PVDF POWDER-BASED PROTON EXCHANGE MEMBRANE PHOSPHONE

Abstract

The present invention relates to a proton exchange membrane based on PVDF in powder form, said PVDF being irradiated, grafted, and phosphonated; the process for preparing said membrane; and the application of said membrane in fields requiring ion exchange, such as electrochemistry or energy. In particular, this membrane is used in the design of fuel cell membranes, such as proton-conducting membranes for fuel cells operating with H2 / 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").

Description

Title of the invention: PVDF POWDER-BASED PROTON EXCHANGE MEMBRANE PHOSPHONE FIELD OF INVENTION

[0001] The present invention relates to a proton exchange membrane based on PVDF in powder form, said PVDF being irradiated, grafted, and phosphonated, the process for preparing said membrane, and the application of said membrane in fields requiring ion exchange, such as electrochemistry or energy. In particular, this membrane is used in the design of fuel cell membranes, such as proton-conducting membranes for fuel cells operating with H2 / 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"). TECHNICAL BACKGROUND

[0002] A fuel cell is an electrochemical generator that converts the chemical energy of a fuel oxidation reaction in the presence of an oxidant into electrical energy, heat, and water. Generally, a fuel cell comprises a plurality of electrochemical cells connected in series, each cell including two electrodes of opposite polarity separated by a proton exchange membrane acting as a solid electrolyte. The membrane allows the passage of protons formed during the oxidation of the fuel at the anode to the cathode.

[0003] The membranes form the core of the fuel cell and must therefore exhibit good proton conduction performance, as well as low permeability to reactant gases (H2 / air or H2 / O2 for PEMFC fuel cells and methanol / air for DMFC fuel cells). The properties of the materials constituting the membranes are essentially thermal stability, resistance to hydrolysis and oxidation, and a certain degree of mechanical flexibility.

[0004] Proton exchange membranes are mostly 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.

[0005] Phosphoric acid-doped polybenzimidazole (PBI) type membrane systems show improved conductivities at higher temperatures (140°C - 170°C), which leads to a better yield due to improved catalytic efficiency. This is counteracted by catalyst poisoning at the cathode, due to the migration of free phosphoric acid to the cathode.

[0006] Immobilizing phosphoric acid allows the battery to be used at higher temperatures, while preventing phosphoric acid poisoning of the cathode. To this end, phosphoric acid was grafted onto a polypentafluorostyrene base in documents DE 102011015212 and EP 4111517. The membranes thus obtained exhibit very good conductivity, but do not exhibit good dimensional stability, due to the low mechanical strength of the styrenic-type systems of poly(pentafluorostyrene), whether cross-linked or not.

[0007] There is a real need for proton exchange membranes with improved properties, including very good mechanical strength and good dimensional stability, as well as good conductivity at temperatures up to 160°C. Summary of the invention

[0008] To meet the aforementioned needs, the inventors have developed a membrane with a very particular morphology obtained from a vinylidene fluoride (PVDF) based polymer in the form of irradiated PVDF powder.

[0009] According to a first aspect, the invention relates to a material consisting of an irradiated PVDF, in powder form, the apparent packed density of said powder being greater than 0.3 g / ml, said irradiated PVDF being grafted with at least one vinyl monomer, then phosphonated, said irradiated and grafted PVDF bearing proton exchange phosphonate groups.

[0010] According to one embodiment, said at least one vinyl monomer is a halogenated vinyl monomer, with a structure of formula I:

[0011] [Chem.l] Formula I

[0012] where:

[0013] • XI, X3 and X4 independently representing an H, a fluorine, a -CF3, a -CH3 or a chlorine;

[0014] • X2 representing a linear, branched or cyclic alkyl chain comprising between 0 and 6 carbons, partially or completely halogenated, a ketone, an ester or an ether;

[0015] • Y1, Y2, Y3, Y4 and Y5 represent a halogen of the fluorine, bromine, iodine or type chlorine, hydrogen, carbonyl, methyl or an alkane chain containing 1 to 4 carbons.

