Ion-conducting membrane, method for manufacturing such membrane, electrochemical cell containing such membrane, and equipment containing such cell.

Abstract

The present invention - Polymer binder 5% to 30% by weight, and - Ceramic powder containing yttrium oxide-doped ceramics and / or cerium oxide-doped ceramics, 70% to 95% by weight The present invention relates to an ion-conducting film (10) for an electrochemical device, comprising a layer of material containing [a specific material]. It is applied to the production of non-porous membranes for low-temperature electrolysis (0°C to 150°C).

Description

Technical Field

[0001] The technical field of the present invention relates to ion-conducting membranes, such as those used particularly in water electrolysis devices. More particularly, the present invention relates to membranes for alkaline water electrolysis (also called separators) and methods for manufacturing such membranes.

Background Art

[0002] Hydrogen is used in many industrial processes, particularly as a starting material in the chemical industry and as a reducing agent in the metallurgical industry. Hydrogen is a basic element in the production of ammonia and thus fertilizers and in the production of methanol used in the production of many polymers. Oil refineries where hydrogen is used in the treatment of intermediate petroleum products are also another field of use.

[0003] Hydrogen is also an important energy vector: it can store and supply energy in a form that can be used. The energy is released by an exothermic combustion reaction with oxygen, thereby forming water. During such combustion reactions, greenhouse gases containing carbon are not emitted.

[0004] As the generation of electricity from renewable energy increases, the need for energy storage and transportation also increases. Many renewable energy sources, particularly sunlight and wind, are located far from population centers and only generate electricity intermittently. Hydrogen can be a complete energy vector for renewable energy. Hydrogen can store energy and distribute it to where it is needed.

[0005] Alkaline water electrolysis is an important method for producing hydrogen. In an alkaline water electrolysis cell, the membrane separates the generated gases, separates electrodes with different polarities, avoids short circuits between these electronically conductive parts (electrodes), and prevents the mixing of H2 (formed at the cathode) and O2 (formed at the anode) to avoid an explosive mixture of these gases. While fulfilling all of these functions simultaneously, the membrane is OH -It is an ion conductor that transports ions from the cathode to the anode.

[0006] In the field of electrolysis, the concept of porosity is important in determining the suitability and definition of membrane-type (airtight) or diaphragm-type (airtight) separators, especially when producing hydrogen.

[0007] In certain electrolysis methods, porous membranes are used, i.e., membranes with pores larger than 1 micrometer (1 μm) in average diameter: these pores are designed to make the membrane ion-conductive, as electrolytes enter through them and, under the influence of the electrolysis voltage, ions (or anions) flow through the electrolyte adsorbed in the pores. However, bubbles also easily enter these pores and pass through the membrane, increasing "crossover" (the passage of gas across the membrane).

[0008] More recent electrolysis methods use airtight membranes (i.e., membranes impermeable to bubbles), meaning membranes with an average pore diameter of less than 1 micrometer (1 μm), or even less than 1 nanometer (1 nm). In this case, the ionic electrolyte is adsorbed by the membrane, but bubbles cannot pass through it. The membrane is said to be airtight or nonporous.

[0009] It is a known technique to produce microporous membranes (or separators) containing hydrophilic inorganic particles, particularly zirconium oxide (also known as zirconia) particles. An example is the Zirfon® membrane, which contains zirconium oxide particles bonded to a polymer. These membranes are microporous (pores with a diameter of approximately 1 μm); however, they also have drawbacks, particularly insufficient mechanical and thermal stability, high permeability to dihydrogen, even higher permeability to dioxygen at temperatures above 100 degrees Celsius, limited ionic conductivity, and therefore limited efficiency. In addition, these membranes have a limited service life due to rapid degradation in alkaline environments and require frequent replacement. All of these drawbacks affect the profitability of large-scale hydrogen production.

