A boron-doped phenolic resin-impregnated carbon fiber paper, a method for preparing the same, and an application thereof

Abstract

The application provides a boron-doped phenolic resin impregnated carbon fiber paper and a preparation method and application thereof, and belongs to the technical field of proton exchange membrane fuel cells. The preparation method comprises the following steps: dispersing polyacrylonitrile-based short carbon fibers in a dispersant aqueous solution, and then sequentially performing papermaking and drying to obtain carbon fiber raw paper; mixing resorcinol, formaldehyde, phenylboronic acid, ammonia water and a solvent, and then performing a polymerization reaction to obtain a boron-doped phenolic resin solution; impregnating the carbon fiber raw paper in the boron-doped phenolic resin solution, and then sequentially performing drying and hot-pressing curing to obtain cured carbon fiber paper; and sequentially performing carbonization treatment and graphitization treatment on the cured carbon fiber paper under a protective atmosphere to obtain the boron-doped phenolic resin impregnated carbon fiber paper. The boron-doped phenolic resin of the application is doped in situ, is uniformly distributed, improves the carbon residue rate and the graphitization degree of the carbon fiber paper, and improves the conductivity of the carbon fiber paper. The process of the application is simple and easy to popularize.

Description

Technical Field

[0001] This invention relates to the field of proton exchange membrane fuel cell technology, and in particular to a boron-doped phenolic resin impregnated carbon fiber paper, its preparation method, and its application. Background Technology

[0002] The gas diffusion layer (GDL) is one of the core components of a PEMFC, responsible for conducting electrons, distributing reactant gases, preventing flooding, and supporting the catalyst layer. Carbon fiber paper, due to its high conductivity, controllable three-dimensional porous structure, excellent chemical stability, and good flexibility and strength, has become the preferred GDL substrate material in commercial PEMFCs, and its performance directly affects the battery's output power and operating life. The preparation of carbon fiber paper typically involves steps such as carbon fiber base paper preparation, resin impregnation, hot pressing and curing, and high-temperature heat treatment (carbonization and graphitization). Among these steps, the type and properties of the impregnation resin are crucial.

[0003] In the selection of impregnation resins, phenolic resins are widely used in the industrial production of carbon fiber paper due to their wide availability of monomers, mature synthesis processes, relatively low cost, and high carbon residue rate during high-temperature pyrolysis. However, after high-temperature carbonization and graphitization, traditional commercial phenolic resins produce resin carbon with mainly disordered layer structures or amorphous carbon, generally exhibiting a low degree of graphitization. This results in poor carbon atom structure regularity, small grain size, and numerous defects, leading to high electron migration resistance and low intrinsic conductivity. This has become a key bottleneck limiting further improvements in the conductivity of carbon fiber paper using phenolic resin as the binder phase.

[0004] To improve the conductivity of carbon materials, elemental doping is an effective method. Due to its unique electronic structure, boron (B) atoms, when introduced into the carbon lattice, can act as electron acceptors, introducing holes into the valence band of carbon and significantly increasing the carrier concentration of the material. More importantly, the introduction of boron can catalyze the structural rearrangement of carbon materials at high temperatures, effectively promoting the transformation of amorphous carbon into a highly ordered graphite lattice, i.e., increasing the graphitization degree of the material, thereby fundamentally reducing its resistivity.

[0005] Currently available technologies for boron modification of carbon fiber paper all have inherent drawbacks. One method, as described in patent CN118581763A, involves physically blending pre-synthesized boron phenolic resin with traditional phenolic resin and adding a transition metal catalyst for synergistic graphitization. This method is essentially still a physical mixing process, making it difficult to achieve uniform dispersion at the molecular level. Furthermore, residual transition metal ions pose a risk of dissolution in the acidic environment of fuel cells, potentially poisoning the catalyst and proton exchange membrane, affecting battery life and GDL stability. Another method involves introducing a boron source during the impregnation process after the phenolic resin synthesis is complete. For example, patent CN113322713A first synthesizes the resin using conventional methods, then adds boric acid powder to the resin solution during the subsequent impregnation of the carbon fiber base paper. Patent CN120250398A, on the other hand, pre-adds boric acid as a modifier during the preparation of the carbon fiber base paper, followed by impregnation with traditional phenolic resin. The above method involves the introduction of boron and the synthesis of phenolic resin separately, following a process route of "resin synthesis first, then addition of boron source." This causes the reaction between boric acid and phenolic resin to occur primarily after the resin skeleton is formed. This post-crosslinking modification makes it difficult for boron to be in situ and uniformly doped during resin network formation, resulting in limited uniformity of boron distribution in carbon fiber paper. Consequently, the catalytic graphitization effect cannot be fully realized, ultimately leading to limited improvement in the conductivity of carbon fiber paper.

