A method for preparing a bipolar membrane intermediate catalyst layer material

Abstract

This invention discloses a method for preparing a bipolar membrane intermediate catalyst layer material, comprising the following steps: S1, mixing 2-aminoterephthalic acid, dimethyl terephthalate, and ferric chloride in a certain proportion, grinding them into particles with a diameter of 1-5 nm and ensuring thorough mixing to obtain a composite support powder; S2, placing the composite support powder in a container, adding N,N-dimethylformamide, and simultaneously adding transition metal oxides and graphene to obtain a raw material slurry; S3, introducing the raw material slurry into a reaction vessel, adding a catalytic medium, heating to 120-130℃ and a pressure of 0.8-1.5 MPa for thorough reaction, and cooling to room temperature; S4, washing and drying the reaction product, pressing it into a thin sheet to obtain the bipolar membrane intermediate catalyst layer material. This invention improves the catalytic site density of the bipolar membrane intermediate layer, enhances the bonding strength between the intermediate layer and the two adjacent anion and cation layers, and reduces ion migration resistance.

Description

Technical Field

[0001] This invention belongs to the field of electrochemical membrane technology, specifically relating to a composite structure of a bipolar membrane intermediate catalyst layer material and its preparation method. Background Technology

[0002] Bipolar membranes (BPMs) are a type of specialized ion exchange membrane composed of an anion exchange layer (AEL), a cation exchange layer (CEL), and an intermediate catalyst layer. They exhibit anion and cation selectivity and can efficiently dissociate water molecules to generate H₂ under reverse bias. + and OH - H + Through the cation exchange membrane, as H + Ion source; OH - Through the anion membrane, as OH - Ion source. H + and OH - The water is replenished primarily through the dissociation of water in the transition zone, while the consumed water is replenished by water from the surrounding solution permeating into the middle of the membrane. Bipolar membranes are widely used in electrodialysis for acid and alkali production, fuel cells, CO2 reduction, and other fields.

[0003] The intermediate catalyst layer of the bipolar membrane is responsible for achieving water dissociation (H2O → H2O). + + OH - The core functional layer of a membrane directly affects its energy consumption, efficiency, and lifespan. In recent years, with the rapid development of electrochemical technology, research on intermediate catalyst layers has mainly focused on material innovation, structural optimization, and interface engineering.

[0004] Traditional intermediate catalyst layers often employ metal hydroxides (such as Fe(OH)3, Cr(OH)3) or physically blended organic / inorganic materials. However, these layers suffer from low and unevenly distributed active sites, requiring high voltage (typically ≥1.2V, 25℃) for water dissociation, resulting in high energy consumption. Furthermore, the catalysts are prone to agglomeration or oxidative deactivation, leading to significant performance degradation after long-term operation. The weak interfacial bonding between the intermediate catalyst layer and the anion / cation layers also contributes to delamination or catalyst loss after prolonged operation. Traditional intermediate catalyst layers lack optimized H... + / OH - Transport path, high ion migration resistance, high membrane resistivity (≥5 Ω·cm) 2 This limits the increase in current density.

[0005] In the preparation process of the intermediate catalyst layer of the bipolar membrane, the present invention enhances the catalytic activity by combining organic catalysts with inorganic materials, and introduces carbon-based materials such as graphene as supported metal catalysts to increase the density of active sites and improve catalytic efficiency by utilizing their high specific surface area and conductivity.

[0006] Patent document CN110898862A discloses a method for preparing bipolar membranes based on electrostatic self-assembly. Ferric hydroxide colloidal solution and deionized water are added to both sides of a dense cross-linked cation exchange membrane layer, respectively, so that metal hydroxide colloidal nanoparticles are electrostatically self-assembled on the dense cross-linked cation exchange membrane layer as an intermediate catalytic layer.

[0007] Patent document CN115714187A discloses a bipolar membrane with an intermediate catalyst layer modified in which the intermediate catalyst layer is composed of a Fe(III)@DMC coordinated complex: 2-methyl-2-acrylate and dimethylaminoethyl methacrylate undergo free radical polymerization in solution to obtain polymer DM. Polymer DM is dissolved in chloroform, and trifluoroacetic acid is added and stirred for hydrolysis to obtain polymer DMC containing carboxyl groups. FeCl3 / ethanol solution and DMC / ethanol solution are mixed and stirred to obtain a solution containing the Fe(III)@DMC coordinated complex. Through the unique coordination between the inherent amine and carboxyl groups on polymer DMC and the trivalent iron ions of the metal catalyst, water dissociation is promoted and catalyst leakage is inhibited.

