Interface polymerization PBI modified alkaline water electrolysis composite diaphragm as well as preparation method and application thereof

Abstract

The invention relates to an interfacial polymerization PBI modified alkaline water electrolysis composite diaphragm as well as a preparation method and application thereof. The alkaline water electrolysis composite diaphragm provided by the invention has excellent super-hydrophilicity, high gas barrier property, low surface resistance and alkali-resistant stability. The method has the advantages of stable physical properties, mild and simple process, green and environment-friendly raw materials, low cost and industrial application potential.

Description

Technical Field

[0001] The present invention belongs to the field of diaphragm materials, and particularly relates to an interfacial polymerization PBI-modified alkaline water electrolysis composite diaphragm, a preparation method thereof, and an application thereof. Background Art

[0002] With the development of social economy, problems such as energy crisis and environmental pollution have become increasingly serious. To ensure China's energy security, it is necessary to develop and utilize new energy. Hydrogen energy has the characteristics of rich reserves, high calorific value, and environmental protection and no pollution, and is considered one of the important energy carriers to replace fossil fuels. In terms of hydrogen production technology, water electrolysis for hydrogen production is considered one of the most promising energy conversion technologies in the 21st century and is the only source of green hydrogen. Among them, alkaline water electrolysis for hydrogen production has the advantages of low cost, simple operation, and mature technology, accounting for more than 70% in the existing structure of water electrolysis for hydrogen production technology. However, problems such as high energy consumption, low efficiency, low purity, and narrow response range in alkaline water electrolysis technology still need to be solved. To further improve the efficiency of the electrolysis water system, it is necessary to start from the key materials and reduce the energy consumption level of the system.

[0003] The diaphragm is one of the core materials in the alkaline electrolyzer and plays a crucial role in improving the system efficiency and gas purity. The existing diaphragms mainly have the following problems: 1) The diaphragm has a large thickness and a high surface resistance. Due to the high thickness of the diaphragm, it leads to a long migration path of hydroxide ions, significantly increasing the ohmic voltage drop of the system. 2) Poor gas barrier property. The existing diaphragms use pore channels to absorb the electrolyte, and allow the electrolyte to pass through the pore channels to achieve the transfer of OH - during the electrolysis process. Such a process will inevitably lead to gas interpenetration and pose a safety risk.

[0004] In response to the above problems, the industry has proposed to use dense AEM or ion solvation membranes to replace traditional diaphragms. AEM has good OH - selectivity and conductivity, and can significantly reduce the concentration of the system electrolyte and reduce the corrosion of equipment. However, AEM has a high cost, is not directly compatible with the existing electrolyzers, and its alkali resistance stability still needs to be further improved. Another alternative is to use ion solvation membranes to replace traditional diaphragms. However, the existing PBI membrane preparation methods are complex and costly, which is not conducive to industrial applications. In addition, the unsupported PBI membrane has poor mechanical strength and is not suitable for direct assembly into the existing alkaline water electrolyzers, with poor versatility. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide an interfacial polymerization PBI-modified alkaline water electrolysis composite diaphragm, a preparation method thereof, and an application thereof.

[0006] The present invention provides a preparation method of a composite diaphragm, comprising:

[0007] (1) Fix the polymer bottom film, and then hydrophilically modify the polymer bottom film with a hydrophilic modifier;

[0008] (2) The hydrophilically modified bottom film is first impregnated with an aqueous solution, then impregnated with an oil-phase solution, washed, and dried to obtain a composite separator.

[0009] Further, in the step (1), fixing the polymer bottom film means fixing the bottom film with a fixture. The fixture is hollowed out up and down, and the polymer bottom film is fixed in the middle of the fixture, and the shape and size of the composite separator can be customized.

[0010] Preferably, in the step (1), the polymer bottom film includes one of polytetrafluoroethylene and expanded polytetrafluoroethylene; the average pore size of the polymer bottom film is 80 - 150 nm.

[0011] Preferably, in the step (1), the hydrophilic modifier includes polyethylene glycol PEG with a weight-average molecular weight of 200 - 20000, and preferably a weight-average molecular weight of 200 - 500.

