Carbon paper for fuel cell, preparation method of carbon paper and fuel cell

Abstract

The invention provides carbon paper for a fuel cell, a preparation method of the carbon paper and the fuel cell, and the preparation method of the carbon paper for the fuel cell comprises the following steps: providing a polytetrafluoroethylene film, and preparing slurry which comprises graphitized carbon fibers, carbon nanotubes, polytetrafluoroethylene emulsion, phenolic resin dry powder, ethylene glycol, deionized water and triton; coining the slurry on the polytetrafluoroethylene film by using the polytetrafluoroethylene film as a substrate and adopting a silk-screen printing process to prepare a carbon paper blank; putting the carbon paper blank into a drying oven for curing, and stripping the polytetrafluoroethylene film in the cured carbon paper blank to obtain initial carbon paper; and putting the initial carbon paper into a drying oven, and sequentially carrying out carbonization treatment and graphitization treatment under atmosphere protection to prepare the carbon paper. The method is simple in process, controllable in cost and easy for large-scale production, and the prepared carbon paper has good porosity, high transverse conductivity and high transverse gas permeability.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of fuel cells, in particular to a carbon paper for fuel cells and a preparation method thereof, and a fuel cell. BACKGROUND

[0002] Proton exchange membrane fuel cell (hereinafter referred to as fuel cell) is a power generation device that converts chemical energy into electrical energy directly through electrochemical reaction of fuel (hydrogen) and oxidant (generally air) without Carnot cycle. As a high-efficiency and clean energy conversion device, the proton exchange membrane fuel cell has become an important development direction of future new energy technology. Gas diffusion layer (GDL) is one of the core components of fuel cell, and the performance of carbon paper as the base material of GDL directly determines the energy output efficiency and long-term durability of the battery.

[0003] The ideal carbon paper needs to have multiple contradictory characteristics at the same time: extremely high longitudinal and lateral conductivity to ensure efficient charge collection and transmission; suitable and uniform pore structure to ensure smooth bidirectional transmission of reaction gas (hydrogen and oxygen) and water vapor (generated water and reaction gas humidification); excellent mechanical strength to support the catalyst layer and microporous layer and maintain structural integrity during battery stack assembly.

[0004] At present, the preparation of carbon paper mostly adopts wet papermaking process combined with subsequent resin impregnation, curing, carbonization and graphitization treatment. However, this traditional process has many inherent defects, which seriously restricts the development and application of high-performance carbon paper: (1) Balance between conductivity and gas permeability: the traditional process is difficult to accurately control the distribution orientation and pore structure of carbon fibers in three-dimensional space. In order to obtain sufficient mechanical strength, a large amount of resin binder is often needed, which will block the pores, resulting in significant reduction of the lateral conductivity and gas permeability of the carbon paper. The existing technology usually makes a difficult choice between the two, and it is difficult to achieve high performance indicators at the same time, which cannot meet the requirements of low mass transfer resistance and high conductivity of carbon paper for high power density and high durability fuel cells.

[0005] (2) Process complexity and material limitations: the wet papermaking process has very strict requirements for the parameters such as the flowability, dispersion stability and fiber length of the slurry. In order to achieve uniform papermaking, the length and diameter ratio of carbon fibers are strictly limited, and it is difficult to build a multi-scale composite structure to optimize the performance. In addition, the process is complicated, involves a large amount of water treatment, has high energy consumption, and has limited production efficiency.

[0006] (3) Difficulty in realizing structure customization and gradient: The carbon paper prepared by traditional methods is usually isotropic or single-structure sheet, which is difficult to customize the carbon paper structure with composition gradient or pore gradient distribution according to the needs of different positions (such as under-land and under-channel) or different working scenarios (such as high humidity or dry operating conditions) of fuel cells. This makes it difficult to optimize the matching of carbon paper and microporous layer (MPL), which limits the further improvement of the overall performance of the battery.

[0007] (4) Challenges of forming and demolding technology: Some new processes try to use coating method to form, but the coating process has high requirements on the rheological properties (such as viscosity and shear thinning behavior) of the slurry, which is difficult to adapt to the slurry system of multiple sizes and multiple components. In addition, it is a great challenge to completely peel off the carbon paper blank from the rigid substrate after curing without damaging its fragile microstructure, which easily leads to surface damage and powder loss of the carbon paper, seriously affecting its integrity and final performance.

[0008] (5) Contradiction between production cost and scale: The traditional wet process production line is large, high in investment cost, and not easy to carry out flexible small-batch customized production. While some laboratory preparation methods (such as vacuum filtration) are flexible, but the production efficiency is extremely low, which is difficult to scale up to realize large-scale and automatic continuous production, resulting in high cost of high-performance carbon paper, which is one of the obstacles to the commercialization of fuel cells. SUMMARY

[0009] The purpose of the present application is to provide a carbon paper for fuel cells and a preparation method thereof, and a fuel cell, which is simple in process, controllable in cost, easy to scale up, and has good porosity, high transverse electrical conductivity and high transverse gas permeability.

[0010] To achieve the above-mentioned purpose, in a first aspect, the present application provides a preparation method of a carbon paper for fuel cells, comprising the following steps: S1, providing a polytetrafluoroethylene film and preparing a slurry, wherein the slurry comprises graphitized carbon fibers, carbon nanotubes, polytetrafluoroethylene emulsion, phenolic resin dry powder, ethylene glycol, deionized water and triton; S2, using the polytetrafluoroethylene film as a substrate and adopting a screen printing process to print the slurry on the polytetrafluoroethylene film to obtain a carbon paper blank; S3, placing the carbon paper blank in an oven for curing, and peeling off the polytetrafluoroethylene film in the cured carbon paper blank to obtain an initial carbon paper; S4, placing the initial carbon paper in an oven and sequentially performing carbonization treatment and graphitization treatment under atmosphere protection to obtain a carbon paper.

