Catalytic graphitizing agent, carbon sheet for gas diffusion layer and its preparation method

Abstract

This invention relates to the field of fuel cell gas diffusion layer technology, specifically to a catalytic graphitizing agent, carbon sheets for gas diffusion layers, their preparation methods, and applications. The catalytic graphitizing agent is a composite particle of a boron-based catalyst loaded on an asphalt surface; the mass ratio of asphalt to boron-based catalyst is 2–20:1. This invention, by loading a boron-based catalyst onto an asphalt surface, allows the molten asphalt to fill the interface between the boron-based catalyst and other components during hot pressing and graphitization, thus optimizing the interface of the asphalt. This solves the problems of rough microstructure of the resin carbon, poor interface between the resin carbon and carbon fibers in the carbon sheet, and high contact resistance caused by using only a boron-based catalyst, thereby improving the conductivity of the carbon sheet. Furthermore, using this catalytic graphitizing agent can increase the graphitization degree of the resin carbon portion in the carbon sheet, reducing energy consumption and cost.

Description

Technical Field

[0001] This invention relates to the field of fuel cell gas diffusion layer technology, and more specifically, to a catalytic graphitizing agent, carbon sheets for gas diffusion layers, and methods for their preparation. Background Technology

[0002] In recent years, proton exchange membrane fuel cell technology, which uses hydrogen and oxygen as energy sources, has developed rapidly as a green energy technology that utilizes hydrogen energy. The gas diffusion layer is an important component of the membrane electrode assembly, a core component of fuel cells. It is located between the catalyst layer and the bipolar plates and plays a role in coordinating the exchange of substances between the water and gas phases, dissipating waste heat from electrochemical reactions, conducting electricity between the anode and cathode, and providing mechanical support for the catalyst layer.

[0003] Current gas diffusion layers primarily use two-dimensional carbon sheets, mainly composed of carbon fibers and resin-based carbon, as a substrate, on which a microporous layer is loaded. The preparation process of the carbon sheet substrate mainly includes papermaking, impregnation, curing, and graphitization, and the specific process is as follows: short-cut carbon fibers are papermade to form virgin carbon sheets; the virgin carbon sheets are resin-impregnated to form impregnated carbon sheets; then, the impregnated carbon sheets are hot-pressed and cured to obtain cured carbon sheets; finally, the cured carbon sheets are placed in a graphitization furnace for graphitization, thus obtaining the final carbon sheet used as the substrate for the gas diffusion layer.

[0004] In the impregnation process of virgin carbon sheets, phenolic resin systems offer advantages such as low cost, good processability, high graphitization residual carbon rate, and good bonding properties of the graphitized resin carbon. Therefore, phenolic resin is typically used as the main component in the resin impregnation solution. However, the chemical structure of phenolic resin makes it difficult to form highly graphitized resin carbon during the graphitization process. Its disordered structure cannot be rearranged into an ordered graphitized crystal structure during high-temperature graphitization, thus limiting the conductivity of the resin carbon formed by phenolic resin, which in turn negatively impacts the conductivity of the carbon sheet. Reduced conductivity of the carbon sheet increases the internal resistance of the fuel cell membrane electrode assembly, affecting ohmic polarization and ultimately leading to a decrease in fuel cell efficiency.

[0005] Furthermore, the commonly used graphitization temperature for resin carbon is in the range of 1800–2800℃. As the graphitization temperature increases, energy consumption and the manufacturing cost of the graphitization furnace also increase significantly. Therefore, minimizing the maximum graphitization temperature can greatly save on equipment and energy costs in the graphitization process.

[0006] To improve the graphitization degree and electrical conductivity of phenolic resin carbon and obtain a higher degree of graphitization at a lower graphitization temperature, one feasible method is to introduce a catalytic graphitizing agent into the resin system before graphitization. However, most catalysts with catalytic graphitization properties will form metal cations during fuel cell operation, causing fuel cell contamination and irreversible performance degradation. Boron-based catalytic graphitizing agents do not cause fuel cell contamination. Therefore, such catalysts can be used to homogenize the graphitization of resin carbon at high temperatures, catalyzing the graphitization process of phenolic resin carbon, thereby reducing the performance requirements of the graphitization furnace equipment, reducing graphitization energy consumption, and saving costs.

[0007] However, in practical applications, boron-based catalytic graphitizing agents can lead to increased surface roughness of the graphitized phenolic resin carbon, resulting in poor interface between the resin carbon and carbon fiber in the carbon sheet and high contact resistance.

[0008] In view of this, the present invention is hereby proposed. Summary of the Invention

[0009] The primary objective of this invention is to provide a catalytic graphitizing agent. By loading a boron-based catalyst onto the surface of asphalt and controlling the ratio between the two, the molten asphalt can fill the interface between the boron-based catalyst and other components during hot pressing and graphitization, thereby optimizing the interface of the asphalt. This solves the problems of rough microstructure of resin carbon, poor interface between resin carbon and carbon fiber in carbon sheets, and high contact resistance caused by using boron-based catalysts alone, thus improving the conductivity of carbon sheets. Furthermore, asphalt is a carbon precursor that is more prone to graphitization than phenolic resin, and introducing asphalt can further enhance the conductivity of carbon sheets.

[0010] The second objective of this invention is to provide a method for preparing a catalytic graphitizing agent based on mechanical grinding. This method utilizes the property that low softening point asphalt is easily fused under mechanical action. By mechanical grinding, a boron-based catalyst is loaded onto the surface of the asphalt. This method has the advantages of simple process, easy operation, and low equipment cost.

[0011] A third objective of this invention is to provide a carbon sheet for a gas diffusion layer. By adding a catalytic graphitizing agent containing pitch and a boron-based catalyst, the graphitization reaction of phenolic resin carbon can be catalyzed, and the microscopic roughness of the resin carbon can be reduced. This solves the problems of poor interface between resin carbon and carbon fiber and high contact resistance, thereby improving the conductivity of the carbon sheet for the gas diffusion layer. Furthermore, using this catalytic graphitizing agent can enhance the graphitization degree of the resin carbon portion in the carbon sheet, while reducing the performance requirements of the graphitization furnace equipment in carbon sheet production, reducing graphitization energy consumption, and lowering production costs.

[0012] The fourth objective of this invention is to provide a method for preparing carbon sheets for gas diffusion layers. The carbon sheets for gas diffusion layers prepared by this method have good electrical conductivity, and the method is simple to operate, has a short process flow, and low production cost.