[0016] According to one embodiment, said halogenated vinyl monomer is chosen from: pentafluorostyrene, pentachlorostyrene, pentabromostyrene, alpha-methyl-2,3,4,5,6-pentafluorostyrene, allylpentafluorobenzene, pentafluorophenyl acrylate, 2-fluorostyrene, 3-fluorostyrene, 4-fluorostyrene, 2-chlorostyrene, 3-chlorostyrene, 4-chlorostyrene, 2-bromostyrene, 3-bromostyrene, 4-bromostyrene, 2-iodostyrene, 3-iodostyrene, 4-iodostyrene, l,2,3,4,5-pentaiodo-6-(l-methylethenyl)benzene, 1-fluoro-4-( 1 -methylethenyl)benzene 1 -bromo-4-( 1 -methylethenyl)benzene 1 -chloro-4-( 1 -methylethenyl)benzene, l-iodo-4-(l-methylethenyl)benzene.

[0017] According to one embodiment, said at least one vinyl monomer is a mixture of a halogenated vinyl monomer, with a nitrilic vinyl monomer.

[0018] According to one embodiment, said nitrilic vinyl monomer is selected from the group: acrylonitrile, 2-methyl-2-butenenitrile, 2-methylene glutaronitrile and methylacrylonitrile.

[0019] The PVDF powder has a particle size having a Dv50 between 30 and 200 pm.

[0020] Said 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, chloro-trifluoroethylene, chlorotrifluoropropene, ethylene, and mixtures thereof.

[0021] According to a second aspect, the invention relates to a method for preparing said material, said method comprising grafting an irradiated PVDF powder with at least one halogenated vinyl monomer, followed by post-treatment of the PVDF powder thus irradiated and grafted, by phosphonation.

[0022] According to a third aspect, the invention relates to a proton exchange polymer electrolyte membrane, said membrane consisting of a film obtained from said PVDF material.

[0023] According to a fourth aspect, the invention relates to a method for manufacturing the proton exchange polymer electrolyte membrane from said irradiated, grafted and phosphonated PVDF material in powder form, said method comprising transforming the PVDF powder into film form.

[0024] 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.

[0025] 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.

[0026] According to another aspect, the invention relates to the applications of the proton exchange polymer electrolyte membrane to the following fields:

[0027] - fuel cells, for example, fuel cells operating with H2 / air or H2 / O2 or running on methanol / air;

[0028] - electrolyzers;

[0029] - lithium batteries, said membranes being able to form part of the constitution of electrolytes.

[0030] The present invention overcomes the drawbacks of the prior art. More particularly, it provides a technology for manufacturing a membrane with very good mechanical strength and dimensional stability, thanks to the PVDF base, and good high-temperature conductivity, namely temperatures up to 160°C, without cathode poisoning, thanks to the good immobilization of the phosphonate groups due to the fact that the phosphonate grafts are chemically bonded to the PVDF.

[0031] Advantageously, the use of a dense powder with a particle size between 30 and or 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 mass grafting rates, determined by NMR, between 5 and 150%, preferably between 10 and 100% and advantageously between 15 and 70%.

[0032] The powder can then be phosphonated to contain proton-exchange phosphonate groups, enabling conductivity at temperatures above 80°C. It can also be used as a binder or membrane after processing, or in both forms for the manufacture of a membrane-electrode assembly, with very good compatibility between the binder and the membrane, and therefore improved efficiency.

[0033] Due to the use of a phosphonated grafted powder, it is also possible to manipulate the morphology of the membrane via transformation techniques conventional film powders, known to those skilled in the art. This allows for a wide variability in properties, particularly proton conductivity / hydrogen permeability ratios, on demand according to application needs.

[0034] DESCRIPTION OF EMBODIMENT METHODS OF 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 an irradiated PVDF, in powder form, the apparent packed density of said powder being greater than 0.3 g / ml, said irradiated PVDF being grafted with at least one vinyl monomer and then phosphonated, said irradiated and grafted PVDF bearing proton exchange phosphonate groups.

