A high-conductivity composite material bipolar plate for fuel cell and preparation method thereof

Abstract

The present invention relates to a highly conductive composite material bipolar plate for a fuel cell and a method for preparing the same. The composite material bipolar plate is composed of a thermosetting resin and a three-dimensional graphite network structure. The present invention first mixes graphite powder and powdered ammonium bicarbonate in a high-pressure mixer, presses the mixed graphite powder and ammonium bicarbonate into a bipolar plate shape at room temperature and high pressure, and then transfers the resulting graphite / ammonium bicarbonate composite plate to a blast oven for heating. After the ammonium bicarbonate volatilizes at high temperature, a three-dimensional graphite skeleton remains. Finally, the three-dimensional graphite skeleton is impregnated with a liquid thermosetting resin under vacuum conditions, and after curing, a composite bipolar plate having a three-dimensional graphite conductive network is obtained. The composite material bipolar plate prepared by the present invention has the advantages of high electrical conductivity, low contact resistance, good thermal conductivity, high bending strength, and good hydrophobicity. The composite bipolar plate can significantly improve the performance of fuel cells.

Description

Technical Field

[0001] The present invention relates to a high-conductivity composite material bipolar plate for fuel cells and a preparation method thereof, and relates to the technical field of fuel cell bipolar plate manufacturing. Background Art

[0002] Proton exchange membrane fuel cells (PEMFCs) are increasingly being used in transportation, energy storage, power generation, and portable power sources due to their high energy conversion efficiency and clean, pollution-free operation. Bipolar plates are crucial multifunctional components of PEMFCs, accounting for approximately 60-80% of the fuel cell stack's weight and 30-50% of its cost. The primary function of bipolar plates is to transport reactant gases to the membrane electrode through the gas flow field on their surface, while also collecting and conducting electrical current and dissipating the heat of the reaction and the resulting water. Therefore, bipolar plates must possess excellent electrical and thermal conductivity, good hydrophobicity, and superior mechanical properties.

[0003] Currently, three main bipolar plate materials are being researched and applied: graphite, metal, and composite. Graphite bipolar plates, with their excellent electrical conductivity and corrosion resistance, were the first material used in fuel cell bipolar plate manufacturing. However, manufacturing and processing are difficult, costly, and exhibit poor airtightness. Metal bipolar plates offer excellent electrical conductivity, thermal conductivity, machinability, and gas tightness, but suffer from poor corrosion resistance. Corrosion of these plates can significantly reduce the lifespan of PEMFC stacks. Composite bipolar plates are made using graphite as a conductive filler and a polymer resin as a binder. Due to their excellent corrosion resistance, processability, and low cost, composite bipolar plates are becoming a new trend in fuel cell bipolar plate development. However, during the processing of composite bipolar plates, the resin flows, making it difficult for the conductive filler to form a continuous conductive network. Furthermore, the resin accumulates on the plate surface, resulting in poor bulk conductivity and high contact resistance. Traditional composite bipolar plates typically use expensive fillers such as carbon nanotubes, graphene, and carbon fibers in combination with graphite. While this method can improve conductivity, the filler content, as high as 70-80%, can severely impact the mechanical and processing properties of the composite bipolar plates. To address the two key issues of poor bulk conductivity and high contact resistance in composite materials, the present invention proposes the following inventive aspects. Summary of the Invention

[0004] In view of the problems that the current composite material bipolar plates have, such as the difficulty in constructing a three-dimensional conductive network due to the flow of polymer resin during the molding process, and the resin enrichment on the surface of the bipolar plate, which affects the conductivity and contact resistance of the composite bipolar plate itself, the purpose of the present invention is to provide a composite material bipolar plate with an efficient three-dimensional conductive network and a preparation method thereof.

[0005] In order to achieve the above technical objectives, the present invention is implemented through the following technical solutions.

