Gel-like polybenzimidazole ionomer membrane with double cross-linked cationic network structure, its preparation method and its application in alkaline water electrolysis for hydrogen production.

Abstract

This invention discloses a gel-state polybenzimidazole ion solvent membrane with a double-crosslinked cationic network structure, its preparation method, and its application in alkaline water electrolysis for hydrogen production. The ion solvent membrane is composed of polybenzimidazole with a double-crosslinked cationic network structure, hydroxide ions, and an ion solvent. It has a wrinkled appearance in the plane and a three-dimensional crosslinked porous microstructure in the cross-section. The ion solvent membrane provided by this invention is prepared by polyphosphoric acid sol-gel process and free radical polymerization reaction. This membrane material combines the advantages of the three-dimensional network porous morphology of gel membranes with cationic groups to obtain additional transport sites with long-range continuous arrangement to improve ion conductivity. It maintains high ion conductivity even at low alkaline concentrations, further improving electrolysis performance and enhancing the dimensional stability of the membrane. It has good application prospects in the field of water electrolysis for hydrogen production.

Description

Technical Field

[0001] This invention relates to ion solvent membranes that can be used in the field of hydrogen production by water electrolysis, and particularly to a gel-state polybenzimidazole (PBI) ion solvent membrane with a double cross-linked cationic network structure, its preparation method, and its application in alkaline water electrolysis for hydrogen production. Background Technology

[0002] Electrolysis of water to produce hydrogen has the advantage of zero carbon emissions and can be combined with renewable energy sources such as wind and solar power, making it a promising industrial application technology. Ion exchange membranes are one of the core components of water electrolysis for hydrogen production; a superior ion exchange membrane ensures efficient and stable operation. An ion exchange membrane is a polymer electrolyte material in which ionic functional groups are covalently bonded to the polymer backbone. These ion exchange membranes are mainly divided into two types: cation exchange membranes (CEMs) and anion exchange membranes (AEMs). Cation exchange membranes connect anionic functional groups (such as sulfonate and carboxylate groups) to the polymer, allowing free conduction of cations (such as hydrogen ions, lithium, sodium, and potassium ions). Anion exchange membranes connect cationic functional groups (such as quaternary ammonium salts and imidazoline salts) to the polymer, allowing free conduction of anions (such as hydroxide, chloride, and carbonate ions). In addition, there are other ion exchange membrane systems such as zwitterionic exchange membranes (AIEMs), bipolar membranes (BPMs), and ion-solubilized membranes (ISMs).

[0003] Polybenzimidazole (PBI) membranes, as a type of ion-exchange solvent membrane, possess excellent chemical stability, high mechanical strength, and superior thermal stability, making them a promising ion conductor due to their amphoteric imidazole properties. Under acid / base doping, PBI ion-exchange solvent membranes can serve as either cationic or anionic conductive solid electrolytes because the imidazole structure on the polymer backbone can act as Lewis acids or Lewis bases in different media.

[0004] Currently, many researchers have applied PBI ion-solvent membranes to flow batteries and water electrolysis for hydrogen production. To improve the electrolytic performance of PBI membranes under low-concentration alkaline solutions, many researchers have introduced cationic groups into the membrane, which effectively increases ion conductivity, thereby enhancing its electrolytic performance and stability, maintaining excellent performance even under low-concentration alkaline electrolytes. Henkensmeier et al. prepared a membrane with cationic groups by combining an FAA anion membrane with m-PBI, achieving a concentration of 166 mS / cm² at room temperature after absorbing 25 wt% (5.5 MKOH). -1 The higher ionic conductivity of ISMs, which is 80% higher than that of m-PBI (Journal of Membrane Science 564(2018)653-662), indicates that the introduction of cationic groups is beneficial to improving the hydroxide conductivity of ISMs and improving their electrolytic performance.

[0005] To address the limitations of traditional casting methods for preparing ionomer membranes, such as limited alkali absorption and poor ion conductivity, this invention proposes a PPA solution-gel phase inversion process to prepare gel-state PBI. This involves nucleophilic substitution and in-situ free radical polymerization, followed by immersion in an alkaline solution to produce a PBI ionomer membrane with a double-crosslinked cationic network structure. This invention combines the advantages of the porous morphology of the gel membrane with functionalized structural design, introducing cationic groups to increase the number of OH groups. - The transport site can achieve high conductivity and high performance, and has excellent water electrolysis performance under low concentration alkaline solution. It can be applied to the field of water electrolysis for hydrogen production and has good application prospects. Summary of the Invention

[0006] To overcome the shortcomings of the prior art, the present invention provides a gel-state polybenzimidazole (PBI) ion solvent membrane with a double cross-linked cationic network structure, its preparation method, and its application in alkaline water electrolysis for hydrogen production.

