A method for preparing a carbon fiber paper for a gas diffusion layer of a fuel cell

Abstract

The application provides a preparation method of a fuel cell gas diffusion layer carbon fiber paper, comprising the following steps: mixing and defibrating carbon fibers, bonding fibers and a dispersing agent to prepare a carbon fiber raw paper by using a wet forming process; preparing a spraying liquid of carbon nano particles, and electrostatically spraying the spraying liquid onto the carbon fiber raw paper to prepare a carbon fiber spraying paper; immersing the carbon fiber spraying paper in a compound system of a resin and an ethanol solution, taking out the carbon fiber spraying paper, and drying, hot pressing and curing the carbon fiber spraying paper to obtain a resin-impregnated carbon fiber paper; carbonizing and graphitizing the resin-impregnated carbon fiber paper in a protective atmosphere to obtain a heat-treated carbon fiber paper; preparing a conductive spraying liquid of conductive particles, a bonding agent and a dispersing liquid, and electrostatically spraying the conductive spraying liquid onto the heat-treated carbon fiber paper to obtain the carbon fiber paper after drying; and based on the preparation of the carbon fiber paper, the modified carbon nano particles and the conductive particles are uniformly attached to the surface of the carbon fibers in stages by using an electrostatic spraying method to obtain a carbon fiber paper with high strength and high conductivity.

Description

Technical Field

[0001] This invention relates to the field of gas diffusion layer preparation technology for fuel cells, and specifically to a method for preparing carbon fiber paper for fuel cell gas diffusion layers. Background Technology

[0002] Fuel cell power generation technology is a clean and efficient power generation technology, and proton exchange membrane fuel cells are the most promising type of fuel cell, with advantages such as small size and weight, high energy density, fast start-up speed, and safe and reliable operation.

[0003] As one of the key components of a proton exchange membrane fuel cell, the gas diffusion layer not only supports the catalyst layer and stabilizes the electrode structure, but also provides gas, proton, electron, and drainage channels for the electrode reaction. Its performance directly affects the battery performance of the fuel cell.

[0004] Gas diffusion layers typically consist of a base layer and a microporous layer. The base layer materials mainly include carbon fiber paper, carbon fiber woven fabric, non-woven fabric, or carbon black paper, among which carbon fiber paper is widely recognized for its excellent performance.

[0005] In the prior art, carbon fiber paper for the gas diffusion layer substrate is usually made by wet forming technology to produce carbon paper base paper from short carbon fibers, which is then processed by resin impregnation, carbonization and graphitization.

[0006] Existing technologies have significant shortcomings: the composite strength of chopped carbon fiber / resin is low, the carbon fiber paper is brittle, and the electrical and thermal conductivity still need to be further improved; the strength, electrical and thermal conductivity of carbon fiber paper are closely related to the intrinsic properties of carbon fiber, while the surface of chopped carbon fiber itself has a large number of defects.

[0007] In view of the above-mentioned background technology and problems, there is a need to provide a preparation method that can improve the strength and conductivity of carbon fiber paper for gas diffusion layer in fuel cells. Summary of the Invention

[0008] This invention addresses the shortcomings of existing carbon fiber paper preparation techniques in terms of strength and conductivity by providing a method for preparing carbon fiber paper for fuel cell gas diffusion layers, comprising the following steps:

[0009] S10: Carbon fiber, bonding fiber and first dispersant are mixed and decomposed, and carbon fiber base paper is prepared by wet forming process;

[0010] S20: Take carbon nanoparticles, add a second dispersant, prepare a spraying liquid, and spray the spraying liquid onto the carbon fiber base paper using an electrostatic spraying method to obtain carbon fiber sprayed paper.

[0011] S30: The carbon fiber coated paper is impregnated in a resin and ethanol compound system, and then dried, hot-pressed and cured in sequence to obtain impregnated carbon fiber paper.

[0012] S40: The impregnated carbon fiber paper is carbonized and graphitized sequentially under a protective atmosphere to obtain heat-treated carbon fiber paper.

[0013] S50: Conductive particles, binder and third dispersant are formulated into a conductive spraying liquid, and the conductive spraying liquid is sprayed onto the heat-treated carbon fiber paper by electrostatic spraying method. After drying, the carbon fiber paper is obtained.

[0014] Furthermore, the carbon fiber is one or more of polyacrylonitrile carbon fiber, pitch-based carbon fiber, and rayon carbon fiber.

