Preparation method of high-conductivity carbon fiber paper

Abstract

A preparation method of high-conductivity carbon fiber paper comprises the following steps: performing surface oxidation modification, washing, filtering and drying on carbon fibers, adding the carbon fibers into an aqueous solution of a dispersing agent, forming through a papermaking process to obtain carbon fiber pre-formed paper, impregnating the carbon fiber pre-formed paper into a resin solution, and drying to obtain the high-conductivity carbon fiber paper. And carrying out hot-pressing curing and high-temperature treatment to obtain the carbon fiber paper. Asphalt resin and phenolic resin are used as binders, in the hot-pressing curing stage, the asphalt resin is heated and melted, carbon fibers are uniformly impregnated, a three-dimensional network structure formed by curing and crosslinking of the phenolic resin is fully filled, and a good conductive network is formed; in the high-temperature treatment stage, the asphalt resin and the phenolic resin are co-carbonized, a polycyclic aromatic hydrocarbon structure of the asphalt resin is combined with free radicals generated by pyrolysis of the phenolic resin to generate dehydrogenation reaction, a wider conjugated carbon network is formed, the graphitization degree of the carbon paper is improved, and the conductivity and mechanical strength of the carbon paper are improved; therefore, the composite membrane has a good effect in the proton exchange membrane fuel cell.

Description

Technical Field

[0001] The present invention belongs to the field of proton exchange membrane fuel cells, and relates to a preparation method of highly conductive carbon fiber paper, specifically to a preparation method of highly conductive carbon fiber paper for fuel cell gas diffusion layers. Background Art

[0002] Proton exchange membrane fuel cells exhibit significant advantages in the new energy field due to their low-temperature operation characteristics, excellent energy conversion efficiency and energy density characteristics, especially the technical feature of only generating water during operation and truly achieving zero pollution emissions. Among them, the gas diffusion layer, as a key component, has attracted much attention. The gas diffusion layer (GDL), as a key functional component in proton exchange membrane fuel cells (PEMFCs), has a decisive impact on the overall performance of the battery. It not only provides support for the membrane electrode assembly (MEA) but also provides channels for the transport of reactants and drainage.

[0003] The preparation process of carbon paper for fuel cell gas diffusion layers includes core processes such as wet forming, resin impregnation, hot pressing, and high-temperature graphitization. As the key raw material of carbon fiber paper, carbon fiber can be divided into three categories according to the type of precursor: polyacrylonitrile-based carbon fiber, pitch-based carbon fiber, and viscose-based carbon fiber. Among them, pitch-based carbon fiber is further subdivided into two types: general-grade and mesophase pitch-based carbon fiber according to the differences in preparation processes. Raw material fibers usually choose polyacrylonitrile-based carbon fiber. Compared with it, mesophase pitch-based carbon fiber exhibits excellent mechanical and thermal properties. Its modulus has reached 950 GPa, which is about 1.5 times that of polyacrylonitrile-based graphite fiber; the thermal conductivity is generally higher than 800 W / m·K, and some models can even reach more than 1000 W / m·K, which is 4-5 times that of polyacrylonitrile-based graphite fiber. This unique performance advantage makes it an ideal reinforcing material for optimizing the performance of carbon fiber paper. By constructing a composite aggregate system with mesophase pitch-based carbon fiber partially replacing polyacrylonitrile-based carbon fiber, the comprehensive performance index of the product can be significantly improved.

[0004] In addition, in the carbon fiber paper impregnation process, phenolic resin solution is usually used to impregnate the fiber substrate. After hot pressing and cross-linking, it is converted into a carbonaceous binder phase during the subsequent high-temperature carbonization process. This carbon phase not only enhances the bonding strength of the fiber network but also constructs a conductive / heat-conductive network path. It should be noted that in the industrial production process, the energy consumption in the high-temperature graphite treatment link accounts for about 60%-70% of the total cost, and the inherent poor graphitization property of phenolic resin carbon exacerbates this technical bottleneck. Specifically, phenolic resin carbon can only be effectively graphitized under ultra-high temperature conditions of 2600-3000 °C, which poses strict requirements on the high-temperature resistance performance of the equipment and causes significant energy loss. The dual constraints of this high-energy-consuming process and the intrinsic properties of the material result in the difficulty of breaking through the theoretical limit of the conductive / heat-conductive performance of the final product.

