Carbon fiber paper as well as preparation method and application thereof

Abstract

The invention relates to the field of proton exchange membrane fuel cells, and discloses carbon fiber paper as well as a preparation method and application thereof. The carbon fiber paper contains short carbon fibers and long carbon fibers; wherein the length of the short carbon fibers ranges from 2 mm to 6.5 mm, and the length of the long carbon fibers ranges from 7 mm to 14 mm; the thickness of the carbon fiber paper is 190-240 [mu] m, and the porosity of the carbon fiber paper is 70-85%. High-length carbon fibers with different proportions are mixed in short-length short carbon fibers, the mechanical performance of the carbon fiber paper can be effectively improved, meanwhile, an effective dispersion method is adopted, the adverse effect of introduction of the long carbon fibers on the uniformity of the carbon fiber paper is reduced as much as possible, and due to the addition of the long carbon fibers, the carbon fiber paper is more uniform. A looser three-dimensional network pore structure can be built, and the high-performance carbon fiber paper with higher porosity and excellent mechanical properties is prepared. As a macroporous substrate of a gas diffusion layer of a fuel cell, the macroporous substrate has better gas transmission performance and water removal capability.

Description

Technical Field

[0001] The invention relates to the field of proton exchange membrane fuel cells, and in particular to carbon fiber paper and a preparation method and application thereof. Background Art

[0002] Proton exchange membrane fuel cells (PEMFC) have become one of the key green energy technologies due to their high power density, high energy conversion efficiency, simple structure, low operating temperature, and complete cleanliness. Membrane electrode assembly (MEA) is a key component of PEMFC, and the gas diffusion layer (GDL) plays an extremely important role. GDL is usually composed of a macroporous substrate (MPS) and a microporous layer (MPL). It not only provides mechanical support for the proton exchange membrane and catalyst layer, but also provides a stable transmission path for the transmission of reaction gases, electrons, and byproduct water during the MEA reaction process. Therefore, the structure and performance of GDL have a decisive influence on the final performance of MEA.

[0003] At present, the carbon fiber paper used in PEMFC at home and abroad is almost monopolized by foreign companies. The main production and supply companies of carbon fiber paper are Toray of Japan, SGL of Germany and AvCarb of the United States. Among them, the carbon fiber paper of Toray of Japan has the best comprehensive performance and the highest market share. The current preparation of carbon fiber paper mainly uses chopped carbon fiber as raw material, and the production process mainly includes carbon fiber dispersion, wet papermaking, resin impregnation, hot pressing, high-temperature carbonization and graphitization. So far, no company in China can industrially produce high-performance carbon fiber paper that meets the needs of PEMFC, because in its production process, the influencing factors are complex, there are situations where the performance is mutually constrained, and the dispersion of carbon fiber in the production process and the uniformity of carbon fiber base paper obtained by wet papermaking are also technical problems. Therefore, it is of great significance to provide an effective method for preparing carbon fiber paper with excellent comprehensive performance. Summary of the invention

[0004] The purpose of the present invention is to overcome the problems that long carbon fibers are difficult to disperse evenly during the papermaking process when preparing carbon fiber paper and that the carbon fiber paper prepared from short carbon fibers has poor mechanical properties and low porosity, and to provide a carbon fiber paper and a preparation method and application thereof.

[0005] In order to achieve the above object, the present invention provides a carbon fiber paper in a first aspect, wherein the carbon fiber paper contains short carbon fibers and long carbon fibers;

[0006] Wherein, the length of the short carbon fiber is 2-6.5 mm, and the length of the long carbon fiber is 7-14 mm;

[0007] The carbon fiber paper has a thickness of 190-240 μm and a porosity of 70-85%.

[0008] Preferably, the length of the short carbon fiber is 3-6 mm, and the length of the long carbon fiber is 8-12 mm.

[0009] Preferably, the content of the short carbon fibers is ≥ the content of the long carbon fibers.

[0010] Preferably, the weight ratio of the short carbon fiber content to the long carbon fiber content is 1-13:1, preferably 1-9:1, and more preferably 1.5-4:1.

[0011] Preferably, the surface density of the carbon fiber paper is 100-150 g / m 2 .

[0012] A second aspect of the present invention provides a method for preparing carbon fiber paper, the preparation method comprising the following steps:

[0013] (1) mixing short carbon fibers, long carbon fibers, a dispersant and water to obtain a fiber slurry;

[0014] (2) preparing carbon fiber base paper from the fiber slurry using a wet papermaking process;

[0015] (3) impregnating the carbon fiber base paper in a phenolic resin solution, and then hot pressing to obtain a carbon fiber paper precursor;

[0016] (4) performing carbonization and graphitization on the carbon fiber paper precursor;

[0017] The length of the short carbon fiber is 2-6.5 mm, and the length of the long carbon fiber is 7-14 mm.

[0018] Preferably, in step (1), the length of the short carbon fiber is 3-6 mm, and the length of the long carbon fiber is 8-12 mm.

[0019] Preferably, the amount of the short carbon fibers is greater than or equal to the amount of the long carbon fibers.

[0020] Preferably, the weight ratio of the short carbon fibers to the long carbon fibers is 1-13:1, preferably 1-9:1, and more preferably 1.5-4:1.

[0021] Preferably, in step (1), the dispersant is selected from one or more of polyethylene oxide, anionic polyacrylamide and Tween-80.

[0022] Preferably, in step (1), the dispersant is mixed with water to obtain a dispersant solution, and the dispersant solution is then mixed with short carbon fibers and long carbon fibers to obtain a fiber slurry.

[0023] Preferably, the concentration of the dispersant in the dispersant solution is 0.1-0.2 wt %.

[0024] Preferably, in the fiber slurry, the total content of short carbon fibers and long carbon fibers is 0.1-0.2 wt %.

[0025] Preferably, in step (3), the content of phenolic resin in the phenolic resin solution is 5-15 wt %.

[0026] Preferably, in step (3), the immersion time is 10-30 minutes.

[0027] Preferably, the conditions for the hot pressing molding include: a temperature of 150-180° C., a time of 30-60 min, and a pressure of 10-15 MPa.

