Fuel cell bipolar plate and preparation method thereof

Abstract

The invention provides a fuel cell bipolar plate and a preparation method thereof. The fuel cell bipolar plate comprises a metal bipolar plate, a self-repairing transition layer covering the surface of the metal bipolar plate and a carbon coating covering the surface of the self-repairing transition layer, and the self-repairing transition layer contains a high-molecular polymer. The main component of the self-repairing transition layer arranged on the surface of the metal bipolar plate is a high-molecular polymer, a network structure formed by the self-repairing transition layer not only can enable a carbon coating to be firmly combined with the metal bipolar plate, but also has relatively high binding force with an oxide film layer on the surface of the metal bipolar plate, and the polymer can continuously grow in an operating environment of a fuel cell, so that the service life of the fuel cell is prolonged. And after the local carbon coating is damaged and corroded, the coating can be self-repaired due to the binding characteristic of the polymer, so that the performance loss of the galvanic pile caused by local carbon corrosion is prevented.

Description

Technical Field

[0001] The present invention relates to the technical field of fuel cell bipolar plates, and in particular to a fuel cell bipolar plate and a preparation method thereof. Background Art

[0002] Proton Exchange Membrane Fuel Cell (PEMFC) is the only energy source in the current new energy field that uses water as its main product to generate electricity. It is very environmentally friendly and its application range has included automobiles, drones, fixed power stations, ships, etc. In the proton exchange membrane fuel cell stack, the fuel cell bipolar plate plays an important role, mainly responsible for gas distribution, heat conduction and a certain support role, accounting for 80% of the weight of the stack and 30% of the stack cost. At present, bipolar plates are mainly divided into metal bipolar plates and graphite bipolar plates. Graphite bipolar plates are limited in the field of fuel cells due to their large size and brittleness; while metal bipolar plates have excellent electrical and thermal conductivity and good mechanical properties, and have become the first choice for fuel cell plate materials. However, unmodified metal bipolar plates will undergo severe electrochemical corrosion in the acidic (pH≈3), high temperature and high humidity environment of the fuel cell, forming a dense oxide film on the surface, causing the conductivity of the bipolar plate to decrease, and a large amount of metal ions will precipitate during the corrosion process to contaminate the catalyst, thereby weakening the output performance of the fuel cell stack.

[0003] In the existing public technology, there are two main ways to improve the corrosion resistance and conductivity of metal plates: 1. Through chemical and physical treatment, such as changing the composition of the substrate material at high temperature, such as using new materials such as adding Ti elements; 2. Prepare and cover the conductive material and corrosion-resistant material on the substrate surface through a single PVD or CVD method, such as Au, Ti, C coating, etc.

[0004] Metal bipolar plates can be divided into stainless steel (SUS) and titanium and other metal materials, but based on the view of high corrosion resistance, more and more studies have shown that the use of low-cost carbon as a coating material combined with titanium plates as substrates can greatly improve the corrosion resistance of bipolar plates. In the process of preparing carbon coatings, the most difficult technical point is how to make the prepared carbon coatings firmly bonded to the surface of the substrate. In most cases, titanium (stainless steel) is exposed to the air to form a dense metal oxide. This layer of oxide usually has low activity, is relatively dense and very strong. Therefore, the most difficult part of the preparation of carbon coating technology is the combination of carbon coating and this layer of oxide. In addition, due to local carbon corrosion in the actual application of carbon coatings, local stainless steel substrates are exposed, which in turn affects the performance of the battery stack. Moreover, the cost of secondary plating of bipolar plates is extremely high. Summary of the invention

[0005] The main purpose of the present invention is to provide a fuel cell bipolar plate and a preparation method thereof, so as to solve the problems in the prior art that the metal bipolar plate and the carbon coating are difficult to firmly bond and the carbon coating bipolar plate may have local corrosion.

