Anion-conducting membrane, method for manufacturing such a membrane, electrochemical cell comprising such a membrane and facility comprising such a cell

Abstract

The invention relates to a layer of catalytic material for an anion-conducting membrane (10) for an electrochemical device; the layer of catalytic material comprises metal nanoparticles bound by a polymer binder. In one embodiment, the metal nanoparticles comprise a mixture of nickel nanoparticles and cobalt nanoparticles. The invention also relates to a membrane comprising a layer of catalytic material and to a method for preparing and depositing a catalytic layer.

Description

DescriptionAnion-conducting membrane, method for manufacturing such a membrane, electrochemical cell comprising such a membrane, and facility comprising such a cell Technical field of the invention [1] The technical field of the invention relates to anion-conducting membranes such as those notably used in water electrolysis devices. More particularly, the invention relates to a membrane for alkaline water electrolysis and to a method for manufacturing such membranes. Prior art [2] Hydrogen is used in many industrial processes, notably as a starting material in the chemical industry and as a reducing agent in the metallurgical industry. Hydrogen is a fundamental element in the manufacture of ammonia, and thus of fertilizers, and in the manufacture of methanol, which is used in the manufacture of many polymers. Refineries, in which hydrogen is used for the treatment of intermediate petroleum products, are another field of use.[3] Hydrogen is also an important energy vector: it can store and supply energy in a usable form. The energy is released through an exothermic combustion reaction with oxygen, thus forming water. No greenhouse gases containing carbon are emitted during such a combustion reaction.[4] As electricity generation from renewable energies increases, the need for energy storage and transport also increases. Many renewable energy sources, in particular solar and wind, are located far from population centers and only produce electricity intermittently. Hydrogen may be the perfect vector for renewable energy. It can store energy and then distribute it where it is needed and at the time it is needed.[5] Alkaline water electrolysis is an important method for manufacturing hydrogen. In an alkaline water electrolysis cell, a membrane is used between two electrodes, a cathode and an anode: the membrane separates the electron-conducting electrodes. Being non-porous to the gases, the membrane also separates the gases produced at the electrodes in order to prevent an explosive mixture of gaseous hydrogen H2 (formed at the cathode) and gaseous O2 (formed at the anode). The membrane is also an ion conductor for transporting OH- ions from the cathode to the anode.[6] It is known to produce proton-exchange membranes (PEM). The most widely used membrane is the Nafion® membrane sold by Dupont de Nemours. The cost of this membrane is particularly high. Furthermore, this membrane generates a highly acidic medium, which is particularly corrosive to the electrodes.[7] New membranes are being developed, known as anion-exchange membranes (AEM, or anion-conducting membranes). For example, mention may be made of anionic membranes such as Piperion® and Sustainion®, and the separator Zirfon®. For example Zirfon®, which is not a conductive membrane but a porous separator, comprises zirconium oxide particles bound by a polymer. Mention may also be made of the membranes comprising ceramic particles, such as the boron carbide membranes described in document D1 = FR3122778 or else the yttria-stabilized zirconia membranes described in document D2 = FR3150048. Produced with a polymer and metal oxide particles and / or ceramic particles, these membranes are quite simple to produce and are less expensive. Also, these membranes are used in an environment that is not acidic but basic, which allows base metals to be used for the production of the electrodes, for example nickel for the cathode and stainless steel for the anode. However, all these membranes and separators are generally less effective than membranes with catalysts, which has an impact on the profitability of large-scale hydrogen production.[8] To improve the effectiveness of the membranes, it is known to deposit, on the membrane, a layer of catalytic materials based on rare materials, for example platinum group metals, also known as PGM metals, which group comprises iridium (Ir), osmium (Om), platinum (Pt), palladium (Pd), rhodium (Rh) and ruthenium (Ru). The effectiveness of the AEM membrane is improved, but in practice it is observed that the resistance of the catalytic layers on the membrane is limited over time and depends even more greatly on the formulation of the catalytic layers and on the method of depositing these layers, anode side and cathode side. Furthermore, PGM metals are rare metals, which greatly increases the cost of the membranes and therefore reduces the profitability of large-scale hydrogen production. Description of the invention [9] The invention proposes novel catalytic layers and a novel membrane that do not have any or some of the abovementioned drawbacks.

[10] To this end, the invention proposes a novel layer of catalytic material for an anion-conducting membrane for an electrochemical device, the layer of catalytic material comprising nanoparticles of active components bound by a polymer binder, the active components being nickel and cobalt.