[0015] Furthermore, the average length of the carbon fiber is 1 mm to 10 mm.

[0016] Furthermore, the bonding fiber is a polyvinyl alcohol fiber.

[0017] Furthermore, the polyvinyl alcohol fiber is a water-soluble polyvinyl alcohol bonding fiber, the length of the water-soluble polyvinyl alcohol bonding fiber is 2 mm to 7 mm, the degree of alcoholysis is 98 mol% to 99 mol%, the degree of polymerization is 1500 to 2000, and after the water-soluble polyvinyl alcohol bonding fiber is prepared into an aqueous solution with a volume concentration of 3.5% to 5.5%, the viscosity is 24 mPa·s to 31 mPa·s. The amount of the water-soluble polyvinyl alcohol bonding fiber is 1% to 10% of the oven-dry mass of the carbon fiber.

[0018] Furthermore, the first dispersant is one or a mixture of several of PEO, anionic polyacrylamide, cationic polyacrylamide, and carboxymethyl cellulose ether, or one or a mixture of several of acrylic dispersants, maleic acid dispersants, and maleic anhydride ester dispersants.

[0019] Furthermore, the carbon nanoparticles are multi-walled carbon nanotubes, graphene, or modified carbon nanotubes, wherein the modified carbon nanotubes are one or more mixtures of hydroxylated carbon nanotubes, carboxylated carbon nanotubes, and aminated carbon nanotubes.

[0020] Furthermore, the modified carbon nanotubes satisfy at least one of the following conditions (A) to (C):

[0021] (A) The content of functionalized groups in the modified carbon nanotubes is 1 wt% to 5 wt% of the mass of the modified carbon nanotubes;

[0022] (B) The modified carbon nanotubes in the spraying liquid have a mass fraction of 10% to 50%;

[0023] (C) The amount of the modified carbon nanotubes sprayed is 0.05% to 5% of the carbon fiber.

[0024] Furthermore, both the second and third dispersants are one of dimethylformamide, dimethylacetamide, acetone, and ethanol, preferably dimethylformamide or dimethylacetamide.

[0025] Furthermore, the resin-ethanol compound system is a phenolic resin-ethanol compound system solution.

[0026] Furthermore, the concentration of the phenolic resin is 8% to 30%.

[0027] Furthermore, the soaking time is 0.5h to 1h.

[0028] Furthermore, the hot pressing temperature is 120°C to 250°C, the pressure is 2MPa to 40MPa, and the time is 10min to 60min.

[0029] Furthermore, the carbonization temperature is 1200℃ to 1700℃, the graphitization temperature is 2400℃ to 3200℃, the holding time is 0.5h to 3h, and the pressure is 10kPa to 300kPa.

[0030] Furthermore, the conductive particles are one or more mixtures of single-walled carbon nanotubes, carbon powder, carbon black powder, acetylene black powder, Ketjen black powder, and graphene.

[0031] Furthermore, the conductive particles must satisfy at least one of the following conditions (D) to (E):

[0032] (D) The mass fraction of the conductive particles in the conductive spraying liquid is 10% to 50%;

[0033] (E) The amount of conductive particles sprayed is 0.1% to 10% of the carbon fiber, preferably calculated based on the oven-dry mass ratio of the carbon fiber to the conductive particles.

[0034] Furthermore, the electrostatic spraying voltage is 10kV to 50kV, the spraying distance is 5cm to 40cm, and the spraying speed is 0.5ml / h to 10ml / h, preferably 5ml / h to 10ml / h.

[0035] The present invention achieves the following technical effects compared to the prior art:

[0036] (1) This invention uses carbon fiber and bonding fiber as raw materials and wet forming technology to prepare carbon fiber base paper as the substrate for electrostatic spraying. The electrostatic spraying technology is used to spray carbon nanoparticles onto the carbon fiber base paper to fill or compensate for the structural defects on the surface of the carbon fiber. Electrostatic spraying can effectively "disperse" the carbon nanoparticles to form a uniform diffusion state. The dispersed carbon nanoparticles are adsorbed and deposited on the carbon fiber paper by high voltage electrostatics, which effectively improves the adsorption strength, fineness and uniformity of carbon nanoparticles on the surface of the carbon fiber paper and improves the intrinsic strength of the carbon fiber. After the carbon fiber sprayed paper is impregnated and compounded in a resin and ethanol compound system, the carbon nanoparticles deposited on the carbon fiber base paper can be further effectively combined with the carbon fiber base paper to achieve the combination of resin and carbon fiber base paper, thereby forming a cross-linked system in structure and improving the interfacial bonding strength between carbon fiber and resin. This improves the intrinsic strength and the interfacial bonding strength between carbon fiber and resin, thereby improving the strength performance of the carbon fiber paper.

