A composite membrane for alkaline water electrolysis, its preparation method and application

Abstract

This invention discloses a composite membrane for alkaline water electrolysis, its preparation method, and its application. The composite membrane comprises, in sequence, a polymer porous layer and a composite porous coating; wherein the composite porous coating contains a mesh-like support structure; the polymer porous layer is composed of polysulfone and chitosan; and the composite porous coating is composed of alkali-resistant polymer and inorganic nanoparticles. The composite membrane provided by this invention possesses high chemical and mechanical stability in strongly alkaline media, high porosity and small pore size, good wettability to alkaline solutions, low gas permeability, and low surface resistivity, while also suppressing the powder shedding problem of modified PPS membranes.

Description

Technical Field

[0001] This invention relates to the field of alkaline water electrolysis technology, and more specifically, to a composite diaphragm for alkaline water electrolysis, its preparation method, and its application. Background Technology

[0002] Hydrogen energy, as a renewable energy source, is characterized by high calorific value, zero pollution, and wide availability, and is considered one of the ideal energy carriers.

[0003] Alkaline water electrolysis is a mature green hydrogen production technology. An alkaline water electrolysis device includes an electrolytic cell, electrodes, and a diaphragm. When electricity is applied, hydrogen gas is generated at the cathode and oxygen gas at the anode. In traditional alkaline aqueous solution electrolysis processes, asbestos cloth or polyphenylene sulfide (PPS) cloth is typically used as a diaphragm to isolate the electrodes while simultaneously conducting hydroxide ions (OH-) from the electrolyte. - Connect the internal circuit. Due to the large pore size of asbestos cloth or polyphenylene sulfide (PPS), in order to avoid the safety hazards caused by the mixing of hydrogen and oxygen generated; at the same time, asbestos cloth and PPS cloth have poor hydrophilicity and high resistance in the tank, resulting in high system energy consumption and excessively high electrolysis cost.

[0004] Improving the membrane is one of the main methods to optimize water electrolysis for hydrogen production. For example, Chinese patent CN115029732A discloses a membrane for alkaline water electrolysis, which is made of organic polymer resin, pore-forming agent, inorganic nanoparticles, and support. This membrane has good wettability, but the interaction force between the polymer and the inorganic nanoparticles is low, resulting in a serious powder shedding problem during use, which prevents the membrane from meeting the performance requirements for water electrolysis for hydrogen production.

[0005] Therefore, how to solve the powder shedding problem of modified PPS membranes and develop membrane materials with high chemical and mechanical stability in strong alkaline media, good wettability to alkaline solutions, low gas permeability, low surface resistivity, simple processing, low cost, and suitability for industrial production to meet the needs of hydrogen production by water electrolysis is an urgent problem to be solved in this field. Summary of the Invention

[0006] The purpose of this invention is to overcome the above-mentioned defects in the prior art and provide a composite membrane for alkaline water electrolysis that has high chemical and mechanical stability in strong alkaline media, good wettability to alkaline solutions, low gas permeability and low surface resistivity, and can suppress the problem of powder shedding from modified PPS membranes, as well as its preparation method and application.

[0007] To achieve the above objectives, the technical solution of the present invention is as follows:

[0008] A composite membrane for alkaline water electrolysis, the composite membrane comprising: a polymer porous layer and a composite porous coating; wherein the composite porous coating contains a support with a mesh structure; the polymer porous layer is composed of polysulfone and chitosan; and the composite porous coating is composed of an alkali-resistant polymer and inorganic nanoparticles.

[0009] Optionally, the alkali-resistant polymer is polysulfone.

[0010] Optionally, the inorganic nanoparticles include at least one of zirconium oxide, titanium dioxide, and cerium oxide, with a particle size of 50-200 nm.

[0011] Optionally, the support is a polyphenylene sulfide mesh; the thickness of the support is 100-300 μm, and the mesh size is 20-200 mesh, preferably 100-150 mesh.

[0012] Optionally, the thickness of the composite membrane is 200-500 μm.

[0013] Optionally, the thickness of the polymer porous layer is 5-50 μm.

[0014] Optionally, the thickness of the composite porous coating is 150-495 μm.

[0015] Optionally, the average pore size of the polymer porous layer is 2-10 μm.

[0016] Optionally, the average pore size of the composite porous coating is 60-150 nm.