[0007] The technical solution of the present invention is as follows:

[0008] A gel-like polybenzimidazole ionomer membrane with a double-crosslinked cationic network structure, comprising a double-crosslinked cationic network structure of polybenzimidazole and hydroxide ions (OH-). - (to balance charge), and composed of ionic solvents;

[0009] in,

[0010] The structural formula of polybenzimidazole with a double crosslinked cationic network structure is as follows:

[0011]

[0012] In the formula, x = 1 to 3, y = 0 to 3, z = 1 to 4, and n = 350 to 400;

[0013] The ionic solvent is an alkaline solution, specifically one or more of potassium hydroxide solution and sodium hydroxide solution.

[0014] The gel-state polybenzimidazole ion solvent membrane with a double cross-linked cationic network structure described in this invention has a network porous structure in its cross-section and a wrinkled shape in its planar surface.

[0015] The preparation process of the gel-state polybenzimidazole ion solvent membrane with a double cross-linked cationic network structure of the present invention includes: using polyphosphoric acid (PPA) as solvent, tetraamine and carboxylic acid monomers directly undergo PBI condensation reaction under nitrogen atmosphere, and obtain phosphoric acid-doped gel-state PBI membrane through solution-gel phase inversion process, then remove the phosphoric acid in the membrane, carry out nucleophilic substitution reaction with haloolefin, carry out free radical polymerization reaction with imidazole salt containing diene group, and finally soak in alkaline solution to obtain the ion solvent membrane.

[0016] Specifically, a method for preparing a gel-state polybenzimidazole ionomer film with a double cross-linked cationic network structure includes the following steps:

[0017] Step 1: Under an inert atmosphere, tetraamine, carboxylic acid monomer, and polyphosphoric acid are mixed, stirred, and heated to 120-200℃ for condensation reaction for 18-24 hours to obtain polybenzimidazole solution;

[0018] Tetraamines are aromatic tetraamines and their derivatives, selected from one or more of 3,3-diaminobenzidine, 1,2,4,5-tetraaminobenzene, and 3,3',4,4'-tetraaminodiphenyl ether.

[0019] The carboxylic acid monomer is selected from one or more of 2-hydroxyterephthalic acid, 2,5-dihydroxyterephthalic acid, 5-hydroxyisophthalic acid, 4,6-dihydroxyisophthalic acid, terephthalic acid, isophthalic acid, and pyromellitic acid.

[0020] Polyphosphoric acid is used as the reaction solvent. It is preferred that the tetraamine, carboxylic acid monomer, and polyphosphoric acid are mixed, and the total mass fraction of the monomers (tetraamine and carboxylic acid monomer) is 1-15 wt%.

[0021] Step 2: The polybenzimidazole solution obtained in Step 1 is coated onto a glass substrate to complete the phase transformation from solution to gel state, resulting in a phosphoric acid-doped gel polybenzimidazole ion solvent film.

[0022] The preferred coating thickness of the polybenzimidazole solution on the glass substrate is 20–500 μm.

[0023] The temperature for the phase transformation process is 0–80℃, and the relative humidity is 40–100%.

[0024] Step 3: Immerse the phosphoric acid-doped gel polybenzimidazole ion solvent film obtained in Step 2 in deionized water until neutral to remove the phosphoric acid doping in the film;

[0025] Soaking in deionized water at room temperature for at least 2 days, changing the water every 24 hours;

[0026] Step 4: Mix the polybenzimidazole gel ion solvent membrane treated in step 3 with a solution containing haloolefins, and carry out a nucleophilic substitution reaction at 60-90℃ for 12-24h. After cleaning, a polybenzimidazole gel ion solvent membrane with side-linked olefins is obtained.

[0027] The concentration of the solution containing haloalkenes is 0.05–0.5 mol / L, and the solvent is one or more of ethanol, methanol, diethyl ether, carbon tetrachloride, chloroform, dichloromethane, deionized water, N,N-dimethylformamide, and N,N-dimethylacetamide.

[0028] The haloalkene is selected from one or more of 3-bromopropene, 3-chloropropene, 4-bromobutene, 4-chlorobutene, 5-bromopentene, and 5-chloropentene;

[0029] After the reaction is complete, the membrane material is cleaned with solvent and deionized water.

[0030] Step 5: The polybenzimidazole gel-type ionic solvent membrane with side-linked branched olefins obtained in Step 4 is subjected to free radical polymerization reaction with an imidazole salt solution containing diene groups at 60-80°C for 20-30 hours under the action of an initiator. After cleaning, it is soaked in an alkaline solution to obtain the gel-state polybenzimidazole ionic solvent membrane with a double crosslinked cationic network structure.

