Bipolar membrane containing monatomic catalyst and preparation method thereof

Abstract

The invention provides a bipolar membrane containing a monatomic intermediate catalyst layer and a preparation method thereof.The bipolar membrane comprises a cation exchange layer, an anion exchange layer and an intermediate catalyst layer located between the cation exchange layer and the anion exchange layer.The monatomic catalyst intermediate layer is introduced, so that the water dissociation voltage is remarkably reduced, and the water dissociation efficiency is improved; the method is suitable for the fields of electrochemical hydrolysis, energy conversion and the like.

Description

Technical Field

[0001] This invention relates to the field of bipolar membrane preparation technology, specifically to a bipolar membrane containing a single-atom catalyst and its preparation method. Background Technology

[0002] A bipolar membrane (BPM) is a composite ion exchange membrane composed of a cation exchange layer (CEL), an anion exchange layer (AEL), and an intermediate catalyst layer (IL). Its core function is to efficiently separate H+ through interfacial water dissociation reaction (WD). + With OH - When a reverse bias voltage is applied, the water molecules in the middle layer dissociate under an extremely high potential gradient, generating H+. + and OH - The water migrates to both sides of the membrane, while the consumed water is replenished through diffusion across the membrane layer. This process generates no gas and consumes little energy, making it a key component in fields such as water electrolysis for hydrogen production, fuel cells, and carbon dioxide reduction. However, the performance of bipolar membranes is highly dependent on the design of the intermediate catalyst layer; the activity, stability, and adhesion of the catalyst to the membrane substrate directly affect the water dissociation efficiency and membrane lifetime.

[0003] Despite continuous advancements in bipolar membrane technology, traditional catalysts (such as MoS2, Pt / C, and IrO2) and novel materials (such as MOFs and nanofibers) exhibit significant drawbacks in applications. First, they are highly dependent on noble metals. For example, noble metal catalysts such as Pt and Ir (e.g., Pt / C and IrO2) are highly active but expensive and prone to dissolution and deactivation at high current densities. Furthermore, noble metal catalysts struggle to maintain stability in both acidic and alkaline environments. Second, nanoparticle aggregation is a problem. Transition metal sulfides (such as MoS2) and oxides (such as Fe3O4) are prone to aggregation due to their high surface energy (as seen in patent CN118186456A, which requires electrochemical exfoliation to improve dispersibility), leading to a decrease in effective specific surface area and insufficient utilization of active sites. Third, interfacial bonding is weak. The catalyst layer and the membrane substrate are mostly bonded by physical adsorption, which can easily lead to delamination due to swelling or mechanical stress during long-term operation (as reported in the literature "Advanced Materials, 2022" regarding the performance degradation of Fe3O4 catalyst due to interfacial exfoliation). Fourth, traditional catalysts have insufficient adsorption / activation capacity for water molecules, resulting in high transmembrane voltage (>2.5V). For example, although MoS2 has high catalytic activity, its adsorption capacity for water molecules is limited, resulting in slow reaction kinetics ("ACS Catalysis, 2023") and significantly increased energy consumption. Finally, the preparation process is complex. For example, metal-organic framework (MOF) materials (such as Fe-MIL-101 in patent CN118743926A) require high-temperature hydrothermal synthesis (>150℃) and have low charge separation efficiency, making them difficult to scale up for application.

[0004] To address the aforementioned problems, this invention introduces an intermediate catalytic layer containing a single-atom catalyst into the bipolar membrane to improve the water dissociation reaction performance and reduce the overpotential of the bipolar membrane electrolyzer, providing a new approach for preparing bipolar membranes with excellent performance and stability in the field of bipolar membrane electrodialysis. Summary of the Invention

[0005] The purpose of this invention is to provide a bipolar membrane containing a single-atom intermediate catalyst layer and its preparation method. The bipolar membrane containing a single-atom intermediate catalyst layer provided by this invention can overcome the defect of poor bonding between the catalyst layer and the electrode substrate in existing bipolar membranes, and significantly reduce the water dissociation voltage and improve the water dissociation efficiency.

