Proton exchange membrane containing PVDF powder and proton-conducting ionic liquid

Abstract

The present invention relates to a proton exchange membrane, to a method for preparing said membrane, and to the use of said membrane in fields requiring ion exchange, such as electrochemistry or energy-related fields. More specifically, the invention relates to a proton-exchange membrane comprising ionic liquids covalently bonded to a polymer containing vinylidene fluoride (PVDF) in powder form.

Description

[0001] DESCRIPTION

[0002] TITLE: PROTON EXCHANGE MEMBRANE BASED ON PVDF POWDER AND PROTON CONDUCTING IONIC LIQUID

[0003] FIELD OF INVENTION

[0004] The present invention relates to a proton exchange membrane, the process for preparing said membrane, and the application of said membrane in fields requiring ion exchange, such as electrochemistry or energy. More specifically, the invention relates to a proton exchange membrane comprising ionic liquids bearing a proton conduction group covalently bonded to a vinylidene fluoride (PVDF) polymer in powder form.In particular, this membrane is used in the design of fuel cell and electrolyzer membranes, such as proton-conducting membranes for fuel cells operating with Ff / air or H2 / O2 (these cells being known by the abbreviation PEMFC for "Proton Exchange Membrane Fuel Cell") or operating with methanol / air (these cells being known by the abbreviation DMFC for "Direct Methanol Fuel Cell") or for electrolyzers operating with FFO / air or H2O / O2 (these electrolyzers being known by the abbreviation PEMWE for "Proton Exchange Membrane Water Electrolysis").

[0005] TECHNICAL BACKGROUND

[0006] Proton exchange membranes are primarily based on the chemistry of perfluorosulfonic acid (PFSA) polymers. Besides their high cost, these membranes cannot be used at operating temperatures above 80°C for extended periods due to their poor mechanical strength at these temperatures. Furthermore, the conductivity of PFSAs drops at temperatures above 90°C due to membrane dehydration at these temperatures.

[0007] Ion-conducting membranes produced by radiation-induced grafting are another option for improving their chemical stability. The radiation grafting reaction is controlled by the diffusion of monomers in the powder and the polymerization reactions of the monomers.

[0008] Ionic liquids, defined as molten salts with a melting point below 100°C, exhibit good ion-conducting properties at temperatures above 80°C, even in anhydrous conditions. However, they tend to migrate towards the membrane surface due to their small size and viscosity at these temperatures. One solution would be to immobilize the ionic liquids to allow the fuel cell to operate at higher temperatures while preventing a loss of ionic conductivity over time.

[0009] The grafting of ionic liquids onto PVDF chains has already been described in the literature. For example, the publication by C. Xing et al., "Immobilization of Ionic Liquids onto the Poly(vinylidene fluoride) by Electron Beam Irradiation" in Ind. Eng. Chem. Res. 2015, 54, 9351-9359, describes the grafting of an unsaturated ionic liquid, l-vinyl-3-butylimidazolium chloride, onto PVDF chains by irradiating a PVDF-ionic liquid film obtained by melt mixing followed by hot pressing. The resulting film is not proton conductive. Nevertheless, it has been shown that grafting significantly reduces the migration of aprotic ionic liquids under the influence of an electric field.

[0010] Document CN104861183 describes the preparation of an anion exchange membrane using an ionic liquid containing a double bond, melt-mixed with PVDF. The resulting mixture is then irradiated to chemically bond the ionic liquid and the PVDF. This ionic liquid has an anion-conducting function, not a proton-type cation-conducting function.

[0011] Finally, the publication by Hongxu Liu et al., “Hydrophilic ionic-liquid grafted poly(vinylidene fluoride) membranes with excellent cationic dye and oil-water emulsion removal performance” in J. Mater. Sci., 2022, 57:4876-4879, also describes the grafting of aprotic ionic liquids such as l-butyl-3-vinylimidazolium bromide or l-allyl-3-vinylimidazolium bromide onto irradiated PVDF powder. The use of PVDF in irradiated powder form allows for the grafting of a larger quantity of ionic liquids.

[0012] These three examples illustrate the possibility of grafting ionic liquids onto a PVDF-type fluoropolymer. However, the ionic liquids used do not contain ionic conducting groups that would allow for proton conduction.

[0013] There remains a real need for proton exchange membranes with improved properties, particularly with regard to proton conduction, durability, mechanical strength and dimensional stability at temperatures above 100°C, up to 160°C.

[0014] SUMMARY OF THE INVENTION

[0015] To meet the aforementioned needs, the inventors developed a membrane obtained from a vinylidene fluoride (PVDF) polymer in powder form. According to a first aspect, the invention relates to a material consisting of PVDF in powder form, irradiated and grafted in powder form with an ionic liquid monomer having a proton-conducting function and a polymerizable function.

