Crosslinkable fluoropolymer composition for sealing fuel cells

Abstract

The present invention relates to a fuel cell incorporating a sealing device, in particular a sealing device for sealing a bipolar plate to a membrane in a PEM fuel cell stack. The resulting fuel cell stack exhibits superior leak resistance and reduced ion leaching in water.

Description

Technical Field

[0001] This application claims priority to patent application number 22184140.6 filed in Europe on July 11, 2022, the entire contents of which are incorporated by reference into this application for all purposes.

[0002] The present invention relates to fuel cells incorporating sealing devices, particularly sealing devices for sealing bipolar plates to membranes in PEM fuel cell stacks. The resulting fuel cell stacks exhibit superior resistance to leakage and reduced ion leaching from water. Background Art

[0003] Fuel cell assemblies employing proton exchange membranes are well known. Such assemblies typically include a stack of fuel cell modules, each module having an anode and a cathode separated by a catalytic proton exchange membrane (PEM), and the modules in the stack are electrically connected in series to provide a desired voltage output. A gaseous fuel in the form of hydrogen or a hydrogen-containing mixture (such as a "reformed" hydrocarbon) flows adjacent to a first side of the membrane, and oxygen, typically in the form of air, flows adjacent to the opposite side of the membrane. Hydrogen is catalytically oxidized at the anode-membrane interface, and the resulting protons H + Migrate through the membrane to the cathode-membrane interface where the protons react with the anionic oxygen O -2 Combine to form water. Protons migrate only in those areas of the fuel cell where the anode and cathode are directly opposite each other across the membrane. Electrons flow from the anode to the cathode through an external circuit, performing electrical work in a load in the circuit.

[0004] A fuel cell assembly typically includes a plurality of fuel cell modules connected in series to form a fuel cell stack. For ease of manufacture, and to provide a more robust assembly, the anode of one cell and the cathode of an adjacent cell are typically formed as rigid plates and then bonded back to back to form a "bipolar plate" as is well known in the art. Thus, a fuel cell assembly typically consists of a stack of alternating bipolar plates and proton exchange membranes.

[0005] The bipolar plates must perform several functions, namely, distributing the fuel and oxidant within the cell, facilitating water management within the cell, carrying electrical current away from the cell, and facilitating thermal management.

[0006] At the outer edges of the assembly, the plates and membranes are sealed together to contain the reactant gases and / or coolant within the assembly. Thus, an important aspect of forming a stacked fuel cell assembly is preventing leakage between the membranes and the plates.

[0007] One prior art approach is to mold a liquid silicone rubber (LSR) gasket directly onto the bipolar plate using liquid injection molding techniques. This has proven difficult due to the complex seal shapes and plate geometries, as well as the very brittle nature of some of the composite materials typically used to form bipolar plates.

[0008] CN113346102 discloses the use of fluororubber as a sealing material for proton exchange membrane fuel cells. Compared with ordinary rubber, fluororubber has the following advantages due to its various excellent properties: high temperature resistance, corrosion resistance, swelling resistance, aging resistance, compression set resistance, mechanical properties, high vacuum resistance, flame retardancy and low temperature resistance.

[0009] US9105884 further discloses the use of fluoroelastomers as fuel cell seals, and such materials can also be applied in the form of a mixture with a curing agent. After heating to a predetermined temperature, or alternatively, reacting with atmospheric moisture or being exposed to ultraviolet (UV) radiation, the material can be cured in situ to form a resilient gasket that adheres to the surface of the component. The gasket so formed can fill the gap between the mating surfaces of various components for their environmental sealing.

[0010] A primary object of the present invention is to economically and reliably seal fuel cell components. Summary of the invention

[0011] The present invention provides a water-based fluoroelastomer crosslinkable composition for fuel cell seals, which can be applied between fuel cell components, such as between a bipolar plate and a proton exchange membrane, in the form of latex using conventional application techniques to simplify the entire application process.

[0012] The resulting fuel cell stack exhibits superior leakage resistance and reduced ion leaching from water, thereby preventing a decrease in fuel cell efficiency.

[0013] Therefore, a first object of the present invention is a method of sealing a plurality of fuel cell components, the method comprising the steps of:

[0014] - step a): depositing an aqueous crosslinkable composition [composition (C)] on at least one surface of at least one of the plurality of fuel cell components;

[0015] - step b): curing the composition (C) so that a seal is formed therethrough;

[0016] Wherein the composition (C) comprises:

[0017] an aqueous latex comprising particles of at least one fluoropolymer based on vinylidene fluoride (VDF) [polymer (A)] comprising recurring units derived from vinylidene fluoride (VDF) and optionally at least one additional comonomer different from VDF;

[0018] - at least one basic compound [base (B)];

[0019] - at least one pyridinium salt conforming to any one of formulae (P-1) to (P-12) [Salt (P)]:

[0020]

[0021]

[0022] in:

[0023] - Each J and J', identical or different from each other, is independently CR* or N at each occurrence, wherein R* is H or Cl-C 12 Hydrocarbon;

[0024] -E is N or has the formula CR° H Groups;

[0025] -Z is a divalent hydrocarbon radical containing 1 to 12 carbon atoms;

[0026] -W is a bond or a bridging group selected from the group consisting of a divalent hydrocarbon group containing 1 to 12 carbon atoms (preferably a divalent aliphatic group containing 1 to 6 carbon atoms) and a divalent fluorocarbon group containing 1 to 12 carbon atoms (preferably a divalent perfluoroaliphatic group containing 1 to 6 carbon atoms);

[0027] - Groups depicted by the following symbols in formulae (P-11) and (P-12):

[0028]

[0029] represents an aromatic mononuclear or polynuclear ring fused to a pyridinium-type aromatic ring, which may contain one or more additional nitrogen atoms, optionally quaternary nitrogen atoms, in the ring or rings;

[0030] -R 1 H , R 2 H , R 3 H , R 4 H , R 5 H , R 6 H , R7 H , R 8 H , R 9 H , R 10 H , R 11 H , R 12 H , R 13 H , R 14 H , R 15 H , R 16 H , R 17 H , R 18 H , R 19 H , R 20 H , R 21 H , R 22 H , R 23 H , R 24 H , R 25 H , R 26 H , R 27 H , R 28 H , R 29 H , R 30 H , R 31 H , R 32 H , R 33 H , R 34 H , R 35 H , R 36 H and R o H Each of, which is the same or different from each other, is independently -H or a group having the formula [group (α-H)] at each occurrence:

[0031]

[0032] Where R a and Rb , which are the same or different from each other, are independently H or a C1-C6 hydrocarbon group;

[0033] -Y, the same or different from each other, are independently oxygen or C1-C 12 A hydrocarbon group, which may be an aliphatic or aromatic group, which may contain one or more heteroatoms selected from N, O, S and halogen;

[0034] -A (m-) It is an anion with a valence of m;

[0035] The premise is

[0036] (i) When the salt (P) has the formula (P-1), R 1 H , R 2 H and R° H At least two of them are groups (α-H);

[0037] (ii) When the salt (P) has the formula (P-2), R 3 H and R 4 H is a group (α-H);

[0038] (iii) When the salt (P) has the formula (P-3), R 5 H , R 6 H , R 7 H and R 8 H At least two of them are groups (α-H);

[0039] (iv) When the salt (P) has the formula (P-4), R 9 H , R 10 H , R 11 H , R 12 H and R° H At least two of them are groups (α-H);

[0040] (v) When the salt (P) has the formula (P-5), R 13 H , R 14 H and R° H At least two of them are groups (α-H);

[0041] (vi) When the salt (P) has the formula (P-6), R 15 H , R 16 H , R 17 H and R° H At least two of them are groups (α-H);

[0042] (vii) When the salt (P) has the formula (P-7), R 18 H , R 19 H , R 20 H , R 21 H and R° H At least two of them are groups (α-H);

[0043] (viii) When the salt (P) has the formula (P-8), R 22 H , R 23 H , R 24 H and R° H At least two of them are groups (α-H);

[0044] (ix) When the salt (P) has the formula (P-9), R 25 H , R 26 H , R 27 H and R 28 H At least two of them are groups (α-H);

[0045] (x) When the salt (P) has the formula (P-10), R 29 H , R 30 H , R 31 H , R 32 H and R 28 H At least two of them are groups (α-H);

[0046] (xi) When the salt (P) has the formula (P-11), R 33 H , R 34 H and R 28 H At least two of them are groups (α-H);

[0047] (xii) When the salt (P) has the formula (P-12), R 35 H , R 36 H and R° H At least two of them are groups (α-H).

