b] furan, indole, benzo [c] thiophene, benzo [c] furan, isoindole, benzoxazole, benzothiazole, benzimidazole, benzisoxazole, benzisothiazole, benzopyra Sol, benzothiadiazole, benzotriazole, dibenzofuran, dibenzothiophene, carbazole, pyridine, bipyridine, pyrazine, pyrazole, pyrimidine, pyridazine, 1,3 , 5-triazine, 1,2,4-triazine, 1,2,4,5-triazine, tetrazine, quinoline, isoquinoline, quinoxaline, quinazoline, cinnoline, 1,8-naphthyridine, 1,5-naphthyridine, 1,6-naphthyridine, 1,7-naphthyridine, phthalazine, pyridopyrimidine, purine, pteridine or quinolizine, 4H-quinolizine, diphenyl ether, Anthracene, benzopyrrole, benzooxadiadiazole, benzooxadiazole, benzopyridine, benzopyrazine, benzopyrazidine, benzopyrimidine, benzotriazine, indolizin, pyridopyridine, imidazopyrimidine, pyrazino Derived from pyrimidine, carbazole, asyridine, phenazine, benzoquinoline, phenoxazine, phenothiazine, acridizin, benzopteridine, phenanthroline and phenanthrene.

Substitution patterns of Ar ¹ , Ar ⁴ , Ar ⁶ , Ar ⁷ , Ar ⁸ , Ar ⁹ , Ar ¹⁰ , Ar ¹¹ are arbitrary, for example, for phenylene, Ar ¹ , Ar ⁴ , Ar ⁶ , Ar ⁷ , Ar ⁸ , Ar ⁹ , Ar ¹⁰ , Ar ¹¹ may be ortho-, meta- or para-phenylene. Particularly preferred groups are derived from benzene and biphenylene which may also be substituted.

Preferred alkyl groups are short-chain alkyl groups having from 1 to 4 carbon atoms such as methyl-, ethyl, n- or i-propyl and t-butyl groups.

Preferred aromatic groups are phenyl and 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 in one repeat unit have the same repeat unit of formula (I).

The polyazoles may also basically have other repeating units, for example different from X radicals. However, it is preferred that there are only identical X radicals in the repeat unit.

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

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

For the purposes of the present invention, polymers containing repeat benzimidazole units are preferred. Some examples of very advantageous polymers comprising repeat benzimidazole units are represented by the formula:

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

Further preferred polyazole polymers are polyimidazole, polybenzimidazole ether ketone, polybenzothiazole, polybenzoxazole, polytriazole, polyoxadiazole, polythiadiazole, polypyrazole, polyquinoxaline, poly (Pyridine), poly (pyrimidine) and poly (tetrazapyrene).

Particularly preferred is Celazole manufactured by Celanese, and specifically, a polymer subjected to a sieving process as described in German patent application 10129458.1 is used.

The polyazoles used, but in particular the polybenzimidazoles, have a high molecular weight. When measured by the intrinsic viscosity, it is preferably 0.2 dl / g or more, in particular 0.8 to 10 dl / g, particularly preferably 1 to 10 dl / g.

Also preferred are polyazoles obtained by the method described in German patent application 10117687.2.

Preferred polymers include polysulfones, especially polysulfones having aromatic and / or heteroaromatic groups in the main chain. According to certain aspects of the invention, preferred polysulfones and polyethersulfones have a melting of 40 cm 3/10 minutes or less, in particular 30 cm 3/10 minutes or less, particularly preferably 20 cm 3/10 minutes or less, measured according to ISO 1133. Volumetric flow rate MVR 300 / 21.6. Here, polysulfone which has the Vicat softening point VST / A / 50 of 180 degreeC-230 degreeC is preferable. In a further 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 containing repeating units having a bonding sulfone group, corresponding to formulas A, B, C, D, E, F and / or G:

Wherein the radicals R are the same or different and each independently represent an aromatic or heteroaromatic group, and these radicals have already been described in detail. These include in particular 1,2-phenylene, 1,3-phenylene, 1, 4-phenylene, 4,4'-biphenyl, pyridine, quinoline, naphthalene and phenanthrene.

Preferred polysulfones for the purposes of the present invention include homopolymers and copolymers such as random copolymers. Particularly preferred polysulfones comprise repeating units of formula H to N:

The polysulfone mentioned above is a brand name Victrex 200P, Victrex 720P, Ultrason E, Ultrason S, Mindel, Radel A, Radel R, Victrex HTA, Astrel and Marketed as Udel.

Moreover, polyether ketone, polyether ketone ketone, polyether ether ketone, polyether ether ketone ketone and polyaryl ketone are particularly preferable. These high performance polymers are known per se, under the trade name Victrex PEEK ^TM , Hostatec and Sold by Kadel.

The polymers mentioned above can be used individually or as mixtures (mixtures). Particular preference is given to blends containing polyazoles and / or polysulfones. By using the admixture, it is possible to improve the mechanical characteristics and to reduce the material cost.

In order to generate free radicals, the polymer is treated at least once with single radiation or various types of radiation in step A) until a sufficient concentration of free radicals is obtained. The type of radiation used is for example electromagnetic radiation, in particular γ-rays, and / or electron beams, for example β-rays. A sufficiently high concentration of free radicals can be achieved with radiation doses of 1 to 500 kGy, preferably 3 to 300 kGy, very particularly preferably 5 to 200 kGy. Irradiation with the electron furnace is especially preferable. Irradiation can be carried out in air or inert gas. After irradiation, the sample can be stored for several weeks at a temperature below -50 ° C. without causing much reduction in free radical activity.

