Ion-conducting membrane, preparation method and applications thereof

Abstract

The invention relates to an ion-conducting membrane comprising a matrix made of a cross-linked polymer and a powder consisting of an ion-conducting material, said powder consisting of an ion-conducting material being dispersed in the continuous solid matrix and representing from 33% to 66% by volume, relative to the total volume of the ion-conducting membrane.

Description

[0001] TITLE: Ionic conductive membrane, preparation process and associated applications

[0002] The present invention relates to an ionic conductive membrane. In particular, the invention relates to an ionic conductive membrane, in particular an anionic and / or cationic membrane, for a fuel cell, in particular of the PEM (“Polymer Exchange Membrane” type).

[0003] One of the essential components for the proper functioning of a PEM fuel cell is the membrane conducting the ions inside the cell. Traditionally, these cells operate in cationic mode and this function is ensured by a cationic (particularly protonic) ionomer conductive material such as Nation®. However, this poses the technical problem of imposing operation in cationic mode. Furthermore, it also requires working with platinum as a catalyst. These technical problems are a hindrance to the development of these devices. Indeed, platinum is a rare and expensive metal that should be replaced, for example, by other less expensive metals such as nickel, etc. Such metals are currently used in high-power stationary installations operating at high temperatures to work in anionic mode and thus replace platinum.However, these processes require working at high temperatures, so it would be advisable to have membranes that can work at room temperature. This should open the door to miniature anionic fuel cells.

[0004] To overcome these difficulties, anionic conductive materials have been developed.

[0005] WO 2015 / 044308 A1 describes in this sense cationic supports consisting of a porous inorganic support, the surface of the pores of which are coated with a silica gel functionalized by cationic groups. The cationic supports described are intended to be used as an anionic membrane in a fuel cell.

[0006] Another strategy was to functionalize Nation® to convert it into an anionic conductive material.

[0007] Such an approach has been described in Salerno Holly LS, et al. (“Anion exchange membranes derived from nation precursor for the alkaline fuel cell”, Journal of Polymer Science Part B: Polymer Physics, 2012, 50, pp. 552-562). This article teaches that robust hydroxide-conducting membranes are necessary for obtaining robust, durable, and inexpensive alkaline fuel cells (AFCs). Nation®-based anion exchange membranes (AEMs) were synthesized by amination of the Nation® precursor membrane with 1,4-dimethylpiperazine. This initial reaction produces an AEM with covalently attached dimethylpiperazinium cations neutralized by fluoride anions, while a subsequent ion exchange reaction produces a hydroxide-conducting membrane. These AEMs possess high thermal stability and different thermal transition temperatures than Nation®

[0008] A modified Nation® membrane is also known from Min-suk J. Jung et al. (“A Perfluorinated Anion Exchange Membrane with a 1,4 Dimethylpiperazinium Cation”, J. Mater. Chem., 2011, 21, (17), pp. 6158-6160) who demonstrated that a perfluorinated anion exchange membrane with a 1,4-dimethylpiperazinium cation exhibits improved hydroxide ion conductivity and a 3-fold reduced water absorption, compared to a hydrocarbon MEA with the same cation. The perfluorinated MEA is stable for 30 days in 2 M KOH at 60°C and has shown good performance in fuel cells.

[0009] A modified Nation® membrane is also known from Schmidt, C. et al. (“Modification of Nation Membranes by Impregnation with Ionic Liquids”, Chemical Engineering & Technology, 2008, 31, No. 1, pp. 13-22) who describe the impregnation of Nation® 117 membranes with different imidazolium (1-hexyl-3-methyl-imidazolium / HMI, 1-butyl-3-methyl-imidazolium / BMI) and pyrrolidinium (1-butyl-1-methyl-pyrrolidinium / BMPyr) anions carrying hydrophobic (tris(pentafluoroethyl)trifluorophosphate / FAP, bis(trifluoromethylsulfonyl)imide / BTSI, hexafluorophosphate / PF 6) and more hydrophilic (tetrafluoroborate / BF4) anions. During this treatment, the cations of the ionic liquids partially replace the protons of the sulfonic acid groups of the Nation®. According to this article, modification of Nation® with ionic liquids carrying the bulky hydrophobic anion FAP appears promising.

[0010] WO 2021 / 083922 A1 also describes a process for converting Nation® by polymerization in the pores of the material of monomers carrying quaternary ammonium groups capable of interacting ionically with the sulfonate groups of Nation®.

[0011] However, the proposed processes are complex to implement.

[0012] Nation®, used as the base material in most of the proposed processes, is also expensive. Furthermore, Nation® is geometrically unstable, making it difficult to integrate into a fuel cell. Finally, the use of a frame is necessary due to its sensitivity to humidity. The present invention aims to solve all or part of the technical problems mentioned above.

[0013] In particular, the invention aims to provide an alternative ionic (cationic or anionic) conductive membrane whose manufacture is simplified, compared to the membranes of the prior art.

