Coating slurry for electrolytic water composite membrane and preparation method of composite membrane

Abstract

The present invention discloses a method for preparing a coating slurry for an alkaline water electrolysis composite membrane and a method for preparing the composite membrane. The coating slurry preparation method comprises providing a drying room for carrying out the coating slurry preparation, wherein the humidity thereof is not higher than 40%; and performing the coating slurry preparation in the drying room. The composite membrane preparation method comprises providing a base membrane; preparing a coating slurry for the alkaline water electrolysis composite membrane; coating the coating slurry on the surface of the base membrane to form a wet film; and drying the wet film to form a composite membrane. The coating slurry dispersion uniformity is improved by controlling the humidity of the coating slurry preparation environment, and the pore size and distribution of the membrane surface are adjusted by controlling the temperature and time of the standing temperature during pre-evaporation to form a relatively dense composite membrane surface layer, thereby improving the composite membrane performance, while also increasing production efficiency and reducing costs.

Description

Technical Field

[0001] The present invention relates to the technical field related to alkaline water electrolysis membranes, and in particular to a method for preparing a coating slurry for an alkaline water electrolysis composite membrane and a composite membrane using the same. Background Art

[0002] Hydrogen production by water electrolysis is a simple process that can be fully automated, produces high-purity hydrogen, and is environmentally friendly. Currently, three types of water electrolysis devices have been developed: solid polymer water electrolyzers, solid oxide water electrolyzers, and alkaline water electrolyzers. Alkaline water electrolyzers are the most mature technology to date, enjoying widespread industrial application due to their simplicity and high efficiency.

[0003] An alkaline water electrolyzer primarily consists of electrodes and a diaphragm. The cell is divided into an anode chamber and a cathode chamber, separated by a diaphragm. The cell is filled with an electrolyte, which has good conductivity. A 30% to 40% KOH or NaOH solution is commonly used. During the electrolysis process, oxygen is generated at the anode and hydrogen is generated at the cathode. The diaphragm prevents the hydrogen and oxygen from mixing.

[0004] Alkaline water electrolysis reaction equation:

[0005] Cathode: 4H2O+4e - →4OH - +2H2

[0006] Anode: 4OH - →2H2O+O2+4e -

[0007] Overall reaction: 2H2O→2H2+O2

[0008] In the process of producing hydrogen by alkaline water electrolysis, the diaphragm functions as follows: on the one hand, it blocks hydrogen and oxygen; on the other hand, it allows hydroxide ions in the solution to pass through, ensuring the electrolysis process continues and minimizing the diaphragm resistance to reduce energy consumption. Diaphragms suitable for alkaline water electrolyzers should meet the following requirements:

[0009] (1) Ensure that H2 and O2 molecules cannot pass through the diaphragm, but allow electrolyte ions to pass through.

[0010] (2) The diaphragm can remain chemically stable under electrolysis temperature and alkaline conditions.

[0011] (3) It has good mechanical strength and can withstand the impact of electrolyte and generated gas for a long time without damaging the diaphragm structure.

[0012] (4) In order to reduce power loss, the diaphragm must have a smaller surface resistance, so the diaphragm porosity should be as high as possible.

[0013] Asbestos has a fibrous structure, consisting of fiber bundles composed of a mixture of various silicates. It exhibits chemical and high temperature resistance, high tensile strength, and strong hydrophilicity. However, asbestos's swelling property reduces the overall tensile strength of the separator, making it susceptible to damage from electrolyte and gas impacts. Furthermore, the swelled separator affects the distribution of electrolyte ions within the electrolyte, increasing the current density, the separator resistance, and the energy consumption of the electrolysis.

[0014] Polyphenylene Sulfide (PPS) has the characteristics of good mechanical properties, resistance to high temperature and high concentration alkali corrosion, and excellent electrical properties. Polyphenylene sulfide diaphragms can be used in alkaline water electrolyzers. However, due to the poor hydrophilicity of polyphenylene sulfide, the electrolyte cannot fully enter the pores of the diaphragm. During the electrolysis process, tiny bubbles gather on the surface of the diaphragm. These phenomena increase the resistance of the diaphragm and lead to increased energy consumption. The poor solubility of polyphenylene sulfide also leads to limitations in the method of preparing polyphenylene sulfide diaphragms. Some scholars have melt-spinned polyphenylene sulfide resin and then woven it to produce a polyphenylene sulfide braided diaphragm, which has effectively overcome the poor solubility of polyphenylene sulfide. By improving the hydrophilicity of polyphenylene sulfide diaphragms, polyphenylene sulfide diaphragms are expected to become a new type of diaphragm that can replace traditional asbestos diaphragms.

[0015] Polysulfone (PSF), abbreviated as PSF, is a polymer compound with phenylene sulfone as a structural unit and is a thermoplastic resin. It has the advantages of strong antioxidant properties, strong acid and alkali corrosion resistance, good solubility, and simple and convenient production. Various existing membrane preparation methods are suitable for the preparation of polysulfone diaphragms. Among them, the phase inversion method is the most commonly used, but the polysulfone diaphragm has poor hydrophilicity. During the water electrolysis process, tiny bubbles of hydrogen and oxygen easily gather on the surface of the diaphragm, affecting the flow of the electrolyte and reducing the current efficiency. This situation is similar to that of polyphenylene sulfide diaphragms. The poor hydrophilicity of the polysulfone diaphragm greatly reduces the performance of the diaphragm. Therefore, if the hydrophilicity of the polysulfone diaphragm can be enhanced through effective means, the polysulfone diaphragm will have a more superior application prospect in the field of water electrolysis diaphragms.