[0016] Advantageously, the polymerizable function allows the said ionic liquid to be chemically bound to the PVDF by irradiation and thus obtain after transformation a membrane or a proton exchange powder based on PVDF bound to a proton-conducting ionic liquid.

[0017] The said PVDF is advantageously chosen from among the poly(vinylidene fluoride) homopolymers and copolymers of vinylidene difluoride with at least one comonomer chosen from the list: vinyl fluoride, tetrafluoroethylene, hexafluoropropylene, 3,3,3-trifluoropropene, 2,3,3,3-tetrafluoropropene, 1,3,3,3-tetrafluoropropene, hexafluoroisobutylene, perfluorobutylethylene, 1,1,3,3,3-pentafluoropropene, 1,2,3,3,3-pentafluoropropene, perfluoropropyl vinyl ether, perfluoromethyl vinyl ether, bromotrifluoroethylene, chlorofluoroethylene, chloro-trifluoroethylene, chlorotrifluoropropene, ethylene, and mixtures thereof.

[0018] Ionic liquid monomers consist solely of organic anions and cations suitable for grafting. In one embodiment, the ionic liquid monomers comprise a polymerizable function from among those listed: vinyl function, acrylic function, methacrylic function, styrenic function, acryloyl function, or methacryloyl function.

[0019] These ionic liquid monomers are protic, that is, they can transfer a proton from a Brønsted acid to a Brønsted base, which allows them to be proton conductors.

[0020] According to another aspect, the invention relates to a method for preparing said material, said method comprising irradiation and grafting of a PVDF in powder form with an ionic liquid monomer having a proton-conducting function and a polymerizable function.

[0021] According to a first embodiment, the PVDF and the ionic liquid monomer are irradiated at the same time.

[0022] According to another embodiment, the PVDF is first irradiated, then the ionic liquid monomer is grafted onto the irradiated PVDF.

[0023] According to one embodiment, the molar grafting rate of the ionic liquid in the grafted PVDF powder is greater than 3% and less than 150%, preferably between 5% and 100%, and more preferably between 10% and 60%. The molar grafting rate is the molar quantity of the ionic liquid in the grafted PVDF powders, as determined by proton NMR. In another aspect, the invention relates to a proton exchange polymer electrolyte membrane, said membrane consisting of a film obtained from said PVDF material.

[0024] According to another aspect, the invention relates to a method for manufacturing the proton exchange polymer electrolyte membrane from said irradiated and grafted PVDF material in powder form, said method comprising the transformation of the PVDF powder into film form.

[0025] According to another aspect, the invention relates to a proton exchange polymer composite membrane, said membrane consisting of a porous polymer support impregnated with said PVDF material by solvent and / or aqueous means.

[0026] According to another aspect, the invention relates to a proton exchange polymer composite membrane, said membrane being at least partly composed of fibers of said PVDF material, the remainder being a polymer. This membrane is then impregnated with said PVDF material by solvent or aqueous means.

[0027] According to another aspect, the invention relates to the applications of the proton exchange polymer electrolyte membrane to the following fields:

[0028] - fuel cells, for example, fuel cells operating with EE / air or H2 / O2 or operating with methanol / air;

[0029] - electrolyzers;

[0030] The present invention overcomes the drawbacks of the prior art. More specifically, it provides a technology that improves the thermal and mechanical strength of the film without any runoff at temperatures below 160°C.

[0031] To achieve this, the use of an ionic liquid with a proton-conducting function allows for good proton conductivity at temperatures ranging from 20°C to 160°C. Furthermore, the ionic liquid is bonded to the PVDF chain and therefore cannot migrate to the surface, ensuring the long-term performance of the proton exchange membrane. This PVDF material can be used in powder form as a binder, or as a membrane after processing, or both forms for manufacturing a membrane-electrode assembly with excellent binder-membrane compatibility, resulting in improved efficiency.

[0032] Because of the use of a grafted powder, it is also possible to manipulate the membrane morphology using conventional powder-to-film transformation techniques. This allows for a wide range of properties, particularly proton conductivity / hydrogen permeability ratios, on demand, according to application requirements.

[0033] The use of a PVDF-type fluorinated polymer also allows for good mechanical resistance of the film, in particular with resistance to temperatures up to 160°C.

[0034] DESCRIPTION OF METHODS OF IMPLEMENTING THE INVENTION

[0035] The invention is now described in more detail and in a non-limiting manner in the following description.

[0036] According to a first aspect, the invention relates to a material consisting of a PVDF in powder form, irradiated and grafted in powder form with an ionic liquid monomer comprising a proton conducting function and a polymerizable function.

[0037] According to another aspect, the invention relates to a proton exchange polymer electrolyte membrane, said membrane being obtained from said PVDF material.

[0038] According to various embodiments, the said material and membrane comprise the following characteristics, possibly combined. The contents indicated are expressed by weight, unless otherwise stated.

[0039] PVDF

[0040] The fluorinated polymer used in the invention, generically designated by the abbreviation PVDF, is a vinylidene difluoride-based polymer.

