A method for manufacturing a carbon fiber paper, a carbon fiber paper, a gas diffusion layer, and a fuel cell

Abstract

The application provides a preparation method of carbon fiber paper, carbon fiber paper, a gas diffusion layer and a fuel cell. The preparation method connects a hydrophobic pretreated carbon fiber paper with an electrode sheet, turns on a direct current power supply to perform a joule heat treatment, the temperature of the joule heat treatment is 300 DEG C-400 DEG C, the time is 10 min-30 min, then the power supply is turned off, and the carbon fiber paper is obtained. The preparation method provided by the application has low energy consumption and short production cycle, and helps the development and utilization of carbon fiber paper.

Description

Technical Field

[0001] This invention relates to a method for preparing carbon fiber paper, and more particularly to a method for preparing carbon fiber paper, carbon fiber paper, a gas diffusion layer, and a fuel cell, belonging to the field of fuel cells. Background Technology

[0002] The gas diffusion layer (GDL) is a crucial component of a fuel cell, playing a vital role in transporting water and gases, conducting electrons and heat during the fuel cell reaction, supporting the catalyst layer, and ensuring the mechanical strength of the electrodes. The GDL is typically composed of a microporous layer and a substrate material. Carbon fiber paper is a commonly used substrate material for fuel cell GDLs, possessing excellent electrical and thermal conductivity, high mechanical strength, and a unique macroporous structure. During fuel cell operation, the reaction product—water—exists in liquid form and must be drained promptly to prevent flooding. Hydrophobic treatment of the carbon fiber paper can improve the fuel cell's hydrothermal management capabilities, enhance gas dispersion and transport, and simultaneously increase the mechanical strength of the carbon fiber paper.

[0003] The general method for hydrophobic treatment of carbon fiber paper involves immersing the carbon fiber paper in a hydrophobic agent solution and then transferring heat to the flowing airflow via forced draft or natural heat convection. The heat is then transferred from the incoming airflow to the carbon fiber paper and maintained for a period of time until hydrophobic sintering is complete.

[0004] However, current methods for preparing carbon fiber paper involve high energy consumption, complex production equipment, and long production cycles, which greatly limit the development and utilization of carbon fiber paper. Summary of the Invention

[0005] This invention provides a method for preparing carbon fiber paper, which uses Joule heat treatment to achieve hydrophobic heat treatment of carbon fiber paper. While maintaining excellent hydrophobic properties, it improves heat conduction efficiency, reduces energy consumption in the hydrophobic heat treatment process of carbon fiber paper, shortens the production cycle of hydrophobic carbon fiber paper, and reduces equipment complexity.

[0006] The present invention also provides a carbon fiber paper, which is prepared by the above preparation method and maintains relatively excellent hydrophobic properties.

[0007] The present invention also provides a gas diffusion layer comprising the aforementioned carbon fiber paper, which has excellent performance.

[0008] The present invention also provides a fuel cell including the above-mentioned gas diffusion layer, which exhibits excellent performance and significant resistance to flooding.

[0009] This invention provides a method for preparing carbon fiber paper, comprising the following steps:

[0010] The hydrophobic carbon fiber paper is connected to the electrode sheet and subjected to Joule heat treatment by connecting a DC power supply. The Joule heat treatment temperature is 300℃-400℃ and the time is 10min-30min. Then the power supply is cut off to obtain the carbon fiber paper.

[0011] In the preparation method described above, the size of the hydrophobic carbon fiber paper is A, and the current of the Joule heat treatment is B, satisfying: 2≤A / B≤20.

[0012] In the preparation method described above, A is B is 2A-20A.

[0013] The preparation method described above includes a pretreated carbon fiber paper and a hydrophobic agent located on at least a portion of the surface of the pretreated carbon fiber paper, wherein the mass percentage of the hydrophobic agent is 1%-10% based on the mass of the hydrophobic carbon fiber paper.

[0014] In the preparation method described above, the hydrophobic agent includes at least one of polytetrafluoroethylene, polyvinylidene fluoride, perfluoroethylene propylene copolymer, and tetrafluoroethylene-perfluoroalkoxy vinyl ether copolymer.