[0006] Currently, boric acid is often chosen as the boron source. However, as an inorganic small molecule, boric acid only undergoes coordination or esterification reactions with phenolic resin after the resin backbone is formed, making it difficult to achieve uniform molecular-level bonding with the phenolic backbone. In contrast, phenylboronic acid, as an organic boron source, has a benzene ring structure highly similar to the phenolic resin backbone. It can directly participate in condensation copolymerization reactions as a reactive monomer, allowing boron atoms to be covalently embedded in the resin backbone in situ, achieving uniform molecular-level doping. Furthermore, organically bonded boron is less prone to volatilization during high-temperature processing, resulting in higher doping efficiency and providing a stable and uniform material basis for subsequent catalytic graphitization.

[0007] Therefore, it is of great significance to provide a boron-doped phenolic resin impregnated carbon fiber paper with higher carbon residue and lower resistivity and its preparation method. Summary of the Invention

[0008] The purpose of this invention is to provide a boron-doped phenolic resin impregnated carbon fiber paper, its preparation method, and its application, addressing the shortcomings of existing technologies. This invention achieves atomic-level uniform doping of boron by in-situ introducing phenylboronic acid during the phenolic resin synthesis stage, resulting in carbon fiber paper with higher carbon residue and lower resistivity.

[0009] To achieve the above-mentioned objectives, the present invention provides the following technical solution: This invention provides a method for preparing boron-doped phenolic resin impregnated carbon fiber paper, comprising the following steps: 1) After dispersing polyacrylonitrile-based short-cut carbon fibers in an aqueous dispersant solution, the fibers are sequentially processed into paper and dried to obtain carbon fiber base paper; 2) Resorcinol, formaldehyde, phenylboronic acid, ammonia and solvent are mixed and then subjected to polymerization to obtain boron-doped phenolic resin solution; 3) After impregnating the carbon fiber base paper in a boron-doped phenolic resin solution, it is sequentially dried and hot-pressed to obtain cured carbon fiber paper; 4) Under a protective atmosphere, the cured carbon fiber paper is sequentially subjected to carbonization and graphitization treatments to obtain boron-doped phenolic resin impregnated carbon fiber paper.

[0010] Preferably, the polyacrylonitrile-based short-cut carbon fibers in step 1) have a length of 3~10mm and a diameter of 5~7μm; The dispersant aqueous solution contains 0.15-0.25% by mass; the dispersant is hydroxymethyl cellulose and / or hydroxyethyl cellulose; and the drying temperature is 80-120°C.

[0011] Preferably, in step 2), the molar ratio of resorcinol, formaldehyde, and phenylboronic acid is 1:1.5~2.5:0.2~0.5, the mass of ammonia is 1~10% of the mass of resorcinol, and the mass concentration of boron-doped phenolic resin solution is 5~25%.

[0012] Preferably, the polymerization reaction in step 2) is carried out at a temperature of 40~60℃ and for a time of 1~3h; the mixing is carried out under stirring conditions at a stirring rate of 200~400rpm; and the solvent is anhydrous ethanol, methanol or water.

[0013] Preferably, the impregnation time in step 3) is 15~35 min, and the impregnation method is atmospheric pressure impregnation or vacuum impregnation; the drying temperature is 60~100℃; the hot-press curing temperature is 140~180℃, the hot-press curing pressure is 10~20MPa, and the hot-press curing time is 20~60 min.

[0014] Preferably, the carbonization temperature in step 4) is 800~1500℃ and the carbonization time is 30~90min; the graphitization temperature is 2400~2800℃ and the graphitization time is 10~30min.

[0015] Preferably, the heating rate to the carbonization temperature is 2~8℃ / min, and the heating rate to the graphitization temperature is 2~8℃ / min.

