Method for preparing flexible carbon nanofiber membrane, flexible carbon nanofiber membrane and proton exchange membrane fuel cell

Abstract

The invention provides a method for preparing a flexible carbon nanofiber membrane, the flexible carbon nanofiber membrane and a proton exchange membrane fuel cell, and belongs to the technical field of functional nanofiber membrane preparation. The method for preparing the flexible carbon nanofiber membrane comprises the step of carrying out hot pressing treatment on the PAN fiber membrane doped with the carbon nanotubes before carbonization treatment. The prepared flexible carbon nanofiber membrane has excellent mechanical strength and conductivity, and is suitable for the fields of high-performance composite materials, fuel cells and the like.

Description

Technical Field

[0001] The present invention relates to the technical field of preparing functional nanofiber membranes, and particularly relates to a method for preparing a flexible carbon nanofiber membrane, the flexible carbon nanofiber membrane, and a proton exchange membrane fuel cell. Background Art

[0002] The gas diffusion layer (GDL) is one of the key components of the membrane electrode assembly in a proton exchange membrane fuel cell (PEMFC), serving as both a functional and a support structure. It plays a crucial role in promoting the transport of reactant gases, controlling the water content, and facilitating electron conduction. The GDL typically has a bilayer structure consisting of a thick macroporous substrate (MPS) and a thin microporous layer (MPL). Carbon-based materials are the mainstream choice for the substrate support layer due to their high electrical conductivity, thermal conductivity, and excellent anti-electrochemical corrosion resistance. The microporous layer is mainly obtained by mixing conductive carbon materials and a hydrophobic agent (usually PTFE) to form a slurry, which is then applied through spraying, doctor blading, or roll pressing, followed by drying and sintering steps.

[0003] However, the comprehensive performance of existing carbon-based materials is poor, so there is a need to provide a new carbon-based material. Summary of the Invention

[0004] To solve the above technical problems, the present invention provides a method for preparing a flexible carbon nanofiber membrane, which can be used for the gas diffusion layer of a hydrogen fuel cell. The present invention combines electrospinning and hot pressing techniques to prepare the flexible carbon nanofiber membrane. By improving the preparation process and further adjusting the electrospinning parameters and concentration ratios to prepare the gas diffusion layer, the comprehensive performance of the GDL is improved, and it has the advantages of good flexibility, good electrical conductivity, and high cell limiting power density.

[0005] To achieve the above object, the present invention adopts the following technical solutions:

[0006] A method for preparing a flexible carbon nanofiber membrane, which includes adding a step of hot pressing the PAN fiber membrane doped with carbon nanotubes before carbonization treatment. The inventors found that adding the hot pressing step can improve the mechanical properties of the flexible carbon nanofiber membrane and improve its electrical conductivity.

[0007] Specifically, in one embodiment, a method for preparing a flexible carbon nanofiber membrane includes the following steps:

[0008] Hot pressing the PAN fiber membrane doped with carbon nanotubes;

[0009] Crosslinking the fiber membrane after hot pressing;

[0010] Heat treating the fiber membrane after crosslinking;

[0011] The flexible carbon nanofiber membrane can be obtained by carbonizing the heat-cured fiber membrane.

[0012] Preferably, the hot pressing treatment is to hot press the PAN fiber membrane doped with carbon nanotubes at a certain temperature and pressure for a certain time; the temperature of the hot pressing treatment is 100 °C to 130 °C; the pressure of the hot pressing treatment is 1 to 3 MPa, and the time of the hot pressing treatment is 5 to 30 min. The hot pressing treatment can be carried out by a flat vulcanizer.

[0013] Preferably, the crosslinking treatment is an impregnation crosslinking treatment, and the impregnation crosslinking treatment is to impregnate the hot-pressed fiber membrane first in a first mixed solution and then in a second mixed solution.