[0011] Preferably, the step of preparing the slurry in step S1 comprises: mixing the graphitized carbon fibers and the carbon nanotubes according to a preset mass percentage to obtain mixed carbon fiber carbon nanotubes; and controlling the content of each component in the mixed carbon fiber carbon nanotubes to be, in terms of mass percentage of the mixed carbon fiber carbon nanotubes: graphitized carbon fibers 60%~80%; carbon nanotubes 40%~20%.

[0012] Preferably, the step of preparing the slurry in the step S1 further comprises: mixing the mixed carbon fiber carbon nanotubes, polytetrafluoroethylene emulsion, phenolic resin dry powder, ethylene glycol, deionized water, triton according to a preset weight ratio and stirring uniformly to obtain the slurry; and controlling the weight parts of each component in the slurry to be: mixed carbon fiber carbon nanotubes 10~50 parts; polytetrafluoroethylene emulsion 2~15 parts; phenolic resin dry powder 2~10 parts; ethylene glycol 20~40 parts; deionized water 20~35 parts; triton 5~10 parts.

[0013] Preferably, the polytetrafluoroethylene emulsion is a polytetrafluoroethylene emulsion with a solid content of 40%~60%.

[0014] Preferably, the length of the graphitized carbon fibers is greater than or equal to 0.5mm and less than or equal to 3mm.

[0015] Preferably, the step of using the polytetrafluoroethylene film as a substrate and adopting a silk screen printing process to press the slurry on the polytetrafluoroethylene film to obtain a carbon paper blank in the step S2 comprises: controlling the speed of the doctor blade in the silk screen printing process to be 10mm / s~50mm / s, and controlling the inclination angle of the doctor blade in the silk screen printing process to be 30°~70°.

[0016] Preferably, the step of placing the carbon paper blank in an oven for curing in the step S3 comprises: controlling the curing temperature to be 200℃~340℃, and controlling the curing time to be 10 minutes~30 minutes.

[0017] Preferably, the step of carbonizing treatment in the step S4 comprises: controlling the temperature of the carbonizing treatment to be 1200℃~1700℃, controlling the time of the carbonizing treatment to be 6h~12h, and adopting inert gas protection in the carbonizing treatment.

[0018] Preferably, the step of the graphitization treatment in the step S4 comprises: controlling the temperature of the graphitization treatment to be 2000℃-3000℃, controlling the time of the graphitization treatment to be 12h-24h, and using inert gas protection in the graphitization treatment.

[0019] Preferably, the thickness of the carbon paper prepared in the step S4 is greater than or equal to 80μm and less than or equal to 250μm.

[0020] Preferably, the carbon loading in the carbon paper prepared in the step S4 is greater than or equal to 1mg / cm² and less than or equal to 4mg / cm².

[0021] Preferably, the contact angle of the polytetrafluoroethylene film provided in the step S1 is greater than or equal to 150° and less than or equal to 170°.

[0022] In the second aspect, the present application provides a carbon paper for fuel cell, which is prepared by the above-mentioned method for preparing carbon paper for fuel cell.

[0023] Preferably, the transverse air permeability of the carbon paper is greater than or equal to 0.5μm² and less than or equal to 1μm².

[0024] Preferably, the transverse electrical conductivity of the carbon paper is greater than or equal to 0.05Ω·cm and less than or equal to 0.2Ω·cm.

[0025] Preferably, the contact angle of the carbon paper is greater than or equal to 150° and less than or equal to 180°.

[0026] In the third aspect, the present application provides a fuel cell, which comprises a proton exchange membrane, a catalytic layer and a gas diffusion layer, and the gas diffusion layer comprises the above-mentioned carbon paper and a microporous layer.

[0027] The carbon paper for fuel cell and the method for preparing the same, and the fuel cell of the present application have the following advantages: (1) The present application prints the slurry made of graphitized carbon fibers and carbon nanotubes with different sizes on a polytetrafluoroethylene film, and then performs solidification demolding, carbonization and high-temperature graphitization to prepare a high-performance carbon paper, so that the carbon paper has excellent transverse electrical conductivity and can also ensure the transverse water vapor transmission effect, i.e., the prepared carbon paper has high transverse electrical conductivity and transverse permeability, which greatly improves the performance and high-current density durability of the fuel cell.

[0028] (2) The use of the screen printing process not only allows the size of the screen holes to be customized as needed, but also has relatively low requirements for the parameters such as the flow casting and viscosity of the slurry compared to the coating process, so that carbonized carbon fibers and carbon nanotubes of different sizes can be screen printed into carbon paper, and it is also more conducive to adjusting the pore distribution and composition gradient of the carbon paper, so as to improve the porosity and transverse conductivity of the carbon paper, make the water vapor permeability of the carbon paper more uniform, and also facilitate the improvement of the conductivity of the fuel cell.

[0029] (3) The use of the screen printing process to prepare the carbon paper blank not only has simple operation, high preparation efficiency, low cost and simple process, but also can be manually operated to meet the needs of small-batch production, can be scaled up for mass production, and can realize automatic production to realize mass production application.

[0030] (4) The slurry formula of the present application is not only conducive to the realization of the screen printing process, but also balances the conductivity and air permeability of the prepared carbon paper.

[0031] (5) The present application uses a polytetrafluoroethylene film as a peelable temporary substrate to realize "dry" or "semi-dry" transfer molding, and it is also conducive to peeling the polytetrafluoroethylene film from the cured carbon paper blank, avoiding the destruction of the integrity and surface properties of the carbon paper; the use of Triton as a surfactant and phenolic resin dry powder as a binder can make the slurry have better stability effect, thereby improving the stability, conductivity, etc. of the carbon paper structure.

