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 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 ionic conductive membranes such as those used in particular in water electrolysis devices. More particularly, 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, 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 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, so does the need for energy storage and transmission. Many renewable energy sources, particularly solar and wind, are located far from population centers and only produce electricity intermittently. Hydrogen can be the perfect energy carrier for renewable energy. It can store energy and distribute it where it is needed.

[0005] Alkaline water electrolysis 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 the electrodes of different polarity in order to avoid 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) by avoiding explosive mixtures of these gases. While performing 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, in particular zirconium oxide particles. Examples include Zirfon® membranes comprising zirconium oxide particles bound by a polymer. However, these microporous membranes have disadvantages, including insufficient mechanical and thermal stability, high hydrogen permeability, higher oxygen permeability at temperatures above 100 degrees Celsius, and limited ionic conductivity. These membranes also show a limited lifespan in use due to rapid degradation in an alkaline environment requiring regular membrane changes. All these disadvantages have an impact on the profitability of large-scale hydrogen production. Statement of the invention

[0007] The invention proposes a new membrane which does not have all or part of the drawbacks mentioned above.

[0008] To this end, the invention proposes a novel ionic 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 the solvated or free electrons present in the electrolyte of an electrolyzer during its operation. The lifetime of the membrane is thus greater than that of membranes known elsewhere, without it being necessary 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, have very good ionic conductivity, so that the efficiency of the electrolysis is improved.

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

[0012] The polymer binder is preferably selected 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 lifetime of the membrane. These polymer binders also have good electrical properties, which improves the efficiency of the production reaction. of hydrogen.

[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 connection 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 figures

[0016] The invention will be better understood, and other characteristics and advantages of the invention will appear in the light of the following description of an example of implementation of the invention. This example is given without limitation. The description is to 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

[0017] As stated previously, the invention relates to an ion-conducting membrane (10) for an electrochemical device, membrane comprising a layer of a material comprising a polymer binder and a powdered ceramic, ceramic 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 seat of the ionic conduction of the membrane, the polymer ensuring the link between the grains and thus the mechanical strength of the membrane. The membrane obtained is non-porous. The proportion by weight of doped powdered ceramic and polymer results from a compromise. The experiments carried out with different proportions of ceramic and polymer show that: - the efficiency of the membrane is satisfactory when the material comprises more than 70% by weight of ceramic, - 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-containing zirconia) has a protective effect against degradation of the binding polymer: tests show that the polymer of a membrane comprising powdered ceramic comprising at least 1% by weight of yttria-containing zirconia degrades little and that the polymer of a membrane comprising powdered ceramic comprising at least 5% by weight of yttria-containing zirconia does not degrade or degrades very little compared to the polymer of a membrane comprising conventional zirconia. Technically, the material constituting the membrane could comprise more than 25% by weight of yttria-containing oxide; however, the cost of yttria being particularly high, the cost of the membrane becomes too high compared to the expected efficiency.

[0022] According to a preferred embodiment, the powdered ceramic grains have an average diameter of between 0.1 and 5 μm, and preferably between 0.2 and 2 μm. The ionic conductivity of the membrane is directly linked to the apparent surfaces (not covered with binder) of the grains in the membrane and more particularly to the contact surfaces or surfaces close to adjacent grains promoting ionic exchanges between the grains. The smaller the grains, the greater the contact or close surfaces between adjacent grains. And at the same time, the smaller the grains, the more they are trapped in the binder which limits the ionic exchange surfaces. Tests show that grains with an average diameter of between 0.1 and 5 μm 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 μm.

[0023] The membrane described above can be produced according to a method comprising a phase inversion step. Such a step here consists of causing the removal of a solvent from a solvent-polymer solution, by immersing a film of solution in a non-solvent. In the context of the invention, such a step allows the transformation of the solvent-polymer solution film into a polymer membrane.

[0024] In more detail, in the example of the production 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 oxide of Yttrium, the method according to the invention comprises the following steps.

[0025] First, (step 1) the polymer is dissolved in a water-immiscible solvent to obtain a polymer solution. In the 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 whole is mixed to obtain a viscous homogeneous membrane solution. In the 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 is obtained that is more viscous than the two initial solutions.

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

[0028] Finally, the film-covered support is then immersed in a non-solvent (step 4) to cause phase inversion. During the phase inversion process, the membrane solution precipitates, the solvent is replaced by non-solvent, particularly on the surface and inside the film. In the example of the PSU / Zirconia-Yttrium oxide membrane, the support on which the film rests is immersed in water (the non-solvent here), which replaces the DMAc (the solvent) remaining in the membrane film. Initially, in the film, two phases are in equilibrium: a solid phase, rich in polymer which forms the structure of the film and a liquid phase (poor in polymer) which constitutes the pores of the membrane filled with water here. As the precipitation progresses, the viscosity of the polymer-rich phase increases until reaching a state where the precipitated polymer is considered a solid.The membrane solution film thus transforms into a membrane, solid, flexible and which 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 rolling step (step 7) of the membrane can be carried out to homogenize the surfaces, remove open porosities to further improve the non-porous character of the membrane and / or improve the mechanical strength of the membrane. The rolling step can be carried out at any time after the end of the transformation of the membrane solution film by phase inversion. The rolling step can thus be carried out before extracting the support and the membrane from the water (step 5), or after extracting the membrane from the water. The rolling step can be repeated several times if necessary to obtain a membrane with the required properties, in particular a non-porous membrane.

[0031] Other post-inversion treatments may be considered to finalize the membrane. For example, a heat treatment step may be performed 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 the production, the membrane can be rolled up and stored.

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

[0034] [Fig. 1] shows a diagram of a known cell for a water electrolysis plant for the production of hydrogen H2 and oxygen O2 gas. [Fig. 2] shows a schematic diagram of a membrane water electrolysis plant. The membrane 10 divides a bath in two, a 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 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 / 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 anode side. Nickel and stainless steel form surface oxides that are catalysts for oxygen release. 316L stainless steel is particularly effective due to its molybdenum content..

[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. Ionic conductive membrane (10) 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.

2. The membrane of 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. The membrane of 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 one of claims 1 to 3 in which the material comprises: - 70 to 95% by weight of powdered ceramic, and - 5 to 30% by weight of polymer.

5. Membrane according to one of claims 1 to 4 in which 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.

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

7. Method of manufacturing a membrane according to one of the preceding claims, comprising a phase inversion step.

8. A method according to claim 7 comprising the following steps:

1. dissolving the polymer in a water-immiscible solvent to obtain a polymer solution, 2. adding the ceramic powder and mixing to obtain a homogeneous membrane solution, 3. casting the membrane solution onto a support to form a film covering the support, 4. immersing the film-covered support in water to cause phase inversion.

9. Method according to the preceding claim, also comprising a step of rolling the membrane.

10. 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 one of claims 1 to 6.

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

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