Composite membrane for water electrolyzer

Abstract

The present application relates to a kind of high conductivity, alkali-resistant water electrolytic cell composite diaphragm and its preparation method.The preparation method includes that support net is dipped casting solution, and the step that support net after dipping casting solution is carried out phase transition in coagulation bath, the preparation method also includes the step that the pressure is applied to the support net after the dipping casting solution before the phase transition, the pressure is 5MPa or less, and the casting solution includes polymer, pore former, hydrophilic agent and solvent.The conductivity of water electrolytic cell composite diaphragm obtained by the foregoing preparation method is improved, resistance is reduced, and tensile strength is also improved, while it can guarantee alkali resistance, and the surface is smooth and flat.

Description

[0001] This invention is a divisional application filed on November 8, 2022, with application number 202211389139.0 and titled "A Highly Conductive, Alkali-Resistant Composite Membrane for a Water Electrolyzer and Its Preparation Method Thereof". Technical Field

[0002] This invention belongs to the field of water electrolysis for hydrogen production technology, specifically relating to a highly conductive, alkali-resistant composite membrane for water electrolysis cells and its preparation method. Background Technology

[0003] Hydrogen energy is a new generation of clean energy carrier for sustainable use. At present, domestic water electrolysis hydrogen production equipment mainly uses alkaline electrolyzers, in which the diaphragm plays a very important role. It is located between the anode and the cathode, and its main function is to prevent the mixing of oxygen on the anode side and hydrogen on the cathode side, thereby improving the purity of the produced hydrogen and oxygen and ensuring safety.

[0004] In the early days, asbestos cloth was used as a diaphragm in industry, but it was phased out due to its poor temperature resistance and high pollution levels. At present, diaphragms are mainly made of polyphenylene sulfide woven fabric, but it has the disadvantages of poor hydrophilicity and poor air tightness. After long-term use, its pores will be filled with air bubbles, which will lead to a decrease in the conductivity of the diaphragm.

[0005] Chinese patent CN101372752A discloses a method to improve the hydrophilicity of polyphenylene sulfide by sulfonating it in sulfuric acid. However, this method has certain problems such as difficulty in cleaning, waste of water resources, environmental pollution, and safety issues.

[0006] Chinese patent CN114432906 A discloses a method for preparing a high-temperature alkaline water electrolysis cell composite membrane using a polyphenylene sulfide (PPS) mesh as a support mesh. The PPS mesh is prepared by mixing polysulfone, polyvinylpyrrolidone (PVP), zirconium dioxide, and metal salts to form a casting solution. The support mesh is then immersed in the casting solution and, after thorough immersion, coated with a doctor blade. However, this method results in partial separation of the casting solution on both sides of the support mesh, making it difficult for the composite membrane to form a solid whole. Furthermore, wrinkles may appear on the side of the composite membrane not in contact with the doctor blade. Additionally, using a larger mesh size PPS mesh reduces its porosity, leading to decreased conductivity of the composite membrane. Moreover, the PPS support mesh is expensive, resulting in high production costs. Summary of the Invention

[0007] The purpose of this invention is to provide a method for preparing a composite membrane for a water electrolyzer with high conductivity and alkali resistance. This method can prepare a composite membrane for a water electrolyzer with high conductivity, alkali resistance, high tensile strength and a uniform and smooth surface.

[0008] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0009] A method for preparing a composite membrane for a water electrolyzer includes the steps of impregnating a support mesh with a casting solution and performing a phase transformation on the impregnated support mesh in a coagulation bath. The preparation method further includes the step of applying pressure to the impregnated support mesh before the phase transformation, wherein the pressure is below 5 MPa, and the casting solution includes a polymer, a pore-forming agent, a hydrophilic agent, and a solvent.

[0010] Further, the pressure is 0.5-5 MPa. Preferably, the pressure is 0.5-3 MPa.

[0011] Furthermore, the pressure is applied at a temperature of 20-60°C. Preferably, the pressure is applied at a temperature of 25-40°C.

[0012] Furthermore, the pressure is applied for 3-10 minutes. Preferably, the pressure is applied for 5-8 minutes.

[0013] Furthermore, pressure is applied using pressure rollers connected to a pneumatic compressor, which is used to adjust the pressure between the pressure rollers.