[0014] Preferably, the first mixed solution is a mixed solution of a crosslinking agent containing polyethyleneimine and absolute ethanol, wherein the concentration of the crosslinking agent containing polyethyleneimine in the first mixed solution is 1 wt% to 10 wt%; the crosslinking agent containing polyethyleneimine can be polyethyleneimine or a mixture of polyethyleneimine and dopamine, a mixture of polyethyleneimine and chitosan, or a mixture of polyethyleneimine, dopamine and chitosan; the mass percentage content of polyethyleneimine in the crosslinking agent containing polyethyleneimine is not less than 70%.

[0015] The second mixed solution is a mixed solution of an aldehyde crosslinking agent and absolute ethanol, and the concentration of the aldehyde crosslinking agent in the second mixed solution is 1 wt% to 10 wt%. The aldehyde crosslinking agent can be glutaraldehyde, adipaldehyde, terephthalaldehyde, etc.

[0016] Preferably, the heat treatment temperature of the heat treatment is 160 °C to 300 °C, and the heat treatment time is 1.5 h to 4 h. Preferably, the heat treatment is carried out using a certain heating program. The preferred heating program is to keep the temperature at 80 - 120 °C for 10 - 20 min, then raise the temperature to 120 - 160 °C and keep it for 20 - 40 min, then raise the temperature to 160 - 200 °C and keep it for 5 - 15 min, and then raise the temperature to 200 - 300 °C and keep it for 1 h to 3 h. More preferably, the heating rate is 1 - 5 °C / min. The heat treatment is carried out in an air atmosphere.

[0017] Preferably, the carbonization temperature of the carbonization treatment is 600 °C to 1500 °C, the heating rate is 1 to 10 °C / min, and the holding time is 1 to 3 h. Preferably, the carbonization treatment is carried out in a nitrogen or inert gas atmosphere.

[0018] In another embodiment, the method includes the following steps:

[0019] Perform hot pressing treatment on the PAN fiber membrane doped with carbon nanotubes;

[0020] The fiber membrane after hot pressing treatment is subjected to pre-oxidation treatment; the temperature of the pre-oxidation treatment is 200 °C to 300 °C, the heating rate is 1 to 5 °C / min, and the heat preservation time is 1 to 3 h;

[0021] The flexible carbon nanofiber membrane can be obtained by carbonizing the fiber membrane after pre-oxidation treatment.

[0022] Preferably, the PAN fiber membrane doped with carbon nanotubes is prepared by electrospinning; a positive voltage of 14 to 20 kV is applied to the spinning needle, and a negative voltage of -1 to -4 kV is applied to the receiver.

[0023] Preferably, the spinning solution used in electrospinning is a mixed solution of carboxylated carbon nanotubes, polyacrylonitrile, and DMF; the proportion of carboxylated carbon nanotubes is 0.1 wt% to 5 wt%, and the proportion of PAN is 6 wt% to 15 wt%. Specifically, a certain amount of carboxylated carbon nanotubes are weighed and mixed in DMF and ultrasonicated, and then polyacrylonitrile (PAN) is mixed with the above solution and stirred overnight to obtain the spinning solution.

[0024] A flexible carbon nanofiber membrane is prepared by the method for preparing a flexible carbon nanofiber membrane described above.

[0025] A proton exchange membrane fuel cell includes the flexible carbon nanofiber membrane described above.

[0026] The beneficial effects of the present invention are as follows:

[0027] 1. The flexible carbon nanofiber membrane prepared by the present invention has excellent comprehensive mechanical properties: the carbon nanofiber membrane after hot pressing treatment is cross-linked by polyethyleneimine (PEI) and GA, which comprehensively improves the mechanical strength of the composite material such as tensile strength, flexural strength, and bending modulus, and is suitable for high-strength composite material applications.

[0028] 2. The flexible carbon nanofiber membrane prepared by the present invention has good electrical conductivity and battery performance: the uniform dispersion of carbon nanotubes and the formation of a good conductive network combined with the cross-linked structure improve the electrical conductivity of the material and increase the power density of the battery performance.

