Composite microporous membranes, methods of making the same, and uses thereof

Abstract

The present application discloses a composite microporous membrane, comprising a hydrophilic base membrane and a coating layer coated on one side or both sides of the hydrophilic base membrane, wherein the hydrophilic base membrane comprises a first fluorine-containing polymer and one or more first hydrophilic grafts grafted thereon, the coating layer comprises a second fluorine-containing polymer and one or more second hydrophilic grafts grafted thereon, and hydrophilic nanoparticles, wherein the first fluorine-containing polymer is the same as the second fluorine-containing polymer, and the composite microporous membrane has low surface resistance, high ionic conductivity and low mass loss rate.

Description

Technical Field

[0001] This invention relates to composite membranes, particularly composite membranes for alkaline water electrolysis, and to slurries and composite membrane processes used in manufacturing such membranes; the invention also relates to fuel cells and hydrogen electrolysis devices using such membranes. Background Technology

[0002] The transition from traditional fossil energy systems to sustainable energy is a major trend in national energy transformation. This transformation can be achieved through the use of low-carbon energy and improved energy efficiency. Hydrogen is a carbon-free energy source, and due to its wide availability, high flexibility, and rich application scenarios, it has been recognized as an ideal energy carrier for achieving efficient conversion of different energy sources and large-scale development of renewable energy.

[0003] Water electrolysis is a highly efficient and carbon-free method for hydrogen production. Alkaline electrolysis (ALK) is widely used in large-scale green hydrogen production due to its advantages such as high technological maturity, a sound industrial chain, low investment, and large production capacity. Currently, commercial ALK electrolysis plants have reached megawatt (GW) scale, and the market capacity is expected to grow rapidly from the current billions to hundreds of billions or even trillions. However, its hydrogen production cost is not yet significantly competitive compared to the cost of producing hydrogen from fossil fuels. Generally speaking, the cost of hydrogen production by water electrolysis is greatly affected by electricity costs. Therefore, reducing the overall power consumption of ALK systems is of great significance for the promotion of this technology.

[0004] The diaphragm is the core component and key material of the ALK electrolyzer. It not only separates the anode and cathode gases, but also provides an effective channel for electrolyte transport. Its performance directly determines the energy consumption, hydrogen purity, and safety of the ALK electrolysis equipment.

[0005] For a long time, the commercial diaphragms used in industrial alkaline electrolyzers in my country have mainly been asbestos cloth and polyphenylene sulfide (PPS) fabrics. Asbestos has gradually withdrawn from the water electrolysis market due to its poor gas barrier properties, high energy consumption, and carcinogenic risks. Although PPS has excellent thermal stability, flame retardancy, and chemical corrosion resistance, PPS fabrics typically exhibit high ion resistance and gas permeability due to their poor hydrophilicity, large membrane thickness (>700μm), and large pore size. This results in low hydrogen production efficiency in the electrolyzer and, when faced with pressure fluctuations caused by frequent start-ups and shutdowns, the hydrogen concentration in oxygen is prone to become too high, affecting the safe operation of the electrolysis system. Summary of the Invention

[0006] Based on the limitations of the aforementioned technical means, the main objective of this invention is to provide a composite microporous membrane. It uses polymers as the porous membrane framework and mixes hydrophilic inorganic fillers to enhance its hydrophilicity. While ensuring the electrochemical performance of the membrane, it also combines the advantages of polymers and inorganic components.

[0007] Therefore, in the embodiments of the present invention, a composite microporous membrane is provided, comprising a hydrophilic base membrane and a coating applied to one or both sides of the hydrophilic base membrane, wherein the hydrophilic base membrane comprises a first fluoropolymer, and the coating comprises a second fluoropolymer and hydrophilic nanoparticles. The first fluoropolymer is the same as the second fluoropolymer.

[0008] In another embodiment of the present invention, a method for preparing a composite microporous membrane is provided, comprising the following steps: Step S1: Take a base film containing the first fluorinated copolymer, and mix it with a plurality of first hydrophilic monomers and / or... Alternatively, multiple third hydrophilic monomers may be grafted onto the first fluorinated copolymer to form a first hydrophilic graft to obtain a hydrophilic base film; Step S2: Take a substrate containing the second fluorinated copolymer, and mix a plurality of second hydrophilic monomers and / or... Alternatively, multiple fourth hydrophilic monomers may be grafted onto the second fluorinated copolymer to form a second hydrophilic graft to obtain a hydrophilic modified substrate, and the hydrophilic modified substrate may be dissolved in an organic solvent to obtain a hydrophilic binder solution, wherein the second fluorinated copolymer is the same as the first fluorinated copolymer. Step S3: Mix the hydrophilic binder solution and hydrophilic nanoparticles to obtain a coating slurry; Step S4: Coat one or both sides of the first hydrophilic base membrane with the coating slurry to obtain the composite microporous membrane.

[0009] In some embodiments, prior to step S1, the preparation method further includes step S10: The substrate film is activated by irradiation with a first irradiation dose; prior to step S2, the preparation method further includes step S20: activating the substrate by irradiation with a second irradiation dose, wherein the irradiation includes γ-rays. X-ray irradiation, plasma irradiation, or electron beam irradiation.