[0017] Optionally, the surface resistivity of the composite diaphragm is ≤0.30Ω / cm. 2 Bubble point pressure ≥ 3 bar.

[0018] Optionally, the contact angle between the composite diaphragm and the 30% KOH alkaline solution is ≤8°.

[0019] Optionally, the porosity of the composite membrane is ≥63%.

[0020] This invention also discloses a method for preparing the composite membrane for alkaline water electrolysis as described above, comprising the following steps:

[0021] S1. Mix the inorganic nanoparticles, alkali-resistant polymer, pore-forming agent and organic solvent 1 evenly to prepare the coating slurry;

[0022] S2. The coating slurry is applied to the surface of the support and cured by non-solvent-induced phase transition to form a composite porous coating, thereby obtaining the first diaphragm.

[0023] S3. Polysulfone and chitosan are miscible with organic solvent 2 to obtain a spinning solution;

[0024] S4. The spinning solution is electrospun onto the surface of the first diaphragm to form a porous polymer layer, which is then subjected to hot pressing to obtain the composite diaphragm for alkaline water electrolysis.

[0025] Optionally, in step S1, the coating slurry is prepared by adding 10-20 wt% polysulfone and 1-5 wt% pore-forming agent to 35-65 wt% organic solvent 1, stirring at 300-2000 r / min for 1-5 h at room temperature to obtain a polymer solution; adding 24-40 wt% zirconium oxide, stirring at 300-2000 r / min for 1-5 h at room temperature, then stirring at 50-100 r / min for 1-3 h, and allowing to stand for degassing for 2-6 h to obtain the coating slurry.

[0026] Optionally, in step S1, the pore-forming agent includes at least one of polyvinylpyrrolidone and polyvinyl alcohol; the organic solvent 1 includes one or more of N-methylpyrrolidone, N,N-dimethylformamide, and N,N-dimethylacetamide.

[0027] Optionally, in step S2, the method for preparing the first diaphragm is as follows:

[0028] The support is placed on a glass plate, and the coating slurry is applied to the support using a scraper to obtain a liquid film with a thickness of 300-650 μm.

[0029] The liquid film was pre-evaporated by being placed in a constant temperature and humidity chamber to obtain a primary film.

[0030] The primary membrane is placed in a coagulation bath for phase inversion for 1-10 minutes, then repeatedly soaked and washed with deionized water until the water is clear and not turbid. Finally, it is dried in an oven at 45-65℃ to obtain the first diaphragm.

[0031] Optionally, the pre-evaporation conditions are: temperature of 60-95℃, humidity of 35-50%, and pretreatment time of 15-45s.

[0032] Optionally, the temperature of the coagulation bath is 5-60°C; the solvent used in the coagulation bath includes a combination of deionized water and a second solvent; wherein the second solvent includes at least one of N-methylpyrrolidone, N,N-dimethylformamide, and N,N-dimethylacetamide; and the mass of the second solvent is 15-40% based on the total mass of deionized water and the second solvent being 100%.

[0033] Optionally, the soaking and washing is performed 3-5 times, with each soak lasting 5-20 minutes; the drying time is 15-30 minutes.

[0034] Optionally, in step S3, the spinning solution is prepared by mixing 5-10 wt% polysulfone, 5-10 wt% chitosan and 80-90 wt% organic solvent 2, and stirring and dissolving them in an oil bath at 50-100°C for 5-10 hours to obtain the spinning solution.

[0035] Optionally, the organic solvent 2 includes one or more of N-methylpyrrolidone, N,N-dimethylformamide, and N,N-dimethylacetamide.

[0036] Optionally, the electrospinning in step S4 includes: adding the spinning solution into a syringe, with the receiving end being a first diaphragm, and performing electrospinning under the conditions of a voltage of 15-30kV, an extrusion speed of 1.5-3ml / h, and a receiving distance of 8-25cm.

[0037] Optionally, the hot pressing treatment includes: hot pressing for 3-15 minutes at 80-120℃ and 5-15MPa.

[0038] The present invention also discloses a composite membrane for alkaline water electrolysis as described above, or the application of a composite membrane for alkaline water electrolysis prepared by the preparation method described above in alkaline water electrolysis for hydrogen production.