[0015] The hydrophobic carbon fiber paper, prepared by the method described above, is obtained through a process including the following steps:

[0016] The pretreated carbon fiber paper is immersed in a hydrophobic agent for 0.5 min to 2 min, and then dried at 80℃ to 100℃. This process is repeated 1 to 10 times to obtain the hydrophobic carbon fiber paper.

[0017] The preparation method described above further includes cleaning the pretreated carbon fiber paper before the impregnation treatment.

[0018] In another aspect, the present invention provides a carbon fiber paper prepared using the preparation method described above.

[0019] In another aspect, the present invention provides a gas diffusion layer comprising carbon fiber paper prepared by the preparation method described above.

[0020] In another aspect, the present invention provides a fuel cell comprising a gas diffusion layer as described above.

[0021] The carbon fiber paper preparation method provided by this invention uses Joule heat treatment. After connecting the hydrophobic carbon fiber paper to the electrode sheet, Joule heat treatment is performed using a DC power supply. By controlling the temperature and time of the Joule heat treatment, the hydrophobic heat treatment of the carbon fiber paper is achieved. This preparation method can rapidly heat up and cool down, improve heat conduction efficiency while maintaining excellent hydrophobic properties, reduce energy consumption in the hydrophobic heat treatment process of carbon fiber paper, shorten the production cycle of hydrophobic carbon fiber paper, and reduce equipment complexity. Attached Figure Description

[0022] Figure 1 This is a partial schematic diagram of the Joule heat treatment apparatus in a specific embodiment of the present invention.

[0023] Figure 2 This is a schematic diagram of the contact angle test point selection range of the present invention.

[0024] Figure 3 The linear sweep current-voltage curves of the fuel cells in Example 2 and Comparative Example 2 are shown.

[0025] Figure 4 This is a partially enlarged view of the linear sweep current-voltage curves of the fuel cells in Example 2 and Comparative Example 2.

[0026] Explanation of reference numerals in the attached figures:

[0027] 1-Ceramic thermal insulation platform; 2-Copper sheet electrode; 3-Conductive silver paste; 4-Hydrophobic carbon fiber paper; 5-DC power supply. Detailed Implementation

[0028] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions in the embodiments of this invention will be clearly and completely described below in conjunction with the embodiments of this invention. Obviously, the described embodiments are only some embodiments of this invention, not all embodiments. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0029] In the prior art, when hydrophobically treating carbon fiber paper, heat is generally transferred to the flowing airflow through a blower or natural heat convection. The heat is then transferred to the carbon fiber paper by the incoming airflow and maintained for a period of time until the hydrophobic sintering process is completed.

[0030] However, due to the low thermal conductivity of gases, typically 0.007-0.17 W / (m·K), their heat transfer efficiency is poor. Therefore, in the hydrophobic sintering process of carbon fiber paper using airflow heat transfer, a large amount of heat is used to heat the flowing gas, resulting in heat consumption far exceeding the actual heat required for the carbon fiber paper to reach the set temperature. This leads to high energy consumption in the production process. Furthermore, considering the practicalities of continuous production, different heating units need to be designed to meet the needs of gradual heating and cooling of the carbon fiber paper. This results in complex production equipment and a large footprint for production line construction.

[0031] This invention provides a method for preparing carbon fiber paper, comprising the following steps:

[0032] The hydrophobic carbon fiber paper is connected to the electrode sheet and subjected to Joule heat treatment by connecting a DC power supply. The Joule heat treatment temperature is 300℃-400℃ and the time is 10min-30min. Then the power supply is cut off to obtain the carbon fiber paper.

[0033] In detail, the carbon fiber paper prepared by the method of the present invention can be used to prepare a gas diffusion layer for fuel cells.

[0034] Specifically, the two ends of the hydrophobic carbon fiber paper are connected to the electrode plates, and then the electrode plates at both ends are connected to the positive and negative terminals of the DC power supply respectively to form a closed circuit. After the DC power supply is turned on, the temperature of the hydrophobic carbon fiber paper reaches 300℃-400℃. After maintaining this temperature for 10min-30min, the power supply is turned off, allowing the temperature to drop rapidly to room temperature, thus obtaining the carbon fiber paper.

