Gas diffusion layer, preparation method thereof and membrane electrode assembly

Abstract

The invention relates to a gas diffusion layer, 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, and the first fiber material and the second fiber material are stacked and assembled according to 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%; the total number of the gas diffusion layers is at least six. The gas diffusion layer can rapidly drain water under a high-humidity condition, and has relatively strong moisture retention performance.

Description

Technical Field

[0001] The present application relates to the field of fuel cell technology, and in particular to a gas diffusion layer and a preparation method thereof, and a membrane electrode assembly. Background Art

[0002] The core components of a proton exchange membrane fuel cell (PEMFC) include the proton exchange membrane (electrolyte), catalyst layer, gas diffusion layer, and bipolar plate. The gas diffusion layer plays a crucial role in fuel cells, supporting the catalyst layer, stabilizing the electrode structure, providing gas transmission channels, and improving water management.

[0003] Traditional gas diffusion layer substrate materials include carbon fiber paper, carbon fiber woven cloth, carbon fiber non-woven material 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] In view of the deficiencies of the prior art, the purpose of the embodiments of the present application includes providing a gas diffusion layer and a preparation method thereof, and a membrane electrode assembly, so as to achieve both rapid drainage and strong moisturizing performance under high humidity conditions.

[0005] In a first aspect, an embodiment of the present application provides 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 layers.

[0006] The present application forms a multilayer structure by alternating a plurality of first fiber materials and a second fiber material. This structure can provide different porosity regions, wherein low-porosity layers (first fiber material layers) and high-porosity layers (second fiber material layers) are arranged alternately. The high-porosity layers have the ability to quickly drain water, while the low-porosity layers have water-retention properties and a self-humidifying effect. This design enables the gas diffusion layer to quickly drain water and maintain appropriate humidity under high humidity conditions, thereby improving the performance, stability, and life of the fuel cell system.

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

[0008] The number of gas diffusion layers within the above range is conducive to achieving the alternating effect of low-porosity layers and high-porosity layers. At the same time, the thickness of the gas diffusion layer is within an appropriate range, which is conducive to reducing resistance.

[0009] In a second aspect, an embodiment of the present application provides a method for preparing the above-mentioned gas diffusion layer, comprising: stacking and assembling a plurality of first fiber materials and a second fiber material 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 having a first porosity, and then sequentially performing a first carbonization process and a first surface treatment on the first fabric material 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 having a second porosity, and then sequentially performing a second carbonization process and a second surface treatment on the second fabric material to obtain a 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 specifically according to needs; 3. It can be applied to the preparation of gas diffusion layers for water electrolysis.

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

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

[0013] Controlling the porosity of the first fabric material and the second fabric material within the above range can better facilitate gas transmission and subsequent molding processing.

[0014] In some embodiments of the present application, the conditions of 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 a first carbonized fiber material and / or a second carbonized fiber material.

[0015] The carbonization process allows the carbon atoms in the first and / or second fabric materials to rearrange and form a stable carbon structure. At high temperatures, the 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 material.

[0016] In the present application, the first heat treatment is carried out under aerobic conditions so that the carbon atoms in the fabric material can react with oxygen atoms in the air. This can increase the oxygen content of the carbon atoms and provide sufficient oxygen for the subsequent carbonization process. Adequate oxygen helps accelerate the subsequent carbonization process and helps to form a stable carbon structure. The second heat treatment is carried out under anaerobic conditions, the purpose of which is 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 to improve the mechanical properties and hydrophobicity of the carbon fiber material.

[0017] In some embodiments of the present 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 these ranges, sufficient oxygen is provided for the subsequent carbonization process, and moisture and volatile substances are removed, thereby improving the thermal stability of the textile material.

[0018] In some embodiments of the present application, 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. By controlling the temperature and time of the second heat treatment within these ranges, the carbon atoms in 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 the present application, the first surface treatment includes: dissolving the first resin in an organic solvent to obtain a first resin solution, soaking the first carbonized fiber material in the first resin solution, so that the first resin solution is adsorbed on the surface of the first carbonized fiber material and wraps the first carbonized fiber material; removing the first resin solution droplets on the surface of the first carbonized fiber material so that the first resin solution only wraps the surface of the first carbonized fiber material; and then drying the first carbonized fiber material.

