Anionic conductive membrane, method of manufacturing such a membrane, electrochemical cell comprising such a membrane and installation comprising such a cell

Abstract

The invention relates to a layer of catalytic material for an anionically conductive membrane (10) for an electrochemical device; the layer of catalytic material comprises metal nanoparticles bound by a polymer binder. According to one embodiment, the metal nanoparticles are nickel particles, metal oxide particles, molybdenum particles, particles of a mixture of nickel and metal oxide, particles of a mixture of nickel and molybdenum or particles of a mixture of nickel, metal oxide and molybdenum. Such a layer is preferably deposited on the anode side of the membrane. Figure 1.

Description

Title of the invention: Anionic conductive membrane, method of manufacturing such a membrane, electrochemical cell comprising such a membrane and installation comprising such a cell Technical field of the invention

[0001] The technical field of the invention relates to anionic conductive membranes such as those used in particular in water electrolysis devices. More particularly, the invention relates to a membrane for the alkaline electrolysis of water and a method for manufacturing such membranes. State of the art

[0002] Hydrogen is used in several industrial processes, including as a raw material in the chemical industry and as a reducing agent in the metallurgical industry. Hydrogen is a fundamental element for the manufacture of ammonia, and therefore fertilizers, and for the manufacture of methanol, used in the manufacture of many polymers. Refineries, where hydrogen is used for the processing of intermediate petroleum products, are another area of use.

[0003] Hydrogen is also an important energy carrier: it can store and provide energy in a usable form. The energy is released by an exothermic combustion reaction with oxygen, thus forming water. During such a combustion reaction, no carbon-containing greenhouse gases are emitted.

[0004] As electricity production from renewable energy increases, the need for energy storage and transmission increases. Many renewable energy sources, particularly solar and wind, are located far from population centers and produce electricity only intermittently. Hydrogen can be the perfect carrier for renewable energy. It can store energy and then distribute it where and when it's needed.

[0005] Alkaline water electrolysis is an important process for producing hydrogen. In an alkaline water electrolysis cell, a membrane is used between two electrodes, a cathode and an anode: the membrane separates the electronically conductive electrodes. Non-porous to gases, the membrane also separates the gases produced at the electrodes to prevent an explosive mixture of hydrogen gas H2 (formed at the cathode) and oxygen gas O2 (formed at the anode). The membrane is also ionically conductive for the transport of OH- ions from the cathode to the anode.

[0006] It is known to produce proton exchange membranes (or PEM for proton- exchange membrane). The most widely used membrane is the Nafion® membrane marketed by Dupont de Nemours. The price of this membrane is particularly high. In addition, this membrane generates a very acidic environment, which is particularly aggressive towards the electrodes.

[0007] New membranes are being developed, called anion exchange membranes (or AEM membrane for anion-exchange membrane or anion-conducting membrane or anionic conducting membrane). Examples include Zirfon® separators comprising zirconium oxide particles bound by a polymer. Also included are membranes comprising ceramic particles, such as the Boron Carbide membranes described in document DI = FR3122778 or the Yttrium Zirconia membranes described in document D2 = FR2306159. Made with a polymer and metal oxide and / or ceramic particles, these membranes are fairly simple to manufacture and less expensive. Also, these membranes are used in a non-acidic or weakly acidic environment, which allows the use of common metals for the production of the electrodes, for example Nickel for the cathode and Stainless Steel for the anode.However, all of these membranes are generally less efficient than membranes with catalysts, which impacts the profitability of large-scale hydrogen production.

[0008] To improve the efficiency of membranes, it is known to deposit on the membrane a layer of catalytic materials based on rare materials, for example metals from the Platinum group, also called PGM metals, a group which includes iridium (Ir), Osmium (Om), platinum (Pt), palladium (Pd), rhodium (Rh) and ruthenium (Ru). The efficiency of the AEM membrane is improved but it is observed in practice that the resistance of the catalytic layers on the membrane is limited in time and depends more strongly on the formulation of the catalytic layers and the method of deposition of these layers, anode side and cathode side. In addition, PGM metals are rare metals, which significantly increase the cost of the membranes and therefore reduce the profitability of large-scale hydrogen production. Statement of the invention

[0009] The invention provides new catalytic layers and a new membrane which do not have all or part of the drawbacks mentioned above.