[0006] To achieve the above-mentioned objectives, the technical solution of the present invention is as follows:

[0007] In a first aspect, the present invention provides a bipolar membrane containing a single-atom intermediate catalyst layer, comprising a cation exchange layer, an anion exchange layer and an intermediate catalyst layer located between the cation exchange layer and the anion exchange layer, wherein the intermediate catalyst layer comprises a single-atom catalyst;

[0008] The preparation method of the single-atom catalyst includes the following steps:

[0009] (a) Preparation of nitrogen-doped carbon support: Nitrogen-containing organic precursors are mixed with carbon sources and then pyrolyzed at low temperature to obtain nitrogen-doped carbon supports;

[0010] (b) Single-atom metal anchoring: The metal salt solution is mixed with a nitrogen-doped carbon support, and the metal atoms are anchored to the surface of the support through a coordination reaction;

[0011] (c) Acid washing purification: Unanchored metal particles are removed by washing with acid solution and dried to obtain single-atom catalyst.

[0012] Preferably, the nitrogen-containing organic precursor in step (a) is selected from at least one of 2,2'-bipyridine, melamine, urea, and polyaniline, and the carbon source is selected from at least one of glucose, sucrose, polyvinyl alcohol, and polyacrylonitrile, with a mass ratio of nitrogen-containing precursor to carbon source of 1:20-1:1.

[0013] Preferably, the temperature of the low-temperature pyrolysis in step (a) is 200-800℃, the heating rate is 5-15℃ / min, the pyrolysis time is 1-6 hours, and the pyrolysis atmosphere is an inert gas, which is selected from nitrogen and argon.

[0014] Preferably, the metal salt in step (b) is Co. 2+ Ni 2+ Fe 3+ Cr 3+ Fe 2+Ru 3+ V 3+ V 5+ Mn 2+ Mn 4+ Ir 3+ Pt 2+ Pt 4+ Eu 3+ Ti 2+ Pd 2+ Ag + Mo 2+ The metal salt is selected from any one or more combinations of soluble sulfates, nitrates, and hydrochlorides; the solvent is water or ethanol, and the amount of metal salt added is 0.01-0.5 mmol / (g carbon), that is, 0.01-0.5 mmol of metal salt is added to 1 gram of porous carbon.

[0015] Preferably, the conditions for the coordination reaction in step (b) include: mixing the nitrogen-doped carbon support with the metal salt solution and stirring at 30-100°C for 2-8 hours.

[0016] Preferably, the acid solution in step (c) is selected from at least one of hydrochloric acid, sulfuric acid, and nitric acid, the concentration of the acid solution is 0.1-1 mol / L, the washing time is 2-12 hours, the drying temperature is 20-120℃, and the drying time is 4-12 hours.

[0017] In a second aspect, the present invention provides a method for preparing the bipolar film containing a single-atom intermediate catalyst layer as described in the first aspect, comprising the following steps:

[0018] (a) Prepare a dispersion of the single-atom catalyst using a solvent and stir until homogeneous;

[0019] (b) Dissolve polyethersulfone in chloroform and mechanically stir at room temperature to obtain a reaction solution. Gradually add chlorosulfonic acid to the reaction solution. After the addition is complete, continue stirring to obtain a sulfonated solution. Slowly pour the obtained sulfonated solution into pure water. After filtration, the polymer is washed with water several times until the pH is neutral. Dry it in a vacuum oven to obtain sulfonated polyethersulfone.

[0020] Sulfonated polyethersulfone was ground into powder, dissolved in N-methylpyrrolidone, and filtered to obtain a homogeneous solution. The homogeneous solution was then poured onto a clean glass plate and dried under vacuum to obtain a cation exchange layer.

[0021] (c) Fix the substrate with the cation exchange layer cast on the heating plate, coat the single-atom catalyst dispersion on the surface of the cation exchange layer, and after the surface dries, cast the anion exchange layer solution onto the intermediate catalyst layer by casting. After the surface dries, a bipolar membrane containing a single-atom intermediate catalyst layer is obtained.

[0022] Preferably, the solvent in step (a) is selected from at least one of water, ethanol, isopropanol, N,N-dimethylformamide (DMF), and N-methylpyrrolidone, and the dispersion concentration of the single-atom catalyst is 0.1-1 g / L.

[0023] Preferably, in step (b), the mass ratio of polyethersulfone to chloroform is 1:15-1:30, the mass ratio of polyethersulfone to chlorosulfonic acid is 1:10-1:15, the chlorosulfonic acid dropping rate is 1-2 drops / second, the reaction temperature is 10-40℃, the stirring time is 1-5 hours, and the degree of sulfonation is adjusted to 10-70%.

