A flexible bipolar plate for hydrogen fuel cells and its preparation method

Abstract

This invention relates to the field of hydrogen fuel cell technology, specifically to a flexible bipolar plate for hydrogen fuel cells and its preparation method. The flexible bipolar plate comprises a metal mesh skeleton and a conductive elastomer that fills and covers the metal mesh skeleton. The metal mesh skeleton is composed of copper mesh materials of different mesh sizes. The conductive elastomer is formed by curing a slurry containing 90-95 wt% silicone potting compound and 5-10 wt% carbon-based conductive filler, forming a three-dimensional interpenetrating conductive network. The metal mesh skeleton is completely covered by the elastomer to avoid direct contact with the reactant gases in the fuel cell. This invention uses a hot press molding process, where the conductive slurry is injected into a mold and hot-pressed to cure the conductive slurry, forming a flexible bipolar plate in the mold. This design features bendability, high conductivity, and light weight, significantly improving the energy density of hydrogen fuel cells. Furthermore, the materials used are inexpensive, and the hot-press molding process is simple and efficient.

Description

Technical Field

[0001] This invention belongs to the field of hydrogen fuel cell technology, specifically relating to a method for preparing a bipolar plate for a hydrogen fuel cell and the prepared bipolar plate. Background Technology

[0002] Bipolar plates, as one of the core components of hydrogen fuel cells, account for 60-80% of the stack's weight and volume, and 40-60% of its total cost. In fuel cells, bipolar plates play a crucial role in supporting the membrane electrode assembly, collecting current, and managing drainage. Excellent bipolar plates suitable for engineering applications should possess: good electrical conductivity, chemical stability, superior mechanical properties, good airtightness, good thermal conductivity, and consistent flow channel stability. Therefore, the performance of bipolar plates has a significant impact on the overall performance of hydrogen fuel cells.

[0003] Currently, the main types of bipolar plates can be divided into: graphite bipolar plates, metal bipolar plates, and composite bipolar plates. Each type has its own advantages and disadvantages, and there is still much room for improvement.

[0004] Graphite bipolar plates have wide applications in various industries such as automotive and energy due to their excellent electrical conductivity and chemical stability. However, the brittleness and porous nature of natural graphite makes it extremely difficult to process graphite bipolar plates to form flow channels and control gas permeation. Moreover, in order to meet the requirements of mechanical strength and gas permeability, graphite bipolar plates usually require a large plate thickness, which leads to an increase in the weight and volume of the fuel cell stack, severely restricting the lightweighting and power density improvement of fuel cells.

[0005] Metal bipolar plates possess superior mechanical properties, machinability, and density, along with excellent thermal and electrical conductivity. Their processing technology is also relatively mature, enabling mass production through methods such as drawing, extrusion, and plastic forming. However, a critical drawback lies in the complex internal working environment of fuel cells, which is typically characterized by complex acid-base, high-temperature, and high-humidity corrosive conditions. This makes metal bipolar plates highly susceptible to corrosion, passivation, or dissolution. The contact resistance of metal bipolar plates increases with usage time, and the metal ions released during corrosion can contaminate the membrane electrode assembly, causing a rapid decrease in conversion efficiency, severely hindering their widespread application. Currently, commercially available metal bipolar plates often require the addition of corrosion-resistant coatings to improve their lifespan and corrosion resistance; however, damage to the coating accelerates substrate corrosion. Furthermore, metal bipolar plates are prone to residual stress and microcracks after bending, making it difficult to simultaneously achieve both flexibility and lightweight design.

[0006] Composite bipolar plates (CBPs) are mainly made of polymers and conductive fillers. By adjusting parameters such as the type and ratio of fillers, the electrical conductivity, thermal conductivity, and corrosion resistance of the bipolar plates can be enhanced, resulting in a product that combines the advantages of the two types of bipolar plates. Therefore, CBPs are currently a very popular type of bipolar plate in research. However, the existing manufacturing process of composite bipolar plates is complex and costly, especially due to the high filler content, which limits their effect on reducing the weight of fuel cells. The high filler content in the raw materials of composite bipolar plates leads to high slurry viscosity, making it difficult to wet and reinforce the framework. Furthermore, the cured plate is brittle and hard. A high filler ratio also significantly increases material density, weakening the weight reduction effect. In addition, the large filler content results in poor flexibility of the composite bipolar plate, leading to poor bending performance and limiting the widespread application of CBPs.

[0007] In conclusion, reducing the weight and volume ratio of bipolar plates in fuel cells is of great significance for improving the overall energy density of hydrogen fuel cells and for promoting the application of hydrogen fuel cells. Summary of the Invention

[0008] The purpose of this invention is to overcome the problems of high volumetric mass ratio of bipolar plates in batteries and low battery energy density in existing technologies. In view of the defects of conventional composite bipolar plates, such as large filler usage, poor filler synergy, poor weight reduction effect and poor toughness of bipolar plates, this invention provides a method for preparing bipolar plates for hydrogen fuel cells and a bipolar plate.