[0031] The concentration of the imidazole salt solution containing diene groups is 0.05–0.5 mol / L, and the solvent is one or more of ethanol, methanol, deionized water, N,N-dimethylformamide, and N,N-dimethylacetamide.

[0032] The general structural formula of imidazole salts containing diene groups is as follows:

[0033]

[0034] In the formula, X is Cl or Br; y = 0 - 3, z = 1 - 4;

[0035] Specifically, the imidazole salt containing a diene group is selected from one or more of the following: 1-allyl-3-vinylimidazolium chloride, 1-allyl-3-vinylimidazolium bromide, 1-enpentyl-3-allylimidazolium chloride, 1-enpentyl-3-allylimidazolium bromide, 1-enhexyl-3-vinylimidazolium chloride, 1-enhexyl-3-vinylimidazolium bromide, 1-enpentyl-3-vinylimidazolium chloride, 1-enpentyl-3-vinylimidazolium bromide, etc.

[0036] The initiator is azobisisobutyronitrile (AIBN), and its content is 1-4% based on the total mass of the reactants.

[0037] After the free radical polymerization reaction is completed, the membrane product is cleaned with N,N-dimethylacetamide, ethanol, and deionized water;

[0038] The alkaline solution is one or more of potassium hydroxide and sodium hydroxide solutions, with a concentration of 0.5–6 mol / L. Immersion in the alkaline solution is carried out at room temperature for ≥48 hours. After immersion in the alkaline solution, the halide anions from the imidazole salt in the polymer membrane are exchanged for OH-. - .

[0039] The gel-state polybenzimidazole ion solvent membrane with a double cross-linked cationic network structure described in this invention can be used for alkaline water electrolysis to produce hydrogen.

[0040] The technical principles of this invention include:

[0041] First, gel-state PBI is prepared using a PPA solution-gel phase inversion process. Nucleophilic substitution and in-situ free radical polymerization are then performed on this gel. Following alkaline solution doping, a PBI ion-solvent membrane with a double-crosslinked cationic network structure is prepared. The ion-solvent membrane prepared in this invention combines the advantages of the three-dimensional network porous morphology of the gel membrane with imidazole cationic groups, obtaining additional transport sites arranged in a long-range continuous pattern to improve ion conductivity. Even under low alkaline conditions, it maintains high ion conductivity, further enhancing electrolysis performance and improving membrane dimensional stability. It shows promising application prospects in the field of alkaline water electrolysis for hydrogen production.

[0042] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0043] (1) The gel-state PBI ion solvent membrane (doped with alkali) with a double cross-linked cation network structure obtained by the present invention has high ion conductivity and high performance. It has excellent water electrolysis performance under low concentration alkali solution and is expected to help the application of alkaline water electrolysis for hydrogen production.

[0044] (2) The ionic conductivity of the ion solvent film (doped with 1M KOH) at 25°C increased from 0.137 S / cm to 0.146 S / cm.

[0045] (3) The ion solvent membrane (doped with 1M KOH) also exhibits excellent performance in the water electrolysis hydrogen production cell, with a current density of 1.96 A / cm² at 60°C and 1M KOH. 2 . Attached Figure Description

[0046] Figure 1 Infrared spectra of gel-state PBI ion solvent membranes in the comparative and examples.

[0047] Figure 2 Mechanical properties of PBI ionomer films in comparative and example cases; (Right: doped with 1M KOH solution, Left: undoped).

[0048] Figure 3 SEM images of PBI ion solvent membranes in comparative and example cases.

[0049] Figure 4 Ionic conductivity of the PBI ion solvent membrane (doped with 1M KOH solution) in the comparative and example cases.

[0050] Figure 5 Ionic conductivity and current density at 2V for the PBI ion solvent membrane (doped with 1M KOH solution) of the comparative example and the embodiment.

[0051] Figure 6 Polarization curves of water electrolysis for hydrogen production using gel-state PBI ion-solvent membranes (doped with 1M KOH solution) at 60°C in comparative and example examples; (electrodes: nickel-iron anode, platinum-carbon cathode).

[0052] Figure 7 Polarization curves of water electrolysis for hydrogen production using gel-state PBI ion-solvent membranes (doped with 1M KOH solution) in comparative examples and embodiments at 60°C; (electrodes: nickel-iron anode, Raney nickel cathode). Detailed Implementation

[0053] To facilitate understanding of the present invention, it will be described more fully in conjunction with the following examples. However, the present invention can be implemented in many different forms, and its scope of protection is not limited to the embodiments described herein. Furthermore, for those skilled in the art, various modifications or improvements to the material composition and dosage in these embodiments, without departing from the spirit and scope of the present invention, are all within the scope of protection claimed by the present invention.