[0035] Understandably, in order to form a closed circuit and improve conductivity, conductive silver paste can be used to connect the hydrophobic carbon fiber paper to the electrode sheet.

[0036] This invention does not limit the specific type of electrode sheet; a suitable electrode sheet, such as a copper sheet, can be selected according to the actual situation.

[0037] like Figure 1 As shown, a closed circuit is formed by copper sheet 2, conductive silver paste 3, hydrophobic carbon fiber paper 4, and DC power supply 5. The circuit consisting of copper sheet 2, conductive silver paste 3, hydrophobic carbon fiber paper 4, conductive silver paste 3, and copper sheet 2 is placed on a ceramic heat-insulating platform 1. To avoid adverse effects of external factors on the Joule heat treatment, the ceramic heat-insulating platform is placed in a transparent sealed cover, which can be filled with inert gases such as nitrogen and argon.

[0038] This invention does not limit the temperature detection method for Joule heat treatment. Common detection methods in the art can be used to detect the temperature during the Joule heat treatment process, such as using an infrared thermometer.

[0039] The carbon fiber paper preparation method provided by this invention has low energy consumption and a short production cycle, which facilitates the development and utilization of carbon fiber paper. As a component in a closed circuit, Joule heat treatment is used to convert electrical energy flowing through the hydrophobic carbon fiber paper into heat energy. The generated heat energy raises the temperature of the hydrophobic carbon fiber paper. By controlling the temperature and time of the Joule heat treatment, the hydrophobic agent in the hydrophobic carbon fiber paper melts, achieving hydrophobic thermal sintering of the carbon fiber paper without damaging its structure. The current applied to the carbon fiber paper can be switched rapidly, enabling rapid heating and cooling. This method obtains hydrophobic carbon paper with excellent hydrophobic properties while reducing the excess energy consumption caused by heat conduction through gas, thus improving heat transfer efficiency.

[0040] During the Joule heat treatment process, adjusting the current according to the size of the hydrophobic carbon fiber paper allows for more precise temperature control, ensuring uniform heating and avoiding localized overheating or underheating, thereby improving the Joule heat treatment effect.

[0041] In one specific embodiment, the size of the hydrophobic carbon fiber paper is A, and the current for Joule heat treatment is B, satisfying: 2≤A / B≤20.

[0042] The size of the hydrophobic carbon fiber paper refers to its area, which can be calculated by measuring the length and width of the carbon paper. The current for Joule heat treatment can be controlled by adjusting the DC power supply.

[0043] In detail, A / B includes, but is not limited to, a range of 2, 3, 5, 8, 10, 12, 15, 18, 20, or any two of these.

[0044] When A / B meets the above range, not only can the temperature and time of Joule heat treatment be precisely controlled to ensure that the material achieves the expected physical and chemical properties, but also the current density distribution can be ensured to be uniform and the carbon fiber paper is heated evenly as a whole, avoiding structural damage or performance reduction caused by local overheating or insufficient heating.

[0045] In one specific embodiment, A is 5cm. 2 -400cm 2 B is 2-20A.

[0046] Specifically, A includes, but is not limited to, 5cm. 2 10cm 2 15cm 2 20cm 2 30cm 2 50cm 2 80cm 2 100cm 2 200cm 2 300cm 2 400cm 2 B is any value in the range of or any combination of any two of them, and B includes, but is not limited to, any value in the range of or any combination of any two of 2A, 3A, 5A, 8A, 10A, 15A, 18A, 20A, etc.

[0047] Hydrophobic carbon fiber paper directly affects the hydrophobic properties and other physicochemical characteristics of carbon fiber paper.

[0048] In one specific embodiment, the hydrophobic carbon fiber paper includes pretreated carbon fiber paper and a hydrophobic agent located on at least a portion of the surface of the pretreated carbon fiber paper, wherein the mass percentage of the hydrophobic agent is 1%-10%.