[0014] The invention also aims to provide an ionic conductive membrane (cationic or anionic) whose manufacturing costs are reduced, compared to the membranes of the prior art. In particular, the invention aims to provide an ionic conductive membrane prepared from materials other than Nation®.

[0015] The present invention also aims to provide an ionic conductive membrane (cationic or anionic) having improved mechanical strength, compared to the membranes of the prior art.

[0016] Another object of the invention is to provide an ionic conductive membrane (cationic or anionic) capable of operating at room temperature in a fuel cell. The present invention also aims to provide an anionic membrane making it possible to replace platinum with other metals, in particular less expensive ones, such as nickel in a fuel cell. The present invention also aims to provide an anionic membrane that is stable in an alkaline medium.

[0017] Thus, the present invention aims to provide an inexpensive, stable membrane whose conductometric performances approach those of conventional proton membranes used in fuel cells.

[0018] The present invention also aims to provide a membrane which can be used in a biologically compatible device, in particular for implantation in a human or animal body.

[0019] Summary of the invention

[0020] The invention firstly relates to an ionic conductive membrane comprising a matrix of a crosslinked polymer and a powder of an ionic conductive material, said powder of an ionic conductive material being dispersed in the continuous solid matrix and representing from 33% to 66% by volume, relative to the total volume of the ionic conductive membrane.

[0021] According to a preferred embodiment, the continuous solid matrix is ​​obtained by crosslinking, in particular by chemical or physical crosslinking, of a crosslinkable polymer chosen from polysiloxanes, thermosetting resins, polyamides, polyesters, polyolefins and any of their mixtures, preferably chosen from polydimethylsiloxanes, epoxy resins and any of their mixtures. Preferably, the powder made of an ionic conductive material has a particle size less than or equal to 20 μm, preferably ranging from 100 nm to 10 μm.

[0022] This small particle size of the ionic conductive material powder contributes to obtaining a membrane with good conductive and mechanical properties. In particular, their small size allows access to membranes of lesser thickness, which improves their flexibility and opens up new perspectives for the application of these membranes.

[0023] Preferably, the powder made of an ionic conductive material has a particle size less than or equal to half the thickness of the ionic conductive membrane.

[0024] Preferably, the ionic conductive material is chosen from inorganic materials based on silicon, optionally functionalized, organic materials such as ion exchange resins, or any of their mixtures.

[0025] Advantageously, the ionic conductive material is chosen from silicates, optionally functionalized, ion exchange resins and any of their mixtures.

[0026] According to one embodiment, the ionic conductive membrane according to the invention is porous, preferably has a porosity ranging from 1% to 25%, more preferably ranging from 3% to 20%.

[0027] The invention also relates to a process for preparing an ionic conductive membrane as defined above and described in detail below, the process comprising: a) providing (i) a crosslinkable polymer and (ii) a powder made of an ionic conductive material, b) dispersing said powder in said crosslinkable polymer so as to form a homogeneous mixture, said powder representing from 33% to 66% by volume, relative to the total volume of the mixture, c) forming a film from the mixture obtained in b), in particular by depositing the mixture on the surface of a support, d) crosslinking the crosslinkable polymer.

[0028] According to a particular embodiment, the method according to the invention comprises a prior step of functionalizing the powder into an ionic conductive material.

[0029] The invention also relates to a fuel cell comprising an ion-conducting membrane as defined above and described in detail below or obtained by a method as defined above and described in detail below. The invention finally relates to a biocompatible device comprising an ion-conducting membrane as defined above and described in detail below or obtained by a method as defined above and described in detail below.

[0030] Detailed description

[0031] The invention firstly relates to an ionic conductive membrane.

[0032] By "ionic conductive membrane" is meant a semi-permeable membrane allowing ionic conduction between a first medium and a second medium located on either side of said membrane. In particular, an ionic conductive membrane according to the material invention is capable of transporting, possibly selectively, ions in order to pass them from the first medium to the second medium through the membrane, while being impermeable to gases such as oxygen or hydrogen.

[0033] The ionic conductive membrane according to the invention typically comprises a matrix of a crosslinked polymer in which a powder of an ionic conductive material is dispersed.

[0034] The crosslinked polymer allows the mechanical properties of the membrane to be controlled (flexible or rigid), while the powder made of an ionic conductive material allows the type of ionic conductivity to be chosen.

[0035] The Matrix

[0036] The matrix of the invention is intended to serve as a support for the ionic conductive material. In particular, it provides the matrix of the invention with good mechanical strength.

[0037] Preferably, the matrix of the invention is solid.

[0038] Also preferably, the matrix of the invention is continuous.

[0039] For the purposes of the present invention, the term crosslinked polymer means a polymer having covalent chemical bonds between the main polymer chains.

[0040] The membrane matrix according to the invention is typically obtained by crosslinking a crosslinkable polymer.

[0041] Preferably, the crosslinkable polymer is a non-fluorinated polymer, i.e. it does not comprise fluorine atoms.