[0054] Comparative Example 1:

[0055] An ion-solvent membrane was prepared using m-PBI (commercial membrane) provided by PBI Performance, Inc., USA. The specific steps are as follows: The m-PBI (commercial membrane) was soaked in acid (such as 85% phosphoric acid) or alkali (such as 1 M KOH) and treated at 25°C for 48 hours to prepare the m-PBI ion-solvent membrane.

[0056] The m-PBI ion solvent film (doped with 1M KOH) obtained in Comparative Example 1 was analyzed and tested:

[0057] Alkali absorption rate: 10wt%; Ionic conductivity: 0.086S / cm@25℃.

[0058] Comparative Example 2:

[0059] (1) Add 3,3-diaminobenzidine (2.7855 g, 0.0130 mol) and terephthalic acid (2.1611 g, 0.0130 mol) to a three-necked reaction flask equipped with a mechanical stirrer, use 160 mL of polyphosphoric acid as solvent, and the monomer content is 3 wt%. Under the protection of nitrogen flow, react at 190 °C for 24 h to obtain a polymer solution.

[0060] (2) The obtained polymer solution is scraped onto a glass substrate for phase inversion. The coating thickness is 0.254 mm. Due to the natural hydrolysis of polyphosphoric acid into phosphoric acid, a PA / PBI gel ion solvent membrane is prepared through a solution-gel phase inversion, i.e. the initial PA / PBI gel membrane.

[0061] The gel-like PBI ion-solvent film (doped with 1M KOH) obtained in Comparative Example 2 was analyzed and tested.

[0062] Alkali absorption rate: 110wt%; Ionic conductivity: 0.137S / cm@25℃.

[0063] Example 1:

[0064] (1) Add 3,3-diaminobenzidine (2.7855 g, 0.130 mol) and terephthalic acid (2.1611 g, 0.0130 mol) to a three-necked reaction flask equipped with a mechanical stirrer, use 160 mL of polyphosphoric acid as solvent, and the monomer content is 3 wt%. Under the protection of nitrogen flow, react at 190 °C for 24 h to obtain a polymer solution.

[0065] (2) The obtained polymer solution was scraped onto a glass substrate for phase inversion. The coating thickness was 0.254 mm. Due to the natural hydrolysis of polyphosphoric acid into phosphoric acid, a PA / PBI gel ion solvent film was prepared through a solution-gel phase inversion.

[0066] (3) The obtained membrane was soaked in deionized water for 3 days (the water was changed every 24 hours) to remove the phosphoric acid contained in the membrane. Then, a nucleophilic reaction was carried out at 70°C for 24 hours with a 0.3 mol / L solution of 3-bromopropene (ethanol as solvent). After cleaning with ethanol, a modified solution of 0.1 mol / L (1-allyl-3-vinyl-imidazolium chloride as crosslinking agent and N,N-dimethylacetamide as solvent) was heated to 60°C under nitrogen atmosphere. Then, 4% initiator (azobisisobutyronitrile) was added, the temperature was raised to 70°C and reacted for 24 hours. After the reaction was completed, the membrane was cleaned with N,N-dimethylacetamide, ethanol and deionized water and then soaked in 1M KOH for 48 hours to obtain a polybenzimidazole gel ion solvent membrane with a double crosslinked cationic network structure.

[0067] The gel-like PBI ion solvent film (doped with 1MKOH) with a double cross-linked cationic network structure obtained in Example 1 was analyzed and tested:

[0068] Alkali absorption rate: 61wt%; Ionic conductivity: 0.140S / cm@25℃.

[0069] Example 2:

[0070] (1) Add 3,3-diaminobenzidine (2.7855 g, 0.0130 mol) and terephthalic acid (2.1611 g, 0.0130 mol) to a three-necked reaction flask equipped with a mechanical stirrer, use 160 mL of polyphosphoric acid as solvent, and the monomer content is 3 wt%. Under the protection of nitrogen flow, react at 190 °C for 24 h to obtain a polymer solution.

[0071] (2) The obtained polymer solution was scraped onto a glass substrate for phase transformation. The coating thickness was 0.254 mm. Due to the natural hydrolysis of polyphosphoric acid into phosphoric acid, a PA / PBI gel ionic solvent film was prepared through a solution-gel phase transformation.

[0072] (3) The obtained membrane was soaked in deionized water for 3 days (the water was changed every 24 hours) to remove the phosphoric acid contained in the membrane. Then, a nucleophilic reaction was carried out at 70°C for 24 hours with a 0.3 mol / L solution of 3-bromopropene (ethanol as solvent). After cleaning with ethanol, a modified solution of 0.2 mol / L (1-allyl-3-vinyl-imidazolium chloride as crosslinking agent and N,N-dimethylacetamide as solvent) was heated to 60°C under nitrogen atmosphere. Then, 4% initiator (azobisisobutyronitrile) was added, the temperature was raised to 70°C and reacted for 24 hours. After the reaction was completed, the membrane was cleaned with N,N-dimethylacetamide, ethanol and deionized water, and then soaked in 1M KOH for 48 hours to obtain a polybenzimidazole gel ion solvent membrane with a double crosslinked cationic network structure.

