Slurry for composite diaphragm, composite diaphragm, preparation method of composite diaphragm and application of composite diaphragm in alkaline water electrolysis

Abstract

The invention discloses slurry for a composite diaphragm, the composite diaphragm, a preparation method of the composite diaphragm and application of the composite diaphragm in alkaline water electrolysis, and belongs to the field of diaphragms for hydrogen production through water electrolysis. The composite diaphragm is prepared from a porous support layer double-sided composite porous coating; wherein the solid components of the porous coating comprise an inorganic nano material, an alkali-resistant high-molecular polymer and a hydrophilic sulfonated polymer; and the porous supporting layer is a polyphenylene sulfide net. The composite diaphragm has a multi-layer structure and sequentially comprises a first compact skin layer, a finger-shaped porous layer, a three-dimensional porous layer and a second compact skin layer, wherein the three-dimensional porous layer contains a porous supporting layer. The composite diaphragm has the advantages of high chemical and mechanical stability, high porosity, small aperture, good wettability to alkali liquor, low gas permeability, low surface resistance and the like in a strong alkali medium.

Description

TECHNICAL FIELD

[0001] The present application relates to a slurry for composite diaphragm, composite diaphragm and its preparation method and application in alkaline water electrolysis, belonging to the field of hydrogen production by electrolysis of water. BACKGROUND

[0002] Hydrogen energy, as a kind of renewable energy, has high combustion heat, no pollution and wide sources, and is regarded as one of the ideal energy carriers. Alkaline water electrolysis, as a mature green hydrogen production technology, has room for further energy consumption reduction. Generally, alkaline water electrolysis device includes electrolytic cell, electrode and diaphragm, hydrogen is generated at the cathode side and oxygen is generated at the anode side when power is on.

[0003] For the diaphragm used in alkaline water electrolysis, it is required to have ion permeability, mechanical strength, gas tightness, electrical insulation and other performances. In the traditional alkaline water electrolysis process, asbestos cloth or polyphenylene sulfide (PPS) cloth is usually used as diaphragm to isolate the electrodes, while conducting the hydroxyl ions (OH-) in the electrolyte to connect the internal circuit. Although the asbestos diaphragm has low cost, it has many disadvantages, such as asbestos fibers easy to fall off, carcinogenicity, high impedance, high energy consumption, etc. Although in recent years, the mainstream diaphragm for hydrogen production by alkaline electrolysis of water has been replaced by PPS diaphragm, there are still problems of low gas tightness, high electrical resistance and high energy consumption.

[0004] Therefore, it is an urgent problem to be solved in the field to develop a diaphragm material with high chemical and mechanical stability, high porosity and small pore size, good wettability to alkaline solution, low gas permeability, low surface resistance, simple process, low cost and suitable for industrial production in strong alkaline medium, to meet the demand of hydrogen production by electrolysis of water. SUMMARY

[0005] According to the first aspect of the present application, a slurry for composite diaphragm is provided. The slurry composition contains hydrophilic sulfonated polymer and alkali-resistant hydrophilic inorganic nanomaterial as hydrophilic component, and alkali-resistant high molecular polymer as film-forming material, pore-forming agent for assisting pore formation, and finally a composite diaphragm material with high liquid affinity, high chemical stability and high porosity can be prepared.

[0006] A slurry for composite diaphragm, the slurry for composite diaphragm comprises 5-10wt% of alkali-resistant high molecular polymer, 5-10wt% of hydrophilic sulfonated polymer, 1-5wt% of pore-forming agent, 35-65wt% of polar solvent, 24-40wt% of inorganic nanomaterial.

[0007] Optionally, the alkali-resistant high molecular polymer is polysulfone;

[0008] The hydrophilic sulfonated polymer is selected from at least one of sulfonated polysulfone, sulfonated polyether sulfone, sulfonated polyether ether ketone, and the sulfonation degree is 20-40%.