[0042] Preferably, the crosslinkable polymer is a non-ionically conductive polymer.

[0043] Preferably, the crosslinkable polymer is chosen from polysiloxanes, thermosetting resins, polyamides, polyesters, polyolefins, epoxy resins, polyacrylamides and any of their mixtures. Preferably, when the crosslinkable polymer is chosen from polysiloxanes, it is chosen from polyalkylsiloxanes, in particular from polyalkylsiloxanes in which the alkyl groups are chosen from C1-C10, more preferably C1-C5, even more preferably C1-C3 alkyl groups.

[0044] Preferably, the polysiloxanes are chosen from polydialkylsiloxanes in which the alkyl groups are chosen independently from C1-C10 alkyl groups, more preferably C1-C5, even more preferably C1-C3.

[0045] More preferably, the alkyl substituents are all identical and are chosen from C1-C10 alkyl groups, more preferably C1-C5, even more preferably C1-C3.

[0046] Advantageously, when the crosslinkable polymer is chosen from polysiloxanes, it is chosen from polydimethylsiloxanes (PDMS).

[0047] Among the thermosetting resins, we can notably cite phenolic resins, ester resins and epoxy resins.

[0048] Preferably, when the crosslinkable polymer is chosen from thermosetting resins, it is chosen from epoxy resins, more preferably from epoxy maleinated castor oil type resins.

[0049] Epoxy maleinated castor oil resins are typically obtained by reacting castor oil with maleic anhydride, followed by an epoxidation step.

[0050] Among the polyamides, we can notably include nylons, polyacrylamides, polybisacrylamides or even copolymers of acrylamide and bisacrylamide.

[0051] Polyesters include polyethylene terephthalate and polybutylene terephthalate.

[0052] Among the polyolefins, we can notably cite homopolymers of olefins such as polyethylene, polypropylene, polybutylene or even copolymers of different olefins.

[0053] Examples of olefinic copolymers include copolymers based on monovinyl aromatic hydrocarbon units, typically copolymers of styrene and divinylbenzene.

[0054] Advantageously, the crosslinkable polymer is chosen from polysiloxanes, thermosetting resins and any of their mixtures.

[0055] More advantageously, the crosslinkable polymer is chosen from polydimethylsiloxanes, epoxy resins and any of their mixtures. The crosslinking of the polymer is carried out according to any method known to those skilled in the art. It can, for example, be carried out by chemical crosslinking, in particular with sulfur, or by physical crosslinking, for example by heat treatment or by irradiation with an electron beam.

[0056] The rigidity and / or flexibility of the final ion-conducting membrane can be adjusted by selecting the starting crosslinkable polymer used to form the matrix. In particular, the selection of one or more polymers with a view to preparing a membrane having particular mechanical properties is within the skill of the art. The invention thus provides access to rigid membranes but also to flexible membranes, depending on the polymer used.

[0057] Preferably, the matrix represents from 33% to 66% by volume, relative to the total volume of the ionic conductive membrane.

[0058] Ionic conductive powder

[0059] The membrane of the invention further comprises at least one powder made of an ionic conductive material, said powder made of an ionic conductive material being dispersed in the matrix.

[0060] According to a preferred embodiment, the powder made of an ionic conductive material is distributed homogeneously in the matrix.

[0061] For the purposes of the invention, the term "ionic conductive material" means a material capable of transporting ions. The ionic conductive behavior of a material is evaluated by measuring its ionic conductivity oi.

[0062] The ionic conductivity of a material can be determined by any method known to those skilled in the art. It can, for example, be measured as follows: a pellet of the material whose electronic conductivity value is to be determined is prepared by pressing powder of said material under 5 t / cm 2 then by sintering at a temperature 30% lower than its melting temperature (expressed in K) for 2 hours. A gold film is then deposited on the surface of the pellet, in order to improve the contact between the current collectors and the sample. The pellet is finally placed between 2 nickel collectors on the surface.

[0063] An impedance measurement is then carried out on the pellet to which a sinusoidal voltage of amplitude of 10mV at different frequencies (between 1MHz and 0.01 Hz) is applied. On the Nyquist diagram, the signal of the blocking electrodes is visible at the lowest frequencies. The intersection between the extrapolation of the signal of the blocking electrodes and the axis of the real values ​​of the impedance RT corresponds to the sum of the ionic resistance Ri and the electronic resistance Re of the pellet. The ionic resistance Ri is calculated from the relation Ri = RT - Re and the ionic conductivity oi is calculated by applying the following formula:

[0064] [Math 1] where oi represents the ionic conductivity of the material (in Sm-1 ), e represents the thickness of the pellet (in m), S the surface area of ​​the pellet (in m 2 ) and Ri the ionic resistance of the material (in Ohm).

[0065] Preferably, the ionic conductive material has an ionic conductivity greater than or equal to 0.1 Sm -1 , preferably greater than or equal to 50 Sm -1 .

