Anion exchange membranes for fuel cells or electrolyzers

Abstract

The invention relates to an anion exchange membrane containing a composite film of an ionomer and zirconium oxide particles of formula ZrO2, the ionomer being a block polymer of formula (AB)nA, the symbol A representing a polyvinylaromatic block bearing quaternary amine groups, the symbol B representing a hydrogenated block of a poly(1,3-diene) or a copolymer comprising monomer units of a 1,3-diene and a vinylaromatic monomer, n being an integer equal to or greater than 1, the zirconium oxide particle content of the composite film being greater than 40% by mass of the composite film mass, the zirconium oxide particles having a median volume size, D50, greater than 100 nm and less than 1 µm. The membrane exhibits good plasticity.

Description

Title of the invention: Anion exchange membranes for fuel cells or electrolyzers

[0001] The field of the present invention is that of anion exchange membranes for fuel cell or electrolyzer.

[0002] It is known to modify thermoplastic elastomers by grafting quaternary amine groups onto their backbone so that they can be used as ionomers in an anion exchange membrane for a fuel cell or electrolyzer. When this ionomer is subjected to mechanical stress, it deforms. The extent of the deformation depends on the intensity of the mechanical stress. Beyond a certain stress, known as the "plasticity threshold," the ionomer undergoes irreversible deformation. The irreversibility of the ionomer's deformation can compromise the dimensional stability of an assembly that includes the ionomer, to the point of jeopardizing the integrity of the assembly and its use. The assembly in question is typically a membrane-electrode assembly (MEA) for a fuel cell or electrolyzer.

[0003] The inventors have discovered a new membrane which makes it possible to solve the aforementioned problem.

[0004] Thus, a first object of the invention is an anion exchange membrane which contains a composite film of an ionomer and zirconium oxide particles of formula ZrO2, the ionomer being a block polymer of formula (I), (AB)nA (I), the symbol A representing a polyvinylaromatic block bearing quaternary amine groups, the symbol B representing a hydrogenated block of a poly(1,3-diene) or of a copolymer comprising monomer units of a 1,3-diene and a vinylaromatic monomer, n being an integer equal to or greater than 1, the content of zirconium oxide particles of the composite film being greater than 40% by mass of the mass of the composite film, the zirconium oxide particles having a median volume size, D50, greater than 100 nm and less than 1 µm.

[0005] A second object of the invention is a method for preparing a membrane according to the invention, which method comprises the following successive steps a) to f): - a) prepare a solution of the ionomer in a solvent, - b) add the zirconium oxide particles to the solution to obtain a suspension, - c) shake the suspension, - d) deposit the suspension onto a support to form a layer, - e) dry the layer on the support to obtain the composite film, - f) remove the composite film from the support.

[0006] Another object of the invention is a membrane-electrode assembly, AME, for a fuel cell or electrolyzer, which assembly comprises an anion exchange membrane according to the invention, which membrane is capable of being obtained by the process according to the invention.

[0007] The invention also relates to a fuel cell or electrolyzer comprising an anion exchange membrane according to the invention, which membrane can be obtained by the process according to the invention. Detailed description of the invention

[0008] The polymers mentioned in the description may be of fossil origin or bio-based. In the latter case, they may be partially or totally derived from biomass or obtained from renewable raw materials derived from biomass. Similarly, they may also come from the recycling of materials already used, that is to say, they may be partially or totally derived from a recycling process, or even obtained from raw materials themselves derived from a recycling process.

[0009] The constituent elements of the composite film are an ionomer and zirconium oxide.

[0010] The ionomer useful for the needs of the invention is a block polymer bearing quaternary amine groups of formula (I) (AB)nA (I), the symbol A representing a polyvinylaromatic block bearing ionic groups which are quaternary amines, the symbol B representing a hydrogenated block of a poly(1,3-diene) or of a copolymer comprising monomeric units of a 1,3-diene and a vinylaromatic monomer, n being an integer equal to or greater than 1.

[0011] According to any one of the embodiments of the invention, the block polymer of formula (I) is preferably a linear polymer.

[0012] Preferably, n is equal to 1, in which case the block polymer of formula (I) is a triblock. The triblock then has the formula ABA in which the symbol A represents a polyvinylaromatic block bearing quaternary amine groups and the symbol B represents a hydrogenated block of a homopolymer of a 1,3-diene or a copolymer comprising monomer units of a 1,3-diene and a vinylaromatic monomer.