[0016] The present invention also provides boron-doped phenolic resin impregnated carbon fiber paper prepared by the above preparation method, wherein the resistivity of the boron-doped phenolic resin impregnated carbon fiber paper is ≤4mΩ·cm, the residual carbon content is ≥54%, and the porosity is ≥70%.

[0017] The present invention also provides the application of the boron-doped phenolic resin impregnated carbon fiber paper in the gas diffusion layer of a proton exchange membrane fuel cell.

[0018] The beneficial effects of this invention are: 1) In-situ doping with uniform distribution: This invention introduces phenylboronic acid during the polycondensation reaction of phenolic resin, allowing boron atoms to be directly embedded into the three-dimensional cross-linked network of the phenolic resin through chemical bonds, achieving atomic-level uniform dispersion of boron. This molecular-level doping method solves the problems of uneven distribution and weak interfacial bonding caused by physical blending, avoids agglomeration and unevenness caused by subsequent doping, and makes boron more stable during subsequent high-temperature treatment.

[0019] 2) Improving Residual Carbon Content and Graphitization Degree: Resorcinol is used as the phenol source, exhibiting higher reactivity and enabling a faster and more complete condensation reaction with formaldehyde, which is beneficial for forming a resin structure with higher crosslinking density and a higher residual carbon content. Phenylboronic acid is used as the boron source, exhibiting higher thermal stability compared to inorganic boric acid and less volatility during resin synthesis and high-temperature treatment. The resulting phenylboronic ester blocks some phenolic hydroxyl groups, shortening the distance between the three benzene rings connected to the central boron atom, thus promoting carbon formation. The introduction of boron inhibits the disordered volatilization of carbon at high temperatures, thereby improving the residual carbon content of the resin. Simultaneously, boron, as a graphitization catalyst, effectively promotes the transformation of amorphous carbon into graphite crystals, significantly improving the graphitization degree of carbon fiber paper.

[0020] 3) Significantly improved conductivity: Due to the higher degree of graphitization and the electronic effect brought by boron, the carbon fiber paper prepared by this invention has a lower resistivity compared with the traditional phenolic resin impregnated carbon fiber paper, thereby reducing the internal resistance of the fuel cell and improving the output performance.

[0021] 4) Simple process and easy to promote: The method of the present invention only adjusts the resin synthesis step, without changing the standard process flow such as impregnation, curing, carbonization, and graphitization, and is easy to realize industrial application on existing production lines. Attached Figure Description

[0022] Figure 1 Here is a SEM image of the carbon fiber paper obtained in Example 1; Figure 2 The Raman spectra of the carbon fiber paper obtained in Example 1 and Comparative Example 2 are shown below. Figure 3 The XRD pattern of the carbon fiber paper obtained in Example 1; Figure 4 The image shows the infrared spectrum of the boron-doped phenolic resin obtained in Example 1. Detailed Implementation

[0023] This invention provides a method for preparing boron-doped phenolic resin impregnated carbon fiber paper, comprising the following steps: 1) After dispersing polyacrylonitrile-based short-cut carbon fibers in an aqueous dispersant solution, the fibers are sequentially processed into paper and dried to obtain carbon fiber base paper; 2) Resorcinol, formaldehyde, phenylboronic acid, ammonia and solvent are mixed and then subjected to polymerization to obtain boron-doped phenolic resin solution; 3) After impregnating the carbon fiber base paper in a boron-doped phenolic resin solution, it is sequentially dried and hot-pressed to obtain cured carbon fiber paper; 4) Under a protective atmosphere, the cured carbon fiber paper is sequentially subjected to carbonization and graphitization treatments to obtain boron-doped phenolic resin impregnated carbon fiber paper.

[0024] In this invention, the length of the polyacrylonitrile-based short-cut carbon fiber in step 1) is preferably 3~10mm, more preferably 5~8mm, and even more preferably 6~7mm, and the diameter is preferably 5~7μm, more preferably 5.5~6.5μm, and even more preferably 6μm; In the aqueous solution of the dispersant, the mass fraction of the dispersant is preferably 0.15~0.25%, more preferably 0.18~0.22%, and even more preferably 0.2%; the dispersant is preferably hydroxymethyl cellulose and / or hydroxyethyl cellulose; the drying temperature is preferably 80~120℃, more preferably 90~110℃, and even more preferably 100℃; the drying time is preferably 1~4h, and even more preferably 2~3h.

