A wet-formed carbon fiber membrane material and a method of making the same

Abstract

This invention relates to a wet-process carbon fiber membrane material and its preparation method. The method includes the following steps: First, phenolic resin powder is dispersed in an aqueous solution of polyvinyl alcohol, and a carboxymethyl cellulose solution is added. The mixture is then freeze-dried to obtain hydrophilic phenolic resin powder. Subsequently, carbon fibers are sequentially washed with acetone and oxidized with hydrogen peroxide. These carbon fibers are then mixed with the hydrophilic phenolic resin powder and a cationic salt in water to form a hydrophilic phenolic resin composite carbon fiber slurry. Finally, the slurry is subjected to paper forming, pressing and drying, hot pressing curing, and pressure carbonization to obtain the wet-process carbon fiber membrane material. This invention achieves uniform dispersion and strong bonding of the resin in the carbon fiber network through the synergistic effect of resin hydrophilic modification, carbon fiber oxidation activation, and cationic bridging. The resulting carbon fiber membrane material exhibits characteristics such as uniform structure, high strength, good conductivity, and controllable porosity.

Description

Technical Field

[0001] This invention belongs to the field of advanced carbon material preparation technology, specifically relating to a wet-process carbon fiber membrane material and its preparation method, particularly a method for preparing high-performance carbon fiber membrane materials by uniformly compounding hydrophilic modified resin with carbon fiber, followed by wet molding and heat treatment. Background Technology

[0002] Proton exchange membrane fuel cells (PEMFCs) are one type of fuel cell with an energy conversion efficiency of up to 90%. They can directly convert the chemical energy of fuels such as hydrogen and methanol into electrical energy, producing virtually no toxic or harmful byproducts. As a clean, efficient, and simple green energy device, fuel cells are considered one of the most promising environmentally friendly energy sources. Therefore, both domestically and internationally, fuel cells are being vigorously developed as a next-generation power source, and numerous experts and scholars are currently researching and developing next-generation fuel cells.

[0003] As an important component of proton exchange membrane fuel cells, the gas diffusion layer plays a crucial role in supporting the catalyst layer, transporting electrons, conveying water vapor, and conducting heat. It also needs to possess stability and corrosion resistance. Currently, gas diffusion layers are mainly classified into three types based on their manufacturing process: carbon fiber paper, carbon fiber woven fabric, and carbon fiber nonwoven fabric. Carbon fiber paper, as a specific form of porous carbon fiber material, is more suitable for use as a backing layer for gas diffusion layers compared to carbon fiber woven fabric. Gas diffusion layer materials need to possess the following characteristics: (1) high porosity to ensure smooth gas passage; (2) excellent electrical conductivity to ensure smooth electron conduction under high current density; (3) good hydrophobic properties to ensure smooth water removal; (4) certain mechanical strength to ensure the integrity of the material during production, transportation, and actual operation; (5) excellent electrochemical stability to ensure efficient operation of the fuel cell; and (6) good thermal conductivity to promptly dissipate excess heat outside the battery.

[0004] Chinese patent CN110129992A discloses a method for preparing carbon fiber paper for fuel cells. The method involves first graphitizing carbon fibers and then preparing carbon paper preforms using a dry papermaking process. This process requires using hot melt adhesive to bond and dry the nonwoven paper sheets at 100-150°C. The carbon paper preform is then impregnated with phenolic resin or pitch resin and cured at 180-220°C for 2-8 hours before carbonization to obtain the carbon paper. Although this invention uses a dry papermaking process to prepare the carbon paper preforms, the use of hot melt adhesive for bonding during the preparation process and the subsequent impregnation with phenolic resin result in poor material uniformity and a still complex manufacturing process.

[0005] Chinese patent CN110512459A describes a method for preparing carbon paper for fuel cells. Carbon fibers, viscose fibers, and cellulose nanofibers are mixed in water, and then a surfactant, polyethylene oxide, and polyvinyl alcohol solution are added sequentially to obtain a mixed slurry. This slurry is then formed into a wet paper web, dried, and a carbon paper precursor is obtained. The carbon paper precursor is impregnated in an ethanol solution of carbon nanotubes and boric acid-cainol modified phenolic resin, dried, hydrophobically treated, and then hot-pressed and heat-treated to obtain the carbon paper. This patent requires impregnating the carbon paper precursor in an ethanol solution of modified phenolic resin, which presents problems such as difficulty in controlling the resin adhesion amount, difficulty in uniformly distributing materials such as carbon nanotubes and boric acid-cainol in the carbon paper, and difficulty in adjusting the porosity of the carbon paper.

[0006] Chinese patent CN113564749A describes a method for preparing a phenolic resin / modified polyvinyl alcohol composite fiber adhesive. Specifically, phenolic resin and modified polyvinyl alcohol are added to a solvent to prepare a spinning solution, and then dry spinning is used to obtain the phenolic resin / modified polyvinyl alcohol composite fiber adhesive. This patent requires the use of a large amount of organic solvent in the preparation of the phenolic resin / modified polyvinyl alcohol composite fiber, which is not environmentally friendly.

[0007] Chinese patent CN111900418A discloses a method for preparing a carbon fiber paper preform for a fuel cell gas diffusion layer. This patent involves mixing short and long carbon fibers with nanocellulose, adding a retention aid for dispersibility to obtain a carbon fiber dispersion, using a wet molding process to obtain a wet carbon fiber paper web, and then using vacuum negative pressure to impregnate the carbon fiber paper, followed by drying to obtain the carbon fiber paper preform. However, using vacuum negative pressure to impregnate the carbon paper still results in uneven distribution of the resin within the carbon paper (due to excessive fluidity), and poor bonding between the resin and the wet paper web with moisture, leading to poor uniformity of the resulting material.