[0013] The polyvinylaromatic block of the ionomer can be a block of a homopolymer of a vinylaromatic monomer or a block of a copolymer of two or more vinylaromatic monomers. The vinylaromatic monomer of the polyvinylaromatic block of the ionomer is also referred to as the "first vinylaromatic." In the present invention, the term vinylaromatic monomer means a monomer of the formula Ar-CH=CH2 or Ar-CR=CH2, the symbol Ar representing an aryl group, substituted or unsubstituted, and the symbol R an alkyl group such as methyl. The aryl represented by the symbol Ar is preferably a phenyl or a phenyl substituted by an alkyl group having 1 to 4 carbon atoms. Examples of vinylaromatic monomers useful for the purposes of the invention include styrene, styrene substituted with an alkyl group in the para, meta, ortho, or alpha positions. The alkyl group is preferably an alkyl group having 1 to 4 carbon atoms.The polyvinyl aromatase block is preferably a polystyrene block, a polyalphamethylstyrene block, or a styrene-alphamethylstyrene copolymer block. The styrene-alphamethylstyrene copolymer block can be stochastic, gradient (tapered), or block-type.

[0014] The polyvinylaromatic block of the ionomer also has the essential characteristic of bearing quaternary amine groups. The polyvinylaromatic block typically contains vinylaromatic monomer units bearing a quaternary amine group, the quaternary amine group being linked to the aromatic ring of the vinylaromatic monomer units via a saturated hydrocarbon chain. In other words, the aromatic ring of each vinylaromatic monomer unit bearing a quaternary amine group is substituted by a saturated hydrocarbon chain substituted with a quaternary amine group. This saturated hydrocarbon chain substituted with a quaternary amine group, present in the block represented by the symbol A, is preferably a linear chain containing 1 to 10 carbon atoms, and more preferably a linear chain containing 2 to 8 carbon atoms.In this application, a linear chain is defined as an acyclic and unbranched chain. As is known, the polyvinylaromatic block bearing quaternary amine groups is obtained by a modification of the aryl groups that occurs in two steps: a haloalkylation reaction of the aromatic ring to form a halogenated polymer, followed by a reaction with a tertiary amine to form the ionomer. Reference may be made, for example, to patent application WO 2010010290.

[0015] According to the invention, the block represented by the symbol B is a hydrogenated block of a poly(1,3-diene) or a hydrogenated block of a copolymer comprising units monomers of a 1,3-diene and a vinylaromatic monomer. The vinylaromatic monomer of the copolymer comprising monomer units of a 1,3-diene and a vinylaromatic monomer is also called the "second vinylaromatic".

[0016] By "hydrogenated block of a poly(1,3-diene) or of a copolymer comprising monomeric units of a 1,3-diene and a vinylaromatic monomer" is meant a block in which the monomeric units of the 1,3-diene are reduced to more than 95%, preferably more than 98%, and more preferably more than 99% by mole of the 1,3-diene monomeric units. The hydrogenation reaction of a poly(1,3-diene) or of a copolymer comprising monomeric units of a 1,3-diene and a vinylaromatic monomer is a well-known reaction. For example, reference can be made to documents EP 1840993 Bl, US 5239010, US 5468574 and US 20070021569 which describe the selective hydrogenation of a poly(1,3-diene) or a copolymer comprising monomer units of a 1,3-diene and a vinylaromatic monomer of a block polymer of formula (I).

[0017] By "a 1,3-diene" is meant one or more 1,3-dienes. By "several" is meant at least two. The 1,3-diene preferably contains 4 to 8 carbon atoms. The 1,3-diene is preferably 1,3-butadiene, isoprene, or a mixture of 1,3-butadiene and isoprene, more preferably 1,3-butadiene.

[0018] According to a first embodiment, the block represented by the symbol B is a hydrogenated block of a poly(1,3-diene). In the present invention, "poly(1,3-diene)" means a polymer whose constituent units are the monomeric units of a 1,3-diene. Poly(1,3-diene) is preferably a homopolymer of a 1,3-diene, in which case the constituent units of poly(1,3-diene) are monomeric units of a single 1,3-diene. Poly(1,3-diene) is more preferably a homopolymer of 1,3-butadiene.

[0019] According to a second embodiment, the block represented by the symbol B is a hydrogenated block of a copolymer comprising monomer units of a 1,3-diene and a vinylaromatic monomer. The copolymer comprising monomer units of a 1,3-diene and a vinylaromatic monomer may be random or gradient. The vinylaromatic monomer constituting the copolymer comprising monomer units of a 1,3-diene and a vinylaromatic monomer may or may not be the same as the vinylaromatic monomer of the polyvinylaromatic block. The vinylaromatic monomer constituting the copolymer comprising monomer units of a 1,3-diene and a vinylaromatic monomer is preferably styrene. The 1,3-diene constituting the copolymer comprising monomer units of a 1,3-diene and a vinylaromatic monomer is preferentially 1,3-butadiene. The copolymer comprising monomeric units of a 1,3-diene and a vinylaromatic monomer preferably contains monomeric units of a vinylaromatic monomer in which the aryl group, preferably phenyl, is substituted by a saturated hydrocarbon chain substituted with a quaternary amine group. Preferably, the 1,3-diene and the vinylaromatic monomer of the copolymer comprising monomeric units of a 1,3-diene and a vinylaromatic monomer are 1,3-butadiene and styrene, respectively. The copolymer comprising monomer units of a 1,3-diene and a vinylaromatic monomer is advantageously a copolymer of a 1,3-diene and a vinylaromatic monomer, copolymer in which some or all of the vinylaromatic monomer units have the aromatic ring of the aryl group, preferably phenyl, substituted by a saturated hydrocarbon chain substituted by a quaternary amine group.The said saturated hydrocarbon chain substituted with a quaternary amine group present in the block represented by the symbol B is preferably a linear chain containing 1 to 10 carbon atoms, more preferably a linear chain containing 2 to 8 carbon atoms. Advantageously, it is identical to the saturated hydrocarbon chain substituted with a quaternary amine group present in the block represented by the symbol A.