[0066] More preferably, the ionic conductive material has an ionic conductivity ranging from 0.1 Sm -1 at 100 Sm -1 , preferably 10 Sm -1 at 100 Sm -1 .

[0067] The nature of the ionic conductive material is not particularly limited. It can be chosen from organic or inorganic materials.

[0068] The organic materials suitable for the invention are typically those comprising charged chemical groups. Examples include ion exchange resins.

[0069] Among the inorganic materials suitable for the invention, mention may in particular be made of silicon-based materials.

[0070] For the purposes of the invention, the term “silicon-based material” means materials comprising a network of silicon atoms linked together, directly or indirectly.

[0071] Examples of silicon-based materials include silicalite, silica gels and silicates.

[0072] Preferably, when the ionic conductive material is chosen from silicates, it is chosen from aluminosilicates, more preferably from zeolites, typically from Y zeolites.

[0073] Preferably, the ionic conductive material is chosen from silicates, ion exchange resins and any of their mixtures.

[0074] More preferably, the ionic conductive material is chosen from aluminosilicates, ion exchange resins and any of their mixtures.

[0075] Advantageously, the ionic conductive material is chosen from zeolites, ion exchange resins and any of their mixtures.

[0076] According to a particular embodiment, the powder made of an ionic conductive material is in the form of a mixture of at least two distinct ionic conductive materials. Preferably, according to this embodiment, the powder made of an ionic conductive material comprises, more preferably consists of, a first powder made of an anionic conductive material and a second powder made of a cationic conductive material. This embodiment is particularly suitable for the preparation of mixed anionic and cationic conductive membranes.

[0077] More preferably, according to this embodiment, the membrane of the invention comprises, preferably consists of:

[0078] - 33% by volume of powder in an anionic conductive material,

[0079] - 33% by volume of powder in a cationic conductive material, and

[0080] - 33% by volume of matrix, preferably 34% by volume of matrix, relative to the total volume of the ionic conductive membrane.

[0081] Advantageously, the powder made of an ionic conductive material has a particle size less than or equal to 50 pm, preferably ranging from 50 nm to 30 pm, more preferably ranging from 100 nm to 10 pm, more preferably ranging from 500 nm to 8 pm, more preferably ranging from 1 pm to 5 pm.

[0082] The particle size of the powder can be measured using any method known to those skilled in the art, for example by laser diffraction or by dynamic light scattering.

[0083] According to a preferred embodiment, the powder made of an ionic conductive material is porous, preferably has open porosity.

[0084] For the purposes of the invention, the term "material having open porosity" means a material whose pores are linked together, so that they form a continuous network within said material.

[0085] Advantageously, the powder made of an ionic conductive material has a porosity ranging from 5% to 40%, more preferably ranging from 10% to 30%.

[0086] The porosity of the powder can be measured by any method known to those skilled in the art, for example by means of a Mercury porosimeter.

[0087] Preferably, the powder of an ionic conductive material represents from 33% to 66% by volume, relative to the total volume of the ionic conductive membrane, preferably ranging from 33% to 55% by volume, preferably ranging from 40 to 50% by volume.

[0088] The volume content of ionic conductive material in the membrane is an essential parameter of the material of the invention. This content results from a percolation law, and the inventors discovered that they could be applied to the matrix of the invention. The fundamental idea of ​​this theory is that when the number of links in a network increases (here, by the volume content of the ionic conductive material), a global cluster of connected nodes suddenly emerges. It is therefore essential that this value is not lower than the three-dimensional percolation threshold (33%), in order to obtain conductivity. Furthermore, the maximum limit in ionic conductive material makes it possible to optimize the mechanical strength and ionic conductivity of the membrane, because too high a content of ionic conductive material will be detrimental to its mechanical strength.The volume content range of ionic conductive material therefore ensures both good conductivity to the membrane and good mechanical strength.

[0089] The ionic conductive membrane

[0090] Preferably, the ionic conductive membrane of the invention is porous.

[0091] More preferably, the ionic conductive membrane of the invention has a porosity ranging from 1% to 25%, more preferably ranging from 3% to 20%.

[0092] The ionic conductive membrane is typically selected from: a cationic membrane, an anionic membrane, and a mixed membrane, partially anionic and partially cationic.

[0093] According to a first embodiment, the ionic conductive membrane is cationic. For the purposes of the invention, the term "cationic membrane" means an ionic conductive membrane capable of transporting cations but not anions.

[0094] A cationic membrane typically comprises a material carrying anionic groups capable of interacting by electrostatic bonds with the cations to be transported.

[0095] The cationic membrane can be generic or universal, that is to say, capable of transporting any type of cations.

[0096] Alternatively, the cationic membrane can be specific, i.e. capable of transporting only certain cations or certain families of cations. Examples of selective cationic membranes include cationic membranes specific to lithium ions, commonly used to extract lithium from seawater.