[0006] A method for preparing a highly conductive composite bipolar plate for a fuel cell comprises the following steps: firstly, graphite powder and ammonium bicarbonate are uniformly mixed in a high-pressure mixer, and then pressed at room temperature and high pressure to form a graphite / ammonium bicarbonate composite plate in the shape of a bipolar plate. Then, the ammonium bicarbonate is heated to volatilize, thereby obtaining a three-dimensional graphite skeleton. Finally, the three-dimensional graphite skeleton is impregnated with a liquid thermosetting resin to obtain a composite bipolar plate having a three-dimensional graphite conductive network.

[0007] More preferably, the method for preparing a highly conductive composite material bipolar plate for a fuel cell is as follows: Figure 1 As shown, the following steps are included:

[0008] 1) Graphite powder and powdered ammonium bicarbonate are uniformly mixed in a high-speed mixer, poured into a bipolar plate forming mold with a flow field, and molded for 5-10 minutes at room temperature and 200-300 MPa to obtain a graphite / ammonium bicarbonate composite plate.

[0009] 2) heating the graphite / ammonium bicarbonate composite plate obtained in step 1) in a forced air oven at 85-100° C. for 5-10 hours to volatilize the ammonium bicarbonate, thereby obtaining a three-dimensional graphite skeleton.

[0010] 3) Impregnating the three-dimensional graphite skeleton obtained in step 2) with a liquid thermosetting resin: impregnating the three-dimensional graphite skeleton with a liquid thermosetting resin at room temperature and vacuum conditions, removing excess thermosetting resin from the surface of the composite bipolar plate after impregnation for 30-60 minutes, and then curing at room temperature for 6-10 hours to finally obtain a composite material bipolar plate with a three-dimensional graphite conductive network.

[0011] More preferably, in the above step 1), the graphite powder is one or more of flake graphite, artificial graphite and expanded graphite; the particle size of the graphite powder is 10-100 μm, and the volume content of the graphite powder is 10%-60%.

[0012] More preferably, in the above step 1), the particle size of the ammonium bicarbonate is 200-300 μm, and the volume content of the ammonium bicarbonate is 40%-90%.

[0013] More preferably, in the above step 3), the liquid thermosetting resin is one or more of epoxy resin, phenolic resin and unsaturated resin that cures at room temperature.

[0014] More preferably, the content of graphite powder in the composite material bipolar plate is 10%-60%, and the content of thermosetting resin is 40%-90%; and the thickness of the composite bipolar plate is 1.0-4.0 mm.

[0015] The present invention also provides a highly conductive composite material bipolar plate for a fuel cell, wherein the bipolar plate has a three-dimensionally interconnected graphite conductive network inside.

[0016] Compared with the prior art, the present invention has the following advantages:

[0017] 1. This invention creates a highly efficient conductive network within the composite bipolar plate. Compared to conventional composite bipolar plates, this invention significantly improves the conductivity of the composite bipolar plate while maintaining a lower graphite content. Furthermore, the composite bipolar plate produced by this invention exhibits advantages such as low contact resistance, high thermal conductivity, excellent mechanical properties, and hydrophobicity.

[0018] 2. Due to the construction of the three-dimensional graphite conductive network, the composite bipolar plate prepared by the present invention can significantly improve the power density of the proton exchange membrane fuel cell.

[0019] 3. The preparation method and principle of the composite material bipolar plate involved in the present invention are simple, the processing conditions and equipment requirements are simple, and the cost is low. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 It is a schematic diagram of the preparation method of the composite material bipolar plate in the present invention. DETAILED DESCRIPTION

[0021] The present invention will be described in further detail below with reference to specific examples, but the embodiments of the present invention are not limited thereto. For process parameters not particularly noted, conventional techniques may be used.

[0022] Example 1

[0023] 1) 40% by volume of flake graphite powder (25 μm) and 60% by volume of ammonium bicarbonate (200 μm) were mixed evenly. The mixed flake graphite powder / ammonium bicarbonate was poured into a bipolar plate mold with a flow channel and pressed into a 2 mm thick flake graphite powder / ammonium bicarbonate composite plate at room temperature and 300 MPa.