[0005] Patent CN108914681A discloses a preparation method of carbon fiber paper, which adds chopped mesophase pitch carbon fiber to improve the conductive and heat-conductive properties of carbon fiber paper. However, it still uses phenolic resin as a binder and requires ultra-high temperature conditions to achieve effective graphitization, resulting in no quantitative improvement in the properties of carbon paper. Patent CN119102143A immerses the carbon fiber substrate in a phenolic resin impregnating solution for primary impregnation, drying, hot pressing and curing, and carbonization, and then secondary impregnation with asphalt / polyimide and carbonization to obtain a carbon fiber-glassy carbon-graphite carbon coating structure, so as to reduce the graphitization temperature. However, this method requires multiple high-temperature treatments of carbonization and graphitization, and the preparation process is complex.

[0006] Therefore, the present invention proposes a strategy of compounding an asphalt-based carbon precursor with a high residual carbon rate and a high degree of graphitization with polyacrylonitrile-based fiber and phenolic resin. Through the co-carbonization of asphalt resin and phenolic resin, the carbon phase composition and structure are optimized, and the process temperature is reduced to achieve the improvement of the conductive and heat-conductive properties of carbon paper while taking into account the mechanical strength. Summary of the Invention

[0007] In order to overcome the deficiencies of the prior art, the object of the present invention is to propose a preparation process of a highly conductive carbon fiber paper for a fuel cell gas diffusion layer. The present invention proposes a strategy of compounding an asphalt-based carbon precursor with a high residual carbon rate and a high degree of graphitization with polyacrylonitrile-based fiber and phenolic resin. Through the co-carbonization of asphalt resin and phenolic resin, a new binder system is constructed. This method effectively reduces the graphitization temperature, facilitates the control of production costs and industrial preparation.

[0008] The technical solution of the present invention:

[0009] A preparation method of a highly conductive carbon fiber paper, comprising the following steps:

[0010] Step 1: Perform surface pretreatment on the carbon fiber, then wash, filter, and dry to obtain pretreated carbon fiber;

[0011] Step 2: Add the pretreated carbon fiber into the aqueous solution of the dispersant and mix evenly to form a carbon fiber suspension slurry;

[0012] Step 3: Form a carbon fiber preformed paper through a papermaking process. Immerse the carbon fiber preformed paper in a binder and then dry it. Obtain the carbon fiber paper after hot pressing and curing and high-temperature treatment.

[0013] In Step 1, the pretreatment process of the carbon fiber includes gas-phase oxidation (oxidizing gases, including but not limited to ozone, air), chemical oxidation (strongly oxidizing liquids, including but not limited to sodium hydroxide, nitric acid, chromic acid), and plasma oxidation.

[0014] In Step 1, the carbon fiber is a mixture of polyacrylonitrile-based carbon fiber and pitch-based carbon fiber with a mass ratio of 9:1 - 5:5; the polyacrylonitrile-based carbon fiber has a length of 3 - 10 mm and a fiber diameter of 5 - 7 μm; the pitch-based carbon fiber has a length of 3 - 10 mm and a fiber diameter of 5 - 10 μm.

[0015] In Step 2, the dispersant is a mixture of sodium carboxymethyl cellulose and polyethylene oxide with a mass ratio of 9:1 - 5:5.

[0016] In Step 3, the binder is a mixture of phenolic resin and pitch resin with a mass ratio of 1:9 - 5:5; the preparation steps of the pitch resin include: using coal tar pitch or petroleum pitch as the raw material, benzaldehyde or terephthaldehyde as the cross-linking agent (the mass ratio of the cross-linking agent to the raw material is 1:4 - 6), p-toluenesulfonic acid or sulfuric acid as the catalyst (the mass ratio of the catalyst to the raw material is 1:15 - 20), controlling the reaction system to be heated to 160 - 190 °C, continuously reacting at this temperature for 2 - 4 h, synthesizing a condensed polycyclic polynuclear aromatic resin through cationic cross-linking, and having a softening point of 80 - 120 °C.

[0017] In Step 3, the temperature of the hot pressing and curing is 140 - 250 °C, the pressure is 1 - 10 MPa, and the time is 20 - 60 minutes.

[0018] In Step 3, the high-temperature treatment process includes two parts: carbonization and graphitization: the carbonization treatment temperature is 800 - 1600 °C, the carbonization treatment heating rate is 1 - 10 °C / min, and the heat preservation time is 0.5 - 2 hours; the graphitization treatment temperature is 2200 - 2500 °C, the graphitization treatment heating rate is 10 - 50 °C / min, and the heat preservation time is 0.5 - 1.5 hours.