[0014] In some embodiments, the polymer is selected from one or more combinations of polyvinyl alcohol, polyetheretherketone, polyimide, polyethersulfone, polysulfone, polybenzimidazole, chitosan, polytetrafluoroethylene, polyetherimide, and polyvinyl chloride. All of the aforementioned polymers are capable of phase inversion in subsequent processes.

[0015] Preferably, the polymer is selected from one or more combinations of polysulfone, polyethersulfone, and polybenzimidazole.

[0016] In some embodiments, the pore-forming agent is selected from one or more combinations of cyclodextrin, polyethylene glycol, urea, polyvinylpyrrolidone, polyacrylamide, starch, sodium chloride, sucrose, and polyurethane.

[0017] Preferably, the pore-forming agent is selected from one or more combinations of polyvinylpyrrolidone, cyclodextrin, and urea.

[0018] In some embodiments, the hydrophilic agent is selected from one or more combinations of polyvinyl alcohol, cellulose, starch, titanium dioxide, silicon dioxide, and zirconium dioxide.

[0019] Preferably, the hydrophilic agent is selected from titanium dioxide and zirconium dioxide.

[0020] Through research, the inventors discovered that applying pressure to the support mesh after impregnation with the casting solution before phase transformation can increase the solid content of the casting solution on the support mesh. Furthermore, the applied pressure ensures that the casting solution on both sides of the support mesh completely adheres to it, avoiding incomplete adhesion caused by the thickness of the support mesh, which leads to pores within the composite membrane. These pores are a major factor contributing to reduced conductivity. Therefore, the composite membrane for the water electrolyzer prepared by this invention exhibits improved conductivity, reduced sheet resistance, and increased tensile strength, while maintaining alkali resistance and low alkali loss. Applying pressure to the support mesh also results in a smooth, wrinkle-free surface of the final composite membrane for the water electrolyzer.

[0021] Furthermore, the mass ratio of the polymer, pore-forming agent, and hydrophilic agent is 10–20:3–15:0.5–6.

[0022] Furthermore, the solvent is selected from one or more combinations of N-methylpyrrolidone, N,N-dimethylformamide and N,N-dimethylacetamide.

[0023] Furthermore, the solid content of the casting solution is 10-40%.

[0024] In some embodiments, the preparation method further includes the steps of melting, drawing, and weaving a polymer material to prepare the support mesh.

[0025] Preferably, the polymer material is a polymer sheet.

[0026] In some embodiments, the polymer material is selected from one or more combinations of polypropylene, polyethylene, polyethylene naphthalate, polyetheretherketone, polyetherketoneketone, polyphenylene ether, polysulfone, polyphenylene sulfide, polytetrafluoroethylene, and polyimide.

[0027] Preferably, the polymer material is selected from polypropylene or polyethylene. Using polypropylene or polyethylene can ensure the tensile strength of the composite membrane, and it is also more cost-effective than polyphenylene sulfide mesh.

[0028] In some embodiments, the melting temperature is 100-400°C.

[0029] In some embodiments, the draw ratio of the drawn wire is 1-10.

[0030] In some embodiments, the warp and weft density of the support mesh is 10–200 strands / inch. This density ensures the support mesh has suitable porosity, facilitating the smooth passage of electrons through the composite membrane during water electrolysis, thereby guaranteeing high conductivity.

[0031] In some embodiments, the immersion time is 10-60 minutes and the immersion temperature is 20-30°C.

[0032] In some embodiments, the preparation method further includes a step of coating the support mesh, after it has been impregnated with the casting solution, with a coating roller before applying pressure. This coating step can further ensure that the support mesh is completely covered by the casting solution, reducing the possibility that some parts of the support mesh are not covered by the casting solution.

[0033] In some embodiments, the preparation method includes the following steps: 1) melting, drawing, and weaving a polymer sheet to prepare the support mesh; 2) dissolving the polymer in the solvent, adding the hydrophilic agent and the pore-forming agent, stirring evenly, filtering, and vacuum degassing to obtain the casting solution; 3) immersing the support mesh in the casting solution, and then coating the support mesh with the casting solution using a coating roller; 4) applying pressure to the support mesh using a pressure roller; 5) allowing the support mesh to stand, and then performing a phase transformation on the support mesh in a first coagulation bath and a second coagulation bath to obtain the water electrolysis cell composite diaphragm.

[0034] In some embodiments, the stirring speed is 200-800 rpm and the stirring time is 1-48 h.