[0039] Implementing the embodiments of the present invention will have the following beneficial effects:

[0040] 1. The composite membrane for alkaline water electrolysis provided by this invention contains a support with a mesh structure to ensure the mechanical strength of the composite membrane; the composite porous coating provides the composite membrane with good hydrophilicity and low gas permeability; the chitosan in the polymer porous layer is rich in hydroxyl groups, which can improve the affinity with the electrolyte, and the cationicity of chitosan can neutralize or form micelles with anions, further improving the hydrophilicity of the composite membrane and reducing the sheet resistance; more importantly, the polymer porous layer can significantly suppress the problem of powder shedding of the modified PPS membrane for alkaline water electrolysis; ultimately endowing the composite membrane with excellent properties such as high chemical and mechanical stability, high porosity and small pore size, good wettability to alkaline solutions, low gas permeability and low sheet resistance in strongly alkaline media.

[0041] 2. The composite membrane for alkaline water electrolysis provided by this invention combines pre-evaporation and phase transformation to ultimately form a composite porous coating with a dense skin layer and a three-dimensional porous layer. The dense skin layer hinders hydrogen permeation and provides a high bubble point pressure; the three-dimensional porous layer imparts good wettability and low surface resistivity while retaining strong mechanical strength. This results in a composite membrane with excellent properties such as high mechanical stability, good wettability to alkaline solutions, low gas permeability, and low surface resistivity. Furthermore, the preparation method is easy to control and readily industrialized. Attached Figure Description

[0042] Figure 1 This is a morphological diagram of the composite membrane in Embodiment 1 of the present invention.

[0043] Figure 2 This is a morphological diagram of the composite diaphragm in Comparative Example 1 of the present invention. Detailed Implementation

[0044] The present invention will be further described below with reference to specific embodiments, but this does not limit the present invention in any way.

[0045] Example 1

[0046] A method for preparing a composite membrane for alkaline water electrolysis includes the following steps:

[0047] S1: Add 20wt% polysulfone and 5wt% polyvinylpyrrolidone to 51wt% N-methylpyrrolidone, and stir at 2000 rpm for 1 h at room temperature to obtain a polymer solution; add 24wt% zirconium oxide (particle size 50 nm), and continue stirring at 2000 rpm for 3 h at room temperature, then reduce the stirring speed to 100 rpm and continue stirring for 3 h, and let stand for 3 h to remove bubbles to obtain a coating slurry; place a polyphenylene sulfide mesh (200 μm thick, 150 mesh) on a glass plate, and use a scraper to apply the coating slurry... The coating slurry is applied to the support to obtain a liquid film with a thickness of 650 μm containing a porous support layer. The liquid film is pre-evaporated for 15 s in a constant temperature and humidity chamber at a temperature of 95℃ and a humidity of 50% to obtain a primary film. The primary film is placed in a 60℃ coagulation bath for phase inversion for 3 min. The solvent used in the coagulation bath is 65% deionized water and 35% N-methylpyrrolidone. The film is then soaked and washed three times with deionized water for 15 min each time until the water is clear and not cloudy. Finally, it is dried in a 45℃ oven for 30 min to obtain the first diaphragm.

[0048] S2: Mix 5wt% polysulfone, 10wt% chitosan and 85wt% N,N-dimethylformamide, and stir in an oil bath at 100℃ for 5h to obtain a spinning solution; add the spinning solution into a syringe, with the receiving end being the first diaphragm; perform electrospinning under the conditions of 18kV voltage, extrusion speed of 1.5ml / h and receiving distance of 12cm, and then hot press at 120℃ and 5MPa for 3min to obtain a composite diaphragm for alkaline water electrolysis with a thickness of 500μm.

[0049] Example 2

[0050] A method for preparing a composite membrane for alkaline water electrolysis includes the following steps:

[0051] S1: 17 wt% polysulfone and 3 wt% polyvinylpyrrolidone were added to 40 wt% N,N-dimethylacetamide and stirred at 1000 r / min for 3 h at room temperature to obtain a polymer solution; 40 wt% zirconium oxide (particle size 100 nm) was added, and stirring was continued at 1000 r / min for 5 h at room temperature, then the stirring speed was reduced to 80 r / min and stirring was continued for 2 h, followed by standing for degassing for 2 h to obtain a coating slurry; a polyphenylene sulfide mesh (thickness 300 μm, 100 mesh) was placed on a glass plate, and the above coating slurry was coated onto the support using a doctor blade to obtain a liquid film with a thickness of 650 μm including a porous support layer; the liquid film was pre-evaporated for 35 s in a constant temperature and humidity chamber at 60 °C and 45% humidity to obtain a primary film; the primary film was placed in a 50 °C coagulation bath for phase inversion for 1 min, and the solvent used in the coagulation bath was 60% deionized water and 40%... N,N-dimethylacetamide was then soaked and washed four times with deionized water for 5 minutes each time until the water was clear and not cloudy. Finally, it was dried in an oven at 65°C for 20 minutes to obtain the first diaphragm.