[0009] To achieve the above objectives, the present invention provides the following technical solution:

[0010] In a first aspect, the present invention provides a flexible bipolar plate for hydrogen fuel cells, which has outstanding properties such as flexibility, high conductivity, and light weight, and can significantly improve the energy density of hydrogen fuel cells when assembled.

[0011] The specific solution is as follows: a flexible bipolar plate for a hydrogen fuel cell, the flexible bipolar plate comprising: A metal mesh skeleton, and a conductive elastomer that fills and covers the metal mesh skeleton; The metal mesh skeleton is made of 40-500 mesh copper mesh material; The conductive elastomer is formed by curing a slurry containing 90-95 wt% silicone potting compound and 5-10 wt% carbon-based conductive filler. The conductive elastomer and the metal mesh skeleton form a three-dimensional interpenetrating conductive network, and the metal mesh skeleton is completely covered by the elastomer to avoid direct contact with the reaction gas of the fuel cell.

[0012] The bipolar plate of this invention is a lightweight and flexible bipolar plate for hydrogen fuel cells. It effectively reduces the volume and weight proportion of bipolar plates in hydrogen fuel cells, while possessing both flexible shaping and high conductivity, thereby effectively improving the energy density of hydrogen fuel cells and expanding the application requirements of hydrogen fuel cells in some special scenarios. Because the conductive elastomer of the composite bipolar plate is formed using a flexible conductive slurry obtained by mixing organosilicon potting compound and various carbon-based conductive fillers, the conductive elastomer has excellent coverage of the metal mesh skeleton. This results in the composite bipolar plate having conductivity and flexibility properties far exceeding those of existing bipolar plate materials, making its application value greater.

[0013] Furthermore, the silicone potting compound is a two-component silicone oil with a viscosity of 5000~8000 cps. Preferably, the weight ratio of the two components is 1:0.95-1.05.

[0014] Furthermore, the silicone potting compound is a two-component vinyl silicone oil with a viscosity of 5500-6000 cps and a weight ratio of 1:0.95-1.05, preferably 1:1. This viscosity range ensures both sufficient dispersion of the filler and suitable flowability.

[0015] Furthermore, the carbon-based conductive filler includes one or a mixture of several of expanded graphite, carbon nanotubes, carbon fiber filaments, and carbon black.

[0016] The carbon-based conductive filler provided by this invention includes expanded graphite, carbon nanotubes, carbon fiber filaments, and carbon black. Expanded graphite has a high specific surface area and a rationally distributed pore structure, which can form a micron-scale three-dimensional conductive network attached to a metal framework. The addition of high aspect ratio carbon nanotubes further increases the density of the three-dimensional conductive network. The addition of carbon fiber filaments and carbon black not only increases the density of the conductive network but also enhances the mechanical strength of the flexible bipolar plate.

[0017] Preferably, the carbon-based conductive filler is a mixture comprising at least two different types of carbon-based conductive fillers.

[0018] Preferably, the carbon-based conductive filler in the conductive elastomer is formed by adding the following raw materials in mass fractions: 1-1.5% graphene precursor, 0.5-1% single-walled carbon nanotubes, 0.5-1% carbon fiber filaments, and 0.25-0.5% conductive carbon black.

[0019] The graphene precursor is converted into expanded graphite during the flexible bipolar plate forming process.

[0020] Furthermore, the graphene precursor has a specific surface area > 50 m². 2 / g of graphene precursor with a median particle size <200 mesh is mixed with organosilicon potting slurry and processed into a conductive elastomer, which is then converted into conductive expanded graphite.

[0021] Using graphene precursors with high specific surface area, a basic conductive network is formed in the slurry. The graphene precursors are formed into worm-shaped high-quality expanded graphite in organosilicon potting slurry, and the graphene interlayers are stretched open, transforming into expanded graphite with high conductivity.

[0022] Natural graphite has a dense structure and tight interlayer bonding, making it difficult to form a continuous conductive network. By selecting high-quality graphene precursors, it is easier to convert into expanded graphite with better performance in organosilicon potting slurry. At the same doping amount, the conductivity can be maximized.

[0023] Furthermore, the carbon nanotubes are single-walled carbon nanotubes with an outer diameter of 20~80 nm.

[0024] Furthermore, the carbon nanotubes are single-walled carbon nanotubes with a length of 10~50 μm.

[0025] Furthermore, the carbon nanotubes are single-walled carbon nanotubes with an electrical conductivity greater than 100 S / cm.

[0026] Preferably, the carbon nanotubes are single-walled carbon nanotubes with an outer diameter of 20-80 nm, a length of 10-50 μm, and an electrical conductivity of >100 S / cm, used to construct nanoscale conductive pathways.

[0027] Furthermore, the carbon fiber filament is an ethylene ester resin compatible carbon fiber with an interlaminar shear strength of 25~50 MPa.

[0028] Preferably, the carbon fiber filament is a ethylene ester resin compatible short-cut fiber with an interlaminar shear strength of 30~45MPa.

[0029] Preferably, the length of the carbon fiber filament is controlled between 0.5 and 3 mm.

