Bipolar membrane containing hydroxyl-based mof catalyst interlayer and method of making and use thereof

Abstract

The application belongs to the technical field of bipolar membrane, and particularly relates to a bipolar membrane containing a hydroxyl MOF catalyst intermediate layer and a preparation method and application thereof. The bipolar membrane is prepared by using cation and anion exchange resins as exchange groups, adding a binder, and using a MOF material containing a hydroxyl group as a hydrolysis catalyst, so that a high-performance and high-stability heterogeneous bipolar membrane is obtained. The raw materials are low in cost, widely available, and excellent in ion exchange capacity, and the prepared bipolar membrane is better in performance and simple in preparation process. The hydroxyl MOF hydrolysis catalyst of the application contains a hydroxyl group and a metal group, can effectively prolong the specific surface area of the catalyst, is helpful to enhancing the transfer of protons from water molecules to fixed charge groups, and thus accelerates the hydrolysis in the bipolar membrane. By adding the binder and adding woven fabric fibers containing carbon, the stability of the membrane structure is improved, the service life of the membrane is prolonged, and the mechanical properties and conductivity of the bipolar membrane are effectively improved.

Description

Technical Field

[0001] This invention belongs to the field of bipolar membrane technology, specifically relating to a bipolar membrane containing a hydroxyl-based MOF catalyst interlayer, its preparation method, and its application. Background Technology

[0002] A bipolar membrane is a layered ion exchange membrane with a special structure. It consists of two polymer layers with fixed opposite charges: one layer allows only anions to pass through (anion exchange membrane layer), while the other layer allows only cations to pass through (cation exchange membrane layer). When a positive bias voltage is applied across the bipolar membrane, the H+ ions on both sides of the bipolar membrane... + and OH - Driven by an electric field, the ions migrate to the interface layer and recombine to form water molecules. When a reverse bias is applied across the bipolar membrane, the positive and negative ions in the intermediate layer migrate through the anion and cation layers into the bulk solution, respectively, driven by the electric field, thereby forcing the water molecules in the intermediate layer to dissociate. The water dissociation product H2 + and OH - Driven by the potential difference between the cathode and anode, water migrates to the bulk solution on both sides of the membrane, while the consumed water diffuses from the bulk solution through the membrane layer to the intermediate layer to replenish it. Compared with conventional water dissociation, this process has the advantages of no gas generation and low energy consumption.

[0003] Bipolar membranes effectively prevent ion cross-linking on both sides of the membrane, providing different reaction environments for each side and broadening their application range. Currently, most bipolar membranes are limited by problems such as high water dissociation voltage, membrane shedding, and catalyst leakage, preventing large-scale application.

[0004] To meet the industrial application requirements of bipolar membranes in various fields, their performance must be continuously improved. Precise control of the bipolar membrane interface layer is a crucial means of enhancing this performance. The control of the water dissociation voltage of the bipolar membrane is mainly achieved by changing the type of catalyst and the preparation process, while problems such as membrane layer detachment are primarily addressed through membrane layer composite processes. Simultaneously, in addition to controlling the materials of the anion and cation membrane layers, the stability of the interface layer catalyst and its immobilization method also significantly impact the stability of the bipolar membrane.

[0005] Since bipolar membranes are currently mainly used in bipolar membrane electrodialysis processes, this invention introduces a method for preparing bipolar membranes with excellent performance and stability, as well as a variety of effective catalysts, providing a new approach for preparing bipolar membranes with excellent performance and stability. Summary of the Invention

[0006] This invention aims to overcome the shortcomings of existing bipolar membranes, such as high water dissociation voltage, slow water dissociation rate, poor membrane structure stability, and high production cost. It provides a bipolar membrane containing a hydroxyl-based MOF catalyst interlayer and its preparation method, and applies it to photo / electrochemical water splitting for hydrogen production, fuel cells, electrochemical ammonia synthesis, and bipolar membrane electrodialysis.

[0007] To achieve the above-mentioned objectives, the present invention is implemented through the following technical solution: A method for preparing a bipolar membrane containing a hydroxyl-based MOF catalyst interlayer includes the following steps: (S.1) Preparation of hydroxyl-based MOF hydrolysis catalysts: Weigh out a hydrated metal chloride and dissolve it in N,N-dimethylformamide solution, add 2-hydroxyterephthalic acid, stir well and then seal it in a reaction vessel. After the reaction is completed, allow it to cool naturally. Take the product, centrifuge, wash and dry it to obtain the hydroxyl MOF hydrolysis catalyst M-MOF-OH. (S.2) Preparation of bipolar films: Anion and cation exchange resin powders were added to the adhesive solution and stirred evenly to obtain anion membrane casting solution and cation membrane casting solution, respectively. The woven fabric was fixed on a clean glass plate and the anion membrane casting solution was cast on it and dried. After drying, anion exchange membrane layer was obtained. An ethanol solution containing the hydroxyl-based MOF hydrolysis catalyst M-MOF-OH was dropped onto the anion exchange membrane layer and dried. After complete drying, the intermediate layer was obtained. A cation exchange membrane layer is formed by coating a cation membrane casting solution onto the intermediate layer and drying it, thus obtaining a bipolar membrane containing a hydroxyl-based MOF catalyst intermediate layer.