[0010] In the above embodiments, the dissolution step of the hydrophilic substrate includes: Step S2a: At a second temperature, the hydrophilic substrate is dissolved in the mixed solvent within a second time period. Obtain a pre-hydrophilic binder solution; Step S2b: At a third temperature, the mixed solvent of the pre-hydrophilic binder solution is replaced with the organic solvent for a third time period to obtain the hydrophilic binder solution.

[0011] In some embodiments, the coating slurry further includes a pore-forming agent selected from at least one of PVP, polyethylene glycol, ethanol, and n-butanol.

[0012] In some embodiments, the mixed solvent comprises water, a first alcohol solvent, and a second alcohol solvent; the organic solvent comprises at least one of NMP, NEP, DMAC, and DMF.

[0013] The above-mentioned composite microporous membrane or the above-mentioned preparation method may further include one or more of the following.

[0014] Generally, the total mass of the first fluoropolymer and the first hydrophilic graft is used as a benchmark. The grafting rate of the first fluoropolymer is 45% to 65%; based on the total mass of the second fluoropolymer and the second hydrophilic graft, the grafting rate of the second fluoropolymer is 45% to 65%.

[0015] Generally, the first fluoropolymer is grafted with one or more first hydrophilic grafts, which include a first hydrophilic monomer containing a hydroxyl group, a carboxyl group, or a heterocyclic aromatic group and / or a third hydrophilic group containing a quaternizable group; and The second fluoropolymer graft has one or more second hydrophilic grafts, which include a second hydrophilic monomer containing a hydroxyl group, a carboxyl group or a heterocyclic aromatic group and / or a fourth hydrophilic group containing a quaternizable group, wherein the first hydrophilic monomer is the same as or different from the second hydrophilic monomer, and the third hydrophilic monomer is the same as or different from the fourth hydrophilic monomer.

[0016] Preferably, the first hydrophilic monomer includes at least one or more of acrylic monomers, imidazole monomers, acrylate monomers, and pyrrolidone monomers; the second hydrophilic monomer includes at least one or more of acrylic monomers, imidazole monomers, acrylate monomers, and pyrrolidone monomers; the third hydrophilic monomer includes an amide monomer; and the fourth hydrophilic monomer includes an amide monomer.

[0017] Generally, the first fluoropolymer includes any one of polytetrafluoroethylene, polytrifluoroethylene, polyvinylidene fluoride, polyvinyl fluoride, polyhexafluoroethylene, tetrafluoroethylene-hexafluoropropylene copolymer, vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-tetrafluoroethylene copolymer, and ethylene-tetrafluoroethylene copolymer; the second fluoropolymer includes any one of polytetrafluoroethylene, polytrifluoroethylene, polyvinylidene fluoride, polyhexafluoroethylene, tetrafluoroethylene-hexafluoropropylene copolymer, vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-tetrafluoroethylene copolymer, and ethylene-tetrafluoroethylene copolymer.

[0018] Generally, the hydrophilic nanoparticles include at least one of aluminum oxide, magnesium oxide, calcium oxide, barium oxide, zinc oxide, silicon dioxide, titanium dioxide, zirconium dioxide, magnesium hydroxide, aluminum hydroxide, and boehmite.

[0019] In some embodiments, when the first hydrophilic graft is polymerized from the first hydrophilic monomer and the third hydrophilic monomer, and / or when the second hydrophilic graft is polymerized from the second hydrophilic monomer and the fourth hydrophilic monomer, the preparation method further includes: Step S5: At the fourth temperature, the composite microporous membrane is brought into contact with the haloalkane for a fourth time to obtain the quaternized composite microporous membrane.

[0020] In another embodiment of the present invention, there is a fuel cell comprising a fuel electrode, an air electrode, and an ion exchange membrane spaced between the fuel electrode and the air electrode, wherein the ion exchange membrane is the aforementioned composite microporous membrane or a composite microporous membrane prepared by the aforementioned preparation method.

[0021] In another embodiment of the present invention, there is an electrolytic cell comprising a cell body and a positive electrode, a negative electrode disposed in the cell body, and a diaphragm spaced between the positive electrode and the negative electrode, wherein the diaphragm is the aforementioned composite microporous membrane or a composite microporous membrane prepared by the aforementioned preparation method.

[0022] The beneficial effects obtained by this invention are that, while ensuring the airtightness and ion permeability of the composite microporous membrane, the membrane thickness is reduced to below 500 μm, which can significantly improve the overall performance of the electrolyzer and has lower internal resistance and higher ionic conductivity; the higher ionic conductivity optimizes the water electrolysis power, enabling the electrolyzer to produce hydrogen more effectively.