[0049] The mass ratio of the hydrophobic agent refers to the ratio of the mass of the hydrophobic agent to the mass of the hydrophobic carbon fiber paper. The mass ratio of the hydrophobic agent can be controlled by controlling the preparation process of the hydrophobic carbon fiber paper, thereby controlling the mass of the hydrophobic agent and the mass of the pretreated carbon fiber paper. Alternatively, the mass of the hydrophobic agent and the total mass of the hydrophobic carbon fiber paper product can be measured using common testing methods in this field, and then the mass ratio of the hydrophobic agent can be calculated.

[0050] In detail, the mass percentage of the hydrophobic agent includes, but is not limited to, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, or any combination thereof.

[0051] When the mass ratio of hydrophobic agent in hydrophobic carbon fiber paper is within the above range, it can not only ensure that the surface of carbon fiber paper is covered with enough hydrophobic agent to form an effective hydrophobic layer, but also avoid the aggregation of hydrophobic agent, which would lead to uneven material properties and prevent excessive hydrophobic agent from affecting the conductivity and mechanical strength of carbon fiber paper.

[0052] It is necessary to select a suitable type of hydrophobic agent. In one specific embodiment, the hydrophobic agent includes at least one of polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), perfluoroethylene propylene copolymer, and tetrafluoroethylene-perfluoroalkoxy vinyl ether copolymer.

[0053] Using the above-mentioned types of hydrophobic agents can provide carbon fiber paper with excellent hydrophobicity, chemical stability, thermal stability and mechanical properties, while meeting the needs of a variety of application scenarios.

[0054] In one specific embodiment, the hydrophobic carbon fiber paper is obtained by a preparation method comprising the following processes:

[0055] The pretreated carbon fiber paper is immersed in a hydrophobic agent for 0.5 min to 2 min, and then dried at 80℃ to 100℃. This process is repeated 1 to 10 times to obtain hydrophobic carbon fiber paper.

[0056] Specifically, the immersion treatment time includes, but is not limited to, a range of 0.5 min, 0.6 min, 0.8 min, 1.0 min, 1.2 min, 1.4 min, 1.6 min, 1.8 min, 2.0 min, or any combination thereof. The drying treatment temperature includes, but is not limited to, 80°C, 82°C, 84°C, 86°C, 88°C, 90°C, 92°C, 94°C, 96°C, 98°C, 100°C, or any combination thereof.

[0057] The present invention does not limit the concentration of the hydrophobic agent, and a suitable concentration range can be selected according to the actual situation, such as 0.2%-5%.

[0058] The impregnation time and drying temperature can be precisely controlled to ensure that the hydrophobic agent content is within the range of 1%-10%. Moreover, through multiple impregnations and drying, the hydrophobic agent can be evenly distributed on the surface and pores of the pretreated carbon fiber paper, avoiding local unevenness and giving the hydrophobic carbon fiber paper excellent hydrophobicity, conductivity and mechanical properties.

[0059] Meanwhile, in order to avoid the influence of impurities on the surface of the pretreated carbon fiber paper on its hydrophobic properties, in one specific embodiment, the pretreated carbon fiber paper is further cleaned before the impregnation treatment.

[0060] The purpose of cleaning is to remove impurities and contaminants from the surface of the pretreated carbon fiber paper to ensure that the hydrophobic agent can adhere evenly and effectively to the surface of the pretreated carbon fiber paper.

[0061] In one specific embodiment, a pretreated carbon fiber paper of appropriate size is ultrasonically treated with acetone and ethanol in sequence to remove dust and organic matter from the carbon fiber paper, and then dried for later use to obtain a clean pretreated carbon fiber paper.

[0062] In another aspect, the present invention provides a carbon fiber paper prepared using the preparation method described above.

[0063] Since the carbon fiber provided by this invention is prepared by the above-described preparation method, it has excellent hydrophobic properties.

[0064] In another aspect, the present invention provides a gas diffusion layer comprising carbon fiber paper prepared by the preparation method described above.

