Coating slurry for composite diaphragm in alkaline electrolytic cell and preparation method of coating slurry

Abstract

The invention belongs to the technical field of water electrolysis hydrogen production diaphragms, and relates to coating slurry for a composite diaphragm in an alkaline electrolytic cell and a preparation method of the coating slurry. The coating slurry comprises a high-molecular polymer, an inorganic hydrophilic oxide, a polymer electrolyte, a pore-foaming agent and an organic solvent. The high-molecular polymer is polysulfone, and the inorganic hydrophilic oxide is titanium dioxide; and the polymer electrolyte is acacia gum. And the pore-foaming agent is polyvinylpyrrolidone. Titanium dioxide is used as a filler, so that the hydrophilicity of the hydrophobic polysulfone membrane can be improved, and the transfer of hydroxyl ions is facilitated. Hydroxyl, amino and other hydrophilic groups of the acacia gum are migrated to a membrane-water interface, and the groups and a membrane matrix are combined to form a hydrogen bond network, so that the stability and the water adsorption capacity of the membrane are enhanced, and the composite membrane with low surface resistance, smooth surface, compact coating and good mechanical capacity is obtained. The nylon and the acacia gum are adopted, cost is low, and large-scale production is facilitated.

Description

Technical Field

[0001] The invention belongs to the technical field of diaphragms for producing hydrogen by electrolysis of water, and relates to a coating slurry for a composite diaphragm in an alkaline electrolytic cell and a preparation method thereof. Background Art

[0002] With the transformation of the global energy structure and growing awareness of environmental protection, the development and utilization of hydrogen, as a clean, efficient, and sustainable energy carrier, has attracted widespread attention and plays a vital role in sustainable social development. Hydrogen can be produced through various methods, such as biofermentation, biomass pyrolysis, and chemical methods. However, alkaline water electrolysis is widely used for hydrogen production worldwide due to its high efficiency and environmental friendliness.

[0003] Alkaline water electrolysis is a key method for large-scale hydrogen production, characterized by its simplicity, stability, and readily available materials. While it produces hydrogen and oxygen directly by electrolyzing water in an electrolyzer, this process easily causes the hydrogen and oxygen to mix, compromising gas purity and requiring secondary purification, increasing costs and safety. Diaphragms play a crucial role in this process. While diaphragms prevent gas mixing and improve safety, they also hinder the flow of ions in the electrolyte, increasing power consumption and thus production costs. Therefore, diaphragm performance is a crucial factor influencing the safety and cost of alkaline hydrogen electrolysis.

[0004] Although asbestos diaphragms are heat-resistant, corrosion-resistant, and highly hydrophilic, they also suffer from shortcomings such as high swelling, poor mechanical properties, and carcinogenicity. Polytetrafluoroethylene resin and polyphenylene sulfide diaphragms, while low swelling and good mechanical properties, have high electrical resistance and poor hydrophilicity, leading to high energy consumption.

[0005] In summary, reducing the surface resistance and material cost of the alkaline electrolytic cell composite membrane and improving the mechanical properties are the key points and difficulties of the existing alkaline water electrolysis composite membrane. Summary of the Invention

[0006] In view of the existing problems, the present invention provides a coating slurry for a composite diaphragm in an alkaline electrolytic cell and a preparation method thereof.

[0007] The technical solution adopted in the present invention is as follows:

[0008] A coating slurry for a composite diaphragm in an alkaline electrolytic cell comprises a high molecular polymer, an inorganic hydrophilic oxide, a high molecular electrolyte, a porogen and an organic solvent.

[0009] The high molecular polymer is polysulfone, with a diameter of 2-2.5 mm and a molecular weight of 80,000 g / mol.

[0010] The inorganic hydrophilic oxide is titanium dioxide, and 99.8% pure 25 nanometer hydrophilic rutile titanium dioxide can be selected.

[0011] The polymer electrolyte is acacia gum, which is in the form of white powder with a density of 1.35 g / ml.

[0012] The porogen is polyvinyl pyrrolidone with an average molecular weight of 220,000.

[0013] The N-methylpyrrolidone is used as the organic solvent.

