A composite anion exchange membrane and its preparation method and application

Abstract

The present invention provides a composite anion exchange membrane, its preparation method, and application. The composite anion exchange membrane comprises a support layer and a modified layer containing a quaternary ammonium base, wherein the support layer is a porous acrylonitrile copolymer support layer. The modified layer is obtained by subjecting the support layer surface to a Mannich reaction with a polyamine and an aldehyde compound, followed by a reaction with an ammonium salt containing an epoxy group, and finally by exchange with hydroxide. The composite anion exchange membrane of the present invention has high ion conductivity, is dimensionally stable in water, and is simple to prepare.

Description

Technical Field

[0001] The present invention relates to the field of membranes, in particular to a composite anion exchange membrane and a preparation method and application thereof. Background Art

[0002] Fuel cell technology is a novel energy technology that uses electrochemical reactions to convert chemical energy stored in fuels into electrical energy. While traditional proton exchange membrane fuel cells offer advantages such as high energy conversion efficiency, high energy density, and environmental friendliness, their catalysts are all relatively precious metals, resulting in high production costs, which significantly limits their industrialization. In this regard, alkaline fuel cells using anion exchange membranes as electrolytes offer significant advantages. Their alkaline operating environment facilitates electrode reaction kinetics, making it feasible to use non-precious metals such as Ag, Ni, and Co as electrocatalysts.

[0003] Anion exchange membranes are one of the key materials in alkaline fuel cells. As a solid electrolyte separator, they separate the active substances at the two electrodes of the battery and transfer anions such as hydroxide, sulfate, or halogen. A review of relevant literature and patents at home and abroad shows that quaternary ammonium anion membranes remain the mainstay of anion membranes. The preparation of quaternary ammonium anion membrane materials often requires a chloromethylation reaction, and the most commonly used chloromethylation agent (chloromethyl methyl ether) is highly carcinogenic. Furthermore, the precise location of the chloromethylation reaction is difficult to control, and cross-linking side reactions are prone to occur.

[0004] Therefore, it is of great significance to develop anion exchange membrane materials that are simple to prepare and environmentally friendly. Summary of the Invention

[0005] In order to solve the above problems existing in the prior art, the present invention provides a composite anion exchange membrane containing quaternary ammonium groups, as well as a preparation method and application thereof. The anion exchange membrane containing quaternary ammonium side groups obtained by this method not only has high ion conductivity, but also has low water absorption and good dimensional stability.

[0006] One objective of the present invention is to provide a composite anion exchange membrane comprising a support layer and a modified layer containing a quaternary ammonium base. The composite anion exchange membrane comprises a two-layer structure: a bottom porous support layer; and a cross-linked dense layer containing quaternary ammonium base groups attached to the surface of the porous support layer.

[0007] The composite anion exchange membrane of the present invention, wherein the support layer is a porous support layer of acrylonitrile copolymer; the modified layer is obtained by allowing the surface of the support layer to undergo a Mannich reaction with polyamine and aldehyde compounds, followed by reaction with ammonium salt containing epoxy groups, and finally exchange with hydroxide.

[0008] In the composite anion exchange membrane of the present invention, the porous support layer is made of acrylonitrile copolymer through phase inversion, and the porosity of the support layer is 10% to 90%, preferably 50 to 70%.

[0009] Preferably, the acrylonitrile copolymer is selected from one or a mixture of polyacrylonitrile, styrene-acrylonitrile copolymer, acrylonitrile-butadiene-styrene copolymer, methyl methacrylate-acrylonitrile copolymer, butadiene-acrylonitrile copolymer, acrylonitrile-methacrylonitrile copolymer, acrylate-acrylonitrile copolymer, and ethylene-propylene-styrene-acrylonitrile copolymer.

[0010] Preferably, the polyamine is selected from one or a mixture of 1,3,5-triaminobenzene, melamine, diethylenetriamine, tetraethylenepentamine, polyethyleneimine, polyethylenepolyamine and polyetheramine, preferably at least one of polyethyleneimine and polyethylenepolyamine.

[0011] Preferably, the aldehyde compound is selected from one or a mixture of formaldehyde, acetaldehyde, propionaldehyde, n-butyraldehyde, n-valeraldehyde, n-heptaldehyde, benzaldehyde and paraformaldehyde.

[0012] Preferably, the ammonium salt containing an epoxy group is selected from ammonium halide salts, more preferably one or more selected from 2,3-epoxypropyltrimethylammonium chloride, 2,3-epoxypropyltriethylammonium chloride, 1,2-epoxypropyldimethyldodecylammonium chloride, diethyl-2,3-epoxypropyl-[3-(methyldimethoxy)]silylpropylammonium chloride, 2,3-epoxypropyltrimethylammonium bromide, 2,3-epoxypropyltriethylammonium bromide, 1,2-epoxypropyldimethyldodecylammonium bromide and diethyl-2,3-epoxypropyl-[3-(methyldimethoxy)]silylpropylammonium bromide.

