Manufacturing method for superhydrophobic separator for hydrogen-producing water electrolysis

Abstract

The present disclosure relates to a manufacturing method for a separator for water electrolysis having a superhydrophobic coating layer. The manufacturing method of the present disclosure not only has high efficiency of manufacturing the separator, but also can reduce manufacturing costs and ultimately product sales costs, and thus has excellent industrial utility value. In addition, the superhydrophobic separator according to the present disclosure has high efficiency of separating hydrogen and oxygen generated in a water electrolysis process, can stably maintain hydrogen purity, and has excellent performance in preventing oxygen from being mixed into hydrogen gas, and thus can fundamentally block the risk of explosion (fire).

Description

Method for manufacturing a superhydrophobic membrane for hydrogen production and electrolysis

[0001] Cross-reference to related applications

[0002] This disclosure claims priority to Patent Application No. 10-2023-0168099, filed November 28, 2023, and Patent Application No. 10-2024-0170319, filed November 26, 2024, the entire contents of each of which are incorporated herein by reference.

[0003] Statement on Government Support

[0004] This disclosure was made possible with support from the '2023 Preliminary Hydrogen Specialized Company Development Support Project' managed by Pohang Technopark, located in Pohang, Gyeongsangbuk-do, Republic of Korea.

[0005] Technology field

[0006] The present disclosure relates to a separation membrane, particularly a separation membrane for water electrolysis for hydrogen production, and a method for producing the same.

[0007] Low-temperature water electrolysis processes are increasingly being used to produce hydrogen. The alkaline electrolysis cell (AEC) process is the primary method used, but research and development on the proton exchange membrane (PEM) and anion exchange membrane (AEM) electrolysis processes, which utilize ion-exchange membranes, are also rapidly increasing.

[0008] While the AEC, PEM, and AEM methods differ in the configuration of their electrolytic modules (cells or stacks) for hydrogen production based on their operating methods, they all share a common requirement: an effective separation method for hydrogen generated at the cathode and oxygen generated at the anode. During the electrolysis process, the separation of the anode and cathode is a critical factor affecting hydrogen production efficiency.

[0009] The series of reactions that occur during the hydrogen production process, where electrons flow through ion movement through the electrolyte (or water between the electrodes), and hydrogen and oxygen are generated, are fundamentally the same regardless of the water electrolysis method.

[0010] In each electrolysis process, maintaining high production efficiency with minimal energy input is crucial. This contradictory situation requires resolving the need for continuous ion exchange while also physically separating the electrolyte (preventing mixing). Membranes are used to achieve this goal.

[0011] The membranes used in each electrolysis process are designed to reflect the characteristics (parameters) required for the process, so there are differences in material, structural, and functional aspects.

[0012] Electrodes for the AEC process are used to separate oxygen and hydrogen generated during the electrolysis of water. The membrane currently used in the AEC process electrodes is not an ion exchange membrane but a simple porous membrane, and as a result, it is referred to as a diaphragm membrane rather than a membrane.

[0013] The PEM method, which is currently under development, uses an ion-exchange membrane to maintain the water electrolysis process through ion migration that causes only the movement of electrons without the movement of water molecules. The fluorinated membrane product commonly known as Nafion® is mainly used. There are only a limited number of companies that can manufacture these Nafion-based membranes, and in particular, due to the characteristics of fluorinated membranes, manufacturing and management are difficult, making them very expensive. In other words, the PEM process using Nafion requires very high equipment costs (CAPEX) and operating costs (OPEX) during the process of building commercial facilities. Meanwhile, the AEM method is currently under research and development, and has a similar structure to the PEM, but with the exception of the anion-exchange membrane characteristics, it has the problem of requiring very high equipment costs and operating costs similar to the PEM process.

[0014] The membrane used in the electrolysis process for hydrogen production must be capable of separating the oxygen and hydrogen produced. Separating the oxygen and hydrogen produced during electrolysis is crucial for maintaining purity and safety. If proper separation is not achieved, the oxygen and hydrogen produced during electrolysis will mix, and the purity of the hydrogen will be affected depending on the concentration (amount) of oxygen mixed in the hydrogen. This can lead to problems such as the inability to maintain the proper purity of the produced hydrogen gas.

