Carbon fiber composite bipolar plate for high-temperature proton exchange membrane fuel cell and preparation method of carbon fiber composite bipolar plate

Abstract

The invention discloses a carbon fiber composite bipolar plate for a high-temperature proton exchange membrane fuel cell and a preparation method of the carbon fiber composite bipolar plate, and belongs to the field of fuel cells. The bipolar plate comprises a conductive supporting framework, an airtight filling phase and an interface conductive layer, the conductive supporting framework is carbon paper or carbon cloth of a porous structure, pores of the conductive supporting framework are filled with the airtight filling phase, and the interface conductive layer is arranged on at least one surface, in contact with the gas diffusion layer, of the bipolar plate. The preparation method comprises the following steps: impregnating carbon paper / carbon cloth and a high-temperature-resistant polymer through a powder solution or performing melt extrusion to prepare pre-impregnated cloth, coating conductive slurry on the surface of the pre-impregnated cloth to form an interface layer, stacking the pre-impregnated cloth in a mold with a flow field structure, performing hot-pressing solidification at the temperature higher than the melting point temperature of the polymer, and coining a flow field, and finally maintaining pressure, cooling and demolding. The corrosion resistance is excellent, the mass and the volume power density of the galvanic pile are greatly improved due to the light and thin characteristics, and densification and flow field forming can be completed at a time through the preparation process.

Description

Technical Field

[0001] This application relates to a carbon fiber composite bipolar plate for high-temperature proton exchange membrane fuel cells and its preparation method, belonging to the field of fuel cell technology. Background Technology

[0002] High-temperature proton exchange membrane fuel cells (HT-PEMFCs) typically operate within a temperature range of 120°C to 180°C and employ phosphoric acid-doped polybenzimidazole (PBI) as the proton exchange membrane. Under these operating conditions, the presence of high concentrations and high temperatures of phosphoric acid inside the cell poses a severe challenge to the bipolar plate (BPP), a core component of the fuel cell stack. The bipolar plate plays a crucial role in separating reactant gases, conducting current, removing reaction products (water), and transferring heat within the fuel cell stack; its performance directly affects the stack's power density, lifespan, and cost.

[0003] Currently, there are two main technical routes for bipolar plates used in HT-PEMFC: graphite and metal.

[0004] Graphite bipolar plates: Traditional graphite bipolar plates possess excellent electrical conductivity and superior corrosion resistance. However, graphite is brittle, and to ensure sufficient airtightness and mechanical strength, graphite bipolar plates typically require a large thickness (usually greater than 1.5 mm), resulting in a bulky fuel cell stack with low volumetric and mass power densities, limiting its application in weight- and volume-sensitive fields such as automotive and drones.

[0005] Metal bipolar plates, represented by stainless steel and titanium alloys, have advantages such as high mechanical strength, good processability, and the ability to be made very thin (e.g., 0.1-0.2 mm), which can significantly improve the power density of the fuel cell stack. However, corrosion resistance is a major challenge in high-temperature phosphoric acid environments. Corrosion not only thins and perforates the metal bipolar plate itself, but more seriously, the metal ions produced by corrosion (such as Fe)... 3+ , Cr 3+ Ni 2+ Corrosion can migrate to the proton exchange membrane and catalyst layer, accelerating battery aging and degradation. Although surface coatings (such as carbon-based coatings or noble metal coatings) can slow down corrosion, coating technology is expensive and poses risks such as coating peeling and pinhole corrosion during long-term operation, making reliability a significant challenge.

[0006] Therefore, developing a new type of bipolar plate material and technology that can resist high-temperature phosphoric acid corrosion and possess the characteristics of being lightweight, thin, highly conductive, and low-cost is a key technical challenge that urgently needs to be solved to promote the commercial application of HT-PEMFC. Summary of the Invention

[0007] To address the aforementioned technical problems, this application provides a carbon fiber composite bipolar plate for high-temperature proton exchange membrane fuel cells and its preparation method.

