Fuel cell gas diffusion layer carbon paper and preparation method thereof

Abstract

The present invention relates to fuel cell gas diffusion layer carbon paper and its preparation method. The method comprises adding carbon fibers to water, adding anionic latex and a cationic agent to the mixture for dispersion, and finally subjecting the mixture to papermaking, pressing, drying, hot pressing, and carbonization to produce the fuel cell gas diffusion layer carbon paper. This preparation method involves adding anionic latex and a cationic agent to a slurry, which undergo an electrical neutralization reaction to form floccules. This allows the carbon fibers to be effectively bonded during the papermaking process through the bridging action of the floccules. The resulting carbon paper exhibits excellent air permeability, good strength, and resistivity. The entire preparation process is simple and environmentally friendly.

Description

Technical Field

[0001] The present invention relates to the technical field of fuel cells, and in particular to a fuel cell gas diffusion layer carbon paper and a preparation method thereof. Background Art

[0002] Hydrogen is currently considered one of the most promising clean energy sources in the low-carbon sector. As one of the most important hydrogen conversion devices, proton exchange membrane fuel cells (PEMFCs) have attracted widespread attention from researchers both domestically and internationally. Due to their low operating temperature, long service life, simple operation, and high startup efficiency, PEMFCs are considered an ideal energy source for various stationary and mobile devices, such as automobiles, distributed thermal power plants, and mobile devices.

[0003] As a core component of proton exchange membrane fuel cells, the gas diffusion layer (GDL) not only supports the catalyst layer but also stabilizes the electrode structure. Furthermore, it provides gas, drainage, ion, and current channels for fuel cell operation. Carbon paper is often used as the substrate material for the GDL in PEMFCs due to its uniform pore structure, good electrical conductivity, and excellent heat and corrosion resistance.

[0004] The main production process for carbon paper involves wet forming of carbon fibers, impregnation with resin, hot pressing and curing, carbonization, and graphitization. However, due to the lack of active groups on the carbon fibers' surfaces, chemical bonds between the fibers are difficult to form after wet forming, making it difficult to produce carbon paper with good strength. Therefore, an adhesive must be added to enhance the strength of the paper. Currently, this method often involves impregnation with phenolic resin. However, the use of phenolic resin results in the volatilization of large amounts of organic solvents, which is detrimental to the ecological environment. Furthermore, the impregnation method makes it difficult to control the amount of phenolic resin applied, resulting in uneven distribution of the adhesive on the carbon paper.

[0005] The Chinese patent with authorization announcement number CN114457620B and authorization announcement date 2023.03.21 uses carbon fiber to prepare a certain amount of vapor-grown carbon fiber and copper powder as the main raw materials, and water-soluble polyvinyl alcohol fiber as the reinforcing fiber. The raw materials are first stirred at high speed in a blender, then stirred at low speed and a dispersant is added to evenly disperse the above raw materials in water. A wet papermaking process is used to make base paper, and then the paper is impregnated with phenolic resin, hot pressed, carbonized, and graphitized to produce carbon paper for proton exchange membrane fuel cells. However, the carbon paper preparation process is complicated, and a large amount of organic solvent (anhydrous ethanol) is required to prepare the phenolic resin impregnation solution. The volatilization of organic solvents is harmful to the environment. In addition, the amount of glue applied by the phenolic resin impregnation method is small, and the tensile strength of the carbon paper is poor.

[0006] The Chinese patent with authorization announcement number CN114457620B and authorization announcement date 2023.03.21 will make a carbon fiber suspension composed of a fibrous binder, water, a dispersant and carbon fibers with different aspect ratios, and then make paper and dry it to obtain a carbon fiber base paper, and then carbonize and graphitize it to obtain a gas diffusion layer carbon paper for a proton exchange membrane fuel cell; the fibrous binder is a composite fiber or blended fiber composed of a phenolic resin and other resins, which reduces the step of impregnating the base paper with resin and reduces the subsequent coating preparation of the microporous layer. However, the fibrous binder in this invention is prepared by dry spinning or wet spinning and then added to the slurry. The process is too complicated, energy consumption is high, and the cost is high. Summary of the Invention

[0007] The technical problem to be solved by the present invention is: In view of the problems that the current preparation process of carbon paper for fuel cell gas diffusion layer is complicated and the use of a large amount of organic solvents causes serious environmental pollution, a fuel cell gas diffusion layer carbon paper and its preparation method are proposed.