[0028] Preferably, in step (4), the carbonization treatment conditions include: temperature of 800-1500° C. and time of 60-120 min.

[0029] Preferably, the graphitization treatment conditions include: temperature of 2200-2900° C. and time of 60-120 min.

[0030] The third aspect of the present invention provides a carbon fiber paper prepared by the above preparation method, wherein the carbon fiber paper has a thickness of 190-240 μm and a porosity of 70-85%.

[0031] Preferably, the surface density of the carbon fiber paper is 100-150 g / m 2 .

[0032] A fourth aspect of the present invention provides a use of the carbon fiber paper in a fuel cell.

[0033] The present invention mixes different proportions of long-length carbon fibers with short-length short carbon fibers, which can effectively improve the mechanical properties of carbon fiber paper. At the same time, an effective dispersion method is adopted to minimize the adverse effects of the introduction of long carbon fibers on the uniformity of carbon fiber paper. Because of the addition of long carbon fibers, a looser three-dimensional network structure can be built, and high-performance carbon fiber paper with higher porosity and excellent mechanical properties can be prepared. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 It is the surface morphology of carbon fiber paper;

[0035] Figure 2 is the cross-sectional morphology of carbon fiber paper;

[0036] Figure 3 The performance of membrane electrodes assembled from different carbon fiber papers. DETAILED DESCRIPTION

[0037] The specific implementation of the present invention is described in detail below in conjunction with the accompanying drawings. It should be understood that the specific implementation described here is only used to illustrate and explain the present invention, and is not used to limit the present invention.

[0038] The endpoints and any values ​​of the ranges disclosed in this article are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of each range, the endpoint values ​​of each range and the individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed in this article.

[0039] A first aspect of the present invention provides a carbon fiber paper, wherein the carbon fiber paper contains short carbon fibers and long carbon fibers;

[0040] Wherein, the length of the short carbon fiber is 2-6.5 mm, and the length of the long carbon fiber is 7-14 mm;

[0041] The carbon fiber paper has a thickness of 190-240 μm and a porosity of 70-85%.

[0042] In the present invention, the short carbon fiber refers to a carbon fiber with a shorter length, and the long carbon fiber refers to a carbon fiber with a longer length, wherein long and short are relative. In the present invention, the length of the carbon fiber is an important influencing factor. The length of the carbon fiber will have a complex and important impact on the uniformity of carbon fiber paper molding, the porosity, conductivity and mechanical properties of the carbon fiber paper. The larger the fiber length, the lower the fiber dispersion, and the uniformity and mechanical properties of the carbon fiber paper also change accordingly. Therefore, the present invention chooses to mix a certain amount of long carbon fibers with a long length into short carbon fibers with a short length, which can greatly alleviate the problem of difficulty in dispersing a single long carbon fiber, ensure the uniformity of the molded paper, and effectively improve the mechanical properties, porosity and conductivity of the carbon fiber paper.

[0043] In order to further improve the mechanical properties, porosity and conductivity of carbon fiber paper, it is necessary to reasonably control the diameters of short carbon fibers and long carbon fibers. Preferably, the length of the short carbon fibers is 3-6 mm, and the length of the long carbon fibers is 8-12 mm.

[0044] The carbon fiber paper of the present invention contains long carbon fibers of relatively long length, which play a role in reinforcing and connecting short carbon fibers of short length in the three-dimensional network structure built between the fibers, and ensure a certain stacking density. After being impregnated with resin of appropriate concentration, the paper has a high porosity, good mechanical properties and low resistivity.

[0045] The thickness and porosity of the carbon fiber paper of the present invention will also affect the comprehensive performance. Therefore, in order to further improve the performance, it is also necessary to reasonably control the thickness and porosity of the carbon fiber paper within the range of the present invention. In a specific embodiment, the thickness of the carbon fiber paper may be 190 μm, 200 μm, 210 μm, 220 μm, 230 μm or 240 μm, and the porosity may be 70%, 75%, 80% or 85%.

[0046] In the present invention, short carbon fibers are equivalent to the matrix to ensure dispersibility. When the amount of long fibers is relatively small, it can play a role in strengthening the matrix without affecting dispersibility. Therefore, in order to obtain carbon fiber paper with better performance, it is necessary to reasonably control the amount of short carbon fibers and long carbon fibers.

[0047] Preferably, in the carbon fiber paper of the present invention, the content of the short carbon fibers is ≥ the content of the long carbon fibers.

[0048] In order to make the carbon fiber paper obtained by the present invention have better performance, the weight ratio of the short carbon fiber content to the long carbon fiber content is 1-13:1, preferably 1-9:1, and more preferably 1.5-4:1.

[0049] In a specific embodiment, the weight ratio of the short carbon fiber content to the long carbon fiber content may be 9:1, 4:1, 7:3, 3:2 or 1:1.

[0050] The surface density of the carbon fiber paper obtained by the present invention is 100-150g / m 2 , specifically 100g / m 2 , 110g / m 2 , 120g / m 2 , 130g / m 2 , 140g / m 2 or 150g / m 2 .

[0051] A second aspect of the present invention provides a method for preparing carbon fiber paper, the preparation method comprising the following steps:

[0052] (1) mixing short carbon fibers, long carbon fibers, a dispersant and water to obtain a fiber slurry;

[0053] (2) preparing carbon fiber base paper from the fiber slurry using a wet papermaking process;

[0054] (3) impregnating the carbon fiber base paper in a phenolic resin solution, and then hot pressing to obtain a carbon fiber paper precursor;

[0055] (4) performing carbonization and graphitization on the carbon fiber paper precursor;

[0056] The length of the short carbon fiber is 2-6.5 mm, and the length of the long carbon fiber is 7-14 mm.

[0057] In the preparation method of the present invention, the length of the carbon fiber is an important influencing factor. The longer the fiber length, the lower the fiber dispersion, and the pore structure and mechanical properties of the carbon fiber paper also change accordingly. Therefore, when preparing the carbon fiber paper, the present invention selects to mix a certain amount of long carbon fibers with short carbon fibers, which can effectively improve the mechanical properties of the carbon fiber paper.