[0041] According to one embodiment, PVDF is a poly(vinylidene fluoride) homopolymer or a mixture of vinylidene fluoride homopolymers.

[0042] According to one embodiment, PVDF is a copolymer of vinylidene difluoride with at least one comonomer compatible with vinylidene difluoride.

[0043] The comonomers compatible with vinylidene difluoride can be halogenated (fluorinated, chlorinated or brominated) or non-halogenated.

[0044] Examples of suitable fluorinated comonomers are: vinyl fluoride, tetrafluoroethylene, hexafluoropropylene, trifluoropropenes and especially 3,3,3-trifluoropropene, tetrafluoropropenes and especially 2,3,3,3-tetrafluoropropene or 1,3,3,3-tetrafluoropropene, hexafluoroisobutylene, perfluorobutylethylene, pentafluoropropenes and especially 1,1,3,3,3-pentafluoropropene or 1,2,3,3,3-pentafluoropropene, perfluoroalkyl vinyl ethers and especially those of general formula Rf-O-CF-CF2, Rf being an alkyl group, preferably at Cl to C4 (preferred examples being perfluoropropyl vinyl ether and perfluoromethyl vinyl ether).

[0045] The fluorinated comonomer may contain a chlorine or bromine atom. In particular, it may be selected from bromotrifluoroethylene, chlorofluoroethylene, chlorotrifluoroethylene, and chlorotrifluoropropene. Chlorofluoroethylene may refer to either 1-chloro-1-fluoroethylene or 1-chloro-2-fluoroethylene. The 1-chloro-1-fluoroethylene isomer is preferred. Chlorotrifluoropropene is preferably 1-chloro-3,3,3-trifluoropropene or 2-chloro-3,3,3-trifluoropropene.

[0046] The VDF copolymer may also include non-halogenated monomers such as ethylene, and / or acrylic or methacrylic comonomers.

[0047] The fluorinated polymer preferably contains at least 50 mole percent vinylidene difluoride.

[0048] According to one embodiment, PVDF is a mixture of a homopolymer poly(vinylidene fluoride) and a copolymer of vinylidene difluoride with at least one comonomer compatible with vinylidene difluoride.

[0049] According to one embodiment, PVDF is a copolymer of vinylidene fluoride (VDF) and hexafluoropropylene (HFP) (P(VDF-HFP)), having a weight percentage of hexafluoropropylene monomer units of 1 to 35%, preferably 2 to 23%, preferably 4 to 20% by weight relative to the weight of the copolymer.

[0050] According to one embodiment, PVDF is a mixture of a homopolymer poly(vinylidene fluoride) and a VDF-HFP copolymer.

[0051] According to one embodiment, PVDF is a vinylidene fluoride homopolymer.

[0052] According to one embodiment, the VDF-HFP copolymer is a melt-processable heterogeneous thermoplastic copolymer, and comprises two or more co-continuous phases, said co-continuous phases comprising: a) 25 to 50% by weight of a first co-continuous phase comprising 90 to 100% by weight of vinylidene fluoride monomer units and 0 to 10% by weight of hexafluoropropylene units, and b) more than 50% by weight to 75% by weight of a second co-continuous phase comprising 65 to 95% by weight of vinylidene fluoride and hexafluoropropylene monomer units, to cause phase separation of the second co-continuous phase from the first continuous phase.

[0053] The heterogeneous copolymer contains two or more phases that form a cocontinuous structure in the solid state. The cocontinuous phases are distinct from one another and can be observed by scanning electron microscopy (SEM). The heterogeneous copolymers according to the invention differ from homogeneous copolymers, which comprise a single phase.

[0054] According to one embodiment, the PVDF has a co-continuous morphology, with a highly crystalline phase rich in VDF that can contain up to 10% HFP and an amorphous phase containing from 0% HFP to up to 35% HFP.

[0055] According to one embodiment, PVDF is a mixture of two or more VDF-HFP copolymers.

[0056] In one embodiment, PVDF comprises monomer units bearing at least one of the following functional groups: vinyl, carboxylic acid, carboxylic acid anhydride, carboxylic acid esters, epoxy groups (such as glycidyl), amide, hydroxyl, carbonyl, mercapto, sulfide, oxazoline, phenolic, ester, ether, siloxane, sulfonic, sulfuric, phosphoric, or phosphonic. The functional group is introduced by a chemical reaction, which may be grafting or copolymerization of the fluorinated monomer with a monomer bearing at least one of said polymerizable functional groups capable of copolymerizing with the fluorinated monomer, according to techniques well known to those skilled in the art.

[0057] According to one embodiment, the functional group carries a carboxylic acid function which is a (meth)acrylic acid type group selected from acrylic acid, methacrylic acid, hydroxy ethyl(meth)acrylate, hydroxypropyl(meth)acrylate and hydroxy ethylhexyl(meth)acrylate.