[0025] In this invention, the preferred mass-to-volume ratio of polyacrylonitrile-based chopped carbon fibers to the dispersant aqueous solution is 1g:4~8L, more preferably 1g:4.5~7L, and even more preferably 1g:5~6L; dispersion is carried out in a fiber disintegrator or a high-speed mixer; the preferred stirring rate during dispersion is 400~600rpm, more preferably 500rpm, and the preferred dispersion time is 3~10min to ensure uniform dispersion of carbon fibers without agglomeration.

[0026] In step 1) of this invention, a wet forming technology is used to transfer a uniformly dispersed carbon fiber dispersion to a standard paper forming machine, and dehydrate and form the paper under vacuum conditions. The vacuum degree is preferably 0.04~0.07MPa, more preferably 0.05~0.06MPa, and the dehydration and forming time is preferably 60~120s, more preferably 100~110s. The formed wet paper is then dried.

[0027] In this invention, the molar ratio of resorcinol, formaldehyde, and phenylboronic acid in step 2) is preferably 1:1.5~2.5:0.2~0.5, more preferably 1:1.8~2.2:0.3~0.4, and even more preferably 1:2.0:0.35. The mass of ammonia is preferably 1~10% of the mass of resorcinol, more preferably 2~7%, and even more preferably 3~5%. The mass concentration of the boron-doped phenolic resin solution (the sum of the mass fractions of resorcinol, formaldehyde, phenylboronic acid, and ammonia in the resin solution) is preferably 5~25%, more preferably 8~20%, and even more preferably 10~15%. The mass fraction of ammonia is preferably 20~28%, and even more preferably 23~25%.

[0028] In this invention, formaldehyde is added in the form of an aqueous formaldehyde solution, and the mass fraction of the aqueous formaldehyde solution is preferably 34-40%, more preferably 37%.

[0029] In this invention, the polymerization temperature in step 2) is preferably 40~60℃, more preferably 45~55℃, and even more preferably 50℃; the polymerization time is preferably 1~3h, more preferably 1.5~2.5h, and even more preferably 2h; the mixing is preferably carried out under stirring conditions, and the stirring rate is preferably 200~400rpm, more preferably 250~350rpm, and even more preferably 300rpm; the solvent is preferably anhydrous ethanol, methanol, or water.

[0030] The boron-doped phenolic resin solution prepared by this invention is sealed and stored at room temperature for later use.

[0031] In this invention, the immersion time in step 3) is preferably 15-35 min, more preferably 20-30 min, and even more preferably 20-25 min; the immersion method is preferably atmospheric pressure immersion or vacuum immersion; the drying temperature is preferably 60-100℃, more preferably 70-90℃, and even more preferably 80℃; the drying time is preferably 80-120 min, and even more preferably 90-100 min.

[0032] In this invention, the temperature for hot pressing curing is preferably 140~180℃, more preferably 150~170℃, and even more preferably 160℃; the pressure for hot pressing curing is preferably 10~20MPa, more preferably 12~18MPa, and even more preferably 15~16MPa; and the time for hot pressing curing is preferably 20~60min, more preferably 25~50min, and even more preferably 30~40min.

[0033] The impregnation process of this invention ensures that the resin solution fully penetrates into the pore structure of the carbon fiber base paper. After impregnation, the impregnated carbon fiber paper is removed and dried to remove the solvent. After drying, hot pressing curing is performed. Hot pressing curing is preferably carried out using a flat vulcanizing machine. The hot pressing curing process causes the resin to undergo a cross-linking reaction, forming a three-dimensional network structure (solid preform).

[0034] In this invention, the carbonization temperature in step 4) is preferably 800~1500℃, more preferably 1000~1400℃, and even more preferably 1200~1300℃, and the carbonization time is preferably 30~90min, more preferably 40~70min, and even more preferably 50~60min; the graphitization temperature is preferably 2400~2800℃, more preferably 2500~2700℃, and even more preferably 2600℃, and the graphitization time is preferably 10~30min, more preferably 15~25min, and even more preferably 20min.