[0037] (2) Using the same electrostatic spraying technology, conductive particles are deposited on the heat-treated carbon fiber paper. The conductive particles are also "dispersed" by electrostatic spraying to form a uniform state. They are then adsorbed onto the heat-treated carbon fiber paper by high voltage electrostatic adsorption to improve the adsorption strength, fineness and uniformity, and to improve the microscopic bonding effect and bonding force between the conductive particles and the carbon fiber. This prevents the problem of weak or unstable conductivity caused by weak or uneven bonding, and effectively improves the conductivity of the carbon fiber paper.

[0038] (3) Both the deposition of carbon nanoparticles and the deposition of conductive particles are carried out by electrostatic spraying. The first spraying is mainly to increase the mechanical strength of carbon fiber paper, and the second spraying is mainly to increase the conductivity of carbon fiber paper. At the same time, the two sprayings promote each other. The high voltage electrostatic formation of the material has a stronger "adsorption" ability, which not only forms physical adsorption, but also promotes the formation of chemical structure. This makes the carbon fiber paper consistent in terms of preparation method and morphology. It prevents the use of multiple preparation methods to splice together, which would have multiple environmental effects on the combination effect of particle state and surface morphology formed by electrostatic spraying, thereby increasing the uncertainty factors in the preparation process, and increasing the particle adhesion, reliability, uniformity and other properties of carbon fiber paper after preparation, and reducing the stability in subsequent use. Attached Figure Description

[0039] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the structures shown in these drawings without creative effort.

[0040] Figure 1 This is a process flow diagram of the preparation method according to an embodiment of the present invention;

[0041] Figure 2 SEM image of the carbon fiber base paper prepared according to an embodiment of the present invention;

[0042] Figure 3 SEM image of carbon fiber coated paper prepared according to an embodiment of the present invention;

[0043] Figure 4 SEM image of heat-treated carbon fiber paper prepared according to an embodiment of the present invention;

[0044] Figure 5 SEM image of the carbon fiber paper prepared according to an embodiment of the present invention;

[0045] Figure 6 This is a physical image of the carbon fiber paper according to an embodiment of the present invention. Detailed Implementation

[0046] To facilitate understanding of the present invention, a more comprehensive description is provided below, along with preferred embodiments. However, the present invention can be implemented in many different forms and is not limited to the embodiments described herein. It should be understood that these embodiments are provided to provide a thorough and complete understanding of the disclosure of the present invention.

[0047] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the specification of this invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention; the term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0048] In the description of this invention, it should be understood that the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features; thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this invention, "a plurality of" means two or more, unless otherwise explicitly specified.

[0049] The weights of the relevant components mentioned in the embodiments of this invention can refer not only to the specific content of each component, but also to the proportional relationship between the weights of each component. Therefore, as long as the content of the relevant components is proportionally increased or decreased according to the embodiments of this invention, it is within the scope disclosed in the embodiments of this invention. Specifically, the weights mentioned in the embodiments of this invention can be well-known mass units in the chemical industry, such as μg, mg, g, kg, cm, mm, wt%, MPa, L, mL, etc.

[0050] First, to verify the strength and electrical conductivity of the carbon fiber paper formed by the preparation method of this embodiment, four comparative tests were conducted as shown in Table 1 below.

[0051] Table 1. Comparison of different preparation methods for forming different carbon fiber papers:

[0052]

[0053] Please see Figures 1 to 5 ; Figure 1 This is a process flow diagram of the preparation method according to an embodiment of the present invention.

[0054] The preparation method of Example 1 is as follows Figure 1 The key process flow for preparation is described in detail below.

[0055] Please see Figures 2 to 6 .

[0056] Figure 2 This is a SEM image of the carbon fiber base paper obtained according to an embodiment of the present invention, wherein... Figure 2 Figure (2a) is a SEM image with a 20 μm scale, and Figure (2b) is a SEM image with a 10 μm scale.

[0057] Figure 3 This is a SEM image of the carbon fiber coated paper obtained according to an embodiment of the present invention, wherein... Figure 3 Figure (3a) is a SEM image with a 10 μm scale, and Figure (3b) is a SEM image with a 10 μm scale.