[0013] In order to achieve the above-mentioned objectives of the present invention, the following technical solution is adopted:

[0014] The present invention first provides a catalytic graphitizing agent, wherein the catalytic graphitizing agent is a composite particle of asphalt loaded with a boron-based catalyst; wherein the mass ratio of the asphalt to the boron-based catalyst is 2 to 20:1.

[0015] Furthermore, the softening point of the asphalt is 80–120°C.

[0016] Furthermore, the coking value of the asphalt is 30% to 60%.

[0017] Furthermore, the toluene-insoluble content in the asphalt is 5 wt.% to 40 wt.%.

[0018] Furthermore, the quinoline insoluble content in the asphalt is less than 10 wt.%.

[0019] Furthermore, the particle size of the asphalt is ≤100μm.

[0020] Furthermore, the asphalt includes at least one of natural asphalt, petroleum asphalt, coal tar pitch, and modified asphalt.

[0021] Furthermore, the boron-based catalyst includes at least one of elemental boron, boron carbide, and boron nitride.

[0022] Furthermore, the average particle size of the boron-based catalyst is 0.5–10 μm.

[0023] The present invention further provides a method for preparing the catalytic graphitizing agent, comprising the following steps: mixing asphalt and a boron-based catalyst and mechanically grinding them to load the boron-based catalyst onto the surface of the asphalt.

[0024] Further, the softening point of the asphalt is 80-120℃; the mechanical grinding method includes ball milling, and the operating conditions of the ball milling include: (1) the ball milling equipment includes a planetary ball mill, and the rotation speed of the equipment is 300-1000 rpm; (2) the ball milling is dry ball milling; (3) the ball milling uses a ball milling jar and grinding balls made of zirconium oxide material, the ball-to-material ratio in the ball milling is 1:1-6:1, and the diameter of the grinding balls is 1-15 mm; (4) the ball milling method includes intermittent ball milling, and the intermittent ball milling method specifically includes: each ball milling for 3-15 minutes, stopping for cooling for 2-10 minutes, and repeating the ball milling and cooling process 10-40 times.

[0025] The present invention also provides a carbon sheet for a gas diffusion layer, which is mainly made of resin impregnation liquid and virgin carbon sheet; wherein, the resin impregnation liquid is mainly composed of the catalytic graphitizing agent and phenolic resin in a mass ratio of 1-15:15-45.

[0026] Further, the resin impregnation solution comprises the following components in parts by mass: 0.1 to 1.5 parts of the catalytic graphitizing agent, 1.5 to 4.5 parts of phenolic resin, 0.01 to 0.2 parts of the anti-settling agent, and 2 to 10 parts of solvent; wherein the anti-settling agent comprises at least one of polyvinylpyrrolidone, polyurea, and polyamide wax.

[0027] Furthermore, the phenolic resin includes thermosetting phenolic resin.

[0028] The present invention also provides a method for preparing the carbon sheet for the gas diffusion layer, comprising the following steps: impregnating a virgin carbon sheet with a resin impregnation solution and then drying it to obtain an impregnated carbon sheet; hot-pressing and curing the impregnated carbon sheet to obtain a cured carbon sheet; and graphitizing the cured carbon sheet to obtain the carbon sheet for the gas diffusion layer.

[0029] Furthermore, the method for preparing the virgin carbon sheet includes: mixing chopped carbon fibers and a dispersion medium to obtain a chopped carbon fiber slurry, then forming the slurry into sheets and drying it.

[0030] Furthermore, the temperature of the hot pressing is 100–180°C.

[0031] Furthermore, the pressure of the hot pressing is ≤5 MPa.

[0032] Furthermore, the hot pressing time is 2 to 120 minutes.

[0033] Furthermore, the graphitization temperature is 1600–2400°C.

[0034] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0035] (1) The catalytic graphitizing agent provided by the present invention loads a boron-based catalyst onto the surface of asphalt. During the hot pressing and graphitization process of the composite particles, the molten asphalt can fill the interface between the boron-based catalyst and other components, thereby playing the role of interface optimization of asphalt. This can solve the problems of rough microstructure of resin carbon, poor interface between resin carbon and carbon fiber in carbon sheet and large contact resistance caused by using boron-based catalyst alone, and improve the conductivity of carbon sheet and the gas diffusion layer made therefrom.

[0036] (2) The catalytic graphitizing agent provided by the present invention can improve the graphitization degree of the resin carbon part in carbon sheets, reduce the performance requirements of graphitization furnace equipment in carbon sheet production, and reduce graphitization energy consumption and production costs.

[0037] (3) The catalytic graphitizing agent provided by the present invention can further reduce the resistivity of carbon sheets and improve the conductivity of carbon sheets by controlling the mass ratio of asphalt and boron-based catalysts while ensuring the carbonization rate.

[0038] (4) The catalytic graphitizing agent provided by the present invention utilizes the property that asphalt with a low softening point is easy to fuse during mechanical grinding. The fused asphalt can act as an adhesive, so that the boron-based catalyst particles are loaded on the surface of the asphalt particles to form a micro-composite structure. The mechanical grinding method is low in cost and simple in equipment, and avoids the solvent use problem that is more common in other composite methods.

[0039] (5) The carbon sheet for gas diffusion layer prepared by the catalytic graphitizing agent provided by the present invention has low planar resistivity and vertical resistivity. Attached Figure Description

[0040] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0041] Figure 1 A schematic flowchart illustrating a method for preparing a carbon sheet for a gas diffusion layer provided by the present invention;

[0042] Figure 2 An optical microscope image of asphalt used in Embodiment 1 of the present invention;

[0043] Figure 3 An optical microscope image of the catalytic graphitizing agent prepared in Example 1 of this invention;

[0044] Figure 4 An optical microscope image of the carbon sheet used for the gas diffusion layer prepared in Example 1 of the present invention;

[0045] Figure 5 An optical microscope image of the carbon sheet used for the gas diffusion layer prepared in Comparative Example 1 provided by the present invention;

[0046] Figure 6 An optical microscope image of the carbon sheet used for the gas diffusion layer prepared in Comparative Example 2 of this invention;

[0047] Figure 7An optical microscope image of the carbon sheet used for the gas diffusion layer prepared in Comparative Example 3 of this invention. Detailed Implementation

[0048] The technical solution of the present invention will be clearly and completely described below with reference to the accompanying drawings and specific embodiments. However, those skilled in the art will understand that the embodiments described below are some embodiments of the present invention, but not all embodiments, and are only used to illustrate the present invention, and should not be regarded as limiting the scope of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall be followed. Where the manufacturers of reagents or instruments are not specified, they are all conventional products that can be purchased commercially.