[0013] In the composite anion exchange membrane of the present invention, the thickness of the support layer is 10 to 60 μm, preferably 20 to 40 μm; the thickness of the modification layer is 10 to 500 nm, preferably 50 to 200 nm.

[0014] A second object of the present invention is to provide a method for preparing the composite anion exchange membrane, comprising the following steps:

[0015] (1) preparing a casting solution containing an acrylonitrile copolymer and an optional porogen, and forming a film to obtain a support layer;

[0016] (2) contacting one surface of the support layer with a solution containing a polyamine and an aldehyde compound to react;

[0017] (3) contacting the surface of the reacted membrane obtained in step (2) with a solution of an ammonium salt containing an epoxy group, heating and drying, to obtain a composite membrane;

[0018] (4) Immersing the composite membrane obtained in step (3) in an aqueous solution of sodium hydroxide and / or potassium hydroxide to obtain the composite anion exchange membrane.

[0019] In the step (1), in the casting solution, the content of the acrylonitrile copolymer is 2.5 to 25 wt%, preferably 5 to 20 wt%, more preferably 5 to 10 wt%; the content of the porogen is 0 to 10 wt%, preferably 0.1 to 5 wt%.

[0020] The porogen is preferably at least one selected from polyvinyl pyrrolidone, polyethylene glycol, lithium chloride, and lithium bromide, and more preferably polyvinyl pyrrolidone.

[0021] The present invention has no particular limitation on the solvent in the casting solution of step (1), as long as it can completely dissolve the acrylonitrile copolymer and is miscible with water. Preferably, it is one of N,N-dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone and dimethyl sulfoxide, preferably N,N-dimethylformamide.

[0022] The present invention has no particular limitation on the film-forming method of step (1), and a conventional phase inversion film-forming method in the art can be used.

[0023] In the step (2), in the solution containing polyamine and aldehyde compound, the content of polyamine is 0.5-10 wt%, preferably 1-5 wt%; the content of aldehyde compound is 0.1-5 wt%, preferably 0.5-2.5 wt%.

[0024] In the step (2), the pH of the solution containing the polyamine and the aldehyde compound is 1 to 4, preferably 2 to 3.

[0025] In step (2), the temperature of the solution containing polyamines and aldehyde compounds is 25 to 100° C., preferably 50 to 80° C.; the time for one surface of the support layer to contact the solution containing polyamines and aldehyde compounds is 30 to 360 minutes, preferably 60 to 180 minutes.

[0026] The present invention has no particular limitation on the solvent in step (2), as long as it can dissolve the polyamine and the aldehyde compound. The solvent is preferably one of water, methanol, and ethylene glycol monomethyl ether, preferably water.

[0027] In the step (3), the content of the quaternary ammonium salt containing epoxy groups in the solution of the ammonium salt containing epoxy groups is 1 to 20 wt %, preferably 1 to 10 wt %, and more preferably 2 to 5 wt %.

[0028] The present invention has no particular limitation on the solvent in step (3), as long as it can dissolve the ammonium salt containing epoxy groups. It is preferably one of water, methanol, and ethylene glycol monomethyl ether, preferably water.

[0029] In the step (3), the temperature of the solution of the ammonium salt containing epoxy groups is 20 to 80° C., preferably 25 to 40° C.; the contact time between the reacted membrane surface and the solution of the ammonium salt containing epoxy groups is 10 seconds to 5 minutes, preferably 30 seconds to 2 minutes.

[0030] In the step (3), the heating temperature is 40 to 120° C., preferably 60 to 100° C.; the heating time is 1 to 30 minutes, preferably 3 to 10 minutes.

[0031] In step (4), the content of sodium hydroxide and / or potassium hydroxide in the aqueous solution is 0.5-10 wt%, more preferably 1-5 wt%; and the soaking time is 10-36 h, preferably 20-30 h.

[0032] The third object of the present invention is to provide a composite anion exchange membrane prepared by the above method.

[0033] The composite anion exchange membrane has high ion conductivity, is dimensionally stable in water, and has a simple preparation method.

[0034] A fourth object of the present invention is to provide the composite anion exchange membrane and the application of the composite anion exchange membrane prepared by the method in the field of fuel cells.

