A method for preparing carbon fiber base paper for proton exchange membrane electrolyzer

Abstract

This invention discloses a method for preparing carbon fiber base paper for proton exchange membrane electrolyzers, comprising the following steps: taking carboxyl-modified polyacrylonitrile fiber pulp, adding a dispersant, and performing descaling and refining treatment to form carboxyl-modified polyacrylonitrile pulp; taking one or two dispersants, adding carbon nanotubes and stirring to obtain a carbon nanotube dispersion; taking two more dispersants and carbon fibers, adding them to water and stirring to form a carbon fiber dispersion; adding carboxyl-modified polyacrylonitrile pulp to the carbon nanotube dispersion, descaling to form a pre-formed liquid; mixing and stirring the carbon fiber dispersion and the pre-formed liquid to obtain a compound system dispersion; wet forming to prepare a wet paper web; coating it with an adhesive; and drying to obtain carbon fiber base paper. By mixing the treated carboxyl-modified polyacrylonitrile pulp with carbon nanotubes, and then uniformly mixing it with carbon fibers to prepare carbon fiber base paper, the bending strength and conductivity of the base paper can be effectively improved, and the process difficulty can be reduced.

Description

Technical Field

[0001] The invention relates to the field of manufacturing carbon fiber base paper, and in particular to a method for preparing carbon fiber base paper for a proton exchange membrane electrolyzer. Background Art

[0002] Among the ways to obtain green hydrogen, proton exchange membrane electrolyzer is one of the mainstream routes for water electrolysis devices. This hydrogen production route has the characteristics of high current density, fast start and stop speed, and fast dynamic response. It can flexibly adapt to the volatility of wind and solar power generation. It is an ideal technology for producing green hydrogen coupled with renewable energy. With the growth of global demand for renewable energy and the focus on reducing carbon emissions, proton exchange membrane electrolyzers will receive more and more attention due to their high efficiency, compact design and rapid response capabilities.

[0003] The membrane electrode assembly (MEA) is the core component of the proton exchange membrane electrolyzer and consists of three key layers: proton exchange membrane (PEM), catalyst layer (CL) and gas diffusion layer (GDL). The three-layer structure works together to ensure efficient mass transfer and electrochemical reaction during the electrolysis process. Among them, the gas diffusion layer is located on the outside of the catalyst layer and is responsible for evenly distributing the reaction gas and discharging the generated gas products. In addition, the gas diffusion layer must also provide good conductivity and thermal management to support effective current transmission and heat dissipation.

[0004] The material selection and production technology of the base layer are the core technologies of the gas diffusion layer; carbon fiber base paper is the widely used base layer for the negative electrode of the gas diffusion layer of the proton exchange membrane electrolyzer, because the carbon fiber base paper has a porous structure, high porosity, certain mechanical strength, good conductivity, high temperature resistance, corrosion resistance, and can meet the operating conditions and performance requirements of the electrolyzer.

[0005] In order to improve the bending strength of carbon fiber base paper to meet the requirements of proton exchange membrane electrolyzer use, it is usually achieved by modifying the carbon fiber synthesis precursor or adding particles such as carbon nanotubes to the carbon fiber base paper; for the latter, the impregnation process is generally used to immerse the carbon fiber base paper in a carbon nanotube dispersion to compound the carbon nanotubes into the carbon fiber base paper.

[0006] To a certain extent, this method is to add carbon nanotubes to the carbon fiber base paper by "physical means". Since more slurry is added to the carbon fiber during its preparation process, the retention of carbon nanotubes is affected, and the carbon fiber is essentially a graphite structure. The impregnation process lacks the effect of "intermediate auxiliary retention substances" and the corresponding processing process. On the other hand, due to the influence of slurry and graphite structure, the retention rate of carbon nanotubes is low, resulting in the formation of carbon fiber base paper. The bending strength is not significantly improved, and the carbon nanotubes formed by the impregnation process are easy to fall off during the application process, and the service life of the carbon fiber base paper is not significantly improved. In addition, the impregnation process and the impregnation liquid have high requirements, so compared with the limited performance improvement, the processing cost is high. At the same time, there is also the problem of poor permeability and uniformity of carbon nanotubes in carbon fiber base paper.

[0007] Therefore, based on the above background and problems, it is necessary to provide a technology that can effectively improve the dispersion uniformity of carbon nanotubes in carbon fiber base paper. Summary of the invention

[0008] The present invention aims at the problems that the prior art method of improving the flexural strength and mechanical strength of carbon fiber base paper by adding carbon nanotubes during the impregnation process has an insignificant improvement in flexural strength, high requirements for the impregnation process and the impregnation liquid, and poor permeability and uniformity of the carbon nanotubes in the carbon fiber base paper. A method for preparing carbon fiber base paper for a proton exchange membrane electrolyzer is provided. The preparation method comprises the following steps:

[0009] S10: taking carboxyl-modified polyacrylonitrile fiber pulp, adding a dispersant, and performing a first pulp disintegration to obtain a carboxyl-modified polyacrylonitrile pulp dispersion; refining the carboxyl-modified polyacrylonitrile pulp dispersion to form carboxyl-modified polyacrylonitrile pulp, and then filtering to obtain a filter cake;

[0010] S20: taking a first dispersant and a second dispersant respectively, adding them into water and stirring to form a dispersion; taking carbon nanotubes, adding them into the dispersion and continuing to stir to obtain a carbon nanotube dispersion;

[0011] S30: taking the first dispersant again and taking the carbon fiber, adding both to water and stirring to form a first carbon fiber dispersion; taking the second dispersant again, adding the second dispersant to the first carbon fiber dispersion and stirring to obtain a second carbon fiber dispersion;

[0012] S40: adding the filter cake into water to perform a second slurry dispersing, and then adding the filter cake into the carbon nanotube dispersion liquid, stirring, and forming a carboxyl-modified polyacrylonitrile fiber composite carbon nanotube prefabricated liquid;

[0013] S50: mixing and stirring the second carbon fiber dispersion liquid and the carboxyl-modified polyacrylonitrile fiber composite carbon nanotube prefabricated liquid to obtain a carbon fiber composite system;

[0014] S60: preparing a wet paper web from the carbon fiber composite system by a wet papermaking process, coating the wet paper web with a binder to form a carbon fiber pre-paper, and drying the wet paper to obtain a carbon fiber base paper.

