High-selectivity composite diaphragm for seawater electrolysis hydrogen production and preparation method of high-selectivity composite diaphragm

Abstract

The invention provides a high-selectivity composite diaphragm for seawater electrolysis hydrogen production and a preparation method of the high-selectivity composite diaphragm, and relates to the technical field of hydrogen energy and seawater resource utilization. The composite diaphragm comprises a matrix layer, a functional layer and a protective layer. The modifier is added to improve the interior of the diaphragm and the surface structure of the diaphragm, the ion selectivity of the diaphragm is improved by adding the ion selective material, efficient screening of Cl <-> / OH <-> is achieved, and the Cl <-> rejection rate is larger than 99%; by reducing the contact angle of the diaphragm, the resistance of ions passing through the diaphragm is reduced, and the effect of reducing the surface resistance of the diaphragm is achieved; the matrix layer and / or the functional layer are / is optimally designed, the micro-nano fiber structure of the matrix layer provides mechanical support, and the bubble point pressure is larger than 5 bar; and an adhesive is added into the functional layer to enhance the interlayer binding force and prevent the coating from falling off. Therefore, the technical problems that an existing diaphragm is insufficient in chloride ion blocking capacity and low in ionic conductivity are solved, and the diaphragm is suitable for efficient and safe electrolytic hydrogen production by directly utilizing seawater.

Description

Technical Field

[0001] The present invention relates to the technical field of hydrogen energy and seawater resource utilization, and particularly relates to a highly selective composite diaphragm for seawater electrolysis hydrogen production and a preparation method thereof. Background Art

[0002] Alkaline electrolytic water hydrogen production technology is one of the most mature green hydrogen production methods at present. However, traditional alkaline electrolyzers require the use of high-purity fresh water as the electrolyte, which limits their application in coastal and water-scarce areas and further exacerbates the problem of water resource shortage.

[0003] Seawater has rich reserves and has natural advantages in large-scale electrolytic hydrogen production. Directly using seawater for electrolytic hydrogen production can significantly reduce the hydrogen production cost. However, due to the complex composition of seawater, the presence of impurities such as Na + , Ca 2+ , Mg 2+ and bacteria, microbial particles, etc. will seriously hinder the progress of the electrolysis reaction. Cations in seawater will form precipitates, such as Ca(OH)2 and Mg(OH)2. Moreover, high-concentration Cl - will also corrode the electrode materials and diaphragms, and compete with the oxygen evolution reaction (OER), reducing the hydrogen production efficiency. Currently, we need to preferentially conduct OH - (alkaline) or H + (acidic), while blocking impurity ions (such as Cl - ). Moreover, the diaphragm is also easily poisoned and blocked by foreign ions.

[0004] Although existing alkaline ion exchange membranes (such as CN 115347318A) can achieve seawater electrolysis, they still have problems such as high chloride ion permeability and insufficient long-term bubble point pressure. While forward osmosis membranes (such as CN 119327288A) can block ions, their hydrophilicity and ionic conductivity are relatively low. In addition, although composite diaphragms (such as CN 118441316A and CN 118996526A) have improved performance through inorganic-organic composite design, the selective separation effect on chloride ions still needs to be improved.

[0005] Therefore, developing a composite diaphragm with high ion selectivity, low resistance, and high bubble point is the key to realizing the industrialization of direct seawater electrolysis hydrogen production. Summary of the Invention

[0006] The object of the present invention is to provide a highly selective composite diaphragm for seawater electrolysis hydrogen production and a preparation method thereof. This composite diaphragm preferentially conducts OH - by adding a certain polymer, and inhibits Cl -Migration endows it with excellent ion selectivity and gas barrier performance, which can effectively inhibit chloride ion penetration and promote hydroxide ion transport, and is suitable for directly using seawater for efficient and safe hydrogen production by electrolysis. It solves the technical problems of insufficient chloride ion barrier ability and low ionic conductivity of existing diaphragms.

