Preparation method of anion exchange membrane, anion exchange membrane and application of anion exchange membrane
Anion exchange membranes were prepared by using ether-free block copolymers. By employing rigid and flexible segment designs and combining click chemistry and processing technology, the chemical instability and conductivity issues of anion exchange membranes under high temperature and high alkalinity environments were solved, achieving a balance between high stability and high conductivity.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-12-16
- Publication Date
- 2026-03-27
AI Technical Summary
Existing anion exchange membranes are chemically unstable in high-temperature and high-alkali environments, leading to main chain degradation and low ion transport efficiency, making it difficult to achieve both high stability and high conductivity.
Anion exchange membranes containing rigid and flexible segments were prepared using ether-free block copolymers. By clicking chemical grafting of N-spirocyclic piperidinium salt cationic groups, combined with solvent annealing, curing and post-treatment, continuous and ordered nanoscale ion channels were formed.
It significantly improves the chemical stability and ionic conductivity of anion exchange membranes under strong alkaline conditions, extends service life, reduces ohmic loss, and ensures mechanical strength and dimensional stability.
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Abstract
Description
Technical Field
[0001] This invention relates to the field of polymer materials technology, and in particular to a method for preparing anion exchange membrane, the anion exchange membrane itself, and its applications. Background Technology
[0002] Anion exchange membranes (AEMs) are a core component in anion exchange membrane water electrolysis (AEMWE) technology, and their performance directly determines the energy conversion efficiency, operational stability, and economic feasibility of the electrolysis system in renewable energy hydrogen production. With the rapid growth of global demand for green hydrogen energy, developing high-performance AEM materials that combine high ionic conductivity, excellent chemical stability, good mechanical strength, and low swelling rate has become a key challenge in promoting the commercial application of AEMWE technology.
[0003] Traditional anion exchange membranes are mostly based on a structural system of polyarylene ether backbone and benzyl quaternary ammonium salt cationic groups. Under actual operating conditions, especially in harsh environments such as high temperatures (above 80°C) and high-concentration alkaline solutions (such as 1-2 M KOH), these materials exhibit significant chemical instability. On the one hand, the ether bonds (–O–) in the polyarylene ether backbone are easily attacked by strongly nucleophilic hydroxyl ions, leading to hydrolytic breakage of the backbone and structural damage to the membrane material. On the other hand, the commonly used benzyl quaternary ammonium salt cationic groups readily undergo Hoffmann elimination or SN2 nucleophilic substitution reactions in high-temperature, strongly alkaline environments, causing degradation of the cationic groups and resulting in loss of ion exchange capacity, severely impacting the long-term service life of the membrane.
[0004] To improve membrane stability, researchers have attempted to replace traditional polyarylether structures with ether-free polymer backbones to fundamentally eliminate the risk of nucleophilic attack from ether bonds. Simultaneously, they have introduced more alkali-resistant cationic groups to enhance the chemical inertness of cations in strongly alkaline environments. However, these improvement strategies face a profound performance trade-off in practice: while the highly rigid backbone introduced to improve chemical stability enhances alkali resistance, it also severely inhibits the chain mobility of the block copolymer, making it difficult to achieve sufficient and ordered microphase separation during film formation. As a result, the expected well-ordered nanochannels often degenerate into disordered, isolated ion clusters, failing to fully realize ion transport efficiency. In other words, current technology faces a dilemma of balancing "high stability" and "high conductivity"—enhancing backbone rigidity to improve stability sacrifices self-assembly capabilities, thus limiting the improvement of ionic conductivity.
[0005] In view of this, the present invention is hereby proposed. Summary of the Invention
[0006] The purpose of this invention is to provide a method for preparing anion exchange membrane, anion exchange membrane and its application, and to solve at least one of the above-mentioned technical problems in the prior art.
[0007] In order to achieve the above-mentioned objectives of the present invention, the following technical solution is adopted: The first aspect of the present invention provides a method for preparing an anion exchange membrane, wherein an ether-free block copolymer is prepared into a casting solution, the casting solution is then coated to prepare a wet membrane, and the wet membrane is finally subjected to solvent annealing, curing and post-treatment to obtain the anion exchange membrane.
[0008] The ether-free block copolymer comprises alternating rigid and flexible segments, and N-spirocyclic piperidinium salt cationic groups grafted onto the ends or side chains of the flexible segments.
[0009] The ether-free block copolymer does not contain ether bonds.
[0010] The rigid chain segment is selected from at least one of carbazole-based structural units, carbazole-based derivative structural units, fluorene-based structural units, and fluorene-based derivative structural units.
[0011] The flexible segments are mainly composed of alkylene chains connecting adamantyl groups to flexible units.
[0012] Furthermore, the molecular weight of the ether-free block copolymer is 50,000 to 200,000 g / mol.
[0013] Preferably, the PDI of the ether-free block copolymer is <1.5.
[0014] Furthermore, the ratio of the number of repeating units of the rigid chain segment to the number of repeating units of the flexible chain segment is 1 to 4:1.
[0015] Preferably, the molecular weight of the rigid segment is 5000~20000 g / mol.
[0016] Preferably, the repeating units of the rigid chain segment are connected by carbon-carbon bonds or aryl-aryl bonds.
[0017] Preferably, the molecular weight of the flexible segment is 1000~10000 g / mol.
[0018] Preferably, the alkylene chain is a straight chain composed of alkylene groups or a branched saturated hydrocarbon chain composed of alkylene groups.
[0019] Preferably, the alkylene group includes at least one selected from butylene, hexaneene, octaneene, decaneene, or dodecylene.
[0020] Furthermore, the carbazole-based structural unit is a 9H-carbazole-derived unit connected to the polymer backbone via a nitrogen atom or a carbon atom on a benzene ring, and has a rigid tricyclic conjugated structure.