[0058] Figure 4 This is a SEM image of the heat-treated carbon fiber paper prepared according to an embodiment of the present invention, wherein... Figure 4 Figure (4a) is a SEM image with a 20 μm scale, and Figure (4b) is a SEM image with a 10 μm scale.

[0059] Figure 5 Here is a SEM image of the carbon fiber paper prepared according to an embodiment of the present invention, wherein... Figure 5 Figure (5a) is a SEM image with a 20 μm scale, and Figure (5b) is a SEM image with a 2 μm scale.

[0060] Figure 6 This is a physical image of the carbon fiber paper according to an embodiment of the present invention.

[0061] Example 1:

[0062] Using the method for preparing carbon fiber paper for a fuel cell gas diffusion layer provided in this embodiment, Example 1 in Table 1 was prepared according to the following steps to form carbon fiber paper ①:

[0063] Step S10: Polyacrylonitrile carbon fibers with an average length of 1 mm to 10 mm, water-soluble polyvinyl alcohol binder fibers with an average length of 2 mm to 7 mm, and a first dispersant are mixed and decomposed, and carbon fiber base paper is obtained by wet forming process (see [link to relevant documentation]). Figure 2 ).

[0064] The water-soluble polyvinyl alcohol bonding fiber has a length of 2 mm to 7 mm, a degree of alcoholysis of 98 mol% to 99 mol%, and a degree of polymerization of 1500 to 2000. After being prepared into an aqueous solution with a volume concentration of 3.5% to 5.5%, its viscosity is 24 mPa·s to 31 mPa·s. The amount used is 1% to 10% of the oven-dry mass of the carbon fiber, preferably 3% to 7%, and more preferably 5%. The water-soluble polyvinyl alcohol used in this embodiment is a special modified fiber. Unlike conventional granular polyvinyl alcohol fibers, it has a filamentous structure, a longer length, and suitable viscosity and aqueous solution viscosity. By controlling its appropriate amount, it can more effectively play a bonding role, providing the basic conditions for the adhesion of carbon nanoparticles and conductive particles by spraying.

[0065] The first dispersant is generally one or a mixture of several of the following: PEO, anionic polyacrylamide, cationic polyacrylamide, and carboxymethyl cellulose ether; or one or a mixture of several of the following: acrylic dispersant, maleic acid dispersant, and maleic anhydride ester dispersant; PEO is preferred.

[0066] Depend on Figure 2 It can be seen that the prepared carbon fiber base paper contains a number of distributed "flocculents" that appear "filamentous". This indicates that the polyvinyl alcohol fibers with filamentous structure are uniformly dispersed in the carbon fiber base paper, which can provide a more convenient and stronger adhesion for the subsequent electrostatic spraying to produce carbon nanoparticles.

[0067] Step S20: Take carboxylated multi-walled carbon nanotubes, add dimethylformamide, and prepare a spraying solution. Under the conditions of 40kV voltage, 15cm spraying distance, and 2ml / h spraying speed, electrostatically spray the solution onto the carbon fiber base paper, and then dry it at 105℃ for 2h to obtain carbon fiber coated paper (see [link to product details]). Figure 3 ).

[0068] Among them, carboxylated carbon nanotubes meet the following conditions:

[0069] (A) The hydroxyl content of the carboxylated carbon nanotubes is 2 wt% of the mass of the modified carboxylated carbon nanotubes;

[0070] (B) The carboxylated carbon nanotubes have a mass fraction of 30% in the spraying liquid;

[0071] (C) The amount of carboxylated carbon nanotubes sprayed is 1% of the carbon fiber, based on the oven-dry mass ratio of the carbon fiber to the carboxylated carbon nanotubes.

[0072] Depend on Figure 3 As can be seen, after the first spraying process, carbon nanoparticles are effectively sprayed onto the carbon fiber base paper and firmly bonded to the carbon fiber filaments. The bonding between the carbon nanoparticles and the carbon fiber base paper is mainly facilitated by the filamentous structure of polyvinyl alcohol fibers. After the first spraying process, the carbon nanoparticles fill the gaps between the carbon fiber filaments in the carbon fiber base paper, repairing defects in the carbon fiber filaments and forming a three-dimensional network structure between the carbon fiber filaments. With its higher tensile strength and elastic modulus, it effectively improves the mechanical strength of the carbon fiber base paper. Preferably, multi-walled carbon nanotubes are used. On the one hand, their relatively large size allows for better bonding with the filamentous structure of polyvinyl alcohol fibers. On the other hand, it provides a foundation of higher-performance carbon nanoparticles for the subsequent fabrication of a three-dimensional network structure to form carbon fiber paper with stronger mechanical properties.

