Classifications

• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M4/00—Electrodes
  • H01M4/86—Inert electrodes with catalytic activity, e.g. for fuel cells
  • H01M4/8663—Selection of inactive substances as ingredients for catalytic active masses, e.g. binders, fillers
  • H01M4/8668—Binders
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M4/00—Electrodes
  • H01M4/86—Inert electrodes with catalytic activity, e.g. for fuel cells
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M8/00—Fuel cells; Manufacture thereof
  • H01M8/02—Details
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M8/00—Fuel cells; Manufacture thereof
  • H01M8/10—Fuel cells with solid electrolytes
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M8/00—Fuel cells; Manufacture thereof
  • H01M8/10—Fuel cells with solid electrolytes
  • H01M8/1004—Fuel cells with solid electrolytes characterised by membrane-electrode assemblies [MEA]
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M2300/00—Electrolytes
  • H01M2300/0017—Non-aqueous electrolytes
  • H01M2300/0065—Solid electrolytes
  • H01M2300/0082—Organic polymers
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
  • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
  • Y02E60/30—Hydrogen technology
  • Y02E60/50—Fuel cells

Definitions

• the present invention relates to membrane electrode assemblies and fuel cells with increased performance which comprise at least two electrochemically active electrodes which are separated by a polymer electrolyte membrane.
• PEM fuel cells are already known.
• sulphonic acid-modified polymers are almost exclusively used in these fuel cells as proton-conducting membranes.
• predominantly perfluorinated polymers are used.
• a relatively high water content is required in the membrane, which typically amounts to 4 - 20 molecules of water per sulphonic acid group.
• the required water content but also the stability of the polymer in connection with acidic water and the reaction gases hydrogen and oxygen, usually restricts the operating temperature of the PEM fuel cell stacks to 80 - 100°C. When applying pressure, the operating temperatures can be increased to >120°C. Otherwise, higher operating temperatures can not be realised without a loss of power in the fuel cell.
• the object of the present invention was to provide membrane electrode assemblies and fuel cells with a performance as high as possible at the cathode of the membrane electrode assembly were the oxygen reduction takes place.
• the improved membrane electrode assemblies should preferably have the following properties:
• the fuel cells should have a service life as long as possible.
• the fuel cells should have an open circuit
• the fuel cells should manage to do without additional humidification of the fuel gas, if possible.
• the fuel cells should be able to withstand permanent or alternate pressure differences between anode and cathodes as good as possible.
• the fuel cells should be robust to different operating conditions (T, p, geometry, etc.) to increase the general reliability as good as possible.
• the fuel cells should have an improved temperature and
• the instant invention relates to a membrane electrode assembly comprising:
• said catalyst layer comprising at least one ionomeric material
• At least the catalyst layer being in contact with the cathode comprises a polymer comprising the recurring units of the general formula (I)
• Ar are identical or different and represent a tetracovalent aromatic group or tetracovalent heteroaromatic group, each can be monocyclic, bicyclic or polycyclic, and
• X are identical or different and represent N, O, S and
• R 1 are identical or different and represent a bicovalent group of the formula
• Ar 1 , Ar 2 are identical or different and represent a bicovalent aromatic group or bicovalent heteroaromatic group, each can be monocyclic, bicyclic or polycyclic, and,
• Z 1 are identical or different and represent an bivalent alkyl group and/or an bivalent aromatic group, both in which at least one hydrogen atom is replaced by a fluorine atom, and
• Ar 3 , Ar 4 are identical or different and represent a tricovalent aromatic group or tricovalent tieteroaromatic group, each can be monocyclic, bicyclic or polycyclic, and,
• Z 2 are identical or different and represent an bivalent alkyl group and/or an bivalent aromatic group, both in which at least one hydrogen atom is replaced by a fluorine atom, and
• X are identical or different and represent N, O, S and
• R 1 are identical or different and represent (i) a bicovalent group of the formula
• Ar 5 , Ar 6 are identical or different and represent a bicovalent aromatic group or bicovalent heteroaromatic group, each can be monocyclic, bicyclic or polycyclic, and,
• Z 3 are identical or different and represent N, O, S
• n 0.1 to 99.9 mol-%
• n is between 40 to 60 mol-%, most preferred 50 mol-%, so that the ration between both subunits of the recurring units is comparable or equal.
• alkyl in Z 1 and/or Z 2 stand for short-chain bivalent alkyl groups having from 1 to 6 carbon atoms, such as, e.g., methyl, ethyl, n-propyl or i-propyl and n-, i-, or t-butyl, n-, i-, or t-pentane, n-, i-, or t-hexane.
• alkyl in Z and/or Z 2 stand for short-chain bivalent alkyl groups having from 1 to 6 carbon atoms, such as, e.g., methyl, ethyl, n-propyl or i-propyl and n-, i-, or t-butyl, n-, i-, or t-pentane, n-, i-, or t-hexane, in which at least one carbon atom is perfluorinated or at least one carbon atom is substituted by at least one (CF 3 )-group, most preferred by two (CF 3 )-groups to form a -C(CF 3 ) 2 - group.
• CF 3 perfluorinated or at least one carbon atom is substituted by at least one (CF 3 )-group, most preferred by two (CF 3 )-groups to form a -C(CF 3 ) 2 - group.
• aromatic group in Z 1 and/or Z 2 independent of each other, stand for bivalent aromatic groups having 5 to 6 carbon atoms, in which one or more carbon atoms can be replaced by a heteroatom selected from N, O or S, in which at least one carbon atom is perfluorinated or at least one carbon atom is substituted by at least one (CF 3 )-group, or an alkyl groups having from 2 to 6 carbon atoms which is substituted by at least one (CF 3 )-group, most preferred by two (CF 3 )-groups to form a -C(CF 3 ) 2 - group or by a terminal -C(CF 3 ) 3 group.
• R 1 independent of each other, stands for bivalent alkyl groups having from 1 to 10 carbon atoms, such as, e.g., methyl, ethyl, n- propyl or i-propyl and n-, i-, or t-butyl, n-, i-, or t-pentane, n-, i-, or t-hexane.
• R 1 independent of each other, stand for bivalent aromatic groups having 5 to 6 carbon atoms, in which one or more carbon atoms can be replaced by a heteroatom selected from N, O or S.
• Preferred bicovalent aromatic or bicovalent heteroaromatic groups Ar 1 , Ar 2 , Ar 5 , Ar 6 independent of each other, stand for monocyclic, bicyclic, or polycyclic, either condensed or not, aromatic or heteroaromatic ring systems having 5 to 20 carbon atoms, in which one or more carbon atoms can be replaced by N, O, S.
• the bicovalent aromatic or bicovalent heteroaromatic groups Ar 1 , Ar 2 , Ar 5 , Ar 6 can be substituted by further radicals.
• bicovalent aromatic or bicovalent heteroaromatic groups Ar 1 , Ar 2 , Ar 5 , Ar 6 independent of each other, are derived from benzene, naphthalene, biphenyl, diphenyl ether, diphenylmethane, diphenyldimethylmethane,
• Preferred tricovalent aromatic or tricovalent heteroaromatic groups Ar 3 , Ar 4 independent of each other, stand for monocyclic, bicyclic, polycyclic, condensed, aromatic or heteroaromatic ring systems having 5 to 20 carbon atoms, in which one or more carbon atoms can be replaced by N, O, S.
• the tricovalent aromatic or tricovalent heteroaromatic groups Ar 3 , Ar 4 can be substituted by further radicals.
• the tricovalent aromatic or tricovalent heteroaromatic groups Ar 3 , Ar 4 are derived from benzene, naphthalene, biphenyl, diphenyl ether, diphenylmethane, diphenyldimethylmethane, bisphenone, diphenylsulphone, quinoline, pyridine, bipyridine, pyridazine, pyrimidine, pyrazine, triazine, tetrazine, pyrrole, pyrazole, anthracene, benzopyrrole, benzotriazole, benzooxathiadiazole, benzooxadiazole, benzopyridine, benzopyrazine,
• benzopyrazidine benzopyrimidine, benzopyrazine, benzotriazine, indolizine, quinolizine, pyridopyridine, imidazopyrimidine, pyrazinopyrimidine, carbazole, aziridine, phenazine, benzoquinoline, phenoxazine, phenothiazine, acridizine, benzopteridine, phenanthroline and phenanthrene which optionally also can be substituted.
• Preferred tetracovalent aromatic or tetracovalent heteroaromatic groups Ar independent of each other, stand for monocyclic, bicyclic, or polycyclic, either condensed or not, aromatic or heteroaromatic ring systems having 5 to 20 carbon atoms, in which one or more carbon atoms can be replaced by N, O, S.
• the tetracovalent aromatic or tetracovalent heteroaromatic groups Ar can be
• tetracovalent aromatic or tetracovalent heteroaromatic groups Ar are derived from benzene, naphthalene, biphenyl, diphenyl ether, diphenylmethane, diphenyldimethylmethane, bisphenone, diphenylsulphone, quinoline, pyridine, bipyridine, pyridazine, pyrimidine, pyrazine, triazine, tetrazine, pyrrole, pyrazole, anthracene, benzopyrrole, benzotriazole, benzooxathiadiazole, benzooxadiazole, benzopyridine, benzopyrazine,
• benzopyrazidine benzopyrimidine, benzopyrazine, benzotriazine, indolizine, quinolizine, pyridopyridine, imidazopyrimidine, pyrazinopyrimidine, carbazole, aziridine, phenazine, benzoquinoline, phenoxazine, phenothiazine, acridizine, benzopteridine, phenanthroline and phenanthrene which optionally also can be substituted.