[0007] To achieve the above object, the present invention adopts the following technical solutions:

[0008] A highly selective composite diaphragm for seawater electrolysis hydrogen production improves the ion selectivity of the diaphragm by adding a modifier to improve the internal and surface structures of the diaphragm and adding an ion-selective material; reduces the contact angle of the diaphragm to reduce the resistance of ions passing through the diaphragm, achieving the effect of reducing the surface resistance of the diaphragm; and optimizes the design of the substrate layer and / or functional layer to improve its bubble point pressure.

[0009] The above-mentioned highly selective composite diaphragm for seawater electrolysis hydrogen production includes a three-layer structure connected in sequence: a substrate layer, a functional layer, and a protective layer.

[0010] For the above-mentioned highly selective composite diaphragm for seawater electrolysis hydrogen production, the substrate layer provides mechanical strength and thermal stability.

[0011] For the above-mentioned highly selective composite diaphragm for seawater electrolysis hydrogen production, the functional layer has high corrosion resistance;

[0012] For the above-mentioned highly selective composite for seawater electrolysis hydrogen production, the functional layer has a high porosity, mostly finger-shaped pores, reducing the surface resistance;

[0013] For the above-mentioned highly selective composite diaphragm for seawater electrolysis hydrogen production, the functional layer adds an adhesive to enhance the interlayer bonding force and make it not easy to peel off;

[0014] For the above-mentioned highly selective composite diaphragm for seawater electrolysis hydrogen production, the protective layer has good ion selectivity and can inhibit the migration of chloride ions;

[0015] For the above-mentioned highly selective composite diaphragm for seawater electrolysis hydrogen production, the thickness of the substrate layer is 100 - 150 μm, and the pore diameter is 50 - 300 μm;

[0016] For the above-mentioned highly selective composite diaphragm for seawater electrolysis hydrogen production, the functional layer is a porous layer with a high porosity, the pore diameter is 30 - 250 nm, the porosity is 60% - 80%, and the thickness is 200 - 300 μm.

[0017] For the above-mentioned highly selective composite diaphragm for seawater electrolysis hydrogen production, the protective layer inhibits Cl - diffusion, the average pore diameter is 10 - 50 nm, and the thickness is 0.5 - 5 μm.

[0018] A highly selective composite membrane for hydrogen production by seawater electrolysis according to the present invention, wherein the matrix support is a composite of one or more of polypropylene, polyphenylene sulfide, polyimide, ceramics, titanium alloy mesh, and carbon fiber, preferably polyphenylene sulfide.

[0019] A highly selective composite membrane for hydrogen production by seawater electrolysis according to the present invention, wherein the fiber diameter of the matrix support is 50 - 150 μm.

[0020] A highly selective composite membrane for hydrogen production by seawater electrolysis according to the present invention, wherein the organic solvent in the casting solution is a combination of one or more of N,N - dimethylacetamide, N - methylpyrrolidone, and N,N - dimethylformamide.

[0021] A highly selective composite membrane for hydrogen production by seawater electrolysis according to the present invention, wherein the polymer material in the casting solution is a combination of one or more of polyethersulfone, polyetheretherketone, polysulfone, polytetrafluoroethylene, chitosan, and polyacrylonitrile.

[0022] A highly selective composite membrane for hydrogen production by seawater electrolysis according to the present invention, wherein the inorganic nanoparticles in the casting solution are a combination of one or more of titanium dioxide, aluminum oxide, silicon oxide, zirconium oxide, and zinc oxide.

[0023] A highly selective composite membrane for hydrogen production by seawater electrolysis according to the present invention, wherein the ion - selective material in the casting solution is a combination of one or more of sulfonamide type, quaternary amine type, tertiary amine type, metal oxide, and polyethersulfone / titanium dioxide composite material.

[0024] A highly selective composite membrane for hydrogen production by seawater electrolysis according to the present invention, wherein the pore - forming agent in the casting solution is a combination of one or more of polyethylene glycol, polyacrylic acid, silicon dioxide, polyoxyethylene ether, and sodium dodecyl sulfate.