[0019] This application also provides a carbon fiber paper, and the carbon fiber paper is prepared by using the preparation method of the carbon fiber paper as described above.

[0020] Advantages of the present invention: a) The present invention adopts a high-temperature synergistic carbonization process with the compounding of asphalt resin and phenolic resin. During the hot pressing and curing stage of the carbon paper, the phenolic resin cures and crosslinks to form a three-dimensional network structure at the low-temperature stage. As the temperature rises, the asphalt resin melts, uniformly impregnates the carbon fiber, and flows and fills in the phenolic resin network structure to form a good conductive network. During the high-temperature treatment stage, the asphalt resin and the phenolic resin undergo co-carbonization, and the polycyclic aromatic hydrocarbon structure of the asphalt resin combines with the free radicals generated by the pyrolysis of the phenolic resin to undergo a dehydrogenation reaction, forming a more extensive conjugated carbon network, improving the graphitization degree of the carbon paper, greatly enhancing the electrical conductivity and mechanical strength of the carbon paper, and enabling it to have good effects in proton exchange membrane fuel cells; b) The present invention uses asphalt-based carbon fibers with more excellent self-conductive and heat-conductive properties and higher graphitization degree to partially replace polyacrylonitrile-based carbon fibers, and uses short-cut carbon fibers with a specific length, which can enable the prepared carbon fiber paper to have a higher tensile strength and uniformity. Since the asphalt-based carbon fiber and the asphalt resin have similar elemental compositions and molecular structures, the interaction force between the two is strong, and they have better carbon compatibility, constructing a fiber-resin structure with excellent electrical conductivity and good porosity; c) The provided preparation method is simple, the raw materials are easy to obtain, and it is easy to scale up production. Brief Description of the Drawings

[0021] Figure 1 It is a schematic diagram of the carbon fiber dispersion in the suspension slurry prepared in Example 1 of the present invention.

[0022] Figure 2 It is a thermogravimetric curve of the asphalt resin prepared in Example 1 of the present invention.

[0023] Figure 3 It is a scanning electron microscope photograph of the carbon fiber paper prepared in Example 1 of the present invention.

[0024] Figure 4 It is a scanning electron microscope photograph of the carbon fiber paper prepared in Comparative Example 1 of the present invention. Detailed Embodiments

[0025] The following further illustrates the detailed embodiments of the present invention in combination with the drawings and technical solutions.

[0026] Example 1

[0027] Step 1: Place the short-cut carbon fiber in a NaOH solution, and place the mixed system in an ultrasonic cleaner for ultrasonic treatment for 30 minutes. After ultrasonic treatment, repeatedly wash with deionized water until the pH value of the filtrate reaches neutral. Dry the washed carbon fiber to obtain a carbon fiber sample pretreated with NaOH. Use a box-type resistance furnace to perform air oxidation modification treatment on the carbon fiber pretreated with NaOH, and the treatment conditions are to treat at 500 °C for 1.5 hours.

[0028] Step 2: Take 70 parts of sodium carboxymethylcellulose and 30 parts of polyethylene oxide as a composite dispersant, add it to water and stir evenly until the dispersion system is clear, transparent and bubble-free. Add 1.75 g of polyacrylonitrile-based carbon fiber with a length of 6 mm and a diameter of 5 μm and 0.75 g of pitch-based carbon fiber with a length of 3 mm and a diameter of 10 μm thereto, and continue to stir at a speed of 350 r / min for 4 hours. Make paper by wet forming process to obtain a carbon fiber preformed paper.

[0029] Step 3: The resin of the resin impregnating solution is selected as a compound of phenolic resin and pitch resin, and the ratio of phenolic resin to pitch resin is 4:6. The pitch resin is prepared using coal tar pitch as the raw material, benzaldehyde as the cross-linking agent (the mass ratio of the cross-linking agent to the raw material is 1:5), and p-toluenesulfonic acid or sulfuric acid as the catalyst (the mass ratio of the catalyst to the raw material is 1:16). Control the reaction system to heat up to 180 °C, and continue to react at this temperature for 4 h. Synthesize condensed polycyclic polynuclear aromatic resin by cationic cross-linking, and the softening point is 90 °C. The crushed and screened pitch resin powder is dissolved in tetrahydrofuran solvent to prepare an impregnating solution with a mass fraction of 12 wt.%.