[0008] To achieve the above objectives, the first aspect of the present invention provides a carbon fiber composite bipolar plate for a high-temperature proton exchange membrane fuel cell, wherein the carbon fiber composite bipolar plate operates at a temperature between 120°C and 180°C, and the high-temperature proton exchange membrane fuel cell employs a phosphate-doped polybenzimidazole (PBI) type proton exchange membrane; comprising: The conductive support framework, airtight filling phase, and interface conductive layer that together constitute the main body of the bipolar plate; The conductive support frame is a porous carbon paper or carbon cloth, used to provide core conductive pathways and mechanical support. The airtight filling phase fills the pores of the conductive support skeleton and is made of a high-temperature resistant polymer. After heat treatment, it forms a dense, non-porous structure. The conductive interfacial layer is disposed on at least one surface of the bipolar plate that is in contact with the gas diffusion layer, and is composed of a mixture of short carbon fibers, carbon nanotubes and carbon powder, and is used to reduce the interfacial contact resistance between the bipolar plate and the gas diffusion layer.

[0009] The carbon fiber composite bipolar plate provided by this invention aims to simultaneously solve the corrosion problem of metal bipolar plates in high-temperature phosphoric acid environments and the problems of bulkiness and complex processing of traditional graphite bipolar plates.

[0010] In one embodiment of the present invention, the material thickness of the carbon fiber composite bipolar plate is 0.1mm-0.4mm, wherein the thickness range in the embodiment is 0.15mm-0.25mm.

[0011] In one embodiment of the present invention, the porosity of the conductive support skeleton is 20%-80%, and the pore structure is uniformly distributed to adapt to the filling of the airtight filling phase and the construction of the conductive path.

[0012] In one embodiment of the present invention, the high-temperature resistant polymer of the gas-tight filling phase is selected from at least one of fluorinated ethylene propylene copolymer (FEP), polytetrafluoroethylene (PTFE), polyphenylene sulfide (PPS) or perfluoroalkoxyalkane (PFA). When the airtight filling phase is FEP, its mass fraction in the carbon fiber composite bipolar plate is 15%-40%.

[0013] In one embodiment of the present invention, the thickness of the interface conductive layer is 2μm-20μm; Among them, the length of the carbon fiber short fiber is 50μm-200μm, the particle size of the carbon powder is 1μm-10μm, and the length of the carbon nanotube is 1μm-25μm. The particle size and length of each component are matched to construct a multi-point conductive network.

[0014] In one embodiment of the present invention, the mass fraction of each component in the interface conductive layer is: The composition consists of 30%-70% carbon fiber short fibers, 30%-70% carbon powder, and 0.5%-2% carbon nanotubes; the interface conductive layer is embedded in the surface of the bipolar plate to form a gradient transition region rich in conductive fillers.

[0015] To achieve the above objectives, a second aspect of the present invention provides a method for preparing a carbon fiber composite bipolar plate for a high-temperature proton exchange membrane fuel cell as described in any one of the first aspects. This method employs a pre-impregnated fabric process and specifically includes the following steps: Step S1: Carbon fiber paper or carbon fiber cloth is mixed with high-temperature resistant polymer through powder solution impregnation or melt extrusion process to prepare carbon fiber / high-temperature resistant polymer prepreg cloth with a predetermined basis weight and polymer content. Step S2: Mix carbon fiber short fibers, carbon nanotubes and carbon powder to form a conductive paste, and uniformly coat it onto at least one surface of the prepreg fabric obtained in step S1. Step S3: Stack one or more prepreg fabrics coated in step S2 in a mold with a preset flow field structure, and hot press them at a temperature higher than the melting point of the high-temperature resistant polymer and a preset pressure to make the high-temperature resistant polymer melt and flow and solidify the multilayer prepreg fabrics into a dense whole, while imprinting gas flow field channels. Preferably, if the prepreg coated in step S2 is a single layer, the single-layer coated prepreg is placed in a mold with a preset flow field structure and hot-pressed at a temperature higher than the melting point of the high-temperature resistant polymer and a preset pressure, so that the high-temperature resistant polymer flows and the single-layer prepreg is solidified into a dense whole. Step S4: Maintain pressure and cool down until the pre-impregnated fabric is completely cured and molded, then release the pressure and demold to obtain the finished carbon fiber composite bipolar plate.