[0016] Phase inversion is currently the most widely used membrane-forming method in the membrane-forming field. The phase inversion membrane-forming process primarily involves the formation of a polymer-rich phase and a polymer-poor phase. These phases are separated under specific conditions, and the polymer-rich phase solidifies into a membrane. Depending on the phase separation method, it can be categorized as thermally induced precipitation phase separation, solvent evaporation precipitation phase separation, vapor phase precipitation phase separation, and immersion precipitation phase separation. Among these, immersion precipitation phase separation is the most widely used and relatively mature membrane-forming method in the membrane-forming field. In the immersion precipitation phase inversion membrane-forming process, a polymer solution is first placed on a specific mold by coating or casting, and the mold is then placed in a non-solvent. During the exchange of the solvent and non-solvent in the polymer solution, a polymer-rich phase gradually forms, ultimately solidifying into a membrane. During the operation, membrane materials with different structures and properties can be produced by controlling factors at different stages, such as polymer concentration, pre-evaporation time, and non-solvent (also known as coagulation bath) temperature.

[0017] Currently, membrane materials made from polyphenylene sulfide (PPS) and polysulfone (PSF) have the problem of poor hydrophilicity, which easily leads to an increase in membrane resistance, thereby greatly reducing the performance of the membrane and affecting the promotion and use of the membrane in the field of alkaline water electrolyzers. Summary of the Invention

[0018] The hydrophilicity of the diaphragm is an important factor affecting the resistance of the diaphragm. In view of this, the present invention hopes to provide a hydrophilic composite membrane to solve the shortcomings of the existing diaphragms, such as poor hydrophilicity and increased resistance, so as to improve the performance of the diaphragm, obtain a diaphragm with high conductivity, increase the utilization rate of hydrophilic compounds, and at the same time improve production efficiency and reduce costs.

[0019] To achieve the above object, the technical solution of the present invention is achieved as follows:

[0020] The present invention provides a method for preparing a coating slurry for an electrolytic water composite membrane, which is characterized by: providing a drying room for implementing the coating slurry preparation, wherein the humidity of the drying room is not higher than 40%; preparing a coating slurry in the drying room, wherein the coating slurry includes a binder, a solvent, a hydrophilic compound and an additive; and stirring and mixing the coating slurry to dissolve the binder and the additive in the solvent.

[0021] Characteristically, the method further comprises performing a degassing treatment on the coating slurry.

[0022] Characteristically, the binder is selected from one of common bisphenol A type polysulfone (PSU), polyethersulfone (PES), polyvinylidene fluoride (PVDF) and polyethylene oxide (PEO) or a combination thereof.

[0023] Characteristically, the solvent is selected from one or a combination of N-ethylpyrrolidone (NEP), N-methylpyrrolidone (NMP), dimethyl sulfoxide (DMSO) and dimethylformamide (DMF).

[0024] Characteristically, the hydrophilic compound is selected from one of zirconium oxide, barium sulfate, zirconium phosphate, titanium oxide, and perovskite oxide materials, or a combination thereof.

[0025] Characteristically, the additive is selected from polyvinyl pyrrolidone (PVP), polyvinyl alcohol (PVA), methyl cellulose (MC) or a combination thereof.

[0026] The present invention also provides a method for preparing a composite membrane for water electrolysis, characterized in that: a base membrane is provided; a coating slurry is prepared for the composite membrane for water electrolysis, wherein the method for preparing the coating slurry for the alkaline water electrolysis composite membrane includes the coating slurry preparation method as described above; the coating slurry is coated on at least one side surface of the base membrane to form a wet film; and the wet film is dried to form a composite membrane.

[0027] Characteristically, the drying step further includes: a pre-evaporation step, in which the wet film is subjected to a pre-evaporation treatment to evaporate the solvent in the wet film; and a co-precipitation step, in which the wet film is placed in a first replacement solvent, so that the solvent in the wet film is replaced by the first replacement solvent and removed from the wet film. Since the binder and the hydrophilic compound are insoluble in the first replacement solvent, the binder and the hydrophilic compound are precipitated from the first replacement solvent. The wet film is taken out of the first replacement solvent and allowed to stand in the air for a period of time to remove the first replacement solvent and the solvent.

[0028] Characteristically, the first replacement solvent comprises water, alcohol or a mixed solvent of water and alcohol in any proportion.

[0029] Characteristically, the co-precipitation step further comprises placing the wet film in a second replacement solvent, so that the additive in the wet film is replaced by the second replacement solvent and removed from the wet film.

[0030] Characteristically, the second replacement solvent comprises water or a mixed solvent of water and alcohol in any proportion.

