Composite bipolar plate, method of making same, and fuel cell

Abstract

This application discloses a composite bipolar plate, its preparation method, and a fuel cell. The preparation method includes: reacting graphite material under nitrogen and hexamethyldisilazane vapor conditions to obtain modified graphite; wet mixing resin and modified graphite to obtain a composite material; and pressing and curing the composite material to obtain the composite bipolar plate. This application modifies the graphite material using HMDS, causing the hydroxyl groups on the graphite surface to react with HMDS to form silane-ether bonds, and also grafting CH3 from HMDS onto the graphite surface. The silane-ether bonds and the grafted CH3 enhance the chemical bonding between graphite and resin, thereby enhancing the compatibility and bonding force between graphite and resin, improving the mechanical strength and airtightness of the composite bipolar plate, and facilitating the preparation of thinner composite bipolar plates.

Description

Technical Field

[0001] This application relates to the field of fuel cell technology, and in particular to a composite bipolar plate, its preparation method, and a fuel cell. Background Technology

[0002] A fuel cell is a device that directly converts the chemical energy of fuel into electrical energy. It is not limited by the Carnot cycle and has high energy conversion efficiency. One type of fuel cell is called a proton exchange membrane (PEM) fuel cell. PEM fuel cells have attracted widespread attention due to their advantages such as high energy density, high theoretical power generation efficiency (85%–90%), long driving range, and clean, pollution-free operation. A PEM fuel cell includes the following basic components: cathode, anode, electrolyte membrane, and bipolar plate (BP). The cathode, anode, and electrolyte membrane are usually located between a pair of bipolar plates, which act as current collectors for the anode and cathode. Furthermore, suitable flow channels and openings are formed in the bipolar plates to distribute the reactant gases of the fuel cell on the surfaces of the cathode and anode.

[0003] Ultrathin bipolar plates with high conductivity, corrosion resistance, and excellent mechanical and gas-tight properties are key to reducing fuel cell weight, lowering costs, and improving fuel cell performance. Currently, composite electrode plates made of graphite and resin have become a research hotspot due to their high overall performance. However, current composite electrode plates are relatively thick (greater than 2 mm). Furthermore, the interfacial compatibility between graphite and resin is poor, and voids easily exist at the interface, leading to substandard gas tightness in the composite bipolar plate, making it prone to gas permeation and affecting battery performance. In addition, stress concentration is easily achieved at these voids, and the connecting pores can easily cause the composite bipolar plate to fracture, affecting its mechanical strength. Summary of the Invention

[0004] In view of this, this application proposes a method for preparing a composite bipolar plate to improve the interfacial compatibility between graphite and resin, enhance the mechanical strength of the composite bipolar plate, and reduce its thickness.

[0005] In addition, it is necessary to provide a composite bipolar plate prepared by the above preparation method and a fuel cell including the composite bipolar plate.

[0006] One embodiment of this application provides a method for preparing a composite bipolar plate, comprising the following steps:

[0007] Modified graphite was obtained by reacting graphite material under nitrogen and hexamethyldisilazane vapor conditions.

[0008] The resin and the modified graphite were mixed using a wet process to obtain a composite material;

[0009] The composite material is pressed and cured to obtain the composite bipolar plate.

[0010] In one embodiment, the mass ratio of the graphite material to the hexamethyldisilazane vapor is (5-10):1.

[0011] In one embodiment, the reaction temperature is greater than or equal to 120°C, the reaction time is 20 min to 60 min, and the flow rate of nitrogen gas in the reaction is 100 mL / min to 150 mL / min.

[0012] In one embodiment, the graphite material includes one or more of expanded graphite, expanded graphite worms, microcrystalline graphite, and flake graphite. The resin includes one or more of polyphenylene sulfide, polyvinylidene fluoride, phenolic resin, and polyimide.

[0013] In one embodiment, the mass ratio of the modified graphite to the resin is (70-80):(10-20).

[0014] In one embodiment, the wet mixing step includes: dissolving the resin, the modified graphite, and the reinforcing material in an organic solvent, stirring and mixing, and removing the organic solvent to obtain the composite material.

[0015] In one embodiment, the organic solvent includes one or more of acetone, N-methylpyrrolidone, anhydrous ethanol, and dimethylformamide. The mixing time is 3 to 6 hours. The method for removing the organic solvent includes stirring and heating, vacuum distillation, or vacuum drying. The reinforcing material includes one or more of nano-carbon black, chopped carbon fibers, and graphene.