[0015] If oxygen generated is mixed with hydrogen, it can pose a serious safety risk. In the case of hydrogen, if oxygen is mixed within a critical concentration (5-70%), the risk of spontaneous combustion without a separate fire source increases. Furthermore, due to the nature of hydrogen, it tends to explode rather than ignite. Therefore, the incorporation of oxygen generated at the anode during the process can cause an explosion and must be prevented.

[0016] Furthermore, to function as an effective separator, it must be capable of effectively separating the electrolyte. The anode and cathode must be electrically connected, but the electrolyte itself must be isolated. Ion transport must occur continuously across the membrane, but the movement of the solution, i.e., water, must be blocked. To achieve this function, most ion exchange membranes currently in use employ polymer membranes with nano-sized pores charged with cations or anions. However, these polymer membranes are often slow to manufacture and expensive due to various manufacturing difficulties.

[0017] The present disclosure aims to improve the low manufacturing efficiency that has been a problem in the manufacturing process of a separation membrane used in a water electrolysis process for hydrogen production, and to reduce the high manufacturing cost and sales cost.

[0018] The present disclosure aims to provide a separation membrane having a superhydrophobic coating layer that has high separation efficiency of hydrogen and oxygen generated in a water electrolysis process for hydrogen production, can stably maintain hydrogen purity, and has excellent performance in preventing oxygen mixing into hydrogen gas, thereby fundamentally blocking the risk of explosion (fire).

[0019] The present disclosure is intended to solve the aforementioned problems, and provides a method for manufacturing a water electrolysis membrane having a superhydrophobic coating layer formed thereon, comprising the steps of: (1) preparing a mesh-like support made of a heat-resistant polymer having a temperature exceeding 90°C, and then washing the surface; (2) preparing a coating solution by mixing PVDF (polyvinylidene fluoride) and NMP (n-methyl-2-pyrrolidone); (3) adjusting the viscosity of the prepared coating solution to obtain a viscosity-adjusted coating solution; (4) spraying the viscosity-adjusted coating solution onto the surface-washed mesh-like support to form a coating layer on both the weft and warp yarns; and (4) applying heat to the support on which the coating layer has been formed to obtain a membrane having a heat-cured superhydrophobic coating layer.

[0020] The method for manufacturing a water electrolysis membrane having a superhydrophobic coating layer according to the present disclosure not only has high membrane manufacturing efficiency but also reduces manufacturing costs and ultimately product sales costs, thus demonstrating excellent industrial utility. The superhydrophobic membrane according to the present disclosure has the advantages of high separation efficiency of hydrogen and oxygen generated during the water electrolysis process, stably maintaining hydrogen purity, and excellent performance in preventing oxygen from mixing into hydrogen gas, thereby fundamentally blocking the risk of explosion (fire).

[0021] Figure 1 schematically illustrates a manufacturing process of a water electrolysis membrane according to one embodiment of the present disclosure.

[0022] FIG. 2 schematically illustrates the structural features of the warp and weft yarns constituting the electrolytic membrane manufactured according to one embodiment of the present disclosure.

[0023] As schematically illustrated in Fig. 1, the present disclosure relates to a method for manufacturing a water electrolysis separation membrane having a superhydrophobic coating layer formed thereon.

[0024] A method for manufacturing a separation membrane for electrolysis according to the present disclosure comprises: (1) a step (S1) of preparing a mesh-shaped support made of a heat-resistant polymer having a temperature exceeding 90°C and then washing the surface; (2) a step (S2) of preparing a coating solution by mixing PVDF (polyvinylidene fluoride) and NMP (n-methyl-2-pyrrolidone); (3) a step (S3) of adjusting the viscosity of the prepared coating solution to obtain a coating solution having an adjusted viscosity; (4) a step (S4) of spraying the viscosity-adjusted coating solution onto the surface-washed mesh-shaped support to form a coating layer on both the weft and warp yarns; and (4) a step (S5) of applying heat to the support on which the coating layer has been formed to obtain a separation membrane having a heat-cured superhydrophobic coating layer.

[0025] Below, the method for manufacturing a water electrolysis separation membrane according to the present disclosure is described in more detail for each step.

[0026] S1 - Preparation of mesh support and surface cleaning step

[0027] In the present disclosure, the mesh-type support may be made of a conventional heat-resistant material that exhibits heat resistance even without undergoing a separate heat-resistant treatment.