In steps B) and C) it is possible to use a solvent. In this case, any organic or inorganic solvent can be used. Organic solvents include in particular polar aprotic solvents such as dimethyl sulfoxide (DMSO), esters such as ethyl acetate and polar protic solvents such as alcohols such as ethanol, propanol, isopropanol and / or butanol. Strong bases such as KOH and / or NaOH can be added to the polar protic solvents, in particular alcohols. Inorganic solvents include especially water, phosphoric acid and polyphosphoric acid.

Preference is given to a solvent which produces a homogeneous mixture of the polymer from step A) and the vinyl containing acid monomer from step B). Preferred solvents are aprotic solvents such as dimethylacetamide, N-methylpyrrolidone, dimethylformamide or dimethyl sulfoxide (DMSO).

Vinyl containing phosphonic acids are known to those skilled in the art. These are compounds containing at least one carbon-carbon double bond and at least one phosphonic acid group. Preferably, the two carbon atoms forming the carbon-carbon double bond comprise two or more, preferably three, bonds in the group leading to minimal steric structural interference of the double bond. Such groups include, among others, hydrogen atoms and halogen atoms, in particular fluorine atoms. In the context of the present invention, polyvinylphosphonic acid is a polymerization product obtained by polymerization of vinyl-containing phosphonic acid alone or polymerization of monomers and / or crosslinkers.

The vinyl containing phosphonic acid may comprise one, two, three or more carbon-carbon double bonds. Furthermore, the vinyl containing phosphonic acid may comprise one, two, three or more phosphonic acid groups.

In general, vinyl containing phosphonic acids comprise 2 to 20, preferably 2 to 10 carbon atoms.

The vinyl containing phosphonic acid used in step B) is preferably of the formula:

(In the formula,

R is a bond, a C1-C15 alkyl group, a C1-C15 alkoxy group, an ethyleneoxy group or a C5-C20 aryl or heteroaryl group, wherein the radicals mentioned above are halogen, -OH, COOZ, -CN, NZ ₂ Can be substituted,

The radicals Z, each independently, represent hydrogen, a C1-C15 alkyl group, a C1-C15 alkoxy group, an ethyleneoxy group or a C5-C20 aryl or heteroaryl group, wherein the radicals mentioned above are halogen, -OH, -CN Can be substituted,

x is 1, 2, 3, 4, 5, 6, 7, 8, 9 or 10,

y is 1, 2, 3, 4, 5, 6, 7, 8, 9 or 10),

And / or the following formula:

(In the formula,

R is a bond, a C1-C15 alkyl group, a C1-C15 alkoxy group, an ethyleneoxy group or a C5-C20 aryl or heteroaryl group, wherein the radicals mentioned above are halogen, -OH, COOZ, -CN, NZ ₂ Can be substituted,

The radicals Z, each independently, represent hydrogen, a C1-C15 alkyl group, a C1-C15 alkoxy group, an ethyleneoxy group or a C5-C20 aryl or heteroaryl group, wherein the radicals mentioned above are halogen, -OH, -CN Can be substituted,

x is 1, 2, 3, 4, 5, 6, 7, 8, 9 or 10),

And / or the following formula:

(In the formula,

A is a group of formula COOR ² , CN, CONR ² ₂ , OR ² and / or R ² , wherein R ² is hydrogen, C 1 -C 15 alkyl group, C 1 -C 15 alkoxy group, ethyleneoxy group or C 5 -C 20 aryl or Heteroaryl group, wherein the radicals mentioned above may be substituted with halogen, -OH, COOZ, -CN, NZ ₂ ,

R is a bond, a divalent C1-C15 alkylene group, a divalent C1-C15 alkoxy group, for example an ethyleneoxy group, or a divalent C5-C20 aryl or heteroaryl group, wherein the radicals mentioned above are halogen, May be substituted with -OH, COOZ, -CN, NZ ₂ ,

The radicals Z, each independently, represent hydrogen, a C1-C15 alkyl group, a C1-C15 alkoxy group, an ethyleneoxy group or a C5-C20 aryl or heteroaryl group, wherein the radicals mentioned above are halogen, -OH, -CN Can be substituted,

x is 1, 2, 3, 4, 5, 6, 7, 8, 9 or 10)

Compound.

Preferred vinyl containing phosphonic acids are in particular alkenes containing phosphonic acid groups such as ethenephosphonic acid, propenephosphonic acid, butenephosphonic acid; Acrylic and / or methacrylic acid compounds containing phosphonic acid groups, such as 2-phosphonomethyl-acrylic acid, 2-phosphonomethyl-methacrylic acid, 2-phosphonomethyl-acryl amide and 2-phosphonomethyl- Methacryl amides.

Particularly preferably used are commercially available vinylphosphonic acids (ethene phosphonic acid) of the type commercially available, for example, from Aldrich or Clariant GmbH. Preferred vinylphosphonic acids have a purity of greater than 70%, preferably greater than 90% and particularly preferably greater than 97%.

In addition, the vinyl-containing phosphonic acid can be used in the form of derivatives, which can then be converted to an acid, which can also take place in the polymerized state. Derivatives of this type specifically include salts, esters, halides and amides of vinyl containing phosphonic acids.

