EP2253036A1 - Material for an electrochemical device - Google Patents

Abstract

The present invention relates to a material for an electrochemical device, especially a fuel cell, an electrolyser or a storage battery, comprising a matrix and activated boron nitride contained in the matrix.

Description

 Material for an electrochemical device

The present invention relates to the materials used for the production of proton exchange membrane comprising boron nitride, intended for the manufacture of electrolysers, fuel cells and / or accumulator and in general of any electrochemical device using ionoselective membranes.

WO 2006/003328 discloses the use of a boron nitride ceramic for collision between protons and electrons and storing hydrogen.

The Nafion ^® commonly used (Dupont de Nemours) to produce membranes for fuel cells, for example in the patent application WO 2004/067611. This material has the disadvantage of a very high cost and can deconstruct at a temperature of use greater than 80 ⁰ C under normal conditions.

There is therefore a need to benefit from a possibly less expensive material that can be used at temperatures up to 200 ^° C., for example of the order of 95 ^° C., better still 120 ^° C. or even 150 ^° C. or 180 ^° C.

The invention aims in particular to provide a new material for electrochemical devices, in particular fuel cells, electrolyzer or accumulator, to ensure good mechanical and thermal stability, and in particular operation at a relatively high temperature as at room temperature .

According to one of its aspects, the subject of the invention is a material for an electrochemical device, in particular a membrane for a fuel cell, comprising a matrix and activated boron nitride contained in the matrix.

According to one of its aspects, the subject of the invention is a material for an electrochemical device, in particular an electrolyser membrane, comprising a matrix and activated boron nitride contained in the matrix.

The material comprising activated boron nitride can be used to manufacture a fuel cell, an accumulator, an electrodialysis device, a Redox system for storing electrical energy, a chlorine electrolyzer or ionoselective electrodes. Activation of boron nitride

By activation of boron nitride is meant a process for promoting proton conduction in boron nitride. In activated boron nitride, the number of bonds B-OH, NH, B-SO ₄ H, B-SO ₃ H, N-SO ₄ H and N-SO ₃ H formed is sufficient to allow the displacement of a proton of a group B-OH or BSOχH or of an NH or N-SOxH group towards an electron pair available on an adjacent oxygen or nitrogen, or on an OH or NH group forming NH ₂ ⁺ , BOH groups ₂ ⁺ ,

Conduction of protons can also be carried out by means of doublets available on oxygen atoms inserted in nitrogen vacancies of boron nitride. Such nitrogen gaps containing oxygen atoms may be especially present when the boron nitride was obtained from B ₂ O ₃ or H ₃ BO ₃ .

The activated boron nitride may comprise bonds B-OH, NH, B-SO ₄ H, B-SO ₃ H, N-SO ₄ H and N-SO ₃ H capable of being converted into B-OH ₂ ⁺ , NH ₂ ⁺ , B-SO _x H ₂ ⁺ and N-SOxH ₂ ⁺ thus allowing a proton transfer by these sites to create thanks to the activation.

The boron nitride may be in the form of grains contiguous to each other, for example percolated or sintered. Percolates are grains that physically touch each other.

The material may comprise percolated boron nitride grains, for example held together by a matrix comprising a compound, for example a compound of the following list: nickel, boron oxide, calcium borate, ethyl cellulose, acid boric, polyvinyl alcohol (PVA), vinylcaprolactam, PTFE (Teflon ^®), sulfonated polyether sulfone, this list not being limiting.

The mass proportion of boron nitride in the material may be between 5% and 100%, for example up to 70%. The material can be made entirely of high pressure sintered boron nitride powder. Alternatively, it may comprise boron nitride and a binder, being manufactured, for example, by a HIP (Hot Isostatic Pressure) process.

The boron nitride used may comprise at least one, for example one or more substituent element (s) from the following list: boron oxide, calcium borate, boric acid, hydrofluoric acid. The presence of such elements can promote activation, especially when present in a mass proportion of between 1 and 10%.

The presence of boric acid, for example present in the pores of boron nitride or in amorphous form, may make it possible to promote the creation of B-OH and NH bonds.

The material may comprise a mineral matrix, for example comprising active carbon or graphite, or else boric acid.

As a variant, the material may comprise an organic matrix, for example comprising at least one of the compounds of the following list: polymer, fluoropolymers,

PVA, epoxy resin, cellulosic compounds. The material may be formed by boron nitride, for example powdery, inserted, in particular dispersed, in a polymer matrix, which can ensure very good proton conductivity to the material.

The polymer, for example PVA, can be used to plug the porosities present in the boron nitride. The addition of the polymer may for example be carried out under vacuum, so that the latter is sucked into the pores of the boron nitride.

The matrix may for example be made from a polymerizable matrix precursor under the action of a stimulus, for example by evaporation of one or more solvents, an increase in temperature or by sending a γ ray. . By way of example, it is possible to use PVA in the matrix, by wetting this mixture and then introducing boron nitride. A crosslinking agent, for example glutaraldehyde, and a crosslinking catalyst, for example acid, is then added, and finally the PVA is thermally crosslinked at 40 ^° C. The PVA may preferably be thermally crosslinked and immersed in an acid bath. It is thus possible to obtain a BN membrane in a PVA matrix having a conductivity of 10 ¹ S / cm.

The matrix can itself be a proton conductor or, on the contrary, not be a protonic conductor.

