A method for preparing a polymer electrolyte membrane based on polymer solution modulation

Abstract

The application belongs to the technical field of high-temperature polymer electrolyte membranes, and particularly relates to a preparation method of a polymer electrolyte membrane based on polymer solution modulation. The method comprises the following steps: (1) polymer dissolution and purification: adding a solvent into a reaction container, adding a polymer while stirring, heating, then stirring again, preparing a polymer solution, and purifying after returning to room temperature; (2) polymer solution modulation: adding the purified polymer solution into the reaction container, stirring, heating, then adding a modulation agent, continuing to stir, and returning to room temperature for use; (3) using a defoaming machine to defoam, then scraping and coating to form, then drying, and obtaining a polymer electrolyte membrane. The modulation agent for modulating the polymer solution is added to improve the interaction between the polymers in the polymer solution, or between the polymer and the solvent, or between the solvents, so as to reduce the interaction between the polymer and water, and change the water absorption property of the solution.

Description

Technical Field

[0001] This invention belongs to the field of high-temperature polymer electrolyte membrane technology, and specifically relates to a method for preparing a polymer electrolyte membrane based on polymer solution modulation. Background Technology

[0002] High-temperature polymer fuel cells (HTFCs) have become a research hotspot due to their strong CO tolerance (CO content in the fuel can reach 5%). As a key material, the HTFC electrolyte membrane is one of the crucial factors determining the performance, reliability, and lifespan of the fuel cell. Currently, the commonly used HTFC electrolyte membrane is the PBI-based electrolyte membrane. The performance of mass-produced PBI-based electrolyte membranes depends not only on the structure, molecular weight, and molecular weight distribution of the key component, the PBI polymer, but also on the preparation of the polymer solution, the membrane preparation method, and the degree of environmental control. The membrane preparation method directly affects the membrane's uniformity, morphology, and even its performance, reliability, and stability to a certain extent. The presence of nitrogen heterocycles in the PBI molecule means that when the humidity in the air during membrane coating preparation is high (≥50% RH), the solution prepared after dissolution easily forms hydrogen bonds with moisture in the air. If the commonly used drying method (one-step or two-step method, with the first step operating at <60℃) is used, the polymer solution used for membrane preparation easily reacts with moisture in the air and absorbs a large amount of moisture (especially after the polymer solution is coated, the solution becomes thinner, and the effect of moisture is significant). As a poor solvent for PBI, water causes the PBI polymer to separate from its good solvent, forming a porous membrane. This not only reduces the mechanical strength of such membranes but can also lead to hydrogen permeation, causing them to lose their insulating properties and rendering them unsuitable for fuel cells. While adding indoor dehumidification and cooling equipment can reduce ambient humidity, this significantly increases production costs and the improvement effect is not substantial. Summary of the Invention

[0003] To address the aforementioned problems, the present invention aims to provide a method for preparing a polymer electrolyte membrane based on polymer solution modulation, thereby mitigating phase separation caused by water entering the polymer solution from the air.

[0004] To achieve the above objectives, the technical solution of the present invention is as follows:

[0005] This invention provides a method for preparing a polymer electrolyte membrane based on polymer solution modulation, the method comprising the following steps:

[0006] (1) Polymer dissolution and purification: Add solvent to reaction vessel, add polymer while stirring, heat, and then stir again to obtain polymer solution. After returning to room temperature, purify.

[0007] (2) Polymer solution modulation: Add the purified polymer solution to the reaction vessel, stir, heat, then add the modifier, continue stirring, and restore to room temperature for later use;

[0008] (3) Degas the membrane using a degassing machine, then coat it with a scraper, and then dry it to obtain a polymer electrolyte membrane.

[0009] In the above technical solution, further, in step (1), the solvent is one or more of N,N-dimethylacetamide, N-methylpyrrolidone, N,N-dimethylformamide, dimethyl sulfoxide, 1,3-dimethyl-2-imidazolinone, and acetonitrile;

[0010] The polymer includes one or more of the following: nitrogen-containing polymers, nitrogen-containing heterocyclic polymers, and polymers containing functional structures that can form hydrogen bonds with water; the nitrogen-containing polymers contain nitrogen structures including RNH2, R2NH, R3N, and quaternary ammonium salt structures containing 2-4 N atoms, including RR'3N. + X - , RR'3N + X - R”N + X - Wherein R is the polymer backbone, and R' and R” are straight-chain alkanes with 1-6 carbon atoms, branched alkanes with 3-8 carbon atoms, or cyclic alkanes with 3-6 carbon atoms; the nitrogen-containing heterocyclic structure includes imidazoles, pyrimidines, piperidines, pyrrolidines, or triazoles; the polymer containing a functional structure that can form hydrogen bonds with water includes polyetheretherketone, polyetherketoneketone, polyvinyl acetate, polymethacrylic acid, polysulfone, acrylate-acrylate copolymer, polyoxymethylene, brominated polyetheretherketone, brominated polyetherketoneketone, or brominated polysulfone; the nitrogen-containing structure or nitrogen-containing heterocyclic structure is located in the polymer backbone or serves as a branch in the polymer side chain.