[0008] Patent document CN119633600A discloses a method for preparing a bipolar membrane based on a charged nanosheet catalytic layer. Modified charged nanosheets (graphene, MOF, etc.) are dissolved into a solution, and the modified charged nanosheet solution is ultrasonically sprayed onto a cation (anion) exchange membrane layer and dried to obtain the intermediate layer of the bipolar membrane.

[0009] Patent document CN116905012A discloses a bipolar membrane with a porous organic cage catalytic intermediate layer. The method involves mixing 1,3,5-benzenetriformaldehyde, trifluoroacetic acid, (R,R)-1,2-diaminocyclohexane, and dichloromethane, and then performing a crystallization reaction to obtain CC3R. An organic solution of CC3R is then mixed with an organic solution of ferric chloride, and the organic solvent is evaporated to obtain FeCl3@CC3R crystals. The FeCl3@CC3R crystals are then placed in a reducing atmosphere and subjected to a reduction reaction to obtain a porous organic cage coated with iron nanoparticles.

[0010] However, the bipolar membranes prepared in the above literature have low water dissociation efficiency in amine liquid environment, which is still a shortcoming. Summary of the Invention

[0011] To address the shortcomings of the existing technologies, this invention provides a bipolar membrane intermediate catalytic layer material and its preparation method, aiming to solve the problems of low catalytic activity, excessively high hydrolysis potential, poor stability, insufficient ion transport efficiency, and easy agglomeration and deactivation of catalysts in traditional bipolar membrane intermediate layers during electrodialysis.

[0012] To achieve the above objectives, the present invention adopts the following technical solution: The present invention provides a method for preparing a bipolar membrane intermediate catalyst layer material, comprising the following steps: S1, 2-aminoterephthalic acid, dimethyl terephthalate and ferric chloride are mixed in proportion, ground into particles with a diameter of 1-5 nm and fully mixed to obtain composite carrier powder; S2, place the composite carrier powder in a container, add N,N-dimethylformamide to form a mixed slurry, and simultaneously add transition metal oxides and graphene, stir until uniform to obtain the raw material slurry; S3, the raw material slurry is introduced into the reactor, a catalytic medium is added, and the mixture is heated to 120-130℃ and subjected to a pressure of 0.8-1.5MPa to carry out a full reaction, and then cooled to room temperature; S4. Soak the reaction product in an organic solvent, wash, filter and dry. The above operation can be repeated multiple times to remove unreacted precursors, impurities and surfactant residues in the catalyst layer, while optimizing the dispersion of catalytic active sites. Press the reaction product into a thin sheet to obtain the bipolar membrane intermediate catalyst layer material.

[0013] In step S1, the composite carrier comprises the following components: 12.5%–22.5% 2-aminoterephthalic acid, 12.5%–22.5% dimethyl terephthalate, and 55%–75% ferric chloride. Preferably, the composite carrier comprises the following components: 12.5%–17.5% 2-aminoterephthalic acid, 12.5%–17.5% dimethyl terephthalate, and 65%–75% ferric chloride.

[0014] In step S2, the transition metal oxide is at least one of zirconium dioxide, molybdenum dioxide, titanium dioxide, and nickel oxide, with an average particle size of 15-35 nm.

[0015] In step S2, the amount of the transition metal oxide added is 10% to 30% of the mass of the composite carrier powder; the graphene is graphene powder with a particle size of 10 to 35 nm and fewer than 10 layers, and its addition amount is 5% to 10% of the mass of the composite carrier powder.

[0016] In step S2, the mass ratio of the composite carrier powder, transition metal oxide and graphene is 20:(2-6):(1-2), preferably 20:6:1, 20:2:1.5 and 20:2:2.

[0017] In step S3, the catalytic medium is a polytetrafluoroethylene (PTFE) dispersion (e.g., Macklin's concentrated PTFE dispersion, P816262-500g, CAS: 9002-84-0, 60wt% dispersion). The PTFE dispersion is added to the raw material slurry at a mass ratio of 1:(9.5-10.5). The reaction time of the raw material slurry is not less than 8 hours at a temperature of 120-130℃ and a pressure of 0.8-1.5MPa. A higher amount of PTFE dispersion results in a larger pore size in the intermediate catalyst layer material of the bipolar membrane; similarly, higher reaction temperature and pressure also result in a larger pore size. However, excessive amounts of PTFE dispersion and excessively high reaction temperatures can cause the catalyst material to become loose and unusable.

[0018] In step S4, the organic solvent is at least one of N,N-dimethylformamide and anhydrous ethanol solution; the soaking temperature is room temperature.