• the polymer comprising the recurring units of the general formula (I) has at least 10 recurring units of the general formula (I), more preferred at least 50 recurring units of the general formula (I).
• the polymer comprising the recurring units of the general formula (I) has a weight averaged molecular weight Mw above 10000 (determined by Gel Permeation Chromatography).
• the polymer comprising the recurring units of the general formula (I) has a number averaged molecular weight Mn above 5000.
• the polymer comprising the recurring units of the general formula (I) has a solubility of at least 0.5%wt in DMAc at a temperature of 25°C.
• the ionomeric material according to the instant invention being present on the catalyst layer at the cathode in a certain ratio to the content of catalyst material.
• the content of catalyst most typically noble metals, in the catalyst layer is 0.1 to 10.0 mg/cm 2 , preferably 0.3 to 6.0 mg/cm 2 and particularly preferably 1 to 4.0 mg/cm 2 . Therefore, it is preferred to have a weight ratio between ionomeric material and catalyst from 100:1 to 1 :100, most preferred from 10:1 to 1 :10. A specific preferred ratio is from 1 :8 to 1 :3.
• the polymer comprising the recurring units of the general formula (I) can be produced by
• step B) heating the mixture from step A) under inert gas to temperatures of up to 350°C, preferably up to 280°C, to form the polymer comprising the recurring units of the general formula (I).
• the mixture obtained from step B) can be directly used to incorporated the polymer comprising the recurring units of the general formula (I) as ionomer in the catalyst layer, in particular in the catalyst layer being later in contact with the cathode.
• the mixture obtained from step B) can be first isolated by precipitating the polymer in a non-solvent, such as water or a media containing water, and, if required, drying. If such pathway is chosen, the polymer comprising the recurring units of the general formula (I) needs be dissolved in a solvent, such as DMAc, phosphoric acid or polyphosphoric acid, for incorporation as ionomer in the catalyst layer, in particular in the catalyst layer being later in contact with the cathode.
• a solvent such as DMAc, phosphoric acid or polyphosphoric acid
• electrolyte matrices are also suitable.
• electrolyte matrices is understood to mean - besides polymer electrolyte matrices - also other matrix materials in which an ion-conducting material or mixture is fixed or immobilised in a matrix.
• polymer electrolyte membranes comprising acids wherein the acids may be covalently bound to the polymers.
• a flat material may be doped with an acid in order to form a suitable membrane.
• doped membranes can, amongst other methods, be produced by swelling flat materials, for example a polymer film, with a fluid comprising acidic
• Polymers suitable for this purpose include, amongst others, polyolefins, such as poly(chloroprene), polyacetylene, polyphenylene, poly(p-xylylene),
• polyarylmethylene polystyrene, polymethylstyrene, polyvinyl alcohol, polyvinyl acetate, polyvinyl ether, polyvinyl amine, poly(N-vinyl acetamide), polyvinyl imidazole, polyvinyl carbazole, polyvinyl pyrrolidone, polyvinyl pyridine, polyvinyl chloride, polyvinylidene chloride, polytetrafluoroethylene,
• polyhexafluoropropylene copolymers of PTFE with hexafluoropropylene, with perfluoropropylvinyl ether, with trifluoronitrosomethane, with
• carbalkoxyperfluoroalkoxyvinyl ether polychlorotrifluoroethylene, polyvinyl fluoride, polyvinylidene fluoride, polyacrolein, polyacrylamide, polyacrylonitrile, polycyanoacrylates, polymethacrylimide, cycloolefinic copolymers, in particular of norbornenes;
• polymers having C-0 bonds in the backbone for example polyacetal,
• polytetrahydrofuran polyphenylene oxide, polyether ketone, polyester, in particular polyhydroxyacetic acid, polyethyleneterephthalate,
• polybutyleneterephthalate polyhydroxybenzoate, polyhydroxypropionic acid, polypivalolacton, polycaprolacton, polymalonic acid, polycarbonate;
• polysulphide ether for example polysulphide ether
• polymeric C-N bonds in the backbone for example polyimines, polyisocyanides, polyetherimine, polyetherimides, polyaniline, polyaramides, polyamides, polyhydrazides, polyurethanes, polyimides, polyazoles, polyazole ether ketone, polyazines;
• liquid crystalline polymers in particular Vectra, as well as
• inorganic polymers for example polysilanes, polycarbosilanes, polysiloxanes, polysilicic acid, polysilicates, silicones, polyphosphazenes and polythiazyl.
• alkaline polymers are preferred wherein this particularly applies to membranes doped with acids.
• Almost all known polymer membranes in which protons can be transported come into consideration as alkaline polymer membranes doped with acid.
• acids are preferred which are able to transport protons without additional water, for example by means of the so-called "Grotthus mechanism”.
• alkaline polymer within the context of the present invention preferably an alkaline polymer with at least one nitrogen atom in a repeating unit is used.
• the repeating unit in the alkaline polymer contains an aromatic ring with at least one nitrogen atom.
• the aromatic ring is preferably a five-membered or six-membered ring with one to three nitrogen atoms which may be fused to another ring, in particular another aromatic ring.
• polymers stable at high temperatures which contain at least one nitrogen, oxygen and/or sulphur atom in one or in different repeating units.
• stable at high temperatures means a polymer which, as a polymeric electrolyte, can be operated over the long term in a fuel cell at temperatures above 120°C. Over the long term means that a
• membrane according to the invention can be operated for at least 100 hours, preferably at least 500 hours, at a temperature of at least 80°C, preferably at least 120°C, particularly preferably at least 160°C, without the performance being decreased by more than 50%, based on the initial performance which can be measured according to the method described in WO 01/18894 A2.
• polymers can be used individually or as a mixture (blend).
• blends which contain polyazoles and/or polysulphones.
• preferred blend components are
• Polyazoles constitute a particularly preferred group of alkaline polymers.
• An alkaline polymer based on polyazole contains recurring azole units of the general formula (I) and/or (II) and/or (III) and/or (IV) and/or (V) and/or (VI) and/or (VII) and/or (VIII) and/or (IX) and/or (X) and/or (XI) and/or (XII) and/or (XIII) and/or (XIV) and/or (XV) and/or (XVI) and/or (XVII) and/or (XVIII) and/or (XIX) and/or (XX) and/or (XXI) and/or (XXII) and/or (XXII))
• Ar are identical or different and represent a tetracovalent aromatic or
• heteroaromatic group which can be monocyclic or polycyclic
• Ar 1 are identical or different and represent a bicovalent aromatic or
• heteroaromatic group which can be monocyclic or polycyclic
• Ar 2 are identical or different and represent a bicovalent or tricovalent aromatic or heteroaromatic group which can be monocyclic or polycyclic,
• Ar 3 are identical or different and represent a tricovalent aromatic or
• heteroaromatic group which can be monocyclic or polycyclic
• Ar 4 are identical or different and represent a tricovalent aromatic or
• heteroaromatic group which can be monocyclic or polycyclic
• Ar 5 are identical or different and represent a tetracovalent aromatic or
• heteroaromatic group which can be monocyclic or polycyclic
• Ar 6 are identical or different and represent a bicovalent aromatic or
• heteroaromatic group which can be monocyclic or polycyclic
• Ar 7 are identical or different and represent a bicovalent aromatic or
• heteroaromatic group which can be monocyclic or polycyclic
• Ar 8 are identical or different and represent a tricovalent aromatic or
• heteroaromatic group which can be monocyclic or polycyclic
• Ar 9 are identical or different and represent a bicovalent or tricovalent or
• tetracovalent aromatic or heteroaromatic group which can be monocyclic or polycyclic
• Ar 10 are identical or different and represent a bicovalent or tricovalent aromatic or heteroaromatic group which can be monocyclic or polycyclic,
• Ar 11 are identical or different and represent a bicovalent aromatic or
• heteroaromatic group which can be monocyclic or polycyclic
• X are identical or different and represent oxygen, sulphur or an amino group which carries a hydrogen atom, a group having 1-20 carbon atoms, preferably a branched or unbranched alkyl or alkoxy group, or an aryl group as a further functional group,
• R are identical or different and represent hydrogen, an alkyl group and an
• R in formula (XX) is not hydrogen
• n, m are each an integer greater than or equal to 10, preferably greater than or equal to 100.
• Preferred aromatic or heteroaromatic groups are derived from benzene, naphthalene, biphenyl, diphenyl ether, diphenylmethane, diphenyldimethylmethane, bisphenone, diphenylsulphone, quinoline, pyridine, bipyridine, pyridazine, pyrimidine, pyrazine, triazine, tetrazine, pyrrole, pyrazole, anthracene, benzopyrrole, benzotriazole, benzooxathiadiazole, benzooxadiazole, benzopyridine, benzopyrazine,
• benzopyrazidine benzopyrimidine, benzotriazine, indolizine, quinolizine, pyridopy dine, imidazopyrimidine, pyrazinopyrimidine, carbazole, aziridine, phenazine, benzoquinoline, phenoxazine, phenothiazine, acridizine,
• benzopteridine phenanthroline and phenanthrene which optionally also can be substituted.
• Ar 1 , Ar 4 , Ar 6 , Ar 7 , Ar 8 , Ar 9 , Ar 10 , Ar 11 can have any substitution pattern, in the case of phenylene, for example, Ar 1 , Ar 4 , Ar 6 , Ar 7 , Ar 8 , Ar 9 , Ar 10 , Ar 11 can be ortho-phenylene, meta-phenylene and 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, e.g., methyl, ethyl, n-propyl or i-propyl and t-butyl groups.
• Preferred aromatic groups are phenyl or naphthyl groups.
• the alkyl groups and the aromatic groups can be substituted.