[0024] Preferably, the mass fraction of sulfonated polyethersulfone in the homogeneous solution prepared in step (b) is 1.5-4 wt%, and the thickness of the cation exchange layer is 80-120 μm.

[0025] Preferably, in step (b), the homogenized solution is vacuum dried on a clean glass plate at a temperature of 50-100°C for 12-48 hours.

[0026] Preferably, the coating and casting temperature in step (c) is 30-80°C, the coating method is selected from at least one of spraying, spin coating, and dipping, the coating thickness is 10-100 nm, the drying temperature is 50-130°C, and the drying time is 1-6 hours.

[0027] Preferably, the loading of the single-atom catalyst interlayer in step (c) is 0.01-0.5 mg / cm³. 2 The preferred concentration is 0.05-0.25 mg / cm³. 2 .

[0028] The beneficial effects of this invention are as follows:

[0029] This invention anchors metal atoms (such as Fe, Co, and Ni) in an atomically dispersed manner onto a nitrogen-doped carbon (NC) support, increasing the specific surface area of ​​the catalyst, fully exposing active catalytic sites, and enhancing atom utilization efficiency. This results in a catalytic layer with ultra-high catalytic performance, promoting water dissociation. The bipolar film containing this single-atom intermediate catalytic layer can significantly reduce the water dissociation voltage and improve the water dissociation efficiency.

[0030] This invention utilizes the combination of one or more different metal cations to effectively enhance conductivity and promote rapid oxidation reactions between different metal sites in the catalyst structure. The synergistic effect between metal ions enhances its reactivity, thereby improving catalytic efficiency.

[0031] This invention utilizes the synergistic effect of the support-interface to enhance the stability of single-atom catalysts by using nitrogen-doped carbon supports to stabilize single atoms through strong coordination of nitrogen atoms.

[0032] This invention provides a method for preparing the above-mentioned bipolar membrane containing a single-atom intermediate catalyst layer. This method is simple and convenient to operate, uses conventional raw materials, and is easy to achieve industrial-scale mass production. Attached Figure Description

[0033] Figure 1 The bipolar membranes of Embodiment 1 and Comparative Example 1 of this invention are used at 100 mA*cm. -2 Cyclic stability curves at current density Detailed Implementation

[0034] To facilitate understanding of the present invention, the following description, in conjunction with embodiments, will further illustrate the invention. It should be understood that the following embodiments are merely for a better understanding of the invention and do not imply that the invention is limited to these embodiments.

[0035] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items. Locational terms such as top and bottom, mentioned or possibly used in this specification, are defined relative to the constructions shown in the accompanying drawings; they are relative concepts and may therefore vary depending on their location and usage.

[0036] Main raw material sources

[0037] The raw materials involved in the following examples are sourced from the following sources:

[0038] Polyethersulfone, chlorosulfonic acid, ferric nitrate, nickel nitrate: Beijing Innocare Technology Co., Ltd.; N-methylpyrrolidone, N,N-dimethylacetamide, ethanol, chloroform: Shanghai Maclean's Biological Reagent Co., Ltd.; Isopropanol, melamine, glucose, concentrated sulfuric acid, hydrochloric acid: Sinopharm Chemical Reagent Co., Ltd.

[0039] Example

[0040] Example 1

[0041] (1) The main material of the cation exchange layer is sulfonated polyether sulfone, and the preparation steps include:

[0042] 1g of polyethersulfone was added to a round-bottom flask and dissolved in 20mL of chloroform. The mixture was mechanically stirred at room temperature to obtain a reaction solution. 15g of chlorosulfonic acid was placed in a constant-pressure dropping funnel and gradually added dropwise to the reaction solution at a dropping rate of 1 drop / second. The reaction temperature was maintained at 20℃. After the addition was completed, the mixture was stirred continuously for 1 hour to obtain a sulfonated solution. The sulfonated solution was slowly poured into pure water and filtered. The resulting polymer was washed with water several times until the pH was neutral. After drying in a vacuum oven, sulfonated polyethersulfone with a degree of sulfonation of 60% was obtained.