[0016] This preparation method employs a hot-pressing process, which can complete the densification and flow field shaping of the sheet material in one step. It boasts high production efficiency, is suitable for large-scale, low-cost manufacturing, and avoids the complex machining processes required for graphite sheets. The raw materials used (carbon paper, FEP, toner, etc.) are all mature industrial products with wide availability and controllable costs, demonstrating strong potential for industrial application.

[0017] In one embodiment of the present invention, in step S1, the high-temperature resistant polymer is FEP, which is in the form of powder or emulsion; The FEP content in the prepreg fabric is 15%-40% by mass.

[0018] In one embodiment of the present invention, in step S2, the preparation process of the conductive paste is as follows: First, mix carbon fiber short fibers, carbon nanotubes, and carbon powder in a mass ratio of 30-70:0.5-2:30-70 until homogeneous, then add a small amount of FEP emulsion and stir until a paste is formed. After processing with the coating process described above, the dry film thickness of the conductive layer at the interface is controlled to be 2μm-20μm.

[0019] In one embodiment of the present invention, in step S3, the preset flow field structure of the mold is a serpentine flow field; The hot pressing temperature is 10℃-100℃ higher than the polymer melting point, the holding time is 10min-20min, and the temperature uniformity deviation of the mold during the hot pressing process does not exceed ±5℃.

[0020] In one embodiment of the present invention, in step S4, the cooling method is liquid cooling or gradient natural cooling, and the cooling rate is controlled at 5℃ / min-15℃ / min.

[0021] The beneficial effects that this application can produce include: 1) The present application provides a carbon fiber composite bipolar plate for high-temperature proton exchange membrane fuel cells, which aims to simultaneously solve the corrosion problem of metal bipolar plates in high-temperature phosphoric acid environment and the problems of bulkiness and complex processing of traditional graphite bipolar plates.

[0022] 2) This application provides a carbon fiber composite bipolar plate for high-temperature proton exchange membrane fuel cells and its preparation method. By organically combining a carbon paper / carbon cloth skeleton, an FEP filling phase, and a carbon fiber short fiber / carbon nanotube / carbon powder interface layer, the carbon skeleton ensures high conductivity and lightweight. FEP, as a thermoplastic fluoropolymer, not only provides excellent resistance to phosphoric acid corrosion and airtightness but also acts as a binder in the hot-pressing process. The unique interface layer design utilizes carbon materials of different scales to construct a multi-point contact network, effectively solving the technical problem of increased contact resistance caused by resin enrichment on the surface of the composite material.

[0023] 3) The carbon fiber composite bipolar plate and its preparation method for high-temperature proton exchange membrane fuel cells provided in this application fundamentally avoid metal corrosion and ion dissolution problems by using carbon and FEP, both of which are highly inert materials in high-temperature phosphoric acid, thus ensuring the long life and stability of the fuel cell stack. Furthermore, due to the use of lightweight carbon fiber materials and the ability to produce thin plates with a thickness of only 0.2-0.4 mm through hot pressing, the mass power density and volumetric power density of the fuel cell stack can be significantly improved.

[0024] 4) This application provides a method for preparing carbon fiber composite bipolar plates for high-temperature proton exchange membrane fuel cells. This method employs a hot-pressing molding process, which can complete the densification and flow field shaping of the plates in one step, resulting in high production efficiency. It is suitable for large-scale, low-cost manufacturing and avoids the complex machining processes required for graphite plates. The raw materials used (carbon paper, FEP, carbon powder, etc.) are all mature industrial products with wide availability and controllable costs, demonstrating strong prospects for industrial application. Attached Figure Description

[0025] Figure 1 This is a schematic diagram of a carbon fiber bipolar plate with an unformed flow field provided in one embodiment of this application; Figure 2 This is a schematic diagram of a carbon fiber bipolar plate with a flow channel after hot pressing containing a single-layer interface layer, provided in one embodiment of this application. Figure 3 This is a schematic diagram of a carbon fiber bipolar plate with flow channels after hot pressing and containing a double-layer interface layer, provided in one embodiment of this application. Figure 4 This is a flowchart illustrating a method for preparing a carbon fiber composite bipolar plate for a high-temperature proton exchange membrane fuel cell according to one embodiment of this application. 100-Conductive support frame; 200 - Airtight packed phase; 300 - Interface conductive layer. Detailed Implementation

[0026] The present application is described in detail below with reference to the embodiments, but the present application is not limited to these embodiments.

