Preparation method and application of carbon paper

Abstract

The present application relates to a method for preparing carbon paper and its application. The method for preparing the carbon paper comprises the following steps: impregnating carbon fiber felt in a resin dispersion, drying, and preparing a carbon paper precursor; hot pressing the carbon paper precursor, and controlling the hot pressing temperature of the first surface of the carbon paper precursor to be higher than the hot pressing temperature of the second surface during the hot pressing treatment, to prepare a carbon paper preform; and carbonizing and graphitizing the carbon paper preform. The first surface and the second surface are two opposite surfaces of the carbon paper precursor. By hot pressing the first surface and the second surface of the carbon paper precursor at different temperatures, carbon paper with a porosity gradient change can be obtained, thereby improving the mass transfer and conduction properties of the carbon paper. In addition, the above-mentioned preparation method has fewer process steps, a simple production process, and is convenient for large-scale production.

Description

Technical Field

[0001] The present application relates to the field of fuel cell technology, and in particular to a method for preparing carbon paper and its application. Background Art

[0002] Proton exchange membrane fuel cells use hydrogen as the anode and oxygen or air as the cathode. They have the advantages of high energy conversion rate, fast low-temperature startup, and environmental friendliness. The gas diffusion layer is an important component of the proton exchange membrane fuel cell, which plays the role of moisture and gas management, electron and heat conduction, and catalyst layer support. The gas diffusion layer is usually made of gas diffusion materials. The gas diffusion material includes a base layer and a microporous layer coated on its surface. Among them, the microporous layer is mainly made of hydrophobic material, which provides hydrophobicity and prevents the generated water from accumulating on the surface of the gas diffusion material. The base layer is usually made of porous materials such as carbon paper, and its porosity and pore structure directly affect the transmission of moisture and gas in the gas diffusion material.

[0003] Studies have shown that under the same average porosity, carbon paper with a porosity gradient is more conducive to the transmission of gas and water. The traditional method first layers carbon fiber slurries of different lengths in sequence, and then prepares a carbon paper precursor with a gradient porosity by papermaking. The carbon paper precursor is then subjected to resin impregnation, hot pressing curing, carbonization, and graphitization to obtain carbon paper with a porosity gradient. This preparation method includes multiple layering steps and a complex process, which is not conducive to mass production. In addition, after multiple steps of treatment, the porosity of the carbon paper precursor will change, and the pore structure of the carbon paper cannot be well maintained.

[0004] Therefore, how to provide a simple preparation method to obtain carbon paper with gradient porosity has become a technical problem that needs to be solved urgently. Summary of the invention

[0005] Based on this, the present application provides a method for preparing carbon paper with a gradient porosity, few preparation steps and a simple production process.

[0006] In a first aspect, a method for preparing carbon paper is provided, comprising the following steps:

[0007] The carbon fiber felt is impregnated in a resin dispersion and dried to prepare a carbon paper precursor;

[0008] Performing a hot pressing treatment on the carbon paper precursor, and controlling the hot pressing temperature of the first surface of the carbon paper precursor to be higher than the hot pressing temperature of the second surface during the hot pressing treatment, to prepare a carbon paper preform; and

[0009] Carrying out carbonization and graphitization treatment on the carbon paper preform;

[0010] The first surface and the second surface are two opposite surfaces of the carbon paper precursor.

[0011] The method for preparing the carbon paper adopts different temperatures to perform hot pressing on the first surface and the second surface of the carbon paper precursor, and controls the curing process of the resin by controlling the hot pressing temperature, thereby adjusting the porosity of the obtained carbon paper. Specifically, on the first surface with a higher hot pressing temperature, the resin curing degree is higher and the uncured resin content is less. During the carbonization treatment, fewer bubbles are generated and fewer pores are formed, so the porosity is relatively low. Correspondingly, on the second surface of the carbon paper precursor, the resin curing degree is lower, and more pores are formed after the carbonization treatment, so the porosity is relatively high. In this way, after the graphitization treatment, a carbon paper with a porosity gradient change can be obtained, and its mass transfer and conduction properties are good. Since the above preparation method only improves the conditions of the hot pressing treatment, no other processes or equipment are added, and the preparation steps are few and the production process is simple, it is convenient for large-scale production.