[0021] Furthermore, the fluorene structural unit is a 9H-fluorene derivative unit with a biphenyl framework and containing a bridging carbon atom, exhibiting a highly rigid planar conjugated structure.
[0022] Furthermore, the carbazoyl derivative structural unit or the fluorenyl derivative structural unit is a derivative having at least one substituent selected from halogen atoms, alkyl, aryl or cyano groups introduced into the carbazoyl or fluorenyl structure, wherein the substituent does not affect the chemical stability of its basic skeleton.
[0023] Furthermore, the adamantyl-containing flexible unit is a unit with adamantane as its backbone, connected to the polymer backbone through multiple substitution sites, and optionally further enhanced with alkyl spacer chains.
[0024] The flexible segment serves as a spacer unit between rigid segments, introducing local degrees of freedom of motion and positioning the N-spirocyclic piperidinium salt cationic group at its end or on its side chain, thus keeping the cationic group away from the polymer backbone.
[0025] Furthermore, the N-spirocyclic piperidinium salt cation group includes 6,6'-spirodipiperidinium or 1,4-diazabicyclo(2.2.2)octane.
[0026] Preferably, the N-spirocyclic piperidinium salt cationic group is grafted onto the end or side chain of the flexible segment via a click chemistry reaction.
[0027] Preferably, the click chemistry reaction is selected from the azide-alkyne cycloaddition reaction (CuAAC) or the thiol-ene click reaction.
[0028] Furthermore, the casting solution also includes epoxy compounds and composite solvents.
[0029] Preferably, the epoxy equivalent (EEW) of the epoxy compound is 100~300 g / eq.
[0030] Preferably, the amount of epoxy compound added is 1 to 10% of the mass of the ether-free block copolymer.
[0031] Preferably, the epoxy compound includes at least one of triepoxypropyl isocyanurate, 5,5-dimethyl-1,3-di(epoxyethylenemethyl)imidazolidine-2,4-dione, N,N,N',N'-tetraepoxypropyl-4,4'-diaminodiphenylmethane, 4-(2,3-epoxypropoxy)-N,N-di(2,3-epoxypropyl)aniline, epichlorohydrin, epibromopropane, vinylcyclohexene dioxide, ethylene oxide, propylene oxide, butane oxide, 3-(chloromethyl)ethylene oxide, and 2[3-(trifluoromethyl)phenyl]-epoxychloropropane.
[0032] Preferably, the composite solvent comprises a first organic solvent and a second organic solvent in a volume ratio of (1~4):1.
[0033] Preferably, the first organic solvent comprises dihydro-L-glucosamine (Cyrene) and / or γ-valerolactone.
[0034] Preferably, the second organic solvent comprises tetrahydrofuran (THF).
[0035] Preferably, the solid content of the casting solution is 5-20 wt%.
[0036] Preferably, the solvent annealing temperature is 25~40℃ and the time is 1~6h.
[0037] Preferably, the solvent annealing is carried out under conditions of relative humidity of 50-80%.
[0038] Furthermore, the curing includes thermal curing.
[0039] Preferably, the thermosetting temperature is 60~100℃ and the time is 1~4h.
[0040] Preferably, the post-treatment involves immersing the cured membrane in a buffer solution with a pH of 8-11 and treating it at 40-60°C for 12-48 hours to complete the non-solvent-induced phase separation and achieve anion exchange functionalization, thereby obtaining the final anion exchange membrane.
[0041] Preferably, the buffer solution comprises a phosphate buffer solution.
[0042] Furthermore, the casting solution also includes a photoinitiator.
[0043] Preferably, the amount of photoinitiator is 0.001 to 0.2% of the mass of the ether-free block copolymer.
[0044] Furthermore, the curing includes photocuring.
[0045] Preferably, the wavelength of the light used for photocuring is 340~400nm, and the time is 10~30min.
[0046] A second aspect of the present invention provides an anion exchange membrane, which is prepared using the preparation method described in the first aspect.
[0047] The anion exchange membrane has a hydroxide ion conductivity greater than 120 mS / cm in an 80°C, 1M KOH aqueous solution.
[0048] The in-plane swelling ratio of the anion exchange membrane is <15%.
[0049] The tensile strength of the anion exchange membrane is >30 MPa.
[0050] After being immersed in 2MKOH aqueous solution at 80°C for 1000 hours, the hydroxide ion conductivity of the anion exchange membrane remained at >90%.
[0051] The third aspect of the present invention provides the application of the anion exchange membrane in water electrolysis.
[0052] Compared with the prior art, the present invention has at least the following beneficial effects: The preparation method provided by this invention utilizes rigid segments with highly conjugated structures and excellent alkali resistance, fundamentally avoiding the degradation problem caused by hydroxyl bonds in the traditional polyarylether backbone being susceptible to nucleophilic attack by hydroxyl groups. This significantly improves the chemical stability of the membrane under strong alkaline conditions. Flexible segments introduce local segmental freedom of movement while providing moderate steric hindrance, effectively promoting microphase separation during the film formation process of ether-free block copolymers, which is beneficial for forming continuous and ordered hydrophilic ion channels. More importantly, highly stable N-spirocyclic piperidinium salt cation groups are grafted onto the ends or side chains of the flexible segments, not only away from the sensitive regions of the backbone to enhance its anti-degradation ability but also achieving uniform distribution in the hydrophilic phase, thereby synergistically improving ionic conductivity and long-term stability. Through solvent annealing-induced ordered self-assembly, solidification-locked microstructure, and subsequent functionalization, an anion exchange membrane with high ionic conductivity, low swelling ratio, excellent mechanical strength, and outstanding durability is finally obtained, providing a reliable material basis for high-performance, long-life water electrolysis hydrogen production technology.