[0009] The pore-forming agent is selected from at least one of polyvinylpyrrolidone, polyvinyl alcohol;

[0010] The polar solvent is selected from at least one of N-methylpyrrolidone, N,N-dimethylformamide, N,N-dimethylacetamide;

[0011] The inorganic nanomaterial is selected from at least one of zirconium dioxide, titanium dioxide, cerium oxide, and has a particle size of 50-200 nm.

[0012] Optionally, the slurry for the composite separator is composed of 5-10 wt% of alkali-resistant high molecular polymer, 5-10 wt% of hydrophilic sulfonated polymer, 1-5 wt% of pore-forming agent, 35-65 wt% of polar solvent, and 24-40 wt% of inorganic nanomaterial.

[0013] According to a second aspect of the present application, a preparation method of a slurry for a composite separator is provided.

[0014] The preparation method of the slurry for the composite separator described above comprises:

[0015] The alkali-resistant high molecular polymer, the hydrophilic sulfonated polymer, and the pore-forming agent are added to the polar solvent, and stirring is performed at 300-2000 r / min at room temperature for 1-5 h to obtain a polymer solution;

[0016] The inorganic nanomaterial is added, and stirring is continued at 300-2000 r / min at room temperature for 1-5 h, the stirring speed is reduced to 50-100 r / min, and stirring is continued for 1-3 h, and standing is performed for 2-6 h to remove bubbles to obtain the slurry for the composite separator.

[0017] According to a third aspect of the present application, a composite separator is provided. The composite separator has excellent properties of high chemical and mechanical stability in a strong alkali medium, high porosity and small pore size, good wettability to lye, low gas permeability, and low surface resistance.

[0018] A composite separator is made of a porous support layer and a porous coating layer on both sides of the porous support layer;

[0019] The solid components of the porous coating layer include inorganic nanomaterial, alkali-resistant high molecular polymer, and hydrophilic sulfonated polymer.

[0020] The porous support layer is a polyphenylene sulfide net.

[0021] Optionally, the composite separator has a multilayer structure, which comprises, in sequence, a first dense skin layer, a finger-shaped porous layer, a three-dimensional porous layer, and a second dense skin layer.

[0022] The three-dimensional porous layer contains a porous support layer;

[0023] The thickness of the composite separator is 200-500 μm;

[0024] The thickness of the first dense skin layer is 1-10 μm;

[0025] The thickness of the porous support layer is 100-300 μm;

[0026] The porosity of the composite separator is ≥65%;

[0027] The pore size of the first dense skin layer is ≤80 nm;

[0028] The size of the polyphenylene sulfide mesh is 20-200 mesh.

[0029] Optionally, the surface resistance of the composite separator is ≤0.25 Ω / cm 2 ;

[0030] The bubble point pressure of the composite separator is ≥3 bar;

[0031] The tensile strength of the composite separator is ≥30 MPa;

[0032] The contact angle of the composite separator with 30% KOH lye is ≤10°.

[0033] In the present application, the porous support layer in a grid-like interwoven manner can significantly enhance the mechanical strength of the composite separator; the addition of inorganic nanoparticles and hydrophilic sulfonated polymers enhances the hydrophilicity of the composite separator.

[0034] In the present application, in the multi-layer structure of the composite separator, the dense skin layer hinders hydrogen permeation, providing a high bubble point pressure; the finger-like porous layer and the three-dimensional porous layer endow the composite separator with good wettability and low surface resistance, while retaining strong mechanical strength. Ultimately, the composite separator is endowed with excellent properties of high mechanical stability, good wettability to lye, low gas permeability and low surface resistance.

[0035] According to a fourth aspect of the present application, a preparation method of a composite separator is provided. The preparation method is convenient to control, and can prepare a composite separator material with high quality.

[0036] The preparation method of the composite separator described above, the preparation method comprises:

[0037] S1 placing a porous support layer polyphenylene sulfide mesh on a substrate, coating the composite separator with a slurry on the porous support layer to obtain a liquid film;

[0038] The slurry for the composite separator is selected from the slurry for the composite separator described above;

[0039] S2 pre-treats the liquid membrane to obtain a primary membrane;

[0040] S3 phase-inverts and post-treats the primary membrane to obtain the composite separator.