[0035] In some embodiments, the filtration is performed using a filter with a pore size of 1-10 μm, and the filtration is performed 2 to 5 times.

[0036] In some embodiments, the vacuum degassing temperature is 20-100°C, and the vacuum degree is 1×10⁻⁶. 5 ~1×10 - 5 Pa.

[0037] In some embodiments, the settling temperature is 25-50°C and the time is 25-60 seconds.

[0038] In some embodiments, the first coagulation bath and the second coagulation bath are selected from one or more combinations of water, ethanol, methanol, acetone, dimethylformamide and dimethylacetamide.

[0039] The present invention also provides a composite diaphragm for a water electrolyzer prepared by the above preparation method.

[0040] Furthermore, the sheet resistivity of the composite diaphragm in the water electrolysis cell is 0.6 Ω·cm. 2 The tensile strength is above 15 MPa. When the composite diaphragm of the water electrolysis cell is immersed in a boiling KOH solution with a mass fraction of 30% for 5 hours, the alkali loss is below 0.35%.

[0041] Preferably, the sheet resistivity of the composite diaphragm in the water electrolysis cell is 0.3 Ω·cm. 2 The tensile strength is above 18 MPa.

[0042] Due to the application of the above technical solution, the present invention has the following advantages compared with the prior art.

[0043] Applying pressure to the support mesh after impregnation with the casting solution before phase transformation can improve the conductivity, reduce the sheet resistance, and increase the tensile strength of the final water electrolysis cell composite diaphragm, while ensuring alkali resistance and low alkali loss.

[0044] Applying pressure to the support mesh can make the surface of the final water electrolyzer composite diaphragm smooth and wrinkle-free. Attached Figure Description

[0045] Figure 1 A photograph of the composite diaphragm of Example 1;

[0046] Figure 2 This is a photograph of the composite diaphragm in Comparative Example 1. Detailed Implementation

[0047] The technical solutions of the present invention will be described in detail below with reference to specific embodiments, so that those skilled in the art can better understand and implement the technical solutions of the present invention, but the present invention is not limited to the scope of the examples described.

[0048] In the following examples, polyethylene was purchased from Sinopharm Group with a molecular weight of 50,000, polypropylene was purchased from Sinopharm Group with a molecular weight of 50,000, polysulfone was purchased from Sinopharm Group with a molecular weight of 80,000, and polyvinylpyrrolidone was purchased from Sinopharm Group with a molecular weight of 40,000.

[0049] Example 1

[0050] This embodiment provides a composite membrane for a water electrolyzer, and its preparation method is as follows:

[0051] 1) After drying, polyethylene chips are placed in a screw extruder for melting at a temperature of 200°C; the polyethylene melt is then drawn into filaments with a draw ratio of 5; the drawn filaments are then woven in parallel into a fiber web with a warp and weft density of 100 threads / inch.

[0052] 2) Dissolve polysulfone in N-methylpyrrolidone and stir until homogeneous. Then add polyvinylpyrrolidone and stir until homogeneous again. Add zirconium dioxide and magnetically stir at 500 rpm for 24 hours. Filter three times using a 5 μm filter and then sterilize under a vacuum of 1 × 10⁻⁶. -5Degassing was performed at 70°C and 80 Pa to obtain the casting solution. The weight ratio of polysulfone, polyvinylpyrrolidone, and zirconium dioxide was 10:3:1, and the solid content of the casting solution was 30%.

[0053] 3) Immerse the aforementioned fiber web in the aforementioned casting solution for 30 minutes, then remove it and use a coating roller to apply the aforementioned casting solution to the fiber web again.

[0054] 4) The fiber web is pressurized at 40℃ and 0.5MPa using a pressure roller connected to the pneumatic compressor for 5 minutes.

[0055] 5) After standing at 30°C for 30 seconds, the fiber web is placed in a mixture of ethanol and acetone (mass ratio of 7:3) for the first and second coagulation baths to obtain the composite membrane for the water electrolysis cell.

[0056] Example 2

[0057] This embodiment provides a composite membrane for a water electrolyzer, which is prepared in a manner similar to that of Embodiment 1, except that polypropylene is used instead of polyethylene, and the weight ratio of polysulfone, polyvinylpyrrolidone and zirconium dioxide in the casting solution is 10:10:3.