[0035] In this invention, the rate of heating from room temperature to carbonization temperature is preferably 2~8℃ / min, more preferably 3~7℃ / min, and even more preferably 4~5℃ / min; the rate of heating from carbonization temperature to graphitization temperature is preferably 2~8℃ / min, more preferably 4~7℃ / min, and even more preferably 5~6℃ / min; the protective atmosphere is preferably high-purity nitrogen or high-purity argon; the gas flow rate is preferably 0.5~2.0L / min, and even more preferably 1.0~1.5L / min.

[0036] The present invention also provides boron-doped phenolic resin impregnated carbon fiber paper prepared by the above preparation method, wherein the resistivity of the boron-doped phenolic resin impregnated carbon fiber paper is ≤4mΩ·cm, the residual carbon content is ≥54%, and the porosity is ≥70%.

[0037] In this invention, the boron-doped phenolic resin impregnated carbon fiber paper is composed of an interlaced carbon fiber network. The fibers are firmly connected by resin carbon formed by the high-temperature conversion of boron-doped phenolic resin, forming abundant conductive pathways and porous structures.

[0038] The present invention also provides the application of the boron-doped phenolic resin impregnated carbon fiber paper in the gas diffusion layer of a proton exchange membrane fuel cell.

[0039] The boron-doped phenolic resin impregnated carbon fiber paper of the present invention has excellent conductivity, high graphitization degree and stable porous structure, which enables it to efficiently perform the functions of gas diffusion and electron conduction.

[0040] This invention employs an in-situ doping strategy: using phenylboronic acid, resorcinol, and formaldehyde as monomers, boron-doped phenolic resin is directly copolymerized during the resin synthesis stage. Using phenylboronic acid as the boron source achieves uniform doping, while the resulting phenylboronic ester ester blocks some phenolic hydroxyl groups, shortening the distance between the three benzene rings connected to the central boron atom, thus promoting carbon formation. Using resorcinol as the phenol source provides higher reactivity, enabling a faster and more complete condensation reaction with formaldehyde, which is beneficial for forming a resin structure with higher crosslinking density and higher residual carbon content. The boron-doped phenolic resin of this invention achieves uniform and stable boron doping and is a novel resin system highly compatible with existing carbon fiber paper preparation processes. This has significant scientific research and engineering application value for preparing next-generation high-performance GDLs with high conductivity, excellent mass transfer capacity, and structural stability, thereby promoting the commercialization of high-performance fuel cells.

[0041] The technical solutions provided by the present invention will be described in detail below with reference to the embodiments, but they should not be construed as limiting the scope of protection of the present invention.

[0042] In the examples and comparative examples, the flow rate of high-purity nitrogen was 1.5 L / min; hydroxymethyl cellulose was purchased from Shanghai Yuanye Biotechnology Co., Ltd., product number: S14014-500g, model specification: AR, viscosity 100,000.

[0043] Example 1

[0044] Two g of polyacrylonitrile-based short-cut carbon fibers (6 mm in length and 6 μm in diameter) were added to 10 L of hydroxymethyl cellulose aqueous solution (0.2% by mass). The solution was dispersed in a fiber standard dissociator at 500 rpm for 3 min until the fibers were uniformly dispersed as monofilaments without obvious flocculent agglomerates, resulting in a homogeneous carbon fiber dispersion. Using a wet forming process, the carbon fiber dispersion was transferred to a paper forming machine and dehydrated under vacuum (0.05 MPa) for 120 s to form a 20 cm × 20 cm sheet of uniform thickness. This sheet was then flattened and dried in a 100 °C oven for 2 h, resulting in a smooth surface, uniform texture, and a basis weight of 50 g / m³. 2 Carbon fiber base paper.

[0045] In a three-necked flask equipped with a stirrer and a condenser, 22.02 g of resorcinol, 32.4 g of formaldehyde aqueous solution (formaldehyde mass fraction 37%), 7.32 g of phenylboronic acid, and 200 mL of methanol were added. The mixture was stirred at 300 rpm to dissolve the substances. Subsequently, 2.00 g of ammonia water (mass fraction 25%) was added, and the mixture was reacted in a 50°C water bath at 300 rpm for 2 hours. The reaction system gradually changed from a colorless and transparent solution to a pale pink, homogeneous, and transparent solution, with a slight increase in viscosity. This yielded a boron-doped phenolic resin solution, denoted as boron-doped phenolic resin solution B1.