The matrix may comprise at least one organic material and one inorganic material. The matrix may comprise one or more compounds of the following list, which is not limited to: inorganic compound, for example silica, such as Aerosil ^®, grafted silica, fumed amorphous silica, organic silica with group thiol, silica with phosphonic acid function, silica with surface-anchored sulfonic acid, alumina, zirconia, sulphated zirconia, titania, sulphonated titania, tungsten trioxide, hydrated tungsten trioxide, heteropoly acid, eg polytriacetylene (PTA ), polyacrylic acid (PTA), STA, SMA, tungstophosphoric acid (TPA), molybdophosphoric acid (MBA), disodium tungstophosphoric acid salt (NA-TPA), phosphomolybdic acid (PMA), lacunary heteropolyacid HsSiWi 1O39, functionalized heteropolyacid sulfonic acid , PWA, silico-tungstic acid, PTA supported on SiO ₂ , ZrO ₂ and TiO ₂ , charged heteropoly acid MCM-41, mesoporous material of tungsten silicate SI-MCM-41, heteropoly acid loaded with Y-zeolyte, silico-tungstic acid, phosphate of zirconia, sulfophenyl zirconia phosphate (ZRSPP), hydrogenated zirconia phosphate ZR (HPO ₄ ) ₂ , zirconia tricarboxybutyl phosphonate, zirconia sulfophenylene phosphonate, Zr ( HPO ₄₎ Io (0 ₃ PC _O H ₄ SO _S H) _IO, sulfophenylene phosphonate zirconium phosphate, zirconia phosphate sulfonated salt of silicotungstic acid of Celsium multilayer nanoparticles silicate, for example montmorillonite, laponite, montmorillonite modified, for example sulphonated montmorillonite, MCM-41, organic montmorillonite (OMMT), montmorillonite grafted with organic sultones and perfluorinated sultones, phosphosilicates (P ₂ Os-SiO ₂ ), phosphato-antimonic acid, noble metals, for example platinum, ruthenium , coated platinum silicate Nafion ^®, silver, zéolyte, chabazite and clinoptylolite, mordonite, phosphate, calcium phosphate, calcium hydroxide phosphate, boron phosphate, organic compound, polymer, Nafion ^®, perfluorosulfonic acid, sulfonated polysulfone, PEO, PTFE , polyaniline, poly (vinylidene) fluoride-chlorotetrafluoroethylene, PEG, DBSA, 4-dodecylbenzene sulfonic acid, SEBSS (styrene sulfone, styrene- (ethylene-butane) ylene) sulfone), PVA, glutaraldéide, Krytox, diphénylsilicate, diphényldiméthoxysilicate, poly (ether sulfone) sulfone, PVDF membrane Nafion ^® NRE-212, Cs _{2, 5} H _{o, 5} PWO _40, PVDF-G-PSSA, polyvinylidene fiuoride, polyacrylonitryl, dodeca-tungstophosphoric acid, (sulfonated poly) ether ether ketone (SPEEK), PEO, sulfonated poly (arylene ether sulfone), polyvinyl alcohol, PEEK (s-polyether ether ketone), cardo sulfonated polyethersulfone, polyphenylene oxide (PPO), polyethylene glycol, silica nanoparticles , tungstosilicate divacant [γ-SiWioθ36] ^{8 ",} PWA, PBI, PEG, polyethylenimine (PEI), poly (arylèneéthersulfone) disulfonated, Teflon ^®, divynilbenzène (crosslinked DVB) sulfone, poly (ethylene-alt-tétrafluroroéthylène) grafted polystyrene, poly (vinyldifluoride), azole polybenzimide, PVDF, cardo sulfonated poly (etheretherketone), poly (fluorinated arylene ether) S, Nafionon 115, polyimide, polyamidimide (PAI), polyvinylidene fluoride (PVDF), styrene-ethylene-butylene-styrene elastomer (SEVS), poly (sulfonated biphenyl ether sulfone), polytetrafluoroethylene (PTFE), PBI. Boron nitride may be activated during or at the end of the membrane manufacturing process.

Obtaining a membrane with boron nitride can be obtained, for example, by one or other of the following two methods: the first method consists in manufacturing a membrane by high temperature sintering of a membrane " raw 'prepared by the usual methods of making ceramic objects. The second method consists in producing a membrane by incorporating boron nitride powder into an organic binder matrix by ensuring percolation between the boron nitride grains.

For example, for the first method, grains of boron nitride are mixed with a polymer binder in liquid form, this mixture being poured on a substrate, then heated to a temperature sufficient to cause calcination of the binder, for example to a temperature of the order of 600 or 700 ⁰ C, so that the grains of boron nitride are percolated between them on the substrate.

In a further step, the result obtained is heated to a temperature of the order of 1000-1500 ^° C. under a neutral atmosphere, for example nitrogen, ammonia or argon, causing the grains to sinter together.

Finally, in a further step, the substrate is removed and a rigid boron nitride sheet composed of sintered grains, for example with a thickness of between 50 μm and 300 μm, is obtained. The activation is carried out after sintering, to avoid the risk that it is destroyed by sintering.

It is also possible, in an alternative embodiment, to incorporate the powdery boron nitride in a molten inorganic binder, for example boric acid. The activation can be carried out under the atmosphere of high temperature steam. The temperature may for example be less than 600 ^° C., or even less than 500 ^° C., better still less than 400 ^° C., or even about 300 ^° C. The material may have sufficient mechanical cohesion to enable it to be in the form of a membrane, for example with a thickness of between 50 μm and 300 μm.

According to the second method, the boron nitride can be activated in its pulverulent form before insertion into the matrix, for example in a polymer, or after insertion into the matrix, for example depending on the matrix used.

The material can be used in the form of a membrane whose tensile strength, between 20 ⁰ C to 180 ⁰ C, is defined by a modulus of elasticity. The modulus of elasticity of a BN membrane with a cross-linked PVA matrix may be, for example, between 10 ⁹ Pa and 10 ⁸ Pa.

The matrix may be insoluble in water. By insoluble, it should be understood that, having remained 600 seconds at 80 ^° C. in the water, less than 10 ^-2 % of the membrane is passed into the solution, even in the presence of an electric field, for example an electric field greater than 11000 V / m, that is to say a voltage of the order of 2.2 V applied to a membrane with a thickness of the order of 200 μm. boron spent in the solution may be less than 10 ^"3 mg / 1.

The boron nitride may be in the form of grains contiguous to each other, for example percolated or sintered. Percolates are grains that physically touch each other. Commercially available boron nitride is electronic and ionic insulation.

The invention further relates, in another of its aspects, an extruded film, screen printed, membrane film alone or with its electrodes, made where can be made from the material as defined above. The invention further relates, in another of its aspects, a proton exchange membrane for an electrochemical device, in particular a fuel cell an electrolyzer or accumulator, comprising a layer of the material as defined above.

According to another of its aspects, the invention also relates to a method of manufacturing such a membrane for fuel cell or other applications, in particular electrolysers or accumulators, in which the membrane is exposed to an acidic solution and then rinsed. . Exposure of the membrane to the acid can advantageously be carried out under an electric field of between 15 and 40,000 / m, or even of the order of 15,000 V / m, which can improve the efficiency of activation. A field of 15000 V / m is equivalent to applying 1.5 V for a thickness of boron nitride of 100 μm or 15 V for a thickness of 1 mm. The field can be at least 15000 V / m, that is to say that a voltage of about 3 V is applied to a membrane of 200 .mu.m thick.

The total impermeability of the wall during production storage can allow to store within the electrode, for example the cathode, the atomic and / or molecular hydrogen formed. The hydrogen adsorption required for this purpose may depend on the nature of the electrode, for example the cathode. Indeed, the presence of water in the electrode, for example the cathode, may risk preventing the establishment of molecular contact within the electrode, for example the cathode, thus preventing the establishment of a conduction satisfactory electrical, and then preventing the formation of hydrogen in the electrode, for example the cathode, or at the interface. On the other hand, the presence of water at the interface of the electrode and the proton exchange membrane may be of no consequence on the system. Indeed, the water behaves as the continuity of the wall permeable to ions because of its ionic conduction power. Moreover, since near the electrode the medium is reducing thanks to the presence of hydrogen, the presence of water is not a problem for storage. At least one electrode, for example the anode, may be made of any electrically conductive material compatible with the H ⁺ ion donor, for example platinum, graphite, a thin layer of a mixture of RuO ₂ , IrO ₂ or RuO ₂ , IrO ₂ and TiO ₂ or RuO ₂ , IrO ₂ and SnO ₂ lined with a porous titanium plate (30 to 50% for example) or a conductive polymer, among others. The thin layer may have a thickness of between 5 microns and 20 microns, for example about 10 microns.