[0073] Step S30: The carbon fiber coated paper is impregnated in a compound solution of phenolic resin and ethanol, wherein the concentration of phenolic resin is 20%, for 0.5 hours. After being removed and dried, it is hot-pressed at a temperature of 150°C and a pressure of 30 MPa for 30 minutes to obtain the impregnated carbon fiber paper.

[0074] Step S40: The impregnated carbon fiber paper is carbonized at 1600°C under an argon atmosphere, and then graphitized at 2700°C for 2.5 hours under a pressure of 100 kPa; heat-treated carbon fiber paper is obtained (see [link to relevant documentation]). Figure 4 ).

[0075] Depend on Figure 4 It can be seen that the heat-treated carbon fiber paper formed after steps S30 and S40 has a three-dimensional network structure of "feather-like" or "webbed" shape in the gaps between the carbon fiber filaments. This not only allows carbon nanoparticles to fully fill and repair the carbon fiber filaments, but also further improves the bonding force between the carbon nanoparticles and the carbon fiber filaments, thereby further enhancing the mechanical strength of the carbon fiber paper.

[0076] Step S50: Single-walled carbon nanotubes, binder, and dimethylformamide are formulated into a conductive spraying liquid. Under conditions of 30kV voltage, 15cm spraying distance, and 2ml / h spraying speed, the conductive spraying liquid is electrostatically sprayed onto the heat-treated carbon fiber paper. After drying, carbon fiber paper is obtained, namely carbon fiber paper ① (see [link to product description]). Figure 5 and Figure 6 ).

[0077] Adhesives generally use PEO, PVA or PAM, with low molecular weight PEO preferred, having a molecular weight of 1,000 to 20,000.

[0078] The carbon black powder meets the following conditions:

[0079] (A) The carbon black powder has a mass fraction of 20% in the conductive spraying liquid;

[0080] (B) The amount of carbon black powder sprayed is 2% of the carbon fiber, based on the oven-dry mass ratio of the carbon fiber to the carbon black powder.

[0081] Depend on Figure 5 It can be seen that, based on the three-dimensional structure of the heat-treated carbon fiber paper formed in the previous process, the second coating makes it easier for single-walled carbon nanotubes to adhere to the heat-treated carbon fiber paper, forming an attachment state that is not easy to fall off, effectively improving the conductivity of the carbon fiber paper.

[0082] It is worth noting that, in the actual processing, for the preparation of the spraying liquid and conductive spraying liquid of this embodiment, other conductive agents (optionally: organic salt ionic compounds, tetrabutylammonium bromide, organic hydroxy quaternary ammonium salts), leveling agents (optionally: acrylic polymers such as epoxy acrylate resins), defoamers (optionally: silicone defoamers such as polydimethylsiloxane, polyoxypropylene-polyoxyethylene block polymers or polyether defoamers such as glycerol polyoxypropylene ether, non-silicone defoamers), surfactants (optionally: dodecylamine polyoxyethylene ether), and other necessary auxiliary components such as pH adjusters, antibacterial agents, anti-aging agents, and plasticizers can be added to improve the industrial processing performance of electrostatic spraying and the sprayed product.

[0083] Comparative Example 1:

[0084] Using the preparation method corresponding to Comparative Example 1 in Table 1, specifically following the preparation process, carbon fiber paper comparative ① was prepared:

[0085] Step S10: Same as S10 in Example 1;

[0086] Step S20: Same as S20 in Example 1;

[0087] Step S30: Same as S30 in Example 1;

[0088] Step S40: Same as S40 in Example 1;

[0089] Step S50: Take conductive particles (one or more of carbon powder, carbon black powder, acetylene black powder, Ketjen black powder, carbon nanotubes, single-walled carbon nanotubes, and graphene); and take a dispersant (dimethylformamide, dimethylacetamide, acetone, or ethanol); ultrasonically disperse to form a conductive particle dispersion; immerse the heat-treated carbon fiber paper in the conductive particle dispersion, heat at 150°C to 160°C until all the dispersant has evaporated, and continue heating for 5 to 10 minutes; obtain carbon fiber paper comparison ①.