[0048] In another object, the present invention provides a seal for a fuel cell component obtainable by curing a composition (C) as defined above.

[0049] In another object, the present invention provides a fuel cell assembly comprising a seal as defined above disposed between fuel cell components; and a fuel cell stack comprising a plurality of said fuel cell assemblies.

[0050] The fuel cell components are advantageously selected from bipolar plates and proton exchange membranes.

[0051] The seal of the present invention comprises a thin layer of a cross-linkable fluoroelastomer disposed between components of a fuel cell, such as a bipolar plate and a membrane. The resulting fuel cell stack exhibits superior leakage resistance and reduced ion leaching from water.

[0052] Some of the compositions (C) used in the method of the invention are novel and represent further aspects of the invention.

[0053] Therefore, in another object, the present invention provides an aqueous crosslinkable composition [composition (C1)] obtained by mixing:

[0054] an aqueous latex comprising particles of at least one fluoropolymer based on vinylidene fluoride (VDF) [polymer (A)] comprising recurring units derived from vinylidene fluoride (VDF) and optionally at least one additional comonomer different from VDF;

[0055] - at least one non-aromatic amine having the formula [base (B1)]

[0056] R bm -NR H 2

[0057] Each R H Independently C1-C 12 Hydrocarbon;

[0058] -R bm is a monovalent non-aromatic hydrocarbon group having 1 to 30 carbon atoms; and

[0059] - at least one pyridinium salt conforming to any one of formulae (P-1) to (P-12) as defined above [salt (P)]. DETAILED DESCRIPTION

[0060] The term "fuel cell assembly" is intended herein to mean each individual cell component, such as a bipolar plate, an electrode, a membrane, or an entire proton exchange membrane.

[0061] The aqueous composition (C) of the present invention is obtained by mixing the latex of the polymer (A) with the salt (P) and the base (B) as described in detail above.

[0062] The expression "latex" is used herein according to its common meaning in the art, i.e. to denote a stable dispersion of particles of polymer (A) in an aqueous medium. Thus, a latex is notably distinguishable from an aqueous slurry which can be prepared by dispersing a polymer powder in an aqueous medium and / or from a solution in a solvent capable of swelling or dissolving polymer (A).

[0063] The term "aqueous medium" is used herein according to its ordinary meaning, i.e. is intended to mean a liquid phase consisting primarily of water, it being understood that small amounts of one or more organic solvents may be present, for example 1% wt or less, without affecting the aqueous nature of the medium.

[0064] The polymer (A) comprises recurring units derived from vinylidene fluoride (VDF) and optionally at least one additional comonomer different from VDF.

[0065] More specifically, according to certain embodiments, polymer (A) comprises:

[0066] - repeating units derived from vinylidene fluoride (VDF) in an amount ranging from 60 mol% to 100 mol%, preferably from 65 mol% to 100 mol%, more preferably from 75 mol% to 100 mol%,

[0067] - and optionally, repeating units derived from at least one additional comonomer different from VDF [comonomer (C)] in an amount ranging from 0 mol% to 40 mol%, preferably 0 mol% to 35 mol%, more preferably 0 mol% to 25 mol%.

[0068] Comonomer (C) may be a hydrogenated comonomer [comonomer (H)] or a fluorinated comonomer [comonomer (F)].

[0069] The term "hydrogenated comonomer [comonomer (H)]" is intended herein to mean an ethylenically unsaturated comonomer containing no fluorine atoms.

[0070] Non-limiting examples of suitable hydrogenated comonomers (H) include notably ethylene, propylene, vinyl monomers such as vinyl acetate, acrylic monomers, and styrene monomers like styrene and p-methylstyrene.

[0071] The term "fluorinated comonomer [comonomer (F)]" is intended herein to mean an ethylenically unsaturated comonomer comprising at least one fluorine atom.

[0072] Comonomer (C) is preferably a fluorinated comonomer [comonomer (F)].

[0073] Non-limiting examples of suitable fluorinated comonomers (F) include notably the following:

[0074] (a) C2-C8 perfluoroolefins, such as tetrafluoroethylene (TFE) and hexafluoropropylene (HFP);

[0075] (b) C2-C8 hydrogen-containing fluoroolefins, such as vinyl fluoride, 1,2-difluoroethylene, trifluoroethylene, pentafluoropropylene and hexafluoroisobutylene;

[0076] (c) having the formula CH2=CH-R f0 Perfluoroalkylethylene, where R f0 is a C1-C6 perfluoroalkyl group;

[0077] (d) Chloro- and / or brominated and / or iodinated C2-C6 fluoroolefins, such as chlorotrifluoroethylene (CTFE);

[0078] (e) having the formula CF2=CFOR f1 (per)fluoroalkyl vinyl ether, wherein R f1 is a C1-C6 fluoroalkyl group or a perfluoroalkyl group, such as -CF3, -C2F5, -C3F7;

[0079] (f) (per)fluoro-oxyalkyl vinyl ethers of the formula CF2=CFOX0, wherein X0 is a C1-C2-alkylene group having one or more ether groups. 12 Oxyalkyl or C1-C 12 (Per)fluorooxyalkyl, for example perfluoro-2-propoxy-propyl;

[0080] (g) having the formula CF2=CFOCF2OR f2 Fluoroalkyl-methoxy-vinyl ether, wherein R f2 is a C1-C6 fluoroalkyl or perfluoroalkyl group, such as -CF3, -C2F5, -C3F7, or a C1-C6 (per)fluorooxyalkyl group having one or more ether groups, such as -C2F5-O-CF3;

[0081] (h) Fluorodioxole having the formula:

[0082]

[0083] Where R f3 , R f4 , R f5 and R f6 Each of them, identical or different from each other, is independently a fluorine atom, a C1-C6 fluoro- or per(halo)fluoroalkyl group, which may optionally contain one or more oxygen atoms, such as -CF3, -C2F5, -C3F7, -OCF3, -OCF2CF2OCF3.

[0084] The most preferred fluorinated comonomers (F) are tetrafluoroethylene (TFE), trifluoroethylene (TrFE), chlorotrifluoroethylene (CTFE), hexafluoropropylene (HFP), perfluoromethyl vinyl ether (PMVE), perfluoropropyl vinyl ether (PPVE) and vinyl fluoride, and among these, HFP is the most preferred.

[0085] According to certain embodiments, polymer (A) comprises repeating units derived from vinylidene fluoride (VDF) and at least one hydrophilic (meth)acrylic monomer (MA) possibly in combination with one or more than one fluorinated comonomer (F).

[0086] The term "at least one hydrophilic (meth)acrylic monomer (MA)" is understood to mean that the polymer (A) may comprise repeating units derived from one or more than one hydrophilic (meth)acrylic monomer (MA) as described above. In the remainder of the text, the expressions "hydrophilic (meth)acrylic monomer (MA)" and "monomer (MA)" are to be understood for the purposes of the present invention both in the plural and in the singular, i.e. they denote both one or more than one hydrophilic (meth)acrylic monomer (MA).

[0087] According to certain embodiments, polymer (A) consists essentially of repeating units derived from VDF and monomer (MA).

[0088] According to other embodiments, polymer (A) consists essentially of repeating units derived from VDF, HFP and monomer (MA).

[0089] The polymer (A) may further include other parts which neither affect nor impair its physicochemical properties, such as defects, terminal groups, etc.