[0014] The above-mentioned method for preparing the composite diaphragm for alkaline electrolytic cell comprises the following steps:

[0015] (1) Dissolve polysulfone in an organic solvent, N-methylpyrrolidone, by thorough stirring to form a colorless transparent liquid; weigh polyvinylpyrrolidone, acacia gum, and titanium dioxide in sequence and add them to the above solution, stirring uniformly at room temperature;

[0016] Wherein, the mass proportion of the organic solvent N-methylpyrrolidone is 60-70%, preferably 65%;

[0017] Polysulfone, polyvinyl pyrrolidone, titanium dioxide + acacia gum, the mass ratio between the three is 4:1:15;

[0018] The mass ratio of titanium dioxide and acacia gum is maintained at 27%;

[0019] (2) Use a vacuum pump to evacuate and defoam until there are no bubbles in the solution to obtain a milky white casting solution; the vacuum environment for defoaming is -0.9 MPa, and the defoaming time is 40-60 minutes;

[0020] (3) First, use a 400±50 μm scraper to apply the casting solution in step (2) on a smooth glass plate; then lay nylon on it; then use a 600±50 μm scraper to apply the casting solution in step (2) on it, perform pre-evaporation for 13±2 seconds, and finally place it in deionized water for phase inversion molding;

[0021] (4) The deionized water was replaced three times within 24 hours to completely precipitate the organic solvent and porogen, and the thickness was 450-550 μm.

[0022] During the preparation process, the stirring temperature, deionized water temperature, pre-evaporation temperature and doctor blade coating temperature involved were all at room temperature.

[0023] The beneficial effects of the present invention are:

[0024] 1. Titanium dioxide as a filler in the present invention can improve the hydrophilicity of the hydrophobic polysulfone membrane, which is beneficial to the transfer of hydroxide ions.

[0025] 2. The hydrophilic groups such as hydroxyl and amino groups of acacia gum in the present invention will migrate to the membrane-water interface. At the same time, the groups will combine with the membrane matrix to form a hydrogen bond network, thereby enhancing the stability of the membrane and its ability to adsorb water, and obtaining a composite diaphragm with low surface resistance, smooth surface, compact coating and good mechanical strength.

[0026] 3. Using nylon as the skeleton not only improves the mechanical properties of the diaphragm, but also nylon is a common material with low cost.

[0027] 4. The acacia gum in the present invention is a renewable green material with low cost and is suitable for large-scale production. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 This is a surface microscopic morphology of the composite diaphragm of the alkaline hydrolysis tank of Example 2 provided by the present invention;

[0029] Figure 2 This is a microscopic morphology of the pores of the composite diaphragm of the alkaline hydrolysis tank of Example 2 provided by the present invention;

[0030] Figure 3 This is a cross-sectional microscopic morphology of the composite diaphragm of the alkaline hydrolysis tank of Example 2 provided by the present invention.

[0031] Figure 4 The surface resistance values of the composite diaphragms of the alkaline hydrolysis tanks of Examples 1-6 and the comparative example Belgian AGFA UTP 500 are provided in the present invention. DETAILED DESCRIPTION

[0032] The specific embodiments of the present invention are described in detail below in conjunction with the technical solutions and drawings.

[0033] Example 1

[0034] A method for preparing a composite diaphragm for an alkaline electrolytic cell comprises the following steps:

[0035] (1) Dissolve 20% polysulfone in a certain amount of N-methylpyrrolidone and stir at 2000 rpm to form a colorless transparent solution; then add 5% polyvinylpyrrolidone and stir at 2000 rpm to form a colorless transparent solution; then add 75% titanium dioxide and stir at 300 rpm for 24 hours until the solution is completely dissolved to obtain a milky white mixed solution; finally, vacuum degassing is performed to obtain a milky white casting solution;

[0036] (2) The casting solution from step (1) was first applied to a smooth glass plate using a 400-μm scraper; nylon was then spread flat on the plate; the casting solution from step (1) was then applied to the plate using a 600-μm scraper, followed by 13-second pre-evaporation. The plate was then placed in deionized water for phase inversion to obtain a diaphragm; the deionized water was replaced three times within 24 hours to completely precipitate the organic solvent and porogen, resulting in a 502-μm thick diaphragm. The surface resistivity was measured to be 0.1697 Ω.cm2.