[0027] Figure 1 This is a schematic diagram of a carbon fiber bipolar plate with an unformed flow field provided in one embodiment of this application. Figure 2 This is a schematic diagram of a carbon fiber bipolar plate with flow channels after hot pressing and containing a single-layer interface layer, according to one embodiment of this application. Figure 3 This is a schematic diagram of a carbon fiber bipolar plate with flow channels after hot pressing and containing a double-layer interface layer, provided in one embodiment of this application.

[0028] Please refer to Figure 1-3 This invention provides a carbon fiber composite bipolar plate for a high-temperature proton exchange membrane fuel cell, wherein the carbon fiber composite bipolar plate operates at a temperature between 120°C and 180°C, and the high-temperature proton exchange membrane fuel cell employs a phosphate-doped polybenzimidazole (PBI) type proton exchange membrane; it comprises: The conductive support frame 100, the airtight filling phase 200 and the interface conductive layer 300 together constitute the main body of the bipolar plate. The conductive support frame 100 is a porous carbon paper or carbon cloth, used to provide core conductive pathways and mechanical support. The airtight filling phase 200 fills the pores of the conductive support skeleton 100, is made of high temperature resistant polymer, and forms a dense non-porous structure after heat treatment. The interface conductive layer 300 is disposed on at least one surface of the bipolar plate that is in contact with the gas diffusion layer, and is composed of a mixture of carbon fiber short fibers, carbon nanotubes and carbon powder, and is used to reduce the interfacial contact resistance between the bipolar plate and the gas diffusion layer.

[0029] The carbon fiber composite bipolar plate provided by this invention aims to simultaneously solve the corrosion problem of metal bipolar plates in high-temperature phosphoric acid environments and the problems of bulkiness and complex processing of traditional graphite bipolar plates.

[0030] In one embodiment of the present invention, the material thickness of the carbon fiber composite bipolar plate is 0.1mm-0.4mm, wherein the thickness range in the embodiment is 0.15mm-0.25mm.

[0031] In one embodiment of the present invention, the porosity of the conductive support skeleton 100 is 20%-80%, and the pore structure is uniformly distributed to adapt to the filling of the airtight filling phase 200 and the construction of conductive pathways.

[0032] In one embodiment of the present invention, the high-temperature resistant polymer of the hermetically sealed filling phase 200 is selected from at least one of fluorinated ethylene propylene copolymer (FEP), polytetrafluoroethylene (PTFE), polyphenylene sulfide (PPS), or perfluoroalkoxyalkane (PFA). When the airtight filling phase is FEP, its mass fraction in the carbon fiber composite bipolar plate is 15%-40%.

[0033] In one embodiment of the present invention, the thickness of the interface conductive layer 300 is 2μm-20μm; Among them, the length of the carbon fiber short fiber is 50μm-200μm, the particle size of the carbon powder is 1μm-10μm, and the length of the carbon nanotube is 1μm-25μm. The particle size and length of each component are matched to construct a multi-point conductive network.

[0034] In one embodiment of the present invention, the mass fraction of each component in the interface conductive layer 300 is as follows: The composition consists of 30%-70% carbon fiber short fibers, 30%-70% carbon powder, and 0.5%-2% carbon nanotubes; and the interface conductive layer 300 is embedded in the surface layer of the bipolar plate to form a gradient transition region rich in conductive fillers.

[0035] Corresponding to the carbon fiber composite bipolar plates for high-temperature proton exchange membrane fuel cells provided in the above embodiments, one embodiment of the present invention also provides a method for preparing carbon fiber composite bipolar plates for high-temperature proton exchange membrane fuel cells.

[0036] Figure 4 This is a flowchart illustrating a method for preparing a carbon fiber composite bipolar plate for a high-temperature proton exchange membrane fuel cell according to one embodiment of this application.