[0032] (7) Wide application range, different structures of carbon paper can be customized for different working scenarios of fuel cells, matched with different microporous layers, which can not only ensure high air permeability but also ensure certain water retention effect. BRIEF DESCRIPTION OF DRAWINGS

[0033] Figure 1 Flowchart of the preparation method of the carbon paper for fuel cells of the embodiments of the present application.

[0034] Figure 2 Scanning electron microscope image of the surface of the carbon paper prepared in Example 1 of the present application.

[0035] Figure 3 Data graph of the surface contact angle of the carbon paper prepared in Example 1 of the present application after hydrophobic treatment.

[0036] Figure 4 Demolding diagram of the carbon paper prepared in Example 1 of the present application. DETAILED DESCRIPTION

[0037] In order to make the objects, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be described clearly and completely below. Obviously, the described embodiments are only some but not all of the embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative efforts should fall into the scope of the present application. Unless otherwise defined, the technical terms or scientific terms used herein should be understood as the common meanings thereof by those of ordinary skill in the art to which the present application belongs. The terms such as "comprise" and the like used herein are intended to cover the elements or components appearing before the terms and the like listed after the terms and equivalents thereof, and do not exclude other elements or components.

[0038] To overcome the problems in the prior art, the embodiments of the present application provide a carbon paper for fuel cells and a preparation method thereof, and a fuel cell, which are simple in process, controllable in cost, easy to scale up, and have good porosity, high transverse electrical conductivity and high transverse gas permeability.

[0039] In some embodiments of the present application, with reference to Figure 1 , the preparation method of the carbon paper for fuel cells comprises the following steps: S1, providing a polytetrafluoroethylene film, and preparing a slurry, wherein the slurry comprises graphitized carbon fibers, carbon nanotubes, a polytetrafluoroethylene emulsion, a phenolic resin dry powder, ethylene glycol, deionized water and triton; S2, using the polytetrafluoroethylene film as a substrate and adopting a screen printing process to press the slurry on the polytetrafluoroethylene film to obtain a carbon paper blank; S3, placing the carbon paper blank into an oven for curing, and peeling off the polytetrafluoroethylene film in the cured carbon paper blank to obtain an initial carbon paper; S4, placing the initial carbon paper into an oven, and sequentially performing carbonization treatment and graphitization treatment under atmosphere protection to obtain a carbon paper.

[0040] The present application prints the slurry of graphitized carbon fibers and carbon nanotubes of different sizes on a polytetrafluoroethylene film by silk screen printing, and processes by solidification demolding, carbonization and high-temperature graphitization to obtain high-performance carbon paper, so that the carbon paper has excellent transverse electrical conductivity and can also ensure the transverse water vapor transmission effect, that is, the prepared carbon paper has high transverse electrical conductivity and transverse permeability, greatly improving the performance and high electrical density durability of the fuel cell. Using the silk screen printing process, not only can the size of the silk screen hole be customized according to needs, but also the requirements for the parameters such as the flowability and viscosity of the slurry are relatively low compared to the coating process, so that the graphitized carbon fibers and carbon nanotubes of different sizes can be silk printed into carbon paper, and it is also beneficial to adjust the pore distribution and composition gradient of the carbon paper, so as to improve the porosity and transverse electrical conductivity of the carbon paper, and make the water vapor permeability of the carbon paper more uniform, and it is also beneficial to improve the electrical conductivity of the fuel cell. The carbon paper blank prepared by the silk screen printing process not only has simple operation, high preparation efficiency, low cost and simple process, but also can be manually operated according to needs to meet the needs of small-batch production, and can be enlarged for mass production, and can realize automatic production to realize mass production application. The slurry formula of the present application is not only beneficial to realize the silk screen printing process, but also balances the electrical conductivity and air permeability of the prepared carbon paper. The present application uses a polytetrafluoroethylene film as a peelable temporary substrate to realize "dry" or "semi-dry" transfer molding, and it is also beneficial to peel the polytetrafluoroethylene film from the solidified carbon paper blank, avoiding damaging the integrity and surface performance of the carbon paper; using Triton as a surfactant and using phenolic resin dry powder as a binder can make the slurry have better stability effect, thereby improving the stability, electrical conductivity, etc. of the carbon paper structure. The application range is wide, and different structures of carbon paper can be customized for different working scenes of fuel cells, matched with different microporous layers, which can ensure high air permeability and certain water retention effect.

[0041] In some embodiments, the contact angle of the polytetrafluoroethylene film provided in step S1 is greater than or equal to 150° and less than or equal to 170°. That is, the polytetrafluoroethylene film has good hydrophobicity, so that the polytetrafluoroethylene film has good demolding properties, avoiding damage to the initial carbon paper due to peeling off the polytetrafluoroethylene film in step S3, which is beneficial to ensure that the initial carbon paper is intact, and avoids damaging the integrity and surface performance of the carbon paper.

[0042] In some embodiments, the step of providing the polytetrafluoroethylene film in step S1 comprises: cutting the polytetrafluoroethylene film, and making the size of the polytetrafluoroethylene film greater than the preset size of the carbon paper. Further, considering that the carbon paper blank will be dehydrated after being treated by solidification demolding, carbonization and high-temperature graphitization, etc., and the size of the obtained carbon paper will be smaller than that of the carbon paper blank due to dehydration, in some specific embodiments, the step of providing the polytetrafluoroethylene film in step S1 comprises: cutting the polytetrafluoroethylene film, and making the size of the polytetrafluoroethylene film greater than the size of the carbon paper blank. Specifically, after determining the preset size of the carbon paper, the size of the polytetrafluoroethylene film can be estimated according to experience, so as to determine the size of the polytetrafluoroethylene film.