[0016] In one embodiment, the preparation method further includes a pretreatment step:

[0017] The graphite material is dried under conditions of nitrogen gas introduction and heating, wherein the flow rate of nitrogen gas is 100 mL / min to 150 mL / min, and the drying temperature is 100℃ to 110℃.

[0018] The hexamethyldisilazane solution is heated to vaporize the hexamethyldisilazane solution and obtain hexamethyldisilazane vapor.

[0019] One embodiment of this application provides a composite bipolar plate, which is prepared by the preparation method described above.

[0020] One embodiment of this application provides a fuel cell that includes the composite bipolar plate described above.

[0021] This application modifies graphite materials using HMDS to react the hydroxyl groups on the graphite surface with HMDS to form silyl ether bonds. Furthermore, CH3 from HMDS is grafted onto the graphite surface. The silyl ether bonds and the grafted CH3 enhance the chemical bonding between graphite and resin, thereby improving the compatibility and bonding strength between graphite and resin. This enhances the mechanical strength and airtightness of the composite bipolar plate, which is beneficial for preparing thinner composite bipolar plates. Attached Figure Description

[0022] Figure 1 This is a flowchart illustrating the preparation of a composite bipolar plate according to one embodiment of this application.

[0023] Figure 2 This is a cross-sectional view of a composite bipolar plate provided in one embodiment of this application.

[0024] Figure 3 The image shows the infrared spectra of expanded graphite in Example 1 of this application before and after HMDS modification.

[0025] Explanation of main component symbols

[0026] Composite bipolar plate 100

[0027] Modified graphite layer 10

[0028] Resin layer 20

[0029] The following detailed description, in conjunction with the accompanying drawings, further illustrates the embodiments of this application. Detailed Implementation

[0030] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which embodiments of this application belong. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the embodiments of this application.

[0031] Please see Figure 1 The first aspect of this application provides a method for preparing a composite bipolar plate, which includes steps S10 to S30.

[0032] Step S10: The graphite material is reacted under the condition of passing nitrogen (N2) and hexamethyldisilazane (HMDS) vapor to obtain modified graphite.

[0033] Step S20: The resin and the modified graphite are mixed by a wet process to obtain a composite material.

[0034] Step S30: Press the composite material into shape and cure it to obtain a composite bipolar plate.

[0035] It is understandable that labeling the steps is intended to clearly describe the specific preparation method, not to restrict the order of the steps.

[0036] In some embodiments, in step S10, the mass ratio of the graphite material to the hexamethyldisilazane vapor is (5-10):1. For example, the mass ratio of the graphite material to the hexamethyldisilazane vapor can be 5:1, 6:1, 7:1, 7.5:1, 8:1, 9:1, 10:1, etc., which will not be listed here.

[0037] In some embodiments, in step S10, the reaction temperature is greater than or equal to 120°C, the reaction time is 20 min to 60 min (e.g., 20 min, 30 min, 40 min, 50 min, 60 min, etc.), the nitrogen flow rate is 100 mL / min to 150 mL / min, and the reaction can be carried out in an oven. The degree of HMDS modification on the graphite material surface is controlled by varying the reaction time. Generally, the longer the time, the more complete the surface reaction. If the time is further extended, the functional groups on the graphite material surface react completely, and the reaction stops. Controlling the reaction time within 20 min to 60 min is sufficient to ensure complete reaction.

[0038] In some embodiments, the graphite material may be one or more of expanded graphite, expanded graphite worms, microcrystalline graphite, and flake graphite, and the resin may be one or more of polyphenylene sulfide (PPS), polyvinylidene fluoride (PVDF), phenolic resin, and polyimide (PI), but is not limited to these.

[0039] In some embodiments, in step S20, the mass ratio of the modified graphite to the resin is (70-80):(10-20). For example, the mass ratio of the modified graphite to the resin can be 70:20, 75:15, 77:20, 80:20, 80:15, 80:10, etc., which will not be listed here.

[0040] In some embodiments, step S20, the wet mixing step, includes: dissolving the resin, the modified graphite, and the reinforcing material in an organic solvent, stirring and mixing, and removing the organic solvent to obtain the composite material. The stirring and mixing can be performed using a magnetic stirrer or a planetary stirrer.