[0031] The present invention also provides a composite membrane for electrolysis of water, characterized by: a base membrane; and a coating layer coated on at least one side of the base membrane to form a composite membrane, wherein the coating layer includes a binder and a hydrophilic compound, the content ratio of the hydrophilic compound is greater than or equal to 60% and less than or equal to 85%, and the surface resistance of the composite membrane is not higher than 1.0Ω*cm 2 .

[0032] Characteristically, the binder is selected from one or a combination of common bisphenol A type polysulfone (PSU), polyethersulfone (PES), polyvinylidene fluoride (PVDF) and polyethylene oxide (PEO), and the hydrophilic compound is selected from one or a combination of zirconium oxide, barium sulfate, zirconium phosphate, titanium oxide, and perovskite oxide materials.

[0033] Characteristically, the preparation method of the coating applied on the base film includes: providing a coating slurry, the coating slurry including a binder, a solvent, a hydrophilic compound and an additive; applying the coating slurry on at least one side surface of the base film to form a wet film; and drying the wet film to form a composite film.

[0034] Characteristically, the coating comprises a retention rate of the hydrophilic compound of 80% to 99.9%, wherein the retention rate of the hydrophilic compound is the retained amount of the hydrophilic compound of the coating divided by the amount of the hydrophilic compound used when the coating slurry is prepared.

[0035] Characteristically, the method for preparing the coating slurry includes: providing a drying room for implementing the coating slurry preparation, the humidity of the drying room being no higher than 40%; preparing the coating slurry in the drying room; and stirring and mixing the coating slurry so that the binder and the additive are dissolved in the solvent.

[0036] Characteristically, the drying step includes: a pre-evaporation step, in which the wet film is subjected to a pre-evaporation treatment to evaporate the solvent in the wet film; and a co-precipitation step, in which the wet film is placed in a first replacement solvent, so that the solvent in the wet film is replaced by the first replacement solvent and removed from the wet film. Since the binder and the hydrophilic compound are insoluble in the first replacement solvent, the binder and the hydrophilic compound will be precipitated from the first replacement solvent. The wet film is taken out of the first replacement solvent and left to stand in the air for a period of time to remove the first replacement solvent and the solvent. The first replacement solvent includes water, alcohol or a mixed solvent of water and alcohol in any ratio.

[0037] Characteristically, the coprecipitation step further comprises placing the wet film in a second displacement solvent, so that the additive in the wet film is displaced by the second displacement solvent and removed from the wet film, wherein the second displacement solvent comprises water or a mixed solvent of water and alcohol in any ratio. The beneficial effects of the present invention are as follows:

[0038] 1) The hydrophilicity of the diaphragm is an important factor affecting the resistance of the diaphragm. Therefore, the present invention starts from the two aspects of improving the hydrophilicity of the diaphragm and the utilization rate of zirconium oxide to prepare a low-resistance diaphragm. Polyphenylene sulfide is selected as the base membrane material, and the immersion precipitation phase transformation method is used to improve the uniformity of slurry dispersion by controlling the humidity of the slurry preparation environment, as well as the temperature and time of the slurry steam bath standing temperature and the co-precipitation time in the displacement solvent and the drying step, to control the proportion and distribution of hydrophilic compounds in the diaphragm, retain more hydrophilic compounds in the composite membrane, increase the utilization rate of hydrophilic compounds to more than 80%, reduce the transfer of hydrophilic compounds to the displacement solvent, increase the conductivity of the composite membrane, and at the same time reduce the cost of recycling hydrophilic compounds from the displacement solvent, improve the performance of the composite membrane, and at the same time improve production efficiency and reduce costs.

[0039] 2) The retention rate of the hydrophilic compound in the slurry is mainly related to the binder, the particle size of the hydrophilic compound and the composite membrane preparation method. The larger the particle size of the hydrophilic compound, the smaller its surface area and the smaller the proportion of binder required. Therefore, under the same ratio conditions, the larger the particle size of the hydrophilic compound, the higher the retention rate. However, the lower the specific surface area, the lower the hydrophilicity and the lower its conductivity. The higher the density of polar groups such as hydroxyl and carboxyl groups in the binder, the better its adhesion. Therefore, it is necessary to select materials such as polysulfone or polyethersulfone with different functional group ratios and molecular weights. In the composite membrane preparation method, the co-precipitation time is the process of exchanging the solvent with the replacement solvent water to precipitate the hydrophilic compound and the binder into a membrane. The displacement solvent gradually penetrates from the surface to the center of the membrane. If this process is too short, the solvent in the membrane center is not completely replaced, resulting in incomplete precipitation, poor membrane uniformity, failed pore formation, and even membrane formation failure. If the process is too long, because the zirconium oxide and binder are still in the forming and uncured stage, the additives are transferred from the membrane to the aqueous phase under the action of the displacement solvent water, also carrying away some zirconium oxide, resulting in zirconium oxide loss. The present invention achieves a high retention rate of the hydrophilic compound in the slurry through better process time control, thereby improving the hydrophilicity of the diaphragm and exhibiting excellent conductivity performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 The present invention provides a flow chart of a method for preparing a coating slurry for an alkaline water electrolysis composite membrane according to an embodiment of the present invention.

[0041] Figure 2 This is a schematic diagram of the composite membrane structure for alkaline water electrolysis according to one embodiment of the present invention.

