Gas diffusion layer and method for manufacturing the same, membrane electrode assembly

Abstract

The application relates to a gas diffusion layer and a preparation method thereof and a membrane electrode assembly, and belongs to the technical field of fuel cells. The gas diffusion layer comprises a first fiber material and a second fiber material, the first fiber material and the second fiber material are assembled in a layer-by-layer mode in an alternating distribution sequence; wherein the porosity of the first fiber material is 55-60%; the porosity of the second fiber material is 65-70%; and the total layer number of the gas diffusion layer is at least 6. The gas diffusion layer can quickly drain water under high humidity conditions and has strong moisture retention performance.

Description

Technical Field

[0001] This application relates to the field of fuel cell technology, and in particular to a gas diffusion layer and its preparation method, and a membrane electrode assembly. Background Technology

[0002] The core components of a proton exchange membrane fuel cell (PEMFC) include a proton exchange membrane (electrolyte), a catalyst layer, a gas diffusion layer, and bipolar plates. Among these, the gas diffusion layer plays a crucial role in the fuel cell, its main functions being to support the catalyst layer, stabilize the electrode structure, provide gas transport channels, and improve water management.

[0003] Traditional gas diffusion layer substrate materials include carbon fiber paper, carbon fiber woven fabric, carbon fiber nonwoven materials, and carbon black paper, but these traditional materials are prone to water accumulation under high humidity conditions and have difficulty in drainage. Summary of the Invention

[0004] To address the shortcomings of existing technologies, the objectives of this application include providing a gas diffusion layer and its preparation method, as well as a membrane electrode assembly, to achieve both rapid drainage and strong moisture retention under high humidity conditions.

[0005] In a first aspect, embodiments of this application provide a gas diffusion layer comprising: a first fiber material and a second fiber material, wherein the first fiber material and the second fiber material are stacked and assembled in an alternating distribution order; wherein the porosity of the first fiber material is 55-60%; the porosity of the second fiber material is 65-70%; and the total number of layers of the gas diffusion layer is at least 6.

[0006] This application employs a multilayer structure composed of multiple first and second fiber materials arranged in an alternating sequence. This structure provides different porosity regions, with low-porosity layers (first fiber material layers) and high-porosity layers (second fiber material layers) alternating. The high-porosity layers possess rapid drainage capabilities, while the low-porosity layers exhibit water retention and self-humidification effects. This design enables the gas diffusion layer to both rapidly drain water and maintain appropriate humidity under high humidity conditions, thereby improving the performance, stability, and lifespan of the fuel cell system.

[0007] In some embodiments of this application, the total number of gas diffusion layers is 6-12.

[0008] Within the range of the number of gas diffusion layers mentioned above, it is beneficial to achieve the alternating effect of low-porosity layers and high-porosity layers. At the same time, the thickness of the gas diffusion layer is within a suitable range, which is beneficial to reduce resistance.

[0009] Secondly, embodiments of this application provide a method for preparing the aforementioned gas diffusion layer, comprising: stacking and assembling multiple first fiber materials and second fiber materials in an alternating distribution order, and then performing a molding process to obtain a gas diffusion layer; wherein, the preparation of the first fiber material comprises: melting a precursor material to form fibers, forming the fibers into a first fabric material with a first porosity, and then sequentially subjecting the first fabric material to a first carbonization treatment and a first surface treatment to obtain the first fiber material; the preparation of the second fiber material comprises: melting a precursor material to form fibers, forming the fibers into a second fabric material with a second porosity, and then sequentially subjecting the second fabric material to a second carbonization treatment and a second surface treatment to obtain the second fiber material.

[0010] The preparation method provided in this application can achieve: 1. Continuous production of carbon paper with high production efficiency; 2. Adjustable porosity and pore size of each layer, which can be designed according to requirements; 3. Applicable to the preparation of gas diffusion layers in water electrolysis.

[0011] In some embodiments of this application, the precursor material includes at least one of polyacrylonitrile, rayon, and petroleum bitumen.

[0012] In some embodiments of this application, the first porosity is 40-50%, and the second porosity is 50-60%.

[0013] By controlling the porosity of the first and second fabric materials within the aforementioned range, gas transmission and subsequent molding processes can be improved.

[0014] In some embodiments of this application, the conditions for the first carbonization treatment and the second carbonization treatment are the same, including: subjecting the first fabric material and / or the second fabric material to a first heat treatment under aerobic conditions, and subjecting the first fabric material and / or the second fabric material that has undergone the first heat treatment to a second heat treatment under anaerobic conditions, to obtain the first carbonized fiber material and / or the second carbonized fiber material.

