Block anion exchange membrane with gapped alkyl chain and method for preparing the same

Abstract

The application belongs to the field of polymer electrolyte membranes, and particularly relates to a block type anion exchange membrane with an interval alkyl chain and a preparation method thereof. A tetrahydrofuran solution of n-butyllithium is added to anhydrous toluene to react, and then an alpha, omega-dihaloalkane is added to obtain an alpha, omega-diphenylalkane; a pre-polymer 1 is obtained by pre-polymerization of biphenyl and 4-imidazole formaldehyde, and a pre-polymer 2 is obtained by pre-polymerization of the alpha, omega-diphenylalkane and 4-imidazole formaldehyde; two pre-polymer solutions are mixed to obtain a fibrous block type polymer with an interval alkane chain; and finally, anion exchange membranes are obtained through quaternization and ion replacement. The application constructs micro-phase separation in the polymer membrane through the block structure to improve the conductivity; the interval alkyl chain is introduced into the main chain of the AEMs to reduce the rigidity of the polybiphenyl and improve the flexibility of the membrane; and the ether bond-free main chain design is used to enhance the alkali resistance of the polymer electrolyte membrane.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of polymer electrolyte membranes, and particularly relates to a block type anion exchange membrane with an interstitial alkyl chain and a preparation method thereof. BACKGROUND

[0002] Fuel cells and water electrolysis technology can realize efficient conversion and circulation of hydrogen energy and various energy forms, and promote the realization of the "carbon neutralization and carbon peak" goal. Anion exchange membrane fuel cells (AEMFCs) and anion exchange membrane water electrolysis (AEMWEs) technologies applied in alkaline environment are widely considered as key technologies for the development of hydrogen energy because they can use non-noble metal catalysts and relatively low-cost anion exchange membranes to replace expensive perfluorosulfonic acid membranes. Anion exchange membranes (AEMs) are the core components of such hydrogen energy conversion technologies, and have received extensive attention from researchers in recent decades. Some commercial anion exchange membranes have been developed, such as Fumasep, Sustainion and Aemion membranes, however, their low conductivity, poor dimensional stability and poor alkaline resistance seriously limit the development of AEMFCs and AEMWEs.

[0003] It has been found that increasing the ion exchange capacity of the membrane can effectively improve the conductivity of the electrolyte membrane, but at the same time it can also cause excessive water absorption into the membrane, resulting in excessive swelling and a decrease in mechanical properties. Constructing hydrophilic / hydrophobic microphase separation structure in the polymer can provide a high-speed channel for ion transport, and the hydrophobic phase in the membrane can effectively limit the swelling of the membrane.

[0004] Recent studies have found that if there is a weak polar bond (such as an ether bond) in the polymer molecular structure, the polymer backbone is easily attacked by OH- nucleophilic attack under high temperature and high alkaline environment, resulting in a decrease in the alkaline resistance of AEMs. Designing and preparing a polymer backbone without weak bonds (such as polyaromatic or polyolefin) as the polymer backbone has become a mainstream method to improve the alkaline resistance of AEMs. However, on the one hand, polyolefin structures have a relatively weak intermolecular interaction, resulting in excessive swelling and poor thermal stability of AEMs based on polyolefin. On the other hand, the rigidity of traditional polyaromatic is usually large, resulting in poor film-forming property and flexibility of AEMs. AMEs based on these two types of backbones need to be further designed and modified to improve the performance of the membranes. Therefore, it is urgent to develop an AEMs with high conductivity, high dimensional stability and high alkaline resistance to meet the practical application of hydrogen energy conversion devices. SUMMARY

[0005] The present application aims to overcome the deficiencies of the prior art and provide a block type anion exchange membrane with high conductivity, high dimensional stability and high alkali resistance, which is designed and prepared from a molecular level with a block type biphenyl polymer with an interstitial alkyl chain. The microphase separation is constructed in the polymer membrane through the block structure to improve the conductivity; the interstitial alkyl chain is introduced into the main chain of the AEMs to reduce the rigidity of the polybiphenyl and improve the flexibility of the membrane; and the ether bond-free main chain design is used to enhance the alkali resistance of the polymer electrolyte membrane.