[0010] To this end, the invention proposes a novel layer of catalytic material for an anionic conductive membrane for an electrochemical device, a layer of catalytic material comprising metal nanoparticles bound by a polymer binder.

[0011] The catalytic layer on the surface of the membrane significantly improves the efficiency electrochemical reactions that take place at the interfaces of the membrane and the electrodes, and the results obtained are generally more interesting than a catalytic deposition on one or other of the electrodes of a cell using an AEM membrane without catalytic deposition.

[0012] According to one embodiment of the catalytic layer, the metal nanoparticles are nickel particles, metal oxide particles, molybdenum particles, particles of a mixture of nickel and metal oxide, particles of a mixture of nickel and molybdenum or particles of a mixture of nickel, metal oxide and molybdenum. Advantageously, such a catalytic layer is deposited on an anionic conductive membrane on the anode side.

[0013] The invention also relates to an anionic conductive membrane comprising at least one catalytic layer as described above, a cell comprising an anionic conductive membrane and a water electrolysis installation comprising an anionic conductive membrane. Presentation of figures

[0014] The invention will be better understood, and other characteristics and advantages of the invention will appear in light of the following description of examples of implementation of the invention. These examples are given without limitation. The description should be read in relation to the appended drawings in which: • [Fig.l] shows a cell suitable for a water electrolysis application • [Fig.2] shows a simplified diagram of a water electrolyser Detailed description

[0015] As previously stated, the invention relates to a layer of catalytic material and an anionic conductive membrane 10 for an electrochemical device. Said membrane can be used to produce a cell for an electrochemical device, for example a water electrolysis installation; the cell comprises: - a 30 anode - a cathode 20 and - between the anode and the cathode, a membrane 10.

[0016] The membrane comprises a main layer known elsewhere, for example a main layer comprising metal oxide particles such as zirconium oxide, or ceramic particles. According to the invention, the main layer is covered with a layer of catalytic material comprising metal nanoparticles bound by a polymer binder.

[0017] In order to compare the performance of the catalytic layers and the membranes on which they are deposited, tests were carried out with a test cell comprising a 30 cm2 membrane, a nickel cathode and a stainless steel anode; the electrolyte used is potassium hydroxide KOH, also known as caustic potash or simply potash. Several types of membranes were tested, including membranes whose main layer comprises ceramic particles such as boron carbide, zirconia or yttria-containing zirconia. The tests were carried out at a temperature T = 90°C.

[0018] In order to compare the performance of the membranes, the HHV (High Heating Value) efficiency of a water electrolysis cell comprising the membrane is calculated. For this, with the membrane placed in the test cell, the voltage V (T, I) between the cathode and the anode of the cell and the current density I flowing between the two electrodes per unit area of membrane are measured. The minimum theoretical voltage for the water dissociation reactions to begin is U0 = 1.48V. The efficiency is calculated by the relation R = V0 / V(T, I), where V(T, I) is the voltage across the cell, for a given temperature T and a given current density I.

[0019] Since the heat produced by the electrolysis itself makes it possible to increase the temperature and then maintain the system at a constant temperature, the efficiency calculation above reflects the efficiency of a cell. To calculate the overall efficiency of an electrolyser comprising such a cell, the amount of energy consumed for the overall operation of the system should be subtracted from the energy consumed directly by the electrolysis. In this document, only the efficiency of the cells is analysed.

[0020] One embodiment of the invention relates to a layer of catalytic material adapted to be positioned on the main layer of the membrane, on the anode side. In this embodiment, the metal particles of the catalytic layer are nickel particles, metal oxide particles, molybdenum particles, particles of a mixture of nickel and metal oxide, particles of a mixture of nickel and molybdenum or particles of a mixture of nickel, metal oxide and molybdenum. When the metal nanoparticles with a catalytic effect comprise metal oxide particles, these are preferably iron oxide particles, preferably iron II / III oxide particles.

[0021] The metal oxide nanoparticles are preferably particles having a so-called Perovskite crystal structure. Perovskites have a crystal structure of type ABX3, where A, B and X represent different ions. The structure is cubic with a B-type ion at the center of a cube formed by A-type ions, and X-type ions occupying the corners of the cube. Perovskites have interesting electrical and magnetic properties, making them useful in particular here as materials for catalysts. Their particular crystalline structure also makes them useful as catalyst supports.