[0090] The hydrophilic (meth)acrylic monomer (MA) preferably conforms to the following formula:

[0091]

[0092] wherein each of R1, R2, and R3, which are the same or different from each other, are independently a hydrogen atom or a C1-C3 hydrocarbon group, and ROH is a hydroxyl group or a C1-C5 hydrocarbon moiety containing at least one hydroxyl group; more preferably, each of R1, R2, and R3 is hydrogen, and R OH has the same meaning as described above, preferably R OH It's OH.

[0093] Non-limiting examples of hydrophilic (meth)acrylic monomers (MA) are, inter alia, acrylic acid, methacrylic acid, hydroxyethyl (meth)acrylate, hydroxypropyl (meth)acrylate; hydroxyethylhexyl (meth)acrylate.

[0094] The monomer (MA) is more preferably selected from:

[0095] - Hydroxyethyl acrylate (HEA) having the formula:

[0096]

[0097] - 2-Hydroxypropyl acrylate (HPA) having any of the following formulas:

[0098]

[0099] - Acrylic acid (AA) having the formula:

[0100]

[0101] - and mixtures thereof.

[0102] More preferably, monomer (MA) is AA and / or HEA, even more preferably AA.

[0103] The determination of the amount of (MA) monomer repeating units in polymer (A) can be carried out by any suitable method. It is worth mentioning that the acid-base titration method, which is well suited for the determination of, for example, acrylic acid content, the NMR method, which is suitable for the quantification of (MA) monomers containing aliphatic hydrogen in the side chain (e.g., HPA, HEA), and the weight balance method based on the total feed (MA) monomer and the unreacted residual (MA) monomer during the production of polymer (A) can be mentioned.

[0104] According to these embodiments, polymer (A) comprises preferably at least 0.1 mol%, more preferably at least 0.2 mol%, of repeating units derived from said hydrophilic (meth)acrylic monomer (MA), and / or polymer (A) comprises preferably at most 10 mol%, more preferably at most 7.5 mol%, even more preferably at most 5 mol%, most preferably at most 3 mol% of repeating units derived from said hydrophilic (meth)acrylic monomer (MA).

[0105] According to these embodiments, when the temperature is adjusted according to ASTM D3835 for 100 sec. -1The polymer (A) generally has a melt viscosity (MV) of at least 15 kpoise when measured at a shear rate of 1.5 % and at a temperature of 230° C. The MV of the polymer (A) is not particularly limited, but it is generally understood that an MV of not more than 100 kpoise, preferably less than 80 kpoise, will be sufficient to ensure optimal properties in coating applications.

[0106] According to certain embodiments, said polymer (A) comprising repeating units derived from vinylidene fluoride (VDF) and optionally at least one additional comonomer different from VDF is a fluoroelastomer [fluoroelastomer (A)].

[0107] For the purposes of the present invention, the term "fluoroelastomer" [fluoroelastomer (A)] is intended to mean a fluoropolymer resin as a base component for obtaining a true elastomer, said fluoropolymer resin comprising more than 10% by weight, preferably more than 30% by weight, of repeating units derived from VDF and from at least one ethylenically unsaturated monomer containing at least one fluorine atom (hereinafter, (per)fluorinated monomer), and optionally from at least one ethylenically unsaturated monomer not containing fluorine atoms (hereinafter, hydrogenated monomer). True elastomers are defined by ASTM, Special Technical Bulletin, No. 184 as materials capable of being stretched to twice their intrinsic length at room temperature and, after keeping them under tension for 5 minutes, recover within the same time to within 10% of their initial length once they are released.

[0108] The fluoroelastomer (A) is generally an amorphous product or has a low crystallinity (less than 20% by volume of the crystalline phase) and a glass transition temperature (T g In most cases, the fluoroelastomer (A) advantageously has a T below 10°C, preferably below 5°C, more preferably below 0°C, even more preferably below -5°C. g .

[0109] Fluoroelastomer (A) typically comprises at least 15 mol%, preferably at least 20 mol%, more preferably at least 35 mol% of recurring units derived from VDF relative to all recurring units of the fluoroelastomer.

[0110] Fluoroelastomer (A) typically comprises at most 85 mol%, preferably at most 80 mol%, more preferably at most 78 mol% of recurring units derived from VDF relative to all recurring units of the fluoroelastomer.

[0111] Non-limiting examples of suitable (per)fluorinated monomers, the repeating units derived from which are comprised in the fluoroelastomer (A) are notably:

[0112] (a) C2-C8 perfluoroolefins, such as tetrafluoroethylene (TFE) and hexafluoropropylene (HFP);

[0113] (b) hydrogen-containing C2-C8 olefins other than VDF, such as vinyl fluoride (VF), trifluoroethylene (TrFE), olefins having the formula CH2=CH-R f Perfluoroalkylethylene, where R f is a C1-C6 perfluoroalkyl group;

[0114] (c) C2-C8 chlorinated and / or brominated and / or iodinated fluoroolefins, such as chlorotrifluoroethylene (CTFE);

[0115] (d) having the formula CF2=CFOR f (per)fluoroalkyl vinyl ether (PAVE), wherein R f is a C1-C6 (per)fluoroalkyl group, such as CF3, C2F5, C3F7;

[0116] (e) (per)fluoro-oxy-alkyl vinyl ethers of the formula CF2=CFOX, wherein X is a C1-C ... 12 ((Per)fluoro)-oxyalkyl, for example perfluoro-2-propoxypropyl;

[0117] (f) (per)fluorodioxoles having the formula:

[0118] Where R f3 , R f4 , R f5 , R f6 , identical or different from each other, independently selected from C1-C6 (per)fluoroalkyl groups containing a fluorine atom and optionally one or more than one oxygen atom, such as notably -CF3, -C2F5, -C3F7, -OCF3, -OCF2CF2OCF3; preferably, perfluorodioxole;

[0119] (g) (per)fluoro-methoxy-vinyl ether (MOVE, hereinafter) having the following formula:

[0120] CFX2=CX2OCF2OR" f

[0121] Where R f is selected from: a linear or branched C1-C6 (per)fluoroalkyl group; a C5-C6 cyclic (per)fluoroalkyl group; and a linear or branched C2-C6 (per)fluorooxyalkyl group containing 1 to 3 chain oxygen atoms, and X2 = F, H; preferably X2 is F and R" fIt is -CF2CF3(MOVE1); -CF2CF2OCF3(MOVE2); or -CF3(MOVE3).

[0122] It is generally preferred that the fluoroelastomer (A) comprises, in addition to recurring units derived from VDF, recurring units derived from HFP.

[0123] In this case, fluoroelastomer (A) typically comprises at least 10 mol%, preferably at least 12 mol%, more preferably at least 15 mol% of recurring units derived from HFP relative to all recurring units of the fluoroelastomer.

[0124] Furthermore, fluoroelastomer (A) typically comprises at most 45 mol%, preferably at most 40 mol%, more preferably at most 35 mol% of recurring units derived from HFP relative to all recurring units of the fluoroelastomer.

[0125] Fluoroelastomer (A) suitable for use in the composition of the present invention may comprise, in addition to repeating units derived from VDF and HFP, one or more of the following:

[0126] - recurring units derived from at least one bis-olefin [bis-olefin (OF)] having the general formula:

[0127]

[0128] wherein R1, R2, R3, R4, R5 and R6 are the same or different from each other and are H, halogen, or a C1-C5 optionally halogenated group which may contain one or more oxygen groups; Z is a linear or branched C1-C 18 Optionally halogenated alkylene or cycloalkylene, optionally containing oxygen atoms, or (per)fluoropolyoxyalkylene;

[0129] - repeating units derived from at least one (per)fluorinated monomer different from VDF and HFP; and

[0130] - repeating units derived from at least one hydrogenated monomer.

[0131] Examples of hydrogenated monomers are notably non-fluorinated alpha-olefins, including ethylene, propylene, 1-butene, diene monomers, styrene monomers, typically using alpha-olefins. C2-C8 non-fluorinated alpha-olefins (O1), and more specifically ethylene and propylene, will be selected to achieve increased alkali resistance.