[0011] Including the following homopolymers:

[0012]

[0013]

[0014] It also includes the following copolymers:

[0015]

[0016] Where n and m are each integers between 150 and 300.

[0017] The mass ratio of the polymer to the volume ratio of the solvent is 1:20-1:5 g / mL.

[0018] In the above technical solution, the stirring speed when adding the polymer is 80-200 rpm to ensure that the solution is completely stirred and the liquid level increases by no more than 5 cm after stirring, so as to promote shearing and prevent the polymer from sticking to the inner wall of the reaction vessel; the heating temperature is 60-160℃, and after the reaction vessel temperature reaches the set temperature, stirring is continued at 80-200 rpm for 30 minutes, followed by stirring again at 280-400 rpm for ≥4 hours; the heating temperature of the reaction vessel is 60-160℃.

[0019] In the above technical solution, the purification method is further described as positive pressure filtration or centrifugation; the positive pressure filtration device is a positive pressure filter or a positive pressure filter bottle and its corresponding funnel; the positive pressure filtration adopts graded filtration, with filter elements of mesh sizes of 1000 mesh, 3000 mesh, and 8000 mesh respectively; the centrifugation adopts a three-step method, with the first step centrifugation speed at 3000-5000 rpm and centrifugation time at 10-15 minutes, the second step centrifugation speed at 6000-8000 rpm and centrifugation time at 10-15 minutes, and the third step centrifugation speed at 8000-10000 rpm and centrifugation time at 5-10 minutes.

[0020] In the above technical solution, further, in step (2), the modulator is one or more of P2O5, sodium hydroxide, potassium hydroxide, lithium hydroxide, sodium carbonate, sodium bicarbonate, potassium carbonate, potassium bicarbonate, sodium phosphate, sodium monohydrogen phosphate, and sodium dihydrogen phosphate.

[0021] The mass ratio of the modulator to the polymer is 1:1000 to 1:100.

[0022] In the above technical solution, the modulator is further added in three stages to the polymer solution. The first addition is half of the total amount added, and the addition time is after the temperature of the reaction vessel rises to the set temperature. The second addition is one-third of the total amount added, and the time interval between the second and third additions is 2-4 hours. The third addition is one-sixth of the total amount added, and the time interval between the second and third additions is 1-2 hours. After the third addition of the modulator, the stirring time is ≥3 hours. The reactor heating temperature is 100-140℃, and a condenser is placed in the reaction vessel to avoid excessive solvent evaporation.

[0023] In the above technical solution, further, in step (3), the drying temperature is 40-65℃ and the drying time is 1-12h.

[0024] The beneficial effects of this invention are as follows:

[0025] 1. This invention improves the interaction between polymers, between polymers and solvents, or between solvents in a polymer solution by adding modulators to modulate the polymer solution, thereby reducing the interaction between polymers and water and changing the water absorption properties of the solution.

[0026] 2. This invention is applicable to the preparation of polymer electrolyte membranes in polymer solutions that are sensitive to water. It can effectively increase the interaction forces between polymer solutions, reduce the absorption of moisture from the air, avoid phase separation of the membrane, and improve the reliability of the electrolyte membrane. Attached Figure Description

[0027] Figure 1 These are photographs showing the state of the polymer electrolyte membrane prepared in Example 1;

[0028] Figure 2 This is a comparison graph showing the changes in tensile strength of the polymer electrolyte membranes prepared in Examples 1, 2 and Comparative Example 1. Detailed Implementation

[0029] The following examples are intended to enable those skilled in the art to more fully understand the present invention, but do not limit the invention in any way.

[0030] Unless otherwise specified, all materials used in the embodiments of this invention are commercially available.

[0031] Example 1

[0032] 1. Polymer dissolution and purification

[0033] 2 L of N,N-dimethylacetamide was added to a 3 L three-necked round-bottom flask, fixed, and mechanically stirred at 150 rpm. 160 g of m-PBI with an intrinsic viscosity of 1.4 dL / g (molecular weight approximately 50,000, repeating unit approximately 160) was heated while stirring. A heating mantle was used to heat the flask at 120 °C. Once the temperature reached 120 °C, stirring was continued at 150 rpm for 1 hour. The stirring speed was then increased to 350 rpm, and stirring continued for 6 hours until dissolution was complete. The heating mantle was then closed, and the flask was removed from it. A blower was used to accelerate cooling. After returning to room temperature, the solution was filtered through a 5 L positive pressure filter. The polymer solution was then filtered sequentially using filter cloths with mesh sizes of 1000 mesh, 3000 mesh, and 8000 mesh to obtain a polymer solution with fewer particulate impurities.