[0020] The molar content of the hydrogenated block of a copolymer comprising monomer units of a 1,3-diene and a vinylaromatic monomer in vinylaromatic monomer units and in vinylaromatic monomer units bearing a quaternary amine group varies preferably in the range of 1% to 25%, more preferably from 5% to 20% of the repeating units constituting the hydrogenated block.

[0021] According to any one of the embodiments of the invention, the block represented by the symbol B is preferably a hydrogenated block of a homopolymer of 1,3-butadiene or a hydrogenated block of a copolymer of 1,3-butadiene and styrene, copolymer in which all or part of the monomer units of styrene have the phenyl group substituted by a saturated hydrocarbon linear chain substituted by a quaternary amine group, the saturated hydrocarbon chain substituted by a quaternary amine group present in the block represented by the symbol B being preferably a linear chain containing 1 to 10 carbon atoms, more preferably a linear chain containing 2 to 8 carbon atoms.

[0022] In the block polymer ionomer of formula (I), the block represented by the symbol B preferentially represents 50% to 90% by mass of the total mass of the block polymer ionomer of formula (I), more preferably 60% to 80% by mass of the total mass of the block polymer ionomer of formula (I).

[0023] The quaternary amine group is preferably of formula (II) or (III) -N+(R!)3 (II) (HD The Rb groups, whether identical or different, are alkyl groups, with R2 representing a divalent, unbranched hydrocarbon chain, saturated or unsaturated, containing 3 to 5 carbon atoms and capable of being interrupted by one or more heteroatoms selected from oxygen, nitrogen, and sulfur. In formulas (II) and (III), the bond attaching the nitrogen atom to the saturated linear hydrocarbon chain substituted by said quaternary amine group is represented by a dash (-), the saturated linear hydrocarbon chain substituted by said quaternary amine group not being shown in formulas (II) and (III). The quaternary amine group is preferably of formula (III), more preferably N-alkylpiperidinium, and even more preferably N-methylpiperidinium.The proportion of vinylaromatic monomers bearing a quaternary amine group in the block polymer of formula (I) can vary widely and is adjusted by those skilled in the art according to the desired ionic conductivity of the membrane. It preferentially varies from 2 to 35 molar percent, a percentage calculated relative to the total number of repeating units constituting the ionomer.

[0024] The counterions of the quaternary amine groups are preferentially halide anions, more preferably bromide anions.

[0025] The number-average molar mass of the ionomer, a block polymer of formula (I), can also vary considerably and is chosen by those skilled in the art according to the desired compromise between the mechanical properties of the composite film and the ionomer's ability to be formed into a film. Preferably, the number-average molar mass of the ionomer, a block polymer of formula (I), is greater than 20,000 g / mol and less than 500,000 g / mol in polystyrene equivalent (values ​​determined by steric chromatography (SEC) coupled with a refractometer).

[0026] The number-average molar mass of the block represented by the symbol A can vary considerably. It preferentially varies from over 1000 g / mol to less than 100,000 g / mol in polystyrene equivalent (values ​​determined by steric chromatography (SEC) coupled with a refractometer). It is chosen by those skilled in the art according to the desired compromise between the mechanical properties of the composite film and the ability of the ionomer to be formed into of a film. A high number-average molar mass, Mn, is more beneficial to the mechanical properties of the composite film than a lower Mn.

[0027] The number-average molar masses of the ionomer, a block polymer of formula (I), are the number-average molar masses of the block polymer before the introduction of the quaternary amine groups into the block polymer. Similarly, the number-average molar masses of the block represented by the symbol A are the number-average molar masses of the block represented by the symbol A before the introduction of the quaternary amine groups into the block polymer.

[0028] The ionomer, a block polymer of formula (I), can be prepared from a starting block polymer. The number-average molar mass of the ionomer can be determined from the number-average molar mass of this starting block polymer, as previously mentioned. The starting block polymer differs from the block polymer of formula (I) in that the aromatic rings are not substituted with groups containing a quaternary amine group and the 1,3-diene monomer units are not reduced. To prepare the ionomer, the 1,3-diene monomer units of the starting block polymer are selectively hydrogenated, and then the vinylaromatic monomer units of the starting block polymer are modified first by a haloalkylation reaction of the aromatic rings, followed by a reaction with a tertiary amine, hereinafter referred to as the quaternization reaction. The reagent used in the haloalkylation reaction is typically a haloalkene. In the haloalkene, the halogen atom and the double bond are preferentially located at opposite ends of the haloalkene's carbon chain. The haloalkene preferentially contains 2 to 10 carbon atoms, and more preferably 4 to 8 carbon atoms. The carbon chain of the haloalkene is preferentially linear. The tertiary amine used in the quaternization reaction is preferably of formula (IV) or (V) N (Rus (IV) (V) The Rb atoms, whether identical or different, are alkyl, with R2 representing a divalent, unbranched hydrocarbon chain, saturated or unsaturated, containing 3 to 5 carbon atoms and potentially interrupted by one or more heteroatoms chosen from oxygen, nitrogen, and sulfur. The tertiary amine is preferably of formula (V), more preferably N-alkylpiperidine, and even more preferably N-methylpiperidine.