[0052] S2: Mix 10wt% polysulfone, 8wt% chitosan and 82wt% N,N-dimethylacetamide, and stir in an oil bath at 80℃ for 7h to obtain a spinning solution; add the spinning solution to a syringe, with the receiving end being the first diaphragm; perform electrospinning under conditions of 15kV voltage, extrusion speed of 2.5ml / h and receiving distance of 8cm, and then hot press at 100℃ and 15MPa for 5min to obtain a composite diaphragm for alkaline water electrolysis with a thickness of 500μm.

[0053] Example 3

[0054] A method for preparing a composite membrane for alkaline water electrolysis includes the following steps:

[0055] S1: 10 wt% polysulfone and 1 wt% polyvinyl alcohol were added to 65 wt% N,N-dimethylformamide and stirred at 300 r / min for 5 h at room temperature to obtain a polymer solution; 24 wt% zirconium oxide (particle size 200 nm) was added, and stirring was continued at 300 r / min for 1 h at room temperature, then the stirring speed was reduced to 50 r / min and stirred for another 1 h. The mixture was allowed to stand for 6 h to remove bubbles, resulting in a coating slurry; a polyphenylene sulfide mesh (100 μm thick, 120 mesh) was placed on a glass plate, and the above coating slurry was coated onto the support using a doctor blade to obtain a liquid film with a thickness of 300 μm containing a porous support layer; the liquid film was pre-evaporated for 45 s in a constant temperature and humidity chamber at 75 °C and 35% humidity to obtain a primary film; the primary film was placed in a 5 °C coagulation bath for phase inversion for 10 min. The solvent used in the coagulation bath was 85% deionized water and 15%... N,N-dimethylformamide was then soaked and washed five times with deionized water for 20 minutes each time until the water was clear and not cloudy. Finally, it was dried in an oven at 55°C for 15 minutes to obtain the first diaphragm.

[0056] S2: Mix 5 wt% polysulfone, 5 wt% chitosan, and 90 wt% N-methylpyrrolidone, and dissolve in an oil bath at 50°C for 10 h to obtain a spinning solution. Add the spinning solution to a syringe, with the receiving end serving as the first diaphragm. Perform electrospinning at a voltage of 30 kV, an extrusion speed of 2 ml / h, and a receiving distance of 25 cm to obtain a composite diaphragm containing a porous polymer layer. Subsequently, hot-press at 80°C and 8 MPa for 10 min to obtain a composite diaphragm for alkaline water electrolysis with a thickness of 200 μm.

[0057] Example 4

[0058] A method for preparing a composite membrane for alkaline water electrolysis includes the following steps:

[0059] S1: Add 20wt% polysulfone and 5wt% polyvinylpyrrolidone to 35wt% N-methylpyrrolidone, and stir at 2000 rpm for 1 h at room temperature to obtain a polymer solution; add 40wt% zirconium oxide (particle size 50 nm), and continue stirring at 2000 rpm for 3 h at room temperature, then reduce the stirring speed to 100 rpm and continue stirring for 3 h, and let stand for 3 h to remove bubbles to obtain a coating slurry; place a polyphenylene sulfide mesh (200 μm thick, 150 mesh) on a glass plate, and use a doctor blade to coat the above coating slurry onto the support to obtain a liquid film with a thickness of 550 μm including a porous support layer; pre-evaporate the liquid film in a constant temperature and humidity chamber at 85℃ and 40% humidity for 25 s to obtain a primary film; place the primary film in a 60℃ coagulation bath for phase inversion for 3 min, using 75% deionized water / 25%... N-methylpyrrolidone was then soaked and washed three times with deionized water for 15 minutes each time until the water was clear and not cloudy. Finally, it was dried in an oven at 45°C for 30 minutes to obtain the first diaphragm.