[0012] In some embodiments, the difference between the hot pressing temperatures of the first surface and the second surface is 20° C. to 140° C.

[0013] In some embodiments, the difference between the hot pressing temperatures of the first surface and the second surface is 60° C. to 120° C.

[0014] In some embodiments, the hot pressing temperature of the first surface is 160°C to 300°C.

[0015] In some embodiments, the hot pressing temperature of the second surface is 140°C to 180°C.

[0016] In some embodiments, the pressure of the hot pressing treatment is 0.1 MPa to 4 MPa;

[0017] In some embodiments, the hot pressing time is 2 min to 60 min.

[0018] In some of these embodiments, the resin in the resin dispersion is a thermosetting resin;

[0019] And / or, the dispersant in the resin dispersion is at least one of ethanol, isopropanol, methanol and acetone.

[0020] In some embodiments, the concentration of the resin dispersion is 0.05 g / mL to 1.0 g / mL.

[0021] In some embodiments, the content of the resin in the carbon paper precursor is 10 g / m 2 ~200g / m 2 .

[0022] In a second aspect, there is provided a use of the carbon paper prepared by the preparation method of the first aspect in the preparation of a fuel cell. DETAILED DESCRIPTION

[0023] In order to make the above-mentioned purposes, features and advantages of the present application more obvious and easy to understand, the specific implementation methods of the present application are described in detail below. In the following description, many specific details are set forth to facilitate a full understanding of the present application. However, the present application can be implemented in many other ways different from those described herein, and those skilled in the art can make similar improvements without violating the connotation of the present application, so the present application is not limited by the specific embodiments disclosed below.

[0024] The terms "first" and "second" used in this article are only used for descriptive purposes and should not be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Thus, the features defined as "first" and "second" may explicitly or implicitly include at least one of the features. In the description of this application, the meaning of "multiple" is at least two, such as two, three, etc., unless otherwise clearly and specifically defined. "At least one" used in this article refers to any one, any two, or any two or more of the listed items. "Above a certain number" used in this article should be understood as a certain number and a range greater than a certain number.

[0025] The terms "and / or", "or / and", and "and / or" used in this document have an optional scope including any one of two or more related listed items, and also including any and all combinations of the related listed items, said any and all combinations including any combination of any two related listed items, any more related listed items, or all related listed items.

[0026] Where “including,” “having,” and “comprising” are used as described herein, it is intended to cover a non-exclusive inclusion, and another component may be added unless an explicit limiting term is used, such as “only,” “consisting of,” etc. Unless mentioned otherwise, a term in the singular form may include a plural form and shall not be construed as being one in number.

[0027] The weight of the relevant components mentioned in the embodiments of the present application specification may not only refer to the specific content of each component, but also indicate the proportional relationship of the weights between the components. Therefore, as long as the content of the relevant components in the embodiments of the present application specification is proportionally enlarged or reduced, it is within the scope disclosed in the embodiments of the present application specification.

[0028] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art to which this application belongs. The terms used herein in the specification of this application are only for the purpose of describing specific embodiments and are not intended to limit this application.

[0029] Carbon paper is one of the ideal substrate materials for fuel cell gas diffusion materials, and its porosity directly affects the mass transfer and conduction performance of fuel cells. Relevant studies have shown that under the same average equivalent porosity, carbon paper with a porosity gradient is more conducive to the transmission of gas and water. Specifically, when there is a porosity difference between the two surfaces of the carbon paper, the gas pressure is smaller on the side with larger porosity, and a pressure difference is formed on both sides of the carbon paper. In the direction of pressure reduction, the diffusion rate of the gas increases, which is beneficial to improve the gas transmission efficiency. In addition, the above-mentioned carbon paper can also allow the water generated by the reaction to be discharged smoothly, effectively preventing the occurrence of flooding.