[0030] Step 4: Cut the pre-prepared carbon fiber preformed paper into a specimen of 10 cm × 10 cm, and immerse it in the pitch resin solution for 1 hour to ensure sufficient infiltration. After the immersion is completed, place the specimen in a flat vulcanizing machine for hot pressing and curing. Set the segmented hot pressing conditions as follows: the pressure is 5 MPa, keep the temperature at 180 °C for 30 minutes, and then raise the temperature to 250 °C and continue to cure for 30 minutes.

[0031] Step 5: Under a nitrogen atmosphere, heat up to 1000 °C at a rate of 1 °C / min and keep it for 1 hour, and heat up to 2500 °C at a rate of 10 °C / min and keep it for 1 hour for graphitization to obtain carbon fiber paper for fuel cells. Finally, the areal density of the carbon paper is 106.8 g / m2, the porosity of the carbon paper is 78%, the resistivity is 2.35 mΩ / cm, and the tensile strength is 35.46 Mpa.

[0032] Example 2

[0033] Step 1: Place the short-cut carbon fiber in a NaOH solution, and place the mixed system in an ultrasonic cleaner for ultrasonic treatment for 30 minutes. After the ultrasonic treatment, wash it repeatedly with deionized water until the pH value of the filtrate reaches neutral. Dry the washed carbon fiber to obtain a carbon fiber sample pretreated with NaOH. Treat the carbon fiber with oxygen plasma, control the treatment pressure to be 15 Pa, the power to be 20 W, the gas flow rate to be 20 L / min, and the treatment time to be 400 seconds.

[0034] Step 2: Take 80 parts of sodium carboxymethylcellulose and 20 parts of polyethylene oxide as a composite dispersant, add it to water and stir evenly until the dispersion system is clear, transparent and bubble-free. Add 2.25 g of polyacrylonitrile-based carbon fiber with a length of 10 mm and a diameter of 7 μm and 0.25 g of pitch-based carbon fiber with a length of 3 mm and a diameter of 7 μm thereto, and continue to stir at a speed of 350 r / min for 4 hours. Then, make paper by wet forming process to obtain a carbon fiber preform paper.

[0035] Step 3: The resin of the resin impregnating solution is a compound of phenolic resin and pitch resin, and the ratio of phenolic resin to pitch resin is 3:7. The pitch resin is prepared using coal tar pitch as the raw material, benzaldehyde as the cross-linking agent (the mass ratio of the cross-linking agent to the raw material is 1:4), and p-toluenesulfonic acid or sulfuric acid as the catalyst (the mass ratio of the catalyst to the raw material is 1:15). Control the reaction system to heat up to 160 °C, and continue to react at this temperature for 2 h to synthesize a condensed polycyclic polynuclear aromatic resin through cationic cross-linking, with a softening point of 80 °C. The crushed and sieved pitch resin powder is dissolved in tetrahydrofuran solvent to prepare an impregnating solution with a mass fraction of 20 wt.%.

[0036] Step 4: Cut the pre-prepared carbon fiber preform paper into a specimen of 10 cm × 10 cm, and impregnate it in the pitch resin solution for 1 hour to ensure full infiltration. After impregnation, place the specimen in a flat vulcanizing machine for hot pressing and curing. Set the segmented hot pressing conditions as follows: the pressure is 10 MPa, keep the temperature at 140 °C for 60 minutes, and then raise the temperature to 200 °C and continue to cure for 20 minutes.

[0037] Step 5: Under a nitrogen atmosphere, heat up to 800 °C at a rate of 10 °C / min and hold for 2 hours, then heat up to 2200 °C at a rate of 20 °C / min and hold for 1.5 hours for graphitization to obtain a carbon fiber paper for fuel cells. Finally, the surface density of the carbon paper is 111 g / m2, the porosity of the carbon paper is 75%, the resistivity is 3.24 mΩ / cm, and the tensile strength is 34.55 Mpa.

[0038] Example 3

[0039] Step 1: Place the short-cut carbon fiber in a concentrated nitric acid solution, and place the mixed system in an ultrasonic cleaner for ultrasonic treatment for 30 minutes. After ultrasonic treatment, wash it repeatedly with deionized water until the pH value of the filtrate reaches neutral. Dry the washed carbon fiber to obtain a pretreated carbon fiber sample. Use a box-type resistance furnace to perform air oxidation modification treatment on the pretreated carbon fiber, and the treatment conditions are to treat at 500 °C for 1.5 hours.