[0012] Preferably, in the step (1), the hydrophilic modification includes: impregnating the polymer bottom film with a hydrophilic modifier; the impregnation time is 5 - 60 min.

[0013] Further, in the step (1), the hydrophilic modification includes: introducing the hydrophilic modifier into the fixture, above the bottom film, and impregnating.

[0014] Preferably, in the step (2), the aqueous solution includes a mixture of an aqueous main body and a solvent; the aqueous main body includes 3,3'-diaminobiphenyl; the solvent of the aqueous solution is water;

[0015] Preferably, in the step (2), the oil-phase solution includes a mixture of an oil-phase main body and a solvent; the oil-phase main body includes mellitic aldehyde; the solvent of the oil-phase solution includes n-hexane.

[0016] Preferably, in the step (2), the mass percentage concentration of the aqueous solution is 0.25% - 2%; the mass percentage concentration of the oil-phase solution is 0.25% - 2%;

[0017] Preferably, in the step (2), the impregnation time of the aqueous solution is 5 - 60 min, and more preferably 30 - 40 min; the impregnation time of the oil-phase solution is 30 - 300 min, and more preferably 120 - 150 min.

[0018] Further, in the step (2), one side or both sides of the hydrophilically modified bottom film are first impregnated with the aqueous solution and then dried, and then impregnated with the oil-phase solution and then dried.

[0019] Further, in step (2), the hydrophilically modified bottom film is first impregnated with an aqueous solution and then with an oil-phase solution, which includes: introducing the aqueous solution into a fixture, impregnating above the bottom film, and then wiping the residual solution on the surface; then introducing the oil-phase solution into the fixture, impregnating above the bottom film, and then wiping the residual solution on the surface.

[0020] Preferably, the drying in step (2) is natural drying at room temperature.

[0021] The present invention provides a fixture used in the preparation method. The fixture is hollowed out up and down, and the polymer bottom film is fixed in the middle of the fixture.

[0022] The present invention provides a composite separator prepared by the method. The thickness of the composite separator is about 230 - 260 μm; and / or, the average pore size of the composite separator is 75 - 100 nm; and / or, the bubble point pressure of the composite separator is 1.0 - 2.0 bar; and / or, the surface resistance of the composite separator is 0.05 - 0.40 Ω·cm 2 ; and / or, the porosity of the composite separator is 40 - 72%, and further preferably the porosity of the composite separator is 40 - 60%; and / or, the water contact angle of the composite separator is ≤90°, and further preferably the water contact angle of the composite separator is ≤60°.

[0023] The present invention provides an application of the composite separator prepared by the method in the field of electrolytic water hydrogen production, such as electrochemical energy devices for electrolytic water hydrogen production, etc.

[0024] The preparation method of the present invention selects expanded polytetrafluoroethylene as the polymer bottom film, which not only has a concentrated pore size distribution, but also has a small thickness and high mechanical strength. After being modified by a hydrophilic modifier, an in-situ interfacial polymerization PBI layer is carried out, so that a functional layer with good gas barrier property is covered on the surface of the separator, and at the same time, it also has a certain KOH absorption effect, improving the conductivity; the composite separator has excellent hydrogen gas barrier performance, low surface resistance and good conductivity.

[0025] Beneficial effects

[0026] The present invention proposes a solution of using a porous polymer bottom film as a support and in-situ interfacial polymerization of a PBI film. The porous polymer bottom film has a fixed pore size, a thin thickness and low cost. By modifying with a hydrophilic modifier, its hydrophilicity can be enhanced to meet the polymerization conditions. A dense and pore-free hydrophilic alkali-resistant PBI film is grown on the porous polymer bottom film by an in-situ polymerization method, which has good gas barrier property and electrolyte doping ability, significantly improving the conductivity of the separator, thereby reducing the system energy consumption of alkaline water electrolysis.