[0024] 2) placing the pressed flake graphite powder / ammonium bicarbonate composite plate in a forced air oven at 90° C. and heating for 10 h to volatilize and remove the ammonium bicarbonate, thereby obtaining a three-dimensional graphite skeleton with a volume fraction of 40%.

[0025] 3) The obtained 40% volume fraction three-dimensional graphite skeleton was placed in a liquid epoxy resin that cures at room temperature. After immersion for 30 minutes at room temperature and vacuum conditions, excess epoxy resin on the surface of the plate was removed, and then the plate was cured at room temperature for 10 hours to obtain a composite bipolar plate 1.

[0026] Example 2

[0027] 1) 60% by volume of flake graphite powder (25 μm) and 40% by volume of ammonium bicarbonate (200 μm) were mixed evenly, the mixed flake graphite powder / ammonium bicarbonate was poured into a bipolar plate mold with a flow channel, and pressed into a 2 mm thick flake graphite powder / ammonium bicarbonate composite plate at room temperature and 300 MPa.

[0028] 2) placing the pressed flake graphite powder / ammonium bicarbonate composite plate in a forced air oven at 90° C. and heating for 10 h to volatilize and remove the ammonium bicarbonate, thereby obtaining a three-dimensional graphite skeleton with a volume fraction of 60%.

[0029] 3) The obtained 60% volume fraction three-dimensional graphite skeleton was placed in a liquid epoxy resin that cures at room temperature. After immersion for 30 minutes at room temperature and vacuum conditions, excess epoxy resin on the surface of the plate was removed, and then the plate was cured at room temperature for 10 hours to obtain a composite bipolar plate 2.

[0030] Example 3

[0031] 1) 60% by volume of expanded graphite powder (25 μm) and 40% by volume of ammonium bicarbonate (200 μm) were mixed evenly, the mixed expanded graphite powder / ammonium bicarbonate was poured into a bipolar plate mold with a flow channel, and pressed into a 2 mm thick expanded graphite powder / ammonium bicarbonate composite plate at room temperature and 300 MPa.

[0032] 2) placing the pressed expanded graphite powder / ammonium bicarbonate composite plate in a forced air oven at 90° C. and heating for 10 h to volatilize and remove the ammonium bicarbonate, thereby obtaining a three-dimensional graphite skeleton with a volume fraction of 60%.

[0033] 3) The obtained 60% volume fraction three-dimensional graphite skeleton was placed in a liquid epoxy resin that cures at room temperature. After immersion for 30 minutes at room temperature and vacuum conditions, excess epoxy resin on the plate surface was removed, and then the plate was cured at room temperature for 10 hours to obtain a composite bipolar plate 3.

[0034] Example 4

[0035] 1) 60% by volume of artificial graphite powder (25 μm) and 40% by volume of ammonium bicarbonate (200 μm) were mixed evenly, the mixed artificial graphite powder / ammonium bicarbonate was poured into a bipolar plate mold with a flow channel, and pressed into a 2 mm thick artificial graphite powder / ammonium bicarbonate composite plate at room temperature and 300 MPa.

[0036] 2) placing the pressed artificial graphite powder / ammonium bicarbonate composite plate in a forced air oven at 90° C. and heating for 10 hours to volatilize and remove the ammonium bicarbonate, thereby obtaining a three-dimensional graphite skeleton with a volume fraction of 60%.

[0037] 3) The obtained 60% volume fraction three-dimensional graphite skeleton was placed in a liquid epoxy resin that cures at room temperature. After immersion for 30 minutes at room temperature and vacuum conditions, excess epoxy resin on the surface of the plate was removed, and then the plate was cured at room temperature for 10 hours to obtain a composite bipolar plate 4.