[0037] Example 2

[0038] (1) Dissolve 20% polysulfone in a certain amount of N-methylpyrrolidone and stir at 2000 rpm to form a colorless transparent solution; then add 5% polyvinylpyrrolidone and stir at 2000 rpm to form a colorless transparent solution; then add 0.5% acacia gum and stir until it becomes colorless and transparent; finally add 74.5% titanium dioxide and stir at 300 rpm for 24 hours until it is completely dissolved to obtain a milky white mixed solution; finally, vacuum degassing is performed to obtain a milky white casting solution;

[0039] (2) First, use a 400-micron scraper to scrape the casting solution in step (1) on a smooth glass plate; then spread nylon on it; then use a 550-micron scraper to scrape the casting solution in step (1) on it, then pre-evaporate it for 15 seconds, and finally put it into deionized water for phase conversion to obtain a diaphragm; finally, replace the deionized water three times within 24 hours to completely precipitate the organic solvent and porogen, and obtain a diaphragm with a thickness of 486 μm. Its surface resistance was measured to be 0.1249 Ω.cm 2 .

[0040] Example 3

[0041] (1) Dissolve 20% polysulfone in a certain amount of N-methylpyrrolidone and stir at 2000 rpm to form a colorless and transparent solution; then add 5% polyvinylpyrrolidone and stir at 2000 rpm to form a colorless and transparent solution; then add 1% acacia gum and stir until it becomes colorless and transparent; finally, add 74% titanium dioxide and stir at 300 rpm for 24 hours until it is completely dissolved to obtain a milky white mixed solution; finally, vacuum degassing is performed to obtain a milky white casting solution;

[0042] (2) First, use a 350-micron scraper to scrape the casting solution in step (1) on a clean glass plate; then spread nylon on it; then use a 650-micron scraper to scrape the casting solution in step (1) on it, then perform pre-evaporation for 11 seconds, and finally place it in deionized water for phase conversion to obtain a diaphragm; finally, replace the deionized water three times within 24 hours to completely precipitate the organic solvent and porogen, and obtain a diaphragm with a thickness of 518 μm. The measured surface resistance is 0.1501Ω.cm2 .

[0043] Example 4

[0044] (1) Dissolve 20% polysulfone in a certain amount of N-methylpyrrolidone and stir at 2000 rpm to form a colorless and transparent solution; then add 5% polyvinylpyrrolidone and stir at 2000 rpm to form a colorless and transparent solution; then add 2% acacia gum and stir until it becomes colorless and transparent; finally, add 73% titanium dioxide and stir at 300 rpm for 24 hours until it is completely dissolved to obtain a milky white mixed solution; finally, vacuum degassing is performed to obtain a milky white casting solution;

[0045] (2) First, use a 350-micron scraper to scrape the casting solution in step (1) on a smooth glass plate; then spread nylon on it; then use a 550-micron scraper to scrape the casting solution in step (1) on it, then perform a 14-second pre-evaporation, and finally place it in deionized water for phase conversion to obtain a diaphragm; finally, replace the deionized water three times within 24 hours to completely precipitate the organic solvent and porogen, and obtain a diaphragm with a thickness of 478 μm. The measured surface resistance is 0.1538 Ω.cm 2 .

[0046] Example 5

[0047] (1) Dissolve 20% polysulfone in a certain amount of N-methylpyrrolidone and stir at 2000 rpm to form a colorless transparent solution; then add 5% polyvinylpyrrolidone and stir at 2000 rpm to form a colorless transparent solution; then add 4% acacia gum and stir until it becomes colorless and transparent; finally add 71% titanium dioxide and stir at 300 rpm for 24 hours until it is completely dissolved to obtain a milky white mixed solution; finally, vacuum degassing is performed to obtain a milky white casting solution;

[0048] (2) The casting solution from step (1) was first applied to a smooth glass plate using a 450 μm scraper; nylon was then spread on the plate; the casting solution from step (1) was then applied to the plate using a 600 μm scraper, followed by 15 s of pre-evaporation, and finally placed in deionized water for phase inversion to obtain a diaphragm; the deionized water was replaced three times within 24 hours to completely precipitate the organic solvent and porogen, resulting in a diaphragm with a thickness of 510 μm. The surface resistivity was measured to be 0.0.1662 Ω.cm2.