[0020] In some embodiments of the present application, the second surface treatment includes: dissolving the second resin in an organic solvent to obtain a second resin solution, soaking the second carbonized fiber material in the second resin solution, allowing the second resin solution to be adsorbed on the surface of the second carbonized fiber material and wrap the second carbonized fiber material; removing the second resin solution droplets on the surface of the second carbonized fiber material so that the second resin solution only wraps the surface of the second carbonized fiber material; and then drying the second carbonized fiber material.

[0021] In this application, surface treatment can improve the wettability and adhesion of the fiber material surface, enabling it to better interact 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 the present application, the surface energy of the first resin is 25-30 dynes / cm, 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 the present 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 the present application, the mass ratio of the first resin to the organic solvent is (1-5):(10-20); and 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 mass ratio of the second resin to the organic solvent within the above ranges, the resin solution can be uniformly coated and dried on the surface of the carbonized fiber material, providing good adhesion and controlling the thickness of the coating layer; this helps to improve the performance and surface characteristics of the carbonized fiber material.

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

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

[0027] In a third aspect, an embodiment of the present application provides a membrane electrode assembly comprising any of the above-mentioned gas diffusion layers. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following is a brief introduction to the drawings required for use in the embodiments. It should be understood that the following drawings only show certain embodiments of the present application and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other relevant drawings can be obtained based on these drawings without creative work.

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

[0030] Figure 2 Schematic diagram of the process for controlling the porosity of the fabric material in this application. DETAILED DESCRIPTION

[0031] To make the purpose, technical solutions and advantages of the examples of the present application clearer, the technical solutions in the examples of the present application will be described clearly and completely below. Where specific conditions are not specified in the examples, conventional conditions or conditions recommended by the manufacturer are used. Where the manufacturer of the reagents or instruments is not specified, they are all conventional products that can be purchased commercially.

[0032] The present invention provides a method for preparing a gas diffusion layer, comprising the following steps:

[0033] 1. Preparation of the First Fiber Material and the Second Fiber Material

[0034] Step S101: melt-treating the precursor material to convert it into fiber form. The fiber is washed and stretched to obtain the desired strength and size.

[0035] In the present application, the precursor material includes but is not limited to at least one of polyacrylonitrile, rayon and petroleum asphalt.

[0036] Step S102: The fibers produced in step S101 are woven into a textile material through a weaving process, wherein the weaving process parameters are adjusted to obtain a first textile material having a first porosity of 40-50% and a second textile material having a second porosity of 50-60%. After the first textile material is adjusted to have a porosity of 40-50%, its pore size is 5-6 μm; after the second textile material is adjusted to have a porosity of 50-60%, its pore size is 8-9 μm.

[0037] In this application, please refer to the schematic diagram of the process for controlling the porosity of the first and second fabric materials. Figure 2 , Figure 2 The polymer melt in the embodiment is equivalent to the precursor material of the present invention, and the receiving device is equivalent to the first fabric material or the second fabric material of the present invention. Figure 2 It can be seen that the present application mainly controls the porosity of the first fabric material and the second fabric material by adjusting the speed of the hot air flow. A higher air flow speed will form smaller pores between the fibers, resulting in a lower porosity. Conversely, a lower air flow speed will form larger pores, which will increase the porosity. Therefore, to achieve a porosity of 40-50% for the first fabric material, it is necessary to adjust the hot air flow speed within the range of 400-450m / s. This will result in smaller pores in the fiber structure, resulting in a lower porosity of the material. Similarly, to achieve a porosity of 50-60% for the second fabric material, it is necessary to adjust the hot air flow speed within the range of 300-350m / s. This will result in larger pores in the fiber structure, resulting in a higher porosity of the material.

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

[0039] As an example, when preparing the second fabric material, the hot air flow rate is adjusted to include but not limited to 300m / s, 305m / s, 310m / s, 315m / s, 320m / s, 325m / s, 330m / s, 335m / s, 340m / s, 345m / s, and 350m / 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 is not limited to this.

[0040] The porosity of the polymer cloth can also be controlled by adjusting other textile process parameters, such as textile density, fabric structure, and fabric thickness, which is not limited in this application.