[0041] In some embodiments, the organic solvent includes one or more of acetone, N-methylpyrrolidone (NMP), anhydrous ethanol, and dimethylformamide. The stirring and mixing time is 3 to 6 hours, and the method for removing the organic solvent may be, but is not limited to, stirring and heating, vacuum distillation, vacuum drying, etc. The reinforcing material may be, but is not limited to, one or more of nano-carbon black, chopped carbon fibers, and graphene. The mass percentage of the reinforcing material, based on the total mass of the resin, modified graphite, and reinforcing material, may be 0% to 10% (e.g., 1%, 5%, or 10%, etc.). In some embodiments, the reinforcing material may be omitted.

[0042] In some embodiments, in step S30, the composite material can be pressed into shape using a bipolar plate mold. The molding pressure can be gradually increased and held from 10 MPa to 90 MPa, with a holding time of 1 minute. The curing process is as follows: the pressed material is placed in a muffle furnace, heated to 150-300°C, then vacuumed and cured at that temperature for 1-2 hours. The curing temperature of the resin is 150-300°C, and the specific curing temperature can be adjusted according to the type of resin. For example, the curing temperature of phenolic resin is 150°C, and the curing temperature of polyimide resin is 270°C.

[0043] In some embodiments, prior to step S10, the preparation method further includes a pretreatment step S00:

[0044] The graphite material is dried under conditions of nitrogen gas introduction and heating. The flow rate of the nitrogen gas can be 100 mL / min to 150 mL / min, and the drying temperature can be 100℃ to 110℃. The drying can be carried out in an oven.

[0045] The HMDS solution is heated (to a temperature above 120°C) to vaporize it and obtain HMDS vapor. It is understood that the mass of the HMDS vapor is equal to the mass of the HMDS solution.

[0046] Please see Figure 2 A second aspect of this application provides a composite bipolar plate 100 manufactured by the preparation method described above, comprising a laminated modified graphite layer 10 and a resin layer 20. The modified graphite layer 10 is formed by modifying graphite with hexamethyldisilazane, and the graphite may be one or more of expanded graphite, expanded graphite worms, microcrystalline graphite, and flake graphite. The resin layer 20 may be one or more of polyphenylene sulfide (PPS), polyvinylidene fluoride (PVDF), phenolic resin, and polyimide (PI), but is not limited to. The thickness of the composite bipolar plate 100 can be as low as 1.18 mm to 1.20 mm.

[0047] A third aspect of this application provides a fuel cell comprising the composite bipolar plate 100 as described above. The fuel cell also includes components such as a cathode, anode, and electrolyte membrane, which will not be described in detail here. The fuel cell can be applied in fields such as automobiles.

[0048] The present application will be described in detail below with reference to embodiments and comparative examples. Those skilled in the art will understand that the following examples are for illustrative purposes only and should not be construed as limiting the invention. The main raw materials and equipment used in the specific embodiments and comparative examples are all conventional commercially available products.

[0049] Graphite: Expanded graphite micro powder, particle size: 30-50μm, TMEGO Graphite Co., Ltd.

[0050] Phenolic resin: Model PR51794, Sumitomo Bakelite Co., Ltd.

[0051] Polyimide: 98% purity, Alpha Chemical Co., Ltd.

[0052] Polyvinylidene fluoride: Model: A937799, Molecular weight: 64.03, Alpha Chemical Co., Ltd.

[0053] Short-cut carbon fiber: 5% carbon content, 0.5mm length, Toray Carbon Fiber Co., Ltd.

[0054] Example 1

[0055] S00: Powdered expanded graphite (EG) is placed in an oven, N2 is introduced at a flow rate of 150 mL / min, heated to 100°C, and dehydrated for 10 min; the HMDS solution is heated to 120°C to vaporize and obtain HMDS vapor. The mass ratio of expanded graphite to HMDS solution is 5:1.

[0056] S10: HMDS vapor is introduced into the oven, and N2 is introduced at a flow rate of 100 mL / min. The reaction is carried out at 120 °C for 60 min to obtain modified graphite (HEG).

[0057] S20: Modified graphite, phenolic resin and chopped carbon fiber (reinforcing material) are dissolved in anhydrous ethanol in a weight percentage of 77:20:3. The mixture is stirred and mixed for 4 hours using a magnetic stirrer. After mixing, most of the anhydrous ethanol is removed by vacuum distillation at 60°C, and then the mixture is dried under vacuum at 60°C to completely remove the anhydrous ethanol, thus obtaining the composite material.