[0027] The alkaline water electrolysis composite diaphragm provided by the present invention has excellent superhydrophilicity, high gas barrier property, and low surface resistance. At the same time, it has stable physical properties, mild and simple process, green and environmentally friendly raw materials, low cost, and has the potential for industrial application.

[0028] Low surface resistance: The PBI membrane prepared in the present invention has good KOH affinity, and its excellent KOH doping ability endows the diaphragm with good OH- conduction ability, significantly reducing the surface resistance.

[0029] Strong gas barrier ability: The average pore diameter of the expanded polytetrafluoroethylene bottom membrane is 100 nm (130 - 150 nm for the zirconium-based composite diaphragm), and the surface of the PBI membrane is dense, endowing the diaphragm with good gas barrier performance.

[0030] High mechanical strength: The expanded polytetrafluoroethylene bottom membrane is composed of a PTFE main layer and a PTFE fiber support layer. The average diameter of the fibers in its fiber layer is 5 μm, making the diaphragm have good mechanical strength and flexibility.

[0031] Having industrial application prospects: The composite diaphragm can be prepared by the solution method at room temperature, and at the same time, the material cost per unit area of the membrane is low, having rich industrial application space. Description of the Drawings

[0032] Figure 1 It is a schematic diagram of the polymer diaphragm fixed in a self-made fixture;

[0033] Figure 2 It is a comparison of the water electrolysis polarization curves of a commercial diaphragm and a PBI-modified composite diaphragm;

[0034] Figure 3 It is a schematic diagram of the microstructure of the expanded polytetrafluoroethylene-based PBI composite diaphragm. Detailed Embodiments

[0035] The present invention will be further described below in conjunction with specific embodiments. It should be understood that these embodiments are only used to illustrate the present invention and not to limit the scope of the present invention. In addition, it should be understood that after reading the content taught by the present invention, those skilled in the art can make various changes or modifications to the present invention, and these equivalent forms also fall within the scope defined by the appended claims of this application.

[0036] Example 1

[0037] This example provides a superhydrophilic hydrotalcite-modified alkaline water electrolysis composite diaphragm, and its preparation method is as follows:

[0038] S1. Fix the expanded polytetrafluoroethylene (purchased from Changzhou Jinchun Environmental Protection Co., Ltd., hydrophilic polytetrafluoroethylene (PTFE) filter membrane, average pore diameter 0.1 μm) in a self-made fixture, as shown in Figure 1 ;

[0039] S2. Prepare an aqueous solution of 3,3'-diaminobiphenyl with a mass concentration of 0.5%, and at the same time prepare a n-hexane solution of mellitene trialdehyde with a mass concentration of 0.5%.

[0040] S3. Introduce polyethylene glycol (PEG 200) into the fixture, above the bottom film, and impregnate for 30 minutes for hydrophilic modification.

[0041] S4. Pour the aqueous solution of 3,3'-diaminobiphenyl into the fixture, above the bottom film, and impregnate for 30 minutes, then wipe dry the residual solution on the surface.

[0042] S5. Pour the n-hexane solution of mellitene trialdehyde into the fixture, above the bottom film, and impregnate for 120 minutes, then wipe dry the residual solution on the surface.

[0043] S6. Wash the prepared composite separator, and naturally dry it at room temperature and atmospheric pressure to obtain an alkaline water electrolysis composite separator modified by interfacial polymerization of PBI.

[0044] Example 2

[0045] This example is the same as Example 1, except that: the mass concentration of the aqueous solution of 3,3'-diaminobiphenyl in step S2 is 0.25%.

[0046] Example 3

[0047] This example is the same as Example 1, except that: the mass concentration of the aqueous solution of 3,3'-diaminobiphenyl in step S2 is 2%.

[0048] Comparative Example 1

[0049] This example is the same as Example 1, except that: the mass concentration of the aqueous solution of 3,3'-diaminobiphenyl in step S2 is 0.1%.

[0050] Comparative Example 2

[0051] This example is the same as Example 1, except that: the mass concentration of the aqueous solution of 3,3'-diaminobiphenyl in step S2 is 5%.

