Ionically conductive membrane, process for manufacturing such a membrane, electrochemical cell comprising such a membrane, and installation comprising such a cell

Abstract

The invention relates to an ionically conductive membrane (10) for an electrochemical device, the membrane comprising a layer of a material comprising a polymer binder and a powdered ceramic, characterized in that the ceramic is doped with Yttrium oxide. Figure 1.

Description

Title of the invention: Ionic 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 ion-conducting membranes such as those used in particular in water electrolysis devices. More specifically, the invention relates to a membrane (also called a separator) 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, forming water. No carbon-containing greenhouse gases are emitted during such a combustion reaction.

[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 energy carrier for renewable energy. It can store energy and distribute it where 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 to separate the produced gases, as well as electrodes of different polarities to prevent a short circuit between these electronically conductive parts (electrodes) and to prevent the mixing of H2 (formed at the cathode) and O2 (formed at the anode), thus avoiding explosive mixtures of these gases. While fulfilling all these functions, the membrane is an ionic conductor for the transport of OH- ions from the cathode to the anode.

[0006] It is known to produce microporous membranes (or separators) comprising hydrophilic inorganic particles, particularly zirconium oxide particles. Zirfon® membranes, comprising zirconium oxide particles bonded by a polymer, are an example. However, these microporous membranes have drawbacks, including insufficient mechanical and thermal stability, high hydrogen permeability, higher oxygen permeability at temperatures above 100 degrees Celsius, and limited ionic conductivity. Furthermore, these membranes exhibit a limited lifespan due to rapid degradation in alkaline environments, necessitating regular membrane replacement. All these drawbacks affect the profitability of large-scale hydrogen production. Description of the invention

[0007] The invention proposes a new membrane not having all or part of the disadvantages mentioned above.

[0008] To this end, the invention proposes a new ionically conductive membrane for an electrochemical device, membrane comprising a layer of a material comprising a polymer binder and a powdered ceramic, characterized in that the ceramic is doped with Yttrium oxide.

[0009] Experience shows that, in the presence of yttrium oxide, the polymer binder is not degraded by solvated or free electrons present in the electrolyte of an electrolyzer during its operation. The membrane's lifespan is thus greater than that of other known membranes, without the need to add a protective layer to the membrane.

[0010] Preferably, the powdered ceramic is chosen from the group consisting of zirconia (or zirconium dioxide ZrO2), boron nitride, and a mixture of zirconia and boron nitride. Experience shows that the membrane comprising boron nitride, and even more so the membrane comprising zirconium oxide, commonly called zirconia, exhibits very good ionic conductivity, thus improving the electrolysis yield.

[0011] The polymer binder can be a hydrophobic thermoplastic polymer. The polymer's tendency to repel water thus enhances its resistance to free electrons and further improves the membrane's lifespan.

[0012] The polymer binder is preferably chosen from the group consisting of polysulfone (PSU), polyethersulfone (PES), polyphenylene sulfone (PPSU), and polytetrafluoroethylene (PTFE). These are chosen for their excellent resistance to heat, oxidation, and hydrolysis in aqueous and alkaline media. This improves the lifespan of the membrane. These polymer binders also exhibit good electrical properties, which improves the efficiency of the hydrogen production reaction.

[0013] The membrane according to the invention is non-porous. The surface of the ceramic grains ensures the ionic conduction of the membrane. The polymer binder ensures the bond between the grains and the mechanical strength of the membrane.

[0014] The invention also relates to a cell for an electrochemical device, cell comprising a membrane as described above; the invention also relates to a water electrolysis installation comprising such a cell.

[0015] The invention finally relates to a method of manufacturing a membrane as described above, according to a phase inversion technique. Presentation of the figures

[0016] The invention will be better understood, and other features and advantages of the invention will become apparent from the following description of an example of an implementation of the invention. This example is 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

[0017] As stated previously, the invention relates to an ionically conductive membrane (10) for an electrochemical device, the membrane comprising a layer of a material including a polymer binder and a powdered ceramic, the ceramic being doped with yttrium oxide. Experience shows that the use of yttrium oxide makes it possible to neutralize the oxidizing effects of solvated electrons during electrochemical reactions, oxidizing effects which degrade the membrane.

[0018] The powdered ceramic is preferably chosen from the group consisting of zirconia, boron nitride and a mixture of zirconia and boron nitride, ceramics chosen for their ionic conduction property.