[0041] Step S103: The first and / or second textile materials prepared in step S102 are subjected to a first carbonization treatment and a second carbonization treatment, wherein the first and second carbonization treatments are performed under the same conditions, including: performing a first heat treatment on the first and / or second textile materials under oxygen conditions (e.g., in air), and then performing a second heat treatment on the first and / or second textile materials that have undergone the first heat treatment under oxygen-free conditions, to obtain a first carbonized fiber material and / or a second carbonized fiber material. During the second heat treatment, to prevent oxygen from entering the carbonization furnace, it is necessary to maintain sealing during the carbonization process, particularly at the inlet and outlet of the carbonization furnace.

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

[0043] The first heat treatment is performed in the presence of oxygen. By heat-treating the first and / or second textile materials at 200-300°C for 30-120 minutes, the carbon atoms in the first and / or second textile materials 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. On the other hand, the presence of moisture and volatile substances may cause the formation of bubbles and pores at high temperatures, thereby affecting the material's density and mechanical properties. The first heat treatment effectively removes these harmful substances, improving the thermal stability of the first and / or second textile materials.

[0044] The second heat treatment is performed under oxygen-free conditions. By heat-treating the first and / or second fabric materials at 1500-3000°C 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 improve the mechanical properties and hydrophobicity of the carbon fiber material. The hydrophobicity of carbon fiber materials is determined by their surface microstructure and chemical composition. At high temperatures, the carbon atoms rearrange to form an ordered carbon structure, making the surface microstructure denser and smoother, thereby enhancing the material's hydrophobicity. At the same time, at high temperatures, the ordered and compact carbon structure reduces the material's grain size and increases its crystallinity, thereby improving the material's strength, stiffness, and wear resistance, making it more suitable for use in high-intensity and high-temperature environments. Moreover, at high temperatures, carbon atoms react with surrounding impurity atoms such as oxygen and nitrogen to form more stable carbon-carbon bonds. This can increase the thermal stability and oxidation resistance of the carbon fiber material, extending its service life.

[0045] Step S104: performing a first surface treatment and a second surface treatment on the first carbonized fiber material and the second carbonized fiber material obtained in step S103, respectively; wherein,

[0046] The first surface treatment includes the following steps: dissolving the first resin in an organic solvent to obtain a first resin solution, soaking the first carbonized fiber material in the first resin solution, allowing the first resin solution to be adsorbed on the surface of the first carbonized fiber material and wrap the first carbonized fiber material; removing the first resin solution droplets on the surface of the first carbonized fiber material, so that the first resin solution only wraps the surface of the first carbonized fiber material; and then drying the first carbonized 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, soaking the second carbonized fiber material in the second resin solution, allowing the second resin solution to be adsorbed on the surface of the second carbonized fiber material and wrap the second carbonized fiber material; removing the second resin solution droplets on the surface of the second carbonized fiber material, so that the second resin solution only wraps the surface of the second carbonized fiber material; and then drying the second carbonized fiber material.

[0048] In the present application, the resin droplets remaining on the surface of the first carbonized fiber material and / or the second carbonized fiber material can be removed by appropriate treatment methods, such as vibration or mechanical scraping, so that the resin is only wrapped on the surface of the first carbonized fiber material and / or the second carbonized fiber material without forming lumps. The surface-treated first carbonized fiber material and / or the second carbonized fiber material is dried to form a uniform coating of the resin on the carbon fibers and to completely solidify the resin. In short, surface treatment of the first carbonized fiber material and / or the second carbonized fiber material can improve its surface properties and characteristics and increase its ability to combine with other materials.

[0049] The first resin has a surface energy of 25-30 dynes / cm, indicating low hydrophobicity; the second resin has a surface energy of 18-22 dynes / cm, indicating high hydrophobicity. In the embodiments of the present 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 the present 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 mass ratio of the second resin to the organic solvent within the aforementioned ranges, the resin can be uniformly infiltrated and adsorbed onto the surface of the carbonized fiber material, forming a uniform coating. 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 carbonized fiber material, thereby improving the strength and durability of the carbonized fiber material.

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

[0053] In this application, a fabric material with a target porosity of 40-50% is carbonized to a porosity of 55-60%, representing the first fiber material; a fabric material with a target porosity of 50-60% is carbonized to a porosity of 65-70%, representing the second fiber material. After carbonization, the first fiber material is adjusted to a porosity of 55-60%, resulting in a pore size of 8-9 μm; and the second fiber material is adjusted to a porosity of 65-70%, resulting in a pore size of 10-12 μm.