[0030] Furthermore, the carbon black is a conductive carbon black with a DBP (dibutyl phthalate) absorbance value of 150~200 mL / g.

[0031] Furthermore, the metal mesh skeleton comprises one or two layers of copper mesh.

[0032] Preferably, the metal mesh skeleton comprises two layers of copper mesh, which are located on both sides of the bipolar plate, and the main body of the conductive elastomer is located between the two layers of copper mesh; and the copper mesh is completely immersed in the conductive elastomer.

[0033] Two layers of copper mesh form a double-layer skeleton structure that embeds / immerses the conductive elastomer within it. The two layers of copper mesh form a double-layer conductive skeleton network structure, resulting in better overall toughness and conductivity of the material.

[0034] Furthermore, the metal mesh skeleton is a 100-300 mesh electrolytic copper mesh with a thickness of 0.05-0.1 mm. The copper mesh and the conductive paste form an interlocking structure, which maintains flexibility while improving mechanical strength.

[0035] Preferably, the copper mesh has a mesh count of 100, 200, or 300.

[0036] Furthermore, the metal mesh skeleton can be any one of copper wire woven mesh, copper plate stretched mesh, or copper plate perforated mesh.

[0037] Preferably, the metal mesh skeleton is a copper wire woven mesh.

[0038] In a second aspect, the present invention provides a method for preparing the above-mentioned flexible bipolar plate for hydrogen fuel cells, ensuring that the obtained bipolar plate possesses key properties such as good flexibility, high conductivity, and light weight. Furthermore, the preparation method uses inexpensive materials and employs a simple and efficient hot-pressing process, thus possessing extremely high commercial value.

[0039] A method for fabricating a flexible bipolar plate for a hydrogen fuel cell includes the following steps: Step 1: Remove the bipolar plate mold and clean it with anhydrous ethanol and deionized water in sequence to ensure that there are no impurities remaining in the mold flow channel.

[0040] Step 2: Wipe the silicone oil onto the mold with polyester cotton to reduce the adhesion between the slurry and the mold.

[0041] Step 3: If the metal mesh skeleton includes two layers of copper mesh, place a copper mesh horizontally on the side surface of the mold runner so that it fits tightly against the edge of the mold; otherwise, proceed directly to step 4.

[0042] Step 4: Slowly pour the conductive paste into the mold, then place the copper mesh horizontally on the surface of the paste and let it stand. After the copper mesh is completely immersed in the paste, cover the mold with the mold cover plate and place it on the molding machine platform.

[0043] Step 5: Hot pressing is performed at 70~140℃, and the plate is demolded after 20~60 min to obtain a flexible bipolar plate.

[0044] The conductive paste is prepared by the following method: (a) Mix the two-component vinyl silicone oil at a mass ratio of 1:0.95-1.05; (b) Add expanded graphite, carbon nanotubes, carbon fiber filaments and carbon black to vinyl silicone oil in a ratio of 1:0.4~0.6:0.4~0.6:0.2~0.3 and mix them evenly to obtain conductive paste.

[0045] The preparation method of this invention uses a hot-pressing molding process to prepare flexible bipolar plates. The conductive slurry is molded and solidified in a mold to finally obtain a flexible bipolar plate that can be used in hydrogen fuel cells. It has the advantages of simple and efficient molding process, which is conducive to significantly reducing the production cost of bipolar plates and accelerating commercialization and application.

[0046] Furthermore, in step 5, hot pressing is performed at 70~120°C.

[0047] Furthermore, in step 5, the hot pressing time is 20~40 minutes.

[0048] Furthermore, in (b), after adding expanded graphite, carbon nanotubes, carbon fiber filaments, and carbon black, the mixture is stirred at a speed of 1000~4000 r / min in a planetary mixer and then sheared by a kneading machine to ensure uniform distribution of the conductive filler.

[0049] Preferably, the rotational speed is set to 2000 r / min.

[0050] Preferably, the stirring time is 3 to 20 minutes. Preferably, the stirring time is 5 minutes.

[0051] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. The flexible bipolar plate prepared by this invention achieves excellent properties such as flexibility, bendability, and low density while ensuring low resistance. Compared with traditional bipolar plates, the density is significantly reduced, which has a significant promoting effect on reducing the weight and volume of the fuel cell stack and improving the overall energy density of the fuel cell, thus greatly expanding the applicable scenarios of fuel cells.

[0052] 2. The flexible bipolar plate of this invention exhibits excellent electrical performance in tests on single hydrogen fuel cells, achieving performance within the same size (effective membrane electrode area 5×5 cm). 2 In single-cell tests, the energy density was significantly improved.

[0053] 3. The flexible conductive material provided by this invention utilizes a simple preparation process, employing inexpensive silicone potting compound combined with multi-level carbon-based conductive fillers and a metal mesh as the conductive framework. The process involves complete encapsulation, followed by hot pressing, significantly improving the conductivity of the flexible film. The film exhibits excellent conductivity near the metal mesh. The high conductivity, flexibility, and lightweight properties enable this bipolar plate to significantly increase the energy density of hydrogen fuel cells. Furthermore, the preparation process avoids complex and difficult-to-implement steps, making it easily suitable for large-scale industrial production.