[0030] Usually, a wet papermaking process is used to prepare carbon paper with gradient porosity. Generally, carbon fibers of different lengths are first made into slurries, and then the slurries are layered in sequence according to the length of the carbon fibers, followed by papermaking, hot pressing and curing, carbonization and graphitization. However, this method includes multiple layering steps, the process is relatively complicated, and in the process of papermaking, carbon fibers of different lengths will be staggered, and the gradient porosity of the carbon paper cannot be well guaranteed. Another preparation method is to first make paper from carbon fiber slurries of different lengths, prepare a variety of fiber felts containing carbon fibers of different lengths, and then stack the above fiber felts in sequence to prepare carbon paper. Although this method can maintain the gradient pore structure of carbon paper, it also involves multiple stackings, and the production process is relatively complicated, making it difficult to plan production.

[0031] As mentioned above, most traditional carbon paper preparation methods use the length difference of different carbon fibers to construct a gradient porosity, so the preparation process is complicated. The present application found that by regulating the resin curing process, the interior of the carbon paper precursor is filled with resins with different degrees of curing, thereby forming a pore structure with a high and low porosity gradient during the carbonization process. The preparation method of the present application forms a gradient porosity in the carbon paper through a simple method, and does not require the addition of additional equipment, does not change the original process, and is easy to scale up production.

[0032] An embodiment of the present application provides a method for preparing carbon paper, including steps S100 to S300.

[0033] Step S100: immersing the carbon fiber felt in a resin dispersion and drying the mixture to prepare a carbon paper precursor.

[0034] In a specific example, carbon fiber is made into carbon fiber felt by wet papermaking. It can be understood that after papermaking, carbon fiber forms a carbon fiber felt with a three-dimensional porous network structure. However, due to the large gaps between carbon fibers and the small contact area, the strength of the carbon fiber felt is insufficient, so it is necessary to fill the gaps between the carbon fibers with resin to increase the density.

[0035] In a specific example, the length of the carbon fibers in the carbon fiber felt is 3 mm to 20 mm. Optionally, the length of the carbon fibers is 6 mm to 12 mm.

[0036] In a specific example, the resin in the resin dispersion is a thermosetting resin. The thermosetting resin can be evenly filled in the gaps between the carbon fibers after curing, and the resin carbon formed after carbonization can be retained in the gaps, making the contact between the carbon fibers more firm and improving the mechanical strength of the product. Furthermore, during carbonization, the thermosetting resin is partially decomposed, and the generated carbon oxides are discharged in the form of bubbles, leaving holes in the resin carbon, increasing the porosity of the product.

[0037] In a specific example, the thermosetting resin includes at least one of a phenolic resin, a furfural resin, an epoxy resin, and a furan resin.

[0038] The dispersant in the resin dispersion is an organic solvent with a relatively low boiling point or a mixed solvent composed of a plurality of low boiling point organic solvents. In a specific example, the dispersant in the resin dispersion is at least one of ethanol, isopropanol, methanol and acetone. The thermosetting resin can be well dispersed in the above organic solvents, thereby improving the impregnation effect of the resin dispersion on the carbon fiber felt.

[0039] In a specific example, the concentration of the resin dispersion is 0.05 g / mL to 1.0 g / mL. Optionally, the concentration of the resin dispersion can be 0.05 g / mL, 0.1 g / mL, 0.15 g / mL, 0.2 g / mL, 0.25 g / mL, 0.3 g / mL, 0.35 g / mL, 0.4 g / mL, 0.45 g / mL, 0.5 g / mL, 0.55 g / mL, 0.6 g / mL, 0.65 g / mL, 0.75 g / mL, 0.8 g / mL, 0.85 g / mL, 0.9 g / mL, 0.95 g / mL or 1.0 g / mL. It can be understood that the concentration of the resin dispersion can also be other suitable selections within the range of 0.05 g / mL to 1.0 g / mL. When the concentration of the resin dispersion is lower than 0.05 g / mL, the resin content in the carbon paper precursor is too low, and the mechanical strength of the obtained carbon paper is low; when the concentration of the resin dispersion is higher than 1.0 g / mL, most of the gaps in the carbon fiber felt are filled with resin, and the porosity of the obtained carbon paper is too low, which reduces the mass transfer and conduction properties of the carbon paper.

[0040] In a specific example, the drying temperature is 40° C. to 70° C., and the drying time is 2 min to 60 min.