[0073] The gel-like PBI ion solvent film (doped with 1MKOH) with a double cross-linked cationic network structure obtained in Example 2 was analyzed and tested:

[0074] Alkali absorption rate: 53wt%; Ionic conductivity: 0.146S / cm@25℃.

[0075] The electrolytic hydrogen production performance of the gel-state PBI ion solvent membrane (doped with 1MKOH) with a double cross-linked cationic network structure obtained in Example 2 was tested:

[0076] To evaluate the performance of the ion-solvent membrane of Example 2 in an alkaline water electrolyzer, the obtained membrane was fabricated into a membrane electrolyte assembly (MEAs, anode: nickel-iron, cathode: Raney nickel / platinum carbon). Electrolyte circulation was performed using 1M KOH solution, and the hydrogen production performance of water electrolysis was tested. Example 2, based on the three-dimensional network porous morphology of the gel-state ion-solvent membrane, introduced imidazole cations. These cations can construct cross-linked networks on their own and can also form cross-linked networks with the polybenzimidazole (PBI) backbone. The constructed double cross-linked network increases the OH- ion-solvent content. - The transport sites enable higher ionic conductivity and better performance at lower concentrations of alkaline solutions.

[0077] The results are as follows Figure 6 , Figure 7 As shown, at 60°C, 1M KOH (anode nickel-iron and cathode platinum-carbon), Example 2 achieved 1.96 A / cm² at 2.05V. 2 Compared to Comparative Example 2, the performance is improved by 19.6%. At 60°C, 1M KOH (anode nickel-iron and cathode Raney nickel), Example 2 achieves 0.65 A / cm at 2V. 2 Compared to Comparative Example 2 (0.53 A / cm) 2 The performance was improved by 22.6%. Therefore, Example 2 shows better performance than Comparative Example 2 under low-alkaline conditions.

[0078] Example 3:

[0079] (1) Add 3,3-diaminobenzidine (2.7855 g, 0.0130 mol) and terephthalic acid (2.1611 g, 0.0130 mol) to a three-necked reaction flask equipped with a mechanical stirrer, use 160 mL of polyphosphoric acid as solvent, and the monomer content is 3 wt%. Under the protection of nitrogen flow, react at 190 °C for 24 h to obtain a polymer solution.

[0080] (2) The obtained polymer solution was scraped onto a glass substrate for phase transformation. The coating thickness was 0.254 mm. Due to the natural hydrolysis of polyphosphoric acid into phosphoric acid, a PA / PBI gel ionic solvent film was prepared through a solution-gel phase transformation.

[0081] (3) The obtained membrane was soaked in deionized water for 3 days (the water was changed every 24 hours) to remove the phosphoric acid contained in the membrane. Then, a nucleophilic reaction was carried out at 70°C for 24 hours with a 0.3 mol / L solution of 3-bromopropene (ethanol as solvent). After cleaning with ethanol, a modified solution of 0.3 mol / L (1-allyl-3-vinyl-imidazolium chloride as crosslinking agent and N,N-dimethylacetamide as solvent) was heated to 60°C under nitrogen atmosphere. Then, 4% initiator (azobisisobutyronitrile) was added, the temperature was raised to 70°C and reacted for 24 hours. After the reaction was completed, the membrane was cleaned with N,N-dimethylacetamide, ethanol and deionized water and then soaked in 1M KOH for 48 hours to obtain a polybenzimidazole gel ion solvent membrane with a double crosslinked cationic network structure.

[0082] The gel-like PBI ion solvent film (doped with 1MKOH) with a double cross-linked cationic network structure obtained in Example 3 was analyzed and tested:

[0083] Alkali absorption rate: 43wt%.

[0084] Example 4:

[0085] (1) Add 3,3-diaminobenzidine (2.7855 g, 0.0130 mol) and terephthalic acid (2.1611 g, 0.0130 mol) to a three-necked reaction flask equipped with a mechanical stirrer, use 160 mL of polyphosphoric acid as solvent, and the monomer content is 3 wt%. Under the protection of nitrogen flow, react at 190 °C for 24 h to obtain a polymer solution.

[0086] (2) The obtained polymer solution was scraped onto a glass substrate for phase inversion. The coating thickness was 0.254 mm. Due to the natural hydrolysis of polyphosphoric acid into phosphoric acid, a PA / PBI gel ion solvent film was prepared through a solution-gel phase inversion.