[0023] In addition, the coating slurry of the composite microporous membrane uses a hydrophilic binder instead of a hydrophobic binder and is applied to the porous framework, giving the membrane better airtightness than PPS fabric. It can effectively block anode and cathode gases and ensure the safe operation of the alkaline water electrolyzer. Furthermore, the composite microporous membrane has a low mass loss rate, which solves the problem of easy detachment of nanoparticles from the coating of previous composite membranes and improves the structural stability of the membrane. Attached Figure Description

[0024] Figures 1A to 1D The specific steps of the preparation method provided by this invention are illustrated by a series of block flowcharts;

[0025] Figure 2 This is a cross-sectional schematic diagram used to illustrate the fuel cell structure provided by the present invention; and

[0026] Figure 3 This is a cross-sectional schematic diagram used to illustrate the electrolytic cell structure provided by the present invention. Detailed Implementation

[0027] The following examples, illustrated with figures, illustrate specific embodiments of the present invention.

[0028] The first embodiment of the present invention provides a composite microporous membrane, which includes a hydrophilic base membrane and a coating applied to one or both sides of the hydrophilic base membrane, wherein the hydrophilic base membrane includes a first fluoropolymer, and the coating includes a second fluoropolymer and hydrophilic nanoparticles, wherein the first fluoropolymer is the same as the second fluoropolymer.

[0029] In a common implementation, based on the total mass of the first fluoropolymer and the first hydrophilic graft, the grafting rate of the first fluoropolymer is 45% to 65%, preferably 50% to 60%; based on the total mass of the second fluoropolymer and the second hydrophilic graft, the grafting rate of the second fluoropolymer is 45% to 65%, preferably 50% to 60%. It is understood that the hydrophilic grafting rate of the base membrane and coating material affects the overall electrochemical performance of the composite microporous membrane. Improved hydrophilicity helps enhance the ion conductivity of the electrolyte, while also improving the filling properties of the coating slurry during application and reducing the asymmetry of the membrane surface resistance. The grafting rate generally refers to the percentage of functional groups introduced into the polymer chain. In this embodiment, the grafting rate of the fluoropolymer can be calculated using the following formula. And thus:

[0030] In a common implementation, the surface resistivity of the composite microporous membrane is less than 0.3 Ω*cm. 2 .

[0031] In a common implementation, the composite microporous membrane has an ionic conductivity greater than 140 mS*cm. -1 , Preferred value is greater than 170mS*cm -1 More preferably greater than 185 mS*cm -1 .

[0032] In a common implementation, the composite microporous membrane experiences a mass loss rate of less than 1% after ultrasonic treatment.

[0033] In a common implementation, the hydrophilic base membrane is a hydrophilic porous material, specifically a screen, fabric, or filter paper.

[0034] In a common implementation, the first fluoropolymer is grafted with one or more first hydrophilic grafts, which include a first hydrophilic monomer containing a hydroxyl group, a carboxyl group or a heterocyclic aromatic group and / or a third hydrophilic group containing a quaternizable group.

[0035] In a common embodiment, the second fluoropolymer is grafted with one or more second hydrophilic grafts, which include a second hydrophilic monomer containing a hydroxyl group, a carboxyl group or a heterocyclic aromatic group and / or a fourth hydrophilic group containing a quaternizable group.

[0036] Understandably, hydrophilic grafts can be either homopolymers or copolymers.

[0037] When the hydrophilic graft is a homopolymer, the first hydrophilic graft is a repeating unit derived from the first or third hydrophilic monomer, and the second hydrophilic graft is a repeating unit derived from the second or fourth hydrophilic monomer. When the hydrophilic graft is a copolymer, the first hydrophilic graft is a non-repeating unit formed by copolymerizing the first and third hydrophilic monomers in different arrangements and combinations, and the second hydrophilic graft is a non-repeating unit formed by copolymerizing the second and fourth hydrophilic monomers in different arrangements and combinations.

[0038] When the hydrophilic graft is a copolymer, its molecular form can be an alternating copolymer, a random copolymer, a block copolymer, or a graft copolymer, without particular limitation; in a specific case, the molar ratio of the first hydrophilic monomer to the third hydrophilic monomer is 1:(0.2 to 0.8), preferably 1:(0.22 to 0.7) or 1:(0.25 to 0.67); the molar ratio of the second hydrophilic monomer to the fourth hydrophilic monomer is 1:(0.2 to 0.8), preferably 1:(0.22 to 0.7) or 1:(0.25 to 0.67).

[0039] In the above embodiments, the first hydrophilic monomer may be the same as or different from the second hydrophilic monomer, and the third hydrophilic monomer may be the same as or different from the fourth hydrophilic monomer; in a preferred embodiment, the first hydrophilic monomer is the same as the second hydrophilic monomer, and the third hydrophilic monomer is the same as the fourth hydrophilic monomer.

[0040] In the above embodiments, the first hydrophilic monomer can be one of acrylic monomers, imidazole monomers, amide monomers, acrylate monomers, and pyrrolidone monomers; the second hydrophilic monomer can be one of acrylic monomers, imidazole monomers, amide monomers, acrylate monomers, and pyrrolidone monomers; the third hydrophilic monomer is any type of amino ester monomer; and the fourth hydrophilic monomer is any type of amino ester monomer.

[0041] The hydrophilic monomers mentioned above can be specifically listed below:

[0042] Acrylic monomers may include, for example, acrylic acid (AA), methacrylic acid (MAA), 2-hydroxypropylacrylic acid (HPA), methacrylonitrile, and acrylonitrile (AN), with acrylic acid (AA) being the most preferred.