[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, said material and said membrane comprise the following characteristics, possibly combined. The contents indicated are expressed by weight, unless otherwise stated. PVDF

[0039] The fluorinated polymer used in the invention, generically designated by the abbreviation PVDF, is a vinylidene difluoride-based polymer.

[0040] According to one embodiment, PVDF is a poly(vinylidene fluoride) homopolymer or a mixture of vinylidene fluoride homopolymers. The term "VDF homopolymer" includes PVDF homopolymers comprising up to 1% by weight of one of the comonomers listed below.

[0041] According to one embodiment, PVDF is a homopolymer poly(vinylidene fluoride) or a copolymer of vinylidene difluoride with at least one comonomer compatible with vinylidene difluoride.

[0042] The comonomers compatible with vinylidene difluoride can be halogenated (fluorinated, chlorinated or brominated) or non-halogenated.

[0043] Examples of suitable fluorinated comonomers are: vinyl fluoride, tetrafluoroethylene, hexafluoropropylene, trifluoropropenes and in particular 3,3,3-trifluoropropene, tetrafluoropropenes and in particular 2,3,3,3-tetrafluoropropene or 1,3,3,3-tetrafluoropropene, hexafluoroisobutylene, perfluorobutylethylene, pentafluoropropenes and in particular 1,1,3,3,3-pentafluoropropene or 1,2,3,3,3-pentafluoropropene, perfluoroalkyl vinyl ethers and in particular 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 1 vinyl ether).

[0044] 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.

[0045] The VDF copolymer may also include non-halogenated monomers such as ethylene, and / or acrylic or methacrylic comonomers.

[0046] The fluorinated polymer preferably contains at least 50 mole percent vinylidene difluoride.

[0047] 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.

[0048] According to one embodiment, PVDF is a mixture of a homopolymer poly(vinylidene fluoride) and a VDF-HFP copolymer.

[0049] According to one embodiment, PVDF is a vinylidene fluoride homopolymer.

[0050] According to one embodiment, the vinylidene fluoride copolymer of the invention is a melt-processable heterogeneous thermoplastic copolymer, and comprises two or more co-continuous phases, said co-continuous phases comprising:

[0051] a) 25 to 50% by weight of a first co-continuous phase comprising 90 to 100% by weight of vinylidene fluoride monomer motifs and 0 to 10% by weight of motifs of at least one other fluorinated monomer, and

[0052] b) from more than 50% by weight to 75% by weight of a second co-continuous phase comprising from 65 to 95% by weight of vinylidene fluoride monomer units and one or more co-monomers selected from the group consisting of hexafluoropropylene and perfluorovinyl ether to cause phase separation of the second co-continuous phase from the first continuous phase.

[0053] Said heterogeneous copolymer contains two or more phases that produce a co-continuous structure in the solid state. The co-continuous 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, PVDF is a mixture of two or more VDF-HFP copolymers.

[0055] According to one embodiment, the PVDF comprises monomeric units bearing at least one of the following functional groups: 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 functional groups and a vinyl function capable of copolymerizing with the fluorinated monomer, according to techniques well known to those skilled in the art.

[0056] 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, hydroxyethyl(meth)acrylate, hydroxypropyl(meth)acrylate and hydroxyethylhexyl(meth)acrylate.

[0057] According to one embodiment, the units bearing the carboxylic acid function further comprise a heteroatom selected from oxygen, sulfur, nitrogen and phosphorus.

[0058] According to one embodiment, the functionality is introduced via the transfer agent used during 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 among 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.

[0059] 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%.

[0060] 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 using a capillary rheometer or a parallel-plate rheometer, according to ASTM D3825. Both methods give similar results.

[0061] The homopolymer PVDFs and VDF copolymers used in the invention can be obtained by known polymerization methods such as emulsion polymerization, or suspension polymerization.

[0062] According to one embodiment, they are prepared by an emulsion polymerization process in the absence of a fluorinated surfactant.