[0034] 2. Polymer solution modulation

[0035] The purified polymer solution was poured into a three-necked round-bottom flask and mechanically stirred. The viscosity of the solution was measured to be 700 cP using a rheometer. The heating temperature was then set to 120°C, and stirring was continued. When the temperature reached 120°C, 0.2 g of potassium bicarbonate powder was added, and stirring was continued for 3 hours. Then, about 0.13 g of potassium hydroxide powder was added, and stirring was continued for 1 hour. Finally, about 0.05 g of P2O5 powder was added, and stirring was continued for 5 hours. The viscosity of the solution was measured to be 2500 cP.

[0036] 3. Preparation of polymer electrolyte membranes

[0037] The modified polymer solution was poured onto a stainless steel sheet and coated using a stainless steel scraper with a fixed gap of 1000 μm. The coated film was then dried in a 50°C oven. The film was characterized and impregnated with phosphoric acid for testing. The mass fraction of phosphoric acid in the film was 400%.

[0038] from Figure 1 It can be seen that the membrane prepared by adjusting the solution viscosity to 2500 cP is completely transparent, and there is no problem of opacity in porous membranes caused by moisture absorption.

[0039] Comparative Example 1

[0040] When the indoor humidity was 40% RH, the unmodulated polymer solution from Example 1 was used for coating and shaping. The film was then prepared using the drying process described in Example 1. The resulting film was almost opaque, with a phosphoric acid doping level comparable to that of Example 1. The tested tensile strength was as follows: Figure 2 As shown.

[0041] from Figure 2 Similarly, it can be seen that the tensile strength of the membrane prepared using the unmodulated solution is only 0.7 MPa, while the tensile strength is significantly improved after the solution viscosity is increased. In particular, the mechanical properties of the membrane are greatly improved (tensile strength increases by 3.4 times) after the solution viscosity is increased to 2500 cP. This indicates that by modulating the forces within the solution, the solution viscosity can be increased, which can significantly improve the problem of membrane absorption of water from the air and improve the reliability of the membrane.

[0042] Example 2

[0043] 1. Polymer dissolution and purification

[0044] 2L of dimethyl sulfoxide was added to a 3L three-necked round-bottom flask, fixed, and mechanical stirring was started at a speed of 150 rpm. 160g of p-PBI with an intrinsic viscosity of 1.4dL / g (molecular weight of about 50,000 and repeating unit of about 160) was heated and dissolved in the flask using a heating mantle. The dissolution process and purification process are as in Example 1.

[0045] 2. Polymer solution modulation

[0046] The solution modulation process is as described in Example 1. The solution viscosity is 700 cP. After heating at 120°C, 0.15 g of sodium hydroxide powder is added and stirring is continued for 3 hours. Then, about 0.1 g of sodium hydroxide powder is added and stirring is continued for 1 hour. Then, about 0.05 g of sodium hydroxide powder is added and stirring is continued for 5 hours. The solution viscosity is measured to be 1500 cP at this time.

[0047] 3. Preparation of polymer electrolyte membranes

[0048] The modified polymer solution was poured onto a stainless steel sheet and coated with a stainless steel scraper roller with a fixed gap of 1000 μm. The film was then dried in a 50°C oven for 6 hours at an indoor humidity of 40% RH.

[0049] The transparency of the film is better than that of the film prepared with the unmodulated solution, but it does not reach the transparency of the film prepared with the 2500 cP solution in Example 1. The tensile strength is as follows: Figure 2 As shown, the mechanical properties are doubled.

[0050] Example 3

[0051] 1. Polymer dissolution and purification

[0052] Electrolyte membranes were prepared by modulating a biphenylpiperidine polymer / dimethyl sulfoxide solution. 60 g of biphenylpiperidine polymer was added to a 1 L three-necked flask, followed by 600 mL of dimethyl sulfoxide. The biphenylpiperidine polymer had a molecular weight of 100,000 and 400 repeating units. The polymer / dimethyl sulfoxide solution was then heated to 60 °C to dissolve the polymer. After dissolution, the solution was purified using the method and process described in Example 1.

[0053] 2. Polymer solution modulation

[0054] The above solution was heated to 120°C, and potassium hydroxide powder was added to it while stirring. The first addition was 0.3g and stirred for 3 hours, then about 0.2g of potassium hydroxide powder was added and stirred for 1 hour, and finally about 0.1g of potassium hydroxide powder was added and stirred for 5 hours. The viscosity of the adjusted solution was 3000 cP.