[0054] 4. The bipolar plate processing method used in this invention is an integral molding method. It only requires pouring the prepared conductive paste into the mold and setting the molding time, temperature and pressure. The method is simple, efficient and has potential for large-scale application. Attached Figure Description

[0055] Figure 1 Optical images of the front and back sides of the fabricated flexible bipolar plate.

[0056] Figure 2 This is the bending strength test curve.

[0057] Figure 3 The results show the conductivity test results of the double-sided copper mesh sample. Detailed Implementation

[0058] The present invention will now be described in further detail with reference to specific embodiments. However, this should not be construed as limiting the scope of the present invention to the following embodiments; all technologies implemented based on the content of the present invention fall within the scope of the present invention.

[0059] Unless otherwise specified, the terms "upper," "lower," "left," "right," "center," "inner," and "outer," etc., used in the description of specific embodiments of the present invention to indicate orientation or positional relationships, are based on the orientation or positional relationships shown in the accompanying drawings, or the orientation or positional relationship in which the product / equipment / device is usually placed during use. These terms are merely for the purpose of facilitating the description of the present invention or simplifying the description in specific embodiments, and for enabling those skilled in the art to quickly understand the solution, and do not indicate or imply that a particular device / component / element must have a specific orientation, or be constructed and operated in a specific positional relationship. Therefore, they should not be construed as limitations on the present invention.

[0060] Furthermore, the use of terms such as "horizontal," "vertical," "suspended," "parallel," and "coaxial" does not imply that the corresponding device / component / element must be absolutely horizontal, vertical, suspended, parallel, or coaxial. Slight tilt or deviation is permissible, as long as it does not affect the normal function of the relevant component. For example, "horizontal" simply means that its direction is more horizontal relative to "vertical," not that the structure must be perfectly horizontal; a slight tilt is acceptable. "Coaxial" means that two components are arranged as coaxially as possible, allowing them to move coaxially or approximately coaxially when their relative positions change. Alternatively, it can be simplified to mean that the corresponding device / component / element, when arranged in "horizontal," "vertical," "suspended," "parallel," or "coaxial" directions, can have an error / deviation of ±10% relative to the corresponding direction, more preferably within ±8%, more preferably within ±6%, more preferably within ±5%, and more preferably within ±4%. For example, the deviation in the "coaxial" direction is controlled within 0.2-1mm, preferably within 0.2-0.5mm. As long as the corresponding device / component / element is within the error / deviation range, it can still achieve its function in the solution of the present invention.

[0061] Furthermore, the use of terms such as "first," "second," and "third" in terminology is merely for distinguishing descriptions of identical or similar components and should not be interpreted as emphasizing or implying the relative importance of a particular component.

[0062] Furthermore, in the description of the embodiments of the present invention, "several", "more than", and "a number of" represent at least two. The number can be any number, such as two, three, four, five, six, seven, eight, or nine, and can even exceed nine.

[0063] Furthermore, in the description of the technical solution of this invention, unless otherwise explicitly specified / limited / restricted, the terms "set up," "install," "connect," "link," "provided with," "laid out," and "arranged" should be interpreted broadly. For example, they can refer to fixed connections, detachable connections, or integral connections; they can refer to connection methods commonly used in the art, such as welding, riveting, bolting, and threaded connections. Such connections can be mechanical, electrical, or communication connections; they can be direct connections or indirect connections through an intermediate medium; and they can refer to the internal communication between two components.

[0064] Example 1 S1. Preparation of conductive paste 90% silicone potting compound, 5% expanded graphite, and 5% carbon fiber filaments were added sequentially to a centrifuge tank according to the following mass ratios. The mixture was stirred at 2000 r / min for 5 min and then ultrasonically treated for 10 min at a frequency of 60 kHz to obtain a conductive slurry.

[0065] S2, Fabrication of flexible bipolar plates Remove the bipolar plate mold and use polyester cotton to wipe the silicone oil on the mold surface and inside the flow channel to reduce the adhesion between the mold and the slurry, making it easier to remove the bipolar plate after molding.

[0066] A double-layer copper mesh scheme was adopted: First, the mold was placed horizontally on the experimental table, and then it was cut into 5×5 cm pieces. 2 A copper mesh is laid flat on the surface of the mold flow channel (as the first layer of copper mesh), so that the copper mesh is tightly attached to the edge of the mold; then the conductive paste is slowly poured into the mold (Note: because the paste has a high viscosity and poor fluidity, it is similar to a semi-solid, so the conductive paste is poured into the mold at a relatively slow speed).

[0067] Then, take 5×5 cm 2A copper mesh (as a second layer of copper mesh) is placed horizontally on the conductive paste. After the second layer of copper mesh is absorbed to a certain depth by the conductive paste (usually 5-20 seconds is sufficient for complete absorption), the mold cover plate is placed on top, and the cover plate is gently pressed to ensure full contact between the mold and the cover plate. The metal mesh skeleton is a 100-mesh electrolytic copper mesh with a thickness of 0.05-0.1 mm and an average wire diameter of 0.05 mm. The copper mesh and the conductive paste form an interlocking structure, maintaining flexibility while improving mechanical strength.