[0008] The present invention provides a method for preparing carbon paper for a fuel cell gas diffusion layer, comprising the following steps:

[0009] (1) adding carbon fiber to water to prepare a carbon fiber slurry with a mass concentration of 0.05% to 0.5%;

[0010] Add 0.05%-0.8% dispersant relative to the mass of carbon fiber and mix well;

[0011] Adding 100% to 600% of anionic latex relative to the mass of the carbon fiber, and mixing again to obtain a carbon fiber / latex suspension;

[0012] (2) stirring the carbon fiber / latex suspension and slowly adding a cationic agent to obtain a carbon fiber suspension adsorbed with an adhesive;

[0013] The suspension is dispersed in a high-speed disperser, and then formed into a sheet in a papermaking machine, pressed, and dried to obtain a carbon paper base;

[0014] The fuel cell gas diffusion layer carbon paper is obtained through hot pressing and carbonization.

[0015] Preferably, the dispersant in step (1) is polyethylene oxide or polyacrylamide.

[0016] Preferably, the latex described in step (1) is nitrile latex, styrene acrylic latex or phenolic resin latex.

[0017] Preferably, the cationic agent in step (2) can be aluminum sulfate, polydimethyldiallylammonium chloride or polyethyleneimine.

[0018] Preferably, the drying temperature in step (2) is 80-120° C., and the drying time is 15-60 min.

[0019] Preferably, the hot pressing treatment temperature in step (2) is 150-210° C., the pressure is 2.5-10 MPa, and the time is 20-120 min.

[0020] Preferably, the carbonization conditions in step (2) are under nitrogen atmosphere, the carbonization temperature is 800-1600° C., and the carbonization time is 30-90 min.

[0021] The present invention also provides a fuel cell gas diffusion layer carbon paper prepared by the above method, which has a basis weight of 40-200 g / m 2 .

[0022] Beneficial effects of the present invention:

[0023] (1) The adhesive used in the present invention is an anionic latex. By slowly adding a cationic agent into the slurry to form floccules, the carbon fibers are effectively combined together, eliminating the subsequent resin impregnation process, simplifying the carbon paper preparation process, avoiding the use of organic solvents, and reducing environmental pollution.

[0024] (2) The present invention uniformly adsorbs the adhesive on the surface of the carbon fiber, so that the adhesive and the carbon fiber form a stable three-dimensional network structure, thereby improving the toughness of the carbon paper, increasing the air permeability of the carbon paper, and improving the uniformity of the carbon paper pores. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 This is a physical picture of the slurry flocculation prepared in Example 1 of the present invention;

[0026] Figure 2 This is a physical picture of the carbon paper base prepared in Example 1 of the present invention;

[0027] Figure 3 This is a physical picture of the carbon paper prepared in Example 1 of the present invention. DETAILED DESCRIPTION

[0028] In order to simplify the carbon paper preparation process and reduce the pollution to the environment caused by organic solvents, the present invention provides a fuel cell gas diffusion layer carbon paper with excellent air permeability, simple process and environmental protection, and a preparation method thereof.

[0029] The method for preparing carbon paper for fuel cell gas diffusion layer provided in the embodiment of the present application is as follows:

[0030] (1) Add carbon fiber to water to prepare a carbon fiber slurry with a mass concentration of 0.05%-0.5%. Add 0.05%-0.8% of a dispersant (which may be polyethylene oxide or polyacrylamide) relative to the mass of the carbon fiber, stir for 1-3 minutes in a stirrer at a speed of 30-300 rpm to mix evenly. Then add 100%-600% of latex (nitrile latex, styrene acrylic latex or phenolic resin latex) relative to the mass of the carbon fiber, stir for 2-8 minutes in a stirrer at a speed of 200-500 rpm to obtain a uniformly mixed carbon fiber / latex suspension.

[0031] (2) The carbon fiber / latex suspension is placed in a stirrer with a rotation speed of 200-500 rpm and stirred. At the same time, a cationic agent (aluminum sulfate, polydimethyldiallyl ammonium chloride or polyethyleneimine) is slowly added to obtain a carbon fiber suspension adsorbed with an adhesive. The suspension is dispersed in a high-speed disperser for 1-5 minutes, then formed in a papermaking machine, pressed, and dried at a temperature of 80-120°C for 15-60 minutes to obtain a carbon paper base. The carbon paper base is hot pressed in a hot press at a temperature of 150-210°C and a pressure of 2.5-10MPa for 20-120 minutes, and finally carbonized in an atmosphere furnace at 800-1600°C for 30-90 minutes to obtain a quantitative carbon paper of 40-200g / m 2 Carbon paper for fuel cell gas diffusion layers.