[0008] Therefore, inventing a fuel cell gas diffusion layer material with high conductivity, high strength, high uniformity, high chemical stability, good permeability, and a simple, stable, and quality-controllable preparation process is a critical problem that urgently needs to be solved. This is essential for developing high-performance, low-cost, and highly stable fuel cells. Summary of the Invention

[0009] The technical problem to be solved by this invention is: to address the problems of complex processes, difficulty in controlling uniformity, and insufficient mechanical strength in the preparation of porous carbon materials (such as carbon paper) for gas diffusion layers in fuel cells, a high-performance wet-formed carbon fiber membrane material and its preparation method are proposed.

[0010] In a first aspect, the present invention provides a method for preparing a wet-formed carbon fiber membrane material, comprising the following steps:

[0011] Step (1) Preparation of hydrophilic phenolic resin powder: Polyvinyl alcohol is dissolved in water to prepare a solution, phenolic resin powder is added, and ultrasonic dispersion is performed to make it mix evenly to obtain a phenolic resin-polyvinyl alcohol suspension system; Carboxymethyl cellulose is dissolved in water to prepare a solution, added to the above suspension system and stirred evenly, and after standing, freeze drying and grinding, hydrophilic phenolic resin powder is obtained.

[0012] Step (2) Carbon fiber pretreatment and preparation of mixed slurry: Carbon fiber is ultrasonically cleaned with acetone and oxidized with hydrogen peroxide to obtain oxidized carbon fiber; carbon fiber slurry is prepared by dispersing oxidized carbon fiber in water, adding hydrophilic phenolic resin powder and cationic salt, and stirring to obtain hydrophilic phenolic resin composite carbon fiber mixed slurry.

[0013] Step (3) Molding and heat treatment of carbon fiber membrane material: The above mixed slurry is wet-molded to obtain a wet-molded preform, which is then subjected to pressing and drying, hot pressing and curing and pressure carbonization treatment in sequence to obtain the wet-molded carbon fiber membrane material.

[0014] In a second aspect, the present invention provides a carbon fiber membrane material prepared by the above method.

[0015] A third aspect of the present invention provides an application of the carbon fiber membrane material prepared by the above method in a gas diffusion layer of a fuel cell.

[0016] The beneficial effects of this invention are:

[0017] (1) This invention replaces the traditional process of multiple resin impregnation-drying-reprocessing steps or vacuum suction steps by pre-preparing hydrophilic phenolic resin powder and directly adding it to carbon fiber slurry for wet blending and papermaking. This integrated molding process significantly simplifies the production process, shortens the preparation cycle, improves production efficiency, and is stable and easy to scale up.

[0018] (2) The hydrophilic modified phenolic resin powder has good dispersibility in water and can achieve uniform and firm bonding with carbon oxide through the bridging effect of cationic salt. This "in-situ composite" mode ensures the uniform distribution and high retention rate of resin in the fiber network, making the internal structure of the final carbon fiber membrane material uniform and dense, and significantly improving the uniformity and mechanical strength of the material.

[0019] (3) By precisely controlling the amount of hydrophilic phenolic resin added, the number and distribution of resin bonding points in the material can be directly and effectively controlled, thereby realizing the active design and precise control of the porosity and pore size distribution of the material to meet the requirements of air permeability and drainage under different working conditions (such as when used as a gas diffusion layer).

[0020] (4) Oxidation pretreatment of carbon fibers increases their surface active groups, further enhancing the interfacial bonding force with hydrophilic phenolic resin. After curing and carbonization, the resin forms a strong conductive carbon network, which not only improves the strength but also ensures excellent electronic conduction pathways within the material, thereby achieving high conductivity.

[0021] (5) The main preparation process uses water as the medium, which avoids the environmental pollution and safety risks caused by the large amount of organic solvents used in traditional processes. At the same time, the resin utilization rate is high and the raw material waste is small, which has good environmental protection and cost control potential. Attached Figure Description

[0022] Figure 1 This is a photograph of a wet paper blank formed in a paper machine using the hydrophilic phenolic resin composite carbon fiber mixed slurry prepared in Example 3 of the present invention.

[0023] Figure 2 This is a photograph of the carbon fiber membrane material precursor obtained in Example 3 of the present invention, after a first stage of pressing and drying.

[0024] Figure 3 This is a scanning electron microscope image of the carbon fiber membrane material (represented as carbon paper) prepared in Example 3 of the present invention, magnified 100 times. Detailed Implementation

[0025] The preparation method of the "wet-formed carbon fiber membrane material" of this application will be described in detail below with reference to specific embodiments.

[0026] The wet-formed carbon fiber membrane material described in this application has an adjustable areal density (basis weight), thickness, and pore structure over a wide range. When the basis weight is in the range of 30-150 g / m², the material exhibits a carbon paper morphology with excellent uniformity and strength, which is a preferred embodiment of this application and is particularly suitable for use as a gas diffusion layer in fuel cells. However, this should not be construed as limiting the scope of protection of this application.

[0027] The method for preparing wet-formed carbon fiber membrane material of this application includes the following steps:

[0028] (1) Preparation of hydrophilic phenolic resin powder

[0029] Polyvinyl alcohol (PVA) with a degree of hydrolysis of 87%-99% and a degree of polymerization of 1000-2500 is dissolved in water at 70-95°C to prepare a 1%-5% (w / w) PVA solution, which is then cooled to room temperature. Thermosetting phenolic resin powder with a particle size of 50-1000 mesh is added to the above PVA solution to prepare a 5%-35% (w / w) phenolic resin suspension. The above phenolic resin suspension is ultrasonically dispersed in an ultrasonic cleaner with an ultrasonic frequency of 50-500 kHz for 5-30 minutes to ensure uniform mixing, resulting in a uniformly dispersed phenolic resin-PVA suspension system.