[0025] A highly selective composite membrane for hydrogen production by seawater electrolysis according to the present invention, wherein the specific composition of the casting solution is by mass fraction: 42 - 50 parts of organic solvent, 15 parts of ion - selective material, 3 - 10 parts of organic polymer, 33 - 40 parts of inorganic nanoparticles, and 0.2 - 3 parts of pore - forming agent.

[0026] A highly selective composite membrane for hydrogen production by seawater electrolysis according to the present invention, wherein the solution of the coagulation bath is a combination of one or more of deionized water, ethanol, N - methylpyrrolidone, and N,N - dimethylformamide.

[0027] A highly selective composite membrane for hydrogen production by seawater electrolysis according to the present invention, wherein the surface resistance of the composite membrane (under room - temperature test conditions) is 0.1 - 0.4 Ω·cm 2 。

[0028] A highly selective composite diaphragm for seawater electrolysis hydrogen production according to the invention, wherein the tensile strength of the composite diaphragm is 10-50 MPa.

[0029] A highly selective composite diaphragm for seawater electrolysis hydrogen production according to the invention, wherein the contact angle of the composite diaphragm is 30-60°.

[0030] A highly selective composite diaphragm for seawater electrolysis hydrogen production according to the invention, wherein the chloride ion interception rate of the composite diaphragm is 99% to 99.7%.

[0031] A highly selective composite diaphragm for seawater electrolysis hydrogen production according to the invention, wherein the composite diaphragm is surface-modified on this basis, and a selective permeable membrane is coated to enhance the selectivity of ions.

[0032] The present invention provides a preparation method for the above-mentioned highly selective composite diaphragm for seawater electrolysis hydrogen production.

[0033] Prepare the casting solution:

[0034] First, weigh the selected organic solvent, organic polymer, ion-selective material, inorganic nanoparticles, and pore-forming agent according to the required weights and set aside. Dissolve the selected organic polymer in the selected organic solvent, first stir well with a glass rod to obtain a uniformly dispersed solution; then sequentially add the weighed ion-selective material and pore-forming agent, and stir well with a constant-temperature magnetic stirrer at room temperature until completely dissolved; then add the weighed inorganic nanoparticles and stir for 20 h until completely dispersed evenly, continue to reduce the stirring speed, stir for 20 h, and perform defoaming treatment to obtain a milky white viscous casting solution;

[0035] Preparation of the composite diaphragm:

[0036] Place the support (mesh) on a clean and appropriately sized glass plate, pour the casting solution obtained in step (1) evenly on the support (mesh), the casting solution fully penetrates into the interior of the support (mesh), and then use a scraper to scrape with a corresponding thickness. Let the diaphragm after scraping stand in the air for pre-evaporation. At this time, a polymer fusion layer is formed on both sides of the support (mesh). At this time, a porous structure has not yet been formed, but the pore-forming agent and ion-selective material have been evenly distributed on the polymer fusion layer; finally, immerse the scraped diaphragm in a coagulation bath for phase inversion. At this time, the polymer fusion layer has completely solidified to form a porous structure; after complete solidification, soak and wash the treated composite diaphragm with deionized water multiple times until there are no suspended substances in the deionized water and it is transparent, and then take it out and dry it to obtain a highly selective composite diaphragm for seawater electrolysis hydrogen production.

[0037] Further, during the preparation of the composite separator, the coagulation bath temperature is 10 - 25°C, and 20°C is preferably selected.

[0038] Further, during the preparation of the composite separator, the pre-evaporation time is 10 - 60 s, and 15 s is preferably selected.

[0039] Advantages of the present invention:

[0040] For the composite separator prepared by the method of the present invention, by adding an ion-selective material, the pore channels are regularized, and sulfonic acid groups or quaternary ammonium groups are formed, realizing the efficient sieving of Cl - / OH - , with a Cl - interception rate > 99%.