[0058] Further preferably, in step (1), the length of the short carbon fiber is 3-6 mm, and the length of the long carbon fiber is 8-12 mm.

[0059] In order to make the prepared carbon fiber paper have better performance, it is also necessary to reasonably control the amount of short carbon fibers and long carbon fibers. Therefore, in the preferred case of step (1), the amount of the short carbon fibers is ≥ the amount of the long carbon fibers.

[0060] In order to make the carbon fiber paper obtained by the present invention have better performance, it is further preferred that in step (1), the weight ratio of the short carbon fiber to the long carbon fiber is 1-13:1, preferably 1-9:1, and more preferably 1.5-4:1.

[0061] In a specific implementation of step (1), the weight ratio of the short carbon fibers to the long carbon fibers can be 9:1, 4:1, 7:3, 3:2 or 1:1.

[0062] In step (1) of the present invention, there is no special requirement for the selection of the dispersant, as long as it has good dispersing performance, and it can be a conventional choice in the art. In a specific embodiment, the dispersant is selected from one or more of polyethylene oxide, anionic polyacrylamide and Tween-80. In order to achieve a better dispersion effect, the dispersant is further selected as polyethylene oxide (PEO).

[0063] In step (1) of the present invention, in order to obtain a better dispersion effect, preferably, the dispersant is first mixed with water to obtain a dispersant solution, and then the dispersant solution is mixed with short carbon fibers and long carbon fibers to obtain a fiber slurry.

[0064] In the preferred case of step (1), the concentration of the dispersant in the dispersant solution is 0.1-0.2 wt%, specifically 0.1 wt%, 0.12 wt%, 0.15 wt%, 0.17 wt% or 0.2 wt%.

[0065] The current carbon fiber paper preparation process mainly includes carbon fiber dispersion, wet papermaking, resin impregnation, hot pressing and high-temperature carbonization and graphitization. During the preparation process, the uniformity of the initial fiber slurry and base paper has an important influence on the comprehensive performance of the final carbon fiber paper. Therefore, in the present invention, in step (1), in order to make the obtained fiber slurry more uniform and thus obtain carbon fiber paper with better performance, in a preferred case, after mixing short carbon fibers, long carbon fibers, dispersants and water, a fiber decompressor can be used to mechanically decompose for 15 minutes at 1000 r / min, and then ultrasonic dispersion is performed to finally obtain a uniformly dispersed fiber slurry.

[0066] In a specific embodiment, in step (1), the frequency of the ultrasonic dispersion is 53 KHz and the time is 30 min.

[0067] Further preferably, in step (1), in the fiber slurry, the total content of short carbon fibers and long carbon fibers is 0.1-0.2wt%, specifically 0.1wt%, 0.12wt%, 0.15wt%, 0.17wt% or 0.2wt%.

[0068] In step (2) of the present invention, the wet papermaking process is a common process in the papermaking field, and the operation of the wet papermaking process includes: placing the fiber slurry in a papermaking forming device with a filtering device, using a copper mesh as a filtering device, and filtering the fiber slurry through the copper mesh to remove water, thereby forming a carbon fiber base paper on the surface of the filtering device.

[0069] In a preferred embodiment, the mesh size of the copper mesh is 100-300 meshes.

[0070] In the method for preparing carbon fiber paper of the present invention, the total weight of the short carbon fiber and the long carbon fiber can be determined according to the preset thickness of the carbon fiber paper and the size of the paper forming area of ​​the paper making forming device used (for example, the paper forming area of ​​the paper making forming device used in the laboratory is 314cm 2 , the total weight of the short carbon fiber and long carbon fiber used is approximately 1.5g-4g).

[0071] In the preparation method described in the present invention, there is no special requirement for the papermaking forming device, and it can be a papermaking machine commonly used in the art.

[0072] In a preferred embodiment, after the carbon fiber base paper is obtained by wet papermaking, the obtained carbon fiber base paper needs to be dried, and then the completely dried carbon fiber base paper is immersed in a phenolic resin solution.

[0073] In step (3) of the present invention, the phenolic resin and ethanol are mixed evenly to obtain a phenolic resin solution.

[0074] In the present invention, the content of phenolic resin in the phenolic acid resin solution will affect the performance of the final carbon fiber paper product, so it is necessary to control the content of phenolic resin in the phenolic resin solution within a reasonable range. Therefore, in the preferred case of step (3), the content of phenolic resin in the phenolic resin solution is 5-15wt%, specifically 5wt%, 8wt%, 10wt%, 13wt% or 15wt%.

[0075] In step (3) of the present invention, during the impregnation operation, the carbon fiber base paper needs to be completely immersed in the phenolic resin solution to ensure that the carbon fiber base paper can be fully impregnated with the phenolic resin.

[0076] In step (3) of the present invention, in order to ensure that the carbon fiber base paper can be fully impregnated with the phenolic resin, the impregnation time is preferably 10-30 minutes, specifically 10 minutes, 15 minutes, 20 minutes, 25 minutes or 30 minutes.

[0077] In a preferred embodiment of the present invention, after the impregnation in step (3) is completed, the impregnated carbon fiber base paper is dried, and after complete drying, a hot pressing molding operation is performed.

[0078] In the preparation method of the present invention, the drying temperature is 50-60°C.

[0079] In step (3) of the present invention, the purpose of hot pressing is to ensure that the phenolic resin can be completely cured so that carbon fiber paper can be finally obtained. If there is no hot pressing operation, the prepolymer in the phenolic resin will quickly dissipate during the subsequent carbonization and graphitization treatments, and no pore structure or graphite structure will be formed between the carbon fibers, and the carbon fiber paper of the present invention will not be obtained.

[0080] In step (3), in order to ensure that the phenolic resin can be completely cured, the conditions for hot pressing molding need to be reasonably controlled. In a preferred embodiment, the conditions for hot pressing molding include: temperature of 150-180°C, time of 30-60 min, and pressure of 10-15 MPa.

