A microporous layer slurry and its preparation method, and a microporous layer and a gas diffusion layer.

Abstract

This invention discloses a method for preparing a microporous layer slurry, comprising the following steps: a) adding a dispersant and a hydrophobic agent to deionized water and stirring and dispersing, then adding conductive carbon material and stirring and dispersing to obtain a first slurry; b) adding conductive carbon nanofibers to the first slurry obtained in step a, and mechanically stirring and dispersing to obtain a microporous layer slurry. The method for preparing the microporous layer slurry of this invention, by adding carbon nanofibers to the microporous layer slurry, results in a microporous layer with high surface smoothness, greatly reducing the contact resistance between the diffusion layer and the catalyst layer; the microporous layer is free of cracks, effectively alleviating water blockage.

Description

Technical Field

[0001] This invention belongs to the field of fuel cell technology, specifically relating to a microporous layer slurry, further relating to a method for preparing the microporous layer slurry, and even further relating to a microporous layer, particularly a gas diffusion layer. Background Technology

[0002] As an important component of the membrane electrode assembly (MEA), a core component of fuel cells, the gas diffusion layer is typically composed of porous materials with good electrical conductivity. It has an anisotropic porous microstructure and plays multiple roles in the fuel cell stack, such as gas transport and distribution, electron conduction, supporting the catalyst layer, and improving water management. It is one of the key components affecting the electrochemical performance of fuel cells.

[0003] For the gas diffusion layer, excellent drainage capacity is particularly important. The catalytic reaction produces a large amount of water, which needs to be drained through the gas diffusion layer. If the water cannot be drained in time, flooding will occur, causing the catalytic layer to be submerged and reducing the utilization rate of the catalyst. At the same time, the pores of the gas diffusion layer will also be blocked by water, making it difficult for gas to diffuse into the catalytic layer, which will severely degrade the performance of the membrane electrode.

[0004] Gas diffusion layers typically consist of carbon paper and carbon cloth. A common structure includes a microporous layer to improve battery water management and reduce interlayer contact resistance. This microporous layer is usually composed of a mixture of carbon powder and PTFE emulsion, uniformly coated onto the surface of the carbon paper or carbon cloth using a specific coating method. The microporous layer is a key factor in improving the performance of the gas diffusion layer. It can be understood as either a portion coated inside the gas diffusion layer or as an independent layer—a three-dimensional, porous network structure formed by impregnating carbon powder with PTFE emulsion and sintering. In high-humidity batteries, numerous studies have confirmed that microporous layers can significantly improve the performance and durability of proton exchange membrane fuel cells, especially at high current densities, and can significantly reduce the "water blockage" phenomenon.

[0005] CN106784883A discloses a method for preparing a smooth, crack-free, low-carbon-load microporous layer for a proton exchange membrane fuel cell. The preparation process includes grinding conductive carbon powder in a ball mill, adding an appropriate amount of dispersant for further grinding and dispersion, adding a hydrophobic emulsion, and ultrasonically dispersing the mixture to form a uniformly distributed microporous slurry. A high-solids-content slurry is coated onto clean carbon paper, followed by an ultrasonically sprayed low-solids-content slurry, dried at room temperature, and finally sintered to form a smooth, crack-free, low-carbon-load microporous layer. The technical solution of CN106784883A is complex, requiring multiple coating processes, making mass production impossible. Furthermore, it does not address the dispersion problem of conductive carbon black, and the spraying process for preparing the microporous layer is inefficient and unsuitable for large-scale production. Therefore, it is necessary to improve the microporous layer technology. Summary of the Invention

[0006] This invention is based on the inventors' discoveries and understanding of the following facts and problems: Due to limitations in the coating process, the coated microporous layer exhibits surface unevenness and numerous cracks, leading to increased contact resistance, unreasonable pore size distribution and pore structure. Furthermore, the presence of cracks easily causes water generated during battery reactions to accumulate, making it difficult for water to drain from the battery in a timely manner, resulting in "flooding." In addition, the number of pore channels for gas transport is relatively reduced, preventing gas from entering the catalyst layer for reaction in a timely manner, thus causing a sharp decline in battery performance. However, existing technologies have limited research on structural design to improve the surface smoothness of microporous layers and reduce surface cracks. Therefore, precisely designing a crack-free and smooth gas diffusion layer for microporous layers has significant research value.