[0008] This invention utilizes anion exchange resins and cation exchange resins as the exchange groups of a bipolar membrane. By adding a binder and using MOF materials containing hydroxyl groups as water dissociation catalysts, a high-performance, high-stability heterogeneous bipolar membrane is fabricated via a casting method. Specifically, this invention uses anion exchange resins and cation exchange resins as raw materials, which are inexpensive, widely available, and easily obtained. Simultaneously, the hydroxyl-based MOF water dissociation catalyst of this invention contains both hydroxyl groups and metal groups. The catalytic effect of the hydroxyl groups and the porous structure of the MOF material itself provide strong adsorption, effectively extending the specific surface area of ​​the catalyst. Furthermore, the metal groups possess excellent hydration capabilities, acting as active surface sites (M-OH) in the ion exchange membrane matrix, which helps enhance the transfer of protons from water molecules to fixed-charge groups, thereby accelerating water dissociation in the bipolar membrane.

[0009] Furthermore, the ion exchange resin selected in this invention possesses excellent ion exchange capacity, resulting in a bipolar membrane with superior performance and a simpler manufacturing process. Additionally, at the physical level, the addition of a binder enhances the membrane's structural stability, contributing to a longer service life. This invention also significantly improves the mechanical properties and conductivity of the bipolar membrane by incorporating carbon-containing woven fibers, thereby ensuring the membrane's stability.

[0010] On the other hand, multimetallic MOF materials exhibit even higher catalytic activity due to their compact structure, good stability, and high electron transfer efficiency. This invention also utilizes the combination of two different metal cations to effectively enhance conductivity and promote rapid oxidation reactions between different metal sites in the MOF structure, thereby improving catalytic efficiency. This controllable integration of functional components helps to construct multifunctional complexes with advanced properties, effectively enhancing the activity of catalytic reactions and other reactions.

[0011] The bipolar film containing a hydroxyl-based MOF catalyst interlayer prepared by the method of this invention achieves a speed of 100 mA / cm². 2 The transmembrane voltage at the current density is only 1.29V. This invention uses different metal ions and MOF materials containing hydroxyl groups to prepare bipolar membranes with different hydroxyl-containing MOF catalyst interlayers. The hydrolysis voltage of these membranes is reduced to varying degrees, and Ni-MOF-OH exhibits the best catalytic effect among the different catalysts prepared. Furthermore, data analysis shows that a catalyst loading of approximately 0.1 g / L is optimal. In the stability test of the bipolar membrane, at 100 mA / cm²... 2 After 10 hours at the current density, the transmembrane voltage of the bipolar membrane containing the hydroxyl-based MOF catalyst interlayer of the present invention increased by only 6%, demonstrating excellent stability.

[0012] Preferably, the hydrated metal chloride in step (S.1) contains Al ions. 3+ Mg 2+ Sn 2+ Any one or more combinations of transition metal ions.

[0013] As a further preferred embodiment, the transition metal ion is Co. 2+ Ni 2+ Cr 3+ Fe 3+ Fe 2+ Ru 3+ V 3+ V 5+ Mn 2 + Mn 4+ Ir 3+ Pt 2+ Pt4+ Eu 3+ Ti 2+ Pd 2+ Ag + Mo 2+ Any one of them.

[0014] Preferably, the molar ratio of the metal ions in the hydrated metal chloride to 2-hydroxyterephthalic acid in step (S.1) is 0.1~1:0.5~1.

[0015] Preferably, the amount of N,N-dimethylformamide solution added in step (S.1) is 30~60 mL.

[0016] Preferably, in step (S.1), the stirring reaction time is 30~100 min; the heating reaction temperature is 120~180℃; and the heating reaction time is 10~18 h.

[0017] Preferably, the cation exchange groups contained in the cation exchange resin powder in step (S.2) are any one or more combinations of sulfonic acid group, carboxyl group, phosphonic acid group, hypophosphonic acid group, arsenic acid group and selenic acid group; The anion exchange groups contained in the anion exchange resin powder are any one or more combinations of quaternary ammonium salts, primary amines, secondary amines, tertiary amines, and tertiary sulfonyl groups. The adhesive solution contains any one or more of the following adhesives: polyacrylonitrile, polyethylene, polyvinyl chloride, polyvinyl alcohol, fluororubber, styrene-butadiene rubber, cellulose derivatives, polytetrafluoroethylene, polychlorotrifluoroethylene, polyvinylidene fluoride, polysulfone, polyetheretherketone, styrene-ethylene-butene-styrene, and polyphenylene ether.