[0029] 3. The preparation method of the present invention has a simple process and a simple operation process, is suitable for large-scale production, and has good industrial application prospects. Description of the Drawings

[0030] Figure 1 It is a scanning electron microscope SEM image of the flexible carbon nanofiber membrane prepared in Example 1 of the present invention. Detailed Embodiments

[0031] In order to make the objectives, technical solutions and advantages of the present invention more clear and understandable, the present invention will be further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0032] The present invention will be further described below through specific embodiments, but the embodiments are only for illustration and cannot limit the scope of the present invention. In addition, it should be understood that after reading the content described in the present invention, those skilled in the art can make various changes or modifications to the present invention, and these equivalent forms also fall within the scope defined by the appended claims of the present application.

[0033] All raw materials used in the present invention, including additives, etc., are commonly used and can be purchased from the market. The methods used for performance testing are all conventional testing methods used in laboratories.

[0034] Example 1

[0035] A method for preparing a flexible carbon nanofiber membrane mainly includes the following steps:

[0036] (1) Weigh a certain amount of CNTs (carboxylated carbon nanotubes) powder (CNTs mass ratio 1.5 wt%) with an electronic balance and place it in a blue-capped bottle. Use a pipette to transfer a certain amount of N-N dimethylformamide DMF (mass ratio 84.5 wt%). Subsequently, ultrasonicate for 6 h, then add 14 wt% PAN (polyacrylonitrile), and mix and heat to 65 °C and stir for 12 hours to finally obtain a spinning solution with relatively uniform dispersion.

[0037] (2) Use an electrospinning device for electrospinning. Connect the positive electrode of the high-voltage generator to the spinneret and the negative electrode to the drum receiver. Adjust and turn on the high-voltage power supply to the set positive voltage of 17 kV and negative voltage of -1.5 kV. When the filaments are stably extruded, obtain a PAN fiber membrane doped with carbon nanotubes through the release paper drum receiver.

[0038] (3) Remove the fiber membrane on the release paper and use a flat vulcanizer to thermocompress it at a pressure of 1 MPa at 130 °C for 5 min.

[0039] (4) Take out the fiber membrane after the thermocompression treatment and immerse it in a 7 wt% polyethyleneimine immersion solution for 5 min, and then take it out and immerse it in a 5 wt% glutaraldehyde immersion solution for 5 min.

[0040] (5) Take out the impregnated fiber membrane and place it in the center of the tubular furnace hearth. Set the temperature to 280 °C, and the heating rate program is as follows: Keep the temperature at 80 °C for 10 min, then heat up to 140 °C and keep it for 30 min, then heat up to 180 °C and keep it for 10 min, then heat up to 280 °C and keep it for 2 h, with a heating rate of 2 °C / min. After the insulation is completed, start to introduce nitrogen purge to prepare for the carbonization stage, and do not take out the fiber membrane.

[0041] (6) Set the carbonization temperature to 1000 °C, the heating rate to 4 °C / min, and the insulation time to 2 h. After naturally cooling to room temperature, take out the sample for testing.

[0042] The SEM image of the prepared flexible carbon nanofiber membrane is shown in Figure 1 , and it can be seen from Figure 1 that the flexible carbon nanofiber membrane prepared in this example has good flexibility and forms a cross-linked structure inside, so it has excellent mechanical properties, electrical conductivity and battery performance.

[0043] Example 2

[0044] A method for preparing a flexible carbon nanofiber membrane, comprising the following steps:

[0045] (1) Weigh a certain amount of CNTs powder (CNTs mass ratio 1.5 wt%) with an electronic balance and place it in a blue-capped bottle. Use a pipette to transfer a certain amount of N-N dimethylformamide DMF (mass ratio 84.5 wt%), then ultrasonicate for 6 h, and then add 14 wt% PAN. Mix and heat to 65 °C and stir for 12 hours to finally obtain a spinning solution with relatively uniform dispersion.