[0087] (3) The obtained membrane was soaked in deionized water for 3 days (the water was changed every 24 hours) to remove the phosphoric acid contained in the membrane. Then, a nucleophilic reaction was carried out at 70°C for 24 hours with a 0.3 mol / L solution of 3-bromopropene (ethanol as solvent). After cleaning with ethanol, a modified solution of 0.4 mol / L (1-allyl-3-vinyl-imidazolium chloride as crosslinking agent and N,N-dimethylacetamide as solvent) was heated to 60°C under nitrogen atmosphere. Then, 4% initiator (azobisisobutyronitrile) was added, the temperature was raised to 70°C and reacted for 24 hours. After the reaction was completed, the membrane was cleaned with N,N-dimethylacetamide, ethanol and deionized water and then soaked in 1M KOH for 48 hours to obtain a polybenzimidazole gel ion solvent membrane with a double crosslinked cationic network structure.

[0088] Example 5:

[0089] (1) Add 3,3-diaminobenzidine (2.7855 g, 0.0130 mol) and terephthalic acid (2.1611 g, 0.0130 mol) to a three-necked reaction flask equipped with a mechanical stirrer, use 160 mL of polyphosphoric acid as solvent, and the monomer content is 3 wt%. Under the protection of nitrogen flow, react at 190 °C for 24 h to obtain a polymer solution.

[0090] (2) The obtained polymer solution was scraped onto a glass substrate for phase inversion. The coating thickness was 0.254 mm. Due to the natural hydrolysis of polyphosphoric acid into phosphoric acid, a PA / PBI gel ion solvent film was prepared through a solution-gel phase inversion.

[0091] (3) The obtained membrane was soaked in deionized water for 3 days (the water was changed every 24 hours) to remove the phosphoric acid contained in the membrane. Then, a nucleophilic reaction was carried out at 70°C for 24 hours with a 0.3 mol / L solution of 3-bromopropene (ethanol as solvent). After cleaning with ethanol, a modified solution of 0.1 mol / L (1-allyl-3-vinyl-imidazolium chloride as crosslinking agent and N,N-dimethylacetamide as solvent) was heated to 60°C under nitrogen atmosphere. Then, 4% initiator (azobisisobutyronitrile) was added, the temperature was raised to 70°C and reacted for 24 hours. After the reaction was completed, the membrane was cleaned with N,N-dimethylacetamide, ethanol and deionized water, and then soaked in 0.5-3 mol / L sulfuric acid for 48 hours to obtain a polybenzimidazole gel ion solvent membrane with a double crosslinked cationic network structure.

[0092] Example 6:

[0093] (1) Add 3,3-diaminobenzidine (2.7855 g, 0.0130 mol) and terephthalic acid (2.1611 g, 0.0130 mol) to a three-necked reaction flask equipped with a mechanical stirrer, use 160 mL of polyphosphoric acid as solvent, and the monomer content is 3 wt%. Under the protection of nitrogen flow, react at 190 °C for 24 h to obtain a polymer solution.

[0094] (2) The obtained polymer solution was scraped onto a glass substrate for phase inversion. The coating thickness was 0.254 mm. Due to the natural hydrolysis of polyphosphoric acid into phosphoric acid, a PA / PBI gel ion solvent film was prepared through a solution-gel phase inversion.

[0095] (3) The obtained membrane was soaked in deionized water for 3 days (the water was changed every 24 hours) to remove the phosphoric acid contained in the membrane. Then, a nucleophilic reaction was carried out at 70°C for 24 hours with a 0.3 mol / L solution of 3-bromopropene (ethanol as solvent). After cleaning with ethanol, a modified solution of 0.2 mol / L (1-allyl-3-vinyl-imidazolium chloride as crosslinking agent and N,N-dimethylacetamide as solvent) was heated to 60°C under nitrogen atmosphere. Then, 4% initiator (azobisisobutyronitrile) was added, the temperature was raised to 70°C and reacted for 24 hours. After the reaction was completed, the membrane was cleaned with N,N-dimethylacetamide, ethanol and deionized water, and then soaked in 0.5-3 mol / L sulfuric acid for 48 hours to obtain a polybenzimidazole gel ion solvent membrane with a double crosslinked cationic network structure.

[0096] Example 7:

[0097] (1) Add 3,3-diaminobenzidine (2.7855 g, 0.0130 mol) and terephthalic acid (2.1611 g, 0.0130 mol) to a three-necked reaction flask equipped with a mechanical stirrer, use 160 mL of polyphosphoric acid as solvent, and the monomer content is 3 wt%. Under the protection of nitrogen flow, react at 190 °C for 24 h to obtain a polymer solution.