[0032] Principle of the present invention:

[0033] The lack of active functional groups on the surface of carbon fibers makes them less likely to bind and react with other compounds. Furthermore, due to their large aspect ratio, carbon fibers tend to agglomerate in water, making them difficult to disperse evenly in water and resulting in poor carbon paper uniformity. The present invention adds a dispersant to the carbon fiber slurry to form a wet film on the carbon fiber surface, enhancing the sliding energy efficiency between the carbon fibers and facilitating their dispersion in water.

[0034] The latex used in this invention is a negatively charged anionic polymer. By first adding the latex to the slurry and then slowly adding the positively charged cationic agent, the anionic and cationic polymers react through a pairing neutralization reaction with zwitterions to form flocs. During the floc formation process, the latex becomes less stable and easily collides with carbon fibers to form larger flocs, promoting the connection between the carbon fibers.

[0035] The present invention utilizes the property that latex and cationic agent undergo electrical neutralization reaction in the pulp to produce floccules, and utilizes the floccules to effectively combine the carbon fibers in the pulp during the formation process. Therefore, no other adhesives need to be applied in the subsequent process, which greatly simplifies the preparation process of carbon paper.

[0036] Traditional carbon paper is mainly made of carbon fibers, and a phenolic resin impregnation method is used to introduce an adhesive between the carbon fibers. However, the resin matrix is ​​very brittle, and the impregnation method causes uneven gluing, resulting in poor toughness and easy breakage of the carbon paper. To improve the bendability of carbon paper, latex can be added to the slurry to improve the bendability. However, since there are no active groups on the surface of the carbon fibers to chemically bond with the latex, adding the latex directly to the slurry will cause a large amount of latex to be lost during wet forming. The present invention utilizes a method of slowly adding a cationic agent to allow the latex to be present in the slurry in the form of flocculent particles. During the stirring process, a stable three-dimensional network structure is formed with the carbon fibers, which is beneficial to the retention and dispersion of the flocculents in the slurry, thereby improving the bendability and air permeability of the carbon paper.

[0037] Example 1

[0038] (1) Carbon fibers were added to water to prepare a carbon fiber slurry having a mass concentration of 0.1%. Polyethylene oxide was then added at 0.5% relative to the mass of the carbon fibers, and the mixture was stirred in a stirrer at 200 rpm for 2 minutes to mix uniformly. A butadiene-acrylonitrile latex was then added at 200% relative to the mass of the carbon fibers, and the mixture was stirred in a stirrer at 400 rpm for 5 minutes to obtain a uniformly mixed carbon fiber / latex suspension.

[0039] (2) The carbon fiber / latex suspension is placed in a stirrer at a speed of 350 rpm and stirred, while aluminum sulfate is slowly added to obtain a carbon fiber suspension adsorbed with an adhesive. The suspension is dispersed in a high-speed disperser for 3 minutes, then formed into a sheet in a papermaking machine, pressed, and dried at a temperature of 90°C for 30 minutes to obtain a carbon paper base. The carbon paper base is hot-pressed in a hot press at a temperature of 180°C and a pressure of 5MPa for 40 minutes, and finally carbonized in an atmosphere furnace at 1000°C for 40 minutes to obtain a carbon paper base with a basis weight of 50g / m 2 Carbon paper for fuel cell gas diffusion layers.

[0040] Example 2

[0041] (1) Carbon fibers were added to water to prepare a carbon fiber slurry having a mass concentration of 0.1%. Polyacrylamide was then added at a concentration of 0.5% relative to the mass of the carbon fibers, and the mixture was stirred in a stirrer at a speed of 250 rpm for 3 minutes to mix uniformly. A butyronitrile latex was then added at a concentration of 200% relative to the mass of the carbon fibers, and the mixture was stirred in a stirrer at a speed of 450 rpm for 4 minutes to obtain a uniformly mixed carbon fiber / latex suspension.

[0042] (2) The carbon fiber / latex suspension is placed in a stirrer at a speed of 400 rpm and stirred, and at the same time, polydimethyldiallyl ammonium chloride is slowly added to obtain a carbon fiber suspension adsorbed with an adhesive. The suspension is dispersed in a high-speed disperser for 4 minutes, then formed into a sheet in a papermaking machine, pressed, and dried at a temperature of 105°C for 40 minutes to obtain a carbon paper base. The carbon paper base is hot pressed in a hot press at a temperature of 180°C and a pressure of 5MPa for 40 minutes, and finally carbonized in an atmosphere furnace at 1100°C for 60 minutes to obtain a carbon paper base with a basis weight of 60g / m 2 Carbon paper for fuel cell gas diffusion layers.