Vinyl containing sulfonic acids are known in the art. These are compounds containing at least one carbon-carbon double bond and at least one sulfonic acid group. Preferably, the two carbon atoms forming the carbon-carbon double bond have at least two, more preferably three bonds in the group leading to the low steric hindrance of the double bond. These groups include in particular hydrogen atoms and halogen atoms, in particular fluorine atoms. Within the scope of the present invention, polyvinylsulfonic acid is a polymerization product obtained by homopolymerization of vinyl containing sulfonic acids or polymerization with other monomers and / or crosslinkers.

The vinyl containing sulfonic acid may comprise one, two, three or more carbon-carbon double bonds. In addition, the vinyl containing sulfonic acid may comprise one, two, three or more sulfonic acid groups.

Usually, vinyl containing sulfonic acids contain 2 to 20, preferably 2 to 10 carbon atoms.

The vinyl containing sulfonic acid used in step B) is preferably of the formula:

(In the formula,

R is a bond, a C1-C15-alkyl group, a C1-C15-alkoxy group, an ethyleneoxy group or a C5-C20-aryl or heteroaryl group, wherein the radicals mentioned above are halogen, -OH, COOZ, -CN, May be substituted with NZ ₂ ,

The radicals Z are each, independently of one another, hydrogen, a C1-C15-alkyl group, a C1-C15-alkoxy group, an ethyleneoxy group or a C5-C20-aryl or heteroaryl group, wherein the radicals mentioned above are halogen, -OH, May be substituted with -CN,

x is 1, 2, 3, 4, 5, 6, 7, 8, 9 or 10,

y is 1, 2, 3, 4, 5, 6, 7, 8, 9 or 10),

And / or the following formula:

(In the formula,

R is a bond, C1-C15-alkyl group, C1-C15-alkoxy group, ethyleneoxy group or C5-C20-aryl or heteroaryl group, wherein the radicals mentioned above are halogen, -OH, C00Z, -CN, May be substituted with NZ ₂ ,

The radicals Z are each, independently of one another, hydrogen, a C1-C15-alkyl group, a C1-C15-alkoxy group, an ethyleneoxy group or a C5-C20-aryl or heteroaryl group, wherein the radicals mentioned above are halogen, -OH, May be substituted with -CN,

x is 1, 2, 3, 4, 5, 6, 7, 8, 9 or 10),

And / or the following formula:

(In the formula,

A is a group of the formula COOR ² , CN, C0NR ² ₂ , OR ² and / or R ² , wherein R ² is hydrogen, C 1 -C 15 -alkyl group, C 1 -C 15 -alkoxy group, ethyleneoxy group or C 5 -C 20 -Aryl or heteroaryl group, wherein the radicals mentioned above can be substituted by halogen, -OH, COOZ, -CN, NZ ₂ ,

R is a bond, a divalent C1-C15-alkylene group, a divalent C1-C15-alkoxy group, for example an ethyleneoxy group or a divalent C5-C20-aryl or heteroaryl group, wherein the radicals mentioned above Halogen, -OH, COOZ, -CN, NZ ₂ ,

The radicals Z are each, independently of one another, hydrogen, a C1-C15-alkyl group, a C1-C15-alkoxy group, an ethyleneoxy group or a C5-C20-aryl or heteroaryl group, wherein the radicals mentioned above are halogen, -OH, May be substituted with -CN,

x is 1, 2, 3, 4, 5, 6, 7, 8, 9 or 10)

Compound.

Preferred vinyl containing sulfonic acids include, in particular, alkenes comprising sulfonic acid groups such as ethene sulfonic acid, propene sulfonic acid, butene sulfonic acid; Acrylic acid and / or methacrylic acid compounds comprising sulfonic acid groups, such as 2-sulfomethyl-acrylic acid, 2-sulfomethyl-methacrylic acid, 2-sulfomethyl-acrylamide and 2-sulfomethyl-methacryl amide.

Particular preference is given to using commercially available vinyl sulfonic acids (ethene sulfonic acids) such as those obtainable from Aldrich or Clariant GmbH. Preferred vinyl sulfonic acids have a purity of greater than 70%, in particular greater than 90%, particularly preferably greater than 97%.

Vinyl containing sulfonic acids can also be used in the form of derivatives which can subsequently be converted to acids, which are also possible in the polymerized state. These derivatives include especially salts, esters, amides and halides of vinyl containing sulfonic acids.

The mixture used in steps B) and C) comprises a vinyl containing phosphonic acid monomer or a vinyl containing sulfonic acid monomer. Furthermore, the mixture may comprise both vinyl containing sulfonic acid monomers and vinyl containing phosphonic acid monomers. The mixing ratio of vinyl containing sulfonic acid monomer to vinyl containing phosphonic acid monomer is preferably in the range of 1:99 to 99: 1, more preferably 1:50 to 50: 1, especially 1:25 to 25: 1.

The content of the vinylsulfonic acid monomer in the composition used for the grafting is preferably in the range of 1% by weight or more, more preferably 5% by weight or more, particularly preferably 10 to 97% by weight.

The content of vinylphosphonic acid monomer in the composition used for grafting is preferably in the range of at least 3% by weight, more preferably at least 5% by weight and particularly preferably in the range of 10 to 99% by weight.

The mixture comprising vinylphosphonic acid / vinylsulfonic acid prepared in step B) and the composition used for grafting may be a solution, which may further contain suspended or dispersed components.