[0007] This invention aims to at least partially solve one of the technical problems in related technologies. To this end, embodiments of this invention propose a microporous layer slurry and its preparation method. Carbon nanofibers are added to the microporous layer slurry, resulting in a microporous layer with high surface smoothness, which greatly reduces the contact resistance between the diffusion layer and the catalyst layer; the microporous layer is free of cracks, alleviating water blockage.

[0008] The method for preparing the microporous layer slurry according to an embodiment of the present invention includes the following steps:

[0009] a. Add the dispersant and hydrophobic agent to deionized water and stir and disperse, then add the conductive carbon material, stir and disperse to obtain the first slurry;

[0010] b. Add conductive carbon nanofibers to the first slurry obtained in step a, and mechanically stir and disperse to obtain a microporous layer slurry.

[0011] The advantages and technical effects of the microporous layer slurry preparation method of this invention are as follows: 1. In the method of this invention, conductive carbon nanofibers are added to the microporous layer slurry. The one-dimensional linear structure of the conductive carbon nanofibers is beneficial for forming a microporous layer with good flatness and no cracks. 2. In the method of this invention, the fibrous conductive carbon nanofibers easily fill the gaps between the granular conductive carbon materials, and through the strong interaction between the carbon fibers and between the carbon fibers and the conductive carbon material particles, the surface of the prepared microporous layer is flat and crack-free. 3. In the method of this invention, the conductive carbon material is added first for stirring and dispersion, and then the conductive carbon nanofibers are added, which helps to improve the uniformity of the microporous layer slurry, obtain a microporous layer with high flatness, and thus improve the performance of the microporous layer. 4. The method of this invention... The method, by adding a dispersant and dispersing with high-speed mechanical stirring, can minimize the uneven mixing of the hydrophobic agent and conductive carbon material caused by the repulsion between the hydrophobic agent and water, resulting in a uniform and stable ink slurry. 5. The microporous layer slurry prepared by the method of this embodiment can produce a high-performance microporous layer with no surface cracks, greatly improving durability and exhibiting excellent electrical properties. It can also effectively improve the surface uniformity and gas diffusion of the gas diffusion layer, significantly reducing the contact resistance between the diffusion layer and the catalyst layer, and alleviating water blockage. 6. The method of this embodiment has a simple, efficient, and uncomplicated process route, suitable for continuous batch production. All raw materials used are commercial products and require no further processing before use. The preparation process is easy to industrialize.

[0012] In some embodiments, the dispersant includes at least one of anionic surfactants, nonionic surfactants, polymeric dispersants, or fluorinated surfactants; and the mass content of the dispersant in the microporous slurry is 0.1-1%.

[0013] In some embodiments, the hydrophobic agent includes at least one of polytetrafluoroethylene emulsion, polyvinylidene fluoride emulsion, and polychlorotrifluoroethylene emulsion; the conductive carbon material includes conductive carbon black.

[0014] In some embodiments, the conductive carbon nanofibers have an average fiber diameter of 100–300 nm, an average fiber length of 1–30 μm, and a specific surface area of ​​10–100 m². 2 / g, with a bulk density of 0.02~0.1g / cm³ 3 .

[0015] In some embodiments, the mass ratio of the conductive carbon nanofibers to the conductive carbon material is 1:2-4.5.

[0016] In some embodiments, step b, the mechanical stirring and dispersion method includes: stirring and dispersing at a first rotational speed of 500 to 2500 rpm for 20-40 minutes, and then stirring and dispersing at a second rotational speed of 4000 to 9000 rpm for 200-300 minutes.

[0017] This invention also provides a microporous layer slurry, prepared using the method described in this invention. The microporous layer slurry of this invention is uniformly dispersed and consistently stable, enabling the preparation of a microporous layer with high smoothness and no cracks.