[0042] Figure 3 The figure is a flow chart of a method for preparing a composite membrane according to an embodiment of the present invention.

[0043] Figure 4 Schematic diagram of the test device for diaphragm resistance.

[0044] Figure 5A This is an electron microscope image of the surface of the composite membrane according to one embodiment of the present invention, with a magnification of 2000 times.

[0045] Figure 5B This is an electron microscope image of the surface of the composite membrane according to one embodiment of the present invention, with a magnification of 10,000 times.

[0046] Figure 5C This is an electron microscope image of a cross section of a composite membrane according to an embodiment of the present invention.

[0047] Component number description

[0048] 1…diaphragm

[0049] 2… Luggin capillary

[0050] 3…Auxiliary electrode

[0051] 4…Saturated KCl salt bridge

[0052] 5…Calomel electrode

[0053] 6…DC power supply

[0054] 7…Ammeter

[0055] 8…Voltmeter

[0056] 9… Composite membrane

[0057] 91…basement membrane

[0058] 92…coating

[0059] S01…Step

[0060] S02…Step

[0061] S03…Step

[0062] S04…Step

[0063] S11…Step

[0064] S12…Step

[0065] S13…Step

[0066] S14…Step DETAILED DESCRIPTION

[0067] The following describes the specific embodiments of the present invention in detail with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are only used to illustrate and explain the present invention and are not intended to limit the present invention.

[0068] The endpoints of the ranges and any values ​​disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoints of each range, the endpoints of each range and individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered to be specifically disclosed herein.

[0069] See also Figure 1 , which is a flow chart of a method for preparing a coating slurry for an alkaline water electrolysis composite membrane according to an embodiment of the present invention. As shown in the figure, a specific embodiment of the present invention in the embodiment provides a method for preparing a coating slurry, comprising the following steps:

[0070] Step S01: providing a drying room for preparing a coating slurry, wherein the humidity in the drying room is not higher than 40%; Step S02: preparing a coating slurry in the drying room, wherein the coating slurry includes a binder, a solvent, a hydrophilic compound, and an additive; Step S03: stirring and mixing the coating slurry to dissolve the binder and the additive in the solvent; and Step S04: further comprising performing a degassing treatment on the coating slurry to remove bubbles from the coating slurry.

[0071] Specifically, the binder is selected from one of common bisphenol A type polysulfone (PSU), polyethersulfone (PES), polyvinylidene fluoride (PVDF) and polyethylene oxide (PEO) or a combination thereof.

[0072] Specifically, the solvent is selected from one or a combination of N-ethylpyrrolidone (NEP), N-methylpyrrolidone (NMP), dimethyl sulfoxide (DMSO) and dimethylformamide (DMF).

[0073] Specifically, the hydrophilic compound is selected from one of zirconium oxide, barium sulfate, zirconium phosphate, titanium oxide, and perovskite oxide materials, or a combination thereof.

[0074] Specifically, the additive is selected from polyvinyl pyrrolidone (PVP), polyvinyl alcohol (PVA), methyl cellulose (MC) or a combination thereof.

[0075] Specifically, the coating slurry preparation in step S02 must be carried out in a dry room with a humidity level no higher than 40%. When the humidity in the laboratory is higher than 40%, the solvent in the slurry prematurely exchanges with water in the air, leading to premature co-precipitation and irreversible reagglomeration of the binder in the slurry. This results in uneven slurry dispersion and poor film-forming properties. Preferably, the humidity in the dry room is controlled at no higher than 10% to more effectively minimize the adverse effects of water in the air on the solvent in the slurry.

[0076] Specifically, the coating slurry prepared in step S02 is sequentially added with a binder (selected from PSU, PES, PVDF, PEO, etc., preferably PSU, PES), a solvent (selected from NEP, NMP, DMSO, DMF, preferably NEP, NMP), an additive with both pore-forming and dispersing effects (selected from PVP, PVA, MC, etc.; preferably PVP), and a hydrophilic compound.

[0077] Specifically, the stirring speed in step S03 is 300-1000 r / min and the stirring time is 2-4 hours. The preparation conditions for degassing the slurry in step S04 are: the degassing speed is 2000-4000 r / min and the degassing time is 10-20 minutes.

[0078] See also Figure 2 , which is a schematic diagram of the composite membrane structure for alkaline water electrolysis according to one embodiment of the present invention. As shown in the figure, in one embodiment, the composite membrane 9 includes a base membrane 91 and a coating 92, and the coating 92 is applied to at least one side of the base membrane 91 to form a composite membrane. The coating includes a binder and a hydrophilic compound, and the content of the hydrophilic compound is greater than or equal to 60% and less than or equal to 85%. The surface resistance of the composite membrane is no more than 1.0Ω*cm. 2 Please also refer to Figure 3 , which is a flow chart of a method for preparing a composite membrane according to an embodiment of the present invention. As shown in the figure, in one embodiment, the method for preparing a composite membrane comprises the following steps:

[0079] Step S11: providing a base film;

[0080] Step S12: preparing a coating slurry for the electrolytic water composite membrane, wherein the coating slurry preparation method for the alkaline electrolytic water composite membrane includes the coating slurry preparation method described above;

[0081] Step S13: coating the coating slurry on at least one side of the base film to form a wet film; and

[0082] Step S14: Drying the wet film to form a composite film.