[0053] The anion exchange membrane provided by this invention employs rigid segments without ether bonds to construct a highly stable polymer backbone, fundamentally resisting nucleophilic attacks on the main chain by hydroxide ions and significantly improving chemical stability. Simultaneously, the introduction of flexible segments not only enhances segment mobility to promote microphase separation but also precisely positions the highly stable N-spirocyclic piperidinium salt cation groups within the hydrophilic channels through click chemistry, effectively inhibiting Hoffmann elimination and SN2 substitution reactions and significantly improving the cation's alkali resistance. This anion exchange membrane forms continuous, ordered nanoscale ion transport channels, exhibiting excellent hydroxide ion conductivity, dimensional stability, mechanical strength, and long-term durability.
[0054] The application provided by this invention, given the advantages of the aforementioned anion exchange membrane, maintains excellent structural integrity and ion exchange capacity even under high-temperature and strong alkaline conditions, significantly extending the service life of the electrolyzer; its ultra-high hydroxide ion conductivity greatly reduces ohmic losses and improves electrolysis efficiency; at the same time, its low swelling rate and high tensile strength ensure the dimensional stability and mechanical reliability of the membrane during long-term operation, effectively preventing the risk of gas cross-contamination and short circuits caused by swelling deformation or rupture, making it suitable for large-scale renewable energy hydrogen production systems. Detailed Implementation
[0055] To make the objectives, technical solutions, and advantages of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.
[0056] In the following, the terms “comprising,” “having,” and their cognates, which may be used in various embodiments of the invention, are intended only to indicate a particular feature, number, step, operation, element, component, or combination thereof, and should not be construed as excluding, firstly, the presence of one or more other features, numbers, steps, operations, elements, components, or combinations thereof, or adding the possibility of one or more features, numbers, steps, operations, elements, components, or combinations thereof.
[0057] The first aspect of the present invention provides a method for preparing an anion exchange membrane, wherein an ether-free block copolymer is prepared into a casting solution, the casting solution is then coated to prepare a wet membrane, and the wet membrane is finally subjected to solvent annealing, curing and post-treatment to obtain the anion exchange membrane.
[0058] The ether-free block copolymer comprises alternating rigid and flexible segments, and N-spirocyclic piperidinium salt cationic groups grafted onto the ends or side chains of the flexible segments.
[0059] The ether-free block copolymer does not contain ether bonds.
[0060] The rigid chain segment is selected from at least one of carbazole-based structural units, carbazole-based derivative structural units, fluorene-based structural units, and fluorene-based derivative structural units.
[0061] The flexible segments are mainly composed of alkylene chains connecting adamantyl groups to flexible units.
[0062] The preparation method provided by this invention utilizes rigid segments with highly conjugated structures and excellent alkali resistance, fundamentally avoiding the degradation problem caused by hydroxyl bonds in the traditional polyarylether backbone being susceptible to nucleophilic attack by hydroxyl groups. This significantly improves the chemical stability of the membrane under strong alkaline conditions. Flexible segments introduce local segmental freedom of movement while providing moderate steric hindrance, effectively promoting microphase separation during the film formation process of ether-free block copolymers, which is beneficial for forming continuous and ordered hydrophilic ion channels. More importantly, highly stable N-spirocyclic piperidinium salt cation groups are grafted onto the ends or side chains of the flexible segments, not only away from the sensitive regions of the backbone to enhance its anti-degradation ability but also achieving uniform distribution in the hydrophilic phase, thereby synergistically improving ionic conductivity and long-term stability. Through solvent annealing-induced ordered self-assembly, solidification-locked microstructure, and subsequent functionalization, an anion exchange membrane with high ionic conductivity, low swelling ratio, excellent mechanical strength, and outstanding durability is finally obtained, providing a reliable material basis for high-performance, long-life water electrolysis hydrogen production technology.
[0063] Furthermore, the molecular weight of the ether-free block copolymer is 50,000 to 200,000 g / mol.
[0064] Typical but not limiting values can be 50,000 g / mol, 80,000 g / mol, 100,000 g / mol, 120,000 g / mol, 150,000 g / mol, 180,000 g / mol or 200,000 g / mol, or any value in the range of 50,000 to 200,000 g / mol.
[0065] Preferably, the PDI of the ether-free block copolymer is <1.5 to ensure the uniformity of polymer chain length, which is beneficial to subsequent microphase separation.
[0066] Furthermore, the ratio of repeating units of the rigid segments to the flexible segments is 1 to 4:1. The rigid segments provide sufficient skeletal stability and mechanical strength, while the flexible segments provide the necessary channel space and segment mobility for ion transport. When the ratio is less than 1:1, the mechanical strength and stability of the membrane are insufficient, while when it is greater than 4:1, segment movement is excessively suppressed, hindering the formation of ordered microphase separation and thus affecting ionic conductivity. At this optimized ratio, the mechanical properties, chemical stability, and ion transport efficiency of the membrane can be balanced, forming nanoscale ion transport channels with good continuity and regularity.
[0067] Typical but not restrictive ratios can be 1:1, 1.5:1, 2:1, 2.5:1, 3:1, 3.5:1 or 4:1, or any ratio within the range of 1 to 4:1.
[0068] Preferably, the rigid segment has a molecular weight of 5000~20000 g / mol to ensure sufficient rigidity and stability on a macroscopic scale. The repeating units of the rigid segment are connected by stable carbon-carbon bonds or aryl-aryl bonds, thereby avoiding any weak links susceptible to nucleophilic attack.