[0028] Heat-resistant materials having a heat-resistant temperature exceeding 90℃ may include, for example, PP (Polypropylene) material, PEEK (Polyetheretherketone) material, or PVDF (Polyvinylidene Fluoride) material.

[0029] Those skilled in the art will readily understand that the mesh-type support of the present disclosure can be used without any particular limitation as long as it basically satisfies the mechanical properties of a water electrolysis membrane and exhibits heat resistance at temperatures of 90°C or higher, 100°C or higher, 110°C or higher, 120°C or higher, 130°C or higher, 140°C or higher, or 150°C or higher.

[0030] The mesh-type support of the present disclosure comprises a heat-resistant polymer fiber woven fabric having a mesh size ranging from 200 to 2000. This heat-resistant woven fabric is characterized in that it can contract and expand within a limited range (approximately 2 to 10%) in response to a temperature increase of the surrounding solution due to the reaction heat (i.e., Joule heat) generated between the anode and cathode for hydrogen production, but does not substantially change its original shape and function.

[0031] In the present disclosure, surface washing of the mesh-type support is performed for the purpose of removing impurities, contaminants, etc. that may remain on the support surface and / or in the pores within the mesh, further increasing the size uniformity of the mesh pores, and also increasing the coating efficiency in the subsequent coating process.

[0032] Washing can be performed using water or purified water at 25 to 35°C, and, if necessary, adding acid or base and / or performing ultrasonic treatment for 1 to 30 minutes.

[0033] S2 - Preparation of coating solution for forming superhydrophobic film

[0034] Mesh supports cannot block the flow of solution, meaning that water naturally moves through the mesh. By spray-coating a coating solution containing PVDF and N-Methyl-2-pyrrolidone (NMP) onto the surface of such mesh supports and then curing it, a superhydrophobic film that prevents the flow / passage of solution can be formed on the mesh surface.

[0035] To form a superhydrophobic film, a coating solution is first prepared by dissolving PVDF powder in an organic solvent such as NMP. In the coating solution, PVDF acts as a binder that binds to the mesh-like support, or more precisely, the surfaces of the weft and warp yarns, while the NMP solvent acts as a solvent that uniformly dissolves the PVDF.

[0036] PVDF is a commercially available powder product with a particle size ranging from 1 to 50 ㎛, preferably from 5 to 45 ㎛, and more preferably from 15 to 35 ㎛, and preferably has high solubility in NMP.

[0037] It is recommended to use NMP with a purity of 99% or higher, commercially available. The NMP stock solution should not contain solid impurities or other organic components.

[0038] PVDF powder and NMP stock solution are mixed to prepare an initial mixed solution. The mixing ratio is 80 to 200 parts by weight, preferably 90 to 150 parts by weight, and more preferably 100 to 130 parts by weight, of NMP stock solution based on 100 parts by weight of PVDF powder. Maintaining the above-mentioned mixing ratio is advantageous in terms of dispersibility of PVDF powder particles in the coating solution, obtaining a coating solution with an appropriate viscosity range, uniformity of current flowing through the electrode during electrolysis, and durability of the coating and electrode.

[0039] Then, PVDF is completely dissolved in NMP through low-speed stirring at a temperature of 10 to 30°C for 1 to 6 hours. The stirring at this time can be performed using a low-speed vibration stirrer at 20 to 100 rpm, preferably 25 to 95 rpm, and more preferably 35 to 85 rpm.

[0040] After low-speed stirring, turbidity measurement can be used to confirm whether the desired coating solution has been produced. Turbidity values ​​confirmed through NTU measurement should preferably be less than 10 NTU, and the solution should be free of undissolved substances or microbubbles.

[0041] If the turbidity exceeds 10 NTU, there is a high possibility that undissolved PVDF components or unwanted microbubbles will remain, which may inhibit the formation of the superhydrophobic coating. Therefore, the turbidity value of the prepared original solution should be maintained at less than 10 NTU, preferably 9.5 NTU, more preferably 8.5 NTU, and most preferably less than 5.5 NTU. If the turbidity value exceeds 10 NTU, it is preferable to perform additional low-speed stirring at 40 to 150 rpm, preferably 55 to 135 rpm, and more preferably 75 to 115 rpm for 30 minutes to 3 hours at a temperature of 25 to 35°C to remove undissolved PVDF and microbubbles.