[0030] In another container, carboxymethyl cellulose powder is slowly added to water at 15–30°C and stirred at 800–1200 rpm to form a uniform suspension. The solution is then heated to 60–80°C and stirred continuously until the carboxymethyl cellulose is completely dissolved, resulting in a stable carboxymethyl cellulose solution with a mass concentration of 0.2%–1%.

[0031] A carboxymethyl cellulose solution at 10%-50% of the mass of polyvinyl alcohol was added to the obtained phenolic resin-polyvinyl alcohol suspension and stirred until homogeneous. The mixture was allowed to stand, and the supernatant was removed. The remaining material was then transferred to a freeze dryer for freeze-drying, followed by grinding to obtain hydrophilic phenolic resin powder.

[0032] (2) Carbon fiber pretreatment and preparation of mixed slurry

[0033] One or more of the following carbon fibers with a diameter of 3-13 μm and a length of 1-8 mm—polyacrylonitrile-based carbon fiber, pitch-based carbon fiber, viscose-based carbon fiber, wood-based carbon fiber, or phenolic resin-based carbon fiber—are immersed in sufficient pure acetone and ultrasonically cleaned at 50-80°C for 0.5-2 hours to remove surface impurities. The cleaned carbon fibers are then treated in a 30% hydrogen peroxide solution at 80°C for 2-4 hours for oxidation modification. Afterward, the fibers are washed with water until neutral and dried to obtain oxidized carbon fibers.

[0034] Carbon dioxide is added to water to prepare a carbon fiber slurry with a mass concentration of 0.05%-0.25%. Hydrophilic phenolic resin powder, at 50%-250% of the carbon fiber mass, is added to the fiber slurry, along with one or more of the following: ferric chloride, ferrous sulfate, aluminum sulfate, aluminum chloride, and polyaluminum chloride, at 0.2%-1.5% of the phenolic resin mass. The mixture is stirred at 100-300 rpm for 1-5 minutes to obtain a hydrophilic phenolic resin composite carbon fiber slurry.

[0035] (3) Molding and heat treatment of carbon fiber membrane materials

[0036] The above-mentioned mixed slurry is formed on a paper machine to obtain a wet-formed preform. The process includes: a first-stage press drying: pressing for 3-10 minutes in a 0.1-0.5 MPa press, followed by drying at 80-110℃ for 5-40 minutes; a second-stage press curing: hot pressing for 20-120 minutes in a hot press at 140-200℃ and 2-15 MPa; and a third-stage pressure carbonization: carbonization for 30-120 minutes in a nitrogen or argon atmosphere furnace at 100-1000 Pa and 600℃-1600℃. The resulting wet-formed carbon fiber membrane material has a basis weight that can be controlled within the range of 30-150 g / m². When the basis weight is within this range, the material exhibits a high-performance carbon paper morphology, making it particularly suitable for fuel cell gas diffusion layers.

[0037] The principle of the method in this application:

[0038] Phenolic resin, as a polymer material, contains benzene rings and phenolic hydroxyl groups in its molecular structure. Therefore, it is soluble in organic solvents such as ethanol and acetone, but insoluble in water. Polyvinyl alcohol is a polymer obtained from vinyl acetate through alcoholysis and polymerization. Its molecules contain a large number of hydroxyl groups, thus exhibiting good water solubility and film-forming properties. Carboxymethyl cellulose is a product obtained by carboxylation modification of cellulose. Its molecular surface is rich in carboxyl groups, making it not only hydrophilic but also an excellent adhesive and stabilizer.

[0039] To impart excellent wetting and dispersing properties to phenolic resin, this application employs a coating method, utilizing polyvinyl alcohol (PVA) and carboxymethyl cellulose (CMC) to synergistically coat and modify the phenolic resin. PVA serves as both a dispersion medium and a surfactant, uniformly coating the surface of phenolic resin particles through ultrasonic treatment, effectively inhibiting their aggregation. CMC further introduces hydrophilic groups such as carboxyl groups, and freeze-drying forms a porous, easily redispersible powder. Hydrogen bonds can form between the phenolic hydroxyl groups in the phenolic resin, the hydroxyl groups in PVA, and the carboxyl groups in CMC. The three polymer chains intertwine and entangle in the solution, forming a physical cross-linked network through hydrogen bonding and electrostatic interactions. This entanglement results in a synergistic reinforcing effect in the mixed system. This process significantly improves the dispersibility and stability of the originally hydrophobic phenolic resin in water, laying the foundation for subsequent uniform and thorough composite with carbon fibers in the aqueous phase.

[0040] Carbon fiber is composed of more than 90% carbon elements and has a disordered graphite crystal structure. Therefore, its surface is both hydrophobic and oleophobic, and it lacks active functional groups, making it difficult to react with other substances. In order to effectively introduce phenolic resin powder into carbon fiber, this application first treats the carbon fiber with acetone and hydrogen peroxide to remove surface organic impurities and introduce oxygen-containing polar functional groups such as hydroxyl and carboxyl groups, thereby enhancing the hydrophilicity and chemical activity of the fiber surface.

[0041] In the mixed slurry, metal cations (such as Al) ionized from the cationic salt 3+ Fe 3+ This substance can simultaneously complex and electrostatically adsorb with the negatively charged sites on the fiber surface and the polar groups on the surface of the hydrophilic phenolic resin powder, thus playing a "bridging" role. Specifically, the negatively charged carboxylate groups on the carbon fiber and hydrophilic phenolic resin surfaces react with the positively charged Al groups... 3+ Coulomb attraction is generated between them, an Al 3+ It can coordinate with multiple carboxyl groups simultaneously to form tetrahedral or octahedral configurations, acting as a crosslinking agent. This bridging effect significantly improves the adhesion efficiency and bonding strength of resin powder on the fiber surface, achieving efficient resin retention and uniform distribution.