[0058] Example 3

[0059] This embodiment provides a composite membrane for a water electrolyzer, which is prepared in a manner similar to that of Embodiment 1, except that: polypropylene is used instead of polyethylene, the weight ratio of polysulfone:polyvinylpyrrolidone:zirconia in the casting solution is 10:15:6, and the solid content of the casting solution is 40%.

[0060] Example 4

[0061] This embodiment provides a composite membrane for a water electrolysis cell. Its preparation method is basically the same as that in Embodiment 1, except that: step 4) uses a pressure roller connected to a pneumatic compressor to pressurize the fiber web at 60°C and 3MPa for 5 minutes.

[0062] Example 5

[0063] This embodiment provides a composite membrane for a water electrolysis cell. Its preparation method is basically the same as that in Embodiment 1, except that: step 4) uses a pressure roller connected to a pneumatic compressor to pressurize the fiber web at 20°C and 2MPa for 5 minutes.

[0064] Example 6

[0065] This embodiment provides a composite membrane for a water electrolysis cell. Its preparation method is basically the same as that in Embodiment 1, except that: step 4) uses a pressure roller connected to a pneumatic compressor to pressurize the fiber web at 40°C and 1MPa for 5 minutes.

[0066] Example 7

[0067] This embodiment provides a composite membrane for a water electrolyzer, which is prepared in a manner similar to that of Embodiment 1, except that titanium dioxide is used instead of zirconium dioxide, and the weight ratio of polysulfone:polyvinylpyrrolidone:titanium dioxide in the casting solution is 15:15:1.5.

[0068] Example 8

[0069] This embodiment provides a composite membrane for a water electrolyzer, which is prepared in a manner similar to that of Embodiment 1, except that titanium dioxide is used instead of zirconium dioxide, and the weight ratio of polysulfone:polyvinylpyrrolidone:titanium dioxide in the casting solution is 15:10:3.

[0070] Example 9

[0071] This embodiment provides a composite membrane for a water electrolyzer, which is prepared in a manner similar to that of Embodiment 1, except that titanium dioxide is used instead of zirconium dioxide, and the weight ratio of polysulfone:polyvinylpyrrolidone:titanium dioxide in the casting solution is 20:15:2.

[0072] Example 10

[0073] This embodiment provides a composite membrane for a water electrolyzer, which is prepared in a manner similar to that of Embodiment 1, except that titanium dioxide is used instead of zirconium dioxide, and the weight ratio of polysulfone:polyvinylpyrrolidone:titanium dioxide in the casting solution is 20:15:3.

[0074] Comparative Example 1

[0075] This comparative example also provides a composite membrane for a water electrolyzer, the preparation method of which is basically the same as that in Example 1, the only difference being that step 4 is not performed.

[0076] For the composite membranes of the water electrolyzers prepared in Examples 1-10 and Comparative Example 1, their surface resistivity (the product of resistance R and cross-sectional area S) was tested using an electrochemical CHI650E station. Specifically, the composite membrane was first soaked in anhydrous ethanol for 2 hours to fully wet it, and then soaked in a 1 mol / L KOH solution for 24 hours. It was then clamped in the middle of the electrolyzer. The middle part of the electrolyzer consisted of two circular plates with small holes, and the membrane was clamped between the two half-electrolyzers using a special stainless steel clamp. Stainless steel plates were inserted into the electrolyzer as auxiliary electrodes, and a 1 mol / L KOH solution was injected onto both sides of the membrane.

[0077] Its tensile strength was tested according to GB1040-79 standard. It was immersed in boiling KOH solution with a mass fraction of 30% for 5 hours. Its alkali loss was tested according to JC211-77 standard. The results are shown in Table 1 below.

[0078] Table 1 Performance of Composite Membrane in Water Electrolysis Cell

[0079] <![CDATA[Sheet Resistance (Ω·cm 2 )]]> Tensile strength (MPa) Alkali loss Example 1 0.24 20.2 0.34％ Example 2 0.23 19.3 0.29％ Example 3 0.26 20.3 0.34％ Example 4 0.41 25.1 0.35％ Example 5 0.30 24.0 0.33％ Example 6 0.27 25.0 0.35％ Example 7 0.32 16.9 0.35％ Example 8 0.64 15.4 0.40％ Example 9 0.35 20.5 0.33％ Example 10 0.30 17.7 0.35％ Comparative Example 1 0.55 12.5 0.36％

[0080] In addition, a photograph of the composite diaphragm for the water electrolyzer prepared in Example 1 is shown below. Figure 1 As shown in the image, its surface is smooth and flat without wrinkles, while the composite diaphragm of the water electrolyzer prepared in Comparative Example 1 is shown in the image. Figure 2 As shown, its surface exhibits obvious wrinkles.