[0006] In order to achieve the above-mentioned purpose, according to one aspect of the present invention, a fuel cell bipolar plate is provided, which comprises: a metal bipolar plate, a self-repairing transition layer covering the surface of the metal bipolar plate and a carbon coating covering the surface of the self-repairing transition layer, wherein the self-repairing transition layer contains a high molecular polymer.

[0007] Furthermore, the high molecular polymer includes any one or more of polyaniline, polypyrrole and polythiophene.

[0008] Furthermore, the thickness of the self-repairing transition layer is 0.05-0.1 μm.

[0009] Furthermore, the self-healing transition layer also includes doping elements; preferably, the doping elements include any one or more of Pt, Au, Ti, Nb, Mo, Si and B; preferably, the content of the doping elements is 1 to 20 wt%.

[0010] Furthermore, the surface of the metal bipolar plate has a metal oxide layer, and the self-repairing transition layer is on the other side of the metal oxide layer.

[0011] According to another aspect of the present application, a method for preparing any of the above-mentioned fuel cell bipolar plates is provided, and the preparation method comprises: step S1, setting a self-repairing transition layer on the surface of the metal bipolar plate substrate by electroplating; step S2, setting a carbon coating on the surface of the self-repairing transition layer.

[0012] Furthermore, step S1 includes immersing the metal bipolar plate substrate in an electroplating solution containing a polymer monomer; preferably, the pH value of the electroplating solution is 4-6.

[0013] Furthermore, the electroplating solution contains doping elements, and preferably, the concentration of the doping elements is 0.5-5 wt %.

[0014] Furthermore, before the self-repairing transition layer is provided on the metal bipolar plate substrate, it is irradiated with ultraviolet light in a vacuum environment; preferably, the wavelength of the ultraviolet light is below 400 nm; preferably, the ultraviolet light irradiation time is 5 to 30 minutes.

[0015] Furthermore, in step S2, the carbon coating is provided by plasma enhanced chemical vapor deposition coating; preferably, step S2 comprises: placing a metal bipolar plate substrate provided with a self-repairing transition layer in a plasma enhanced chemical vapor deposition device, and performing vapor deposition with a hydrocarbon gas as a carbon source, preferably, the hydrocarbon gas comprises any one or more of acetylene, methane, butane and ethylene, preferably, the RF power of the plasma enhanced chemical vapor deposition device is 50 to 200 W, the gas flow rate is 1 to 30 sccm, the deposition pressure is 0.1 to 1 Pa, preferably, the deposition time is 1 to 3 h, and the chamber temperature is 400 to 600 ° C.

[0016] By applying the technical solution of the present invention, a self-repairing transition layer and a carbon coating are arranged on the surface of the metal bipolar plate, wherein the main component of the self-repairing transition layer is a high molecular polymer, and the network structure formed by the self-repairing transition layer can not only make the carbon coating firmly bonded to the metal bipolar plate substrate, especially with the oxide film layer on the surface of the metal bipolar plate, but also the polymer can continue to grow in the operating environment of the fuel cell. When the local carbon coating is damaged and corroded, due to the binding characteristics of the polymer, the coating can be self-repaired, thereby preventing the loss of battery stack performance caused by local carbon corrosion. The above-mentioned composite coating can increase the conductivity and corrosion resistance of the bipolar plate on the one hand, and on the other hand, it can also greatly reduce the cost of coating preparation. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] The drawings constituting a part of the present application are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the drawings:

[0018] Figure 1 A schematic diagram of the preparation process of a self-repairing transition layer according to an embodiment of the present invention is shown;

[0019] Figure 2 A schematic diagram of the preparation process of a carbon coating according to an embodiment of the present invention is shown;

[0020] Figure 3 A schematic diagram of the structure of the bipolar plate composite coating according to Example 1 of the present invention is shown;

[0021] Figure 4 The Raman images of carbon elements of the composite coatings of Examples 1 to 3 of the present application are shown;

[0022] Figure 5 The IV curves and IP curves of Examples 1, 3, and 8 of the present application are shown.