[0019] The present invention also provides a bipolar membrane intermediate catalyst layer material prepared by the aforementioned method for preparing the bipolar membrane intermediate catalyst layer material.

[0020] Compared with the prior art, the beneficial effects of the present invention are as follows: The bipolar membrane intermediate catalytic layer material of the present invention uses 2-aminoterephthalic acid-dimethyl terephthalate-ferric chloride as a composite support, with graphene and transition metal oxides attached to the support. The introduction of transition metal oxides increases the catalytic site density of the bipolar membrane intermediate layer; the introduction of CN and OCO covalent bonds enhances the bonding strength between the intermediate layer and the anion and cation layers on both sides; and the introduction of graphene to construct a composite ion channel reduces the ion migration resistance. Attached Figure Description

[0021] Figure 1 The infrared spectrum is the original solution (post-reaction solution) of the intermediate layer of the bipolar film.

[0022] Figure 2 The infrared spectrum is for the intermediate catalytic layer material of the bipolar membrane. Detailed Implementation

[0023] The technical solution of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0024] Example 1 A method for preparing a bipolar membrane intermediate catalyst layer material includes the following steps: S1, 125 mg of 2-aminoterephthalic acid, 125 mg of dimethyl terephthalate and 750 mg of ferric chloride were placed in a ball mill jar, and grinding balls were added to the ball mill jar at the same time; the ball mill jar was sent to a planetary ball mill for grinding and thorough mixing. The ball mill speed was 400 r / min and the grinding time was 240 min to obtain composite carrier powder with a particle size of 1.5-3 nm; S2, place 500mg of composite carrier powder in a container, add 100mg of zirconium dioxide and 200mg of graphene, and stir to mix evenly; then add 40ml of N,N-dimethylformamide, and stir with a magnetic stirrer until uniform. The magnetic stirrer speed is 400r / min, and the stirring time is 20min to obtain the raw material slurry. S3. The raw material slurry is introduced into a high-temperature and high-pressure reactor. 5 ml of polytetrafluoroethylene dispersion (approximately 80 mg) is added to the reactor using a dropper. The temperature is increased to 120°C at a rate of 5°C / min. During the heating process, nitrogen gas with a purity of 99.999% is purged into the reactor. The reactor is kept at 120°C and 1.0 MPa for 12 hours to increase the molecular activation energy and ensure that the raw material slurry reacts fully to achieve molecular polymerization. Then, the temperature is reduced to room temperature at a rate of 5°C / min, and the reaction product is removed. S4. The reaction product was soaked in 100 ml of dimethylformamide at 100°C for 4 hours. The product was then washed with dichloromethane, filtered, and dried in a drying oven at 80°C for 1 hour. The reaction product was then soaked in 100 ml of anhydrous ethanol at 75°C for 4 hours. The product was then washed with dichloromethane. Repeated soaking and washing were performed to remove unreacted precursors, impurities, and surfactant residues from the catalyst layer, while optimizing the dispersion of catalytic active sites. The product was then filtered and dried in a drying oven at 80°C for 1 hour. The reaction product was then pressed into thin sheets with a thickness of 2–3 mm using a tablet press to obtain the intermediate catalyst layer material of the bipolar membrane.

[0025] Infrared spectroscopy was performed on the intermediate layer stock solution slurry of Example 1 and the reaction product (the final bipolar membrane intermediate catalyst layer material). The results showed that the functional group composition and content of the two were similar, but CN covalent bonds were present in the reaction product. The conductivity of the reaction product was tested using an electrochemical device, and the results showed that its conductivity was 8.69 S / cm.