[0029] Typically, the starting block polymer is a thermoplastic elastomer, preferably a triblock. According to any one of the embodiments of the invention, the starting block polymer is preferably a linear polymer.

[0030] The starting block polymer may be a commercial product, available for example from Kraton or Kuraray, or may be prepared according to any of the synthesis processes known and described below: - a) anionic polymerization of 1,3-diene or its copolymerization with the second vinylaromatic initiated by a dilithiated compound such as the diisopropenylbenzene and sec-butyllithium adduct described for example in document EP 1237941 or 1,1,4,4-tetraphenyl-1,4-dilithiobutane, followed by the polymerization of the first vinylaromatic to form a triblock polymer, the synthesis of block polymers containing more than 3 blocks being able to be carried out by successively continuing the polymerization of 1,3-diene and where appropriate of the second vinylaromatic and that of the first vinylaromatic; - b) anionic polymerization of the first vinylaromatic initiated by a monolithic compound such as butyllithium, followed by the polymerization of 1,3-diene or its copolymerization with the second vinylaromatic, then reaction with a coupling agent, for example a dichlorosilane to form a triblock, the synthesis of block polymers containing more than 3 blocks being able to be carried out by successively carrying out the polymerization of the first vinylaromatic and that of 1,3-diene and where appropriate of the second vinylaromatic before the coupling reaction.

[0031] A person skilled in the art understands that the methods for preparing the starting block polymer can lead to mixtures containing the starting block polymer. They understand that the method for preparing the starting block polymer according to process b) can lead to the formation of a mixture containing the starting block polymer, a polyvinylaromatic compound, and a diblock formed respectively during the third, first, and second steps described in the process. Similarly, they understand that process a) can lead to a mixture containing the starting block polymer and a homopolymer or copolymer of a 1,3-diene formed during the first step.

[0032] For the modification of the vinylaromatic monomer units, reference can be made for example to document WO 2010010290; for the hydrogenation reaction, reference can be made for example to document WO 03008467.

[0033] Alternatively, the ionomer, a block polymer of formula (I), can be prepared from a commercial product, available for example from Kraton, for example under the name "Kraton G", or from Kuraray, for example under the trade name "SEPTON", which commercial product is an already hydrogenated block polymer which differs from the ionomer in that it does not carry quaternary amine groups.

[0034] When one of these methods of preparing the starting block polymer results in a mixture containing the starting block polymer, the hydrogenation and modification reactions of the vinylaromatic monomer units are generally carried out on the mixture containing the starting block polymer. In the case where the hydrogenation and modification reactions of the vinylaromatic monomer units are carried out on the mixture containing the starting block polymer, the ionomer is obtained in the form of a mixture and is generally used without being isolated from this mixture.

[0035] The zirconium oxide particles useful for the purposes of the invention have the chemical structure ZrO2. As zirconium oxide particles have the formula ZrO2, they are hygroscopic. They are generally spherical or nearly spherical. They are generally commercially available products, for example from Inframat under the trade name "40R-0801". They are present in the composite film at a concentration greater than 40% by mass of the composite film and preferably at a concentration less than 90% by mass of the composite film. Advantageously, the concentration of zirconium oxide particles in the composite film is greater than 50% by mass of the composite film. More advantageously, the concentration of zirconium oxide particles in the composite film is greater than or equal to 70% by mass of the composite film. The zirconium oxide particles have a median volume size, D50, greater than 100 nm and less than 1 pm. Preferably, they have a median volume size, D50, greater than 200 nm and less than 800 nm.

[0036] The composite film has a thickness that can vary considerably and is chosen by a person skilled in the art according to the intended application of the composite film. Typically, it can vary from 10 µm to several hundred microns, for example, from 10 µm to 500 µm. The composite film constitutes all or part of the membrane according to the invention.

[0037] The membrane according to the invention can be prepared by a process, another object of the invention, which comprises the following successive steps a) to f): - a) prepare a solution of the ionomer in a solvent, - b) add zirconium oxide particles to the solution to obtain a suspension, - c) stir the suspension, - d) deposit the suspension on a support to form a layer, - e) dry the layer on the support to obtain the composite film, - f) remove the composite film from the support.