[0132] The diene (OF) is preferably selected from the group consisting of dienes conforming to formula (OF-1), (OF-2) and (OF-3):

[0133] (OF-1)

[0134]

[0135] wherein j is an integer between 2 and 10, preferably between 4 and 8, and R1, R2, R3, R4, identical or different from each other, are H, F or C 1-5 Alkyl or (per)fluoroalkyl;

[0136] (OF-2)

[0137]

[0138] wherein each A is the same or different from each other and, at each occurrence, is independently selected from F, Cl, and H; each B is the same or different from each other and, at each occurrence, is independently selected from F, Cl, H, and OR B , where R B is a branched or straight-chain alkyl group which may be partially, substantially or completely fluorinated or chlorinated; E is an optionally fluorinated divalent group having 2 to 10 carbon atoms which may be interrupted by an ether bond; preferably, E is -(CF2) m -group, wherein m is an integer from 3 to 5; a preferred diene of type (OF-2) is F2C=CF-O-(CF2)5-O-CF=CF2.

[0139] (OF-3)

[0140]

[0141] wherein E, A and B have the same meanings as defined above; R5, R6, R7 are the same as or different from each other and are H, F or C 1-5 Alkyl or (per)fluoroalkyl.

[0142] The most preferred fluoroelastomers (A) are those having the following composition (in mol % relative to the total number of moles of units of the fluoroelastomer):

[0143] (i) Vinylidene fluoride (VDF) 45%-85%; Hexafluoropropylene (HFP) 15%-45%; Tetrafluoroethylene (TFE) 0-30%;

[0144] (ii) vinylidene fluoride (VDF) 20%-30%; hexafluoropropylene (HFP) 18%-27%; C2-C8 non-fluorinated olefin (Ol) 5%-30%; perfluoroalkyl vinyl ether (PAVE) 0-35%; bis-olefin (OF) 0%-5%;

[0145] (iii) Vinylidene fluoride (VDF) 60%-75%; Hexafluoropropylene (HFP) 10%-25%; Tetrafluoroethylene (TFE) 0-20%; Perfluoroalkyl vinyl ether (PAVE) 1%-15%.

[0146] Regardless of the nature of polymer (A), typically, the particles of polymer (A) have an average primary particle size of less than 1 μm. For the purposes of the present invention, the term "primary particles" is intended to mean primary particles of polymer (A) that are derived directly from aqueous emulsion polymerization without isolating the polymer from the latex (i.e., a stable emulsion of particles). Thus, the primary particles of polymer (A) are intended to be distinguishable from agglomerates (i.e., collections of primary particles) that can be obtained by recovery and conditioning steps of such polymer manufacturing (e.g., concentrating and / or agglomerating an aqueous latex of polymer (A) and subsequently drying and homogenizing to produce the corresponding powder).

[0147] Preferably, the particles of polymer (A) in dispersion (D) have an average primary particle size of greater than 20 nm, more preferably greater than 30 nm, even more preferably greater than 50 nm, and / or as low as 600 nm, more preferably below 400 nm and even more preferably below 350 nm, as measured according to ISO 13321.

[0148] Preferred salts (P) of formula (P-1) are those conforming to formulae (P-1-a) to (P-1-e):

[0149]

[0150]

[0151] in:

[0152] -R a and R b has the meaning as defined above, preferably R a and R b It is H;

[0153] -Y has the meaning as defined above, preferably Y is methyl;

[0154] - Each R p and R q , the same or different from each other, are H or C1-C 12 Hydrocarbon;

[0155] -A and m have the meanings as defined above.

[0156] More preferably, the salt (P) having the formula (P-1) is one having any one of the formulae (P-1-g) to (P-1-p):

[0157]

[0158]

[0159] wherein A and m have the meanings as detailed above.

[0160] Preferred salts (P) of formula (P-2) are those conforming to formula (P-2-a):

[0161]

[0162] in:

[0163] -R a and R b has the meaning as defined above, preferably R a and R b It is H;

[0164] -Y has the meaning as defined above, preferably Y is methyl;

[0165] - Each R p and R q , the same or different from each other, are H or C1-C 12 Hydrocarbon;

[0166] -A and m have the meanings as defined above.

[0167] More preferably, the salts (P) having the formula (P-2) are those having the formula (P-2-b)

[0168]

[0169] wherein A and m have the meanings as detailed above.

[0170] Preferred salts (P) of formula (P-3) are those conforming to formula (P-3-a):

[0171]

[0172] in:

[0173] -R a and R b has the meaning as defined above, preferably R a and R b It is H;

[0174] -Y has the meaning as defined above, preferably Y is methyl;

[0175] -A and m have the meanings as defined above.

[0176] More preferably, the salts (P) having the formula (P-3) are those having the formula (P-3-b)

[0177]

[0178] wherein A and m have the meanings as detailed above.

[0179] Preferred salts (P) of formula (P-4) are those conforming to formula (P-4-a):

[0180]

[0181] in:

[0182] -R a and R b has the meaning as defined above, preferably R a and R b It is H;

[0183] - w is an integer from 1 to 12, preferably from 1 to 6, most preferably equal to 3;

[0184] -A and m have the meanings as defined above.

[0185] More preferably, the salts (P) of formula (P-4) are those of formula (P-4-b) or (P-4-c):

[0186]

[0187] wherein A and m have the meanings as detailed above, and w=3.

[0188] Preferred salts (P) of formula (P-5) are those conforming to formula (P-5-a):

[0189]

[0190] in:

[0191] -R a and R b has the meaning as defined above, preferably R a and R b It is H;

[0192] -Y has the meaning as defined above, preferably Y is methyl;

[0193] -A and m have the meanings as defined above.

[0194] More preferably, the salts (P) having the formula (P-5) are those having the formula (P-5-b) or (P-5-c):

[0195]

[0196] wherein A and m have the meanings as detailed above.

[0197] Preferred salts (P) of formula (P-11) are those conforming to formula (P-11-a):

[0198]

[0199] in:

[0200] -R a and R b has the meaning as defined above, preferably R a and R b It is H;

[0201] -Y has the meaning as defined above, preferably Y is methyl;

[0202] -A and m have the meanings as defined above.

[0203] More preferably, the salts (P) having the formula (P-11) are those having the formula (P-11-b):

[0204]

[0205] wherein A and m have the meanings as detailed above.

[0206] Preferred salts (P) of formula (P-12) are those conforming to formula (P-12-a):

[0207]

[0208] in:

[0209] -R a and R b has the meaning as defined above, preferably R a and R b It is H;

[0210] -Y has the meaning as defined above, preferably Y is methyl;

[0211] -A and m have the meanings as defined above.

[0212] More preferably, the salts (P) having the formula (P-12) are those having the formula (P-12-b):

[0213]

[0214] wherein A and m have the meanings as detailed above.

[0215] The choice of anion A in formulae (P-1) to (P-12) is not particularly critical; however, it will be appreciated that, due to their rapid availability from a synthetic point of view, particular preference may be given to anions selected from the group consisting of: arylsulfonates, in particular toluenesulfonates (p-toluenesulfonates); (fluoro)alkylsulfonates having a C1-C6 (fluoro)alkyl chain, including fluorine-free alkylsulfonates, for example, methanesulfonates (methanesulfonates) and fluorine-containing (especially perfluorinated) alkylsulfonates, for example trifluoromethanesulfonates (trifluoromethanesulfonates); halides (iodide, bromide, chloride).

[0216] The Applicant has surprisingly found that salts (P) of any one of formulae (P-1) to (P-12) comprising a cyclic quaternized pyridinium nitrogen and having at least two groups comprising said reactive hydrogen atoms in ortho or para position relative to said cyclic quaternized pyridinium nitrogen are effective crosslinkers for crosslinking VDF polymers when combined with a basic compound in an aqueous medium.

[0217] Without being bound by this theory, the Applicant believes that the group in the ortho or para position comprising at least one hydrogen atom in the alpha position relative to the aromatic ring has an acidic character, thereby generating a corresponding carbon anion in the presence of a base (B); the carbon anion thus formed has a sufficiently reactive / nucleophilic character to ensure the activation and grafting of the VDF polymer chains, thereby generating a three-dimensional crosslinked network in the coated membranes and layers obtained therefrom.