[0015] Carbonization allows carbon atoms in the first and / or second fabric materials to rearrange and form a stable carbon structure. At high temperatures, carbon atoms can recombine and rearrange to form a more ordered lattice structure, which helps improve the mechanical properties and hydrophobicity of the resulting carbon fiber materials.

[0016] In this application, the first heat treatment is carried out under aerobic conditions, allowing the carbon atoms in the fabric material to react with oxygen atoms in the air. This increases the oxygen content of the carbon atoms, providing sufficient oxygen for the subsequent carbonization process. Sufficient oxygen accelerates the subsequent carbonization process and helps form a stable carbon structure. The second heat treatment is carried out under anaerobic conditions to allow the carbon atoms in the fabric material to rearrange and form a stable carbon structure. At high temperatures, carbon atoms can recombine and rearrange to form a more ordered lattice structure, which helps improve the mechanical properties and hydrophobicity of the carbon fiber material.

[0017] In some embodiments of this application, the conditions for the first heat treatment include: a heat treatment temperature of 200-300°C and a heat treatment time of 30-120 minutes. By controlling the temperature and time of the first heat treatment within the above range, sufficient oxygen can be provided for the subsequent carbonization process, and moisture and volatile substances can be removed, thereby improving the thermal stability of the fabric material.

[0018] In some embodiments of this application, the conditions for the second heat treatment include: a heat treatment temperature of 1500-3000℃ and a heat treatment time of 5-20 minutes. By controlling the temperature and time of the second heat treatment within the above range, the carbon atoms of the carbon fiber material can be rearranged to form a stable carbon structure, thereby improving the hydrophobicity, mechanical strength, and thermal stability of the material.

[0019] In some embodiments of this application, the first surface treatment includes: dissolving a first resin in an organic solvent to obtain a first resin solution; immersing a first carbon fiber material in the first resin solution to allow the first resin solution to adsorb onto the surface of the first carbon fiber material and coat the first carbon fiber material; removing droplets of the first resin solution from the surface of the first carbon fiber material so that the first resin solution only coats the surface of the first carbon fiber material; and then drying the first carbon fiber material.

[0020] In some embodiments of this application, the second surface treatment includes: dissolving the second resin in an organic solvent to obtain a second resin solution; immersing the second carbon fiber material in the second resin solution so that the second resin solution is adsorbed onto the surface of the second carbon fiber material and coats the second carbon fiber material; removing the droplets of the second resin solution from the surface of the second carbon fiber material so that the second resin solution only coats the surface of the second carbon fiber material; and then drying the second carbon fiber material.

[0021] In this application, surface treatment can improve the wettability and adhesion of the fibrous material surface, enabling it to interact better with other materials or liquids. For example, surface treatment can increase the contact area between the gas diffusion layer and the electrolyte or catalyst, thereby improving the efficiency of energy devices such as proton exchange membrane fuel cells.

[0022] In some embodiments of this application, the surface energy of the first resin is 25-30 dynes / cm, and the surface energy of the second resin is 18-22 dynes / cm. The first resin is a low hydrophobic resin, and the second resin is a high hydrophobic resin.

[0023] In some embodiments of this application, the first resin includes at least one of polyvinylidene fluoride, polyvinyl fluoride, polypropylene, and polyethylene, and the second resin includes polytetrafluoroethylene and / or polytrifluoroethylene.

[0024] In some embodiments of this application, the mass ratio of the first resin to the organic solvent is (1-5):(10-20); the mass ratio of the second resin to the organic solvent is (2-8):(15-30). By controlling the mass ratio of the first resin to the organic solvent and the second resin to the organic solvent within the above ranges, uniform coating and drying of the resin solution on the surface of the carbon fiber material can be achieved, providing good adhesion and control of the coating layer thickness; this helps to improve the performance and surface properties of the carbon fiber material.

[0025] In some embodiments of this application, the organic solvent includes at least one of ethanol, n-propanol, and acetone.

[0026] In some embodiments of this application, the drying conditions include a drying temperature of 50-100°C and a drying time of 5-10 minutes. Within the above-mentioned drying temperature and time range, the carbonized fiber material can be dried quickly without causing shape changes or structural damage; it can also remove organic solvents from the carbonized fiber material.