[0015] Preferably, the carboxyl-modified polyacrylonitrile fiber has a diameter of 5 μm to 10 μm and a length of 1 mm to 4 mm; the carbon fiber has a diameter of 3 μm to 8 μm and a length of 3 mm to 10 mm.

[0016] Preferably, the dispersant is sodium polyacrylate, polyoxyethylene alkylphenol ether, polyvinyl pyrrolidone or a mixture of several thereof.

[0017] Preferably, the carboxyl content of the carboxyl-modified polyacrylonitrile fiber is 0.6 mmol / g to 2 mmol / g.

[0018] Preferably, the carbon nanotubes are single-walled carbon nanotubes, multi-walled carbon nanotubes, amino-modified multi-walled carbon nanotubes, or a mixture of the foregoing; the diameter of the single-walled carbon nanotubes is 0.4 nm to 2.0 nm; the diameter of the multi-walled carbon nanotubes or amino-modified multi-walled carbon nanotubes is 2.0 nm to 100.0 nm; and the amino-modified content of the amino-modified multi-walled carbon nanotubes is 0.2 wt % to 0.5 wt %.

[0019] Preferably, the preparation process of the amino-modified multi-walled carbon nanotubes comprises:

[0020] S210: taking multi-walled carbon nanotubes, subjecting them to plasma treatment, and then washing and drying them to form activated carbon nanotubes;

[0021] S220: Take 3-aminopropyltriethoxysilane or 4,4'-diaminodiphenylmethane, add it into water and stir continuously to form an amino-modified precursor solution;

[0022] S230: ultrasonically dispersing the activated carbon nanotubes into a sodium hydroxide solution, continuously stirring, then washing, and drying to obtain hydroxylated carbon nanotubes;

[0023] S240: adding the hydroxylated carbon nanotubes into anhydrous ethanol, and mixing with the amino-modified precursor solution, performing ultrasonic dispersion, and then stirring and washing to obtain the amino-modified multi-walled carbon nanotubes.

[0024] Preferably, the first dispersant is one component of acrylic acid dispersant, maleic acid dispersant, maleic anhydride ester dispersant or a mixture of several thereof; the second dispersant is one component of anionic polyacrylamide, cationic polyacrylamide, polyethylene oxide, carboxymethyl cellulose ether or a mixture of several thereof.

[0025] Preferably, the mass ratio of the first dispersant content to the carbon fiber content in the second carbon fiber dispersion is 1:1 to 10:1.

[0026] Preferably, the mass ratio of the second dispersant content to the carbon fiber content in the second carbon fiber dispersion is 1:1 to 10:1.

[0027] Preferably, the carbon fiber base paper contains 40% to 70% by mass of the carbon fiber, 5% to 20% by mass of the carboxyl-modified polyacrylonitrile pulp, 5% to 20% by mass of the carbon nanotubes, and 5% to 20% by mass of the binder.

[0028] The present invention performs pulping treatment on carboxyl modified polyacrylonitrile pulp to screen out a suitable fiber system, increase the fine fiber content, effectively improve the degree of fibrillation, form different mesh structures, improve the capture of conductive particles, and greatly improve the bending strength of the final carbon fiber base paper; by preparing a uniformly dispersed carbon nanotube dispersion, adding carbon nanotubes in the stirring and mixing stage of wet forming, the carbon nanotube dispersion and the uniformly dispersed carboxyl modified polyacrylonitrile pulp are uniformly mixed, and the carbon nanotubes are uniformly adsorbed on the carboxyl modified polyacrylonitrile pulp, ensuring During the molding process, the carbon nanotubes are fully mixed with the carbon fibers to improve the uniformity of the carbon nanotubes inside the carbon fiber base paper, and then evenly mixed with the carbon fiber dispersion liquid. After wet molding, the carbon nanotubes attached to the carboxyl-modified polyacrylonitrile pulp are evenly distributed inside and on the surface of the carbon fiber base paper. Compared with the carbon fiber base paper in which carbon nanotubes are added during the impregnation process in the prior art, the bending strength and flexibility are significantly improved, thereby improving the utilization rate of the carbon fiber base paper in subsequent applications. The overall preparation method effectively simplifies the impregnation process and reduces the requirements for the impregnation process and the impregnation liquid. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the structures shown in these drawings without paying creative work.

[0030] Figure 1is a process flow chart of a preparation method according to an embodiment of the present invention;

[0031] Figure 2 A flow chart of preparing and forming carbon fiber base paper according to an embodiment of the present invention;

[0032] Figure 3 This is a diagram of the preparation process of amino-modified multi-walled carbon nanotubes according to an embodiment of the present invention;

[0033] Figure 4 This is a physical picture of a carbon fiber base paper prepared by using 5% carbon nanotubes and 5% carboxyl-modified polyacrylonitrile pulp in Example 1 of the embodiment of the present invention;

[0034] Figure 5 This is a physical picture of a carbon fiber base paper prepared by using 20% ​​carbon nanotubes and 20% carboxyl-modified polyacrylonitrile pulp in Example 4 of the embodiment of the present invention;

[0035] Figure 6 This is a physical picture of a carbon fiber base paper prepared by using 20% ​​amino-modified multi-walled carbon nanotubes and 20% carboxyl-modified polyacrylonitrile pulp in Example 5 of the embodiment of the present invention;

[0036] Figure 7 This is a physical picture of the carbon nanotube composite carbon fiber base paper prepared by the impregnation process in Comparative Example 1;

[0037] Figure 8 This is a photo of the carbon fiber base paper prepared in Comparative Example 3 using 20% ​​plant fiber and 20% carbon nanotubes;

[0038] Fig. 9 This is the SEM image of pure carbon fiber base paper;

[0039] Fig.10 This is a SEM image of the carbon fiber base paper of Example 5 according to the embodiment of the present invention.