[0041] Optionally, in step S1, the thickness of the liquid membrane is 300-650 μm;

[0042] In step S2, the pre-treatment comprises: pre-evaporating the liquid membrane while standing, the pre-evaporation being under the conditions of a temperature of 60-95 ℃, a humidity of 35-50%, and a pre-treatment time of 15-45 s;

[0043] In step S3, the primary membrane is placed in a coagulation bath for phase inversion for 1-10 min, then immersed in water for cleaning until the water is transparent and not turbid, and finally dried in an oven at 45-65 ℃ to obtain the composite separator.

[0044] Optionally, the liquid membrane comprises a porous support layer.

[0045] Optionally, the liquid membrane is pre-evaporated while standing in a constant-temperature and constant-humidity box, which is easy to form a thin dense skin layer on the surface of the membrane and is also helpful to adjust the pore size of the membrane.

[0046] Optionally, in step S3, the temperature of the coagulation bath is 5-60 ℃;

[0047] The coagulation bath is selected from a combination of water and an organic solvent, wherein the organic solvent is at least one selected from N-methylpyrrolidone, N,N-dimethylformamide and N,N-dimethylacetamide;

[0048] The mass of the organic solvent is 15-40% based on the total mass of water and the organic solvent being 100%;

[0049] The number of times of the immersion cleaning is 3-5, and the time of each immersion is 5-20 min;

[0050] The time of the drying is 15-30 min.

[0051] In the present application, the slurry composition for the composite separator contains hydrophilic sulfonated polymer and alkali-resistant hydrophilic inorganic nano-material as the hydrophilic component, which endows the separator with extremely high liquid affinity; the alkali-resistant polymer is used as the film-forming material, which endows the separator with high alkali resistance; the pore-forming agent is used to assist pore formation, and the pre-evaporation and phase inversion are combined, so that a multi-layer structure composite separator is finally obtained, which has high mechanical strength, low gas permeability and low surface resistance. Finally, a composite separator material with high liquid affinity, high chemical stability, high porosity, low gas permeability and low surface resistance can be obtained.

[0052] According to a fifth aspect of the present application, a composite separator is provided.

[0053] The application of the composite diaphragm described above in alkaline water electrolysis, the composite diaphragm is used as an alkaline electrolytic water diaphragm.

[0054] The composite diaphragm has the advantages of high chemical and mechanical stability, high porosity and small pore size, good wetting property to alkaline solution, low gas permeability and low surface resistance in a strong alkali medium.

[0055] The beneficial effects that can be produced by the present application include:

[0056] 1) The composite diaphragm provided by the present application has extremely high liquid affinity, which is due to the fact that the hydrophilic sulfonated polymer and the alkali-resistant hydrophilic inorganic nanomaterials are used as the hydrophilic components. The composite diaphragm has the advantages of high liquid affinity, high chemical stability, high porosity, low gas permeability and low surface resistance.

[0057] 2) The preparation method of the composite diaphragm provided by the present application combines pre-evaporation and phase inversion to finally obtain a composite diaphragm with a multi-layer structure. In the multi-layer structure of the composite diaphragm, the dense skin layer hinders hydrogen permeation and provides a high bubble point pressure; the finger-shaped porous layer and the three-dimensional porous layer endow the composite diaphragm with good wettability and low surface resistance, while retaining strong mechanical strength. Finally, the composite diaphragm has excellent properties such as high mechanical stability, good wettability to alkaline solution, low gas permeability and low surface resistance. BRIEF DESCRIPTION OF DRAWINGS

[0058] Figure 1 is a morphology diagram of the composite diaphragm in Example 1 of the present application. DETAILED DESCRIPTION

[0059] The present application will be described in detail below in conjunction with examples, but the present application is not limited to these examples.

[0060] Unless otherwise specified, the raw materials in the examples of the present application are purchased through commercial channels.

[0061] Unless otherwise specified, the test methods all use conventional methods, and the instrument settings all use the recommended settings of the manufacturers.