[0098] (2) The obtained polymer solution was scraped onto a glass substrate for phase inversion. The coating thickness was 0.254 μm. Due to the natural hydrolysis of polyphosphoric acid into phosphoric acid, a PA / PBI gel ion solvent film was prepared through a solution-gel phase inversion.

[0099] (3) The obtained membrane was soaked in deionized water for 3 days (the water was changed every 24 hours) to remove the phosphoric acid contained in the membrane. Then, a nucleophilic reaction was carried out at 70°C for 24 hours with a 0.3 mol / L solution of 3-bromopropene (ethanol as solvent). After cleaning with ethanol, a modified solution of 0.3 mol / L (1-allyl-3-vinyl-imidazolium chloride as crosslinking agent and N,N-dimethylacetamide as solvent) was heated to 60°C under nitrogen atmosphere. Then, 4% initiator (azobisisobutyronitrile) was added, the temperature was raised to 70°C and reacted for 24 hours. After the reaction was completed, the membrane was cleaned with N,N-dimethylacetamide, ethanol and deionized water, and then soaked in 0.5-3 mol / L sulfuric acid for 48 hours to obtain a polybenzimidazole gel ion solvent membrane with a double crosslinked cationic network structure.

[0100] Example 8:

[0101] (1) Weigh out 3,3'-diaminobenzidine, 2,5-dihydroxyterephthalic acid, and trimesic acid respectively, and pour them into a three-necked reactor. Then add solvent and polyphosphoric acid as a condensation agent to the reactor. The ratio of 2,5-dihydroxyterephthalic acid to trimesic acid monomers is 100 / 10. The reaction is carried out under a nitrogen atmosphere and an oil bath heating method is used, with the temperature gradually increased to 190℃ and the reaction lasting for more than 15 hours.

[0102] (2) Pour the polymer solution onto the glass substrate, use a film scraper to scrape the film, and control the casting film thickness to 250 μm. Since polyphosphoric acid is naturally hydrolyzed into phosphoric acid, a functional branched high-temperature ionic solvent film is prepared through a solution-gel phase transition.

[0103] (3) The obtained membrane was soaked in deionized water for 3 days (the water was changed every 24 hours) to remove the phosphoric acid contained in the membrane. Then, a nucleophilic reaction was carried out at 70°C for 24 hours with a 0.3 mol / L solution of 3-bromopropene (ethanol as solvent). After cleaning with ethanol, a modified solution of 0.3 mol / L (1-allyl-3-vinyl-imidazolium chloride as crosslinking agent and N,N-dimethylacetamide as solvent) was heated to 60°C under nitrogen atmosphere. Then, 4% initiator (azobisisobutyronitrile) was added, the temperature was raised to 70°C and reacted for 24 hours. After the reaction was completed, the membrane was cleaned with N,N-dimethylacetamide, ethanol and deionized water, and then soaked in 85% phosphoric acid for 48 hours to obtain a polybenzimidazole gel ion solvent membrane with a double crosslinked cationic network structure.

[0104] Table 1 shows the alkali absorption rate analysis in some comparative examples and case studies (doped with 1 mol / L potassium hydroxide).

[0105]

[0106] Anion exchange membranes (AEMs) offer numerous advantages for water electrolysis, but their commercialization is hampered by the low alkalinity stability of most AEMs due to the fragility of their quaternary ammonium groups. Ion solvation membranes (ISMs) can be an alternative, but so far require high alkalinity concentrations. The gel-state PBI ion solvation membrane with a double-crosslinked cationic network structure provided by this invention combines the advantages of the three-dimensional network porous morphology of gel membranes with cationic groups to construct a double-crosslinked network structure. This structure provides additional long-range, continuously arranged transport sites to enhance ion conductivity, resulting in high ion conductivity and water electrolysis performance even at low alkalinity concentrations. Furthermore, the introduction of imidazole cations allows them to form a crosslinked network layer, and they can also form a crosslinked network with the polybenzimidazole PBI backbone. This double-crosslinked network formation results in better dimensional stability compared to Comparative Example 2.