[0018] This invention also provides a microporous layer, which is prepared by blade coating or screen printing using the microporous layer slurry of this invention. The microporous layer of this invention has a high surface smoothness, which greatly reduces the contact resistance between the diffusion layer and the catalyst layer. The microporous layer is free of cracks, thus alleviating water blockage.

[0019] In some embodiments, the thickness of the microporous layer is 20–50 μm, and the total carbon loading is 1.7–2.5 mg / cm³. 2 .

[0020] This invention also provides a gas diffusion layer, including a microporous layer as described in this embodiment. The gas diffusion layer of this invention possesses all the advantages of the microporous layer of this invention, which will not be elaborated further here. Attached Figure Description

[0021] Figure 1 These are polarization curves of the membrane electrodes assembled with diffusion layers obtained in Example 1 and Comparative Example 1.

[0022] Figure 2 This is a scanning electron microscope image of the diffusion layer microporous layer obtained in Example 1;

[0023] Figure 3 This is a scanning electron microscope image of the diffusion layer microporous layer prepared in Comparative Example 1. Detailed Implementation

[0024] Embodiments of the present invention are described in detail below, examples of which are illustrated in the accompanying drawings. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain the present invention, and should not be construed as limiting the present invention.

[0025] The method for preparing the microporous layer slurry according to an embodiment of the present invention includes the following steps:

[0026] a. Add the dispersant and hydrophobic agent to deionized water and stir and disperse, then add the conductive carbon material, stir and disperse to obtain the first slurry;

[0027] b. Add conductive carbon nanofibers to the first slurry obtained in step a, and mechanically stir and disperse to obtain a microporous layer slurry.

[0028] The method for preparing a microporous layer slurry according to embodiments of the present invention involves adding conductive carbon nanofibers to the microporous layer slurry. The one-dimensional linear structure of the conductive carbon nanofibers facilitates the formation of a smooth, crack-free microporous layer. In the method of the present invention, the fibrous conductive carbon nanofibers easily fill the gaps between the granular conductive carbon materials, and through the strong interaction between the carbon fibers and between the carbon fibers and the conductive carbon material particles, the surface of the prepared microporous layer is smooth and crack-free. In the method of the present invention, the conductive carbon material is added first for stirring and dispersion, and then the conductive carbon nanofibers are added, which helps to improve the uniformity of the microporous layer slurry, obtain a microporous layer with high smoothness, and thus improve the performance of the microporous layer. The method of the present invention, by adding dispersants and high... Rapid mechanical stirring and dispersion can minimize the uneven mixing of hydrophobic agents and conductive carbon materials caused by the repulsion between hydrophobic agents and water, resulting in a uniform and stable ink slurry. The microporous layer slurry prepared by the method of this invention can produce a high-performance microporous layer with no surface cracks, greatly improving durability and exhibiting excellent electrical properties. It can also effectively improve the surface uniformity and gas diffusion of the gas diffusion layer, significantly reducing the contact resistance between the diffusion layer and the catalyst layer, and alleviating water blockage. The method of this invention has a simple, efficient, and uncomplicated process route, suitable for continuous batch production. All raw materials used are commercial products and require no further processing before use, making the preparation process easy to industrialize.

[0029] In some embodiments, the dispersant includes at least one of anionic surfactants, nonionic surfactants, polymeric dispersants, or fluorinated surfactants; the mass content of the dispersant in the microporous slurry is 0.1-1%. Preferably, the hydrophobic agent includes at least one of polytetrafluoroethylene emulsion, polyvinylidene fluoride emulsion, and polychlorotrifluoroethylene emulsion. Preferably, the conductive carbon material includes conductive carbon black; preferably, the conductive carbon black is one or a mixture of Vulcan XC72(R) and Acetylene Black, wherein the specific surface area of ​​Acetylene Black is 50-70 m². 2 / g, with a particle size of 40-50nm, and a specific surface area of ​​250m². 2 / g, with a particle size of approximately 30nm. In the method of this invention embodiment, dispersants, hydrophobic agents, and conductive carbon materials are preferably used, which is beneficial for further improving the performance of the microporous layer slurry.