[0042] S3 - Step for obtaining a viscosity-adjusted coating solution

[0043] Maintaining an appropriate viscosity is crucial for evenly coating the mesh support with the prepared coating solution. The viscosity of the coating solution can be adjusted depending on the thickness and shape of the yarns (weft and warp) that make up the mesh support.

[0044] When the viscosity of the coating solution is in the range of 5 to 250 cP, preferably in the range of 10 to 200 cP, more preferably in the range of 30 to 150 cP, and most preferably in the range of 50 to 100 cP, a superhydrophobic film can be uniformly and stably formed on the mesh-like support.

[0045] Surprisingly, the present inventors have found that by adjusting the mixing ratio of PVDF powder and NMP stock solution and the stirring conditions within the aforementioned range, the viscosity of the coating solution can be appropriately controlled, and that when the viscosity of the coating solution is set to a range of 5 to 250 cP, 10 to 200 cP, 30 to 150 cP, or 50 to 100 cP, the miscibility of the binder component and the solvent is excellent, a coating layer can be formed with a desired thickness, the heat treatment time is shortened, and the coating structure after the heat treatment is also stably maintained for a long period of time.

[0046] S4 - Step of spraying coating solution with adjusted viscosity onto mesh support

[0047] In this step, a coating solution with adjusted viscosity is applied using an air brush to form a film of a certain thickness on the surface of the mesh-shaped support.

[0048] The thickness of the film can be adjusted in the range of 1 to 50 ㎛ taking into account the mesh gap, desired blocking efficiency, etc.

[0049] This step may be repeated several times to ensure that the coating solution applied to the mesh-like support forms a coating layer of a desired thickness.

[0050] S5 - Film hardening stage through heat treatment

[0051] After the spray coating is completed, the coating is cured initially by first heat treatment at 30 to 80°C for 30 to 60 minutes to evaporate the solvent component. This first heat treatment is also referred to as the initial curing stage, or soft baking stage. This stage can be repeated several times to ensure that the coating solution applied to the mesh support forms a coating layer of the desired thickness.

[0052] Afterwards, the secondary hardening of the coating layer structure is performed through a secondary heat treatment in the range of 80℃ to 200℃ for 30 to 120 minutes, thereby completing the heat treatment. At this time, the heat treatment can be performed using a hot air dryer at atmospheric pressure.

[0053] By sequentially performing the first and second heat treatment processes, the adhesion of the coating layer formed on the weft and warp of the mesh-type substrate can be strengthened, the density and structural rigidity of the coating structure can be increased, and the superhydrophobicity of the coating can be enhanced accordingly.

[0054] As shown in Fig. 2, a water electrolysis separation membrane having a superhydrophobic coating layer formed on both the weft and warp surfaces of a mesh-shaped support can be obtained through the aforementioned steps S1 to S5.

[0055] The manufacturing method according to the present disclosure has the advantage of being able to easily manufacture a superhydrophobic coating layer of a desired thickness compared to existing membrane manufacturing methods, and also has the advantage of being able to reduce the production cost of the final product by performing simple steps, requiring relatively little energy to be invested in the manufacturing process, and being able to easily manufacture a superhydrophobic coating layer of a desired thickness compared to existing membrane manufacturing methods.

[0056] A separator having a superhydrophobic coating layer produced by a manufacturing method according to the present disclosure may have a contact angle with water on the surface of the separator of 150° or more, preferably 157° or more.

[0057] Typically, voids generated by the attachment of bubbles to electrodes act as a factor in increasing the voltage between the electrodes, resulting in voltage fluctuations of 5 to 10%. In contrast, the separator having a superhydrophobic coating layer according to the present disclosure is applied to a typical hydrogen production device, effectively preventing the generation of voids due to the attachment of bubbles (electrolyte) to the surface of the separator even during continuous operation, and exhibits improved characteristics with voltage fluctuations of less than 3%.

[0058] The electrolytic separation membrane having a superhydrophobic coating layer obtained by the manufacturing method according to the present disclosure is particularly useful because it not only has sufficient heat resistance and chemical resistance compared to the product in use, but also can achieve effective separation of the electrolyte solution by the superhydrophobic coating layer, has high separation efficiency of hydrogen and oxygen, can stably maintain hydrogen purity, and has excellent performance in preventing oxygen mixing into hydrogen gas, so that the risk of explosion can be fundamentally blocked.