[0049] Unless otherwise specified, in this invention, terms such as "first aspect," "second aspect," "third aspect," and "fourth aspect" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or quantity, nor should they be construed as implicitly indicating the importance or quantity of the indicated technical features. Moreover, terms such as "first," "second," "third," and "fourth" serve only as a non-exhaustive enumeration and should be understood not to constitute a closed limitation on quantity.

[0050] Unless otherwise specified, the terms "comprising" and "including" as used in this invention can be open-ended or closed-ended. For example, "comprising" and "including" can mean that other components not listed may also be included, or that only the listed components may be included.

[0051] Unless otherwise specified, in this invention, "one or more" or "at least one" refers to any one, any two, or any two or more of the listed items. "Several" refers to any two or more.

[0052] In a first aspect, the present invention provides a catalytic graphitizing agent, wherein the catalytic graphitizing agent is a composite particle of a boron-based catalyst loaded on the surface of asphalt.

[0053] The mass ratio of the asphalt to the boron-based catalyst is 2 to 20:1, including but not limited to any one of the following: 2:1, 3:1, 4:1, 5:1, 6:1, 7:1, 8:1, 9:1, 10:1, 11:1, 12:1, 13:1, 14:1, 15:1, 16:1, 17:1, 18:1, 19:1, 20:1, or any range between the two.

[0054] The catalytic graphitizing agent provided by this invention loads a boron-based catalyst onto the surface of asphalt. During the hot pressing and graphitization process of the composite particles, the molten asphalt can fill the interface between the boron-based catalyst and other components, thereby optimizing the interface of the asphalt. This solves the problems of rough microstructure of resin carbon, poor interface between resin carbon and carbon fiber in carbon sheets, and high contact resistance caused by using boron-based catalysts alone, and improves the conductivity of carbon sheets and the gas diffusion layer made therefrom.

[0055] The catalytic graphitizing agent provided by this invention can catalyze the graphitization reaction of phenolic resin carbon in the graphitization process. This catalytic graphitizing agent is used to prepare the gas diffusion layer of a fuel cell. By catalyzing the graphitization reaction of the resin carbon during the graphitization treatment stage, the performance of the carbon sheet material used in the fuel cell gas diffusion layer can be optimized.

[0056] Specifically, as a graphite precursor material, asphalt possesses advantages such as high residual carbon content, good residual carbon conductivity, and improved interfacial properties. Furthermore, the physicochemical properties of asphalt, such as its melting and graphitization behavior, are compatible with existing carbon sheet manufacturing processes (it can be adapted to the process parameters of each step in carbon sheet preparation). Moreover, compared to phenolic resin, asphalt is a carbon precursor that is more easily graphitized; therefore, the introduction of asphalt will not adversely affect the conductivity of the system itself.

[0057] Meanwhile, boron-based catalysts can catalyze the graphitization process of asphalt and phenolic resins, further enhancing the catalyst's effectiveness.

[0058] Furthermore, using this catalytic graphitizing agent can improve the graphitization degree of the resin carbon portion in carbon sheets, and can also reduce the performance requirements of graphitization furnace equipment in carbon sheet production, thereby reducing graphitization energy consumption and production costs.

[0059] Furthermore, by controlling the mass ratio of asphalt to boron-based catalyst, this invention can further reduce the resistivity of carbon sheets and improve their electrical conductivity while ensuring the carbonization rate.

[0060] In some specific embodiments, the softening point of the asphalt is 80–120°C; including but not limited to any one of 80°C, 85°C, 90°C, 95°C, 100°C, 105°C, 110°C, 115°C, and 120°C, or a range between any two. Asphalt with a low softening point is easily fused during grinding. The fused asphalt acts as a binder, allowing boron-based catalyst particles to be loaded onto the surface of the asphalt particles, forming composite particles. This avoids the solvent usage problem commonly found in other composite methods.

[0061] In some specific embodiments, the coking value of the asphalt is 30% to 60%; including but not limited to point values ​​of any one of 30%, 35%, 40%, 45%, 55%, and 60%, or ranges between any two. It is understood that the coking value is related to the softening point.

[0062] In some specific embodiments, the toluene-insoluble content in the asphalt is 5 wt.% to 40 wt.%, including but not limited to point values ​​or ranges between any one of 5 wt.%, 10 wt.%, 15 wt.%, 20 wt.%, 25 wt.%, 30 wt.%, 35 wt.%, and 40 wt.%. The toluene-insoluble content is mainly composed of large-molecule asphaltenes, which have a significant positive effect on the graphitization process of asphalt.

[0063] In some specific embodiments, the quinoline insoluble content in the asphalt is less than 10 wt.%; including but not limited to point values ​​or ranges between any one of 9 wt.%, 8 wt.%, 7 wt.%, 6 wt.%, 5 wt.%, 4 wt.%, 3 wt.%, and 1 wt.%. The quinoline insoluble content is mainly a difficult-to-graphitize component, and controlling its content at a low level is beneficial to improving the performance of the catalytic graphitizing agent.

[0064] In some specific embodiments, the particle size of the asphalt is ≤100μm; including but not limited to point values ​​or ranges between any one of 100μm, 80μm, 60μm, 50μm, 30μm, 20μm, 10μm, 5μm, and 1μm. If the particle size of the asphalt is too large, it will lead to a decrease in the stability of the resin impregnation solution; if the particle size of the asphalt is too small, the pretreatment process of the asphalt powder, including crushing and sieving, will be more complex and time-consuming.

[0065] In some specific embodiments, the asphalt is subjected to crushing and sieving.

[0066] In some specific embodiments, the asphalt includes at least one of natural asphalt, petroleum asphalt, coal tar pitch, and modified asphalt. Modified asphalt includes, but is not limited to, naphthalene-modified asphalt, rubber-modified asphalt, or thermoplastic resin-modified asphalt, etc., and this invention does not limit the specific types.

[0067] In some specific embodiments, the boron-based catalyst includes at least one of elemental boron, boron carbide, and boron nitride.

[0068] The boron-based catalyst is preferably boron carbide. When boron carbide is used, it acts as a grinding aid and lubricant during the grinding process, thereby improving grinding efficiency.

[0069] In some specific embodiments, the average particle size (i.e., Dv50 particle size) of the boron-based catalyst is 0.5–10 μm, including but not limited to point values ​​or ranges between any one of 0.5 μm, 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, and 10 μm. If the boron-based catalyst particle size is too small, it is difficult to load onto the asphalt surface during grinding; while if the particle size is too large, even approaching the particle size of the asphalt particles, it is difficult to form a microscopic composite structure.