[0043] In some embodiments, the step of preparing the slurry in step S1 comprises: mixing the graphitized carbon fibers and the carbon nanotubes uniformly according to a preset mass percentage to obtain mixed carbon fiber carbon nanotubes; and the content of each component in the mixed carbon fiber carbon nanotube is controlled as follows, in terms of mass percentage of the mixed carbon fiber carbon nanotube: graphitized carbon fibers 60%~80%; carbon nanotubes 40%~20%.

[0044] In this embodiment, the graphitized carbon fibers and carbon nanotubes are first mixed uniformly, and then mixed with other components, which is beneficial to improve the uniformity of the slurry. The ratio of the graphitized carbon fibers and carbon nanotubes is more beneficial to screen the slurry made of graphitized carbon fibers and carbon nanotubes of different sizes onto the polytetrafluoroethylene film, so as to improve the porosity, transverse conductivity and mechanical strength of the carbon paper, and make the water vapor permeability of the carbon paper more uniform, and also beneficial to improve the conductivity of the fuel cell.

[0045] In some embodiments, the length of the graphitized carbon fibers is greater than or equal to 0.5 mm and less than or equal to 3 mm. This makes the slurry more uniformly dispersed, which is beneficial to realize the screen printing process, and can make the conductivity and air permeability of the obtained carbon paper reach a good balance.

[0046] In some embodiments, the step of preparing the slurry in step S1 further comprises: mixing the mixed carbon fiber carbon nanotube, polytetrafluoroethylene emulsion, phenolic resin dry powder, ethylene glycol, deionized water and triton according to a preset weight ratio and stirring uniformly to obtain the slurry; and the weight parts of each component in the slurry are controlled as follows: mixed carbon fiber carbon nanotube 10~50 parts; polytetrafluoroethylene emulsion 2~15 parts; Phenolic resin dry powder 2~10 parts; Ethylene glycol 20~40 parts; Deionized water 20~35 parts; Triton 5~10 parts.

[0047] The weight parts of the mixed carbon fiber and carbon nanotube in this embodiment are conducive to adjusting the solid content of the slurry, thereby facilitating the realization of the screen printing process, ensuring that the carbon paper blank is not broken, avoiding the poor flowability of the slurry leading to the agglomeration of carbon nanotubes, the slurry being unable to be screen printed, and the poor conductivity of the prepared carbon paper. When the weight parts of triton are less than 5 parts, the carbon nanotubes will be seriously agglomerated, and the slurry cannot be screen printed. When the weight parts of triton are more than 10 parts, excessive surfactant will decompose and leave too many pores in the carbonization process, damaging the structural strength of the carbon paper. When the weight parts of the polytetrafluoroethylene emulsion are more than 15 parts, it may cause some pores formed by the graphitized carbon fibers and nanotubes to be blocked, thereby affecting the air permeability of the prepared carbon paper, and excessive coating will make the conductivity of the prepared carbon paper worse. The weight parts of ethylene glycol and deionized water ensure that the slurry neither dries too quickly to block the screen printing plate nor dries too slowly. The weight parts of the phenolic resin dry powder are conducive to improving the stability of the carbon paper structure, and can form hydrophobic channels in the post-processing, which is conducive to improving the air permeability of the prepared carbon paper.

[0048] In some embodiments, the step of preparing the slurry in step S1 further includes controlling the mixing temperature to be 5℃~10℃ and the mixing time to be greater than 1 hour, so as to more favorably improve the uniformity of the slurry mixing, and the agglomeration does not occur in the low-temperature mixing process, nor is the occurrence of side reactions conducive.

[0049] In some embodiments, the polytetrafluoroethylene emulsion is a polytetrafluoroethylene emulsion with a solid content of 40%~60%. A high proportion of polytetrafluoroethylene emulsion can not only act as a binder, but also form hydrophobic channels in the post-processing, which is conducive to improving the air permeability of the prepared carbon paper.

[0050] In some embodiments, the polytetrafluoroethylene emulsion is a polytetrafluoroethylene emulsion with a solid content of 50%, and the prepared carbon paper has better air permeability.

[0051] In some embodiments, the step of using the polytetrafluoroethylene film as a substrate and adopting the screen printing process to press the slurry onto the polytetrafluoroethylene film in step S2 to prepare a carbon paper blank includes: S21, clamping the base material: placing the polytetrafluoroethylene film on the vacuum adsorption platform of the screen printing machine and starting the vacuum adsorption device to fix the polytetrafluoroethylene film and prevent it from warping; S22, mounting the screen plate and feeding: after positioning and clamping the screen frame with the fixed screen plate on the printing head of the printing machine and making the lower surface of the screen plate parallel to the upper surface of the PTFE film, the slurry is injected to the side of the starting position of the squeegee on the screen plate through the feeding system, the squeegee is moved for preliminary spreading, until the slurry completely fills the screen holes of the screen plate and evenly overflows at the front end in the direction of the squeegee advancement, and there is no visible air bubble, the injection is stopped, so that there is no air mixed in the material cavity of the screen plate, thereby facilitating continuous and uninterrupted printing process; S23, squeegee printing and parameter control: the squeegee is driven to scrape across the surface of the screen plate at a constant speed, the pressure of the squeegee forces the slurry to be printed (or transferred) on the PTFE film through the transparent screen holes on the screen plate to form the carbon paper blank.

[0052] In some embodiments, the step S23 is followed by the step of: turning off the vacuum device and taking out the prepared carbon paper blank.