• Preferred substituents are halogen atoms, such as, e.g., fluorine, amino groups, hydroxy groups or short-chain alkyl groups, such as, e.g., methyl or ethyl groups.
• the polyazoles can in principle also have different recurring units wherein their functional groups X are different, for example. However, there are preferably only identical functional groups X in a recurring unit.
• polyazole polymers are polyimidazoles, polybenzothiazoles, polybenzoxazoles, polyoxadiazoles, polyquinoxalines, polythiadiazoles,
• the polymer containing recurring azole units is a copolymer or a blend which contains at least two units of the formulae (I) to (XXII) which differ from one another.
• the polymers can be in the form of block copolymers (diblock, triblock), random copolymers, periodic copolymers and/or alternating polymers.
• the polymer containing recurring azole units is a polyazole which only contains units of the formulae (I) and/or (II).
• the number of recurring azole units in the polymer is preferably an integer greater than or equal to 10.
• Particularly preferred polymers contain at least 100 recurring azole units.
• benzimidazole units are preferred. Some examples of the most useful polymers containing recurring benzimidazole units are represented by the following formulae:
• n and m are each an integer greater than or equal to 10, preferably greater than or equal to 100.
• the polyazoles used are characterized by a high molecular weight. Measured as the intrinsic viscosity, this is preferably at least 0.2 dl/g, preferably 0.8 to 10 dl/g, in particular 1 to 10 dl/g.
• aromatic carboxylic acids are, amongst others, dicarboxylic and tricarboxylic acids and tetracarboxylic acids or their esters or their anhydrides or their acid chlorides.
• aromatic carboxylic acids likewise also comprises heteroaromatic carboxylic acids.
• the aromatic dicarboxylic acids are isophthalic acid, terephthalic acid, phthalic acid, 5-hydroxyisophthalic acid, 4-hydroxyisophthalic acid, 2- hydroxyterephthalic acid, 5-aminoisophthalic acid, 5-N,N-dimethylaminoisophthalic acid, 5-N,N-diethylaminoisophthalic acid, 2,5-dihydroxyterephthalic acid, 2,6- dihydroxyisophthalic acid, 4,6-dihydroxyisophthalic acid, 2,3-dihydroxyphthalic acid, 2,4-dihydroxyphthalic acid, 3,4-dihydroxyphthalic acid, 3-fluorophthalic acid, 5-fluoroisophthalic acid, 2-fluoroterephthalic acid, tetrafluorophthalic acid, tetrafluoroisophthalic acid, tetrafluoroterephthalic acid,1 ,4-naphthalenedicarboxylic acid, 1 ,5-naphthalenedicarboxylic acid, 1
• aromatic tricarboxylic acids, tetracarboxylic acids or their C1-C20 alkyl esters or C5-C12 aryl esters or their acid anhydrides or their acid chlorides are preferably 1 ,3,5-benzenetricarboxylic acid (trimesic acid), 1 ,2,4-benzenetricarboxylic acid (trimellitic acid), (2-carboxyphenyl)iminodiacetic acid, 3,5,3'-biphenyltricarboxylic acid or 3,5,4'-biphenyltricarboxylic acid.
• aromatic tetracarboxylic acids or their C1-C20 alkyl esters or C5-C12 aryl esters or their acid anhydrides or their acid chlorides are preferably 3, 5,3', 5'- biphenyltetracarboxylic acid, 1 ,2,4,5-benzenetetracarboxylic acid,
• benzophenonetetracarboxylic acid S.S' ⁇ '-biphenyltetracarboxylic acid, 2, 2', 3,3'- biphenyltetracarboxylic acid, 1 ,2,5,6-naphthalenetetracarboxylic acid or 1 ,4,5,8- naphthalenetetracarboxylic acid.
• heteroaromatic carboxylic acids used are preferably heteroaromatic dicarboxylic acids, tricarboxylic acids and tetracarboxylic acids or their esters or their anhydrides.
• Heteroaromatic carboxylic acids are understood to mean aromatic systems which contain at least one nitrogen, oxygen, sulphur or phosphorus atom in the aromatic group.
• pyridine-2,5- dicarboxylic acid pyridine-3,5-dicarboxylic acid, pyridine-2,6-dicarboxylic acid, pyridine-2,4-dicarboxylic acid, 4-phenyl-2,5-pyridinedicarboxylic acid, 3,5- pyrazoledicarboxylic acid, 2,6-pyrimidinedicarboxylic acid, 2,5- pyrazinedicarboxylic acid, 2,4,6-pyridinetricarboxylic acid or benzimidazole-5,6- dicarboxylic acid and their C1-C20 alkyl esters or C5-C12 aryl esters or their acid anhydrides or their acid chlorides.
• the content of tricarboxylic acids or tetracarboxylic acids is between 0 and 30 mol-%, preferably 0.1 and 20 mol-%, in particular 0.5 and 10 mol-%.
• the aromatic and heteroaromatic diaminocarboxylic acids used are preferably diaminobenzoic acid or its monohydrochloride and dihydrochloride derivatives.
• mixtures of at least 2 different aromatic carboxylic acids are used.
• mixtures are used which also contain heteroaromatic carboxylic acids in addition to aromatic carboxylic acids.
• the mixing ratio of aromatic carboxylic acids to heteroaromatic carboxylic acids is between 1 :99 and 99:1 , preferably 1 :50 to 50:1.
• N-heteroaromatic dicarboxylic acids and aromatic dicarboxylic acids are in particular mixtures of N-heteroaromatic dicarboxylic acids and aromatic dicarboxylic acids.
• Non-limiting examples of these are isophthalic acid, terephthalic acid, phthalic acid, 2,5-dihydroxyterephthalic acid, 2,6- dihydroxyisophthalic acid, 4,6-dihydroxyisophthalic acid, 2,3-dihydroxyphthalic acid, 2,4-dihydroxyphthalic acid, 3,4-dihydroxyphthalic acid, 1 ,4- naphthalenedicarboxylic acid, 1 ,5-naphthalenedicarboxylic acid, 2,6- naphthalenedicarboxylic acid, 2,7-naphthalenedicarboxylic acid, diphenic acid, 1 ,8-dihydroxynaphthalene-3,6-dicarboxylic acid, diphenyl ether-4,4'-dicarboxylic acid, benzo
• the preferred aromatic tetraamino compounds include, amongst others, 3,3',4,4'- tetraaminobiphenyl, 2,3,5,6-tetraaminopyridine, 1 ,2,4,5-tetraaminobenzene, 3,3',4,4'-tetraaminodiphenyl sulphone, 3,3',4,4'-tetraaminodiphenyl ether, 3,3',4,4'- tetraaminobenzophenone, 3,3',4,4'-tetraaminodiphenylmethane and 3,3',4,4'- tetraaminodiphenyldimethylmethane as well as their salts, in particular their monohydrochloride, dihydrochloride, trihydrochloride and tetrahydrochloride derivatives.
• Preferred polybenzimidazoles are commercially available under the trade name ® Celazole.
• Preferred polymers include polysulphones, in particular polysulphone having aromatic and/or heteroaromatic groups in the backbone.
• preferred polysulphones and polyethersulphones have a melt volume rate MVR 300/21.6 of less than or equal to 40 cm 3 /10 min, in particular less than or equal to 30 cm 3 /10 min and particularly preferably less than or equal to 20 cm 3 /10 min, measured in accordance with ISO 1133.
• MVR 300/21.6 of less than or equal to 40 cm 3 /10 min, in particular less than or equal to 30 cm 3 /10 min and particularly preferably less than or equal to 20 cm 3 /10 min, measured in accordance with ISO 1133.
• the number average of the molecular weight of the polysulphones is greater than 30,000 g/mol.
• the polymers based on polysulphone include in particular polymers having recurring units with linking sulphone groups according to the general formulae A, B, C, D, E, F and/or G:
• the functional groups R independently of another, are identical or different and represent aromatic or heteroaromatic groups, these functional groups having been explained in detail above.
• these functional groups include in particular 1 ,2-phenylene, 1 ,3-phenylene, 1 ,4-phenylene, 4,4'-biphenyl, pyridine, quinoline, naphthalene, phenanthrene.
• polysulphones preferred within the scope of the present invention include homopolymers and copolymers, for example random copolymers.
• Particularly preferred polysulphones comprise recurring units of the formulae H to N:
• the previously described polysulphones can be obtained commercially under the trade names ® Victrex 200 P, ® Victrex 720 P, ® Ultrason E, ® Ultrason S, ® Mindel, ® Radel A, ® Radel R, ® Victrex HTA, ® Astrel and ® Udel.
• polyether ketones, polyether ketone ketones, polyether ether ketones, polyether ether ketone ketones and polyaryl ketones are particularly preferred. These high-performance polymers are known per se and can be obtained commercially under the trade names Victrex ® PEEKTM, ® Hostatec, The polysulphones mentioned above and the polyether ketones, polyether ketone ketones, polyether ether ketones, polyether ether ketone ketones and polyaryl ketones mentioned can be, as already set forth, present as a blend component with alkaline polymers.
• polysulphones mentioned above and the polyether ketones, polyether ketone ketones, polyether ether ketones, polyether ether ketone ketones and polyaryl ketones mentioned above can be used in sulphonated form as a polymer electrolyte wherein the sulphonated materials can also feature alkaline polymers, in particular polyazoles as a blend material.
• alkaline polymers or polyazoles also apply to these embodiments.
• a polymer preferably an alkaline polymer, in particular a polyazole can be dissolved in an additional step in polar, aprotic solvents such as dimethylacetamide (DMAc) and a film can be produced by means of classical methods.