[0046] (2) Use an electrospinning device for electrospinning. Connect the positive electrode of the high-voltage generator to the spinneret and the negative electrode to the drum receiver. Adjust and turn on the high-voltage power supply to the set positive voltage of 20 kV and negative voltage of -4 kV. When the fiber is stably extruded, obtain a PAN fiber membrane doped with carbon nanotubes through the release paper drum receiver.

[0047] (3) Remove the fiber membrane on the release paper and use a flat vulcanizer to thermocompress it at a pressure of 3 MPa and a constant temperature of 120 °C for 10 min.

[0048] (4) Take out the thermocompressed fiber membrane and immerse it in a 5 wt% polyethyleneimine impregnating solution for 5 min, and then take it out and immerse it in a 5 wt% glutaraldehyde impregnating solution for 5 min.

[0049] (5) Take out the fiber membrane after impregnation and crosslinking, place it in the center of the tubular furnace hearth, set the pre-oxidation temperature at 300 °C, and the heating rate program is as follows: keep the temperature at 80 °C for 10 min, heat up to 140 °C and keep the temperature for 30 min, heat up to 180 °C and keep the temperature for 10 min, heat up to 300 °C and keep the temperature for 2 h, keep the temperature for 2 h, the heating rate is 2 °C / min. After the heat preservation ends, start to introduce nitrogen for purging to prepare for the carbonization stage, and do not take out the fiber membrane.

[0050] (6) Set the carbonization temperature at 1000 °C, the heating rate at 4 °C / min, and the heat preservation time at 2 h. After naturally cooling to room temperature, take out the sample for testing.

[0051] Example 3

[0052] A method for preparing a flexible carbon nanofiber membrane, comprising the following steps:

[0053] (1) Weigh a certain amount of CNTs powder (CNTs mass ratio 1.5 wt%) with an electronic balance and place it in a blue-capped bottle. Use a pipette to transfer a certain amount of N,N-dimethylformamide DMF (mass ratio 84.5 wt%), then ultrasonicate for 6 h, and then add 14 wt% PAN. Mix and heat to 65 °C and stir for 12 hours to finally obtain a spinning solution with relatively uniform dispersion.

[0054] (2) Use an electrospinning device for electrospinning. Connect the positive pole of the high-voltage generator to the spinneret and the negative pole to the drum receiver. Adjust and turn on the high-voltage power supply to the set positive voltage of 14 kV and negative voltage of -4 kV. When the filaments are stably ejected, obtain a doped carbon nanotube nanofiber membrane through the release paper drum receiver.

[0055] (3) Remove the fiber membrane on the release paper and thermocompress it at a pressure of 1 MPa and a constant temperature of 130 °C for 30 min with a flat vulcanizer.

[0056] (4) Take out the fiber membrane after thermocompression treatment, immerse it in a 5 wt% polyethyleneimine impregnating solution for 5 min, and then take it out and immerse it in a 5 wt% glutaraldehyde impregnating solution for 5 min.

[0057] (5) Take out the fiber membrane after impregnation and crosslinking, place it in the center of the tubular furnace hearth, set the pre-oxidation temperature at 260 °C, and the heating rate program is as follows: keep the temperature at 80 °C for 10 min, heat up to 140 °C and keep the temperature for 30 min, heat up to 180 °C and keep the temperature for 10 min, heat up to 260 °C and keep the temperature for 2 h, the heating rate is 2 °C / min. After the heat preservation ends, start to introduce nitrogen for purging to prepare for the carbonization stage, and do not take out the fiber membrane.

[0058] (6) Set the carbonization temperature at 1500 °C, the heating rate at 4 °C / min, and the heat preservation time at 2 h. After naturally cooling to room temperature, take out the sample for testing.

[0059] Example 4

[0060] A method for preparing a flexible carbon nanofiber membrane mainly includes the following steps:

[0061] (1) Weigh a certain amount of CNTs (carboxylated carbon nanotubes) powder (CNTs mass ratio 0.1 wt%) using an electronic balance and place it in a blue-capped bottle. Use a pipette to transfer a certain amount of N,N-dimethylformamide DMF (mass ratio 93.9 wt%). Then, ultrasonicate for 4 h, add 6 wt% PAN (polyacrylonitrile), mix and heat to 70 °C, and stir for 10 hours to finally obtain a spinning solution with relatively uniform dispersion.