[0043] Sulfonated polyethersulfone was ground into powder, dissolved in N-methylpyrrolidone, and filtered to obtain a 2.5 wt% homogeneous solution. The homogeneous solution was then poured onto a clean glass plate and dried under vacuum at 80 °C for 24 h to obtain a cation exchange layer with a thickness of 100 μm.

[0044] (2) The anion exchange layer solution is a 5wt% quaternary ammonium polyphenylene ether solution, the solute is quaternary ammonium polyphenylene ether, and the solvent is a mixed solvent composed of 85vol% ethanol and 15vol% N,N-dimethylformamide.

[0045] (3) Weigh 3g of melamine and 15g of glucose into a mortar, grind them thoroughly until uniform, transfer them to a crucible, and then place them in a tube furnace. Carbonize at 500℃ in a N2 atmosphere for 2 hours, with a heating rate of 5℃ / min. -1 Nitrogen-doped carbon material (NC) was finally obtained. 1.0 g of NC, 0.02 mmol Ni(NO3)2, and 0.02 mmol Fe(NO3)3 were added to 10 ml of deionized water to form a transparent solution. The solution was stirred at 80 °C for 5 h to promote adsorption on the surface of the nitrogen-doped carbon material. After stirring, the solution was slowly evaporated in a beaker at 60 °C. Finally, the solution was acid-washed with 0.5 M H2SO4 for 12 h to remove any nanoparticles that may have formed during the process. The solution was then dried at 80 °C for 6 h to obtain a single-atom catalyst (Fe / Ni-NC). The obtained single-atom catalyst was dispersed in isopropanol at a concentration of 0.1 g / L to obtain the Fe / Ni-NC catalyst dispersion.

[0046] (4) Fix the glass plate coated with the cation exchange layer onto the heating plate, and at a heating temperature of 80°C, uniformly coat the catalyst dispersion onto the surface of the cation exchange layer by ultrasonic spraying (the catalyst loading is 0.25 mg / cm³). 2 After the catalyst dispersion is dried at 80℃ for 4 hours, the anion exchange layer solution is cast onto the catalyst layer at a heating temperature of 60℃. After the surface dries, an anion exchange layer with a thickness of 50 μm is formed, thus obtaining a bipolar film containing an Fe / Ni-NC intermediate catalyst layer.

[0047] Example 2

[0048] (1) The cation exchange membrane is the same as in Example 1.

[0049] (2) The anion exchange layer solution is the same as in Example 1.

[0050] (3) Weigh 3g of polyaniline and 15g of polyacrylonitrile into a mortar, grind them thoroughly until uniform, transfer them to a crucible, and then place them in a tube furnace. Carbonize at 500℃ in a N2 atmosphere for 2 hours, with a heating rate of 5℃ / min. -1 Nitrogen-doped carbon material (NC) was finally obtained. 1.0 g of NC and 0.04 mmol of FeCl3 were added to 10 mL of deionized water to form a transparent solution. The solution was stirred at 80 °C for 5 h to promote adsorption on the surface of the nitrogen-doped carbon material. After stirring, the solution was slowly evaporated in a beaker at 60 °C. Finally, the solution was acid-washed with 0.5 M H₂SO₄ for 12 h to remove any nanoparticles that may have formed during the process. The solution was then dried at 80 °C for 6 h to obtain a single-atom catalyst (Fe-NC). The obtained single-atom catalyst was dispersed in water at a concentration of 0.1 g / L to obtain the Fe-NC catalyst dispersion.

[0051] (4) The bipolar film preparation method is the same as that in Example 1.

[0052] Example 3

[0053] (1) The cation exchange membrane is the same as in Example 1.

[0054] (2) The anion exchange layer solution is the same as in Example 1.

[0055] (3) Weigh 3g of melamine and 15g of glucose into a mortar, grind them thoroughly until uniform, transfer them to a crucible, and then place them in a tube furnace. Carbonize at 500℃ in a N2 atmosphere for 2 hours, with a heating rate of 5℃ / min. -1 Nitrogen-doped carbon material (NC) was finally obtained. 1.0 g of NC and 0.04 mmol of NiCl2 were added to 10 mL of deionized water to form a transparent solution. The solution was stirred at 80 °C for 5 h to promote adsorption on the surface of the nitrogen-doped carbon material. After stirring, the solution was slowly evaporated in a beaker at 60 °C. Finally, the solution was acid-washed with 0.5 M HCl for 12 h to remove any nanoparticles that may have formed during the process. The solution was then dried at 80 °C for 6 h to obtain a single-atom catalyst (Ni-NC). The obtained single-atom catalyst was dispersed in ethanol at a concentration of 0.1 g / L to obtain a Ni-NC catalyst dispersion.