[0041] For the composite separator prepared by the method of the present invention, the micro-nano fiber structure of the matrix layer provides mechanical support, improving the fracture strength; the addition of an adhesive in the functional layer enhances the interlayer bonding force, preventing the coating from peeling off.

[0042] For the composite separator prepared by the method of the present invention, it can stably operate for 1000 hours without attenuation under the conditions of 80°C and 30 wt% KOH.

[0043] The composite separator prepared by the method of the present invention solves the technical problems of insufficient chloride ion barrier ability and low ionic conductivity of the existing separator.

[0044] In the present invention, the above technical solutions can also be combined with each other to achieve more preferred combination schemes. Other features and advantages of the present invention will be described in the subsequent specification, and some advantages can be made obvious from the specification or understood by implementing the present invention. Description of the Drawings

[0045] Figure 1 It is a schematic structural diagram of the composite separator of the present invention; Detailed Embodiments

[0046] The technical solutions in the embodiments of the present application will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments in the present application without making creative efforts shall fall within the protection scope of the present application.

[0047] In the description of this specification, the reference terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" mean that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the embodiment of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art can combine and combine different embodiments or examples described in this specification and features of different embodiments or examples without contradiction.

[0048] In some of the following examples of the present invention, the support (ie, base membrane) used is PPS mesh, which was purchased from Shanghai Haifan Filter Material Co., Ltd.

[0049] In the following examples of the present invention, the organic solvents, polymer materials, inorganic nanoparticles, pore-forming agents, etc. used were purchased from regular commercial channels unless otherwise specified.

[0050] In some of the following examples of the present invention, the solution in the coagulation bath used was homemade in the laboratory.

[0051] In some of the following examples of the present invention, the organic solvent used is N,N-dimethylacetamide (DMAC) with a purity of 99.8%.

[0052] In some of the following embodiments of the present invention, the polymer material used is polysulfone (PSU), injection molding grade.

[0053] Example 1

[0054] The preparation method of this embodiment is as follows:

[0055] (1) Prepare the casting solution: First, 50% wt of the organic solvent N,N-dimethylacetamide (DMAC) is measured and poured into a beaker. 10% wt of polysulfone (PSU) is then added. A magnetic stirrer is placed in the beaker and the mixture is rapidly stirred on a strong magnetic stirrer. 5% wt of polyethylene glycol (PEG) is then added to the solution as a pore-forming agent, followed by stirring. Finally, 5% wt of the ion-selective material perfluorosulfonic acid resin is added and stirred evenly. 30% wt of inorganic nanoparticles of titanium dioxide (TiO2) are then added and stirred thoroughly at room temperature using a constant temperature magnetic stirrer for 20 hours until the mixture is completely dispersed. The stirring speed is then reduced and the mixture is stirred for 20 hours. Degassing is then performed to obtain a milky white, viscous casting solution.

[0056] (2) Preparation of composite diaphragm: The support (mesh cloth) is repeatedly rinsed with deionized water or ethanol and then dried. The treated support (mesh cloth) is placed on a clean glass plate of appropriate size. The casting solution obtained in step (1) is evenly poured onto the support (mesh cloth) (during the pouring process, the beaker should be close to the support to prevent the generation of bubbles). The casting solution fully penetrates into the interior of the support (mesh cloth). Then, a scraper is used to scrape at a corresponding thickness. The cast film is left standing in the air for pre-evaporation for 15 s. At this time, a polymer fusion layer is formed on both the front and back sides of the support (mesh cloth) by the casting solution. At this point, a porous structure has not yet been formed, but the pore-forming agent and the ion-selective material have been evenly distributed on the polymer fusion layer. Finally, the scraped film is immersed in a coagulation bath at a temperature of 20 °C. At this time, phase inversion occurs between the solvent and the non-solvent, and the liquid casting solution becomes gel-like, forming a porous structure. After complete solidification, the film spontaneously detaches from the glass plate. The treated composite film is soaked and washed several times with deionized water to remove the residual solvent in the film until there are no suspended substances in the deionized water and it is transparent. Then, the film is taken out and placed in a drying oven for drying, thus obtaining the required composite film, which is cut into an appropriate size for testing.