[0030] In some embodiments, the conductive carbon nanofibers have an average fiber diameter of 100–300 nm, an average fiber length of 1–30 μm, and a specific surface area of ​​10–100 m². 2 / g, with a bulk density of 0.02~0.1g / cm³ 3 Preferably, the mass ratio of the conductive carbon nanofibers to the conductive carbon material is 1:2-4.5. In this embodiment of the invention, the preferred mass ratio of conductive carbon nanofibers to conductive carbon material is used. If too much conductive carbon nanofiber is added, it will cause cracking and peeling on the surface of the microporous layer, resulting in an uneven surface. If too little is added, it will not be able to fill the gaps between the carbon powder particles effectively, thus failing to achieve the purpose of a smooth and crack-free surface.

[0031] In some embodiments, step b, the mechanical stirring and dispersion method includes: stirring and dispersing at a first rotational speed of 500-2500 rpm for 20-40 minutes, followed by stirring and dispersing at a second rotational speed of 4000-9000 rpm for 200-300 minutes. In this embodiment of the invention, the preferred mechanical stirring speed and the method of gradually increasing the stirring speed are beneficial for better dispersion of the conductive carbon material, further improving the smoothness of the obtained microporous layer, thereby improving the performance of the microporous layer. If the stirring speed is too low, it will be detrimental to the uniform dispersion of the conductive carbon material; if the stirring speed is too high, it will damage the hydrophobic substances, failing to achieve a good hydrophobic effect, and also failing to achieve a good dispersion effect. Furthermore, in this embodiment of the invention, the preferred method of gradually increasing the stirring speed from low to high allows for segmented pre-uniform mixing of different materials, thereby promoting uniform mixing between different materials.

[0032] This invention also provides a microporous layer slurry, prepared using the method described in this invention. The microporous layer slurry of this invention is uniformly dispersed and consistently stable, enabling the preparation of a microporous layer with high smoothness and no cracks.

[0033] This invention also provides a microporous layer, which is prepared by doctor blade coating or screen printing using the microporous layer slurry of this invention. The microporous layer of this invention has a high surface smoothness, greatly reducing the contact resistance between the diffusion layer and the catalyst layer. The microporous layer is crack-free, alleviating water blockage. Furthermore, the viscosity of the microporous layer slurry of this invention is approximately 1000–6500 cp, making it suitable for preparing microporous layers by doctor blade coating or screen printing.

[0034] In some embodiments, the thickness of the microporous layer is 20–50 μm, and the total carbon loading is 1.7–2.5 mg / cm³. 2Total carbon loading refers to the total loading of conductive carbon materials and conductive carbon nanofibers. In this embodiment of the invention, the microporous layer thickness is uniform and controllable, capable of completely covering the rough carbon paper surface, and the surface is smooth and crack-free.

[0035] This invention also provides a gas diffusion layer, including a microporous layer as described in this embodiment. The gas diffusion layer of this invention possesses all the advantages of the microporous layer of this invention, which will not be elaborated further here.

[0036] The present invention will now be described in detail with reference to the embodiments and accompanying drawings.

[0037] Example 1

[0038] I. Hydrophobic treatment of carbon paper

[0039] Commercial carbon paper is hydrophobically treated by diluting the hydrophobic agent emulsion to 25 wt%, immersing the carbon paper in the hydrophobic agent solution for 2 minutes, and then taking it out and placing it in a forced-air drying oven for drying to obtain a carbon paper substrate support layer.