[0022] In terms of efficiency for water electrolysis, good HHV yields have been obtained with a membrane comprising a catalytic layer in which the nanoparticles comprise 30 to 70% by weight of iron oxide, 15 to 35% by weight of nickel and 15 to 35% by weight of molybdenum, and better, 40 to 60% by weight of iron oxide, 20 to 30% by weight of nickel and 20 to 30% by weight of molybdenum. With a membrane having a layer of catalytic material at the anode comprising a mixture of metal nanoparticles comprising 50% by weight of iron oxide, 25% by weight of nickel and 25% by weight of molybdenum, an efficiency of 75%HHV was obtained for a current density of 1A / cm2 and an efficiency of 79%HHV was obtained for a current density of 0.7A / cm2.

[0023] The efficiency of the membranes depends in particular on the quantity of nanoparticles present in the catalytic layer on the anode side. The best efficiencies have been obtained for membranes in which the layer of catalytic material comprises, on the surface, 0.1 to 7 mg / cm2 of metal nanoparticles. The catalytic layer preferably has a thickness of 100 pm to 100 pm.

[0024] The tests have also shown that the efficiency of the membranes also depends on the size of the metal nanoparticles used for the catalytic layer on the anode side, and more precisely that the catalytic activity of the nanoparticles increases when the number of electrochemical reaction sites for dissociating water molecules increases. The sites of the chemical reactions are present on the surfaces of the catalytic materials; to increase the number of sites, one solution is to increase the specific surface area (ratio between the surface area and the mass) of the catalytic materials. Thus, in the context of the invention, the nanoparticles chosen have a size of less than 50 nm, preferably less than 20 nm and even more preferably less than 5 nm.

[0025] The performance of the membranes also depends on the good cohesion of the nanoparticles between them, on the good cohesion of the catalytic layer to the main layer of the membrane and on the durability of this cohesion over time. For this purpose, the polymer binder used is an ionomer chosen for its resistance over time in aggressive chemical environments and at high temperatures up to 120°C, but also for its ionic conduction properties, but also depending on its ionic conduction properties. By polymerizing, the binder acts as a glue in the catalytic layer and keeps the particles and nanoparticles of this layer together. It also allows good adhesion of the catalytic layer with the membrane. Finally, an essential point in the context of the invention, due to its ionic conduction, the ionomer allows the catalytic layer to remain electrically conductive and ionic. The preferred ionomer is known as Nafion®, derived from the polymerization of a monomer called tetrafluoroethylene-perfluoro-sulfonic acid. The proportion of polymer binder is 10% to 40% of the weight of the mixture. The proportion by weight of polymer binder is 10% to 40% of the total mass of the mixture.

[0026] The performance of membranes with a catalytic layer also depends on the method of producing the catalytic layer on the main layer of the membrane.

[0027] For this purpose, the invention proposes a method for depositing a catalytic layer on an anionic conductive membrane, method comprising a step of preparing a liquid ink comprising metal nanoparticles and a polymer binder, the step of preparing the liquid ink comprises the following steps consisting of: - mixing the metal nanoparticles in a liquid such as water or ethanol, - grind the mixture of metal particles in a liquid medium until a homogeneous mixture is obtained, - add the liquid polymer binder.

[0028] The quantity of liquid chosen is adapted to wet the nanoparticles, so as to facilitate the following grinding step and to limit an operator's exposure to the nanoparticle dust that will be generated during the grinding step. The mixing and then grinding of the nanoparticles makes it possible to obtain smaller nanoparticles, of the chosen size, less than 50 nm and even more preferably less than 5 nm, and particles of the most homogeneous size possible. The mixing and then grinding of the nanoparticles also makes it possible to have a homogeneous mixture of the materials, in particular when two or more types of nanoparticles are used (for example Nickel and Cobalt, or Ni, iron oxide and Molybdenum). The grinding of the nanoparticles is carried out in an aqueous medium, for example in a planetary mill / mixer (or bowlmilling in English).

[0029] The preparation step described above makes it possible to obtain an ink comprising catalytic nanoparticles in suspension, a composition which will also be called “catalytic ink”.