The invention further relates, in another of its aspects, an electrode for an electrochemical device, in particular a fuel cell, made at least partially in the material as defined above. The electrode may for example be a cathode or anode. The material according to the invention may be metallized before activation.

At least one of the electrodes, for example the cathode, may also comprise activated boron nitride and activated carbon or graphite. Said electrode, for example the cathode may be embedded in a mass of boron nitride. The electrode may comprise, for example, a metal foam or any conductive material, for example active carbon or graphite, embedded in a mass of boron nitride.

At least one of the electrodes, for example the anode, may for example comprise a thin layer of a mixture of RuO ₂ , IrO ₂ or RuO ₂ , IrO ₂ and TiO _2, or

RuO ₂ , IrO ₂ and SnO ₂ lined with a porous titanium plate (from 30% to 50% for example).

The thin layer may have a thickness of between 5 μm and 20 μm, for example

About 10 μm.

One or the other of the electrodes may be made in a powder form, being sprayed on the membrane constituted by the boron nitride layer mentioned above. After spraying, this layer can be compressed in press at a pressure of between 5 and 40 kg / m ² , for example about 20 kg / m ² , at a temperature of between 15 ^° C. and 200 ^° C., for example between 25 ⁰ C to 150 ⁰ C to improve the adhesion of the electrodes to the membrane. The temperature depends on the nature of the layer, according to for example whether or not it comprises a polymer sensitive to the maximum temperature applied.

Another subject of the invention is, according to another of its aspects, a fuel cell, electrolyzer or accumulator cell comprising: a cathode, and a proton exchange membrane, at least one of the cathode and the membrane comprising or even consisting of the material as defined above, in particular the protonic exchange membrane.

The cell may further comprise an anode. The cathode of the cell may be as defined above. As a variant, one or both of the electrodes, anode and / or cathode, may comprise at least one of the compounds of the following list, which is not limiting: platinum, for example in the form of nanograins, activated carbon, a binder, for example ethanol or a polymer compound, for example PTFE, or a mixture of these elements. Either of the electrodes can be made in a powder form, being sprayed onto the proton exchange membrane. In an alternative embodiment, the entire outer surface of the cathode may be covered with a material comprising boron nitride, for example activated boron nitride. The cathode can be immersed in boron nitride, which can to be powdery. The cathode can be wound on itself, in a spiral shape.

The cell may be generally cylindrical in shape, the proton exchange membrane constituting a cylindrical envelope surrounding the cathode. The proton exchange membrane may be impermeable to hydrogen. By

"Impermeable", it should be understood that a quantity of hydrogen less than 2% can pass through a membrane of thickness 150 microns. The proton exchange membrane may be non-porous. By "non-porous", it should be understood that less than 2% of gas can pass through a 150 μm thick membrane. The proton exchange membrane may have a non-zero surface porosity.

At least one of the electrodes, for example the anode, may comprise at least one layer of a metal compound in contact with the protonic exchange membrane. The metal compound can be chosen from: platinum, gold, nickel and their alloys.

One or both of the electrodes, anode and / or cathode, may be as defined above. One or both of the electrodes, anode and / or cathode may for example comprise at least one of the compounds of the following list, which is not limiting: platinum, for example in the form of nanograins, boron nitride , especially activated boron nitride as mentioned below, activated carbon, a binder, for example ethanol or a polymer compound, for example PVA or PTFE, or a mixture of these elements.

The thickness of the proton exchange membrane may be less than or equal to 1 mm, being for example between 50 microns and 300 microns.

The cell may further comprise a substrate for supporting the proton exchange membrane. The substrate may be chosen from: alumina, zirconia, porous boron nitride and mixtures thereof.

The substrate may for example comprise a grid, one or more son, a foam, a film or a plate, for example a pierced plate. The substrate may comprise, for example, a thin woven fabric made of a polymer, for example polyamide, for example Nylon ^® . The invention further relates, in one aspect, to an electrolyzer comprising a cell as defined above. According to one of its aspects, the subject of the invention is also a fuel cell comprising a cell as defined above, as well as a fuel supply circuit on the cathode side and a fuel circuit. supply of an oxidant on the side of the anode. The fuel may be hydrogen gas. The oxidant may be air or oxygen. Hydrogen for supplying the cell may be stored as hydride in the material defined above.

The use of the electrolyser or the fuel cell in accordance with the invention can be carried out at relatively high temperatures, for example of the order of 80 ^° C. for the electrolyzer and 150 ^° C. for the fuel cell. .

The invention further relates, in one of its aspects, to a method for activating a material for an electrochemical device, comprising a matrix and boron nitride contained in the matrix, in which the material is exposed to a fluid making it possible to provide hydroxyl radicals -OH and / or ions H ₃ O ⁺ or SO ₄ ^{2 "} and to create in the boron nitride bonds B-OH and / or B-SO ₄ H, B-SO ₃ H, N-SO ₄ H, N-SO ₃ H and / or NH bonds.

For this activation, the boron nitride, or the membrane, can be exposed to a fluid making it possible to provide ions H ₃ O ⁺ or SO ₄ ^{2 "} and to create in the boron nitride bonds B-OH and / or B S0 ₄ H, B-SO ₃ H, N-SO ₄ H, N-SO ₃ H and / or NH bonds The fluid may for example be an acidic solution containing H ₃ O ⁺ ions, for example acids such as HCl, H ₂ SO ₄ , H ₃ PO ₄ , H ₂ S ₂ O ₇ , or weak acids for example in the presence of an electric field, or else not be an acid solution, but for example a solution basic containing OH ^" ions, for example a solution of soda, potassium hydroxide. The concentration of the solution can have an influence on the speed and the level of activation obtained, ie on the level of proton conductivity obtained, but not on the appearance of the activation itself. The acid concentration may for example be between 1 and 18 mol / L and the concentration of sodium hydroxide be between 0.5 and 1 mol / L.

In order to promote the creation of bonds B-OH, B-SO ₄ H, B-SO ₃ H, N-SO ₄ H, N-SO ₃ H and / or NH, the membrane containing boron nitride can be subjected to an electric field, for example an electric field between 15 and 40000 V / m, or even of the order of 15000 V / m, in the presence of a 1 molar H ₂ SO ₄ acid solution for example. A field of 15000 V / m is equivalent to applying a voltage of 1.5 V for a material thickness of 100 μm or else 15 V for a thickness of 1 mm.

The electric field can be delivered by an external generator.

The applied voltage may be for example between 1.5 V and 50 V, for example of the order of 30 V. The voltage source may be constant, or, alternatively, non-constant. It can be configured to detect the end of the activation automatically, for example when the current density in the material increases sharply. The intensity of the current flowing during the activation in the material can be of the order of 10 mA / cm ² at 1000 mA / cm ² . The electrodes used, cathode and anode, may for example be platinum, or titanium platinum cathode and titanium with IrO ₂ at the anode. The shape of the electrodes may for example be flat or non-planar variant. They may for example be in the form of a sintered porous (sinter).