[0070] In a second aspect, the present invention provides a method for preparing the catalytic graphitizing agent, comprising the following steps: mixing asphalt and a boron-based catalyst and mechanically grinding them to load the boron-based catalyst onto the surface of the asphalt, thereby obtaining the catalytic graphitizing agent.

[0071] The method for preparing a catalytic graphitizing agent provided by this invention modifies a boron-based catalyst by introducing asphalt. After mechanical grinding, the boron-based catalyst particles adhere to the surface of the asphalt particles. During the hot pressing and graphitization process, the molten asphalt in this micro-composite structure can fill the interface between the boron-based catalyst and other components, thereby playing an interface optimization role. This solves the problems of rough microstructure of resin carbon, poor interface between resin carbon and carbon fiber in carbon sheets, and high contact resistance caused by using boron-based catalysts alone, and thus improves the conductivity of carbon sheets and the gas diffusion layer made therefrom.

[0072] Furthermore, this method has advantages such as simple process, short process, easy operation, low equipment cost, and suitability for mass production.

[0073] In some specific embodiments, the softening point of the asphalt is 80 to 120°C, including but not limited to any one of 80°C, 85°C, 90°C, 95°C, 100°C, 105°C, 110°C, 115°C, and 120°C, or a range between any two.

[0074] By utilizing the characteristic of low-softening-point asphalt to readily fuse during grinding, the fused asphalt acts as a binder, allowing boron-based catalyst particles to be loaded onto the surface of the asphalt particles, forming a catalytic graphitizer with a microscopic composite structure. This method avoids the solvent usage problems commonly found in other composite methods, further reducing production costs.

[0075] In some specific embodiments, the mechanical grinding method includes, but is not limited to, ball milling.

[0076] The powder mixture of asphalt and boron-based catalysts should be subjected to dry mechanical grinding with an appropriate intensity (the intensity is determined by parameters such as the rotation speed, time, and structure of the equipment components). If the grinding intensity is too high, the prepared catalytic graphitizer will clump together; if the grinding intensity is too low, the boron-based catalyst will be difficult to load onto the asphalt surface through the micro-melting and coagulation of the asphalt during grinding, and will not be able to form an effective micro-composite structure.

[0077] Taking ball milling as an example, the operating conditions of this invention are as follows: (1) The equipment used in the ball milling method is a planetary ball mill with a rotation speed of 300 to 1000 rpm, such as 500 rpm, 600 rpm, or 800 rpm; (2) The ball milling method is a dry ball milling method; (3) The ball milling method uses a zirconium oxide ball mill jar and grinding balls, the ball-to-material ratio in the ball milling ranges from 1:1 to 6:1, such as 3:1, 4:1, or 5:1, and the diameter of the grinding balls ranges from 1 to 15 mm. For example, 3mm, 5mm, 8mm, 10mm or 13mm; (4) The ball milling method includes intermittent ball milling, which specifically includes: milling for 3 to 15 minutes (e.g. 5 minutes, 6 minutes, 8 minutes, 10 minutes or 12 minutes), stopping the machine to cool for 2 to 10 minutes (e.g. 3 minutes, 5 minutes or 8 minutes), and repeating the ball milling and cooling process 10 to 40 times (e.g. 15 times, 20 times, 30 times or 35 times).

[0078] During the grinding process, by controlling parameters such as grinding time and grinding intensity, and by setting intervals during grinding to allow the sample in the equipment to cool sufficiently, it is possible to ensure that the boron-based catalyst is loaded onto the surface of the asphalt particles. If the grinding time is too long, the grinding intensity is too high, or the cooling is insufficient, the asphalt will undergo large-scale coalescence during grinding, causing the sample to clump together; while if the grinding time and intensity are too low, it will be difficult to load the boron-based catalyst onto the surface of the asphalt particles.

[0079] Thirdly, the present invention provides a carbon sheet for a gas diffusion layer, which is mainly made of resin impregnation liquid and virgin carbon sheet.

[0080] The resin impregnation solution is mainly composed of the catalytic graphitizing agent and phenolic resin in a mass ratio of 1-15:15-45. The mass ratio of the catalytic graphitizing agent to the phenolic resin includes, but is not limited to, any one of the following values ​​or a range between any two: 1:15, 1:20, 1:25, 1:30, 1:35, 1:40, 1:45, 5:15, 5:20, 5:25, 5:30, 5:35, 5:40, 5:45, 10:15, 10:20, 10:25, 10:30, 10:35, 10:40, 10:45, 15:15, 15:20, 15:25, 15:30, 15:35, 15:40, and 15:45.

[0081] This invention catalyzes the graphitization reaction of phenolic resin carbon by adding a catalytic graphitizing agent containing asphalt and boron-based catalysts, thereby reducing the roughness of the resin carbon's microstructure and solving the problems of poor interface between resin carbon and carbon fiber and high contact resistance. This reduces the resistivity of carbon sheets, improves the conductivity of carbon sheets used in gas diffusion layers, and reduces energy consumption and production costs.

[0082] Meanwhile, by controlling the ratio of catalytic graphitizing agent and phenolic resin, this invention can improve the homogeneous graphitization effect of catalytic graphitizing agent on resin carbon, catalyze the graphitization process of phenolic resin carbon, improve the graphitization degree of phenolic resin carbon and the conductivity of carbon sheets used in gas diffusion layer.

[0083] In some specific embodiments, in order to further improve the graphitization degree of phenolic resin carbon and the conductivity of carbon sheets for gas diffusion layers, the resin impregnation liquid includes the following components in parts by mass: 0.1 to 1.5 parts of the catalytic graphitizing agent, 1.5 to 4.5 parts of phenolic resin, 0.01 to 0.2 parts of the anti-settling agent, and 2 to 10 parts of solvent.

[0084] The catalytic graphitizing agent, by weight parts, includes, but is not limited to, any one of the following point values ​​or any range between any two: 0.1 parts, 0.3 parts, 0.4 parts, 0.5 parts, 0.6 parts, 0.8 parts, 1 part, 1.2 parts, 1.3 parts, and 1.5 parts; the phenolic resin, by weight parts, includes, but is not limited to, any one of the following point values ​​or any range between any two: 1.5 parts, 1.8 parts, 2 parts, 2.3 parts, 2.5 parts, 2.8 parts, 3 parts, 3.2 parts, 3.5 parts, 3.7 parts, 4 parts, 4.3 parts, and 4.5 parts; and the anti-settling agent. The values, by mass parts, include but are not limited to, any one of the following point values ​​or any range between any two: 0.01 parts, 0.02 parts, 0.03 parts, 0.04 parts, 0.05 parts, 0.06 parts, 0.07 parts, 0.08 parts, 0.09 parts, 0.1 parts, 0.15 parts, and 0.2 parts; the values, by mass parts, include but are not limited to, any one of the following point values ​​or any range between any two: 2 parts, 3 parts, 4 parts, 4.5 parts, 5 parts, 5.8 parts, 6 parts, 6.5 parts, 7 parts, 7.5 parts, 8 parts, 8.5 parts, 9 parts, and 10 parts.