[11] Advantageously, such a catalytic layer is deposited on an anion-conducting membrane on the cathode side.

[12] The catalytic layer according to the invention, deposited on the surface of the membrane, substantially improves the effectiveness of the electrochemical reactions which take place at the interfaces of the membrane and the electrodes, and the results obtained are generally more advantageous than a catalytic deposition on one or other of the electrodes of a cell using an AEM membrane without catalytic deposition.

[13] Also, the efficiencies obtained deteriorate much less over time.

[14] Lastly, the metals used in the catalytic layer according to the invention, nickel and cobalt, are not rare materials and make it possible to produce a membrane with a catalytic layer at a reasonable cost, which makes it possible to produce hydrogen on a large-scale at a reasonable cost.

[15] The invention also relates to an anion-conducting membrane comprising at least one catalytic layer as described above, to a cell comprising an anion-conducting membrane and to a water electrolysis unit comprising an anion-conducting membrane.

[16] The invention lastly relates to a method for depositing a catalytic layer as described above on an anion-conducting membrane. Presentation of the figures 

[17] The invention will be better understood, and other features and advantages of the invention will become apparent in light of the following description of examples of implementation of the invention. These examples are given without implied limitation. The description should be read in conjunction with the accompanying drawings, in which:[Fig. 1] shows a cell suitable for a water electrolysis application,[Fig. 2] shows a simplified diagram of a water electrolyzer,[Fig. 3] shows the size dispersion of a component used for the implementation of the invention,[Fig. 4] shows an intermediate result from a method according to invention,[Fig. 5] shows results of tests performed with layers of catalytic material according to the invention. Detailed description 

[18] As stated previously, the invention relates to a layer of catalytic material and an anion-conducting membrane 10 for an electrochemical device. Said membrane may be used to produce a cell for an electrochemical device, for example a water electrolysis unit; the cell comprises:an anode 30,a cathode 20, andbetween the anode and the cathode, a membrane 10.

[19] The membrane comprises a main layer which is moreover known. The main layer is for example a main layer comprising particles of metal oxide such as zirconium oxide and yttrium oxide as described in D2, or else a main layer comprising particles of ceramic as described in D1.

[20] Unless otherwise further specified locally, the following terms are defined here for the whole of the description. A “particle” is a cluster of several atoms or molecules of a single component or of different components. The “size” of a particle corresponds to the value of its largest dimension; for example, the largest dimension of a particle of substantially rhomboidal shape is its length. The numerical values given correspond to average values measured on a batch of particles of the same type. The measurements of the size of the nanoparticles may be carried out by scanning electron microscopy (SEM) or by transmission electron microscopy (TEM). The term “nanoparticles” corresponds to particles for which the average value of the size is between 1 and 100 nm. The expression “submicron particles” corresponds to particles with an average size of between 0.010 μm and 1 μm and the term “microparticles” corresponds to particles with an average size of between 1 μm and 10 μm.

[21] Unless otherwise further specified locally, the term “nanoparticles” is used here and throughout the description to refer to particles for which the average value of the size is between 1 and 100 nm, the size being defined as being the largest dimension of a particle. The measurements of the size of the nanoparticles may be carried out by scanning electron microscopy (SEM) or by transmission electron microscopy (TEM). Each nanoparticle is a cluster of several atoms or molecules of a single component or of different components.

[22] In order to compare the performance of the membranes, R, the HHV (High Heating Value) efficiency of a water electrolysis cell comprising the membrane is calculated. For this, the membrane is placed in the test cell, a current density I flowing between the cathode and anode per unit area of membrane is imposed and the voltage V (T, I) between the cathode and anode of the cell is measured.

[23] For a given current density, it is sought to obtain the lowest possible voltage for obtaining the dissociation of a given amount of water molecules.

[24] The minimum theoretical voltage for the water dissociation reactions to begin is V0 = 1.48V HHV and it corresponds, by convention, to an efficiency R of 100% HHV. The efficiency R is calculated by the equation R = V0 / V(T, I), where V(T, I) is the voltage at the terminals of the cell, for a given temperature T and a given current density I.

[25] Insofar as the heat produced by the electrolysis itself makes it possible to increase the temperature and then to maintain the system at a constant temperature, the above efficiency calculation clearly reflects the efficiency of a cell. For the calculation of the overall efficiency of an electrolyzer comprising such a cell, it would be necessary to subtract the amount of energy consumed for the overall operation of the system from the energy consumed directly by the electrolysis. In this document, only the efficiency of the cells is analyzed.