[0041] In a specific example, the content of the resin in the carbon paper precursor is 10 g / m 2 ~200g / m 2Optionally, the resin content in the carbon paper precursor may be 10 g / m 2 , 20g / m 2 , 40g / m 2 , 60g / m 2 , 80g / m 2 , 100g / m 2 , 120g / m 2 , 140g / m 2 , 160g / m 2 , 180g / m 2 , 2000g / m 2 It is understandable that the content of the resin in the carbon paper precursor can also be 10 g / m 2 ~2000g / m 2 Further optionally, the content of the resin in the carbon paper precursor can be 20 g / m 2 ~140g / m 2 It should be noted that the content of resin in the carbon paper precursor can be regulated by controlling the concentration of the resin dispersion. Those skilled in the art can select process parameters such as the impregnation time according to the concentration of the resin dispersion and actual needs. 2 When the resin content is lower than 10 g / m 2 When the carbon paper is heated, the carbon paper contains less resin carbon, which will reduce the mechanical strength of the carbon paper.

[0042] Step S200: hot-pressing the carbon paper precursor, and controlling the hot-pressing temperature of the first surface of the carbon paper precursor to be higher than the hot-pressing temperature of the second surface during the hot-pressing process, to prepare a carbon paper preform. The first surface and the second surface are two opposite surfaces of the carbon paper precursor.

[0043] It is understandable that the resin solidifies during hot pressing and fills the gaps in the carbon fiber felt. Since the degree of curing of thermosetting resins is mainly affected by the curing temperature, the curing process of the resin can be regulated by controlling the hot pressing temperature, so that the carbon paper preform is filled with resins of different curing degrees. Further, the higher the hot pressing temperature, the higher the degree of curing of the resin as a whole, the less the content of incompletely cured resin, the fewer bubbles generated during carbonization, the fewer holes formed after carbonization, and therefore the lower the porosity. Therefore, the first surface and the second surface of the carbon paper precursor are hot pressed at different temperatures, and carbon paper with different porosities in the top and bottom layers can be obtained after carbonization and graphitization. Moreover, since the temperature inside the carbon paper precursor presents a gradient change, a gradient porosity is formed inside the obtained carbon paper. In addition, the higher the degree of curing of the resin, the more resin carbon remains in the gaps between the carbon fibers after carbonization, and the higher the mechanical strength. Similarly, the lower the hot pressing temperature, the more holes are formed, but the less resin carbon remains, and the mechanical strength is reduced.

[0044] In a specific example, the hot pressing temperature difference between the first surface and the second surface is 20°C to 140°C. Optionally, the hot pressing temperature difference between the first surface and the second surface can be 20°C, 30°C, 40°C, 50°C, 60°C, 70°C, 80°C, 90°C, 100°C, 110°C, 120°C, 130°C or 140°C. It is understandable that the hot pressing temperature difference between the first surface and the second surface can also be other suitable choices within the range of 20°C to 140°C. By regulating the hot pressing temperature difference between the first surface and the second surface, the top layer and the bottom layer of the carbon paper can have a suitable porosity difference, which is beneficial to the diffusion of the reaction gas and the discharge of the product water when used to prepare the gas diffusion layer.

[0045] In a specific example, the hot pressing temperature difference between the first surface and the second surface is 60° C. to 120° C. When the hot pressing temperature difference between the first surface and the second surface satisfies the above relationship, the gradient pore structure of the carbon paper can be further improved.

[0046] In a specific example, the hot pressing temperature of the first surface is 160°C to 300°C. Optionally, the hot pressing temperature of the first surface can be 160°C, 170°C, 180°C, 190°C, 200°C, 210°C, 220°C, 230°C, 240°C, 250°C, 260°C, 270°C, 280°C, 290°C or 300°C. It is understandable that the hot pressing temperature of the first surface can also be other suitable selections within the range of 160°C to 300°C. When the hot pressing temperature is within the above range, the curing degree of the resin on the first surface is high, the porosity of the surface after carbonization is low, but the residual carbon rate is high, and the mechanical strength of the surface is high.