[0035] After extensive research, the inventors discovered that because the cross-linked, densely modified layer containing quaternary ammonium base groups is very thin, hydroxide ions can easily transfer from one side of the dense layer to the pores of the porous support layer. The pores of the porous support layer are filled with water molecules, and without the obstruction of solid polymer, hydroxide ions are quickly transferred to the cathode. As a result, the thin-layer composite anion exchange membrane has high ionic conductivity. Furthermore, because the porous support layer contains no ionic groups, it has low water absorption, which limits the swelling of the composite membrane in water and ensures its dimensional stability in water.

[0036] Other features and advantages of the present invention will be described in detail in the following detailed description. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 This is the infrared spectrum of the composite membrane (PAN-NH4Cl) modified with the porous support layer (PAN) and 2,3-epoxypropyltrimethylammonium chloride.

[0038] Figure 2 This is a scanning electron microscope image of the surface of the porous support layer (PAN).

[0039] Figure 3 This is a surface scanning electron microscope photograph of the anion exchange membrane (PAN-NH4OH). DETAILED DESCRIPTION

[0040] The present invention will be described in detail below with reference to specific embodiments. It is necessary to point out that the following embodiments are only used to further illustrate the present invention and are not to be construed as limiting the scope of protection of the present invention. Non-essential improvements and adjustments made by those skilled in the art to the present invention based on the contents of the present invention still fall within the scope of protection of the present invention.

[0041] The invention provides a composite anion exchange membrane having a two-layer structure: a bottom layer is an acrylonitrile copolymer porous support layer; and a cross-linked dense modification layer containing quaternary ammonium base groups is attached to the surface of the porous support layer.

[0042] According to the present invention, the thickness of the porous support layer and the modified layer containing quaternary ammonium base groups is not particularly limited, and can be a conventional choice in the field. However, in order to enable the two layers to play a better synergistic role and enable the obtained composite anion exchange membrane to have better ion conductivity and fuel permeation barrier properties, preferably, the thickness of the porous support layer is 10 to 60 μm, preferably 20 to 40 μm; the thickness of the modified layer containing quaternary ammonium base groups is 10 to 500 nm, preferably 50 to 200 nm.

[0043] According to a preferred embodiment of the present invention, the present invention does not specifically limit the porosity of the porous support layer, which can be a conventional choice in the field. However, in order to enable the two layers to play a better synergistic role and enable the obtained composite anion exchange membrane to have better ion conductivity and fuel permeation barrier properties, preferably, the porosity of the porous support layer is 10% to 90%, more preferably 50 to 70%.

[0044] The present invention also provides a method for preparing a composite anion exchange membrane, and a preferred embodiment is as follows: (1) an acrylonitrile copolymer solution containing or not containing a porogen is scraped onto a glass plate using a scraper, and the solution is immediately immersed in deionized water to prepare a high-porosity porous support layer; (2) one surface of the porous support layer is contacted with an aqueous solution containing a polyamine and an aldehyde compound; (3) after washing with water, the surface of the porous support layer modified with the polyamine is contacted with an aqueous solution of a quaternary ammonium salt containing an epoxy group, and after draining, the solution is heated and dried; (4) the obtained composite membrane is immersed in an aqueous sodium hydroxide solution, and washed with water to prepare a composite anion exchange membrane.

[0045] According to a preferred embodiment of the present invention, in step (1), the acrylonitrile copolymer is a mixture of one or more of the polyacrylonitrile polymer selected from the group consisting of polyacrylonitrile, styrene-acrylonitrile copolymer, acrylonitrile-butadiene-styrene copolymer, methyl methacrylate-acrylonitrile copolymer, butadiene-acrylonitrile copolymer, acrylonitrile-methacrylonitrile copolymer, acrylate-acrylonitrile copolymer and ethylene-propylene-styrene-acrylonitrile copolymer.

[0046] According to a preferred embodiment of the present invention, in step (1), the porogen is one of polyvinyl pyrrolidone, polyethylene glycol, lithium chloride and lithium bromide, preferably polyvinyl pyrrolidone.

[0047] According to a preferred embodiment of the present invention, in step (1), the solvent for preparing the polymer solution is one of N,N-dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone and dimethyl sulfoxide.

[0048] According to a preferred embodiment of the present invention, in step (2), the polyamine is one or a mixture of 1,3,5-triaminobenzene, melamine, diethylenetriamine, tetraethylenepentamine, polyethyleneimine, polyethylenepolyamine and polyetheramine, preferably polyethyleneimine and polyethylenepolyamine; the aldehyde compound is one or a mixture of formaldehyde, acetaldehyde, propionaldehyde, n-butyraldehyde, n-valeraldehyde, n-heptaldehyde, benzaldehyde and paraformaldehyde.