[0069] Typical but not limiting values can be 5000 g / mol, 8000 g / mol, 10000 g / mol, 12000 g / mol, 15000 g / mol, 18000 g / mol or 20000 g / mol, or any value in the range of 5000 to 20000 g / mol.
[0070] Preferably, the repeating units of the rigid chain segment are connected by carbon-carbon bonds or aryl-aryl bonds.
[0071] Preferably, the molecular weight of the flexible segment is 1000~10000 g / mol.
[0072] Typical but not limiting values can be 1000 g / mol, 2000 g / mol, 4000 g / mol, 6000 g / mol, 8000 g / mol or 10000 g / mol, or any value in the range of 1000 to 10000 g / mol.
[0073] Preferably, the alkylene chain is a straight chain composed of alkylene groups or a branched saturated hydrocarbon chain composed of alkylene groups.
[0074] Preferably, the alkylene group includes at least one selected from butylene, hexaneene, octaneene, decaneene, or dodecylene.
[0075] The presence of the flexible segments introduces local degrees of freedom of movement within the overall rigid framework, effectively increasing the flexibility and thermodynamic mobility of the polymer segments. This provides the necessary conditions for achieving sufficient and ordered microphase separation during film formation of the ether-free block copolymer. This design overcomes the challenge of self-assembly of a purely rigid backbone.
[0076] The adamantyl-containing flexible unit refers to a unit with adamantane as its backbone, connected to the polymer backbone through multiple substitution sites, and potentially further enhanced in flexibility by introducing alkyl spacer chains. The adamantyl group itself has a three-dimensional cage-like structure and a certain degree of rigidity, but its combination with alkylene chains provides unique steric hindrance and limited flexibility, helping to promote nanophase separation while maintaining a certain degree of membrane rigidity.
[0077] The introduction of the flexible segments not only serves as a spacer between the rigid segments but also positions the highly stable N-spirocyclic piperidinium salt cationic groups at their ends or on their side chains. This positioning keeps the cationic groups away from the vulnerable polymer backbone, further enhancing its stability in strongly alkaline environments.
[0078] Furthermore, the carbazole-based structural unit is a 9H-carbazole-derived unit connected to the polymer backbone via a nitrogen atom or a carbon atom on a benzene ring, and has a rigid tricyclic conjugated structure.
[0079] Furthermore, the fluorene structural unit is a 9H-fluorene derivative unit with a biphenyl framework and containing a bridging carbon atom, exhibiting a highly rigid planar conjugated structure.
[0080] Furthermore, the carbazoyl derivative structural unit or the fluorenyl derivative structural unit is a derivative having at least one substituent selected from halogen atoms, alkyl, aryl or cyano groups introduced into the carbazoyl or fluorenyl structure, wherein the substituent does not affect the chemical stability of its basic skeleton.
[0081] Furthermore, the adamantyl-containing flexible unit is a unit with adamantane as its backbone, connected to the polymer backbone through multiple substitution sites, and optionally further enhanced with alkyl spacer chains.
[0082] The flexible segment serves as a spacer unit between rigid segments, introducing local degrees of freedom of motion and positioning the N-spirocyclic piperidinium salt cationic group at its end or on its side chain, thus keeping the cationic group away from the polymer backbone.
[0083] Furthermore, the N-spirocyclic piperidinium salt cation group includes 6,6'-spirodipiperidinium or 1,4-diazabicyclo(2.2.2)octane.
[0084] Preferably, the N-spirocyclic piperidinium salt cationic group is grafted onto the end or side chain of the flexible segment via a click chemistry reaction.
[0085] Preferably, the click chemistry reaction is selected from the azide-alkyne cycloaddition reaction (CuAAC) or the thiol-ene click reaction.
[0086] Furthermore, the casting solution also includes epoxy compounds and composite solvents.
[0087] The epoxy compound undergoes ring-opening polymerization with specific active sites (e.g., pre-introduced hydroxyl, carboxyl, or amine groups) on the rigid segments of the etherless block copolymer through its internal epoxy groups, forming a covalent crosslinked network.
[0088] Preferably, the epoxy equivalent (EEW) of the epoxy compound is 100~300 g / eq.
[0089] Typical but not restrictive values can be 100g / eq, 150g / eq, 200g / eq, 250g / eq, or 300g / eq, or any value within the range of 100 to 300g / eq.
[0090] Preferably, the amount of epoxy compound added is 1 to 10% of the mass of the ether-free block copolymer to ensure that a suitable crosslinking density is formed in subsequent steps, which can effectively lock the microstructure without excessively restricting chain segment movement, thereby maintaining ion transport efficiency.
[0091] Typical but not restrictive percentages can be 1%, 2%, 4%, 6%, 8%, or 10%, or any percentage within the range of 1% to 10%.
[0092] Preferably, the epoxy compound includes at least one of triepoxypropyl isocyanurate, 5,5-dimethyl-1,3-di(epoxyethylenemethyl)imidazolidine-2,4-dione, N,N,N',N'-tetraepoxypropyl-4,4'-diaminodiphenylmethane, 4-(2,3-epoxypropoxy)-N,N-di(2,3-epoxypropyl)aniline, epichlorohydrin, epibromopropane, vinylcyclohexene dioxide, ethylene oxide, propylene oxide, butane oxide, 3-(chloromethyl)ethylene oxide, and 2[3-(trifluoromethyl)phenyl]-epoxychloropropane.
[0093] Preferably, the composite solvent comprises a first organic solvent and a second organic solvent in a volume ratio of (1~4):1.
[0094] Typical, but not limiting, volume ratios can be, for example, 1:1, 2:1, 3:1 or 4:1, or any volume ratio within the range of (1 to 4):1.
[0095] Preferably, the first organic solvent comprises dihydro-L-glucosamine (Cyrene) and / or γ-valerolactone.