[0046] Carbon fiber paper was cut into 10cm × 10cm samples, weighed, and the initial mass was recorded. The samples were completely immersed in a glass petri dish containing boron-doped phenolic resin solution B1. The entire petri dish was then placed in a vacuum drying oven for vacuum impregnation at room temperature (vacuum degree 130 Pa) for 20 minutes. After removal, it was dried in an 80℃ forced-air drying oven for 2 hours. The dried carbon fiber paper was then hot-pressed and cured using a flat vulcanizing machine at a temperature of 160℃, a pressure of 15 MPa, and a time of 30 minutes.

[0047] The hot-pressed and cured carbon fiber paper is first placed in a box furnace and heated from room temperature to 1300℃ at a heating rate of 5℃ / min under the protection of high-purity nitrogen, and held at this temperature for 60 minutes for carbonization treatment. Then it is placed in a high-temperature graphitization furnace and heated from 1300℃ to 2600℃ at a heating rate of 5℃ / min under the protection of high-purity nitrogen, and held at this temperature for 20 minutes for graphitization treatment. After the graphitization treatment is completed, it is naturally cooled to room temperature to obtain boron-doped phenolic resin impregnated carbon fiber paper (denoted as carbon fiber paper S1).

[0048] The carbon fiber paper S1 prepared in this embodiment was tested for performance. Its carbon residue rate was 60.7%, resistivity was 3.11 mΩ·cm, and porosity was 72.5%.

[0049] Example 2

[0050] Two g of polyacrylonitrile-based short-cut carbon fibers (6 mm in length and 6 μm in diameter) were added to 10 L of hydroxymethyl cellulose aqueous solution (0.2% by mass). The solution was dispersed in a fiber standard dissociator at 500 rpm for 3 min until the fibers were uniformly dispersed as monofilaments without obvious flocculent agglomerates, resulting in a homogeneous carbon fiber dispersion. Using a wet forming process, the carbon fiber dispersion was transferred to a paper forming machine and dehydrated under vacuum (0.05 MPa) for 120 s to form a 20 cm × 20 cm sheet of uniform thickness. This sheet was then flattened and dried in a 100 °C oven for 2 h, resulting in a smooth surface, uniform texture, and a basis weight of 50 g / m³. 2 Carbon fiber base paper.

[0051] In a three-necked flask equipped with a stirrer and a condenser, 22.02 g of resorcinol, 32.4 g of formaldehyde aqueous solution (37% by mass), 7.32 g of phenylboronic acid, and 200 mL of methanol were added. The mixture was stirred at 300 rpm to dissolve the substances. Subsequently, 2.00 g of ammonia water (25% by mass) was added, and the mixture was reacted in a 50°C water bath at 300 rpm for 2 hours. The reaction system gradually changed from a colorless and transparent solution to a pale pink, homogeneous, and transparent solution, with a slight increase in viscosity. This yielded a boron-doped phenolic resin solution, denoted as boron-doped phenolic resin solution B1.

[0052] Carbon fiber paper was cut into 10cm × 10cm samples, weighed, and the initial mass was recorded. The samples were completely immersed in a glass petri dish containing boron-doped phenolic resin solution B1. The entire petri dish was then immersed for 20 minutes at room temperature (25℃) under normal pressure. After removal, it was dried in an 80℃ forced-air drying oven for 2 hours. The dried carbon fiber paper was then hot-pressed and cured using a flat vulcanizing machine at a temperature of 160℃, a pressure of 15MPa, and a time of 30 minutes.

[0053] The hot-pressed and cured carbon fiber paper is first placed in a box furnace and heated from room temperature to 1300℃ at a heating rate of 5℃ / min under the protection of high-purity nitrogen, and held at this temperature for 60 minutes for carbonization treatment. Then it is placed in a high-temperature graphitization furnace and heated from 1300℃ to 2600℃ at a heating rate of 5℃ / min under the protection of high-purity nitrogen, and held at this temperature for 20 minutes for graphitization treatment. After the graphitization treatment is completed, it is naturally cooled to room temperature to obtain boron-doped phenolic resin impregnated carbon fiber paper (denoted as carbon fiber paper S2).