[0043] Example 3

[0044] (1) Carbon fibers were added to water to prepare a carbon fiber slurry having a mass concentration of 0.1%. Polyethylene oxide was then added at 0.5% relative to the mass of the carbon fibers, and the mixture was stirred in a stirrer at 280 rpm for 2 minutes to mix uniformly. Styrene acrylic latex was then added at 200% relative to the mass of the carbon fibers, and the mixture was stirred in a stirrer at 250 rpm for 4 minutes to obtain a uniformly mixed carbon fiber / latex suspension.

[0045] (2) The carbon fiber / latex suspension was stirred in a stirrer at a speed of 300 rpm, and polyethyleneimine was slowly added at the same time to obtain a carbon fiber suspension adsorbed with an adhesive. The suspension was dispersed in a high-speed disperser for 3 minutes, and then formed into a sheet in a papermaking machine, pressed, and dried at a temperature of 105°C for 40 minutes to obtain a carbon paper base. The carbon paper base was hot pressed in a hot press at a temperature of 150°C and a pressure of 5MPa for 20 minutes, and finally carbonized in an atmosphere furnace at 900°C for 30 minutes to obtain a carbon paper with a basis weight of 80g / m 2 Carbon paper for fuel cell gas diffusion layers.

[0046] Example 4

[0047] (1) Carbon fibers were added to water to prepare a carbon fiber slurry having a mass concentration of 0.1%. Polyethylene oxide was then added at 0.5% relative to the mass of the carbon fibers, and the mixture was stirred in a stirrer at 250 rpm for 2 minutes to mix uniformly. Phenolic resin latex was then added at 200% relative to the mass of the carbon fibers, and the mixture was stirred in a stirrer at 450 rpm for 7 minutes to obtain a uniformly mixed carbon fiber / latex suspension.

[0048] (2) The carbon fiber / latex suspension is placed in a stirrer at a speed of 400 rpm and stirred, while aluminum sulfate is slowly added to obtain a carbon fiber suspension adsorbed with an adhesive. The suspension is dispersed in a high-speed disperser for 4 minutes, then formed into sheets in a papermaking machine, pressed, and dried at a temperature of 105°C for 25 minutes to obtain a carbon paper base. The carbon paper base is hot pressed in a hot press at a temperature of 170°C and a pressure of 5MPa for 20 minutes, and finally carbonized in an atmosphere furnace at 1100°C for 60 minutes to obtain a carbon paper base with a basis weight of 90g / m 2 Carbon paper for fuel cell gas diffusion layers.

[0049] Comparative Example 1

[0050] (1) Carbon fibers were added to water to prepare a carbon fiber slurry having a mass concentration of 0.1%. Then, nitrile butadiene rubber latex (200% by mass relative to the mass of the carbon fibers) was added, and the mixture was stirred in a stirrer at a speed of 400 rpm for 5 minutes to obtain a uniformly mixed carbon fiber / latex suspension.

[0051] (2) The carbon fiber / latex suspension was stirred in a stirrer at a speed of 350 rpm, while aluminum sulfate was slowly added to obtain a carbon fiber suspension adsorbed with an adhesive. The suspension was dispersed in a high-speed disperser for 3 minutes, then formed into sheets in a papermaking machine, pressed, and dried at 90°C for 30 minutes to obtain a carbon paper base. The carbon paper base was hot pressed in a hot press at a temperature of 180°C and a pressure of 5 MPa for 40 minutes, and finally carbonized in an atmosphere furnace at 1000°C for 40 minutes to obtain a fuel cell gas diffusion layer carbon paper.

[0052] Comparative Example 2

[0053] (1) Carbon fibers were added to water to prepare a carbon fiber slurry with a mass concentration of 0.1%. Then, 0.5% of polyethylene oxide and 10% of polyvinyl alcohol fibers were added relative to the mass of the carbon fibers. The mixture was stirred in a stirrer at 400 rpm for 5 minutes to obtain a uniformly mixed carbon fiber / polyvinyl alcohol fiber suspension.

[0054] (2) The carbon fiber / polyvinyl alcohol fiber suspension was formed in a papermaking machine, pressed, and dried at 105°C for 30 minutes to obtain a carbon paper base. The carbon paper base was impregnated with a phenolic resin / ethanol solution, dried at 80°C for 20 minutes, and then hot-pressed in a hot press at 180°C and 5 MPa for 40 minutes. Finally, it was carbonized in an atmosphere furnace at 1000°C for 40 minutes to obtain a fuel cell gas diffusion layer carbon paper.