[26] One embodiment of the invention relates to a layer of catalytic material suitable for being positioned on the main layer of the membrane, on the side of the cathode. The layer of catalytic material here comprises nanoparticles of active components (in the sense of catalysts for the electrolysis reaction) which are nickel, cobalt or a mixture of nickel and cobalt.

[27] The nanoparticles of active components used for the implementation of the invention may be purchased mail order; for example, for the tests carried out, the nanoparticles of nickel, molybdenum and cobalt were purchased from the Chinese company HEBEI Flance Nanotechnology Co. Ltd.

[28] The nanoparticles of the active components are preferably supported by carbon particles and bound by the polymer binder; the carbon is for example in the form of activated carbon or graphite. The carbon particles are preferably of micrometer size (1 μm to 100 μm) or of submicron size (0.01 to 1 μm). The carbon particles are commercially available and may be purchased mail order. For example, activated carbon particles can be purchased from the company Sigma Aldrich or from the company Cabot Corp; for example, for certain tests, the Vulcan XC-72R particles of the Vulcan brand from the company Cabot Corp were used; they have an average size of around 0.60 μm and the size dispersion of a batch of these particles is represented in figure 3.

[29] In the mixture of carbon particles / nanoparticles of active components, per 100% by weight of mixture, the proportion of carbon is from 40% to 80% by weight and the proportion of active components is from 20% to 60% by weight. The use of carbon particles for supporting the particles of active components further improves the specific surface area of the layer of catalytic material. Carbon, and in particular activated carbon, itself having a high specific surface area. With the proportions indicated above, a catalytic layer is obtained with a specific surface area equal to 250 m2 / g to 370 m2 / g. it is recalled that the specific surface area (or surface area by mass) represents the total surface area per unit mass accessible to the atoms and molecules for the reaction, open porosities included. The physical principle, universally acknowledged for the determination of the specific surface area, is based on the adsorption of gases at low temperature.

[30] Also, the use of carbon particles helps with good distribution of the nanoparticles of active components in the catalytic layer (figure 4) and further improves the accessibility of the sites of the chemical reactions to the particles of active components; specifically, this facilitates firstly the circulation of the electrolyte between the nanoparticles of active components and secondly the discharging of the gases produced at these sites.

[31] In terms of effectiveness for water electrolysis, good HHV efficiencies were obtained with a membrane comprising a catalytic layer in which the nanoparticles of active components in the layer of catalytic material comprise, per 100% by weight of nanoparticles, 65% to 85% by weight of nickel nanoparticles and 15% to 35% by weight of cobalt particles, and better still with 70% to 80% by weight of nickel nanoparticles and 20% to 30% by weight of cobalt particles. With a membrane having a layer of catalytic material at the cathode comprising a mixture of nanoparticles of active components comprising 75% by weight of nickel and 25% by weight of cobalt, an efficiency of 80% HHV was obtained for a current density of 1 A / cm2 and an efficiency of 85% HHV was obtained for a current density of 0.7 A / cm2 applied between the electrodes of the test cell.

[32] Figure 5 shows results of tests for assessing the change over time in the efficiency of the cell with a catalytic layer according to the invention. The tests are carried out with the test cell described above comprising a 30 cm² membrane, a nickel cathode and a stainless steel anode; the electrolyte used is potassium hydroxide KOH at a concentration of 4 mol / l; the membrane is composed of yttria-stabilized zirconia with a PTFE binder, covered on the cathode side with a catalytic layer. The tests were carried out at a temperature T = 90°C, an applied current density of 0.7 A / cm2 and over a period of several tens of hours.

[33] The light grey curve shows the change in voltage for a membrane comprising, on the cathode side, a catalytic layer comprising 60% carbon and 40% active nanoparticles comprising 100% nickel.

[34] The dark grey curve shows the change in voltage for a membrane comprising, on the cathode side, a catalytic layer comprising 60% carbon and 40% active nanoparticles comprising 80% nickel and 20% cobalt.

[35] At the start, in the first hour, the catalytic activity of the catalytic layer comprising only nickel is higher (the voltage, around 1.85 V, is lower) than the catalytic activity of the catalytic layer comprising nickel and cobalt (voltage around 1.91 V).