[0019] The polymer binder is a hydrophobic thermoplastic polymer, preferably chosen from the group consisting of polysulfone (PSU), polyethersulfone (PES), polyphenylene sulfone (PPSU) and polytetrafluoroethylene (PTFE), polymers chosen for their mechanical, chemical and electrical properties.

[0020] The material preferably comprises: - 70 to 95% by weight of powdered ceramic, and - 5 to 30% by weight of polymer. In the membrane according to the invention, the surface of the powdered ceramic grains is the site of ionic conduction of the membrane, the polymer ensuring the bond between the grains and thus the mechanical strength of the membrane. The resulting membrane is non-porous. The proportion by weight of Powder-doped ceramic and polymer results from a compromise. Experiments carried out with different proportions of ceramic and polymer show that: - the membrane efficiency is satisfactory when the material comprises more than 70% ceramic by weight, - the mechanical strength of the membrane is sufficient for the applications envisaged when the material comprises more than 5% by weight of polymer binder.

[0021] When made with zirconia, the doped ceramic may comprise: - 75 to 99%, and preferably 75 to 95%, by weight of zirconia and - 1 to 25%, and preferably 5 to 25%, by weight of Yttrium oxide. Yttrium oxide is, for example, yttrium dioxide (Y₂O₃). Yttrium-stabilized zirconia (also called yttria zirconia) has a protective effect against the degradation of the binding polymer: tests show that the polymer in a membrane containing powdered ceramic with at least 1% by weight of yttria zirconia degrades very little, and that the polymer in a membrane containing powdered ceramic with at least 5% by weight of yttria zirconia degrades little or not at all compared to the polymer in a membrane containing conventional zirconia. Technically, the membrane material could contain more than 25% by weight of yttrium oxide; however, since the cost of yttrium oxide is particularly high, the cost of the membrane becomes too great relative to the expected performance.

[0022] According to a preferred embodiment, the powdered ceramic grains have an average diameter of between 0.1 and 5 pm, and preferably between 0.2 and 2 pm. The ionic conductivity of the membrane is directly related to the apparent (unbound) surfaces of the grains in the membrane, and more particularly to the contact surfaces or surfaces near adjacent grains that promote ion exchange between the grains. The smaller the grains, the larger the contact surfaces or surfaces near adjacent grains. At the same time, the smaller the grains, the more they are trapped in the binder, which limits the ion exchange surfaces. Tests show that grains with an average diameter of between 0.1 and 5 pm are a good compromise, regardless of the ceramic used. The best test results were obtained with grains with an average diameter of between 0.2 and 2 pm.

[0023] The membrane described above can be produced by a process comprising a phase inversion step. Such a step consists of removing a solvent from a solvent-polymer solution by immersing a film of the solution in a non-solvent. In the context of the invention, such a step enables the transformation of the solvent-polymer solution film into a polymer membrane.

[0024] In more detail, in the example of the fabrication of a PSU / Zirconia membrane doped with Yttrium comprising 10% by weight of PSU and 90% by weight of doped ceramic comprising 85% by weight of Zirconia and 15% by weight of Yttrium oxide, the process according to the invention comprises the following steps.

[0025] First, (step 1) the polymer is dissolved in a solvent immiscible in water to obtain a polymer solution. In this example, a mass of polymer, polysulfone (PSU), is dissolved in a volume of solvent such as dimethylacetamide (DMAc), which is an oily liquid. If necessary, the mixture is stirred at a temperature above 70°C until the polymer is completely dissolved and a homogeneous polymer solution is obtained.

[0026] The ceramic powder is then added (step 2) to the polymer solution, and the mixture is blended to obtain a homogeneous, viscous membrane solution. In this example, to facilitate mixing, a mass of doped zirconia powder is dispersed in DMAc solvent, and then the solution containing the ceramic and the polymer solution obtained in the previous step are mixed for 45 to 60 minutes until a membrane solution more viscous than the two initial solutions is obtained.

[0027] The membrane solution is then poured (step 3) onto a support to form a film. The support is preferably flat. If necessary, particularly depending on its viscosity, the membrane solution is stretched simultaneously with the pouring. The pouring parameters are adjusted according to the desired dimensions of the membrane and the parameters of the membrane solution (in particular the viscosity of the membrane solution and the shrinkage capacity of the polymer binder during the subsequent steps).