[0081] In a specific embodiment, in step (3), the temperature of the hot pressing molding can be 150°C, 160°C, 170°C or 180°C, the time of the hot pressing molding can be 30 min, 40 min, 50 min or 60 min, and the pressure of the hot pressing molding can be 10 MPa, 11 MPa, 12 MPa, 13 MPa, 14 MPa or 15 MPa.

[0082] In the present invention, the pressure refers to absolute pressure.

[0083] In step (4) of the present invention, the carbonization treatment refers to a high-temperature treatment carried out in a carbonization furnace under the protection of an inert atmosphere, during which the impregnated phenolic resin is converted into carbon; the graphitization treatment refers to a high-temperature treatment carried out at a higher temperature under the protection of an inert atmosphere, during which the structure of the carbon material is further completed and the degree of graphitization is further improved.

[0084] In the present invention, the inert atmosphere may be a common inert atmosphere in the art. In order to reduce costs, the inert atmosphere in the present invention is preferably nitrogen and / or argon.

[0085] In a preferred embodiment of the present invention, in step (4), the carbonization treatment conditions include: a temperature of 800-1500° C. and a time of 60-120 min.

[0086] In a specific implementation of step (4), the temperature of the carbonization treatment can be 800°C, 900°C, 1000°C, 1100°C, 1200°C, 1300°C, 1400°C or 1500°C, and the time of the carbonization treatment can be 60 min, 70 min, 80 min, 90 min, 100 min, 110 min or 120 min.

[0087] Preferably, in step (4), the carbonization treatment conditions include: temperature of 1300-1500° C. and time of 60 min.

[0088] In a preferred embodiment of the present invention, in step (4), the conditions of the graphitization treatment include: a temperature of 2200-2900° C. and a time of 60-120 min.

[0089] In a specific implementation of step (4), the temperature of the graphitization treatment can be 2200°C, 2300°C, 2400°C, 2500°C, 2600°C, 2700°C, 2800°C, 2900°C, and the time of the carbonization treatment can be 60 min, 70 min, 80 min, 90 min, 100 min, 110 min or 120 min.

[0090] Preferably, in step (4), the conditions of the graphitization treatment include: a temperature of 2800-2900° C. and a time of 60 min.

[0091] In a preferred embodiment of the present invention, for a laboratory paper forming area of ​​300cm 2The papermaking forming device is about 2.1 g, the total weight of short carbon fiber and long carbon fiber is 2.1 g, the length of short carbon fiber is 6 mm, the length of long carbon fiber is 10 mm, the weight ratio of the amount of short carbon fiber to the amount of long carbon fiber is 6:4, the concentration of dispersant (PEO) in the dispersant solution is 0.1 wt%, the total content of short carbon fiber and long carbon fiber in the fiber slurry is 0.1 wt%, the number of copper mesh is 200 mesh, the content of phenolic resin in the phenolic resin solution is 10 wt%, the impregnation time is 15 min, the temperature and pressure of hot pressing are 180 ° C and 10 MPa respectively, the temperature of carbonization treatment is 1400 ° C, the time of carbonization treatment is 60 min, the temperature of graphitization treatment is 2800 ° C, and the time of graphitization treatment is 60 min; the properties of the obtained carbon fiber paper are as follows: the thickness is 190 μm, the porosity is 80.3%, the tensile strength is 21.7 MPa, and the in-plane resistivity is 0.95 mΩ cm -2 The maximum power density of the membrane electrode assembled with it as the substrate is 1034.7 mW cm -2 .

[0092] The third aspect of the present invention provides a carbon fiber paper prepared by the above preparation method. The carbon fiber paper prepared by the above preparation method has a thickness of 190-240 μm and a surface density of 100-150 g / m 2 , the porosity is 70-85%.

[0093] A fourth aspect of the present invention provides a use of the carbon fiber paper in a fuel cell.

[0094] The high-performance carbon fiber paper obtained by the present invention can improve its tensile strength by more than 30% compared with the carbon fiber paper prepared from short-cut carbon fibers of a single length. When the high-performance carbon fiber paper is used as the base layer of the gas diffusion layer of a hydrogen / oxygen fuel cell to assemble a membrane electrode, the maximum power density during power generation can be improved by more than 20% compared with the membrane electrode assembled with the carbon fiber paper prepared from short-cut carbon fibers of a single length.

[0095] The present invention mixes a certain amount of long carbon fibers with short carbon fibers, and prepares the carbon fiber base paper by dispersing, mixing and papermaking, wet impregnating phenolic resin and then hot pressing. The carbon fiber base paper can be effectively improved in mechanical properties after carbonization and high-temperature carbonization and graphitization. At the same time, a dispersion method combining mechanical disintegration with ultrasonic dispersion is adopted to minimize the adverse effect of the introduction of long carbon fibers on the uniformity of the carbon fiber paper. Because of the addition of long carbon fibers, a looser three-dimensional network structure can be built to prepare high-performance carbon fiber paper with higher porosity, higher tensile strength, electrical conductivity and excellent mechanical properties, which can be used as a substrate material for membrane electrodes of proton exchange membrane fuel cells.

[0096] The present invention will be described in detail below through examples, but the protection scope of the present invention is not limited thereto.

[0097] In the following examples and comparative examples, wet papermaking was performed on a paper area of ​​314 cm 2 The test was carried out on a laboratory vacuum filtration wet papermaking machine. Short carbon fibers and long carbon fibers treated with a surface hydrophilic sizing agent provided by Shanghai Petrochemical were used as raw materials. The diameters of the short carbon fibers and long carbon fibers were both 7 μm.