The presence of an electric field may, for example, make it possible to overcome the natural hydrophobicity of boron nitride. Hydrogen can be produced at the cathode during activation and then oxygen at the anode. The dihydrogen formed at the cathode and the oxygen formed at the anode can be recovered in tanks.

The fluid can be forced to flow on either side of the boron nitride, for example by means of a pump. Activation by a fluid can be carried out at a temperature between

0 and 90 ⁰ C, for example of the order of 60 ⁰ C, or at room temperature.

Boron nitride can be activated in a basic solution, for example sodium hydroxide, with or without the application of an electric field.

After being exposed to the solution, the boron nitride can be rinsed and optionally dried before being used to make a fuel cell, electrolyzer or accumulator. The fluid can be removed so that its residual content is less than 2%.

The fluid exposure step may have a duration of between 10 and 50 hours, or even between 15 and 72 hours, better between 10 and 40 hours for example, better still between 10 and 20 hours. Boron nitride

The boron nitride used may preferably be crystallized in hexagonal form. The material may for example comprise turbostratic boron nitride, that is to say whose crystallization planes may be slightly offset with respect to the theoretical crystallization position, for example hexagonal crystallization of boron nitride, which leads to a shift stacks of plans and a less good maintenance planes between them, the latter being slightly further apart.

The material may comprise hexagonal boron nitride grains contiguous to each other, for example grains having a median size greater than 1 nm, even greater than 10 nm, or even greater than 5 μm, and less than 20 μm. The boron nitride may be in the form of grains, for example having a median size of between 5 and 15 μm, or even between 7 and 11 μm, or even of the order of 10 μm. The grains can themselves be composed of crystallites of average size between 0.1 and 0.5 microns.

When the material is in the form of a layer, the boron nitride grains may be oriented preferably not all parallel to the layer, but for example perpendicular to it, so as to ensure a better mechanical strength, or still heterogeneously, in order to ensure better proton conduction of the material.

Matrix The material may comprise percolated boron nitride grains, for example held together by a matrix-forming compound. This matrix can be obtained from all kinds of organic or inorganic or hybrid materials, both organic and inorganic.

According to a particular embodiment of the invention, the inorganic material may be a glass or a gel, obtained for example from boric acid or borates, silica, silicates, silica gels, alumina, gels alumina, clays or clays modified with zeolites, or any suitable combination, this list not being limiting.

The organic matrices can be constituted from natural, artificial or synthetic macro-molecular compounds, for example cellulose, modified celluloses, vinyl polymers, polyvinyl alcohol (PVA), polyamides, polyesters, polyethers, resins epoxy polymers, such as polyetherketone, polyether sulfone, sulfonated polyether sulfone, poly polyphenylene ether, poly phenylene sulfide, fluorinated and perfluorinated polymers (PVDF, PTFE, Teflon ^® ...) and any organic material obtained from the foregoing by chemical modification, grafting and / or crosslinking in order to obtain a matrix thermomechanical properties adapted to the chosen application. The mass proportion of boron nitride in the material may be between 5% and 100%, for example around 70%, even 80%, or even 980%. The proportion 100% or neighboring means a material entirely made of high temperature sintered boron nitride powder having only a small proportion of binder if any. The material can also be obtained from boron nitride and a binder. The method of preparation of the material will be chosen according to the properties of the matrix material and the desired properties.

The material may be formed by boron nitride, for example powdery, inserted, in particular dispersed, in a polymer membrane, which can ensure very good proton conductivity to the material. The polymer, for example PVA, can also be used to seal the porosities present in the boron nitride. The addition of the polymer may for example be carried out under vacuum, from a viscous solution, such that the latter is sucked into the pores of the boron nitride, and then stabilized by crosslinking according to a known method. The matrix can also be made from a polymerizable precursor under the action of a stimulus, for example by evaporation of one or more solvents, an increase in temperature or by sending a gamma ray, or thermal decomposition of polymerization initiator.

By way of example, the PVA matrix can be used, by dissolving this polymer in water at 80 ^° C., and then introducing boron nitride. A crosslinking agent, for example glutaraldehyde, is then added, and a crosslinking catalyst, for example acid, after pouring and evaporation, the PVA is thermally crosslinked at 40 ^° C. The membrane obtained may preferably be thermally crosslinked. by being immersed in an acid bath. It is thus possible to obtain a BN membrane in a PVA matrix having a conductivity of 10 5 S / cm 3 in a 0.5 molar sulfuric acid electrolyte. additives

The matrix may itself be a proton conductor or may not be a proton conductor, or may contain a proton conductor. The matrix may comprise a mixture of organic and inorganic compounds

The matrix can thus comprise one or more of the following list of compounds, which is not limited to: inorganic compound, for example silica, such as Aerosil ^®, amorphous silica gel, bonded silica with organic groups with phosphonic acid, or sulphonic acid, alumina, zirconia, zirconium acid sulphate, titanium oxide, sulphonated titanium oxide, tungsten trioxide, hydrated tungsten trioxide, phosphomolybdic acid (PMA), tungstophosphoric acid (TPA), molybdophosphoric acid, zeolite loaded with heteropolyacid hetero polyacid lacunary H ₈ SiWnθ39, silicate multilayer nanoparticles, for example montmorillonite, laponite, modified montmorillonite, for example sulphonated montmorillonite, MCM-41, montmorillonite grafted with organic sultones and sultones perfluorinated, phosphosilicates (P ₂ Os-SiO ₂ ), cellulosic compounds, this list not being limiting. The matrix may also contain an organic proton conductor material, for example, Nafion ^®, perfluorosulfonic acid, sulfonated polysulfone, sulfonated poly styrene, poly styrene- (ethylene-butylene) sulfonated poly (ether ether ketone) sulfonated cardo, poly vinyl sulfonic acid, acid polyamido methyl propane acrylosulfonic PAMPS) and its copolymers, this list not being limiting. The invention further relates, in another of its aspects, an extruded film, forming itself the membrane used. The extrusion can be carried out by means of an extruder equipped with a head leading to form an output film. The extruded material may consist of a suspension of activated boron nitride in a viscous solution of suitable polymer, capable of being crosslinked after extrusion. The resulting film can be used as is or modified. For example, electrodes may be deposited on its surface by screen printing.

The invention further relates, in another of its aspects, to a proton exchange membrane for an electrochemical device, in particular a fuel cell, an electrolyzer or accumulator, comprising a layer of the material as defined above and other layers. of material adapted to the desired use. The ion-permeable wall may preferably have a water permeability of less than 5% of the mass of ions transported, for example the mass of hydrogen produced, in the case where H ₂ is produced.

The ion-permeable wall may have a zero water permeability, measured under normal conditions of temperature and pressure, with liquid water, or even in the form of steam, at a temperature below 600 ^° C. and a difference pressure on both sides of the membrane not exceeding 4 bar.

Total impermeability of the wall to water may be particularly useful for hydriding water-sensitive metal alloys. During the production and storage of hydrogen, it can make it possible to ensure the storage within a cathode (electrode to which the H + ions are directed) hydrogenuric alloy atomic hydrogen and / or molecular formed at during an electrolysis. This prevents water corrosion of the hydridable alloy. The hydrided material obtained can in turn serve as an anode, reversing the flow direction, and provide H + ions that migrate without water through the membrane containing the activated boron nitride.