[0047] In a specific example, the hot pressing temperature of the second surface is 140°C to 180°C. Optionally, the hot pressing temperature of the second surface may be 140°C, 145°C, 150°C, 155°C, 160°C, 165°C, 170°C, 175°C or 180°C. It is understandable that the hot pressing temperature of the second surface may also be other suitable choices within the range of 140°C to 180°C. When the hot pressing temperature is within the above range, the degree of curing of the resin on the second surface is low, the residual carbon rate of the surface after carbonization is low, and the mechanical strength is poor; however, the porosity of the surface is high, and it can form a suitable porosity difference with the first surface, which is beneficial to the diffusion of the reaction gas and the discharge of the product water when used to prepare the gas diffusion layer.

[0048] In a specific example, the pressure of the hot pressing treatment is 0.1MPa to 4MPa. Optionally, the pressure of the hot pressing treatment can be 0.1MPa, 0.5MPa, 1MPa, 1.5MPa, 2MPa, 2.5MPa, 3MPa, 3.5MPa or 4MPa. It is understandable that the pressure of the hot pressing treatment can also be other suitable selections within the range of 0.1MPa to 4MPa. When the hot pressing pressure is less than 0.1MPa, the obtained carbon paper is not flat enough, which is not conducive to processing and assembly when used to prepare a gas diffusion layer. When the hot pressing pressure is greater than 4MPa, it may cause the carbon fiber to break and reduce the mechanical strength of the carbon paper.

[0049] In a specific example, the time of the hot pressing treatment is 2 minutes to 60 minutes. Optionally, the time of the hot pressing treatment can be 2 minutes, 10 minutes, 20 minutes, 30 minutes, 40 minutes, 50 minutes or 60 minutes.

[0050] It is understandable that in actual production, different hot pressing temperatures can be obtained by controlling the heating temperatures of the upper mold and the lower mold of the hot pressing equipment. Exemplarily, the carbon paper precursor is placed in a hot pressing device, and the first surface is in contact with the upper mold, and the second surface is in contact with the lower mold. The heating temperatures of the upper mold and the lower mold are set according to the hot pressing temperatures of the first surface and the second surface, respectively, and hot pressing treatment is performed under a preset pressure and time to solidify the resin. It should be noted that the temperature of the upper mold and the lower mold can be controlled relatively independently. The above method does not require additional processes and equipment, and is simple to operate, which is convenient for large-scale production.

[0051] Step S300: performing carbonization and graphitization treatment on the carbon paper preform.

[0052] In a specific example, the temperature of the carbonization treatment is 800° C. to 1800° C., and the time of the carbonization treatment is 1 hour to 100 hours.

[0053] In a specific example, the temperature of the graphitization treatment is 2000° C. to 2800° C., and the time of the graphitization treatment is 0.5 h to 100 h.

[0054] The method for preparing the carbon paper adopts different temperatures to perform hot pressing on the first surface and the second surface of the carbon paper precursor, and controls the curing process of the resin by controlling the hot pressing temperature, thereby adjusting the porosity of the obtained carbon paper. Specifically, on the first surface with a higher hot pressing temperature, the resin curing degree is higher and the uncured resin content is less. During the carbonization treatment, fewer bubbles are generated and fewer pores are formed, so the porosity is relatively low. Correspondingly, on the second surface of the carbon paper precursor, the resin curing degree is lower, and more pores are formed after the carbonization treatment, so the porosity is relatively high. In this way, after the graphitization treatment, a carbon paper with a porosity gradient change can be obtained, and its mass transfer and conduction properties are good. Since the above preparation method only improves the conditions of the hot pressing treatment, no other processes or equipment are added, and the preparation steps are few and the production process is simple, it is convenient for large-scale production.

[0055] One embodiment of the present application provides an application of the carbon paper obtained according to the above preparation method in the preparation of a fuel cell.

[0056] In one specific example, the fuel cell is a proton exchange membrane fuel cell.

[0057] In a specific example, a fuel cell includes a gas diffusion material, the gas diffusion material includes a stacked substrate layer and a microporous layer, and the material for preparing the substrate layer includes carbon paper prepared by the above preparation method. The gas diffusion material has good mass transfer and conductivity performance, can improve the diffusion rate of the reaction gas; and can timely discharge the water generated by the reaction to avoid flooding.

[0058] In order to make the purpose and advantages of the present application more clearly understood, the present application is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and are not used to limit the present application.

[0059] Example 1

[0060] (1) A 0.1 g / mL phenolic resin dispersion is provided, wherein the dispersant is ethanol.