[0058] According to one embodiment, the units bearing the carboxylic acid function further comprise a heteroatom selected from oxygen, sulfur, nitrogen and phosphorus.

[0059] In one embodiment, the functionality is introduced via the transfer agent used in the synthesis process. The transfer agent is a polymer with a molar mass less than or equal to 20,000 g / mol and bearing functional groups selected from the following: carboxylic acid, carboxylic acid anhydride, carboxylic acid esters, epoxy groups (such as glycidyl), amide, hydroxyl, carbonyl, mercapto, sulfide, oxazoline, phenolic, ester, ether, siloxane, sulfonic, sulfuric, phosphoric, and phosphonic groups. An example of such a transfer agent is acrylic acid oligomers.

[0060] The functional group content of PVDF is at least 0.01 mol%, preferably at least 0.1 mol%, and at most 15 mol%, preferably at most 10 mol%.

[0061] The PVDF preferably has a high molecular weight. By high molecular weight, as used here, is meant a PVDF having a molten viscosity greater than 100 Pa·s, preferably greater than 500 Pa·s, more preferably greater than 1000 Pa·s, advantageously greater than 2000 Pa·s. The viscosity is measured at 232°C, at a shear rate of 100 s⁻¹. 1 using a capillary rheometer or a parallel plate rheometer, according to ASTM D3825. Both methods give similar results.

[0062] The homopolymer PVDFs and VDF copolymers used in the invention can be obtained by known polymerization methods such as emulsion polymerization or suspension polymerization.

[0063] According to one embodiment, they are prepared by an emulsion polymerization process in the absence of fluorinated surfactant.

[0064] The polymerization of PVDF results in a latex typically having a solids content of 10 to 60% by weight, preferably 10 to 50%, and a weight-average particle size of less than 1 micrometer, preferably less than 1000 nm, preferably less than 800 nm, and most preferably less than 600 nm. The weight-average particle size is generally at least 10 nm, preferably at least 50 nm, and advantageously in the range of 100 to 400 nm. The polymer particles may form agglomerates, called secondary particles, with a weight-average size of less than 5000 µm, preferably less than 1000 µm, advantageously in the range of 1 to 80 micrometers, and preferably in the range of 2 to 50 micrometers. The agglomerates may break down into discrete particles during formulation and application to a substrate.

[0065] In some embodiments, homopolymer PVDF and VDF copolymers are composed of bio-based VDF. The term "bio-based" means "derived from biomass." This improves the membrane's environmental footprint. Bio-based VDF can be characterized by a renewable carbon content—that is, carbon of natural origin from a biomaterial or biomass—of at least 1 atomic percent, as determined by the 14C content according to standard NF EN 16640. The term "renewable carbon" indicates that the carbon is of natural origin and comes from a biomaterial (or biomass), as described below.According to some embodiments, the bio-carbon content of VDF may be greater than 5%, preferably greater than 10%, preferably greater than 25%, preferably greater than or equal to 33%, preferably greater than 50%, preferably greater than or equal to 66%, preferably greater than 75%, preferably greater than 90%, preferably greater than 95%, preferably greater than 98%, preferably greater than 99%, advantageously equal to 100%.

[0066] In one embodiment, they are prepared by a suspension polymerization process, comprising a step of polymerizing VDF, alone or with at least one comonomer compatible with vinylidene difluoride, in the presence of water, a radical initiator, optionally a dispersing agent, and optionally a chain transfer agent. In the suspension process, the VDF and the optional comonomer(s) are loaded into a stirred reactor filled with deionized water, optionally a dispersing agent, and optionally a chain transfer agent. The reactor is then heated to the desired initiation temperature, which is maintained during polymerization. The initiator is then injected into the reactor to start polymerization. The consumption of the monomers leads to a pressure drop, which is compensated by a continuous supply of water. The reactor is then cooled and degassed.The product is discharged and collected as a suspension. This suspension is filtered, and the wet powder is washed and then dried.

[0067] A PVDF powder from synthesis is used as is or is melted using a single-screw, twin-screw co- or contra-rotating extruder, Buss co-mixer, or a desiccant extruder in order to obtain, via water cooling and depending on the type of cutting system, granules in lenticular or cylindrical form with a size of a few millimeters.

[0068] The resulting granules are then ground in a mill such as a hammer mill, knife mill, air jet mill, ball mill, or spherical mill. Grinding can be done at ambient temperature or under liquid nitrogen cooling, a process known as cryo-grinding.

[0069] The PVDF powder obtained from synthesis or by cryo-milling of the granules has a particle size defined by a Dv50 less than or equal to 200 pm, preferably between 10 and 150 micrometers.

[0070] The Dv50 referred to here is the median volume diameter, which corresponds to the particle size value that divides the examined particle population exactly in half. Dv50 is measured according to ISO 9276 - parts 1 to 6. In this description, a Malvern System INSITEC particle size analyzer is used, and the measurement is performed using a dry method by laser diffraction on the powder.