[0018] Preferably, the concentration of the adhesive solution in step (S.2) is 2-15%; The mass ratio of anion and cation exchange resin powder in the casting solution to binder in the binder solution is 0.2~1.5:1; The concentrations of both the anion exchange membrane casting solution and the cation exchange membrane casting solution are 5-20%. The concentration of the ethanol solution containing the hydroxyl-based MOF hydrolysis catalyst M-MOF-OH is 0.05~0.2 g / L.

[0019] Preferably, the drying temperature in step (S.2) is 50~60℃.

[0020] The bipolar membrane containing a hydroxyl-based MOF catalyst intermediate layer prepared by the method described above comprises, in sequence, an anion exchange membrane layer, an intermediate layer with water dissociation catalysis, and a cation exchange membrane layer, characterized in that the intermediate layer comprises a MOF catalyst containing hydroxyl groups.

[0021] The preparation method of bipolar membrane containing hydroxyl-based MOF catalyst intermediate layer as described above has applications in photo / electrochemical water splitting hydrogen production processes, fuel cells, electrochemical ammonia synthesis processes, and bipolar membrane electrodialysis.

[0022] Therefore, the present invention has the following beneficial effects: (1) This invention utilizes anion exchange resin and cation exchange resin as the exchange groups of the bipolar membrane, and adds a binder and uses MOF material containing hydroxyl groups as a water dissociation catalyst to produce a high-performance, high-stability heterogeneous bipolar membrane by casting. The raw materials are inexpensive and widely available, have excellent ion exchange capacity, and the resulting bipolar membrane has better performance and a simple manufacturing process; (2) The hydroxyl-based MOF water dissociation catalyst of the present invention contains both hydroxyl groups and metal groups. The catalytic effect of hydroxyl groups and the porous structure of the MOF material itself have strong adsorption properties, which can effectively extend the specific surface area of ​​the catalyst. In addition, the metal groups also have excellent hydration capabilities and act as active surface sites (M-OH) in the ion exchange membrane matrix, which helps to enhance the transfer of protons from water molecules to fixed charge groups, thereby accelerating water dissociation in the bipolar membrane; (3) This invention enhances the stability of the membrane structure by adding an adhesive, which helps to extend the service life of the membrane. Furthermore, the addition of carbon-containing woven fibers significantly improves the mechanical properties and conductivity of the bipolar membrane, thereby ensuring its stability. (4) The present invention utilizes the combination of two or more different metal cations to effectively enhance conductivity and promote the rapid oxidation reaction between different metal sites in the MOF structure, thereby effectively enhancing reaction activity and improving catalytic efficiency. Attached Figure Description

[0023] Figure 1 This is a route diagram for the preparation of hydroxyl-based MOF hydrolysis catalysts.

[0024] Figure 2 This is a route diagram for the preparation of bipolar membranes containing a hydroxyl-based MOF catalyst interlayer.

[0025] Figure 3 The results show the scanning electron microscope (SEM) images of the hydroxyl-based MOF water dissociation catalyst and the cross-sectional SEM images of the bipolar membrane containing the hydroxyl-based MOF catalyst interlayer compared with the cross-sectional SEM images of the blank bipolar membrane.

[0026] Figure 4 The figure shows the test results of bipolar film current-voltage curves under different metal group conditions.

[0027] Figure 5The figure shows the test results of bipolar membrane current-voltage curves under different concentrations of hydroxyl-based MOF water dissociation catalysts.

[0028] Figure 6 For bipolar films containing hydroxyl-based MOF catalyst interlayers at 100 mA / cm 2 Cyclic stability curves at current density.

[0029] Figure 7 The graph shows the test results of current-voltage curves for different bipolar films. Detailed Implementation

[0030] The present invention will be further described below with reference to the accompanying drawings and specific embodiments. Those skilled in the art will be able to implement the present invention based on these descriptions. Furthermore, the embodiments of the present invention described below are generally only some, not all, of the embodiments of the present invention. Therefore, all other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort should fall within the scope of protection of the present invention.

[0031] Example 1 This embodiment provides a method for preparing a bipolar membrane containing a hydroxyl-based MOF catalyst interlayer.

