Sodium carboxymethyl cellulose modified ultrathin alkaline water electrolysis composite diaphragm as well as preparation method and application thereof

Abstract

The invention relates to a sodium carboxymethyl cellulose modified ultrathin alkaline water electrolysis composite diaphragm as well as a preparation method and application thereof. The alkaline electrolytic water diaphragm provided by the invention not only has excellent hydrophilicity and low surface resistance, but also has high gas barrier property and excellent mechanical property. In addition, the diaphragm is simple in preparation process and low in cost, and has industrial application potential.

Description

Technical Field

[0001] The present invention belongs to the field of diaphragm materials, and particularly relates to a sodium carboxymethylcellulose-modified ultra-thin alkaline water electrolysis composite diaphragm and its preparation method and application. Background Art

[0002] Hydrogen energy is an ideal energy source in the 21st century. As a renewable secondary energy source, hydrogen has rich sources, high energy density, and the advantages of no carbon emissions and environmental friendliness. In the current development pattern of our country, actively developing and making full use of hydrogen energy resources has great and far-reaching strategic significance for reshaping our country's energy structure and effectively ensuring energy supply security. Currently, the main sources of hydrogen are fossil fuel reforming for hydrogen production, biological hydrogen production, and industrial by-product hydrogen, etc. Renewable energy sources such as solar energy and wind energy have the characteristics of intermittency and volatility, and their power generation is unstable, and a large amount of electric energy is difficult to be directly connected to the grid for efficient utilization. And electrolytic water hydrogen production just provides an ideal way out for these "extra" electric energies. By storing unstable electric energy in the form of hydrogen, it can play the role of "peak shaving and valley filling", effectively improving the utilization efficiency and consumption capacity of renewable energy.

[0003] In the field of electrolytic water hydrogen production, alkaline electrolytic water hydrogen production is widely used due to its low cost, rich operation experience, and simple operation. As the core component of the alkaline electrolytic cell, the diaphragm, on the one hand, has the function of conducting hydroxide ions to ensure the continuous progress of electrolysis. On the other hand, it isolates the gases generated at the anode and cathode to ensure the purity of hydrogen. The development of the diaphragm has gone through three stages, from the first-generation traditional diaphragm represented by asbestos, to the second-generation organic diaphragm represented by polyphenylene sulfide non-woven fabric, to the current third-generation composite diaphragm composed of hydrophilic ceramic materials and hydrophobic polymers as slurries and a PPS mesh as a support. However, the various performances of the composite diaphragm still need to be improved, mainly including the following problems: 1) The diaphragm is relatively thick (usually >500um), resulting in a large electrode spacing and a long ion migration distance, thus leading to an increase in ohmic impedance and energy consumption; 2) Poor hydrophilicity, there is a dense polymer layer on the surface of the diaphragm, increasing the hydrophobicity of the diaphragm. The hydrophobic surface is beneficial to the desorption of bubbles, increasing the ohmic resistance between the diaphragm and the electrode; 3) Poor gas barrier property, the pore size of the support of the composite diaphragm is large, and the proportion of large pores is high, which easily leads to gas crossover between the anode and cathode, resulting in safety risks. Therefore, how to develop a diaphragm with low surface resistance, good hydrophilicity and gas barrier property through hydrophilic modification and thickness control, and at the same time develop a diaphragm that can be continuously and stably applied in alkaline media is of great significance for the field of alkaline electrolytic water hydrogen production. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide a sodium carboxymethylcellulose-modified ultra-thin alkaline water electrolysis composite diaphragm and its preparation method and application, solving the problem of how to reduce the diaphragm thickness and shorten OH -The conduction path reduces the surface resistance while taking into account technical issues such as the hydrophilicity, gas barrier property, and long-term stability of the separator.