[0071] This powder has an apparent density greater than 0.3 g / ml, preferably between 0.4 and 1.2 g / ml, advantageously between 0.5 and 1.0 g / ml, which defines it as a dense powder.

[0072] To measure the apparent packed density, a known quantity of PVDF powder is placed in a precision graduated cylinder. The mass is weighed using a precision balance accurate to 0.1 g. The powder is then compacted in a STAV 2003 type compaction device capable of delivering 220 to 250 drops per minute. After 2500 compactions, the volume Vx is measured. The apparent density (ADD), or density, is then calculated as follows:

[0073] [Math 1] n

[0074] MVA compressed = — -

[0075] V x

[0076] Ionic liquid

[0077] The ionic liquid monomer comprising the material according to the invention consists solely of anions and organic cations. The ionic liquid monomer includes a proton-conducting function that can be located on either the anion or the cation. The ionic liquid can be formed by proton transfer from a Brønsted acid to a Brønsted base, thus enabling it to be proton-conducting. In this case, it is said to be protic. The ionic liquid monomer is suitable for grafting, as it contains a polymerizable function.

[0078] The polymerizable function can be located on the cation or on the anion, and preferably consists of a vinylic, styrenic, acrylic, methacrylic, acryloyl or methacryloyl function.

[0079] According to one embodiment, the cation also comprises a protic conduction group which is selected from the list: an imidazolium group, a pyridinium group, a pyrrolidinium group, a pyrimidium group, a piperidinium group, a benzimidazolium group, a triazinium group, a phosphonium group, an ammonium group, or a benzene group substituted with an acid such as boric acid, boronic acid, sulfuric acid, sulfonic acid, phosphoric acid, phosphonic acid, or carboxylic acid.

[0080] According to one embodiment, the anion of the ionic liquid monomer which is chosen from the list: PF6, Br, CL, I, NO3, CF3CO2, CH3COO, HSO4, H2PO4, SCN, N(CN)2, [N(SO2CF3)2]', [N(SO2F)2]', [NFCF3(SO2)2]L CéFisP-, and CF3SO3'.

[0081] According to one embodiment, the anion also includes a group enabling protic conduction which is chosen from the list: a sulfonate group, a phosphonate group, a carboxylic group or a sulfonyl imide group.

[0082] According to one embodiment, the ionic liquid monomer comprises a monomer having at least one imidazolium group.

[0083] According to one embodiment, the ionic liquid monomers are imidazolium salts having the general formula Formula I: [Chem 1]

[0084] Formula I in which: R is a hydrogen atom or a C1-C24 alkyl group comprising a protic conduction group, R' is a C2-C24 alkenyl group, and X is a monovalent anion.

[0085] According to one embodiment, the ionic liquid monomer is 1H-3-vinylimidazolium bis(trifluoromethanesulfonyl)imide.

[0086] PVDF material in powder form

[0087] According to a second aspect, the invention relates to a method for preparing said material, said method comprising the irradiation and grafting of a PVDF in powder form with an ionic liquid monomer having a proton-conducting function and a polymerizable function.

[0088] In one embodiment, the PVDF is first irradiated, and then the ionic liquid monomer is grafted onto the irradiated PVDF. The PVDF powder is first exposed to ionizing radiation to introduce active sites into the PVDF polymer chain. The powder is irradiated by an electron beam, gamma rays, or X-ray source at a dose between 25 and 150 kgrays, and preferably between 50 and 125 kgrays. Irradiation is carried out under vacuum, air, or nitrogen. This yields an irradiated PVDF powder.

[0089] The homopolymer or copolymer of VDF is semi-crystalline, exhibiting a Tg lower than the grafting temperature, between 20 and 160°C, and thus allowing better diffusion of monomers within the powder.

[0090] Advantageously, the use of a dense powder with a particle size between 30 and 200 pm having an apparent packed density greater than 0.3 g / ml promotes the diffusion of monomers within the powder and thus leads to molar grafting rates determined by NMR of between 5 and 150%, preferably between 10 and 100% and preferably between 15 and 60%.

[0091] The irradiated PVDF powder then undergoes a grafting step using an ionic liquid monomer.

[0092] Grafting involves polymerizing an ionic liquid monomer containing a polymerizable functional group using radicals created on the PVDF chain during irradiation. This allows for the addition of covalently grafted pendant chains to the main fluorinated chain. These grafted chains then support proton-conducting groups.

[0093] In one embodiment, the irradiated powder is placed in a bath at a temperature between 60°C and 80°C containing an ionic liquid monomer comprising a polymerizable function. The grafted powder is then purified, rinsed, and air-dried.