[36] Over time, it is observed that the catalytic activity of the catalytic layer comprising only nickel increases gradually: from around 1.88 V after around 10 h, the voltage increases to around 1.92 V after around 250 h. The efficiency thus decreases gradually over time.

[37] On the contrary, surprisingly, the catalytic activity of the catalytic layer comprising nickel and cobalt gradually decreases and stabilizes: from around 1.91 V at the start, the voltage decreases to 1.88 V after around 10 h, decreases further and stabilizes at a value of around 1.875 V which is still maintained after around 250 h. The combination of nickel and cobalt thus makes it possible to obtain a better efficiency and an efficiency that is stable over time.

[38] The efficiency of the membranes depends notably on the amount of nanoparticles present in the catalytic layer. The best efficiencies were obtained for membranes in which the layer of catalytic material comprises, on the surface, 0.1 to 6 mg / cm2 of nanoparticles of active components, more precisely 0.1 to 7 mg of nanoparticles in a volume corresponding to 1 cm2 of membrane area multiplied by the thickness of the catalytic layer.

[39] The catalytic layer preferably has a thickness of 50 μm to 250 μm.

[40] The efficiency of the membranes also depends on the catalytic activity of the nanoparticles which increases when the number of sites of electrochemical reactions for dissociation of the water molecules increases. The sites of the chemical reactions are present on the surfaces of the catalytic materials.

[41] To increase the number of reaction sites on particles of active components such as nickel and cobalt, the tests have shown that an effective solution is to increase the specific surface area of the catalytic materials. For this purpose, in the context of the invention, the nanoparticles of active components have a size of less than 50 nm, preferably less than 20 nm and even more preferentially less than 5 nm. The particles have a substantially spherical or convex polyhedral general shape and their size corresponds to their largest dimension.

[42] The tests have also shown that, for a size of given particles, the catalytic activity of the particles is improved by improving the homogeneity of the size of the particles; this is true when the particles comprise a mixture of particles of active components, and even more true when the particles comprise particles of active components and carbon particles.

[43] The tests have also shown that the homogeneity (in terms of type of particles) of a mixture of particles of active components or of a mixture of particles of active components and carbon particles further improves the catalytic activity.

[44] The efficiency of the membranes also depends on good cohesion of the nanoparticles with one another, on good cohesion of the catalytic layer to the main layer of the membrane and on the durability of this cohesion over time. After tests, the polymer binder is an ionomer chosen as a function of its resistance over time to corrosive chemical environments and to high temperatures up to 120°C, but also as a function of its ionic conduction properties. By polymerizing, the binder acts as an adhesive in the catalytic layer and holds the particles and nanoparticles of this layer together. It also allows good adhesion of the catalytic layer with the membrane. Lastly, an essential point in the context of the invention, owing to its ionic conduction, the ionomer enables the catalytic layer to remain electrically and ionically conductive. The ionomer preferentially used is known under the name Nafion®, and is derived from the polymerization of a monomer referred to as tetrafluoroethylene-perfluorosulfonic. The proportion of polymer binder is from 10% to 40% of the weight of the binder / particles of active components mixture (or where appropriate of the binder / particles of active components + carbon particles mixture).

[45] The efficiency of the membranes also depends on the method for producing the catalytic layer on the main layer of the membrane.

[46] For this purpose, the invention proposes a method for depositing a catalytic layer on an anion-conducting membrane, the catalytic layer comprising nanoparticles of at least two active components and a polymer binder, the method comprising a step of preparing a liquid ink comprising nanoparticles and a polymer binder, the nanoparticles comprising particles of at least two active components;the step of preparing the liquid ink comprises the following steps consisting in:mixing the nanoparticles in a liquid, the liquid being water, a solvent or mixture of water and solvent, the solvent being an alcohol for example,grinding the mixture of particles in a liquid medium until a homogeneous mixture is obtained,adding the liquid polymer binder.

[47] In the example of the catalyst according to the invention, the particles of active components are nickel particles and cobalt particles.

[48] The liquid is water or a solvent or a mixture of water and solvent. The solvent is suitable for diluting the binder. The solvent is an alcohol for example. Conclusive tests were carried out for example with water, with ethanol, and with a mixture of water and isopropanol.

[49] The amount of liquid chosen is suitable for wetting the solid nanoparticles, so as to facilitate the following grinding step and limit the exposure of an operator to the nanoparticle dust which will be generated during the grinding step.

[50] The amount of liquid is also chosen so that the resulting ink can be sprayed onto the membrane. In the conclusive tests carried out, use was made of an amount of liquid, the weight of which corresponded to 10 to 25 times the weight of the solid particles.

