Carbon fiber woven cloth composite bipolar plate with sandwich structure and preparation method

Abstract

The application discloses a kind of composite bipolar plate with sandwich structure and preparation method thereof, comprising the following steps: 1: weighed electrically conductive filler and electrically conductive reinforcing material are respectively added to a resin solution, respectively A solution and B solution are obtained, and A solution and B solution are stirred uniformly respectively;2: prepare two groups of carbon fiber woven cloth, two carbon fiber woven cloth in each group of carbon fiber woven cloth are stacked together respectively, then using coater, first evenly coat a layer of A solution on the two groups of stacked carbon fiber woven cloth, coat a layer of B solution on any one group of carbon fiber woven cloth;3: two groups of carbon fiber woven cloth coated with different solutions are folded together, so that the coated B solution is in the middle layer of the folded material, after molding into vacuum laminating machine, it is taken out;4: remove the metal cation that causes damage to proton exchange membrane, and the method has broad development prospects in the field of proton exchange membrane fuel cell.

Description

Technical Field

[0001] This invention belongs to the field of bipolar plate technology, specifically relating to a carbon fiber woven fabric composite bipolar plate with a sandwich structure and its preparation method. Background Technology

[0002] Hydrogen energy, as a crucial component of energy structure transformation, boasts advantages such as cleanliness, flexibility, renewability, and large energy storage capacity. Accelerating the development and utilization of hydrogen energy is a vital measure to reduce dependence on fossil fuels. Fuel cells, as the most widespread and convenient way to use hydrogen energy, can directly convert chemical energy into electrical energy using hydrogen and oxygen as fuel, playing a significant role in future energy systems. For proton exchange membrane fuel cells (PEMFCs), bipolar plates are a key component, and their development influences the commercialization process of PEMFCs. Although previous researchers have conducted extensive studies in this field, a definitive technological roadmap remains elusive.

[0003] Previous research has found that bipolar plates fabricated by combining graphite-based and carbon-based conductive fillers all have some problems, preventing the materials from achieving their ideal performance. Therefore, this invention attempts to introduce metal elements to prepare composite bipolar plates, hoping that the excellent electrical and thermal conductivity of metal elements can produce composite bipolar plates with satisfactory performance. However, due to the "metal cation effect" of perfluorosulfonic acid proton exchange membranes, the most critical issue in determining whether metal elements can be used to prepare composite bipolar plates is whether the damage caused by metal cations to the proton exchange membrane can be avoided. Summary of the Invention

[0004] To address the aforementioned issues, some embodiments of the present invention propose a carbon fiber woven fabric composite bipolar plate with a sandwich structure and a method for its preparation.

[0005] A method for preparing a bipolar plate made of carbon fiber woven fabric composite material with a sandwich structure, characterized by comprising the following steps:

[0006] Step 1: Add the weighed conductive filler and conductive reinforcing material to a resin solution respectively to obtain solution A and solution B. Then use a stirrer to stir solution A and solution B evenly.

[0007] Step 2: Prepare two sets of carbon fiber woven fabrics. Each set of carbon fiber woven fabrics includes two pieces of carbon fiber woven fabric. Stack the two pieces of carbon fiber woven fabric in each set together. Then, use a coater to evenly coat a layer of solution A on the two sets of stacked carbon fiber woven fabrics. Then, use a coater to evenly coat a layer of solution B on any one of the sets of carbon fiber woven fabrics coated with solution A.

[0008] Step 3: Combine the two sets of carbon fiber woven fabrics coated with different solutions, so that the coated solution B is in the middle layer of the combined material. Then place the mold with raised flow channels on it and send them into the vacuum press. After vacuum hot pressing for a certain time under the set temperature and pressure, take it out to obtain a carbon fiber woven fabric composite bipolar plate with sandwich structure.

[0009] Step 4: After the bipolar plate with a sandwich structure made of carbon fiber woven fabric is prepared, it is subjected to constant potential test in a simulated fuel cell working environment to reduce and remove metal cations that damage the proton exchange membrane.