[0058] S30: The composite material is placed in a bipolar plate mold, and then pressurized stepwise from 10MPa to 90MPa and held for 1 minute to prepare a bipolar plate with flow channel characteristics. Then, it is placed in a muffle furnace and heated to 150℃, and then vacuum-cured for 1 hour to obtain a graphite / phenolic resin composite bipolar plate with a thickness of 1.18mm (denoted as PF). 20 EG 77 CF3-H).

[0059] Example 2

[0060] The difference between this embodiment and Embodiment 1 is that in step S20, the modified graphite and phenolic resin are dissolved in anhydrous ethanol in a weight ratio of 80:20, and the mixture is stirred and mixed for 4 hours using a magnetic stirrer. After the mixture is homogeneous, most of the anhydrous ethanol is removed by vacuum distillation at 60°C, and then the mixture is dried under vacuum at 60°C to completely remove the anhydrous ethanol and obtain the composite material.

[0061] The remaining steps are the same as in Example 1, and will not be repeated here.

[0062] Example 2 prepared a graphite / phenolic resin composite bipolar plate (denoted as PF) with a thickness of 1.20 mm. 20 EG 80 -H).

[0063] Example 3

[0064] The difference between this embodiment and embodiment 2 is that in step S00, the mass ratio of expanded graphite to HMDS solution (vapor) is 10:1.

[0065] The remaining steps are the same as in Example 1, and will not be repeated here.

[0066] Example 3 prepared a graphite / phenolic resin composite bipolar plate (denoted as PF) with a thickness of 1.20 mm. 20 EG 80 -H).

[0067] Example 4

[0068] The difference between this embodiment and Example 1 is that the reaction time in step S10 is 30 min; in step S20, the modified graphite and phenolic resin are dissolved in anhydrous ethanol in a weight ratio of 80:20, and the mixture is stirred and mixed for 4 h with a magnetic stirrer. After the mixture is homogeneous, most of the anhydrous ethanol is removed by vacuum distillation at 60 °C, and then the mixture is dried under vacuum at 60 °C to completely remove the anhydrous ethanol and obtain the composite material.

[0069] The remaining steps are the same as in Example 1, and will not be repeated here.

[0070] Example 4 prepared a graphite / phenolic resin composite bipolar plate (denoted as PF) with a thickness of 1.20 mm. 20 EG 80 -H).

[0071] Example 5

[0072] The difference between this embodiment and Embodiment 1 is as follows: In step S20, modified graphite, polyimide resin, and chopped carbon fiber (reinforcing material) are dissolved in NMP in sequence according to a weight percentage of 77:20:3. The mixture is stirred and mixed for 4 hours using a planetary stirrer. After uniform mixing, most of the NMP is removed by vacuum distillation at 100°C, and then vacuum dried at 100°C to completely remove the NMP, thus obtaining the composite material. In step S30, the composite material is placed in a bipolar plate mold, and then pressure is gradually increased from 10MPa to 90MPa and held (holding time is 1min) to prepare a bipolar plate with flow channel characteristics. Then, it is placed in a muffle furnace and heated to 270°C, and vacuum-insulated and cured for 1 hour to obtain the composite bipolar plate.

[0073] The remaining steps are the same as in Example 1, and will not be repeated here.

[0074] Example 5 prepared a graphite / polyimide composite bipolar plate (denoted as PI) with a thickness of 1.18 mm. 20 EG 77 CF3-H).

[0075] Example 6

[0076] The difference between this embodiment and Embodiment 1 is as follows: In step S20, modified graphite, polyvinylidene fluoride, and chopped carbon fibers are dissolved sequentially in a compound solution (NMP:ethanol:H2O = 20:11:2, volume ratio) according to a weight percentage of 77:20:3. The mixture is stirred and mixed for 4 hours using a magnetic stirrer. After uniform mixing, most of the solvent is removed by vacuum distillation at 60°C and 100°C, and then vacuum dried at 110°C to obtain the composite material. In step S30, the composite material is placed in a bipolar plate mold, and pressure is applied and held at 10MPa-90MPa in stages (holding time is 1min) to prepare a bipolar plate with flow channel characteristics. Then, it is placed in a muffle furnace and heated to 200°C, and vacuum-insulated and cured for 1 hour to obtain the composite bipolar plate.