[0027] Thirdly, embodiments of this application provide a membrane electrode assembly including any of the aforementioned gas diffusion layers. Attached Figure Description

[0028] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of this application and should not be regarded as a limitation of the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0029] Figure 1 A schematic diagram of the gas diffusion layer provided in this application under different states;

[0030] Figure 2 This is a schematic diagram of the process for controlling the porosity of fabric materials in this application. Detailed Implementation

[0031] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions in the embodiments of this application will be clearly and completely described below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased commercially.

[0032] This application provides a gas diffusion layer, the preparation method of which includes the following steps:

[0033] I. Preparation of the First and Second Fiber Materials

[0034] Step S101. Melt the precursor material to transform it into a fibrous form. Wash and stretch the fibers to obtain the desired strength and dimensions.

[0035] In this application, the precursor materials include, but are not limited to, at least one of polyacrylonitrile, rayon, and petroleum bitumen.

[0036] Step S102. The fibers obtained in step S101 are processed into fabric materials through a textile process. By adjusting the textile process parameters, a first fabric material with a first porosity and a second fabric material with a second porosity are obtained. The first porosity is 40-50%, and the second porosity is 50-60%. After adjusting the porosity to 40-50%, the pore size of the first fabric material is 5-6 μm; after adjusting the porosity to 50-60%, the pore size of the second fabric material is 8-9 μm.

[0037] Please refer to the schematic diagram of the porosity control process for the first and second fabric materials in this application. Figure 2 , Figure 2 The polymer melt in the middle corresponds to the precursor material of this application, and the receiving device corresponds to the first or second fabric material of this application. Figure 2 As can be seen, this application primarily controls the porosity of the first and second fabric materials by adjusting the speed of the hot airflow. Higher airflow speeds create smaller pores between fibers, resulting in lower porosity. Conversely, lower airflow speeds create larger pores, increasing porosity. Therefore, to achieve a porosity of 40-50% for the first fabric material, the hot airflow speed needs to be adjusted to the range of 400-450 m / s. This results in smaller pores in the fiber structure, leading to a lower porosity. Similarly, to achieve a porosity of 50-60% for the second fabric material, the hot airflow speed needs to be adjusted to the range of 300-350 m / s. This results in larger pores in the fiber structure, leading to a higher porosity.

[0038] As an example, when preparing the first fabric material, the hot air flow velocity can be adjusted to include, but is not limited to, 400 m / s, 405 m / s, 410 m / s, 415 m / s, 420 m / s, 425 m / s, 430 m / s, 435 m / s, 440 m / s, 445 m / s, and 450 m / s. As long as the porosity of the first fabric material can reach 40-50%, it can be adjusted according to the specific working conditions, and this application does not limit it.

[0039] As an example, when preparing the second fabric material, the hot air flow velocity can be adjusted to include, but is not limited to, 300 m / s, 305 m / s, 310 m / s, 315 m / s, 320 m / s, 325 m / s, 330 m / s, 335 m / s, 340 m / s, 345 m / s, and 350 m / s. As long as the porosity of the second fabric material can reach 50-60%, it can be adjusted according to the specific working conditions, and this application does not limit it.

[0040] The porosity of polymer fabrics can also be controlled by adjusting other textile process parameters, such as textile density, fabric structure and fabric thickness, but this application does not limit this.

[0041] Step S103. The first and / or second fabric materials obtained in step S102 are subjected to a first carbonization treatment and a second carbonization treatment, wherein the conditions for the first and second carbonization treatments are the same, including: subjecting the first and / or second fabric materials to a first heat treatment under aerobic conditions (e.g., in air), and subjecting the first and / or second fabric materials after the first heat treatment to a second heat treatment under anaerobic conditions, to obtain the first and / or second carbonized fiber materials. During the second heat treatment, in order to prevent oxygen from entering the carbonization furnace, it is necessary to maintain the airtightness of the carbonization process, especially at the inlet and outlet during carbonization.

[0042] In this application, the temperature of the first heat treatment is 200-300℃, and the heat treatment time is 30-120 min. The temperature of the second heat treatment is 1500-3000℃, and the heat treatment time is 5-20 min.

[0043] The first heat treatment is carried out under aerobic conditions. By heat-treating the first and / or second fabric materials at 200-300℃ for 30-120 minutes, the carbon atoms in the first and / or second fabric materials can react with oxygen atoms in the air. This increases the oxygen content of the carbon atoms, providing sufficient oxygen for the subsequent carbonization process. Sufficient oxygen is beneficial for accelerating the subsequent carbonization process and helps to form a stable carbon structure. On the other hand, the presence of moisture and volatile substances may cause the formation of bubbles and pores at high temperatures, thus affecting the density and mechanical properties of the material. The first heat treatment can effectively remove these harmful substances and improve the thermal stability of the first and / or second fabric materials.