[0068] The mold is then moved onto the molding platform of the molding machine, and the heating temperature is set to 120℃, the pressure to 10MPa, and the time to 40 minutes. The molding platform is raised and lowered three times to expel air from the mold. Finally, the flexible bipolar plate preform is removed after the molding time is completed.

[0069] S3, Bipolar Plate Post-processing and Testing After removing the bipolar plate, it was cleaned sequentially with anhydrous ethanol and deionized water. The solidified slurry that had overflowed from the edges of the bipolar plate was then removed using a scalpel. The final optical images of the front and back of the flexible bipolar plate are shown below. Figure 1 As shown, the obtained flexible bipolar plate is assembled with the membrane electrode assembly of a hydrogen fuel cell. The gap between the bipolar plate and the membrane electrode assembly is sealed with silicone potting compound. The assembled hydrogen fuel cell is placed on a test bench for electrical performance testing, wherein the electrical performance is the cell open-circuit voltage.

[0070] Example 2 S1. Preparation of conductive paste 90% silicone potting compound, 5% expanded graphite, and 5% carbon fiber filaments were added sequentially to a centrifuge tank according to the mass ratio. After stirring at 2000 r / min for 5 min, the mixture was then ultrasonically treated for 10 min at an ultrasonic frequency of 60 kHz to obtain a conductive slurry.

[0071] S2, Fabrication of flexible bipolar plates Remove the bipolar plate mold and wipe the surface and inside the flow channel with silicone oil to reduce its adhesion to the slurry, making it easier to remove the bipolar plate after molding.

[0072] A single-layer copper mesh solution was used: the mold was placed horizontally on the experimental table, the conductive paste was slowly poured into the mold, and then the copper mesh was cut into 5×5 cm pieces. 2 The copper mesh is shaped like a mold and placed horizontally on the conductive paste. After the copper mesh is absorbed to a certain depth by the conductive paste, the mold cover plate is placed on top, and the cover plate is gently pressed to ensure full contact between the mold and the cover plate. The metal mesh skeleton is a 100-mesh electrolytic copper mesh with a thickness of 0.05-0.1 mm and an average wire diameter of 0.05 mm. The copper mesh and the conductive paste form an interlocking structure, which maintains flexibility while improving mechanical strength.

[0073] The mold is then moved onto the molding platform of the molding machine, and the heating temperature is set to 120℃, the pressure to 10MPa, and the time to 40 minutes. The molding platform is raised and lowered three times to expel air from the mold. Finally, the flexible bipolar plate preform is removed after the molding time is completed.

[0074] S3, Bipolar Plate Post-processing and Testing After removing the bipolar plate, it is cleaned sequentially with anhydrous ethanol and deionized water. The solidified slurry overflowing from the edges of the bipolar plate is then removed using a tool. The resulting flexible bipolar plate is assembled with the hydrogen fuel cell membrane electrode assembly (MEA). The gap between the bipolar plate and the MEA is sealed with silicone potting compound. The assembled hydrogen fuel cell is then placed on a test bench for electrical performance testing. The electrical performance is defined as the cell's open-circuit voltage.

[0075] Example 3 S1. Preparation of conductive paste 95% silicone potting compound, 2% expanded graphite, 1% carbon nanotubes, 1% carbon fiber filaments and 1% carbon black were added to a centrifuge tank in the following proportions by mass. The mixture was stirred at 2000 r / min for 5 min and then ultrasonically treated for 10 min at a frequency of 60 kHz to obtain a conductive slurry.

[0076] S2, Fabrication of flexible bipolar plates Remove the bipolar plate mold and wipe the surface and inside the flow channel with silicone oil to reduce its adhesion to the slurry, making it easier to remove the bipolar plate after molding.

[0077] A single-layer copper mesh solution was used: the mold was placed horizontally on the experimental table, the conductive paste was slowly poured into the mold, and then the copper mesh was cut into 5×5 cm pieces. 2 The copper mesh is shaped like a mold and placed horizontally on the conductive paste. After the copper mesh is absorbed to a certain depth by the conductive paste, the mold cover plate is placed on top, and the cover plate is gently pressed to ensure full contact between the mold and the cover plate. The metal mesh skeleton is a 100-mesh electrolytic copper mesh with a thickness of 0.05-0.1 mm and an average wire diameter of 0.05 mm. The copper mesh and the conductive paste form an interlocking structure, which maintains flexibility while improving mechanical strength.

[0078] The mold is then moved onto the molding platform of the molding machine, and the heating temperature is set to 120℃, the pressure to 10MPa, and the time to 40 minutes. The molding platform is raised and lowered three times to expel air from the mold. Finally, the flexible bipolar plate preform is removed after the molding time is completed.