On the other hand, the presence of water at the interface of the electrode and the proton exchange membrane may be beneficial for other systems. In fact, the water containing acid, for example 0.5 mol, behaves like the continuity of the ion-permeable wall because of its ionic conduction power. Depending on the desired properties, the catalyst material may comprise a metallic or electronically conductive inorganic material, for example active carbon or graphite, or any kind of material used in electrochemical devices: noble metals, ruthenium, platinum, divided nickel, silver , cobalt, eg platinum coated Nafion ^®, this list not being limiting, for forming the catalytic layers of by both sides of the membrane in contact with the anode and cathode electrodes.

The anode can be made with any electrically conductive material, for example platinum, graphite, for example deposited on a porous titanium plate (30 to 50% porosity for example) on which is deposited a thin layer of catalysts such as as IrO ₂ or RuO ₂ , a mixture of RuO ₂ and IrO ₂ and TiO ₂ , IrO ₂ and SnO ₂ . The thin layer may have a thickness of between 5 μm and 50 μm, or even between 5 and 20 microns, for example about 10 microns. The amount of catalyst per cm ² may be of the order of 1 to 10 mg / cm ² , more preferably between 1 and 3 mg / cm ² , or even of the order of 2 mg / cm ² .

The cathode may also comprise activated boron nitride and activated carbon or graphite. The cathode may be embedded in a mass of boron nitride. The electrode may comprise, for example, a porous titanium plate (30 to 50% porosity, for example) containing a thin layer of catalysts such as platinum, palladium or a mixture of platinum palladium and nickel cobalt. The thin layer may have a thickness of between 5 microns and 20 microns, for example about 10 microns. The amount of catalyst per cm ² is of the order of 0.1 to 1 mg, or of the order of 0.5 mg / cm ² . One or the other of the catalytic layers can be made in a powder form, being sprayed on the membrane constituted by the boron nitride layer mentioned above. After spraying, this layer can be compressed in a press at a pressure of between 5 and 40 kg / cm ² , for example about 20 kg / cm ² , at a temperature of between 15 ^° C. and 200 ^° C., for example between 25 ⁰ C to 150 ⁰ C, to improve the adhesion of the electrodes to the membrane. The temperature depends on the nature of the layer, according to for example whether or not it comprises a polymer sensitive to the maximum temperature applied.

Another subject of the invention, according to another of its aspects, is a fuel cell, electrolyzer or accumulator cell comprising: a cathode, for example a catalytic layer for the cathode, a protonic exchange membrane, for example a catalytic layer; for the anode and an anode, at least one of the cathode with its catalytic layer and the membrane comprising, or even consisting of, the material as defined above, in particular the proton exchange membrane. The proton exchange membrane may be preferably non-porous. The proton exchange membrane will have, for example, zero surface porosity on at least one face. The proton exchange membrane may preferably be impermeable to hydrogen. By "waterproof", it should be understood that an amount of hydrogen less than 2% of the amount produced or used can pass through a 150 μm thick membrane.

The one or both catalytic thin layers of the anode and / or the cathode, may for example comprise at least one of the compounds of the following list, which is not limiting: platinum, for example in the form of nanograins, boron nitride, especially activated boron nitride as mentioned below, activated carbon, a binder, for example a polymeric compound, for example Nafilon®, PVA or PTFE, or a mixture of these elements. The thickness of the proton exchange membrane may be less than or equal to 1 mm, being for example between 50 microns and 300 microns.

The cell may also include a substrate supporting the proton exchange membrane. The substrate may be chosen from various inorganic or organic materials compatible with the chosen application: for example alumina, zirconia, porous boron nitride and their mixtures, this list not being limiting.

The substrate may for example comprise a grid, one or more son, nano son, a foam, a film or a plate, for example a pierced plate. The substrate may comprise for example fine-woven, made of a polymer, e.g., polyamide, for example Teflon ^®. The invention further relates, in one aspect, to an electrolyzer comprising a cell as defined above.

The invention can be better understood on reading the following detailed description of an example of non-limiting implementation thereof, and on examining the appended drawing, in which: FIG. a schematic and partial view of a fuel cell comprising activated boron nitride according to the invention,

FIG. 2 is a schematic and partial view of a proton exchange membrane for producing an electrolyzer membrane,

FIG. 3 is a schematic and partial view of a proton exchange membrane for producing an accumulator, FIG. 4 is a schematic and partial perspective view of an activation device, FIG. 5 is a view from above. , schematic and partial, of a variant of activation device, - Figure 6 is a block diagram illustrating the method according to the invention, FIG. 7 illustrates the variation of the current density during the activation of a membrane according to the invention according to one of the electrochemical activation methods,

FIG. 8 represents the infrared spectra of activated boron nitride and of crude boron nitride,

FIG. 9 illustrates the X-ray diffractogram of an activated boron nitride powder pellet, and

- Figures 10 and 11 illustrate the characteristic curve of the membranes of Examples 2 and 4. In the drawing, the relative proportions of the various elements have not always been respected, for the sake of clarity.

FIG. 1 schematically and partially shows a fuel cell 1 comprising a proton exchange membrane 2 formed of a material comprising a matrix and activated boron nitride contained in this matrix. In the example described, these are hexagonal boron nitride grains activated h-BN bonded with a polymer. The fuel cell 1 has an anode 3 on one side of the proton exchange membrane 2 and a cathode 4 on the other side thereof.

The anode 3 comprises for example a layer for the oxidation reaction, for example a metal compound such as platinum or gold, or composite such as platinum graphite or gold graphite, and the cathode 4 a layer of a catalyst for the reduction reaction, for example a layer of platinum, nickel, nickel graphite, platinum graphite, platinum activated carbon, platinum activated carbon PVA or platinum activated carbon with activated BN, each layer being be in contact with the membrane 2.

The proton exchange membrane 2 as well as the two layers disposed on either side of it may be supported by a porous substrate 6, such as for example a porous titanium layer as a current collector.

Electrical conductors can contact the anode 3 and the cathode 4. The anode 3 may for example comprise on the layer for the oxidation reaction a deposit of gold, for example in the form of a frame 10, so to collect the electric current. The thickness of the exchange membrane 2 is, for example, 100 μm and that of the layers used for the oxidation and catalyst reaction ranges, for example, from 10 to 50 μm, or even to 30 μm.

In an exemplary implementation of the invention, the proton exchange membrane 2 is made from an H-BN boron nitride ceramic HIP reference of the company SAINT-GOBAIN, activated by exposure to acid sulfuric.

The exposure to the acid can be carried out for example for several hours, at room temperature for example or at a higher temperature, for example up to 300 ⁰ C, the sulfuric acid being for example 0.1 concentration. M to 18 M, for example 18 M. During this exposure, the membrane can, if necessary, be exposed to an electric field of about 30 000 V / m, that is to say at a voltage of 3 V when the thickness of the membrane is 100 microns, which can improve the quality of the activation for example in case of exposure to a low molarity acid. The ceramic is rinsed after exposure to the acid. Without being bound by theory, the activation can make it possible to modify the pendant bonds of boron nitride grains.