[0044] The second heat treatment is carried out under oxygen-free conditions. By heat-treating the first and / or second fabric materials at 1500-3000℃ for 5-20 minutes, the carbon atoms in the first and / or second fabric materials can rearrange and form a stable carbon structure. At high temperatures, carbon atoms can recombine and rearrange to form a more ordered lattice structure, which helps to improve the mechanical properties and hydrophobicity of carbon fiber materials. The hydrophobicity of carbon fiber materials is determined by their surface microstructure and chemical composition. At high temperatures, the rearrangement of carbon atoms to form an ordered carbon structure results in a denser and smoother surface microstructure, thus enhancing the hydrophobicity of the material. Simultaneously, at high temperatures, the ordered and compact carbon structure reduces the grain size and increases the crystallinity of the material, thereby improving its strength, stiffness, and wear resistance, making it more suitable for use in high-strength and high-temperature environments. Furthermore, at high temperatures, carbon atoms react with surrounding oxygen, nitrogen, and other impurity atoms to form more stable carbon-carbon bonds. This increases the thermal stability and oxidation resistance of carbon fiber materials, extending their service life.

[0045] Step S104. The first carbonized fiber material and the second carbonized fiber material obtained in step S103 are subjected to a first surface treatment and a second surface treatment, respectively; wherein,

[0046] The first surface treatment includes the following steps: dissolving a first resin in an organic solvent to obtain a first resin solution; immersing a first carbon fiber material in the first resin solution so that the first resin solution is adsorbed onto the surface of the first carbon fiber material and coats the first carbon fiber material; removing droplets of the first resin solution from the surface of the first carbon fiber material so that the first resin solution only coats the surface of the first carbon fiber material; and then drying the first carbon fiber material.

[0047] The second surface treatment includes the following steps: dissolving the second resin in an organic solvent to obtain a second resin solution; immersing the second carbon fiber material in the second resin solution so that the second resin solution is adsorbed onto the surface of the second carbon fiber material and coats the second carbon fiber material; removing the droplets of second resin solution from the surface of the second carbon fiber material so that the second resin solution only coats the surface of the second carbon fiber material; and then drying the second carbon fiber material.

[0048] In this application, resin droplets remaining on the surface of the first and / or second carbon fiber materials can be removed by appropriate processing methods, such as vibration or mechanical scraping, so that the resin only coats the surface of the first and / or second carbon fiber materials without forming clumps. Drying the surface-treated first and / or second carbon fiber materials allows the resin to form a uniform coating on the carbon fibers and fully cures the resin. In summary, surface treatment of the first and / or second carbon fiber materials can improve their surface properties and characteristics, and increase their bonding ability with other materials.

[0049] The first resin has a surface energy of 25-30 dynes / cm and is a low hydrophobic resin; the second resin has a surface energy of 18-22 dynes / cm and is a high hydrophobic resin. In the embodiments of this application, the first resin includes, but is not limited to, at least one of polyvinylidene fluoride, polyvinyl fluoride, polypropylene, and polyethylene, and the second resin includes, but is not limited to, polytetrafluoroethylene and / or polytrifluoroethylene.

[0050] In this application, the mass ratio of the first resin to the organic solvent is (1-5):(10-20); the mass ratio of the second resin to the organic solvent is (2-8):(15-30). The organic solvent includes, but is not limited to, at least one of ethanol, n-propanol, and acetone.

[0051] By controlling the mass ratio of the first resin to the organic solvent and the second resin to the organic solvent within the aforementioned range, the resin can be uniformly wetted and adsorbed onto the surface of the carbon fiber material, forming a uniform coating layer. The concentration of the resin solution can also be controlled to provide good adhesion, ensuring a good bond and adhesion between the resin and the carbon fiber material, thus contributing to improved strength and durability of the carbon fiber material.

[0052] In this application, the drying temperature is 50-100℃, and the drying time is 5-10 minutes. The purpose of drying is to remove organic solvents from the carbonized fiber material. Within the above-mentioned drying temperature and time range, the carbonized fiber material can be dried quickly without causing shape changes or structural damage.

[0053] In this application, a fabric material with a target porosity of 40-50% undergoes carbonization treatment, resulting in a porosity of 55-60%, and is designated as the first fiber material. A fabric material with a target porosity of 50-60% undergoes carbonization treatment, resulting in a porosity of 65-70%, and is designated as the second fiber material. After carbonization treatment, the first fiber material is adjusted to achieve a porosity of 55-60%, and its pore size is 8-9 μm. The second fiber material is adjusted to achieve a porosity of 65-70%, and its pore size is 10-12 μm.