[0079] S3, Bipolar Plate Post-processing and Testing After removing the bipolar plate, it is cleaned sequentially with anhydrous ethanol and deionized water. The solidified slurry overflowing from the edges of the bipolar plate is then removed using a tool. The resulting flexible bipolar plate is assembled with the hydrogen fuel cell membrane electrode assembly (MEA). The gap between the bipolar plate and the MEA is sealed with silicone potting compound. The assembled hydrogen fuel cell is then placed on a test bench for electrical performance testing. The electrical performance is defined as the cell's open-circuit voltage.

[0080] Example 4-16 Referring to the processing method of the flexible bipolar plate for hydrogen fuel cells in Example 1, a composite bipolar plate was prepared. First, a conductive slurry was prepared: 90-95% silicone rubber potting compound (composition shown in the table below) was added, along with carbon-based conductive filler (composition and dosage shown in the table below). The mixture was stirred at 2000 r / min for 5 min, and then ultrasonically treated for 10 min at a frequency of 60 kHz to obtain the conductive slurry.

[0081] Then, after cleaning the surface of the bipolar plate mold, silicone oil is wiped off, a copper mesh is arranged, and conductive paste is poured in.

[0082] For a double-layer copper mesh design, refer to the procedure in Example 1. First, place the bipolar plate mold horizontally and insert a metal copper mesh (as the first layer of copper mesh), then slowly pour in the conductive paste. Next, place a 5×5 cm... 2 The metal copper mesh with the shape and mesh size shown in the table below (as the second layer of copper mesh) is used. After the second layer of copper mesh is immersed in the conductive paste, the mold cover plate is placed on top, and the cover plate is gently pressed to ensure full contact between the mold and the cover plate. The first layer of copper mesh and the second layer of copper mesh can be the same or different. In this series of embodiments, the same 100-mesh electrolytic copper mesh is used, with a thickness of 0.05-0.1 mm and an average wire diameter of 0.05 mm.

[0083] For a single-layer copper mesh solution, refer to the procedure in Example 2: place the mold horizontally on the experimental table, slowly pour the conductive paste into the mold, and then cut the copper mesh into 5×5 cm pieces. 2 Shape it and place it horizontally on the conductive paste. After the copper mesh is absorbed into the conductive paste to a certain depth, cover it with the mold cover plate and press the cover plate lightly to make the mold and the cover plate fully contact.

[0084] Finally, the entire mold is moved onto the molding platform of the molding machine. The heating temperature, pressure, and hot pressing time are set as shown in the table below. The molding platform is raised and lowered repeatedly three times to expel air from the mold. Finally, after the molding time is completed, the flexible bipolar plate preform is removed. After hot pressing, the composite bipolar plate is removed and cleaned sequentially with anhydrous ethanol and deionized water, and any excess cured slurry overflowing from the edges is removed.

[0085] Table 1: Raw materials and process parameters for flexible composite bipolar plates in Examples 4-16

[0086] This invention, based on the selection and proportioning control of raw materials for preparing composite bipolar plates in Example 1, compares the impact of different raw material selections and process parameter controls on the performance of the final composite bipolar plates. The potential of various two-component silicone rubbers in preparing composite bipolar plates was compared. Dow Corning 184 addition-cure two-component silicone rubber elastomer showed better performance and better bonding with carbon-based conductive fillers and copper mesh, with the copper mesh being fully coated and without voids. Various combinations of carbon-based fillers and different proportions were selected, and three-dimensional, two-dimensional, and one-dimensional multi-level compounding schemes of expanded graphite, carbon nanotubes, carbon fiber filaments, and carbon black powder were explored. Planetary mixers and conventional mechanical stirring were also tested for material mixing.

[0087] In Examples 11 and 13, the same double-layer copper mesh scheme as in Example 1 was used. Examples 4-10, 12, and 14-16 used a single-layer copper mesh scheme (similar to Example 2). Conductive paste was poured in first, then the copper mesh was placed in. After the copper mesh was absorbed to a certain depth by the conductive paste, the mold cover was placed on top. In all single-layer copper mesh examples, the depth to which the copper mesh was absorbed by the conductive paste was determined by the complete immersion of the copper mesh. In all double-layer copper mesh examples, the depth to which the second layer of copper mesh was absorbed by the conductive paste was determined by the complete immersion of the copper mesh. During the specific experiments, a certain amount of time was allowed to ensure that the copper mesh placed after the conductive paste was poured was completely wrapped / covered by the paste.

[0088] Test Example 1 The key raw material selection and process parameters for preparing flexible bipolar plates for hydrogen fuel cells were compared through various embodiments. After the bipolar plates prepared in the above embodiments were removed from the mold, they were washed sequentially with anhydrous ethanol and deionized water, and the solidified slurry overflowing from the edges of the bipolar plates was removed. Then, the resulting flexible composite bipolar plates were subjected to performance testing.