[0097] The generic / universal or specific nature of the membrane depends on the chemical nature of the ionic conductive material dispersed in the matrix. The selection of a suitable conductive material is a matter for the person skilled in the art, depending on the desired final properties of the membrane.

[0098] According to a second embodiment, the ionic conductive membrane is anionic. For the purposes of the invention, the term "anionic membrane" means an ionic conductive membrane capable of transporting anions but not cations. An anionic membrane typically comprises a material carrying cationic groups capable of interacting by electrostatic bonds with the cations to be transported.

[0099] The anionic membrane can be generic or universal, i.e., capable of transporting all anions. Alternatively, the anionic membrane can be specific, i.e., capable of transporting only certain anions or certain families of anions.

[0100] The generic / universal or specific nature of the membrane depends on the chemical nature of the ionic conductive material dispersed in the matrix. The selection of a suitable conductive material is a matter for the person skilled in the art, depending on the desired final properties.

[0101] According to a third embodiment, the ionic conductive membrane is mixed, partially anionic and partially cationic. For the purposes of the invention, the term “mixed, partially anionic and partially cationic membrane” means an ionic conductive membrane capable of transporting both anions and cations. This type of membrane is typically obtained from a mixture of several ionic conductive materials comprising at least one anionic material and at least one cationic material.

[0102] As with cationic and anionic membranes, the generic / universal or specific character can be adjusted by the selection of ionic conducting materials, on the one hand with respect to cations and on the other hand with respect to anions.

[0103] According to a particular embodiment, the ionic conductive membrane of the invention is made of an electronic insulating material. The electronic insulating nature of the membranes of the invention is not essential for all applications. However, it is particularly suitable in the case of an ionic conductive membrane intended for a fuel cell.

[0104] For the purposes of the invention, the term "electronic insulating material" means a material incapable of transporting electrons. Typically, in the context of the invention, an electronic insulating material has an electronic resistance greater than or equal to 1 Megohm (MO).

[0105] The electronic resistance of a material can be determined by any method known to those skilled in the art. For example, it can be measured as follows:

[0106] A pellet of the material whose electronic resistance value is to be determined is prepared by pressing powder of the said material under 5t / cm 2 then by sintering at a temperature 30% lower than its melting temperature (expressed in K) for 2 hours. A gold film is then deposited on the surface of the pellet, in order to improve the contact between the current collectors and the sample. The pellet is finally placed between 2 nickel collectors on the surface. A voltage is applied to the terminals of the electrodes in order to measure the evolution of the current flowing in the pellet as a function of time. The graph obtained plotting the evolution of this current as a function of the applied voltage is a straight line whose slope corresponds to the electronic resistance Re of the pellet.

[0107] Preferably, the ionic conductive membrane according to the invention has a thickness ranging from 1 μm to 1 mm, more preferably ranging from 10 μm to 500 μm, even more preferably from 20 μm to 100 μm, typically 50 μm.

[0108] The invention is advantageous in that it allows the preparation of ionic conductive membranes, in particular anionic and / or cationic membranes, which can have varied mechanical properties, in particular in terms of rigidity and flexibility. In particular, the invention allows, by the selection of the materials forming the matrix, to adjust the mechanical properties of the final membrane, in particular with a view to its final use. For example, the invention allows the preparation of flexible ionic conductive membranes, suitable for integration into flexible assemblies / devices, such as for example in clothing, in particular for the manufacture of connected clothing. Conversely, the invention allows the preparation of rigid ionic conductive membranes, particularly suitable for industrial installations or even cars.

[0109] Manufacturing process

[0110] The invention also relates to a process for preparing an ionic conductive membrane according to the invention, as defined above.

[0111] Preferably, the method according to the invention comprises the following steps: a) providing (i) a crosslinkable polymer as defined above and (ii) a powder made of an ionic conductive material as defined above, b) dispersing said powder in said crosslinkable polymer so as to form a homogeneous mixture, c) forming a film from the mixture obtained in b), in particular by depositing the mixture on the surface of a support, d) crosslinking the crosslinkable polymer, preferably in an oven.

[0112] Preferably, during step b), the powder made of an ionic conductive material is dispersed in the crosslinkable polymer so that said powder represents from 33% to 66% by volume, relative to the total volume of the mixture of the powder and the crosslinkable polymer.

[0113] Preferably, the method according to the invention comprises the following steps: a) providing (i) a crosslinkable polymer as defined above and (ii) a powder made of an ionic conductive material as defined above, b) dosing by weighing the crosslinkable polymer and the powder made of an ionic conductive material so that each of these two components has a volume greater than 33% and less than 66% of the total volume of the membrane, taking into account their respective density in order to comply with the percolation rule, c) mixing said powder with said crosslinkable polymer so as to form a homogeneous mixture, d) forming a film of desired thickness from the mixture obtained in c), in particular by depositing the mixture on the surface of a support, e) crosslinking the crosslinkable polymer by heating, preferably in an oven.