[0005] The present invention provides a method for preparing a composite separator, comprising:

[0006] S1. Dissolve a binder in a solvent and stir to obtain a homogeneous solution;

[0007] S2. Add a pore regulator to the solution obtained in S1 and stir to form a homogeneous dispersion;

[0008] S3. Add a hydrophilic material to the dispersion obtained in S2, stir, and defoam to obtain a slurry;

[0009] S4. Coat the slurry on a polymer substrate through a slit to obtain a polymer substrate, then immerse it in a coagulation bath for phase inversion, take it out and dry to obtain a composite separator.

[0010] Preferably, the mass ratio of the solvent, binder, pore regulator, and hydrophilic material is (14-18):(3-4):(1-3):(16-18).

[0011] Preferably, the binder in step S1 includes polysulfone, and the weight average molecular weight of the binder is 40,000-86,000, and more preferably the weight average molecular weight is 70,000-80,000;

[0012] Preferably, the solvent in step S1 includes one or more of N-methylpyrrolidone, N,N-dimethylformamide, and N,N-dimethylacetamide.

[0013] Preferably, the pore regulator in step S2 includes polyvinylpyrrolidone, and the weight average molecular weight is 10,000-100,000, and more preferably the weight average molecular weight is 10,000-30,000.

[0014] Preferably, the hydrophilic material in step S3 includes a hydrophilic modifier and / or a hydrophilic ceramic filler. More preferably, the hydrophilic ceramic filler is zirconia, and the average nano particle size is 80-100 nm. The hydrophilic modifier includes sodium carboxymethyl cellulose;

[0015] Preferably, the mass ratio of the hydrophilic ceramic filler to the hydrophilic modifier is 77:8-83:2, and more preferably 80:5-83:2. Preferably, the defoaming in step S3 is natural static defoaming.

[0016] Preferably, the polymer substrate in step S4 includes a polyphenylene sulfide woven mesh, and the mesh number is 120-150 meshes;

[0017] Preferably, the coagulation bath in step S4 is anhydrous ethanol, and the phase inversion time is 8-15 h.

[0018] Preferably, after placing the polymer substrate in the slit and pouring the slurry, the polymer substrate is vertically and uniformly passed through the slit to achieve uniform coating of the slurry. The slit width is 350 μm to 650 μm, and more preferably the slit width is 340 to 350 μm.

[0019] Furthermore, the device used for slit coating in step S4 is a slit coater, which includes a bracket, a wire bar, a gasket, and a slurry tank; furthermore, the slit width is adjusted by the gasket. After placing the polymer substrate in the slit and pouring the slurry, the polymer substrate is vertically and uniformly passed through the slit to achieve uniform coating of the slurry.

[0020] The drying in step S4 is drying under natural conditions.

[0021] The present invention provides an ultra-thin composite separator prepared by the above method. The separator has dense and uniform sponge-like pores, and the thickness of the composite separator is 200 to 450 μm.

[0022] Furthermore, the thickness of the composite separator is preferably 200 to 240 μm;

[0023] and / or, the bubble point pressure of the composite separator is 2.0 to 4.0 bar;

[0024] and / or, the surface resistance of the composite separator is 0.05 to 0.30 Ω·cm 2 ;

[0025] and / or, the porosity of the composite separator is 50 to 80%;

[0026] and / or, the average pore size of the composite separator is 90 to 150 nm;

[0027] and / or, the water contact angle of the composite separator is ≤80°.

[0028] The present invention provides an electrochemical energy device, and the electrochemical energy device includes the composite separator.

[0029] The present invention provides an application of the composite separator or the electrochemical energy device in the field of electrolytic water hydrogen production.

[0030] The preparation method of the present invention can effectively reduce the separator thickness by adjusting the slit width of the self-made fixture. At the same time, the hydrophilic filler sodium carboxymethylcellulose is used for hydrophilic modification, and polyvinylpyrrolidone cooperates to effectively regulate the pore size and pore size distribution. The composite separator prepared by the present invention has excellent hydrogen barrier performance, low surface resistance, and good conductivity. At the same time, the separator has good mechanical properties, simple preparation process, low cost, and has the potential for industrial application.