[0043] Amide monomers may include, for example, acrylamide (AM), N,N-dimethylacrylamide (DMAA), N-isopropylacrylamide (NIPAM), methacrylamide (MAM), maleimide, N-vinylacetamide, N-vinylformamide, N-acrylpiperazine, or N-acrylpyrrolidine.

[0044] Imidazole monomers may include, for example, N-vinylimidazole (NVI), N-methylimidazole (1-Vinyl-2-Methylimidazole), 1-(3-aminopropyl)imidazole (N-(3-Aminopropyl)-imidazole), or 1-vinyl-3-methylimidazole (1-Vinyl-3-Methylimidazole).

[0045] Acrylate monomers may include, for example, 2-Hydroxyethyl Methacrylate (HEMA), methyl methacrylate (EMA), n-Butyl Methacrylate (n-BMA), methyl acrylate (MA), ethyl acrylate (EA), glycidyl methacrylate (GMA), isopropyl acrylate (IPA), benzyl acrylate (BzA), n-Butyl acrylate (n-BA), or isobutyl methacrylate (iBMA), preferably hydroxyethyl methacrylate (HEMA).

[0046] Pyrrolidone monomers include, for example, N-vinylpyrrolidone (NVP). N-Methylpyrrolidone (NMP) or 2-pyrrolidone (2-Pyrrolidone).

[0047] Examples of amino ester monomers include dimethylaminoethyl methacrylate (DMAEMA), diethylaminoethyl methacrylate (DEAEMA), dimethylaminoethyl acrylate (DMAEA), diethylaminoethyl acrylate (DEAEA), dimethylaminoethyl acrylate (DMAAP), or dimethylaminopropyl methacrylate (DMAPMA), with dimethylaminoethyl methacrylate (DMAEMA) being the most preferred.

[0048] In a common implementation, the first fluoropolymer includes any one of polytetrafluoroethylene, polytrifluoroethylene, polyvinylidene fluoride, polyvinyl fluoride, polyhexafluoroethylene, tetrafluoroethylene-hexafluoropropylene copolymer, vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-tetrafluoroethylene copolymer, and ethylene-tetrafluoroethylene copolymer, preferably ethylene-tetrafluoroethylene copolymer; the second fluoropolymer includes any one of polytetrafluoroethylene, polytrifluoroethylene, polyvinylidene fluoride, polyvinyl fluoride, polyhexafluoroethylene, tetrafluoroethylene-hexafluoropropylene copolymer, vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-tetrafluoroethylene copolymer, and ethylene-tetrafluoroethylene copolymer, preferably ethylene-tetrafluoroethylene copolymer.

[0049] In a common implementation, the hydrophilic nanoparticles include at least one of aluminum oxide, magnesium oxide, calcium oxide, barium oxide, zinc oxide, silicon dioxide, titanium dioxide, zirconium dioxide, magnesium hydroxide, aluminum hydroxide, and boehmite, preferably zirconium dioxide.

[0050] Please see Figure 1A The second embodiment of the present invention provides a method for preparing a composite microporous membrane. It includes the following steps: Step S1: Take a base film containing the first fluorinated copolymer, and mix it with a plurality of first hydrophilic monomers and / or... Alternatively, multiple third hydrophilic monomers may be grafted onto the first fluorinated copolymer to form a first hydrophilic graft to obtain a hydrophilic base film; Step S2: Take a substrate containing the second fluorinated copolymer, and mix a plurality of second hydrophilic monomers and / or... Alternatively, multiple fourth hydrophilic monomers may be grafted onto the second fluorinated copolymer to form a second hydrophilic graft to obtain a hydrophilic modified substrate, and the hydrophilic modified substrate may be dissolved in an organic solvent to obtain a hydrophilic binder solution. Step S3: Mix the hydrophilic binder solution and hydrophilic nanoparticles to obtain a coating slurry; Step S4: Coat one or both sides of the first hydrophilic base membrane with the coating slurry to obtain the composite microporous membrane.

[0051] In a common implementation, the second fluorinated copolymer is the same as the first fluorinated copolymer.

[0052] In a common implementation, the base membrane is a porous material, including a screen, fabric, or filter paper. The substrate may be a porous material similar to the base film, or a raw material used to form the base film, such as powder, fiber, or slurry.

[0053] In a common implementation, the coating slurry has a solid content of 10 to 20 wt%, preferably. 10 to 15 wt% or 15 to 20 wt%.

[0054] In a common implementation, the mass ratio of the hydrophilic modified substrate to the hydrophilic nanoparticles is 1:(3 to 8), preferably 1:(4 to 6).

[0055] In a common implementation, the coating slurry further includes a pore-forming agent selected from at least one of PVP, polyethylene glycol, ethanol, and n-butanol.

[0056] In a common embodiment, the organic solvent may be at least one of N-methylpyrrolidone (NMP), N-ethylpyrrolidone (NEP), N,N-dimethylacetamide (DMAC), and dimethylformamide (DMF).

[0057] In a common implementation, the polymerization grafting reaction is carried out at a first temperature of 40 to 80°C for a first time of 30 to 90 minutes, preferably at 50 to 60°C for 50 to 70 minutes.