[0098] Example 1

[0099] (1) A dispersant (PEO) and water are mixed to obtain a dispersant solution with a concentration of 0.1 wt%, short carbon fibers with a length of 6 mm and long carbon fibers with a length of 10 mm are added to the dispersant solution (the total weight of the short carbon fibers and the long carbon fibers is 2.1 g, and the weight ratio of the short carbon fibers to the long carbon fibers is 9:1), and a fiber decomposer is used to mechanically decompose for 15 min at 1000 r / min and then ultrasonically disperse (the frequency of the ultrasonic dispersion is 53 KHz, and the time of the ultrasonic dispersion is 30 min) to obtain a uniformly dispersed fiber slurry, wherein the total content of the short carbon fibers and the long carbon fibers in the fiber slurry is 0.1 wt%;

[0100] (2) The fiber slurry obtained in step (1) is poured into a vacuum filtration wet papermaking machine, and a copper mesh with a mesh number of 200 is used as a filtering device (filter screen). Water is removed by filtration through the filter screen, and a uniform carbon fiber base paper is obtained after forming on the surface of the filter screen. The surface density of the obtained carbon fiber base paper is 67 g / m 2 ;

[0101] (3) mixing phenolic resin and ethanol uniformly to obtain a phenolic resin solution, wherein the content of phenolic resin in the phenolic resin solution is 10 wt %. The carbon fiber base paper obtained in step (2) is completely dried at 60° C. and then immersed in the resin solution. After immersion for 15 min, the base paper is taken out and completely dried at 60° C., and then hot-pressed at 180° C. and 10 MPa for 60 min to completely cure the phenolic resin, thereby obtaining a carbon fiber paper precursor.

[0102] (4) The carbon fiber paper precursor obtained in step (3) was subjected to carbonization treatment (temperature of 1400° C., time of 60 min) and graphitization treatment (temperature of 2800° C., time of 60 min) under a nitrogen atmosphere to obtain carbon fiber paper A1.

[0103] Example 2

[0104] (1) A dispersant (PEO) and water are mixed to obtain a dispersant solution with a concentration of 0.1 wt%, short carbon fibers with a length of 6 mm and long carbon fibers with a length of 10 mm are added to the dispersant solution (the total weight of the short carbon fibers and the long carbon fibers is 2.1 g, and the weight ratio of the short carbon fibers to the long carbon fibers is 8:2), and a fiber decomposer is used to mechanically decompose for 15 min at 1000 r / min and then ultrasonically disperse (the frequency of the ultrasonic dispersion is 53 KHz, and the time of the ultrasonic dispersion is 30 min) to obtain a uniformly dispersed fiber slurry, wherein the total content of the short carbon fibers and the long carbon fibers in the fiber slurry is 0.1 wt%;

[0105] (2) The fiber slurry obtained in step (1) is poured into a vacuum filtration wet papermaking machine, and a copper mesh with a mesh number of 200 is used as a filtering device (filter screen). Water is removed by filtration through the filter screen, and a uniform carbon fiber base paper is obtained after forming on the surface of the filter screen. The surface density of the obtained carbon fiber base paper is 67 g / m 2 ;

[0106] (3) mixing phenolic resin and ethanol uniformly to obtain a phenolic resin solution, wherein the content of phenolic resin in the phenolic resin solution is 10 wt %. The carbon fiber base paper obtained in step (2) is completely dried at 60° C. and then immersed in the resin solution. After immersion for 15 min, the base paper is taken out and completely dried at 60° C., and then hot-pressed at 180° C. and 10 MPa for 60 min to completely cure the phenolic resin, thereby obtaining a carbon fiber paper precursor.

[0107] (4) The carbon fiber paper precursor obtained in step (3) was subjected to carbonization treatment (temperature of 1400° C., time of 60 min) and graphitization treatment (temperature of 2800° C., time of 60 min) under a nitrogen atmosphere to obtain carbon fiber paper A2.

[0108] Example 3

[0109] (1) A dispersant (PEO) and water are mixed to obtain a dispersant solution with a concentration of 0.1 wt%, short carbon fibers with a length of 6 mm and long carbon fibers with a length of 10 mm are added to the dispersant solution (the total weight of the short carbon fibers and the long carbon fibers is 2.1 g, and the weight ratio of the short carbon fibers to the long carbon fibers is 7:3), and a fiber decomposer is used to mechanically decompose for 15 min at 1000 r / min and then ultrasonically disperse (the frequency of the ultrasonic dispersion is 53 KHz, and the time of the ultrasonic dispersion is 30 min) to obtain a uniformly dispersed fiber slurry, wherein the total content of the short carbon fibers and the long carbon fibers in the fiber slurry is 0.1 wt%;

[0110] (2) The fiber slurry obtained in step (1) is poured into a vacuum filtration wet papermaking machine, and a copper mesh with a mesh number of 200 is used as a filtering device (filter screen). Water is removed by filtration through the filter screen, and a uniform carbon fiber base paper is obtained after forming on the surface of the filter screen. The surface density of the obtained carbon fiber base paper is 67 g / m 2 ;

[0111] (3) mixing phenolic resin and ethanol uniformly to obtain a phenolic resin solution, wherein the content of phenolic resin in the phenolic resin solution is 10 wt %. The carbon fiber base paper obtained in step (2) is completely dried at 60° C. and then immersed in the resin solution. After immersion for 15 min, the base paper is taken out and completely dried at 60° C., and then hot-pressed at 180° C. and 10 MPa for 60 min to completely cure the phenolic resin, thereby obtaining a carbon fiber paper precursor.

[0112] (4) The carbon fiber paper precursor obtained in step (3) was subjected to carbonization treatment (temperature of 1400° C., time of 60 min) and graphitization treatment (temperature of 2800° C., time of 60 min) under a nitrogen atmosphere to obtain carbon fiber paper A3.

[0113] Example 4

[0114] (1) A dispersant (PEO) and water are mixed to obtain a dispersant solution with a concentration of 0.1 wt%, short carbon fibers with a length of 6 mm and long carbon fibers with a length of 10 mm are added to the dispersant solution (the total weight of the short carbon fibers and the long carbon fibers is 2.1 g, and the weight ratio of the short carbon fibers to the long carbon fibers is 6:4), and a fiber decomposer is used to mechanically decompose for 15 min at 1000 r / min and then ultrasonically disperse (the frequency of the ultrasonic dispersion is 53 KHz, and the time of the ultrasonic dispersion is 30 min) to obtain a uniformly dispersed fiber slurry, wherein the total content of the short carbon fibers and the long carbon fibers in the fiber slurry is 0.1 wt%;

[0115] (2) The fiber slurry obtained in step (1) is poured into a vacuum filtration wet papermaking machine, and a copper mesh with a mesh number of 200 is used as a filtering device (filter screen). Water is removed by filtration through the filter screen, and a uniform carbon fiber base paper is obtained after forming on the surface of the filter screen. The surface density of the obtained carbon fiber base paper is 67 g / m 2 ;

[0116] (3) mixing phenolic resin and ethanol uniformly to obtain a phenolic resin solution, wherein the content of phenolic resin in the phenolic resin solution is 10 wt %. The carbon fiber base paper obtained in step (2) is completely dried at 60° C. and then immersed in the resin solution. After immersion for 15 min, the base paper is taken out and completely dried at 60° C., and then hot-pressed at 180° C. and 10 MPa for 60 min to completely cure the phenolic resin, thereby obtaining a carbon fiber paper precursor.