[0010] Another known method from EP2373833 is to produce non-porous films consisting solely of yttrium oxide-doped zirconia-type ceramics, where yttrium oxide is chosen for its high-temperature ion-conducting effect. These films are fabricated from ceramic particles by a sintering method at high temperatures (approximately 1400-1600°C), which rearranges the ceramic crystals, causing them to fuse together and form a hard film. However, these films have drawbacks: they are brittle because they are hard and can only be used for high-temperature electrolysis (above 600°C). Furthermore, the method for manufacturing these films is particularly difficult and costly to implement because it requires a sintering step. [Overview of the project] [Problems that the invention aims to solve]

[0011] This invention proposes a novel film that does not have any or some of the aforementioned drawbacks. [Means for solving the problem]

[0012] For this purpose, the present invention - Polymer binder 5% to 30% by weight, and - Ceramic powder containing yttrium oxide-doped ceramics and / or cerium oxide-doped ceramics, 70% to 95% by weight We propose a novel ion-conducting film for electrochemical devices, comprising a layer of material containing [specific material].

[0013] In doping methods, impurities (yttrium oxide or cerium oxide in the context of this invention) are added to a pure substance (ceramic in the context of this invention) to modify the crystal structure of the pure substance and, ultimately, its physicochemical properties. Therefore, in the context of this invention, the doped substances used, in this case yttrium oxide-doped ceramics and / or cerium oxide-doped ceramics, are substances that differ from the original pure substance (the ceramic) with respect to their crystal structure and, as a result, have at least one different physicochemical property compared to the original ceramic.

[0014] Surprisingly, in the film according to the present invention, which consists of a polymer binder and yttrium oxide-doped ceramic and / or cerium oxide-doped ceramic, the polymer binder is solvated or free electrons present in the electrolyte within the electrolytic cell during electrolytic cell operation, or particularly aggressive nascent oxygen atoms "O · Tests showed that it does not degrade due to [the substance]. Therefore, tests show that yttrium oxide-doped ceramics and cerium oxide-doped ceramics have a protective effect against oxidation of polymer binders. Consequently, the lifespan of the film according to the present invention is longer than that of other known films, and there is no need to add a protective layer to the film against oxidation.

[0015] In a particular embodiment of the film according to the present invention, the ceramic powder is - Yttrium oxide-doped zirconia, - Cerium oxide-doped zirconia, or - A mixture of yttrium oxide-doped zirconia and cerium oxide-doped zirconia. It may include.

[0016] Yttrium-stabilized zirconia, also known as YSZ, is a ceramic made of zirconium dioxide (ZrO2) whose crystalline structure is stabilized at ambient temperature by yttrium oxide in its cubic or tetragonal form. Zirconia has very good ionic conductivity, which improves the efficiency of electrolysis. Doping zirconia with yttrium oxide imparts a specific antioxidant effect to the doped zirconia that is advantageous in the context of this invention. Doping with cerium oxide also provides an advantageous antioxidant effect, and cerium oxide is not more expensive than yttrium oxide.

[0017] In another embodiment, the ceramic powder is - A mixture of yttrium oxide-doped zirconia and boron nitride, - A mixture of cerium oxide-doped zirconia and boron nitride, or - A mixture of yttrium oxide-doped zirconia, cerium oxide-doped zirconia, and boron nitride. It may include.

[0018] Thanks to its excellent ionic conductivity, boron nitride is a good additive for zirconia.

[0019] The polymer binder may be a hydrophobic thermoplastic polymer. Therefore, the polymer's water-repellent properties enhance its resistance to electrons, further improving the film's lifespan.

[0020] The polymer binder is preferably polysulfone (PSU), polyethersulfone (PES), polyphenylene sulfone (PPSU), polytetrafluoroethylene (PTFE), or a mixture of at least two of the above polymers. These polymers are selected because they have excellent resistance to heat, oxidation, and hydrolysis in aqueous and alkaline environments. This improves the service life of the membrane. These polymer binders also have good electrical properties, thereby improving the efficiency of the hydrogen production reaction.