[0094] In another embodiment, the PVDF powder is irradiated in the presence of an ionic liquid monomer. The PVDF powder-ionic liquid monomer mixture is irradiated by an electron beam, gamma ray, or X-ray source at a dose between 25 and 150 kgrays. Irradiation is carried out under vacuum, air, or nitrogen. The grafted powder is then purified, rinsed, and air-dried.

[0095] The molar grafting rate thus obtained is greater than 3% and less than 150%, preferably between 5 and 100%, preferably between 10 and 60%.

[0096] Polymer electrolyte membrane

[0097] In another aspect, the invention relates to a method for manufacturing a proton exchange polymer electrolyte membrane from said irradiated and grafted PVDF material in powder form, said method comprising transforming the PVDF powder into a film that constitutes the membrane. This step of transforming the PVDF powder into a film is carried out by all techniques known to those skilled in the art: blow molding, flatbed extrusion, but also, for example, solvent film manufacturing.

[0098] According to one embodiment, the grafted PVDF powder can then be used as a binder for the manufacture of electrodes for the fuel cell and / or electrolyzer.

[0099] According to another aspect, the invention relates to a proton exchange polymer electrolyte membrane, said membrane consisting of a film obtained from said PVDF material.

[0100] In another aspect, the invention relates to a method for manufacturing a proton exchange polymer electrolyte membrane from a mixture of said irradiated and grafted PVDF material in powder form and another polymer selected from: polymethyl methacrylate and its copolymers, fluoropolymers, polyurethanes, and polyesters. This mixture comprises from 100% to 30% by mass of said irradiated and grafted PVDF in powder form. The method includes transforming the mixture into a film. This step of transforming the mixture into a film is carried out by all techniques known to those skilled in the art: blow molding, flatbed extrusion, and also, for example, solvent-based film manufacturing.

[0101] According to another aspect, the invention relates to a proton exchange polymer composite membrane, said membrane consisting of a porous support impregnated with said PVDF material by solvent and / or aqueous means, said porous support being a polymer selected from: polyethylene, polypropylene, polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), polysulfone (PSU), polyethersulfone (PESU), polyimide (PI), the polyaryletherketone (PAEK) family such as PEEK or PEKK. This porous support can be produced according to techniques known to those skilled in the art, such as phase inversion, extrusion followed by sequential stretching, meltblown or spunbond extrusion, and electrospinning.

[0102] According to another aspect, the invention relates to a proton exchange polymer composite membrane, said membrane being at least partially composed of fibers of said PVDF material, the remainder being one of the following polymers selected from: polymethyl methacrylate and its copolymers, fluoropolymers, polyurethanes, polyesters, polyethylene, polypropylene, polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), polysulfone (PSU), polyethersulfone (PESU), polyimide (PI), and the polyaryletherketone (PAEK) family such as PEEK or PEKK. This composite membrane is manufactured by electrospinning. This membrane is then impregnated with said PVDF material by solvent or aqueous means.

[0103] In membrane-electrode assemblies (MEA), this powder can be used as a binder between the catalyst, other additives such as electronic conductive agents, and the membrane.

[0104] According to another aspect, the invention relates to the applications of the proton exchange polymer electrolyte membrane to the following fields:

[0105] - fuel cells, for example, fuel cells operating with EE / air or H2 / O2 or operating with methanol / air;

[0106] - electrolyzers; According to one embodiment, the polymer electrolyte membrane is intended to be inserted into a fuel cell device within an electrode-membrane-electrode assembly.

[0107] These membranes are advantageously presented in the form of thin films, having, for example, a thickness of 10 to 200 micrometers.

[0108] To prepare such an assembly, the membrane can be placed between two electrodes. The assembly formed by the membrane positioned between the two electrodes is then pressed at a suitable temperature to obtain good electrode-membrane adhesion.

[0109] The electrode-membrane-electrode assembly is then placed between two plates that ensure electrical conduction and the supply of reactants to the electrodes. These plates are commonly referred to as bipolar plates.

[0110] EXAMPLES

[0111] The following examples illustrate the invention without limiting it.

[0112] Examples A and B according to the invention

[0113] A PVDF powder was irradiated and grafted according to two embodiments with an ionic liquid monomer having a polymerizable function and bearing ionic groups allowing proton conduction. This monomer is 1H-3-vinylimidazolium bis(trifluoromethanesulfonyl)imide [HVIM][TFSI].

[0114] The PVDF powder is a VDF-HFP copolymer that was in powder form at the synthesis output and then extruded through a co-rotating twin-screw extruder. The resulting lenticular granules were then ground in a cryo-hammer mill.

[0115] In Example A, according to a first embodiment, the PVDF powder is first irradiated, and then the ionic liquid monomer is grafted onto the irradiated PVDF. The PVDF powder was irradiated at 25 kgray under an electron beam and then stored at -30°C to preserve the radicals. The powder was then immersed in a [HVIM][TFSI] solution with a mass ratio of 20 / 80 PVDF / [HVIM][TFSI] at 60°C for 6 hours.