[0010] Further optimization involves the conductive filler comprising natural flake graphite, artificial flake graphite, expandable graphite, and carbon black, and the conductive reinforcing material comprising copper, silver, aluminum, and platinum.

[0011] Further optimization involves the resin being either a thermosetting resin or a thermoplastic resin. The thermosetting resin is any one of epoxy resin, phenolic resin, or vinyl ester resin, and the thermoplastic resin is any one of polyvinylidene fluoride or polypropylene.

[0012] Further optimization involves using carbon fiber woven fabrics, including plain weave carbon fiber woven fabrics and twill weave carbon fiber woven fabrics. The stacking arrangement of a set of carbon fiber woven fabrics includes any one of the following: a stacking arrangement of plain weave carbon fiber woven fabrics and twill weave carbon fiber woven fabrics, a stacking arrangement of twill weave carbon fiber woven fabrics and twill weave carbon fiber woven fabrics, or a stacking arrangement of plain weave carbon fiber woven fabrics and plain weave carbon fiber woven fabrics.

[0013] Further optimization involves using carbon fiber woven fabric with more than just two layers.

[0014] Further optimization involves the following: in solution A, the ratio of resin:curing agent:accelerator is 1:0.8:0.01, and the conductive filler accounts for 10%-40% of the total weight of the resin, curing agent, and accelerator.

[0015] The resin:curing agent:accelerator ratio in solution B is 1:0.8:0.01, and the content of conductive reinforcing material in solution B is less than 10% of the total weight of resin, curing agent and accelerator.

[0016] Further optimization involves using methyltetrahydrophthalic anhydride as the curing agent.

[0017] Further optimization revealed that the accelerator is diaminodiphenylmethane.

[0018] To further optimize the process, the prepared carbon fiber woven fabric composite bipolar plate with a sandwich structure was placed in a simulated fuel cell working environment, namely an H2SO4 solution with pH=3. Using an electrochemical workstation, a 4-hour constant potential test was performed at a potential of 0.6V vs SCE. During the test, the carbon fiber woven fabric composite bipolar plate with a sandwich structure was simultaneously purged with air. The concentration of metal in the conductive reinforcement material precipitated in the simulated fuel cell working environment was measured every 1 hour using inductively coupled plasma atomic emission spectrometry (ICP-AES). After the metal concentration in the conductive reinforcement material measured in the two consecutive measurements stabilized, the plate was removed and rinsed clean.

[0019] The carbon fiber woven fabric composite bipolar plate with a sandwich structure of the present invention is prepared by the above-mentioned preparation method of carbon fiber woven fabric composite bipolar plate with a sandwich structure, and then assembled into a PEMFC single cell after the above-mentioned processing.

[0020] The present invention has the following beneficial effects:

[0021] (1) Traditional composite bipolar plates cannot simultaneously optimize conductivity and mechanical strength. To achieve excellent conductivity, the content of conductive filler needs to be increased. The poor mechanical strength of the conductive filler and the reduction of resin content together lead to a decrease in mechanical strength. This is because the added conductive filler cannot be effectively utilized and needs to spontaneously form a conductive network during the molding process. Therefore, in this invention, carbon fiber woven fabric is used as the conductive network introduced into the composite bipolar plate to reduce the difficulty of the conductive filler contacting each other to form a conductive network. The interlaced carbon fiber woven fabric can also improve the problem of poor uniformity of in-plane conductivity caused by resin enrichment on the surface.