[0040] The realization of the purpose, functional features and advantages of the present invention will be further explained in conjunction with embodiments and with reference to the accompanying drawings. DETAILED DESCRIPTION

[0041] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0042] It should be noted that all directional indications in the embodiments of the present invention (such as up, down, left, right, front, back, inside, outside...) are only used to explain the relative position relationship, movement status, etc. between the components under a certain specific posture (as shown in the accompanying drawings). If the specific posture changes, the directional indication will also change accordingly.

[0043] In addition, in the present invention, descriptions such as "first", "second", etc. are only used for descriptive purposes and cannot be understood as indicating or implying their relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" or "second" may explicitly or implicitly include at least one of the features. In the description of the present invention, the meaning of "plurality" is at least two, such as two, three, etc., unless otherwise clearly and specifically defined.

[0044] In addition, the technical solutions between the various embodiments of the present invention can be combined with each other, but it must be based on the fact that ordinary technicians in the field can implement it. When the combination of technical solutions is contradictory or cannot be implemented, it should be deemed that such combination of technical solutions does not exist and is not within the scope of protection required by the present invention.

[0045] See also Figure 1 and Figure 2 ; Figure 1 is a process flow chart of a preparation method according to an embodiment of the present invention; Figure 2 The present invention is a flowchart of preparing carbon fiber base paper according to an embodiment of the present invention.

[0046] The method for preparing carbon fiber base paper for proton exchange membrane electrolyzer provided in the embodiment of the present invention comprises: Figure 1 Steps and follow Figure 2 The specific description is as follows.

[0047] Step S10:

[0048] Take carboxyl modified polyacrylonitrile fiber pulp with a diameter of 5 μm to 10 μm and a length of 1 mm to 4 mm, add a dispersant, the dispersant is one or a mixture of several of sodium polyacrylate (PAA), polyoxyethylene alkylphenol ether (AEO), polyvinyl pyrrolidone (PVP), and then carry out the first pulp deflaking in a fiber standard deflaking machine, the deflaking speed is 20000r to 70000r, and obtain a carboxyl modified polyacrylonitrile pulp dispersion, in which the mass fraction of the dispersant is 1% to 5%.

[0049] The carboxyl modified polyacrylonitrile pulp dispersion is refined by a refiner, the refining concentration is 5% to 15%, the refining gap is 0.2 mm to 1.0 mm, the beating degree after refining is measured to be 30°SR to 70°SR, the fiber length is 1.0 mm to 3.0 mm, and the fine fiber content is increased from 50% to 60% when no dispersant is added to 75% to 85% after the dispersant is added in this embodiment, and the carboxyl modified polyacrylonitrile pulp is processed to form the carboxyl modified polyacrylonitrile pulp, which is then filtered to form a filter cake.

[0050] The carboxyl content of the carboxyl modified polyacrylonitrile fiber is 0.6 mmol / g to 2 mmol / g. The carboxyl modified polyacrylonitrile fiber is selected so that the formed carboxyl and water molecules are easily cross-linked, thereby improving the hydrophilicity of the fiber. However, the carboxyl content should not be too high, otherwise the negative effect of too strong hydrophilicity will appear. Too strong hydrophilicity will lead to the weakening of the interface bonding between the fiber and the matrix material in the composite material, thereby affecting the overall mechanical properties of the material. Too strong hydrophilicity may interfere with the electron transmission path between the carbon fibers, thereby reducing the conductivity of the composite material. In the pulping process, the carboxyl modified polyacrylonitrile pulp and water can fully react with each other and are easy to separate into fibers.

[0051] The present embodiment selects carboxyl-modified polyacrylonitrile pulp, the carboxyl groups and water molecules formed in the molecules of which are easily cross-linked, thereby improving the hydrophilicity of the fibers. During the pulping process, the fibers and water can fully react with each other and are easily fibrillated and broomed. The feather-like fibers after fibrillation and brooming are easier to form complexes with a variety of conductive particles than the fibers without fibrillation and brooming, thereby enhancing the compatibility of the pulp with the conductive particles. The feather-like fibers after fibrillation and brooming form a stable and tough network structure, which is convenient for the subsequent adsorption of carbon nanotubes in the pores, thereby improving the retention rate of carbon nanotubes, and improving the bending strength and flexibility of the carbon fiber base paper. The carboxyl-modified polyacrylonitrile fibers still have good conductivity, so they will not affect the conductivity of the carbon fiber base paper.

[0052] Step S20:

[0053] The first dispersant and the second dispersant are added into water and stirred to form a dispersion; single-walled carbon nanotubes, multi-walled carbon nanotubes, amino-modified multi-walled carbon nanotubes or a mixture of several thereof are added into the dispersion and stirred continuously to obtain a carbon nanotube dispersion having a mass concentration of 5% to 20% of carbon nanotubes.

[0054] The diameter of the single-walled carbon nanotube is 0.4nm to 2.0nm, the diameter of the multi-walled carbon nanotube or the amino-modified multi-walled carbon nanotube is 2.0nm to 100.0nm; the amino (-NH2) modification content of the amino-modified multi-walled carbon nanotube is 0.2wt% to 0.5wt%.

[0055] The first dispersant is a component of a surfactant, an acrylic dispersant, a maleic acid dispersant, a maleic anhydride ester dispersant, or a mixture of several of them.