[0040] 2. Weigh 50g of 60% polytetrafluoroethylene (PTFE) emulsion and add it to 1300g of deionized water. Sonicate and stir for 30min to prepare a homogeneous mixed solution A. Add 5g of sulfonic acid-based fluorosurfactant to solution A and disperse and stir at low speed (1500 rpm) for 60min to form a homogeneous mixed solution B. Add 150g of conductive carbon black Vulcan XC72(R) to mixed solution B and disperse and stir at low speed (900 rpm) for 60min to form slurry C. Add 50g of conductive carbon nanofibers (average fiber diameter 150nm, average fiber length 15μm, specific surface area 30m²) to slurry C. 2 / g, with a bulk density of 0.06g / cm³ 3 The conductive carbon nanofibers and conductive carbon materials were mixed at a mass ratio of 1:3. The mixture was dispersed and stirred at a high speed of 2000 rpm for 30 minutes. Then, the stirring speed was increased and the mixture was stirred at a second stirring speed of 6500 rpm for 240 minutes to finally obtain a microporous slurry with a viscosity of 1800 cp.

[0041] III. Preparation of Gas Diffusion Layer

[0042] The microporous layer slurry was screen-printed onto commercially available carbon paper treated with hydrophobicity to form a microporous layer with a thickness of 45 μm. The layer was then dried in a forced-air drying oven at 60°C for 30 min and transferred to a box furnace for sintering at 350°C for 1 h to obtain a smooth, crack-free microporous gas diffusion layer.

[0043] IV. Single-cell electrical performance testing: Polarization curves were tested under high humidity conditions.

[0044] The gas diffusion layer prepared in this embodiment was used as the anode and cathode gas diffusion layers, and assembled with a standard CCM to form an MEA for testing. Test conditions were: battery temperature 80℃, hydrogen and air flow rates set to 0.3 / 0.7 L / M, excess coefficients of 1.5 / 2.0, back pressure of 100 kPa / 40 kPa, activation for 2 hours under a voltage mode of 0.1–0.3–0.5 V, and testing under 40% humidity. Test results are shown in [Figure / Reference]. Figure 1 The gas diffusion layer prepared in Example 1 exhibits superior mass transfer polarization in the concentration polarization region.

[0045] The scanning electron microscope image of the microporous gas diffusion layer prepared in this embodiment is shown below. Figure 2 It can be seen that there are no cracks or fissures on the surface of the microporous layer of the gas diffusion layer.

[0046] The physical property test data of the gas diffusion layer microporous layer prepared in this embodiment are shown in Table 1.

[0047] Example 2

[0048] The method is the same as in Example 1, except that the amount of conductive carbon nanofibers added is 75g, that is, the mass ratio of conductive carbon nanofibers to conductive carbon material is 1:2, and a microporous layer slurry with a viscosity of 950cp is obtained.

[0049] The physical property test data of the gas diffusion layer microporous layer prepared in this embodiment are shown in Table 1.

[0050] Example 3

[0051] The method is the same as in Example 1, except that the amount of conductive carbon nanofibers added is 33g, that is, the mass ratio of conductive carbon nanofibers to conductive carbon material is 1:4.5, and a microporous layer slurry with a viscosity of 2440cp is obtained.

[0052] The physical property test data of the gas diffusion layer microporous layer prepared in this embodiment are shown in Table 1.

[0053] Example 4

[0054] The method is the same as in Example 1, except that after adding conductive carbon nanofibers, the first stirring speed is 900 rpm, and a microporous slurry with a viscosity of 6500 cp is obtained.

[0055] The physical property test data of the gas diffusion layer microporous layer prepared in this embodiment are shown in Table 1.

[0056] Example 5

[0057] The method is the same as in Example 1, except that after adding conductive carbon nanofibers, the second stirring speed is 9000 rpm, and a microporous slurry with a viscosity of 3010 cp is obtained.

[0058] The physical property test data of the gas diffusion layer microporous layer prepared in this embodiment are shown in Table 1.

[0059] Example 6

[0060] Similar to the method in Implementation 1, except that after adding conductive carbon nanofibers, the same stirring speed is used for stirring and dispersion, that is, the first and second stirring speeds are both 2000 rpm, to obtain a microporous layer slurry with a viscosity of 1020 cp.

[0061] The physical property test data of the gas diffusion layer microporous layer prepared in this embodiment are shown in Table 1.