[0053] In some embodiments, the step S2 of using the PTFE film as the substrate and adopting the screen printing process to print the slurry on the PTFE film to prepare the carbon paper blank includes: controlling the speed of the squeegee in the screen printing process to be 10 mm / s-50 mm / s, and controlling the inclination angle of the squeegee in the screen printing process to be 30°-70°. The speed of the squeegee is related to the viscosity of the slurry. If the viscosity of the slurry is relatively small, the speed of the squeegee can be set to be relatively large, and if the viscosity of the slurry is relatively large, the speed of the squeegee needs to be set to be relatively small. The speed of the squeegee and the inclination angle of the squeegee set in the application can better cooperate with the setting of the weight parts of each component in the slurry, which is conducive to ensuring the continuous and uninterrupted printing process and reducing or avoiding defects of the carbon paper blank.

[0054] In some embodiments, the height of the screen printing plate in the screen printing process is set according to the thickness of the PTFE film and the preset thickness of the carbon paper, that is, the distance between the screen printing plate and the substrate, i.e. the PTFE film, in the screen printing process is set. In some embodiments, the distance between the screen printing plate and the PTFE film in the screen printing process is 100 μm-300 μm, that is, the thickness of the slurry layer printed on the PTFE film is 100 μm-300 μm (i.e. the thickness of the carbon paper blank minus the thickness of the PTFE film).

[0055] In some embodiments, the step of placing the carbon paper blank in the oven for curing in the step S3 includes: controlling the curing temperature to be 200°C-340°C and the curing time to be 10 minutes-30 minutes.

[0056] In some embodiments, the carbonization treatment in step S4 includes controlling the temperature of the carbonization treatment to be 1200-1700°C, controlling the time of the carbonization treatment to be 6-12 hours, and using inert gas protection during the carbonization treatment. The relatively low temperature of the carbonization treatment is conducive to forming a carbon skeleton from the organic precursor of the phenolic resin, thereby producing a carbon layer with a stable structure.

[0057] In some embodiments, the graphitization treatment in step S4 includes controlling the temperature of the graphitization treatment to be 2000-3000°C, controlling the time of the graphitization treatment to be 12-24 hours, and using inert gas protection during the graphitization treatment. The high-temperature environment of the graphitization treatment is conducive to forming ordered graphite crystal structures from amorphous carbon, greatly improving the durability of the carbon paper, such as corrosion resistance and high potential resistance.

[0058] In some embodiments, the inert gas includes nitrogen or argon, etc. The parameters such as the gas flow of the inert gas are conventional means in the art, and will not be described here.

[0059] In some embodiments, the thickness of the carbon paper produced in step S4 is greater than or equal to 80 μm and less than or equal to 250 μm. The thinner the carbon paper, the better the air permeability, but the stability may not be sufficient, and the thicker the carbon paper, the better the stability, but the air permeability will be worse. The preparation method of the present application balances the stability and air permeability of the produced carbon paper through the synergistic cooperation of the slurry formulation and the screen printing process, so that carbon papers of different thicknesses can be produced as needed, and the application range is wider.

[0060] In some embodiments, the carbon loading in the carbon paper produced in step S4 is greater than or equal to 1 mg / cm² and less than or equal to 4 mg / cm². The carbon loading is related to the thickness of the carbon paper. At the same thickness, a high carbon loading means a high density and a relatively low porosity, good electrical conductivity, but possibly poor air and water permeability. The preparation method of the present application balances the electrical conductivity and air and water permeability of the produced carbon paper through the synergistic cooperation of the slurry formulation and the screen printing process, that is, it is conducive to ensuring that the carbon paper not only has good porosity and electrical conductivity, but also has good air and water permeability, so that carbon papers of different carbon loadings can be produced as needed, and the application range is wider.

[0061] In some embodiments, the carbon paper for fuel cells is prepared by the preparation method of the carbon paper for fuel cells described in the preceding embodiments.

[0062] In some embodiments, the carbon paper has a transverse air permeability greater than or equal to 0.5 μm² and less than or equal to 1 μm². The carbon paper has a good transverse air permeability, which is beneficial to improve the water vapor transmission of the fuel cell during operation.

[0063] In some embodiments, the carbon paper has a transverse electrical conductivity greater than or equal to 0.05 Ω·cm and less than or equal to 0.2 Ω·cm. The carbon paper has a low electrical resistivity, which is beneficial to improve the electrical conductivity of the fuel cell.

[0064] In some embodiments, the carbon paper has a contact angle greater than or equal to 150° and less than or equal to 180°. The carbon paper has a large contact angle, which is a super-hydrophobic carbon paper. The carbon paper has a high water vapor permeability, so that water vapor is more easily discharged and does not remain on the carbon paper.

[0065] In some embodiments, the fuel cell includes a proton exchange membrane, a catalyst layer, and a gas diffusion layer, the gas diffusion layer including the carbon paper and a microporous layer.

[0066] To enable the above-mentioned implementation details and operations of the present application to be clearly understood by those skilled in the art, and the further performance of the carbon paper for fuel cells and the preparation method thereof, and the fuel cell of the embodiments of the present application to be significantly embodied, the following will be illustrated by multiple embodiments. Embodiment 1

[0067] A polytetrafluoroethylene film was purchased from RIKEN NEW MATERIALS (SHENZHEN) CO., LTD., and the model number was NO. 900UL.