[0056] The surface of carbon nanotubes is smooth and has a high specific surface area. Due to the overlap of the π-π electron clouds between carbon atoms, there is a strong van der Waals force between carbon nanotubes, which makes the carbon nanotubes tend to attract each other and form bundle structures (agglomerates) or agglomerates. Dispersants can effectively prevent the overlap between carbon atoms, and in subsequent processes can increase the effective connection between carbon nanotubes and carboxyl-modified polyacrylonitrile fibers and carbon fibers, thereby improving bending strength and flexibility.

[0057] The second dispersant is a component of a surfactant, anionic polyacrylamide, cationic polyacrylamide, polyethylene oxide, carboxymethyl cellulose, cellulose ether, or a mixture of several of them.

[0058] The negatively charged side groups of this type of dispersant can be adsorbed on the surface of carbon nanotubes, giving the carbon nanotubes a negative charge. Since like charges repel each other, negatively charged carbon nanotubes will move away from each other in the dispersion medium, thereby preventing them from aggregating. In some cases, they can also play a bridging flocculation role, that is, connecting multiple particles through the molecular chains of the dispersant to form larger flocs.

[0059] See also Figure 3 ; Figure 3 This is a diagram of the preparation process of amino-modified multi-walled carbon nanotubes according to an embodiment of the present invention.

[0060] The preparation process of the amino-modified multi-walled carbon nanotubes includes: Figure 3 The steps are as follows:

[0061] S210: taking multi-walled carbon nanotubes, subjecting them to plasma treatment, washing them with deionized water, and drying them at a temperature of 60° C. to 70° C. to form activated carbon nanotubes;

[0062] S220: Take 3-aminopropyltriethoxysilane or 4,4'-diaminodiphenylmethane, add it into water and stir it continuously, and add an appropriate amount (mass fraction is 1% to 2%) of ethanol to increase the solubility to form an amino-modified precursor solution;

[0063] S230: ultrasonically dispersing the activated carbon nanotubes into a 0.1 mol / L to 0.2 mol / L sodium hydroxide solution, stirring continuously for 12 hours, then washing at a temperature of 5° C. to 20° C., and drying to obtain hydroxylated carbon nanotubes;

[0064] S240: adding the hydroxylated carbon nanotubes into anhydrous ethanol and mixing with the amino-modified precursor solution, performing ultrasonic dispersion for 20 minutes, then stirring at 80° C. for 5 hours, and then washing with deionized water for 3 times to obtain the amino-modified multi-walled carbon nanotubes.

[0065] The above plasma treatment is carried out using domestically produced plasma equipment. The entire amino modification process is simple and clear. The amino-modified multi-walled carbon nanotubes modified with amino groups can improve surface hydrophilicity and polarity, improve the dispersibility of carbon nanotubes in polymers, and the amino groups can undergo acylation reaction with the carboxyl groups in carboxyl-modified polyacrylonitrile pulp to form amide bonds, thereby increasing the interfacial bonding strength between the two and thereby increasing the retention rate of carbon nanotubes in carboxyl-modified polyacrylonitrile pulp.

[0066] Step S30:

[0067] Take the first dispersant again, and take carbon fiber with a diameter of 3μm to 8um and a length of 3mm to 10mm, add it to water and stir and disperse it for 5min to 20min to form a first carbon fiber dispersion; the mass ratio of the first dispersant to the carbon fiber here is 1:1 to 10:1; take the second dispersant again, add it to the first carbon fiber dispersion and stir and disperse it for 5min to 20min to obtain a second carbon fiber dispersion; the mass ratio of the second dispersant to the carbon fiber here is 1:1 to 10:1.

[0068] In the present embodiment, the carbon fiber uses polyacrylonitrile-based carbon fiber, which is a good base raw material for the negative electrode carbon fiber paper of the gas diffusion layer and has good conductivity, mechanical strength, and high temperature resistance.

[0069] Since carbon fiber is made through the processes of pre-oxidation and carbonization of polyacrylonitrile fiber, the chain structure of polyacrylonitrile fiber undergoes cyclocross-linking in the pre-oxidation stage to form a heat-resistant trapezoidal structure, forms a carbon-based surface in the carbonization stage, and finally forms a graphite-like structure. Therefore, the graphite-like structure does not have grinding and pulping properties, and its structure contains more slurry, making it difficult to retain carbon nanotubes. Polyacrylonitrile fiber is a chain polymer formed by the polymerization of acrylonitrile, which has good grinding and pulping properties, as well as the ability to retain carbon nanotubes, which is equivalent to providing a bridge of "intermediate auxiliary retention substance" for carbon nanotubes and carbon fibers, while using its own properties to improve the mechanical properties of carbon fiber paper.

[0070] Therefore, the embodiment of the present invention adopts an overall ternary composite framework system of carbon fiber, polyacrylonitrile and carbon nanotubes, and undergoes a specific preparation process of overall design such as pulping, refining and dispersion to form a system that complements and enhances each other in performance, thereby effectively improving the comprehensive performance of carbon fiber base paper.

[0071] Step S40:

[0072] The filter cake is added into water to perform a second slurry dispersal to 5000r, and then the carbon nanotube dispersion is added and stirred to form a carboxyl-modified polyacrylonitrile fiber composite carbon nanotube prefabricated liquid.

[0073] Step S50:

[0074] The second carbon fiber dispersion liquid and the carboxyl-modified polyacrylonitrile fiber composite carbon nanotube prefabricated liquid are mixed and stirred to obtain a carbon fiber composite system.

[0075] Step S60:

[0076] The carbon fiber composite system is prepared by a wet papermaking process to form a wet paper web, a binder is applied to the wet paper web to form a carbon fiber preformed paper, and the carbon fiber base paper is prepared by drying at a temperature of 150° C. to 180° C. for 5 to 15 minutes.

[0077] The main function of the binder is to bond the carbon fiber wet paper web together after high-temperature curing. The main component is one of acrylic acid, acrylate, and polyurethane, or a mixed solution of several of them.