[0022] (2) Traditional composite bipolar plates introduce new elements directly during stirring or mixing, followed by hot pressing after uniform mixing. However, this method cannot control the distribution of elements. This invention uses copper and other metal elements as conductive reinforcing materials and designs a sandwich structure to regulate the distribution of copper elements in the composite bipolar plate, concentrating them as much as possible inside, thereby avoiding the decrease in corrosion resistance caused by the addition of copper. Experimental results show that the carbon fiber woven fabric composite bipolar plate with a sandwich structure prepared using the method of this invention has better conductivity and mechanical strength than composite bipolar plates prepared by traditional blending methods. The construction of the sandwich structure also successfully protects the copper elements, improving the electrochemical corrosion of the composite bipolar plate. Furthermore, through certain treatment methods, metal cations that may harm the proton exchange membrane are removed, thereby avoiding the occurrence of metal cation effects. Finally, the prepared composite bipolar plate was applied to a PEMFC single cell, showing good operating conditions with a peak power density of 0.520 W / cm³. 2 . Attached Figure Description

[0023] Figure 1 This is a schematic diagram of the preparation process of the carbon fiber woven fabric composite bipolar plate with a sandwich structure according to the present invention.

[0024] Figure 2 This study investigates the effect of the amount of flake graphite added on the conductivity and flexural strength of carbon fiber woven fabric composite bipolar plates when only flake graphite / resin solution is used to prepare them.

[0025] Figure 3 This is a comparison of the electrical conductivity and mechanical properties of Examples 1 and 2.

[0026] Figure 4 This is a comparison of the electrical conductivity and mechanical properties of Examples 1 and 3.

[0027] Figure 5 This is a comparison of the electrical conductivity and mechanical properties of Examples 4 and 5.

[0028] Figure 6 The electrochemical corrosion conditions are shown in Examples 4 and 5.

[0029] Figure 7 These are images of the microstructure and elemental distribution of Examples 4 and 5.

[0030] Figure 8 These are the ICP-AES test results for Examples 6 and 7.

[0031] Figure 9 The test results include the single-cell assembly method (a), the assembled single cell (b), and the IV and IP curves of the single cells assembled using Examples 6 and 7.

[0032] Figure 10 This is a schematic diagram showing the conductivity and flexural strength test results of Examples 7, 8, and 9. Detailed Implementation

[0033] Embodiments of the present invention are described in detail below, examples of which are illustrated in the accompanying drawings. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain the present invention, and should not be construed as limiting the present invention.

[0034] like Figure 1 As shown, the method for preparing a carbon fiber woven fabric composite bipolar plate with a sandwich structure according to the present invention includes the following steps:

[0035] Step 1: Add the weighed conductive filler and conductive reinforcing material to the same resin solution to obtain solution A and solution B respectively. Then use a stirrer to stir solution A and solution B evenly.

[0036] In the above steps, the conductive filler is flake graphite, and the conductive reinforcing material is copper.

[0037] In the solution A, the ratio of resin:curing agent:accelerator is 1:0.8:0.01, and the conductive filler accounts for 10%-40% of the total weight of resin, curing agent and accelerator; the resin is epoxy resin, the curing agent is methyltetrahydrophthalic anhydride, and the accelerator is diaminodiphenylmethane.

[0038] The resin:curing agent:accelerator ratio in solution B is 1:0.8:0.01, and the content of conductive reinforcing material in solution B is less than 10% of the total weight of resin, curing agent and accelerator; the resin is epoxy resin, the curing agent is methyltetrahydrophthalic anhydride, and the accelerator is diaminodiphenylmethane.

[0039] Step 2: Prepare two sets of carbon fiber woven fabrics. Each set includes one plain weave carbon fiber woven fabric and one twill weave carbon fiber woven fabric, both with a specification of 3k200g. Stack the plain weave and twill weave carbon fiber woven fabrics from each set together. Then, use a coater to evenly coat a layer of solution A onto both sets of stacked carbon fiber woven fabrics. Next, use a coater to evenly coat a layer of solution B onto any one of the sets coated with solution A. When the plain weave and twill weave carbon fiber woven fabrics are stacked together, the mesh density is significantly increased, which is beneficial for improving electrical conductivity and mechanical properties.