[0021] The membrane according to the invention is non-porous. The surface of the ceramic particles ensures the ionic conduction of the membrane. The polymer binder ensures the mechanical bonding between the particles; thereby a flexible membrane is also obtained.

[0022] The invention also relates to a ceramic comprising yttrium-doped ceramic and / or cerium-doped ceramic, preferably yttrium-doped zirconia and / or cerium-doped zirconia, which is particularly advantageous for the production of non-porous membranes for low-temperature electrolysis (0 °C to 150 °C).

[0023] The invention also relates to a cell for an electrochemical device comprising the above membrane; the invention also relates to a water electrolysis facility comprising such a cell.

[0024] Finally, the invention relates to a method for producing the above membrane by phase conversion technology.

[0025] In light of the following description of the implementation examples of the invention, the invention will be better understood and other features and advantages of the invention will become apparent. This example is shown as a non-limiting illustration. The description should be read in conjunction with the accompanying drawings.

Brief Description of the Drawings

[0026] [Figure 1] It is a diagram showing a cell suitable for water electrolysis applications. [Figure 2]This diagram shows a simplified scheme for a water electrolysis cell. [Figure 3] This figure shows the results of tests performed on the film according to the present invention. [Modes for carrying out the invention]

[0027] As mentioned above, the present invention is - Polymer binder 5% to 30% by weight, and - Ceramic powder containing yttrium oxide-doped ceramic or cerium oxide-doped ceramic, 70% to 95% by weight The present invention relates to an ion-conducting film (10) for an electrochemical device, comprising a layer of material containing [a specific material].

[0028] Experience has shown that the use of doped ceramics can neutralize the oxidative effects of solvated electrons and lone atoms in electrochemical reactions, and that these oxidative effects degrade the film, and more specifically, the film binder.

[0029] In a particular embodiment, the ceramic powder is: - Yttrium oxide-doped zirconia, - Cerium oxide-doped zirconia, or a mixture of yttrium oxide-doped zirconia and cerium oxide-doped zirconia. It may include. In other embodiments, the ceramic powder is: - A mixture of yttrium oxide-doped zirconia and boron nitride, - A mixture of cerium oxide-doped zirconia and boron nitride, or - A mixture of yttrium oxide-doped zirconia, cerium oxide-doped zirconia, and boron nitride. It may include.

[0030] The polymer binder is a hydrophobic thermoplastic polymer, preferably polysulfone (PSU), polyethersulfone (PES), polyphenylenesulfone (PPSU), polytetrafluoroethylene (PTFE), or a mixture of at least two of these polymers; these polymers are selected for their mechanical, chemical, and electrical properties.

[0031] As disclosed above, the materials that make up the component are: - Ceramic powder 70% to 95% by weight, and - Polymer 5% to 30% by weight Includes.

[0032] In the film according to the present invention, the surface of the ceramic powder particles, more specifically the contact surfaces between the ceramic particles, are the sites of ion conduction in the film. Therefore, it is important to maximize these contact surfaces in order to obtain the most efficient film possible in terms of ion conduction, i.e., electrolytic efficiency. In the film according to the present invention, the polymer provides interparticle bonding and therefore the mechanical strength of the film. The resulting film is non-porous, and ion conduction occurs on the contact surfaces of the ceramic particles. Therefore, the weight ratio of ceramic powder to polymer is a compromise. Experiments performed with different ratios of ceramic and polymer showed: - The efficiency of the film, particularly with respect to ionic conductivity, is satisfactory when the material contains more than 70% by weight of ceramic. - The mechanical strength of the film is sufficient for the intended application when the material contains 5% by weight of polymer binder. I found out. In one embodiment, the doped ceramic is: - Ceramic (e.g., zirconia) 75% to 99% by weight, preferably 75% to 95% by weight, and - Yttrium oxide or cerium oxide in an amount of 1% to 25% by weight, preferably 5% to 25% by weight. It may include.