[0056] (4) The bipolar film preparation method is the same as that in Example 1.

[0057] Example 4

[0058] (1) Add 1g of polyethersulfone to a round-bottom flask and dissolve it in 15mL of chloroform. Stir mechanically at room temperature to obtain a reaction solution. Put 20g of chlorosulfonic acid into a constant pressure dropping funnel and gradually add it to the reaction solution. The chlorosulfonic acid dropping rate is 2 drops / second. The reaction temperature is maintained at 40℃. After the addition is complete, stir continuously for 3h to obtain a sulfonated solution. Slowly pour the obtained sulfonated solution into pure water. After filtration, the obtained polymer is washed with water several times until the pH is neutral. After drying in a vacuum oven, sulfonated polyethersulfone with a sulfonation degree of 70% is obtained.

[0059] Sulfonated polyethersulfone was ground into powder, dissolved in N-methylpyrrolidone, and filtered to obtain a 4 wt% homogeneous solution. The homogeneous solution was then poured onto a clean glass plate and dried under vacuum at 80 °C for 24 h to obtain a cation exchange layer with a thickness of 120 μm.

[0060] (2) The anion exchange layer solution is the same as in Example 1.

[0061] (3) Weigh 10g of urea and 10g of sucrose into a mortar, grind them thoroughly until uniform, transfer them to a crucible, and then place them in a tube furnace. Carbonize at 800℃ in a N2 atmosphere for 1 hour, with a heating rate of 15℃ / min. -1 Nitrogen-doped carbon material (NC) was finally obtained. 1.0 g of NC, 0.1 mmol Ni(NO3)2, and 0.1 mmol FeCl3 were added to 10 mL of deionized water to form a transparent solution. The solution was stirred at 30 °C for 8 h to promote adsorption on the surface of the nitrogen-doped carbon material. After stirring, the solution was slowly evaporated in a beaker at 60 °C. Finally, the solution was acid-washed with 0.1 M HCl for 8 h to remove any nanoparticles that may have formed during the process. The solution was then dried at 20 °C for 12 h to obtain a single-atom catalyst (FeNi-NC-2). The obtained single-atom catalyst was dispersed in N,N-dimethylamide at a concentration of 0.1 g / L to obtain the FeNi-NC-2 catalyst dispersion.

[0062] (4) The difference between the bipolar membrane preparation method and Example 1 is that the anion exchange layer solution casting temperature is 80℃ and the catalyst loading is 0.5 mg / cm³. -2 The catalyst was dried on the membrane surface at a temperature of 50°C for 6 hours.

[0063] Example 5

[0064] (1) Add 1g of polyethersulfone to a round-bottom flask and dissolve it in 30mL of chloroform. Stir mechanically at room temperature to obtain a reaction solution. Place 10g of chlorosulfonic acid in a constant pressure dropping funnel and gradually add it to the reaction solution. The chlorosulfonic acid dropping rate is 2 drops / second. The reaction temperature is maintained at 10℃. After the addition is complete, stir continuously for 1h to obtain a sulfonated solution. Slowly pour the obtained sulfonated solution into pure water. After filtration, the obtained polymer is washed with water several times until the pH is neutral. After drying in a vacuum oven, sulfonated polyethersulfone with a sulfonation degree of 40% is obtained.

[0065] Sulfonated polyethersulfone was ground into powder, dissolved in N-methylpyrrolidone, and filtered to obtain a 1.5 wt% homogeneous solution. The homogeneous solution was then poured onto a clean glass plate and dried under vacuum at 80 °C for 24 h to obtain a cation exchange layer with a thickness of 80 μm.

[0066] (2) The anion exchange layer solution is the same as in Example 1.