[0068] The slurry includes: Graphitized carbon fibers, purity greater than 98%, diameter 100 nm, length 0.5 mm-3 mm, surface area 39 m² / g, purchased from MERCK CHEMICAL TECHNOLOGY (SHANGHAI) CO., LTD.; Carbon nanotubes, multi-walled carbon nanotubes, purity greater than 98%, diameter 6 nm-13 nm, length 2.5 μm-20 μm, surface area 220 m² / g, purchased from MERCK CHEMICAL TECHNOLOGY (SHANGHAI) CO., LTD.; Phenolic resin dry powder, particle size 250 mesh, purity greater than 95%, purchased from Shanghai Aladdin Biochemical Technology Co., Ltd.; Polytetrafluoroethylene emulsion, solid content 50%, purchased from Shanghai Branch of DuPont China Group Co., Ltd.; Ethylene glycol, brand 10009818, analytical pure, purity greater than 99.5%, purchased from China Reagent Co., Ltd.; Triton, model X-100, brand 30188983, purchased from China Reagent Co., Ltd.; Deionized water.

[0069] The carbon paper for the fuel cell is prepared by the following steps: S100, cutting the polytetrafluoroethylene film according to the preset size of the target carbon paper; S200, preparing the slurry: taking 30 parts of mixed carbon fiber carbon nanotubes, wherein the content of graphitized carbon fiber is 70% and the content of carbon nanotube is 30% based on the mass percentage of the mixed carbon fiber carbon nanotube, i.e. 21 parts of graphitized carbon fiber, 9 parts of carbon nanotube, 8 parts of polytetrafluoroethylene film with a solid content of 50%, 6 parts of phenolic resin dry powder, 30 parts of ethylene glycol, 28 parts of deionized water, and 7 parts of triton, placing the above raw materials in a planetary mixer, stirring at 500 r / min for 30 minutes, and then high-speed dispersing at 1500 r / min for 60 minutes to obtain a uniform and stable slurry; S300, screen printing: A 200-mesh nylon screen printing screen is selected, the distance between the screen printing screen and the polytetrafluoroethylene film is set to 200 μm, the screen printing length is 300 mm, the width is 150 mm, the speed of the squeegee is 30 mm / s, and the inclination angle of the squeegee is 45℃; The polytetrafluoroethylene film with a thickness of 100 μm is placed on the vacuum adsorption platform of the screen printing machine, and the vacuum adsorption device is started; Slowly inject the slurry, and stop injecting when the slurry uniformly overflows from the material cavity of the screen printing screen and there is no air bubble, so as to ensure that there is no air mixed in the material cavity; Drive the squeegee to perform screen printing operation according to the above parameters, so that the slurry is printed (or transferred) on the polytetrafluoroethylene film through the through holes on the screen printing screen to form the carbon paper embryo; After obtaining the carbon paper embryo, the vacuum device is turned off; S400, curing treatment: after the carbon paper embryo is dried, it is transferred into an oven, the temperature of the oven is set to 200℃, and after curing treatment for 30 minutes, the cured carbon paper embryo is taken out, the polytetrafluoroethylene film in the cured carbon paper embryo is peeled off, i.e. demolding treatment is performed, to obtain the initial carbon paper; S500, carbonization treatment and graphitization treatment: the initial carbon paper is placed in a high-temperature atmosphere furnace, heated to 1500℃ at a rate of 5℃ / min under nitrogen atmosphere protection, and then heated to 2200℃ at a rate of 5℃ / min for 12 h for graphitization treatment, and then naturally cooled to room temperature to obtain the carbon paper.

[0070] Example 2, Example 3, Comparative Example 1, Comparative Example 2, Comparative Example 3 Table 1

[0071] The difference between any one of Example 2, Example 3, Comparative Example 1, Comparative Example 2 and Comparative Example 3 and Example 1 is that the weight ratio of each component of the slurry is different, and the weight ratio of each component of the slurry in Example 2, Example 3, Comparative Example 1, Comparative Example 2 and Comparative Example 3 is shown in Table 1. The selection, configuration and preparation steps of other raw materials of any one of Example 2, Example 3, Comparative Example 1, Comparative Example 2 and Comparative Example 3 are the same as those of Example 1, and will not be repeated here.

[0072] Comparative Example 4 The difference between Comparative Example 4 and Example 1 is that in S300, Comparative Example 4 uses a traditional wet papermaking process to prepare the carbon paper blank. The other preparation steps of the carbon paper, the selection of raw materials, and the weight ratio of each component of the slurry in Comparative Example 4 are the same as those of Example 1, and will not be repeated here.

[0073] Specifically, the steps of using a traditional wet papermaking process to prepare the carbon paper blank in Comparative Example 4 include: delivering the dispersed slurry to an inclined screen paper machine, and the slurry flows onto a moving forming screen (filter screen). Under the action of gravity, water is separated and flows through the mesh, and carbon fibers are left on the screen surface to form a “wet carbon fiber paper”, which is then dehydrated and dried; and then the dried carbon fiber paper is placed into a phenolic resin impregnation tank, so that the resin penetrates into the gaps of the fibers to obtain the carbon paper blank.

[0074] Comparative Example 5 The difference between Comparative Example 5 and Example 1 is that a polyethylene terephthalate film (PET film) is selected to replace the polytetrafluoroethylene film as the substrate, i.e., the polyethylene terephthalate film is used as the substrate and a screen printing process is used to press the slurry onto the polyethylene terephthalate film to obtain the carbon paper blank. The selection of other raw materials, the weight ratio of each component of the slurry, and the preparation steps of the carbon paper in Comparative Example 5 are the same as those of Example 1, and will not be repeated here.

[0075] Performance test and result A four-probe resistance tester is used to measure the transverse conductivity of the carbon paper prepared in Example 1 to Example 3 and Comparative Example 1, Comparative Example 3 and Comparative Example 4 according to GB_T 20042.7-2014 “Carbon Paper Properties Test Method”.

[0076] A soap film flowmeter is used to measure the transverse air permeability of the carbon paper prepared in Example 1 to Example 3 and Comparative Example 1, Comparative Example 3 and Comparative Example 4 according to ASTM D737-19 “Standard Test Method for Air Permeability of Textile Fabrics”.