[0038] Example 5

[0039] 1) 60% by volume of graphite powder (flake graphite (25 μm): expanded graphite (25 μm) volume ratio = 1:1) and 40% by volume of ammonium bicarbonate (200 μm) were mixed uniformly. The mixed graphite powder / ammonium bicarbonate was poured into a bipolar plate mold with a flow channel and pressed at room temperature and 300 MPa to form a 2 mm thick flake graphite powder / ammonium bicarbonate composite plate.

[0040] 2) placing the pressed graphite powder / ammonium bicarbonate composite plate in a forced air oven at 90° C. and heating for 10 h to volatilize and remove the ammonium bicarbonate, thereby obtaining a three-dimensional graphite skeleton with a volume fraction of 60%.

[0041] 3) The obtained 60% volume fraction three-dimensional graphite skeleton was placed in a liquid epoxy resin that cures at room temperature. After immersion for 30 minutes at room temperature and vacuum conditions, excess epoxy resin on the plate surface was removed, and then the plate was cured at room temperature for 10 hours to obtain a composite bipolar plate 5.

[0042] Example 6

[0043] 1) 60% by volume of graphite powder (flake graphite (25 μm): expanded graphite (25 μm) volume ratio = 1:1) and 40% by volume of ammonium bicarbonate (200 μm) were mixed uniformly. The mixed graphite powder / ammonium bicarbonate was poured into a bipolar plate mold with a flow channel and pressed at room temperature and 300 MPa to form a 2 mm thick flake graphite powder / ammonium bicarbonate composite plate.

[0044] 2) placing the pressed graphite powder / ammonium bicarbonate composite plate in a forced air oven at 90° C. and heating for 10 h to volatilize and remove the ammonium bicarbonate, thereby obtaining a three-dimensional graphite skeleton with a volume fraction of 60%.

[0045] 3) The obtained 60% volume fraction three-dimensional graphite skeleton was placed in a liquid unsaturated resin that was cured at room temperature. After immersion for 30 minutes at room temperature and vacuum conditions, excess epoxy resin on the plate surface was removed, and then the plate was cured at room temperature for 10 hours to obtain a composite bipolar plate 6.

[0046] In order to further highlight the advantages of the composite bipolar plate prepared by the present invention, the performance of the composite bipolar plate prepared by the traditional method with the same filler content was compared.

[0047] Comparative Example 1

[0048] 40% volume fraction of flake graphite powder (25 μm) was evenly mixed with liquid epoxy resin, and the mixed flake graphite powder / epoxy resin mixture was poured into a bipolar plate mold with a flow channel. The mixture was molded at room temperature and 20 MPa for 2 hours to obtain a flake graphite / epoxy resin composite plate with a flow channel (thickness 2 mm); it was then cured at room temperature for 10 hours to finally obtain the comparative composite bipolar plate 1.

[0049] Comparative Example 2

[0050] 60% volume fraction of flake graphite powder (25 μm) and 40% volume fraction of liquid epoxy resin were mixed evenly, and the mixed flake graphite powder / epoxy resin mixture was poured into a bipolar plate mold with a flow channel. The mixture was molded at room temperature and 20 MPa for 2 hours to obtain a flake graphite / epoxy resin composite plate with a flow channel (thickness 2 mm); then it was cured at room temperature for 10 hours to finally obtain the comparative composite bipolar plate 2.

[0051] Comparative Example 3

[0052] 60% volume fraction of expanded graphite powder (25 μm) and 40% volume fraction of liquid epoxy resin were evenly mixed. The mixed expanded graphite powder / epoxy resin mixture was poured into a bipolar plate mold with a flow channel. The mixture was molded at room temperature and 20 MPa for 2 hours to obtain an expanded graphite / epoxy resin composite plate with a flow channel (thickness 2 mm); the plate was then cured at room temperature for 10 hours to finally obtain the comparative composite bipolar plate 3.