[0065] Since the gas diffusion layer provided by the present invention includes the aforementioned carbon fiber paper, it can effectively improve gas dispersion and transport, and enhance the performance of the gas diffusion layer.

[0066] The present invention does not limit the preparation method of the gas diffusion layer, and it can be prepared by common preparation methods in the art, such as blade coating, slot extrusion coating, comma roller transfer coating, and ultrasonic atomization spraying.

[0067] In another aspect, the present invention provides a fuel cell comprising the gas diffusion layer as described above.

[0068] The fuel cell provided by the present invention includes the above-mentioned gas diffusion layer, and therefore has excellent performance.

[0069] It is understood that the fuel cell provided by the present invention comprises five main parts: a single cell, an air supply system, a hydrogen supply system, a hydrothermal management system, and a load system.

[0070] The fuel cell stack is the core component of a fuel cell system, maintaining the energy output of the entire system and largely determining key factors such as overall performance, lifespan, and cost. A fuel cell stack mainly consists of single fuel cells, and common stack structures include end plates, current collectors, bipolar plates, and membrane electrode assemblies (MEAs). The MEA comprises a gas diffusion layer, a catalyst layer, and a proton exchange membrane. The gas diffusion layer, located between the catalyst electrode and the bipolar plates, plays a crucial role in supporting the catalyst layer, collecting current, conducting gas, and removing the reaction product water.

[0071] The carbon fiber paper provided by the present invention will be described in detail below through specific embodiments.

[0072] Example 1

[0073] The method for preparing carbon fiber paper provided in this embodiment includes the following steps:

[0074] 1. Clean the pretreated carbon fiber paper (10cm x 10cm) in acetone and ethanol by ultrasonic cleaning to remove organic matter and surface impurities. After drying, weigh the pretreated carbon fiber paper.

[0075] 2. Immerse the pretreated carbon fiber paper in a polytetrafluoroethylene dispersion diluted to 0.5% by mass for 1 minute, remove it and dry it at 80°C. Repeat this process twice until the polytetrafluoroethylene content in the pretreated carbon fiber paper reaches 1% by mass, and then obtain hydrophobic carbon fiber paper.

[0076] 3. Press the dried hydrophobic carbon fiber paper into... Figure 1 As shown, the carbon fiber paper, conductive silver paste, and copper sheet are connected together and placed on a ceramic heat-insulating platform. The entire device is placed in a transparent sealed enclosure, and nitrogen gas is continuously purged as a protective gas. A pulsed current is applied to the carbon fiber paper-conductive silver paste-copper sheet connector using a DC power supply, and the current value is gradually increased to 10A until the average temperature of the carbon fiber paper, as measured by an infrared thermometer, reaches 350°C for Joule heat treatment. After the carbon fiber paper is held at this temperature for 20 minutes, the current is cut off, and after cooling to room temperature, the carbon fiber paper is removed to obtain the carbon fiber paper.

[0077] Example 2

[0078] The preparation method of carbon fiber paper provided in this embodiment is basically the same as that in Example 1, except that:

[0079] The Joule heat treatment in step 3 lasts for 10 minutes.

[0080] Example 3

[0081] The preparation method of carbon fiber paper provided in this embodiment is basically the same as that in Example 1, except that:

[0082] In step 2, the process is repeated 4 times to achieve a polytetrafluoroethylene (PTFE) content of 2% by mass in the pretreated carbon fiber paper.

[0083] Example 4

[0084] The preparation method of carbon fiber paper provided in this embodiment is basically the same as that in Example 1, except that:

[0085] In step 2, the process is repeated 10 times to ensure that the polytetrafluoroethylene content in the pretreated carbon fiber paper reaches 5% by mass.

[0086] Example 5

[0087] The method for preparing carbon fiber paper provided in this embodiment includes the following steps:

[0088] 1. Clean the pretreated carbon fiber paper (10cm x 20cm) in acetone and ethanol by ultrasonic cleaning to remove organic matter and surface impurities. After drying, weigh the pretreated carbon fiber paper.