[0063] The polymerization of PVDF results in a latex generally having a solids content of 10 to 60% by weight, preferably 10 to 50%, and having a weight-average particle size of less than 1 micrometer, preferably less than 800 nm, and more preferably less than 600 nm. The weight-average particle size is generally at least 10 nm, preferably at least 50 nm, and advantageously the average size is 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 between 1 and 80 micrometers, and preferably between 2 and 50 micrometers. The agglomerates may break down into discrete particles during formulation and application to a substrate.

[0064] In certain 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, i.e., 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 certain 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%.

[0065] Emulsion polymerization allows the manufacture of latex particles of approximately 200 nm, which after drying, for example by spraying, leads to obtaining particles having a volume average diameter (Dv50) ranging from 10 to 50 µm.

[0066] According to 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 brought to the initiation temperature. The desired temperature is maintained during polymerization. The initiator is then injected into the reactor to start polymerization. Monomer consumption leads to a pressure drop, which is compensated for 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 such or is melted by means of a single screw extruder, twin screw co or contra rotating, Buss co-mixer, or a dehydrating extruder in order to obtain, via water cooling and depending on the type of cutting system, granules in lenticular or cylindrical form having a size of a few millimeters.

[0068] The granules thus obtained are then ground in a hammer mill, knife mill, air jet mill, ball mill or spherical mill. The grinding can be carried out at ambient temperature or under liquid nitrogen cooling, known as cryo-grinding.

[0069] The PVDF powder obtained at the end of 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 30 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. The 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 introduced into 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 apparatus 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.l] MVA WA ™ —-- V PVDF material in powder form

[0074] The material according to the invention consists of a PVDF in the form of irradiated powder, onto which is grafted at least one vinyl monomer, said irradiated and grafted PVDF bearing proton exchange phosphonate groups.

[0075] According to one embodiment, said at least one vinyl monomer is a vinyl monomer comprising halogenated aromatic groups.

[0076] According to one embodiment, the material according to the invention consists of a PVDF in the form of irradiated powder, onto which pentafluorostyrene is grafted, said irradiated and grafted PVDF bearing proton exchange phosphonate groups.

[0077] According to one embodiment, said at least one vinyl monomer is a mixture of a halogenated vinyl monomer, such as pentafluorostyrene, with a nitrilic vinyl monomer, such as methylene glutaronitrile.

[0078] According to one embodiment, the material according to the invention consists of a PVDF in the form of irradiated powder, onto which is grafted the halogenated vinyl monomer and methylene glutaronitrile, said irradiated and grafted PVDF bearing proton exchange phosphonate groups.

[0079] This material is prepared according to a process which includes grafting an irradiated PVDF with at least one halogenated vinyl monomer, or with a mixture of halogenated vinyl monomer and nitrillic vinyl monomer, followed by post-treatment of the PVDF powder thus irradiated and grafted, by phosphonation.

[0080] Each step of this process is detailed below.

[0081] According to one embodiment, the PVDF powder defined above is first exposed to ionizing radiation to introduce active sites into the PVDF polymer chain. The powder is irradiated by an electron beam, gamma ray, or X-ray source at a dose of between 25 and 150 kgrays, and preferably between 30 and 125 kgrays. The irradiation is carried out under vacuum, air, or nitrogen. This yields an irradiated PVDF powder.

[0082] PVDF is a semi-crystalline homopolymer with a Tg lower than the grafting temperature (between 20 and 160°C), thus allowing better diffusion of monomers within the powder.

[0083] PVDF-HFP also exhibits lower Tg at the grafting temperature and amorphous zones, due to the presence of HFP groups, thus allowing better diffusion of monomers within the powder.

[0084] Grafting consists of diffusing a halogenated vinyl monomer, such as pentafluorostyrene, within the PVDF, and then polymerizing it, with or without a nitrilic vinyl comonomer, from the radicals created on the PVDF chain during irradiation, thus allowing the addition of pendant chains covalently grafted onto the main fluorinated chain.