[0062] Example 1

[0063] The preparation of the composite diaphragm includes the following steps:

[0064] 1) Preparation of slurry: 5wt% polysulfone, 5wt% sulfonated polysulfone and 1wt% polyvinylpyrrolidone were added to 65wt% N-methylpyrrolidone, and stirred at 1000r / min for 5h at room temperature to obtain a polymer solution; 24wt% zirconium dioxide was added, and the stirring was continued at 1000r / min for 1h at room temperature, the stirring speed was then reduced to 50r / min, and the stirring was continued for 3h, and the slurry was left to stand for 3h to remove bubbles, obtaining a milky white slurry.

[0065] 2) Composite separator preparation: The polyphenylene sulfide net was placed on a glass plate, and the above-mentioned milky white slurry was coated on the porous support layer using a doctor blade to obtain a liquid film with a thickness of 400 pm including the porous support layer; the liquid film was pretreated in a constant temperature and humidity box at a temperature of 60°C and a humidity of 50% for 15 s to obtain a primary film; the primary film was placed in a coagulation bath at 40°C for phase inversion for 1 min, then soaked and washed with deionized water for 3 times, each time for 5 min, until the water was transparent and not turbid, and finally placed in a 65°C oven for drying for 30 min, to obtain the composite separator.

[0066] In this embodiment, the sulfonation degree of the sulfonated polysulfone is 30%; the particle size of the zirconium dioxide is 50 nm; the thickness of the polyphenylene sulfide net is 100 pm, and the specification is 150 mesh; and the coagulation bath is 65% deionized water / 35% N-methyl pyrrolidone.

[0067] The composite separator obtained in this embodiment has a thickness of 200 pm; a porosity of 70%; a pore size of the first dense skin layer of 70 nm, a thickness of the first dense skin layer of 10 pm; a surface resistance of 0.2 Ω / cm 2 ; a bubble point pressure of 3.5 bar; a tensile strength of 35 MPa; and a contact angle with 30% KOH lye of 5°.

[0068] Example 2

[0069] Composite separator preparation, including the following steps:

[0070] 1) Slurry preparation: 10 wt% polysulfone, 6 wt% sulfonated polyether sulfone, and 5 wt% polyvinylpyrrolidone were added to 39 wt% N,N-dimethylformamide, stirred at 2000 r / min at room temperature for 4 h to obtain a polymer solution; 30 wt% zirconium dioxide and 10 wt% titanium dioxide were added, and stirring was continued at 2000 r / min at room temperature for 3 h, the stirring speed was reduced to 100 r / min, and stirring was continued for 1 h, and the solution was left to stand for 2 h to remove bubbles to obtain a milky white slurry.

[0071] 2) Composite separator preparation: The polyphenylene sulfide net was placed on a glass plate, and the above-mentioned milky white slurry was coated on the porous support layer using a doctor blade to obtain a liquid film with a thickness of 650 pm including the porous support layer; the liquid film was pretreated in a constant temperature and humidity box at a temperature of 95°C and a humidity of 35% for 20 s to obtain a primary film; the primary film was placed in a coagulation bath at 5°C for phase inversion for 3 min, then soaked and washed with deionized water for 4 times, each time for 6 min, until the water was transparent and not turbid, and finally placed in a 50°C oven for drying for 15 min, to obtain the composite separator.

[0072] In this example, the sulfonation degree of the sulfonated polyether sulfone is 40%; the particle size of the zirconium dioxide is 50 nm, and the particle size of the titanium dioxide is 100 nm; the thickness of the polyphenylene sulfide net is 300 μm, and the specification is 100 mesh; the coagulation bath is 60% deionized water / 40% N,N-dimethylformamide.

[0073] In this example, the thickness of the composite separator obtained is 500 μm; the porosity is 65%; the pore size of the first dense skin layer is 80 nm, and the thickness of the first dense skin layer is 8 μm; the surface resistance is 0.25 Ω / cm 2 ; the bubble point pressure is 3 bar; the tensile strength is 40 MPa; and the contact angle with 30% KOH lye is 8°.