[0038] The solvent for the ionomer solution is chosen by those skilled in the art based on its boiling point and the solubility of the ionomer in said solvent, in particular its ability to solubilize the ionomer at the desired concentrations of the ionomer solution. The concentration of the ionomer solution generally ranges from 1 to 15% by mass of the ionomer. The solvent for the ionomer solution preferably has a relatively low boiling point, typically less than or equal to 100°C, so that it can be easily removed from the layer formed by the ionomer and the zirconium oxide particles, notably by evaporation under vacuum, air currents, or an inert gas such as nitrogen or argon.

[0039] The support typically takes the form of a plate with a surface onto which a layer of the suspension is deposited. The dimensions of this surface are chosen by those skilled in the art, generally according to the desired dimensions of the composite film. They may be comparable to the desired dimensions of the composite film or, alternatively, larger, in which case the step of peeling the composite film from the support may be followed by cutting to obtain the composite film to the desired dimensions. The support may be made of an organic material such as PET (polyethylene terephthalate), PTFE (polytetrafluoroethylene), PP (polypropylene), PE (polyethylene), or an inorganic material, particularly a metallic one such as aluminum, stainless steel, preferably PTFE.

[0040] In step a), the concentration of the ionomer solution is adjusted by a person skilled in the art so that the suspension formed by mixing the ionomer solution and zirconium oxide particles can be poured onto a support at near-ambient temperature to form a layer. It preferably varies from 5% to 15% by weight. Step a) is generally carried out at near-ambient temperature (23°C), typically from 22°C to 25°C. In step c), the suspension is agitated to obtain a suspension in which the zirconium oxide particles are homogeneously distributed.

[0041] Step e) can be carried out in an oven, in a drying cabinet known as a fume hood, under ambient atmosphere, under an inert atmosphere such as nitrogen or under vacuum. Depending on the solvent used in step a), step e) can be carried out at a temperature above ambient temperature to promote solvent evaporation.

[0042] Typically, at the end of step e) the film is considered dry for a residual solvent content of less than 5% by mass of the mass of the composite film, preferably less than 2% by mass of the mass of the composite film.

[0043] Following step e), a membrane activation step can be carried out. As is well known to those skilled in the art, a membrane is saturated with water before being put into operation in a membrane-electrode assembly, which constitutes a fuel cell or electrolyzer. Saturating the membrane with water is generally part of the membrane break-in or activation operation. Generally, during this saturating process, the counterions of the ionomer constituting the composite film, which are halides, can be replaced by hydroxide anions, which are known to have much better ionic mobility than halide anions.The replacement of halide counterions with hydroxide anions can be achieved by impregnating the composite film of the membrane with an aqueous solution, for example, by bringing the composite film into contact with an aqueous solution containing hydroxide anions, such as an aqueous solution of a strong base. Suitable strong bases include potassium hydroxide and sodium hydroxide, preferably potassium hydroxide. Preferably, the replacement of halide counterions with hydroxide anions is carried out during the membrane break-in or activation process.

[0044] The membrane-electrode assembly, Membrane-Electrode Assembly (MEA), another object of the invention, has as its essential characteristic the inclusion of an anion exchange membrane according to the invention. MEAs are well-known basic components of fuel cells or electrolyzers. An MEA generally comprises five layers: an electrolytic layer, two catalytic layers, and two gas diffusion layers. The electrolytic layer, which may be a polymer ion-exchange membrane, constitutes the central layer of the MEA; on either side of the electrolytic layer is a catalytic layer; the layer adjacent to the catalytic layer is a gas diffusion layer. The assembly formed by the gas diffusion layers, the catalytic layers, and the electrolytic layer is held together by two bipolar plates. One of the two catalytic layers forms the anode, the other the cathode. The anion exchange membrane according to the invention is constitutive of the electrolytic layer of the AME.

[0045] In summary, the invention is advantageously implemented according to any one of the following embodiments 1 to 22:

[0046] Mode 1: Anion exchange membrane containing a composite film of an ionomer and zirconium oxide particles of formula ZrO2, the ionomer being a block polymer of formula (I), (AB)nA (I), the symbol A representing a polyvinylaromatic block bearing quaternary amine groups, the symbol B representing a hydrogenated block of a poly(1,3-diene) or a copolymer comprising monomer units of a 1,3-diene and a vinylaromatic monomer, n being an integer equal to or greater than 1, the content of zirconium oxide particles in the composite film being greater than 40% by mass of the mass of the composite film, the zirconium oxide particles having a median volume size, D50, greater than 100 nm and less than 1 sqm.

[0047] Mode 2: Membrane according to mode 1 in which the content of zirconium oxide particles of the composite film is greater than 50% by mass of the mass of the composite film.

[0048] Mode 3: Membrane according to mode 1 or 2 in which the content of zirconium oxide particles of the composite film is greater than or equal to 70% by mass of the mass of the composite film.

[0049] Mode 4: Membrane according to any one of modes 1 to 3 in which the zirconium oxide particle content of the composite film is less than 90% by mass of the mass of the composite film.