[0078] The carbon fiber preformed paper formed above contains 40% to 70% carbon fiber by mass, 5% to 20% carboxyl modified polyacrylonitrile pulp by mass, 5% to 20% carbon nanotubes by mass, and 5% to 20% binder by mass.

[0079] That is, in step S30 to step S60, if 100 parts of carbon fiber preformed paper need to be prepared, 40 parts to 70 parts of carbon fiber are used in step S30, 5 parts to 20 parts of carboxyl-modified polyacrylonitrile pulp are used in step S40, a carbon nanotube dispersion containing 5 parts to 20 parts of carbon nanotubes is used in step S50, and 5 parts to 20 parts of a binder are used in step S60.

[0080] The prepared carbon fiber base paper has a porous structure, which is conducive to the smooth discharge of water generated by the proton exchange membrane electrolyzer during operation.

[0081] The following typical examples are provided to further illustrate the effects of the carboxyl-modified polyacrylonitrile pulp content and the carbon nanotube content on the electrical conductivity, flexural strength and mechanical properties of the prepared carbon fiber base paper in the embodiments of the present invention.

[0082] Example 1 (70% carbon fiber-5% carboxyl-modified polyacrylonitrile fiber-5% carbon nanotube):

[0083] See also Figure 4 ; Figure 4This is a photo of the carbon fiber base paper prepared by using 5% carbon nanotubes and 5% carboxyl-modified polyacrylonitrile pulp in Example 1 of the embodiment of the present invention.

[0084] (1) Take the 5% carboxyl-modified polyacrylonitrile pulp prepared in step S10 and the 5% carbon nanotube dispersion prepared in step S20, mix them evenly according to step 4, and obtain a carboxyl-modified polyacrylonitrile fiber composite carbon nanotube prefabricated solution①;

[0085] (2) taking the second carbon fiber dispersion containing 70% carbon fiber obtained in step S30, according to step S50, adding the carboxyl-modified polyacrylonitrile fiber composite carbon nanotube prefabricated solution ① thereto, stirring and dispersing evenly to obtain a carbon fiber composite system ①;

[0086] (3) According to step S60, the carbon fiber composite system ① is made into a wet paper web, 20% of a binder is applied, and the paper is dried at 160° C. for 10 min to obtain a carbon fiber base paper ① containing 5% carbon nanotubes, 5% carboxyl-modified polyacrylonitrile pulp, and 70% carbon fibers.

[0087] Example 2 (55% carbon fiber-5% carboxyl-modified polyacrylonitrile fiber-20% carbon nanotube):

[0088] (1) Take the 5% carboxyl-modified polyacrylonitrile pulp prepared in step S10 and the 20% carbon nanotube dispersion prepared in step S20, mix them evenly according to step 4, and obtain a carboxyl-modified polyacrylonitrile fiber composite carbon nanotube prefabricated solution ②;

[0089] (2) taking the second carbon fiber dispersion containing 55% carbon fiber obtained in step S30, according to step S50, adding the carboxyl-modified polyacrylonitrile fiber composite carbon nanotube preformed liquid ② thereto, stirring and dispersing evenly to obtain a carbon fiber composite system ②;

[0090] (3) According to step S60, the carbon fiber composite system ② is made into a wet paper web, 20% of a binder is applied, and the paper is dried at 160° C. for 10 min to obtain a carbon fiber base paper ② containing 20% ​​carbon nanotubes, 5% carboxyl-modified polyacrylonitrile pulp, and 55% carbon fibers.

[0091] Example 3 (55% carbon fiber-20% carboxyl-modified polyacrylonitrile fiber-5% carbon nanotube):

[0092] (1) Take the 20% carboxyl-modified polyacrylonitrile pulp prepared in step S10 and the 50% carbon nanotube dispersion prepared in step S20, mix them evenly according to step 4, and obtain a carboxyl-modified polyacrylonitrile fiber composite carbon nanotube prefabricated solution ③;

[0093] (2) taking the second carbon fiber dispersion containing 55% carbon fiber obtained in step S30, according to step S50, adding the carboxyl-modified polyacrylonitrile fiber composite carbon nanotube prefabricated solution ③ thereto, stirring and dispersing evenly to obtain a carbon fiber composite system ③;

[0094] (3) According to step S60, the carbon fiber composite system ③ is made into a wet paper web, 20% of a binder is applied, and the paper is dried at 160° C. for 10 min to obtain a carbon fiber base paper ③ containing 5% carbon nanotubes, 20% carboxyl-modified polyacrylonitrile pulp, and 55% carbon fibers.

[0095] Example 4 (40% carbon fiber-20% carboxyl-modified polyacrylonitrile fiber-20% carbon nanotube):

[0096] See also Figure 5 ; Figure 5 This is a photo of a carbon fiber base paper prepared by using 20% ​​carbon nanotubes and 20% carboxyl-modified polyacrylonitrile pulp in Example 4 of the embodiment of the present invention.

[0097] (1) taking the 20% carboxyl-modified polyacrylonitrile pulp prepared in step S10 and the 20% carbon nanotube dispersion prepared in step S20, and mixing them evenly according to step 4 to obtain a carboxyl-modified polyacrylonitrile fiber composite carbon nanotube prefabricated solution④;

[0098] (2) taking the second carbon fiber dispersion containing 40% carbon fiber obtained in step S30, according to step S50, adding the carboxyl-modified polyacrylonitrile fiber composite carbon nanotube prefabricated liquid ④ thereto, stirring and dispersing evenly to obtain a carbon fiber composite system ④;

[0099] (3) According to step S60, the carbon fiber composite system ④ is made into a wet paper web, 10% of a binder is applied, and the paper is dried at 160° C. for 10 min to obtain a carbon fiber base paper ④ containing 20% ​​carbon nanotubes, 20% carboxyl-modified polyacrylonitrile pulp, and 40% carbon fibers.