[0074] Example 3

[0075] The preparation of the composite separator includes the following steps:

[0076] 1) Preparation of the slurry: 8 wt% of polysulfone, 10 wt% of sulfonated polyether ether ketone, and 2 wt% of polyvinyl alcohol are added to 45 wt% of N,N-dimethylacetamide, stirred at 2000 r / min at room temperature for 1 h to obtain a polymer solution; 30 wt% of zirconium dioxide and 5 wt% of cerium oxide are added, and stirring is continued at 300 r / min at room temperature for 5 h, the stirring speed is reduced to 80 r / min, and stirring is continued for 2 h, and the slurry is left to stand for 6 h to remove bubbles to obtain a milky white slurry.

[0077] 2) Preparation of the composite separator: the polyphenylene sulfide net is placed on a glass plate, and the above-mentioned milky white slurry is coated on the porous support layer using a doctor blade to obtain a liquid film with a thickness of 300 μm containing the porous support layer; the liquid film is pretreated in a constant temperature and humidity box at a temperature of 65°C and a humidity of 40% for 45 s to obtain a primary film; the primary film is placed in a coagulation bath at 60°C for phase inversion for 10 min, and then immersed in deionized water for cleaning 5 times, each time for 20 min, until the water is transparent and not turbid, and finally placed in a 45°C oven for drying for 20 min to obtain the composite separator.

[0078] In this example, the sulfonation degree of the sulfonated polyether ether ketone is 20%; the particle size of the zirconium dioxide is 50 nm, and the particle size of the cerium oxide is 200 nm; the thickness of the polyphenylene sulfide net is 150 μm, and the specification is 100 mesh; the coagulation bath is 85% deionized water / 15% N,N-dimethylacetamide.

[0079] In this example, the thickness of the composite separator obtained is 220 μm; the porosity is 75%; the pore size of the first dense skin layer is 60 nm, and the thickness of the first dense skin layer is 2 μm; the surface resistance is 0.25 Ω / cm 2 ; the bubble point pressure is 3 bar; the tensile strength is 31 MPa; and the contact angle with 30% KOH lye is 10°.

[0080] Example 4

[0081] Preparation of the composite separator, comprising the following steps:

[0082] 1) Preparation of the slurry: 10wt% polysulfone, 10wt% sulfonated polysulfone, 5wt% polyvinylpyrrolidone were added into 35wt% N-methylpyrrolidone, stirred at 300r / min for 5h at room temperature, to obtain a polymer solution; 40wt% zirconium dioxide was added, and stirring was continued at 2000r / min for 2h at room temperature, the stirring speed was reduced to 100r / min, and stirring was continued for 3h, and the slurry was left to stand for 3h to remove bubbles, to obtain a milky white slurry.

[0083] 2) Preparation of the composite separator: the polyphenylene sulfide net was placed on a glass plate, and the above-mentioned milky white slurry was coated on the porous support layer using a scraper to obtain a liquid film with a thickness of 400μm containing the porous support layer; the liquid film was pretreated in a constant temperature and humidity box at a temperature of 60℃ and a humidity of 50% for 15s to obtain a primary film; the primary film was placed in a coagulation bath at 50℃ for phase inversion for 2min, and then soaked and washed with deionized water for 3 times, each for 5min, until the water was transparent and not turbid, and finally dried in an oven at 65℃ for 20min, to obtain the composite separator.

[0084] In this example, the sulfonation degree of the sulfonated polysulfone was 20%; the particle size of the zirconium dioxide was 50nm; the thickness of the polyphenylene sulfide net was 100μm, and the specification was 150 mesh; and the coagulation bath was 70% deionized water / 30% N-methylpyrrolidone.

[0085] The composite separator obtained in this example had a thickness of 200μm; a porosity of 75%; a pore size of the first dense skin layer of 80nm, a thickness of the first dense skin layer of 1μm; a surface resistance of 0.2Ω / cm 2 ; a bubble point pressure of 3.8bar; a tensile strength of 30MPa; and a contact angle with 30% KOH lye of 5°.