[0033] This combination forms a 100% by weight doped ceramic. Yttrium oxide is, for example, yttrium dioxide Y2O3. Ceramics doped with yttrium oxide or cerium oxide have a protective effect against oxidative degradation of the polymer binder: compared to the polymer of a conventional zirconia-containing film, for example, a polymer of a film containing ceramic powder with doped zirconia containing at least 1% by weight of yttrium oxide showed little degradation, and a polymer of a film containing ceramic powder with doped zirconia containing at least 5% by weight of yttrium oxide showed no degradation or only very slight degradation, as has been found in tests. Technically, in the material constituting the film according to the present invention, the doped ceramic may contain 25% by weight of yttrium oxide; however, since the price of yttrium oxide is particularly high, the price of the film would be too high compared to the expected efficiency.

[0034] According to a preferred embodiment, the average diameter of the ceramic powder particles is 0.1–5 μm, preferably 0.2–2 μm. The ionic conductivity of the film is directly related to the visible surface of the particles in the film (not covered by the binder), and more particularly to the contact surface or the proximity surface between adjacent particles that promotes ion exchange between particles. The smaller the particles, the larger the contact surface or the proximity surface between adjacent particles. At the same time, the smaller the particles, the more they are trapped in the binder, thereby limiting the ion exchange surface. Tests have shown that particles with an average diameter of 0.1–5 μm are a good compromise, regardless of the ceramic used. The best test results were obtained with particles with an average diameter of 0.2–2 μm.

[0035] The above-described film can be produced by a method comprising a phase conversion step. In such a step, the solvent is removed from the solvent-polymer solution by immersing the film of the solution in a non-solvent. In the context of the present invention, this step converts the film of the solvent-polymer solution into a polymer film.

[0036] More specifically, in an example of producing a PSU (polysulfone) / YSZ (yttrium oxide-doped zirconia) film containing 10 wt% PSU and 90 wt% doped ceramic (yttrium oxide-doped zirconia containing 85 wt% zirconia and 15 wt% yttrium oxide), the method according to the present invention includes the following steps:

[0037] First, (Step 1) the polymer is dissolved in a water-immiscible solvent to obtain a polymer solution. In the example, a certain mass of polymer, polysulfone (PSU), is dissolved in a certain amount of an oily liquid solvent such as dimethylacetamide (DMAc). If necessary, this mixture is stirred at a temperature above 70°C until the polymer is completely dissolved to obtain a homogeneous polymer solution.

[0038] Next, ceramic powder is added to the polymer solution (Step 2). The amount of ceramic powder added is such that the polymer accounts for 5% to 30% by weight and the ceramic accounts for 70% to 95% by weight relative to the total weight of the polymer and ceramic. The ceramic powder includes yttrium oxide-doped ceramic and / or cerium oxide-doped ceramic, preferably cerium oxide-doped zirconia and / or, as in this embodiment, yttrium oxide-doped zirconia (YSZ). The mixture is blended to obtain a homogeneous viscous film solution. In this embodiment, to facilitate mixing, a certain mass of doped zirconia powder is dispersed in a 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 film solution with a higher viscosity than the first two solutions is obtained.

[0039] Next, the film solution is poured onto the support (step 3) to form a film. The support is preferably flat. If necessary, and especially depending on its viscosity, the film solution is poured and stretched at the same time. The casting parameters are adjusted according to the desired dimensions of the film and the parameters of the film solution (particularly the viscosity of the film solution and the shrinkage force of the polymer binder in the steps below).

[0040] Finally, the film-covered support is then immersed in a non-solvent (step 4) to induce a phase transition. During the phase transition process, the film solution precipitates, replacing the solvent with the non-solvent, particularly on the surface and within the film. In the example of a PSU / yttrium oxide-stabilized zirconia film, the support on which the film rests is immersed in water (the non-solvent in this case) to replace the DMAc (solvent) remaining in the film. Initially, the two phases are in equilibrium within the film: the polymer-rich solid phase forms the structure of the film, and the liquid phase (less polymer) constitutes the pores of the film, which in this case are filled with water. As precipitation gradually progresses, the viscosity of the polymer-enriched phase increases until the precipitated polymer reaches a state where it is considered solid. Thus, the film solution is transformed into a solid, soft film that captures ceramic particles.