[0040] Step 3: Two sets of carbon fiber woven fabrics coated with different solutions are joined together, with solution B coating in the middle layer of the joined materials. A mold with raised flow channels is then placed on top, and the two are fed into a vacuum press. Under set temperature and pressure, they are vacuum-pressed for a certain time, and then removed to obtain a carbon fiber woven fabric composite bipolar plate with a sandwich structure. The vacuum press is set at 150℃, 3000kg, and vacuum pressure held for 20 minutes. The molds need to be customized according to the battery design requirements; there is no single form. The purpose is to process the carbon fiber woven fabric into the corresponding shape according to the battery requirements. Here, a mold with raised flow channels is used.

[0041] Step 4: The prepared composite bipolar plate was placed in a simulated fuel cell operating environment (H2SO4 solution at pH=3) and subjected to a 4-hour constant potential test at 0.6V vs SCE using an electrochemical workstation, with air purging during the test. The concentration of copper precipitated in the solution was measured every 1 hour using inductively coupled plasma atomic emission spectrometry (ICP-AES). After stabilization, the plate was removed, rinsed clean, and assembled into a PEMFC single cell, and its power was tested.

[0042] Further optimization involves the carbon fiber woven fabric composite bipolar plate with a sandwich structure, which is prepared by the above-mentioned method for preparing a carbon fiber woven fabric composite bipolar plate with a sandwich structure, and then assembled into a PEMFC single cell after the above-mentioned processing.

[0043] The conductive filler includes natural flake graphite, artificial flake graphite, expandable graphite, and carbon black, and the conductive reinforcing material includes copper, silver, aluminum, platinum, carbon fiber, graphene, carbon nanotubes, and carbon microspheres.

[0044] When carbon-based conductive reinforcing materials such as carbon fibers, graphene, carbon nanotubes, and carbon microspheres are used, the subsequent processing in step 4 is unnecessary. The processing described in this invention is for metallic materials that produce a "metal cation effect." If only carbon-based conductive fillers are used, no processing is required.

[0045] The advantages of this technical solution are illustrated below through comparative examples, and the preferred technical values ​​are selected. In the embodiments described later in the patent, solution A mainly consists of epoxy resin and flake graphite, while solution B mainly consists of epoxy resin and copper powder. Considering that the concentration of solution A (EP / G mixture) used in the carbon fiber woven fabric composite bipolar plate with a sandwich structure prepared in this paper has a certain influence on the conductivity and mechanical properties of the composite bipolar plate, the effect of the flake graphite concentration in solution A (EP / G mixture) on the composite bipolar plate was first studied. The results show that the effect of the amount of flake graphite added on conductivity and flexural strength is as follows: Figure 2 As shown.

[0046] In addition, to investigate whether the coating thickness affects the performance of the final composite bipolar plate, this embodiment uses several different thicknesses of the coater in combination to examine the conductivity of the composite bipolar plates prepared by different thickness combinations in order to screen out the best-performing thickness combination. The thickness combinations are arranged such that the thickness of solution A (EP / G) is always greater than or equal to the thickness of solution B (EP / Cu). This is to minimize the contact between copper and the outside environment. The coater has four thicknesses: 150μm, 100μm, 75μm, and 50μm, resulting in 10 combinations. The average conductivity of the composite bipolar plates prepared by different thickness combinations is shown in the table below.

[0047]

[0048] Conductivity of composite bipolar plates prepared with different thickness combinations

[0049] In the experiment, the concentration of solution A (EP / G layer) was 40 wt%, the concentration of solution B (EP / Cu layer) was 5 wt%, and the process conditions were: vacuum curing at 150℃ and 3000kg pressure for 30 min.

[0050] The resistivity of the sample surface was measured using a four-probe resistivity meter, and the conductivity was then calculated. Based on the average conductivity test value, the composite bipolar plate prepared by combining solution layer A (epoxy resin-flake graphite layer) and solution layer B (epoxy resin-copper layer at 100μm / 75μm) has the best conductivity. Therefore, the sample below was prepared according to this thickness combination.