[0058] Please see Figure 1B In some embodiments, in order to activate the base film and substrate to generate free radicals for subsequent free radical grafting polymerization, before step S1, the preparation method further includes step S10: activating the base film with a first irradiation dose; and / or before step S2, the preparation method further includes step S20: activating the substrate with a second irradiation dose, wherein the irradiation includes gamma ray irradiation, plasma irradiation or electron beam irradiation.

[0059] In some embodiments, the irradiation is electron beam irradiation, the first irradiation dose is 40 to 200 kGy, preferably 60 to 120 kGy; the second irradiation dose is 40 to 200 kGy, preferably 60 to 120 kGy; preferably, the first irradiation dose is the same as the second irradiation dose.

[0060] Please see Figure 1C In a common implementation, the dissolution step of the hydrophilic substrate includes the following sub-steps: Step S2a: At a second temperature, the hydrophilic substrate is dissolved in the mixed solvent within a second time period to obtain a pre-hydrophilic binder solution; and Step S2b: At a third temperature, the mixed solvent of the pre-hydrophilic binder solution is replaced with the organic solvent for a third time period to obtain the hydrophilic binder solution.

[0061] In the above embodiments, the hydrophilic substrate is placed at a second temperature of 100 to 300°C to dissolve for at least 5 hours, and the pre-hydrophilic binder solution is subjected to solvent replacement at a third temperature below 80°C for 4 to 36 hours, preferably 12 to 24 hours.

[0062] In the above embodiments, the mixed solvent is an alcohol-water solution, which includes water, a first alcohol solvent and a second alcohol solvent, wherein the first alcohol solvent is, for example, n-propanol, isopropanol, n-butanol, isobutanol or a mixture thereof, and the second alcohol solvent is, for example, methanol or ethanol; in some specific cases, the mixing ratio of the water, the first alcohol solvent and the second alcohol solvent is 3:(3 to 5):(1 to 2), preferably 3:(3.5 to 4.0):(1.1 to 1.3).

[0063] In some embodiments, when the first hydrophilic graft is polymerized from the first hydrophilic monomer and the third hydrophilic monomer, and / or when the second hydrophilic graft is polymerized from the second hydrophilic monomer and the fourth hydrophilic monomer, the quaternizable groups in the composite microporous membrane may be further quaternized to improve the overall hydrophilicity; accordingly, please refer to Figure 1D The preparation method further includes step S5: contacting the composite microporous membrane with a haloalkane at a fourth temperature for a fourth time to obtain a quaternized composite microporous membrane, wherein the fourth temperature is 50 to 200°C, preferably 60 to 100°C, the fourth time is 4 to 16 hours, preferably 8 to 10 hours, and the haloalkane includes one or more of iodomethane, bromoethane, bromobutane, and bromohexane, preferably iodomethane.

[0064] Please see Figure 2 The third embodiment of the present invention provides a fuel cell (100) comprising a fuel electrode (1), an air electrode (2) and an ion exchange membrane (3) spaced between the fuel electrode (1) and the air electrode (2), wherein the ion exchange membrane (3) is a composite microporous membrane provided by the first embodiment or a composite microporous membrane prepared by the preparation method provided by the second embodiment.

[0065] Please see Figure 3 The fourth embodiment of the present invention provides an electrolytic cell (200), which includes a cell body (2a) and a positive electrode (10) and a negative electrode (20) disposed in the cell body (2a) and a diaphragm (30) spaced between the positive electrode (10) and the negative electrode (20). The diaphragm (30) is a composite microporous membrane provided by the first embodiment or a composite microporous membrane prepared by the preparation method provided by the second embodiment.

[0066] In a common implementation, the electrolysis power of the electrolyzer (200) is greater than 0.55W, preferably greater than 0.65W, and more preferably greater than 0.75W, under a cell voltage of 1.5 to 2.0V.

[0067] The following examples illustrate the technical effects achieved by the present invention, but are not intended to limit the invention.

[0068] Example 1

[0069] Step S10: Take a 5×10cm ETFE fabric with a thickness of 290μm, activate it with a 100kGy electron beam, and store it at -25℃ for later use.

[0070] Step S1: Add 60 g of DMF and 40 g of hydroxyethyl methacrylate (HEMA) to a double-walled glass reactor connected to a reflux device. Stir continuously and purge the solution with nitrogen to remove air. After 20 minutes, heat the reaction solution to 60°C. Add activated ETFE fabric and allow the grafting reaction to proceed for 60 minutes. Remove the solution. HEMA grafted onto modified ETFE fabric (hereinafter referred to as ETFE-g-pHEMA), and repeatedly washed with isopropanol.

[0071] Step S2: Take 2×2cm ETFE fabric with a thickness of 290μm and repeat steps S10 to S1. ETFE-g-pHEMA was obtained; 1 unit weight of ETFE-g-pHEMA was weighed and mixed with a mixed solvent (water, n-propanol, and ethanol in a unit weight ratio of 3:3.8:1.2) in a reaction vessel, and dissolved at 230°C for 5 hours to obtain a pre-hydrophilic binder solution with a solid content of 10%; the pre-hydrophilic binder solution was poured into a separatory funnel and allowed to stand for 24 hours, the lower half of the solution was taken, and evaporated to dryness at 80°C to perform solvent replacement, resulting in an NMP solution with a solid content of 20% as the hydrophilic binder solution.