[0218] In general, exemplary compounds that have been found to be particularly useful in the compositions of the present invention are those listed below having formulae (Ex-1) to (Ex-9):

[0219]

[0220] The composition of the present invention generally comprises the salt (P) in an amount of at least 0.1 part by weight, preferably at least 0.5 part by weight, more preferably at least 1 part by weight per 100 parts by weight of polymer (A) (phr).

[0221] The composition of the invention generally comprises the salt (P) in an amount of up to 30 parts by weight, preferably up to 20 parts by weight, more preferably up to 15 parts by weight per 100 parts by weight of polymer (A).

[0222] The base (B) suitable for use in the composition (C) of the present invention is not particularly limited. One or more than one organic base (B) may be used.

[0223] Among the organic bases (B), mention may be made notably of:

[0224] (j) Non-aromatic amines or amides according to the general formula (B1m) or (B1d):

[0225] R bm -[C(O)] t -NR H 2(B1m)

[0226] R H 2N-[C(O)] t’ -R dm -[C(O)] t” -NR H 2(B1d)

[0227] in:

[0228] - each t, ​​t' and t", are the same or different from each other and are zero or 1 at each occurrence;

[0229] - Each R H are independently H or C1-C 12 Hydrocarbon;

[0230] -R bm is a monovalent non-aromatic hydrocarbon group having 1 to 30 carbon atoms;

[0231] -R bm is a divalent non-aromatic hydrocarbon group having 1 to 30 carbon atoms; and

[0232] (jj) an alicyclic secondary or tertiary amine conforming to the general formula (B2m) or (B2d):

[0233]

[0234] in:

[0235] -Cy represents a divalent aliphatic group comprising at least 4 carbon atoms, optionally comprising one or more than one ethylenically unsaturated double bonds, and optionally comprising one or more catenary nitrogen atoms forming a ring with the nitrogen atoms attached thereto;

[0236] -Cy' represents a trivalent aliphatic group comprising at least 5 carbon atoms, optionally comprising one or more than one ethylenically unsaturated double bonds, and optionally comprising one or more catenary nitrogen atoms forming a ring with the nitrogen atoms attached thereto;

[0237] (jjj) Aromatic amines or amides conforming to the general formula (B3):

[0238] Ar b -{[C(O)] t -NR H 2} w (B3)

[0239] in:

[0240] -t, which are identical or different from each other and are either zero or 1 at each occurrence;

[0241] -w is an integer from 1 to 4;

[0242] - Each R H are independently H or C1-C 12 Hydrocarbon;

[0243] -Ar b is a mononuclear or polynuclear aromatic group, which may contain one or more catenary heteroatoms selected from the group consisting of S and O;

[0244] (jv) heteroaromatic amines containing at least one nitrogen atom contained in a heteroaromatic ring, in particular pyridine derivatives;

[0245] (v) Guanidine derivatives having the formula (B4) or (B5):

[0246]

[0247] in:

[0248] - Each R 1 , R 2 , R 3 , R 4 , R 5 , R 6 , R 7 and R 8 , the same or different from each other, independently H or C1-C 12 Hydrocarbon

[0249] and the corresponding salts of the guanidines (B4) and (B5), in particular the corresponding N-quaternary ammonium hydrohalides (preferably hydrochlorides);

[0250] (vj) Metal alkoxides, preferably alkoxides of aliphatic alcohols.

[0251] Among the bases of formula (B1m) and (B1d), wherein:

[0252] -R bm is a monovalent aliphatic linear radical having 6 to 30 carbon atoms, which may contain one or more than one ethylenically unsaturated double bond; and

[0253] -R dm is a divalent aliphatic straight-chain radical having 6 to 30 carbon atoms, which may contain one or more than one ethylenically unsaturated double bond,

[0254] It is particularly preferred.

[0255] Among the non-aromatic amines or amides, mention may in particular be made of:

[0256] -Has the formula CH3(CH2) 17 -NH2-octadecylamine;

[0257] - having the formula H2N-C(O)-(CH2) 11 -Erucamide of CH=CH-(CH2)7CH3;

[0258] - oleamide having the formula H2N-C(O)-(CH2)7-CH=CH-(CH2)7CH3;

[0259] - hexamethylenediamine having the formula H2N-(CH2)6-NH2;

[0260] -N,N-dimethyloctylamine;

[0261] -N,N-dimethyldodecylamine;

[0262] -Trioctylamine;

[0263] -trimethylamine;

[0264] -Trihexylamine.

[0265] Among the alicyclic secondary or tertiary amines, mention may be made of 1,8-diazabicycloundec-7-ene (DBU) having the following formula:

[0266]

[0267] Exemplary embodiments of the guanidine derivative having the formula (B-4) are notably guanidine hydrochloride and di-o-tolylguanidine.

[0268] Exemplary embodiments of the metal alkoxides are notably potassium tert-butoxide, sodium ethoxide and sodium methoxide.

[0269] Exemplary embodiments of the heteroaromatic amines are notably collidine isomers.

[0270] In a preferred embodiment of the present invention, the base (B) is a non-aromatic amine having the formula

[0271] R bm -NR H 2

[0272] Each R H Independently C1-C 12 Hydrocarbon;

[0273] -R bm It is a monovalent hydrocarbon non-aromatic group having 1 to 30 carbon atoms.

[0274] In a more preferred embodiment of the present invention, the base (B) is trihexylamine.

[0275] The amount of base (B) will be adjusted by a person skilled in the art taking into account the nature and basicity of the base (B) used.

[0276] However, it is understood that composition (C) generally comprises at least 0.1 parts by weight, preferably at least 0.2 parts by weight, more preferably at least 0.25 parts by weight of said base (B) (as detailed above) per 100 parts by weight of polymer (A).

[0277] Further, the composition (C) generally comprises at most 30 parts by weight, preferably at most 25 parts by weight, more preferably at least 20 parts by weight of the base (B) per 100 parts by weight of the polymer (A).

[0278] The base (B) and the salt (P) may be added in a preparatory step during the preparation of the composition (C) in order to generate the corresponding carbanion of the salt (P).

[0279] As stated, composition (C) is an aqueous composition, ie it is a composition comprising a liquid medium comprising water as the main component.

[0280] Although small amounts of organic solvents may be present, it is generally understood that the liquid medium of composition (C) consists essentially of water and that the solvent is preferably present in limited amounts, e.g. less than 1% wt relative to the total weight of composition (C), so as not to adversely modify the aqueous nature of the composition and all its favorable environmental aspects.

[0281] The present invention further relates to a process for the manufacture of a composition (C) as detailed above, said process comprising mixing an aqueous latex of a polymer (A) as detailed above, a base (B) and a salt (P).

[0282] Typically, the process according to the invention comprises a first step of mixing a base (B) and a salt (P) so as to obtain a premix, and a second step of mixing said premix with an aqueous latex of a polymer (A).

[0283] Typically, in a first step, the base (B) and the salt (P) are mixed in a liquid medium, and more specifically in an aqueous medium, i.e. a liquid medium consisting essentially of water. A small amount of one or more organic solvents may be tolerated in the aqueous medium in which the base (B) and the salt (P) are mixed, provided that their amount does not exceed 1% wt based on the aqueous medium. Examples of one or more organic solvents that may be present as solubilizing aids for the salt (P) are notably tetrahydrofuran (THF) and acetonitrile.

[0284] In a first step, the base (B) and the salt (P) are mixed in the aqueous medium at a temperature of advantageously at least 10°C, preferably at least 15°C and generally at most 60°C, more preferably at most 50°C, it being understood that mixing at room temperature may be preferred and is generally fully effective.

[0285] Without being bound by this theory, the Applicant believes that in this first step of forming the premix of base (B) and salt (P), a reactive hydrogen atom in the ortho or para position relative to the ring-quaternized pyridinium nitrogen of the salt (P) is removed so as to provide the corresponding carbanion which is the actual effective crosslinker for polymer (A).

[0286] Mixing of the base (B) and the salt (P) in the aqueous medium can be carried out in customary mixing apparatuses, usually in a vessel equipped with stirring means.