[0051] Example 1:

[0052] Solution A (G / EP mixture) with a flake graphite concentration of 40% and solutions B (μm Cu / EP mixture) with concentrations of 1%, 5%, 10%, and 15% were prepared and stirred thoroughly. Four test samples were prepared by combining solution A with solutions B of different concentrations of conductive reinforcing materials. The preparation process for each sample is described below.

[0053] Two identical twill fabric pieces were stacked alternately, preparing two sets. First, solution A was evenly coated onto each set of carbon fiber fabric using a coater. Then, solution B was evenly coated onto one set using the coater. The sets were then joined together and placed in a vacuum press at 150°C and 3000 kg pressure for 20 minutes, after which a test sample was obtained. Using this method, four test samples were ultimately obtained.

[0054] Example 2:

[0055] Solution A (G / EP mixture) with a flake graphite concentration of 40% and solutions B (μm Cu / EP mixtures) with concentrations of 1%, 5%, 10%, and 15% were prepared and stirred thoroughly. Four test samples were prepared by combining solution A with solutions B of different concentrations of conductive reinforcing materials. The preparation process for each sample is described below.

[0056] Two identical pieces of cross-weave and twill woven fabric were stacked alternately to prepare two sets. First, solution A was evenly coated onto each set of carbon fiber woven fabric using a coater. Then, solution B was evenly coated onto one set using a coater. The sets were then joined together and placed in a vacuum press at 150°C and 3000 kg pressure for 20 minutes, after which a test sample was obtained. Using this method, four test samples were ultimately obtained.

[0057] Example 3:

[0058] Solution A (G / EP mixture) with a flake graphite concentration of 40% and solutions B (nmCu / EP mixture) with concentrations of 1%, 5%, 10%, and 15% were prepared and stirred thoroughly. Four test samples were prepared by combining solution A with solutions B of different concentrations of conductive reinforcing materials. The preparation process for each sample is described below.

[0059] Two identical twill fabric pieces were stacked alternately, preparing two sets. First, solution A was evenly coated onto each set of carbon fiber fabric using a coater. Then, solution B was evenly coated onto one set using the coater. The sets were then joined together and placed in a vacuum press at 150°C and 3000 kg pressure for 20 minutes, after which a test sample was obtained. Using this method, four test samples were ultimately obtained.

[0060] Example 4:

[0061] Two identical twill woven fabrics were stacked alternately, one on top of the other, to prepare two sets. A G / EP mixture with a flake graphite concentration of 40% was then prepared and stirred thoroughly. Subsequently, the prepared G / EP solution was evenly coated onto each set of carbon fiber woven fabrics using a coater. The pieces were then assembled and placed in a vacuum press at 150°C and 3000 kg pressure for 20 minutes. The resulting sample was then removed to obtain a test sample.

[0062] Example 5:

[0063] Solution A (G / EP mixture) with a flake graphite concentration of 40% and solutions B (μm Cu / EP mixture) with concentrations of 1%, 3%, 5%, 7%, and 10% were prepared and stirred thoroughly. Five test samples were prepared by combining solution A with solutions B of different concentrations of conductive reinforcing materials. The preparation process for each sample is described below.

[0064] Two identical twill fabric pieces were stacked alternately, preparing two sets. First, solution A was evenly coated onto each set of carbon fiber fabric using a coater. Then, solution B was evenly coated onto one set using the coater. The sets were then joined together and placed in a vacuum press at 150℃ and 3000kg pressure for 20 minutes, after which a test sample was obtained. Following this method, five test samples were ultimately obtained.