[51] The grinding of the nanoparticles is carried out in an aqueous medium, for example in planetary mixer / mill (or ball mill). The grinding of a mixture of particles of at least two different components (which may also be referred to as co-grinding) makes it possible to obtain smaller nanoparticles, of the chosen size, of less than 50 nm, preferably less than 20 nm and even more preferentially less than 5 nm, and particles with an average size that is as homogeneous as possible.

[52] In the method according to the invention, the grinding makes it possible to obtain a ground material comprising not only particles comprising atoms or molecules of the first active component, and particles comprising atoms or molecules of a second active component but also, surprisingly, particles comprising atoms or molecules of two (or more) different active components. For example, the grinding of a mixture of nickel particles and cobalt particles makes it possible to obtain a ground material comprising nickel particles, cobalt particles and particles of an Ni-Co alloy. The grinding thus makes it possible to physically agglomerate particles together by physically compressing the particles against one another. The ground material obtained thus has a higher catalytic activity than the mixture of particles before grinding.

[53] The mixture of nanoparticles in the liquid also makes it possible to have a homogeneous mixture (in terms of distribution of particles of various types) of the materials notably when use is made of two or more types of nanoparticles (for example nickel and cobalt here, or else nickel, metal oxide and / or molybdenum or else platinum, copper, zinc).

[54] If carbon is used to support the nanoparticles of active components, the preparation step also comprises, before addition of the polymer binder, the following steps consisting in:adding carbon particles to the ground material of nanoparticles of active components, andgrinding the mixture of particles of active components and carbon particles until a homogeneous mixture is obtained.

[55] The carbon is for example in the form of activated carbon or graphite, with particles of the order of 0.2 to 0.9 μm.

[56] This second grinding step makes it possible to incorporate the nanoparticles of active components into the carbon particles of large specific surface area. It makes it possible to homogenize the size of the carbon particles and that of the particles of active components, it also makes it possible to properly distribute the particles of active components in the midst of the carbon particles and make them adhere as best possible to the carbon particles. This step may also be carried out with a support material other than carbon.

[57] After adding the polymer binder, a mixing step is carried out to obtain a homogeneous ink.

[58] The preparation step described above makes it possible to obtain an ink comprising catalytic nanoparticles in suspension, which composition will also be referred to as “catalytic ink”.

[59] The catalytic ink thus prepared is sprayed by ultrasonic coating onto the main layer of an anion-conducting membrane. The deposition of the catalytic ink by an ultrasonic spray coating method, combined with the fluidity of the ink makes it possible to properly separate the nanoparticles from one another to avoid the agglomeration thereof during spraying. This method also makes it possible to keep the ink homogeneous throughout the duration of the spraying. This spraying method also makes it possible, by a pressure effect, to obtain a good adhesion of the ink on the main layer of the membrane. The result is a catalytic layer where the distribution of the nanoparticles is particularly homogeneous and uniform; also, the layer obtained has a very thin thickness, of the order of 50 μm to 250 μm at the cathode for a layer comprising nickel, cobalt and carbon, and is particularly constant over the surface of the membrane. Finally, this method makes it possible to obtain a porous catalytic layer which thus has a high specific surface area (ratio between the active surface area and the weight of the catalytic layer), of from 5 m2 / g to 200 m2 / g depending on the formulation of the catalytic ink.

[60] After thorough drying, the membrane can be stored.

[61] Drying enables the evaporation of the liquid, water or water and solvent mixture. The catalytic layer deposited on the membrane then comprises only the particles bound by the polymer binder.

[62] The method according to the invention can be carried out to deposit a first catalytic layer on a first face of the main layer of the membrane, then optionally a second catalytic layer on a second face of the main layer of the membrane.

[63] Thus, the method according to the invention can be carried out to produce an anion-conducting membrane 10 comprising a main layer covered by:- a layer of a first catalytic material comprising nanoparticles of active components bound by a polymer binder, the active components being nickel and cobalt,- or, on one side of the main layer, by a layer of the first catalytic material and, on another side of the main layer, by a layer of a second catalytic material.

[64] The second catalytic material comprises for example nanoparticles of active components bound by a polymer binder, the active components being nickel, a metal oxide and / or molybdenum.