[0100] Example 5 (40% carbon fiber-20% carboxyl-modified polyacrylonitrile fiber-20% amino-modified carbon nanotubes):

[0101] See also Figure 6 ; Figure 6 This is a photo of the carbon fiber base paper prepared by using 20% ​​amino-modified multi-walled carbon nanotubes and 20% carboxyl-modified polyacrylonitrile pulp in Example 5 of the embodiment of the present invention.

[0102] (1) taking the 20% carboxyl-modified polyacrylonitrile pulp prepared in step S10 and the 20% amino-modified multi-walled carbon nanotube dispersion prepared in step S20, and mixing them evenly according to step 4 to obtain a carboxyl-modified polyacrylonitrile fiber composite carbon nanotube prefabricated solution ⑤;

[0103] (2) taking the second carbon fiber dispersion containing 40% carbon fiber obtained in step S30, according to step S50, adding the carboxyl-modified polyacrylonitrile fiber composite carbon nanotube prefabricated liquid ⑤ thereto, stirring and dispersing evenly to obtain a carbon fiber composite system ⑤;

[0104] (3) According to step S60, the carbon fiber composite system ⑤ is made into a wet paper web, 20% of a binder is applied, and the paper is dried at 160° C. for 10 min to obtain a carbon fiber base paper ⑤ containing 20% ​​amino-modified carbon nanotubes, 20% carboxyl-modified polyacrylonitrile pulp, and 40% carbon fibers.

[0105] In order to more fully illustrate the effect of carboxyl-modified polyacrylonitrile pulp on the flexural strength of carbon fiber base paper, the following preparation processes of Comparative Examples 1 to 3 and different carbon fiber base papers prepared are also provided.

[0106] Comparative Example 1 (carbon fiber-carbon nanotube prepared by impregnation process):

[0107] See also Figure 7 ; Figure 7 This is a real picture of the carbon nanotube composite carbon fiber base paper prepared by the impregnation process in comparative example 1.

[0108] (1) taking the second carbon fiber dispersion containing 60% carbon fiber obtained in step S30;

[0109] (2) According to step S60, the second carbon fiber dispersion is made into a wet paper web, 20% of a binder is applied, and the paper is dried at 160° C. for 10 minutes to obtain a carbon fiber paper base containing 60% of carbon fibers.

[0110] (3) taking carbon nanotubes with a mass fraction of 20% relative to carbon fibers and dissolving them in ethanol to form a mixed solution;

[0111] (4) The carbon fiber paper obtained in step 1 is immersed in the mixed solution, and after the ethanol evaporates at room temperature, it is dried at 160° C. for 10 min to obtain a carbon fiber paper containing 60% carbon fiber and 20% carbon nanotubes (i.e., carbon fiber-carbon nanotubes made by the impregnation process).

[0112] Comparative Example 2 (carbon nanotube-carbon fiber):

[0113] Take the carbon nanotube dispersion with a mass fraction of 5% to 20% in step S20, add it to the second carbon fiber dispersion obtained in step S30, stir and disperse, and obtain a carbon nanotube composite carbon fiber mixed liquid. Use a method similar to the above step S60 to prepare the carbon nanotube composite carbon fiber mixed liquid by a wet papermaking process to form a wet paper web, apply a binder to the wet paper web, and dry it at 160°C for 10 minutes to obtain a carbon nanotube composite carbon fiber base paper.

[0114] In order to verify the good role of carboxyl-modified polyacrylonitrile fiber pulp as a bridge for promoting the "intermediate auxiliary retention substance" to be compounded into carbon fiber base paper in this embodiment, plant fiber pulp and aramid pulp are specially selected as the bridge of "intermediate auxiliary retention substance", and the preparation process of this embodiment is adopted to form plant fiber-carbon nanotube-carbon fiber base paper and aramid-carbon nanotube-carbon fiber base paper for further comparison.

[0115] The comparative proportions are as follows:

[0116] Comparative Example 3 (plant fiber-carbon nanotube-carbon fiber):

[0117] See also Figure 8 ; Figure 8 This is a real picture of the carbon fiber base paper prepared in comparative example 3 using 20% ​​plant fiber and 20% carbon nanotubes.

[0118] Take the carbon nanotube dispersion with a mass fraction of 5% to 20% in step S20, add it to the second carbon fiber dispersion obtained in step S30, stir and disperse, and add plant fiber with a mass fraction of 5% to 20%, stir and disperse evenly to obtain a plant fiber-carbon nanotube-carbon fiber mixed liquid, adopt a method similar to the above step S60, use a wet papermaking process to prepare the plant fiber-carbon nanotube-carbon fiber mixed liquid to form a wet paper web, apply a binder to the wet paper web, and dry it at 160°C for 10 minutes to obtain a plant fiber-carbon nanotube-carbon fiber base paper; wherein the plant fiber is one or a mixture of coniferous wood pulp, broadleaf wood pulp, cotton pulp, and hemp pulp.

[0119] Comparative Example 4 (aramid-carbon nanotube-carbon fiber):

[0120] Take the carbon nanotube dispersion with a mass fraction of 5% to 20% in step S20, add it to the second carbon fiber dispersion obtained in step S30, stir and disperse, and add aramid pulp with a mass fraction of 5% to 20%, stir and disperse evenly to obtain an aramid-carbon nanotube-carbon fiber mixed liquid, adopt a method similar to the above step S60, use a wet papermaking process to prepare the aramid-carbon nanotube-carbon fiber mixed liquid to form a wet paper web, apply a binder to the wet paper web, and dry it at 160°C for 10 minutes to obtain an aramid-carbon nanotube-carbon fiber base paper; wherein the aramid pulp is one of para-aramid pulp and meta-aramid pulp, or a mixture of several of them.