[0052] Example 4

[0053] This example is the same as Example 1, except that: the mass concentration of the n-hexane solution of mellitene trialdehyde in step S2 is 0.25%.

[0054] Example 5

[0055] This example is the same as Example 1, except that: the mass concentration of the n-hexane solution of mellitene trialdehyde in step S2 is 2%.

[0056] Comparative Example 3

[0057] This example is the same as Example 1, except that: the mass concentration of the phloroglucinol trimethaldehyde n-hexane solution in step S2 is 0.1%.

[0058] Comparative Example 4

[0059] This example is the same as Example 1, except that: the mass concentration of the phloroglucinol trimethaldehyde n-hexane solution in step S2 is 5%.

[0060] Example 6

[0061] This example is the same as Example 1, except that: the impregnation time of the 3,3'-diaminobiphenyl aqueous solution in step S4 is 5 minutes.

[0062] Example 7

[0063] This example is the same as Example 1, except that: the impregnation time of the 3,3'-diaminobiphenyl aqueous solution in step S4 is 60 minutes.

[0064] Comparative Example 5

[0065] This example is the same as Example 1, except that: the impregnation time of the 3,3'-diaminobiphenyl aqueous solution in step S4 is 2 minutes.

[0066] Comparative Example 6

[0067] This example is the same as Example 1, except that: the impregnation time of the 3,3'-diaminobiphenyl aqueous solution in step S4 is 120 minutes.

[0068] Example 8

[0069] This example is the same as Example 1, except that: the impregnation time of the phloroglucinol trimethaldehyde n-hexane solution in step S5 is 30 minutes.

[0070] Example 9

[0071] This example is the same as Example 1, except that: the impregnation time of the phloroglucinol trimethaldehyde n-hexane solution in step S5 is 300 minutes.

[0072] Comparative Example 7

[0073] This example is the same as Example 1, except that: the impregnation time of the phloroglucinol trimethaldehyde n-hexane solution in step S5 is 10 minutes.

[0074] Comparative Example 8

[0075] This example is the same as Example 1, except that: the impregnation time of the phloroglucinol trimethaldehyde n-hexane solution in step S5 is 600 minutes.

[0076] Test Example 1

[0077] This test example conducted electrolytic water performance tests on a commercial separator (purchased from Tianjin Respect Technology Co., Ltd.) and the composite separator prepared in Example 1. The results are as Figure 3 shown.

[0078] The alkaline water electrolysis experiment was carried out in a single-chamber zero-gap electrolytic cell, which was purchased from Maiqi New Energy Technology Co., Ltd., model LSCF-261000, with an effective electrode area of 15 cm 2 . Replace the separator in it with this product, use 30% KOH as the electrolyte, and control the cell temperature at 80 °C. Use a DC power supply for power supply, with the current density range of 0 - 10000 A / m 2 , and the step size is 1000 A / m 2 , and record the corresponding voltage. As Figure 2 can be seen, due to the alkali absorption ability of the surface ion solvation membrane PBI, the composite separator with surface PBI polymerization is more excellent in water electrolysis performance than the commercial separator. When the cell voltage is 2 V, the current density reaches 5000 A / m 2 (For the commercial separator UTP 500: the current density reaches nearly 3000 A / m when the cell voltage is 2 V 2 ).

[0079] Test Example 2

[0080] This test measured the average pore size, alkali absorption rate, surface resistance, porosity, and the water contact angle and wetting time of the separators in the above Examples 1 - 9 and Comparative Examples 1 - 8. The measurement results are shown in Table 1.

[0081] The average pore size can reflect the pore size of the separator, which is of great significance for the OH - permeability and gas barrier performance of the separator. The test method refers to GBT 21650.1 - 2008 "Determination of Pore Size Distribution and Porosity of Solid Materials by Mercury Intrusion Method and Gas Adsorption Method".

[0082] The surface resistance of the separator has an important impact on the conductivity of the separator. The surface resistance refers to the resistance value per unit area of the separator, indicating the resistance of the current passing through the separator. The lower the surface resistance, the smaller the resistance value per unit area, and the smaller the resistance of the current passing through the separator. The test method refers to SJT10171.5 - 1991 "Test Methods for the Performance of Separators for Alkaline Storage Batteries".