[0089] (1) Refer to GB / T 9341-2008 "Determination of Bending Properties of Plastics" for bending strength and bending deflection tests. First, place the flexible bipolar plate sample in a standard environment of 23±2℃ and 50±10% RH for at least 24 hours. Place the sample flat on the support blocks with a spacing of 30 mm. The width direction of the sample is perpendicular to the axis of the indenter. Align the axis of the indenter with the center of the sample and position it in the middle of the two support blocks. Perform the loading test at a speed of 1 mm / min. First, apply a force of 0.1 N, and then gradually press down until the pressure value drops by 30% or the deflection reaches 20 mm. Record the load-deflection curve (sampling frequency 10 Hz). If the sample breaks during bending, record the maximum force value (denoted as ). F maxIf it does not break, then the pressure at which the specified deflection is 1.5 times the thickness is taken (denoted as ). F s ).

[0090] Flexural strength: (A) If the sample breaks, the flexural strength is calculated according to the following formula:

[0091] (B) If the sample is not broken,

[0092] In the formula, Flexural strength, in MPa; L is the span, L = 30 mm; h is the sample thickness, h = 2 mm; b is the width of the sample, b=50mm.

[0093] Bending deflection is measured by mid-span compression displacement gauges, in mm, representing the amount of bipolar plate compression deformation.

[0094] (2) Conduct conductivity tests were performed in accordance with GB / T 20042.6-2011 "Proton Exchange Membrane Fuel Cells Part 6: Test Methods for Bipolar Plate Characteristics". The prepared flexible bipolar plates were placed in a standard environment of 23±2℃ and 50±10% RH for at least 24 hours. Resistivity tests were performed using a fully automated four-probe resistivity meter.

[0095] (3) The density was tested in accordance with GB / T 20042.6-2011 "Proton Exchange Membrane Fuel Cell Part 6: Test Method for Bipolar Plate Characteristics". The bipolar plate was weighed using a precision balance and the volume was determined by the immersion method. The mass-to-volume ratio was calculated to determine the density of the bipolar plate.

[0096] (4) Corrosion current density was tested according to GB / T 20042.6-2011 "Proton Exchange Membrane Fuel Cells Part 6: Test Methods for Bipolar Plate Characteristics". The corrosion resistance test was conducted in a 3.5% sodium chloride solution at an ambient temperature of 25°C. After polishing the sample surface, it was rinsed with deionized water and anhydrous ethanol, air-dried naturally, and then dried in a desiccator for 24 hours. Then, the sample was immersed in a 3.5 wt.% sodium chloride standard test solution. The three-electrode system was connected to the electrochemical workstation, and the test sample was connected to conduct the corrosion current density test.

[0097] (5) Calculate the cost based on the price of the raw materials used in the preparation.

[0098] The flexible composite bipolar plates of Examples 1 to 16 were subjected to various performance tests and analyses according to the above test methods, and the specific results are shown in the table below.

[0099] Table 2: Performance Test Results of Flexible Composite Bipolar Plates in Examples 4-16

[0100] Note: The conductivity measurement of a single-sided copper mesh is the conductivity of the side without the copper mesh. The addition of a double-sided copper mesh will make the actual conductivity measurement closer to the conductivity of copper, thus differing by orders of magnitude.

[0101] Density is measured by weighing. The lightness of the copper mesh is not the determining factor for the density of the finished bipolar plate. The main determining factors for the density of the bipolar plate are the different fillers used in the slurry during processing and the differences in the molding process. The use of single-layer or double-layer copper mesh has little impact on the density of the composite bipolar plate. Therefore, the final measured result does not depend entirely on the single-layer / double-layer copper mesh structure.

[0102] #The cost is calculated based on the cost and usage ratio of the raw materials used.

[0103] As can be seen from the table above, the flexible bipolar plate of this invention exhibits excellent performance, particularly in bending strength and bending deflection, achieving flexible and bendable characteristics. This allows the bipolar plate to be used in fuel cells with certain bending resistance, demonstrating better flexibility compared to rigid bipolar plates. Furthermore, the flexible bipolar plate of this invention has a density of only 1.2 g / cm³. 3 Compared to pure metal bipolar plates, the density is significantly reduced, which can reduce the weight and volume of the fuel cell stack and improve the overall energy density of the fuel cell.

[0104] The flexible bipolar plate prepared in Example 16 was subjected to bending strength testing, and the results are as follows: Figure 2 As shown. Calculations show that the bending strength of this bipolar plate is approximately 9.6 MPa, which meets the requirements for normal use in flexible hydrogen fuel cells.

[0105] The conductivity of the flexible bipolar plate samples from Example 1 (sample 1) and Example 13 (sample 2) was tested, and the results are as follows: Figure 3 As shown, the surface conductivity of the bipolar plates using the double-sided copper mesh design is greater than 300 S / cm, which meets the conductivity requirements for normal use of hydrogen fuel cells.

[0106] The flexible bipolar plate of this invention exhibits extremely low corrosion current density during testing because the carbon-based conductive filler inside the silicone rubber potting material does not undergo continuous corrosion damage. Simultaneously, the carbon-based conductive filler forms a continuous conductive network, organically combining with the copper mesh, resulting in high overall conductivity and excellent electrical performance, making it particularly suitable for current collection in fuel cell current collectors.