[0032] A method for preparing a bipolar membrane containing a hydroxyl-based MOF catalyst interlayer includes the following steps: (S.1) Preparation of hydroxyl-based MOF hydrolysis catalyst (Ni-MOF-OH): Weigh 0.2377 g (0.001 mol) of NiCl2•6H2O and dissolve it in 40 mL of N,N-dimethylformamide (DMF) solution, then add 1.811 g of 2-hydroxyterephthalic acid to maintain the concentration of Ni ions in the entire system. 2+ The molar ratio of 2-hydroxyterephthalic acid to hydroxyl-2-hydroxyterephthalic acid was 1:1. After stirring for 60 min, the mixture was encapsulated in a polytetrafluoroethylene reactor and heated at 150 °C for 12 h. After the reaction was completed, the mixture was allowed to cool naturally, and the product was centrifuged, washed three times with anhydrous ethanol, and finally vacuum dried at 80 °C for 24 h to obtain the hydroxyl-based MOF water dissociation catalyst (Ni-MOF-OH). The preparation route of the hydroxyl-based MOF water dissociation catalyst is as follows: Figure 1 As shown; (S.2) Preparation of bipolar films: The purchased anion and cation exchange resin particles were crushed separately to a diameter of less than 10 μm using a ball mill (QM-3SP2 planetary ball mill from Nanjing Nanda Instrument Co., Ltd.) to obtain anion and cation exchange resin powders. Then, the anion and cation exchange resin powders were added separately to an 8% polyacrylonitrile solution and stirred for at least 12 hours to ensure uniform dispersion of the anion and cation exchange resin particles, yielding 10% anion membrane casting solutions and 10% cation membrane casting solutions, respectively. The mass ratio of anion and cation exchange resin powder in the anion and cation membrane casting solutions to polyacrylonitrile in the polyacrylonitrile solution was 1.2:1. Carbon-containing woven fabric fibers were fixed to a clean glass plate with tape, and the anion membrane casting solution was poured onto it. The solution was then smoothed to a thickness of 200 μm using a scraper. After complete drying, an anion exchange membrane layer was obtained. The thickness of the dried anion exchange membrane layer was 70–120 μm, depending on the concentration of the anion membrane casting solution. After the anion exchange membrane layer is completely dry, in an area of ​​12.56 cm²... 2 1 mL of a 0.1 g / L ethanol solution containing a hydroxyl-based MOF water dissociation catalyst (Ni-MOF-OH) was dropped onto the anion exchange membrane layer. After complete drying, an intermediate layer was obtained. A cation exchange membrane casting solution was then poured onto the intermediate layer and dried completely, forming a cation exchange membrane layer on the upper surface of the intermediate layer. The thickness of the cation exchange membrane layer was controlled to be similar to that of the anion exchange membrane layer, and the drying temperature was maintained at 60℃. Finally, a bipolar membrane containing a hydroxyl-based MOF catalyst intermediate layer was obtained. The bipolar membrane containing the hydroxyl-based MOF catalyst intermediate layer was immersed in a 0.1–0.5 mol / L sodium chloride solution for at least 2 hours before analysis. The preparation route of the bipolar membrane containing the hydroxyl-based MOF catalyst intermediate layer is as follows: Figure 2 As shown.

[0033] Example 2 The difference between this embodiment and Embodiment 1 is that: This embodiment provides a method for preparing a bipolar film containing a hydroxyl-based MOF catalyst interlayer. In step (S.1), 0.2703 g (0.001 mol) of FeCl3•6H2O is used to replace 0.2377 g (0.001 mol) of NiCl2•6H2O. The final step (S.1) yields a hydroxyl-based MOF water dissociation catalyst (Fe-MOF-OH). In step (S.2), a membrane with an area of ​​12.56 cm² is prepared. 2 1 mL of an ethanol solution containing a hydroxyl-based MOF hydrolysis catalyst (Fe-MOF-OH) with a concentration of 0.1 g / L was dropped onto the anion exchange membrane. Everything else was the same as in Example 1.

[0034] Example 3 The difference between this embodiment and Embodiment 1 is that: This embodiment provides a method for preparing a bipolar film containing a hydroxyl-based MOF catalyst interlayer. In step (S.1), 0.1188 g (0.0005 mol) of NiCl2•6H2O and 0.1352 g (0.0005 mol) of FeCl3•6H2O are used to replace 0.2377 g (0.001 mol) of NiCl2•6H2O. The final step (S.1) yields a hydroxyl-based MOF water dissociation catalyst (Ni / Fe-MOF-OH). In step (S.2), a membrane with an area of ​​12.56 cm² is prepared. 2 1 mL of an ethanol solution containing a hydroxyl-based MOF hydrolysis catalyst (Ni / Fe-MOF-OH) with a concentration of 0.1 g / L was dropped onto the anion exchange membrane. Everything else was the same as in Example 1.