[0049] According to a preferred embodiment of the present invention, in step (2), the mass concentration of the polyamine in the solution containing the polyamine and the aldehyde compound is 0.5-10 wt%, preferably 1-5 wt%; the mass concentration of the aldehyde compound is 0.1-5 wt%, preferably 0.5-2.5 wt%.

[0050] According to a preferred embodiment of the present invention, in step (2), the pH of the solution containing the polyamine and the aldehyde compound is 1 to 4, preferably 2 to 3.

[0051] According to a preferred embodiment of the present invention, in step (2), the contact time between the surface of the porous support layer and the polyamine and aldehyde compound solution is 30 min to 360 min, preferably 60 min to 180 min; the temperature of the polyamine and aldehyde compound solution is 25 to 100°C, preferably 50 to 80°C.

[0052] According to a preferred embodiment of the present invention, in step (3), the quaternary ammonium salt containing an epoxy group is selected from one or more of 2,3-epoxypropyltrimethylammonium chloride, 2,3-epoxypropyltriethylammonium chloride, 1,2-epoxypropyldimethyldodecylammonium chloride, diethyl-2,3-epoxypropyl-[3-(methyldimethoxy)]silylpropylammonium chloride, 2,3-epoxypropyltrimethylammonium bromide, 2,3-epoxypropyltriethylammonium bromide, 1,2-epoxypropyldimethyldodecylammonium bromide and diethyl-2,3-epoxypropyl-[3-(methyldimethoxy)]silylpropylammonium bromide.

[0053] According to a preferred embodiment of the present invention, in step (3), there is no special limitation on the mass concentration of the quaternary ammonium salt containing epoxy groups, and it can be a conventional choice in the art. However, in order to enable the obtained composite anion exchange membrane to have better ion conductivity and fuel permeation barrier properties, preferably, the content of the quaternary ammonium salt containing epoxy groups is 1 to 20 wt%, preferably 1 to 10 wt%, and more preferably 2 to 5 wt%.

[0054] According to a preferred embodiment of the present invention, in step (3), the conditions for treating the membrane with the aqueous solution of quaternary ammonium salt containing epoxy groups are not particularly limited and can be conventionally selected in the art. However, in order to enable the obtained composite anion exchange membrane to have better ion conductivity and fuel permeation barrier properties, preferably, the temperature of the aqueous solution of quaternary ammonium salt containing epoxy groups is 20 to 80° C., preferably 25 to 40° C.; and the contact time between the membrane surface and the aqueous solution of quaternary ammonium salt containing epoxy groups is 10 s to 5 min, preferably 30 s to 2 min.

[0055] According to a preferred embodiment of the present invention, in step (3), there is no special limitation on the heating treatment conditions and they can be conventionally selected in the art. However, in order to enable the obtained composite anion exchange membrane to have better ion conductivity and fuel permeation barrier properties, preferably, the heating temperature is 40 to 120°C, preferably 60 to 100°C; and the heating time is 1 min to 30 min, preferably 3 min to 10 min.

[0056] According to a preferred embodiment of the present invention, in step (4), there is no particular limitation on the concentration of the sodium hydroxide and it can be a conventional choice in the art. However, in order to enable the obtained composite anion exchange membrane to have better ion conductivity and fuel permeation barrier properties, preferably, the content of sodium hydroxide is 0.5 to 10 wt%, more preferably 1 to 5 wt%.

[0057] According to a preferred embodiment of the present invention, in step (4), there is no special limitation on the time for soaking the membrane in the sodium hydroxide aqueous solution, and it can be a conventional choice in the art. However, in order to enable the obtained composite anion exchange membrane to have better ion conductivity and fuel permeation barrier properties, preferably, the soaking time is 10h to 36h, preferably 20h to 30h.

[0058] In the following examples and comparative examples:

[0059] (1) Proton conductivity test: The proton conductivity was measured by AC impedance spectroscopy (Salton 1260) using the four-electrode method. The proton conductivity was calculated using the following formula: σ = L / RS, where L is the distance between the electrodes (cm); S is the cross-sectional area of the membrane (cm 2 ), R is the resistance of the membrane (Ω).

[0060] (2) Membrane water absorption and swelling rate test: The membrane was soaked in 80°C distilled water for 24 hours, then removed and quickly dried. The membrane surface was weighed and its dimensions were measured. The water absorption and swelling rates are the percentage changes in mass and dimensions of the membrane after saturation with water.