[0121] Comparative Example 5 (40% carbon fiber-20% polyacrylonitrile fiber-20% amino-modified carbon nanotubes):

[0122] (1) taking ordinary polyacrylonitrile fiber pulp that has not been modified with carboxyl groups, and taking the 20% polyacrylonitrile pulp prepared in step S10, and taking the 20% carbon nanotube dispersion prepared in step S20, and mixing them evenly according to step 4 to obtain a polyacrylonitrile fiber composite carbon nanotube prefabricated solution ⑥;

[0123] (2) taking the second carbon fiber dispersion containing 40% carbon fiber obtained in step S30, adding the polyacrylonitrile fiber composite carbon nanotube prefabricated liquid ⑥ thereto according to step S50, stirring and dispersing evenly to obtain a carbon fiber composite system ⑥;

[0124] (3) According to step S60, the carbon fiber composite system ⑥ is made into a wet paper web, 20% of a binder is applied, and the paper is dried at 160° C. for 10 min to obtain a carbon fiber base paper ⑥ of 40% carbon fiber-20% polyacrylonitrile fiber-20% amino-modified carbon nanotubes.

[0125] The carbon fiber base papers prepared in the above Examples 1 to 5 and Comparative Examples 1 to 5 were tested respectively, and the test items included: test resistivity; bending strength; tensile strength; the test results are shown in Table 1.

[0126] Table 1:

[0127]

[0128] It can be seen from the test results of (Example 1, Example 2, Example 3 or Example 4) and (Comparative Example 1) that the carbon fiber base paper formed by the present embodiment adopts specific overall processing processes such as pulping, refining, dispersion, and decomposition, and adopts a ternary system of carbon nanotubes, carboxyl-modified polyacrylonitrile fibers, and carbon fibers. The resistivity of the carbon fiber base paper does not change much, but the flexural strength and tensile strength are significantly improved, indicating that the formula and method of the present embodiment are compared with the carbon nanotube composite carbon fiber base paper formed by the impregnation process in the prior art, and the flexural strength and tensile strength are greatly improved.

[0129] By comparing (Example 2, Example 3 or Example 4) with Comparative Example 2, it can be seen that the resistivity of the carbon fiber base paper formed in this embodiment is not much changed compared to the carbon fiber base paper formed without adding carboxyl-modified polyacrylonitrile fiber, but the bending strength and tensile strength are improved, which fully demonstrates the bridge effect of the carboxyl-modified polyacrylonitrile fiber on the "intermediate auxiliary retention substance" for the retention of carbon nanotubes in the carbon fiber, making the carbon nanotubes have a greater effect on the carbon fiber base paper.

[0130] By comparing Example 1, Example 2, Example 3 and Example 4, it can be seen that appropriately increasing the amount of carbon nanotubes and carboxyl-modified polyacrylonitrile pulp does not change the resistivity of the formed carbon fiber base paper much, but improves the flexural strength and tensile strength, further illustrating the bridging effect of carboxyl-modified polyacrylonitrile fiber on the retention of carbon nanotubes, and illustrating that an appropriate ratio can further improve the flexural strength and tensile strength.

[0131] By comparing (Example 2, Example 3 or Example 4) with (Comparative Example 3 or Comparative Example 4), it can be seen that the use of carboxyl-modified polyacrylonitrile fiber is significantly better than the use of plant fiber pulp or aramid pulp in promoting the retention and composite of carbon nanotubes in carbon fiber base paper, indicating that carboxyl-modified polyacrylonitrile fiber is superior to the use of plant fiber or aramid material in terms of the similarity of material properties between carbon nanotubes and carbon fibers, and the degree of easier formation of molecular chains and copolymerization.

[0132] By comparing Example 4 with Example 5, it can be seen that the carbon fiber base paper ⑤ prepared by the amino-modified multi-walled carbon nanotubes through the method process has better flexural strength and tensile strength than the carbon fiber base paper ④ prepared by the ordinary carbon nanotubes through the method process. The reason for this phenomenon is that the ordinary carbon nanotubes have poor surface inertness and dispersibility, and are easy to agglomerate themselves. Due to interface and dispersion factors, in the method of physical blending or oxidation of carbon nanotubes, the carbon nanotubes have poor compatibility with solvents, and it is difficult to significantly improve the mechanical properties of the resin at a low addition amount; the amino-modified multi-walled carbon nanotubes modified by amino groups effectively improve the surface hydrophilicity and polarity, thereby improving the dispersibility in the polymer, and the amino groups and the carboxyl groups in the carboxyl-modified polyacrylonitrile pulp undergo acylation reaction to form amide bonds, thereby increasing the interfacial bonding force between the two, thereby increasing the retention rate of the carbon nanotubes in the carboxyl-modified polyacrylonitrile pulp.

[0133] By comparing Example 5 with Comparative Example 5, it can be seen that, under the same other conditions, the carbon fiber base paper made of carboxyl-modified polyacrylonitrile fiber (Example 5) has significantly higher flexural strength and tensile strength than that of ordinary polyacrylonitrile fiber which has not been carboxyl-modified, indicating that the carboxyl groups and water molecules formed by carboxyl-modified polyacrylonitrile fiber pulp are more easily cross-linked, and during the pulping process, the carboxyl-modified polyacrylonitrile fiber pulp and water can fully react with each other and are easy to be fibrillated. The feather-like fibers after fibrillation and fibrillation form a stable and tough network structure, which is convenient for the subsequent adsorption of carbon nanotubes in the pores, thereby improving the retention rate of carbon nanotubes and improving the flexural properties and tensile strength of the carbon fiber base paper.

[0134] See also Fig. 9 and Fig.10 , Fig. 9 This is the SEM image of pure carbon fiber base paper; Fig.10 This is a SEM image of the carbon fiber base paper of Example 5 according to the embodiment of the present invention.