[0060] S2: Mix 10 wt% polysulfone, 10 wt% chitosan, and 80 wt% N,N-dimethylformamide, and stir in an oil bath at 100°C for 5 h to obtain a spinning solution. Add the spinning solution to a syringe, with the receiving end serving as the first diaphragm. Perform electrospinning at a voltage of 18 kV, an extrusion speed of 1.5 ml / h, and a receiving distance of 12 cm to obtain a composite diaphragm containing a porous polymer layer. Subsequently, hot-press at 120°C and 5 MPa for 35 min to obtain a composite diaphragm with a thickness of 450 μm for alkaline water electrolysis.

[0061] Comparative Example 1

[0062] A method for preparing a composite membrane for alkaline water electrolysis includes the following steps:

[0063] S1: Add 20wt% polysulfone and 5wt% polyvinylpyrrolidone to 51wt% N-methylpyrrolidone, and stir at 2000 rpm for 1 h at room temperature to obtain a polymer solution; add 24wt% zirconium oxide (particle size 50 nm), and continue stirring at 2000 rpm for 3 h at room temperature, then reduce the stirring speed to 100 rpm and continue stirring for 3 h, and let stand for 3 h to remove bubbles to obtain a coating slurry; place a polyphenylene sulfide mesh (200 μm thick, 150 mesh) on a glass plate, and use a scraper to apply the coating slurry... The coating slurry is applied to the support to obtain a liquid film with a thickness of 450 μm containing a porous support layer. The liquid film is pre-evaporated for 15 s in a constant temperature and humidity chamber at 95 °C and 50% humidity to obtain a primary film. The primary film is placed in a 60 °C coagulation bath for phase inversion for 3 min. The solvent used in the coagulation bath is 65% deionized water and 35% N-methylpyrrolidone. The film is then soaked and washed three times with deionized water for 15 min each time until the water is clear and non-turbid. Finally, it is dried in a 45 °C oven for 30 min to obtain the first diaphragm.

[0064] S2: The first diaphragm obtained in the previous step is hot-pressed at 120℃ and 5MPa for 3 minutes to obtain a composite diaphragm for alkaline water electrolysis with a thickness of 480μm.

[0065] Comparative Example 2

[0066] This comparative example uses a commercially available polyphenylene sulfide membrane with a thickness of 700 μm.

[0067] Test case

[0068] Performance Test 1: The membranes of Examples 1-4 and Comparative Examples 1-2 were subjected to performance tests. The specific test methods are as follows, and the test results are shown in Table 1 and 2. Figure 1-2 .

[0069] Porosity: The porosity of the composite membrane was determined using a gravimetric method. A 5cm x 5cm membrane sheet was thoroughly wetted with deionized water. The surface moisture was quickly and gently wiped away with filter paper, and the mass of the wet membrane was accurately weighed using an electronic analytical balance. Then, the membrane was vacuum dried at 60℃ for at least 3 hours, and the mass of the dry membrane was accurately weighed again. The formula for membrane porosity is as follows:

[0070]

[0071] Where ε is the porosity (%); ρ is the density of water (g / mL); and A is the membrane area (cm²). 2 ); l is the thickness of the membrane in the wet state (cm); m2 and m1 are the masses of the membrane in the wet and dry states (g), respectively.

[0072] Sheet resistance: Sheet resistance was determined using electrochemical impedance spectroscopy. A two-electrode system was employed. A 20.1mm × 20.1mm square window was cut between two 75mm × 75mm × 8mm PTFE plates. Two 20mm × 20mm × 0.5mm platinum plates were placed inside the window, with a diaphragm placed 3mm away from the platinum plates. The PTFE plates were securely fixed with PTFE screws and nuts. The plate was then placed in a beaker containing 30% KOH solution and placed in a water bath at a constant temperature of 30℃. Electrochemical impedance spectroscopy was measured using an electrochemical workstation.

[0073] The surface resistance of the diaphragm is calculated using the following formula:

[0074] Rs=(R1-R0)×S

[0075] In the formula: RS: sheet resistance of the diaphragm, Ω·cm 2 R0: Solution resistance between the two electrodes without a diaphragm, Ω; R1: Resistance between the chambers after adding a diaphragm, Ω; S: Electrode or diaphragm area, cm² 2 .