The polymerization of the vinyl containing phosphonic acid / sulfonic acid monomer in step C) is carried out at temperatures above room temperature (20 ° C.) and below 200 ° C., preferably at a temperature in the range from 40 ° C. to 150 ° C., in particular at 50 ° C. to 120 ° C. do. The polymerization is preferably carried out at atmospheric pressure, but can also be carried out at superatmospheric pressure. The polymerization is preferably carried out under an inert gas such as nitrogen. Polymerization results in an increase in volume and weight. The degree of grafting is characterized by an increase in weight during grafting and is at least 10%, preferably greater than 20% and very particularly preferably greater than 50%. The grafting degree is calculated from the mass m ₀ of the dry film before grafting and the mass m ₁ of the dry film after grafting and washing (step D) according to the following formula.

Grafting degree = (m ₁ -m ₀ ) / m ₀ * 100

After these steps, they can be repeated several times in the order described. The number of iterations depends on the degree of grafting desired.

The polymer obtained in step C) comprises 0.5 to 96% by weight of organic polymer and 99.5 to 4% by weight of polyvinylphosphonic acid and / or polyvinylsulfonic acid. The polymer obtained in step C) preferably comprises 3 to 90% by weight of organic polymer and 97 to 10% by weight of polyvinylphosphonic acid and / or polyvinylsulfonic acid.

The casting of the sheet-like structure, in particular the polymer film, from the polymer solution comprising the polymer obtained according to step C) (step D) is carried out by means known per se from the prior art. For example, the mixture obtained according to step C) can be used for casting. In addition, the grafted polymer obtained is first separated from the mixture from step C), and then the separated polymer is dissolved in the solvent exemplified above, and then cast to prepare a film.

After casting according to step D), the monomer residues present in the sheet-like structure can be thermally, photochemically, chemically and / or electrochemically polymerized. Depending on the proportion of solvent residues, drying according to step E) is achieved, whereby a freestanding membrane is produced.

The polymerization can be carried out by way of example of IR or NIR (IR = infrared, ie light having a wavelength greater than 700 nm; NIR = near infrared, ie light having a wavelength in the range of approximately 700 to 2,000 nm or energy in the range of approximately 0.6 to 1.75 eV). By action.

The polymerization can be carried out, for example, by the action of UV light having a wavelength of less than 400 nm. Such polymerization processes are known per se and are described, for example, in Hans Joerg Elias, Makromolekulare Chemie, 5 Auflage, Volume 1, pp. 492-511; D.R. Arnold, N.C. Baird, J.R. Bolton, J. C. D. Brand, P.W.M Jacobs, P.de Mayo, W.R. Ware, Photochemistry-An Introduction, Academic Press, New York und M.K. Mishra, Radical Photopolymerization of Vinyl Monomers, J. Macromol. Sci.-Revs. Macromol. Chem. Phys. C22 (1982-1983) 409.

The polymerization can also be carried out by the action of β-, γ- and / or electron beams. According to a particular embodiment of the invention, the membrane is irradiated with a radiation dose in the range of 1 to 300 kGy, preferably 3 to 200 kGy and particularly preferably 20 to 100 kGy.

Any polymerization of the vinyl containing sulfonic acid and / or vinyl containing phosphonic acid monomers is preferably at temperatures above room temperature (20 ° C.) and below 200 ° C., especially at temperatures in the range from 40 ° C. to 150 ° C., particularly preferably at 50 ° C. To 120 ° C. The polymerization is preferably carried out under atmospheric pressure, but can also be carried out under superatmospheric pressure. Polymerization results in strengthening of the sheet-like structure, which can be monitored by microhardness measurement. The increase in hardness caused by the polymerization is preferably at least 20% relative to the hardness of the sheet-like structure obtained in step A).

According to certain embodiments of the invention, the membrane has high mechanical stability. This parameter is given by the hardness of the membrane measured by microhardness measurement according to DIN 50539. For this reason, the membrane is continuously pressed for 20 seconds with a Vickers diamond up to a force of 3 mN, and the depth of penetration is determined. According to this, the hardness at room temperature is 0.01 N / mm 2 or more, preferably 0.1 N / mm 2 Above, particularly preferably 1 N / mm 2 As mentioned above, it is not limited to this. The force is then kept constant for 5 seconds at 3 mN, and creep is calculated from the depth of penetration. In a preferred membrane, the creep C _HU 0,003 / 20/5 under these conditions is less than 20%, preferably less than 10%, particularly preferably less than 5%. The YHU coefficient determined using micro-hardness measurement is at least 0.5 MPa, in particular at least 5 MPa, particularly preferably at least 10 MPa, but is not limited thereto.

Depending on the type of composition used for the grafting and any surface polymerization / crosslinking, drying may be advantageous. Drying of the sheet-like structure in step E) can be carried out at a temperature in the range from room temperature to 300 ° C. Drying is carried out at atmospheric or reduced pressure. Drying time depends on the thickness of the film and is 10 seconds to 24 hours. If the sheet-like structure formed in step D) is a film, it is dried in accordance with step E), which is then self-supported and can be separated from the support without damage and, if appropriate, further processed. Drying is carried out by conventional drying methods in the film industry.

The solvent can be removed very significantly, for example by drying carried out in step E). Therefore, the residual content of the organic solvent is usually less than 30% by weight, preferably less than 20% by weight, particularly preferably less than 10% by weight.

By increasing the drying temperature and drying time, the residual solvent content can be further reduced to less than 2% by weight. In one variation, drying may also be combined with a cleaning step. Particularly suitable methods for the workup and removal of residual solvents are described in German patent application 10109829.4.