[0085] Nuclear magnetic resonance (NMR) measurements, via calculation based on the ratio between a specific peak of the aromatic group and / or a specific peak of the nitrile group relative to a reference peak of the PVDF, show a mass rate of grafting of the PVDF between 10 and 100%.

[0086] According to one embodiment, when a mixture of halogenated vinyl and nitrillic vinyl monomers is used for grafting PVDF, the molar ratio of halogenated monomer to nitrillic monomer in the material varies from 0.7 to 1.3.

[0087] According to one embodiment, the irradiated PVDF powder is passed through a bath containing between 50 and 100% pentafluorostyrene and between 0 and 50% 2-methylene glutaronitrile for 1 to 48 hours.

[0088] According to one embodiment, grafting pentafluorostyrene (PFS) onto irradiated PVDF powder leads to obtaining a PFS-grafted PVDF.

[0089] The grafted chains then support proton exchange groups via a nucleophilic SN1-type substitution reaction of tris(trimethylsilyl) phosphite (TSP) on the halogenated aromatic groups of the halogenated vinyl monomers. The TSP grafted onto the aromatic is then hydrolyzed to phosphonyl acid by immersion in water for 16 hours under reflux.

[0090] According to one embodiment, phosphonation is carried out by adding a phosphonation agent such as tris(trimethylsilyl) phosphite to the PVDF-grafted PFS.

[0091] According to one embodiment, the process for preparing the material according to the invention comprises the following steps:

[0092] - exposing said PVDF powder to ionizing radiation selected from the electron beams, gamma rays, or X-rays;

[0093] - expose the irradiated powder to at least one halogenated vinyl monomer, or with a mixture of halogenated vinyl monomer and nitrilic vinyl monomer, said halogenated vinyl monomer having the aforementioned formula I; said nitrilic vinyl monomer being selected from the group: acrylonitrile, 2-methyl-2-butenenitrile, 2-methylene glutaronitrile and methylacrylonitrile;

[0094] - subject the grafted PVDF powder to a post-functionalization reaction with a phosphonation agent such as tris(trimethylsilyl) phosphite, followed by hydrolysis in water.

[0095] According to one embodiment, the material according to the invention consists of a PVDF irradiated and grafted with a halogenated vinyl monomer and phosphonated with tris(trimethylsilyl) phosphite.

[0096] According to one embodiment, the material according to the invention consists of a PVDF irradiated and grafted with a mixture of pentafluorostyrene and 2-methylene glutaronitrile, then phosphonated with tris(trimethylsilyl) phosphite.

[0097] According to one embodiment, the PFS-grafted PVDF is dissolved under heat in the presence of the phosphonating agent, optionally with the addition of another solvent or a combination of different solvents, at temperatures between 40 and 200°C. The reaction mixture is heated for between 30 minutes and 12 hours and then cooled, after which the excess phosphonating agent is removed by washing. The phosphonated polymer is then immersed in refluxing water to obtain a proton-conducting phosphonyl group. The powder is then isolated by centrifugation and subsequently dried.

[0098] The phosphonated grafted PVDF powder exhibits good conductivity at temperatures above 80°C. Polymer electrolyte membrane

[0099] According to another aspect, the invention relates to a method for manufacturing the proton exchange polymer electrolyte membrane from said irradiated, grafted, and functionalized 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, or even solvent-based film production or impregnation of a woven or non-woven substrate.

[0100] 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.

[0101] According to another aspect, the invention relates to a method for manufacturing a proton exchange polymer electrolyte membrane from a mixture of said irradiated, grafted, and phosphonated 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 50% by mass of said irradiated, grafted, and functionalized 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 film manufacturing.