[0041] Next, the membrane-covered support is removed from the water (step 5), and the membrane is separated from the support (step 6).

[0042] If necessary, a lamination step (step 7) can be performed to homogenize the surface, eliminate open pores to further improve the non-porous properties of the film, and / or improve the mechanical strength of the film. The lamination step can be performed at any point after the completion of the phase conversion of the film solution. Thus, the lamination step can be performed before removing the support and film from water (step 5), or after removing the film from water. The lamination step also yields a film of uniform thickness. The lamination step can be repeated several times as needed to obtain a film with the required properties, particularly a non-porous film. Thus, it was possible to demonstrate from testing that the residual pore diameter of the PSU / YSZ film according to the present invention is 0.2 μm, and the residual pore diameter of the PTFE / YSZ film according to the present invention is 0.1 μm.

[0043] Other post-phase-transition treatments may be considered to complete the film formation. For example, a heat treatment step may be performed to strengthen the bond between the polymer and ceramic particles and / or to further reduce the size of pores in the film.

[0044] Finally, the membrane can be rolled up and stored.

[0045] The above membrane, especially when made with PTFE, 1. Suspend the polytetrafluoroethylene (PTFE) polymer in water. 2. A step of adding and mixing ceramic powder in an amount such that the polymer is equivalent to 5% to 30% by weight and the ceramic is equivalent to 70% to 95% by weight relative to the total weight of the polymer and ceramic, in order to obtain a uniform film paste, wherein the ceramic powder includes yttrium oxide-doped ceramic and / or cerium oxide-doped ceramic, preferably yttrium oxide-doped zirconia and / or cerium oxide-doped zirconia, 3. Laminating the paste onto a support to form a film of a desired thickness. It can also be generated using other methods, including [mentioning a specific method].

[0046] The amount of water used here is limited so that the lamination process is sufficient to remove water from the paste.

[0047] The above-mentioned film according to the present invention is particularly - Anode 30, - Cathode 20, and - Between the anode and cathode, the above film 10 It can be used to prepare electrochemical cells containing [the specified element].

[0048] Figure 1 shows a scheme of a known cell for a water electrolysis apparatus for producing hydrogen (H2) and oxygen (O2) gases. Figure 2 shows an operating scheme of a membrane-based water electrolysis apparatus. The membrane 10 divides the cell into two parts, the cell containing a mixture of water and electrolyte. The cathode 20 and anode 30 are located on either side of the membrane and are connected to the negative and positive terminals of the power supply, respectively. The membrane 10 enables the effective separation of hydrogen gas produced at the cathode and oxygen gas produced at the anode. The cathode and / or anode may be porous. The cathode and anode may be made of a metal, e.g., nickel, stainless steel, or a metal oxide, particularly on the anode side. Nickel and stainless steel form surface oxides that act as catalysts for oxygen release. 316L stainless steel is particularly effective in terms of its molybdenum content.

[0049] Figure 1 shows a single cell. However, in reality, industrial equipment may contain several cells or even 100 cells.

[0050] Figure 3 shows the results of a test conducted at approximately 90°C in an electrolytic cell containing a 4 mol / l water and potassium hydroxide (KOH) mixture bath using the PSU / YSZ film according to the present invention. Figure 3 more accurately shows the change in voltage between cell terminals as a function of the current density flowing between electrodes. For a given current density value, the HHV (higher heating value) efficiency of the cell can be calculated by dividing 1.48V by the voltage between cell terminals; 1.48V is a reference value corresponding to the thermodynamic voltage of water dissociation, and is the reference value at which theoretical efficiency is considered to be 100%. Current density 0.39 A / cm 2 In this case, the voltage between the electrode terminals is 1.6V, which corresponds to an efficiency of 1.48 / 1.6 = 93% HHV. The current density is 0.70 A / cm². 2 In this case, corresponding to the cell's nominal operating point, the voltage across the electrode terminals is 1.72V, which corresponds to an efficiency of 86% HHV. For comparison, the voltage across the terminals of a known cell containing a Zirfon film is 2.1V, which corresponds to an efficiency of 70% HHV.