[0031] Beneficial effects

[0032] (1) Good gas barrier property: The composite diaphragm of the present invention has a relatively high bubble point pressure, which can effectively prevent the gas crossover generated by the anode and cathode, and greatly reduce potential safety hazards.

[0033] (2) Low surface resistance: The composite diaphragm of the present invention has an ultra-low surface resistance, which can quickly conduct hydroxide ions, reduce the electrolysis voltage, and decrease the energy consumption.

[0034] (3) Good hydrophilicity: The composite diaphragm of the present invention has good hydrophilicity, which can be quickly wetted by the lye, accelerate the conduction rate of hydroxide ions, and thus improve the electrolysis rate.

[0035] (4) Simple operation and easy to scale up: The operation of the present invention is simple, the method is efficient, and it has good potential for industrial application. Description of the drawings

[0036] Figure 1 It is a schematic diagram of a self-made slit coater;

[0037] Figure 2 They are scanning electron microscope images of the surface (a) and cross-section (b) of the composite diaphragm prepared in Example 1;

[0038] Figure 3 They are the porosity test results of the composite diaphragms prepared in Examples 1-3 and Comparative Example 1;

[0039] Figure 4 They are the comparison of the water electrolysis polarization curves between the commercial diaphragm and the composite diaphragm prepared in Example 1;

[0040] Figure 5 They are the alkali absorption rate test results of the composite diaphragms prepared in Examples 1-3 and Comparative Example 1. Detailed implementation manners

[0041] 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.

[0042] Unless otherwise specified, the raw materials used in the embodiments of the present invention are all commercially available raw materials, and the equipment used is all conventional equipment in the technical field.

[0043] Example 1

[0044] S1. Dissolve polysulfone (Mw~76800) in N-methylpyrrolidone, and control the mass ratio of polysulfone to N-methylpyrrolidone to be 3:14, and stir for 12 h to obtain a homogeneous solution;

[0045] S2. Add polyvinylpyrrolidone (Mw ~ 10000) to the above solution, and control the mass ratio of polyvinylpyrrolidone to polysulfone to be 1:3, and stir for 6 h to form a homogeneous dispersion;

[0046] S3. Add sodium carboxymethyl cellulose to the dispersion obtained in S2, stir to form a homogeneous dispersion, then add zirconia (average particle size 100 nm), and control the mass ratio of polysulfone, sodium carboxymethyl cellulose and zirconia to be 15:2:83, and continue to stir until the slurry is uniformly dispersed, and then let it stand naturally to defoam to obtain a uniformly dispersed slurry;

[0047] S4. Pass a 150-mesh PPS mesh through a self-made slot coater and introduce the slurry, adjust the slot width to 350 μm, make the PPS mesh pass through the slot at a constant speed, and then immerse it in a coagulation bath for phase inversion for 12 h;

[0048] S5. Take out the sample film and dry it under natural conditions to obtain a composite separator with a thickness of 220 μm.

[0049] Example 2

[0050] This example is the same as Example 1, except that: in step S3, a certain amount of sodium carboxymethyl cellulose is added, and the mass ratio of it to polysulfone and zirconia is 15:5:80.

[0051] Example 3

[0052] This example is the same as Example 1, except that: in step S3, a certain amount of sodium carboxymethyl cellulose is added, and the mass ratio of it to polysulfone and zirconia is 15:8:77.

[0053] Comparative Example 1

[0054] This example is the same as Example 1, except that: in step S3, a certain amount of sodium carboxymethyl cellulose is added, and the mass ratio of it to polysulfone and zirconia is 15:0:85.

[0055] Comparative Example 2

[0056] This example is the same as Example 1, except that: in step S3, a certain amount of sodium carboxymethyl cellulose is added, and the mass ratio of it to polysulfone and zirconia is 15:12:73.