[0062] (2) Perform electrospinning using an electrospinning device. Connect the positive electrode of the high-voltage generator to the spinneret and the negative electrode to the drum receiver. Adjust and turn on the high-voltage power supply to the set positive voltage of 17 kV and negative voltage of -1 kV. When the stable filament is produced, obtain a PAN fiber membrane doped with carbon nanotubes through the release paper drum receiver.

[0063] (3) Remove the fiber membrane on the release paper and use a flat vulcanizer to thermally press it at a pressure of 3 MPa and a constant temperature of 100 °C for 5 min.

[0064] (4) Take out the fiber membrane after the hot pressing treatment and immerse it in a mixed immersion solution of 1 wt% polyethyleneimine and dopamine (mass ratio of polyethyleneimine to dopamine is 8:2) for 6 min. Then, take it out and immerse it in a 10 wt% glutaraldehyde immersion solution for 10 min.

[0065] (5) Take out the fiber membrane after impregnation and crosslinking, place it in the center of the tubular furnace hearth, set the temperature to 260 °C, and the heating rate program is as follows: keep the temperature at 100 °C for 15 min, raise the temperature to 160 °C and keep it for 20 min, raise the temperature to 200 °C and keep it for 15 min, raise the temperature to 260 °C and keep it for 2.5 h, heating rate 1 °C / min. After the heat preservation ends, start to introduce nitrogen for purging to prepare for the carbonization stage, and do not take out the fiber membrane.

[0066] (6) Set the carbonization temperature to 600 °C, heating rate 10 °C / min, heat preservation time 1 h. After naturally cooling to room temperature, take out the sample for testing.

[0067] Example 5

[0068] A method for preparing a flexible carbon nanofiber membrane mainly includes the following steps:

[0069] (1) Weigh a certain amount of CNTs (carboxylated carbon nanotubes) powder (CNTs mass ratio 5 wt%) using an electronic balance and place it in a blue-capped bottle. Use a pipette to transfer a certain amount of N,N-dimethylformamide DMF (mass ratio 85 wt%), then ultrasonicate for 4 h, and then add 10 wt% PAN (polyacrylonitrile). Mix and heat to 70 °C and stir for 10 hours to finally obtain a spinning solution with relatively uniform dispersion.

[0070] (2) Electrospinning is carried out using an electrospinning device. Connect the positive electrode of the high-voltage generator to the spinneret and the negative electrode to the drum receiver. Adjust and turn on the high-voltage power supply to the set positive voltage of 17 kV and negative voltage of -1 kV. When the stable filament is produced, obtain a PAN fiber membrane doped with carbon nanotubes through the release paper drum receiver.

[0071] (3) Remove the fiber membrane on the release paper and use a flat vulcanizer to thermally press at a pressure of 2 MPa and a constant temperature of 100 °C for 5 min.

[0072] (4) Take out the fiber membrane after the hot pressing treatment and immerse it in a 10 wt% polyethyleneimine impregnating solution for 4 min, and then take it out and immerse it in a 1 wt% glutaraldehyde crosslinking solution for 20 min.

[0073] (5) Take out the fiber membrane after impregnation and crosslinking, place it in the center of the tubular furnace hearth, set the temperature to 300 °C, and the heating rate program is as follows: keep the temperature at 120 °C for 10 min, heat up to 160 °C and keep the temperature for 40 min, heat up to 220 °C and keep the temperature for 15 min, heat up to 300 °C and keep the temperature for 2.5 h, and the heating rate is 5 °C / min. After the heat preservation ends, start to introduce nitrogen purge to prepare for the carbonization stage, and the fiber membrane is not taken out.