[0030] The catalytic ink thus prepared is sprayed by ultrasound onto the main layer of an anionic conductive membrane. The deposition of the catalytic ink by an ultrasonic spraying process, combined with the fluidity of the ink, makes it possible to separate the nanoparticles well from each other to avoid their agglomeration during spraying. This process also makes it possible to keep the ink homogeneous throughout the spraying. This process also makes it possible, by a pressure effect, to obtain good adhesion of the ink to the main layer of the membrane. The result is a catalytic layer where the distribution of the nanoparticles is particularly homogeneous and regular; also, the layer obtained has a very low thickness, of the order of 100 pm to 100 pm at the anode and 50 pm to 250 pm at the cathode, and particularly constant over the entire surface of the membrane.

[0031] After complete drying, the membrane can be stored.

[0032] The method according to the invention can be implemented 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.

[0033] Thus the method according to the invention can be implemented to produce an anionic conductive membrane 10 comprising a main layer covered by: - a layer of a first catalytic material, for example produced according to the embodiment described above, based on iron, nickel and / or molybdenum oxide - a layer of a second catalytic material, for example a layer based on Nickel and / or Cobalt, - or, on one side, by a first layer of catalytic material produced according to the embodiment described above and on the other side by a second layer of catalytic material, for example a layer based on Nickel and / or Cobalt.

[0034] [Fig.l] shows a diagram of a cell suitable for a water electrolysis plant 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. [Fig.2] shows a schematic diagram of a water electrolysis plant comprising a cell according to the invention. The membrane 10 divides a bath into two, a bath comprising a mixture of water and electrolyte, in one example potash KOH. The membrane is covered on one side by a layer 40 of catalytic material based on Nickel and Molybdenum and on the other side by a layer 50 of catalytic material based on Nickel and Cobalt. 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 energy source. The membrane 10 allows good separation of the hydrogen gas produced on the cathode and the oxygen gas produced on the anode.The cathode and the anode are metallic, for example nickel, respectively stainless steel. With such a membrane, with a main layer based on zirconia and with two layers of catalyst 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.

[0035] A single cell is shown in [Fig.l]. However, in practice, an industrial installation may comprise several cells, or even a hundred cells.

Claims

Claims

1. Layer of catalytic material for an anionic conductive membrane (10) for an electrochemical device, layer of catalytic material comprising metal nanoparticles bound by a polymer binder, the metal nanoparticles are Nickel particles, metal oxide particles, Molybdenum particles, particles of a mixture of Nickel and metal oxide, particles of a mixture of Nickel and Molybdenum or particles of a mixture of Nickel, metal oxide and Molybdenum.

2. Layer according to claim 1 in which the metal nanoparticles comprise metal oxide particles, preferably metal oxide particles having a so-called Perovskite crystalline structure.

3. Layer according to one of the preceding claims in which the metallic nanoparticles comprise iron oxide particles, preferably iron II / III oxide particles.

4. Layer according to one of the preceding claims in which the metallic nanoparticles comprise 30 to 70% by weight of iron oxide, 15 to 35% by weight of nickel and 15 to 35% by weight of molybdenum, preferably 40 to 60% by weight of iron oxide, 20 to 30% by weight of nickel and 20 to 30% by weight of molybdenum, and even more preferably 50% by weight of iron oxide, 25% by weight of nickel and 25% by weight of molybdenum.

5. Layer according to one of the preceding claims in which the layer of catalytic material comprises, on the surface, 0.1 to 7 mg / cm2 of metallic nanoparticles.

6. Layer according to one of the preceding claims in which the polymer binder is an ionomer, preferably a fluoropolymer copolymer based on sulfonated tetrafluoroethylene (Nafion).

7. Layer according to one of the preceding claims in which the nanoparticles have a size less than 50 nm, and preferably less than 20 nm, and even more preferably less than 5 nm.

8. Anionic conductive membrane (10) for an electrochemical device, membrane comprising a main layer covered by a layer of catalytic material according to one of the preceding claims.

9. Cell for an electrochemical device, cell comprising: - an anode (30) - a cathode (20) and - between the anode and the cathode, a membrane (10) according to claim 8.

10. Water electrolysis installation comprising at least one cell according to the preceding claim.

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