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

Abstract

The invention relates to a catalytic material layer for an anionically conductive membrane (10) for an electrochemical device; the catalytic material layer comprises metallic nanoparticles bonded by a polymer binder. In one embodiment, the metallic 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 for 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 specifically, 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, notably as a raw material in the chemical industry and as a reducing agent in the metallurgical industry. Hydrogen is a fundamental element for the production of ammonia, and therefore fertilizers, and for the production 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 ​​application.

[0003] Hydrogen is also an important energy carrier: it can store and supply energy in a usable form. 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 sources increases, so does the need for energy storage and transport. Many renewable energy sources, particularly solar and wind power, 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 is needed.

[0005] The electrolysis of alkaline water 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. Being 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] Proton exchange membranes (or PEMs) are known to be manufactured. The most widely used membrane is the Nafion® membrane marketed by DuPont de Nemours. This membrane is particularly expensive. Furthermore, it generates a highly acidic environment, which is particularly aggressive towards the electrodes.

[0007] New membranes are being developed, called anion-exchange membranes (AEMs, also known as anion-conducting membranes or anionic-conducting membranes). Examples include Zirfon® separators comprising zirconium oxide particles bonded by a polymer. Other examples include membranes comprising ceramic particles, such as boron carbide membranes described in document DI = FR3122778 or yttria zirconia membranes described in document D2 = FR2306159. Made with a polymer and metal oxide and / or ceramic particles, these membranes are relatively simple to manufacture and less expensive. Furthermore, these membranes are used in non-acidic or slightly acidic environments, which allows the use of common metals for the electrodes, for example, nickel for the cathode and stainless steel for the anode.However, all these membranes are generally less efficient than membranes with catalysts, which impacts the profitability of large-scale hydrogen production.

[0008] To improve membrane efficiency, it is known to deposit a layer of catalytic materials based on rare earth elements onto the membrane, for example, platinum group metals, 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 in practice, the adhesion of the catalytic layers to the membrane is limited over time and depends heavily on the formulation of the catalytic layers and the deposition process of these layers, on both the anode and cathode sides. Furthermore, PGM metals are rare earth elements, which significantly increase the cost of the membranes and therefore reduce the profitability of large-scale hydrogen production. Description of the invention

[0009] The invention proposes new catalytic layers and a new membrane not exhibiting all or part of the disadvantages mentioned above.

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

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

[0012] According to one embodiment of the catalytic layer, the metallic 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 anionically 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 the figures

[0014] The invention will be better understood, and other features and advantages of the invention will become apparent from the following description of examples of implementation of the invention. These examples are given by way of non-limiting example. The description is to be read in conjunction with the accompanying drawings in which: • Fig. 1 shows a cell adapted for a water electrolysis application • Figure 2 shows a simplified diagram of a water electrolyzer Detailed description

[0015] As stated previously, the invention relates to a layer of catalytic material and an anionic conductive membrane 10 for an electrochemical device. This membrane can be used to construct a cell for an electrochemical device, for example, a water electrolysis installation; the cell comprises: - an anode 30 - 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 metallic nanoparticles linked 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 was potassium hydroxide (KOH), also known as caustic potash or simply potash. Several types of membranes were tested, including membranes whose main layer comprised ceramic particles of the boron carbide, zirconia, or yttria-stabilized zirconia type. The tests were carried out at a temperature T = 90°C.

[0018] To compare the performance of the membranes, the HHV (High Heating Value) efficiency of a water electrolysis cell including the membrane is calculated. For this purpose, with the membrane placed in the test cell, the voltage V(T, I) between the cathode and anode of the cell and the current density I flowing between the two electrodes per unit area of ​​the membrane are measured. The minimum theoretical voltage for the water dissociation reactions to begin is U0 = 1.48V. The efficiency is calculated using 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 allows the temperature to be raised and then maintained at a constant temperature, the efficiency calculation above accurately reflects the efficiency of a single cell. To calculate the overall efficiency of an electrolyzer including such a cell, the amount of energy consumed for the overall operation of the system, excluding the energy consumed directly by electrolysis, would need to be subtracted. In this document, only the efficiency of the cells is analyzed.

[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 metallic 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 metallic nanoparticles with 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 crystalline structure. Perovskites have a crystalline structure of the ABX3 type, where A, B, and X represent different ions. The structure is cubic, with a type B ion at the center of a cube formed by type A ions, and type X ions occupying the corners of the cube. Perovskites exhibit interesting electrical and magnetic properties, making them particularly useful here as catalyst materials. Their specific crystal 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 wt% of Iron oxide, 15 to 35 wt% of Nickel and 15 to 35 wt% of Molybdenum, and better, 40 to 60 wt% of Iron oxide, 20 to 30 wt% of Nickel and 20 to 30 wt% of Molybdenum. With a membrane having an anode catalytic material layer comprising a mixture of metallic 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 were obtained for membranes in which the catalytic material layer comprises, on its surface, 0.1 to 7 mg / cm² of metallic nanoparticles. The catalytic layer preferably has a thickness of 100 µm to 100 µm.