[0085] The main function of the anti-settling agent is to maintain the stability of the catalytic graphitizing agent in the resin impregnation solution system and optimize the resin impregnation process.

[0086] In some specific embodiments, the phenolic resin includes thermosetting phenolic resin.

[0087] In some specific embodiments, the free phenol content of the phenolic resin is 10% to 20%, including but not limited to any one of 10%, 12%, 13%, 15%, 18%, and 20%, or any range between two of them.

[0088] In some specific embodiments, the solid content of the phenolic resin is 40% to 70%, including but not limited to any one of 40%, 45%, 50%, 55%, 60%, 65%, and 70%, or any range between two of them.

[0089] In some specific embodiments, the antisettling agent includes at least one of polyvinylpyrrolidone, polyurea, and polyamide wax.

[0090] In some specific embodiments, the solvent includes, but is not limited to, an organic solvent, such as at least one of methanol, ethanol, isopropanol and toluene.

[0091] Fourthly, the present invention provides a method for preparing the carbon sheet for the gas diffusion layer, or a catalytic graphitization method for the carbon sheet for the gas diffusion layer of a fuel cell, comprising the following steps: impregnating a virgin carbon sheet with a resin impregnation solution and then drying it to obtain an impregnated carbon sheet; hot-pressing and curing the impregnated carbon sheet to obtain a cured carbon sheet; graphitizing the cured carbon sheet and cooling it to obtain the carbon sheet for the gas diffusion layer. The resin impregnation solution mainly consists of the catalytic graphitizing agent and phenolic resin in a mass ratio of 1–15:15–45.

[0092] The method for preparing carbon sheets for gas diffusion layers provided by this invention is simple to operate, has a short process flow, is suitable for mass production, and has low production costs. Furthermore, the carbon sheets for gas diffusion layers prepared by this method have good electrical conductivity.

[0093] In some specific embodiments, the preparation method of the virgin carbon sheet includes wet papermaking, which specifically includes: mixing chopped carbon fibers and a dispersion medium to obtain a chopped carbon fiber slurry, then using a papermaking machine to form a sheet, followed by drying.

[0094] Figure 1 This is a schematic flowchart illustrating a method for preparing a carbon sheet for a gas diffusion layer provided by the present invention.

[0095] In some specific embodiments, the chopped carbon fibers include at least one of polyacrylonitrile-based carbon fibers, pitch-based carbon fibers, and viscose-based carbon fibers.

[0096] In some specific embodiments, the average length of the chopped carbon fiber is 1 to 20 mm, including but not limited to any one of 1 mm, 3 mm, 5 mm, 8 mm, 10 mm, 12 mm, 15 mm, 17 mm, and 20 mm, or any range between two of them; the average diameter of the chopped carbon fiber is 1 to 15 μm, including but not limited to any one of 1 μm, 3 μm, 5 μm, 8 μm, 10 μm, 12 μm, and 15 μm, or any range between two of them.

[0097] In some specific embodiments, the areal density of the virgin carbon sheet is 15–60 g / m². 2 ; including but not limited to 15g / m 2 20g / m 2 25g / m 2 30g / m 2 35g / m 2 40g / m 2 45g / m 2 50g / m 2 60g / m 2 The point value of any one of them or the range value between any two.

[0098] In some specific embodiments, the average thickness of the virgin carbon sheet is 120 to 600 μm; including but not limited to a point value of any one of 120 μm, 200 μm, 300 μm, 400 μm, 500 μm, and 600 μm or a range between any two.

[0099] In some specific implementations, the dispersion medium includes water.

[0100] In some specific implementations, short-cut carbon fiber slurry is prepared using a high-speed dispersion device.

[0101] In some specific implementations, the immersion time in the immersion process is 10 to 300 seconds; including but not limited to any one of 10 seconds, 30 seconds, 50 seconds, 80 seconds, 100 seconds, 150 seconds, 200 seconds, 250 seconds, and 300 seconds, or any range between two of them.

[0102] In some specific embodiments, the drying temperature in the impregnation process is 60 to 150°C, including but not limited to any one of 60°C, 70°C, 80°C, 100°C, 120°C, 130°C, and 150°C, or any range between two of them.

[0103] In some specific embodiments, the drying time in the impregnation process is 1 to 30 minutes, including but not limited to any one of 1 minute, 3 minutes, 5 minutes, 8 minutes, 10 minutes, 15 minutes, 20 minutes, 25 minutes, and 30 minutes, or any range between two of them.

[0104] In some specific embodiments, the hot pressing temperature is 100 to 180°C, including but not limited to any one of 100°C, 110°C, 120°C, 130°C, 140°C, 150°C, 160°C, and 180°C, or a range between any two.

[0105] In some specific embodiments, the pressure of the hot pressing is ≤5 MPa, including but not limited to a point value of any one of 0.1 MPa, 0.5 MPa, 1 MPa, 2 MPa, 3 MPa, 4 MPa, and 5 MPa, or a range between any two.

[0106] In some specific embodiments, the hot pressing time is 2 to 120 minutes, including but not limited to any one of 2 minutes, 3 minutes, 5 minutes, 10 minutes, 15 minutes, 20 minutes, 30 minutes, 40 minutes, 60 minutes, 80 minutes, 90 minutes, 100 minutes, and 120 minutes, or any range between two of them.

[0107] In some specific embodiments, the hot pressing equipment includes, but is not limited to, a flat vulcanizing machine.

[0108] In some specific embodiments, the graphitization temperature is 1600–2400°C, including but not limited to any one of 1600°C, 1700°C, 1800°C, 1900°C, 2000°C, 2100°C, 2200°C, 2300°C, and 2400°C, or a range between any two. The method for preparing carbon sheets for gas diffusion layers provided by this invention, by adding a catalytic graphitizing agent during the preparation process, can obtain phenolic resin carbon with a high degree of graphitization at a relatively low graphitization temperature. The resulting carbon sheets for gas diffusion layers have good electrical conductivity and low energy consumption and production cost.

[0109] In some specific embodiments, the graphitization time is determined by the heating rate and the final temperature during the graphitization process, and can be, for example, 16 min to 240 min, but is not limited to.