In certain embodiments of the invention, the membrane comprises at least 3% by weight, preferably at least 5% by weight and particularly preferably at least 7% by weight of phosphorus (element) relative to the total weight of the membrane. The proportion of phosphorus can be determined by elemental analysis. For this purpose, the membrane is dried under reduced pressure (1 mbar) at 110 ° C. for 3 hours. In certain embodiments of the invention, the membrane comprises at least 3% by weight, preferably at least 5% by weight and particularly preferably at least 7% by weight of phosphorus (element) relative to the total weight of the membrane. The proportion of phosphorus can be determined by elemental analysis. For this purpose, the membrane is dried under reduced pressure (1 mbar) at 110 ° C. for 3 hours. The ratio is particularly preferably determined after an optional washing step.

The polymer membranes of the present invention have improved material properties compared to acid known doped polymer membranes. In particular, it exhibits inherent conductivity at temperatures above 100 ° C., unlike known undoped polymer membranes, and is free of humidification. This is due in particular to polymeric polyvinylphosphonic acid and / or polyvinylsulfonic acid covalently bound to the polymer backbone.

At 80 ° C. temperature, optionally by humidification, the intrinsic conductivity of the membranes of the invention is generally at least 0.1 mS / cm, preferably at least 1 mS / cm, in particular at least 2 mS / cm, particularly preferably at least 5 mS / cm That's it.

At a ratio of more than 10% by weight of polyvinylphosphonic acid relative to the total weight of the membrane, the membrane is generally at least 1 mS / cm, preferably at least 3 mS / cm, in particular at least 5 mS / cm, particularly preferably at 160 ° C. It has a conductivity of 10 mS / cm or more. These figures are achieved without humidification.

Specific conductivity is measured using a platinum electrode (0.25 mm diameter wire) by an impedance spectrometer in a 4-pole array potentiostatic mode. The distance between the current collecting electrodes is 2 cm. The spectra obtained are evaluated using a simple model consisting of parallel arrangements of ohmic resistors and capacitors. The sample cross sectional area of the phosphate-doped membrane is measured immediately prior to sample introduction. To measure the temperature dependence, the test cell is heated in the oven to the desired temperature and the temperature is controlled by a Pt-100 thermocouple placed in the immediate vicinity of the sample. After reaching this temperature, the sample is held at this temperature for 10 minutes before the start of the measurement.

The crossover current density is preferably less than 100 mA / cm 2, in particular less than 70 mA / cm 2, particularly preferably less than 50 mA / cm 2 when operating at 90 ° C. with 0.5 M methanol solution in a liquid direct methanol fuel cell. More preferably less than 10 mA / cm 2. The crossover current density is preferably less than 100 mA / cm 2, in particular less than 50 mA / cm 2, particularly preferably less than 10 mA / cm 2 when operating at 160 ° C. with a 2 M methanol solution in a gas direct current methanol fuel cell. to be.

To determine the crossover current density, the amount of carbon dioxide emitted from the cathode is measured using a CO ₂ sensor. The crossover current density is [P. Zelenay, SC Thomas, S. Gottesfeld in S. Gottesfeld, TF Fuller "Proton Conducting Membrane Fuel Cells II" ECS Proc. Vol. 98-27 pp. 300-308, as determined from the numerical values of the amount of CO ₂ obtained.

Following the treatment according to step E), the sheet-like structure can be further crosslinked on the surface by the action of heat in the presence of atmospheric oxygen. Curing of this membrane surface achieves further improvement of the properties of the membrane.

Crosslinking is also the action of IR or NIR (IR = infrared, ie light having a wavelength greater than 700 nm; NIR = near infrared, ie light having a wavelength in the range of approximately 700 to 2,000 nm or energy in the range of approximately 0.6 to 1.75 eV). Can be performed by Another method is irradiation by β-rays. The radiation dose ranges from 5 to 200 kGy.

In another step, the grafted membrane prepared according to the present invention may be free of unreacted components by washing with alcohol or water such as methanol, 1-propanol, isopropanol or butanol or mixtures thereof. The washing is carried out at temperatures from room temperature (20 ° C.) to 100 ° C., in particular at room temperature to 80 ° C., very particularly preferably at room temperature to 60 ° C.

To further improve the use properties, fillers, in particular proton conductive fillers, and additional acids can also be added to the membrane. The addition can be carried out in step A) or after polymerization.

Non-limiting examples of proton conductive fillers include:

Sulfates such as CsHSO ₄ , Fe (SO ₄ ) ₂ , (NH ₄ ) ₃ H (SO ₄ ) ₂ , LiHSO ₄ , NaHSO ₄ , KHSO ₄ , RbSO ₄ , LiN ₂ H ₅ SO ₄ , NH ₄ HSO ₄ ,

Phosphates such as Zr (PO ₄ ) ₄ , Zr (HPO ₄ ) ₂ , HZr ₂ (PO ₄ ) ₃ , UO ₂ PO ₄ 3H ₂ O, H ₈ UO ₂ PO ₄ , Ce (HPO ₄ ) ₂ , Ti ( HPO ₄ ) ₂ , KH ₂ PO ₄ , NaH ₂ PO ₄ , LiH ₂ PO ₄ , NH ₄ H ₂ PO ₄ , CsH ₂ PO ₄ , CaHPO ₄ , MgHPO ₄ , HSbP ₂ O ₈ , HSb ₃ P ₂ O ₁₄ , H ₅ Sb ₅ P ₂ O ₂₀ ,