[0061] (3) Methanol permeability test: 150 mL of high-purity water and an equal amount of methanol solution (10 M) were placed in the two half-cells A and B of the stainless steel diffusion cell, respectively. The two half-cells were separated by a polymer membrane. After magnetic stirring for several hours, the liquid on the high-purity water side was removed and the methanol concentration was measured using a SHIMADZU GC-8A gas chromatograph. The methanol permeability was calculated using the following formula:

[0062]

[0063] Among them, C A :Methanol concentration in pool A (10mol L -1 ,), C B :Methanol concentration in pool B (mol L -1 ), V B is the volume of methanol solution in pool B (L), P: methanol permeability (cm 2 s -1 ), A: the area of the opening between pool A and pool B (cm 2 ):L is the film thickness (cm).

[0064] (4) Film thickness: The cross-sectional morphology of the film was observed using a Hitachi S-4800 high-resolution field emission scanning electron microscope (FESEM) to obtain the film thickness.

[0065] (5) The molecular structure of the membrane surface was measured by infrared spectrometer (ATR-FTIR) (Nicolet 6700).

[0066] In addition, in the following examples and comparative examples:

[0067] Polyacrylonitrile was purchased from Maclean (number average molecular weight of 80,000), polyvinylpyrrolidone (number average molecular weight of 58,000), branched polyethyleneimine (weight average molecular weight of 25,000), polyethylene polyamine, melamine, diethylenetriamine, tetraethylenepentamine, 2,3-epoxypropyltrimethylammonium chloride, 2,3-epoxypropyltriethylammonium chloride, 1,2-epoxypropyldimethyldodecylammonium chloride, 2,3-epoxypropyltrimethylammonium bromide, etc. were all purchased from J&K Technology Co., Ltd., and other chemical reagents were purchased from Sinopharm Chemical Reagent Co., Ltd.

[0068] Preparation Example 1

[0069] A certain amount of polyacrylonitrile (number-average molecular weight of 80,000) and polyvinylpyrrolidone (number-average molecular weight of 58,000) were dissolved in N,N-dimethylformamide to prepare a uniform casting solution with a polyacrylonitrile concentration of 10% by weight and a polyvinylpyrrolidone concentration of 2.5% by weight. The solution was degassed at 25°C for 120 minutes. The polyacrylonitrile solution was then coated on a glass plate using a spatula to obtain an initial membrane. The membrane was then immersed in water at 25°C for 60 minutes to allow the polyacrylonitrile to undergo phase transformation into a porous membrane. The membrane was then washed three times with water to obtain a support layer with a thickness of 25 μm and a porosity of 52%.

[0070] Preparation Example 2

[0071] The method is the same as that of Preparation Example 1, except that the concentration of polyvinyl pyrrolidone in the casting solution is 5% by weight. Finally, a support layer with a thickness of 29 μm and a porosity of 60% is obtained.

[0072] Preparation Example 3

[0073] The method is the same as that of Preparation Example 1, except that the concentration of polyvinyl pyrrolidone in the casting solution is 7.5% by weight. Finally, a support layer with a thickness of 35 μm and a porosity of 73% is obtained.

[0074] Preparation Example 4

[0075] The method is the same as that of Preparation Example 1, except that the casting solution does not contain polyvinyl pyrrolidone. Finally, a support layer with a thickness of 22 μm and a porosity of 41% is obtained.

[0076] Preparation Example 5

[0077] The method is the same as that of Preparation Example 1, except that styrene-acrylonitrile copolymer is used instead of polyacrylonitrile, and finally a support layer with a thickness of 32 μm and a porosity of 34% is prepared.

[0078] Example 1

[0079] The upper surface of the porous polyacrylonitrile support layer obtained in Preparation Example 1 was exposed to an aqueous solution containing 1 wt% polyethyleneimine and 0.5 wt% formaldehyde at a pH of 2 for 180 minutes at 50°C, and then rinsed with deionized water. The upper surface of the porous polyacrylonitrile support layer was then exposed to an aqueous solution containing 2 wt% 2,3-epoxypropyltrimethylammonium chloride at 25°C for 60 seconds. The membrane was then placed in an oven and heated at 70°C for 5 minutes. The resulting composite membrane was then immersed in a 4 wt% aqueous NaOH solution for 24 hours, removed, and rinsed with deionized water until neutral, yielding composite anion exchange membrane N1. The support layer had a thickness of 25 microns, and the modified layer had a thickness of 0.15 microns.

[0080] The reaction mechanism during the membrane preparation process is given below.

[0081]

[0082] First, the active hydrogen on polyacrylonitrile can undergo a Mannich reaction with formaldehyde and polyethyleneimine to modify the amino group on the surface of the polyacrylonitrile porous membrane; then, the amino group on the membrane surface undergoes a ring-opening reaction with epoxy to modify the ammonium chloride group on the surface of the polyacrylonitrile porous membrane; finally, chloride ions and hydroxide ions achieve ion exchange to produce anion exchange membrane material.