[0023] Among them, the above-mentioned drawings include the following figure marks: 1. substrate; 2. active metal oxide film; 3. self-healing transition layer; 4. carbon coating. DETAILED DESCRIPTION

[0024] It should be noted that, in the absence of conflict, the embodiments and features in the embodiments of the present application can be combined with each other. The present invention will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0025] As analyzed in the background technology of the present application, in the process of preparing the surface coating of the bipolar plate, a dense, hard and stable metal oxide film is often formed on the surface of the original substrate in the atmosphere. Since this layer structure has relatively stable performance and few active functional groups in the molecular structure, it is extremely difficult to combine the carbon film with this metal oxide layer. In the prior art, there are problems such as difficulty in firmly combining the metal bipolar plate and the carbon coating and local corrosion of the carbon coated bipolar plate. In order to solve this problem, the present application provides a fuel cell bipolar plate and a preparation method thereof.

[0026] According to a typical embodiment of the present application, a fuel cell bipolar plate is provided, which includes: a metal bipolar plate, a self-healing transition layer covering the surface of the metal bipolar plate, and a carbon coating covering the surface of the self-healing transition layer, wherein the self-healing transition layer contains a high molecular polymer.

[0027] The present application sets a self-repairing transition layer and a carbon coating on the surface of the metal bipolar plate, wherein the main component of the self-repairing transition layer is a high molecular polymer, and the network structure formed by it can not only make the carbon coating firmly bonded to the metal bipolar plate, especially with the oxide film layer on the surface of the metal bipolar plate, but also the polymer can continue to grow in the operating environment of the fuel cell. When the local carbon coating is damaged and corroded, due to the binding characteristics of the polymer, the coating can be self-repaired, thereby preventing the performance loss of the battery stack caused by local carbon corrosion. The above-mentioned composite coating can increase the conductivity and corrosion resistance of the bipolar plate on the one hand, and on the other hand, it can also greatly reduce the cost of coating preparation.

[0028] The metal bipolar plate of the present application can be titanium or stainless steel, and both can improve the bonding ability with the carbon coating and further improve the conductivity and corrosion resistance of the bipolar plate by setting the above-mentioned self-repairing transition layer.

[0029] In some preferred embodiments of the present application, the polymer includes any one or more of polyaniline, polypyrrole and polythiophene. These polymers are easy to grow in the operating environment of the fuel cell, and the transition layer formed has good self-repairing ability and strong binding ability to metals and metal oxides, which is conducive to further improving the corrosion resistance of the bipolar plate.

[0030] In order to further improve the conductivity and corrosion resistance of the metal bipolar plate, in some embodiments of the present application, the thickness of the self-repairing transition layer is 0.05 to 0.1 μm.

[0031] In some embodiments of the present application, in order to further improve the conductivity of the composite coating, the self-repairing transition layer may also include doping elements. Preferably, the doping elements include any one or more of Pt, Au, Ti, Nb, Mo, Si and B. The above doping elements can be used as the structural center of the transition layer unit, with the polymer as the skeleton, which can improve the self-repairing and conductivity of the self-repairing transition layer, thereby better solving the bonding force between the metal oxide (such as titanium oxide) and the carbon film layer and the problem of coating shedding and exposing the substrate. Especially when the doping element is titanium, not only the performance of the composite coating is significantly improved, but also the cost is low. Preferably, the content of the doping element is 1-20wt%, which has a more significant effect on improving the performance of the composite coating, and more preferably 5-15wt%, such as 5wt%, 6wt%, 7wt%, 8wt%, 9wt%, 10wt%, 11wt%, 12wt%, 13wt%, 14wt%, 15wt% or any range between the two.

[0032] In some embodiments of the present application, the surface of the metal bipolar plate has a metal oxide layer, and the above-mentioned self-healing transition layer is arranged on the surface of the metal oxide layer of the metal bipolar plate, that is, on the other side of the metal oxide layer. Due to the special composition of the self-healing transition layer, it can be firmly combined with the metal oxide layer on the surface of the metal bipolar plate, which not only increases the conductivity and corrosion resistance of the bipolar plate, but also eliminates the influence of metal oxide, thereby simplifying the preparation process of the bipolar plate.