[0050] Mode 5: Membrane according to any one of modes 1 to 4 in which the zirconium oxide particles have a median volume size, D50, greater than 200 nm and less than 800 nm.

[0051] Mode 6: Membrane according to any one of the modes 1 to 5 in which n is equal to 1.

[0052] Mode 7: Membrane according to any one of modes 1 to 6 in which the polyvinylaromatic block is a polystyrene block, a polyalphamethylstyrene block or a styrene and alphamethylstyrene copolymer block.

[0053] Mode 8: Membrane according to any one of modes 1 to 7 in which the polyvinylaromatic block contains vinylaromatic monomer units bearing a quaternary amine group, the quaternary amine group being linked to the aromatic ring of the vinylaromatic monomer units via a saturated hydrocarbon chain.

[0054] Mode 9: Membrane according to any one of modes 1 to 8 in which the copolymer comprising monomer units of a 1,3-diene and a vinylaromatic monomer is a copolymer of a 1,3-diene and a monomer vinylaromatic, a copolymer in which some or all of the vinylaromatic monomer units have the aromatic ring of the aryl group, preferably phenyl, substituted by a saturated hydrocarbon chain substituted by a quaternary amine group.

[0055] Mode 10: Membrane according to mode 8 or 9 in which the saturated hydrocarbon chain is a linear chain containing 1 to 10 carbon atoms, preferably a linear chain containing 2 to 8 carbon atoms.

[0056] Mode 11: Membrane according to any one of modes 1 to 10 in which the 1,3-diene and the vinylaromatic monomer of the copolymer comprising monomer units of a 1,3-diene and a vinylaromatic monomer are respectively 1,3-butadiene and styrene.

[0057] Mode 12: Membrane according to any one of modes 1 to 11 in which the molar content of the hydrogenated block of a copolymer comprising monomer units of a 1,3-diene and a vinylaromatic monomer in vinylaromatic monomer units and in vinylaromatic monomer units bearing a quaternary amine group varies in a range from 1% to 25%, preferably from 5% to 20% of the repeat motifs constituting the hydrogenated block.

[0058] Mode 13: Membrane according to any one of modes 1 to 12 in which the block represented by the symbol B represents from 50% to 90% by mass of the total mass of the ionomer, preferably from 60% to 80% by mass of the total mass of the ionomer.

[0059] Mode 14: Membrane according to any one of modes 1 to 13 in which the quaternary amine group is of formula (II) or (III) -N+(R!)3 (II) (HD —NR, R, the Rb identical or different, being alkyl, R2 representing a divalent unbranched hydrocarbon chain, saturated or unsaturated, containing 3 to 5 carbon atoms and which can be interrupted by one or more heteroatoms chosen from oxygen, nitrogen and sulfur.

[0060] Mode 15: Membrane according to mode 14 in which the quaternary amine group has formula (III) Ri being alkyl, R2 representing a divalent unbranched hydrocarbon chain, saturated or unsaturated, containing 3 to 5 carbon atoms and which can be interrupted by one or more heteroatoms chosen from oxygen, nitrogen and sulfur.

[0061] Mode 16: Membrane according to mode 15 in which the quaternary amine group is N-alkylpiperidinium.

[0062] Mode 17: Membrane according to any one of modes 1 to 16 in which the quaternary amine group is N-methylpiperidinium.

[0063] Mode 18: Membrane according to any one of modes 1 to 17 in which the proportion of vinylaromatic monomers bearing a quaternary amine group in the block polymer of formula (I) varies from 2 to 35 molar percent, the percentage calculated in relation to the total number of repeat motifs constituting the ionomer.

[0064] Mode 19: Membrane according to any one of modes 1 to 18 in which the number-average molar mass of the ionomer, block polymer of formula (I), is greater than 20,000 g / mol and less than 500,000 g / mol in polystyrene equivalent, the number-average molar mass of the block represented by the symbol A varies from more than 1,000 g / mol to less than 100,000 g / mol in polystyrene equivalent.

[0065] Mode 20: A method for preparing a membrane defined in any one of modes 1 to 19 which comprises the following successive steps a) to f): - a) prepare a solution of the ionomer in a solvent, - b) add zirconium oxide particles to the solution to obtain a suspension, - c) stir the suspension, - d) deposit the suspension on a support to form a layer, - e) dry the layer on the support to obtain the composite film, - f) remove the composite film from the support.

[0066] Mode 21: Membrane-Electrode Assembly, MEA, for fuel cell or electrolyzer, which assembly comprises an anion exchange membrane defined in any one of modes 1 to 19.

[0067] Mode 22: Fuel cell or electrolyzer which includes an anion exchange membrane defined in any one of modes 1 to 19.

[0068] The aforementioned features of the present invention, as well as others, will be better understood upon reading the following description of several examples of embodiments of the invention, given by way of illustration. Examples

[0069] Measurement of the median volume size, D50, of zirconium oxide particles: The values ​​of D50, median volume size, are determined by Laser diffraction which allows the particle size distribution to be determined as a volume percentage by means of a dry particle size analyzer.