[0083] Figure 1 This is the infrared spectrum of the surface of the polyacrylonitrile porous support membrane (PAN) modified with 2,3-epoxypropyltrimethylammonium chloride (PAN-NH4Cl). Figure 1 It can be seen that after the surface modification of PAN membrane, the -1 and 3300cm -1 New absorption peaks appeared at 100 nm and 100 nm, corresponding to the ammonium chloride groups and the hydroxyl groups generated after the epoxy ring opening, respectively. This proves that the ammonium chloride groups were successfully modified onto the surface of the PAN porous support layer through the two-step modification method.

[0084] Figure 2 and Figure 3The surface morphologies of the porous polyacrylonitrile support layer and the modified anion exchange membrane were compared. As can be seen, the surface of the porous polyacrylonitrile support layer is covered with nanoscale pores, while the surface of the modified anion exchange membrane exhibits a dense structure. This demonstrates that polyethyleneimine, under the action of formaldehyde, successfully modified the surface of the porous polyacrylonitrile layer. Furthermore, the reaction of 2,3-epoxypropyltrimethylammonium chloride with amino groups further branched and cross-linked the porous support layer, forming a dense layer on the surface of the porous support layer.

[0085] The obtained composite anion exchange membrane N1 was immersed in 80°C water for 24 hours, and the water absorption and swelling rate of the membrane were tested. The results are shown in Table 1. The hydroxide conductivity of the membrane in 80°C water and the methanol permeability at room temperature are also shown in Table 1.

[0086] Example 2

[0087] The upper surface of the porous polyacrylonitrile support layer obtained in Preparation Example 2 was exposed to an aqueous solution containing 2.5 wt% polyethylene polyamine and 1 wt% acetaldehyde at pH 2 for 60 minutes at 80°C, after which the surface was rinsed with deionized water. The upper surface of the porous polyacrylonitrile support layer was then exposed to an aqueous solution containing 4 wt% 2,3-epoxypropyltriethylammonium chloride at 25°C for 60 seconds. The membrane was then placed in an oven and heated at 70°C for 5 minutes. The resulting composite membrane was then immersed in a 4 wt% aqueous NaOH solution for 24 hours, removed, and rinsed with deionized water until neutral, yielding composite anion exchange membrane N2. The support layer had a thickness of 29 microns, and the modified layer had a thickness of 0.20 microns.

[0088] The obtained composite anion exchange membrane N2 was immersed in 80°C water for 24 hours, and the water absorption and swelling rate of the membrane were tested. The results are shown in Table 1. The hydroxide conductivity of the membrane in 80°C water and the methanol permeability at room temperature are also shown in Table 1.

[0089] Example 3

[0090] The upper surface of the porous polyacrylonitrile support layer obtained in Preparation Example 3 was exposed to an aqueous solution containing 5 wt% tetraethylenepentamine and 2.5 wt% propionaldehyde at pH 2 for 120 minutes at 80°C, and then rinsed with deionized water. The upper surface of the porous polyacrylonitrile support layer was then exposed to an aqueous solution containing 5 wt% 1,2-epoxypropyldimethyldodecylammonium chloride at 25°C for 60 seconds. The membrane was then placed in an oven and heated at 70°C for 5 minutes. The resulting composite membrane was then immersed in a 4 wt% NaOH aqueous solution for 24 hours, removed, and rinsed with deionized water until neutral, yielding composite anion exchange membrane N3. The support layer had a thickness of 35 microns, and the modified layer had a thickness of 0.23 microns.

[0091] The obtained composite anion exchange membrane N3 was immersed in 80°C water for 24 hours, and the water absorption and swelling rate of the membrane were tested. The results are shown in Table 1. The hydroxide conductivity of the membrane in 80°C water and the methanol permeability at room temperature are also shown in Table 1.

[0092] Example 4

[0093] An anion exchange membrane N4 was prepared according to the method of Example 1, except that melamine was used instead of polyethyleneimine, and the thickness of the modified layer was 0.12 μm.

[0094] The obtained composite anion exchange membrane N4 was immersed in 80°C water for 24 hours, and the water absorption and swelling rate of the membrane were tested. The results are shown in Table 1. The hydroxide conductivity of the membrane in 80°C water and the methanol permeability at room temperature are also shown in Table 1.

[0095] Example 5

[0096] An anion exchange membrane N5 was prepared according to the method of Example 1, except that diethylenetriamine was used instead of polyethyleneimine. The thickness of the modified layer was 0.13 μm.