[0042] Hydrophilic phenolic resin powder is directly added to the aqueous phase slurry of carbon fiber. Utilizing its excellent hydrophilicity and the flocculating and bridging effect of cationic salts, the resin particles can be uniformly adhered to the fiber surface and fiber interlacing points under gentle stirring, forming a uniformly composite wet paper web of fiber and resin. This wet blending process avoids the resin distribution gradient problems caused by uneven resin solution penetration or vacuum suction in traditional impregnation methods, ensuring the uniformity of the final material structure from the source.

[0043] This application employs a one-step molding process by directly introducing hydrophilic phenolic resin into an aqueous system. The carbon fiber membrane material is then obtained through a three-stage gradient heating process. The first stage, pressing and drying, aims to remove free water from the preform, soften the phenolic resin, and achieve pre-bonding with the fiber. The second stage, pressing and curing, further removes bound water and promotes cross-linking and curing of the phenolic resin through a hydroxymethyl reaction. The third stage, pressure carbonization, removes non-carbon elements such as H, O, and N, ultimately yielding the carbon fiber membrane material. Therefore, this application not only improves the affinity and dispersibility of the phenolic resin in water and enhances its retention in the slurry, but also optimizes the material preparation process, forming a synergistic effect of "resin hydrophilic modification → fiber activation → aqueous phase bridging and composite → staged thermal conversion," ultimately achieving the goal of controllable and efficient preparation of carbon fiber membrane materials.

[0044] Example 1

[0045] (1) Preparation of hydrophilic phenolic resin powder:

[0046] Polyvinyl alcohol with a degree of hydrolysis of 87% and a degree of polymerization of 1000 was dissolved in water at 95°C to prepare a 2% (w / w) polyvinyl alcohol solution, which was then cooled to room temperature. Thermosetting phenolic resin powder with a particle size of 60 mesh was added to the above polyvinyl alcohol solution to prepare a 30% (w / w) phenolic resin suspension. The above phenolic resin suspension was ultrasonically dispersed in an ultrasonic cleaner with an ultrasonic frequency of 100 kHz for 30 minutes to ensure uniform mixing, resulting in a uniformly dispersed phenolic resin-polyvinyl alcohol suspension system.

[0047] In another container, carboxymethyl cellulose powder was slowly added to water at 15°C and stirred at 1200 rpm to form a uniform suspension. The solution was then heated to 80°C and stirred continuously until the carboxymethyl cellulose was completely dissolved, resulting in a stable carboxymethyl cellulose solution with a mass concentration of 0.8%.

[0048] A carboxymethyl cellulose solution at 10% (by weight of polyvinyl alcohol) was added to the resulting phenolic resin-polyvinyl alcohol suspension and stirred until homogeneous. After allowing the mixture to stand, the supernatant was removed, and the remaining material was transferred to a freeze dryer for freeze-drying. The resulting powder was then ground to obtain hydrophilic phenolic resin powder.

[0049] (2) Carbon fiber pretreatment and preparation of mixed slurry:

[0050] Wood-based carbon fibers with a diameter of 12 μm and a length of 7 mm were immersed in sufficient pure acetone and ultrasonically cleaned at 70 °C for 0.6 hours to remove surface impurities. The cleaned carbon fibers were then treated in a 30% hydrogen peroxide solution at 80 °C for 4 hours for oxidation modification. After washing with water until neutral, the carbon fibers were dried to obtain oxidized carbon fibers.

[0051] Carbon fiber slurry with a mass concentration of 0.2% was prepared by adding oxidized carbon fiber to water. Hydrophilic phenolic resin powder (50% by weight of carbon fiber) was added to the slurry, along with ferric chloride (0.5% by weight of phenolic resin). The mixture was stirred at 100 rpm for 5 minutes to obtain a hydrophilic phenolic resin composite carbon fiber slurry.

[0052] (3) Molding and heat treatment of carbon fiber membrane materials:

[0053] The above-mentioned mixed slurry was formed on a paper machine to obtain a wet-formed preform. The process included: a first-stage press drying: pressing for 10 minutes in a 0.2 MPa press, followed by drying at 80°C for 40 minutes; a second-stage press curing: hot pressing for 30 minutes in a 14 MPa hot press at 150°C; and a third-stage pressure carbonization: carbonization for 120 minutes in a nitrogen atmosphere furnace at 1500°C and 200 Pa. This yielded a preform with a basis weight of 100 g / m³. 2 Carbon fiber membrane material (appearing as carbon paper).

[0054] Example 2

[0055] (1) Preparation of hydrophilic phenolic resin powder:

[0056] Polyvinyl alcohol with a degree of hydrolysis of 99% and a degree of polymerization of 2500 was dissolved in water at 75°C to prepare a 5% (w / w) polyvinyl alcohol solution, which was then cooled to room temperature. Thermosetting phenolic resin powder with a particle size of 1000 mesh was added to the above polyvinyl alcohol solution to prepare a 10% (w / w) phenolic resin suspension. The above phenolic resin suspension was ultrasonically dispersed in an ultrasonic cleaner with an ultrasonic frequency of 500 kHz for 5 minutes to ensure uniform mixing, resulting in a uniformly dispersed phenolic resin-polyvinyl alcohol suspension system.

[0057] In another container, carboxymethyl cellulose powder was slowly added to water at 30°C and stirred at 800 rpm to form a uniform suspension. The solution was then heated to 80°C and stirred continuously until the carboxymethyl cellulose was completely dissolved, resulting in a stable carboxymethyl cellulose solution with a mass concentration of 0.3%.

[0058] A carboxymethyl cellulose solution at 40% of the mass of polyvinyl alcohol was added to the resulting phenolic resin-polyvinyl alcohol suspension and stirred until homogeneous. After allowing the mixture to stand, the supernatant was removed, and the remaining material was transferred to a freeze dryer for freeze-drying. The resulting powder was then ground to obtain hydrophilic phenolic resin powder.