[0035] Example 4 The difference between this embodiment and Embodiment 1 is that: This embodiment provides a method for preparing a bipolar film containing a hydroxyl-based MOF catalyst interlayer. In step (S.1), 0.2664 g (0.001 mol) of CrCl3•6H2O is used to replace 0.2377 g (0.001 mol) of NiCl2•6H2O. The final step (S.1) yields a hydroxyl-based MOF water dissociation catalyst (Cr-MOF-OH). In step (S.2), a membrane with an area of ​​12.56 cm² is prepared. 2 1 mL of an ethanol solution containing a hydroxyl-based MOF hydrolysis catalyst (Cr-MOF-OH) with a concentration of 0.1 g / L was dropped onto the anion exchange membrane. Everything else was the same as in Example 1.

[0036] Example 5 The difference between this embodiment and Embodiment 1 is that: This embodiment provides a method for preparing a bipolar film containing a hydroxyl-based MOF catalyst interlayer. In step (S.1), 0.2379 g (0.001 mol) of CoCl2•6H2O is weighed and dissolved in 30 mL of DMF solution, and 1.8213 g of 2-hydroxyterephthalic acid is added to maintain the metal ion concentration (CoCl2•6H2O) in the entire system. 2+The molar ratio of 2-hydroxyterephthalic acid to hydroxyl MOF was 0.1:1; the stirring reaction time was 30 min; the reaction was heated at 120 °C for 10 h; thus, a hydroxyl MOF hydrolysis catalyst (Co-MOF-OH) was obtained. In step (S.2), anion and cation exchange resin powders were added to a 2% polyethylene solution to obtain a 5% anion membrane casting solution and a 5% cation membrane casting solution, respectively; wherein the mass ratio of anion and cation exchange resin powders in the anion and cation membrane casting solutions to polyethylene in the polyethylene solution was 0.2:1; the drying temperature was maintained at 50 °C. Everything else was the same as in Example 1.

[0037] Example 6 The difference between this embodiment and Embodiment 1 is that: This embodiment provides a method for preparing a bipolar film containing a hydroxyl-based MOF catalyst interlayer. In step (S.1), 0.2033 g (0.001 mol) of MgCl₂•6H₂O is weighed and dissolved in 60 mL of DMF solution, and 0.0911 g of 2-hydroxyterephthalic acid is added to maintain the metal ion concentration (MgCl₂•6H₂O) in the entire system. 2+ The molar ratio of 2-hydroxyterephthalic acid to 2-hydroxyterephthalic acid was 2:1; the stirring reaction time was 100 min; the reaction was heated at 180 °C for 18 h; a hydroxyl-based MOF hydrolysis catalyst (Mg-MOF-OH) was obtained. In step (S.2), anion and cation exchange resin powders were added to a 15% polyvinylidene fluoride solution to obtain anion membrane casting solution and cation membrane casting solution with a concentration of 20% respectively; wherein, the mass ratio of anion and cation exchange resin powders in the anion and cation membrane casting solutions to polyvinylidene fluoride in the polyvinylidene fluoride solution was 1.5:1; the drying temperature was maintained at 55 °C. Everything else was the same as in Example 1.

[0038] Comparative Example 1 The difference between this comparative example and Example 1 is as follows: This comparative example provides a method for preparing a blank bipolar film, wherein in step (S.2), a film with an area of ​​12.56 cm² is prepared. 2 1 mL of ethanol was added dropwise onto the anion exchange membrane layer instead of 1 mL of the 0.1 g / L ethanol solution containing the hydroxyl-based MOF hydrolysis catalyst (Ni-MOF-OH). This resulted in a blank bipolar membrane without the hydroxyl-based MOF catalyst interlayer. Everything else was the same as in Example 1.

[0039] Comparative Example 2 The difference between this comparative example and Example 1 is as follows: This comparative example provides a method for preparing a bipolar film containing a hydroxyl-based MOF catalyst interlayer, wherein in step (S.2), a film with an area of ​​12.56 cm² is prepared. 2 1 mL of an ethanol solution containing a hydroxyl-based MOF hydrolysis catalyst (Ni-MOF-OH) with a concentration of 0.05 g / L was dropped onto the anion exchange membrane. Everything else was the same as in Example 1.

[0040] Comparative Example 3 The difference between this comparative example and Example 1 is as follows: This comparative example provides a method for preparing a bipolar film containing a hydroxyl-based MOF catalyst interlayer, wherein in step (S.2), a film with an area of ​​12.56 cm² is prepared. 2 1 mL of an ethanol solution containing a hydroxyl-based MOF hydrolysis catalyst (Ni-MOF-OH) with a concentration of 0.2 g / L was dropped onto the anion exchange membrane. Everything else was the same as in Example 1.