[0096] Preferably, the second organic solvent includes tetrahydrofuran (THF), which reduces the overall viscosity of the casting solution, promotes the uniform dispersion of polymer segments in the solution, and can induce a concentration gradient of hydrophilic / hydrophobic segments through its faster evaporation rate during subsequent solvent evaporation, thereby synergistically promoting the occurrence of microphase separation.
[0097] Preferably, the solid content of the casting solution is 5-20 wt%.
[0098] Typical but not limiting, for example, can be 5wt%, 8wt%, 10wt%, 12wt%, 15wt%, 18wt%, or 20wt%, or any percentage in the range of 5 to 20wt%.
[0099] The casting process can employ techniques such as doctor blade coating, spin coating, or slot-die coating to uniformly coat a clean and smooth substrate (e.g., a glass plate or PET film) with a thickness of 50 μm to 200 μm.
[0100] Preferably, the solvent annealing temperature is 25~40℃ and the time is 1~6h.
[0101] Typical, but not limiting, temperatures can be, for example, 25°C, 30°C, 35°C, or 40°C, or any value within the range of 25°C to 40°C; times can be, for example, 1h, 2h, 3h, 4h, 5h, or 6h, or any duration within the range of 1h to 6h.
[0102] Within a range of 1 to 6 hours, the solvent can fully evaporate, while the polymer chain segments have enough time to undergo microphase separation and reach a quasi-equilibrium state in thermodynamics, thereby forming continuous ion transport channels with regular lamellar, cylindrical, or spherical nanoscale morphologies.
[0103] Preferably, the solvent annealing is carried out under conditions of relative humidity of 50-80%.
[0104] Typical, but not limiting, relative humidity can be, for example, 50%, 60%, 70% or 80%, or any percentage within the range of 50% to 80%.
[0105] The solvent annealing temperature affects the solvent diffusion rate and the thermal mobility of polymer segments. Within a specified temperature range, polymer segments possess sufficient kinetic energy for thermodynamic rearrangement while preventing excessively rapid solvent evaporation that could lead to pre-freezing disorder. The regulation of relative humidity, by influencing solvent vapor pressure and the evaporation kinetics of the solvent on the film surface, synergistically regulates the solvent evaporation rate. A high-humidity environment can slow down the solvent evaporation rate, providing a longer relaxation time for polymer segment self-assembly and promoting the formation of a more ordered structure.
[0106] The curing step aims to permanently fix the nanoscale ordered structure formed by the GISAA process, preventing deformation or disintegration due to swelling or thermal disturbance during subsequent processing or in actual working environments. The in-situ crosslinking is characterized by its selectivity. The epoxy compound preferentially reacts with the highly chemically active rigid segments in the ether-free block copolymer. This selective crosslinking mechanism ensures the integrity and continuity of the ion transport channels formed by the flexible segments are unimpeded, while simultaneously enhancing the overall mechanical strength and dimensional stability of the membrane.
[0107] Furthermore, the curing includes thermal curing.
[0108] Preferably, the thermosetting temperature is 60~100℃ and the time is 1~4h, ensuring that the reaction between the epoxy groups and the active sites on the rigid chain segments proceeds fully, forming a stable covalent network, while avoiding thermal damage to the formed nanostructure and sensitive cationic groups. The thermosetting can be carried out in a vacuum oven or in an inert gas atmosphere to prevent oxidation.
[0109] Typical, but not limiting, temperatures can be, for example, 60°C, 70°C, 80°C, 90°C, or 100°C, or any value within the range of 60°C to 100°C; times can be, for example, 1h, 2h, 3h, or 4h, or any duration within the range of 1h to 4h.
[0110] Preferably, the post-treatment involves immersing the cured membrane in a buffer solution with a pH of 8-11 and treating it at 40-60°C for 12-48 hours to complete the non-solvent-induced phase separation and achieve anion exchange functionalization, resulting in the final anion exchange membrane. The post-treatment further removes residual solvent from the membrane, promotes the final separation and hydration of the hydrophilic / hydrophobic phases, and activates the anionic groups in the membrane into hydroxide ions, thereby enabling it to have ion exchange function.
[0111] The pH value ensures that the N-spirocyclic piperidinium salt cation groups in the membrane can efficiently perform anion exchange, completely replacing the paired counterions (such as halide ions that may be present during synthesis) with hydroxide ions, while avoiding potential degradation of the cation groups or polymer backbone under extreme pH conditions.
[0112] The pH value can typically, but is not limiting, be 8, 9, 10, or 11, or any value within the range of 8 to 11; the treatment temperature can be 40°C, 45°C, 50°C, 55°C, or 60°C, or any value within the range of 40 to 60°C. This temperature range helps to accelerate the diffusion of the solvent and the rate of ion exchange, while ensuring that the structural integrity of the membrane material is not damaged by excessively high temperatures; the treatment time can be 12h, 24h, 36h, or 48h, or any duration within the range of 12 to 48 hours.
[0113] Using a buffer solution as a non-solvent (water), a solvent-non-solvent exchange process is employed to promote further rearrangement of polymer chains within the membrane. The hydrophilic phase swells sufficiently to form continuous hydrated ion channels, while the hydrophobic phase maintains its structural integrity, thereby achieving more thorough phase separation and optimizing membrane performance. The resulting membrane is then washed and dried before use in the AEMWE system.
[0114] Preferably, the buffer solution comprises a phosphate buffer solution.
[0115] Furthermore, the casting solution also includes a photoinitiator.
[0116] Preferably, the amount of photoinitiator is 0.001 to 0.2% of the mass of the ether-free block copolymer.