[0024] The tests also showed that the membrane efficiency depends on the size of the metallic nanoparticles used for the catalytic layer on the anode side, and more specifically that the catalytic activity of the nanoparticles increases as the number of electrochemical reaction sites for the dissociation of water molecules increases. These chemical reaction sites are present on the surfaces of the catalytic materials; to increase the number of sites, one solution is to increase the specific surface area (surface area to mass ratio) 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 with each other, the good cohesion of the catalytic layer to the main layer of the membrane, and the durability of this cohesion over time. To this end, 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, as well as for its ionic conductivity. Upon polymerization, the binder acts as a It adheres to the catalytic layer and holds the particles and nanoparticles of this layer together. It also ensures good adhesion of the catalytic layer to the membrane. Finally, and crucially for the purposes of this invention, due to its ionic conductivity, the ionomer allows the catalytic layer to remain electrically and ionically conductive. The preferred ionomer is known as Nafion®, which is derived from the polymerization of a monomer called tetrafluoroethylene-perfluorosulfonic acid. The proportion of polymer binder is 10% to 40% by weight of the mixture.

[0026] The efficiency of membranes with a catalytic layer also depends on the process of making the catalytic layer on the main layer of the membrane.

[0027] To this end, the invention proposes a method for depositing a catalytic layer on an anionic conductive membrane, a method comprising a step of preparing a liquid ink comprising metallic nanoparticles and a polymer binder. The step of preparing the liquid ink comprises the following steps consisting of: - mixing the metallic nanoparticles in a liquid such as water or ethanol, - Grind the mixture of metallic 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 subsequent grinding step and limit operator exposure to the nanoparticle dust that will be generated during the grinding step. Mixing and then grinding 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. Mixing and then grinding the nanoparticles also makes it possible to obtain a homogeneous mixture of the materials, particularly 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 bowl mill).

[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 ultrasonically sprayed 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, allows for good separation of the nanoparticles from one another to prevent their agglomeration. during spraying. This process also ensures that the ink remains homogeneous throughout the entire spraying process. Furthermore, through a pressure effect, this process achieves good adhesion of the ink to the main layer of the membrane. The result is a catalytic layer where the distribution of nanoparticles is particularly homogeneous and regular; also, the resulting layer has a very thin profile, on the order of 100 µm to 100 µm at the anode and 50 µm to 250 µm at the cathode, and is remarkably consistent across 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, and then optionally a second catalytic layer on a second face of the main layer of the membrane.

[0033] Thus, the process 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 made according to the embodiment described above, based on iron oxide, nickel and / or molybdenum; - 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 made 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] Figure 1 shows a schematic diagram of a cell adapted for a water electrolysis plant for the production of hydrogen (H2) and gaseous oxygen (O2). The cell comprises a cathode 20, an anode 30, and a membrane 30 between them. Figure 2 shows a schematic diagram of a water electrolysis plant comprising a cell according to the invention. The membrane 10 divides a bath in two, the bath comprising a mixture of water and electrolyte, in this example, potassium hydroxide (KOH). The membrane is coated on one side by a layer 40 of nickel-molybdenum-based catalytic material and on the other side by a layer 50 of nickel-cobalt-based catalytic material. 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 for good separation of the hydrogen gas produced at the cathode and the oxygen gas produced at the anode.The cathode and anode are metallic, for example nickel and stainless steel respectively. With such a membrane, with a zirconia-based main layer and two layers of catalyst material on either side of the main layer, the efficiency is [missing value]. 84%HHV was obtained for a current density of 1A / cm2 and an efficiency of 90%HHV was obtained for a current density of 0.7A / cm2.

[0035] A single cell is shown in [Fig.1]. However, in practice, an industrial installation may include several cells, or even a hundred cells.

Claims

Demands

1. A catalytic material layer for an anionically conductive membrane (10) for an electrochemical device, a catalytic material layer comprising nanoparticles linked by a polymer binder, the nanoparticles being 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 nanoparticles comprise metal oxide particles, preferably metal oxide particles having a so-called Perovskite crystalline structure.

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

4. A layer according to any one of the preceding claims wherein the nanoparticles comprise 30 to 70 wt% of Iron oxide, 15 to 35 wt% of Nickel and 15 to 35 wt% of Molybdenum, preferably 40 to 60 wt% of Iron oxide, 20 to 30 wt% of Nickel and 20 to 30 wt% of Molybdenum, and even more preferably 50 wt% of Iron oxide, 25 wt% of Nickel and 25 wt% of Molybdenum.

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

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

7. A layer according to any one of the preceding claims, wherein the nanoparticles have a size less than 50 nm, and preferably less than 20 nm, and even more preferably less than 5

8. 11111. Anionic conductive membrane (10) for an electrochemical device, membrane comprising a main layer covered by a layer of catalytic material according to any 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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