[0041] Comparative Example 4 The difference between this comparative example and Example 1 is as follows: This comparative example provides a method for preparing a bipolar film containing a MOF catalyst interlayer, wherein the preparation process of the MOF water dissociation catalyst (Ni-NH2-MOF) in step (S.1) is as follows: Weigh 2.377 g of NiCl2•6H2O and dissolve it in 45 mL of a mixed solvent (obtained by mixing N,N-dimethylformamide, ethanol, and deionized water in a volume ratio of 10:1:5), and add 1.811 g of 2-aminoterephthalic acid to maintain the concentration of Ni ions in the entire system. 2+ The molar ratio of 2-aminoterephthalic acid to 2-aminoterephthalic acid was 1:1. After stirring for 60 min, the mixture was sealed in a polytetrafluoroethylene reactor and heated at 180 °C for 8 h. After the reaction, the mixture was allowed to cool naturally, and the product was centrifuged and washed three times with DMF. Finally, it was vacuum dried at 80 °C for 24 h to obtain the MOF water dissociation catalyst (Ni-NH2-MOF). In step (S.2), the mass ratio of anion and cation exchange resin powder in the anion and cation membrane casting solution to polyacrylonitrile in the polyacrylonitrile solution was 1.5:1; the thickness of the anion exchange membrane layer formed after drying was 70~200 μm, with the most preferred thickness being 150 μm; the area was 12.56 cm². 2 1 mL of an aqueous solution containing a 0.1 g / L MOF water dissociation catalyst (Ni-NH2-MOF) was dropped onto the anion exchange membrane layer; the drying temperature was maintained at 50 °C. Everything else was the same as in Example 1.

[0042] [Performance Testing and Analysis] Hydroxyl-based MOF water dissociation catalyst (Ni-MOF-OH), bipolar membranes containing a hydroxyl-based MOF catalyst interlayer, and blank bipolar membranes without a hydroxyl-based MOF catalyst interlayer were prepared according to the methods in Example 1 and Comparative Example 1, respectively. Scanning electron microscopy (SEM) tests were performed on each, and the results are as follows: Figure 3 As shown. Figure 3 The results show the scanning electron microscope (SEM) images of the hydroxyl-based MOF water dissociation catalyst and the cross-sectional SEM images of the bipolar membrane containing the hydroxyl-based MOF catalyst interlayer, compared with the cross-sectional SEM images of the blank bipolar membrane.

[0043] from Figure 3 Analysis revealed that the cross-sectional image of the bipolar membrane containing a hydroxyl-based MOF catalyst interlayer prepared in Example 1 showed a clear interface between the anion exchange membrane layer and the cation exchange membrane layer, with no interpenetration between the interlayer and the two ion exchange membrane layers. Each unipolar membrane layer of the bipolar membrane was obtained by dispersing anion and cation exchange resin powders in a binder solution layer by layer. The presence of anion and cation exchange resins in the membrane layers increased the surface roughness of the bipolar membrane, increasing the reaction area at the site of water dissociation.

[0044] Bipolar film current-voltage curve testing (IV): The current-voltage curve testing apparatus uses a four-chamber electrodialysis unit, consisting of a cathode chamber, an anode chamber, an acid chamber, an alkali chamber, and cathode and anode components. This apparatus, along with a regulated power supply, a peristaltic pump, a multimeter, and a reference electrode, forms the testing system. During testing, a 1.0 mol / L sodium chloride solution is circulated through the acid and alkali chambers, while a 1.0 mol / L sodium sulfate solution is circulated through the cathode and anode chambers. The test current density is 0 mA / cm². 2 -200mA / cm 2 .

[0045] Different hydroxyl-based MOF water dissociation catalysts and their corresponding bipolar membranes containing hydroxyl-based MOF catalyst interlayers and blank bipolar membranes without hydroxyl-based MOF catalyst interlayers were prepared according to the methods in Examples 1-3 and Comparative Example 1, respectively. Current-voltage curve (IV) tests were then performed on each. The test results are as follows: Figures 4-5 As shown in the figure. The test results of the bipolar film current-voltage curves under different metal group conditions are as follows. Figure 4 As shown in the figure. The test results of bipolar membrane current-voltage curves under different concentrations of hydroxyl-based MOF water dissociation catalysts are as follows. Figure 5 As shown.

[0046] from Figures 4-5Data analysis revealed that the voltage of the bipolar membranes with added hydroxyl-based MOF water dissociation catalysts (Examples 1-3) was significantly lower than that of the blank bipolar membrane without catalyst (Comparative Example 1). This indicates that the introduction of hydroxyl-based MOF water dissociation catalysts is beneficial for water dissociation in the bipolar membrane. As expected, MOF catalysts containing hydroxyl groups (-OH) and metal groups can accelerate water dissociation in the bipolar membrane. Furthermore, the current-voltage curve of the bipolar membrane was found to be closely related to the catalyst loading concentration. With increasing addition of hydroxyl-based MOF water dissociation catalyst, the voltage drop first decreased and then increased. This indicates that there exists an optimal loading concentration when using hydroxyl-based MOF materials as the interfacial catalyst for bipolar membranes. Concentrations higher or lower than this optimal level are unlikely to achieve the best catalytic effect.