[0067] (3) Weigh 1g of urea and 20g of glucose into a mortar, grind them thoroughly until homogeneous, transfer them to a crucible, and then place them in a tube furnace. Carbonize at 200℃ in an Ar2 atmosphere for 6 hours, with a heating rate of 10℃ / min. -1 Nitrogen-doped carbon material (NC) was finally obtained. 1.0 g of NC, 0.5 mmol Ni(NO3)2, and 0.5 mmol CoCl2 were added to 10 mL of deionized water to form a transparent solution. The solution was stirred at 100 °C for 2 h to promote adsorption on the surface of the nitrogen-doped carbon material. After stirring, the solution was slowly evaporated in a beaker at 60 °C. Finally, the solution was acid-washed with 1 M H2SO4 for 2 h to remove any nanoparticles that may have formed during the process. The solution was then dried at 120 °C for 4 h to obtain a single-atom catalyst (NiCo-NC). The obtained single-atom catalyst was dispersed in N-methylpyrrolidone at a concentration of 0.1 g / L to obtain the NiCo-NC catalyst dispersion.

[0068] (4) The difference between the bipolar membrane preparation method and Example 1 is that the anion exchange layer solution casting temperature is 30℃, and the catalyst loading is 0.01 mg / cm³. -2 The catalyst was dried on the membrane surface at a temperature of 130°C for 1 hour.

[0069] Comparative Example

[0070] Comparative Example 1

[0071] The difference between this comparative example and Example 1 is that this comparative example provides a method for preparing a bipolar film of a nitrogen-doped porous carbon catalyst intermediate layer, wherein the catalyst intermediate layer is nitrogen-doped porous carbon.

[0072] (1) The cation exchange membrane is the same as in Example 1.

[0073] (2) The anion exchange layer solution is the same as in Example 1.

[0074] (3) Weigh 3g of melamine and 15g of glucose into a mortar, grind them thoroughly until uniform, transfer them to a crucible, and then place them in a tube furnace. Carbonize at 500℃ in a N2 atmosphere for 2 hours, with a heating rate of 5℃ / min. -1 Nitrogen-doped carbon material (NC) was finally obtained. The obtained carbon material was dispersed in isopropanol at a concentration of 0.1 g / L to obtain the NC catalyst dispersion.

[0075] (4) The bipolar film preparation method is the same as that in Example 1.

[0076] Comparative Example 2:

[0077] The difference between this comparative example and Example 1 is that this comparative example provides a method for preparing a bipolar film of a single-atom catalyst intermediate layer, wherein no nitrogen-containing precursor is added during the preparation of carbon materials, and the prepared single-atom catalyst is not doped with nitrogen.

[0078] (1) The cation exchange membrane is the same as in Example 1.

[0079] (2) The anion exchange layer solution is the same as in Example 1.

[0080] (3) Weigh 15g of glucose into a mortar, grind it thoroughly until homogeneous, transfer it to a crucible, and then place it in a tube furnace. Carbonize at 500℃ in a N2 atmosphere for 2 hours, with a heating rate of 5℃ / min. -1 The porous carbon material (C) was finally obtained. 1.0 g of porous carbon, 0.02 mmol Ni(NO3)2, and 0.02 mmol Fe(NO3)3 were added to 10 ml of deionized water to form a transparent solution. The solution was stirred at 80 °C for 5 h to promote adsorption on the surface of the nitrogen-doped carbon material. After stirring, the solution was slowly evaporated in a beaker at 60 °C. Finally, the solution was acid-washed with 0.5 M H2SO4 for 12 h to remove any nanoparticles that may have formed during the process. The solution was then dried at 80 °C for 6 h to obtain a single-atom catalyst (Fe / Ni-C). The obtained single-atom catalyst was dispersed in isopropanol at a concentration of 0.1 g / L to obtain the Fe / Ni-NC catalyst dispersion.

[0081] (4) The bipolar film preparation method is the same as that in Example 1.

[0082] Comparative Example 3

[0083] The difference between this comparative example and Example 1 is that this comparative example provides a method for preparing a bipolar membrane without a catalyst intermediate layer, and there is no catalyst between the anion and cation membrane layers.

[0084] (1) The cation exchange membrane is the same as in Example 1.

[0085] (2) The anion exchange layer solution is the same as in Example 1.

[0086] (3) The cation exchange layer is fixed on a heating plate, and the anion exchange layer solution is cast onto the catalyst layer at a heating temperature of 60°C. After the surface dries, an anion exchange layer with a thickness of 50 μm is formed, thus obtaining a bipolar membrane without an intermediate catalyst layer.