[0083] Specifically, the composite membrane includes a base membrane and a coating, and the coating includes a retention rate of the hydrophilic compound of 80% to 99.9%, wherein the retention rate of the hydrophilic compound is the retention amount of the hydrophilic compound of the coating divided by the amount of the hydrophilic compound used when the coating slurry is configured.

[0084] Specifically, the base film in step S11 includes a film material made of polyphenylene sulfide or polysulfone.

[0085] Specifically, the coating step in step S13 includes a film forming method, in which the coating slurry is coated on the base film by means of blade coating or the like.

[0086] Specifically, the drying step in step S14 further includes: a pre-evaporation step, in which the wet film is subjected to a pre-evaporation treatment to evaporate the solvent in the wet film; and a co-precipitation step, in which the wet film is placed in a first replacement solvent, so that the solvent in the wet film is replaced by the first replacement solvent and removed from the wet film. Since the binder and the hydrophilic compound are insoluble in the first replacement solvent, the binder and the hydrophilic compound are precipitated from the first replacement solvent. The wet film is then taken out of the first replacement solvent and allowed to stand in air for a period of time to remove the first replacement solvent and the solvent.

[0087] Specifically, the first replacement solvent includes water, alcohol, or a mixed solvent of water and alcohol in any ratio.

[0088] Specifically, the pre-evaporation step involves standing the membrane at 50°C for 2 minutes to form a dense pore structure on the surface, reducing the loss of hydrophilic compounds. This process can only be performed once. The pre-evaporation process primarily occurs on the surface layer of the composite membrane, where water in the air and the solvent on the composite membrane surface are pre-exchanged. This causes the binder and hydrophilic compounds in the composite membrane to rearrange, forming a surface structure with a smaller pore size, which facilitates the retention of more hydrophilic compounds in the intermediate layer of the composite membrane during the subsequent co-precipitation process. However, during the co-precipitation process, the first displacement solvent has already been essentially replaced by the solvent, making further pre-evaporation impossible.

[0089] Specifically, the co-precipitation step further includes placing the wet film in a second replacement solvent, so that the additive in the wet film is replaced by the second replacement solvent and removed from the wet film.

[0090] Specifically, the second replacement solvent includes water or a mixed solvent of water and alcohol in any ratio.

[0091] Specifically, the co-precipitation method includes placing the wet film in a first replacement solvent, such as water, for 10 to 25 minutes. During this process, the first replacement solvent and the solvent NEP are exchanged. The first replacement solvent and the solvent are compatible, but because the binder precipitates when it comes into contact with water and the hydrophilic compound is also insoluble in the first replacement solvent, when a large amount of the first replacement solvent enters the wet film, the solvent is gradually diluted by the first replacement solvent until the binder and the hydrophilic compound are precipitated. The time of the co-precipitation method can be controlled between 10 minutes and 18 hours. If the time is controlled between 10 and 25 minutes, the solvent is not completely replaced due to the time being too short, and the precipitation is incomplete; if the time is too long, the first replacement solvent will take away some of the hydrophilic compound while taking away the PVP. Therefore, it is best to take the wet film out of the first replacement solvent and let it stand in the air for a period of time, about 4-24 hours, to remove most of the first replacement solvent and the solvent, to ensure that the film is formed and stable; then the wet film is placed in a second replacement solvent for 20-30 minutes, and a large amount of the second replacement solvent replaces the PVP in the wet film. At this time, the hydrophilic compound has been fixed in the film by the binder.

[0092] Micromorphology and pore size measurement

[0093] The surface and cross-sectional morphologies of the diaphragm were observed using a JSM-6700F field-emission scanning electron microscope (FESEM) manufactured in Japan. To observe the membrane's cross-sectional structure, the membrane was freeze-quenched in liquid nitrogen and affixed vertically to the sample stage with conductive double-sided tape. Due to the membrane's poor conductivity, it was gold-plated to prevent electron accumulation. The surface and cross-sectional microstructures of the membrane were then observed under a FESEM. Five holes were randomly measured in the membrane's SEM image, and the average value was used as the membrane pore size.

[0094] Sheet resistance measurement

[0095] See also Figure 4 , which is a schematic diagram of the test device for diaphragm resistance. The test device includes a diaphragm 1, a Luggin capillary 2, an auxiliary electrode 3, a saturated KCl salt bridge 4, a calomel electrode 5, a DC power supply 6, an ammeter 7, and a voltmeter 8. Before the test, the diaphragm was cut into samples with a diameter of about 3 cm, soaked in anhydrous ethanol for 2 hours, and then soaked in a 30wt% KOH solution for 24 hours, with the alkali solution changed once in the middle. The saturated potassium chloride solution and salt bridge were prepared in advance, and the saturated potassium chloride solution and salt bridge were prepared according to the following method. Figure 4 Connect the test system as shown. Then, clamp the diaphragm in the middle of the electrolytic cell. Turn on the regulated DC power supply and adjust the current to 10mA, 20mA, 30mA, 40mA, and 50mA, recording the voltage corresponding to each current. For each sample, a straight line plotting the voltage vs. current will be obtained. The slope of this line represents the system resistance. Subtract the system resistance without the diaphragm from this resistance to obtain the diaphragm's sheet resistance. Divide the sheet resistance by the diaphragm's thickness to obtain the resistivity.