[0077] The viscosity of the slurries prepared in Examples 1 to 3 and Comparative Examples 1 to 5 was measured using a rotational rheometer, referring to the standard ASTM D2196 - "Standard Test Method for Determination of Rheological Properties of Non-Newtonian Materials by Rotational Viscometer".

[0078] The stability of the slurries prepared in Examples 1 to 3 and Comparative Examples 1 to 5 was measured by visual inspection to determine whether there was any sedimentation or agglomeration.

[0079] The stability and viscosity of the slurries prepared in Examples 1 to 3, and Comparative Examples 1 to 5, as well as the measurement data of the transverse electrical conductivity and transverse air permeability of the prepared carbon paper, are shown in Table 2.

[0080] Table 2

[0081] Based on the test data in Table 2, the following conclusions can be drawn.

[0082] The carbon paper prepared in Example 1 has a lateral electrical conductivity of 0.05 Ω·cm and a lateral air permeability of 1 μm²; the carbon paper prepared in Example 2 has a lateral electrical conductivity of 0.1 Ω·cm and a lateral air permeability of 0.8 μm²; and the carbon paper prepared in Example 3 has a lateral electrical conductivity of 0.08 Ω·cm and a lateral air permeability of 0.6 μm². This indicates that the carbon papers prepared in Examples 1, 2, and 3 all possess good lateral electrical conductivity and lateral air permeability.

[0083] The scanning electron microscope image of the surface of the carbon paper prepared in Example 1 is shown below. Figure 2 As shown in the figure, the carbon paper prepared in Example 1 has good porosity. The surface contact angle data of the carbon paper prepared in Example 1 after hydrophobic treatment is shown in the figure below. Figure 3 As shown, the contact angles can reach 162.92° and 165.02°, indicating that the carbon paper has good hydrophobicity and high water permeability.

[0084] It is evident that the carbon paper prepared by the slurry formulation and screen printing process used in this application not only has high lateral electrical conductivity and lateral air permeability, as well as high water permeability and good porosity, but also achieves low-cost and high-efficiency preparation of carbon paper for fuel cells.

[0085] The carbon paper prepared in Comparative Example 1 without the addition of carbon nanotubes had a transverse electrical conductivity of only 0.3 Ω·cm and a transverse air permeability of 0.2 μm², and its structure was loose and prone to collapse. This demonstrates that the synergistic effect of the combination of carbon nanotubes and graphitized carbon fibers (carbon nanotubes have bridging and network reinforcement effects) is superior to that of a single filler, namely graphitized carbon fibers.

[0086] In Comparative Example 2, without the addition of Triton, the resulting slurry exhibited severe agglomeration and stratification after standing, making it impossible to uniformly screen print carbon paper. Performance data was not measured in this case. This demonstrates that Triton plays a crucial role in dispersing carbon materials, preventing agglomeration, and forming a stable and uniform slurry, thus contributing to improved slurry stability and making it an indispensable component.

[0087] The carbon paper prepared in Comparative Example 3 has a transverse electrical conductivity of only 0.5 Ω·cm and a transverse air permeability of 0.3 μm². Furthermore, compared to the slurry prepared in Example 1, the slurry in Comparative Example 3 exhibits excessively high viscosity and reduced stability due to the high carbon nanotube content. Therefore, it is evident that controlling the content of graphitized carbon fibers to 60%–80% and the carbon nanotube content to 40%–20% by mass percentage of the mixed carbon fibers and carbon nanotubes yields carbon paper with optimal overall performance.

[0088] Comparative Example 4 uses a traditional wet papermaking process to prepare carbon paper preforms. The resulting carbon paper has a transverse electrical conductivity of 0.3 Ω·cm and a transverse air permeability of 0.4 μm². It is evident that the carbon paper preforms prepared using the screen printing process of this invention exhibit significantly improved electrical conductivity and air permeability.

[0089] Comparative Example 5, which uses PET film and screen printing to prepare carbon paper, suffers from surface damage and powdering when the PET film is peeled off, resulting in incomplete carbon paper and making it impossible to effectively measure performance data. (Reference) Figure 4 As shown, Example 1 uses the polytetrafluoroethylene film as a substrate, which can completely peel the polytetrafluoroethylene film from the cured carbon paper blank. The white part is the polytetrafluoroethylene film, and the black part is the initial carbon paper. It can be seen that this application helps to ensure that the initial carbon paper is intact and avoids damaging the integrity and surface properties of the carbon paper.

[0090] The carbon paper prepared in Examples 1 to 3, Comparative Examples 1, 3 and 4 was used to prepare a gas diffusion layer with a microporous layer. The gas diffusion layer was then hot-pressed with a proton exchange membrane and a catalyst layer to prepare a membrane electrode. Finally, the membrane electrode and bipolar plates were assembled into a fuel cell single cell (effective area 5cm*5cm).

[0091] Electrochemical tests were conducted under the following conditions: battery temperature 70℃, open cathode, hydrogen pressure 50 kPa, hydrogen flow rate 2.77 slpm, and ambient humidity 50%. The test results are shown in Table 3 below.

[0092] Table 3

[0093] As can be seen from Table 3, the voltage values of the fuel cells prepared by using the carbon papers prepared in Examples 1 to 3 are higher than those of the fuel cells prepared by using the carbon papers prepared in Comparative Examples 1, 3 and 4, and the fuel cells prepared by using the carbon papers prepared in Examples 1 to 3 exhibit better conductivity at low current density, higher voltage at high current density, less mass transfer loss, and good water vapor transfer effect, especially the fuel cell prepared by using the carbon paper prepared in Example 1 exhibits the best effect, which indicates that the carbon paper prepared by using the present application effectively improves the performance of the battery.