[0102] 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: polymethyl methacrylate and its copolymers, polyethylene, polypropylene, polytetrafluoroethylene (PTFE), fluoropolymers, polyurethanes, polyesters, poly(vinylidene fluoride) (PVDF), polysulfone (PSU), polyethersulfone (PESU), polyimide (PI), the family of Polyaryletherketones (PAEK) such as PEEK or PEKK. This porous support can be produced using techniques known to those skilled in the art such as phase inversion, extrusion followed by sequenced drawing, meltblown or spunbond extrusion, electrospinning.

[0103] Dynamic mechanics analysis (DMA) between -40°C and 230°C shows that the membrane has a thermal resistance greater than 140°C. Its elongation at break, measured at 23°C under 50% relative humidity at a speed of 10 mm / minute, for a film thickness of 20 pm, is greater than 100%.

[0104] In membrane-electrode assemblies (MEA), this powder can be used as a binder between the catalyst, other electronically conductive agent type additives and the membrane.

[0105] According to another aspect, the phosphonated grafted PVDF powder can serve as a binder for the manufacture of electrodes for fuel cells and / or electrolyzers.

[0106] According to another aspect, the phosphonated grafted PVDF powder can be transformed into a membrane for use as such in fuel cells.

[0107] It is also possible to combine the use of phosphonated grafted powder in the form of a membrane and binder for the production of an MEA with improved efficiency due to the high compatibility between the binder and the membrane.

[0108] According to another aspect, the invention relates to the applications of the proton exchange polymer electrolyte membrane to the following fields:

[0109] - fuel cells, for example, fuel cells operating with H2 / air or H2 / O2 or running on methanol / air;

[0110] - electrolyzers;

[0111] - lithium batteries, said membranes being able to form part of the constitution of electrolytes.

[0112] According to one embodiment, the electrolyte polymer membrane is intended to be inserted into a fuel cell device within an electrode-membrane-electrode assembly.

[0113] These membranes are advantageously in the form of thin films, having, for example, a thickness of 10 to 200 micrometers.

[0114] 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.

[0115] The electrode-membrane-electrode assembly is then placed between two plates ensuring electrical conduction and the supply of reactants to the electrodes. These plates are commonly referred to as bipolar plates.

Claims

1.

2. Demands Material consisting of an irradiated PVDF, in powder form, onto which is grafted at least one vinyl monomer, the apparent packed density of said powder being greater than 0.3 g / ml, preferably between 0.4 and 1.2 g / ml, said irradiated PVDF being grafted with at least one vinyl monomer, then phosphonated, said irradiated and grafted PVDF bearing proton exchange phosphonate groups. Material according to claim 1, wherein said vinyl monomer is a halogenated vinyl monomer having a structure of formula I: [Chem.2]

3. Formula I Or : • XI, X3 and X4 independently represent H, fluorine, -CF3, -CH3 or chlorine; ; • X2 representing a linear, branched or cyclic alkyl chain comprising between 0 and 6 carbons, partially or completely halogenated, a ketone, an ester or an ether; •Y1,Y2,Y3,Y4 andY5 represent a halogen of the type fluorine, bromine, iodine or chlorine, a hydrogen, a carbonyl, a methyl or an alkane chain containing 1 to 4 carbons. Material according to claim 1 or 2, wherein said vinyl monomer is selected from: pentafluorostyrene, pentachlorostyrene, pentabromostyrene, alpha-methyl-2,3,4,5,6-pentafluorostyrene, allylpentafluorobenzene, pentafluorophenyl acrylate, 2-fluorostyrene, 3-fluorostyrene, 4-fluorostyrene, 2-chlorostyrene, 3-chlorostyrene, 4-chlorostyrene, 2-bromostyrene, 3-bromostyrene, 4-bromostyrene, 2-iodostyrene, 3-iodostyrene, 4-iodostyrene, l,2,3,4,5-pentaiodo-6-(l-methylethenyl)benzene, l-fluoro-4-(l-methylethenyl)benzene l-bromo-4-(l-methylethenyl)benzene l-chloro-4-(l-methylethenyl)benzene, 1-iodo-4-(1-methylethenyl)benzene.

4. Material according to claim 1, wherein said vinyl monomer is a halogenated vinyl monomer subsequently phosphonated by nucleophilic substitution.