[0057] Example 2

[0058] The preparation method of this example is as follows:

[0059] (1) Prepare the casting solution: First, measure 50% wt of the organic solvent N,N-dimethylacetamide (DMAC) and pour it into a beaker. Then, add 10% wt of polysulfone (psu) in sequence. A magnetic stir bar is placed in the beaker and it is quickly stirred evenly with a strong magnetic stirrer. Then, continue to add 5% wt of polyethylene glycol (peg) as the pore-forming agent to this solution, followed by stirring. Then, add 5% wt of the ion-selective material quaternized silica (obtained by grafting a silane coupling agent onto the surface of SiO2), and continue to stir it evenly. Then, add 30% wt of the inorganic nanoparticle titanium dioxide (TiO2). It is fully stirred with a constant-temperature magnetic stirrer at room temperature for 20 h until it is completely dispersed evenly. Then, the stirring speed is reduced and stirred for 20 h for defoaming treatment, obtaining a milky white viscous casting solution;

[0060] (2) Preparation of the composite film: The support (mesh) is repeatedly rinsed with deionized water or ethanol and dried. The treated support (mesh) is placed on a clean and appropriately sized glass plate, and the casting liquid obtained in step (1) is evenly poured onto the support (mesh) (the beaker should be close to the support during the pouring process to prevent bubbles from forming). The casting liquid is fully immersed in the interior of the support (mesh), and then a scraper is used to select the corresponding thickness for scraping. The scraped membrane is placed in the air for pre-evaporation for 15 seconds. At this time, the casting liquid forms a polymer fusion layer on both sides of the support (mesh). At this time, a porous structure has not yet been formed, but the pore-forming agent and the ion-selective material have been evenly coated. is distributed on the polymer fusion layer; finally, the coated diaphragm is immersed in a coagulation bath with a temperature of 20°C. At this time, a phase transition occurs between the solvent and the non-solvent, and the liquid casting liquid becomes gel-like, forming a porous structure; after being completely solidified, the diaphragm falls off from the glass plate by itself, and the treated composite diaphragm is soaked and cleaned multiple times with deionized water to remove the residual solvent in the diaphragm until there is no suspended matter in the deionized water and it is transparent. Then, the diaphragm is taken out and placed in a drying oven for drying, and the required composite diaphragm is obtained, which is cut into appropriate sizes for testing.

[0061] Example 3

[0062] The preparation method of this embodiment is as follows:

[0063] (1) Prepare the casting solution: First, 50% wt of the organic solvent N,N-dimethylacetamide (DMAC) was measured and poured into a beaker. 10% wt of polysulfone (PSU) was then added. A magnetic stir bar was placed in the beaker and the mixture was rapidly stirred using a strong magnetic stirrer. 5% wt of polyethylene glycol (PEG) was then added to the solution as a pore-forming agent. Stirring was continued, followed by 5% wt of the ion-selective material tetramethylammonium chloride (TMAC) and continued stirring. 30% wt of inorganic nanoparticles of titanium dioxide (TiO2) were then added. The mixture was stirred thoroughly using a constant-temperature magnetic stirrer at room temperature for 20 hours until it was completely dispersed. The stirring speed was then reduced and the mixture was stirred for 20 hours. Degassing was performed to obtain a milky white, viscous casting solution.