[0074] (6) Set the carbonization temperature to 800 °C, the heating rate to 1 °C / min, and the heat preservation time to 3 h. After naturally cooling to room temperature, take out the sample for testing.

[0075] Example 6

[0076] A method for preparing a flexible carbon nanofiber membrane mainly includes the following steps:

[0077] (1) Weigh a certain amount of CNTs (carboxylated carbon nanotubes) powder (CNTs mass ratio 1.5 wt%) using an electronic balance and place it in a blue-capped bottle. Use a pipette to transfer a certain amount of N,N-dimethylformamide DMF (mass ratio 84.5 wt%), then ultrasonicate for 6 h, and then add 14 wt% PAN (polyacrylonitrile). Mix and heat to 65 °C and stir for 12 hours to finally obtain a spinning solution with relatively uniform dispersion.

[0078] (2) Electrospinning was carried out using an electrospinning device. The positive electrode of the high-voltage generator was connected to the spinneret, and the negative electrode was connected to the roller receiver. The high-voltage power supply was adjusted to the set positive voltage of 17 kV and negative voltage of -1.5 kV. When the fiber spinning was stable, a PAN fiber membrane doped with carbon nanotubes was obtained through the release paper roller receiver.

[0079] (3) The fiber membrane on the release paper was removed and hot-pressed at a pressure of 1 MPa and a constant temperature of 130 °C for 5 min using a flat vulcanizer.

[0080] (4) The fiber membrane after hot-pressing was taken out and placed in the center of the tube furnace hearth. The pre-oxidation temperature was set at 280 °C, the heating rate was 2 °C / min, and the holding time was 2 h. After the holding was completed, nitrogen was purged to prepare for the carbonization stage, and the fiber membrane was not taken out.

[0081] (5) The carbonization temperature was set at 1000 °C, the heating rate was 4 °C / min, and the holding time was 2 h. After naturally cooling to room temperature, the sample was taken out for testing.

[0082] Comparative Example 1

[0083] It was basically the same as the process of Example 1, but carboxylated carbon nanotubes were not doped. The performance comparison of the prepared flexible carbon nanofiber membrane is shown in Table 1.

[0084] Comparative Example 2

[0085] It was basically the same as the process of Example 6, but the hot-pressing process was not carried out. The performance comparison of the prepared flexible carbon nanofiber membrane is shown in Table 1.

[0086] Table 1 Performance Comparison

[0087]

[0088] [Note]: Tested in accordance with GB / T 20042.7-2014 "Proton Exchange Membrane Fuel Cells - Part 7: Test Methods for the Characteristics of Carbon Paper"

[0089] The performance comparison of Examples 1, 2, 3, 6 and Comparative Examples 1 and 2 is shown in Table 1. It can be seen from Table 1 that compared with Comparative Example 2 without hot-pressing, the electrical conductivity of the flexible carbon nanofiber membranes obtained in Examples 1 to 3 and Example 6 after hot-pressing has been greatly improved, and their limiting current density and limiting power density of the hydrogen fuel cell have also been greatly improved. Compared with Comparative Example 1 without doping carboxylated carbon nanotubes, the comprehensive performance has been greatly improved after adding doped carboxylated carbon nanotubes.

[0090] The present invention illustrates the detailed operation process of the present invention through the above embodiments, but the present invention is not limited to the above detailed operation step parameters, that is, it does not mean that the present invention must rely on the above detailed operation step parameters to be implemented. Those skilled in the art should understand that any improvement to the present invention, replacement, change, addition or reduction of the operation steps and operation parameters selected by the present invention all fall within the protection scope and the disclosure scope of the present invention.

[0091] The preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited to the specific details in the above embodiments. Within the technical concept scope of the present invention, various simple modifications can be made to the technical solution of the present invention, and these simple modifications all belong to the protection scope of the present invention.

[0092] In addition, it should be noted that, in the case of no conflict, the various specific technical features described in the above specific embodiments can be combined in any suitable manner. To avoid unnecessary repetition, the present invention will not separately describe various possible combination manners.