[0077] The remaining steps are the same as in Example 1, and will not be repeated here.

[0078] Example 6 yielded a graphite / polyvinylidene fluoride composite bipolar plate (denoted as PVDF) with a thickness of 1.18 mm. 20 EG 77 CF3-H).

[0079] Comparative Example 1

[0080] The difference between Comparative Example 1 and Example 1 is that HMDS vapor is not used to modify the expanded graphite, while the remaining steps are the same as in Example 1.

[0081] In Comparative Example 1, a graphite / phenolic resin composite bipolar plate with a thickness of 1.28 mm (denoted as PF) was prepared. 20 EG 77 CF3).

[0082] Comparative Example 2

[0083] The difference between Comparative Example 2 and Example 2 is that HMDS vapor is not used to modify the expanded graphite, while the remaining steps are the same as in Example 2.

[0084] In Comparative Example 2, a graphite / phenolic resin composite bipolar plate with a thickness of 1.31 mm (denoted as PF) was prepared. 20 EG 80 ).

[0085] Comparative Example 3

[0086] The difference between Comparative Example 3 and Example 5 is that HMDS vapor is not used to modify the expanded graphite, while the remaining steps are the same as in Example 5.

[0087] In Comparative Example 3, a graphite / polyimide composite bipolar plate with a thickness of 1.29 mm (denoted as PI) was prepared. 20 EG 80 ).

[0088] Performance testing

[0089] (I) Infrared characterization

[0090] Infrared characterization was performed on expanded graphite (EG) before and after HMDS modification in Example 1 to observe changes in functional groups on the graphite surface. The infrared spectra are shown in [link to infrared spectrum]. Figure 3 .Depend on Figure 3 It can be seen that both the unmodified EG and the modified HEG have a diameter of 3449 cm. -1 The tensile vibration peak of OH is present at 1633 cm⁻¹. -1 A C=C aromatic vibration peak is present at 1580 cm⁻¹. -1 The peaks at this location represent the benzene ring framework, and these peaks are characteristic of the expanded graphite matrix. The difference lies in the presence of peaks at 1210 cm⁻¹ in EG. -1 The -OH vibration peak was present at 3449 cm⁻¹, but this peak disappeared in HEG obtained after HMDS modification, and was present in EG at 3449 cm⁻¹. -1 The OH vibration peak at the chromatogram also weakened, indicating that the hydroxyl groups on the expanded graphite surface reacted during the HMDS treatment. Simultaneously, a 1381 cm⁻¹ peak was observed in the HEG infrared spectrum. -1 1088cm-1 and 1052cm -1 Three new peaks were observed, namely the -CH3 vibration peak and the stretching vibration absorption peaks of CO-Si and Si-O-Si. These three new peaks indicate that the hydroxyl groups on the surface of expanded graphite and HMDS successfully reacted to form silyl ether bonds, and that CH3 in HMDS was also grafted onto the surface of expanded graphite, indicating that expanded graphite was successfully modified by HMDS.

[0091] (II) Testing of flexural strength, electrical conductivity and gas permeability

[0092] Referring to GB / T20042.6-2011 "Proton Exchange Membrane Fuel Cells - Part 6: Test Methods for Bipolar Plate Characteristics", the composite bipolar plates prepared in Examples 1-6 and Comparative Examples 1-3 were tested for the above-mentioned performance.

[0093] The performance test results of the composite bipolar plates prepared in Examples 1-6 and Comparative Examples 1-3 are shown in Table 1.

[0094] Table 1

[0095]

[0096] Comparing Example 1 with Comparative Example 1, it can be found that the composite bipolar plate obtained by HMDS modification of expanded graphite in Example 1 exhibits a 15.7% increase in flexural strength (mechanical strength) compared to the composite bipolar plate without HMDS modification ((50.69-43.81) / 43.81). This increase in mechanical strength is attributed to the reaction of hydroxyl groups on the graphite surface with HMDS to form silyl ether bonds, and the grafting of CH3 groups from HMDS onto the graphite surface. These silyl ether bonds and the grafted CH3 groups enhance the chemical bonding between graphite and resin, thereby improving their compatibility and adhesion. This increased mechanical strength facilitates the fabrication of thinner composite bipolar plates, enabling them to achieve a balance between high mechanical strength and low thickness. Furthermore, when unmodified expanded graphite is combined with resin, small molecule water will be adsorbed on the graphite with high specific surface energy, reducing the adhesion between the resin and graphite and affecting the mechanical strength of the bipolar plate. Modified graphite is conducive to forming a dry, hydrophobic surface, reducing the impact of small molecule water on performance, and further enhancing the adhesion between graphite and resin.