[0090] Comparative Example 2:

[0091] Using the preparation method corresponding to Comparative Example 2 in Table 1, carbon fiber paper comparative ② was prepared according to the following preparation process:

[0092] Step S10: Same as S10 in Example 1;

[0093] Step S20: Take carbon nanoparticles (multi-walled carbon nanotubes, graphene, or modified carbon nanotubes, wherein the modified carbon nanotubes are one or more mixtures of hydroxylated carbon nanotubes, carboxylated carbon nanotubes, and aminated carbon nanotubes); and take a dispersant (dimethylformamide, dimethylacetamide, acetone, or ethanol); ultrasonically disperse to form a carbon nanoparticle dispersion; immerse the carbon fiber base paper in the carbon nanoparticle dispersion for 10 to 20 minutes, then remove it and dry it in an oven; thus obtaining carbon fiber paper-impregnated paper.

[0094] Step S30: The carbon fiber paper impregnated with the above carbon fiber paper is prepared by the same method as step S30 in Example 1 to obtain impregnated carbon fiber paper;

[0095] Step S40: The above-mentioned impregnated carbon fiber paper is processed using the same method as step S40 in Example 1 to obtain heat-treated carbon fiber paper;

[0096] Step S50: The above-mentioned impregnated carbon fiber paper is processed using the same method as step S50 of Example 1 to obtain carbon fiber paper, namely carbon fiber paper comparison ②.

[0097] Comparative Example 3:

[0098] Using the preparation method corresponding to Comparative Example 3 in Table 1, carbon fiber paper comparative ③ was prepared according to the following preparation process:

[0099] Step S10: Same as S10 in Example 1;

[0100] Step S20: Take carbon nanoparticles (multi-walled carbon nanotubes, graphene, or modified carbon nanotubes, wherein the modified carbon nanotubes are one or more mixtures of hydroxylated carbon nanotubes, carboxylated carbon nanotubes, and aminated carbon nanotubes); and take a dispersant (dimethylformamide, dimethylacetamide, acetone, or ethanol); ultrasonically disperse to form a carbon nanoparticle dispersion; immerse the carbon fiber base paper in the carbon nanoparticle dispersion for 10 to 20 minutes, then remove it and dry it in an oven; thus obtaining carbon fiber paper-impregnated paper.

[0101] Step S30: The carbon fiber paper impregnated with the above carbon fiber paper is prepared by the same method as step S30 in Example 1 to obtain impregnated carbon fiber paper;

[0102] Step S40: The above-mentioned impregnated carbon fiber paper is processed using the same method as step S40 in Example 1 to obtain heat-treated carbon fiber paper;

[0103] Step S50: Take conductive particles (one or more of carbon powder, carbon black powder, acetylene black powder, Ketjen black powder, carbon nanotubes, single-walled carbon nanotubes, and graphene); and take a dispersant (dimethylformamide, dimethylacetamide, acetone, or ethanol); ultrasonically disperse to form a conductive particle dispersion; immerse the heat-treated carbon fiber paper in the conductive particle dispersion, heat at 150°C to 160°C until all the dispersant evaporates, and continue heating for 5 to 10 minutes; obtain carbon fiber paper comparison ③.

[0104] The carbon fiber papers prepared above were tested, and the results are shown in Table 2 below.

[0105] Table 2: Performance test results of the various carbon fiber papers prepared in Table 1 (data are average values ​​from the tests):

[0106]

[0107] As can be seen from the performance test results in Table 2 above, the mechanical strength (including tensile strength and bending strength) of the carbon fiber paper ① prepared by this embodiment is greater than that of carbon fiber paper comparison ② and carbon fiber paper comparison ③, and its electrical conductivity (parallel resistivity and perpendicular resistivity) is better than that of carbon fiber paper comparison ② and carbon fiber paper comparison ③.

[0108] This embodiment employs electrostatic spraying technology to spray carbon nanoparticles onto carbon fiber base paper, filling or compensating for structural defects on the carbon fiber surface. Electrostatic spraying effectively "disperses" the carbon nanoparticles, creating a uniform diffusion state. High-voltage electrostatics then adsorb and deposit the dispersed carbon nanoparticles onto the impregnated carbon fiber paper, effectively enhancing the adsorption strength, fineness, and uniformity of the carbon nanoparticles on the impregnated carbon fiber paper surface, thereby improving the intrinsic strength of the carbon fiber. Furthermore, after impregnating the carbon fiber-coated paper in a resin and ethanol compound system, the carbon nanoparticles deposited on the carbon fiber base paper can further effectively bond with the carbon fiber base paper, achieving resin-carbon fiber base paper bonding and forming a structural cross-linked system. This enhances the interfacial bonding strength between the carbon fiber and the resin, thereby improving the intrinsic strength and the interfacial bonding strength between the carbon fiber and the resin, ultimately improving the strength properties of the carbon fiber paper.