[0006] To achieve the above object, the technical scheme adopted by the present application is that the block type anion exchange membrane with an interstitial alkyl chain has a chemical structure general formula comprising the following repeating unit:

[0007]

[0008] In the formula, n is the length of the interstitial alkyl chain, which is an integer of 2-12; x is the content of the biphenyl unit, which is greater than 0 and less than 1, and m represents the degree of polymerization.

[0009] Another object of the present application is to provide a preparation method of the high-performance block type anion exchange membrane with an interstitial alkyl chain, which mainly comprises the following steps:

[0010] (a) Synthesis of alpha, omega-diphenylalkane

[0011] The tetrahydrofuran solution of n-butyllithium is slowly added to the dehydrated toluene at -78°C and stirred at room temperature for 3 hours. Then, the alpha, omega-dihaloalkane is added to the reaction solution and reacted at room temperature for 12-24 hours. The reaction solution is quenched with water and extracted with ethyl acetate. The extracted solution is dried to obtain a crude product, which is finally separated and purified by column chromatography to obtain the target alpha, omega-diphenylalkane.

[0012] The molar ratio of n-butyllithium to alpha, omega-dihaloalkane is 2:1, the molar ratio of toluene to alpha, omega-dihaloalkane is greater than 2:1, the separation and purification eluent is n-hexane, and the stationary phase is silica gel.

[0013] (b) Preparation of block type polymer

[0014] The biphenyl and 4-imidazole formaldehyde are dissolved in dichloromethane (the material concentration is 10-30 wt%, and the molar amount of 4-imidazole formaldehyde is 1.1 times that of biphenyl), the mixed acid of trifluoromethanesulfonic acid and methanesulfonic acid (volume ratio 3:4) is added under ice water bath, and the prepolymer solution 1 is obtained by pre-polymerization under ice water bath for 5 hours.

[0015] The α,ω-diphenylalkane and 4-imidazole carboxaldehyde in step (a) are dissolved in dichloromethane (10-30wt%, 4-imidazole carboxaldehyde is 1.1 times of α,ω-diphenylalkane in molar amount), and the mixed acid of trifluoromethanesulfonic acid and methane sulfonic acid (volume ratio 3:4) is added under ice water bath, and the prepolymer solution is pre-polymerized for 5 hours under ice water bath. The prepolymer solution 2 is obtained.

[0016] Finally, the two prepolymer solutions are mixed, and further mechanically stirred at room temperature for 12-24 hours. The mixture becomes highly viscous, and the mixture is washed out with deionized water until the washing liquid is neutral, to obtain a fibrous block polymer with an interstitial alkane chain.

[0017] The ratio of the two prepolymer solutions ensures that the content of biphenyl or α,ω-diphenylalkyl group is greater than 0 and less than 1, and the total sum is 1.

[0018] (c) Quaternization

[0019] The block polymer in step (b) is dissolved in dimethyl sulfoxide, and potassium carbonate and iodomethane are added (the molar ratio of potassium carbonate to polymer is 2:1, and the molar ratio of iodomethane to polymer is 1:10), and the reaction is stirred at 60°C for 24 hours. The reaction liquid is precipitated with ethanol, and washed with water to obtain the target quaternary ammonium polymer. Finally, the quaternary ammonium polymer is re-dissolved in dimethyl sulfoxide, and the membrane solution is dropped into a clean glass mold, and placed in an oven at 80°C to dry into a film. Finally, the film is soaked in a 60°C potassium hydroxide solution for 24 hours for ion replacement to obtain an OH-type anion exchange membrane.

[0020] The block anion exchange membrane with an interstitial alkane chain prepared by the present application can be applied in the fields of fuel cells, flow batteries, water electrolysis, electrodialysis or separation membranes, etc.

[0021] Compared with the prior art, the present application has the following advantages due to the use of the above technical solutions:

[0022] (1) The design of the block structure is beneficial to the construction of micro-phase separation inside the membrane, thereby providing a high-speed channel for ion transmission and improving the ion conductivity. At the same time, the hydrophobic phase can limit the excessive swelling of the membrane;

[0023] (2) The introduction of flexible interstitial alkyl chains in the rigid polybiphenyl can improve the flexibility of the aromatic ring polymer and improve the film forming ability;

[0024] (3) The design of the main chain without weak bonds (such as ether bonds) can effectively enhance the alkali resistance stability of AEMs. BRIEF DESCRIPTION OF DRAWINGS

[0025] Figure 1 NMR hydrogen spectrum of 1,6-diphenylhexane synthesized in Example 1.