[0081] As can be seen from the results of the above embodiments and comparative examples, the present invention can improve the various properties of the final composite membrane by pressurizing the support network after impregnation with the casting solution before phase transformation.

[0082] The above embodiments are only for illustrating the technical concept and features of the present invention, and are intended to enable those skilled in the art to understand the content of the present invention and implement it accordingly. They should not be construed as limiting the scope of protection of the present invention. All equivalent changes or modifications made in accordance with the spirit and essence of the present invention should be covered within the scope of protection of the present invention.

Claims

1. A composite diaphragm for a water electrolyzer, characterized in that: The composite diaphragm is prepared by a method including the following steps: 1) melting, drawing, and weaving polymer sheets to prepare a support mesh; 2) dissolving the polymer in a solvent, adding a hydrophilic agent and a pore-forming agent, stirring evenly, filtering, and vacuum degassing to obtain a casting solution; 3) immersing the support mesh in the casting solution, and then coating the support mesh with the casting solution using a coating roller. 4) Apply pressure to the support mesh using pressure rollers; 5) Let the support mesh stand still, and then perform phase transformation on the support mesh in the first coagulation bath and the second coagulation bath to obtain the composite diaphragm for the water electrolysis cell. The pressure is 0.5-5 MPa; The polymer sheet is selected from one or more of polypropylene, polyethylene, and polytetrafluoroethylene.

2. The composite diaphragm for a water electrolyzer according to claim 1, characterized in that: The sheet resistivity of the composite diaphragm is 0.6 Ω·cm. 2 The tensile strength is above 15 MPa. When the composite diaphragm of the water electrolysis cell is immersed in a boiling KOH solution with a mass fraction of 30% for 5 hours, the alkali loss is below 0.35%.

3. The composite diaphragm for a water electrolyzer according to claim 1, characterized in that: The sheet resistivity of the composite diaphragm is 0.35 Ω·cm. 2 The tensile strength is above 19.3 MPa, and the alkali loss is below 0.35% when the composite diaphragm of the water electrolysis cell is immersed in a boiling KOH solution with a mass fraction of 30% for 5 hours.

4. The composite diaphragm for a water electrolyzer according to claim 1, characterized in that: The pressure is applied at 20-60°C; and / or the pressure is applied for 3-10 minutes.

5. The composite diaphragm for a water electrolyzer according to claim 1, characterized in that: The pressure is 0.5-3 MPa; and / or the pressure is applied at 25-40°C; and / or the pressure is applied for 5-8 minutes.

6. The composite diaphragm for a water electrolyzer according to claim 1, characterized in that: The polymer is selected from one or more combinations of polyvinyl alcohol, polyetheretherketone, polyimide, polyethersulfone, polysulfone, polybenzimidazole, chitosan, polytetrafluoroethylene, polyetherimide, and polyvinyl chloride; and / or the porogen is selected from one or more combinations of cyclodextrin, polyethylene glycol, urea, polyvinylpyrrolidone, polyacrylamide, starch, sodium chloride, sucrose, and polyurethane; and / or the hydrophilic agent is selected from one or more combinations of polyvinyl alcohol, cellulose, starch, titanium dioxide, silicon dioxide, and zirconium dioxide.

7. The composite diaphragm for a water electrolyzer according to claim 1, characterized in that: The mass ratio of the polymer, pore-forming agent, and hydrophilic agent is 10~20:3~15:0.5~6; and / or, the solvent is selected from one or more combinations of N-methylpyrrolidone, N,N-dimethylformamide, and N,N-dimethylacetamide; and / or, the solid content of the casting solution is 10~40%.

8. The composite diaphragm for a water electrolyzer according to claim 7, characterized in that: The melting temperature is 100-400℃; and / or the drawing ratio is 1-10.

9. The composite diaphragm for a water electrolyzer according to claim 1, characterized in that: The immersion time is 10-60 minutes, and the immersion temperature is 20-30℃.

10. The composite diaphragm for a water electrolyzer according to claim 1, characterized in that: The support net has a warp and weft density of 10-200 strands per inch.

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