[0116] In Example B, according to a second embodiment, the PVDF powder and the ionic liquid monomer are irradiated simultaneously. The PVDF powder is first impregnated with [HVIM][TFSI] at a mass ratio of 20 / 80 PVDF / [HVIM][TFSI] and then irradiated at 25 kgray under an electron beam. The [HVIM][TFSI]-grafted PVDF powders were washed with ethanol to remove residual ionic liquid monomer and the poly([HVIM][TFSI]) homopolymer not grafted onto the PVDF chain.

[0117] The molar grafting rate is the molar amount of [HVIM][TFSI] in [HVIM][TFSI] grafted PVDF powders as measured by proton NMR.

[0118] Counter-example C

[0119] In the same embodiment as in Example A, a PVDF powder was mixed with a proton-conducting ionic liquid lacking a polymerizable function. This ionic liquid is [EIM][TFSI] and was incorporated at 60% into the PVDF matrix. As in the previous examples, a membrane was then prepared from this mixture.

[0120] Counter-example D

[0121] A PVDF powder was mixed with an ionic liquid containing a polymerizable but non-proton-conducting function. This ionic liquid monomer is l-vinyl-3-ethylimidazole tetrafluoroborate [VEIM][BF4]. The PVDF powder was first irradiated, and then the ionic liquid monomer was grafted onto the irradiated PVDF. The PVDF powder was irradiated at 25 kg-rays under an electron beam and then stored at -30°C to preserve the radicals. The powder was then immersed in a solution of l-vinyl-3-ethylimidazole tetrafluoroborate with a mass ratio of 20 / 80 PVDF / [VEIM][BF4] at 60°C for 6 hours.

[0122] The grafted PVDF powder was washed with ethanol to remove residual ionic liquid monomer and non-grafted ionic liquid homopolymer on the PVDF chain.

[0123] The molar grafting rate is the molar amount of ionic liquid in grafted PVDF powders measured by proton NMR.

[0124] For all examples, the exudation of ionic liquids (% exudation) is measured by the difference in mass before and after immersion in water at 80°C for 7 days according to the following formula:

[0125] In this case, minitiaie is the initial mass of the membrane, mf maie is the mass of the membrane after immersion in hot water, and minitiaie LI is the mass of ionic liquid incorporated into the membrane, obtained by subtracting the initial mass of PVDF powder from the mass of the powder after grafting and purification. For all examples, proton conductivity is measured in the plane. The sample is 1 cm wide and is placed in a Bekketch BT-121x cell so that the distance between the two electrodes is 20 mm. The cell containing the sample is then placed in a chamber that allows it to be heated to 140°C under dry conditions. The cell is connected to an LCR-type impedance meter to measure the proton resistance of the sample.

[0126] The conductivity (δ) in the plane is then calculated according to the following formula:

[0127] [Math 2] where R is the ohmic resistance of the sample. The initial conductivity is measured without immersion in water. The conductivity after aging is measured after immersing the membrane in water at 80°C for 7 days and conditioning it in the chamber.

[0128] The results obtained are illustrated in Table 1.

[0129] Table 1

Claims

DEMANDS 1. Material consisting of a PVDF in powder form, irradiated and grafted in powder form with an ionic liquid monomer, said ionic liquid monomer having a proton-conducting function and a polymerizable function.

2. Material according to claim 1, wherein the PVDF is selected from poly(vinylidene fluoride) homopolymers and copolymers of vinylidene difluoride with at least one comonomer selected from the list: vinyl fluoride, tetrafluoroethylene, hexafluoropropylene, 3,3,3-trifluoropropene, 2,3,3,3-tetrafluoropropene, 1,3,3,3-tetrafluoropropene, hexafluoroisobutylene, perfluorobutylethylene, 1,1,3,3,3-pentafluoropropene, 1,2,3,3,3-pentafluoropropene, perfluoropropyl vinyl ether, perfluoromethyl vinyl ether, bromotrifluoroethylene, chlorofluoroethylene, chlorotrifluoroethylene, chlorotrifluoropropene, ethylene, and mixtures thereof.

3. Material according to claim 1 or 2, wherein PVDF is a vinylidene fluoride homopolymer.

4. Material according to any one of claims 1 or 2, wherein PVDF is a copolymer of vinylidene fluoride and hexafluoropropylene, having a weight percentage of hexafluoropropylene monomer units of 1 to 35%, preferably 2 to 23%, preferably 4 to 20% by weight relative to the weight of the copolymer.

5. Material according to claim 1 or 2, wherein PVDF is a heterogeneous thermoplastic copolymer, and comprises two or more co-continuous phases, said co-continuous phases comprising: a) 25 to 50% by weight of a first co-continuous phase comprising 90 to 100% by weight of vinylidene fluoride monomer units and 0 to 10% by weight of hexafluoropropylene units, and b) more than 50% by weight to 75% by weight of a second co-continuous phase comprising 65 to 95% by weight of vinylidene fluoride and hexafluoropropylene monomer units, to cause the phase separation of the second co-continuous phase from the first continuous phase.