[0033] The carbon coating can be selected from the prior art, such as an amorphous carbon layer, and there is no special requirement for this application.

[0034] According to another typical embodiment of the present application, a method for preparing a bipolar plate as described above is provided, the method comprising: step S1, providing a self-repairing transition layer on the surface of a metal bipolar plate substrate by electroplating; step S2, providing a carbon coating on the surface of the self-repairing transition layer.

[0035] The fuel cell bipolar plate prepared by the above method has a self-repairing transition layer of a composite coating whose main component is a high molecular polymer. The network structure formed by the composite coating can not only make the carbon coating firmly bonded to the metal bipolar plate substrate, especially with the oxide film layer on the surface of the metal bipolar plate, but also the polymer can continue to grow in the fuel cell operation environment. When the local carbon coating is damaged and corroded, the coating can be self-repaired due to the binding characteristics of the polymer, thereby preventing the loss of stack performance caused by local carbon corrosion. The composite coating can increase the conductivity and corrosion resistance of the bipolar plate on the one hand, and on the other hand, it can also greatly reduce the cost of coating preparation.

[0036] The above-mentioned metal bipolar plate substrate can be prepared by a method in the prior art, and the present application has no limitation on the preparation method of the metal bipolar plate. For example, the anode plate and the cathode plate are prepared by stamping, molding, rolling or 3D printing, and then the cathode plate and the anode plate are connected by welding, bonding or other methods to form the metal bipolar plate substrate.

[0037] In some typical embodiments of the present application, the above-mentioned step S1 includes immersing the metal bipolar plate substrate in an electroplating solution containing a polymer monomer; preferably, the pH value of the electroplating solution is 4 to 6, which is conducive to the formation of a polymer network structure, and the formed network self-healing transition layer has a better effect.

[0038] In some embodiments of the present application, in order to prepare a self-repairing transition layer containing doping elements, the above-mentioned electroplating solution contains doping elements, and the doping elements include any one or more of Ti, Nb, Mo, Si and B. Preferably, the concentration of the doping element is 0.1-5wt%. By adjusting the concentration of the doping element in the electroplating solution, the content of the doping element in the self-repairing transition layer can be controlled. By using the electroplating solution with the doping element content, a self-repairing transition layer with a doping element content of 0.1-1wt% can be prepared. For example, when the content of the doping element titanium in the electroplating solution is 1wt%, the content of the corresponding doping element titanium in the self-repairing transition layer after electroplating is generally 5-10wt%; when the content of the doping element titanium in the electroplating solution is 5wt%, the content of the corresponding doping element titanium in the self-repairing transition layer after electroplating is generally 10-15wt%.

[0039] In some preferred embodiments of the present application, in order to improve the efficiency of electroplating or other properties of the coating, the electroplating solution may also contain additives, such as tetrabutylammonium. There is no special limitation on the type and amount of the additives in the present application. Those skilled in the art can selectively add them according to specific needs, which will not be introduced in detail here.

[0040] In order to further improve the bonding strength between the transition layer and the metal bipolar plate substrate, before setting the self-repairing transition layer, the surface of the metal bipolar plate substrate can be cleaned to remove impurities and contaminants such as grease on the surface of the metal bipolar plate substrate. The surface treatment method can be selected from the existing technology, such as ultrasonic treatment in an acidic solution.

[0041] In some preferred embodiments of the present application, before the self-repairing transition layer is set, the metal bipolar plate substrate is irradiated with ultraviolet light in a vacuum environment to remove pollutants on the surface of the metal bipolar plate substrate. The ultraviolet light irradiation on the substrate surface not only has a good surface cleaning effect, but also due to the photocatalytic effect, the metal oxide coating is activated, the surface free energy of the layer is increased, and the bonding ability between the metal bipolar plate substrate and the self-repairing transition layer containing a high molecular polymer is greatly improved. Furthermore, laser cleaning is used instead of traditional acid washing and active alkaline washing, which not only reduces pollution to the environment but also, more importantly, does not cause chemical damage to the substrate and thus affect the subsequent coating preparation process. Preferably, the gas pressure of the above-mentioned vacuum environment is less than or equal to 1Pa; preferably, the wavelength of the ultraviolet light is below 400nm, which has a better surface activation effect on the metal bipolar plate substrate; preferably, the ultraviolet light irradiation time is 5 to 20 minutes.