[0110] In some specific embodiments, the heating rate of graphitization is 10 to 100 °C / min, including but not limited to any one of 10 °C / min, 20 °C / min, 30 °C / min, 40 °C / min, 50 °C / min, 60 °C / min, 70 °C / min, 80 °C / min, 90 °C / min, and 100 °C / min, or a range between any two.

[0111] In some specific embodiments, the graphitization atmosphere includes an inert atmosphere, such as argon or nitrogen.

[0112] In some specific embodiments, the graphitization equipment includes, but is not limited to, a graphitization furnace.

[0113] The embodiments of the present invention will be described in detail below with reference to examples. However, those skilled in the art will understand that the following examples are for illustrative purposes only and should not be considered as limiting the scope of the invention. Unless otherwise specified in the examples, conventional conditions or conditions recommended by the manufacturer are followed. Reagents or instruments whose manufacturers are not specified are all commercially available conventional products.

[0114] Example 1

[0115] The preparation method of the catalytic graphitizing agent provided in this embodiment includes the following steps: Medium-temperature coal tar pitch with a softening point of 85℃, a coking value of 45.6%, a toluene-insoluble content of 9.5 wt.%, and a quinoline-insoluble content of 0.2 wt.% is used. The coal tar pitch is pulverized using a blade pulverizer and then sieved to obtain coal tar pitch powder with a particle size ≤100 μm. Boron carbide powder with an average particle size of 2 μm is used as a boron-based catalyst. Coal tar pitch powder and boron carbide powder are weighed at a mass ratio of 6:1, and the two powders are mixed and mechanically ground using a planetary ball mill at a speed of 800 rpm. Dry ball milling is used, and the grinding jar and grinding balls are made of zirconium oxide with a ball-to-powder ratio of 3:1 and a grinding ball diameter of 4 mm. The grinding process is repeated 12 times, with a 3-minute cooling period after every 5 minutes of grinding, to obtain the catalytic graphitizing agent. The catalytic graphitizing agent comprises composite particles, which include asphalt and a boron-based catalyst supported on the asphalt surface. For example... Figure 2 The image shown is an optical microscope image of the asphalt used in Example 1 after it has been crushed and sieved; as shown... Figure 3 The image shown is an optical microscope image of the catalytic graphitizing agent prepared in Example 1. By comparison... Figure 2 and Figure 3 It can be seen that, through mechanical grinding, some of the white boron carbide crystal particles are loaded onto the surface of the black asphalt particles under the fusion effect of asphalt, forming a catalytic graphitizing agent with a micro-composite structure.

[0116] The method for preparing the carbon sheet for the gas diffusion layer provided in this embodiment includes the following steps:

[0117] (1) Short-cut polyacrylonitrile-based carbon fibers with an average length of 4 mm and an average diameter of 7 μm were used. Water was used as the dispersion medium, and the carbon fibers were dispersed using a high-speed dispersion device to prepare a slurry. After forming the slurry using a sheet-forming machine, the slurry was dried at 100 °C for 30 min to obtain a surface density of 25 g / m³. 2 Native carbon sheet with an average thickness of 240μm.

[0118] (2) Weigh 6 parts of ethanol (solvent) by mass, then add 3 parts of thermosetting phenolic resin to the ethanol under stirring, then add 0.1 parts of polyurea anti-settling agent, and finally add 0.6 parts of the above-prepared catalytic graphitizing agent (i.e., the mass ratio of catalytic graphitizing agent to phenolic resin is 6:30). Then disperse the mixed solution using a dispersion disc mixer to obtain a resin impregnation solution. Then immerse the virgin carbon sheet obtained in step (1) into the resin impregnation solution for 120s, take it out and dry it at 100℃ for 10min to obtain the impregnated carbon sheet.

[0119] (3) The impregnated carbon sheet obtained in step (2) is hot-pressed and cured in a flat vulcanizing machine, wherein the temperature, pressure and time of hot pressing are 140℃, 4MPa and 30min respectively, to obtain the cured carbon sheet.

[0120] (4) Under the protection of argon, the solidified carbon sheet obtained in step (3) is heated to 2000℃ at a heating rate of 15℃ / min to be graphitized, so as to obtain a carbon sheet that can be used as a gas diffusion layer or a gas diffusion layer substrate for fuel cells.

[0121] like Figure 4 The image shown is an optical microscope image of the carbon sheet used for the gas diffusion layer prepared in Example 1.

[0122] Example 2

[0123] The preparation method of the catalytic graphitizing agent provided in this embodiment is basically the same as that in Example 1, except that the coal tar pitch is replaced with petroleum pitch with a softening point of 120°C, a coking value of 55.4%, a toluene insoluble content of 13.1 wt.%, and a quinoline insoluble content of 0.4 wt.%.

[0124] Using the catalytic graphitizing agent obtained in this embodiment, carbon sheets for gas diffusion layers are prepared according to the preparation method of carbon sheets for gas diffusion layers in Example 1.

[0125] Example 3

[0126] The preparation method of the catalytic graphitizing agent provided in this embodiment is basically the same as that in Example 1, except that the coal tar pitch is replaced with naphthalene-modified pitch with a softening point of 115°C, a coking value of 50.4%, a toluene insoluble content of 18.1 wt.%, and a quinoline insoluble content of 0.4 wt.%.

[0127] Using the catalytic graphitizing agent obtained in this embodiment, carbon sheets for gas diffusion layers are prepared according to the preparation method of carbon sheets for gas diffusion layers in Example 1.

[0128] Example 4

[0129] The preparation method of the catalytic graphitizing agent provided in this embodiment is basically the same as that in Example 1, except that boron carbide is replaced with boron element with an average particle size of 5 μm.

[0130] Using the catalytic graphitizing agent obtained in this embodiment, carbon sheets for gas diffusion layers are prepared according to the preparation method of carbon sheets for gas diffusion layers in Example 1.

[0131] Example 5

[0132] The preparation method of the catalytic graphitizing agent provided in this embodiment is basically the same as that in Example 1, except that boron carbide is replaced with boron nitride with an average particle size of 10 μm.

[0133] Using the catalytic graphitizing agent obtained in this embodiment, carbon sheets for gas diffusion layers are prepared according to the preparation method of carbon sheets for gas diffusion layers in Example 1.

[0134] Example 6

[0135] The preparation method of the catalytic graphitizing agent provided in this embodiment is basically the same as that in Example 1, except that the grinding equipment speed is 600 rpm, the ball mill jar and grinding balls are made of zirconium oxide, the ball-to-material ratio is 3:1, and the diameter of the grinding balls is 4 mm. The grinding process is repeated 10 times, with a 3-minute cooling period after every 3 minutes of grinding.