[0096] Example 1

[0097] A method for preparing an alkaline water hydrogen production composite membrane comprises the following steps: 1. Slurry preparation: Prepare the slurry in a dry room with a humidity no higher than 5%. Add 4.41g of polysulfone and 25g of NEP solvent to the slurry in sequence and stir to dissolve. After the polysulfone dissolves, add 2.95g of PVP and dissolve for half an hour. Finally, add 17.64g of zirconium oxide. Stir at 750 rpm for 2 hours. 2. Slurry degassing: 4000 rpm for 15 minutes. 3. Film formation: Apply the slurry to a PPS base film on both sides with a knife. The wet film thickness is 300 microns. 4. Pre-evaporation: Allow to stand at 50°C for 2 minutes. 5. Co-precipitation: Place the wet film in water for 10 minutes, exchange the water and solvent, and then allow to stand for 18 hours. Place the membrane in water for 30 minutes and air-dry. The zirconium oxide retention rate is 98%, and then performance testing is performed. The zirconium oxide utilization rate was 94.3%. The membrane was immersed in ethanol for two hours, ultrasonically shaken, and immersed in 3Mol / L potassium hydroxide for 24 hours. The surface resistance was tested to be 0.40Ω*cm. 2 .

[0098] See also Figures 5A-5C , which is an electron microscope image of the composite membrane surface and cross section, Figures 5A-5B It can be seen that the surface morphology of the composite membrane is porous, the pore distribution is relatively uniform, and the pore size range is 300-500 nanometers. Figure 5C It can be seen that the composite membrane has a relatively dense stratification on the surface of the membrane, and the pore types inside the membrane are sponge-like and finger-like. The proportion of finger-like pores is higher, and the pore distribution is relatively uniform.

[0099] Example 2

[0100] A method for preparing an alkaline water hydrogen production composite membrane comprises the following steps: In Example 1, "IV. Pre-evaporation method: standing at 50°C for 2 minutes" is changed to "standing at 50°C for 0 minutes." Other operations are the same as in Example 1. The zirconium oxide retention rate is 95%, and performance testing is performed. The tested zirconium oxide utilization rate is 90%. The tested surface resistance is 0.45Ω*cm 2 .

[0101] Example 3

[0102] A method for preparing an alkaline water hydrogen production composite membrane comprises the following steps: In Example 1, "IV. Pre-evaporation method: standing at 50°C for 2 minutes" is changed to "standing at room temperature for 2 minutes." Other operations are the same as in Example 1. The zirconium oxide retention rate is 93%, and performance testing is performed. The tested zirconium oxide utilization rate is 87%. The tested surface resistance is 0.43Ω*cm. 2 .

[0103] Example 4

[0104] A method for preparing an alkaline water hydrogen production composite membrane comprises the following steps: "In Example 1: Coprecipitation method, placing the wet membrane in water for 10 minutes" is replaced with "Place the wet membrane in water for 25 minutes." Other operations are the same as in Example 1. The zirconium oxide retention rate is 85%, and performance testing is performed. The tested zirconium oxide utilization rate is 82%. The tested surface resistance is 0.49 Ω*cm. 2 .

[0105] Example 5

[0106] A method for preparing an alkaline water hydrogen production composite membrane comprises the following steps: "In Example 1: Coprecipitation method, place the wet membrane in water for 10 minutes, wait for the water and solvent to exchange, and then let it stand for 18 hours" is changed to: "Place the wet membrane in water for 10 minutes, wait for the water and solvent to exchange, and then let it stand for 4 hours." Other operations are the same as in Example 1. Performance testing was conducted. The zirconium oxide utilization rate was tested to be 80%. The surface resistance was tested to be 0.55 Ω*cm. 2 .

[0107] Example 6

[0108] A method for preparing an alkaline water hydrogen production composite membrane comprises the following steps: "In Example 1: Coprecipitation method, place the wet membrane in water for 10 minutes, wait for the water and solvent to exchange, and then let it stand for 18 hours" is changed to: "Place the wet membrane in water for 10 minutes, wait for the water and solvent to exchange, and then let it stand for 24 hours." Other operations are the same as in Example 1. Performance testing was conducted. The zirconium oxide utilization rate was tested to be 95%. The surface resistance was tested to be 0.39 Ω*cm. 2 .

[0109] Comparative Example 1

[0110] A method for preparing an alkaline water hydrogen production composite membrane comprises the following steps: 1. Slurry preparation: Prepare the slurry in a dry room with a humidity of 70%; add 4.41g of polysulfone and 25g of NEP solvent to the slurry in sequence and stir to dissolve; after the polysulfone dissolves, add 2.95g of PVP and dissolve for half an hour, and finally add 17.64g of zirconium oxide. Stir at 750 rpm for 2 hours. 2. Slurry degassing: Conditions: 4000 rpm for 15 minutes. 3. Film formation: Apply the slurry to both sides of a PPS base film with a knife to a wet film thickness of 300 microns. 4. Pre-evaporation: Allow to stand at 50°C for 2 minutes. 5. Co-precipitation: Place the wet film in water for 10 minutes. After the water and solvent are exchanged, significant zirconium oxide loss occurs. The membrane pores are observed to be large, at the level of 500 microns, visible to the naked eye. This pore size is too high for use as an alkaline water membrane, and the membrane formation is therefore determined to have failed.