[0287] In the second step, the method comprises mixing the premix and the aqueous latex of polymer (A). Typically, the premix is ​​gradually added to the aqueous latex of polymer (A); more specifically, the formed premix may be added dropwise to the aqueous medium.

[0288] Mixing of the aqueous latex of polymer (A) with the base (B) and the salt (P) or a premix thereof is generally carried out in a mixing apparatus (generally operating at low shear rates) in order to minimize shear stress-induced coagulation phenomena.

[0289] Mixing is typically carried out at a temperature of from 10°C to 45°C, preferably 15°C to 35°C, it being understood that mixing at room temperature may be preferred and is generally fully effective.

[0290] In step a) of the method of the present invention, the aqueous crosslinkable sealing composition (C) can be applied in latex form to at least one surface of at least one of the multiple fuel cell components using conventional coating application techniques such as spraying, dipping, cast film, immersion, and screen printing.

[0291] After applying composition (C) to at least one surface of the fuel cell component, the composition layer is preferably dried before subjecting it to step b). Drying is preferably carried out at a temperature comprised between 30°C and 100°C, preferably between 40°C and 50°C.

[0292] In step b) of the method, once the aqueous crosslinkable sealing composition (C) is applied to at least one side of a fuel cell component, such as to at least one surface of a proton exchange membrane or to at least one surface of a bipolar plate, curing of the composition (C) can be obtained by thermally crosslinking it, thereby providing a fuel cell component with improved performance, in particular in terms of leakage resistance, such that the overall metal ion content that may be found to be leached in water during fuel cell operation is reduced.

[0293] Thermal crosslinking may be performed by heating the composition (C) at a temperature which may vary from about 150°C to about 400°C, preferably at a temperature below 300°C, more preferably below 200°C.

[0294] In another object, the present invention provides a seal for a fuel cell component obtainable by curing a composition (C) as defined above.

[0295] The seal of the present invention comprises a thin layer of a cross-linkable fluoroelastomer disposed between components of a fuel cell, such as a bipolar plate and a proton exchange membrane. When the seal of the present invention is used in a fuel cell stack, a reduced amount of ions are present due to the specific components of the composition (C) used; in addition, due to the superior leakage resistance of the seal of the present invention, ion leaching is prevented and the efficiency of the fuel cell is maintained.

[0296] Some of the compositions (C) used in the method of the invention are novel and represent further aspects of the invention.

[0297] Therefore, in another object, the present invention provides an aqueous composition [composition (C1)] obtained by mixing:

[0298] an aqueous latex comprising particles of at least one fluoropolymer based on vinylidene fluoride (VDF) [polymer (A)] comprising recurring units derived from vinylidene fluoride (VDF) and optionally at least one additional comonomer different from VDF;

[0299] - at least one non-aromatic amine [base (B1)] having the formula

[0300] R bm -NR H 2

[0301] Each R H Independently C1-C 12 Hydrocarbon;

[0302] -R bm is a monovalent non-aromatic hydrocarbon group having 1 to 30 carbon atoms;

[0303] - at least one pyridinium salt conforming to any one of formulae (P-1) to (P-12) as defined above [salt (P)].

[0304] In a more preferred embodiment of the present invention, the base (B) in composition (C1) is trihexylamine.

[0305] Should the disclosure of any patents, patent applications, and publications incorporated herein by reference conflict with the description of the present application to the extent that it might render a term unclear, the present description shall take precedence.

[0306] The present invention will now be described with reference to the following examples, which are for illustrative purposes only and are not intended to limit the scope of the present invention.

[0307] Experimental Section

[0308] raw material

[0309] TN latex, commercially available from Solvay Specialty Polymers; solids content equal to 65-68 wt%.

[0310] Examples

[0311] Preparation Example 1 - 1,2,4,6-Tetramethyl-pyridinium p-toluenesulfonate having the formula:

[0312]

[0313] Into a three-necked round-bottom flask equipped with a thermometer, a condenser and stirring, CH2Cl2 (85 ml) and methyl p-toluenesulfonate (25.50 g) were charged. Then 2,4,6-trimethylpyridine (16.59 g) was added dropwise at room temperature. The reaction was stirred at 50°C and the reaction was completed after 22 hours. The liquid phase was removed by vacuum evaporation to obtain a white powder, which was dispersed in diethyl ether (50 ml) under stirring. The liquid phase was filtered off, and 39.13 g of pure product was recovered as a white powder with a 93% yield (melting point 161°C; 1% weight loss: 266°C).

[0314] 1 H NMR (solvent D2O, TMS reference): +7.70 ppm (d; 2H; o-H; p-toluenesulfonate); +7.55 (s; 2H; m-H; 1,2,4,6-tetramethyl-pyridinium); +7.39 (d; 2H; m-H; p-toluenesulfonate); +4.0 (s; 3H; NCH3; 1,2,4,6-tetramethyl-pyridinium); +2.74 (s; 6H; o-CH3; 1,2,4,6-tetramethyl-pyridinium); 2.53 (s; 3H; p-CH3; 1,2,4,6-tetramethyl-pyridinium); +2.44 ppm (s; 3H; p-CH3; p-toluenesulfonate).

[0315] Preparation Example 2: Preparation of pyridinium salt and trihexylamine solution

[0316] To a solution of 1,2,4,6-tetramethyl-pyridinium p-toluenesulfonate (13.7 g; 0.05 mol) in water (90 ml) was added trihexylamine (24 g, 0.1 mol) in water (17.5 ml).The mixture (Preparation A) was stirred at room temperature for 2.5 hours.

[0317] Preparation Example 3: Preparation of pyridinium salt and sodium hydroxide (comparison)

[0318] To a solution of 1,2,4,6-tetramethyl-pyridinium p-toluenesulfonate (13.7 g; 0.05 mol) in water (90 ml) was added a solution of sodium hydroxide (4.2 g, 0.1 mol) in water (17.5 ml). The mixture (Preparation B) was stirred at room temperature for 2.5 hours.

[0319] Example 1: Preparation of Composition CA

[0320] To 140 g of TN latex, 9.2 g of Formulation A was added dropwise.

[0321] The system was kept under agitation at room temperature for 60 minutes. The aqueous dispersion thus obtained was then cast on a chromated aluminum Q panel test substrate. The coated panel was dried at 40° C. for 1 hour; then baked in an air oven at 190° C. for 60 minutes.

[0322] Example 2-Comparative: Preparation of Composition CB

[0323] To 140 g of TN latex, 9.7 g of Formulation B was added dropwise.

[0324] The system was kept under agitation (at 18°C-22°C) for 60 minutes. The aqueous dispersion thus obtained was then cast on a chromated aluminum Q panel test substrate. The coated panel was dried at 40°C for 1 hour; then baked in an air oven at 190°C for 60 minutes.

[0325] Soak test

[0326] The coated panels (from both CA and CB compositions) were placed in a jar filled with deionized water according to ASTM D1193 Type I. The conductivity of the solution was measured. The jar was then placed in an oven at 80°C for 15 days. The final conductivity of the aqueous solution was then measured to check the amount of ionic species leached into the water.

[0327] The leachate water was then injected into the fuel cell and the change in current before and after the injection of the leachate solution was measured: a lower ΔI means that the leachate water has less impact on the membrane efficiency and the power produced.

[0328] The results are summarized in Table 1.

[0329] Determination of metal ion content

[0330] The amount of metals in Composition CA and Composition CB was determined by Inductively Coupled Plasma Optical Emission Spectroscopy (ICP-OES).

[0331] Composition CA and composition CB were preheated to remove water; the residue was then calcined (at 550° C. by a Bunsen burner flame or a semi-assisted muffle furnace), and then dissolved in acid (H 2 SO 4 ).

[0332] The acid solution thus obtained is injected into a high temperature energy source (ICP).

[0333] The excited atoms emit radiation with a typical and defined wavelength, producing an emission spectrum. The intensity of this emission is proportional to the concentration of free atoms within the source.

[0334] The concentration of each element was obtained by comparison with the calibration curve.

[0335] The results are reported in Table 1.