[0040] Step 2: Take 60 parts of sodium carboxymethylcellulose and 40 parts of polyethylene oxide as a composite dispersant, add them to water and stir evenly until the dispersion system is clear, transparent and bubble-free. Add 1.5 g of polyacrylonitrile-based carbon fiber with a length of 3 mm and a diameter of 5 μm and 1 g of pitch-based carbon fiber with a length of 10 mm and a diameter of 5 μm thereto, and continue to stir at a speed of 350 r / min for 4 hours. Then, make paper by wet forming process to obtain a carbon fiber preformed paper.

[0041] Step 3: The resin of the resin impregnating solution is a compound of phenolic resin and pitch resin, and the ratio of phenolic resin to pitch resin is 2:8. The pitch resin is prepared using petroleum pitch as the raw material, benzaldehyde as the cross-linking agent (the mass ratio of the cross-linking agent to the raw material is 1:5), and p-toluenesulfonic acid or sulfuric acid as the catalyst (the mass ratio of the catalyst to the raw material is 1:20). Control the reaction system to be heated to 190 °C, and continue to react at this temperature for 3 h to synthesize a condensed polycyclic polynuclear aromatic resin through cationic cross-linking, with a softening point of 120 °C. The pulverized and sieved pitch resin powder is dissolved in a tetrahydrofuran solvent to prepare an impregnating solution with a mass fraction of 6 wt.%.

[0042] Step 4: Cut the pre-prepared carbon fiber preformed paper into specimens of 10 cm × 10 cm, and immerse them in the pitch resin solution for 1 hour to ensure sufficient infiltration. After immersion, place the specimens in a flat vulcanizing machine for hot pressing and curing, and set the segmented hot pressing conditions as follows: the pressure is 1 MPa, keep the temperature at 180 °C for 60 minutes, and then raise the temperature to 250 °C and continue to cure for 30 minutes.

[0043] Step 5: Under a nitrogen atmosphere, heat up to 1600 °C at a rate of 10 °C / min and hold for 0.5 hour, then heat up to 2500 °C at a rate of 50 °C / min and hold for 0.5 h for graphitization to obtain a carbon fiber paper for fuel cells. Finally, the surface density of the carbon paper is 92.3 g / m2, the porosity of the carbon paper is 82%, the resistivity is 4.6 mΩ / cm, and the tensile strength is 26.78 Mpa.

[0044] Example 4

[0045] Step 1: Place the short-cut carbon fiber in a chromic acid solution, and place the mixed system in an ultrasonic cleaner for ultrasonic treatment for 30 minutes. After ultrasonic treatment, wash repeatedly with deionized water until the pH value of the filtrate reaches neutral. Dry the washed carbon fiber to obtain a pretreated carbon fiber sample. Use a box-type resistance furnace to carry out air oxidation modification treatment on the pretreated carbon fiber, and the treatment conditions are to treat at 500 °C for 1.5 hours.

[0046] Step 2: Take 50 parts of sodium carboxymethylcellulose and 50 parts of polyethylene oxide as a composite dispersant, add them to water and stir evenly until the dispersion system is clear, transparent and bubble-free. Add 2 g of polyacrylonitrile-based carbon fiber with a length of 3 mm and a diameter of 5 μm and 0.5 g of pitch-based carbon fiber with a length of 3 mm and a diameter of 10 μm thereto, and continue to stir at a speed of 350 r / min for 4 hours. Then, make paper by wet forming process to obtain a carbon fiber preformed paper.

[0047] Step 3: The resin of the resin impregnating solution is a compound of phenolic resin and pitch resin, and the ratio of phenolic resin to pitch resin is 1:9. The pitch resin is prepared using coal tar pitch as the raw material, benzaldehyde as the cross-linking agent (the mass ratio of the cross-linking agent to the raw material is 1:6), and p-toluenesulfonic acid or sulfuric acid as the catalyst (the mass ratio of the catalyst to the raw material is 1:16). Control the reaction system to heat up to 180 °C, and continue to react at this temperature for 3 h to synthesize a condensed polycyclic polynuclear aromatic resin through cationic cross-linking, with a softening point of 85 °C. The pulverized and sieved pitch resin powder is dissolved in tetrahydrofuran solvent to prepare an impregnating solution with a mass fraction of 14 wt.%.

[0048] Step 4: Cut the pre-prepared carbon fiber preformed paper into specimens of 10 cm × 10 cm, and immerse them in the pitch resin solution for 1 hour to ensure sufficient infiltration. After immersion, place the specimens in a flat vulcanizing machine for hot pressing and curing, and set the segmented hot pressing conditions as follows: the pressure is 3 MPa, keep the temperature constant at 140 °C for 30 minutes, and then raise the temperature to 200 °C and continue to cure for 20 minutes.