[0117] (4) The carbon fiber paper precursor obtained in step (3) was subjected to carbonization treatment (temperature of 1400° C., time of 60 min) and graphitization treatment (temperature of 2800° C., time of 60 min) under a nitrogen atmosphere to obtain carbon fiber paper A4.

[0118] Example 5

[0119] (1) A dispersant (PEO) and water are mixed to obtain a dispersant solution with a concentration of 0.1 wt%, short carbon fibers with a length of 6 mm and long carbon fibers with a length of 10 mm are added to the dispersant solution (the total weight of the short carbon fibers and the long carbon fibers is 2.1 g, and the weight ratio of the short carbon fibers to the long carbon fibers is 5:5), and a fiber decomposer is used to mechanically decompose for 15 min at 1000 r / min and then ultrasonically disperse (the frequency of the ultrasonic dispersion is 53 KHz, and the time of the ultrasonic dispersion is 30 min) to obtain a uniformly dispersed fiber slurry, wherein the total content of the short carbon fibers and the long carbon fibers in the fiber slurry is 0.1 wt%;

[0120] (2) The fiber slurry obtained in step (1) is poured into a vacuum filtration wet papermaking machine, and a copper mesh with a mesh number of 200 is used as a filtering device (filter screen). Water is removed by filtration through the filter screen, and a uniform carbon fiber base paper is obtained after forming on the surface of the filter screen. The surface density of the obtained carbon fiber base paper is 67 g / m 2 ;

[0121] (3) mixing phenolic resin and ethanol uniformly to obtain a phenolic resin solution, wherein the content of phenolic resin in the phenolic resin solution is 10 wt %. The carbon fiber base paper obtained in step (2) is completely dried at 60° C. and then immersed in the resin solution. After immersion for 15 min, the base paper is taken out and completely dried at 60° C., and then hot-pressed at 180° C. and 10 MPa for 60 min to completely cure the phenolic resin, thereby obtaining a carbon fiber paper precursor.

[0122] (4) The carbon fiber paper precursor obtained in step (3) was subjected to carbonization treatment (temperature of 1400° C., time of 60 min) and graphitization treatment (temperature of 2800° C., time of 60 min) under a nitrogen atmosphere to obtain carbon fiber paper A5.

[0123] Example 6

[0124] (1) A dispersant (PEO) and water are mixed to obtain a dispersant solution with a concentration of 0.1 wt%, short carbon fibers with a length of 6 mm and long carbon fibers with a length of 8 mm are added to the dispersant solution (the total weight of the short carbon fibers and the long carbon fibers is 2.1 g, and the weight ratio of the short carbon fibers to the long carbon fibers is 6:4), and a fiber decomposer is used to mechanically decompose for 15 min at 1000 r / min and then ultrasonically disperse (the frequency of the ultrasonic dispersion is 53 KHz, and the time of the ultrasonic dispersion is 30 min) to obtain a uniformly dispersed fiber slurry, wherein the total content of the short carbon fibers and the long carbon fibers in the fiber slurry is 0.1 wt%;

[0125] (2) The fiber slurry obtained in step (1) is poured into a vacuum filtration wet papermaking machine, and a copper mesh with a mesh number of 200 is used as a filtering device (filter screen). Water is removed by filtration through the filter screen, and a uniform carbon fiber base paper is obtained after forming on the surface of the filter screen. The surface density of the obtained carbon fiber base paper is 67 g / m 2 ;

[0126] (3) mixing phenolic resin and ethanol uniformly to obtain a phenolic resin solution, wherein the content of phenolic resin in the phenolic resin solution is 10 wt %. The carbon fiber base paper obtained in step (2) is completely dried at 60° C. and then immersed in the resin solution. After immersion for 15 min, the base paper is taken out and completely dried at 60° C., and then hot-pressed at 180° C. and 10 MPa for 60 min to completely cure the phenolic resin, thereby obtaining a carbon fiber paper precursor.

[0127] (4) The carbon fiber paper precursor obtained in step (3) was subjected to carbonization treatment (temperature of 1400° C., time of 60 min) and graphitization treatment (temperature of 2800° C., time of 60 min) under a nitrogen atmosphere to obtain carbon fiber paper A6.

[0128] Example 7

[0129] (1) A dispersant (PEO) and water are mixed to obtain a dispersant solution with a concentration of 0.1 wt%, short carbon fibers with a length of 6 mm and long carbon fibers with a length of 12 mm are added to the dispersant solution (the total weight of the short carbon fibers and the long carbon fibers is 2.1 g, and the weight ratio of the short carbon fibers to the long carbon fibers is 6:4), and a fiber decomposer is used to mechanically decompose for 15 min at 1000 r / min and then ultrasonically disperse (the frequency of the ultrasonic dispersion is 53 KHz, and the time of the ultrasonic dispersion is 30 min) to obtain a uniformly dispersed fiber slurry, wherein the total content of the short carbon fibers and the long carbon fibers in the fiber slurry is 0.1 wt%;

[0130] (2) The fiber slurry obtained in step (1) is poured into a vacuum filtration wet papermaking machine, and a copper mesh with a mesh number of 200 is used as a filtering device (filter screen). Water is removed by filtration through the filter screen, and a uniform carbon fiber base paper is obtained after forming on the surface of the filter screen. The surface density of the obtained carbon fiber base paper is 67 g / m 2 ;

[0131] (3) mixing phenolic resin and ethanol uniformly to obtain a phenolic resin solution, wherein the content of phenolic resin in the phenolic resin solution is 10 wt %. The carbon fiber base paper obtained in step (2) is completely dried at 60° C. and then immersed in the resin solution. After immersion for 15 min, the base paper is taken out and completely dried at 60° C., and then hot-pressed at 180° C. and 10 MPa for 60 min to completely cure the phenolic resin, thereby obtaining a carbon fiber paper precursor.