6. Material according to any one of claims 1 to 5, wherein the molar grafting rate of the ionic liquid in the grafted PVDF powder is greater than 3% and less than 150%, preferably between 5 and 100%, preferably between 10 and 60%.

7. Material according to any one of claims 1 to 6, wherein the PVDF powder is formed of particles having a volume mean diameter (Dv50) less than or equal to 200 pm, preferably between 30 and 150 micrometers.

8. Material according to any one of claims 1 to 7, wherein said polymerizable function of the ionic liquid monomer is located on the cation thereof, and is constituted of a vinylic, styrenic, acrylic, methacrylic, acryloyl or methacryloyl function.

9. Material according to any one of claims 1 to 7, wherein said polymerizable function of the ionic liquid monomer is located on the anion thereof, and is constituted of a vinyl, styrenic, acrylic, methacrylic, acryloyl or methacryloyl function.

10. Material according to any one of claims 1 to 9, wherein the cation of the ionic liquid monomer also comprises a protic conduction group which is selected from the list: an imidazolium group, a pyridinium group, a pyrrolidinium group, a pyrimidium group, a piperidinium group, a benzimidazolium group, a triazinium group, a phosphonium group, an ammonium group, or a benzene group substituted with an acid such as boric acid, boronic acid, sulfuric acid, sulfonic acid, phosphoric acid, phosphonic acid, or carboxylic acid.

11. Material according to any one of claims 1 to 8 and 10, wherein the anion of the ionic liquid monomer is selected from the list: PFÔ, Br, CD, I", NO3, CF3CO2, CH3COO, HSO4, H2PO4, SCN", N(CN)2, [N(SO2CF3)2]-, [N(SO2F)2], [NFCF3(SO2)2]", C6FI8P-, and CF3SO3.

12. Material according to any one of claims 1 to 7 and 9, wherein the anion also comprises a protic conduction group which is selected from the list: a sulfonate group, a phosphonate group, a carboxylic group or a sulfonyl imide group.

13. Material according to any one of claims 1 to 8, 10 and 11, wherein the ionic liquid monomers are imidazolium salts having the general formula Formula I: [Chem 2] Formula I in which: R is a hydrogen atom or a C1-C24 alkyl group comprising a protic conduction group, R' is a C2-C24 alkenyl group, and X is a monovalent anion.

14. A method for preparing the material according to any one of claims 1 to 13, said method comprising irradiation and grafting of a PVDF in powder form with an ionic liquid monomer having a proton-conducting function and a polymerizable function.

15. A method according to claim 14, wherein the PVDF powder and the ionic liquid monomer are irradiated at the same time.

16. A method according to claim 14, wherein the PVDF powder is first irradiated, and then the ionic liquid monomer is grafted onto the irradiated PVDF.

17. A method according to any one of claims 14 to 16, wherein the irradiation is carried out by means of ionizing radiation selected from electron beams, gamma rays, or X-rays.

18. A method for manufacturing a proton exchange polymer electrolyte membrane from PVDF material according to any one of claims 1 to 13, said method comprising transforming grafted PVDF powder into film form.

19. Method of manufacturing a proton exchange polymer electrolyte membrane from a mixture of the PVDF material according to any one of claims 1 to 13, and another polymer selected from: polymethyl methacrylate and its copolymers, fluorinated polymers, polyurethanes and polyesters, said method comprising transforming said mixture into film form.

20. Proton exchange polymer electrolyte membrane, said membrane consisting of a film obtained from the PVDF material according to any one of claims 1 to 13.

21. Proton exchange polymer composite membrane, said membrane consisting of a porous support impregnated with PVDF material according to any one of claims 1 to 13 by solvent and / or aqueous means, said porous support being a polymer selected from: polyethylene, polypropylene, polytetrafluoroethylene (PTFE), poly(vinylidene fluoride) (PVDF), polysulfone (PSU), polyethersulfone (PESU), polyimide (PI), and polyaryletherketones (PAEK).

22. Proton exchange polymer composite membrane, said membrane being at least partly made up of fibers of the PVDF material according to any one of claims 1 to 13, the remainder being one of the polymers selected from: polymethyl methacrylate and its copolymers, fluorinated polymers, polyurethanes, polyesters, polyethylene, polypropylene, polytetrafluoroethylene (PTFE), poly(vinylidene fluoride) (PVDF), polysulfone (PSU), polyethersulfone (PESU), polyimide (PI), and polyaryletherketones (PAEK), said electrospinning membrane being subsequently impregnated with said PVDF material by solvent or aqueous means.

23. Fuel cell comprising a membrane as defined in any one of claims 20 to 22.

24. Electrolyzer comprising a membrane as defined in any one of claims 20 to 22.

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