• aprotic solvents such as dimethylacetamide (DMAc)
• the film thus obtained can be treated with a washing liquid, as is described in WO 02/07518. Due to the cleaning of the polyazole film to remove residues of solvent described patent application mentioned above, the mechanical properties of the film are surprisingly improved. These properties include in particular the E-modulus, the tear strength and the break strength of the film.
• the polymer film can have further modifications, for example by cross- linking, as described in WO 02/070592 or in WO 00/44816.
• the polymer film used consisting of an alkaline polymer and at least one blend component additionally contains a cross-linking agent, as described in WO 03/016384.
• the thickness of the polyazole films can be within wide ranges.
• the thickness of the polyazole film before its doping with acid is in the range of 5 pm to 2000 pm, particularly preferably in the range of 10 pm to 1000 pm; however, this should not constitute a limitation.
• these films are doped with an acid.
• acids include all known Lewis und Bronsted acids, preferably inorganic Lewis und Bronsted acids.
• polyacids are also possible, in particular isopolyacids and heteropolyacids as well as mixtures of different acids.
• heteropolyacids define inorganic polyacids with at least two different central atoms, each formed of weak, polybasic oxygen acids of a metal (preferably Cr, MO, V, W) and a non-metal (preferably As, I, P, Se, Si, Te) as partial mixed anhydrides.
• a metal preferably Cr, MO, V, W
• non-metal preferably As, I, P, Se, Si, Te
• the conductivity of the polyazole film can be influenced via the degree of doping.
• the conductivity increases with an increasing concentration of the doping substance until a maximum value is reached.
• the degree of doping is given as mole of acid per mole of repeating unit of the polymer.
• a degree of doping between 3 and 50, in particular between 5 and 40 is preferred.
• Particularly preferred doping substances are sulphuric acid and phosphoric acid or compounds releasing these acids, for example during hydrolysis.
• the particularly preferred doping substance is phosphoric acid (H 3 PO 4 ).
• highly concentrated acids are generally used.
• the concentration of the phosphoric acid is at least 50% by weight, in particular at least 80% by weight, based on the weight of the doping substance.
• proton-conductive membranes can also be obtained by a method comprising the steps of
• step II heating the mixture obtainable in accordance with step A) under inert gas to temperatures of up to 400°C,
• step IV treating the membrane formed in step III) until it is self-supporting.
• doped polyazole films can be obtained by a method comprising the steps of
• aromatic carboxylic acids or their esters which contain at least two acid groups per carboxylic acid monomer, or mixing one or more aromatic and/or heteroaromatic diaminocarboxylic acids in polyphosphonc acid with formation of a solution and/or dispersion,
• step B) applying a layer using the mixture in accordance with step A) to a support or to an electrode
• step C) heating the flat structure/layer obtainable in accordance with step B) under inert gas to temperatures of up to 350°C, preferably up to 280°C, with formation of the polyazole polymer,
• step D) treating the membrane formed in step C) (until it is self-supporting).
• step A The aromatic or heteroaromatic carboxylic acid and tetraamino compounds to be used in step A) have been described above.
• the polyphosphonc acid used in step A) is a customary polyphosphonc acid as is available, for example, from Riedel-de Haen.
• H n+2 P n O 3n+1 (n>1) usually have a concentration of at least 83%, calculated as P2O5 (by acidimetry). Instead of a solution of the monomers, it is also possible to produce a dispersion/suspension.
• the mixture produced in step A) has a weight ratio of polyphosphonc acid to the sum of all monomers of 1 :10,000 to 10,000:1 , preferably 1 :1000 to 1000:1 , in particular 1 :100 to 100:1.
• the layer formation in accordance with step B) is performed by means of measures known per se (pouring, spraying, application with a doctor blade) which are known from the prior art of polymer film production. Every support that is considered as inert under the conditions is suitable as a support.
• phosphoric acid cone, phosphoric acid, 85%
• the viscosity can be adjusted to the desired value and the formation of the membrane be facilitated.
• the layer produced in accordance with step B) has a thickness of 10 to 4000 pm, preferably 20 to 4000 pm, very preferably of 30 to 3500 ⁇ , in particular of 50 to 3000 pm.
• step A) also contains tricarboxylic acids or tetracarboxylic acid, branching/cross-linking of the formed polymer is achieved therewith. This contributes to an improvement in the mechanical property.
• the treatment of the polymer layer produced in accordance with step C) is performed in the presence of moisture at temperatures and for a sufficient period of time until the layer exhibits a sufficient strength for use in fuel cells. The treatment can be effected to the extent that the membrane is self-supporting so that it can be detached from the support without any damage.
• step C) the flat structure obtained in step B) is heated to a temperature of up to 350°C, preferably up to 280°C and particularly preferably in the range of 200°C to 250°C.
• the inert gases to be used in step C) are known to those in professional circles. These include in particular nitrogen as well as noble gases, such as neon, argon, helium.
• the formation of oligomers and/or polymers can already be brought about by heating the mixture from step A) to temperatures of up to 350°C, preferably up to 280°C. Depending on the selected temperature and duration, it is then possible to dispense partly or fully with the heating in step C).
• This variant is also an object of the present invention.
• the treatment of the membrane in step D) is performed at temperatures of more than 0°C and less than 150°C, preferably at temperatures between 10°C and 120°C, in particular between room temperature (20°C) and 90°C, in the presence of moisture or water and/or steam and/or water-containing phosphoric acid of up to 85%.
• the treatment is preferably performed at normal pressure, but can also be carried out with action of pressure. It is essential that the treatment takes place in the presence of sufficient moisture whereby the polyphosphoric acid present contributes to the solidification of the membrane by means of partial hydrolysis with formation of low molecular weight polyphosphoric acid and/or phosphoric acid.
• the hydrolysis fluid may be a solution wherein the fluid may also contain suspended and/or dispersed constituents.
• the viscosity of the hydrolysis fluid can be within wide ranges wherein an addition of solvents or an increase in
• the dynamic viscosity is preferably in the range of 0.1 to 10,000 mPa*s, in particular 0.2 to 2000 mPa * s, wherein these values can be measured in accordance with DIN 53015, for example.
• the treatment in accordance with step D) can take place with any known method.
• the membrane obtained in step C) can, for example, be immersed in a fluid bath.
• the hydrolysis fluid can be sprayed onto the membrane.
• the hydrolysis fluid can be poured onto the membrane.
• the oxo acids of phosphorus and/or sulphur include in particular phosphinic acid, phosphonic acid, phosphoric acid, hypodiphosphonic acid, hypodiphosphoric acid, oligophosphoric acids, sulphurous acid, disulphurous acid and/or sulphuric acid. These acids can be used individually or as a mixture.
• the oxo acids of phosphorus and/or sulphur comprise monomers that can be processed by free-radical polymerisation and comprise phosphonic acid and/or sulphonic acid groups.
• Monomers comprising phosphonic acid groups are known in professional circles. These are compounds having 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 have at least two, preferably 3, bonds to groups which lead to minor steric hindrance of the double bond. These groups include, amongst others, hydrogen atoms and halogen atoms, in particular fluorine atoms.
• the polymer comprising phosphonic acid groups results from the polymerisation product which is obtained by polymerising the monomer comprising phosphonic acid groups alone or with other monomers and/or cross-linking agents.
• the monomer comprising phosphonic acid groups may comprise one, two, three or more carbon-carbon double bonds. Furthermore, the monomer comprising phosphonic acid groups may contain one, two, three or more phosphonic acid groups.
• the monomer comprising phosphonic acid groups contains 2 to 20, preferably 2 to 10 carbon atoms.
• the monomer comprising phosphonic acid groups is preferably a compound of the formula wherein
• R represents a bond, a bicovalent C1-C15 alkylene group, a bicovalent C1- C15 alkyleneoxy group, for example ethyleneoxy group, or a bicovalent C5- C20 aryl or heteroaryl group wherein the above-mentioned functional groups themselves can be substituted with halogen, -OH, COOZ, -CN, NZ 2 ,
• Z represent, independently of 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 above-mentioned functional groups themselves can be substituted with halogen, -OH, -CN, and
• x represents an integer 1 , 2, 3, 4, 5, 6, 7, 8, 9 or 10
• y represents an integer 1 , 2, 3, 4, 5, 6, 7, 8, 9 or 10,
• R represents a bond, a bicovalent C1 -C15 alkylene group, a bicovalent C1- C15 alkyleneoxy group, for example ethyleneoxy group, or a bicovalent C5- C20 aryl or heteroaryl group wherein the above-mentioned functional groups themselves can be substituted with halogen, -OH, COOZ, -CN, NZ 2 ,
• Z represent, independently of 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 above-mentioned functional groups themselves can be substituted with halogen, -OH, -CN, and
• x represents an integer 1 , 2, 3, 4, 5, 6, 7, 8, 9 or 10,
• A represents a group of the formulae COOR 2 , CN, CONR 2 2 , OR 2 and/or R 2 , wherein R 2 is hydrogen, a C1-C15 alkyl group, a C1-C15 alkoxy group, an ethyleneoxy group or a C5-C20 aryl or heteroaryl group, wherein the above-mentioned functional groups themselves can be substituted with halogen, -OH, COOZ, -CN, NZ 2 , R represents a bond, a bicovalent C1-C15 alkylene group, a bicovalent C1- C15 alkyleneoxy group, for example ethyleneoxy group, or a bicovalent C5- C20 aryl or heteroaryl group wherein the above-mentioned functional groups themselves can be substituted with halogen, -OH, COOZ, -CN, NZ 2 ,
• Z represent, independently of 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 above-mentioned functional groups themselves can be substituted with halogen, -OH, -CN, and
• x represents an integer 1 , 2, 3, 4, 5, 6, 7, 8, 9 or 10.