[0114] Preferably, the amount of powder dispersed in the polymer during step b) is adjusted so as to obtain a mixture having good spreading capacity at room temperature, in particular with viscoelastic properties suitable for allowing the formation of a film during step c).

[0115] Preferably, the film obtained at the end of step c) has a thickness ranging from 1 μm to 1 mm, more preferably ranging from 10 μm to 500 μm, even more preferably from 20 μm to 100 μm, typically 50 μm.

[0116] The crosslinking of the polymer during step d) can be carried out according to any method known to those skilled in the art. It can, for example, be carried out by chemical crosslinking, in particular with sulfur, or by physical crosslinking, for example by heat treatment or by irradiation with an electron beam.

[0117] According to a particular embodiment, the method of the invention comprises, before step b), a preliminary step of preparing the powder into an ionic conductive material, typically by functionalization of a precursor material. Such a functionalization step typically makes it possible to modify the ionic conductivity of the precursor material, before its dispersion in the crosslinkable polymer.

[0118] According to a first embodiment, the precursor material is non-ionically conductive. Thus, according to this first embodiment, the prior preparation step consists of a step of functionalizing the precursor material making it possible to graft charged organic groups onto the surface of the precursor material, so as to make it ionically conductive. Such a grafting step is typically carried out according to any method known to those skilled in the art. According to a second embodiment, the precursor material is ionically conductive. Thus, according to this second embodiment, the prior preparation step makes it possible to modify the conductivity of the precursor material. For example, the functionalization step can be carried out so as to convert an anionically conductive material into a cationically conductive material.Such a step of modifying the conductivity of a material can be carried out according to any known method, for example according to the grafting method described in WO 2021 / 083922 A1.

[0119] Applications

[0120] The invention also relates to a device integrating an ionic conductive membrane as defined above or obtained according to the method described above.

[0121] The nature of this device is not particularly limited. It can consist, for example, of a fuel cell, an electrolyzer, a desalination plant (or device for desalination), a device for extracting lithium from seawater, etc.

[0122] Thus, the invention relates in particular to a fuel cell comprising an ionic conductive membrane as defined above or obtained according to the method described above.

[0123] Methods for preparing fuel cells are described in the prior art and can be applied by analogy.

[0124] Current micro-batteries consist of a stack of membranes and electrodes which are compressed to ensure watertightness.

[0125] The micro-batteries according to the invention can be mass-produced using automated means in the semiconductor industry. The size and geometric arrangement of the cells can be easily adapted.

[0126] Preferably, a fuel cell according to the invention comprises:

[0127] - a cathode part comprising a cathode;

[0128] - an anode part comprising an anode;

[0129] - one or more devices for bringing a source of water and / or a source of oxygen into contact with the cathode part;

[0130] - a hydrogenated porous silicon in contact with the anode part;

[0131] - said cathode part and said anodic part being physically separated by an ionic conductive membrane according to the present invention. The invention also relates to a process for producing dihydrogen, for example from water and oxygen.

[0132] According to the invention, the operating temperature of said fuel cell is generally between approximately 10°C and approximately 70°C, and preferably at room temperature (20-25°C). The reaction preferably takes place at atmospheric pressure or at slightly higher pressures, generally less than or equal to approximately 2 bars, between approximately 1 bar and 1.5 bar.

[0133] The diffusion medium of a fuel cell is generally an electron conductor and consists, for example, of woven carbon fibers in which porous graphite particles are embedded. In this case, the gas molecules pass through the woven fiber grid and the electrons are carried by the carbon fibers. According to another embodiment, it also consists of a gas-permeable crosslinked polymer such as PDMS (polydimethylsiloxane) loaded with porous graphite particles.

[0134] Several methods can be used to stack the active layers of a fuel cell. One method involves stacking the layers on top of each other, usually from the anode to the cathode, to form a complete stack of a micro-cell. A second method involves producing the anode and cathode separately and then assembling them, for example, in a press. Although different in their final assembly method, these two methods use similar layer deposition techniques.

[0135] The invention also relates to an electrolyser comprising an ionic conductive membrane as defined above or obtained according to the method described above.

[0136] Methods for preparing electrolysers are described in the prior art and can be applied by analogy.

[0137] Electrolysers typically consist of a stack of two electrodes, possibly coated with a catalyst, between which an ionic conductive membrane is placed.

[0138] Typically, the device of the invention, and more particularly the fuel cell, can be transportable or fixed.

[0139] Advantageously, the device may be biocompatible and comprise an ionic conductive membrane as defined above or obtained according to the method described above.

[0140] The invention is advantageous in that it allows the preparation of ionic conductive membranes, in particular suitable for use in fuel cells, according to a simplified process compared to the techniques of the prior art.

[0141] In addition, the invention makes it possible to considerably reduce the manufacturing cost of ionic conductive membranes, on the one hand by making it possible to do without expensive polymers such as Nation®, and on the other hand thanks to a manufacturing process that is simple to implement.