[0072] Step S3: Under conditions where the humidity does not exceed 40%, weigh 62 grams of hydrophilic adhesive solution and 37.2 grams of... Add 0.8 g of zirconium dioxide (ZrO2) and stir at 750 r / min for 2 hours, then add 0.8 g of PVP and stir at 750 r / min for another 2 hours to degas and obtain the coating slurry.

[0073] Step S4: Coat both sides of the coating slurry onto the ETFE-g-pHEMA obtained in step 1, with a wet film thickness of about 800 micrometers. After heat treatment at 140°C for 10 minutes, vertically immerse the non-solvent phase with a water-to-alcohol mass ratio of 1:1 for 20 minutes to obtain a composite microporous membrane.

[0074] Example 2

[0075] The method steps are largely the same as in Example 1, except that HEMA is replaced with acrylic acid (AA) to obtain... AA grafted and modified ETFE fabric (ETFE-g-pAA).

[0076] Example 3

[0077] The method steps are largely the same as those in Example 1, except that 29.2 g of HEMA and 10.8 g of AA are added in step S1 to obtain HEMA-AA copolymer grafted modified ETFE fabric (ETFE-gp(HEMA-co-AA)); and in step S2, a NMP solution with a solid content of 10% is obtained as a hydrophilic adhesive solution.

[0078] Example 4

[0079] The method steps are largely the same as in Example 1, with the following differences: In step S1, 30.7 g of HEMA and 9.3 g of DMAEMA were added to obtain HEMA-DMAEMA copolymer grafted modified ETFE fabric (ETFE-gp(HEMA-co-DMAEMA)). Step S2 yields an NMP solution with a solid content of 10% as a hydrophilic binder solution; and Following step S4, there is further step S5: the composite microporous membrane obtained in step 4 is immersed in an ethanol solution containing 0.2M iodomethane and reacted at 60°C for 10 hours to obtain a quaternized composite microporous membrane, which is then repeatedly rinsed with isopropanol.

[0080] Example 5

[0081] The method steps are largely the same as those in Example 1, except that boehmite is added in step S3.

[0082] Comparative Example 1

[0083] The method steps are largely the same as in Example 1, except that the ETFE fabric was not grafted.

[0084] Comparative Example 2

[0085] The method steps are largely the same as in Example 1, except that the ETFE fabric is activated with a 30kGy electron beam.

[0086] Comparative Example 3

[0087] The steps are largely the same as in Example 1, except that the grafting reaction takes 30 minutes.

[0088] Comparative Example 4

[0089] The method steps are largely the same as those in Example 1, except that in step S2, 2×2cm thick polyvinylidene fluoride (PVDF) is taken and subjected to steps S10 to S1 to obtain PVDF-g-pHEMA, which is then used to manufacture a hydrophilic adhesive solution.

[0090] Comparative Example 5

[0091] The method steps are largely the same as in Example 1, except that 100g of hydrophilic binder solution is added in step S3, and zirconium dioxide (ZrO2) is not added.

[0092] Comparative Example 6

[0093] The steps are largely the same as in Example 1, except that the ETFE fabric is activated with a 200 kGy electron beam.

[0094] Comparative Example 7

[0095] The steps are largely the same as in Example 1, except that the grafting reaction is 120 minutes.

[0096] Surface resistivity and ionic conductivity

[0097] Take a composite microporous membrane of a certain thickness, 2.5*2.5cm (the test area is a circle with a diameter of 2cm), and test it at 30%. After soaking in KOH for 24 hours, the membrane was placed in a stainless steel test chamber. The impedance spectrum of the composite microporous membrane was obtained using an electrochemical workstation. The readings at the intersections of the high-frequency part of the spectrum with the real axis were taken as the impedance values ​​and converted into surface resistance and ionic conductivity.

[0098] Quality loss rate

[0099] A 5×5cm composite microporous membrane was dried at 100℃ for 1 hour, and its mass W1 was measured. After being ultrasonically treated with 360W power for 5 minutes, it was dried again at 100℃ for 1 hour, and its mass W2 was measured. Then, according to… The following formula is used to calculate the mass loss rate:

[0100] Alkaline electrolysis water test

[0101] With an active area of ​​15cm 2 The LSCF single-cell electrolytic cell uses a composite microporous membrane to replace the original membrane. It operates with 30% KOH as the electrolyte at 80°C, powered by a DC power supply, with a cell voltage ranging from 1.5 to 2.0 kJ / mL. V, with a step size of 0.05V, and a current density of 0.4A*cm-2 After running for 200 hours, the current-voltage curve of the composite microporous membrane was tested, and the power of the system at 1.8V was calculated.

[0102] The test results obtained after the above tests for individual embodiments and comparative examples are summarized in Table 1.