When the membrane is activated in the presence of an electric field, this electric field can be generated between two electrodes. The anode may or may not be in contact with the membrane and is in contact with the acidic electrolyte and water. The cathode must be in contact only with the membrane, and not in contact with the acidic electrolyte and water. Alternatively, the cathode may also be immersed in the acid in a cathode compartment. In this case, there are two compartments, anode and a cathode, separated in a sealed manner by the membrane. Each compartment contains acid and the electrodes are in contact or not with the membrane.

In another variant, the boron nitride may be deposited in the form of powder in a crucible 2 in which the cathode 15 is also inserted, as illustrated in FIG. 4. The crucible may be made of boron nitride, in order to favor the activation. The whole is then immersed in the electrolyte.

In a further variant, the cathode 15 may have a spiral shape, as illustrated in FIG. 5. It may be electrodes that serve only for the activation process and are not useful thereafter, for example being not found again. not in the system using the membrane. he can also be electrodes, one of which is found in the final system, including the cathode, for example.

At least one or both of the activating electrodes may be in contact with the membrane and be permanently attached thereto, for example. One of the electrodes for activation is, for example, a platinum anode, other electrically conductive elements that can be used provided that they do not oxidize or degrade rapidly.

The anode can still be porous platinum if it is in contact with the membrane. The other electrode, also porous, is a cathode made of a suitable electrically conductive material. These electrodes may be plated, for example by thin layer deposition methods, against the membrane.

In a variant, electrically conductive layers are deposited on either side of the boron nitride layer, for example porous titanium layers containing platinum on the surface. The membrane thus coated is then exposed to the acid in order to activate it, in the presence of an electric field applied thanks to the conductive layers.

Once the acid has been exposed, the membrane can be rinsed.

Of course, it is not beyond the scope of the present invention by making modifications to the examples which have just been given above.

In particular, the exchange membrane can be coated with platinum only on the cathode and a porous titanium plate can be used as a current collector. It is also possible to coat only an oxide alloy, the exchange membrane on the anode and use only a porous titanium plate as a current collector.

In another variant, one or both of the electrodes, anode and / or cathode, may be made at least partially in a material comprising a matrix and activated boron nitride contained in the matrix.

The proton exchange membrane may have various shapes, for example a planar or cylindrical shape.

In the example of FIG. 2, the protonic exchange membrane 2 is used in an electrolyser comprising a porous titanium cathode 20 coated with platinum on the surface, the anode 30 being, for example, porous titanium coated on the surface of the iridium oxide IrO _2. In the example of FIG. 3, the exchange membrane 2 is used in an accumulator, the anode 40 being for example made of porous titanium coated on the surface with iridium oxide IrO ₂ and platinum and with contact with an aqueous acidic electrolyte, for example a sulfuric acid solution, while the cathode 50 comprises a hydrurable material.

In another variant, at least one of the electrodes, in particular the cathode, can be made at least partially in the material according to the invention.

An example of an activation method according to the invention will now be described with reference to FIG. Boron nitride, which may be hexagonal or even hexagonal turbostratic, is used and which is in one embodiment of the invention in a powder form. Activation can be facilitated. The grains of boron nitride can be percolated. The boron nitride may contain at least one additive that can promote activation, for example oxygen and boron oxide. The boron nitride selected is, in a first step 61, exposed to a fluid for providing -OH hydroxyl radicals, for example an acidic or basic solution, or even simply water.

The activation of the boron nitride can for example be carried out as follows. 18M acid (99.99% pure) can be used. Powdered boron nitride is made up of polycrystalline grains of variable size, which depends on the manufacturing methods used. Each BN crystal, contained in a BN polycrystalline grain, is in contact with other crystals at the edge of the sheet. This crystalline structure can be schematically represented as a stack of sheets.

In the case of an activation of the BN powder with acid, the infrared spectroscopic signature under FTIR spectroscopy (Fourier Transformed InfraRed spectroscopy) changes according to the degree of activation.

The powdery boron nitride may be placed in a crucible itself made of boron nitride, in order to ensure the proton conductivity, or in another material. In a second step 62, bonds are created between the boron nitride and the hydroxyl radicals, in particular B-OH bonds, and possibly also bonds with nitrogen atoms of the boron nitride, in particular between the protons and the atoms. boron nitride nitrogen, for example NH bonds, or even bonds B-SO ₃ H, B-SO ₄ H, N-SO ₃ H and / or N-SO ₄ H.

The activation can be promoted by applying an electric field in step 63, for example by means of a cathode and an anode soaked in the solution, one or both of these two electrodes being able to be used and stored later for the manufacture of the fuel cell.

Activation can be promoted by increasing the temperature of the boron nitride-acid mixture.

After activation, it is possible to recover in a step 64 the activated boron nitride which may optionally in a step 65 be rinsed before proceeding to the manufacture of a fuel cell in a step 66.

The boron nitride used may be associated with the matrix, for example a polymer, before activation, or after activation and before the manufacture of the fuel cell. The result of activation on boron nitride will now be described with reference to FIGS. 7 and 8.

FIG. 7 illustrates the evolution of the current density and the voltage during the activation of the boron nitride. It is found that the current density D increases abruptly after a certain time, namely around thirty hours in the example described, which illustrates the fact that the proton conduction in boron nitride is ensured.

FIG. 4 illustrates infrared spectra of activated boron nitride A and crude boron nitride B, that is to say before activation.

It is observed by observing these spectra A and B that they are of different shape. It can be noted the presence of two troughs on the spectrum A which are not present on the spectrum B. These troughs illustrate the presence of the B-OH and N-H bonds, which result from the activation of the boron nitride.

The activation of boron nitride can also be observed by measuring the proton conductivity of the latter. Raw boron nitride, that is to say non-activated nitride, may have a proton conductivity of the order of 10 ^-5 Siemens / cm, whereas activated boron nitride may have a proton conductivity of the order of 10 ^"2 to 10 ^{" 1} Siemens / cm, for example 10 ^"1 Siemens / cm. By way of comparison, the Nafion may have a proton conductivity of the order of 8.6 × 10 ^-2 Siemens / cm.

For example, it is possible to use a process for producing a boron nitride membrane with a SPS (Spark Plasma Sintering) type apparatus. This technique consists in passing a strong electric current between two graphite electrodes which by Joule effect will undergo a fast and strong increase of the temperature. Between the two electrodes is placed a graphite mold containing the boron nitride powder, the powder-mold interface being made by paper. When the current is applied, the powder is pressed.

The SPS technique, unlike the usual press techniques, makes it possible to dispense with the presence of a sintering element, so that a pellet consisting exclusively of the desired material, in this case boron nitride, results therefrom.