• Preferred monomers comprising phosphonic acid groups include, inter alia, alkenes which contain phosphonic acid groups, such as ethenephosphonic acid, propenephosphonic acid, butenephosphonic acid; acrylic acid compounds and/or methacrylic acid compounds which contain phosphonic acid groups, such as for example 2-phosphonomethylacrylic acid, 2-phosphonomethylmethacrylic acid, 2- phosphonomethylacrylamide and 2-phosphonomethylmethacrylamide.
• vinylphosphonic acid ethenephosphonic acid
• ethenephosphonic acid is available from the companies Aldrich or Clariant GmbH, for example.
• a preferred vinylphosphonic acid has a purity of more than 70%, in particular 90% and particularly preferably a purity of more than 97%.
• the monomers comprising phosphonic acid groups can furthermore be used in the form of derivatives which can subsequently be converted to the acid, wherein the conversion to the acid may also take place in the polymerised state.
• derivatives include in particular the salts, the esters, the amides and the halides of the monomers comprising phosphonic acid groups.
• the monomers comprising phosphonic acid groups can also be introduced onto and into the membrane after the hydrolysis. This can be
• the ratio of the weight of the sum of phosphoric acid, polyphosphoric acid and the hydrolysis products of the polyphosphoric acid to the weight of the monomers that can be processed by free-radical polymerisation, for example the monomers comprising phosphonic acid groups is preferably greater than or equal to 1 :2, in particular greater than or equal to 1 :1 and particularly preferably greater than or equal to 2:1.
• the ratio of the weight of the sum of phosphoric acid, polyphosphoric acid and the hydrolysis products of the polyphosphoric acid to the weight of the monomers that can be processed by free-radical polymerisation is in the range of 1000:1 to 3:1 , in particular 100:1 to 5:1 and particularly preferably 50:1 to 10:1.
• This ratio can easily be determined by means of customary methods in which, in many cases, the phosphoric acid, polyphosphoric acid and their hydrolysis products can be washed out of the membrane. Through this, the weight of the polyphosphoric acid and its hydrolysis products can be obtained after the completed hydrolysis to phosphoric acid. In general, this also applies to the monomers which can be processed by free-radical polymerisation.
• Monomers comprising sulphonic acid groups are known in professional circles. These are compounds having at least one carbon-carbon double bond and at least one sulphonic acid group. Preferably, the two carbon atoms forming the carbon-carbon double bond have at least two, preferably 3, bonds to groups which lead to minor steric hindrance of the double bond. These groups include, amongst others, hydrogen atoms and halogen atoms, in particular fluorine atoms.
• the polymer comprising sulphonic acid groups results from the polymerisation product which is obtained by polymerisation of the monomer comprising sulphonic acid groups alone or with further monomers and/or cross-linking agents.
• the monomer comprising sulphonic acid groups may comprise one, two, three or more carbon-carbon double bonds. Furthermore, the monomer comprising sulphonic acid groups can contain one, two, three or more sulphonic acid groups.
• the monomer comprising sulphonic acid groups contains 2 to 20, preferably 2 to 10 carbon atoms.
• the monomer comprising sulphonic acid groups is preferably a compound of the formula
• R represents a bond, a bicovalent C1-C15 alkylene group, a bicovalent C1- C15 alkyleneoxy group, for example ethyleneoxy group, or a bicovalent C5- C20 aryl or heteroaryl group, wherein the above-mentioned functional groups themselves can be substituted with halogen, -OH, COOZ, -CN, NZ 2 ,
• Z represent, independently of 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 above-mentioned functional groups themselves can be substituted with halogen, -OH, -CN, and
• x represents an integer 1 , 2, 3, 4, 5, 6, 7, 8, 9 or 10,
• y represents an integer 1 , 2, 3, 4, 5, 6, 7, 8, 9 or 10, and/or of the formula
• R represents a bond, a bicovalent C1-C15 alkylene group, a bicovalent C1- C15 alkyleneoxy group, for example ethyleneoxy group, or a bicovalent C5- C20 aryl or heteroaryl group, wherein the above-mentioned functional groups themselves can be substituted with halogen, -OH, COOZ, -CN, NZ 2 ,
• Z represent, independently of 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 above-mentioned functional groups themselves can be substituted with halogen, -OH, -CN, and
• x represents an integer 1 , 2, 3, 4, 5, 6, 7, 8, 9 or 10, and/or of the formula
• A represents a group of the formulae COOR 2 , CN, CONR 2 2 , OR 2 and/or R 2 , wherein R 2 is hydrogen, a C1-C15 alkyl group, a C1-C15 alkoxy group, an ethyleneoxy group or a C5-C20 aryl or heteroaryl group, wherein the above-mentioned functional groups themselves can be substituted with halogen, -OH, COOZ, -CN, NZ 2 ,
• R represents a bond, a bicovalent C1-C15 alkylene group, a bicovalent C1- C15 alkyleneoxy group, for example ethyleneoxy group, or a bicovalent C5- C20 aryl or heteroaryl group, wherein the above-mentioned functional groups themselves can be substituted with halogen, -OH, COOZ, -CN, NZ 2 ,
• Z represent, independently of 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 above-mentioned functional groups themselves can be substituted with halogen, -OH, -CN, and
• x represents an integer 1 , 2, 3, 4, 5, 6, 7, 8, 9 or 10.
• Preferred monomers comprising sulphonic acid groups include, inter alia, alkenes which contain sulphonic acid groups, such as ethenesulphonic acid,
• propenesulphonic acid butenesulphonic acid
• acrylic acid compounds and/or methacrylic acid compounds which contain sulphonic acid groups such as for example 2-sulphonomethylacrylic acid, 2-sulphonomethylmethacrylic acid, 2-sulphonomethylacrylamide and 2-sulphonomethylmethacrylamide.
• vinylsulphonic acid such as it is available from the companies Aldrich or Clariant GmbH, for example, is
• a preferred vinylsulphonic acid has a purity of more than 70%, in particular 90% and particularly preferably a purity of more than 97%.
• the monomers comprising sulphonic acid groups can furthermore be used in the form of derivatives which can subsequently be converted to the acid, wherein the conversion to the acid may also take place in the polymerised state.
• derivatives include in particular the salts, the esters, the amides and the halides of the monomers comprising sulphonic acid groups.
• the monomers comprising sulphonic acid groups can also be introduced onto and into the membrane after the hydrolysis. This can be
• monomers capable of cross-linking can be used. These monomers can be added to the hydrolysis fluid. Furthermore, the monomers capable of cross-linking can also be applied to the membrane obtained after the hydrolysis.
• the monomers capable of cross-linking are in particular compounds having at least 2 carbon-carbon double bonds. Preference is given to dienes, trienes, tetraenes, dimethylacrylates, trimethylacrylates, tetramethylacrylates, diacrylates, triacrylates, tetraacrylates.
• R represents a C1-C15 alkyl group, a C5-C20 aryl or heteroaryl group, NR', - S0 2 , PR', Si(R')2, wherein the above-mentioned functional groups
• R' represent, independently of another, hydrogen, a C1-C15 alkyl group, a C1- C15 alkoxy group, a C5-C20 aryl or heteroaryl group, and
• n is at least 2.
• the substituents of the above-mentioned functional group R are preferably halogen, hydroxyl, carboxy, carboxyl, carboxylester, nitriles, amines, silyl, siloxane groups.
• cross-linking agents are silyl methacrylate, ethylene glycol dimethacrylate, diethylene glycol dimethacrylate, triethylene glycol dimethacrylate, tetraethylene glycol dimethacrylate and polyethylene glycol dimethacrylate, 1 ,3- butanediol dimethacrylate, glycerol dimethacrylate, diurethane dimethacrylate, trimethylpropane trimethacrylate, epoxy acrylates, for example ebacryl,
• ⁇ ', ⁇ -methylenebisacrylamide carbinol, butadiene, isoprene, chloroprene, divinylbenzene and/or bisphenol A dimethylacrylate.
• CN120, CN104 and CN980 commercially available from Sartomer Company Exton, Pennsylvania under the designations CN120, CN104 and CN980, for example.
• cross-linking agents are optional wherein these compounds can typically be used in the range of 0.05 to 30% by weight, preferably 0.1 to 20% by weight, particularly preferably 1 to 10% by weight, based on the weight of the membrane.
• the cross-linking monomers can be introduced onto and into the membrane after the hydrolysis. This can be performed by means of measures known per se (e.g., spraying, immersing etc.) which are known from the prior art.
• the monomers comprising phosphonic acid and/or sulphonic acid groups or the cross-linking monomers can be polymerised wherein the polymerisation is preferably a free- radical polymerisation.
• the formation of radicals can take place thermally, photochemically, chemically and/or electrochemically.
• a starter solution containing at least one substance capable of forming radicals can be added to the hydrolysis fluid.
• a starter solution can be applied to the membrane after the hydrolysis. This can be performed by means of measures known per se (e.g., spraying, immersing etc.) which are known from the prior art.
• Suitable radical formers are, amongst others, azo compounds, peroxy
• Non-limiting examples are dibenzoyl peroxide, dicumene peroxide, cumene hydroperoxide, diisopropyl peroxydicarbonate, bis(4-t-butylcyclohexyl) peroxydicarbonate, dipotassium persulphate, ammonium peroxydisulphate, 2,2'-azobis(2-methylpropionitrile) (AIBN), 2,2'-azobis(isobutyric acid amidine)hydrochloride, benzopinacol, dibenzyl derivatives, methyl ethylene ketone peroxide, 1 ,1-azobiscyclohexanecarbonitrile, methyl ethyl ketone peroxide, acetyl acetone peroxide, dilauryl peroxide, didecanoyl peroxide, tert-butylper-2-ethyl hexanoate, ketone peroxide, methyl is
• radical formers which form free radicals when exposed to radiation.