[0026] Example 2 A method for preparing a bipolar membrane intermediate catalyst layer material includes the following steps: S1, 150 mg of 2-aminoterephthalic acid, 150 mg of dimethyl terephthalate and 700 mg of ferric chloride were placed in a ball mill jar, and grinding balls were added to the ball mill jar at the same time; the ball mill jar was sent to a planetary ball mill for grinding and thorough mixing. The ball mill speed was 400 r / min and the grinding time was 300 min to obtain composite carrier powder with a particle size of 1.5-3 nm; S2, place 500mg of composite carrier powder in a container, add 150mg of zirconium dioxide and 150mg of graphene, and stir to mix evenly; then add 40ml of N,N-dimethylformamide, and stir with a magnetic stirrer until uniform. The magnetic stirrer speed is 400r / min, and the stirring time is 20min to obtain the raw material slurry. S3. The raw material slurry is introduced into a high-temperature and high-pressure reactor. 5 ml of polytetrafluoroethylene dispersion (approximately 80 mg) is added to the reactor using a dropper. The temperature is increased to 120°C at a rate of 5°C / min. During the heating process, nitrogen gas with a purity of 99.999% is purged into the reactor. The reactor is kept at 120°C and 1.2 MPa for 12 hours to increase the molecular activation energy and ensure that the raw material slurry reacts fully to achieve molecular polymerization. Then, the temperature is reduced to room temperature at a rate of 5°C / min, and the reaction product is removed. S4. The reaction product was soaked in 100 ml of dimethylformamide at 100°C for 4 hours. The product was then washed with dichloromethane, filtered, and dried in a drying oven at 80°C for 1 hour. The reaction product was then soaked in 100 ml of anhydrous ethanol at 75°C for 4 hours. The product was then washed with dichloromethane. The soaking and washing were repeated to remove unreacted precursors, impurities, and surfactant residues from the catalyst layer, while optimizing the dispersion of catalytic active sites. The product was then filtered and dried in a drying oven at 80°C for 1 hour. The reaction product was then pressed into sheets with a thickness of 2-3 mm using a tablet press to obtain the bipolar membrane intermediate catalyst layer material.

[0027] Infrared spectroscopy was performed on the intermediate layer slurry (i.e., the raw material slurry in S2) and the reaction product (the final bipolar membrane intermediate catalyst layer material) of Example 2. The conductivity of the reaction product was tested using an electrochemical apparatus, and the results showed that its conductivity was 11.04 S / cm.

[0028] Example 3 A method for preparing a bipolar membrane intermediate catalyst layer material includes the following steps: S1, 175 mg of 2-aminoterephthalic acid, 175 mg of dimethyl terephthalate and 650 mg of ferric chloride were placed in a ball mill jar, and grinding balls were added to the jar at the same time; the ball mill jar was then fed into a planetary ball mill for grinding and thorough mixing. The ball mill speed was 400 r / min and the grinding time was 200 min to obtain a composite carrier powder with a particle size of 1.5-3 nm; S2, place 500mg of composite carrier powder in a container, add 50mg of zirconium dioxide and 250mg of graphene, and stir to mix evenly; then add 40ml of N,N-dimethylformamide, and stir with a magnetic stirrer until uniform. The magnetic stirrer speed is 400r / min, and the stirring time is 20min to obtain the raw material slurry. S3. The raw material slurry is introduced into a high-temperature and high-pressure reactor. 5 ml of polytetrafluoroethylene dispersion (approximately 80 mg) is added to the reactor using a dropper. The temperature is increased to 120°C at a rate of 5°C / min. During the heating process, nitrogen gas with a purity of 99.999% is purged into the reactor. The reactor is kept at 120°C and 0.9 MPa for 12 hours to increase the molecular activation energy and ensure that the raw material slurry reacts fully to achieve molecular polymerization. Then, the temperature is reduced to room temperature at a rate of 5°C / min, and the reaction product is removed. S4. The reaction product was soaked in 100 ml of dimethylformamide at 100°C for 4 hours. The product was then washed with dichloromethane, filtered, and dried in a drying oven at 80°C for 1 hour. The reaction product was then soaked in 100 ml of anhydrous ethanol at 75°C for 4 hours. The product was then washed with dichloromethane. The soaking and washing were repeated to remove unreacted precursors, impurities, and surfactant residues from the catalyst layer, while optimizing the dispersion of catalytic active sites. The product was then filtered and dried in a drying oven at 80°C for 1 hour. The reaction product was then pressed into sheets with a thickness of 2-3 mm using a tablet press to obtain the bipolar membrane intermediate catalyst layer material.

[0029] Infrared spectroscopy was performed on the intermediate layer stock solution (i.e., the raw material slurry in S2) and the reaction product (the final bipolar membrane intermediate catalyst layer material) of Example 3. The conductivity of the reaction product was tested using an electrochemical apparatus, and the results showed that its conductivity was 9.83 S / cm.

[0030] Comparative Example 1 is a comparative example of Example 1, except that in step S3 of Comparative Example 1, the raw material slurry is introduced into a high-temperature and high-pressure reactor, and 8 ml of polytetrafluoroethylene dispersion (about 125 mg) is added to the reactor using a dropper.

[0031] Comparative Example 2 is a comparative example of Example 1, except that in step S3 of Comparative Example 2, the raw material slurry is introduced into a high-temperature and high-pressure reactor, and 3 ml of polytetrafluoroethylene dispersion (about 48 mg) is added to the reactor using a dropper.