[0026] Figure 2 Figure 1 shows the H2 / O2 fuel cell performance of the block type AEMs prepared in Example 1 and the random copolymer type AEMs in Comparative Example 1.

[0027] Figure 3 Figure 2 shows the H2 / O2 fuel cell performance of the block type AEMs prepared in Example 3 with spacer alkyl chains and the random copolymer type AEMs in Comparative Example 1. DETAILED DESCRIPTION

[0028] The application will now be further described with reference to some specific examples.

[0029] Example 1

[0030] (a) n-BuLi (8 mL, 20 mmol, 2.5 M in hexane) was slowly added dropwise to 10 mL of dry toluene at -78 °C under nitrogen. Then 10 mL of dry THF was slowly added dropwise. The mixture was allowed to react at room temperature for 3 hours, then 1,6-dibromohexane (2.44 g, 10 mmol) was slowly added and the mixture was allowed to react at room temperature for 12 hours. The reaction was quenched with water and extracted with ethyl acetate. The organic layer was dried to give the crude product, which was finally purified by column chromatography using hexane to give clean 1,6-diphenylhexane.

[0031] (b) Biphenyl (1.54 g, 10 mmol) and 4-imidazole carboxaldehyde (1.05 g, 11 mmol) were stirred and dissolved in 10 mL of dichloromethane. The mixed acid of trifluoromethanesulfonic acid and methanesulfonic acid (6 mL / 8 mL) was slowly added dropwise under ice water bath. The pre-polymer solution 1 was obtained by mechanical stirring for 5 hours. 1,6-Diphenylhexane (2.38 g, 10 mmol) and 4-imidazole carboxaldehyde (1.05 g, 11 mmol) were stirred and dissolved in 10 mL of dichloromethane. The mixed acid of trifluoromethanesulfonic acid and methanesulfonic acid (6 mL / 8 mL) was slowly added dropwise under ice water bath. The pre-polymer solution 2 was obtained by mechanical stirring for 5 hours. Finally, the two solutions were mixed and mechanical stirring was continued for 24 hours. The reaction became highly viscous and was poured into deionized water to precipitate and wash until the washing solution was neutral to give the fibrous block type polymer.

[0032] (c) The block polymer in step (b) was dissolved in dimethyl sulfoxide, then potassium carbonate and iodomethane (molar ratio of potassium carbonate, iodomethane and polymer was 2:10:1) were added, the reaction was stirred at 60°C for 12 hours, then the reaction solution was poured into ethanol to precipitate and wash, followed by further washing with water, and finally dried to obtain the quaternized block polymer. The quaternized block polymer was re-dissolved in dimethyl sulfoxide, and the membrane solution was poured into a clean glass mold and dried into a film in an oven at 80°C. Finally, the membrane was immersed in a potassium hydroxide solution at 60°C for 24 hours for ion exchange to obtain an OH-type anion exchange membrane. The structural formula of the target AEMs obtained is as follows:

[0033]

[0034] The water absorption, swelling degree and ionic conductivity of the prepared AEMs were 72%, 26% and 115 mS cm -1 at 80°C, the tensile strength and elongation at break in the wet state were 15 MPa and 152%, the H2 / O2 fuel cell performance at 80°C reached 1.21 W cm -2 , and the voltage of the electrolytic water tank at a current density of 1 A cm -2 was 2.05 V.

[0035] Example 2

[0036] Example 2 was similar to Example 1, except that the α,ω-dihaloalkane selected in step (a) was 1,2-dibromoethane, and 1,2-diphenylethane was prepared.