[0136] Using the catalytic graphitizing agent obtained in this embodiment, carbon sheets for gas diffusion layers are prepared according to the preparation method of carbon sheets for gas diffusion layers in Example 1.

[0137] Example 7

[0138] The preparation method of the catalytic graphitizing agent provided in this embodiment is basically the same as that in Example 1, except that the mass ratio of coal tar pitch powder and boron carbide powder is replaced with 15:1.

[0139] Using the catalytic graphitizing agent obtained in this embodiment, carbon sheets for gas diffusion layers are prepared according to the preparation method of carbon sheets for gas diffusion layers in Example 1.

[0140] Example 8

[0141] The preparation method of the catalytic graphitizing agent provided in this embodiment is basically the same as that in Example 1, except that the mass ratio of coal tar pitch powder and boron carbide powder is replaced with 3:1.

[0142] Using the catalytic graphitizing agent obtained in this embodiment, carbon sheets for gas diffusion layers are prepared according to the preparation method of carbon sheets for gas diffusion layers in Example 1.

[0143] Example 9

[0144] The preparation method of the catalytic graphitizing agent provided in this embodiment is the same as that in Example 1.

[0145] The preparation method of the carbon sheet for the gas diffusion layer provided in this embodiment is basically the same as that in Example 1. The difference is that in step (2), the amount of catalytic graphitizing agent added is replaced with 0.3 parts (that is, the mass ratio of catalytic graphitizing agent and phenolic resin is 3:30).

[0146] Example 10

[0147] The preparation method of the catalytic graphitizing agent provided in this embodiment is the same as that in Example 1.

[0148] The preparation method of the carbon sheet for the gas diffusion layer provided in this embodiment is basically the same as that in Example 1. The difference is that in step (2), the amount of catalytic graphitizing agent added is replaced with 1.2 parts (i.e., the mass ratio of catalytic graphitizing agent and phenolic resin is 12:30).

[0149] Comparative Example 1

[0150] The preparation method of the carbon sheet for gas diffusion layer provided in this comparative example is basically the same as that in Example 1. The difference is that in step (2), no catalytic graphitizing agent is added, and the amount of thermosetting phenolic resin added is replaced with 3.6 parts.

[0151] Comparative Example 2

[0152] The preparation method of the catalytic graphitizing agent provided in this comparative example is the same as that in Example 1.

[0153] The preparation method of the carbon sheet for gas diffusion layer provided in this comparative example is basically the same as that in Example 1. The difference is that in step (2), the catalytic graphitizing agent is replaced with boron carbide powder with an average particle size of 2 μm of equal mass.

[0154] Comparative Example 3

[0155] The preparation method of the catalytic graphitizing agent provided in this comparative example is the same as that in Example 1.

[0156] The preparation method of the carbon sheet for the gas diffusion layer provided in this comparative example is basically the same as that in Example 1. The difference is that in step (2), the catalytic graphitizing agent is replaced with an equal mass of coal tar powder prepared in Example 1.

[0157] Comparative Example 4

[0158] The preparation method of the catalytic graphitizing agent provided in this comparative example is basically the same as that in Example 1, except that the coal tar pitch is replaced with coal tar pitch with a softening point of 160°C, a coking value of 66.4%, a toluene insoluble content of 33.1 wt.%, and a quinoline insoluble content of 11.3 wt.%.

[0159] Using the catalytic graphitizing agent prepared in this comparative example, carbon sheets for gas diffusion layers were prepared according to the preparation method of carbon sheets for gas diffusion layers in Example 1.

[0160] Experimental Example

[0161] According to the testing standard GB / T20042.7-2014, Proton Exchange Membrane Fuel Cell Part 7: Test Methods for Carbon Paper Characteristics, the performance of the carbon sheets for the gas diffusion layer obtained in the above embodiments and comparative examples was tested. The planar resistivity and vertical resistivity of the carbon sheets for the gas diffusion layer were calculated. The carbonization rate was calculated as: (mass of carbon sheets for the gas diffusion layer / mass of carbon sheets after curing) × 100%. The test results are shown in Table 1.

[0162] Table 1 Results of carbonization rate, planar resistivity and vertical resistivity

[0163] Group Carbonization rate (%) Planar resistivity (mΩ·cm) Vertical resistivity (mΩ·cm) Example 1 67.9 8.57 515 Example 2 66.5 9.88 496 Example 3 66.8 8.67 520 Example 4 68.1 8.30 531 Example 5 68.3 9.44 591 Example 6 68.1 9.19 657 Example 7 65.9 10.48 580 Example 8 69.7 9.22 722 Example 9 66.8 9.77 540 Example 10 68.2 9.34 550 Comparative Example 1 68.6 12.53 588 Comparative Example 2 72.6 9.54 934 Comparative Example 3 64.3 11.33 595 Comparative Example 4 71.7 9.24 747

[0164] As can be seen from Table 1, each embodiment has a lower resistivity.

[0165] Specifically, Comparative Example 1 can serve as a control group, as it does not contain asphalt or boron carbide, and its resin component is mainly phenolic resin, resulting in carbon sheet performance. Example 1 uses a composite catalytic graphitizing agent of asphalt and boron carbide, which significantly improves both planar and vertical resistivity compared to Comparative Example 1, with the improvement in planar resistivity being the most pronounced.

[0166] Example 10 used a higher proportion of catalytic graphitizer than Example 1, but its conductivity was slightly worse than that of Example 1; Example 9 used a lower proportion of catalytic graphitizer than Example 1, and its conductivity was slightly worse than that of Example 1, indicating that the amount of catalytic graphitizer has a certain impact on the planar resistivity and vertical resistivity of the carbon sheet used in the gas diffusion layer.

[0167] Example 8 reduced the ratio of asphalt to boron carbide and increased the amount of boron carbide. It was found that the vertical resistance increased significantly compared to Example 1, indicating that when the boron carbide content is too high, the asphalt cannot effectively fill the interface, and the problem of poor contact resistance still exists.

[0168] Example 7 increased the ratio of coal tar pitch to boron carbide and found that both the vertical resistance and the planar resistance increased compared to Example 1, indicating that the amount of boron carbide used was too small to effectively catalyze graphitization.

[0169] Comparative Example 2 is a scheme that simply adds boron carbide. Its carbonization rate is higher than that of Example 1, which illustrates the catalytic graphitization effect of boron carbide. The addition of boron carbide significantly optimizes the planar resistivity, but causes a significant deterioration in the vertical resistivity. This illustrates the problem of poor interface and contact resistance caused by boron-based catalysts.