[0054] 2. Preparation of Gas Diffusion Layer

[0055] The prepared plurality of first and second fiber materials are stacked and assembled in an alternating order to form a multilayer structure. This multilayer structure is then composite-hot-pressed at a temperature of 250-350°C and a pressure of 0.2-0.3 MPa to securely bond the layers together, resulting in a gas diffusion layer with alternating low and high porosity. The gas diffusion layer comprises at least six layers, namely, three layers of the first fiber material and three layers of the second fiber material, with the first and second fiber materials alternating in arrangement.

[0056] For example, the total number of gas diffusion layers is 6-12. Too few layers prevent the alternating effect from being fully realized, resulting in wasted functionality. Too many layers increase the thickness of the gas diffusion layer (GDL), increasing resistance and increasing the stack volume. Furthermore, when there are too many layers and the original thickness is to be maintained, the thickness of each layer must be reduced, and thinning a single layer greatly increases the difficulty of manufacturing.

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

[0058] In this application, hot pressing can be performed with reference to existing technologies. For example, 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; and the pressure includes, but is not limited to, 0.2 MPa, 0.25 MPa, and 0.3 MPa; this application does not impose any limitations on this.

[0059] During use, the low-porosity layer (first fiber material layer) is close to the catalyst layer in the proton exchange membrane fuel cell (PEMFC), and the surface of the first fiber material near the catalyst layer needs to be coated with a microporous layer (MPL). The microporous layer is usually composed of carbon black and a hydrophobic agent, with a thickness of 10-100μm. It is used to improve the substrate pore structure, reduce the contact resistance between the substrate and the catalyst layer, guide the reaction gas to quickly pass through the diffusion layer and evenly distribute it to the surface of the catalyst layer, and drain the water generated by the reaction to prevent "flooding". The high-porosity layer (second fiber material layer) is close to the bipolar plate in the proton exchange membrane fuel cell (PEMFC).

[0060] Figure 1 The schematic diagram of the gas diffusion layer in different states provided in this application is as follows: Figure 1 It can be seen that under normal (dry) conditions, both the low-porosity layer (first fiber material layer) and the high-porosity layer (second fiber material layer) can smoothly transmit gas; after the humidity increases, the low-porosity layer will first condense liquid due to capillary action, causing the gas flow rate to slow down, and the flow rate of the high-porosity layer to accelerate, and the accelerated flow rate can drive the volatilization of water in the low-porosity layer; when the machine is turned off after use, that is, in the shutdown state, due to the capillary action of the low-porosity layer, some water will remain, which plays a role of self-humidification.

[0061] The present application forms a multilayer structure by alternating the order of multiple first fiber materials and second fiber materials. This structure can provide different porosity regions, in which the low porosity layer (first fiber material layer) and the high porosity layer (second fiber material layer) are arranged alternately. Among them, the low porosity layer has a strong water retention property and can absorb and retain an appropriate amount of water. When the fuel cell system is under low humidity conditions, the low porosity layer can increase the moisture content by absorbing water vapor in the gas, providing the required humidity conditions, thereby improving the performance of the fuel cell. On the contrary, when the humidity is high, the low porosity layer can absorb excess water, allowing the high porosity layer to maintain good gas flow and prevent flooding. At the same time, at the same humidity, the low porosity layer can more easily produce liquid water and adsorb the water in the fiber material through capillary action. This helps to reduce the accumulation of liquid water in the fuel cell, reduce the risk of flooding of the stack, and reduce the corrosion damage of the catalyst layer and the bipolar plate. The high porosity layer plays a role in rapid drainage in 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 transmission and rapidly removes the water through airflow, preventing it from accumulating and clogging the 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 leverage the capillary action and water retention of the low-porosity layer to achieve rapid liquid water transport and evaporation; at the same time, the high-porosity layer can quickly remove gas. This design allows the gas diffusion layer to both quickly drain water under humid conditions and maintain appropriate humidity, resulting in strong moisture retention.