[0054] The carbon fiber paper S2 prepared in this embodiment was tested for performance. Its carbon residue rate was 56.8%, resistivity was 3.98 mΩ·cm, and porosity was 73.2%.

[0055] Example 3

[0056] The 7.32g of phenylboronic acid in Example 1 was replaced with 4.88g of phenylboronic acid, and other process conditions were the same as in Example 1, to obtain boron-doped phenolic resin impregnated carbon fiber paper (denoted as carbon fiber paper S3).

[0057] The carbon fiber paper S3 prepared in this embodiment was tested for performance. Its carbon residue rate was 60.3%, resistivity was 3.56 mΩ·cm, and porosity was 71.6%.

[0058] Example 4

[0059] The 7.32g phenylboronic acid in Example 1 was replaced with 9.76g phenylboronic acid, and other process conditions were the same as in Example 1, to obtain boron-doped phenolic resin impregnated carbon fiber paper (denoted as carbon fiber paper S4).

[0060] The carbon fiber paper S4 prepared in this embodiment was tested for performance. Its carbon residue rate was 55.7%, resistivity was 3.08 mΩ·cm, and porosity was 73.5%.

[0061] Example 5

[0062] The length of the polyacrylonitrile-based short-cut carbon fiber in Example 1 was changed to 10 mm, the volume of the hydroxymethyl cellulose aqueous solution was changed to 10 L, and other process conditions were the same as in Example 1, to obtain boron-doped phenolic resin impregnated carbon fiber paper (denoted as carbon fiber paper S5).

[0063] The carbon fiber paper S5 prepared in this embodiment was subjected to performance testing, and its resistivity was 3.18.

[0064] The tensile strength was tested at mΩ·cm, and it was 12% higher than that of carbon fiber paper S1 in Example 1.

[0065] Comparative Example 1

[0066] Omit the 7.32g phenylboronic acid from Example 1 and prepare a common phenolic resin solution, denoted as common phenolic resin solution C1. The graphitization time is changed to 30min, and other process conditions are the same as in Example 1, to obtain phenolic resin impregnated carbon fiber paper (denoted as carbon fiber paper D1).

[0067] The carbon fiber paper D1 prepared in this comparative example was tested for performance. Its carbon residue rate was 56.1%, resistivity was 4.52 mΩ·cm, and porosity was 72.4%.

[0068] Comparative Example 2

[0069] The boron-doped phenolic resin solution B1 in Example 1 was replaced with a commercial boron-phenolic resin impregnation solution C2. The preparation method of commercial boron-phenolic resin impregnation solution C2 was as follows: 20.00 g of commercially available thermosetting boron-phenolic resin (Shandong Jining Huakai Resin Co., Ltd.) was placed in a dry beaker, and 180 g of methanol was added. The beaker was placed on a magnetic stirrer and stirred continuously at 300 r / min at room temperature until the resin was completely dissolved, resulting in a homogeneous, slightly yellow, transparent solution. Measurements showed that the resin impregnation amount was comparable to that of the resin solution prepared in Example 1. Carbon fiber base paper was impregnated in commercial boron-phenolic resin impregnation solution C2, with other process conditions the same as in Example 1, to obtain carbon fiber paper D2.

[0070] The carbon fiber paper D2 prepared in this comparative example was tested for performance. Its carbon residue rate was 60.4%, resistivity was 4.45 mΩ·cm, and porosity was 71.4%.

[0071] The SEM image of the carbon fiber paper obtained in Example 1 is shown below. Figure 1 As shown; by Figure 1 It is known that the boron-doped phenolic resin-impregnated carbon fiber paper consists of an interwoven fiber network, with the fibers interconnected by the resin carbon. The graphitized resin did not exhibit cracks, ensuring good bonding between the fibers.

[0072] The Raman spectra of the carbon fiber paper obtained in Example 1 and Comparative Example 2 are as follows: Figure 2 As shown, the smaller the ID / IG value, the more regular the crystal structure of the carbon paper. Figure 2 It can be seen that in Example 1, the G peak, representing structural regularity, gradually becomes narrower and sharper, while the D peak, representing structural defects, gradually becomes smaller. The ID / IG value of Example 1 is smaller than that of Comparative Example 2, proving that boric acid has a catalytic effect on the graphitization of carbon paper.