[0061] (2) The carbon fiber felt (wherein the carbon fiber length in the carbon fiber felt is 10 mm) is immersed in the resin dispersion of step (1) and dried at 70° C. to obtain a resin dispersion having a content of 20 g / m 2 Carbon paper precursor.

[0062] (3) The carbon paper precursor prepared in step (2) is placed in a flat vulcanization press for hot pressing to prepare a carbon paper preform. The temperature of the upper mold of the flat vulcanization press is 220°C, the temperature of the lower mold of the flat vulcanization press is 160°C, the hot pressing pressure is 2.0MPa, and the time is 10min. It should be noted that the temperature of the upper mold is the hot pressing temperature of the first surface, the temperature of the lower mold is the hot pressing temperature of the second surface, and the upper mold and the lower mold of the flat vulcanization press are independently controlled to maintain a constant temperature.

[0063] (4) The carbon paper preform prepared in step (3) is carbonized at 1200° C. for 30 h, and then graphitized at 2400° C. for 2 h to obtain carbon paper.

[0064] Example 2

[0065] The method is basically the same as Example 1, except that the temperature of the upper mold in step (3) is 300°C.

[0066] Example 3

[0067] It is basically the same as Example 1, except that the temperature of the upper mold in step (3) is 250°C.

[0068] Example 4

[0069] The method is basically the same as Example 1, except that in step (3), the temperature of the upper mold is 160°C and the temperature of the lower mold is 140°C.

[0070] Example 5

[0071] The same as Example 1, except that the concentration of the resin dispersion in step (1) is 0.05 g / mL, and the resin content is 10 g / mL. 2 Carbon paper precursor.

[0072] Example 6

[0073] The same as Example 1, except that the concentration of the resin dispersion in step (1) is 0.2 g / mL, and the resin content is 40 g / mL. 2 Carbon paper precursor.

[0074] Example 7

[0075] The same as Example 1, except that the concentration of the resin dispersion in step (1) is 0.4 g / mL, and the resin content is 80 g / mL. 2 Carbon paper precursor.

[0076] Example 8

[0077] The same as Example 1, except that the concentration of the resin dispersion in step (1) is 0.6 g / mL, and the resin content is 120 g / mL. 2 Carbon paper precursor.

[0078] Example 9

[0079] The same as Example 1, except that the concentration of the resin dispersion in step (1) is 1 g / mL, and the resin content is 200 g / mL. 2 Carbon paper precursor.

[0080] Example 10

[0081] It is basically the same as Example 1, except that the pressure of the hot pressing treatment in step (3) is 0.1 MPa.

[0082] Embodiment 11

[0083] It is basically the same as Example 1, except that the pressure of the hot pressing treatment in step (3) is 1 MPa.

[0084] Example 12

[0085] It is basically the same as Example 1, except that the pressure of the hot pressing treatment in step (3) is 3 MPa.

[0086] Example 13

[0087] It is basically the same as Example 1, except that the pressure of the hot pressing treatment in step (3) is 4 MPa.

[0088] Comparative Example 1

[0089] It is basically the same as Example 1, except that in step (3), the temperature of the upper mold is 160°C, and the temperature of the lower mold is 160°C.

[0090] Comparative Example 2

[0091] It is basically the same as Example 1, except that in step (3), the temperature of the upper mold is 200°C, and the temperature of the lower mold is 200°C.

[0092] Comparative Example 3

[0093] It is basically the same as Example 1, except that in step (3), the temperature of the upper mold is 250°C, and the temperature of the lower mold is 250°C.

[0094] Performance Testing

[0095] The carbon papers prepared in the embodiments and comparative examples were tested, and the results are shown in Table 1. A three-dimensional micro / nano imaging X-ray microscope (model: 3D Micro / NanoXCT) was used to directly read the porosity of the first surface and the second surface corresponding to each embodiment and comparative example. "P1" represents the porosity of the first surface (i.e., the surface in contact with the upper mold), and "P2" represents the porosity of the second surface (i.e., the surface in contact with the lower mold). "P2-P1" represents the difference between the porosity of the second surface and the first surface of the carbon paper.