[0059] (2) Carbon fiber pretreatment and preparation of mixed slurry:

[0060] Viscose-based carbon fibers with a diameter of 4 μm and a length of 2 mm were immersed in sufficient pure acetone and ultrasonically cleaned at 50°C for 2 hours to remove surface impurities. The cleaned carbon fibers were then treated in a 30% hydrogen peroxide solution at 80°C for 2 hours to perform oxidation modification. After washing with water until neutral, the carbon fibers were dried to obtain oxidized carbon fibers.

[0061] Carbon dioxide was added to water to prepare a carbon fiber slurry with a mass concentration of 0.05%. Hydrophilic phenolic resin powder (250% by weight of the carbon fiber) was added to the slurry, along with polyaluminum chloride (1.4% by weight of the phenolic resin). The mixture was stirred at 300 rpm for 1 minute to obtain a hydrophilic phenolic resin composite carbon fiber slurry.

[0062] (3) Molding and heat treatment of carbon fiber membrane materials:

[0063] The above-mentioned mixed slurry was formed on a paper machine to obtain a wet-formed preform. The process included: a first-stage press drying: pressing for 3 minutes in a 0.5 MPa press, followed by drying at 110°C for 5 minutes; a second-stage press curing: hot pressing for 100 minutes in a hot press at 190°C and 2 MPa; and a third-stage pressure carbonization: carbonization for 30 minutes in an argon atmosphere furnace at 800 Pa and 800°C. A preform with a basis weight of 40 g / m³ was obtained. 2 Carbon fiber membrane material (appearing as carbon paper).

[0064] Example 3

[0065] (1) Preparation of hydrophilic phenolic resin powder:

[0066] Polyvinyl alcohol with a degree of hydrolysis of 95% and a degree of polymerization of 2000 was dissolved in water at 80°C to prepare a 3% (w / w) polyvinyl alcohol solution, which was then cooled to room temperature. Thermosetting phenolic resin powder with a particle size of 200 mesh was added to the above polyvinyl alcohol solution to prepare a 25% (w / w) phenolic resin suspension. The above phenolic resin suspension was ultrasonically dispersed in an ultrasonic cleaner with an ultrasonic frequency of 250 kHz for 20 min to ensure uniform mixing, resulting in a uniformly dispersed phenolic resin-polyvinyl alcohol suspension system.

[0067] In another container, carboxymethyl cellulose powder was slowly added to water at 25°C and stirred at 1000 rpm to form a uniform suspension. The solution was then heated to 80°C and stirred continuously until the carboxymethyl cellulose was completely dissolved, resulting in a stable carboxymethyl cellulose solution with a mass concentration of 0.5%.

[0068] A carboxymethyl cellulose solution at 25% of the mass of polyvinyl alcohol was added to the obtained phenolic resin-polyvinyl alcohol suspension and stirred until homogeneous. After allowing the mixture to stand, the supernatant was removed, and the remaining material was transferred to a freeze dryer for freeze-drying. After grinding, hydrophilic phenolic resin powder was obtained.

[0069] (2) Carbon fiber pretreatment and preparation of mixed slurry:

[0070] Polyacrylonitrile-based carbon fibers with a diameter of 8 μm and a length of 3 mm were immersed in sufficient pure acetone and ultrasonically cleaned at 70 °C for 1 hour to remove surface impurities. The cleaned carbon fibers were then placed in a 30% hydrogen peroxide solution at 80 °C for 3 hours for oxidation modification. After washing with water until neutral, the carbon fibers were dried to obtain oxidized carbon fibers.

[0071] Carbon dioxide was added to water to prepare a carbon fiber slurry with a mass concentration of 0.1%. Hydrophilic phenolic resin powder (200% by weight of the carbon fiber) was added to the slurry, along with aluminum sulfate (0.1% by weight of the phenolic resin). The mixture was stirred at 200 rpm for 3 minutes to obtain a hydrophilic phenolic resin composite carbon fiber slurry.

[0072] (3) Molding and heat treatment of carbon fiber membrane materials:

[0073] The above-mentioned mixed slurry was formed on a paper machine to obtain a wet-formed preform. The process included: a first-stage press drying: pressing for 5 minutes in a 0.3 MPa press, followed by drying at 105°C for 20 minutes; a second-stage press curing: hot pressing for 30 minutes in a hot press at 180°C and 8 MPa; and a third-stage pressure carbonization: carbonization for 60 minutes in a nitrogen atmosphere furnace at 500 Pa and 1200°C. This yielded a preform with a basis weight of 80 g / m³. 2 Carbon fiber membrane material (appearing as carbon paper).

[0074] The hydrophilic phenolic resin composite carbon fiber mixed slurry prepared in this embodiment, after being formed by a paper machine, yields a wet-formed preform as shown in the following photograph. Figure 1 As shown in the figure, the hydrophilic phenolic resin particles are effectively retained and uniformly attached to the carbon fiber surface, and fully dispersed in the fiber network, ensuring the overall uniformity of the matrix structure of the resulting membrane material. Figure 2 The image shown is a photograph of the carbon fiber membrane material precursor after pressing and drying. In this stage, the hydrophilic solid phenolic resin melts upon heating, further coating the carbon fibers and penetrating to the fiber interlacing points, thereby significantly improving the density and uniformity of the matrix structure. The microstructure of the carbon fiber membrane material obtained after further carbonization treatment was observed using a scanning electron microscope, and the results are as follows: Figure 3 As shown, the phenolic resin has been transformed into resin carbon and is firmly bonded to the surface of the carbon fibers and their intersections, forming a stable three-dimensional carbon network. These reinforcing anchor points not only significantly enhance the mechanical strength of the material but also retain a through-pore structure suitable for gas diffusion.