[0073] The XRD pattern of the carbon fiber paper obtained in Example 1 is as follows: Figure 3 As shown, by Figure 3 It can be seen that the graphitization characteristic peaks in the XRD pattern of boron-doped phenolic resin-impregnated carbon fiber paper are high in intensity and sharp, which fully demonstrates that boric acid has a catalytic effect on the graphitization of carbon paper.

[0074] The infrared spectrum of the boron-doped phenolic resin obtained in Example 1 is shown below. Figure 4 As shown, by Figure 4 It can be seen that at 1335cm -1 The absorption peak at this point is a characteristic peak of the BO bond, indicating that the boron-doped phenolic resin was successfully synthesized.

[0075] This invention introduces boron in situ during the resin synthesis stage. Phenylboronic acid enters the framework as a reactant during resin synthesis and is not easily lost due to volatilization during high-temperature treatment. The generated phenylboronic ester blocks some phenolic hydroxyl groups and shortens the distance between the three benzene rings connected to the central boron atom, which is conducive to carbon formation. This significantly improves the residual carbon rate of the resin and the graphitization degree of the carbon fiber paper, thereby giving it superior electrical conductivity. It is particularly suitable for the gas diffusion layer of high-performance proton exchange membrane fuel cells.

[0076] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing boron-doped phenolic resin impregnated carbon fiber paper, characterized in that, It includes the following steps: 1) After dispersing polyacrylonitrile-based short-cut carbon fibers in an aqueous dispersant solution, the fibers are sequentially processed into paper and dried to obtain carbon fiber base paper; 2) Resorcinol, formaldehyde, phenylboronic acid, ammonia and solvent are mixed and then subjected to polymerization to obtain boron-doped phenolic resin solution; 3) After impregnating the carbon fiber base paper in a boron-doped phenolic resin solution, it is sequentially dried and hot-pressed to obtain cured carbon fiber paper; 4) Under a protective atmosphere, the cured carbon fiber paper is sequentially subjected to carbonization and graphitization treatments to obtain boron-doped phenolic resin impregnated carbon fiber paper.

2. The preparation method according to claim 1, characterized in that, Step 1) The length of the polyacrylonitrile-based short-cut carbon fiber is 3~10mm and the diameter is 5~7μm; The dispersant aqueous solution contains 0.15-0.25% by mass; the dispersant is hydroxymethyl cellulose and / or hydroxyethyl cellulose; and the drying temperature is 80-120°C.

3. The preparation method according to claim 1 or 2, characterized in that, In step 2), the molar ratio of resorcinol, formaldehyde, and phenylboronic acid is 1:1.5~2.5:0.2~0.5, the mass of ammonia is 1~10% of the mass of resorcinol, and the mass concentration of boron-doped phenolic resin solution is 5~25%.

4. The preparation method according to claim 3, characterized in that, Step 2) The polymerization reaction temperature is 40~60℃, and the polymerization reaction time is 1~3h; the mixing is carried out under stirring conditions, and the stirring rate is 200~400rpm; the solvent is anhydrous ethanol, methanol or water.

5. The preparation method according to claim 1 or 4, characterized in that, Step 3) The impregnation time is 15~35min, and the impregnation method is atmospheric pressure impregnation or vacuum impregnation; the drying temperature is 60~100℃; the hot pressing curing temperature is 140~180℃, the hot pressing curing pressure is 10~20MPa, and the hot pressing curing time is 20~60min.

6. The preparation method according to claim 5, characterized in that, Step 4) The carbonization temperature is 800~1500℃ and the carbonization time is 30~90min; the graphitization temperature is 2400~2800℃ and the graphitization time is 10~30min.

7. The preparation method according to claim 6, characterized in that, The heating rate to the carbonization temperature is 2~8℃ / min, and the heating rate to the graphitization temperature is 2~8℃ / min.

8. The boron-doped phenolic resin-impregnated carbon fiber paper prepared by the preparation method according to any one of claims 1 to 7, characterized in that, The boron-doped phenolic resin impregnated carbon fiber paper has a resistivity of ≤4mΩ·cm, a carbon residue rate of ≥54%, and a porosity of ≥70%.

9. The application of the boron-doped phenolic resin impregnated carbon fiber paper of claim 8 in the gas diffusion layer of a proton exchange membrane fuel cell.

Images