[0059] The method for manufacturing a water electrolysis membrane having a superhydrophobic coating layer according to the present disclosure not only has high membrane manufacturing efficiency but also reduces manufacturing costs and ultimately product sales costs, so it has very high industrial utility. In addition, the superhydrophobic membrane according to the present disclosure has high separation efficiency of hydrogen and oxygen generated in the water electrolysis process, can stably maintain hydrogen purity, and has excellent performance in preventing oxygen mixing into hydrogen gas, thereby fundamentally blocking the risk of explosion (fire). Therefore, it is expected to have a remarkable ripple effect in the hydrogen production-related industry.

Claims

1. A method for manufacturing a water electrolysis separation membrane having a superhydrophobic coating layer formed thereon, (1) A step of preparing a mesh-shaped support made of a heat-resistant polymer exceeding 90℃, and then washing the surface; (2) A step of preparing a coating solution by mixing PVDF (polyvinylidene fluoride) and NMP (n-methyl-2-pyrrolidone); (3) A step of adjusting the viscosity of the manufactured coating solution to obtain a coating solution with adjusted viscosity; (4) a step of spraying a viscosity-adjusted coating solution onto a surface-washed mesh-shaped support to form a coating layer on both the weft and warp yarns; and (5) A step of applying heat to a support on which a coating layer is formed to obtain a separator having a heat-cured superhydrophobic coating layer. A method for manufacturing a water electrolysis separation membrane having a superhydrophobic coating layer formed thereon.

2. In claim 1, A method for manufacturing a water electrolysis separation membrane having a superhydrophobic coating layer formed thereon, characterized in that the mesh-shaped support is a heat-resistant polymer fiber woven fabric having a mesh range of 200 to 2000 mesh.

3. In claim 1, A method for manufacturing a water electrolysis membrane having a superhydrophobic coating layer formed thereon, characterized in that in step (1), washing is performed using water or purified water at 25 to 35°C for 1 to 30 minutes, optionally with ultrasonic treatment.

4. In claim 1, A method for manufacturing a water electrolysis separation membrane having a superhydrophobic coating layer formed thereon, characterized in that in step (2), the coating solution is manufactured by mixing 80 to 200 parts by weight, 90 to 150 parts by weight, or 100 to 130 parts by weight of NMP solution based on 100 parts by weight of PVDF powder.

5. In claim 1, A method for manufacturing a water electrolysis separation membrane having a superhydrophobic coating layer formed thereon, characterized in that in step (2), the coating solution is stirred at low speed at a speed of 20 to 100 rpm for 1 to 6 hours at a temperature of 10 to 30°C.

6. In claim 1, A method for manufacturing a water electrolysis separation membrane having a superhydrophobic coating layer formed thereon, characterized in that the turbidity value of the coating solution is less than 10 NTU.

7. In claim 1, A method for manufacturing a water electrolysis separation membrane having a superhydrophobic coating layer formed thereon, characterized in that in step (3), the viscosity of the coating solution is adjusted to a range of 5 to 250 cP.

8. In claim 1, A method for manufacturing a water electrolysis separation membrane having a superhydrophobic coating layer formed thereon, characterized in that in step (4), a coating solution whose viscosity is adjusted is sprayed through an airbrush so that a coating layer having a thickness of 1 to 50 ㎛ is formed on both the weft and warp of the mesh-shaped support.

9. In claim 1, A method for manufacturing a water electrolysis separation membrane having a superhydrophobic coating layer formed, characterized in that the heat treatment in step (5) includes a step of first curing while volatilizing the solvent component through a first heat treatment at 30 to 80°C for 30 to 60 minutes.

10. In claim 9, A method for manufacturing a water electrolysis membrane having a superhydrophobic coating layer formed thereon, characterized in that it comprises a step of secondary hardening of a film structure through secondary heat treatment in a range of 80°C to 200°C for 30 to 120 minutes after a primary heat treatment.

11. In claim 1, A method for manufacturing a water electrolysis separation membrane having a superhydrophobic coating layer formed thereon, characterized in that the contact angle of water molecules on the superhydrophobic surface is 150° or more.

12. A water electrolysis separation membrane having a superhydrophobic coating layer formed thereon, obtainable by the manufacturing method of any one of claims 1 to 11.

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