[0064] (2) Preparation of composite diaphragm: The support (mesh) is repeatedly rinsed with deionized water or ethanol and dried. The treated support (mesh) is placed on a clean and appropriately sized glass plate, and the casting liquid obtained in step (1) is evenly poured onto the support (mesh) (the beaker should be close to the support during pouring to prevent bubbles from forming). The casting liquid is fully immersed in the interior of the support (mesh), and then a scraper is used to select the corresponding thickness for scraping. The scraped diaphragm is placed in the air for pre-evaporation for 15 seconds. At this time, the casting liquid forms a polymer fusion layer on both sides of the support (mesh). At this time, a porous structure has not yet been formed, but the pore-forming agent and the ion-selective material have been evenly coated. Evenly distribute on the polymer fusion layer; finally, immerse the coated diaphragm in a coagulation bath with a coagulation bath temperature of 20°C. At this time, phase transformation occurs between the solvent and the non-solvent, and the liquid casting liquid becomes gel-like, forming a porous structure; after complete solidification, the diaphragm falls off from the glass plate by itself, and the treated composite diaphragm is soaked and cleaned multiple times with deionized water to remove the residual solvent in the diaphragm until there is no suspended matter in the deionized water and it is transparent. Then take out the diaphragm and place it in a drying oven for drying to obtain a composite diaphragm, which is cut into appropriate sizes for testing.

[0065] Example 4

[0066] The preparation method of this embodiment is as follows:

[0067] (1) Prepare the casting solution: First, 50% wt of the organic solvent N,N-dimethylacetamide (DMAC) is measured and poured into a beaker. 10% wt of polysulfone (PSU) is then added. A magnetic stirrer is placed in the beaker and the mixture is rapidly stirred with a strong magnetic stirrer. 5% wt of polyethylene glycol (PEG) is then added to the solution as a pore-forming agent. The mixture is then stirred. Finally, 5% wt of an ion-selective material (compounded in a ratio of 1:1:1 perfluorosulfonic acid resin, quaternized silica, and tetramethylammonium chloride) is added and stirred. 30% wt of inorganic nanoparticles of titanium dioxide (TiO2) are then added. The mixture is stirred thoroughly with a constant temperature magnetic stirrer at room temperature for 20 hours until it is completely dispersed. The stirring speed is then reduced and the mixture is stirred for 20 hours. Degassing is then performed to obtain a milky white, viscous casting solution.

[0068] (2) Preparation of composite diaphragm: The support (mesh) is repeatedly rinsed with deionized water or ethanol and dried. The treated support (mesh) is placed on a clean and appropriately sized glass plate, and the casting liquid obtained in step (1) is evenly poured onto the support (mesh) (the beaker should be close to the support during pouring to prevent bubbles from forming). The casting liquid is fully immersed in the interior of the support (mesh), and then a scraper is used to select the corresponding thickness for scraping. The scraped diaphragm is placed in the air for pre-evaporation for 15 seconds. At this time, the casting liquid forms a polymer fusion layer on both sides of the support (mesh). At this time, a porous structure has not yet been formed, but the pore-forming agent and the ion-selective material have been evenly coated. Evenly distribute on the polymer fusion layer; finally, immerse the coated diaphragm in a coagulation bath with a coagulation bath temperature of 20°C. At this time, phase transformation occurs between the solvent and the non-solvent, and the liquid casting liquid becomes gel-like, forming a porous structure; after complete solidification, the diaphragm falls off from the glass plate by itself, and the treated composite diaphragm is soaked and cleaned multiple times with deionized water to remove the residual solvent in the diaphragm until there is no suspended matter in the deionized water and it is transparent. Then take out the diaphragm and place it in a drying oven for drying to obtain a composite diaphragm, which is cut into appropriate sizes for testing.

[0069] Comparative Example 1

[0070] The ion selective material in Example 1 was removed, and the rest remained unchanged to obtain a composite membrane. The preparation method is as follows:

[0071] (1) Prepare the casting solution: First, 50% wt of the organic solvent N,N-methylacetamide (DMAC) was measured and poured into a beaker. 10% wt of polysulfone (PSU) was then added. A magnetic stir bar was placed in the beaker and the mixture was rapidly stirred using a strong magnetic stirrer. 5% wt of polyethylene glycol (PEG) was then added to the solution as a pore-forming agent and further stirred. 30% wt of inorganic nanoparticles of titanium dioxide (TiO2) were then added and stirred thoroughly using a constant-temperature magnetic stirrer at room temperature for 20 hours until the mixture was completely dispersed. The stirring speed was then reduced and the mixture was stirred for 20 hours. Degassing was then performed to produce a milky white, viscous casting solution.