[0097] The obtained composite anion exchange membrane N5 was immersed in 80°C water for 24 hours, and the water absorption and swelling rate of the membrane were tested. The results are shown in Table 1. The hydroxide conductivity of the membrane in 80°C water and the methanol permeability at room temperature are also shown in Table 1.

[0098] Example 6

[0099] An anion exchange membrane N6 was prepared according to the method of Example 1, except that 2,3-epoxypropyltrimethylammonium bromide was used instead of 2,3-epoxypropyltrimethylammonium chloride. The thickness of the modified layer was 0.15 μm.

[0100] The obtained composite anion exchange membrane N6 was immersed in 80°C water for 24 hours, and the water absorption and swelling rate of the membrane were tested. The results are shown in Table 1. The hydroxide conductivity of the membrane in 80°C water and the methanol permeability at room temperature are also shown in Table 1.

[0101] Example 7

[0102] An anion exchange membrane N7 was prepared according to the method of Example 1, except that the polyacrylonitrile porous support membrane obtained in Preparation Example 4 was used instead of the polyacrylonitrile porous support membrane obtained in Preparation Example 1. The thickness of the modified layer was 0.13 μm.

[0103] The obtained composite anion exchange membrane N7 was immersed in 80°C water for 24 hours, and the water absorption rate and swelling rate of the membrane were tested. The results are shown in Table 1. The hydroxide conductivity of the membrane in 80°C water and the methanol permeability at room temperature are also shown in Table 1.

[0104] Example 8

[0105] An anion exchange membrane N8 was prepared according to the method of Example 1, except that the styrene-polyacrylonitrile porous support membrane obtained in Preparation Example 5 was used instead of the polyacrylonitrile porous support membrane obtained in Preparation Example 1. The thickness of the modified layer was 0.08 μm.

[0106] The obtained composite anion exchange membrane N8 was immersed in 80°C water for 24 hours, and the water absorption and swelling rate of the membrane were tested. The results are shown in Table 1. The hydroxide conductivity of the membrane in 80°C water and the methanol permeability at room temperature are also shown in Table 1.

[0107] Table 1

[0108]

[0109] As shown in Table 1, because the cross-linked dense layer containing quaternary ammonium base groups is very thin, hydroxide ions can easily transfer from one side of the dense layer to the pores of the porous support layer. The pores of the porous support layer are filled with water molecules, and without the obstruction of the solid polymer, hydroxide ions are quickly transferred to the cathode. Therefore, the thin-layer composite anion exchange membrane has high ionic conductivity. Furthermore, the cross-linked structure of the modified dense layer prevents methanol penetration. Furthermore, because the porous support layer lacks ionic groups, it has low water absorption, which limits the swelling of the composite membrane in water and ensures its dimensional stability in water.

Claims

1. A composite anion exchange membrane comprising a support layer and a modifying layer containing a quaternary ammonium base, wherein the support layer is a porous support layer of polyacrylonitrile or acrylonitrile copolymer; the modifying layer is obtained by allowing the surface of the support layer to undergo a Mannich reaction with a polyamine and an aldehyde compound, followed by reaction with an ammonium salt containing an epoxy group, and finally exchange with hydroxide.

2. The composite anion exchange membrane according to claim 1, characterized in that: The acrylonitrile copolymer is selected from at least one of styrene-acrylonitrile copolymer, acrylonitrile-butadiene-styrene copolymer, methyl methacrylate-acrylonitrile copolymer, butadiene-acrylonitrile copolymer, acrylonitrile-methacrylonitrile copolymer, acrylate-acrylonitrile copolymer, and ethylene-propylene-styrene-acrylonitrile copolymer; and / or The polyamine is selected from at least one of 1,3,5-triaminobenzene, melamine, diethylenetriamine, tetraethylenepentamine, polyethyleneimine, polyethylenepolyamine, and polyetheramine; and / or The aldehyde compound is selected from at least one of formaldehyde, acetaldehyde, propionaldehyde, n-butyraldehyde, n-valeraldehyde, benzaldehyde, n-heptanal, and paraformaldehyde; and / or, The ammonium salt containing an epoxy group is selected from ammonium halides.

3. The composite anion exchange membrane according to claim 2, characterized in that: The ammonium salt containing an epoxy group is selected from at least one of 2,3-epoxypropyltrimethylammonium chloride, 2,3-epoxypropyltriethylammonium chloride, 1,2-epoxypropyldimethyldodecylammonium chloride, diethyl-2,3-epoxypropyl-[3-(methyldimethoxy)]silylpropylammonium chloride, 2,3-epoxypropyltrimethylammonium bromide, 2,3-epoxypropyltriethylammonium bromide, 1,2-epoxypropyldimethyldodecylammonium bromide and diethyl-2,3-epoxypropyl-[3-(methyldimethoxy)]silylpropylammonium bromide.