[0117] Typical but not limiting, for example, can be 0.001%, 0.01%, 0.05%, 0.1%, 0.15% or 0.2%, or any percentage in the range of 0.001 to 0.2%.
[0118] Furthermore, the curing includes photocuring.
[0119] Preferably, the wavelength of the photocuring light is 340-400 nm, and the time is 10-30 min. Ultraviolet light within this wavelength range has suitable energy, which can efficiently initiate the photoinitiator to produce active substances, thereby catalyzing the cross-linking reaction of epoxy groups. The irradiation time ensures the thoroughness of the cross-linking reaction. The photocuring process is usually carried out under the protection of an inert gas (such as nitrogen) to avoid oxygen inhibition of polymerization.
[0120] Through the curing step, a three-dimensional cross-linked network is formed, which firmly fixes the hydrophilic and hydrophobic water phases of the microphase separation in their respective positions. This allows the microstructure of the membrane material to maintain a high degree of order and stability during the subsequent water absorption and swelling process, thereby significantly improving the mechanical strength and dimensional stability of the membrane while maintaining high ionic conductivity.
[0121] Typically, but not limitingly, the light wavelength can be, for example, 340 nm, 350 nm, 360 nm, 370 nm, 380 nm or 400 nm, or any wavelength in the range of 340 to 400 nm; the time can be, for example, 10 min, 15 min, 20 min, 25 min or 30 min, or any duration in the range of 10 to 30 min.
[0122] A second aspect of the present invention provides an anion exchange membrane, which is prepared using the preparation method described in the first aspect.
[0123] The anion exchange membrane has a hydroxide ion conductivity greater than 120 mS / cm in an 80°C, 1 MkOH aqueous solution.
[0124] The in-plane swelling ratio of the anion exchange membrane is <15%.
[0125] The tensile strength of the anion exchange membrane is >30 MPa.
[0126] After being immersed in 2M KOH aqueous solution at 80℃ for 1000 hours, the hydroxide ion conductivity of the anion exchange membrane retained >90%, which fully demonstrates the excellent long-term chemical stability of the anion exchange membrane under harsh strong alkaline and high-temperature conditions. This stability stems from the resistance of the rigid backbone without ether bonds to nucleophilic attack, and the inhibitory effect of the N-spirocyclic piperidinium salt cation group on Hoffmann elimination and SN2 substitution reactions. These two aspects work synergistically to extend the membrane's lifespan and improve the operational reliability and economy of the AEMWE system.
[0127] The anion exchange membrane provided by this invention employs rigid segments without ether bonds to construct a highly stable polymer backbone, fundamentally resisting nucleophilic attacks on the main chain by hydroxide ions and significantly improving chemical stability. Simultaneously, the introduction of flexible segments not only enhances segment mobility to promote microphase separation but also precisely positions the highly stable N-spirocyclic piperidinium salt cation groups within the hydrophilic channels through click chemistry, effectively inhibiting Hoffmann elimination and SN2 substitution reactions and significantly improving the cation's alkali resistance. This anion exchange membrane forms continuous, ordered nanoscale ion transport channels, exhibiting excellent hydroxide ion conductivity, dimensional stability, mechanical strength, and long-term durability.
[0128] The third aspect of the present invention provides the application of the anion exchange membrane in water electrolysis.
[0129] The application provided by this invention, given the advantages of the aforementioned anion exchange membrane, maintains excellent structural integrity and ion exchange capacity even under high-temperature and strong alkaline conditions, significantly extending the service life of the electrolyzer; its ultra-high hydroxide ion conductivity greatly reduces ohmic losses and improves electrolysis efficiency; at the same time, its low swelling rate and high tensile strength ensure the dimensional stability and mechanical reliability of the membrane during long-term operation, effectively preventing the risk of gas cross-contamination and short circuits caused by swelling deformation or rupture, making it suitable for large-scale renewable energy hydrogen production systems.
[0130] The present invention is further illustrated below with specific embodiments and comparative examples. However, it should be understood that these embodiments are merely for illustrative purposes and should not be construed as limiting the invention in any way. Unless otherwise specified, the raw materials used in the embodiments and comparative examples of the present invention were carried out under conventional conditions or conditions recommended by the manufacturer. Reagents or instruments used, unless otherwise specified, are all commercially available conventional products.
[0131] Example 1 This embodiment provides an anion exchange membrane, and the specific preparation method is as follows: (1) Etherless block copolymer: comprising rigid and flexible segments with alternating repeating units in a ratio of 3:1; wherein the rigid segments contain several carbazole structural units. The average molecular weight of the rigid segments is 15,000 g / mol.
[0132] The flexible segment consists of a hexane chain linking flexible units containing adamantyl groups, with N-spirocyclic piperidinium salt cationic groups grafted onto the ends or side chains of the flexible segment. The average molecular weight of the flexible segment is 5,000 g / mol.
[0133] The polydispersity index (PDI) of the ether-free block copolymer is 1.32.
[0134] (2) Add 10.0 g of ether-free block copolymer and 0.5 g of trioxypropyl isocyanurate (EEW=130 g / eq) to 200 mL of mixed solvent to obtain a mixture.
[0135] The mixed solvent is composed of dihydro-L-glucosamine (Cyrene) and tetrahydrofuran (THF) in a volume ratio of 3:1.
[0136] The mixture was mechanically stirred at 60°C for 15 hours until a clear and transparent homogeneous solution was formed. Subsequently, the homogeneous solution was filtered under reduced pressure through a 0.45 μm PTFE membrane to remove any particles and bubbles, resulting in a final solids content of 5.2 wt% in the casting solution.