Polyacids such as H ₃ PW ₁₂ O ₄₀ nH ₂ O (n = 21-29), H ₃ SiW ₁₂ O ₄₀ nH ₂ O (n = 21-29), H _x WO ₃ , HSbWO ₆ , H ₃ PMo ₁₂ O ₄₀ , H ₂ Sb ₄ O ₁₁ , HTaWO ₆ , HNbO ₃ , HTiNbO ₅ , HTiTaO ₂ , HSbTeO ₆ , H ₅ Ti ₄ O ₉ , HSbO ₃ , H ₂ MoO ₄ ,

Selenides and argenides such as (NH ₄ ) ₃ H (SeO ₄ ) ₂ , UO ₂ AsO ₄ , (NH ₄ ) ₃ H (SeO ₄ ) ₂ , KH ₂ AsO ₄ , Cs ₃ H (SeO ₄ ) ₂ , Rb ₃ H (SeO ₄ ) ₂ ,

Oxides such as Al ₃ O ₃ , Sb ₂ O ₅ , ThO ₂ , SnO ₂ , ZrO ₂ , MoO ₃ ,

Silicates, such as zeolites, zeolite (NH ₄ ^+), sheet silicates, silicate skeleton, H- or trolley agent, H- mordenite, NH ₄ - Anal Shin, NH ₄ - bovine Dalits, NH ₄ - gallate, H- Montmorillonite,

Acids such as HClO ₄ , SbF ₅ ,

Fillers such as carbides, in particular SiC, Si ₃ N ₄ , fibers, in particular glass fibers, glass powders and / or polymer fibers, preferably polyazole substrates.

These additives may be present in conventional amounts in the proton conductive polymer membrane, but by excessive addition, the ultimate properties such as high conductivity, long life and high mechanical stability of the membrane should not be overly impaired. Typically, the membrane after polymerization in step C) contains up to 80% by weight, preferably up to 50% by weight, particularly preferably up to 20% by weight of additives.

The membrane may also contain a perfluorinated sulfonic acid additive (0.1-20% by weight, preferably 0.2-15% by weight, particularly preferably 0.2-10% by weight). These additives result in performance enhancements that increase oxygen solubility and oxygen diffusion near the cathode and reduce the adsorption of phosphates and phosphates on platinum (Electrolyte additives for phophoric acid fuel cells.Gang, Xiao; Hjuler, HA; Olsen, C .; Berg, RW; Bjerrum, NJ Chem.Dep.A, Tech.Univ.Denmark, Lyngby, Den.J. Electrochem.Soc. (1993), 140 (4), 896-902, and Perfluorosulphonimide as an additive in phophoric acid fuel cell.Razaq, M .; Razaq, A .; Yeager, E .; DesMarteau, Darryl D .; Singh, S. Case Cent.Electrochem.Sci., Case West.Reservation Univ., Cleveland, OH, USA J. Electrochem.Soc. (1989), 136 (2), 385-90).

Non-limiting examples of persulfonated additives include the following:

Trifluoromethanesulfonic acid, potassium trifluoromethanesulfonate, sodium trifluoromethanesulfonate, lithium trifluoromethanesulfonate, ammonium trifluoromethanesulfonate, potassium perfluorohexanesulfonate, sodium perfluoro Hexanesulfonate, lithium perfluorohexanesulfonate, ammonium perfluorohexanesulfonate, perfluorohexanesulfonic acid, potassium nonafluorobutanesulfonate, sodium nonafluorobutanesulfonate, lithium nonafluorobutanesulfonate, Ammonium nonafluorobutanesulfonate, cesium nonafluorobutanesulfonate, triethylammoniumperfluorohexanesulfonate, perfluorosulfonimide and nafion.

Furthermore, as described in JP2001118591 A2, the membrane may also comprise additives which eliminate (primary antioxidant) or destroy (secondary antioxidant) free peroxide radicals produced by the reduction of oxygen, thereby -The life and stability of the electrode unit can be improved. The mode of operation and molecular structure of the additives is described in F. Gugumus in Plastics Additives, Hanser Verlag, 1990; N.S. Allen, M. Edge Fundamentals of Polymer Degradation and Stability, Elsevier, 1992; Or H. Zweifel, Stabilization of Polymeric Materials, Springer, 1998].

Non-limiting examples of such additives are as follows:

Bis (trifluoromethyl) nitroxide, 2,2-diphenyl-1-piclinylhydrazyl, phenol, alkylphenol, steric hindrance alkyl phenols such as Irganox, in particular Irganox 1135 (Ciba Geigy), aromatic Amines, steric hindrance amines such as Chimassorb; Steric hindrance hydroxylamine, steric hindrance alkylamine, steric hindrance hydroxylamine, steric hindrance hydroxylamine ether, phosphites such as Irgafos, nitrosobenzene, methyl-2-nitrosopropane, Benzophenone, benzaldehyde tert-butyl nitron, cysteamine, melanin, lead oxide, manganese oxide, nickel oxide and cobalt oxide.

In another variant of the invention, the polymerization according to step C) can take place after the formation of the sheet-like structure according to step D). In this case, the polymerization is carried out in a thin layer.

Possible fields of use of the polymer membranes of the present invention include in particular use in fuel cells, electrolysis, capacitors and cell systems. Thanks to their characteristic profile, the polymer membranes are preferably used in fuel cells, very particularly preferably in direct current methanol fuel cells. The invention also provides a polymer solution obtainable according to step C). These represent very useful intermediates. The solution can also be used as an ionomer to coat the electrode or after solvent removal.

The present invention similarly provides a polymer obtainable by separating or evaporating the solvent from step C). The polymers and solutions can also be used for electrode coating or as porous polymer substrates, such as expanded Teflon filling ionomers.