[0083] The porosity is directly related to the conductivity of the separator. A larger porosity means a larger electrolyte flux and a smaller surface resistance of the separator. In this test example, the composite separators prepared in the above examples and comparative examples were respectively cut into squares with a size of 2 cm * 2 cm, and the dry weight was measured. Then they were respectively immersed in deionized water for 12 h; after that, they were taken out and the porosity of the composite separator was calculated by measuring the mass and volume differences of the dry and wet membranes before and after water absorption.

[0084] The bubble point pressure refers to the pressure at which gas in the separator begins to permeate at a certain temperature. A higher bubble point pressure indicates that the separator has better gas barrier performance and can more effectively prevent gas permeation. The test method refers to GB / T 26204-2010 "Test Method for Performance of Liquid Phase Filter Materials - Air Bubble Point Test".

[0085] The water contact angle can reflect the wetting performance of the film. The test method refers to GB / T 30693-2014 "Measurement of Water Contact Angle of Plastic Films". The wetting time is the time difference from when the water droplet contacts the separator and starts to generate a contact angle until the contact angle becomes 0.

[0086] After in-situ polymerization of the PBI membrane, the obtained separators all have a porosity of ~60%, and the bubble point pressures are all between 1.0 bar and 2.0 bar, indicating that this strategy can effectively locally fill the macropores, enabling the separators to have better gas barrier performance. The water contact angles of all the surface-polymerized PBI membrane separators are ≤60°. This superhydrophilicity greatly improves the performance of the separator during the water electrolysis process and reduces the system energy consumption.

[0087] Table 1 shows the performance parameters of the PBI-modified composite separators prepared in Examples 1-9 and Comparative Examples 1-8

[0088]

[0089]

Claims

1. A method for preparing a composite separator, comprising: (1) Fixing a polymer base film, and then hydrophilically modifying the polymer base film with a hydrophilic modifier; (2) The hydrophilically modified base film is first impregnated with an aqueous solution, and then impregnated with an oil phase solution, washed, and dried to obtain a composite separator.

2. The preparation method according to claim 1, characterized in that, In the step (1), the fixing of the polymer base film is to fix the base film with a fixture.

3. The preparation method according to claim 1, characterized in that, In the step (1), the polymer base film includes one of polytetrafluoroethylene and expanded polytetrafluoroethylene; In the step (1), the hydrophilic modifier includes polyethylene glycol PEG with a weight average molecular weight of 200-20000.

4. The preparation method according to claim 1, characterized in that, In the step (1), the hydrophilic modification includes: impregnating the polymer base film with a hydrophilic modifier; the impregnation time is 5-60 min.

5. The preparation method according to claim 1, characterized in that, In the step (2), the aqueous solution includes a mixture of an aqueous main body and a solvent; the aqueous main body includes 3,3'-diaminobiphenyl; the solvent of the aqueous solution is water; In the step (2), the oil phase solution includes a mixture of an oil phase main body and a solvent; the oil phase main body includes mellitic aldehyde; The solvent of the oil phase solution includes n-hexane.

6. According to the preparation method described in claim 1, characterized in that, In the step (2), the mass percentage concentration of the aqueous solution is 0.25%-2%; the mass percentage concentration of the oil phase solution is 0.25%-2%; In the step (2), the impregnation time of the aqueous solution is 5-60 min; the impregnation time of the oil phase solution is 30-300 min.

7. A fixture used in the preparation method according to claim 1, characterized in that, The fixture is hollowed out up and down, and the polymer base film is fixed in the middle of the fixture.

8. A composite separator prepared by the method according to claim 1.

9. An electrochemical energy device, characterized in that, The electrochemical energy device includes the composite separator prepared by the method according to claim 1.

10. An application of the composite separator prepared by the method according to claim 1 or the electrochemical energy device according to claim 9 in the field of hydrogen production by electrolyzing water.

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