[0072] (2) Preparation of composite diaphragm: The support (mesh) is repeatedly rinsed with deionized water or ethanol and then dried. The treated support (mesh) is placed on a clean glass plate of appropriate size. The casting solution obtained in step (1) is evenly poured onto the support (mesh) (during the pouring process, the beaker should be close to the support to prevent the generation of bubbles). The casting solution fully penetrates into the interior of the support (mesh). Then, a scraper is used to scrape at a corresponding thickness. The cast film is left standing in the air for pre-evaporation for 15 s. At this time, a polymer fusion layer is formed on both sides of the support (mesh) by the casting solution. At this point, a porous structure has not yet been formed, but the pore-forming agent and the ion-selective material have been evenly distributed on the polymer fusion layer. Finally, the scraped film is immersed in a coagulation bath at a temperature of 20 °C. At this time, phase inversion occurs between the solvent and the non-solvent, and the liquid casting solution becomes gel-like, forming a porous structure. After complete coagulation, the film spontaneously detaches from the glass plate. The treated composite film is soaked and washed multiple times with deionized water to remove the residual solvent in the film until there are no suspended solids in the deionized water and it is transparent. Then, the film is taken out and placed in a drying oven for drying, thus obtaining the composite film, which is cut into an appropriate size for testing.

[0073] Perform performance tests on the composite membranes in the examples and comparative examples.

[0074] (1) Porosity measurement:

[0075] The porosity of the membrane refers to the ratio of the volume of pores in the membrane to the total volume. In experiments, the weighing method is usually used to measure it.

[0076]

[0077] (2) Contact angle measurement:

[0078] Use a contact angle measuring instrument to measure the contact angle of pure water on the membrane surface. Place the sample flat on the sample stage, and use a syringe to drop 1 μL of deionized water on the membrane surface. Quickly save and fit the image to measure the contact angle.

[0079] (3) Surface resistance measurement:

[0080] Use electrochemical impedance spectroscopy to measure the surface resistance of the membrane. Immerse the sample in room temperature simulated seawater (3.5% NaCl solution) for a whole day, and use an electrochemical workstation to test the surface resistance.

[0081] (4) Chloride ion rejection rate test:

[0082] By measuring the Cl - concentration changes on both sides (anode side and cathode side) of the membrane, calculate the rejection rate.

[0083]

[0084] The measurement results are shown in Table 1.

[0085] Table 1

[0086] From the data of the above embodiments, it can be seen that a highly selective composite diaphragm for seawater electrolysis hydrogen production provided by the present invention, by adding an ion-selective material, the Cl - interception rate > 99%, realizing the efficient screening of Cl - / OH - , significantly improving the ion selectivity of the diaphragm. Among them, Example 4 has the best effect. It provides the possibility for large-scale direct electrolysis of seawater to produce hydrogen and reduces the cost.

[0087] Finally, it should be noted that the above are only the preferred embodiments of the present invention and are not used to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements on some of the technical features. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A highly selective composite diaphragm for hydrogen production by seawater electrolysis and its preparation method, characterized in that, Improve the internal and surface structures of the separator by adding modifiers to enhance the ion selectivity of the separator; reduce the contact angle of the separator to lower the resistance of ions passing through the separator, achieving the effect of reducing the surface resistance of the separator; optimize the design of the substrate layer and / or functional layer to increase its bubble point pressure.

2. The highly selective composite diaphragm for seawater electrolysis hydrogen production according to claim 1, characterized in that, It includes three layers connected in sequence: a substrate layer, a functional layer, and a protective layer. The substrate layer provides mechanical strength and thermal stability. The functional layer has high ion selectivity and high gas selectivity, can effectively prevent the passage of chloride ions, and separate hydrogen and oxygen; High porosity, reducing surface resistance; Add adhesives to enhance the interfacial bonding force and prevent peeling. The protective layer has good ion selectivity and can inhibit the migration of chloride ions.