[0042] In some embodiments of the present application, the process of setting the self-repairing transition layer is as follows: Figure 1 As shown, the bipolar plate is cleaned with alkaline solution to remove oil stains on the surface of the metal bipolar plate substrate, and the cleaned bipolar plate is immersed in an electrolyte, which is an acidic polymer monomer solution. A voltage is applied to electroplate a polymer coating on the surface of the bipolar plate. After plating, it is cleaned and dried.

[0043] The method for setting the above-mentioned carbon coating can be selected from the existing technology, such as plasma enhanced chemical vapor deposition coating, i.e. PECVD. In some embodiments of the present application, step S2 includes: placing a metal bipolar plate substrate provided with a self-repairing transition layer in a plasma enhanced chemical vapor deposition device, and performing vapor deposition with hydrocarbon gas as a carbon source, which is conducive to forming a carbon coating with good thickness uniformity, and the sample preparation is not limited by size. Preferably, the hydrocarbon gas includes any one or more of acetylene, methane, butane and ethylene. Preferably, the RF power of the plasma enhanced chemical vapor deposition device is 50 to 200 W, the gas flow rate is 1 to 30 sccm, and the deposition pressure is 0.1 to 1 Pa. Preferably, the deposition time is 1 to 3 hours, and the chamber temperature is 400 to 600 ° C.

[0044] In some embodiments of the present application, the process of setting the carbon coating on the bipolar plate is as follows: Figure 2As shown, the metal bipolar plate substrate provided with a self-repairing transition layer is pickled to remove surface impurities and then dried, and then put into a furnace, that is, transferred into a plasma enhanced chemical vapor deposition equipment, evacuated, and PECVD is performed. The deposition time is 1 to 3 hours, the chamber temperature is 400 to 600°C, and the pressure is restored to the atmospheric value after the deposition is completed, and the carbon coating is prepared.

[0045] The beneficial effects that can be achieved by the present application will be further illustrated below in combination with embodiments and comparative examples.

[0046] Example 1

[0047] (1) A bare stainless steel plate was placed in a vacuum atmosphere (0.01 Pa), and ultraviolet light (400 nm) was used to irradiate the surface of the substrate for 15 min. The treated stainless steel plate was electroplated to prepare a polymer self-healing layer, polyaniline.

[0048] (2) Aniline was dissolved in tetrabutylammonium solution to prepare an acidic aqueous solution with a concentration of 0.5 M (M represents mol / L, the same below) (including 20 mM HCl, mM represents mmol / L, the same below), and the mixture was mixed to prepare an acidic solution with an aniline concentration of 0.5 M and a pH value of 5. Nano-titanium powder was added to the prepared acidic aniline solution to finally prepare an aniline acidic solution containing 1 wt% nano-titanium powder, which was used as an electrolyte for later use.

[0049] (3) A transition layer polymer polyaniline material is prepared by a three-electrode method. Specifically, a stainless steel plate surface-treated in step (1) and ultrasonically cleaned with 1% HF is immersed in the above electrolyte, Ag / AgCl is used as a reference electrode, Pt is used as a counter electrode, and cyclic voltammetry is used. The voltage is set at -0.3 V to 1.9 V, the scan rate is 50 mV / s, and the cycle is repeated for 30 times. A polymer self-healing transition layer containing a polyaniline network structure with good conductivity and corrosion resistance, namely a polyaniline layer, is formed on the surface of the stainless steel plate. The thickness of the polyaniline layer is 0.05 μm.