[0062] Comparative Example 1

[0063] The method is the same as in Example 1, except that conductive carbon nanofibers are not added. After adding conductive carbon black, high-speed dispersion is carried out using the same mechanical stirring dispersion method as in Example 1, that is, dispersion and stirring at a stirring speed of 900 rpm for 60 min, stirring and dispersing at a first stirring speed of 2000 rpm for 30 min, and then stirring and dispersing at a second stirring speed of 6500 rpm for 240 min to obtain a microporous layer slurry with a viscosity of 2600 cp.

[0064] The membrane electrode was fabricated using the same method as in Example 1, and the single-cell electrical performance was tested. The test results are shown in [Figure 1]. Figure 1 In contrast, the gas diffusion layer prepared in Comparative Example 1 exhibits a rapid voltage drop and performance degradation in the concentration polarization region.

[0065] The scanning electron microscope image of the microporous gas diffusion layer prepared in Comparative Example 1 is shown below. Figure 3 Numerous cracks exist on the surface of the microporous layer of the gas diffusion layer.

[0066] The physical property test data of the gas diffusion layer microporous layer prepared in Comparative Example 1 are shown in Table 1.

[0067] Comparative Example 2

[0068] The method is the same as in Example 1, except that the amount of conductive carbon nanofibers added is 150g, that is, the mass ratio of conductive carbon nanofibers to conductive carbon material is 1:1, and a microporous layer slurry with a viscosity of 230cp is obtained.

[0069] The physical property test data of the gas diffusion layer microporous layer prepared in Comparative Example 2 are shown in Table 1.

[0070] Comparative Example 3

[0071] The method is the same as in Example 1, except that the timing of the addition of conductive carbon nanofibers is different. Conductive carbon nanofibers are added at the same time as conductive carbon black. High-speed dispersion is carried out using the same mechanical stirring and dispersion method as in Example 1, that is, dispersion and stirring at a stirring speed of 900 rpm for 60 min, stirring and dispersing at a first stirring speed of 2000 rpm for 30 min, and then stirring and dispersing at a second stirring speed of 6500 rpm for 240 min to obtain a microporous layer slurry with a viscosity of 3600 cp.

[0072] The physical property test data of the gas diffusion layer microporous layer prepared in Comparative Example 3 are shown in Table 1.

[0073] Comparative Example 4

[0074] The method is the same as in Example 1, except that the order of adding conductive carbon black and conductive carbon nanofibers is different. First, 50g of conductive carbon nanofibers are added to the mixed solution B and dispersed at low speed for 60min to form slurry C. Then, 150g of conductive carbon black Vulcan XC72(R) is added to slurry C and stirred and dispersed at the first stirring speed for 30min. Then, the slurry is stirred and dispersed at the second stirring speed for 240min to obtain a microporous layer slurry with a viscosity of 1600cp.

[0075] The physical property test data of the gas diffusion layer microporous layer prepared in Comparative Example 4 are shown in Table 1.

[0076] Comparative Example 5

[0077] The method is the same as in Example 1, except that conductive carbon nanofibers are replaced with carbon nanotubes, that is, 50g of carbon nanotubes (average specific surface area 260m²) are added to slurry C. 2 A microporous slurry with a viscosity of 610 cp was prepared by using a method with an average tube diameter of 10 nm and a tube diameter of 1 g.

[0078] The physical property test data of the gas diffusion layer microporous layer prepared in Comparative Example 5 are shown in Table 1.

[0079] The gas diffusion layers prepared in Examples 1-6 and Comparative Examples 1-5 were subjected to physical property tests, and the results are shown in Table 1. The air permeability value measured by the air permeability tester represents the time required for a certain flow rate (100cc) of gas to pass through. A longer time indicates poorer air permeability, while a shorter time indicates better air permeability.