[0037] Please refer to Figure 4 This invention provides a method for preparing carbon fiber composite bipolar plates for high-temperature proton exchange membrane fuel cells. The method employs a pre-impregnated fabric process and specifically includes the following steps: Step S1: Carbon fiber paper or carbon fiber cloth is mixed with high-temperature resistant polymer through powder solution impregnation or melt extrusion process to prepare carbon fiber / high-temperature resistant polymer prepreg cloth with a predetermined basis weight and polymer content. Step S2: Mix carbon fiber short fibers, carbon nanotubes and carbon powder to form a conductive paste, and uniformly coat it onto at least one surface of the prepreg fabric obtained in step S1. Step S3: Stack one or more prepreg fabrics coated in step S2 in a mold with a preset flow field structure, and hot press them at a temperature higher than the melting point of the high-temperature resistant polymer and a preset pressure to make the high-temperature resistant polymer melt and flow and solidify the multilayer prepreg fabrics into a dense whole, while imprinting gas flow field channels. Preferably, if the prepreg coated in step S2 is a single layer, the single-layer coated prepreg is placed in a mold with a preset flow field structure and hot-pressed at a temperature higher than the melting point of the high-temperature resistant polymer and a preset pressure, so that the high-temperature resistant polymer flows and the single-layer prepreg is solidified into a dense whole. Step S4: Maintain pressure and cool down until the pre-impregnated fabric is completely cured and molded, then release the pressure and demold to obtain the finished carbon fiber composite bipolar plate.

[0038] This preparation method employs a hot-pressing process, which can complete the densification and flow field shaping of the sheet material in one step. It boasts high production efficiency, is suitable for large-scale, low-cost manufacturing, and avoids the complex machining processes required for graphite sheets. The raw materials used (carbon paper, FEP, toner, etc.) are all mature industrial products with wide availability and controllable costs, demonstrating strong potential for industrial application.

[0039] In one embodiment of the present invention, in step S1, the high-temperature resistant polymer is FEP, which is in the form of powder or emulsion. The FEP content in the prepreg fabric is 15%-40% by mass.

[0040] In one embodiment of the present invention, in step S2, the preparation process of the conductive paste is as follows: First, mix carbon fiber short fibers, carbon nanotubes, and carbon powder in a mass ratio of 30-70:0.5-2:30-70 until homogeneous, then add a small amount of FEP emulsion and stir until a paste is formed. After processing with the coating process described above, the dry film thickness of the conductive layer at the interface is controlled to be 2μm-20μm.

[0041] In one embodiment of the present invention, in step S3, the preset flow field structure of the mold is a serpentine flow field; The hot pressing temperature is 10℃-100℃ higher than the polymer melting point, the holding time is 10min-20min, and the temperature uniformity deviation of the mold during the hot pressing process does not exceed ±5℃.

[0042] In one embodiment of the present invention, in step S4, the cooling method is liquid cooling or gradient natural cooling, and the cooling rate is controlled at 5℃ / min-15℃ / min.

[0043] The preparation method is explained in detail below: Example 1 Step 1, Substrate Selection: Freudenberg's H23C2 commercial carbon paper was selected as the conductive support skeleton 100.

[0044] Step 2, Pre-impregnation: FEP film (thickness ~200μm) is hot-melted with H23C2 to obtain carbon paper prepreg with FEP attached.

[0045] Step 3, Interface layer preparation and coating: Carbon fiber short fibers with an average length of 100 μm, graphite powder with an average particle size of 5 μm, and carbon nanotubes with an average length of 20 μm were mixed at a mass ratio of 1:2:0.03. This mixture was then combined with a small amount of FEP emulsion and stirred until a paste-like conductive paste was formed. The paste was then screen-printed evenly onto both sides of a prepreg, with the dry film thickness controlled to approximately 10 μm.

[0046] Step 4, hot pressing: Preheat the steel mold with the serpentine flow field channel to 320°C. Place the prepared composite billet into the mold and hot-press it at a pressure of 10 MPa for 15 minutes.

[0047] Step 5, Cooling and Demolding: While maintaining constant pressure, the mold is cooled to below 100°C. The pressure is released and the sample is removed, yielding a thin composite bipolar plate with a thickness of approximately 0.25 mm and clear flow field channels on its surface.