[0050] (4) The stainless steel bipolar plate containing the polyaniline transition layer prepared above was dried, and then the bipolar plate was placed in a PECVD device, acetylene was used as a carbon source; the RF power, gas flow rate and deposition pressure were 150 W, 10 sccm, and 0.5 Pa, respectively, the deposition time was 1.5 h, the chamber temperature was 600 ° C, and a carbon film was prepared. The final composite coating structure is as shown Figure 3 As shown, on the surface of the stainless steel substrate 1 there is an active metal oxide film 2, a self-repairing transition layer 3 mainly composed of high molecular weight polyaniline material formed by the above process, and an amorphous carbon film, namely a carbon coating 4 as a conductive layer.

[0051] The Raman image of the carbon element of the composite coating of this embodiment is as follows Figure 4The IV curve and IP curve are shown in curve (c). Figure 5 shown.

[0052] Example 2

[0053] The difference from Example 1 is that when preparing the carbon film in step (4), the chamber temperature is 500°C.

[0054] The Raman image of the carbon element of the composite coating of this embodiment is as follows Figure 4 The curve in (b).

[0055] Example 3

[0056] The difference from Example 1 is that when preparing the carbon film in step (4), the chamber temperature is room temperature (RT).

[0057] The Raman image of the carbon element of the composite coating of this embodiment is as follows Figure 4 The IV curve and IP curve are shown in (a). Figure 5 shown.

[0058] Example 4

[0059] The difference from Example 1 is that in step (2) the electrolyte is replaced by pyrrole of the same concentration in place of aniline.

[0060] Example 5

[0061] The difference from Example 1 is that in step (2) the electrolyte is replaced by aniline with thiophene of the same concentration.

[0062] Example 6

[0063] The difference from Example 1 is that no titanium is added to the electrolyte in step (2).

[0064] Example 7

[0065] The difference from Example 1 is that the base stainless steel plate was not subjected to step (1).

[0066] Example 8

[0067] The difference from Example 1 is that when preparing the carbon film in step (4), a Ti target is used as a transition layer.

[0068] The IV curve and IP curve of this embodiment are as follows Figure 5 shown.

[0069] Example 9

[0070] The difference from Example 1 is that in step (3), the thickness of the polyaniline layer is 0.1 μm.

[0071] Example 10

[0072] The difference from Example 1 is that in step (3), the thickness of the polyaniline layer is 0.15 μm.

[0073] Embodiment 11

[0074] The difference from Example 1 is that in step (3), the thickness of the polyaniline layer is 0.02 μm.

[0075] Example 12

[0076] The difference from Example 1 is that in step (2), the pH value of the electrolyte is 4.

[0077] Embodiment 13

[0078] The difference from Example 1 is that in step (2), the pH value of the electrolyte is 6.

[0079] Embodiment 14

[0080] The difference from Example 1 is that in step (2), no acid is added to the electrolyte.

[0081] Embodiment 15

[0082] The difference from Example 1 is that in step (2), the content of nano titanium powder in the electrolyte is 5 wt %.

[0083] Example 16

[0084] The difference from Example 1 is that in step (2), the content of nano titanium powder in the electrolyte is 7 wt %.

[0085] Embodiment 17

[0086] The difference from Example 1 is that in step (2), the electrolyte contains 1 wt% nano silicon powder.

[0087] Comparative Example 1

[0088] The stainless steel bipolar plate was cleaned with 1% HF to remove surface impurities and dried. Then the bipolar plate was placed in a PECVD device and ethylene was used as a carbon source. The RF power, gas flow rate and deposition pressure were 150W, 10sccm and 0.5Pa respectively. The deposition time was 1.5h and the chamber temperature was 600°C to prepare a carbon film.

[0089] Among them, the intensity of the carbon films prepared in Examples 1 to 3 at different Raman shifts gradually increases with the content of ID / IG, indicating that the higher the content and purity of amorphous carbon, the better the performance. Figure 4 shown.