[0054] II. Preparation of Gas Diffusion Layer

[0055] Multiple prepared first and second fiber materials are stacked and assembled in an alternating distribution to form a multilayer structure. This multilayer structure is then subjected to composite hot pressing at a temperature of 250-350℃ and a pressure of 0.2-0.3 MPa, resulting in a strong bond between the layers and a gas diffusion layer with alternating low and high porosity. This gas diffusion layer has at least six layers, comprising three layers of first fiber material and three layers of second fiber material, with the first and second fiber materials alternating in distribution.

[0056] As an example, the total number of gas diffusion layers is 6-12. Too few layers will result in the inability of alternating effects to function properly, leading to wasted functionality; too many layers will increase the thickness of the gas diffusion layer (GDL), increase the resistance, and increase the volume of the fuel cell stack. Moreover, when there are too many layers and the original thickness must be maintained, the thickness of each layer must be reduced, which will greatly increase the difficulty of fabrication.

[0057] As an example, the total number of gas diffusion layers provided in this application includes, but is not limited to, 6, 7, 8, 9, 10, 11, and 12 layers. This application does not limit the number of layers.

[0058] In this application, hot pressing can be performed with reference to existing technology. As an example, in hot pressing, the hot pressing temperature includes, but is not limited to, 250°C, 270°C, 290°C, 300°C, 310°C, 330°C, and 350°C; the pressure includes, but is not limited to, 0.2MPa, 0.25MPa, and 0.3MPa; this application does not limit these.

[0059] In operation, the low-porosity layer (first fiber material layer) is positioned close to the catalyst layer in the proton exchange membrane fuel cell (PEMFC). The surface of the first fiber material near the catalyst layer needs to be coated with a microporous layer (MPL). This microporous layer, typically composed of carbon black and a hydrophobic agent, is 10-100 μm thick and serves to improve the substrate's pore structure, reduce the contact resistance between the substrate and the catalyst layer, guide the reactant gas through the diffusion layer and distribute it uniformly to the catalyst surface, and remove water generated during the reaction to prevent flooding. The high-porosity layer (second fiber material layer) is positioned close to the bipolar plates in the PEMFC.

[0060] Figure 1 This is a schematic diagram of the gas diffusion layer provided in this application under different states, from Figure 1 As can be seen, under normal (dry) conditions, both the low-porosity layer (first fiber material layer) and the high-porosity layer (second fiber material layer) can smoothly carry out gas transmission. After the humidity increases, the low-porosity layer will first have liquid condensation due to capillary action, causing the gas flow rate to slow down, while the high-porosity layer will have a faster flow rate. The faster flow rate can drive the evaporation of water from the low-porosity layer. When the machine is turned off after use, i.e. in the off state, some water will remain due to the capillary action of the low-porosity layer, which plays a role in self-humidification.

[0061] This application employs a multilayer structure composed of multiple first and second fiber materials arranged in an alternating sequence. This structure provides different porosity regions, with low-porosity layers (first fiber material layers) and high-porosity layers (second fiber material layers) arranged alternately. The low-porosity layers possess strong water retention capabilities, adsorbing and retaining appropriate amounts of moisture. When the fuel cell system operates under low humidity conditions, the low-porosity layers can increase the moisture content by adsorbing water vapor from the introduced gas, providing the necessary humidity conditions and thus improving fuel cell performance. Conversely, when humidity is high, the low-porosity layers absorb excess moisture, allowing the high-porosity layers to maintain good gas flow and preventing flooding. Simultaneously, at the same humidity, the low-porosity layers are more prone to generating liquid water, which is adsorbed into the fiber materials through capillary action. This helps reduce the accumulation of liquid water in the fuel cell, lowering the risk of stack flooding and reducing corrosion damage to the catalyst layer and bipolar plates. The high-porosity layers act as rapid drainage layers within the gas diffusion layer. When excessive liquid water is generated in a fuel cell system, the high porosity layer, with its high pore volume and permeability, ensures high-speed gas transport, rapidly expelling the water through the gas flow and preventing water accumulation and blockage of gas channels. This helps maintain the normal operation of the fuel cell and reduces the interference of liquid water on the electrochemical reaction.