[0075] Example 4

[0076] (1) Preparation of hydrophilic phenolic resin powder:

[0077] Polyvinyl alcohol with a degree of hydrolysis of 87% and a degree of polymerization of 1000 was dissolved in water at 95°C to prepare a 2% (w / w) polyvinyl alcohol solution, which was then cooled to room temperature. Thermosetting phenolic resin powder with a particle size of 60 mesh was added to the above polyvinyl alcohol solution to prepare a 30% (w / w) phenolic resin suspension. The above phenolic resin suspension was ultrasonically dispersed in an ultrasonic cleaner with an ultrasonic frequency of 100 kHz for 30 minutes to ensure uniform mixing, resulting in a uniformly dispersed phenolic resin-polyvinyl alcohol suspension system.

[0078] In another container, carboxymethyl cellulose powder was slowly added to water at 15°C and stirred at 1200 rpm to form a uniform suspension. The solution was then heated to 80°C and stirred continuously until the carboxymethyl cellulose was completely dissolved, resulting in a stable carboxymethyl cellulose solution with a mass concentration of 0.8%.

[0079] A carboxymethyl cellulose solution at 10% (by weight of polyvinyl alcohol) was added to the resulting phenolic resin-polyvinyl alcohol suspension and stirred until homogeneous. After allowing the mixture to stand, the supernatant was removed, and the remaining material was transferred to a freeze dryer for freeze-drying. The resulting powder was then ground to obtain hydrophilic phenolic resin powder.

[0080] (2) Carbon fiber pretreatment and preparation of mixed slurry:

[0081] Wood-based carbon fibers with a diameter of 12 μm and a length of 7 mm were immersed in sufficient pure acetone and ultrasonically cleaned at 70 °C for 0.6 hours to remove surface impurities. The cleaned carbon fibers were then treated in a 30% hydrogen peroxide solution at 80 °C for 4 hours for oxidation modification. After washing with water until neutral, the carbon fibers were dried to obtain oxidized carbon fibers.

[0082] Carbon fiber slurry with a mass concentration of 0.2% was prepared by adding oxidized carbon fiber to water. Hydrophilic phenolic resin powder (250% by weight of carbon fiber) was added to the slurry, along with ferric chloride (0.5% by weight of phenolic resin). The mixture was stirred at 100 rpm for 5 minutes to obtain a hydrophilic phenolic resin composite carbon fiber slurry.

[0083] (3) Molding and heat treatment of carbon fiber membrane materials:

[0084] The above-mentioned mixed slurry was formed on a paper machine to obtain a wet-formed preform. The process included: a first-stage press drying: pressing for 10 minutes in a 0.2 MPa press, followed by drying at 80°C for 40 minutes; a second-stage press curing: hot pressing for 30 minutes in a 14 MPa hot press at 150°C; and a third-stage pressure carbonization: carbonization for 120 minutes in a nitrogen atmosphere furnace at 1500°C and 200 Pa. This yielded a preform with a basis weight of 100 g / m³. 2 Carbon fiber membrane material (appearing as carbon paper).

[0085] Comparative Example 1

[0086] The preparation of a comparative material using unmodified hydrophilic phenolic resin includes the following steps:

[0087] Polyacrylonitrile-based carbon fibers with a diameter of 8 μm and a length of 3 mm were immersed in sufficient pure acetone and ultrasonically cleaned at 70 °C for 1 hour to remove surface impurities. The cleaned carbon fibers were then placed in a 30% hydrogen peroxide solution at 80 °C for 3 hours for oxidation modification. After washing with water until neutral, the carbon fibers were dried to obtain oxidized carbon fibers.

[0088] Carbon fiber oxide was added to water to prepare a carbon fiber slurry with a mass concentration of 0.1%. Unmodified phenolic resin powder (200% by weight of the carbon fiber) was added to the slurry, along with aluminum sulfate (0.1% by weight of the phenolic resin). The mixture was stirred at 200 rpm for 3 minutes to obtain a general phenolic resin composite carbon fiber slurry.

[0089] The above-mentioned mixed slurry was formed on a paper machine to obtain a wet-formed preform. The process included: a first-stage press drying: pressing for 5 minutes in a 0.3 MPa press, followed by drying at 105°C for 20 minutes; a second-stage press curing: hot pressing for 30 minutes in a hot press at 180°C and 8 MPa; and a third-stage pressure carbonization: carbonization for 60 minutes in a nitrogen atmosphere furnace at 500 Pa and 1200°C. This yielded a preform with a basis weight of 80 g / m³. 2 Comparative material (represented by carbon paper).

[0090] Comparative Example 2

[0091] The preparation of unoxidized modified carbon fiber comparative materials includes the following steps:

[0092] Polyvinyl alcohol with a degree of hydrolysis of 95% and a degree of polymerization of 2000 was dissolved in water at 80°C to prepare a 3% (w / w) polyvinyl alcohol solution, which was then cooled to room temperature. Thermosetting phenolic resin powder with a particle size of 200 mesh was added to the above polyvinyl alcohol solution to prepare a 25% (w / w) phenolic resin suspension. The above phenolic resin suspension was ultrasonically dispersed in an ultrasonic cleaner with an ultrasonic frequency of 250 kHz for 20 min to ensure uniform mixing, resulting in a uniformly dispersed phenolic resin-polyvinyl alcohol suspension system.

[0093] In another container, carboxymethyl cellulose powder was slowly added to water at 25°C and stirred at 1000 rpm to form a uniform suspension. The solution was then heated to 80°C and stirred continuously until the carboxymethyl cellulose was completely dissolved, resulting in a stable carboxymethyl cellulose solution with a mass concentration of 0.5%.