[0336] Table 1

[0337]

[0338] As shown in Table 1, when the composition containing trihexylamine was used instead of the composition containing an inorganic base, the water conductivity after the soaking test was lower.

[0339] Furthermore, in the case of the composition containing trihexylamine, when the leachate water was injected into the fuel cell, the change in current was also much lower, thus satisfying the high purity requirement required for fuel cell applications.

[0340] Furthermore, the results show that, due to the presence of certain non-aromatic amines, the aqueous crosslinkable compositions according to the invention have a lower metal ion content compared to compositions comprising an inorganic base; this makes the compositions of the invention particularly suitable for preparing seals for fuel cells.

[0341] In view of the above, it has been discovered that the compositions of the present invention are suitable for easy application to fuel cell components to provide fluoroelastomer latex compositions crosslinked with pyridinium salts and certain organic bases that allow effective sealing and minimize reduction in fuel cell efficiency due to ion leaching.

Claims

1. A method for sealing a plurality of fuel cell components, the method comprising the steps of: - step a): depositing an aqueous crosslinkable composition [composition (C)] on at least one surface of at least one of the plurality of fuel cell components; - step b): curing the composition (C) so that a seal is formed therethrough; Wherein the composition (C) comprises: an aqueous latex comprising particles of at least one fluoropolymer based on vinylidene fluoride (VDF) [polymer (A)] comprising recurring units derived from vinylidene fluoride (VDF) and optionally at least one additional comonomer different from VDF; - at least one basic compound [base (B)]; - at least one pyridinium salt conforming to any one of formulae (P-1) to (P-12) [Salt (P)]: in: - Each J and J', identical or different from each other, is independently CR* or N at each occurrence, wherein R* is H or Cl-C 12 Hydrocarbon; -E is N or has the formula CR° H Groups; -Z is a divalent hydrocarbon radical containing 1 to 12 carbon atoms; -W is a bond or a bridging group selected from the group consisting of a divalent hydrocarbon group containing 1 to 12 carbon atoms (preferably a divalent aliphatic group containing 1 to 6 carbon atoms) and a divalent fluorocarbon group containing 1 to 12 carbon atoms (preferably a divalent perfluoroaliphatic group containing 1 to 6 carbon atoms); - Groups depicted by the following symbols in formulae (P-11) and (P-12): represents an aromatic mononuclear or polynuclear ring fused to a pyridinium-type aromatic ring, which may contain one or more additional nitrogen atoms, optionally quaternary nitrogen atoms, in the ring or rings; -R 1 H 、R 2 H 、R 3 H 、R 4 H 、R 5 H 、R 6 H 、R 7 H 、R 8 H 、R 9 H 、R 10 H 、R 11 H 、R 12 H 、R 13 H 、R 14 H 、R 15 H 、R 16 H 、R 17 H 、R 18 H 、R 19 H 、R 20 H 、R 21 H 、R 22 H 、R 23 H 、R 24 H 、R 25 H 、R 26 H 、R 27 H 、R 28 H 、R 29 H 、R 30 H 、R 31 H 、R 32 H 、R 33 H 、R 34 H 、R 35 H 、R 36 H and R o H Each of, which is the same or different from each other, is independently -H or a group having the formula [group (α-H)] at each occurrence: Where R a and R b , which are the same or different from each other, are independently H or a C1-C6 hydrocarbon group; -Y, the same or different from each other, are independently oxygen or C1-C 12 a hydrocarbon radical which may in particular be an aliphatic or aromatic radical which may contain one or more than one heteroatom selected from N, O, S and halogen; -A (m-) It is an anion with a valence of m; The premise is (i) When the salt (P) has the formula (P-1), R 1 H , R 2 H and R° H At least two of them are groups (α-H); (ii) When the salt (P) has the formula (P-2), R 3 H and R 4 H is a group (α-H); (iii) When the salt (P) has the formula (P-3), R 5 H , R 6 H , R 7 H and R 8 H At least two of them are groups (α-H); (iv) When the salt (P) has the formula (P-4), R 9 H , R 10 H , R 11 H , R 12 H and R° H At least two of them are groups (α-H); (v) When the salt (P) has the formula (P-5), R 13 H , R 14 H and R° H At least two of them are groups (α-H); (vi) When the salt (P) has the formula (P-6), R 15 H , R 16 H , R 17 H and R° H At least two of them are groups (α-H); (vii) When the salt (P) has the formula (P-7), R 18 H , R 19 H , R 20 H , R 21 H and R° H At least two of them are groups (α-H); (viii) When the salt (P) has the formula (P-8), R 22 H , R 23 H , R 24 H and R° H At least two of them are groups (α-H); (ix) When the salt (P) has the formula (P-9), R 25 H , R 26 H , R 27 H and R 28 H At least two of them are groups (α-H); (x) When the salt (P) has the formula (P-10), R 29 H , R 30 H , R 31 H , R 32 H and R 28 H At least two of them are groups (α-H); (xi) When the salt (P) has the formula (P-11), R 33 H , R 34 H and R 28 H At least two of them are groups (α-H); (xii) When the salt (P) has the formula (P-12), R 35 H , R 36 H and R° H At least two of them are groups (α-H).

2. The method according to claim 1, wherein: The polymer (A) comprises: - repeating units derived from vinylidene fluoride (VDF) in an amount ranging from 60 mol% to 100 mol%, preferably from 65 mol% to 100 mol%, more preferably from 75 mol% to 100 mol%, - and optionally, repeating units derived from at least one additional comonomer different from VDF [comonomer (C)] in an amount ranging from 0 mol% to 40 mol%, preferably 0 mol% to 35 mol%, more preferably 0 mol% to 25 mol%.

3. The method according to claim 1 or claim 2, wherein: The comonomer (C) is a hydrogenated comonomer [comonomer (H)], which is an ethylenically unsaturated comonomer containing no fluorine atoms, preferably selected from the group consisting of ethylene, propylene, vinyl monomers such as vinyl acetate, acrylic acid monomers, and styrene monomers like styrene and p-methylstyrene; or a fluorinated comonomer [comonomer (F)], which is an ethylenically unsaturated comonomer containing at least one fluorine atom, preferably selected from the group consisting of: (a) C2-C8 perfluoroolefins, such as tetrafluoroethylene (TFE) and hexafluoropropylene (HFP); (b) C2-C8 hydrogen-containing fluoroolefins, such as vinyl fluoride, 1,2-difluoroethylene, trifluoroethylene, pentafluoropropylene and hexafluoroisobutylene; (c) having the formula CH2=CH-R f0 Perfluoroalkylethylene, where R f0 is a C1-C6 perfluoroalkyl group; (d) Chloro- and / or brominated and / or iodinated C2-C6 fluoroolefins, such as chlorotrifluoroethylene (CTFE); (e) having the formula CF2=CFOR f1 (per)fluoroalkyl vinyl ether, wherein R f1 is a C1-C6 fluoroalkyl group or a perfluoroalkyl group, such as -CF3, -C2F5, -C3F7; (f) (per)fluoro-oxyalkyl vinyl ethers of the formula CF2=CFOX0, wherein X0 is a C1-C2-alkylene group having one or more ether groups. 12 Oxyalkyl or C1-C 12 (Per)fluorooxyalkyl, for example perfluoro-2-propoxy-propyl; (g) having the formula CF2=CFOCF2OR f2 Fluoroalkyl-methoxy-vinyl ether, wherein R f2 is a C1-C6 fluoroalkyl or perfluoroalkyl group, such as -CF3, -C2F5, -C3F7, or a C1-C6 (per)fluorooxyalkyl group having one or more ether groups, such as -C2F5-O-CF3; (h) Fluorodioxole having the formula: Where R f3 , R f4 , R f5 and R f6 Each of them, identical or different from each other, is independently a fluorine atom, a C1-C6 fluoro- or per(halo)fluoroalkyl group, which may optionally contain one or more oxygen atoms, such as -CF3, -C2F5, -C3F7, -OCF3, -OCF2CF2OCF3.