[0142] The membranes according to the invention also have improved mechanical strength compared to the membranes of the prior art.

[0143] Finally, the invention is advantageous in that it allows access to ionic conductive membranes having variable flexibility, depending on the polymer used to form the matrix.

[0144] Examples:

[0145] Example 1- Preparation of an anionic membrane according to the invention from Zeolite Y-Na and a polydimethylsiloxane polymer

[0146] Material

[0147] - Y-Na zeolite (CAS 1318-02-01),

[0148] - ion exchange resin, commercially available from DuPont under the name Amberlite™ H;

[0149] - 3-(Trimethoxysilyl)propyl-N,N,N-trimethylammonium-15N chloride (TMSPA, CAS 35141-36-7);

[0150] - polydimethylsiloxane polymer + curing agent, commercially available in the form of a mixture from DOW CHEMICALS under the name Sylgard® 184,

[0151] - polytetrafluoroethylene (PTFE) support.

[0152] Preparation of the anionic membrane

[0153] 1 ère step: Conversion of zeolite Y-Na to zeolite YH

[0154] 300 mg of zeolite Y-Na powder is mixed with 5 ml of water. 300 mg of Amberlite H +are then added to the solution. The mixture is left to react with stirring for 24 hours. An infrared spectrometric analysis confirms the production of zeolite YH (by substitution of the free sodium cations Na + by hydrogen ions H + ).

[0155] 2 ème Step: Conversion of cationic conductive YH zeolite into an anionic conductive material

[0156] The TH zeolite powder is dried and mixed with 5 mL of TMSPA to convert cationic conduction to anionic conduction. The mixture is left to react for 10 hours. The product is then rinsed and dried. Infrared spectrometry analysis confirms the conversion of the zeolite.

[0157] 3 èmeStep: Membrane Preparation The converted zeolite powder is then mixed with an equal mass of the polydimethylsiloxane polymer and curing agent mixture. The resulting mixture is deposited on a PTFE support to form a 100 μm thick film, the thickness being controlled by using strips of adhesive tape as a template. The film is then placed for 24 hours at a temperature of 50°C to cause the polymer to crosslink. The film is then peeled off the support and die-cut to obtain a disc 11 mm in diameter.

[0158] Example 2 - Preparation of a cationic membrane according to the invention from an ion exchange resin and a polydimethylsiloxane polymer

[0159] Material

[0160] - cationic ion exchange resin, strongly acidic, in the form of sodium Na +, commercially available from DuPont under the name Amberlite™ IRP69;

[0161] - polydimethylsiloxane polymer + curing agent, commercially available in the form of a mixture from DOW CHEMICALS under the name Sylgard® 184,

[0162] - polytetrafluoroethylene (PTFE) support.

[0163] Preparation of the cationic membrane

[0164] 900 mg of the ion exchange resin is mixed with 400 mg of the mixture of polydimethylsiloxane polymer and curing agent. The resulting mixture is deposited on a PTFE support to form a 100 μm thick film, the thickness being controlled by using strips of adhesive tape as a template. The film is then placed for 24 hours at a temperature of 50°C, in order to cause the polymer to crosslink. The film is then peeled off the support and placed for 12 hours under a water-saturated atmosphere, in order to rehydrate it. The film is then die-cut to obtain a disc 11 mm in diameter.

[0165] Example 3 - Preparation of electrolysers from the membranes according to the invention and evaluation of the conduction of the membranes

[0166] The ionic conductivity of the membranes prepared in Examples 1 and 2 was evaluated in electrolyzer-type devices.

[0167] Preparation of the electrolyzers

[0168] An electrolyser was prepared from each of the membranes. In particular, the electrolysers were prepared by superimposing the following layers: - a woven carbon electrode,

[0169] - the membrane to be evaluated, and

[0170] - a woven carbon electrode.

[0171] Evaluation of electrolyzer performance

[0172] The electrical conduction of the different electrolysers was evaluated by measuring the variation in the intensity of the current measured at the terminals of the electrolyser as a function of the imposed voltage.

[0173] The results obtained are presented in Figures 1 and 2.

[0174] [Fig 1] Figure 1 is a curve representing the evolution of the intensity measured at the terminals of an electrolyser integrating the composite membrane prepared in example 1, as a function of the imposed voltage.

[0175] [Fig 2] Figure 2 is a curve representing the evolution of the intensity measured at the terminals of an electrolyser integrating the composite membrane prepared in example 2 or a Nation® type membrane, as a function of the imposed voltage.

[0176] Curve 1 was obtained from an electrolyzer incorporating the composite membrane prepared in Example 2.

[0177] Curve 2 (comparative) was obtained from an electrolyser incorporating a Nation® type membrane.