[0070] Measurement of the plasticity values ​​of films: The plasticity threshold values ​​of the films are determined by tensile testing at 23°C on a TA Instruments TA HR20 device. A rectangular sample measuring 5 cm x 1 cm is placed between the jaws of the device and is deformed at a speed of 50 mm / min until the sample breaks. Preparation of the ionomer:

[0071] The commercial product, "G1652" from Kraton, is a hydrogenated triblock polymer whose central block is a copolymer of 1,3-butadiene and styrene, and whose terminal blocks are polystyrenes, the degree of hydrogenation of the butadiene units being greater than 99%. Table 1 gives the composition of the commercial product, its macrostructure (number-average molar mass Mn measured by size-exclusion chromatography analysis, PS calibration).

[0072] The ionomer is prepared from the commercial product according to the following procedure which is broken down into two steps, step 1 and step 2.

[0073] Table 1: Styrene (mol%) Ethylene (mol%) Butylene (mol%) Mn (g / mol) G1652 12.1 68.4 19.5 68 513

[0074] Step 1: Bromoalkylation of the commercial product:

[0075] Put the polymer and the dichloromethane solvent into a bottle while stirring until completely dissolved (approximately 2 hours at room temperature (23°C)) then put the bottle at 5°C for 12 hours; Allow the polymer solution to be bubbled through nitrogen at 5°C for 10 min; Cool the solution to 0°C in an ice bath for 30 min; With stirring, add trifluoroacetic acid drop by drop (0.6 acid equivalent / styrene) in less than 1 min at 0°C (yellow / orange colouring); Leave under agitation for 30 minutes at 0°C (yellow / orange colouring); After the stirring time, allow the solution to return to room temperature; Add the 6-bromo-l-hexene alkene drop by drop using a syringe pump for 45 min (the solution turns red), while stirring; Leave under agitation for an additional 90 minutes at room temperature (23°C) (colour becomes dark red); Add methanol as a reaction stopper (decolorization of the medium); Neutralize by fractional addition of a KOH solution in methanol (IM), until pH reaches 7-8 (formation of a small precipitate and decolorization from whitish to mauve); Coagulate in methanol (3 times the reaction volume) by pouring the methanol drop by drop into the vortex and then recover the polymer using a filter; Wash the polymer by pouring it into a bath of deionized water under agitation for 10 min (to remove the salts) then recover the polymer using a filter; Retrieve the polymer and let it dry for 24 hours in an oven at 40°C, 150 mbar.

[0076] The levels in the brominated polymer of the ethylene, butylene, styrene and substituted styrene motifs are measured by NMR analysis and are shown in Table 2; the term "substituted styrene" refers to styrene motifs substituted by an alkyl group substituted by a bromine atom.

[0077] Table 2: Molecular composition Substituted styrene (%mol) Styrene (%mol) Ethylene (%mol) Butylene (%mol) Kylated bromoal polymer 5.7 6.4 68.4 19.5

[0078] Step 2: Quaternization of the bromoalkylated polymer:

[0079] The polymer is dissolved in dichloromethane to form a 2.5% by weight polymer solution. Ten equivalents of N-methylpiperidine per bromine atom grafted onto the polymer are then added. The mixture is stirred for 48 hours at 40°C, then coagulated and washed in methanol. The ionomer is recovered and then oven-dried at 40°C for 24 hours. Preparation of the Fl to F4 composite films:

[0080] Four composite films are prepared according to the following procedure: The ionomer (9g) is dissolved in dichloromethane to form a 6% wt% ionomer solution. Zirconium oxide particles (Inframat 40R-0801, D50: 300-700 nm) are added to the ionomer solution and the mixture is stirred at 350 rpm for 3 days at room temperature (23°C) to obtain a homogeneous suspension. In a fume hood, the suspension is deposited onto a PTFE plate measuring 150 mm x 300 mm to form a layer 400 µm thick. To eliminate dichloromethane, the coated support is treated with the layer. The composite film is left in a fume hood at room temperature (23°C) under ambient air. The composite film is considered dry when the residual dichloromethane content is less than 2% by mass of the composite film. The composite film is recovered by peeling it from the substrate. The zirconium oxide and ionomer contents of the composite film are given in Table 3 and are expressed as mass percentages relative to the mass of the composite film.

[0081] A FO film is also prepared according to the procedure described for the preparation of composite films, but omitting the addition of zirconium oxide particles. The plasticity values ​​for each of the films are measured according to the method described above. The results are shown in Table 3.

[0082] Table 3: F0 Fl F2 F3 F4 % Ionomer 100 80 60 30 15 % ZrO2 0 20 40 70 85 Plasticity threshold (MPa) 4.2 2.4 4.0 6.2 7.5

[0083] Composite films F0, Fl, and F2 have zirconium oxide mass contents of 40% or less. Only composite films F3 and F4, which have zirconium oxide mass contents greater than 40% (70% and 85%, respectively), are suitable for the purposes of the invention. The film thickness varies from 100 to 150 µm.