4. The method according to claim 3, wherein: The polymer (A) comprises repeating units derived from vinylidene fluoride (VDF) and at least one hydrophilic (meth)acrylic monomer (MA) possibly in combination with one or more than one fluorinated comonomer (F), wherein the hydrophilic (meth)acrylic monomer (MA) conforms to the following formula: wherein each of R1, R2, and R3, which are the same or different from each other, are independently a hydrogen atom or a C1-C3 hydrocarbon group, and R OH is a hydroxyl group or a C1-C5 hydrocarbon moiety containing at least one hydroxyl group; more preferably, each of R1, R2, and R3 is hydrogen, and R OH has the same meaning as described above, preferably R OH It's OH.

5. A method according to any one of the preceding claims, wherein: The polymer (A) is chosen from fluoroelastomers (A) having the following composition (in mol % relative to the total number of moles of units of the fluoroelastomer): (i) Vinylidene fluoride (VDF) 45%-85%; Hexafluoropropylene (HFP) 15%-45%; Tetrafluoroethylene (TFE) 0-30%; (ii) vinylidene fluoride (VDF) 20%-30%; hexafluoropropylene (HFP) 18%-27%; C2-C8 non-fluorinated olefin (Ol) 5%-30%; perfluoroalkyl vinyl ether (PAVE) 0-35%; bis-olefin (OF) 0%-5%; (iii) Vinylidene fluoride (VDF) 60%-75%; Hexafluoropropylene (HFP) 10%-25%; Tetrafluoroethylene (TFE) 0-20%; Perfluoroalkyl vinyl ether (PAVE) 1%-15%.

6. A method according to any one of the preceding claims, wherein: The salts (P) of formula (P-1) are those of any one of formulae (P-1-g) to (P-1-p): Among them A (m-) It is an anion with a valence of m.

7. A method according to any one of the preceding claims, wherein: The composition (C) comprises the salt (P) in an amount of at least 0.1 parts by weight, preferably at least 0.5 parts by weight, more preferably at least 1 parts by weight per 100 parts by weight of polymer (A) (phr) and / or in an amount of at most 20 parts by weight, preferably at most 15 parts by weight, more preferably at most 10 parts by weight per 100 parts by weight of polymer (A).

8. A method according to any one of the preceding claims, wherein: The base (B) is selected from non-aromatic amines having the formula R bm -NR H 2 Each R H Independently C1-C 12 Hydrocarbon; -R bm It is a monovalent hydrocarbon non-aromatic group having 1 to 30 carbon atoms.

9. A method according to any one of the preceding claims, wherein: In step a), the composition (C) is applied in latex form to at least one surface of at least one of the plurality of fuel cell components using conventional coating application techniques such as spraying, dip coating, cast film, dipping, screen printing.

10. A method according to any one of the preceding claims, wherein: In step b) of the process, curing of the composition (C) is obtained by thermally crosslinking it by heating it at a temperature ranging from about 150°C to about 400°C, preferably at a temperature below 300°C, more preferably below 200°C.

11. A method according to any one of the preceding claims, wherein: The plurality of fuel cell assemblies are composed of bipolar plates and proton exchange membranes.

12. A seal for a fuel cell component, the seal being obtainable by curing a composition (C), the composition (C) comprising: an aqueous latex comprising particles of at least one fluoropolymer based on vinylidene fluoride (VDF) [polymer (A)] comprising recurring units derived from vinylidene fluoride (VDF) and optionally at least one additional comonomer different from VDF; - at least one basic compound [base (B)]; - at least one pyridinium salt conforming to any one of formulae (P-1) to (P-12) [Salt (P)]: in: - Each J and J', identical or different from each other, is independently CR* or N at each occurrence, wherein R* is H or Cl-C 12 Hydrocarbon; -E is N or has the formula CR° H Groups; -Z is a divalent hydrocarbon radical containing 1 to 12 carbon atoms; -W is a bond or a bridging group selected from the group consisting of a divalent hydrocarbon group containing 1 to 12 carbon atoms (preferably a divalent aliphatic group containing 1 to 6 carbon atoms) and a divalent fluorocarbon group containing 1 to 12 carbon atoms (preferably a divalent perfluoroaliphatic group containing 1 to 6 carbon atoms); - Groups depicted by the following symbols in formulae (P-11) and (P-12): represents an aromatic mononuclear or polynuclear ring fused to a pyridinium-type aromatic ring, which may contain one or more additional nitrogen atoms, optionally quaternary nitrogen atoms, in the ring or rings; -R 1 H 、R 2 H 、R 3 H 、R 4 H 、R 5 H 、R 6 H 、R 7 H 、R 8 H 、R 9 H 、R 10 H 、R 11 H 、R 12 H 、R 13 H 、R 14 H 、R 15 H 、R 16 H 、R 17 H 、R 18 H 、R 19 H 、R 20 H 、R 21 H 、R 22 H 、R 23 H 、R 24 H 、R 25 H 、R 26 H 、R 27 H 、R 28 H 、R 29 H 、R 30 H 、R 31 H 、R 32 H 、R 33 H 、R 34 H 、R 35 H 、R 36 H and R o H Each of, which is the same or different from each other, is independently -H or a group having the formula [group (α-H)] at each occurrence: Where R a and R b , which are the same or different from each other, are independently H or a C1-C6 hydrocarbon group; -Y, the same or different from each other, are independently oxygen or C1-C 12 a hydrocarbon radical which may in particular be an aliphatic or aromatic radical which may contain one or more than one heteroatom selected from N, O, S and halogen; -A (m-) It is an anion with a valence of m; The premise is (i) When the salt (P) has the formula (P-1), R 1 H , R 2 H and R° H At least two of them are groups (α-H); (ii) When the salt (P) has the formula (P-2), R 3 H and R 4 H is a group (α-H); (iii) When the salt (P) has the formula (P-3), R 5 H , R 6 H , R 7 H and R 8 H At least two of them are groups (α-H); (iv) When the salt (P) has the formula (P-4), R 9 H , R 10 H , R 11 H , R 12 H and R° H At least two of them are groups (α-H); (v) When the salt (P) has the formula (P-5), R 13 H , R 14 H and R° H At least two of them are groups (α-H); (vi) When the salt (P) has the formula (P-6), R 15 H , R 16 H , R 17 H and R° H At least two of them are groups (α-H); (vii) When the salt (P) has the formula (P-7), R 18 H , R 19 H , R 20 H , R 21 H and R° H At least two of them are groups (α-H); (viii) When the salt (P) has the formula (P-8), R 22 H , R 23 H , R 24 H and R° H At least two of them are groups (α-H); (ix) When the salt (P) has the formula (P-9), R 25 H , R 26 H , R 27 H and R 28 H At least two of them are groups (α-H); (x) When the salt (P) has the formula (P-10), R 29 H , R 30 H , R 31 H , R 32 H and R 28 H At least two of them are groups (α-H); (xi) When the salt (P) has the formula (P-11), R 33 H , R 34 H and R 28 H At least two of them are groups (α-H); (xii) When the salt (P) has the formula (P-12), R 35 H , R 36 H and R° H At least two of them are groups (α-H).

13. The seal according to claim 11, wherein: The at least one basic compound [base (B)] in composition (C) is selected from non-aromatic amines having the formula R bm -NR H 2 Each R H Independently C1-C 12 Hydrocarbon; -R bm It is a monovalent hydrocarbon non-aromatic group having 1 to 30 carbon atoms.

14. A fuel cell assembly comprising a seal according to claim 12 or 13 disposed between fuel cell components.

15. A fuel cell stack comprising a plurality of fuel cell assemblies according to claim 14.

16. An aqueous crosslinkable composition [composition (C1)] obtained by mixing: an aqueous latex comprising particles of at least one fluoropolymer based on vinylidene fluoride (VDF) [polymer (A)] comprising recurring units derived from vinylidene fluoride (VDF) and optionally at least one additional comonomer different from VDF; - at least one non-aromatic amine having the formula [base (B1)] R bm -NR H 2 Each R H Independently C1-C 12 Hydrocarbon; - at least one pyridinium salt conforming to any one of formulae (P-1) to (P-12) [Salt (P)]

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