[0032] Table 1. Test results of Examples 1-3 and Comparative Examples 1-2

[0033] Studies have shown that the bipolar membrane intermediate catalyst layer material prepared in this invention uses 2-aminoterephthalic acid-dimethyl terephthalate-ferric chloride as a composite support, with graphene and transition metal oxides attached to the support. It possesses appropriate pore volume and pore size, providing stable and efficient channels for H- and OH- ions while maintaining a certain specific surface area, and is not easily blocked. This effectively reduces membrane voltage, decreases ion diffusion resistance, and improves conductivity. The bipolar membrane made using the intermediate catalyst layer material of this invention has a thickness of approximately 0.3 mm, a water dissociation start-up voltage of 1.5 V, and a voltage fluctuation of less than 1 V during continuous operation.

[0034] Compared to Example 1, Comparative Example 1, while improving conductivity, suffers from excessively large pore size and volume, leading to a loose internal structure of the catalyst layer, pore collapse, component shedding, reduced mechanical properties, and consequently, decreased operational performance. Excessively large pore size also reduces specific surface area, decreasing water dissociation efficiency. Conversely, the small pore size and volume of Comparative Example 1 result in a significant increase in ion diffusion resistance and susceptibility to impurity blockage, leading to increased membrane resistance. Therefore, only a combination of high specific surface area and mesoporous dominance can achieve high catalytic activity and low conduction resistance. The product of this invention exhibits suitable porosity and pore size, resulting in optimal performance.

Claims

1. A method for preparing a bipolar membrane intermediate catalyst layer material, characterized in that, Includes the following steps: S1, 2-aminoterephthalic acid, dimethyl terephthalate and ferric chloride are mixed in proportion, ground into particles with a diameter of 1-5 nm and fully mixed to obtain composite carrier powder; S2, place the composite carrier powder in a container, add N,N-dimethylformamide, and simultaneously add transition metal oxides and graphene, stir until uniform, and obtain the raw material slurry; S3, the raw material slurry is introduced into the reactor, a catalytic medium is added, and the mixture is heated to 120-130℃ and subjected to a pressure of 0.8-1.5MPa to carry out a full reaction, and then cooled to room temperature; S4. The reaction product is soaked in an organic solvent, washed, filtered, and dried; the reaction product is pressed into a thin sheet to obtain the bipolar membrane intermediate catalyst layer material.

2. The method for preparing the bipolar film intermediate catalyst layer material according to claim 1, characterized in that, In step S1, the composite carrier has the following composition: 12.5% ​​to 22.5% 2-aminoterephthalic acid, 12.5% ​​to 22.5% dimethyl terephthalate, and 55% to 75% ferric chloride.

3. The method for preparing the bipolar film intermediate catalyst layer material according to claim 1, characterized in that, In step S1, the composite carrier has the following composition: 12.5%–17.5% 2-aminoterephthalic acid, 12.5%–17.5% dimethyl terephthalate, and 65%–75% ferric chloride.

4. The method for preparing the bipolar film intermediate catalyst layer material according to claim 1, characterized in that, In step S2, the transition metal oxide is at least one of zirconium dioxide, molybdenum dioxide, titanium dioxide, and nickel oxide, with an average particle size of 15-35 nm.

5. The method for preparing the bipolar film intermediate catalyst layer material according to claim 1, characterized in that, In step S2, the amount of the transition metal oxide added is 10% to 30% of the mass of the composite carrier powder; the graphene is graphene powder with a particle size of 10 to 35 nm and fewer than 10 layers, and its addition amount is 5% to 10% of the mass of the composite carrier powder.

6. The method for preparing the bipolar film intermediate catalyst layer material according to claim 1, characterized in that, In step S2, the mass ratio of the composite carrier powder, transition metal oxide and graphene is 20:(2-6):(1-2).

7. The method for preparing the bipolar film intermediate catalyst layer material according to claim 1, characterized in that, In step S3, the catalytic medium is a polytetrafluoroethylene dispersion; the polytetrafluoroethylene dispersion is added to the raw material slurry at a mass ratio of 1:(9.5-10.5).

8. The method for preparing the bipolar film intermediate catalyst layer material according to claim 1, characterized in that, In step S3, the reaction time of the raw material slurry at a temperature of 120-130℃ and a pressure of 0.8-1.5MPa shall not be less than 8 hours.

9. The method for preparing the bipolar film intermediate catalyst layer material according to claim 1, characterized in that, In step S4, the organic solvent is at least one of N,N-dimethylformamide and anhydrous ethanol solution; the soaking temperature is room temperature.

10. The bipolar membrane intermediate catalyst layer material prepared by the preparation method according to any one of claims 1 to 9.

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