[0065] Example 6:

[0066] Two identical twill woven fabrics were stacked alternately to prepare two sets. A solution (G / EP mixture) with a flake graphite concentration of 40% and a solution (μmCu / EP mixture) with a concentration of 5% were prepared and stirred thoroughly. Solution A was then uniformly coated onto each set of carbon fiber woven fabrics using a coater. Solution B was then uniformly coated onto one set using the coater. A mold with raised flow channels was placed on top, and the mold was then closed and placed in a vacuum press at 150℃ and 3000kg pressure for 20 minutes. The molded sample with flow channels was then removed. Under simulated fuel cell operating conditions (H2SO4 solution at pH=3), a 4-hour constant potential test was performed using an electrochemical workstation at a potential of 0.6V vs SCE, while the sample was simultaneously purged with air. The concentration of copper precipitated in the solution was measured every 1 hour using inductively coupled plasma atomic emission spectrometry (ICP-AES). Figure 8 As shown, the rate of change of element concentration in the solution is different. When the concentration difference between the solution after 3 hours and 4 hours is not significant, it can be considered stable. After it stabilizes, it is taken out, rinsed clean and assembled into a PEMFC single cell.

[0067] Example 7:

[0068] Two identical twill woven fabrics are stacked alternately, preparing two sets. Then, a 40% flake graphite concentration solution A (G / EP mixture) and a 5% concentration solution B (μmCu / EP mixture) are prepared and stirred thoroughly. Next, solution A is uniformly coated onto each set of carbon fiber woven fabrics using a coater. Then, solution B is uniformly coated onto one set using the coater. A mold with raised flow channels is placed on top, then the mold is closed and fed into a vacuum press. After vacuum pressing at 150℃ and 3000kg for 20 minutes, the mold is removed, yielding a composite bipolar plate with flow channels, without undergoing step 4.

[0069] Example 8:

[0070] Two identical twill woven fabrics are stacked alternately, preparing two sets. An EP mixture with a concentration of 40% G + 5% μm Cu is prepared and stirred until homogeneous. This mixture is then evenly coated onto each set of carbon fiber woven fabric using a coater. A mold with raised flow channels is placed on top, closed, and fed into a vacuum press. The press is held under vacuum at 150°C and 3000 kg for 20 minutes, yielding a composite bipolar plate with flow channels.

[0071] Example 9:

[0072] Two identical twill woven fabrics were stacked alternately, preparing two sets. Then, a 40% flake graphite concentration solution A (G / EP mixture) and a 5% concentration solution B (nmCu / EP mixture) were prepared and stirred thoroughly. Next, solution A was uniformly coated onto each set of carbon fiber woven fabrics using a coater. Then, solution B was uniformly coated onto one set using the coater. A mold with raised flow channels was placed on top, then the mold was closed and fed into a vacuum press. After vacuum pressing at 150℃ and 3000kg for 20 minutes, the mold was removed, yielding a composite bipolar plate with flow channels.

[0073] By comparing the above embodiments, we can conclude that:

[0074] Figure 3 The conductivity and mechanical properties test results of Examples 1 and 2 clearly show that the composite bipolar plates prepared using plain weave and twill carbon fiber woven fabrics generally have better conductivity and mechanical strength, indicating that the composite bipolar plates prepared using plain weave and twill carbon fiber woven fabrics have better performance.

[0075] Figure 4 The conductivity and mechanical properties test results of Examples 1 and 3 show that the composite bipolar plate prepared with nmCu has a higher average conductivity. However, the optimal conductivity appears in the composite bipolar plate prepared with 5% μmCu. Considering the large redundancy in mechanical strength, μmCu is selected for subsequent preparation in order to pursue better conductivity. This way, the manufacturing cost can be lower while obtaining the best conductivity.

[0076] Figure 5 The conductivity and mechanical property test results of Examples 4 and 5 clearly show that the composite bipolar plate prepared using 5% μm Cu exhibits the best conductivity, and the samples prepared using the sandwich method described in this invention generally have higher mechanical strength. This indicates that constructing a sandwich structure is beneficial for achieving superior conductivity and mechanical properties.

[0077] Depend on Figure 6As shown in the Tafel curves (left) and corrosion current densities (right) of Examples 4 and 5, it is evident that the composite bipolar plate with a sandwich structure prepared using the method of this invention exhibits significantly better corrosion resistance. Compared to composite bipolar plates prepared using only flake graphite, the composite bipolar plate prepared using the method of this invention, even with the addition of 7% micron-sized copper, achieved a corrosion current density similar to that of the composite bipolar plate prepared using only flake graphite. This indicates that the sandwich structure successfully provides protection for the added copper.