[0049] Step 5: Under a nitrogen atmosphere, heat up to 1500 °C at a rate of 10 °C / min and keep it warm for 1.5 hours, then heat up to 2500 °C at a rate of 50 °C / min and keep it warm for 1.5 hours for graphitization to obtain a carbon fiber paper for fuel cells. Finally, the surface density of the carbon paper is 105.3 g / m2, the porosity of the carbon paper is 76.8%, the resistivity is 5.28 mΩ / cm, and the tensile strength is 27.72 Mpa.

[0050] Example 5

[0051] Step 1: Place the chopped carbon fiber in a NaOH solution, and place the mixed system in an ultrasonic cleaner for ultrasonic treatment for 30 minutes. After ultrasonic treatment, wash it repeatedly with deionized water until the pH value of the filtrate reaches neutral. Dry the washed carbon fiber to obtain a pretreated carbon fiber sample. Further oxidize the carbon fiber with ozone, with an ozone concentration of 50 mg / L, a gas flow rate of 0.5 L / min, and an oxidation time of 400 seconds.

[0052] Step 2: Take 90 parts of sodium carboxymethylcellulose and 10 parts of polyethylene oxide as a composite dispersant, add it to water and stir evenly until the dispersion system is clear, transparent and bubble-free. Add 1.25 g of polyacrylonitrile-based carbon fiber with a length of 6 mm and a diameter of 5 μm and 1.25 g of pitch-based carbon fiber with a length of 3 mm and a diameter of 10 μm thereto, and continue to stir at a speed of 350 r / min for 4 hours. Then, make paper by wet forming process to obtain a carbon fiber preformed paper.

[0053] Step 3: The resin of the resin impregnating solution is a compound of phenolic resin and pitch resin, and the ratio of phenolic resin to pitch resin is 5:5. The pitch resin is prepared using coal tar pitch as the raw material, benzaldehyde as the cross-linking agent (the mass ratio of the cross-linking agent to the raw material is 1:5), and p-toluenesulfonic acid or sulfuric acid as the catalyst (the mass ratio of the catalyst to the raw material is 1:16). Control the reaction system to heat up to 180 °C, and continue to react at this temperature for 4 h to synthesize a condensed polycyclic polynuclear aromatic resin through cationic cross-linking, with a softening point of 90 °C. The pulverized and sieved pitch resin powder is dissolved in a tetrahydrofuran solvent to prepare an impregnating solution with a mass fraction of 16 wt.%.

[0054] Step 4: Cut the pre-prepared carbon fiber preformed paper into specimens of 10 cm × 10 cm, and immerse them in the pitch resin solution for 1 hour to ensure sufficient infiltration. After impregnation, place the specimens in a flat vulcanizing machine for hot pressing and curing. Set the segmented hot pressing conditions as follows: the pressure is 1 MPa, keep the temperature at 180 °C for 30 minutes, and then raise the temperature to 250 °C and continue to cure for 30 minutes.

[0055] Step 5: Under a nitrogen atmosphere, heat up to 1500 °C at a rate of 5 °C / min and hold for 1 hour, then heat up to 2500 °C at a rate of 30 °C / min and hold for 1 hour for graphitization to obtain a carbon fiber paper for fuel cells. Finally, the areal density of the carbon paper is 101 g / m2, the porosity of the carbon paper is 75.75%, the resistivity is 5.67 mΩ / cm, and the tensile strength is 25.02 Mpa.

[0056] Comparative Example 1

[0057] Step 1: Place the short-cut carbon fiber in an NaOH solution, and place the mixed system in an ultrasonic cleaner for ultrasonic treatment for 30 minutes. After ultrasonic treatment, wash it repeatedly with deionized water until the pH value of the filtrate reaches neutral. Dry the washed carbon fiber to obtain a carbon fiber sample pretreated with NaOH. Use a box-type resistance furnace to perform air oxidation modification treatment on the carbon fiber pretreated with NaOH, and the treatment conditions are treatment at 500 °C for 1.5 hours.

[0058] Step 2: Take 70 parts of sodium carboxymethylcellulose and 30 parts of polyethylene oxide as a composite dispersant, add them to 1000 ml of water, and stir evenly at a speed of 350 r / min until the dispersion system is clear, transparent and bubble-free. Add 1.75 g of polyacrylonitrile-based carbon fiber with a length of 6 mm and a diameter of 5 μm and 0.75 g of pitch-based carbon fiber with a length of 3 mm and a diameter of 10 μm thereto, and continue to stir at a speed of 350 r / min for 4 hours. Through the wet forming process of papermaking, a carbon fiber preform paper is obtained.