[0132] (4) The carbon fiber paper precursor obtained in step (3) was subjected to carbonization treatment (temperature of 1400° C., time of 60 min) and graphitization treatment (temperature of 2800° C., time of 60 min) under a nitrogen atmosphere to obtain carbon fiber paper A7.

[0133] Comparative Example 1

[0134] The method of Example 1 is followed, except that in step (1), long carbon fibers are not used, i.e., 2.1 g of short carbon fibers with a length of 6 mm are added to the dispersant solution; the content of phenolic resin in the phenolic resin solution used in step (3) is 5 wt%; and carbon fiber paper D1 is obtained.

[0135] Comparative Example 2

[0136] The method of Example 1 is followed, except that in step (1), long carbon fibers are not used, i.e., 2.1 g of short carbon fibers with a length of 6 mm are added to the dispersant solution; the content of phenolic resin in the phenolic resin solution used in step (3) is 10 wt%; and carbon fiber paper D2 is obtained.

[0137] Comparative Example 3

[0138] The method of Example 3 is followed, except that in step (1), long carbon fibers are not used, i.e., 2.1 g of short carbon fibers with a length of 6 mm are added to the dispersant solution; the resin content in the resin solution used in step (3) is 15 wt%; and carbon fiber paper D3 is obtained.

[0139] Comparative Example 4

[0140] The method of Example 6 was followed, except that in step (1), short carbon fibers were not used, and 2.1 g of long carbon fibers with a length of 8 mm were added to the dispersant solution; thus obtaining carbon fiber paper D4.

[0141] Comparative Example 5

[0142] The method of Example 6 was followed, except that in step (1), short carbon fibers were not used, and 2.1 g of long carbon fibers with a length of 10 mm were added to the dispersant solution; thus obtaining carbon fiber paper D5.

[0143] Comparative Example 6

[0144] The method of Example 6 was followed, except that in step (1), short carbon fibers were not used, and 2.1 g of long carbon fibers with a length of 12 mm were added to the dispersant solution; thus obtaining carbon fiber paper D6.

[0145] Comparative Example 7

[0146] The method of Example 4 was followed, except that in step (1), the length of the short carbon fibers used was 1 mm, and the length of the long carbon fibers used was 4 mm; and carbon fiber paper D7 was obtained.

[0147] Comparative Example 8

[0148] The method of Example 2 was followed, except that the weight ratio of the short carbon fibers to the long carbon fibers was 2:8, to obtain carbon fiber paper D8.

[0149] Test Example 1

[0150] The surface morphology and cross-sectional morphology of the carbon fiber paper A4 obtained in Example 4 were respectively detected by field emission scanning electron microscopy (accelerating voltage 5 KV). The results are as follows: Figure 1 and Figure 2 As shown, from the surface morphology ( Figure 1 ) It can be seen that carbon fiber paper is generally composed of carbon fiber and resin carbon. The carbon fiber is distributed isotropically, and the resin carbon is mainly distributed at the contact points of the fibers. It can be seen that the resin carbon content is relatively small; from the cross-sectional morphology ( Figure 2 ) It can be observed that the resin carbon is evenly distributed in the three-dimensional network-like pore structure constructed by carbon fiber, playing a bonding role.

[0151] Test Example 2

[0152] The thickness, surface density, in-plane resistivity, porosity, tensile strength and maximum power density of A1-A7 and D1-D8 were tested respectively. The testing methods are as follows:

[0153] The thickness was tested using a thickness gauge: five points were taken on a 5×5 cm carbon fiber paper to test and the average value was taken;

[0154] Surface density test method: GB / T 20042.7-2014 Proton exchange membrane fuel cell, Part 7: Carbon paper properties determination method to test the surface density of carbon fiber paper;

[0155] The in-plane resistivity was tested by a four-probe in-plane resistance tester: five points were taken on a 5×5 cm carbon fiber paper to test and the average value was taken;

[0156] The porosity was measured by the liquid infiltration method: 5×5 cm carbon fiber paper was immersed in n-butanol solution, and vacuum filtration was used to make the n-butanol solution completely infiltrate the carbon fiber paper. The porosity was calculated by weighing the carbon fiber paper before and after infiltration using the following formula;

[0157]

[0158] Wherein, P: porosity, %; m2: weight of carbon fiber paper after complete impregnation; m1: weight of carbon fiber paper before impregnation; ρ: density of n-butanol solution, g / cm 3 ; V: volume of carbon fiber paper;

[0159] The tensile strength was tested by a universal testing machine: the carbon fiber paper was cut into a size of 2 × 4 cm and the tensile rate was 2 mm / min to obtain the tensile strength;

[0160] Maximum power density: The prepared carbon fiber paper and commercially available carbon fiber paper were assembled with commercial CCM (a collection of proton exchange membrane and catalyst) into a membrane electrode (MEA), where commercial carbon black (XC-72) and PTFE were used to construct the microporous layer, and the carbon loading was 3 mg / cm 2 The power generation performance of the membrane electrode was tested on the Scribner 850G fuel cell workstation. The cell temperature was 80°C, the relative humidity of the gas was 30%, and the gas flow rates of the cathode and anode were 0.8 / 0.3 L min -1 , the back pressure is 100KPa, the results are as follows Figure 3 As shown, CCP is a commercial carbon paper (TGP-H-060) purchased from Toray, CP1 is carbon fiber paper D2, CP2 is carbon fiber paper A2, and CP3 is carbon fiber paper A4. Figure 3 The maximum power density is read from the peak power density on the curve.

[0161] The results are shown in Table 1.