[65] Figure 1 shows a diagram of a cell suitable for a water electrolysis unit for the production of gaseous hydrogen H2 and oxygen O2. The cell comprises a cathode 20, an anode 30 and between the two a membrane 30. Figure 2 shows a schematic diagram of a water electrolysis unit comprising a cell according to the invention. The membrane 10 divides a bath in two, the bath comprising a solution of water and electrolyte, in one example potassium hydroxide KOH. The membrane is covered on one side by a layer 40 of catalytic material comprising nickel and cobalt nanoparticles supported by activated carbon and on the other side by a layer 50 of catalytic material comprising nickel and molybdenum nanoparticles. The cathode 20 and the anode 30 are positioned on either side of the membrane and are connected respectively to the negative and positive terminals of an electrical power source. The membrane 10 allows effective separation of the hydrogen gas produced at the cathode and of the oxygen gas produced at the anode. The cathode and anode may be metallic, for example made of nickel and stainless steel respectively. With such a membrane, with a main layer based on zirconia and with two layers of catalytic material on either side of the main layer, an efficiency of 84% HHV was obtained for a current density of 1 A / cm2 and an efficiency of 90% HHV was obtained for a current density of 0.7 A / cm2 applied between the electrodes of the cell.1. A single cell is represented in Figure 1. However, in practice, an industrial unit may comprise several cells, or even around a hundred cells.

Claims

1. A layer of catalytic material for an anion-conducting membrane (10) for an electrochemical device, the layer of catalytic material comprising nanoparticles of active components bound by a polymer binder, the active components being nickel and cobalt.

2. The layer of catalytic material as claimed in claim 2, wherein the active components comprise 65% to 85% by weight of nickel and 15% to 35% by weight of cobalt, preferably 70% to 80% by weight of nickel and 20% to 30% by weight of cobalt, and even more preferentially 75% by weight of nickel and 25% by weight of cobalt.

3. The layer of catalytic material as claimed in either of claims 1 and 2, wherein the nanoparticles of active components are supported by carbon particles, the nanoparticles of active components and the carbon particles being mixed and bound by the polymer binder.

4. The layer of catalytic material as claimed in claim 3, wherein the carbon is in the form of activated carbon or graphite.

5. The layer of catalytic material as claimed in either of claims 3 and 4, wherein the mixture of active components and carbon comprises:40% to 80% by weight of carbon, and20% to 60% by weight of active components.

6. The layer of catalytic material as claimed in either of claims 3 and 4 comprising:60% to 90% by weight of active components or of a mixture of active components and carbon, in the form of particles, and10% to 40% by weight of binder.

7. The layer of catalytic material as claimed in one of claims 1 to 3 comprising, on the surface, 0.1 to 6 mg / cm2 of active components.

8. The layer of catalytic material as claimed in one of claims 1 to 4, wherein the polymer binder is an ionomer, preferably a sulfonated tetrafluoroethylene based fluoropolymer-copolymer (Nafion).

9. The layer as claimed in one of claims 1 to 5, wherein the nanoparticles of active components and / or the carbon nanoparticles have a size of less than 50 nm, preferably less than 20 nm and even more preferentially less than 5 nm.

10. An anion-conducting membrane (10) for an electrochemical device, the membrane comprising a main layer covered by a layer of catalytic material as claimed in one of claims 1 to 9 or, on one side, by a layer of catalytic material as claimed in one of claims 1 to 9 and, on another side, by a layer of a second catalytic material.

11. A method for depositing a catalytic layer on a main layer of an anion-conducting membrane, the catalytic layer comprising nanoparticles of at least two active components and a polymer binder,the method comprising a step of preparing a liquid ink comprising the following steps consisting in:mixing the nanoparticles of active components in a liquid, the liquid being water, a solvent or a mixture of water and solvent, the solvent being an alcohol for example,grinding the mixture of nanoparticles of active components and liquid,adding the polymer binder to the ground material and mixing.

12. The method as claimed in claim 11, wherein the preparation step also comprises, before adding the polymer binder, the following steps consisting in: adding carbon particles to the ground material of nanoparticles of active components, andgrinding the mixture of particles of active components and carbon particles until a homogeneous mixture is obtained.

13. The method as claimed in either of claims 8 and 9, also comprising a step of ultrasonic spray coating of said liquid ink onto the main layer of the anion-conducting membrane.

14. A cell for an electrochemical device, the cell comprising:an anode (30)a cathode (20) andbetween the anode and the cathode, a membrane (10) as claimed in claim 10.

15. A water electrolysis unit comprising at least one cell as claimed in the preceding claim.

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