• Preferred compounds include, amongst others, ⁇ , ⁇ - diethoxyacetophenone (DEAP, Upjon Corp), n-butyl benzoin ether (®Trigonal-14, AKZO) and 2,2-dimethoxy-2-phenylacetophenone ( ⁇ Igacure 651) and 1 -benzoyl cyclohexanol ( ⁇ Igacure 184), bis-(2,4,6-trimethylbenzoyl)phenylphosphine oxide ( ⁇ Irgacure 819) and 1-[4-(2-hydroxyethoxy)phenyl]-2-hydroxy-2-phenylpropan-1- one ( ⁇ Irgacure 2959), each of which are commercially available from the company Ciba Geigy Corp.
• radical formers typically, between 0.0001 and 5% by weight, in particular 0.01 to 3% by weight (based on the weight of the monomers that can be processed by free-radical polymerisation; monomers comprising phosphonic acid groups and/or sulphonic acid groups or the cross-linking monomers, respectively) of radical formers are added.
• the amount of radical formers can be varied according to the degree of polymerisation desired.
• IR infrared, i.e. light having a wavelength of more than 700 nm
• NIR near-IR, i.e. light having a wavelength in the range of about 700 to 2000 nm and an energy in the range of about 0.6 to 1.75 eV
• the polymerisation can also take place by action of UV light having a wavelength of less than 400 nm.
• This polymerisation method is known per se and described, for example, in Hans Joerg Elias, Makromolekulare Chemie, 5th edition, 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 and M. K. Mishra, Radical Photopolymerization of Vinyl
• a membrane is irradiated with a radiation dose in the range of 1 to 300 kGy, preferably 3 to 200 kGy and very particularly preferably 20 to 100 kGy.
• the polymerisation of the monomers comprising phosphonic acid groups and/or sulphonic acid groups or the cross-linking monomers, respectively, preferably takes place at temperatures of more than room temperature (20°C) and less than 200°C, in particular at temperatures between 40°C and 150°C, particularly preferably between 50°C and 120°C.
• the polymerisation is preferably performed at normal pressure, but can also be carried out with action of pressure.
• the polymerisation leads to a solidification of the flat structure, wherein this
• the increase in hardness caused by the polymerisation is at least 20%, based on the hardness of a correspondingly hydrolysed membrane without polymerisation of the monomers.
• the molar ratio of the molar sum of phosphoric acid, polyphosphoric acid and the hydrolysis products of polyphosphoric acid to the number of moles of the phosphonic acid groups and/or sulphonic acid groups in the polymers obtainable by polymerisation of monomers comprising phosphonic acid groups and/or monomers comprising sulphonic acid groups is preferably greater than or equal to 1 :2, in particular greater than or equal to 1 :1 and particularly preferably greater than or equal to 2:1.
• the molar ratio of the molar sum of phosphoric acid, polyphosphoric acid and the hydrolysis products of polyphosphoric acid to the number of moles of the phosphonic acid groups and/or sulphonic acid groups in the polymers obtainable by polymerisation of monomers comprising phosphonic acid groups and/or monomers comprising sulphonic acid groups lies in the range of 1000:1 to 3:1 , in particular 100:1 to 5:1 and particularly preferably 50:1 to 10:1.
• the molar ratio can be determined by means of customary methods. To this end, especially spectroscopic methods, for example, NMR spectroscopy can be used.
• the phosphonic acid groups are present in the formal oxidation stage 3 and the phosphorus in phosphoric acid, polyphosphoric acid or hydrolysis products thereof, respectively, in oxidation stage 5.
• the flat structure which is obtained after polymerisation is a self-supporting membrane.
• the degree of polymerisation is at least 2, in particular at least 5, particularly preferably at least 30 repeating units, in particular at least 50 repeating units, very particularly preferably at least 100 repeating units. This degree of polymerisation is
• the conversion achieved in a comparative polymerisation is preferably greater than or equal to 20%, in particular greater than or equal to 40% and particularly preferably greater than or equal to 75%, based on the monomers comprising phosphonic acid groups used.
• the hydrolysis fluid comprises water wherein the concentration of the water generally is not particularly critical.
• the hydrolysis fluid comprises 5 to 80% by weight, preferably 8 to 70% by weight and particularly preferably 10 to 50% by weight, of water.
• the amount of water which is formally included in the oxo acids is not taken into account in the water content of the hydrolysis fluid.
• phosphoric acid and/or sulphuric acid are particularly preferred wherein these acids comprise in particular 5 to 70% by weight, preferably 10 to 60% by weight and particularly preferably 15 to 50% by weight, of water.
• step D The partial hydrolysis of the polyphosphoric acid in step D) leads to a solidification of the membrane due to a sol-gel transition. This is also connected with a reduction in the layer thickness to 15 to 3000 pm, preferably between 20 and 2000 ⁇ , in particular between 20 and 1500 pm; the membrane is self-supporting.
• the upper temperature limit for the treatment in accordance with step D) is typically 150°C. With extremely short action of moisture, for example from overheated steam, this steam can also be hotter than 150°C. The duration of the treatment is substantial for the upper limit of the temperature.
• the partial hydrolysis (step D) can also take place in climatic chambers where the hydrolysis can be specifically controlled with defined moisture action.
• the moisture can be specifically set via the temperature or saturation of the surrounding area in contact with it, for example gases such as air, nitrogen, carbon dioxide or other suitable gases, or steam.
• gases such as air, nitrogen, carbon dioxide or other suitable gases, or steam.
• the duration of the treatment depends on the parameters chosen as aforesaid.
• the duration of the treatment depends on the membrane
• the duration of the treatment amounts to between a few seconds to minutes, for example with the action of overheated steam, or up to whole days, for example in the open air at room temperature and low relative humidity.
• the duration of the treatment is between 10 seconds and 300 hours, in particular 1 minute to 200 hours.
• the duration of the treatment is between 1 and 200 hours.
• the membrane obtained in accordance with step D) can be formed in such a way that it is self-supporting, i.e. it can be detached from the support without any damage and then directly processed further, if applicable.
• the concentration of phosphoric acid and therefore the conductivity of the polymer membrane can be set via the degree of hydrolysis, i.e. the duration, temperature and ambient humidity.
• the concentration of the phosphoric acid is given as mole of acid per mole of repeating unit of the polymer.
• Membranes with a particularly high concentration of phosphoric acid can be obtained by the method comprising the steps A) to D).
• a concentration (mol of phosphoric acid, based on a repeating unit of formula (I), for example polybenzimidazole) of 10 to 50, in particular between 12 and 40 is preferred. Only with very much difficulty or not at all is it possible to obtain such high degrees of doping (concentrations) by doping polyazoles with commercially available orthophosphoric acid.
• doped polyazole films are produced by use of polyphosphoric acid
• the production of these films can be carried out by a method comprising the following steps:
• aromatic carboxylic acids or their esters which contain at least two acid groups per carboxylic acid monomer, or one or more aromatic and/or heteroaromatic diaminocarboxylic acids in the melt at temperatures of up to 350°C, preferably up to 300°C,
• step 3 heating the solution obtainable in accordance with step 2) under inert gas to temperatures of up to 300°C, preferably up to 280°C, with formation of the dissolved polyazole polymer,
• step 5) treating the membrane formed in step 4) until it is self-supporting.
• a membrane particularly a membrane based on polyazoles, can further be cross- linked at the surface by action of heat in the presence of atmospheric oxygen. This hardening of the membrane surface further improves the properties of the membrane.
• the membrane can be heated to a temperature of at least 150°C, preferably at least 200°C and particularly preferably at least 250°C.
• the oxygen concentration usually is in the range of 5 to 50% by volume, preferably 10 to 40% by volume; however, this should not constitute a limitation.
• IR infrared, i.e. light having a wavelength of more than 700 nm
• NIR near-IR, i.e. light having a wavelength in the range of from about 700 to 2000 nm and an energy in the range of from about 0.6 to 1.75 eV
• Another method is ⁇ -ray irradiation.
• the irradiation dose is from 5 to 200 kGy.
• the duration of the cross-linking reaction can be within a wide range. In general, this reaction time lies in the range of 1 second to 10 hours, preferably 1 minute to 1 hour; however, this should not constitute a limitation.
• Particularly preferred polymer membranes display a high performance.
• the reason for this is in particular improved proton conductivity. This is at least
• the membranes are suitable as so called high-temperature, polymer electrolyte membrane fuel cells and to produce high-temperature membrane electrode assemblies.
• the aforementioned high-temperature proton conductivity can be accomplished by proton-conducting polymer electrolyte membranes and matrices comprising (i) a basic polymer material or matrix and an acid which allows for the so-called “Grotthus mechanism” or a (ii) a polymer material having covalently bound groups which allows for the so-called “Grotthus mechanism”. In the latter case, this is typically achieved by incorporating at least 10% by weight of polymers derived from the aforementioned monomers comprising phosphonic acid groups.
• the specific conductivity is measured by means of impedance spectroscopy in a 4-pole arrangement in potentiostatic mode and using platinum electrodes (wire, diameter of 0.25 mm).
• the gap between the current-collecting electrodes is 2 cm.
• the spectrum obtained is evaluated using a simple model comprised of a parallel arrangement of an ohmic resistance and a capacitor.
• the cross section of the sample of the membrane doped with phosphoric acid is measured immediately prior to mounting of the sample. To measure the temperature dependency, the measurement cell is brought to the desired temperature in an oven and regulated using a Pt-100 thermocouple arranged in the immediate vicinity of the sample. Once the temperature is reached, the sample is held at this temperature for 10 minutes prior to the start of measurement.