[0062] Therefore, by designing this alternating multilayer structure, the gas diffusion layer can utilize the capillary action and water retention properties of the low-porosity layer to achieve rapid transport and evaporation of liquid water; simultaneously, the high-porosity layer can quickly expel gas. This design allows the gas diffusion layer to possess both rapid drainage characteristics and the ability to maintain appropriate humidity under humid conditions, exhibiting strong moisture retention performance.

[0063] The features and performance of this application will be further described in detail below with reference to the embodiments.

[0064] Example 1

[0065] This embodiment provides a gas diffusion layer, the preparation method of which includes the following steps:

[0066] (1) Preparation of the first fiber material and the second fiber material

[0067] The precursor material is melt-treated to form fibers, which are then washed and stretched. These fibers are then used to create a first fabric material with a porosity of 45-50% and a second fabric material with a porosity of 55-60%. The first and second fabric materials are first heat-treated in air at 280°C for 1.5 hours; then, under anaerobic conditions, they are heat-treated at 2600°C for 15 minutes. The first fabric material, after two heat treatments, is then immersed in a first resin solution (acetic acid 90% by mass, polypropylene 10% by mass, i.e., acetic acid / polypropylene = 90 / 10), and the second fabric material is immersed in a second resin solution (ethanol 85% by mass, polytetrafluoroethylene 15% by mass, i.e., ethanol / polytetrafluoroethylene = 85 / 15), allowing the resin solution to adsorb onto and encapsulate the carbon fiber material. The resin solution droplets on the surface of the carbon fiber material are removed, leaving only the surface coated with resin solution. Finally, the two carbon fiber materials are dried at 80°C for 10 minutes to obtain the first and second fiber materials. The porosity of the first fiber material is 56%, and the porosity of the second fiber material is 68%.

[0068] (2) Preparation of gas diffusion layer

[0069] The multiple first fiber materials and second fiber materials prepared in step (1) above are stacked and assembled in an alternating distribution order, wherein the first fiber material and the second fiber material each have 4 layers. Then, the assembled 8-layer material structure is composite hot-pressed to obtain a gas diffusion layer with a total of 8 layers.

[0070] Example 2

[0071] This embodiment is basically the same as embodiment 1, except that: in step (1), the first fabric material and the second fabric material are not subjected to heat treatment under oxygen conditions, that is, the step of heat treatment at 280°C for 1.5h in air is not performed; only the first fabric material and the second fabric material are heat treated at 2600°C for 15min under oxygen-free conditions.

[0072] (1) Preparation of the first fiber material and the second fiber material

[0073] The precursor material is melt-treated to form fibers, which are then washed and stretched. These fibers are then used to create a first fabric material with a porosity of 45-50% and a second fabric material with a porosity of 55-60%. The first and second fabric materials are heat-treated at 2600℃ for 15 minutes under anaerobic conditions. The first fabric material, after two heat treatments, is then immersed in a first resin solution (acetic acid 90% by mass, polypropylene 10% by mass, i.e., acetic acid / polypropylene = 90 / 10), and the second fabric material is immersed in a second resin solution (ethanol 85% by mass, polytetrafluoroethylene 15% by mass, i.e., ethanol / polytetrafluoroethylene = 85 / 15). This allows the resin solution to adsorb onto and encapsulate the carbon fiber material. The resin solution droplets on the surface of the carbon fiber material are removed, leaving only the surface coated with the resin solution. Finally, the two carbon fiber materials are dried at 80℃ for 10 minutes to obtain the first and second fiber materials.

[0074] Example 3

[0075] This embodiment is basically the same as Embodiment 1, except that the heat treatment at 2600℃ for 15 minutes is changed to heat treatment at 3500℃ for 15 minutes.

[0076] Example 4

[0077] This embodiment is basically the same as Embodiment 1, except that the heat treatment at 2600℃ for 15 minutes is changed to heat treatment at 1000℃ for 15 minutes.

[0078] Example 5

[0079] This embodiment is basically the same as Embodiment 1, except that: acetic acid, ethanol, polypropylene (first resin) and polytetrafluoroethylene (second resin) are mixed and dissolved in a mass ratio of 40 / 40 / 10 / 10 to obtain a mixed resin solution. Then, the first fabric material and the second fabric material are respectively immersed in the mixed resin solution, so that the resin solution is adsorbed on the surface of the carbon fiber material and wraps the carbon fiber material.

[0080] Example 6

[0081] This embodiment is basically the same as Embodiment 1, except that the resin solution droplets on the surface of the carbonized fiber material are not removed, and the subsequent drying steps are carried out directly.