[0063] The features and performance of the present application are 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) Preparing 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; then formed into a first fabric material with a porosity of 45-50% and a second fabric material with a porosity of 55-60%; the first fabric material and the second fabric material are first heat-treated in air at 280°C for 1.5 hours; then heat-treated at 2600°C for 15 minutes under anaerobic conditions; the first fabric material after the two heat treatments is then immersed in a first resin solution (acetic acid accounts for 90% by mass and polypropylene accounts for 10% by mass, i.e., acetic acid / polypropylene = 90 / 10), and the second fabric material is immersed in a second resin solution (ethanol accounts for 85% by mass and polytetrafluoroethylene accounts for 15% by mass, i.e., ethanol / polytetrafluoroethylene = 85 / 15), so that the resin solution is adsorbed on the surface of the carbonized fiber material and wraps the carbonized fiber material; the resin solution droplets on the surface of the carbonized fiber material are removed so that the resin solution only wraps the surface of the carbonized fiber material; and the above-mentioned two carbonized fiber materials are then dried at 80°C for 10 minutes to obtain the first fiber material and the second fiber material. 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 the second fiber materials prepared in the above step (1) are stacked and assembled in an alternating distribution order, wherein the first fiber material and the second fiber material each have 4 layers, and then the assembled 8-layer material structure is composite hot-pressed to obtain a gas diffusion layer with a total number 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 aerobic conditions, that is, the step of heat treatment at 280°C in air for 1.5 hours is not performed; only the first fabric material and the second fabric material are heat treated at 2600°C for 15 minutes under anaerobic conditions.

[0072] (1) Preparing 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; then formed into a first fabric material with a porosity of 45-50%, and a second fabric material with a porosity of 55-60%; the first fabric material and the second fabric material are heat-treated at 2600°C for 15 minutes under anaerobic conditions; the first fabric material after the two heat treatments is then immersed in a first resin solution (acetic acid accounts for 90% by mass, polypropylene accounts for 10% by mass, that is, acetic acid / polypropylene = 90 / 10), and the second fabric material is immersed in a second resin solution (ethanol accounts for 85% by mass, polytetrafluoroethylene accounts for 15% by mass, that is, ethanol / polytetrafluoroethylene = 85 / 15), so that the resin solution is adsorbed on the surface of the carbonized fiber material and wraps the carbonized fiber material; the resin solution droplets on the surface of the carbonized fiber material are removed so that the resin solution only wraps the surface of the carbonized fiber material; and the above-mentioned two carbonized fiber materials are dried at 80°C for 10 minutes to obtain the first fiber material and the second fiber material.

[0074] Example 3

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

[0076] Example 4

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

[0078] Example 5

[0079] This embodiment is basically the same as Example 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, and 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 carbonized fiber material and wraps the carbonized fiber material.

[0080] Example 6

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

[0082] Example 7

[0083] This embodiment is basically the same as Example 1, except that the first fabric material after two heat treatments is immersed in a first resin solution (the mass proportion of ethanol is 85%, and the mass proportion of polytetrafluoroethylene is 15%, that is, ethanol / polytetrafluoroethylene = 85 / 15), and the second fabric material is immersed in a second resin solution (the mass proportion of acetic acid is 90%, and the mass proportion of polypropylene is 10%, that is, 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] Some parameters of the examples and comparative examples of this application are detailed in Table 1.

[0093] Table 1

[0094]

[0095]

[0096] Table 1 (Continued)

[0097]

[0098]

[0099] Test example

[0100] In this test example, the gas diffusion layers provided in Examples 1-7 and Comparative Examples 1-4 were subjected to performance tests. The test items included thickness test, tensile strength, surface density, bulk resistance, gas flux, and contact angle. For the measurement methods of the above items, please refer to 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, defined as the contact angle of a liquid on a solid surface, is an important parameter for measuring the wettability of a liquid on a material. Contact angle measurement reveals the degree of water binding to the surface. The larger the contact angle, the easier it is for water to detach from the surface. Contact angles 1 and 2 in Table 2 correspond to the first and second fiber materials, respectively.

[0106] As can be seen from Table 2, by comparing Example 1 and Example 2, the carbon cloth surface is partially oxidized by first heat treatment at 280°C (first heat treatment) and then carbonized, thereby improving the strength of the carbonized gas diffusion layer. The carbon cloth that is not partially oxidized (without the first heat treatment) has uneven carbonization, resulting in decreased strength.

[0107] By comparing Examples 1, 3, and 4, it can be found that the second heat treatment temperature specified in this application (1500-3000°C) is more conducive to improving fiber strength. When the second heat treatment temperature (carbonization temperature) is higher than 3000°C, the carbon fiber strength deteriorates and the overall tensile strength decreases. When the second heat treatment temperature (carbonization temperature) is lower than 1500°C, the carbon fiber cannot be completely carbonized, and a large amount of polymer remains, which in turn leads to a small change in porosity and an increase in bulk resistance, making it unusable.