[0076] Bubble point pressure: The bubble point pressure of the diaphragm is determined by the bubble point method according to GB / T 2679.14-1996. First, the membrane is completely wetted with the test liquid water. Then, the gas pressure on the inlet side of the membrane is increased slowly, and the bubbling of the gas permeating through the membrane is observed. The pressure corresponding to the first continuous string of bubbles when the gas passes through the liquid seal layer of the membrane is the bubble point pressure.

[0077] Average pore size: The average pore size of the diaphragm was determined using the bubble point method according to GB / T 2679.14-1996. First, the membrane was completely wetted with the test liquid water. Then, the gas pressure on the inlet side of the membrane was increased slowly, and the bubbling of the gas permeating through the membrane side was observed. Finally, the average pore size of the diaphragm was output.

[0078] Tensile strength: The tensile strength of the diaphragm was tested using an electronic universal testing machine in accordance with the national standard GB1039-79. First, the diaphragm was cut into a strip sample with a length of 60 mm and a width of 10 mm. Then, a static tensile load was applied to the diaphragm under test on a tensile testing machine at 25±2℃ and a relative humidity of 65±5% to determine the tensile strength of the sample.

[0079] Contact angle: The contact angle of the membrane was measured using a contact angle meter. During the test, the membrane sample was placed flat on the sample stage, and 2 μL of 30wt% KOH was dropped onto the membrane surface using a graduated syringe. The baseline position was adjusted, and the data was recorded after 15 seconds. Each sample was tested at least three times.

[0080] Anti-detachment weight loss ratio (%): The diaphragm was placed in an ultrasonic vibrator and vibrated at 180W for 60s, and the diaphragm weight loss ratio was calculated.

[0081] Table 1. Test results of Examples 1-4 and Comparative Examples 1-2

[0082]

[0083] Depend on Figure 1 and Figure 2 As can be seen, the composite membrane in Example 1 of the present invention has a multilayer structure, comprising, in sequence: a porous polymer layer containing polysulfone and chitosan; a composite porous coating bonded to the porous polymer layer; and a support containing a mesh structure contained within the composite porous coating. Compared with Example 1, the composite membrane in Comparative Example 1 is identical to that without the porous polymer layer, except for the remaining components and structure.

[0084] As shown in Table 1, compared with Comparative Examples 1-2, the composite membranes described in Examples 1-4 exhibit high porosity, low sheet resistivity, high bubble point pressure, and high hydrophilicity, while maintaining high mechanical strength despite a relatively low thickness. The reasons for this are as follows: the multilayer structure of the composite membrane in this invention includes a support with a mesh-like structure that provides mechanical strength; the composite porous coating provides good hydrophilicity and low gas permeability; the chitosan in the polymer porous layer is rich in hydroxyl groups, which improves affinity with the electrolyte; and the cationic nature of chitosan can neutralize or form micelles with anions, further enhancing the hydrophilicity of the composite membrane and reducing sheet resistivity.

[0085] Furthermore, observation of Comparative Examples 1-2 reveals that the composite membrane in the embodiments of the present invention exhibits increased resistance to shedding. This is because, compared to Comparative Examples 1-2, the embodiments of the present invention incorporate a porous polymer layer, which significantly suppresses the powder shedding problem of the modified PPS membrane used in alkaline water electrolysis.

[0086] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the patent application. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the scope of protection of the present invention. Therefore, the scope of protection of this patent should be determined by the appended claims.

Claims

1. A composite separator for alkaline water electrolysis, characterized by, The composite diaphragm comprises, in sequence, a high-molecular porous layer and a composite porous coating layer; wherein the composite porous coating layer contains a support body with a grid structure; The high-molecular porous layer is composed of polysulfone and chitosan; The composite porous coating layer is composed of an alkali-resistant high-molecular polymer and inorganic nanoparticles; The inorganic nanoparticles include at least one of zirconium oxide, titanium dioxide and cerium oxide; The preparation method of the composite diaphragm for alkaline water electrolysis comprises the following steps: S1. Mixing inorganic nanoparticles, an alkali-resistant high-molecular polymer, a pore-forming agent and an organic solvent 1 uniformly to prepare a coating slurry; S2. Coating the coating slurry on the surface of a support body and curing by non-solvent induced phase inversion to form a composite porous coating layer, thereby obtaining a first diaphragm; S3. Dissolving polysulfone and chitosan in an organic solvent 2 to obtain a spinning solution; S4. Electrospinning the spinning solution on the surface of the first diaphragm to form a high-molecular porous layer, and then performing heat pressing treatment to obtain the composite diaphragm for alkaline water electrolysis; In step S2, the preparation method of the first diaphragm is as follows: Place the support body on a glass plate, use a doctor blade to coat the coating slurry on the support body, and obtain a liquid film with a thickness of 300-650 µm; Place the liquid film in a constant-temperature and constant-humidity box for pre-evaporation to obtain a primary film; Place the primary film in a coagulation bath for phase inversion for 1-10 min, then immerse and clean it in deionized water for multiple times until the water is transparent and not turbid, and finally place it in an oven at 45-65 °C for drying to obtain the first diaphragm.