[0089] 2. Immerse the pretreated carbon fiber paper in a polyvinylidene fluoride dispersion diluted to 5% by mass for 30 seconds, remove it and dry it at 100°C. Repeat this process 4 times until the polyvinylidene fluoride content in the pretreated carbon fiber paper reaches 10% by mass, and then obtain hydrophobic carbon fiber paper.

[0090] 3. Press the dried hydrophobic carbon fiber paper into... Figure 1 As shown, the carbon fiber paper, conductive silver paste, and copper sheet are connected together and placed on a ceramic heat-insulating platform. The entire device is placed in a transparent sealed enclosure, and nitrogen gas is continuously purged as a protective gas. A pulsed current is applied to the carbon fiber paper-conductive silver paste-copper sheet connector using a DC power supply, and the current value is gradually increased to 18A until the average temperature of the carbon fiber paper, as measured by an infrared thermometer, reaches 400℃ for Joule heat treatment. After the carbon fiber paper is held at this temperature for 10 minutes, the current is cut off, and after cooling to room temperature, the carbon fiber paper is removed to obtain the carbon fiber paper.

[0091] Example 6

[0092] The preparation method of carbon fiber paper provided in this embodiment is basically the same as that in Example 1, except that:

[0093] In step 1, the size of the pretreated carbon fiber paper is 3cm × 3cm.

[0094] Example 7

[0095] The preparation method of carbon fiber paper provided in this embodiment is basically the same as that in Example 1, except that:

[0096] In step 2, the process is repeated once, and the mass percentage of polytetrafluoroethylene in the pretreated carbon fiber paper is 0.5%.

[0097] Comparative Example 1

[0098] The preparation method provided in this comparative example is basically the same as the preparation method provided in Example 1, except that:

[0099] Step 3: Place the hydrophobic carbon fiber paper in a vacuum atmosphere furnace, continuously introduce nitrogen gas, set the heating program, raise the temperature to 350°C within 60 minutes, hold for 20 minutes, and then allow it to cool naturally. After that, take it out to obtain the carbon fiber paper.

[0100] Comparative Example 2

[0101] The preparation method provided in this comparative example is basically the same as the preparation method provided in Comparative Example 1, except that:

[0102] In step 3, the heat preservation time is 1 hour.

[0103] Comparative Example 3

[0104] The preparation method provided in this comparative example includes the following steps:

[0105] The method for preparing carbon fiber paper provided in this embodiment includes the following steps:

[0106] 1. Clean the pretreated carbon fiber paper (10cm x 10cm) in acetone and ethanol by ultrasonic cleaning to remove organic matter and surface impurities. After drying, weigh the pretreated carbon fiber paper.

[0107] 2. Immerse the pretreated carbon fiber paper in water, remove it and dry it at 80°C to obtain dried pretreated carbon fiber paper.

[0108] 3. Arrange the dried pretreated carbon fiber paper according to... Figure 1 As shown, the carbon fiber paper, conductive silver paste, and copper sheet are connected together and placed on a ceramic heat-insulated platform. The entire device is placed in a transparent sealed enclosure, and nitrogen gas is continuously purged as a protective gas. A pulsed current is applied to the carbon fiber paper-conductive silver paste-copper sheet connector using a DC power supply, and the current value is gradually increased to 10A until the average temperature of the carbon fiber paper, as measured by an infrared thermometer, reaches 350°C for Joule heat treatment. The carbon fiber paper is held at this temperature for 20 minutes, then the current is cut off, and it is cooled to room temperature before being removed to obtain the carbon fiber paper.

[0109] Test Example 1

[0110] 1. Weigh the hydrophobic carbon fiber paper obtained in step 2) and the carbon fiber paper obtained in step 3 of the preparation methods provided in all embodiments and comparative examples, and calculate the mass loss ratio.

[0111] The mass loss ratio is calculated as: |mass of carbon fiber paper - mass of hydrophobic carbon fiber paper| / mass of hydrophobic carbon fiber paper. Specific test results are shown in Table 1.