[0055] 3. Preparation of polymer electrolyte membranes

[0056] The modified solution was poured onto a thin stainless steel plate with a fixed gap of 600 μm.

[0057] The film was coated by scraping and dried in an oven at 50°C for 12 hours. The resulting film was light yellow and transparent, with a phosphoric acid doping mass fraction of 350% and a tensile strength of 3 MPa.

[0058] The above embodiments are merely preferred embodiments of the present invention and are not intended to limit the implementation. The scope of protection of the present invention should be determined by the scope defined in the claims. Other variations or modifications can be made based on the above description. Obvious variations or modifications derived therefrom are still within the scope of protection of the present invention.

Claims

1. A method for preparing a polymer electrolyte membrane based on polymer solution modulation, characterized in that, The method includes the following steps: (1) Polymer dissolution and purification: Add solvent to reaction vessel, add polymer while stirring, heat, and then stir again to obtain polymer solution. After returning to room temperature, purify. (2) Polymer solution modulation: Add the purified polymer solution to the reaction vessel, stir, heat, then add the modifier, continue stirring, and restore to room temperature for later use; (3) Degas the membrane using a degassing machine, then coat it with a scraper, and then dry it to obtain a polymer electrolyte membrane; The modulator is added to the polymer solution in three stages. The first addition is 2 / 5 to 3 / 5 of the total amount; the second addition is 3 / 10 to 7 / 20 of the total amount, with an interval of 2 to 4 hours between the first and second additions; the third addition is 3 / 20 to 1 / 4 of the total amount, with an interval of 1 to 2 hours between the second and second additions. After the third addition of the modulator, stirring is continued for ≥3 hours. The reaction vessel is heated to a temperature of 100-140℃.

2. The preparation method according to claim 1, characterized in that, In step (1), the solvent is one or more of N,N-dimethylacetamide, N-methylpyrrolidone, N,N-dimethylformamide, dimethyl sulfoxide, 1,3-dimethyl-2-imidazolinone, and acetonitrile; The polymer includes one or more of the following: nitrogen-containing polymers, nitrogen-containing heterocyclic polymers, and polymers containing functional structures that can form hydrogen bonds with water; the nitrogen-containing polymers contain nitrogen structures including RNH2, R2NH, R3N, and quaternary ammonium salt structures containing 2-4 N atoms, including RR'3N. + X - RR'3N + X - R”N + X - Wherein R is the polymer backbone, and R' and R” are straight-chain alkanes with 1-6 carbon atoms, branched alkanes with 3-8 carbon atoms, or cyclic alkanes with 3-6 carbon atoms; the nitrogen-containing heterocyclic polymers include imidazoles, pyrimidines, piperidines, pyrrolidines, or triazoles; the polymers containing functional structures that can form hydrogen bonds with water include polyetheretherketones, polyetherketoneketones, polyvinyl acetate, polymethacrylic acid, polysulfones, acrylate-acrylate copolymers, polyoxymethylene, brominated polyetheretherketones, brominated polyetherketoneketones, or brominated polysulfones; the nitrogen-containing structures and nitrogen-containing heterocyclic structures are located in the polymer backbone or serve as branches in the polymer side chains; The mass ratio of the polymer to the volume ratio of the solvent is 1:20-1:5 g / mL.

3. The preparation method according to claim 1, characterized in that, In step (1), when the polymer is added, the stirring speed is 80-200 rpm. After the temperature of the reaction vessel is raised to the set temperature, the stirring speed is continued at 80-200 rpm for 30 minutes. Then, the stirring speed is increased to 280-400 rpm and the stirring time is ≥4h. The reaction vessel is heated to a temperature of 60-160℃.

4. The preparation method according to claim 1, characterized in that, In step (1), the purification method is positive pressure filtration or centrifugation; the positive pressure filtration adopts graded filtration, and the mesh size of the filter element is 1000 mesh, 3000 mesh and 8000 mesh respectively; the centrifugation adopts a three-step method, the first step centrifugation speed is 3000-5000 rpm and the centrifugation time is 10-15 minutes, the second step centrifugation speed is 6000-8000 rpm and the centrifugation time is 10-15 minutes, and the third step centrifugation speed is 8000-10000 rpm and the centrifugation time is 5-10 minutes.

5. The preparation method according to claim 1, characterized in that, In step (2), the modulator is one or more of P2O5, sodium hydroxide, potassium hydroxide, lithium hydroxide, sodium carbonate, sodium bicarbonate, potassium carbonate, potassium bicarbonate, sodium phosphate, sodium monohydrogen phosphate, and sodium dihydrogen phosphate. The mass ratio of the modulator to the polymer is 1:1000 to 1:

100.

6. The preparation method according to claim 1, characterized in that, In step (3), the drying temperature is 40-65℃ and the drying time is 1-12h.

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