[0109] In the deposition and preparation process of conductive particles, electrostatic spraying technology is also used to deposit conductive particles onto the heat-treated carbon fiber paper. On the one hand, the conductive particles are also "dispersed" by electrostatic spraying to form a uniform state. Then, they are adsorbed onto the heat-treated carbon fiber paper by high voltage electrostatic adsorption, which improves the adsorption strength, fineness and uniformity, and enhances the microscopic bonding effect and bonding force between conductive particles and carbon fiber. This prevents the problem of weak or unstable conductivity caused by weak or uneven bonding, and effectively improves the conductivity of carbon fiber paper.

[0110] Using electrostatic spraying in both processes ensures consistency between the preparation method and the final form of the carbon fiber paper. This prevents the use of multiple preparation methods in combination, which could lead to multiple environmental influences on the bonding effect of the particle state and surface morphology formed by electrostatic spraying. This would increase uncertainties in the preparation process, improve the particle adhesion, reliability, and uniformity of the carbon fiber paper after preparation, and reduce its stability during subsequent use.

[0111] Furthermore, the gas permeability and porosity of the four types of carbon fiber paper in Table 2 remain unchanged, indicating that the carbon fiber paper ① prepared in this way can improve strength and reduce resistance without affecting porosity and gas permeability, thus exhibiting a better overall effect than existing methods. Gas permeability and porosity work together to determine the discharge efficiency of water vapor and liquid water inside the fuel cell. If the permeability is insufficient, liquid water may accumulate in the diffusion layer or catalyst layer, blocking gas channels (i.e., causing "flooding"), leading to a sharp drop in battery performance. In addition, higher gas permeability can reduce the transmission resistance of reactant gases such as hydrogen and oxygen in the diffusion layer, accelerate the diffusion rate of gas to the catalyst layer, thereby improving the reaction efficiency and output power of the fuel cell.

[0112] To further verify and illustrate the influence of the amount of each electrostatic spraying in the first electrostatic spraying (i.e., electrostatic spraying to obtain carbon fiber coated paper) and the second electrostatic spraying (i.e., electrostatic spraying to obtain carbon fiber paper) on the mechanical strength and electrical conductivity of the prepared carbon fiber paper, the examples in Table 3 below are used for comparison.

[0113] Table 3: Effect of Coating Amount on Mechanical Strength and Electrical Conductivity (Example Table)

[0114]

[0115] Using the preparation process of Example 1 described above, and with the corresponding coating amounts in Table 3, the various carbon fiber papers shown in Table 3 were prepared.

[0116] Table 4: Performance test results of the various carbon fiber papers prepared in Table 3 (data are average values ​​from the tests):

[0117]

[0118] As can be seen from the performance test results in Table 4 above, among the carbon fiber paper ①, carbon fiber paper A, carbon fiber paper B, carbon fiber paper C, and carbon fiber paper D prepared using this embodiment, the mechanical strength (including tensile strength and bending strength) of carbon fiber paper ① is greater than that of the other carbon fiber papers, and its electrical conductivity (parallel resistivity and perpendicular resistivity) is better than that of the other carbon fiber papers.

[0119] Comparing the mechanical strength of carbon fiber paper ①, carbon fiber paper A, and carbon fiber paper C, it can be seen that when the second coating amount remains constant at 3%, and the first coating amount (corresponding to 2%, 0.6%, and 0.03% respectively) decreases sequentially, the mechanical strength of the carbon fiber paper decreases significantly. This indicates that when using electrostatic spraying to deposit carbon nanoparticles, the smaller the coating amount, the smaller the deposition effect of carbon nanoparticles, and the lower the resulting mechanical strength. At the same time, when the first coating amount is reduced to a relatively small amount of 0.03%, the conductivity (vertical resistivity) of carbon fiber paper C also weakens, indicating that the second coating amount and coating effect are affected to some extent by the first coating amount and coating effect.