[0090] The metal bipolar plates prepared in the above embodiments and comparative examples were tested respectively. The test method was as follows: the tested samples were measured by transverse potential method. The measuring conditions were pH=3, H2SO4, 2ppm HF, 80°C, three-electrode system, 0.84Vvs SHE-24h. The test results are shown in Table 1 below.

[0091] Table 1

[0092]

[0093] From the above description, it can be seen that the above-mentioned embodiments of the present invention achieve the following technical effects: a self-repairing transition layer and a carbon coating are arranged on the surface of the metal bipolar plate, wherein the main component of the self-repairing transition layer is a high molecular polymer, and the network structure formed by it can not only make the carbon coating firmly bonded to the metal bipolar plate substrate, especially with the oxide film layer on the surface of the metal bipolar plate, but also the polymer can continue to grow in the operating environment of the fuel cell. When the local carbon coating is damaged and corroded, due to the binding characteristics of the polymer, the coating can be self-repaired, thereby preventing the loss of battery stack performance caused by local carbon corrosion. The above-mentioned composite coating can increase the conductivity and corrosion resistance of the bipolar plate on the one hand, and on the other hand, it can also greatly reduce the cost of coating preparation.

[0094] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A fuel cell bipolar plate, characterized in that: include: A metal bipolar plate, a self-repairing transition layer covering the surface of the metal bipolar plate, and a carbon coating covering the surface of the self-repairing transition layer, Wherein, the self-repairing transition layer contains a high molecular polymer.

2. The fuel cell bipolar plate according to claim 1, characterized in that: The high molecular polymer includes any one or more of polyaniline, polypyrrole and polythiophene.

3. The fuel cell bipolar plate according to claim 1, characterized in that: The thickness of the self-repairing transition layer is 0.05-0.1 μm.

4. The fuel cell bipolar plate according to any one of claims 1 to 3, characterized in that: The self-repairing transition layer further includes a doping element; Preferably, the doping element includes any one or more of Pt, Au, Ti, Nb, Mo, Si and B; Preferably, the content of the doping element is 1-20 wt %.

5. The fuel cell bipolar plate according to any one of claims 1 to 3, characterized in that: The metal bipolar plate has a metal oxide layer on its surface, and the self-repairing transition layer is on the other side of the metal oxide layer.

6. The method for preparing a fuel cell bipolar plate according to any one of claims 1 to 5, characterized in that: include: Step S1, providing a self-repairing transition layer on the surface of the metal bipolar plate substrate by electroplating; Step S2, providing a carbon coating on the surface of the self-repairing transition layer.

7. The preparation method according to claim 6, characterized in that: The step S1 comprises immersing the metal bipolar plate substrate in an electroplating solution containing a polymer monomer; preferably, the pH value of the electroplating solution is 4-6.

8. The preparation method according to claim 7, characterized in that: The electroplating solution contains a doping element, and preferably, the concentration of the doping element is 0.5-5 wt %.

9. The preparation method according to claim 6, characterized in that: The metal bipolar plate substrate is irradiated with ultraviolet light in a vacuum environment before the self-repairing transition layer is provided; Preferably, the wavelength of the ultraviolet light is below 400 nm; Preferably, the ultraviolet light irradiation time is 5 to 30 minutes.

10. The preparation method according to claim 6, characterized in that: In the step S2, the carbon coating is provided by plasma enhanced chemical vapor deposition coating; Preferably, step S2 includes: placing a metal bipolar plate substrate provided with a self-repairing transition layer in a plasma enhanced chemical vapor deposition device, and performing vapor deposition using a hydrocarbon gas as a carbon source. Preferably, the hydrocarbon gas includes any one or more of acetylene, methane, butane and ethylene. Preferably, the RF power of the plasma enhanced chemical vapor deposition device is 50 to 200 W, the gas flow rate is 1 to 30 sccm, and the deposition pressure is 0.1 to 1 Pa. Preferably, the deposition time is 1 to 3 hours, and the chamber temperature is 400 to 600°C.

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