[0087] Main testing methods

[0088] Bipolar films were prepared according to the preparation methods of Examples 1-3 and Comparative Examples 1-2, respectively, and then subjected to physical and electrochemical characterization tests. The test methods are shown below:

[0089] Water absorption rate test and swelling degree: The bipolar membrane was dried in a 100℃ oven, and then the mass and volume of the membrane were measured. It was then placed in distilled water and soaked at room temperature for 24 hours. The membrane was then removed and the water was absorbed with filter paper until no water dripped when the membrane was placed on an inclined glass slide. The mass and volume were then measured.

[0090] Tensile strength test: The membrane sample was cut to dimensions of 10 mm wide and 40 mm long, and the tensile rate was 5 mm·min. -1 .

[0091] The test results of water absorption rate, swelling degree and tensile strength of bipolar membrane are shown in Table 1.

[0092] Table 1:

[0093] sample Water absorption rate % Swelling degree % Tensile strength / MPa Example 1 27.6 6.5 33.2 Example 2 29.6 6.9 34.2 Example 3 28.9 7.3 31.4 Example 4 31.4 6.6 32.8 Example 5 29.4 7.1 31.6 Comparative Example 1 32.4 6.7 32.6 Comparative Example 2 31.3 6.8 32.4 Comparative Example 3 28.6 6.7 31.7

[0094] Water dissociation voltage test: The bipolar membranes prepared in Examples 1-3 and Comparative Examples 1-2 were immersed in a 1 mol / L sodium sulfate solution for 24 hours, respectively. A test system was constructed using a four-compartment electrodialysis apparatus, a regulated power supply, a peristaltic pump, a multimeter, and a reference electrode. During the test, 1M sodium hydroxide solution was used in the two compartments on the anode side, and 0.5M sulfuric acid was used in the two compartments on the cathode side. The test current density was 100 mA*cm². -2 The test results of bipolar membranes with different catalysts are shown in Table 2. As can be seen from Table 2, compared with the bipolar membranes prepared in Comparative Examples 1-3, the bipolar membranes prepared in Examples 1-5 have lower water dissociation voltages, and therefore have higher water dissociation efficiencies.

[0095] Table 2:

[0096]

[0097]

[0098] Stability testing: A bipolar membrane containing a single-atom catalyst interlayer was prepared according to the preparation method in Example 1, and the change in transmembrane voltage of the bipolar membrane over time was monitored under constant current. The testing apparatus was the same as that used for water dissociation voltage testing. The current was set to 100 mA / cm². 2 The voltage test interval was 30 minutes, and the total test time was set to 10 hours. The test results are as follows: Figure 1 As shown.

[0099] from Figure 1 Data analysis shows that during the 10-hour constant current density test, the transmembrane voltage of the prepared bipolar membrane containing the MOF catalyst intermediate layer increased from 1.31V to 1.37V, with a transmembrane voltage increase rate of only 4.5%. This indicates that the bipolar membrane containing the Fe / Ni-NC intermediate catalyst layer has excellent stability during long-term operation.

[0100] It is readily understood that the above embodiments are merely illustrative examples for clear explanation and do not imply that the invention is limited thereto. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A bipolar membrane comprising a monatomic intermediate catalytic layer, comprising a cation exchange layer, an anion exchange layer and an intermediate catalytic layer between the cation exchange layer and the anion exchange layer, wherein the intermediate catalytic layer comprises a monatomic catalyst; The preparation method of the monatomic catalyst comprises the following steps: (a) preparing a nitrogen-doped carbon carrier: mixing a nitrogen-containing organic precursor with a carbon source to obtain a nitrogen-doped carbon carrier by low-temperature pyrolysis; (b) monatomic metal anchoring: mixing a metal salt solution with the nitrogen-doped carbon carrier to anchor metal atoms on the surface of the carrier through coordination reaction; (c) acid washing purification: removing unanchored metal particles by washing with an acid solution, and drying to obtain a monatomic catalyst.

2. The bipolar membrane containing a monatomic intercatalytic layer according to claim 1, wherein In step (a), the nitrogen-containing organic precursor is selected from at least one of 2,2'-dipyridyl, melamine, urea and polyaniline, the carbon source is selected from at least one of glucose, sucrose, polyvinyl alcohol and polyacrylonitrile, and the mass ratio of the nitrogen-containing precursor to the carbon source is 1:20-1:1;and / or, in step (a), the temperature of the low-temperature pyrolysis is 200-800℃, the heating rate is 5-15℃ / min, the pyrolysis time is 1-6 hours, and the pyrolysis atmosphere is an inert gas selected from nitrogen and argon.