In this example, a commercial HCV boron nitride powder is used. HCV commercial BN powder provides a pellet. After pressing, the pellet is polished to remove the paper remaining on the surface of the sample. The pellet obtained is analyzed by X-ray diffraction. The diffractogram obtained is shown in FIG. 9 on the curve C as well as the diffractogram of the commercial HCV powder which has not undergone SPS treatment on the curve D. It can be noted that the pellet has a much higher crystallinity than the untreated HCV powder. Plan families such as the unobserved (103) or (104) families for the untreated HCV powder appear on the diffractogram of the pellet. It can also be noted that the intensities of the lines are not in agreement with the standard intensities of a hexagonal boron nitride powder. Such a difference can be explained by the fact that, in the case of the pellet, the grains may not have a completely random orientation, as in the case of a powder, thus favoring the diffraction of certain families of planes.

Thus, it can be observed in particular that the relative intensities of the lines of the families (104), (110) and (112) are not in agreement with the intensities normally expected for hexagonal crystalline boron nitride. Indeed the lines (110), (112) are too intense compared to the line (104). Examples of embodiments of a membrane of activated boron nitride with PVA will now be described. Among the various polymers proposed, polyvinyl alcohol (PVA) is a cheap biocompatible polymer having a good film-forming ability, by casting a solution of PVA (in water or in an organic solvent), having excellent mechanical properties and good chemical stability. It also has the advantage of being easily crosslinkable, because of a high number of OH groups, which gives it good mechanical strength in a humid environment. The PVA used is provided by Celanese; it is the grade Celvol E 4/98 (degree of hydrolysis 98.3 mol%) of molecular mass 31000. Many methods are proposed in the literature for the crosslinking of PVA, we opted for the crosslinking by by acid glutaraldehyde in acid medium [8] A.Martinelli, A.Matic, P.Jacobsson, L.Borjesson, MANavarra, A.Fernicola, S.Panero, B.Scrosati, Solid State Ionics, 177, 2431- 2435 (2006).

Example 1 We manufacture a membrane containing 20g of activated BN for 10g of

PVA.

In a beaker of 15OmL, 70mL of water are introduced with 10g of PVA; the whole is brought to 90 ⁰ C, and stirred with a paddle stirrer until complete dissolution of the polymer (about 30 minutes) and then, with continued stirring, 20 g of activated powdered BN are added in rain (90 ⁰ C) until a complete wetting of the BN.

The solution is brought to room temperature and 0.2 ml of GA (50% solution) are added by mixing. The solution is divided into two parts. In the first part is added 0.5mL of sulfuric acid (2M).

The final mixture is rapidly poured into petri dishes (diameter 10 cm). Drying is done under a hood at room temperature (12h). The membrane A is obtained.

Tests were conducted in parallel, by casting the mixture PVA / BN / GA when the membrane is dry, (about 12h at room temperature or 3h in an oven at 60 ⁰ C), it is soaked in H2SO4 2M about Ih, gets the membrane B.

The membranes obtained have thicknesses of 200 to 500 μm. The membrane obtained is not rigid, but it requires to be used hydrated to have a soft consistency. The permeability test with an aqueous solution of erythrosine 0.2% is consistent, the liquid does not cross and does not migrate to the surface for the membranes thus prepared.

The conductivity measurements on both membranes are as follows:

It is therefore noted that these membranes are conductive.

Scanning electron microscope examinations show that the cast membranes have different surfaces depending on the contacts.

The surface dried in the open air is homogeneous with few visible pores

The surface dried in contact with the glass (petri dish) has many pores although each grain of BN is coated with PVA and is bound in them by the polymer.

Example 2 Another method of manufacture is used to make membranes

BN / PVA with a proportion of 35 g activated BN for 15 g of PVA.

Activation of the BN powder: To 35 gr of BN powder is added 35 ml of 18 molar sulfuric acid. 12 hours later, the mixture is rinsed and filtered twice with 500 ml of water each time. Preparation of the PVA: 10 g of PVA 186000 molecular weight (non-limiting, other molecular weights can be used) is heated to 80 ⁰ C in 140 ml of demineralized water. 10 g of PVA of molecular weight 31000 (not limiting, other molecular weights can be used) is heated to 80 ^° C. in 70 ml of demineralized water.

Preparation of the "casting" ink (manufacture) of the membrane: a homogeneous mixture of the activated powder BN is obtained with the PVA 186000 and 39 g of the solution of PVA 31000. To this mixture is added a crosslinking agent for PVA. In this example, it is 0.7 ml of Gutaraldehyde with 7 ml of 1 molar sulfuric acid.

This final mixture allows the casting of membranes that can be crosslinked under different conditions of temperature and humidity. In the case of this example: the membranes were crosslinked at a temperature of 18 ° C and 23% humidity.

The characteristics of these membranes are as follows:

Conductivity in acid 1 molar: 2.10 ^"1 SZCm.

They are soft in the water.

They are hydrogen tight under a pressure of 1 bar. The behavior in electrolysis is illustrated in FIG.

To obtain these characteristic curves, we deposited catalytic layers of iridium oxide (anode side, 3mg / cm ² ) and platinum (cathode side, lmg / cm ² ) nano structured according to the state of the art on both sides of the membrane.

In the context of using the fuel cell membrane, the two catalytic layers are formed of nano-structured platinum.

Example 3 Teflonated BN Membrane

One of the techniques for making carbon electrodes is to use teflon as a binder between the carbon grains. This technique is applied to BN in order to obtain flexible and more thermally stable membranes than PVA-based membranes.

The proportions of 7 g of BN and 8 g of aqueous teflon suspension (60%) are used, ie approximately 5 g of pure teflon.

The mixture is kneaded by hand by moistening with water and ethyl alcohol to obtain a very soft paste that can be spread using a rolling mill.

In a second series of tests, the amount of Teflon is decreased in order to reduce the hydrophobicity of this membrane. Thus, it is formulated with 7 g of activated BN and 3 g of Teflon suspension (ie about 2 g of pure Teflon). The membranes obtained in both cases can have thicknesses of 120 to 250 μm. The membranes obtained are porous, and the pores are closed with PVA. The PVA deposit is then made from the 10 g solution in 70 mL with 0.2 mL GA, (see previous example).

The membrane is cut to be deposited in a Bϋchner whose filtering part is covered with a nylon filter, 2OmL of this mixture is poured on the BN / Teflon membrane, inverted to wet well both sides, then the excess is removed by filtration under vacuum (water jet). In the next step: either the acid solution is poured into the Bϋchner, after 10 minutes of reaction the excess is filtered and the membrane is dried under a hood (12h), or the membrane is removed from the Bϋchner and immersed in the acid solution at least 2 hours, then dried in the open air.

In both cases, the membranes are extremely flexible and fragile, in fact BN and Teflon are two materials used as lubricants.

Their conductivity in 1M H2SO4 was measured between 0.1 and 0.2 S / cm.

Better mechanical properties are obtained by incorporating silica into the mixture. Better properties were still obtained by adding a little sulfonated polyether sulfone.

Example N ⁰ 4

The following example describes the preparation of silica / BN or silica membranes

/ PESS / BN.