• the membrane electrode assembly according to the invention has two gas diffusion layers which are separated by the polymer electrolyte membrane.
• Mechanically stabilizing materials which are very light, not necessarily electrically conductive, but mechanically stable and contain fibres, for example, in the form of non-woven fabrics, paper or woven fabrics are used as the starting material for the gas diffusion layers according to the invention. These include, for example, graphite-fibre paper, carbon-fibre paper, graphite fabric and/or paper which was rendered conductive by addition of carbon black.
• the mechanically stabilizing material preferably contains carbon fibres, glass fibres or fibres containing organic polymers, for example polypropylene, polyester (polyethylene terephthalate), polyphenylenesulphide or polyether ketones, to name only a few.
• materials with a weight per unit area for example polypropylene, polyester (polyethylene terephthalate), polyphenylenesulphide or polyether ketones, to name only a few.
• ⁇ 150 g/m 2 preferably with a weight per unit area in the range of 10 to 100 g/m 2 are particularly well suited.
• non-woven fabrics made of carbonised or graphitised fibres with weights per unit area within the preferred range are particularly suited.
• Using such materials has two advantages: Firstly, they are very light and secondly, they have a high open porosity.
• the open porosity of the stabilizing materials used with preference is within the range of 20 to 99.9%, preferably 40 to 99%, such that they can easily be filled with other materials and the porosity, conductivity and hydrophobicity of the finished gas diffusion layer thus can be adjusted in a directed manner, namely throughout the entire thickness of the gas diffusion layer.
• this layer has a thickness in the range of 80 pm to 2000 pm, in particular 100 pm to 1000 pm and particularly preferably 150 pm to 500 pm.
• gas diffusion layers or gas diffusion electrodes is described in detail in WO 97/20358, for example.
• the production methods set out therein are also part of the present description.
• the hydrophobicity of the gas diffusion layer can be set by using perfluorinated polymers together with non- fluorinated binders. Subsequently, the equipped gas diffusion layers are dried and after-treated thermally, for example by sintering at temperatures of more than 200°C. Furthermore, it is possible to construct the gas diffusion layer with several layers. In a preferred embodiment of the gas diffusion layer, it has at least 2
• At least one of the gas diffusion layers can consist of a compressible material.
• a compressible material is characterized by the property that the gas diffusion layer can be compressed to half, in particular a third of its original thickness without losing its integrity.
• the gas diffusion layers according to the invention have a low electrical surface resistivity which is in the range of ⁇ 100 mOhm per cm 2 , preferably ⁇ 60 mOhm per cm 2 .
• gas diffusion layer made of graphite fabric and/or graphite paper which were rendered conductive by addition of carbon black.
• the gas diffusion layers are usually also optimised in respect of their hydrophobicity and mass transfer properties by the addition of further materials.
• the gas diffusion layers are equipped with fluorinated or partially fluorinated materials, for example PTFE.
• the catalyst layer or catalyst layers contains or contain catalytically active substances. These include, amongst others, precious metals of the platinum group, i.e. Pt, Pd, Ir, Rh, Os, Ru, or also the precious metals Au and Ag.
• alloys of all the above-mentioned metals may also be used.
• At least one catalyst layer can contain alloys of the elements of the platinum group with non-precious metals, such as for example Fe, Co, Ni, Cr, Mn, Zr, Ti, Ga, V, etc.
• the oxides of the above-mentioned precious metals and/or non-precious metals can also be used.
• the catalytically active particles which comprise the above-mentioned substances can be used as metal powder, in particular platinum and/or platinum alloy powder, so-called black precious metal. Such particles generally have a size in the range of 5 nm to 200 nm, preferably in the range of 7 nm to 100 nm. So-called nano particles are also used.
• the metals can also be used on a support material.
• this support comprises carbon which particularly may be used in the form of carbon black, graphite or graphitised carbon black.
• electrically conductive metal oxides such as for example, SnO x , TiO x , or phosphates, such as e.g.
• FePO x , NbPO x , Zr y (PO x ) z can be used as support material.
• the indices x, y and z designate the oxygen or metal content of the individual compounds which can lie within a known range as the transition metals can be in different oxidation stages.
• the content of these metal particles on a support is generally in the range of 1 to 80% by weight, preferably 5 to 60% by weight and particularly preferably 10 to 50% by weight; however, this should not constitute a limitation.
• the particle size of the support in particular the size of the carbon particles, is preferably in the range of 20 to 1000 nm, in particular 30 to 100 nm.
• the size of the metal particles present thereon is preferably in the range of 1 to 20 nm, in particular 1 to 10 nm and particularly preferably 2 to 6 nm.
• the sizes of the different particles represent mean values and can be determined via transmission electron microscopy or X-ray powder diffractometry.
• the catalytically active particles set forth above can generally be obtained commercially.
• catalyst nano particles made of platinum-containing alloys in particular based on Pt, Co and Cu or Pt, Ni and Cu, respectively, can also be used in which the particles in the outer shell have a higher Pt content as in the core.
• Such particles were described by P. Strasser et al. in Angewandte Chemie 2007.
• the catalytically active layer may contain customary additives. These include, amongst others, fluoropolymers, such as e.g. polytetrafluoroethylene (PTFE), proton-conducting ionomers and surface-active substances.
• PTFE polytetrafluoroethylene
• the weight ratio of fluoropolymer to catalyst material comprising at least one noble metal and optionally one or more support materials is greater than 0.1 , this ratio preferably lying within the range of 0.2 to 0.6.
• the catalyst layer has a thickness in the range of 1 to 1000 pm, in particular from 5 to 500, preferably from 10 to 300 pm.
• This value represents a mean value, which can be determined by using cross-section images of the layer that can be obtained with a scanning electron microscope (SEM).
• the content of noble metals of the catalyst layer is 0.1 to 10.0 mg/cm 2 , preferably 0.3 to
• the ionomeric material according to the instant invention being present on the catalyst layer at the cathode in a certain ratio to the content of catalyst material.
• a weight ratio between ionomeric material and catalyst from 100:1 to 1 :100, most preferred from 10:1 to 1 :10.
• a specific preferred ratio is from 1 :8 to 1 :3.
• the catalyst layer is in general not self-supporting but is usually applied to the gas diffusion layer and/or the membrane.
• a part of the catalyst layer can, for example, diffuse into the gas diffusion layer and/or the membrane, resulting in the formation of transition layers. This can also lead to the catalyst layer being understood as part of the gas diffusion layer.
• the thickness of the catalyst layer results from measuring the thickness of the layer onto which the catalyst layer was applied, for example the gas diffusion layer or the membrane, the measurement providing the sum of the catalyst layer and the corresponding layer, for example the sum of the gas diffusion layer and the catalyst layer.
• the catalyst layers preferably feature gradients, i.e. the content of precious metals increases in the direction of the membrane while the content of hydrophobic materials is behaving contrarily.
• gaskets used or generated within the scope of the method according to the invention are either produced in a separate step and applied or else directly generated on the circumferential edge of the gas diffusion layer and the
• the gasket in the formed, constructional inner boundary area overlaps inwards and thus overlaps the outer boundary area of the gas diffusion layer or the gas diffusion layer provided with a catalyst layer.
• the gas diffusion layer is fixed in the bipolar plate such that further positioning or fixing frames can be dispensed with. Additionally, no longer does the boundary area of the gas diffusion layer have to be interspersed with sealing material or does the sealing material have to penetrate the boundary area of the gas diffusion layer to achieve the sealing function.
• the gasket possesses a sufficient mechanical stability and/or integrity such that in a subsequent compression step, for example, the gas diffusion layer and/or the membrane/electrolyte matrix will not be
• a so-called hard stop function may be integrated into the gasket in an advantageous manner. This embodiment is particularly preferred when the gasket is produced on a bipolar plate without a raised edge.
• Production of the gasket can be performed in a separate step or else the gasket is generated directly on the circumferential edge of the gas diffusion layer towards the bipolar plate. Formation of the gasket can be performed by means of all the known methods, preferably by the spray-application of thermoplastic elastomers or cross-linkable rubbers or the application and/or cross-linking of these by means of printing methods.
• the gaskets according to the invention are formed from meltable polymers or rubbers which can be processed thermally.
• silicone rubber Q
• EPDM ethylene-propylene-diene rubber
• EPM ethylene-propylene rubber
• MR butadiene rubber
• SBR styrene-butadiene rubber
• SIR styrene-isoprene rubber
• IBR isoprene-butadiene rubber
• IR isoprene rubber
• NBR acrylonitrile-butadiene rubber
• CR chloroprene rubber
• ACM acrylate rubber
• fluoropolymers are used as sealing material, preferably
• poly(tetrafluoroethylene-co-hexafluoropropylene) FEP polyvinylidene fluoride PVDF
• perfluoroalkoxy polymer PFA perfluoroalkoxy polymer
• poly(tetrafluoroethylene-co- perfluoro(methylvinyl ether) MFA poly(tetrafluoroethylene-co- perfluoro(methylvinyl ether) MFA.
• sealing materials based on polyimides can also be used.
• the class of polymers based on polyimides also includes polymers also containing, besides imide groups, amide (polyamideimides), ester (polyesterimides) and ether groups (polyetherimides) as components of the backbone.
• Preferred polyimides have recurring units of the formula (VI)
• the functional group Ar has the meaning set forth above and the functional group R represents an alkyl group or a bicovalent aromatic or heteroaromatic group with 1 to 40 carbon atoms.
• the functional group R represents a bicovalent aromatic or heteroaromatic group derived from benzene, naphthalene, biphenyl, diphenyl ether, diphenyl ketone,
• diphenylmethane diphenyldimethylmethane
• bisphenone diphenylsulphone
• quinoline pyridine
• bipyridine anthracene, thiadiazole and phenanthrene which optionally also can be substituted.