[0051] Furthermore, when the film's lifespan was tested for 2500 hours under normal operating conditions, no degradation of the film occurred.

Claims

1. - Polymer binder 5% to 30% by weight, and - 70% to 95% by weight of ceramic powder containing yttrium oxide-doped ceramic or cerium oxide-doped ceramic An ion-conducting film (10) for an electrochemical device, comprising a layer of material containing the following:

2. The aforementioned ceramic powder - Yttrium oxide-doped zirconia, - Zirconia doped with cerium oxide, - A mixture of yttrium oxide-doped zirconia and cerium oxide-doped zirconia. - A mixture of yttrium oxide-doped zirconia and boron nitride, - A mixture of cerium oxide-doped zirconia and boron nitride, or - A mixture of yttrium oxide-doped zirconia, cerium oxide-doped zirconia, and boron nitride. The film according to claim 1, comprising:

3. The film according to claim 1 or 2, wherein the polymer binder is a hydrophobic thermoplastic polymer, preferably polysulfone (PSU), polyethersulfone (PES), polyphenylenesulfone (PPSU), or polytetrafluoroethylene (PTFE), or a mixture of at least two of the above polymers.

4. The doped ceramic, - Ceramic 75% to 99% by weight, preferably 75% to 95% by weight, and - 1% to 25% by weight, preferably 5% to 25% by weight, of yttrium oxide or cerium oxide A film according to any one of claims 1 to 3, comprising:

5. The film according to any one of claims 1 to 4, wherein the average diameter of the ceramic powder particles is between 0.1 and 5 μm, preferably between 0.2 and 2 μm.

6. A membrane according to any one of claims 1 to 5, which is nonporous with respect to gas.

7. 1. Dissolve the polymer in a water-immiscible solvent to obtain a polymer solution.

2. A step of adding and mixing ceramic powder in an amount such that the polymer is equivalent to 5% to 30% by weight and the ceramic is equivalent to 70% to 95% by weight, relative to the total weight of the polymer and ceramic, to obtain a homogeneous film solution, wherein the ceramic powder includes yttrium oxide-doped ceramic and / or cerium oxide-doped ceramic, preferably yttrium oxide-doped zirconia and / or cerium oxide-doped zirconia, 3. A step of pouring the film solution onto a support to form a film that covers the support.

4. The step of immersing the film-covered support in water to bring about a phase change. A method for producing a membrane, including [a specific component].

8. The method according to claim 7, further comprising the step of laminating the aforementioned films.

9. 1. The step of suspending the polytetrafluoroethylene (PTFE) polymer in water, 2. A step of adding and mixing ceramic powder in an amount such that the polymer is equivalent to 5% to 30% by weight and the ceramic is equivalent to 70% to 95% by weight, relative to the total weight of the polymer and ceramic, to obtain a uniform film paste, wherein the ceramic powder includes yttrium oxide-doped ceramic and / or cerium oxide-doped ceramic, preferably yttrium oxide-doped zirconia and / or cerium oxide-doped zirconia, 3. Laminating the paste onto a support to form a film of a desired thickness. A method for producing a membrane, including [a specific component].

10. A ceramic comprising yttrium oxide-doped ceramic and / or cerium oxide-doped ceramic, preferably yttrium oxide-doped zirconia and / or cerium oxide-doped zirconia, Ceramics for the manufacture of non-porous membranes for low-temperature electrolysis (0°C to 150°C).

11. - Anode (30), - Cathode (20), and - A film (10) according to any one of claims 1 to 6 between the anode and the cathode. Cells for electrochemical devices, including those mentioned above.

12. A water electrolysis apparatus comprising at least one cell as described in claim 11.

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