[0084] Activation of the MO to M4 membranes by impregnation of the composite films F0 to F4:

[0085] Each of the composite films F0 to F4 is used to constitute a membrane, respectively MO to M4. The membranes are prepared according to the following procedure: The composite film is immersed for 24 hours in an aqueous potassium hydroxide (MH) solution at room temperature (23°C) to activate the membrane. The membrane is then removed from the solution and its surface is wiped. Only membranes M3 to M4, composed of films F3 and F4 respectively, conform to the invention.

[0086] To determine the ionic conductivity of the prepared membrane, its electrochemical impedance is measured across the plane of the membrane at 23 °C, the measurement parameters being an amplitude variation of 10 mV and an applied potential of 0 V. The ionic conductivity results are shown in Table 4.

[0087] Table 4: Membrane MO M1 M2 M3 M4 Ionic conductivity θ (S / cm) 13.8 2.1 1.1 0.6 0.4

[0088] Exhibiting ionic conductivity, the MO to M4 membranes can be used in an AME in a fuel cell or electrolyzer. It appears that only the M3 and M4 membranes according to the invention exhibit the best plasticity.

Claims

Demands

1. Anion exchange membrane containing a composite film of an ionomer and zirconium oxide particles of formula ZrO2, the ionomer being a block polymer of formula (I), (AB)nA (I), the symbol A representing a polyvinylaromatic block bearing quaternary amine groups, the symbol B representing a hydrogenated block of a poly(1,3-diene) or a copolymer comprising monomer units of a 1,3-diene and a vinylaromatic monomer, n being an integer equal to or greater than 1, the zirconium oxide particle content of the composite film being greater than 40% by mass of the mass of the composite film, the zirconium oxide particles having a median volume size, D50, greater than 100 nm and less than 1 pm.

2. Membrane according to claim 1 in which the content of zirconium oxide particles of the composite film is greater than 50% by mass of the mass of the composite film.

3. Membrane according to claim 1 or 2 wherein the content of zirconium oxide particles of the composite film is greater than or equal to 70% by mass of the mass of the composite film.

4. Membrane according to any one of claims 1 to 3 wherein the zirconium oxide particle content of the composite film is less than 90% by mass of the mass of the composite film.

5. Membrane according to any one of claims 1 to 4 in which the zirconium oxide particles have a median volume size, D50, greater than 200 nm and less than 800 nm.

6. Membrane according to any one of claims 1 to 5 in which n equals 1.

7. Membrane according to any one of claims 1 to 6 wherein the polyvinylaromatic block is a polystyrene block, a polyalphamethylstyrene block or a styrene and alphamethylstyrene copolymer block.

8. Membrane according to any one of claims 1 to 7 wherein the polyvinylaromatic block contains vinylaromatic monomer units bearing a quaternary amine group, the quaternary amine group being linked to the aromatic ring of vinylaromatic monomer units via a saturated hydrocarbon chain.

9. Membrane according to any one of claims 1 to 8 wherein the copolymer comprising monomer units of a 1,3-diene and a vinylaromatic monomer is a copolymer of a 1,3-diene and a vinylaromatic monomer, copolymer wherein some or all of the vinylaromatic monomer units have the aromatic ring of the aryl group, preferably phenyl, substituted by a saturated hydrocarbon chain substituted by a quaternary amine group.

10. Membrane according to any one of claims 1 to 9 wherein the 1,3-diene and the vinylaromatic monomer of the copolymer comprising monomer units of a 1,3-diene and a vinylaromatic monomer are respectively 1,3-butadiene and styrene.

11. Membrane according to any one of claims 1 to 10 wherein the block represented by the symbol B represents from 50% to 90% by mass of the total mass of the ionomer, preferably from 60% to 80% by mass of the total mass of the ionomer.

12. Membrane according to any one of claims 1 to 11 wherein the quaternary amine group is of formula (III) (HD Ri being alkyl, R2 representing an unbranched, saturated or unsaturated divalent hydrocarbon chain containing 3 to 5 carbon atoms and capable of being interrupted by one or more heteroatoms selected from oxygen, nitrogen and sulfur, preferably the quaternary amine group is N-alkylpiperidinium, more preferably the quaternary amine group is N-methylpiperidinium.

13. A method for preparing a membrane defined in any one of claims 1 to 12 comprising the following successive steps a) to f): - a) preparing a solution of the ionomer in a solvent, - b) add zirconium oxide particles to the solution to obtain a suspension, - c) stir the suspension, - d) deposit the suspension onto a support to form a layer, - e) dry the layer on the support to obtain the composite film, - f) remove the composite film from the support.

14. Membrane-Electrode Assembly, MEA, for fuel cell or electrolyzer, which assembly comprises an anion exchange membrane as defined in any one of claims 1 to 12.

15. Fuel cell or electrolyzer comprising an anion exchange membrane as defined in any one of claims 1 to 12.