[0094] Although the embodiments of the present application have been described in detail above, it is obvious to those skilled in the art that various modifications and changes can be made to the embodiments. However, it should be understood that such modifications and changes are within the scope and spirit of the present application described in the claims. Moreover, the present application described herein can have other embodiments and can be implemented or realized in various ways.

Claims

1. A method for producing a carbon paper for fuel cells, characterized by, The method comprises the following steps: S1, providing a polytetrafluoroethylene film and preparing a slurry, wherein the slurry comprises graphitized carbon fibers, carbon nanotubes, a polytetrafluoroethylene emulsion, a phenolic resin dry powder, ethylene glycol, deionized water and triton; S2, using the polytetrafluoroethylene film as a substrate and adopting a screen printing process to print the slurry on the polytetrafluoroethylene film to obtain a carbon paper blank; S3, placing the carbon paper blank in an oven for curing, and peeling off the polytetrafluoroethylene film in the cured carbon paper blank to obtain an initial carbon paper; S4, placing the initial carbon paper in an oven and sequentially performing carbonization treatment and graphitization treatment under atmosphere protection to obtain a carbon paper.

2. The method of claim 1, wherein the carbon paper for fuel cells is prepared by the steps of: The step of preparing the slurry in the step S1 comprises: mixing the graphitized carbon fibers and the carbon nanotubes uniformly according to a preset mass percentage to obtain mixed carbon fiber carbon nanotubes; and controlling the content of each component in the mixed carbon fiber carbon nanotubes according to a mass percentage of the mixed carbon fiber carbon nanotubes as follows: graphitized carbon fibers 60%~80%; carbon nanotubes 40%~20%.

3. The method for preparing carbon paper for fuel cells according to claim 2, characterized in that, The step of preparing the slurry in the step S1 further comprises: mixing the mixed carbon fiber carbon nanotubes, the polytetrafluoroethylene emulsion, the phenolic resin dry powder, the ethylene glycol, the deionized water and the triton according to a preset weight ratio and stirring uniformly to obtain the slurry; and controlling the weight parts of each component in the slurry as follows: mixed carbon fiber carbon nanotubes 10~50 parts; polytetrafluoroethylene emulsion 2~15 parts; phenolic resin dry powder 2~10 parts; ethylene glycol 20~40 parts; deionized water 20~35 parts; triton 5~10 parts.

4. The method for producing a carbon paper for fuel cells according to claim 1 or 3, characterized by, The polytetrafluoroethylene emulsion is a polytetrafluoroethylene emulsion with a solid content of 40%~60%.

5. The method for preparing carbon paper for fuel cells according to claim 2, characterized in that, The length of the graphitized carbon fibers is greater than or equal to 0.5 mm and less than or equal to 3 mm.

6. The method of claim 1, wherein the carbon paper for fuel cells is prepared by the steps of: The step of using the polytetrafluoroethylene film as a substrate and adopting a screen printing process to print the slurry on the polytetrafluoroethylene film to obtain a carbon paper blank in the step S2 comprises: controlling the speed of a doctor blade in the screen printing process to be 10 mm / s~50 mm / s and controlling the inclination angle of the doctor blade in the screen printing process to be 30°~70°.

7. The method for preparing carbon paper for fuel cells according to claim 1, characterized in that, The step of placing the carbon paper blank in an oven for curing in the step S3 comprises: controlling the curing temperature to be 200℃~340℃ and controlling the curing time to be 10 minutes~30 minutes.

8. The method of claim 1, wherein the carbon paper for fuel cells is prepared by the steps of: The step of the carbonization treatment in the step S4 comprises: controlling the temperature of the carbonization treatment to be 1200℃~1700℃, controlling the time of the carbonization treatment to be 6h~12h, and adopting inert gas protection in the carbonization treatment.

9. The method for preparing carbon paper for fuel cells according to claim 1, characterized in that, The step of the graphitization treatment in the step S4 comprises: controlling the temperature of the graphitization treatment to be 2000℃~3000℃, controlling the time of the graphitization treatment to be 12h~24h, and adopting inert gas protection in the graphitization treatment.

10. The method of claim 1, wherein the carbon paper for fuel cells is prepared by the steps of: The thickness of the carbon paper obtained in the step S4 is greater than or equal to 80μm and less than or equal to 250μm.

11. The method of claim 1, wherein the carbon paper for fuel cells is prepared by the steps of: The carbon loading in the carbon paper prepared in the step S4 is greater than or equal to 1 mg / cm2 and less than or equal to 4 mg / cm2.

12. The method for preparing carbon paper for fuel cells according to claim 1, characterized in that, The contact angle of the polytetrafluoroethylene film provided in the step S1 is greater than or equal to 150° and less than or equal to 170°.

13. A carbon paper for fuel cells, characterized by, The carbon paper for fuel cells is prepared by the method according to any one of claims 1 to 12.

14. The carbon paper for fuel cells according to claim 13, characterized by The transverse air permeability of the carbon paper is greater than or equal to 0.5 μm2 and less than or equal to 1 μm2.

15. The carbon paper for fuel cells according to claim 13, wherein The transverse electrical conductivity of the carbon paper is greater than or equal to 0.05 Ω·cm and less than or equal to 0.2 Ω·cm.

16. The carbon paper for fuel cells according to claim 13, wherein The contact angle of the carbon paper is greater than or equal to 150° and less than or equal to 180°.

17. A fuel cell, characterized by A fuel cell comprising a proton exchange membrane, a catalytic layer and a gas diffusion layer, the gas diffusion layer comprising a microporous layer and the carbon paper for fuel cells according to any one of claims 13 to 16.

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