[0049] Example 6

[0050] (1) Dissolve 20% polysulfone in a certain amount of N-methylpyrrolidone and stir at 2000 rpm to form a colorless transparent solution; then add 5% polyvinylpyrrolidone and stir at 2000 rpm to form a colorless transparent solution; then add 6% acacia gum and stir until it becomes colorless and transparent; finally add 69% titanium dioxide and stir at 300 rpm for 24 hours until it is completely dissolved to obtain a milky white mixed solution; finally, vacuum degassing is performed to obtain a milky white casting solution;

[0051] (2) The casting solution from step (1) was first applied to a smooth glass plate using a 450 μm scraper; nylon was then spread on the plate; the casting solution from step (1) was then applied to the plate using a 650 μm scraper, followed by 11 seconds of pre-evaporation. The plate was then placed in deionized water for phase inversion to obtain a diaphragm; the deionized water was replaced three times within 24 hours to completely precipitate the organic solvent and porogen, resulting in a diaphragm with a thickness of 523 μm. The surface resistivity was measured to be 0.1816 Ω.cm2.

[0052] Example 7: Testing

[0053] Thickness test: Tested in accordance with SJ T 10171-2016 standard.

[0054] Surface resistance test: tested in accordance with SJ T 10171-2016 standard.

[0055] (1) Microstructure of composite diaphragm surface

[0056] The surface micrograph of the composite diaphragm prepared in Example 2 was obtained by scanning electron microscopy. Figure 1 and Figure 2 As shown, Figure 1 The surface of the composite diaphragm is smooth and flat, without burrs, which helps to reduce the friction between the electrolyte and gas on the membrane, thereby increasing its service life; Figure 2 The pore size and distribution are uniform, the density is good, and the pores are very small.

[0057] (2) Composite diaphragm cross section

[0058] The cross-sectional micrograph of the composite diaphragm prepared in Example 3 was obtained by scanning electron microscopy. Figure 3 As shown in the figure, it can be seen that the slurry adheres well to the nylon mesh cloth skeleton, and the channels in the middle of the composite diaphragm are finger-shaped. At the same time, the channels at the membrane interface are smaller than the internal channels, which is conducive to blocking the gas without affecting the flow of hydroxide ions.

[0059] (3) Composite diaphragm surface resistance

[0060] The composite membranes obtained in Examples 1-6 of the present invention were electrochemically tested at room temperature in a 30% KOH electrolyte to measure the surface resistance. AGFA UTP 500 from Belgium was used as a comparative example. The results are shown in FIG. Figure 4 The results show that, under the same thickness range and test conditions, the resistance of commonly used separators on the market is 0.28Ω.cm2, while the resistance of the separator of the present invention is below 0.18Ω.cm2, with a minimum of 0.12Ω.cm2. The surface resistance of this composite separator is much lower than that of commercial products, and this membrane will significantly reduce the energy consumption required for electrolytic hydrogen production. Acacia gum is a green and renewable material, and this composite separator is suitable for large-scale market production and application.

Claims

1. A coating slurry for a composite diaphragm in an alkaline electrolytic cell, characterized in that: Including high molecular polymer, inorganic hydrophilic oxide, polymer electrolyte, porogen and organic solvent; The high molecular weight polymer is polysulfone, with a diameter of 2-2.5 mm and a molecular weight of 80,000 g / mol; The inorganic hydrophilic oxide is titanium dioxide, which can be 99.8% pure 25 nanometer hydrophilic rutile titanium dioxide. The polymer electrolyte is acacia gum, which is a white powder with a density of 1.35 g / ml. The porogen is polyvinyl pyrrolidone with an average molecular weight of 220,000; The N-methylpyrrolidone is used as the organic solvent.

2. The method for preparing a composite diaphragm for an alkaline electrolytic cell according to claim 1, wherein: The steps are as follows: (1) Dissolve polysulfone in an organic solvent, N-methylpyrrolidone, by thorough stirring to form a colorless transparent liquid; weigh polyvinylpyrrolidone, acacia gum, and titanium dioxide in sequence and add them to the above solution, stirring uniformly at room temperature; Among them, the mass proportion of organic solvent N-methylpyrrolidone is 60-70%; Polysulfone, polyvinyl pyrrolidone, titanium dioxide + acacia gum, the mass ratio between the three is 4:1:15; The mass ratio of titanium dioxide and acacia gum is maintained at 27%; (2) Use a vacuum pump to evacuate and defoam until there are no bubbles in the solution to obtain a milky white casting solution; the vacuum environment for defoaming is -0.9 MPa, and the defoaming time is 40-60 minutes; (3) First, use a 400±50 μm scraper to apply the casting solution in step (2) on a smooth glass plate; then lay nylon on it; then use a 600±50 μm scraper to apply the casting solution in step (2) on it, perform pre-evaporation for 13±2 seconds, and finally place it in deionized water for phase inversion molding; (4) The deionized water was replaced three times within 24 hours to completely precipitate the organic solvent and porogen, and the thickness was 450-550 μm.