[0086] Comparative Example 1

[0087] Comparative Example 1 was a commercial polyphenylene sulfide separator with a thickness of 700μm.

[0088] Comparative Example 2

[0089] Preparation of the composite separator, comprising the following steps:

[0090] 1) Preparation of the slurry: 10wt% polysulfone, 1wt% polyvinylpyrrolidone were added into 65wt% N-methylpyrrolidone, stirred at 1000r / min for 5h at room temperature, to obtain a polymer solution; 24wt% zirconium dioxide was added, and stirring was continued at 1000r / min for 1h at room temperature, the stirring speed was reduced to 50r / min, and stirring was continued for 3h, and the slurry was left to stand for 3h to remove bubbles, to obtain a milky white slurry.

[0091] 2) Composite separator preparation: The polyphenylene sulfide net was placed on a glass plate, and the above-mentioned milky white slurry was coated on the porous support layer using a doctor blade to obtain a liquid film with a thickness of 400 μm comprising the porous support layer; the liquid film was pretreated in a constant temperature and humidity chamber at a temperature of 60°C and a humidity of 50% for 15 s to obtain a primary film; the primary film was placed in a coagulation bath at 40°C for phase inversion for 1 min, and then soaked and washed with deionized water for 3 times, each time for 5 min, until the water was transparent and not turbid, and finally placed in an oven at 65°C for drying for 30 min to obtain the composite separator.

[0092] In this embodiment, the particle size of zirconium dioxide was 50 nm; the thickness of the polyphenylene sulfide net was 100 μm, and the specification was 150 meshes; and the coagulation bath was 65% deionized water / 35% N-methyl pyrrolidone.

[0093] The composite separator obtained in this embodiment had a thickness of 200 μm.

[0094] Performance test:

[0095] The separators obtained in Examples 1 to 4 and Comparative Examples 1 to 2 were subjected to performance tests, and the specific test methods were as follows, and the test results are shown in Table 1 and Table 2. Figure 1 .

[0096] Porosity: The porosity of the composite separator was determined by weighing method. A 5 cm*5 cm film piece was taken and fully wetted with deionized water. The water on the surface of the separator was quickly and lightly wiped off with filter paper, and the mass of the wet film was accurately weighed with an electronic analytical balance. Then the film was vacuum dried at 60°C for more than 3 h, and the mass of the dry film was accurately weighed. The porosity formula of the film is as follows:

[0097] ε = (m2-m1) / (p*A*l)

[0098] Wherein ε is the porosity;

[0099] p is the density of water (g / mL);

[0100] A is the area of the film piece (cm 2 );

[0101] L is the thickness of the film piece in wet state (cm);

[0102] m2 and m1 are the masses of the film piece in wet state and dry state respectively (g).

[0103] Surface resistance: The surface resistance was measured by electrochemical impedance method. A two-electrode system was used. A 20.1 mm x 20.1 mm square window was opened in the middle of two 75 mm x 75 mm x 8 mm polytetrafluoroethylene plates, two 20 mm x 20 mm x 0.5 mm platinum plates were placed in the window, a separator was placed in the middle of the platinum plates, and the separator was 3 mm away from the platinum plates. The polytetrafluoroethylene plates were tightly fixed with polytetrafluoroethylene screws and nuts. The system was placed in a beaker containing 30% KOH solution, and the beaker was placed in a water bath at 30°C. The electrochemical impedance was measured by an electrochemical workstation.

[0104] The surface resistance of the separator was calculated by the following formula:

[0105] Rs = (R1 - R0) x S

[0106] In the formula: Rs - surface resistance of the separator, Ω-cm 2 ; R0 - solution resistance between the two electrodes without a separator, Ω; R1 - resistance between the two chambers after adding the separator, Ω; S - electrode or separator area, cm 2 .