[0111] Comparative Example 2

[0112] A method for preparing an alkaline water hydrogen production composite membrane comprises the following steps: 1. Slurry preparation: Prepare the slurry in a dry room at 45% humidity; add 4.41g of polysulfone and 25g of NEP solvent to the slurry in sequence and stir to dissolve; after the polysulfone dissolves, add 2.95g of PVP and dissolve for half an hour, followed by 17.64g of zirconium oxide. Stir at 750 rpm for 2 hours. 2. Slurry degassing: Conditions: 4000 rpm for 15 minutes. 3. Film formation: Apply the slurry to a PPS base film on both sides with a knife to a wet film thickness of 300 microns. 4. Pre-evaporation: Allow to stand at 50°C for 2 minutes. 5. Co-precipitation: Place the wet film in water for 10 minutes, allow the water and solvent to exchange, and then allow to stand for 18 hours. Place the membrane in water for 30 minutes, allow it to air dry, and then perform performance testing. The zirconium oxide utilization rate was 40.2%. The test surface resistance is 2.0Ω*cm 2 .

[0113] Comparative Example 3

[0114] A method for preparing an alkaline water hydrogen production composite membrane comprises the following steps: In Example 1, "IV. Pre-evaporation method: standing at 50°C for 2 minutes" is changed to "standing at 50°C for 5 minutes." Other operations are the same as in Example 1. Performance testing is performed. The zirconium oxide utilization rate is 90%. The surface resistance is 1.3 Ω*cm. 2 .

[0115] Comparative Example 4

[0116] A method for preparing an alkaline water hydrogen production composite membrane comprises the following steps: In Example 1, "coprecipitation method, placing the wet membrane in water for 10 minutes" is replaced with "place the wet membrane in water for 1 hour." Other operations are the same as in Example 1. Performance testing is performed. The zirconium oxide utilization rate is tested to be 75%. The surface resistance is tested to be 1.5 Ω*cm. 2 .

[0117] Comparative Example 5

[0118] A method for preparing an alkaline water hydrogen production composite membrane comprises the following steps: "In Example 1: Coprecipitation method, place the wet membrane in water for 10 minutes, wait for the water and solvent to exchange, and then let it stand for 18 hours" is changed to: "Place the wet membrane in water for 10 minutes, wait for the water and solvent to exchange, and then let it stand for 3 hours." Other operations are the same as in Example 1. Performance testing is conducted. The zirconium oxide utilization rate is tested to be 80%. The membrane is immersed in ethanol for two hours, ultrasonically shaken, and immersed in 3 mol / L potassium hydroxide for 24 hours. The surface resistance is tested to be 1.1 Ω*cm. 2 .

[0119] It is worth mentioning that the hydrophilicity of the diaphragm is an important factor affecting the resistance of the diaphragm. Therefore, the present invention starts from the two aspects of improving the hydrophilicity of the diaphragm and the utilization rate of zirconium oxide to prepare a low-resistance composite membrane. Polyphenylene sulfide is selected as the base membrane material, and the immersion precipitation phase conversion method is used to improve the uniformity of slurry dispersion by controlling the humidity of the slurry preparation environment, and by controlling the steam bath standing temperature and time during slurry pre-evaporation, the co-precipitation time in the replacement solvent, and the drying step, the proportion and distribution of hydrophilic compounds in the composite membrane are controlled, more hydrophilic compounds are retained in the composite membrane, the utilization rate of hydrophilic compounds is increased to more than 80%, the transfer of hydrophilic compounds to the replacement solvent is reduced, the conductivity of the composite membrane is increased, and the cost of recycling hydrophilic compounds from the replacement solvent is reduced, the performance of the composite membrane is improved, and the production efficiency is improved and the cost is reduced. The calculation method of the hydrophilic compound utilization rate (retention rate) is as follows: the amount of hydrophilic compound used during slurry preparation W0; the amount of hydrophilic compound retained in the coating layer of the membrane after the diaphragm preparation is completed W1. Hydrophilic compound utilization rate (retention rate) = W1 / W0*100%.

[0120] The retention rate of hydrophilic compounds in the slurry is primarily related to the binder, the particle size of the hydrophilic compound, and the composite membrane preparation method. The larger the hydrophilic compound particle size, the smaller its surface area, and the smaller the binder ratio required. Therefore, under the same ratio conditions, the larger the hydrophilic compound particle size, the higher the retention rate. However, the lower the specific surface area, the lower the hydrophilicity, resulting in lower conductivity. The higher the density of polar groups such as hydroxyl and carboxyl groups in the binder, the better its adhesion. Therefore, it is necessary to select materials such as polysulfone or polyethersulfone with different functional group ratios and molecular weights. In the composite membrane preparation method, the coprecipitation time is the process of exchanging the solvent with the displacement solvent to precipitate the hydrophilic compound and binder into a membrane. The displacement solvent gradually penetrates from the surface to the center of the membrane. If this process is too short, the solvent in the membrane center is not completely replaced, resulting in incomplete precipitation, poor membrane uniformity, failed pore formation, and even membrane formation failure. If the process is too long, because the zirconium oxide and binder are still in the forming and uncured stage, the additives are transferred from the membrane to the aqueous phase under the action of the displacement solvent water, also carrying away some zirconium oxide, resulting in zirconium oxide loss. The present invention achieves a high retention rate of the hydrophilic compound in the slurry through better process time control, thereby improving the hydrophilicity of the diaphragm and exhibiting excellent conductivity performance.