[0096] Table 1

[0097]

[0098]

[0099] As can be seen from Table 1, the porosity of the first surface and the second surface of the carbon paper prepared by the preparation method of the embodiment is quite different. Comparative Examples 1 to 3 use the same temperature to hot press the first surface and the second surface of the carbon paper precursor, and the porosity of the two surfaces of the carbon paper is basically the same, wherein the temperature of the lower mold of Comparative Example 1 is the same as that of Example 1, and the only difference is the temperature of the upper mold, but the difference between the porosity of the upper and lower surfaces of the two is quite different; similarly, the temperature of the upper mold of Comparative Example 3 is the same as that of Example 3, and the only difference is the temperature of the lower mold, and the difference in porosity between the two is also quite different. When the carbon paper has a gradient porosity, there is a pressure difference on both sides, and the greater the difference in porosity on both sides, the greater the pressure difference. Such a structure can not only promote the diffusion of the reaction gas, but more importantly, it is conducive to the discharge of the generated water. In addition, compared with Example 1, the concentration of the resin dispersion used in Example 5 is lower, so its tensile strength is lower, while the concentration of the resin dispersion used in Examples 6 to 9 is higher, so its tensile strength is higher.

[0100] The technical features of the above-described embodiments may be arbitrarily combined. To make the description concise, not all possible combinations of the technical features in the above-described embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0101] The above-described embodiments only express several implementation methods of the present application, and the descriptions thereof are relatively specific and detailed, but they cannot be construed as limiting the scope of the patent application. It should be pointed out that, for a person of ordinary skill in the art, several variations and improvements can be made without departing from the concept of the present application, and these all belong to the protection scope of the present application. Therefore, the protection scope of the patent application shall be subject to the attached claims, and the description may be used to interpret the content of the claims.

Claims

1. A method for preparing carbon paper, characterized in that: The steps include: The carbon fiber felt is impregnated in a resin dispersion and dried to prepare a carbon paper precursor; the resin in the resin dispersion is a thermosetting resin; the concentration of the resin dispersion is 0.05 g / mL to 1.0 g / mL; the content of the resin in the carbon paper precursor is 10 g / mL. 2 ~200g / m 2 ; Performing a hot pressing treatment on the carbon paper precursor, and controlling the hot pressing temperature of the first surface of the carbon paper precursor to be higher than the hot pressing temperature of the second surface during the hot pressing treatment, to prepare a carbon paper preform; as well as Carrying out carbonization and graphitization treatment on the carbon paper preform; Among them, the first surface and the second surface are two opposite surfaces of the carbon paper precursor; the hot pressing temperature of the first surface is 160℃~300℃; the hot pressing temperature of the second surface is 140℃~180℃; the hot pressing temperature difference between the first surface and the second surface is 20℃~140℃.

2. The method for preparing carbon paper according to claim 1, characterized in that: The hot pressing temperature difference between the first surface and the second surface is 60° C. to 120° C.

3. The method for preparing carbon paper according to any one of claims 1 to 2, characterized in that: The pressure of the hot pressing treatment is 0.1 MPa to 4 MPa.

4. The method for preparing carbon paper according to any one of claims 1 to 2, characterized in that: The hot pressing time is 2 minutes to 60 minutes.

5. The method for preparing carbon paper according to any one of claims 1 to 2, characterized in that: The dispersant in the resin dispersion is at least one of ethanol, isopropanol, methanol and acetone.

6. The method for preparing carbon paper according to any one of claims 1 to 2, characterized in that: The length of the carbon fibers in the carbon fiber felt is 3 mm to 20 mm.

7. The method for preparing carbon paper according to any one of claims 1 to 2, characterized in that: The thermosetting resin includes at least one of phenolic resin, furfural resin, epoxy resin and furan resin.

8. The method for preparing carbon paper according to any one of claims 1 to 2, characterized in that: The temperature of the carbonization treatment is 800° C. to 1800° C., and the time of the carbonization treatment is 1 hour to 100 hours.

9. The method for preparing carbon paper according to any one of claims 1 to 2, characterized in that: The temperature of the graphitization treatment is 2000° C. to 2800° C., and the time of the graphitization treatment is 0.5 h to 100 h.

10. Use of the carbon paper obtained by the preparation method according to any one of claims 1 to 9 in the preparation of a fuel cell.

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