[0112] 2. According to Figure 2 The ranges A, B, C, D, and E in the figure represent the contact angles of the carbon fiber paper provided in the embodiments and comparative examples at the four corner positions and the center position, respectively. The average value was then calculated. The process includes the following steps: placing each embodiment and comparative example on the platform of a contact angle tester, using pure water as the test liquid, and dropping water droplets onto the surface of the paper. Figure 2 The contact angle was measured at the indicated location using testing software. Specific test results are shown in Table 1.

[0113] 3. Analyze the energy consumption in the preparation methods of all embodiments and comparative examples, including the following steps:

[0114] For Examples 1-7 and Comparative Example 3, energy consumption was calculated using the voltage and current values ​​during the heating and holding periods; for Comparative Examples 1-2, energy consumption was calculated using the average power during the heating and holding periods. The energy consumption figures for all examples and comparative examples only represent the energy consumption of carbon fiber paper during the hydrophobic sintering process and do not include the energy consumption of preceding steps. Specific results are shown in Table 1.

[0115] Table 1

[0116]

[0117] As shown in Table 1, the mass loss percentage in Comparative Example 3 is extremely low, indicating that heating the carbon fiber paper to 350°C using Joule heating does not significantly affect its properties. The mass loss ratios of Examples 1 and 2 are similar, demonstrating that even with the Joule heat treatment time shortened to 10 minutes, sufficient heating and sintering of the carbon fiber paper can still be achieved, resulting in hydrophobic treatment. The operating conditions for Comparative Example 1 and Comparative Example 2 are identical except for the holding time during heat treatment. However, the mass loss differs significantly between the two, indicating that in Comparative Example 1, the insufficient holding time prevented the complete removal of other components in the hydrophobic agent, inevitably negatively impacting the hydrophobic effect of the sintered carbon fiber paper.

[0118] The contact angle of Comparative Example 3, which was not impregnated with a hydrophobic agent, was less than 90°, indicating that its surface was hydrophilic. The contact angle test results of Examples 1 and 2 were similar, demonstrating that Joule heat treatment can achieve hydrophobic sintering in a short time. Compared to Comparative Examples 1 and 2, the impregnation amount of the hydrophobic agent in Example 3 was 2%. The contact angle test results showed that the contact angle of Example 3 was similar to that of Comparative Example 2, while the contact angle of Comparative Example 1 was smaller. This indicates that Joule heat hydrophobic sintering and convection heating hydrophobic sintering methods can achieve nearly the same hydrophobic effect. In Example 4, the hydrophobic agent content in the carbon fiber paper was relatively high, and after 20 minutes of Joule heat hydrophobic sintering, the contact angle test results showed that it had a uniform hydrophobic effect.

[0119] From an energy consumption perspective, in different embodiments and comparative examples, the energy consumption of carbon paper hydrophobic sintering using Joule heating is significantly lower than that of gas convection heating. When obtaining hydrophobic carbon paper with similar properties, the Joule heating sintering method provided by this invention can save more energy and reduce costs.

[0120] Test Example 2

[0121] The hydrophobic carbon fiber paper obtained in Example 2 and Comparative Example 2 was coated with a microporous layer to obtain two gas diffusion layers, which were then tested in a fuel cell single cell test system.

[0122] The preparation steps of the gas diffusion layer include: mixing 10g of conductive carbon black, 4g of 60% PTFE emulsion, 45g of deionized water, 1.2g of Triton, 2g of methylcellulose and 25g of anhydrous ethanol, and dispersing the mixture at a rate of 4000r / min for 1h using a high-speed shear disperser, while simultaneously obtaining a microporous layer slurry under circulating cold water heat preservation. The microporous layer slurry is then screen-printed onto hydrophobic carbon fiber paper to form a microporous layer with a thickness of 20μm. After that, it is transferred to an 80℃ forced-air drying oven for drying for 30min, and then transferred to a vacuum atmosphere furnace for sintering at 350℃ for 1h to finally obtain the gas diffusion layer.