3. The monatomic intercatalytic layer-containing bipolar membrane as claimed in claim 1 or 2, characterized in that, The metal salt in step (b) is Co 2+ , Ni 2+ , Fe 3+ , Cr 3+ , Fe 2+ , Ru 3+ , V 3+ , V 5+ , Mn 2+ , Mn 4+ , Ir 3+ , Pt 2+ , Pt 4+ , Eu 3+ , Ti 2+ , Pd 2+ , Ag + , Mo 2+ ; any one or more combinations of soluble sulfate, nitrate, chloride salts thereof; the solvent is water or ethanol, and the metal salt is added in an amount of 0.01-0.5 mmol / (1 g of carbon).

4. The bipolar membrane containing a monolayer intercatalytic layer according to any one of claims 1 to 3, wherein In step (b), the conditions of the coordination reaction include: mixing the nitrogen-doped carbon carrier with the metal salt solution, and then stirring at 30-100℃ for 2-8 hours;and / or, in step (c), the acid solution is selected from at least one of hydrochloric acid, sulfuric acid and nitric acid, the concentration of the acid solution is 0.1-1mol / L, the washing time is 2-12 hours, the drying temperature is 20-120℃, and the drying time is 4-12 hours. 5.The preparation method of the bipolar membrane comprising a monatomic intermediate catalytic layer according to any one of claims 1-4, comprising the following steps: (a) preparing a monatomic catalyst dispersion liquid by using a solvent, and stirring uniformly; (b) dissolving polyether sulfone in chloroform under mechanical stirring at room temperature to obtain a reaction solution, gradually adding chlorosulfonic acid to the reaction solution, continuing to stir after the addition is completed, slowly pouring the obtained completed sulfonation liquid into pure water, filtering the obtained polymer, washing with water for multiple times until the pH is neutral, drying the polymer in a vacuum oven to obtain sulfonated polyether sulfone; grinding the sulfonated polyether sulfone into powder, dissolving in N-methyl pyrrolidone, filtering to obtain a homogeneous solution;then pouring the homogeneous solution on a clean glass plate, vacuum drying to obtain a cation exchange layer; (c) fixing the substrate with the cation exchange layer on a heating plate, coating the monatomic catalyst dispersion on the surface of the cation exchange layer, and then casting the anion exchange layer solution on the intermediate catalytic layer by flow casting, and obtaining the bipolar membrane comprising a monatomic intermediate catalytic layer after the surface is dried.

6. The production method according to claim 5, wherein In step (a), the solvent is selected from at least one of water, ethanol, isopropanol, N,N-dimethylformamide (DMF) and N-methyl pyrrolidone, and the dispersion concentration of the monatomic catalyst is 0.1-1g / L.

7. The production method according to claim 5 or 6, characterized by, The mass ratio of polyether sulfone to chloroform in step (b) is 1:15-1:30, the mass ratio of polyether sulfone to chlorosulfonic acid is 1:10-1:15, the dropwise adding speed of chlorosulfonic acid is 1-2 drops per second, the reaction temperature is 10-40℃, the stirring time is 1-5 hours, and the sulfonation degree is controlled to 10-70%.

8. The production method according to any one of claims 5 to 7, wherein The mass fraction of sulfonated polyether sulfone in the homogeneous solution prepared in step (b) is 1.5-4wt%, and the thickness of the cation exchange layer is 80-120um; and / or, the temperature for vacuum drying the homogeneous solution poured on a clean glass plate in step (b) is 50-100℃, and the time is 12-48h.

9. The production method according to any one of claims 5 to 8, wherein The temperature for coating and casting in step (c) is 30-80°C, the coating method is selected from at least one of spraying, spin coating, dipping, the coating thickness is 10-100 nm, the drying temperature is 50-130°C, and the drying time is 1-6 hours; and / or, the loading of the monatomic catalyst intermediate layer in step (c) is 0.01-0.5 mg / cm 2 , preferably 0.05-0.25 mg / cm 2 .

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