[0170] Comparative Example 3 is a scheme that simply adds asphalt. Its electrical conductivity is similar to that of Comparative Example 1. The lower carbonization rate is because the carbonization rate of asphalt is lower than that of phenolic resin.

[0171] Comparative Example 4 uses asphalt with an excessively high softening point. Since asphalt with a high softening point is difficult to trigger micro-coalescence during grinding to form a micro-composite structure with the boron-based catalyst, it is impossible to optimize the interface and contact resistance problems of the boron-based catalyst.

[0172] Furthermore, an optical microscope image of the carbon sheet used for the gas diffusion layer prepared in Example 1 can be found here. Figure 4 For the optical microscope image of the gas diffusion layer prepared in Comparative Example 1 using carbon sheet, see [image of the gas diffusion layer prepared in Comparative Example 1]. Figure 5 The optical microscope image of the gas diffusion layer prepared using carbon sheet in Comparative Example 2 is shown below. Figure 6 The optical microscope image of the gas diffusion layer prepared using carbon sheet in Comparative Example 3 is shown below. Figure 7 .

[0173] It can be seen that, Figure 5 In Comparative Example 1, the surface of the phenolic resin carbon without boron carbide and pitch was relatively smooth. This is because Comparative Example 1 did not add a boron-based catalyst, and therefore did not have the problem of a rough surface of the phenolic resin carbon. Figure 7 In Comparative Example 3, the surface of the resin carbon with added asphalt showed some pores due to the decomposition of asphalt during the graphitization process. Figure 4 Example 1 and Comparative Example 2 Figure 6 It can be seen that catalytic graphitizers with composite structures can improve the roughness of resin carbon to a certain extent, thereby optimizing the interface and contact resistance.

[0174] In summary, this invention utilizes the easy melting and coalescence properties of low-softening-point asphalt during mechanical grinding and the easy graphitization of carbon precursors from asphalt. Combined with the catalytic effect of boron-based catalysts in the resin graphitization process, and by combining asphalt and boron-based catalysts and controlling their ratio, it improves upon the problems of rough resin carbon, poor interface, and poor contact resistance that exist when using boron-based catalysts alone. This method can catalyze the graphitization process of resin carbon in the graphitization process, optimize the planar and vertical conductivity of the carbon sheets used in the gas diffusion layer, and reduce the graphitization temperature, thereby achieving the goal of saving equipment and graphitization energy costs.

[0175] Although the present invention has been illustrated and described with specific embodiments, it should be understood that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; those skilled in the art should understand that modifications can be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein, without departing from the spirit and scope of the present invention; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention; therefore, this means that all such substitutions and modifications that fall within the scope of the present invention are included in the appended claims.

Claims

1. A catalytic graphitization agent, characterized in that, The catalytic graphitizing agent is a composite particle of boron-based catalyst supported on the surface of asphalt; The mass ratio of the asphalt to the boron-based catalyst is 2~20:1; The softening point of the asphalt is 80~120℃.

2. The catalytic graphitizing agent according to claim 1, characterized in that, At least one of the following conditions must be met: (1) The coking value of the asphalt is 30%~60%; (2) The toluene-insoluble content in the asphalt is 5 wt.%~40 wt.%; (3) The content of quinoline insoluble matter in the asphalt is less than 10 wt.%; (4) The particle size of the asphalt is ≤100μm; (5) The asphalt includes at least one of natural asphalt, petroleum asphalt, coal tar pitch and modified asphalt.

3. The catalytic graphitizing agent according to claim 1, characterized in that, At least one of the following conditions must be met: (1) The boron-based catalyst includes at least one of elemental boron, boron carbide, and boron nitride; (2) The average particle size of the boron-based catalyst is 0.5~10μm.

4. The method for preparing the catalytic graphitizing agent according to any one of claims 1 to 3, characterized in that, The process includes the following steps: mixing asphalt and a boron-based catalyst and mechanically grinding them to load the boron-based catalyst onto the asphalt surface.

5. The method for preparing the catalytic graphitizing agent according to claim 4, characterized in that, The softening point of the asphalt is 80~120℃.

6. The method for preparing the catalytic graphitizing agent according to claim 4, characterized in that, The mechanical grinding method includes ball milling, and the operating conditions of the ball milling include: (1) the ball milling equipment includes a planetary ball mill, and the rotation speed of the equipment is 300~1000 rpm; (2) the ball milling is dry ball milling; (3) the ball milling uses a ball milling jar and grinding balls made of zirconium oxide material, the ball-to-material ratio in the ball milling is 1:1~6:1, and the diameter of the grinding balls is 1~15 mm; (4) the ball milling method includes intermittent ball milling, and the intermittent ball milling method specifically includes: each ball milling for 3~15 min, stopping for cooling for 2~10 min, and repeating the ball milling and cooling process 10~40 times.

7. A carbon sheet for a gas diffusion layer, characterized in that, It is mainly made of resin impregnation liquid and virgin carbon sheet; The resin impregnation solution is mainly composed of a catalytic graphitizing agent and a phenolic resin as described in any one of claims 1 to 3, in a mass ratio of 1 to 15: 15 to 45.

8. The carbon sheet for the gas diffusion layer according to claim 7, characterized in that, At least one of the following conditions must be met: (1) The resin impregnation solution comprises the following components in parts by mass: 0.1 to 1.5 parts of the catalytic graphitizing agent, 1.5 to 4.5 parts of phenolic resin, 0.01 to 0.2 parts of the anti-settling agent and 2 to 10 parts of solvent; wherein the anti-settling agent comprises at least one of polyvinylpyrrolidone, polyurea and polyamide wax; (2) The phenolic resin includes thermosetting phenolic resin.

9. The method for preparing the carbon sheet for the gas diffusion layer as described in claim 7 or 8, characterized in that, Includes the following steps: The virgin carbon sheet is impregnated with a resin impregnation solution and then dried to obtain the impregnated carbon sheet. The impregnated carbon sheet is hot-pressed and cured to obtain a cured carbon sheet. The cured carbon sheet is graphitized to obtain the carbon sheet for the gas diffusion layer.

10. The method for preparing the carbon sheet for the gas diffusion layer according to claim 9, characterized in that, At least one of the following conditions must be met: (1) The preparation method of the virgin carbon sheet includes: mixing short carbon fibers and a dispersion medium to obtain a short carbon fiber slurry, then forming the slurry and drying it; (2) The temperature of the hot pressing is 100~180℃; (3) The pressure of the hot pressing is ≤5MPa; (4) The hot pressing time is 2~120 min; (5) The graphitization temperature is 1600~2400℃.

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