[0162] Table 1

[0163]

[0164]

[0165] As can be seen from Table 1, as the proportion of mixed long carbon fibers increases, the thickness of the carbon fiber paper decreases, the in-plane resistivity decreases, and the porosity and tensile strength increase. This is because as the proportion of mixed long carbon fibers increases, the three-dimensional network structure built between the fibers becomes looser. During the impregnation process, the phenolic resin is easier to enter the interior, and the impregnation is more uniform. After hot pressing carbonization and graphitization, the resin carbon content reaches a certain value and the distribution tends to be uniform, the in-plane resistivity decreases, the bonding between the fibers is better, and the thickness decreases. There is a balance between the looser structure between the fibers and the resin carbon content. Therefore, when the ratio of short carbon fibers with a length of 6 mm and long carbon fibers with a length of 10 mm is 6:4, the highest porosity, tensile strength and power density are shown. Comparison of carbon fiber paper composed of single-length carbon fibers shows that the increase in length leads to a decrease in porosity, which is mainly attributed to the difficulty of uniform dispersion of carbon fibers, thereby reducing the output power density of the fuel cell as a substrate. Therefore, when the length of the short carbon fiber is 6 mm, the length of the long carbon fiber is 10 mm, and the short carbon fiber and the long carbon fiber are mixed in a ratio of 6:4, the comprehensive performance of the carbon fiber paper is better than that of the carbon fiber paper prepared with a single length carbon fiber.

[0166] As the resin concentration increases, the thickness, in-plane resistivity and porosity of carbon fiber paper all decrease. This is because the resin carbon also increases, making the bonding between fibers tighter and reducing the thickness; at the same time, a better conductive path is formed, which is conducive to the transmission of electrons, so the in-plane resistivity decreases; the porosity decreases because the excessive resin carbon content blocks the pore structure between fibers, resulting in a decrease in porosity, which seriously affects the mass transfer and water management of the membrane electrode as a substrate. Therefore, the optimized concentration of resin impregnation is 10wt%.

[0167] The carbon fiber paper prepared by mixing two carbon fibers of different lengths has better performance than the carbon fiber paper prepared by carbon fiber of a single length, taking into account the dispersion of fibers, the uniformity of paper, and the porosity, resistivity and mechanical properties of the paper.

[0168] The preferred embodiments of the present invention are described in detail above, but the present invention is not limited thereto. Within the technical concept of the present invention, the technical solution of the present invention can be subjected to a variety of simple modifications, including the combination of various technical features in any other suitable manner, and these simple modifications and combinations should also be regarded as the contents disclosed by the present invention and belong to the protection scope of the present invention.

Claims

1. A carbon fiber paper, characterized in that: The carbon fiber paper contains short carbon fibers and long carbon fibers; Wherein, the length of the short carbon fiber is 2-6.5 mm, and the length of the long carbon fiber is 7-14 mm; The carbon fiber paper has a thickness of 190-240 μm and a porosity of 70-85%.

2. The carbon fiber paper according to claim 1, characterized in that: The length of the short carbon fiber is 3-6 mm, and the length of the long carbon fiber is 8-12 mm; Preferably, the content of the short carbon fibers is ≥ the content of the long carbon fibers; Preferably, the weight ratio of the short carbon fiber content to the long carbon fiber content is 1-13:1, preferably 1-9:1, and more preferably 1.5-4:

1.

3. The carbon fiber paper according to claim 1 or 2, characterized in that: The surface density of the carbon fiber paper is 100-150g / m 2 .

4. A method for preparing carbon fiber paper, characterized in that: The preparation method comprises the following steps: (1) mixing short carbon fibers, long carbon fibers, a dispersant and water to obtain a fiber slurry; (2) preparing carbon fiber base paper from the fiber slurry using a wet papermaking process; (3) impregnating the carbon fiber base paper in a phenolic resin solution, and then hot pressing to obtain a carbon fiber paper precursor; (4) performing carbonization and graphitization on the carbon fiber paper precursor; The length of the short carbon fiber is 2-6.5 mm, and the length of the long carbon fiber is 7-14 mm.

5. The preparation method according to claim 4, characterized in that: In step (1), the length of the short carbon fiber is 3-6 mm, and the length of the long carbon fiber is 8-12 mm; Preferably, the amount of the short carbon fiber is ≥ the amount of the long carbon fiber; Preferably, the weight ratio of the short carbon fibers to the long carbon fibers is 1-13:1, preferably 1-9:1, and more preferably 1.5-4:

1.

6. The preparation method according to claim 4 or 5, characterized in that: In step (1), the dispersant is selected from one or more of polyethylene oxide, anionic polyacrylamide and Tween-80.

7. The preparation method according to claim 4, characterized in that: In step (1), the dispersant is mixed with water to obtain a dispersant solution, and the dispersant solution is then mixed with short carbon fibers and long carbon fibers to obtain a fiber slurry; Preferably, the concentration of the dispersant in the dispersant solution is 0.1-0.2 wt %; Preferably, in the fiber slurry, the total content of short carbon fibers and long carbon fibers is 0.1-0.2 wt %.

8. The preparation method according to claim 4 or 5, characterized in that: In step (3), the content of phenolic resin in the phenolic resin solution is 5-15 wt%.

9. The preparation method according to claim 3, characterized in that: In step (3), the immersion time is 10-30 min; Preferably, the conditions for the hot pressing molding include: a temperature of 150-180° C., a time of 30-60 min, and a pressure of 10-15 MPa.

10. The preparation method according to claim 4, characterized in that: In step (4), the carbonization treatment conditions include: temperature of 800-1500°C and time of 60-120 min; Preferably, the graphitization treatment conditions include: temperature of 2200-2900° C. and time of 60-120 min.

11. The carbon fiber paper prepared by the preparation method according to any one of claims 5 to 10, characterized in that: The carbon fiber paper has a thickness of 190-240 μm and a porosity of 70-85%; Preferably, the surface density of the carbon fiber paper is 100-150 g / m 2 .

12. Use of the carbon fiber paper according to any one of claims 1 to 3 or the carbon fiber paper according to claim 11 in a fuel cell.

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