[0057] Example 4

[0058] This example is the same as Comparative Example 1, except that: in step S4, the slot width is adjusted to 500 μm.

[0059] Example 5

[0060] This example is the same as Comparative Example 1, with the difference being that in step S4, the slit width is adjusted to 650 μm.

[0061] Comparative Example 3

[0062] This example is the same as Comparative Example 1, with the difference being that in step S4, the slit width is adjusted to 280 μm.

[0063] Comparative Example 4

[0064] This example is the same as Comparative Example 1, with the difference being that in step S4, the slit width is adjusted to 800 μm.

[0065] Test Example 1

[0066] In this test example, the surface and cross-sectional microtopographies of the ultrathin highly hydrophilic composite separator prepared in Example 1 were characterized by scanning electron microscopy (SEM), and the results are as Figure 1 shown.

[0067] As can be seen from Figure 1 , the separator surface in this test example has a uniform and dense pore structure. This pore structure can conduct hydroxide ions more rapidly, improving the efficiency of water electrolysis. At the same time, the dense pores can effectively block gas crossover, ensuring the safety of separator use. The separator in this test example forms a porous framework structure from polysulfone, and zirconia and sodium carboxymethylcellulose are interspersed between the porous frameworks, forming a gradient sponge-like pore structure and improving the hydrophilicity of the separator. At the same time, polyvinylpyrrolidone acts as a pore regulator to synergistically promote the narrow distribution of the pore structure.

[0068] Test Example 2

[0069] In this test example, the porosity of the composite separators prepared in Example 1, Example 2, Example 3, Comparative Example 1, and the commercial separator (Zirfon UTP 500) was measured, and the experimental results are as Figure 3 shown. As can be seen from the figure, after adding a certain amount of sodium carboxymethylcellulose, the porosity of the separator has been improved. Among them, when the mass ratio of sodium carboxymethylcellulose to zirconia is 2:83, the porosity of the separator reaches 67.5%, indicating that adding sodium carboxymethylcellulose can significantly increase the porosity of the separator. The high porosity can effectively improve the rate of hydroxide ion conduction of the separator, thereby reducing ohmic polarization and improving the efficiency of water electrolysis.

[0070] Test Example 3

[0071] In this test example, the water electrolysis performance of the commercial separator (purchased from Tianjin Respected Technology Co., Ltd.) and the composite separator prepared in Example 1 was tested. The results are as Figure 4 shown.

[0072] The alkaline water electrolysis experiment was carried out in a single-chamber zero-gap electrolyzer, which was purchased from Maiqi New Energy Technology Co., Ltd., model LSCF-261000, with an effective electrode area of 4.84 cm 2 . Replace the diaphragm 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 - 23000 A / m 2 , and the step size is 1000 A / m 2 , and record the corresponding voltage. As can be seen from Figure 4 , thanks to the ultra-thin thickness of the composite diaphragm, the super hydrophilicity of sodium carboxymethyl cellulose, and the improvement of the pore structure, the 83 / 2 composite diaphragm is applied to water electrolysis to obtain an ultra-high current density of 22000 A / m 2 @2V, which is significantly better than the performance of commercial diaphragms (11000 A / m 2 @2V - UTP 500).

[0073] Test Example 4

[0074] In this test, the surface resistance, bubble point pressure, diaphragm water contact angle, porosity, and pore size of the diaphragms in the above Examples 1 - 5 and Comparative Examples 1 - 4 were measured, and the measurement results are shown in Table 1.

[0075] The surface resistance of the diaphragm has an important impact on the electrical conductivity of the diaphragm. The surface resistance refers to the resistance value per unit area of the diaphragm, indicating the resistance of the current passing through the diaphragm. The lower the surface resistance, the smaller the resistance value per unit area, and the smaller the resistance of the current passing through the diaphragm. The test method refers to SJT10171.5 - 1991 "Test Methods for the Performance of Alkaline Battery Diaphragms".