[0047] Bipolar film stability test: A bipolar membrane containing a hydroxyl-based MOF catalyst interlayer was prepared according to the preparation method in Example 1, and the change of the transmembrane voltage of the bipolar membrane over time was monitored under constant current. The testing apparatus was the same as that used for current-voltage curve testing. The current was set to 100 mA / cm². 2 The test voltage interval was 30 minutes, and the total test time was set to 10 hours. The bipolar membrane containing a hydroxyl-based MOF catalyst interlayer was tested at 100 mA / cm². 2 The cyclic stability curve at current density is as follows Figure 6 As shown.

[0048] from Figure 6 Data analysis shows that during the 10-hour constant current density test, the transmembrane voltage of the prepared bipolar membrane containing the hydroxyl-based MOF catalyst interlayer increased from 1.29V to 1.36V, with a transmembrane voltage increase rate of only 6%. This indicates that the bipolar membrane containing the hydroxyl-based MOF catalyst interlayer exhibits excellent stability during long-term operation. This further confirms that the coordination effect and special structure of the hydroxyl-based MOF water dissociation catalyst in the bipolar membrane containing the hydroxyl-based MOF catalyst interlayer not only effectively improves the water dissociation efficiency but also significantly enhances the stability of the bipolar membrane.

[0049] Hydroxyl-based MOF water dissociation catalysts and bipolar membranes containing hydroxyl-based MOF catalyst interlayers, blank bipolar membranes without hydroxyl-based MOF catalyst interlayers, MOF water dissociation catalysts (Ni-NH2-MOF) and bipolar membranes containing MOF catalyst interlayers were prepared according to the methods in Example 1, Comparative Example 1, and Comparative Example 4, respectively. Current-voltage curves (IV) were then performed on these membranes. The test results are as follows: Figure 7 As shown.

[0050] from Figure 7Data analysis reveals that, under identical conditions, there is a significant difference in the water dissociation voltage between the bipolar membrane containing a MOF catalyst interlayer (Ni-NH2-MOF, Comparative Example 4) and the bipolar membrane containing a hydroxyl-based MOF catalyst interlayer (Ni-MOF-OH, Example 1). The reaction mechanism of amino (-NH2) ions primarily involves the basic properties of the amino group. The basicity of amino groups stems from the isolated electron pairs on their nitrogen atoms, which can accept protons or free hydrogen ions (H+). + It combines with protons or free hydrogen ions to form the positively charged conjugate acid form of the amino group, often represented as NH3. + The reaction mechanism of hydroxyl (-OH) groups with water molecules mainly involves hydrogen bonding. The hydroxyl group is a hydrophilic group, and its interaction with water molecules is similar to that of an alcohol group. The oxygen atom in the hydroxyl group can form hydrogen bonds with the hydrogen atoms in the water molecule. This interaction is stronger than ordinary intermolecular forces but weaker than chemical bonds. The formation of hydrogen bonds gives the hydroxyl group good solubility and compatibility. Although both amino (-NH2) and hydroxyl (-OH) groups can catalyze the dissociation of water molecules, comparative results show that the bipolar film containing the hydroxyl-based MOF catalyst interlayer has a better catalytic effect. It not only increases the effective active area of ​​the water dissociation reaction but also enhances the interfacial field strength, further promoting the polarization effect of water molecules and accelerating the kinetic process of the water dissociation reaction.

[0051] In summary, this invention utilizes anion exchange resins and cation exchange resins, adds a binder, uses hydroxyl-based MOF materials as water dissociation catalysts, and fabricates a high-performance and highly stable bipolar membrane containing a hydroxyl-based MOF catalyst interlayer via a casting method. The preparation method of this invention uses inexpensive raw materials, is simple to implement, and produces a bipolar membrane with a stable structure and long service life. This invention utilizes hydroxyl-based MOF materials as water dissociation catalysts, which contain both hydroxyl and metal groups. The catalytic effect of the hydroxyl groups and the porous structure of the MOF material itself provide strong adsorption, effectively extending the specific surface area of ​​the catalyst. The metal groups have hydration capabilities and function as active surface sites in the ion exchange membrane matrix, enhancing the transfer of protons from water molecules to fixed-charge groups, accelerating water dissociation in the bipolar membrane, and thus promoting a faster hydrolysis rate in the bipolar membrane containing the hydroxyl-based MOF catalyst interlayer. This invention demonstrates that in bipolar membrane research, the design of bipolar membrane materials and the selection of hydroxyl-based MOF water dissociation catalysts hold broad prospects for developing novel and superior bipolar membranes.