[0028] Finally, the film-coated support is then immersed in a non-solvent (step 4) to induce phase inversion. During the phase inversion process, the membrane solution precipitates, and the solvent is replaced by the non-solvent, particularly on the surface and within the film. In the example of the PSU / Zircone-Yttrium oxide membrane, the support on which the film rests is immersed in water (the non-solvent in this case), which replaces the DMAc (the solvent) remaining in the membrane film. Initially, two phases are in equilibrium within the film: a solid, polymer-rich phase that forms the film structure and a liquid (polymer-poor) phase that constitutes the water-filled pores of the membrane. As precipitation progresses, the viscosity of the polymer-rich phase increases until it reaches a state where the precipitated polymer is considered a solid.The membrane solution film thus transforms into a solid, flexible membrane that traps ceramic grains.

[0029] The membrane-covered support is then extracted from the water (step 5) and the membrane is separated from the support (step 6).

[0030] If necessary, a lamination step (step 7) of the membrane can be carried out to homogenize the surfaces, eliminate open porosities to further improve the non-porous nature of the membrane and / or improve mechanical strength of the membrane. The lamination step can be performed at any time after the phase inversion transformation of the membrane solution film is complete. The lamination step can therefore be carried out before extracting the support and membrane from the water (step 5), or after extracting the membrane from the water. The lamination step can be repeated several times if necessary to obtain a membrane with the required properties, including a non-porous membrane.

[0031] Other post-inversion treatments can be considered to finalize the membrane. For example, a heat treatment step can be carried out to strengthen the bond between the polymer and the ceramic grains and / or to reduce the pore size in the membrane.

[0032] At the end of production, the membrane can be rolled up and stored.

[0033] The membrane according to the invention as described above can be used to make an electrochemical cell comprising in particular - an anode 30 - a cathode 20, and - between the anode and the cathode, a membrane 10 as described above.

[0034] Figure 1 shows a diagram of a known cell for water electrolysis plants for the production of hydrogen (H2) and oxygen (O2) gas. Figure 2 shows a schematic diagram of a membrane-based water electrolysis plant. The membrane 10 divides a bath into two parts, the bath comprising a mixture of water and electrolyte. 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 / or the anode may be porous. The cathode and the anode may be metallic, for example, nickel, stainless steel, or metal oxides, particularly on the anodic side. Nickel and stainless steel form oxides on their surface that act as catalysts for oxygen release. 316L stainless steel is particularly effective due to its molybdenum content..

[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. Ionic conductive membrane (10) for an electrochemical device, membrane comprising a layer of a material comprising: - 5 to 30% of a polymer binder and - 70 to 95% by weight of a powdered ceramic, said ceramic being doped with Yttrium oxide.

2. Membrane according to claim 1 wherein the powdered ceramic is selected from the group consisting of zirconia, boron nitride and a mixture of zirconia and boron nitride.

3. Membrane according to claim 1 wherein the polymer binder is a hydrophobic thermoplastic polymer, preferably selected from the group consisting of polysulfone (PSU), polyethersulfone (PES), polyphenylene sulfone (PPSU) and polytetrafluoroethylene (PTFE).

4. Membrane according to any one of claims 1 to 3 wherein the ceramic comprises: - 75 to 99%, and preferably 75 to 95%, by weight of ceramic and - 1 to 25%, and preferably 5 to 25%, by weight of Yttrium oxide.

5. Membrane according to any one of the preceding claims wherein the grains of the powdered ceramic have an average diameter of between 0.1 and 5 pm, and preferably between 0.2 and 2 pm.

6. A method for manufacturing a membrane according to claim 5 comprising the following steps, consisting of:

1. dissolving a polymer in a solvent immiscible in water to obtain a polymer solution, 2. adding a ceramic powder, in an amount such that, relative to the total weight of the polymer and the ceramic, the polymer represents 5 to 30% by weight and the ceramic represents 70 to 95% by weight, the ceramic powder being ceramic doped with Yttrium oxide, and mixing to obtain a homogeneous membrane solution, 3. pouring the membrane solution onto a support to form a film covering the support, 4. immersing the support covered with the film in water to cause a phase inversion.

7. A method according to the preceding claim, also comprising a step of laminating the membrane.

8. 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 any one of claims 1 to 5.

9. Water electrolysis installation comprising at least one cell according to claim 8.