2. The composite separator for alkaline water electrolysis according to claim 1, characterized by, The alkali-resistant high-molecular polymer is polysulfone; The particle size of the inorganic nanoparticles is 50-200 nm; The support body is polyphenylene sulfide mesh; The thickness of the support body is 100-300 µm, and the mesh opening number is 20-200.

3. The composite separator for alkaline water electrolysis according to claim 1, characterized by, The thickness of the composite diaphragm is 200-500 µm; The thickness of the high-molecular porous layer is 5-50 µm; The thickness of the composite porous coating layer is 150-495 µm; The average pore size of the high-molecular porous layer is 2-10 µm; The average pore size of the composite porous coating layer is 60-150 nm; The surface resistance of the composite separator is ≤0.30 Ω / cm 2 , the bubble point pressure is ≥3 bar; The contact angle of the composite diaphragm with 30% KOH lye is ≤8°; The porosity of the composite diaphragm is ≥63%.

4. The composite separator for alkaline water electrolysis according to claim 1, characterized by, In step S1, the preparation method of the coating slurry is as follows: add 10-20 wt% polysulfone and 1-5 wt% pore-forming agent to 35-65 wt% organic solvent 1, stir at 300-2000 r / min at room temperature for 1-5 h to obtain a polymer solution; add 24-40 wt% zirconium oxide, stir at 300-2000 r / min at room temperature for 1-5 h, then reduce the stirring speed to 50-100 r / min and continue stirring for 1-3 h, and stand for 2-6 h for defoaming to obtain the coating slurry; The pore-forming agent includes at least one of polyvinylpyrrolidone and polyvinyl alcohol; and the organic solvent 1 includes one or two or more of N-methylpyrrolidone, N,N-dimethylformamide and N,N-dimethylacetamide.

5. The composite separator for alkaline water electrolysis according to claim 1, characterized by, The pre-evaporation condition is that the temperature is 60-95℃, the humidity is 35-50%, and the pre-treatment time is 15-45s; The temperature of the coagulation bath is 5-60℃; The solvent used by the coagulation bath includes a combination of deionized water and a second solvent; wherein the second solvent includes at least one of N-methyl pyrrolidone, N,N-dimethylformamide, N,N-dimethylacetamide; the mass of the second solvent is 15-40% based on 100% of the total mass of deionized water and the second solvent; The number of times of the soaking cleaning is 3-5, and the time of each time is 5-20min; The drying time is 15-30min.

6. The composite separator for alkaline water electrolysis according to claim 1, characterized by, In the step S3, the preparation method of the spinning solution is that 5-10wt% of polysulfone, 5-10wt% of chitosan and 80-90wt% of an organic solvent 2 are mixed, stirred and dissolved under the condition of 50-100℃ oil bath for 5-10h to obtain the spinning solution; The organic solvent 2 includes one or two or more of N-methyl pyrrolidone, N,N-dimethylformamide and N,N-dimethylacetamide.

7. The composite separator for alkaline water electrolysis according to claim 1, characterized by, In the step S4, the electrospinning includes that the spinning solution is added into a syringe, the receiving end is a first diaphragm, and the electrospinning is performed under the condition that the voltage is 15-30kV, the extrusion speed is 1.5-3ml / h, and the receiving distance is 8-25cm. The heat pressing treatment includes that heat pressing is performed under the condition that the temperature is 80-120℃ and the pressure is 5-15MPa for 3-15min.

8. The application of the composite diaphragm for alkaline water electrolysis in claim 1-7 in the hydrogen production by alkaline water electrolysis.

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