[0076] The bubble point pressure refers to the pressure at which the gas in the diaphragm begins to permeate at a certain temperature. A higher bubble point pressure indicates that the diaphragm has better gas barrier performance and can more effectively prevent gas permeation. The test method refers to GB / T26204 - 2010 "Test Methods for the Performance of Liquid Phase Filter Materials - Air Bubble Point Test".

[0077] The water contact angle can reflect the wetting performance of the film. The test method refers to GB / T 30693 - 2014 "Measurement of the Contact Angle of Plastic Films with Water". The wetting time is the time difference from when the water droplet contacts the diaphragm and starts to generate a contact angle until the contact angle becomes 0. After reducing the diaphragm thickness and adding sodium carboxymethyl cellulose, the surface resistance of the diaphragm is ≤0.2 Ωcm 2, the bubble point pressure is ≥ 2.5 bar, indicating that reducing the thickness of the diaphragm can greatly shorten the ion transport path and significantly reduce the surface resistance. By using a PPS mesh with a higher mesh number, the pore size of the PPS mesh can be reduced, making it difficult for gas to pass through the diaphragm and endowing the diaphragm with better gas barrier performance. By adding sodium carboxymethylcellulose, the water contact angle of the diaphragm can be significantly reduced, thereby improving the hydrophilicity of the diaphragm. This hydrophilic property greatly enhances the performance of the diaphragm during the water electrolysis process and reduces the system energy consumption.

[0078] Table 1 shows the performance parameters of the composite diaphragms prepared in Examples 1-8 and Comparative Examples 1-8

[0079]

Claims

1. A method for preparing a composite separator, comprising: S1. Dissolving a binder in a solvent and stirring to obtain a homogeneous solution; S2. Adding a pore regulator to the solution obtained in S1 and stirring to form a homogeneous dispersion; S3. Adding a hydrophilic material to the dispersion obtained in S2, stirring, and degassing to obtain a slurry; S4. Coating the slurry on a polymer substrate through a slit to obtain a polymer substrate, then impregnating it in a coagulation bath for phase inversion, taking it out and drying to obtain a composite separator.

2. The preparation method according to claim 1, wherein The mass ratio of the solvent, binder, pore regulator and hydrophilic material is (14 - 18):(3 - 4):(1 - 3):(16 - 18).

3. The preparation method according to claim 1, characterized in that, In step S1, the binder includes polysulfone, and the weight average molecular weight of the binder is 40,000 - 86,000; In step S1, the solvent includes one or more of N-methylpyrrolidone NMP, N,N-dimethylformamide DMF, and N,N-dimethylacetamide DMAC.

4. The preparation method according to claim 1, wherein, In step S2, the pore regulator includes polyvinylpyrrolidone, and the weight average molecular weight is 10,000 - 100,000.

5. The preparation method according to claim 1, characterized in that In step S3, the hydrophilic material includes a hydrophilic modifier and / or a hydrophilic ceramic filler.

6. The preparation method according to claim 5, characterized in that, The hydrophilic ceramic filler includes zirconia, and the average nano-particle size is 80 - 100 nm; the hydrophilic modifier includes sodium carboxymethyl cellulose. The mass ratio of the hydrophilic ceramic filler to the hydrophilic modifier is 73:12 - 83:

2.

7. The preparation method according to claim 1, wherein In step S4, the polymer substrate includes a polyphenylene sulfide mesh, and the mesh number of the polymer substrate is 120 - 150 mesh; in step S4, the coagulation bath is anhydrous ethanol.

8. According to the preparation method described in claim 1, characterized in that, In step S4, the polymer substrate is placed in a slit and the slurry is poured in, so that the polymer substrate vertically passes through the slit at a constant speed to achieve uniform coating of the slurry.

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

10. An electrochemical energy device, characterized in that, The electrochemical energy device includes the composite separator according to claim 1.

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

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