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

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

[0110] By comparing Example 1 and Example 7, it can be found that exchanging the first resin solution and the second resin solution will increase the contact angle of the low-porosity layer and decrease 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 the porosity of the first fabric material is more conducive to exhaust in the range of 40-50%. When the porosity of the first fabric is lower than 40%, exhaust will be difficult and the resistance will increase. When the porosity of the first fabric is higher than 50%, due to the high porosity, the tensile strength will be seriously reduced, and it will not be pressure-resistant. It will be severely compressed under 1Mpa and cannot be used.

[0112] Comparison of Example 1, Comparative Example 3, and Comparative Example 4 reveals that a porosity of 50-60% for the second fabric material is more conducive to high-speed gas transmission. A porosity of greater than 60% significantly reduces the tensile strength of the gas diffusion layer. This excessive porosity also results in a lower contact angle and a surface tension similar to that of the first fabric material, hindering directional water distribution. A porosity of less than 50% reduces gas flux, failing to meet operational requirements.

[0113] The embodiments described above are part of the embodiments of the present application, rather than all of the embodiments. The detailed description of the embodiments of the present application is not intended to limit the scope of the present application for protection, but merely represents selected embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this application.

Claims

1. A gas diffusion layer, characterized in that: The method comprises 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%; The total number of gas diffusion layers is at least 6.

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

3. A method for preparing a gas diffusion layer according to claim 1 or 2, characterized in that: include: stacking and assembling a plurality of first fiber materials and a second fiber material in an alternating distribution order, and then performing a molding process to obtain the gas diffusion layer; The preparation of the first fiber material comprises: melting a precursor material to form fibers, forming the fibers into a first fabric material having a first porosity, and then sequentially performing a first carbonization treatment and a first surface treatment on the first fabric material to obtain the first fiber material; 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 sequentially performing a second carbonization treatment and a second surface treatment on the second fabric material to obtain the second fiber material.

4. The preparation method according to claim 3, characterized in that The precursor material includes at least one of polyacrylonitrile, rayon and petroleum asphalt; Optionally, the first porosity is 40-50%, and the second porosity is 50-60%.

5. The preparation method according to claim 3, characterized in that The conditions of 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 subjected to the first heat treatment are subjected to a second heat treatment under anaerobic conditions to obtain a first carbonized fiber material and / or a second carbonized fiber material.

6. The preparation method according to claim 5, characterized in that The conditions of the first heat treatment include: a heat treatment temperature of 200-300°C and a heat treatment time of 30-120 minutes; Optionally, the conditions of the second heat treatment include: a heat treatment temperature of 1500-3000° C., and a heat treatment time of 5-20 min.

7. The preparation method according to claim 5, characterized in that The first surface treatment comprises: dissolving a first resin in an organic solvent to obtain a first resin solution, and soaking the first carbonized fiber material in the first resin solution so that the first resin solution is adsorbed on the surface of the first carbonized fiber material and wraps the first carbonized fiber material; removing the first resin solution droplets on the surface of the first carbonized fiber material, so that the first resin solution is only wrapped on the surface of the first carbonized fiber material; Then drying the first carbonized fiber material; Optionally, the second surface treatment includes: dissolving a second resin in an organic solvent to obtain a second resin solution, and soaking the second carbonized fiber material in the second resin solution so that the second resin solution is adsorbed on the surface of the second carbonized fiber material and wraps the second carbonized fiber material; removing the second resin solution droplets on the surface of the second carbonized fiber material, so that the second resin solution is only wrapped on the surface of the second carbonized fiber material; The second carbonized fiber material is then dried.

8. The preparation method according to claim 7, characterized in that 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; Optionally, the first resin includes at least one of polyvinylidene fluoride, polyvinyl fluoride, polypropylene and polyethylene, and the second resin includes polytetrafluoroethylene and / or polytrifluoroethylene.

9. The preparation method according to claim 7, 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); Optionally, the organic solvent includes at least one of ethanol, n-propanol and acetone; Optionally, the drying conditions include: a drying temperature of 50-100° C. and a drying time of 5-10 minutes.

10. A membrane electrode assembly, characterized in that: Comprising the gas diffusion layer according to claim 1 or 2.

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