[0094] A carboxymethyl cellulose solution at 25% of the mass of polyvinyl alcohol was added to the obtained phenolic resin-polyvinyl alcohol suspension and stirred until homogeneous. After allowing the mixture to stand, the supernatant was removed, and the remaining material was transferred to a freeze dryer for freeze-drying. After grinding, hydrophilic phenolic resin powder was obtained.

[0095] Unoxidized polyacrylonitrile-based carbon fibers with a diameter of 8 μm and a length of 3 mm were added to water to prepare a carbon fiber slurry with a mass concentration of 0.1%. Hydrophilic phenolic resin powder (200% of the carbon fiber mass) was added to the slurry, along with aluminum sulfate (0.1% of the phenolic resin mass). The mixture was stirred at 200 rpm for 3 minutes to obtain a hydrophilic phenolic resin composite carbon fiber slurry.

[0096] The above-mentioned mixed slurry was formed on a paper machine to obtain a wet-formed preform. The process included: a first-stage press drying: pressing for 5 minutes in a 0.3 MPa press, followed by drying at 105°C for 20 minutes; a second-stage press curing: hot pressing for 30 minutes in a hot press at 180°C and 8 MPa; and a third-stage pressure carbonization: carbonization for 60 minutes in a nitrogen atmosphere furnace at 500 Pa and 1200°C. This yielded a preform with a basis weight of 80 g / m³. 2 Comparative material (represented by carbon paper).

[0097] Comparative Example 3

[0098] The preparation of the comparative material without the addition of a cation salt includes the following steps:

[0099] Polyvinyl alcohol with a degree of hydrolysis of 95% and a degree of polymerization of 2000 was dissolved in water at 80°C to prepare a 3% (w / w) polyvinyl alcohol solution, which was then cooled to room temperature. Thermosetting phenolic resin powder with a particle size of 200 mesh was added to the above polyvinyl alcohol solution to prepare a 25% (w / w) phenolic resin suspension. The above phenolic resin suspension was ultrasonically dispersed in an ultrasonic cleaner with an ultrasonic frequency of 250 kHz for 20 min to ensure uniform mixing, resulting in a uniformly dispersed phenolic resin-polyvinyl alcohol suspension system.

[0100] In another container, carboxymethyl cellulose powder was slowly added to water at 25°C and stirred at 1000 rpm to form a uniform suspension. The solution was then heated to 80°C and stirred continuously until the carboxymethyl cellulose was completely dissolved, resulting in a stable carboxymethyl cellulose solution with a mass concentration of 0.5%.

[0101] A carboxymethyl cellulose solution at 25% of the mass of polyvinyl alcohol was added to the obtained phenolic resin-polyvinyl alcohol suspension and stirred until homogeneous. After allowing the mixture to stand, the supernatant was removed, and the remaining material was transferred to a freeze dryer for freeze-drying. After grinding, hydrophilic phenolic resin powder was obtained.

[0102] Polyacrylonitrile-based carbon fibers with a diameter of 8 μm and a length of 3 mm were immersed in sufficient pure acetone and ultrasonically cleaned at 70 °C for 1 hour to remove surface impurities. The cleaned carbon fibers were then placed in a 30% hydrogen peroxide solution at 80 °C for 3 hours for oxidation modification. After washing with water until neutral, the carbon fibers were dried to obtain oxidized carbon fibers.

[0103] Carbon oxidized carbon fiber was added to water to prepare a carbon fiber slurry with a mass concentration of 0.1%. Hydrophilic phenolic resin powder, at a mass ratio of 200% relative to the carbon fiber, was added to the fiber slurry. (No cationic salts were added.) The mixture was stirred at 200 rpm for 3 minutes to obtain a hydrophilic phenolic resin composite carbon fiber slurry.

[0104] The above-mentioned mixed slurry was formed on a paper machine to obtain a wet-formed preform. The process included: a first-stage press drying: pressing for 5 minutes in a 0.3 MPa press, followed by drying at 105°C for 20 minutes; a second-stage press curing: hot pressing for 30 minutes in a hot press at 180°C and 8 MPa; and a third-stage pressure carbonization: carbonization for 60 minutes in a nitrogen atmosphere furnace at 500 Pa and 1200°C. This yielded a preform with a basis weight of 80 g / m³. 2 Comparative material (represented by carbon paper).

[0105] Carbon fiber membrane material performance testing:

[0106] The materials prepared in the above examples and comparative examples were subjected to tests for tensile strength, porosity, resistivity, and air permeability. The test results are shown in Table 1.

[0107] Table 1. Performance Comparison of Carbon Fiber Film Materials (Carbon Paper Form)

[0108]

[0109] A comparison of the data from Example 3 and Comparative Example 1 in Table 1 shows that the comparative material prepared using unmodified phenolic resin exhibits significantly reduced tensile strength and increased resistivity. This indicates that unmodified phenolic resin is difficult to effectively adsorb and bind with oxidized carbon fibers, leading to resin loss during molding and a decrease in the internal bonding strength of the material. This result demonstrates that hydrophilic modification of phenolic resin is a prerequisite for achieving uniform dispersion in the aqueous phase and a stable bond with fibers, and is an indispensable key step. The comparison between Example 1 and Example 4 shows that increasing the content of hydrophilic phenolic resin can significantly enhance the bonding force between carbon fibers, making the three-dimensional network structure more compact, thereby improving the strength of the membrane material while reducing porosity and pore size. This proves that by controlling the content of hydrophilic phenolic resin, the mechanical properties and porous structure of the material can be effectively coordinated.

[0110] Comparing Example 3 with Comparative Example 2, it can be seen that the material prepared using oxidized carbon fiber exhibits superior tensile strength and electrical conductivity compared to unmodified carbon fiber. This is because oxidation treatment introduces polar oxygen-containing functional groups such as hydroxyl and carboxyl groups onto the carbon fiber surface, increasing the number of surface active sites. This not only enhances the interfacial contact with phenolic resin but also improves the adsorption capacity for cations. Therefore, the oxidation activation of carbon fiber is crucial for improving surface polarity and enhancing chemical bonding and electrostatic adsorption with hydrophilic resins.