3. The method for preparing a composite diaphragm for an alkaline electrolytic cell according to claim 1, wherein: The steps are as follows: (1) Dissolve polysulfone in an organic solvent, N-methylpyrrolidone, by thorough stirring to form a colorless transparent liquid; weigh polyvinylpyrrolidone, acacia gum, and titanium dioxide in sequence and add them to the above solution, stirring uniformly at room temperature; Among them, the mass proportion of organic solvent N-methylpyrrolidone is 65%; Polysulfone, polyvinyl pyrrolidone, titanium dioxide + acacia gum, the mass ratio between the three is 4:1:15; The mass ratio of titanium dioxide and acacia gum is maintained at 27%; (2) Use a vacuum pump to evacuate and defoam until there are no bubbles in the solution to obtain a milky white casting solution; the vacuum environment for defoaming is -0.9 MPa, and the defoaming time is 40-60 minutes; (3) First, use a 400±50 μm scraper to apply the casting solution in step (2) on a smooth glass plate; then lay nylon on it; then use a 600±50 μm scraper to apply the casting solution in step (2) on it, perform pre-evaporation for 13±2 seconds, and finally place it in deionized water for phase inversion molding; (4) The deionized water was replaced three times within 24 hours to completely precipitate the organic solvent and porogen, and the thickness was 450-550 μm.

4. The preparation method according to claim 2 or 3, characterized in that During the preparation process, the stirring temperature, deionized water temperature, pre-evaporation temperature and doctor blade coating temperature involved were all at room temperature.

5. The preparation method according to claim 2 or 3, characterized in that The steps are as follows; (1) Dissolve 20% polysulfone in N-methylpyrrolidone and stir at 2000 rpm to form a colorless transparent solution; then add 5% polyvinylpyrrolidone and stir at 2000 rpm to form a colorless transparent solution; Then, 75% titanium dioxide was added and stirred at 300 rpm for 24 hours until it was completely dissolved to obtain a milky white mixed solution; finally, vacuum degassing was performed to obtain a milky white casting solution; (2) First, a 400-micron scraper was used to apply the casting solution in step (1) on a smooth glass plate; then, nylon was spread flat on it; then, a 600-micron scraper was used to apply the casting solution in step (1) on it, followed by 13-second pre-evaporation, and finally, it was placed in deionized water for phase conversion to obtain a diaphragm; finally, the deionized water was replaced 3 times within 24 hours to completely precipitate the organic solvent and porogen, to obtain a diaphragm with a thickness of 502 μm; the surface resistance was measured to be 0.1697 Ω.cm2.

6. The preparation method according to claim 2 or 3, characterized in that The steps are as follows; (1) Dissolve 20% polysulfone in N-methylpyrrolidone and stir at 2000 rpm to form a colorless transparent solution; then add 5% polyvinylpyrrolidone and stir at 2000 rpm to form a colorless transparent solution; then add 0.5% acacia gum and stir until it becomes colorless and transparent; finally add 74.5% titanium dioxide and stir at 300 rpm for 24 hours until it is completely dissolved to obtain a milky white mixed solution; finally, vacuum degassing is performed to obtain a milky white casting solution; (2) First, the casting solution in step (1) was applied on a smooth glass plate using a 400 μm scraper; then, nylon was spread on the plate; then, the casting solution in step (1) was applied on the plate using a 550 μm scraper, followed by 15 s of pre-evaporation, and finally, the plate was placed in deionized water for phase conversion to obtain a diaphragm; finally, the deionized water was replaced 3 times within 24 hours to completely precipitate the organic solvent and porogen, thereby obtaining a diaphragm with a thickness of 486 μm; the surface resistance thereof was measured to be 0.1249 Ω.cm 2 .