[0078] like Figure 7 As shown, the microstructure and elemental distribution of composite bipolar plates prepared with different copper addition amounts are illustrated. The first column (Figures a1, b1, c1, d1, e1) are cross-sectional views of copper addition amounts of 1wt%, 3wt%, 5wt%, 7wt%, and 10wt%. The second column (Figures a2, b2, c2, d2, e2) are EDS images corresponding to the first column, where the red part represents C element and the blue part represents Cu element. The third column (Figures a3, b3, c3, d3, e3) are microstructure images of the corresponding amounts. It can be clearly seen that as the copper content increases, the sandwich structure formed inside the composite bipolar plate gradually becomes more obvious. This indicates that the preparation method described in this invention can successfully construct a sandwich structure inside the composite bipolar plate, thereby forming a protection for the copper element.

[0079] Depend on Figure 9 As shown, Examples 4 and 5 illustrate the single-cell assembly method (a), the assembled single cell (b), and the IV and IP curve test results of Examples 4 and 5 (c). It can be seen that the composite bipolar plate, after the post-processing described in this invention, exhibits superior performance in PEMFC single-cell performance testing, achieving a peak power density of 0.520 W / cm². 2 Compared to the peak power density of 0.450 W / cm² for the unprocessed sample, this represents a significant improvement. 2 This represents a significant improvement.

[0080] Depend on Figure 10 It is known that the construction of sandwich structures optimizes the conductivity and mechanical strength of composite bipolar plates.

[0081] In summary, the present invention has the following beneficial effects:

[0082] (1) Traditional composite bipolar plates cannot simultaneously optimize conductivity and mechanical strength. To achieve excellent conductivity, the content of conductive filler needs to be increased. The poor mechanical strength of the conductive filler and the reduction of resin content together lead to a decrease in mechanical strength. This is because the added conductive filler cannot be effectively utilized and needs to spontaneously form a conductive network during the molding process. Therefore, in this invention, carbon fiber woven fabric is used as the conductive network introduced into the composite bipolar plate to reduce the difficulty of the conductive filler contacting each other to form a conductive network. The interlaced carbon fiber woven fabric can also improve the problem of poor uniformity of in-plane conductivity caused by resin enrichment on the surface.

[0083] (2) Traditional composite bipolar plates introduce new elements directly during stirring or mixing, followed by hot pressing after uniform mixing. However, this method cannot control the distribution of elements. This invention uses copper and other metal elements as conductive reinforcing materials and designs a sandwich structure to regulate the distribution of copper elements in the composite bipolar plate, concentrating them as much as possible inside, thereby avoiding the decrease in corrosion resistance caused by the addition of copper. Experimental results show that the carbon fiber woven fabric composite bipolar plate with a sandwich structure prepared using the method of this invention has better conductivity and mechanical strength than composite bipolar plates prepared by traditional blending methods. The construction of the sandwich structure also successfully protects the copper elements, improving the electrochemical corrosion of the composite bipolar plate. Furthermore, through certain treatment methods, metal cations that may harm the proton exchange membrane are removed, thereby avoiding the occurrence of metal cation effects. Finally, the prepared composite bipolar plate was applied to a PEMFC single cell, showing good operating conditions with a peak power density of 0.520 W / cm³. 2 .

[0084] In this invention, the terms "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., refer to a specific feature, structure, material, or characteristic described in connection with that embodiment or example, which is included in at least one embodiment or example of the invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0085] Although the above embodiments have been shown and described, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Any changes, modifications, substitutions and variations made to the above embodiments by those skilled in the art are within the protection scope of the present invention.