[0053] Comparative Example 4

[0054] 60% volume fraction of artificial graphite powder (25 μm) and 40% volume fraction of liquid epoxy resin were mixed evenly, and the mixed artificial graphite powder / epoxy resin mixture was poured into a bipolar plate mold with a flow channel. The mixture was molded at room temperature and 20 MPa for 2 hours to obtain an artificial graphite / epoxy resin composite plate with a flow channel (thickness 2 mm); then it was cured at room temperature for 10 hours to finally obtain the comparative composite bipolar plate 4.

[0055] Comparative Example 5

[0056] A 60% volume fraction of graphite powder (volume ratio of flake graphite (25 μm): expanded graphite (25 μm) = 1:1) was evenly mixed with liquid epoxy resin. The mixed graphite powder / epoxy resin mixture was poured into a bipolar plate mold with a flow channel and molded at room temperature and 20 MPa for 2 hours to obtain a graphite / epoxy resin composite plate with a flow channel (thickness 2 mm); then cured at room temperature for 10 hours to finally obtain the comparative composite bipolar plate 5.

[0057] Comparative Example 6

[0058] A 60% volume fraction of graphite powder (volume ratio of flake graphite (25 μm): expanded graphite (25 μm) = 1:1) was evenly mixed with a liquid unsaturated resin. The mixed graphite powder / unsaturated resin mixture was poured into a bipolar plate mold with a flow channel, and molded at room temperature and 20 MPa for 2 hours to obtain a graphite / unsaturated resin composite plate with a flow channel (thickness 2 mm); then cured at room temperature for 10 hours to finally obtain a comparative composite bipolar plate 6.

[0059] Performance testing.

[0060] The electrical conductivity and contact resistance of the composite bipolar plates prepared in Examples 1-6 and Comparative Examples 1-6 were tested, respectively. The test results are shown in Table 1.

[0061] Table 1 Comparison of performance of composite bipolar plates between examples and comparative examples

[0062]

[0063] Through actual testing, it can be seen from the conductivity test results of the composite bipolar plates of the embodiment and the comparative example in Table 1 that, compared with the composite material bipolar plates prepared by the traditional method, the conductivity of the composite bipolar plates of the present invention can be significantly improved, and the contact resistance can be greatly reduced because an efficient conductive network is constructed in the composite bipolar plates.

[0064] The present invention compared the thermal conductivity, mechanical strength, and hydrophobicity of the composite bipolar plates prepared in Examples 1-6. The composite bipolar plates prepared in Examples 1-6 were also assembled in fuel cells for testing. The test results are shown in Table 2.

[0065] Table 2 Basic performance test results of composite bipolar plates of various examples

[0066]

[0067] Among them, compared with Example 2, Example 1 changes the volume fraction of flake graphite. The volume fraction of flake graphite in the composite bipolar plate of Example 1 is 40%, and the volume fraction of flake graphite in the composite bipolar plate of Example 2 is 60%. Comparing Examples 1-2, as the graphite content increases, the electrical conductivity, thermal conductivity, hydrophobicity and fuel cell performance of the composite bipolar plate are significantly improved. This is because the graphite content increases, and the composite bipolar plate in Example 2 has a more efficient graphite conduction network than that in Example 1. The increase in graphite content and the decrease in bending strength and hydrogen permeability are due to the reduction in resin matrix, but the bending strength and hydrogen permeability in Examples 1-2 meet the use standards of bipolar plates.

[0068] Compared to Examples 3 and 4, Example 2 differs in the type of graphite powder used: Example 2 uses flake graphite powder, Example 3 uses expanded graphite powder, and Example 4 uses artificial graphite powder. The volume fraction of the graphite powder in each of Examples 2, 3, and 4 is 60%, and the particle size is 25 μm. Comparing Examples 2-4, the composite bipolar plate prepared from flake graphite exhibits the best performance. This is likely because the flaky structure of flake graphite, compared to the blocky structures of expanded and artificial graphite, allows for a more easily formed, tightly connected conductive network.