In another method variant, the polymer after the solvent is separated or evaporated after step C) can also be processed by a typical thermoplastic molding method, for example injection molding or extrusion, to yield a proton conductive membrane.

The abovementioned auxiliaries and fillers may be present in or in the above method variants.

The invention also provides a membrane-electrode unit comprising at least one polymer membrane according to the invention. The membrane-electrode unit exhibits high performance even with a small amount of catalytically active material such as platinum, ruthenium or palladium. Gas diffusion layers with catalytically active layers can be used for this.

The gas diffusion layer generally exhibits electron conductivity. On the sheet, electrically conductive and acid resistant structures are commonly used for this. These include, for example, sheet-like structures imparted with conductivity by addition of carbon fiber paper, graphitized carbon fiber paper, carbon fiber fabric, graphitized carbon fiber fabric and / or carbon black.

The catalytically active layer comprises a catalytically active material. These include in particular precious metals such as platinum, palladium, rhodium, iridium and / or ruthenium. These materials can also be used in the form of each alloy. In addition, these materials can also be used as alloys with non-noble metals such as Cr, Zr, Ni, Co and / or Ti. In addition, oxides of the above-mentioned noble metals and / or non-noble metals may also be used. According to certain aspects of the invention, the catalytically active compound is preferably used in the form of particles having a size in the range from 1 to 1,000 nm, in particular from 10 to 200 nm, preferably from 20 to 100 nm.

In addition, the catalytically active layer may comprise conventional additives. These include, in particular, fluoropolymers such as polytetrafluoroethylene (PTFE) and surface-active materials.

In certain embodiments of the invention, the weight ratio of the fluoropolymer and the catalyst material comprising at least one precious metal and, where appropriate, at least one support material, is greater than 0.1, preferably in the range of 0.2 to 0.6.

In certain embodiments of the invention, the catalyst layer has a thickness in the range from 1 to 1,000 μm, in particular from 5 to 500 μm, preferably from 10 to 300 μm. This figure represents the average value determinable by measuring the layer thickness in the cross section of the photograph obtained using a scanning electron microscope (SEM).

In certain embodiments of the invention, the precious metal content of the catalyst layer is 0.1 to 10.0 mg / cm 2, preferably 0.3 to 6.0 mg / cm 2, particularly preferably 0.2 to 3.0 mg / cm 2. These values can be determined by elemental analysis of the sheet phase sample.

For further information on the membrane-electrode unit, refer to the technical literature, in particular the patent applications WO 01/18894 A2, DE 195 09 748, DE 195 09 749, WO 00/26982, WO 92/15121 and DE 197 57 492. can do. The structure and manufacture of membrane-electrode units, and also those disclosed in the above-mentioned documents with respect to electrodes, gas diffusion layers and selected catalysts, are incorporated by reference in the detailed description of the invention.

In another variant, the catalytically active layer can be applied to the membrane of the present invention, which can be bonded to the gas diffusion layer.

The present invention similarly provides a membrane-electrode unit comprising at least one polymer membrane according to the invention in combination with another polyazole based polymer membrane or polymer blend membrane, as appropriate.

Claims (15)