7. The preparation method according to claim 2 or 3, characterized in that The steps are as follows; (1) Dissolve 20% polysulfone in N-methylpyrrolidone and stir at 2000 rpm to form a colorless transparent solution; then add 5% polyvinylpyrrolidone and stir at 2000 rpm to form a colorless transparent solution; then add 1% acacia gum and stir until it becomes colorless and transparent; finally add 74% titanium dioxide and stir at 300 rpm for 24 hours until it is completely dissolved to obtain a milky white mixed solution; finally, vacuum degassing is performed to obtain a milky white casting solution; (2) First, the casting solution in step (1) was applied on a smooth glass plate using a 350 μm scraper; then, nylon was spread on the plate; then, the casting solution in step (1) was applied on the plate using a 650 μm scraper, followed by 11 s of pre-evaporation, and finally, the plate was placed in deionized water for phase inversion to obtain a diaphragm; finally, the deionized water was replaced 3 times within 24 hours to completely precipitate the organic solvent and porogen, thereby obtaining a diaphragm with a thickness of 518 μm; the surface resistance was measured to be 0.1501 Ω.cm 2 .

8. The preparation method according to claim 2 or 3, characterized in that The steps are as follows; (1) Dissolve 20% polysulfone in N-methylpyrrolidone and stir at 2000 rpm to form a colorless transparent solution; then add 5% polyvinylpyrrolidone and stir at 2000 rpm to form a colorless transparent solution; Then add 2% acacia gum and stir until it becomes colorless and transparent. Finally, add 73% titanium dioxide and stir at 300 rpm for 24 hours until it is completely dissolved to obtain a milky white mixed solution. Finally, vacuum degassing is performed to obtain a milky white casting solution. (2) First, the casting solution in step (1) was applied on a smooth glass plate using a 350 μm scraper; then, nylon was spread on the plate; then, the casting solution in step (1) was applied on the plate using a 550 μm scraper, followed by 14 s of pre-evaporation, and finally, the plate was placed in deionized water for phase conversion to obtain a diaphragm; finally, the deionized water was replaced 3 times within 24 hours to completely precipitate the organic solvent and porogen, thereby obtaining a diaphragm with a thickness of 478 μm; the surface resistance was measured to be 0.1538 Ω.cm 2 .

9. The preparation method according to claim 2 or 3, characterized in that The steps are as follows; (1) Dissolve 20% polysulfone in N-methylpyrrolidone and stir at 2000 rpm to form a colorless transparent solution; then add 5% polyvinylpyrrolidone and stir at 2000 rpm to form a colorless transparent solution; then add 4% acacia gum and stir until it becomes colorless and transparent; finally add 71% titanium dioxide and stir at 300 rpm for 24 hours until it is completely dissolved to obtain a milky white mixed solution; finally, vacuum degassing is performed to obtain a milky white casting solution; (2) First, use a 450-micron scraper to scrape the casting solution in step (1) on a smooth glass plate; then spread nylon on it; then use a 600-micron scraper to scrape the casting solution in step (1) on it, and then pre-evaporate it for 15 seconds, and finally put it into deionized water for phase conversion to obtain a diaphragm; finally, replace the deionized water three times within 24 hours to completely precipitate the organic solvent and porogen, and obtain a diaphragm with a thickness of 510 μm; the measured surface resistance is 0.0.1662 Ω.cm2.

10. The preparation method according to claim 2 or 3, characterized in that: The steps are as follows; (1) Dissolve 20% polysulfone in N-methylpyrrolidone and stir at 2000 rpm to form a colorless transparent solution; then add 5% polyvinylpyrrolidone and stir at 2000 rpm to form a colorless transparent solution; then add 6% acacia gum and stir until it becomes colorless and transparent; finally, add 69% titanium dioxide and stir at 300 rpm for 24 hours until it is completely dissolved to obtain a milky white mixed solution; finally, vacuum degassing is performed to obtain a milky white casting solution; (2) First, use a 450-micron scraper to apply the casting solution in step (1) on a smooth glass plate; then spread nylon on it; then use a 650-micron scraper to apply the casting solution in step (1) on it, and then perform pre-evaporation for 11 seconds, and finally put it into deionized water for phase conversion to obtain a diaphragm; finally, replace the deionized water three times within 24 hours to completely precipitate the organic solvent and porogen, and obtain a diaphragm with a thickness of 523 μm; the measured surface resistance is 0.1816 Ω.cm2.

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