[0103] As can be seen from the comparison between Examples 1 to 5 and Comparative Example 1, after the base film and coating materials were hydrophilically modified, the performance of the composite microporous membrane in all aspects was significantly improved, not only reducing the surface resistivity to 0.3 Ω*cm. 2 The following increases in ionic conductivity are at least 30.8%, 52.6%, 41.3%, 45.1%, and 27.1%, respectively, while the mass loss rate after ultrasonic treatment is reduced to less than 1%, and the electrolysis power is enhanced by at least 43%. Table 1

[0104] As can be seen from the comparison of Examples 1 to 5 with Comparative Examples 2 and 3, the grafting rate of the hydrophilic grafts in the base film and coating materials directly affects the performance of the composite microporous membrane in various aspects. The grafting rate produced by low irradiation (30 kGy) and short polymerization time (30 minutes) is low, and there is no significant improvement in surface resistance, ionic conductivity, mass loss rate and water electrolysis power.

[0105] On the other hand, compared with Example 1, Comparative Example 4 shows that preparing the base film and coating with different substrates actually increases the mass loss rate; Comparative Example 5 shows that the conductivity of the coating is significantly reduced when nanoparticles are lacking; Comparative Example 6 shows that activating ETFE fabric with high irradiation (200 kGy) significantly increases the grafting rate, but the mass loss rate and water electrolysis power are not significantly improved; similarly, Comparative Example 7 increases the grafting rate by extending the grafting reaction time (120 minutes), but the mass loss rate increases instead of decreasing, and the water electrolysis power is not significantly improved.

[0106] The above content involving common knowledge will not be described in detail, as those skilled in the art will understand.

[0107] The embodiments described above are merely illustrative of the principles and effects of the present invention and are not intended to limit the invention. Any person skilled in the art can modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by those skilled in the art without departing from the spirit and technical concept disclosed in the present invention should still be covered by the claims of the present invention.

Claims

1. A composite microporous membrane, characterized in that, The composite microporous membrane includes a hydrophilic base membrane and a coating applied to one or both sides of the hydrophilic base membrane. The hydrophilic base membrane includes a first fluoropolymer and one or more first hydrophilic grafts grafted thereon. The coating includes a second fluoropolymer and one or more second hydrophilic grafts grafted thereon, as well as hydrophilic nanoparticles. The first fluoropolymer is the same as the second fluoropolymer. Based on the total mass of the first fluoropolymer and the first hydrophilic grafts, the grafting rate of the first fluoropolymer is 45% to 65%. Based on the total mass of the second fluoropolymer and the second hydrophilic grafts, the grafting rate of the second fluoropolymer is 45% to 65%.

2. The composite microporous membrane as described in claim 1, characterized in that, The first hydrophilic graft comprises a first hydrophilic monomer containing a hydroxyl group, a carboxyl group, or a heterocyclic aromatic group and / or a third hydrophilic monomer containing a quaternizable group; and The second hydrophilic graft comprises a second hydrophilic monomer containing a hydroxyl group, a carboxyl group or a heterocyclic aromatic group and / or a fourth hydrophilic monomer containing a quaternizable group, wherein the first hydrophilic monomer is the same as or different from the second hydrophilic monomer, and the third hydrophilic monomer is the same as or different from the fourth hydrophilic monomer.

3. The composite microporous membrane as described in claim 2, characterized in that: The first hydrophilic monomer includes at least one or more of acrylic monomers, imidazole monomers, amide monomers, acrylate monomers, and pyrrolidone monomers; The second hydrophilic monomer includes at least one or more of acrylic monomers, imidazole monomers, amide monomers, acrylate monomers, and pyrrolidone monomers; The third hydrophilic monomer includes amino ester monomers; The fourth hydrophilic monomer includes amino ester monomers.

4. The composite microporous membrane as described in claim 3, characterized in that, The acrylic monomers include acrylic acid (AA), the acrylate monomers include hydroxyethyl methacrylate (HEMA), and the amino ester monomers include dimethylaminoethyl methacrylate (DMAEMA).

5. The composite microporous membrane as described in claim 1, characterized in that, The first fluoropolymer includes any one of polytetrafluoroethylene, polytrifluoroethylene, polyvinylidene fluoride, polyvinyl fluoride, polyhexafluoroethylene, tetrafluoroethylene-hexafluoropropylene copolymer, vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-tetrafluoroethylene copolymer, and ethylene-tetrafluoroethylene copolymer; the second fluoropolymer includes any one of polytetrafluoroethylene, polytrifluoroethylene, polyvinylidene fluoride, polyvinyl fluoride, polyhexafluoroethylene, tetrafluoroethylene-hexafluoropropylene copolymer, vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-tetrafluoroethylene copolymer, and ethylene-tetrafluoroethylene copolymer.

6. The composite microporous membrane as described in claim 1, characterized in that, The hydrophilic nanoparticles include at least one of aluminum oxide, magnesium oxide, calcium oxide, barium oxide, zinc oxide, silicon dioxide, titanium dioxide, zirconium dioxide, magnesium hydroxide, aluminum hydroxide, and boehmite.