A proton conductive electrolyte membrane obtainable by a process comprising the following steps: A. irradiating the polymer to generate free radicals, B. preparing a mixture of the polymer irradiated in step A) with a monomer comprising vinyl phosphonic acid and / or a monomer comprising vinyl sulfonic acid, if appropriate by adding a solvent or solvent mixture, C. polymerizing monomers comprising vinyl phosphonic acid and / or vinyl sulfonic acid, D. casting a sheet-like structure comprising the polymer obtained according to step C), E. Drying the sheet-like structure to form a freestanding film. 2. The membrane according to claim 1, wherein the polymer used in step A) is a polymer containing at least one fluorine, nitrogen, oxygen and / or sulfur atom in one repeating unit or another repeating unit. The vinyl-containing phosphonic acid monomer of claim 1 wherein the vinyl-containing phosphonic acid monomer used in step B) is (In the formula, R is a bond, a C1-C15 alkyl group, a C1-C15 alkoxy group, an ethyleneoxy group or a C5-C20 aryl or heteroaryl group, wherein the radicals mentioned above are halogen, -OH, COOZ, -CN, NZ ₂ Can be substituted, The radicals Z, each independently, represent hydrogen, a C1-C15 alkyl group, a C1-C15 alkoxy group, an ethyleneoxy group or a C5-C20 aryl or heteroaryl group, wherein the radicals mentioned above are halogen, -OH, -CN Can be substituted, x is 1, 2, 3, 4, 5, 6, 7, 8, 9 or 10, y is 1, 2, 3, 4, 5, 6, 7, 8, 9 or 10), And / or the following formula: (In the formula, R is a bond, a C1-C15 alkyl group, a C1-C15 alkoxy group, an ethyleneoxy group or a C5-C20 aryl or heteroaryl group, wherein the radicals mentioned above are halogen, -OH, COOZ, -CN, NZ ₂ Can be substituted, The radicals Z, each independently, represent hydrogen, a C1-C15 alkyl group, a C1-C15 alkoxy group, an ethyleneoxy group or a C5-C20 aryl or heteroaryl group, wherein the radicals mentioned above are halogen, -OH, -CN Can be substituted, x is 1, 2, 3, 4, 5, 6, 7, 8, 9 or 10), And / or the following formula: (In the formula, A is a group of formula COOR ² , CN, CONR ² ₂ , OR ² and / or R ² , wherein R ² is hydrogen, C 1 -C 15 alkyl group, C 1 -C 15 alkoxy group, ethyleneoxy group or C 5 -C 20 aryl or Heteroaryl group, wherein the radicals mentioned above may be substituted with halogen, -OH, COOZ, -CN, NZ ₂ , R is a bond, a divalent C1-C15 alkylene group, a divalent C1-C15 alkyleneoxy group, such as an ethyleneoxy group, or a divalent C5-C20 aryl or heteroaryl group, wherein the radicals mentioned above are halogen , -OH, COOZ, -CN, NZ ₂ can be substituted, The radicals Z, each independently, represent hydrogen, a C1-C15 alkyl group, a C1-C15 alkoxy group, an ethyleneoxy group or a C5-C20 aryl or heteroaryl group, wherein the radicals mentioned above are halogen, -OH, -CN Can be substituted, x is 1, 2, 3, 4, 5, 6, 7, 8, 9 or 10) Membrane characterized in that the compound. The vinyl-containing sulfonic acid monomer of claim 1, wherein the vinyl-containing sulfonic acid monomer used in step B) is (In the formula, R is a bond, a C1-C15-alkyl group, a C1-C15-alkoxy group, an ethyleneoxy group or a C5-C20-aryl or heteroaryl group, wherein the radicals mentioned above are halogen, -OH, COOZ, -CN, May be substituted with NZ ₂ , The radicals Z are each, independently of one another, hydrogen, a C1-C15-alkyl group, a C1-C15-alkoxy group, an ethyleneoxy group or a C5-C20-aryl or heteroaryl group, wherein the radicals mentioned above are halogen, -OH, May be substituted with -CN, x is 1, 2, 3, 4, 5, 6, 7, 8, 9 or 10, y is 1, 2, 3, 4, 5, 6, 7, 8, 9 or 10), And / or the following formula: (In the formula, R is a bond, C1-C15-alkyl group, C1-C15-alkoxy group, ethyleneoxy group or C5-C20-aryl or heteroaryl group, wherein the radicals mentioned above are halogen, -OH, C00Z, -CN, May be substituted with NZ ₂ , The radicals Z are each, independently of one another, hydrogen, a C1-C15-alkyl group, a C1-C15-alkoxy group, an ethyleneoxy group or a C5-C20-aryl or heteroaryl group, wherein the radicals mentioned above are halogen, -OH, May be substituted with -CN, x is 1, 2, 3, 4, 5, 6, 7, 8, 9 or 10), And / or the following formula: (In the formula, A is a group of the formula COOR ² , CN, C0NR ² ₂ , OR ² and / or R ² , wherein R ² is hydrogen, C 1 -C 15 -alkyl group, C 1 -C 15 -alkoxy group, ethyleneoxy group or C 5 -C 20 -Aryl or heteroaryl group, wherein the radicals mentioned above can be substituted by halogen, -OH, COOZ, -CN, NZ ₂ , R is a bond, a divalent C1-C15-alkylene group, a divalent C1-C15-alkyleneoxy group, for example an ethyleneoxy group or a divalent C5-C20-aryl or heteroaryl group, wherein the radicals mentioned above May be substituted with halogen, -OH, COOZ, -CN, NZ ₂ , The radicals Z are each, independently of one another, hydrogen, a C1-C15-alkyl group, a C1-C15-alkoxy group, an ethyleneoxy group or a C5-C20-aryl or heteroaryl group, wherein the radicals mentioned above are halogen, -OH, May be substituted with -CN, x is 1, 2, 3, 4, 5, 6, 7, 8, 9 or 10) Membrane characterized in that the compound. The membrane of claim 1 wherein the solution of vinyl containing phosphonic acid / sulfonic acid monomer further comprises an additional monomer capable of crosslinking. 2. The membrane according to claim 1, wherein the polymerization according to step C) is carried out after formation of the sheet-like structure according to step D). The membrane of claim 1, having an intrinsic conductivity of at least 0.001 S / cm. Proton conductive electrolyte membrane comprising 0.5 to 96% by weight of the polymer as defined in claim 2 and 99.5 to 4% by weight of polyvinylphosphonic acid and polyvinylsulfonic acid obtainable by polymerization of the monomers as defined in claims 3 and 4. . Proton conductive polymer blends obtainable by methods comprising the following steps: A. irradiating the polymer with electromagnetic radiation to generate free radicals, B. preparing a mixture of the polymer irradiated in step A) with a monomer comprising vinyl phosphonic acid and / or a monomer comprising vinyl sulfonic acid, if appropriate by adding a solvent or solvent mixture, C. polymerizing monomers comprising vinyl phosphonic acid and / or vinyl sulfonic acid. 10. The proton conductive polymer blend according to claim 9, wherein the polymer used in step A) is the polymer material as defined in claim 2. 10. The proton conductive polymer blend according to claim 9, wherein the vinyl containing monomer used in step B) comprises the compound as defined in claims 3 and 4. Membrane-electrode unit comprising at least one electrode and at least one membrane according to claim 1. A membrane-electrode unit comprising at least one electrode and the proton conductive polymer blend according to claim 9 in combination with at least one membrane according to any one of claims 1 to 8 as appropriate. The at least one membrane-electrode unit according to claim 12 and / or 13 and / or the at least one membrane according to any one of claims 1 to 8 and / or the proton conductive polymer blend according to claim 9 Fuel cell included. Use of the proton conductive polymer blend according to claim 9 as ionomer in a fuel cell.