[0137] (3) The casting solution was uniformly coated onto a smooth glass substrate measuring 20cm × 20cm using a doctor blade coating method, with the doctor blade gap set to 100 μm, to form a wet film. The coated wet film was immediately transferred to a specially designed solvent annealing chamber. The temperature of the solvent annealing chamber was precisely controlled at 35°C, and the relative humidity was maintained at 70%. Solvent evaporation and annealing were carried out under this controlled environment for 3 hours.
[0138] (4) The film that has undergone solvent annealing, together with the glass substrate, is transferred to a vacuum oven and subjected to heat curing at 80°C for 2 hours.
[0139] (5) The thermocured membrane was carefully peeled off from the glass substrate and immersed in a phosphate buffer water bath (45°C) with a pH of 10.5. The water bath solution was changed every 12 hours, and the total immersion time was 36 hours. After immersion, the membrane was thoroughly washed several times with deionized water to remove the residual buffer salts on the surface, and finally vacuum dried at room temperature for 24 hours to obtain the anion exchange membrane.
[0140] Example 2 This embodiment provides an anion exchange membrane. Unlike Example 1, in step (2), the mixed solvent is composed of γ-valerol and tetrahydrofuran (THF) in a volume ratio of 4:1. In step (3), the temperature of the solvent annealing chamber is precisely controlled at 25°C, and the relative humidity is maintained at 80%. The solvent evaporates and annealing is carried out for 5 hours under this controlled environment. The remaining steps are the same as in Example 1 and will not be repeated here.
[0141] Example 3 This embodiment provides an anion exchange membrane, which differs from Embodiment 1 in that the casting solution also includes 0.1g of photoinitiator (triphenyl phosphite); and the curing in step (4) is performed using ultraviolet light curing (365nm, intensity 20 mW / cm). 2 (Irradiation for 20 minutes) instead of heat curing, the remaining steps are the same as in Example 1, and will not be repeated here.
[0142] Example 4 This embodiment provides an anion exchange membrane. Unlike Example 1, the rigid segments in the ether-free block copolymer are composed of alternating carbazole and fluorene derivative units (9,9-dimethylfluorene) in a 1:1 ratio, with a total rigid segment molecular weight of approximately 15,000 g / mol. The remaining raw materials and preparation methods are the same as in Example 1 and will not be repeated here.
[0143] Example 5 This embodiment provides an anion exchange membrane. Unlike Example 1, the cationic group grafted onto the flexible segment is a 1,4-diazabicyclo(2.2.2)octane (DABCO) quaternary ammonium salt, rather than a 6,6'-spiropiperidinium salt. This group is grafted onto the flexible segment containing the terminal alkyne group via the same azide-alkyne click chemistry reaction (CuAAC). The remaining preparation steps are the same as in Example 1 and will not be repeated here.
[0144] Example 6 This embodiment provides an anion exchange membrane. Unlike embodiment 1, step (3) takes 6 hours. The remaining preparation steps are the same as in embodiment 1 and will not be repeated here.
[0145] Comparative Example 1 This comparative example provides an anion exchange membrane. An ether-free block copolymer (with parameters and specifications the same as in Example 1) and triglycidyl isocyanurate (EEW = 130 g / eq) were dissolved in DMF to prepare a casting solution with a solid content of 5.2 wt%. After casting the solution into a film, the solvent was removed directly in a vacuum drying oven at 60°C. The film was then heat-cured at 80°C for 2 hours, and then immersed in a 1M KOH aqueous solution for 24 hours at 60°C. Subsequently, it was thoroughly washed with deionized water and vacuum-dried at room temperature for 24 hours to obtain the anion exchange membrane.
[0146] Comparative Example 2 This comparative example provides an anion exchange membrane. The difference from Example 1 is that the solvent annealing step in step (3) is omitted, and the coated wet membrane is directly transferred to a vacuum oven for subsequent steps. The other raw materials and preparation methods are the same as in Example 1, and will not be repeated here.
[0147] Comparative Example 3 This comparative example provides an anion exchange membrane. The difference from Example 1 is that step (5) is omitted, and the thermo-cured membrane is directly used as an anion exchange membrane. The other raw materials and preparation methods are the same as in Example 1, and will not be repeated here.
[0148] Test Example 1 The anion exchange membranes obtained in the examples and comparative examples were subjected to performance tests under the following conditions: ionic conductivity was measured by AC impedance spectroscopy in 1M KOH aqueous solution at 80°C. Swelling rate was calculated by measuring the dimensional changes of the membrane before and after immersion in 1M KOH solution at 80°C for 24 hours. Tensile strength was tested using a universal testing machine at room temperature. Long-term chemical stability was assessed by measuring the hydroxide ion conductivity again and calculating the retention rate after immersion in 2M KOH aqueous solution at 80°C for 1000 hours.
[0149] The obtained data is recorded in Table 1.
[0150] Table 1
[0151] As shown in Table 1, the ionic conductivity of all examples under 80℃ and 1M KOH conditions exceeded 120 mS / cm, reaching a maximum of 140 mS / cm; and after immersion in 80℃ and 2M KOH for 1000 hours, the conductivity retention rate was not less than 91%, fully demonstrating its excellent chemical stability. Compared with the traditional DMF solvent system used in Comparative Example 1 and the method of omitting post-treatment in Comparative Example 3, this invention significantly reduces the in-plane swelling rate of the membrane by adopting key technologies such as an ether-free rigid-flexible alternating copolymer structure, a green composite solvent system, solvent annealing-induced ordered microphase separation, and buffer post-treatment: the swelling rate of Example 2 was as low as 22.74%, far superior to 30.41% of Comparative Example 1 and 31.92% of Comparative Example 3, and improved tensile strength and structural integrity.
[0152] Meanwhile, Example 3, by introducing a photocuring process, further controlled the swelling rate to 15.69%, increased the tensile strength to 37.08 MPa, and achieved a conductivity retention rate of 97.02%, demonstrating the best overall performance.