5. Material according to any one of claims 1 to 4, wherein said at least vinyl monomer is a mixture of a halogenated vinyl monomer, with a nitrilic vinyl monomer.

6. Material according to claim 5, wherein said nitrilic vinyl monomer is selected from the group: acrylonitrile, 2-methyl-2-butenenitrile, 2-methylene glutaronitrile and methylacrylonitrile.

7. Material according to any one of claims 1 to 6, 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.

8. Material according to any one of claims 1 to 7, wherein PVDF is a vinylidene fluoride homopolymer.

9. Material according to any one of claims 1 to 7, 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.

10. A material according to any one of claims 1 to 7, 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 units of at least one other fluorinated monomer, 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 monomer units and one or more co-monomers selected from the group consisting of hexafluoropropylene and perfluorovinyl ether to cause phase separation of the second co-continuous phase from the first continuous phase.

11. Material according to any one of claims 1 to 10, wherein said powder is derived from ground PVDF granules having a particle size defined by a Dv50 less than or equal to 200 pm, preferably between 30 and 150 micrometers.

12. Material according to any one of claims 1 to 11, wherein said PVDF is grafted with pentafluorostyrene and 2-methylene glutaronitrile, and is functionalized with tris(trimethylsilyl) phosphite.

13. A method for preparing the material according to any one of claims 1 to 12, said method comprising grafting an irradiated PVDF with at least one halogenated vinyl monomer, or with a mixture of halogenated vinyl monomer and nitrillic vinyl monomer, followed by post-treatment of the PVDF powder thus irradiated and grafted, by phosphonation.

14. A process according to claim 13, comprising the following steps: - exposing said PVDF powder to ionizing radiation selected from electron beams, gamma rays, or X-rays; - exposing the irradiated powder to at least one halogenated vinyl monomer, or to a mixture of halogenated vinyl monomer and nitrillic vinyl monomer, said halogenated vinyl monomer having the structure of formula I; said nitrillic vinyl monomer being selected from the group: acrylonitrile, 2-methyl-2-butenenitrile, 2-methylene glutaronitrile and methylacrylonitrile; - subjecting the grafted PVDF powder to a post-functionalization reaction with a phosphonation agent such as tris(trimethylsilyl) phosphite, followed by hydrolysis in water.

15. A method for manufacturing a proton exchange polymer electrolyte membrane from PVDF material according to one any of claims 1 to 12, said process comprising the transformation of PVDF powder into film form.

16. A method for manufacturing a proton exchange polymer electrolyte membrane from a mixture of the PVDF material according to any one of claims 1 to 12, and another polymer selected from: polymethyl methacrylate and its copolymers, fluorinated polymers, polyurethanes and polyesters, said method comprising transforming said mixture into a film.

17. Proton exchange polymer electrolyte membrane, said membrane consisting of a film obtained from PVDF material according to any one of claims 1 to 12.

18. Proton exchange polymer composite membrane, said membrane consisting of a porous support impregnated with PVDF material according to any one of claims 1 to 12 by solvent and / or aqueous means, said porous support being a polymer selected from: polymethyl methacrylate and its copolymers, polyethylene, polypropylene, polytetrafluoroethylene (PTFE), fluorinated polymers, polyurethanes, polyesters, poly(vinylidene fluoride) (PVDF), polysulfone (PSU), polyethersulfone (PESU), polyimide (PI), the polyaryletherketone (PAEK) family such as PEEK or PEKK.

19. Fuel cell comprising a membrane as defined in one of claims 17 and 18.

20. Binder for the manufacture of electrodes for fuel cells and / or electrolyzers, said binder comprising the material in the form of phosphon-grafted PVDF powder according to any one of claims 1 to 12.

21. Binder between the catalyst, electronic conductive agent type additives and the membrane in membrane-electrode assemblies, said binder comprising the material in the form of phosphon-grafted PVDF powder according to any one of claims 1 to 12.