[0107] Compared to the significantly increased costs associated with surface plating of metal bipolar plates using titanium, silver, or other precious metals, flexible bipolar plates with a fully encapsulated metal mesh have extremely low processing costs. This significantly improves the output current density of hydrogen fuel cells, which is crucial for enhancing fuel cell conversion efficiency. Calculations show that by avoiding titanium or silver plating, both production and material costs are reduced. Furthermore, the entire manufacturing process avoids complex and difficult-to-implement steps, making it easily suitable for large-scale industrial production.

[0108] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A flexible bipolar plate for hydrogen fuel cells, characterized in that, The flexible bipolar plate comprises: A metal mesh skeleton, and a conductive elastomer that fills and covers the metal mesh skeleton; The metal mesh skeleton is made of 40-500 mesh copper mesh material; The conductive elastomer is formed by curing a slurry containing 90-95 wt% silicone potting compound and 5-10 wt% carbon-based conductive filler. The conductive elastomer and the metal mesh skeleton form a three-dimensional interpenetrating conductive network, and the metal mesh skeleton is completely covered by the elastomer to avoid direct contact with the reaction gas of the fuel cell.

2. The flexible bipolar plate for a hydrogen fuel cell as described in claim 1, characterized in that, The silicone potting compound is a two-component silicone oil with a viscosity of 5000~8000 cps, and the weight ratio of the two components is 1:0.95-1.05; The carbon-based conductive filler includes one or a mixture of several of expanded graphite, carbon nanotubes, carbon fiber filaments, and carbon black.

3. The flexible bipolar plate for a hydrogen fuel cell as described in claim 2, characterized in that, The carbon-based conductive filler is a mixture comprising at least two different types of carbon-based conductive fillers.

4. The flexible bipolar plate for a hydrogen fuel cell as described in claim 3, characterized in that, The carbon-based conductive filler in the conductive elastomer is formed by adding the following raw materials in the indicated mass fractions: 1-1.5% graphene precursor, 0.5-1% single-walled carbon nanotubes, 0.5-1% carbon fiber filaments, and 0.25-0.5% conductive carbon black.

5. A flexible bipolar plate for a hydrogen fuel cell as described in claim 4, characterized in that, The graphite precursor has a specific surface area > 50 m². 2 / g, graphene precursor with a median particle size <200 mesh.

6. A flexible bipolar plate for a hydrogen fuel cell as described in claim 2, characterized in that, The carbon nanotubes are single-walled carbon nanotubes with an outer diameter of 20~80 nm; The carbon nanotubes are single-walled carbon nanotubes with a length of 10~50 μm; The carbon nanotubes are single-walled carbon nanotubes with an electrical conductivity greater than 100 S / cm; The carbon fiber filaments are vinyl ester resin compatible carbon fibers with an interlaminar shear strength of 25~50 MPa.

7. A flexible bipolar plate for a hydrogen fuel cell as described in claim 1, characterized in that, The metal mesh skeleton includes two layers of copper mesh, which are located on both sides of the bipolar plate, and the main body of the conductive elastomer is located between the two layers of copper mesh; and the copper mesh is completely immersed in the conductive elastomer.

8. A flexible bipolar plate for a hydrogen fuel cell as described in claim 1, characterized in that, The metal mesh skeleton is a 100-300 mesh electrolytic copper mesh with a thickness of 0.05-0.1 mm.

9. A method for preparing a flexible bipolar plate for a hydrogen fuel cell according to any one of claims 1-8, characterized in that, Includes the following steps: Step 1: Remove the bipolar plate mold and clean it with anhydrous ethanol and deionized water in sequence to ensure that there are no impurities remaining in the mold flow channels; Step 2: Wipe the silicone oil onto the mold with polyester cotton to reduce the adhesion between the slurry and the mold. Step 3: If the metal mesh skeleton includes two layers of copper mesh, place a copper mesh horizontally on the side surface of the mold flow channel so that it fits tightly against the edge of the mold; otherwise, proceed directly to step 4. Step 4: Slowly pour the conductive paste into the mold, then place the copper mesh horizontally on the surface of the paste and let it stand. After the copper mesh is completely immersed in the slurry, cover it with the mold cover plate and place it on the molding machine platform; Step 5: Hot pressing is performed at 70~140℃, and the plate is demolded after 20~60 min to obtain a flexible bipolar plate; The conductive paste is prepared by the following method: (a) Mix the two-component vinyl silicone oil at a mass ratio of 1:0.95-1.05; (b) Add expanded graphite, carbon nanotubes, carbon fiber filaments and carbon black to vinyl silicone oil in a ratio of 1:0.4~0.6:0.4~0.6:0.2~0.3 and mix them evenly to obtain conductive paste.

10. The preparation method according to claim 9, characterized in that, In (b), after adding expanded graphite, carbon nanotubes, carbon fiber filaments and carbon black, the planetary mixer is set to a speed of 1000~4000 r / min and stirred until homogeneous. The conductive filler is then evenly distributed by shearing the slurry through an internal mixer.

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