[0135] It can be seen that the pure carbon fiber base paper only forms a mesh structure in which the fibers are interwoven with each other, while the carbon fiber base paper prepared by the present embodiment not only forms a mesh structure in which the fibers are interwoven with each other, but also forms a microscopic membrane between some mesh holes, which is similar to the structure of a "flipper", effectively retaining the carbon nanotubes, which not only improves the bending strength and tensile strength, but also improves the service life of the membrane; and the reason why the conductive performance is not greatly weakened is that the conductive performance of the carbon fiber base paper is mainly because the carbon fibers are connected and overlapped with each other to form a continuous conductive network, and after the addition of carbon nanotubes and carboxyl-modified polyacrylonitrile pulp, there is no obvious effect on this performance of the carbon fiber, and therefore does not affect its conductivity.

[0136] The above are only preferred embodiments of the present invention, and are not intended to limit the patent scope of the present invention. All equivalent structural changes made using the contents of the present invention's specification and drawings, or directly / indirectly applied in other related technical fields, are included in the patent protection scope of the present invention.

Claims

1. A method for preparing carbon fiber base paper for proton exchange membrane electrolyzer, characterized in that: The preparation method comprises the following steps: S10: taking carboxyl-modified polyacrylonitrile fiber pulp, adding a dispersant, and performing a first pulp disintegration to obtain a carboxyl-modified polyacrylonitrile pulp dispersion; refining the carboxyl-modified polyacrylonitrile pulp dispersion to form carboxyl-modified polyacrylonitrile pulp, and then filtering to obtain a filter cake; The dispersant is one or a mixture of sodium polyacrylate, polyoxyethylene alkylphenol ether, and polyvinyl pyrrolidone; The carboxyl content of the carboxyl-modified polyacrylonitrile fiber is 0.6 mmol / g to 2 mmol / g; S20: taking a first dispersant and a second dispersant respectively, adding them into water and stirring to form a dispersion; taking carbon nanotubes, adding them into the dispersion and continuing to stir to obtain a carbon nanotube dispersion; The carbon nanotubes are single-walled carbon nanotubes, multi-walled carbon nanotubes, amino-modified multi-walled carbon nanotubes, or a mixture of several thereof; S30: taking the first dispersant again and taking the carbon fiber, adding both to water and stirring to form a first carbon fiber dispersion; taking the second dispersant again, adding the second dispersant to the first carbon fiber dispersion and stirring to obtain a second carbon fiber dispersion; The first dispersant is one component or a mixture of acrylic acid dispersants, maleic acid dispersants, maleic anhydride ester dispersants; the second dispersant is one component or a mixture of anionic polyacrylamide, cationic polyacrylamide, polyethylene oxide, carboxymethyl cellulose ether; S40: adding the filter cake into water to perform a second slurry dispersing, and then adding the filter cake into the carbon nanotube dispersion liquid, stirring, and forming a carboxyl-modified polyacrylonitrile fiber composite carbon nanotube prefabricated liquid; S50: mixing and stirring the second carbon fiber dispersion liquid and the carboxyl-modified polyacrylonitrile fiber composite carbon nanotube prefabricated liquid to obtain a carbon fiber composite system; S60: preparing a wet paper web from the carbon fiber composite system by a wet papermaking process, coating the wet paper web with a binder to form a carbon fiber pre-paper, and drying the wet paper to obtain a carbon fiber base paper.

2. The method for preparing a carbon fiber base paper for a proton exchange membrane electrolyzer according to claim 1, characterized in that: The carboxyl modified polyacrylonitrile fiber has a diameter of 5 μm to 10 μm and a length of 1 mm to 4 mm; the carbon fiber has a diameter of 3 μm to 8 μm and a length of 3 mm to 10 mm.

3. The method for preparing a carbon fiber base paper for a proton exchange membrane electrolyzer according to claim 1, characterized in that: The diameter of the single-walled carbon nanotube is 0.4 nm to 2.0 nm; the diameter of the multi-walled carbon nanotube or the amino-modified multi-walled carbon nanotube is 2.0 nm to 100.0 nm; and the amino-modified content of the amino-modified multi-walled carbon nanotube is 0.2 wt % to 0.5 wt %.

4. The method for preparing a carbon fiber base paper for a proton exchange membrane electrolyzer according to claim 1, characterized in that: The preparation process of the amino-modified multi-walled carbon nanotubes comprises: S210: taking multi-walled carbon nanotubes, subjecting them to plasma treatment, and then washing and drying them to form activated carbon nanotubes; S220: Take 3-aminopropyltriethoxysilane or 4,4'-diaminodiphenylmethane, add it into water and stir continuously to form an amino-modified precursor solution; S230: ultrasonically dispersing the activated carbon nanotubes into a sodium hydroxide solution, continuously stirring, then washing, and drying to obtain hydroxylated carbon nanotubes; S240: adding the hydroxylated carbon nanotubes into anhydrous ethanol, and mixing with the amino-modified precursor solution, performing ultrasonic dispersion, and then stirring and washing to obtain the amino-modified multi-walled carbon nanotubes.

5. The method for preparing a carbon fiber base paper for a proton exchange membrane electrolyzer according to claim 1, characterized in that: The mass ratio of the first dispersant content to the carbon fiber content in the second carbon fiber dispersion is 1:1 to 10:

1.

6. The method for preparing a carbon fiber base paper for a proton exchange membrane electrolyzer according to claim 1, characterized in that: The mass ratio of the second dispersant content to the carbon fiber content in the second carbon fiber dispersion is 1:1 to 10:

1.

7. The method for preparing a carbon fiber base paper for a proton exchange membrane electrolyzer according to claim 1, 5 or 6, characterized in that: The carbon fiber base paper contains 40% to 70% carbon fiber by mass, 5% to 20% carboxyl modified polyacrylonitrile pulp by mass, 5% to 20% carbon nanotubes by mass, and 5% to 20% binder by mass.

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