[0037] In addition, in step (b) of pre-polymerization, biphenyl (2.31 g, 15 mmol) and 4-imidazole formaldehyde (1.59 g, 16.5 mmol) were stirred and dissolved in 15 mL of dichloromethane. The mixed acid of trifluoromethanesulfonic acid and methanesulfonic acid (9 mL / 12 mL) was slowly added under ice water bath, and the pre-polymerization was mechanically stirred for 5 hours. Meanwhile, 1,2-diphenylethane (0.91 g, 5 mmol) and 4-imidazole formaldehyde (0.53 g, 5.5 mmol) were stirred and dissolved in 10 mL of dichloromethane. The mixed acid of trifluoromethanesulfonic acid and methanesulfonic acid (3 mL / 4 mL) was slowly added under ice water bath, and the pre-polymerization was mechanically stirred for 5 hours. Finally, the two were mixed and mechanically stirred for 24 hours, and the reaction solution became highly viscous, which was poured into deionized water to precipitate and wash until the washing liquid was neutral to obtain a fibrous block polymer.

[0038] The structural formula of the target AEMs obtained is as follows:

[0039]

[0040] The water uptake, swelling degree, and ionic conductivity of the prepared AEMs were 40%, 16%, and 76 mS cm at 80 °C -1 ; the tensile strength and elongation at break in wet state were 29 MPa and 77%; the H2 / O2 fuel cell performance reached 0.81 W cm at 80 °C -2 ; the voltage of the electrolysis cell was 2.58 V at 1 A cm -2 at 60 °C.

[0041] Example 3

[0042] Example 3 was similar to Example 2, except that in step (b) for the prepolymerization, diphenyl (1.54 g, 10 mmol) and 4-imidazole carboxaldehyde (1.05 g, 11 mmol) were stirred and dissolved in 10 mL of dichloromethane. A mixed acid of trifluoromethanesulfonic acid and methanesulfonic acid (6 mL / 8 mL) was slowly added under an ice water bath, and the prepolymerization was mechanically stirred for 5 hours. Meanwhile, 1,6-diphenylhexane (1.82 g, 10 mmol) and 4-imidazole carboxaldehyde (1.05 g, 11 mmol) were stirred and dissolved in 10 mL of dichloromethane. A mixed acid of trifluoromethanesulfonic acid and methanesulfonic acid (6 mL / 8 mL) was slowly added under an ice water bath, and the prepolymerization was mechanically stirred for 5 hours. Finally, the two were mixed, and mechanical stirring was continued for 24 hours. The reaction liquid became highly viscous, and it was poured into deionized water for precipitation and washing until the washing liquid was neutral, to obtain a fibrous block-type polymer.

[0043] The structural formula of the obtained target AEMs was as follows:

[0044]

[0045] The water uptake, swelling degree, and ionic conductivity of the prepared AEMs were 48%, 19%, and 88 mS cm at 80 °C -1 ; the tensile strength and elongation at break in wet state were 25 MPa and 110%; the H2 / O2 fuel cell performance reached 0.92 W cm at 80 °C -2 ; the voltage of the electrolysis cell was 2.42 V at 1 A cm -2 at 60 °C.

[0046] Example 4

[0047] Example 4 is similar to Example 2, except that in step (b) the pre-polymerization, diphenyl (0.77 g, 5 mmol) and 4-imidazole carboxaldehyde (0.53 g, 5.5 mmol) were stirred and dissolved in 5 mL of dichloromethane. The mixed acid of trifluoromethanesulfonic acid and methanesulfonic acid (3 mL / 4 mL) was added slowly under ice water bath, and the pre-polymerization was mechanically stirred for 5 hours. Meanwhile, 1,6-diphenylhexane (2.73 g, 15 mmol) and 4-imidazole carboxaldehyde (1.59 g, 16.5 mmol) were stirred and dissolved in 15 mL of dichloromethane. The mixed acid of trifluoromethanesulfonic acid and methanesulfonic acid (9 mL / 12 mL) was added slowly under ice water bath, and the pre-polymerization was mechanically stirred for 5 hours. Finally, the two were mixed, and the mechanical stirring was continued for 24 hours. The reaction solution became highly viscous, and it was poured into deionized water for precipitation and washing until the washing solution was neutral, to obtain a fibrous block polymer.