[0121] Compared with the prior art, the present invention has the following positive effects:

[0122] By controlling the humidity of the slurry preparation environment, the uniformity of slurry dispersion is improved. By controlling the temperature and time of the steam bath during pre-evaporation, the pore size and distribution on the membrane surface are adjusted to form a relatively dense composite membrane surface layer. By controlling the co-precipitation time in the displacement solvent, the proportion and distribution of hydrophilic agent particles in the middle layer of the diaphragm are controlled. The subsequent drying step retains more hydrophilic compounds in the composite membrane, increasing the utilization rate of the hydrophilic compounds to over 80% and reducing the transfer of hydrophilic compounds to the displacement solvent. Finally, the membrane is placed in the displacement solvent again to displace the additives, completing the pore formation in the middle layer of the composite membrane. This method increases the conductivity of the composite membrane while reducing the cost of recycling hydrophilic compounds from the displacement solvent, improving the performance of the composite membrane, and at the same time increasing production efficiency and reducing costs.

[0123] The above contents involving common knowledge are not described in detail and can be understood by those skilled in the art.

[0124] The above descriptions are merely specific embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention shall be included within the scope of protection of the present invention. The technical scope of the present invention is not limited to the contents of the specification and must be determined according to the scope of the claims.

Claims

1. A method for preparing a composite membrane for water electrolysis, characterized in that: include: providing a base film; Providing a drying room for preparing the coating slurry, wherein the humidity in the drying room is not higher than 5%; A coating slurry is prepared in the drying chamber, wherein the coating slurry includes a binder, a solvent, a hydrophilic compound, and an additive, wherein the binder is selected from one or a combination of common bisphenol A type polysulfone (PSU), polyethersulfone (PES), polyvinylidene fluoride (PVDF), and polyethylene oxide (PEO); the solvent is selected from one or a combination of N-ethyl-pyrrolidone (NEP), N-methylpyrrolidone (NMP), dimethyl sulfoxide (DMSO), and dimethylformamide (DMF); the hydrophilic compound is selected from one or a combination of zirconium oxide, barium sulfate, zirconium phosphate, and titanium oxide; and the additive is selected from one or a combination of polyvinyl pyrrolidone (PVP), polyvinyl alcohol (PVA), and methyl cellulose (MC); Stirring and mixing the coating slurry in the drying chamber to dissolve the binder and additives in the solvent; Degassing the coating slurry; Applying the coating slurry on at least one side of the base film to form a wet film; and drying the wet film to form a composite film; The drying step comprises: a pre-evaporation step of performing a pre-evaporation treatment on the wet film to evaporate the solvent in the wet film, wherein the pre-evaporation treatment is performed at 50° C. for 0 or 2 minutes, or at room temperature for 2 minutes; and In the co-precipitation step, the wet film is placed in a first replacement solvent for 10 to 25 minutes so that the solvent in the wet film is replaced by the first replacement solvent and removed from the wet film. Since the binder and the hydrophilic compound are insoluble in the first replacement solvent, the binder and the hydrophilic compound are precipitated from the first replacement solvent. The wet film is taken out of the first replacement solvent and allowed to stand in the air for 4 to 24 hours to remove the first replacement solvent and the solvent. The wet film is then placed in a second replacement solvent so that the additives in the wet film are replaced by the second replacement solvent and removed from the wet film.

2. The method for preparing a composite membrane for water electrolysis according to claim 1, wherein: The first replacement solvent includes water, alcohol or a mixed solvent of water and alcohol in any proportion.

3. The method for preparing a composite membrane for water electrolysis according to claim 1, wherein: The wet film is placed in the second displacement solvent for 20 to 30 minutes, so that the additive in the wet film is replaced by the second displacement solvent and removed from the wet film.

4. The method for preparing a composite membrane for water electrolysis according to claim 1, wherein: The second replacement solvent includes water or a mixed solvent of water and alcohol in any proportion.

5. A composite membrane for water electrolysis, characterized in that: include: a basement membrane; and A coating layer is applied on at least one side of the base film to form a composite film, wherein the coating layer includes a binder and a hydrophilic compound, the content of the hydrophilic compound is greater than or equal to 60% and less than or equal to 85%, and the surface resistance of the composite film is not higher than 1.0Ω*cm 2 ; wherein the coating comprises a retention rate of the hydrophilic compound of 80% to 99.9%, and the retention rate of the hydrophilic compound is the retained amount of the hydrophilic compound of the coating divided by the amount of the hydrophilic compound used when the coating slurry is prepared; The composite membrane for water electrolysis is prepared by the method for preparing a composite membrane for water electrolysis according to any one of claims 1 to 4.

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