[0107] Bubble point pressure: The bubble point pressure of the separator was measured by the bubble point method according to GB / T 2679.14-1996. First, the membrane was completely immersed in the test liquid water, then the gas pressure on the membrane side was increased at a slow speed, and the bubbling of the gas through the membrane side was observed. When the first continuous bubble string appeared through the liquid seal layer of the membrane, the corresponding pressure was the bubble point pressure.

[0108] Tensile strength: The tensile strength of the separator was tested according to the national standard GB1039-79 using an electronic universal testing machine. First, the separator was cut into a long strip-shaped sample with a length of 60 mm and a width of 10 mm, then under the conditions of 25±2°C and relative humidity of 65±5%, the measured separator was subjected to static tensile load on the tensile testing machine to determine the tensile strength of the sample.

[0109] Contact angle: The contact angle of the membrane was measured by a contact angle measuring instrument. During testing, the membrane sample was placed flat on the sample stage, 2 μL of 30 wt% KOH was dropped on the membrane surface with a graduated syringe, the baseline position was adjusted, and the data was recorded after 15 s. Each sample was tested at least three times.

[0110] Table 1

[0111]

[0112]

[0113] From Figure 1It can be known that the composite diaphragm in the embodiment 1 of the application comprises a plurality of layers, and sequentially comprises a first dense skin layer, a finger-shaped porous layer, a three-dimensional porous layer and a second dense skin layer; wherein the three-dimensional porous layer comprises a porous support layer.

[0114] As shown in Table 1, compared with the comparative example 1, the composite diaphragm in the embodiment 1-4 has high porosity, low surface resistance, high bubble point pressure and high wettability, and meanwhile, has high mechanical strength in the case of low thickness. The reason is analyzed as follows: the hydrophilic sulfonated polymer and the alkali-resistant hydrophilic inorganic nano-material in the application are used as the hydrophilic component together, which endows the diaphragm with extremely high wettability; and the commercial polyphenylene sulfide film has poor wettability, so that the composite diaphragm in the application has extremely high affinity with the 30wt% KOH electrolyte. Meanwhile, the pre-evaporation and phase inversion are used in the application, and finally the composite diaphragm with a plurality of layers is prepared. In the plurality of layers of the composite diaphragm, the dense skin layer hinders the hydrogen permeation, and provides high bubble point pressure; the finger-shaped porous layer and the three-dimensional porous layer endow the diaphragm with good wettability and low surface resistance, and meanwhile, retain high mechanical strength. Finally, the composite diaphragm is endowed with high mechanical stability, good wettability to the alkali solution, low gas permeability and low surface resistance.

[0115] In addition, it can be found from the observation of the comparative example 2 that the composite diaphragm in the comparative example 2 also has the advantages of high porosity, low surface resistance, high bubble point pressure, high wettability and high mechanical strength, but compared with the composite diaphragm in the embodiment of the application, the composite diaphragm in the embodiment of the application has better affinity with the alkali solution. This is because compared with the comparative example 2, the hydrophilic sulfonated polymer material is added in the embodiment of the application, which further improves the wettability of the composite diaphragm.

[0116] The above is only several embodiments of the application, and does not limit the application in any form. Although the application is disclosed with the preferred embodiments, it is not intended to limit the application. Any skilled person in the art can make some changes or modifications to the above disclosed technical contents without departing from the scope of the technical solution of the application, and the equivalent embodiments are equivalent to the equivalent embodiments, which are all within the scope of the technical solution.

Claims

1. A slurry for composite diaphragms, characterized in that, The composite diaphragm slurry comprises 5-10 wt% of alkali-resistant polymer, 5-10 wt% of hydrophilic sulfonated polymer, 1-5 wt% of pore-forming agent, 35-65 wt% of polar solvent, and 24-40 wt% of inorganic nanomaterials.

2. The slurry for composite diaphragms according to claim 1, characterized in that, The alkali-resistant polymer is polysulfone; The hydrophilic sulfonated polymer is selected from at least one of sulfonated polysulfone, sulfonated polyethersulfone, and sulfonated polyether ether ketone, and the degree of sulfonation is 20-40%. The pore-forming agent is selected from at least one of polyvinylpyrrolidone and polyvinyl alcohol; The polar solvent is selected from at least one of N-methylpyrrolidone, N,N-dimethylformamide, and N,N-dimethylacetamide; The inorganic nanomaterial is selected from at least one of zirconium dioxide, titanium dioxide, and cerium oxide, and has a particle size of 50-200 nm.