[0048] The bipolar plates prepared above were subjected to performance testing: Air tightness test: At a pressure difference of 150 kPa, the hydrogen permeability is less than 10. -6 ml·cm -2 s -1 It meets the sealing requirements.

[0049] Conductivity test: The through-plane conductivity is greater than 120 S / cm.

[0050] Interface contact resistance (ICR) test: The interfacial contact resistance with carbon paper (simulating a gas diffusion layer) is less than 8 mΩ·cm².

[0051] Corrosion resistance test: When immersed in 85% phosphoric acid at 160℃ for 500 hours, the mass loss rate was less than 0.1%, there were no obvious changes on the surface, and no significant degradation of various electrical properties.

[0052] In summary, the test results show that the composite bipolar plate prepared by this invention fully meets the stringent requirements for use in HT-PEMFC.

[0053] Example 2 Step 1, Preparation of pre-impregnated fabric: Short carbon fibers with an average length of 3 mm were added to water, and after adding a dispersant, the mixture was stirred at high speed to form a uniform fiber suspension.

[0054] FEP powder with an average particle size of 5 μm was added to the above suspension and stirred continuously to allow the FEP powder to be uniformly adsorbed on the carbon fiber surface.

[0055] Using a process similar to "wet papermaking", the mixed slurry is filtered, dehydrated and dried on a forming wire L to produce a pre-impregnated felt material (i.e., pre-impregnated cloth) that is uniformly mixed with carbon fiber and FEP powder, with its surface density controlled at 150 g / m², of which the mass fraction of FEP is about 30%.

[0056] Step 2, Interface layer coating: Similar to Example 1, a conductive paste was prepared by mixing carbon fiber short fibers with an average length of 100 μm and graphite powder with an average particle size of 5 μm (mass ratio 1:2) with FEP emulsion.

[0057] The slurry was uniformly coated on both sides of the pre-impregnated fabric using a scraping process, and the dry film coating thickness was controlled to be 15μm.

[0058] Step 3, hot pressing: Place a prepreg cloth coated with interface into a mold engraved with a symmetrical serpentine flow field.

[0059] The mold is heated to 320°C, a pressure of 10 MPa is applied, and the pressure is maintained for 15 minutes. During this process, the FEP resin completely melts, impregnates all the carbon fibers, and fills all the micropores to form a dense composite material sheet.

[0060] Step 4, Cooling and Demolding: Maintain pressure, cool the mold with water to below 100°C, then release the pressure, open the mold, and remove the finished product.

[0061] The final product is a thin composite bipolar plate with a thickness of approximately 0.3 mm, uniform performance, smooth surface, and clear flow field.

[0062] The above description is merely a few embodiments of this application and is not intended to limit this application in any way. Although this application discloses preferred embodiments as described above, it is not intended to limit this application. Any changes or modifications made by those skilled in the art without departing from the scope of the technical solution of this application using the disclosed technical content are equivalent to equivalent implementation cases and fall within the scope of the technical solution.

Claims

1. A carbon fiber composite bipolar plate for high temperature proton exchange membrane fuel cells, characterized by, The working temperature of the carbon fiber composite bipolar plate is between 120-180℃, and the high-temperature proton exchange membrane fuel cell adopts a phosphoric acid doped polybenzimidazole proton exchange membrane; It comprises: The conductive support framework, the airtight filling phase and the interface conductive layer cooperatively constitute the bipolar plate body; The conductive support framework is a porous carbon paper or carbon cloth, which is used to provide core conductive paths and mechanical support; The airtight filling phase is filled in the pores of the conductive support framework, which is composed of high-temperature resistant polymers and forms a dense and pore-free structure after heat treatment; The interface conductive layer is arranged on at least one surface of the bipolar plate in contact with the gas diffusion layer, which is composed of a mixture of carbon fiber short fibers, carbon nanotubes and carbon powder, and is used to reduce the interface contact resistance between the bipolar plate and the gas diffusion layer.

2. The carbon fiber composite bipolar plate of claim 1, wherein, The material thickness of the carbon fiber composite bipolar plate is 0.1-0.4mm, and the thickness range in the implementation state is 0.15-0.25mm.