[0153] The above results demonstrate that the present invention effectively solves the technical challenge of balancing high conductivity and high stability in traditional anion exchange membranes through the synergistic effect of molecular structure design and membrane formation process, providing a membrane material basis with great application prospects for high-performance water electrolysis hydrogen production.
[0154] Finally, it should be noted that the above-described embodiments are merely specific implementations of the present invention, used to illustrate the technical solutions of the present invention, and not to limit it. The scope of protection of the present invention is not limited thereto. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that any person skilled in the art can still modify or easily conceive of changes to the technical solutions described in the foregoing embodiments within the technical scope disclosed in the present invention, or make equivalent substitutions for some of the technical features; and these modifications, changes, or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention, and should all be covered within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.
Claims
1. A method for preparing an anion exchange membrane, characterized in that, A casting solution was prepared by using a non-etheric block copolymer, and then a wet membrane was prepared by coating the casting solution. Finally, the wet membrane was subjected to solvent annealing, curing and post-treatment to obtain the anion exchange membrane. The ether-free block copolymer comprises alternating rigid and flexible segments, and N-spirocyclic piperidinium salt cationic groups grafted onto the ends or side chains of the flexible segments. The ether-free block copolymer does not contain ether bonds; The rigid chain segment is selected from at least one of carbazoyl structural units, carbazoyl derivative structural units, fluorenyl structural units, and fluorenyl derivative structural units; The flexible segments are mainly composed of alkylene chains connecting adamantyl groups to flexible units.
2. The preparation method according to claim 1, characterized in that, The molecular weight of the ether-free block copolymer is 50,000 to 200,000 g / mol; Preferably, the PDI of the ether-free block copolymer is <1.
5.
3. The preparation method according to claim 1, characterized in that, The ratio of the number of repeating units of the rigid chain segment to the number of repeating units of the flexible chain segment is 1 to 4:1; Preferably, the molecular weight of the rigid segment is 5000~20000 g / mol; Preferably, the repeating units of the rigid chain segment are connected by carbon-carbon bonds or aryl-aryl bonds; Preferably, the molecular weight of the flexible segment is 1000~10000 g / mol; Preferably, the alkylene chain is a straight chain composed of alkylene groups or a branched saturated hydrocarbon chain composed of alkylene groups. Preferably, the alkylene group includes at least one selected from butylene, hexaneene, octaneene, decaneene, or dodecylene.
4. The preparation method according to any one of claims 1 to 3, characterized in that, The N-spirocyclic piperidinium salt cation group includes 6,6'-spirodipiperidinium or 1,4-diazabicyclo(2.2.2)octane; Preferably, the N-spirocyclic piperidinium salt cationic group is grafted onto the end or side chain of the flexible segment via a click chemistry reaction; Preferably, the click chemistry reaction is selected from azide-alkyne cycloaddition reaction or thiol-ene click reaction.
5. The preparation method according to any one of claims 1 to 3, characterized in that, The casting solution also includes epoxy compounds and composite solvents; Preferably, the epoxy equivalent of the epoxy compound is 100~300 g / eq; Preferably, the amount of epoxy compound added is 1-10% of the mass of the ether-free block copolymer; Preferably, the epoxy compound comprises at least one selected from the following: triepoxypropyl isocyanurate, 5,5-dimethyl-1,3-di(epoxyethylenemethyl)imidazolidine-2,4-dione, N,N,N',N'-tetraepoxypropyl-4,4'-diaminodiphenylmethane, 4-(2,3-epoxypropoxy)-N,N-di(2,3-epoxypropyl)aniline, epichlorohydrin, epibromopropane, vinylcyclohexene dioxide, ethylene oxide, propylene oxide, butane oxide, 3-(chloromethyl)ethylene oxide, and 2[3-(trifluoromethyl)phenyl]-epoxychloropropane; Preferably, the composite solvent comprises a first organic solvent and a second organic solvent in a volume ratio of (1~4):1; Preferably, the first organic solvent comprises dihydro-L-glucosidone and / or γ-valerolactone; Preferably, the second organic solvent comprises tetrahydrofuran; Preferably, the solid content of the casting solution is 5-20 wt%; Preferably, the solvent annealing temperature is 25~40℃ and the time is 1~6h; Preferably, the solvent annealing is carried out under conditions of relative humidity of 50-80%.
6. The preparation method according to any one of claims 1 to 3, characterized in that, The curing includes thermosetting; Preferably, the thermosetting temperature is 60~100℃ and the time is 1~4h; Preferably, the post-treatment involves immersing the cured membrane in a buffer solution with a pH of 8-11 and treating it at 40-60°C for 12-48 hours to complete the non-solvent-induced phase separation and achieve anion exchange functionalization, thereby obtaining the final anion exchange membrane. Preferably, the buffer solution comprises a phosphate buffer solution.
7. The preparation method according to claim 5, characterized in that, The casting solution also includes a photoinitiator; Preferably, the amount of photoinitiator is 0.001 to 0.2% of the mass of the ether-free block copolymer.
8. The preparation method according to claim 7, characterized in that, The curing includes photocuring; Preferably, the wavelength of the light used for photocuring is 340~400nm, and the time is 10~30min.
9. An anion exchange membrane, characterized in that, It was prepared by the preparation method according to any one of claims 1 to 8; The anion exchange membrane has a hydroxide ion conductivity greater than 120 mS / cm in 80℃ and 1M KOH aqueous solution. The in-plane swelling ratio of the anion exchange membrane is <15%; The tensile strength of the anion exchange membrane is >30 MPa.
10. The application of the anion exchange membrane according to claim 9 in water electrolysis.