Claims

1. A gel-state polybenzimidazole ionomer film having a double cross-linked cationic network structure, characterized in that, It is composed of polybenzimidazole with a double cross-linked cationic network structure, hydroxide ions, and ionic solvents; in, The structural formula of polybenzimidazole with a double crosslinked cationic network structure is as follows: In the formula, x = 1 to 3, y = 0 to 3, z = 1 to 4, and n = 350 to 400; The ionic solvent is an alkaline solution; The preparation method of the gel-state polybenzimidazole ion solvent membrane with a double cross-linked cationic network structure is as follows: Step 1: Under an inert atmosphere, tetraamine, carboxylic acid monomer, and polyphosphoric acid are mixed, stirred, and heated to 120-200℃ for condensation reaction for 18-24 hours to obtain polybenzimidazole solution; The tetraamine is selected from one or more of 3,3-diaminobenzidine, 1,2,4,5-tetraaminobenzene, and 3,3',4,4'-tetraaminodiphenyl ether; The carboxylic acid monomer is selected from one or more of 2-hydroxyterephthalic acid, 2,5-dihydroxyterephthalic acid, 5-hydroxyisophthalic acid, 4,6-dihydroxyisophthalic acid, terephthalic acid, isophthalic acid, and pyromellitic acid. Step 2: The polybenzimidazole solution obtained in Step 1 is coated onto a glass substrate to complete the phase transformation from solution to gel state, resulting in a phosphoric acid-doped gel polybenzimidazole ion solvent film. Step 3: Immerse the phosphoric acid-doped gel polybenzimidazole ion solvent film obtained in Step 2 in deionized water until neutral to remove the phosphoric acid doping in the film; Step 4: Mix the polybenzimidazole gel ion solvent membrane treated in step 3 with a solution containing haloolefins, and carry out a nucleophilic substitution reaction at 60-90℃ for 12-24h. After cleaning, a polybenzimidazole gel ion solvent membrane with side-linked olefins is obtained. The haloalkene is selected from one or more of 3-bromopropene, 3-chloropropene, 4-bromobutene, 4-chlorobutene, 5-bromopentene, and 5-chloropentene; Step 5: The polybenzimidazole gel-type ionic solvent membrane with side-linked branched olefins obtained in Step 4 is subjected to free radical polymerization reaction with an imidazole salt solution containing diene groups at 60-80°C for 20-30 hours under the action of an initiator. After cleaning, it is soaked in an alkaline solution to obtain the gel-state polybenzimidazole ionic solvent membrane with a double crosslinked cationic network structure. The general structural formula of imidazole salts containing diene groups is as follows: In the formula, X is Cl or Br; y = 0 - 3, z = 1 - 4; The initiator is azobisisobutyronitrile.

2. The gel-state polybenzimidazole ionomer membrane with a double cross-linked cationic network structure as described in claim 1, characterized in that, In step 1 of the preparation method, polyphosphoric acid is used as the reaction solvent. After mixing tetraamine, carboxylic acid monomer, and polyphosphoric acid, the total mass fraction of the monomer is 1-15 wt%.

3. The gel-state polybenzimidazole ionomer membrane with a double cross-linked cationic network structure as described in claim 1, characterized in that, In step 2 of the preparation method, the temperature of the phase transformation process is 0–80℃ and the relative humidity is 40–100%.

4. The gel-state polybenzimidazole ionomer membrane with a double cross-linked cationic network structure as described in claim 1, characterized in that, In step 4 of the preparation method, the concentration of the solution containing the haloalkene is 0.05–0.5 mol / L, and the solvent is one or more of ethanol, methanol, diethyl ether, carbon tetrachloride, chloroform, dichloromethane, deionized water, N,N-dimethylformamide, and N,N-dimethylacetamide.

5. The gel-state polybenzimidazole ionomer membrane with a double cross-linked cationic network structure as described in claim 1, characterized in that, In step 5 of the preparation method, the concentration of the imidazole salt solution containing diene groups is 0.05–0.5 mol / L, and the solvent is one or more of ethanol, methanol, deionized water, N,N-dimethylformamide, and N,N-dimethylacetamide.

6. The gel-state polybenzimidazole ionomer membrane with a double cross-linked cationic network structure as described in claim 1, characterized in that, In step 5 of the preparation method, the imidazole salt containing a diene group is selected from one or more of the following: 1-allyl-3-vinylimidazolium chloride, 1-allyl-3-vinylimidazolium bromide, 1-allyl-3-allylimidazolium chloride, 1-allyl-3-allylimidazolium bromide, 1-allyl-3-vinylimidazolium chloride, 1-allyl-3-vinylimidazolium bromide, 1-allyl-3-vinylimidazolium bromide, 1-allyl-3-vinylimidazolium chloride, 1-allyl-3-vinylimidazolium bromide, etc.

7. The gel-state polybenzimidazole ionomer membrane with a double cross-linked cationic network structure as described in claim 1, characterized in that, In step 5 of the preparation method, the alkaline solution is one or more of potassium hydroxide solution and sodium hydroxide solution, and the concentration of the alkaline solution is 0.5-6 mol / L; the soaking in the alkaline solution is carried out at room temperature, and the soaking time is ≥48h.

8. The application of the gel-state polybenzimidazole ionomer membrane with a double cross-linked cationic network structure as described in claim 1 in alkaline water electrolysis for hydrogen production.

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