3. The highly selective composite diaphragm for seawater electrolysis hydrogen production according to claim 2, characterized in that, The thickness of the substrate layer is 100 - 300 μm, and the pore diameter is 50 - 300 μm; the functional layer is a porous layer with high porosity, the pore diameter is 30 - 250 nm, the porosity is 60% - 80%, and the thickness is 200 - 250 μm. The protective layer inhibits Cl diffusion, the average pore diameter is 10 - 50 nm, and the thickness is 0.5 - 5 μm.

4. The highly selective composite diaphragm for seawater electrolysis hydrogen production according to claim 2, wherein, The substrate support used is one or a combination of several of polypropylene, polyphenylene sulfide, polyimide, ceramics, titanium alloy mesh, and carbon fiber, preferably polyphenylene sulfide; the fiber diameter of the support is 50 - 150 μm.

5. In the preparation method of a highly selective composite diaphragm for seawater electrolysis hydrogen production according to claim 1, it is characterized in that The organic solvents in the casting solution used are one or a combination of several of N,N - dimethylacetamide, N - methylpyrrolidone, and N,N - dimethylformamide; the polymer materials are one or a combination of several of polyethersulfone, polyetheretherketone, polysulfone, polytetrafluoroethylene, chitosan, and polyacrylonitrile; the inorganic nanoparticles are one or a combination of several of titanium dioxide, alumina, silica, zirconia, and zinc oxide; the ion - selective materials are one or a combination of several of sulfonamide - type, quaternary - amine - type, tertiary - amine - type, metal oxides, and polyethersulfone / titanium dioxide composites; the pore - forming agents are one or a combination of several of polyethylene glycol, polyacrylic acid, silica, polyoxyethylene ether, and sodium dodecyl sulfate.

6. In the preparation method of a highly selective composite diaphragm for seawater electrolysis hydrogen production according to claim 5, it is characterized in that, The specific composition in the casting solution used is by mass fraction: organic solvents 42 - 50 parts, ion - selective materials 15 parts, organic polymer 3 - 10 parts, inorganic nanoparticles 33 - 40 parts, pore - forming agents 0.2 - 3 parts.

7. In the method for preparing a highly selective composite diaphragm for seawater electrolysis for hydrogen production according to claim 5, it is characterized in that, The solution of the coagulation bath used is one or a combination of several of deionized water, ethanol, N - methylpyrrolidone, and N,N - dimethylformamide.

8. A highly selective composite separator for hydrogen production by seawater electrolysis and its preparation process according to claims 1 - 7, characterized in that S1. First, weigh the selected organic solvents, organic polymers, ion - selective materials, inorganic nanoparticles, and pore - forming agents as required and set aside. S2. Dissolve the selected organic polymer in the selected organic solvent. First, stir it well with a glass rod to obtain a uniformly dispersed solution. Then, sequentially add the weighed ion-selective material and pore former, and stir well with a constant-temperature magnetic stirrer at room temperature until it is completely dissolved. Next, add the weighed inorganic nanoparticles and stir for 20 h until they are completely dispersed uniformly. Then, continue to reduce the stirring speed and stir for 20 h for defoaming treatment to obtain a milky viscous casting solution. S3. Pour the casting solution evenly onto the support placed on a glass plate, and use a suitable doctor blade to scrape it evenly. Pre-evaporate the scraped diaphragm in the air. Then, place it in a coagulation bath for phase inversion. S4. Wait for the diaphragm to automatically peel off on the glass plate, then rinse it with deionized water and then perform a drying treatment to obtain a highly selective composite diaphragm for seawater electrolysis hydrogen production.

9. A highly selective composite diaphragm for seawater electrolysis hydrogen production according to claims 1-8.

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