[0048] The structural formula of the obtained target AEMs is as follows:

[0049]

[0050] The water absorption, swelling degree, and ionic conductivity of the prepared AEMs were 54%, 22%, and 105 mS cm -1 at 80°C, respectively. The tensile strength and elongation at break in the wet state were 19 MPa and 139%, respectively. The H2 / O2 fuel cell performance at 80°C reached 1.07 W cm -2 . The voltage of the electrolysis tank at 1 A cm -2 current density at 60°C was 2.18 V.

[0051] Example 5

[0052] Example 5 is similar to Example 1, except that in step (a) the selected α,ω-dihaloalkane was 1,12-dibromododecane, and 1,12-diphenyldodecane was prepared. The monomer ratio in the pre-polymerization in step (b) was the same as in Example 1. The structural formula of the obtained AEMs is as follows:

[0053]

[0054] The water absorption, swelling degree, and ionic conductivity of the prepared AEMs were 84%, 35%, and 122 mS cm -1 at 80°C, respectively. The tensile strength and elongation at break in the wet state were 11 MPa and 172%, respectively. The H2 / O2 fuel cell performance at 80°C reached 1.28 W cm -2 . The voltage of the electrolysis tank at 1 A cm -2 current density at 60°C was 1.95 V.

[0055] Example 6

[0056] Example 6 is similar to Example 1 except that the a, w-dihaloalkane used in step (a) is 1,4-dibromobutane, and 1,4-diphenylbutane is produced. The monomer ratio in the prepolymerization in step (b) is the same as in Example 1. The structure of the AEMs produced is as follows:

[0057]

[0058] The water uptake, swelling degree, and ionic conductivity of the AEMs produced are 60%, 23%, and 108 mS cm -1 at 80°C, respectively. The tensile strength and elongation at break in the wet state are 20 MPa and 132%, respectively. The H2 / O2 fuel cell performance at 80°C is 1.02 W cm -2 ; the current density is 1 A cm -2 ; and the voltage of the electrolysis cell is 2.20 V.

[0059] Comparative Example 1

[0060] Comparative Example 1 produces a random copolymer AEM having the same molecular structure as Example 3. The preparation method is as follows. Biphenyl (1.54 g, 10 mmol), 1,6-diphenylhexane (1.82 g, 10 mmol), and 4-imidazole carboxaldehyde (2.11 g, 22 mmol) are stirred and dissolved in 20 mL of dichloromethane. Trifluoromethane sulfonic acid and methane sulfonic acid (12 mL / 16 mL) mixed acid is slowly added under an ice water bath, and mechanical stirring is continued for 48 hours. The reaction solution becomes highly viscous, and is poured into deionized water to precipitate and wash until the washing solution is neutral. A fibrous random polymer is obtained. The random polymer is dissolved in dimethyl sulfoxide, and then potassium carbonate and iodomethane (the molar ratio of potassium carbonate, iodomethane, and polymer is 2:10:1) are added. Stirring is continued at 60°C for 12 hours, and then the reaction solution is poured into ethanol to precipitate and wash. Further washing is performed with water, and finally drying is performed to obtain a quaternized random polymer. The quaternized random polymer is redissolved in dimethyl sulfoxide, and the membrane solution is poured into a clean glass mold. Drying is performed in an oven at 80°C to form a film. Finally, ion exchange is performed by immersing the film in a 60°C potassium hydroxide solution for 24 hours to obtain an OH- type anion exchange membrane. The structure of the random AEM produced is as follows:

[0061]

[0062] The water uptake, swelling degree, and ionic conductivity of the AEMs produced are 35%, 10%, and 68 mS cm -1 at 80°C, respectively. The tensile strength and elongation at break in the wet state are 36 MPa and 48%, respectively. The H2 / O2 fuel cell performance at 80°C is 0.58 W cm-2 60 °C 1 A cm -2 The voltage of the water electrolysis tank was 2.73 V at a current density of 1 A / cm2.

[0063] The above examples are only for illustrating the technical concept and characteristics of the present application, and the purpose is to enable the skilled in the art to understand the content of the present application and to implement it, and cannot limit the protection scope of the present application. Any equivalent changes or modifications made according to the spirit and essence of the present application shall be covered within the protection scope of the present application.