[0120] Comparing the conductivity of carbon fiber paper ①, carbon fiber paper B, and carbon fiber paper D, it can be seen that when the first coating amount remains constant at 2%, and the second coating amount (corresponding to 3%, 0.8%, and 0.06% respectively) decreases sequentially, the conductivity of the carbon fiber paper significantly decreases. This indicates that when electrostatic spraying is used to deposit conductive particles, the smaller the coating amount, the weaker the deposition effect of conductive particles, and the lower the conductivity. At the same time, when the second coating amount is reduced to a relatively small amount of 0.06%, the mechanical strength of carbon fiber paper D also decreases, indicating that the first coating amount and effect are affected to some extent by the second coating amount and effect.

[0121] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0122] The above-described embodiments are merely illustrative of several implementation methods of the present invention, facilitating a detailed understanding of the technical solutions of the present invention. However, they should not be construed as limiting the scope of protection of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the scope of protection of the present invention. It should be understood that technical solutions obtained by those skilled in the art based on the technical solutions provided by the present invention through logical analysis, reasoning, or limited experimentation are all within the scope of protection of the appended claims. Therefore, the scope of protection of this invention patent should be determined by the content of the appended claims, and the specification can be used to interpret the content of the claims.

Claims

1. A method for preparing carbon fiber paper for a fuel cell gas diffusion layer, characterized in that: The preparation method includes the following steps: S10: Carbon fiber, bonding fiber and first dispersant are mixed and decomposed, and carbon fiber base paper is prepared by wet forming process; S20: Take carbon nanoparticles, add a second dispersant, prepare a spraying liquid, and spray the spraying liquid onto the carbon fiber base paper using an electrostatic spraying method to obtain carbon fiber sprayed paper. The carbon nanoparticles are graphene or modified carbon nanotubes, and the modified carbon nanotubes are one or more mixtures of hydroxylated carbon nanotubes, carboxylated carbon nanotubes and aminated carbon nanotubes. S30: The carbon fiber coated paper is impregnated in a resin and ethanol compound system, and then dried, hot-pressed and cured in sequence to obtain impregnated carbon fiber paper. S40: The impregnated carbon fiber paper is carbonized and graphitized sequentially under a protective atmosphere to obtain heat-treated carbon fiber paper. S50: Conductive particles, binder and third dispersant are formulated into a conductive spraying liquid, and the conductive spraying liquid is sprayed onto the heat-treated carbon fiber paper by electrostatic spraying method. After drying, the carbon fiber paper is obtained. The conductive particles are one or more of single-walled carbon nanotubes, acetylene black powder, and graphene.

2. The preparation method according to claim 1, characterized in that: The bonding fiber is polyvinyl alcohol fiber.

3. The preparation method according to claim 2, characterized in that: The polyvinyl alcohol fiber is a water-soluble polyvinyl alcohol bonding fiber. The length of the water-soluble polyvinyl alcohol bonding fiber is 2 mm to 7 mm, the degree of alcoholysis is 98 mol% to 99 mol%, and the degree of polymerization is 1500 to 2000. After the water-soluble polyvinyl alcohol bonding fiber is prepared into an aqueous solution with a volume concentration of 3.5% to 5.5%, the viscosity is 24 mPa·s to 31 mPa·s. The amount of the water-soluble polyvinyl alcohol bonding fiber is 1% to 10% of the oven-dry mass of the carbon fiber.

4. The preparation method according to claim 1, characterized in that: The first dispersant is one or a mixture of several of PEO, anionic polyacrylamide, cationic polyacrylamide, and carboxymethyl cellulose ether, or one or a mixture of several of acrylic dispersants, maleic acid dispersants, and maleic anhydride ester dispersants.

5. The preparation method according to claim 1, characterized in that: The modified carbon nanotubes must satisfy at least one of the following conditions (A) to (C): (A) The content of functionalized groups in the modified carbon nanotubes is 1 wt% to 5 wt% of the mass of the modified carbon nanotubes; (B) The modified carbon nanotubes in the spraying liquid have a mass fraction of 10% to 50%; (C) The amount of the modified carbon nanotubes sprayed is 0.05% to 5% of the carbon fiber.

6. The preparation method according to claim 1, characterized in that: The second and third dispersants are both one of dimethylformamide, dimethylacetamide, acetone, and ethanol.

7. The preparation method according to claim 1, characterized in that: The resin-ethanol compound system is a solution of phenolic resin and ethanol.

8. The preparation method according to claim 1 or 7, characterized in that: The conductive particles must satisfy at least one of the following conditions (D) to (E): (D) The mass fraction of the conductive particles in the conductive spraying liquid is 10% to 50%; (E) The amount of conductive particles sprayed is 0.1% to 10% of the carbon fiber.

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