[0111] Furthermore, a comparison between Example 3 and Comparative Example 3 shows that the material properties with added cationic salt are significantly better than those without. This confirms that cationic salt plays a crucial "bridging" role between phenolic resin and carbon fiber. In summary, the synergistic effect of hydrophilic phenolic resin, oxidized carbon fiber, and cationic salt is indispensable in the material molding process. The introduction of cationic salt can effectively improve the resin retention rate and bonding strength on the fiber surface, which is key to optimizing the uniformity of the composite.

[0112] This application significantly improves the tensile strength and reduces the resistivity of the obtained carbon fiber membrane material by introducing hydrophilic phenolic resin powder, while also reducing porosity and air permeability to some extent. This is mainly because hydrophilic modification significantly improves the dispersibility of phenolic resin in water, enhances the uniformity of the slurry, and thus makes the material structure more uniform; the resin strengthens the bonding force between fibers, thereby greatly improving tensile strength; the continuous spatial network formed between fibers after resin carbonization increases the conductive pathway and reduces resistivity; and the partial filling of the gaps between fibers by the resin leads to a reasonable decrease in porosity and air permeability.

[0113] In summary, the carbon fiber membrane material preparation process provided in this application is simple and efficient, and the resulting product has excellent comprehensive performance. In particular, through multi-stage synergy, the structural stability and durability of the material as a gas diffusion layer in fuel cells are effectively improved.

[0114] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention in any other way. Any person skilled in the art may make changes or equivalent variations based on the above-disclosed technical content. Any simple modifications, equivalent variations, and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the protection scope of the present invention.

Claims

1. A method for preparing a wet-formed carbon fiber membrane material, characterized in that, Includes the following steps: Step (1) Preparation of hydrophilic phenolic resin powder: Polyvinyl alcohol is dissolved in water to prepare a solution, phenolic resin powder is added, and ultrasonic dispersion is performed to make it mix evenly to obtain a phenolic resin-polyvinyl alcohol suspension system; Carboxymethyl cellulose is dissolved in water to prepare a solution, added to the above suspension system and stirred evenly, and after standing, freeze drying and grinding, hydrophilic phenolic resin powder is obtained. Step (2) Carbon fiber pretreatment and preparation of mixed slurry: Carbon fiber is ultrasonically cleaned with acetone and oxidized with hydrogen peroxide to obtain oxidized carbon fiber; carbon fiber slurry is prepared by dispersing oxidized carbon fiber in water, adding hydrophilic phenolic resin powder and cationic salt, and stirring to obtain hydrophilic phenolic resin composite carbon fiber mixed slurry. Step (3) Molding and heat treatment of carbon fiber membrane material: The above mixed slurry is wet-molded to obtain a wet-molded preform, which is then subjected to pressing and drying, hot pressing and curing and pressure carbonization treatment in sequence to obtain the wet-molded carbon fiber membrane material.

2. The preparation method according to claim 1, characterized in that, The degree of alcoholysis of the polyvinyl alcohol mentioned in step (1) is 87%-99%, and the degree of polymerization is 1000-2500; the mass concentration of the polyvinyl alcohol solution is 1%-5%.

3. The preparation method according to claim 1 or 2, characterized in that, The phenolic resin mentioned in step (1) is a thermosetting phenolic resin with a powder particle size of 50-1000 mesh; the mass concentration of the phenolic resin in the suspension system is 5%-35%.

4. The preparation method according to claim 3, characterized in that, The mass concentration of the carboxymethyl cellulose solution in step (1) is 0.2%-1%, and the amount of carboxymethyl cellulose solution added is 10%-50% relative to the mass of polyvinyl alcohol.

5. The preparation method according to claim 3, characterized in that, The ultrasonic frequency for ultrasonic dispersion in step (1) is 50-500kHz, and the dispersion time is 5-30min.

6. The preparation method according to claim 1, characterized in that, The carbon fiber mentioned in step (2) is one or more of polyacrylonitrile-based carbon fiber, pitch-based carbon fiber, viscose-based carbon fiber, wood-based carbon fiber and phenolic resin-based carbon fiber; the carbon fiber diameter is 3-13μm and the length is 1-8mm.

7. The preparation method according to claim 1 or 6, characterized in that, The temperature for ultrasonic cleaning with acetone in step (2) is 50-80℃ and the time is 0.5-2 hours; the conditions for hydrogen peroxide oxidation modification are: temperature 80℃, 30% hydrogen peroxide solution, and treatment time 2-4 hours.

8. The preparation method according to claim 7, characterized in that, The mass concentration of the carbon fiber slurry in step (2) is 0.05%-0.25%; the amount of hydrophilic phenolic resin powder added is 50%-250% relative to the mass of carbon fiber; and the amount of cationic salt added is 0.2%-1.5% relative to the mass of phenolic resin.

9. The preparation method according to claim 1 or 8, characterized in that, The cationic salt mentioned in step (2) is one or more of ferric chloride, ferrous sulfate, aluminum sulfate, aluminum chloride and polyaluminum chloride.

10. The preparation method according to claim 9, characterized in that, The pressing and drying conditions in step (3) are: pressure 0.1-0.5MPa, pressing time 3-10min, drying temperature 80-110℃, drying time 5-40min; the hot pressing and curing conditions are: temperature 140-200℃, pressure 2-15MPa, hot pressing time 20-120min; the pressurized carbonization conditions are: pressure 100-1000Pa, temperature 600℃-1600℃, carbonization time 30-120min, and the atmosphere is nitrogen or argon.

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