[0178] From Figure 1, it is observed that a non-zero current is measured at the terminals of the electrolyser incorporating the composite membrane (according to the invention) prepared in Example 1. The prepared electrolyser is therefore indeed electrically conductive, thus proving the capacity of the membrane (according to the invention) prepared in Example 1 to conduct ions through the membrane. The membrane prepared in Example 1 is therefore indeed ionically conductive.

[0179] From Figure 2, it is observed that a non-zero current is measured at the terminals of the electrolyser incorporating the composite membrane (according to the invention) prepared in Example 2. The electrolyser is therefore indeed electrically conductive, thus proving the capacity of the membrane prepared in Example 2 to conduct ions through the membrane. The membrane (according to the invention) prepared in Example 2 is therefore indeed ionically conductive.

[0180] Furthermore, still according to Figure 2, the electric current measured at the terminals of the electrolyser incorporating the membrane prepared in Example 2 (curve 1) is significantly higher than that measured at the terminals of the electrolyser incorporating a Nation® membrane (curve 2). The membrane (according to the invention) prepared in Example 2 therefore has an ionic conductivity significantly higher than that of the Nation® membrane.

[0181] Example 4 - Preparation of batteries from the membranes according to the invention The performance of the membranes prepared in Examples 1 and 2 was also evaluated in batteries.

[0182] Material

[0183] Batteries are prepared from the following materials:

[0184] - electrode consisting of a woven carbon fabric substrate coated with a Vulcan carbon-supported catalyst (20%) and a Nation® surface coating, commercially available from the FuelCell Store company under the reference W1 S1011, and

[0185] - crosslinked polyacrylic acid polymer, commercially available under the reference Carbopol® 940.

[0186] Preparing the battery

[0187] As a preliminary step, the surface coating of the electrodes is modified to convert it into an anionic conductive material by applying the method described in WO 2021 / 083922 A1. Similarly, the crosslinked polyacrylic acid polymer is modified using the same method. These preliminary steps ensure good ionic conduction between the membrane and the supported catalyst of the electrode.

[0188] A stack is then prepared from each of the membranes prepared above. In particular, the stacks are prepared by superimposing the following layers:

[0189] - an electrode modified according to the method described above,

[0190] - a layer of a crosslinked polyacrylic acid polymer modified according to the process described above,

[0191] - the membrane to be evaluated,

[0192] - a layer of a crosslinked polyacrylic acid polymer modified according to the process described above, and

[0193] - an electrode modified according to the method described above.

[0194] Battery Evaluation

[0195] OCV, voltage and power measurements were then carried out from the different batteries. The following results were obtained.

[0196] For the cell incorporating the membrane (according to the invention) prepared in example 1, the measured OCV is equal to 700 mV.

[0197] For the cell incorporating the membrane (according to the invention) prepared in Example 2, the measured OCV is equal to 700 mV. In addition, the measured power density is equal to 100 mW / cm 2 .

Claims

CLAIMS 1. Ionic conductive membrane comprising a matrix of a crosslinked polymer and a powder of an ionic conductive material, said powder of an ionic conductive material being dispersed in the continuous solid matrix and representing from 33% to 66% by volume, relative to the total volume of the ionic conductive membrane.

2. Membrane according to claim 1, in which the continuous solid matrix is ​​obtained by crosslinking, in particular by chemical or physical crosslinking, of a crosslinkable polymer chosen from polysiloxanes, thermosetting resins, polyamides, polyesters, polyolefins and any of their mixtures, preferably chosen from polydimethylsiloxanes, epoxy resins and any of their mixtures.

3. Membrane according to claim 1 or according to claim 2, in which the powder made of an ionic conductive material has a particle size less than or equal to 20 pm, preferably ranging from 100 nm to 10 pm.

4. Membrane according to any one of the preceding claims, in which the ionic conductive material is chosen from inorganic materials based on silicon, optionally functionalized, organic materials such as ion exchange resins, or any of their mixtures.

5. Membrane according to claim 4, in which the ionic conductive material is chosen from silicates, optionally functionalized, ion exchange resins and any of their mixtures.

6. Membrane according to any one of the preceding claims, characterized in that said ion-conducting membrane is porous, preferably has a porosity ranging from 1% to 25%, more preferably ranging from 3% to 20%.

7. A method of preparing an ionic conductive membrane according to any one of the preceding claims, the method comprising: a) providing (i) a crosslinkable polymer and (ii) a powder made of an ionic conductive material, b) dispersing said powder in said crosslinkable polymer so as to form a homogeneous mixture, said powder representing from 33% to 66% by volume, relative to the total volume of the mixture, c) forming a film from the mixture obtained in b), in particular by depositing the mixture on the surface of a support, d) crosslinking the crosslinkable polymer.

8. Method according to claim 7, comprising a prior step of functionalizing the powder into an ionic conductive material.

9. Fuel cell comprising a membrane according to any one of claims 1 to 6 or obtained by a method according to claim 7 or according to claim 8.

10. Biocompatible device comprising a membrane according to any one of claims 1 to 6 or obtained by a method according to claim 7 or according to claim 8.

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