• the index n suggests that the recurring units represent parts of polymers.
• Such polymers are commercially available under the trade names ⁇ Kapton, ®Vespel, ®Toray and ⁇ Pyralin from DuPont as well as ®Ultem from GE Plastics and ⁇ Upilex from Ube Industries.
• Combinations of the above-mentioned materials with the property combination soft/hard are also suitable as sealing material, in particular when the above- mentioned hard stop function is to be integrated.
• Particularly preferred sealing materials have a Shore A hardness of 5 to 85, in particular of 25 to 80.
• the Shore hardness is determined according to DIN 53505.
• the permanent set is determined according to DIN ISO 815.
• the thickness of the gaskets is influenced by several factors.
• An essential factor is how high the elevation in the boundary area of the bipolar plate is chosen.
• the thickness of the gasket generated or applied is 5 pm to 5000 pm, preferably 10 pm to 1000 pm and in particular 25 pm to 150 pm. In particular in the case of bipolar plates without a raised boundary area, the thickness can also be higher.
• the gaskets can also be constructed with several layers.
• different layers are connected with each other using suitable polymers, in particular fluoropolymers being well suited to establish an adequate connection.
• suitable fluoropolymers are known to those in professional circles. These include, amongst others, polytetrafluoroethylene (PTFE) and poly(tetrafluoroethylene-co- hexafluoropropylene) (FEP).
• PTFE polytetrafluoroethylene
• FEP poly(tetrafluoroethylene-co- hexafluoropropylene)
• the layer made of fluoropolymers present on the sealing layers described above in general has a thickness of at least 0.5 pm, in particular at least 2.5 pm. If expanded fluoropolymers are applied, the thickness of the layer can be 5 to 250 ⁇ , preferably 10 to 150 pm.
• the gaskets or sealing materials described above are such that they fix the gas diffusion layer in the recess which is formed together with the bipolar plate. To this end, it is advantageous when the gasket overlaps the outer boundary area of the gas diffusion layer circumferentially.
• the overlap of the gasket with the boundary area of the gas diffusion layer is preferably 0.1 to 5 mm, preferably 0.1 to 3 mm, based on the outermost edge of the gas diffusion layer. A greater overlap is possible, but leads to a strong loss in catalytically active surface. For this reason, the degree of overlapping has to be balanced in a critical way so that an
• the bipolar plates or also separator plates used within the scope of the present invention are typically provided with process media channels (flow field channels) to permit the distribution of the reactants and other fluids typical for fuel cells, for example cooling fluids.
• the bipolar plates are usually formed from electrically conductive materials; these may be metallic or non-metallic materials.
• composite materials are composites made of a matrix material which are provided with electrically conductive fillers.
• Polymeric materials in particular organic polymers are preferably suited as the matrix material.
• high- performance polymers in particular thermally stable polymers can also be required.
• polymers are used whose long-term service temperature is at least 80°C, preferably at least 120°C, particularly preferably at least 180°C.
• Thermoplastics in particular polypropylene (PP), polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyphenylene sulphide (PPS) and liquid- crystalline polymers (LCP) are used with particular preference, it also being possible to use these as compounds, i.e. admixed with other polymers and typical additives, respectively.
• thermoplastics thermosetting plastics and resins are also preferred. In particular, phenol resins (PF), melamine resins (MF), polyester (UP) and epoxy resins (EP) are used.
• Particulate substances which permit a distribution as homogenous as possible in the matrix are used as electrically conductive fillers.
• these fillers possess a bulk conductivity of at least 10 mS/cm.
• Carbons, graphites and carbon blacks are used with particular preference. These can also be treated to achieve a better wettability with the matrix material.
• the particle size is not subject to any particular limitation, but has to permit the production of such bipolar plates.
• electrically conductive fillers even further additives which are to improve the application properties can be added to the matrix materials. Fibre reinforcements are also possible, in particular if the mechanical load can otherwise not be ensured.
• Producing such bipolar plates is preferably performed by means of suitable forming methods, in particular by means of injection moulding techniques as well as injection embossing and embossing techniques.
• the bipolar plates can also have further ducts or openings or bores through which coolants or reaction gases, for example, can be supplied and discharged.
• the thickness of the non-metallic bipolar plates is preferably within the range of 0.3 to 10 mm, in particular within the range of 0.5 to 5 mm and particularly preferably within the range of 0.5 to 2 mm.
• the conductivity of the non-metallic bipolar plates is greater than or equal to 25 S/cm.
• the bipolar plates are constructed from metallic materials, more cost-efficient integral designs are possible.
• the construction of such metallic bipolar plates is not subject to any substantial limitation.
• Corrosion-resistant and acid-resistant steels are preferred as metallic materials, in particular those based on V2A and V4A steels as well as those made of nickel- based alloys.
• Plated or coated metals are further preferred, in particular those with corrosion-resistant surfaces made of precious metals, nickel, ruthenium, niobium, tantalum, chromium, carbon as well as metals coated with ceramic materials, in particular coats made of CrN, TIN, TiAIN, complex nitrides, carbides, silicides and oxides of metals and transition metals.
• the metallic bipolar plates can additionally have such coats which, on the one hand, reduce the electrical surface resistivity of the junction of gas diffusion layer/bipolar plate or else increase the chemical and/or physical resistance of the bipolar plate towards the media present or formed in fuel cells.
• the construction of metallic bipolar plates can take place from individual plates, it thus being possible in a simple manner to form voids for coolants or reaction media which have to be supplied and discharged.
• the connection of the individual plates can be performed by material bonding methods, such as, for example, welding or soldering. If necessary, the voids are additionally sealed with respect to each other, e.g. by means of further internal coats such that leakages can be avoided.
• the bipolar plates or individual bipolar plates in the stack may also be manufactured from only one metallic or non-metallic individual plate.
• the thickness of the metallic bipolar plates is preferably within the range of 0.03 to 1 mm, in particular within the range of 0.05 to 0.5 mm and particularly preferably within the range of 0.05 to 0.15 mm.
• the bipolar plates used within the scope of the present invention may have a raised boundary area such that the area of the bipolar plate containing the channels of the flow field forms a recess.
• the exact height of the boundary area in relation to the highest elevation of the area of the bipolar plate having the process media channels is adapted to the thickness of the gas diffusion layer or the gas diffusion layer with a catalyst layer. If the gas diffusion layer or the gas diffusion layer with a catalyst layer is not to be subjected to any further compression during the subsequent compression step, the elevation of the boundary area of the bipolar plate corresponds to the thickness of the gas diffusion layer or the gas diffusion layer with a catalyst layer.
• the thickness of the gas diffusion layer or the gas diffusion layer with a catalyst layer is higher than the height of the boundary area opposite the highest elevation of the area of the bipolar plate having the process media ducts, a compression of the gas diffusion layer results during the subsequent compression step.
• the degree of compression is determined via the thickness and formability of the sealing material such that the sealing material acts as a hard stop. This embodiment is particularly advantageous when soft or easily formable polymer electrolyte membranes are used as damage to the membrane can be avoided.
• the above-described elevation of the boundary area is chosen such that the compression is at least 5%.
• a compression of more than 50%, in particular of more than 30% is chosen as the upper limit, it being possible to also exceed this through the choice of other parameters.
• the compression of the components is performed by the action of pressure and temperature such that an intimate connection of the components with each other is formed. In general, this is carried out at a temperature in the range of 10 to 300°C, in particular 20°C to 200°C and with a pressure in the range of 1 to 1000 bar, in particular of from 3 to 300 bar.
• the above-mentioned compression can also take place during the production of the stack and/or when starting-up the fuel cell stack.
• the electrochemical cell in particular individual cell for fuel cells is operational and can be used.
• the underlying individual cells for fuel cells are arranged as a stack.
• the production of the fuel cell stack can be performed by using the semi-finished parts according to the invention, it being possible to provide these beforehand with the required membrane.
• the membrane is previously available as rolled goods, for example, and can be cut individually to be adapted to the respective bipolar plate design, with minimal use of materials. No handling frame needs to be added.
• the production of fuel cell stacks from individual cells for fuel cells is generally known.
• the electrodes and membrane electrode assembly according to the instant invention provides, as described in the examples below, polymer which contains fluorine and at the same time imino group that allows adsorption of phosphoric acid.
• polymer which contains fluorine and at the same time imino group that allows adsorption of phosphoric acid.
• ionomer coated on electrodes gives significantly higher oxygen reduction current is obtained. Accordingly, it was shown that the
• Polymer 1 Polybenzimidazole (PBI)
• poly(2,2'-m-phenylene-5,5'-bibenzimidazole) from BASF Fuel Cell GmbH is used.
• Polymer 2 Fluorine-containing polymer 1
• This polymer was soluble in organic solvents, such as Dimethyl Acetamide and NMP (N-Methylpyrrolidone).
• Polymer 3 Fluorine-containing polymer 2
• This polymer was soluble in organic solvents, such as Acetoamide and NMP (N- Methylpyrrolidone).
• Polymer 4 Fluorine-containing polymer 3
• Sebacic acid shown in Formula 5
• 2,2-Bis (3- amino-4-hydroxyphenyl) Hexafluoropropane dihydrochloride shown in Formula 6, was used as a monomer containing amino group.
• polyphosphoric acid 117% phosphoric acid
• the reaction took place at 130°C for 1 hour, and further at 180°C for 24 hours.
• the reaction mixture became highly viscous.
• This polymer was soluble in organic solvents, such as Dimethyl Acetamide and NMP (N-Methylpyrrolidone).
• the electrochemical measurements are performed by pressing the

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