Claims

1. A method for preparing a bipolar plate of carbon fiber woven fabric composite material with a sandwich structure, characterized in that, Includes the following steps: Step 1: Add the weighed conductive filler to the resin solution to obtain solution A, and then use a stirrer to stir solution A evenly; add the weighed conductive reinforcing material to the resin solution to obtain solution B, and then use a stirrer to stir solution B evenly; wherein, the conductive filler includes natural flake graphite, artificial flake graphite, expandable graphite and carbon black, and the conductive reinforcing material includes copper, silver, aluminum and platinum; Step 2: Prepare two sets of carbon fiber woven fabrics. Each set of carbon fiber woven fabrics includes two pieces of carbon fiber woven fabric. Stack the two pieces of carbon fiber woven fabric in each set together. Then, use a coater to evenly coat a layer of solution A on the two sets of stacked carbon fiber woven fabrics. Then, use a coater to evenly coat a layer of solution B on any one of the sets of carbon fiber woven fabrics coated with solution A. Step 3: Combine the two sets of carbon fiber woven fabrics coated with different solutions, so that the coated solution B is in the middle layer of the combined material. Then place the mold on it and send them into the vacuum press. After vacuum hot pressing for a certain time under the set temperature and pressure, take it out to obtain a carbon fiber woven fabric composite bipolar plate with a sandwich structure. Step 4: After the bipolar plate with a sandwich structure made of carbon fiber woven fabric is prepared, it is subjected to constant potential test in a simulated fuel cell working environment to reduce and remove metal cations that damage the proton exchange membrane.

2. The method for preparing the composite material bipolar plate according to claim 1, characterized in that: The resin is a thermosetting resin or a thermoplastic resin. The thermosetting resin is any one of epoxy resin, phenolic resin or vinyl ester resin, and the thermoplastic resin is any one of polyvinylidene fluoride or polypropylene.

3. The method for preparing the composite material bipolar plate according to claim 1, characterized in that: The carbon fiber woven fabric used includes plain weave carbon fiber woven fabric and twill weave carbon fiber woven fabric. The stacking arrangement of a group of carbon fiber woven fabrics includes any one of the following: plain weave carbon fiber woven fabric and twill weave carbon fiber woven fabric stacked arrangement, twill weave carbon fiber woven fabric and twill weave carbon fiber woven fabric stacked arrangement, plain weave carbon fiber woven fabric and plain weave carbon fiber woven fabric stacked arrangement.

4. The method for preparing the composite material bipolar plate according to claim 1, characterized in that, In the A solution, the ratio of resin:curing agent:accelerator is 1:0.8:0.01, and the conductive filler accounts for 10%-40% of the total weight of resin, curing agent and accelerator; The resin:curing agent:accelerator ratio in solution B is 1:0.8:0.01, and the content of conductive reinforcing material in solution B is less than 10% of the total weight of resin, curing agent and accelerator.

5. The method for preparing the composite material bipolar plate according to claim 4, characterized in that, The curing agent is methyltetrahydrophthalic anhydride.

6. The method for preparing the composite material bipolar plate according to claim 4, characterized in that, The accelerator is diaminodiphenylmethane.

7. The method for preparing a carbon fiber woven fabric composite bipolar plate with a sandwich structure according to claim 1, characterized in that: Step 4 involves placing the prepared carbon fiber woven fabric composite bipolar plate with a sandwich structure into a simulated fuel cell working environment, i.e., an H2SO4 solution with pH=3. Using an electrochemical workstation, a constant potential test is performed for 4 hours at a potential of 0.6V vs SCE. During the test, the carbon fiber woven fabric composite bipolar plate with a sandwich structure is simultaneously purged with air. The concentration of metal in the conductive reinforcing material precipitated in the simulated fuel cell working environment is measured every 1 hour using inductively coupled plasma atomic emission spectrometry (ICP-AES). After the concentration of metal in the conductive reinforcing material measured in the two consecutive measurements stabilizes, the plate is removed and rinsed clean.

8. A bipolar plate made of carbon fiber woven fabric composite material with a sandwich structure, characterized in that, The composite material electrode plate is prepared by the method for preparing the composite material bipolar plate according to any one of claims 1-7.

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