[0059] Step 3: Select a phenolic resin ethanol solution with a mass fraction of 10 wt.% as the binder system. Cut the pre-prepared carbon fiber preform paper into specimens of 10 cm × 10 cm, and immerse them in the phenolic resin solution for 1 hour to ensure sufficient infiltration. After immersion, take out the specimens and air them for 1 hour to remove the residual ethanol solvent on the surface. Under the condition of a pressure of 5 MPa, first carry out a constant temperature treatment at 140 °C for 30 minutes, and then raise the temperature to 160 °C to continue curing for 30 minutes.

[0060] Step 4: Under a nitrogen atmosphere, heat up to 1500 °C at a rate of 2 °C / min and keep it warm for 1 hour, and then heat up to 3000 °C at a rate of 50 °C / min and keep it warm for 1 hour for graphitization to obtain a carbon fiber paper for fuel cells. Finally, the areal density of the carbon paper obtained is 78.4 g / m2, the porosity of the carbon paper is 75.75%, the resistivity is 16.63 mΩ / cm, and the tensile strength is 10.79 Mpa.

[0061] Compared with Examples 1-5, the difference in this comparative example is that phenolic resin is used as the binder. It can be seen from the results that the resistivity of the carbon fiber paper increases several times, and the mechanical properties are significantly reduced. This is because the carbonization product of phenolic resin is amorphous hard carbon, with a high proportion of sp 3 hybrid carbon, which is difficult to be highly graphitized, ultimately resulting in poor electrical conductivity and mechanical properties of the carbon paper.

[0062] Comparative Example 2

[0063] Step 1: Place the chopped carbon fiber in a NaOH solution, and place the mixed system in an ultrasonic cleaner for ultrasonic treatment for 30 minutes. After ultrasonic treatment, wash it repeatedly with deionized water until the pH value of the filtrate reaches neutral. Dry the washed carbon fiber to obtain a carbon fiber sample pretreated with NaOH. Use a box-type resistance furnace to carry out air oxidation modification treatment on the carbon fiber pretreated with NaOH, and the treatment conditions are to treat it at 500 °C for 1.5 hours.

[0064] Step 2: Take 70 parts of sodium carboxymethylcellulose and 30 parts of polyethylene oxide as a composite dispersant, add them to 1000 ml of water, and stir evenly at a speed of 350 r / min until the dispersion system is clear, transparent and bubble-free. Add 1.75 g of polyacrylonitrile-based carbon fiber with a length of 6 mm and a diameter of 5 μm and 0.75 g of pitch-based carbon fiber with a length of 3 mm and a diameter of 10 μm thereto, and continue to stir at a speed of 350 r / min for 4 hours. Then, make paper by wet forming process to obtain a carbon fiber preform paper.

[0065] Step 3: The resin of the resin impregnating solution is selected as pitch resin. Using coal tar pitch as the raw material and benzaldehyde as the cross-linking agent (the mass ratio of the cross-linking agent to the raw material is 1:5), and p-toluenesulfonic acid or sulfuric acid as the catalyst (the mass ratio of the catalyst to the raw material is 1:16), control the reaction system to heat up to 180 °C, and continue to react at this temperature for 4 h. Condensed polycyclic polynuclear aromatic resin is synthesized by cationic cross-linking, and the softening point is 90 °C. The pulverized and sieved pitch resin powder is dissolved in tetrahydrofuran solvent to prepare an impregnating solution with a mass fraction of 12 wt.%.

[0066] Step 4: Cut the pre-prepared carbon fiber preform paper into 10 cm × 10 cm specimens, and immerse them in the pitch resin solution for 1 hour to ensure sufficient infiltration. After immersion, place the specimens in a flat vulcanizing machine for hot pressing and curing. Set the segmented hot pressing conditions as follows: the pressure is 5 MPa, keep the temperature at 180 °C for 30 minutes, and then raise the temperature to 250 °C and continue to cure for 30 minutes.

[0067] Step 5: Under a nitrogen atmosphere, heat up to 1000 °C at a rate of 1 °C / min and keep it for 1 hour, then heat up to 2500 °C at a rate of 10 °C / min and keep it for 1 hour for graphitization to obtain a carbon fiber paper for fuel cells. Finally, the areal density of the carbon paper is 90.8 g / m2, the porosity of the carbon paper is 78%, the resistivity is 12.35 mΩ / cm, and the tensile strength is 15.46 Mpa.