[0097] As can be seen from the comparison between Examples 1-6 and Comparative Examples 1-3, the gas permeability of the composite bipolar plate prepared after modification is increased by about two orders of magnitude, thus improving the airtightness of the composite bipolar plate. The improved airtightness is because the modification treatment generates silyl ether bonds and grafts CH3 onto the graphite surface, thereby enhancing the interfacial bonding between graphite and resin, reducing porosity, and thus reducing gas permeation.

[0098] Compared to Examples 3 and 4, Example 1 had a higher relative content of HMDS (the mass ratio of expanded graphite to HMDS was 5:1), a longer reaction time (60 min), and produced a composite bipolar plate with superior performance (higher flexural strength and conductivity, and lower gas permeability). This indicates that the graphite modification was more complete, and the interfacial bonding between the resin and graphite was tighter.

[0099] This application modifies graphite materials using HMDS to react the hydroxyl groups on the graphite surface with HMDS to form silyl ether bonds. Furthermore, CH3 from HMDS is grafted onto the graphite surface. The silyl ether bonds and the grafted CH3 enhance the chemical bonding between graphite and resin, thereby improving the compatibility and bonding strength between graphite and resin. This enhances the mechanical strength and airtightness of the composite bipolar plate, which is beneficial for preparing thinner composite bipolar plates.

[0100] The above description describes some specific embodiments of this application, but in actual applications, the application should not be limited to these embodiments. For those skilled in the art, other modifications and alterations made based on the technical concept of this application should fall within the protection scope of this application.

Claims

1. A method for preparing a composite bipolar plate, characterized in that, The preparation method includes the following steps: Modified graphite was obtained by reacting graphite material under nitrogen and hexamethyldisilazane vapor conditions. The resin and the modified graphite were mixed using a wet process to obtain a composite material; The composite material is pressed and cured to obtain the composite bipolar plate.

2. The method for preparing the composite bipolar plate as described in claim 1, characterized in that, The mass ratio of the graphite material to the hexamethyldisilazane vapor is (5-10):

1.

3. The method for preparing the composite bipolar plate as described in claim 1, characterized in that, The reaction temperature is greater than or equal to 120°C, the reaction time is 20 min to 60 min, and the flow rate of nitrogen gas in the reaction is 100 mL / min to 150 mL / min.

4. The method for preparing the composite bipolar plate as described in claim 1, characterized in that, The graphite material includes one or more of expanded graphite, expanded graphite worms, microcrystalline graphite, and flake graphite, and the resin includes one or more of polyphenylene sulfide, polyvinylidene fluoride, phenolic resin, and polyimide.

5. The method for preparing the composite bipolar plate as described in claim 1, characterized in that, The mass ratio of the modified graphite to the resin is (70-80):(10-20).

6. The method for preparing the composite bipolar plate as described in claim 1, characterized in that, The wet mixing step includes: dissolving the resin, the modified graphite, and the reinforcing material in an organic solvent, stirring and mixing, and removing the organic solvent to obtain the composite material.

7. The method for preparing the composite bipolar plate as described in claim 6, characterized in that, The organic solvent includes one or more of acetone, N-methylpyrrolidone, anhydrous ethanol, and dimethylformamide; the mixing time is 3h to 6h; the method for removing the organic solvent includes stirring and heating, vacuum distillation, or vacuum drying; the reinforcing material includes one or more of nano carbon black, chopped carbon fibers, and graphene.

8. The method for preparing the composite bipolar plate as described in claim 1, characterized in that, The preparation method further includes a pretreatment step: The graphite material is dried under conditions of nitrogen gas introduction and heating, wherein the flow rate of nitrogen gas is 100 mL / min to 150 mL / min, and the drying temperature is 100℃ to 110℃. The hexamethyldisilazane solution is heated to vaporize the hexamethyldisilazane solution and obtain hexamethyldisilazane vapor.

9. A composite bipolar plate, characterized in that, The composite bipolar plate is prepared by the preparation method according to any one of claims 1 to 8.

10. A fuel cell, characterized in that, Including the composite bipolar plate as described in claim 9.

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