[0080] Table 1

[0081]

[0082] As shown in Table 1, the gas diffusion layers prepared in Examples 1-6 of this application exhibit low contact resistance, high porosity, excellent air permeability, and good hydrophobicity, demonstrating superior overall physical properties. In Comparative Examples 1-5, the uneven mixing and dispersion of the prepared slurries resulted in the inability to achieve excellent overall performance. Comparative Example 1, lacking conductive carbon nanofibers, resulted in an uneven and cracked surface of the microporous layer, leading to a contact resistance as high as 13.9 mΩ*cm. 2 In Comparative Example 2, the addition of excessive conductive carbon nanofibers resulted in a very low viscosity of the microporous layer slurry, only 230 cp, leading to poor slurry condition and a significant decrease in the porosity and permeability of the resulting gas diffusion layer. In Comparative Examples 3 and 4, the order of addition of conductive carbon nanofibers was changed. Whether the conductive carbon nanofibers and conductive carbon black were added simultaneously or after the conductive carbon black, the conductive carbon black and conductive carbon nanofibers could not be effectively dispersed. This resulted in a significant decrease in the hydrophobic properties of the resulting gas diffusion layer, and a marked decrease in both permeability and porosity. This is because carbon nanofibers are difficult to disperse uniformly in aqueous solvents and tend to agglomerate. By adding carbon nanofibers later, the carbon nanofibers can be evenly dispersed in the already relatively uniformly mixed conductive carbon black solution, forming a good conductive network between the already relatively uniformly mixed conductive carbon black particles, creating point-line contact with the conductive carbon black, and also ensuring uniform mixing between the conductive carbon black and the hydrophobic agent. In Comparative Example 5, carbon nanotubes were used instead of conductive carbon nanofibers. The viscosity of the resulting microporous layer slurry was only 610 cp. The contact resistance was significantly lower than that in Example 1, and the porosity, air permeability, and hydrophobic properties also decreased.

[0083] In this invention, the terms "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., refer to a specific feature, structure, material, or characteristic described in connection with that embodiment or example, which is included in at least one embodiment or example of the invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0084] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention.

Claims

1. A method for preparing a microporous layer slurry for a gas diffusion layer in a proton exchange membrane fuel cell, characterized in that, Includes the following steps: a. Add the dispersant and the hydrophobic agent to deionized water and stir and disperse, then add the conductive carbon material, stir and disperse to obtain the first slurry, wherein the conductive carbon material includes conductive carbon black; b. Add conductive carbon nanofibers to the first slurry obtained in step a, and mechanically stir and disperse to obtain a microporous layer slurry, wherein the mass ratio of the conductive carbon nanofibers to the conductive carbon material is 1:2-4.5, and the mechanical stirring and dispersion method includes: stirring and dispersing at a first speed of 2000~2500 rpm for 20-40 minutes, and then stirring and dispersing at a second speed of 4000~6500 rpm for 200-300 minutes.

2. The method for preparing the microporous layer slurry according to claim 1, characterized in that, The dispersant includes at least one of anionic surfactants, nonionic surfactants, polymeric dispersants, or fluorinated surfactants; the mass content of the dispersant in the microporous slurry is 0.1-1%.

3. The method for preparing the microporous layer slurry according to claim 1, characterized in that, The water-repellent agent includes at least one of polytetrafluoroethylene emulsion, polyvinylidene fluoride emulsion, and polychlorotrifluoroethylene emulsion.

4. The method for preparing the microporous layer slurry according to claim 1, characterized in that, The conductive carbon nanofibers have an average fiber diameter of 100–300 nm, an average fiber length of 1–30 μm, and a specific surface area of ​​10–100 m². 2 / g, with a bulk density of 0.02~0.1 g / cm³. 3 .

5. A microporous layer slurry, characterized in that, It is prepared by any one of claims 1-4.

6. A microporous layer, characterized in that, The microporous layer slurry as described in claim 5 is prepared by doctor blade coating or screen printing coating.

7. The microporous layer according to claim 6, characterized in that, The microporous layer has a thickness of 20–50 μm and a total carbon loading of 1.7–2.5 mg / cm³. 2 .

8. A gas diffusion layer, characterized in that, Includes the microporous layer as described in claim 7.

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