[0068] Compared with Example 1, the difference in this comparative example is that pitch resin is used as the binder. It can be seen from the results that the electrical conductivity and mechanical properties of the carbon fiber paper are significantly improved compared with Comparative Example 1. This is because the pitch resin has a high char yield and contains a large number of highly conjugated aromatic ring systems in its molecules, and can gradually transform into a graphite crystal structure through orientation, interlayer stacking and ordered carbonization during the pyrolysis process. Due to the similar elemental composition and the interaction of functional groups between the pitch-based carbon fiber and the pitch resin, the interaction force between the two is strong, and they have better carbon compatibility. Its high graphitization potential and high char yield endow the carbon paper with good electrical and thermal conductivity.

[0069] Meanwhile, compared with the carbon papers prepared by using a single resin binder in Comparative Example 1 and Comparative Example 2, the resistivity of the carbon papers in Examples 1-5 increased by 3-8 times, and the mechanical properties decreased by about 50%. This result also reconfirmed the superiority of the high-temperature synergistic carbonization process with the compounding of pitch resin and phenolic resin. The carbon paper prepared by compounding phenolic resin and pitch resin at a ratio of 4:6 had a resistivity of 2.35 mΩ / cm and a tensile strength of 35.46 Mpa, and its performance was far superior to the theoretical sum value of using the two resins as binders respectively.

Claims

1. A preparation method of a highly conductive carbon fiber paper, characterized in that, It includes the following steps: Step 1: Perform surface pretreatment on carbon fiber, then wash, filter, and dry it to obtain pretreated carbon fiber; Step 2: Add the pretreated carbon fiber into an aqueous solution of a dispersant and mix evenly to form a carbon fiber suspension slurry; Step 3: Form a carbon fiber preformed paper through a papermaking process. Impregnate the carbon fiber preformed paper with a binder and then dry it. Obtain the carbon fiber paper through hot pressing curing and high-temperature treatment.

2. The preparation method according to claim 1, characterized in that, In Step 1, the carbon fiber is a mixture of polyacrylonitrile-based carbon fiber and pitch-based carbon fiber with a mass ratio of 9:1 - 5:5; the length of the polyacrylonitrile-based carbon fiber is 3 - 10 mm, and the fiber diameter is 5 - 7 μm; the length of the pitch-based carbon fiber is 3 - 10 mm, and the fiber diameter is 5 - 10 μm.

3. The preparation method according to claim 1, characterized in that, In Step 1, the pretreatment process of the carbon fiber is gas-phase oxidation, chemical oxidation, or plasma oxidation.

4. The preparation method according to claim 1, wherein In Step 2, the dispersant is a mixture of sodium carboxymethyl cellulose and polyethylene oxide with a mass ratio of 9:1 - 5:

5.

5. The preparation method according to claim 1, characterized in that, In Step 3, the binder is a mixture of phenolic resin and pitch resin with a mass ratio of 1:9 - 5:

5.

6. The preparation method according to claim 5, characterized in that, In Step 3, the preparation steps of the pitch resin include: using coal tar pitch or petroleum pitch as the raw material, benzaldehyde or terephthalaldehyde as the crosslinking agent, the mass ratio of the crosslinking agent to the raw material is 1:4 - 6, p-toluenesulfonic acid or sulfuric acid as the catalyst, the mass ratio of the catalyst to the raw material is 1:15 - 20, control the reaction system to heat up to 160 - 190 °C, continuously react at this temperature for 2 - 4 h, synthesize a condensed polycyclic polynuclear aromatic resin through cationic crosslinking, and the softening point is 80 - 120 °C.

7. The preparation method according to claim 1, characterized in that, In Step 3, the temperature of hot pressing curing is 140 - 250 °C, the pressure is 1 - 10 MPa, and the time is 20 - 60 minutes.

8. The preparation method according to claim 1, characterized in that, In Step 3, the high-temperature treatment process includes two parts: carbonization and graphitization: the carbonization treatment temperature is 800 - 1600 °C, the carbonization treatment heating rate is 1 - 10 °C / min, and the holding time is 0.5 - 2 hours; the graphitization treatment temperature is 2200 - 2500 °C, the graphitization treatment heating rate is 10 - 50 °C / min, and the holding time is 0.5 - 1.5 hours.

9. A carbon fiber paper is prepared from the highly conductive carbon fiber paper obtained by the preparation method according to any one of claims 1 - 8.

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