4. The composite anion exchange membrane according to claim 1 or 2, characterized in that: The thickness of the support layer is 10 to 60 μm; and / or, The thickness of the modified layer is 10 to 500 nm; and / or The porosity of the support layer is 10-90%.

5. The composite anion exchange membrane according to claim 4, characterized in that: The thickness of the support layer is 20 to 40 μm; and / or, The thickness of the modified layer is 50 to 200 nm; and / or The porosity of the support layer is 50-70%.

6. A method for preparing the composite anion exchange membrane according to any one of claims 1 to 5, comprising the following steps: (1) preparing a casting solution containing polyacrylonitrile or acrylonitrile copolymer and an optional porogen, and forming a membrane to obtain a support layer; (2) contacting one surface of the support layer with a solution containing a polyamine and an aldehyde compound to react; (3) contacting the surface of the reacted membrane obtained in step (2) with a solution of an ammonium salt containing an epoxy group, and heating and drying; (4) Immersing the composite membrane obtained in step (3) in an aqueous solution of sodium hydroxide and / or potassium hydroxide to obtain the composite anion exchange membrane.

7. The method for preparing a composite anion exchange membrane according to claim 6, wherein In the step (1): In the casting solution, the content of polyacrylonitrile or acrylonitrile copolymer is 2.5 to 25 wt%; and / or, The content of the porogen in the casting solution is 0-10 wt%; and / or, The porogen is selected from at least one of polyvinyl pyrrolidone, polyethylene glycol, lithium chloride and lithium bromide.

8. The method for preparing a composite anion exchange membrane according to claim 7, wherein: In the casting solution, the content of polyacrylonitrile or acrylonitrile copolymer is 5 to 20 wt%; and / or, The content of the porogen in the casting solution is 0.1-5 wt%.

9. The method for preparing a composite anion exchange membrane according to claim 6, wherein In the step (2): In the solution containing polyamine and aldehyde compound, the content of polyamine is 0.5-10 wt%; the content of aldehyde compound is 0.1-5 wt%; and / or, The pH of the solution containing the polyamine and the aldehyde compound is 1 to 4; and / or, The temperature of the solution containing polyamine and aldehyde compound is 25-100° C.; and / or, The contact time is 30 to 360 minutes.

10. The method for preparing a composite anion exchange membrane according to claim 9, wherein: In the solution containing polyamine and aldehyde compound, the content of polyamine is 1-5 wt%; the content of aldehyde compound is 0.5-2.5 wt%; and / or, The pH of the solution containing the polyamine and the aldehyde compound is 2 to 3; and / or, The temperature of the solution containing polyamine and aldehyde compound is 50-80° C.; and / or, The contact time is 60 to 180 minutes.

11. The method for preparing a composite anion exchange membrane according to claim 6, characterized in that In the step (3): The content of the quaternary ammonium salt containing epoxy groups in the solution of the ammonium salt containing epoxy groups is 1 to 20 wt %; and / or, The temperature of the solution of the ammonium salt containing epoxy groups is 20 to 80° C.; and / or, The contact time is 10 seconds to 5 minutes; and / or, The heating temperature is 40-120°C; the heating time is 1-30 minutes.

12. The method for preparing a composite anion exchange membrane according to claim 11, wherein: In the solution of the ammonium salt containing epoxy groups, the content of the quaternary ammonium salt containing epoxy groups is 1 to 10 wt%; and / or, The temperature of the solution of the ammonium salt containing epoxy groups is 25-40° C.; and / or, The contact time is 30 seconds to 2 minutes; and / or, The heating temperature is 60-100°C; the heating time is 3-10 minutes.

13. The method for preparing a composite anion exchange membrane according to claim 6, characterized in that In the step (4): The content of sodium hydroxide and / or potassium hydroxide in the aqueous solution is 0.5 to 10 wt%; and / or, The soaking time is 10 to 36 hours.

14. The method for preparing a composite anion exchange membrane according to claim 13, wherein: The aqueous solution contains sodium hydroxide and / or potassium hydroxide in an amount of 1 to 5 wt %; and / or The soaking time is 20 to 30 hours.

15. A composite anion exchange membrane obtained by the preparation method according to any one of claims 6 to 14.

16. Use of the composite anion exchange membrane according to any one of claims 1 to 5 and the composite anion exchange membrane obtained by the preparation method according to any one of claims 6 to 14 in a fuel cell.

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