[0082] Example 7

[0083] This embodiment is basically the same as Embodiment 1, except that: the first fabric material after two heat treatments is immersed in the first resin solution (ethanol accounts for 85% by mass and polytetrafluoroethylene accounts for 15% by mass, i.e., ethanol / polytetrafluoroethylene = 85 / 15), and the second fabric material is immersed in the second resin solution (acetic acid accounts for 90% by mass and polypropylene accounts for 10% by mass, i.e., acetic acid / polypropylene = 90 / 10).

[0084] Comparative Example 1

[0085] This comparative example is basically the same as Example 1, except that a first fabric material with a porosity of 32% (30-35%) is selected.

[0086] Comparative Example 2

[0087] This comparative example is basically the same as Example 1, except that a first fabric material with a porosity of 57% (55-60%) is selected.

[0088] Comparative Example 3

[0089] This comparative example is basically the same as Example 1, except that a second fabric material with a porosity of 43% (40-45%) is selected.

[0090] Comparative Example 4

[0091] This comparative example is basically the same as Example 1, except that a second fabric material with a porosity of 73% (70-75%) is selected.

[0092] Please refer to Table 1 for some parameters of the embodiments and comparative examples of this application.

[0093] Table 1

[0094]

[0095]

[0096] Table 1 (continued)

[0097]

[0098]

[0099] Test case

[0100] This test example uses the gas diffusion layers provided in Examples 1-7 and Comparative Examples 1-4 to perform performance tests. The test items include thickness, tensile strength, areal density, volume resistivity, gas flux, and contact angle. The determination methods for the above items are in accordance with GB / T 20042.7-2014.

[0101] The measurement results of the above items are shown in Table 2.

[0102] Table 2

[0103]

[0104]

[0105] The contact angle refers to the contact angle between a liquid and the surface of a solid material, and it is an important parameter for measuring the wettability of the liquid on the material surface. By measuring the contact angle, the degree of bonding between water and the material surface can be obtained. The larger the contact angle, the easier it is for water to detach from the material surface. In Table 2, contact angle 1 and contact angle 2 correspond to the first fiber material and the second fiber material, respectively.

[0106] As can be seen from Table 2, by comparing Example 1 and Example 2, the carbon cloth surface can be partially oxidized by first undergoing heat treatment at 280℃ (first heat treatment) and then carbonization, which results in better strength of the carbonized gas diffusion layer; the carbon cloth that has not undergone partial oxidation (without the first heat treatment) has a reduced strength due to uneven carbonization.

[0107] Comparing Examples 1, 3, and 4 reveals that the second heat treatment temperature (1500-3000℃) specified in this application is more conducive to improving fiber strength. When the second heat treatment temperature (carbonization temperature) is higher than 3000℃, the carbon fiber strength deteriorates, and the overall tensile strength decreases. When the second heat treatment temperature (carbonization temperature) is lower than 1500℃, the carbon fiber cannot be completely carbonized, resulting in a large amount of polymer residue, which in turn leads to a small change in porosity and an increase in volume resistivity, rendering the fiber unusable.

[0108] By comparing Examples 1 and 5, it can be found that using a mixed resin solution will cause the contact angle of the low porosity layer to increase and the contact angle of the high porosity layer to decrease, which is not conducive to the directional aggregation of water.

[0109] By comparing Examples 1 and 6, it can be found that if the excess resin solution on the surface of the carbon fiber material is not removed, the resin will block the pores, and the gas cannot be transmitted normally.

[0110] By comparing Examples 1 and 7, it can be found that interchangeing the first resin solution and the second resin solution will result in an increase in the contact angle of the low porosity layer and a decrease in the contact angle of the high porosity layer, which is not conducive to the directional aggregation of water.

[0111] By comparing Example 1, Comparative Example 1 and Comparative Example 2, it can be found that a porosity of 40-50% for the first fabric material is more conducive to air venting. When the porosity of the first fabric is less than 40%, it will cause difficulty in air venting and increase the resistance. When the porosity of the first fabric is greater than 50%, the tensile strength will be severely reduced due to the excessive porosity, and it will not withstand pressure. It will be severely compressed at 1 MPa and cannot be used.

[0112] By comparing Example 1, Comparative Example 3, and Comparative Example 4, it can be found that a porosity of 50-60% in the second fabric material is more conducive to high-speed gas transport. When the porosity of the second fabric material is higher than 60%, the tensile strength of the gas diffusion layer will be significantly reduced. Furthermore, due to the excessively high porosity, the contact angle will also be lower, and the surface tension will be similar to that of the first fabric material, which is not conducive to the directional distribution of water. When the porosity of the second fabric is lower than 50%, the gas flux will be reduced, failing to meet the usage requirements.