[0093] In addition, minor adjustments outside the range can also be made between various different operation parameters of the present invention, as long as it does not violate the idea of the present invention, it should also be regarded as the content disclosed by the present invention.

Claims

1. A method for preparing a flexible carbon nanofiber membrane, characterized in that: A step of hot pressing the carbon nanotube-doped PAN fiber membrane is added before the carbonization treatment.

2. The method for preparing a flexible carbon nanofiber membrane according to claim 1, characterized in that: The method comprises the following steps: The carbon nanotube-doped PAN fiber membrane is subjected to hot pressing treatment; Cross-linking the fiber membrane after the heat pressing treatment; heat treating the fiber membrane after cross-linking treatment; The flexible carbon nanofiber membrane can be obtained by carbonizing the fiber membrane after the heat treatment.

3. The method for preparing a flexible carbon nanofiber membrane according to claim 2, characterized in that: The hot pressing treatment is to hot press the carbon nanotube-doped PAN fiber membrane at a certain temperature and pressure for a certain time; the temperature of the hot pressing treatment is 100°C to 130°C; the pressure of the hot pressing treatment is 13 Mpa, and the time of the hot pressing treatment is 5 to 30 minutes.

4. The method for preparing a flexible carbon nanofiber membrane according to claim 2, characterized in that: The cross-linking treatment is an immersion cross-linking treatment, and the immersion cross-linking treatment is to immerse the heat-pressed fiber membrane in a first mixed liquid first, and then in a second mixed liquid.

5. The method for preparing a flexible carbon nanofiber membrane according to claim 4, characterized in that: The first mixed solution is a mixed solution of a cross-linking agent containing polyethylene imine and anhydrous ethanol, wherein the concentration of the cross-linking agent containing polyethylene imine in the first mixed solution is 1 wt% to 10 wt%; The second mixed solution is a mixed solution of an aldehyde cross-linking agent and anhydrous ethanol, and the concentration of the aldehyde cross-linking agent in the second mixed solution is 1 wt % to 10 wt %.

6. The method for preparing a flexible carbon nanofiber membrane according to claim 2, characterized in that: The heat treatment temperature is 160°C to 300°C, and the heat treatment time is 1.5 h to 4 h.

7. The method for preparing a flexible carbon nanofiber membrane according to claim 1, characterized in that: The method comprises the following steps: The carbon nanotube-doped PAN fiber membrane is subjected to hot pressing treatment; Performing pre-oxidation treatment on the fiber membrane after the heat pressing treatment; The flexible carbon nanofiber membrane can be obtained by carbonizing the pre-oxidized fiber membrane.

8. The method for preparing a flexible carbon nanofiber membrane according to any one of claims 1 to 7, characterized in that: The carbonization temperature of the carbonization treatment is 600° C. to 1500° C., the heating rate is 1 to 10° C. / min, and the heat preservation time is 1 to 3 hours.

9. The method for preparing a flexible carbon nanofiber membrane according to any one of claims 1 to 8, characterized in that: The carbon nanotube-doped PAN fiber membrane is prepared by electrostatic spinning, wherein a positive voltage of 14 to 20 kV is applied to the spinning needle and a negative voltage of -1 to -4 kV is applied to the receiver.

10. The method for preparing a flexible carbon nanofiber membrane according to claim 9, characterized in that: The spinning solution used in electrospinning is a mixed solution of carboxylated carbon nanotubes, polyacrylonitrile and DMF; the carboxylated carbon nanotubes account for 0.1wt% to 5wt%, and PAN accounts for 6wt% to 15wt%.

11. A flexible carbon nanofiber membrane, characterized in that: The flexible carbon nanofiber membrane is prepared by the method for preparing the flexible carbon nanofiber membrane according to any one of claims 1 to 10.

12. A proton exchange membrane fuel cell, characterized in that: Comprising the flexible carbon nanofiber membrane as claimed in claim 11.

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