An agate mortar is used. Quality of the silicas tested: - Merck Silicagel - 40-63 μm pore 60 - reference 9385

Silicagel for TCL standard grade: 28 850 0 - 2 à25μm - Sigma reference Lichrosphère 8.7 to 15.4μm (average 12μm) pore 60 Â- Merck reference 19654

Davisil gel gel grade 633 - 38 to 75μm pore 60 Â Sigma reference 236772

Davisil gel gel grade 643 - 38 to 75μm pore 150 Å Sigma reference 236810 - Sulfonated sulfonated polyether (PESS) produced ERAS reference UDEL P3500 (acid form) ion exchange charge 0.76meq / monomer unit. The activated BN must be dry. BN silica membrane The quantity of silica required is weighed and introduced into a mortar then the amount of BN required.

An intimate mixture is made using the pestle and a spatula. The suspension of PTFE is then introduced into the mixture, then about 2 ml of ethanol (60%) are deposited. The mixture is mixed in the mortar until an ink is formed, then a soft film.

This film is extracted from the mortar, 60% ethanol is added and the paste is worked manually by folding and stretching with a glass roll until a soft paste is obtained. This paste is then worked by rolling mill (folding stretch) a maximum of 4 times taking care to gradually reduce the thickness (150μm to 200μm to have a membrane manipulable). The membrane is dried at 40 ^° C. for approximately 1 hour. Silica Membrane / PESS / BN

Solutions of PESS in tetrahydrofuran (the solution is slightly cloudy) 2.5g / 25ml or 2.5g / 50ml were made in the laboratory.

Preparation of silica impregnated with PESS

A quantity of known silica is introduced into the mortar, a sufficiently large volume (approximately 5 to 10 ml / g of SiO 2) of PESS solution (choose a concentration as a function of the desired final% PESS) is introduced onto the silica so as to wet it and form a friable paste.

Under a hood, mix with the mortar until the solvent has evaporated and a fine, unagglomerated homogeneous powder has been obtained. Finish evaporation of the solvent leaving the powder 15h in an oven at 40 ^° C.

The quantity of silica / PESS mixture required is weighed and introduced into a mortar and the quantity of BN required is then introduced. An intimate mixture is made using the pestle and a spatula. The suspension of PTFE is then introduced into the mixture, then about 2 ml of ethanol (60%).

The mixture is mixed in the mortar until an ink is formed, then a soft film.

This film is extracted from the mortar, 60% ethanol is added and the dough is manually worked by folding and stretching with a glass roll until a smooth homogeneous smooth paste is obtained.

This paste is then worked in the rolling mill (folding stretching) at most 4 times taking care to gradually reduce the thickness, (up to 150μm to 200μm to have a membrane manipulable). The membrane is dried at 40 ^° C. for approximately 1 hour.

The behavior in electrolysis is illustrated in FIG.

Assembly and determination of the electrochemical characteristics of the membranes All the assemblies were carried out with membranes of 2.25 cm 2 useful in an H-TEK stack.

The membrane is moistened by soaking in a sulfuric acid solution

IM at least 4 hours before stacking. The electrodes are platinum carbon E-

TEK reference ELT 120EW. The membrane is moistened with a few drops of sulfuric acid IM before mounting the electrodes, a plastic spring maintains contact between electrode-current collector.

The terminal voltage is read (emf), during the current sweep (zero current up to maximum current for a voltage of 0 mV) the maximum power is defined (Pmax in mW / cm2) with the corresponding current density ( J mA / cm 2). The resistance of the membrane is measured by impedencemetry

The first two sweeps are carried out, then the stack is opened, a few drops of acid are again deposited on the membrane and the following scans are carried out. Stack performance results

Trials with membranes without activated BN all lead to high membrane resistances.

The phrase "with one" should be understood as being synonymous with "having at least one".

Claims

1. Material for an electrochemical device, in particular a fuel cell, an electrolyzer or an accumulator, comprising a matrix and activated boron nitride contained in the matrix.

2. Material according to the preceding claim, wherein the boron nitride is in the form of percolated grains.

3. Material according to claim 1, wherein the boron nitride is in the form of sintered grains.

4. The material according to any one of the preceding claims, wherein the boron nitride is crystallized in a hexagonal form.

5. Material according to any one of the preceding claims, wherein the boron nitride is turbostratic.

6. Material according to any one of the preceding claims, comprising a mineral matrix.

7. Material according to any one of claims 1 to 3, comprising a matrix comprising at least one of an organic material and an inorganic material.

8. Material according to one of the preceding claims, wherein the boron nitride is present in the material in a mass proportion of less than 70%.

An extruded film made or obtainable from a material as defined in any one of the preceding claims.

10. Proton exchange membrane for an electrochemical device, in particular a fuel cell, electrolyzer or accumulator, comprising a layer of the material as defined in any one of Claims 1 to 8.

Electrode for an electrochemical device, in particular a fuel cell, made at least partially in the material as defined in any one of Claims 1 to 8.

Fuel cell cell, electrolyzer or accumulator, comprising: an anode, a cathode, and a proton exchange membrane, at least one of the cathode and the membrane comprising the material as defined in any one of Claims 1 to 8.

13. Cell according to the preceding claim, comprising a cathode or anode according to claim 11.

14. Cell according to claim 12, wherein the entire outer surface of the cathode covered with a material comprising boron nitride.

15. Cell according to the preceding claim, wherein the boron nitride is powdery.

16. Cell according to any one of the two preceding claims, wherein the cathode is wound on itself.

17. Cell according to any one of claims 12 to 16, being of cylindrical general shape, the proton exchange membrane constituting a cylindrical envelope surrounding the cathode.

18. Cell according to any one of claims 12 to 17, the proton exchange membrane being impermeable to hydrogen.

19. Cell according to any one of claims 12 to 18, the proton exchange membrane being non-porous.

20. Cell according to any one of claims 12 to 19, the proton exchange membrane having a non-zero surface porosity.

21. Cell according to any one of claims 12 to 20, the thickness of the proton exchange membrane being less than or equal to 300 microns.

22. Cell according to any one of claims 12 to 20, comprising a support substrate of the proton exchange membrane.

23. Electrolyser comprising a cell as defined in any one of claims 12 to 22.

24. A fuel cell comprising a cell as defined in any one of claims 12 to 22, and a fuel supply circuit on the cathode side and a supply circuit of an oxidant of the side of the anode.

25. Battery according to the preceding claim, wherein the hydrogen for supplying the cell is stored as hydride in the material according to any one of claims 1 to 8.

26. A method for activating a material for an electrochemical device, comprising a matrix and boron nitride contained in the matrix, in which the material is exposed to a fluid that makes it possible to provide hydroxyl radicals -OH and / or ions H ₃ O ⁺ and / or SO ₄ ^{2 "} ions and create in the boron nitride bonds B-OH, B-SO ₄ H, B-SO ₃ H, N-SO ₄ H, N-SO ₃ H and / or NH ₂ bonds.

27. Method according to the preceding claim, the activation taking place in the presence of an electric field.

28. A process according to any one of the two preceding claims, wherein the material is exposed to an acidic solution.

The method of any of claims 26 or 27, wherein the material is exposed to a basic solution.