3. The method for preparing the slurry for composite diaphragms according to claim 1 or 2, characterized in that, The preparation method includes: An alkali-resistant polymer, a hydrophilic sulfonated polymer, and a pore-forming agent are added to a polar solvent and stirred at 300-2000 r / min for 1-5 h at room temperature to obtain a polymer solution. Add inorganic nanomaterials and continue stirring at 300-2000 r / min for 1-5 h at room temperature. Reduce the stirring speed to 50-100 r / min and continue stirring for 1-3 h. Let stand to degas for 2-6 h to obtain the slurry for the composite diaphragm.

4. A composite diaphragm, characterized in that, The composite diaphragm is made of a porous support layer with a double-sided composite porous coating. The solid components of the porous coating include inorganic nanomaterials, alkali-resistant polymers, and hydrophilic sulfonated polymers. The porous support layer is a polyphenylene sulfide mesh.

5. The composite diaphragm according to claim 4, characterized in that, The composite membrane has a multi-layer structure, which includes, in sequence: a first dense skin layer, a finger-like porous layer, a three-dimensional porous layer, and a second dense skin layer. The three-dimensional porous layer contains a porous support layer; The thickness of the composite diaphragm is 200–500 μm; The thickness of the first dense cortex is 1–10 μm; The thickness of the porous support layer is 100-300 μm; The porosity of the composite membrane is ≥65%; The pore size of the first dense skin layer is ≤80nm; The polyphenylene sulfide mesh has a mesh size of 20 to 200.

6. The composite diaphragm according to claim 4, characterized in that, The surface resistivity of the composite diaphragm is ≤0.25Ω / cm. 2 ; The bubble point pressure of the composite diaphragm is ≥3 bar; The tensile strength of the composite diaphragm is ≥30MPa; The contact angle between the composite diaphragm and the 30% KOH alkaline solution is ≤10°.

7. The method for preparing the composite diaphragm according to any one of claims 4 to 6, characterized in that, The preparation method includes: S1. A porous support layer of polyphenylene sulfide mesh is placed on a substrate, and a composite membrane is coated onto the porous support layer with a slurry to obtain a liquid film. The slurry for the composite diaphragm is selected from the slurry for the composite diaphragm as described in claim 1 or 2; S2 pre-treats the liquid membrane to obtain the primary membrane; S3 involves phase transformation and post-processing of the primary membrane to obtain the composite membrane.

8. The preparation method according to claim 7, characterized in that, In step S1, the thickness of the liquid film is 300–650 μm; In step S2, the pretreatment includes: allowing the liquid film to stand for pre-evaporation, wherein the pre-evaporation conditions are: temperature 60-95℃, humidity 35-50%, and pretreatment time 15-45s. In step S3, the primary membrane is placed in a coagulation bath for phase inversion for 1 to 10 minutes, then soaked and washed with water until the water is clear and not cloudy, and finally dried in an oven at 45 to 65°C to obtain the composite membrane.

9. The preparation method according to claim 8, characterized in that, In step S3, the temperature of the coagulation bath is 5–60°C; The coagulation bath is selected from a combination of water and an organic solvent, wherein the organic solvent is selected from at least one of N-methylpyrrolidone, N,N-dimethylformamide, and N,N-dimethylacetamide; The organic solvent comprises 15-40% of the total mass of water and organic solvent, with the total mass of water and organic solvent being 100%. The soaking and cleaning is performed 3 to 5 times, with each soak lasting 5 to 20 minutes. The drying time is 15 to 30 minutes.

10. The application of the composite diaphragm according to any one of claims 4 to 6 in alkaline water electrolysis, characterized in that, The composite membrane is used as an alkaline water electrolysis membrane.

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