[0113] The embodiments described above are some, but not all, of the embodiments of this application. The detailed description of the embodiments of this application is not intended to limit the scope of the claimed application, but merely to illustrate selected embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of this application without inventive effort are within the scope of protection of this application.

Claims

1. A gas diffusion layer, characterized in that, It includes a first fiber material and a second fiber material, which are stacked and assembled in an alternating distribution order; The porosity of the first fiber material is 55-60%, and the porosity of the second fiber material is 65-70%. The total number of gas diffusion layers is at least 6; The gas diffusion layer is prepared by the following method: Multiple first fiber materials and second fiber materials are stacked and assembled in an alternating distribution order, and then molded to obtain the gas diffusion layer; The preparation of the first fiber material includes: melting a precursor material to make fibers, making the fibers into a first fabric material with a first porosity, and then subjecting the first fabric material to a first carbonization treatment and a first surface treatment in sequence to obtain the first fiber material. The first surface treatment includes: dissolving the first resin in an organic solvent to obtain a first resin solution, wherein the first resin solution only coats the surface of the first carbon fiber material; Then the first carbonized fiber material is dried; The surface energy of the first resin is 25-30 dynes / cm, and the first resin includes at least one of polyvinylidene fluoride, polyvinyl fluoride, polypropylene, and polyethylene. The preparation of the second fiber material includes: melting a precursor material to form fibers, forming the fibers into a second fabric material with a second porosity, and then subjecting the second fabric material to a second carbonization treatment and a second surface treatment in sequence to obtain the second fiber material. The second surface treatment includes: dissolving the second resin in an organic solvent to obtain a second resin solution, wherein the second resin solution only coats the surface of the second carbonized fiber material; Then the second carbonized fiber material is dried; The surface energy of the second resin is 18-22 dynes / cm; the second resin includes polytetrafluoroethylene and / or polytrifluoroethylene; The precursor material includes at least one of polyacrylonitrile, rayon, and petroleum pitch. The first porosity is 40-50%, and the second porosity is 50-60%.

2. The gas diffusion layer according to claim 1, characterized in that, The total number of gas diffusion layers is 6-12.

3. The gas diffusion layer according to claim 1, characterized in that, The conditions for the first carbonization treatment and the second carbonization treatment are the same, including: The first fabric material and / or the second fabric material are subjected to a first heat treatment under aerobic conditions, and the first fabric material and / or the second fabric material after the first heat treatment are subjected to a second heat treatment under anaerobic conditions to obtain the first carbonized fiber material and / or the second carbonized fiber material.

4. The gas diffusion layer according to claim 3, characterized in that, The conditions for the first heat treatment include: a heat treatment temperature of 200-300°C and a heat treatment time of 30-120 min; The conditions for the second heat treatment include: a heat treatment temperature of 1500-3000°C and a heat treatment time of 5-20 minutes.

5. The gas diffusion layer according to claim 1, characterized in that, The first surface treatment includes: The first resin is dissolved in an organic solvent to obtain a first resin solution. The first carbonized fiber material is then immersed in the first resin solution, so that the first resin solution is adsorbed onto the surface of the first carbonized fiber material and encapsulates the first carbonized fiber material. Remove the droplets of the first resin solution from the surface of the first carbonized fiber material, so that the first resin solution only coats the surface of the first carbonized fiber material; Then the first carbonized fiber material is dried; The second surface treatment includes: The second resin is dissolved in an organic solvent to obtain a second resin solution. The second carbonized fiber material is then immersed in the second resin solution, so that the second resin solution is adsorbed onto the surface of the second carbonized fiber material and encapsulates the second carbonized fiber material. Remove the droplets of the second resin solution from the surface of the second carbon fiber material, so that the second resin solution only coats the surface of the second carbon fiber material; The second carbonized fiber material is then dried.

6. The gas diffusion layer according to claim 5, characterized in that, The mass ratio of the first resin to the organic solvent is (1-5):(10-20); the mass ratio of the second resin to the organic solvent is (2-8):(15-30). The organic solvent includes at least one of ethanol, n-propanol, and acetone; The drying conditions include: a drying temperature of 50-100°C and a drying time of 5-10 minutes.

7. A membrane electrode assembly, characterized in that, Includes the gas diffusion layer as described in any one of claims 1-6.

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