Metal bipolar plate and preparation method thereof

Abstract

The invention provides a metal bipolar plate and a preparation method thereof, and belongs to the technical field of fuel cell bipolar plate materials.By controlling the thickness and composition of a metal sub-layer, a metal two-phase healing layer and a compact anti-corrosion three-phase ceramic layer in a self-healing coating of the metal bipolar plate, the coating has the advantages of being high in density, uniform in component, good in corrosion resistance and the like. No obvious boundary exists between layers, the anti-seismic property and the heat resistance are high, the conductivity and the corrosion resistance are high, the stability of the fuel cell is improved, and the service life of the fuel cell is prolonged; the binding force of the coating and the base material is enhanced through the metal sub-layer, so that the coating is prevented from falling off during stress deformation; according to the metal two-phase healing layer, when cracks and holes are generated in the coating, formed oxide can promote penetration crack healing of the coating, reduce the porosity of the coating, promote crack healing and prevent cracking, Al is introduced into the metal two-phase healing layer, the binding force of the metal two-phase healing layer and the compact corrosion-resistant three-phase ceramic layer is improved, and the corrosion resistance of the coating is improved. And the coating is prevented from falling off or cracking.

Description

Technical Field

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

[0002] Fuel cell bipolar plates play an important role in proton exchange membrane fuel cells. Their main functions include supporting membrane electrodes, distributing reactants, conducting electricity, and resisting corrosion. Metal bipolar plates are the most widely used fuel cell bipolar plates due to their excellent corrosion resistance, electrical conductivity, and low cost. The commonly used material is stainless steel. Although stainless steel bipolar plates have the characteristics of low cost and easy processing, stainless steel is prone to severe corrosion, which reduces its electrical conductivity. During the operation of fuel cell bipolar plates, they often face relatively harsh working environments, such as acidic conditions, high electric potential, uneven temperature and humidity distribution, etc. And in the actual operation of vehicles, the working conditions are also relatively complex, often experiencing conditions such as start-stop and variable load. An effective way to solve the problems of reduced electrical conductivity and severe corrosion of fuel cell bipolar plates under corrosive conditions is to prepare a corrosion-resistant and conductive coating on the surface of metal bipolar plates.

[0003] Metal bipolar plate coatings include various corrosion-resistant and conductive coatings, such as noble metal coatings, metal carbide coatings, conductive polymer coatings, amorphous carbon coatings, and ceramic coatings, etc. Among them, noble metal coatings have a relatively high cost, amorphous carbon coatings have insufficient corrosion resistance, and the preparation process of conductive polymer coatings is complex, which limits their application in the fuel cell field. That is to say, traditional solutions require the use of noble metal coatings with relatively high costs and also need to prepare multi-layer composite coatings through complex deposition processes to meet the application requirements of bipolar plate coatings. And there are many limitations in the selection of coating materials, and multiple modifications are required during the process of process preparation, which increases the time cost. For example, when increasing the working voltage and working pressure during the PVD preparation process, the intensity of plasma bombardment increases, which may increase the internal stress and surface defects of the coating. Moreover, during the actual operation of fuel cells, the phenomenon of instantaneous gas supply shortage often occurs, generating local reverse high electric potential. The reverse high electric potential will oxidize the catalyst, reduce the performance of the membrane electrode, and also cause severe corrosion of the bipolar plate. In addition, during the operation of the whole vehicle, the bipolar plate is usually in extreme temperature and humidity cycles and strong vibration conditions, which are likely to cause problems such as stress cracking of the coating. Therefore, it is an urgent technical problem to be solved by the existing technology to provide a metal bipolar plate with low cost, simple preparation process, which can significantly improve the corrosion resistance and electrical conductivity of stainless steel, avoid stress cracking problems, enable stainless steel bipolar plates to break through their own service limits, and improve the stability and service life of fuel cells. Summary of the Invention

[0004] The object of the present invention is to provide a metal bipolar plate and a preparation method thereof. By using the metal bipolar plate provided by the present invention, which includes a substrate and a self-healing coating, the self-healing coating has both high conductivity and corrosion resistance, is applicable to the variable load / start-stop, high and low temperature and humidity cycling conditions, and the operating environment with strong vibration of a fuel cell, and the self-healing coating has the functions of promoting the healing of coating cracks and preventing coating cracking, can avoid problems such as stress cracking, and the preparation process of the metal bipolar plate is simple and the cost is low.