7. A method for preparing a composite microporous membrane, characterized in that, Includes the following steps: Step S1: Take a base film containing a first fluoropolymer, and graft a plurality of first hydrophilic monomers and / or a plurality of third hydrophilic monomers onto the first fluoropolymer to form a first hydrophilic graft, thereby obtaining a hydrophilic base film; Step S2: Take a substrate containing a second fluoropolymer, and graft polymerize a plurality of second hydrophilic monomers and / or a plurality of fourth hydrophilic monomers onto the second fluoropolymer to form a second hydrophilic graft to obtain a hydrophilic modified substrate, and dissolve the hydrophilic modified substrate in an organic solvent to obtain a hydrophilic binder solution, wherein the second fluoropolymer is the same as the first fluoropolymer. Step S3: Mix the hydrophilic binder solution and hydrophilic nanoparticles to obtain a coating slurry; Step S4: Coat one or both sides of the hydrophilic base membrane with the coating slurry to obtain the composite microporous membrane. Based on the total mass of the first fluoropolymer and the first hydrophilic graft, the grafting rate of the first fluoropolymer is 45% to 65%; based on the total mass of the second fluoropolymer and the second hydrophilic graft, the grafting rate of the second fluoropolymer is 45% to 65%.

8. The preparation method according to claim 7, characterized in that: Prior to step S1, the preparation method further includes step S10: activating the base film by irradiation with a first irradiation dose; Prior to step S2, the preparation method further includes step S20: activating the substrate by irradiation with a second irradiation dose, wherein the irradiation includes gamma ray irradiation, plasma irradiation, or electron beam irradiation.

9. The preparation method according to claim 7, characterized in that, The graft polymerization in steps S1 and S2 is carried out at a first temperature of 40 to 80°C for a first time of 30 to 90 minutes.

10. The preparation method according to claim 7, characterized in that: The first hydrophilic monomer includes a hydroxyl group, a carboxyl group, or a heterocyclic aromatic group; The third hydrophilic monomer includes a quaternizable group; The second hydrophilic monomer includes a hydroxyl group, a carboxyl group, or a heterocyclic aromatic group; The fourth hydrophilic monomer includes a quaternizable group, wherein the first hydrophilic monomer is the same as or different from the second hydrophilic monomer, and the third hydrophilic monomer is the same as or different from the fourth hydrophilic monomer.

11. The preparation method according to claim 10, characterized in that: The first hydrophilic monomer includes at least one or more of acrylic monomers, imidazole monomers, amide monomers, acrylate monomers, and pyrrolidone monomers; The second hydrophilic monomer includes at least one or more of acrylic monomers, imidazole monomers, amide monomers, acrylate monomers, and pyrrolidone monomers; The third hydrophilic monomer includes amino ester monomers; The fourth hydrophilic monomer includes amino ester monomers.

12. The preparation method according to claim 11, characterized in that, The acrylic monomers include acrylic acid (AA), the acrylate monomers include hydroxyethyl methacrylate (HEMA), and the amino ester monomers include dimethylaminoethyl methacrylate (DMAEMA).

13. The preparation method according to claim 11, characterized in that, When the first hydrophilic graft is polymerized from the first hydrophilic monomer and the third hydrophilic monomer, and / or when the second hydrophilic graft is polymerized from the second hydrophilic monomer and the fourth hydrophilic monomer, the preparation method further includes: Step S5: Contact the composite microporous membrane with the haloalkane for a fourth time to obtain the quaternized composite microporous membrane, wherein the haloalkane includes one or more of iodomethane, bromoethane, bromobutane, and bromohexane.

14. The preparation method according to claim 7, characterized in that, The first fluoropolymer includes any one of polytetrafluoroethylene, polytrifluoroethylene, polyvinylidene fluoride, polyvinyl fluoride, polyhexafluoroethylene, tetrafluoroethylene-hexafluoropropylene copolymer, vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-tetrafluoroethylene copolymer, and ethylene-tetrafluoroethylene copolymer; the second fluoropolymer includes any one of polytetrafluoroethylene, polytrifluoroethylene, polyvinylidene fluoride, polyvinyl fluoride, polyhexafluoroethylene, tetrafluoroethylene-hexafluoropropylene copolymer, vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-tetrafluoroethylene copolymer, and ethylene-tetrafluoroethylene copolymer.

15. The preparation method according to claim 7, characterized in that, The hydrophilic nanoparticles include at least one of aluminum oxide, magnesium oxide, calcium oxide, barium oxide, zinc oxide, silicon dioxide, titanium dioxide, zirconium dioxide, magnesium hydroxide, aluminum hydroxide, and boehmite.

16. The preparation method according to claim 7, characterized in that, The coating slurry further includes a pore-forming agent selected from at least one of polyvinylpyrrolidone (PVP), polyethylene glycol, ethanol, and n-butanol.

17. A fuel cell, characterized in that, The fuel cell includes a fuel electrode, an air electrode, and an ion exchange membrane spaced between the fuel electrode and the air electrode. The ion exchange membrane is the composite microporous membrane of claim 1 or a composite microporous membrane prepared by the preparation method of claim 7.

18. An electrolytic cell, characterized in that, The electrolytic cell includes a cell body and a positive electrode, a negative electrode, and a separator between the positive electrode and the negative electrode disposed in the cell body. The separator is the composite microporous membrane of claim 1 or the composite microporous membrane prepared by the preparation method of claim 7.

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