[0055] Comparative Example 3

[0056] (1) Carbon fibers were added to water to prepare a carbon fiber slurry having a mass concentration of 0.1%. Then, nitrile butadiene rubber latex (200% by mass relative to the mass of the carbon fibers) was added, and the mixture was stirred in a stirrer at a speed of 400 rpm for 5 minutes to obtain a uniformly mixed carbon fiber / latex suspension.

[0057] (2) The carbon fiber / latex suspension was formed into a sheet in a papermaking machine, pressed, and dried at 90°C for 30 minutes to obtain a carbon paper base. The carbon paper base was hot pressed in a hot press at 180°C and 5 MPa for 40 minutes, and finally carbonized in an atmosphere furnace at 1000°C for 40 minutes to obtain a fuel cell gas diffusion layer carbon paper.

[0058] Gas diffusion layer carbon paper performance test:

[0059] The carbon papers prepared in the above examples and comparative examples were tested for properties such as bending stiffness, air permeability, resistivity, and tensile strength. The test results are shown in Table 1.

[0060] Table 1 Comparison of gas diffusion layer carbon paper properties

[0061]

[0062]

[0063] As shown in Examples 1-2 and Comparative Example 1 (without adding a dispersant) in Table 1, adding a dispersant can significantly improve the air permeability, electrical conductivity, and tensile strength of carbon paper. This is mainly because uniformity is one of the main factors affecting the performance of carbon paper, and the addition of a dispersant improves the uniformity of carbon paper, thereby improving its performance. As shown in Examples 1-4 and Comparative Example 2 (impregnated with phenolic resin) in Table 1, carbon paper prepared using latex has good resistivity and tensile strength, and its bendability and air permeability are better than those prepared using the traditional process (impregnated with phenolic resin). As shown in Examples 1-4 and Comparative Example 3 (without adding a cationic agent) in Table 1, adding a cationic agent helps retain the latex and increases the bonding force between the carbon fibers, thereby increasing the tensile strength of the carbon paper, and effectively improving its bendability and electrical conductivity.

[0064] In summary, the carbon paper of the present invention has excellent comprehensive performance. While ensuring good electrical conductivity and mechanical properties, it not only has excellent bending and deformation capabilities, but also has good air permeability, so it has good practical application value.

[0065] The above description is only a preferred embodiment of the present invention and does not limit the invention in any other form. Any technician familiar with the profession may use the technical content disclosed above to change or modify it into an equivalent embodiment with equivalent changes. However, any simple modification, equivalent change and modification made to the above embodiment based on the technical essence of the present invention without departing from the content of the technical solution of the present invention still falls within the scope of protection of the technical solution of the present invention.

Claims

1. A method for preparing carbon paper for a fuel cell gas diffusion layer, characterized in that: (1) Add carbon fiber to water to prepare a carbon fiber slurry with a mass concentration of 0.05%-0.5%; Add 0.05%-0.8% dispersant relative to the mass of carbon fiber and mix well; Adding 100% to 600% of the anionic latex relative to the mass of the carbon fiber, and mixing again to obtain a carbon fiber / latex suspension; (2) stirring the carbon fiber / latex suspension and slowly adding a cationic agent to obtain a carbon fiber suspension adsorbed with an adhesive; the cationic agent is aluminum sulfate, polydimethyldiallylammonium chloride or polyethyleneimine; The suspension is dispersed in a high-speed disperser, and then formed into a sheet in a papermaking machine, pressed, and dried to obtain a carbon paper base; The fuel cell gas diffusion layer carbon paper is obtained through hot pressing and carbonization.

2. The method for preparing carbon paper for a fuel cell gas diffusion layer according to claim 1, wherein: The dispersant in step (1) is polyethylene oxide or polyacrylamide.

3. The method for preparing carbon paper for a fuel cell gas diffusion layer according to claim 1, wherein: The latex described in step (1) is nitrile latex, styrene acrylic latex or phenolic resin latex.

4. The method for preparing carbon paper for a fuel cell gas diffusion layer according to claim 1, wherein: The drying temperature in step (2) is 80-120° C., and the drying time is 15-60 min.

5. The method for preparing carbon paper for a fuel cell gas diffusion layer according to claim 1, wherein: The hot pressing treatment temperature in step (2) is 150-210°C, the pressure is 2.5-10 MPa, and the time is 20-120 min.

6. The method for preparing carbon paper for a fuel cell gas diffusion layer according to claim 1, wherein: The carbonization conditions in step (2) are in a nitrogen atmosphere, the carbonization temperature is 800-1600° C., and the carbonization time is 30-90 min.

7. A fuel cell gas diffusion layer carbon paper, obtained by the preparation method according to any one of claims 1 to 6, having a basis weight of 40-200 g / m 2 .

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