[0052] The above description is merely a detailed explanation of preferred embodiments and principles of the present invention. For those skilled in the art, there may be changes in specific implementation methods based on the ideas provided by the present invention, and these changes should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing a bipolar film containing a hydroxyl-based MOF catalyst interlayer, characterized in that, Includes the following steps: (S.1) Preparation of hydroxyl-based MOF hydrolysis catalysts: Weigh out a hydrated metal chloride and dissolve it in N,N-dimethylformamide solution, add 2-hydroxyterephthalic acid, stir well and then seal it in a reaction vessel. After the reaction is completed, allow it to cool naturally. Take the product, centrifuge, wash and dry it to obtain the hydroxyl MOF hydrolysis catalyst M-MOF-OH. (S.2) Preparation of bipolar films: Anion and cation exchange resin powders were added to the adhesive solution and stirred evenly to obtain anion membrane casting solution and cation membrane casting solution, respectively. The woven fabric was fixed on a clean glass plate and the anion membrane casting solution was cast on it and dried. After drying, anion exchange membrane layer was obtained. An ethanol solution containing the hydroxyl-based MOF hydrolysis catalyst M-MOF-OH was dropped onto the anion exchange membrane layer and dried. After complete drying, the intermediate layer was obtained. A cation exchange membrane layer is formed by coating a cation membrane casting solution onto the intermediate layer and drying it, thus obtaining a bipolar membrane containing a hydroxyl-based MOF catalyst intermediate layer.

2. The method for preparing a bipolar film containing a hydroxyl-based MOF catalyst interlayer according to claim 1, characterized in that, The hydrated metal chloride in step (S.1) contains Al ions. 3+ Mg 2+ Sn 2+ Any one or more combinations of transition metal ions.

3. The method for preparing a bipolar film containing a hydroxyl-based MOF catalyst interlayer according to claim 1, characterized in that, The molar ratio of the metal ions in the hydrated metal chloride to 2-hydroxyterephthalic acid in step (S.1) is 0.1~1:0.5~1.

4. The method for preparing a bipolar film containing a hydroxyl-based MOF catalyst interlayer according to claim 1, characterized in that, In step (S.1), the amount of N,N-dimethylformamide solution added is 30~60 mL.

5. The method for preparing a bipolar film containing a hydroxyl-based MOF catalyst interlayer according to claim 1, characterized in that, In step (S.1), the stirring reaction time is 30~100 min; the heating reaction temperature is 120~180℃, and the heating reaction time is 10~18 h.

6. The method for preparing a bipolar film containing a hydroxyl-based MOF catalyst interlayer according to claim 1, characterized in that, In step (S.2), the cation exchange resin powder contains any one or more combinations of sulfonic acid groups, carboxyl groups, phosphonic acid groups, hypophosphonic acid groups, arsenic acid groups, and selenic acid groups. The anion exchange groups contained in the anion exchange resin powder are any one or more combinations of quaternary ammonium salts, primary amines, secondary amines, tertiary amines, and tertiary sulfonyl groups. The adhesive solution contains any one or more of the following adhesives: polyacrylonitrile, polyethylene, polyvinyl chloride, polyvinyl alcohol, fluororubber, styrene-butadiene rubber, cellulose derivatives, polytetrafluoroethylene, polychlorotrifluoroethylene, polyvinylidene fluoride, polysulfone, polyetheretherketone, styrene-ethylene-butene-styrene, and polyphenylene ether.

7. The method for preparing a bipolar film containing a hydroxyl-based MOF catalyst interlayer according to claim 1, characterized in that, The concentration of the adhesive solution in step (S.2) is 2-15%; The mass ratio of anion and cation exchange resin powder in the casting solution to binder in the binder solution is 0.2~1.5:1; The concentrations of both the anion exchange membrane casting solution and the cation exchange membrane casting solution are 5-20%. The concentration of the ethanol solution containing the hydroxyl-based MOF hydrolysis catalyst M-MOF-OH is 0.05~0.2 g / L.

8. The method for preparing a bipolar film containing a hydroxyl-based MOF catalyst interlayer according to claim 1, characterized in that, The drying temperature in step (S.2) is 50~60℃.

9. A bipolar membrane containing a hydroxyl-based MOF catalyst interlayer prepared by the preparation method according to any one of claims 1 to 8, comprising, in sequence, an anion exchange membrane layer, an interlayer with water dissociation catalysis, and a cation exchange membrane layer, characterized in that, The intermediate layer includes a MOF catalyst containing hydroxyl groups.

10. The preparation method of the bipolar membrane containing a hydroxyl-based MOF catalyst interlayer as described in any one of claims 1 to 8, and its application in the fields of photo / electrochemical water splitting for hydrogen production, fuel cells, electrochemical ammonia synthesis, and bipolar membrane electrodialysis.

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