3. The carbon fiber composite bipolar plate of claim 1, wherein, The porosity of the conductive support framework is 20-80%, and the pore structure is uniformly distributed to adapt to the filling of the airtight filling phase and the construction of the conductive path.

4. The carbon fiber composite bipolar plate of claim 1, wherein, The high-temperature resistant polymer of the airtight filling phase is selected from at least one of fluorinated ethylene-propylene copolymer, polytetrafluoroethylene, polyphenylene sulfide or perfluoroalkoxy alkane; When the airtight filling phase is fluorinated ethylene-propylene copolymer, the mass fraction of the airtight filling phase in the carbon fiber composite bipolar plate is 15-40%.

5. The carbon fiber composite bipolar plate of claim 1, wherein The thickness of the interface conductive layer is 2-20μm; The length of the carbon fiber short fiber is 50-200μm, the particle size of the carbon powder is 1-10μm, and the length of the carbon nanotube is 1-25μm, and the particle size and length of each component are matched to construct a multi-point conductive network. Preferably, the mass fraction of each component in the interface conductive layer is: Carbon fiber short fiber 30-70%, carbon powder 30-70%, and carbon nanotube 0.5-2%; and the interface conductive layer is embedded in the surface layer of the bipolar plate to form a gradient transition zone rich in conductive fillers.

6. A method of making a carbon fiber composite bipolar plate for high temperature proton exchange membrane fuel cells according to any one of claims 1-5, characterized in that, The pre-impregnated cloth process specifically includes the following steps: Step S1, carbon fiber paper or carbon fiber cloth is impregnated with high-temperature resistant polymers by powder solution impregnation or melt extrusion process to prepare carbon fiber / high-temperature resistant polymer pre-impregnated cloth with a predetermined grammage and polymer content; Step S2, carbon fiber short fibers, carbon nanotubes and carbon powder are mixed to prepare a conductive slurry, which is uniformly coated on at least one surface of the pre-impregnated cloth obtained in step S1; Step S3, one or more pre-impregnated cloths coated by step S2 are stacked in a mold with a pre-set flow field structure, and heat pressing is carried out at a temperature higher than the melting point of the high-temperature resistant polymer and a pre-set pressure, so that the high-temperature resistant polymer melts and flows, and the multi-layer pre-impregnated cloth is solidified into a dense whole, and at the same time, the gas flow field channel is pressed out; Preferably, if the pre-impregnated cloth coated by step S2 is single-layer, the single-layer coated pre-impregnated cloth is placed in a mold with a pre-set flow field structure, and heat pressing is carried out at a temperature higher than the melting point of the high-temperature resistant polymer and a pre-set pressure, so that the high-temperature resistant polymer flows and the single-layer pre-impregnated cloth is solidified into a dense whole. Step S4, keeping the pressure state, cooling to completely solidify the pre-impregnated cloth, then unloading the pressure to get the finished carbon fiber composite bipolar plate.

7. The method of claim 6, wherein the method further comprises, In the step S1, the high-temperature-resistant polymer is fluorinated ethylene-propylene copolymer, which is in the form of powder or emulsion; The mass fraction of the fluorinated ethylene-propylene copolymer in the pre-impregnated cloth is 15%-40%.

8. The method of claim 6, wherein, In the step S2, the preparation process of the conductive paste is as follows: First, mix the carbon fiber short fiber, carbon nanotube and carbon powder according to the mass ratio of 30-70:0.5-2:30-70, then add a small amount of fluorinated ethylene-propylene copolymer emulsion and stir until it is paste-like; After the coating process is adopted, the dry film thickness of the coated interface conductive layer is controlled to be 2-20 microns.

9. The method of claim 6, wherein, In the step S3, the preset flow field structure of the mold is a serpentine flow field. The hot-pressing temperature is 10-100 degrees Celsius higher than the melting point of the polymer, the pressure holding time is 10-20 minutes, and the uniformity deviation of the mold temperature during the hot-pressing process is not more than ±5 degrees Celsius.

10. The method of claim 6, wherein, In the step S4, the cooling method is liquid cooling or gradient natural cooling, and the cooling rate is controlled to be 5-15 degrees Celsius per minute.

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