[0123] The gas diffusion layer obtained above was tested in a fuel cell. The battery assembly steps included: coating the prepared gas diffusion layer with a catalyst-coated proton exchange membrane (CCM), with anode and cathode loadings of 0.30 / 0.15 mg / cm³, respectively. 2 ), frame, sealing assembly membrane assembly (MEA). Place the MEA in an effective area of ​​10cm² 2 The fuel cell was tested in a single-cell fuel cell fixture. The fuel cell fixture consists of metal end plates, current collectors, and a graphite plate with a flow field. The test conditions for the fuel cell were: cell temperature 80℃, stoichiometric ratio of hydrogen to air at the anode / cathode of 1.5 / 3, relative humidity of hydrogen and air of 90%, and back pressure of the anode / cathode gases of 200 kPa / 200 kPa.

[0124] The linear sweep current-voltage curves of the fuel cells in Example 2 and Comparative Example 2 are shown below. Figure 3 and Figure 4 , Figure 4 for Figure 3 A magnified view of the details. A comparison of the current-voltage curves shows that the hydrophobic carbon fiber paper obtained by Joule heating rapid hydrophobic sintering and vacuum atmosphere furnace hydrophobic sintering exhibits similar performance in fuel cell testing. This demonstrates the applicability of hydrophobic carbon fiber paper obtained by Joule heating rapid hydrophobic sintering in fuel cells, as the internal carbon fiber structure of the carbon paper does not change significantly with the application of current. Furthermore, in the high-current testing range (current density greater than 1500 mA cm⁻¹),...-2 In the example, at the same current density, the voltage was significantly higher than that of the comparative example, at 2000 mA cm⁻¹. -2 At that time, the test voltage of the embodiment was 7mV higher than that of the comparative example, at 2500mAcm -2 At that time, the test voltage of the example was 114mV higher than that of the comparative example, at 3000mA cm -2 At that time, the test voltage of the embodiment was 24mV higher than that of the comparative example. This indicates that the hydrophobic carbon fiber paper obtained in the embodiment has better drainage capacity and can promptly remove water generated during the battery reaction, avoiding flooding.

[0125] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing carbon fiber paper, characterized in that, Includes the following steps: The hydrophobic carbon fiber paper is connected to the electrode sheet and subjected to Joule heat treatment by connecting a DC power supply. The Joule heat treatment temperature is 300℃-400℃ and the time is 10min-30min. Then the power supply is cut off to obtain the carbon fiber paper.

2. The preparation method according to claim 1, characterized in that, The size of the hydrophobic carbon fiber paper is A, and the current of the Joule heat treatment is B, satisfying: 2≤A / B≤20.

3. The preparation method according to claim 2, characterized in that, A is 5cm 2 -400cm 2 B is 2A-20A.

4. The preparation method according to any one of claims 1-3, characterized in that, The hydrophobic carbon fiber paper includes pretreated carbon fiber paper and a hydrophobic agent located on at least a portion of the surface of the pretreated carbon fiber paper, wherein the mass percentage of the hydrophobic agent is 1%-10% based on the mass of the hydrophobic carbon fiber paper.

5. The preparation method according to claim 4, characterized in that, The hydrophobic agent includes at least one of polytetrafluoroethylene, polyvinylidene fluoride, perfluoroethylene propylene copolymer, and tetrafluoroethylene-perfluoroalkoxy vinyl ether copolymer.

6. The preparation method according to claim 4, characterized in that, Hydrophobic carbon fiber paper is obtained by a preparation method including the following processes: The pretreated carbon fiber paper is immersed in a hydrophobic agent for 0.5 min to 2 min, and then dried at 80℃ to 100℃. This process is repeated 1 to 10 times to obtain the hydrophobic carbon fiber paper.

7. The preparation method according to claim 6, characterized in that, The impregnation process also includes cleaning the pretreated carbon fiber paper before the impregnation process.

8. A carbon fiber paper, characterized in that, It is prepared using the preparation method described in any one of claims 1-7.

9. A gas diffusion layer, characterized in that, This includes carbon fiber paper prepared by the preparation method described in any one of claims 1-7.

10. A fuel cell, characterized in that, Includes the gas diffusion layer as described in claim 9.

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