[0069] Compared to Example 2, Example 5 varied the graphite powder ratio. Example 5 employed a mixture of flake graphite (25 μm) and expanded graphite (25 μm) at a volume ratio of 1:1, while Example 2 employed only flake graphite. Comparing Example 5 with Example 2, the composite bipolar plate in Example 5 exhibited superior performance compared to Example 2, attributed to the synergistic effect of the two different dimensional graphite powders: flake graphite and expanded graphite.

[0070] Compared to Example 5, Example 6 uses a different thermosetting resin: an unsaturated resin in Example 6 and an epoxy resin in Example 5. Comparing Examples 5 and 6, it can be seen that the change in the resin matrix significantly affects only the flexural strength of the composite bipolar plate. This is due to the inherent mechanical property differences between epoxy and unsaturated resins.

[0071] The terms used in this specification are for the purpose of describing specific embodiments only and are not intended to limit this specification. As used in one or more embodiments of this specification and the appended claims, the singular forms "a," "an," "the," and "the" are intended to include the plural forms, unless the context clearly indicates otherwise. It should also be understood that the term "and / or" used in one or more embodiments of this specification refers to and encompasses any and all possible combinations of one or more of the associated listed items.

Claims

1. A method for preparing a highly conductive composite material bipolar plate for a fuel cell, characterized in that: First, graphite powder and powdered ammonium bicarbonate are mixed uniformly, and then pressed at room temperature and high pressure to form a graphite / ammonium bicarbonate composite plate in the shape of a bipolar plate. The ammonium bicarbonate is then heated to volatilize, thereby obtaining a three-dimensional graphite skeleton. Finally, a liquid thermosetting resin is impregnated into the three-dimensional graphite skeleton under vacuum conditions, and after curing, a composite bipolar plate with a three-dimensional graphite conductive network is obtained. The following steps are involved: 1) Graphite powder and powdered ammonium bicarbonate are uniformly mixed in a high-speed mixer, poured into a bipolar plate forming mold with a flow field, and pressed at room temperature and 200-300 MPa for 5-10 minutes to obtain a graphite / ammonium bicarbonate composite plate; 2) heating the graphite / ammonium bicarbonate composite plate obtained in step 1) in a forced air oven at 85-100° C. for 5-10 hours to volatilize the ammonium bicarbonate, thereby obtaining a three-dimensional graphite skeleton; 3) impregnating the three-dimensional graphite skeleton obtained in step 2) with a liquid thermosetting resin: impregnating the three-dimensional graphite skeleton with the liquid thermosetting resin at room temperature under vacuum conditions, removing excess thermosetting resin from the surface of the composite bipolar plate after impregnation for 30-60 minutes, and then curing at room temperature for 5-10 hours to obtain a composite material bipolar plate having a three-dimensional graphite conductive network; The particle size of the graphite powder is 10-100 μm; In step 1), the particle size of the ammonium bicarbonate is 200-300 μm; based on the total volume of the graphite powder and the ammonium bicarbonate, the volume content of the ammonium bicarbonate is 40%-90%, and the volume content of the graphite powder is 10%-60%; The volume content of the graphite powder in the composite material bipolar plate is 10%-60%, and the volume content of the thermosetting resin in the composite material bipolar plate is 40%-90%.

2. The method for preparing a highly conductive composite material bipolar plate for a fuel cell according to claim 1, wherein: In step 1), the graphite powder is one or more of flake graphite, artificial graphite and expanded graphite.

3. The method for preparing a highly conductive composite material bipolar plate for a fuel cell according to claim 1, wherein: In step 3), the liquid thermosetting resin is one or more of epoxy resin, phenolic resin and unsaturated resin that cures at room temperature.

4. The method for preparing a highly conductive composite material bipolar plate for a fuel cell according to claim 1, wherein: The thickness of the composite bipolar plate is 1.0-4.0 mm.

5. A highly conductive composite bipolar plate for a fuel cell prepared by the preparation method according to any one of claims 1 to 4.

6. The highly conductive composite bipolar plate for fuel cells according to claim 5, characterized in that: The bipolar plate has a three-dimensional interconnected graphite conductive network inside.

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