Claims

1. A block type anion exchange membrane having a gapped alkyl chain, characterized by: The chemical structure of the block type anion exchange membrane is as follows: In the formula, n is the length of the gap alkyl chain, which is an integer of 2-12; x is the content of the biphenyl unit, which is greater than 0 and less than 1, and m represents the degree of polymerization.

2. A method for producing the block-type anion exchange membrane with a gapped alkyl chain according to claim 1, characterized by, The preparation method comprises the following steps: (a) Synthesis of α, ω-diphenylalkane A tetrahydrofuran solution of n-butyllithium is added to dehydrated toluene at -78°C and stirred at room temperature for 3 hours, then α, ω-dihaloalkane is added to the reaction solution, and the reaction is carried out at room temperature for 12-24 hours. The reaction solution is quenched with water and extracted with ethyl acetate. The extracted solution is dried to obtain a crude product, which is finally separated and purified by column chromatography to obtain the target product α, ω-diphenylalkane; (b) Preparation of block polymer ①Dissolve biphenyl and 4-imidazole formaldehyde in dichloromethane, add a mixed acid of trifluoromethanesulfonic acid and methanesulfonic acid under ice water bath, and pre-polymerize for 5 hours under ice water bath to obtain a pre-polymer 1 solution; ②Dissolve α, ω-diphenylalkane and 4-imidazole formaldehyde in dichloromethane in step (a), add a mixed acid of trifluoromethanesulfonic acid and methanesulfonic acid under ice water bath, and pre-polymerize for 5 hours under ice water bath to obtain a pre-polymer 2 solution; ③Mix the two pre-polymer solutions, mechanically stir at room temperature for 12-24 hours, and wash the mixture with deionized water until the washing liquid is neutral to obtain a fibrous block polymer with a gap alkane chain; (c) Quaternization Dissolve the block polymer in step (b) in dimethyl sulfoxide, add potassium carbonate and iodomethane, and stir at 60°C for 24 hours. The reaction solution is precipitated with ethanol and washed with water to obtain a quaternized polymer. Finally, the quaternized polymer is redissolved in dimethyl sulfoxide, the solution is dropped into a clean glass mold, and the mold is placed in an 80°C oven to dry into a film. The film is soaked in a 60°C potassium hydroxide solution for 24 hours for ion exchange to obtain an OH-type anion exchange membrane.

3. The method for producing a block type anion exchange membrane with a gapped alkyl chain according to claim 2, characterized by, In step (a), the molar ratio of n-butyllithium to α, ω-dihaloalkane is 2:1, the molar ratio of toluene to α, ω-dihaloalkane is greater than 2:1, the eluent for separation is n-hexane, and the stationary phase is silica gel.

4. The method for producing a block-type anion exchange membrane with a gapped alkyl chain according to claim 2, characterized by, In step (b) ①, the concentration of biphenyl and 4-imidazole formaldehyde in dichloromethane is 10-30 wt%, the molar amount of 4-imidazole formaldehyde is 1.1 times that of biphenyl, and the volume ratio of trifluoromethanesulfonic acid to methanesulfonic acid is 3:

4.

5. The method for producing a block type anion exchange membrane with a gapped alkyl chain according to claim 2, characterized by, In step (b) ②, the concentration of α, ω-diphenylalkane and 4-imidazole formaldehyde in dichloromethane is 10-30 wt%, the molar amount of 4-imidazole formaldehyde is 1.1 times that of α, ω-diphenylalkane, and the volume ratio of trifluoromethanesulfonic acid to methanesulfonic acid is 3:

4.

6. The method for producing a block-type anion exchange membrane with a gapped alkyl chain according to claim 2, characterized by, In step (b), the proportion of the two pre-polymer solutions ensures that the content of the biphenyl or α, ω-diphenylalkane group is greater than 0 and less than 1, and the total is 1.

7. The method for producing a block type anion exchange membrane with a gapped alkyl chain according to claim 2, characterized by, In step (c), the molar ratio of potassium carbonate to block polymer is 2:1, and the molar ratio of iodomethane to block polymer is 1:

10.

8. Use of the block anion exchange membrane with a gapped alkyl chain according to claim 1, characterized in that, The block type anion exchange membrane is applied to fuel cells, flow batteries, water electrolysis, electrodialysis or separation membranes.

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