[0005] In order to achieve the above object of the invention, the present invention provides the following technical solutions:

[0006] The present invention provides a metal bipolar plate, which includes a substrate and a self-healing coating. The self-healing coating includes a metal sub-layer, a metal two-phase healing layer, and a dense corrosion-resistant three-phase ceramic layer that are sequentially arranged from the inside to the outside on the surface of the substrate;

[0007] The material of the metal sub-layer is Ti, Cr, Zr or Nb; the metal two-phase healing layer is composed of Al and alloying elements, and the alloying elements are Ti, Cr, Zr or Nb;

[0008] The dense corrosion-resistant three-phase ceramic layer is a MAX phase.

[0009] Preferably, the thickness of the metal sub-layer is 15-60 nm, the thickness of the metal two-phase healing layer is 80-600 nm, and the thickness of the dense corrosion-resistant three-phase ceramic layer is 40-300 nm.

[0010] Preferably, the thickness of the metal sub-layer is 20-50 nm, the thickness of the metal two-phase healing layer is 100-500 nm, and the thickness of the dense corrosion-resistant three-phase ceramic layer is 50-290 nm.

[0011] Preferably, the MAX phase is a nanocrystalline structure, and the crystallinity of the MAX phase > 80%.

[0012] The present invention also provides a preparation method of the metal bipolar plate according to the above technical solution, including the following steps:

[0013] (1) Ultrasonically clean the stainless steel and dry it with nitrogen to obtain a substrate;

[0014] (2) Perform a first deposition on the surface of the substrate obtained in the step (1) to form a metal sub-layer, and obtain a substrate after the first deposition;

[0015] (3) Perform a second deposition on the surface of the metal sub-layer of the substrate after the first deposition obtained in the step (2) to form a metal two-phase healing layer, and obtain a substrate after the second deposition;

[0016] (4) Perform a third deposition on the surface of the metal two-phase healing layer of the second deposited substrate obtained in step (3) to form a three-phase ceramic layer;

[0017] Perform vacuum heat treatment on the three-phase ceramic layer to form a dense corrosion-resistant three-phase ceramic layer with a composition of MAX phase, realizing the preparation of a self-healing coating on the substrate surface to obtain a metal bipolar plate.

[0018] Preferably, the method of the first deposition in step (1) is multi-arc ion plating, high-power pulsed magnetron sputtering or vacuum cathodic arc ion plating, and the temperature of the first deposition is 180-700 °C.

[0019] Preferably, in step (2), an Al metal target and an alloy element metal target are used for the second deposition, and the deposition current ratio of the alloy element metal target to the Al metal target is (1:5)-(5:1).

[0020] Preferably, the method of the third deposition in step (4) is high-power pulsed magnetron sputtering, and the temperature of the third deposition is 150-700 °C.

[0021] Preferably, in step (4), a gaseous carbon source is used as the working gas for the third deposition, and the volume content of the gaseous carbon source in the working gas is 10%-50%.

[0022] Preferably, the temperature of the vacuum heat treatment in step (4) is 150-900 °C, the heating rate of the vacuum heat treatment is 0.5-12 °C / min, and the time of the vacuum heat treatment is 20-50 min.

[0023] The present invention provides a metal bipolar plate, comprising a substrate and a self-healing coating. The self-healing coating includes a metal sub-layer, a metal two-phase healing layer, and a dense corrosion-resistant triple-phase ceramic layer, which are sequentially arranged from the inside to the outside on the surface of the substrate. The material of the metal sub-layer is Ti, Cr, Zr or Nb. The metal two-phase healing layer is composed of Al and alloying elements, and the alloying elements are Ti, Cr, Zr or Nb. The dense corrosion-resistant triple-phase ceramic layer is a MAX phase. In the metal bipolar plate provided by the present invention, the self-healing coating (also known as the MAX phase multi-layer composite coating) is composed of a metal sub-layer, a metal two-phase healing layer, and a dense corrosion-resistant triple-phase ceramic layer, which are sequentially arranged from the inside to the outside on the surface of the substrate. By controlling the thickness and composition of the metal sub-layer, the metal two-phase healing layer, and the dense corrosion-resistant triple-phase ceramic layer, the coating has high density, uniform composition, and no obvious boundary between layers. Under a relatively thin dense corrosion-resistant triple-phase ceramic layer, excellent seismic performance and heat resistance can still be achieved, and it has high conductivity and high corrosion resistance. It can enable the stainless steel bipolar plate to break through its own service limit, improve the stability and service life of the fuel cell, and is suitable for variable load / start-stop, high and low temperature and humidity cycling conditions, and operating environments with strong vibration of the fuel cell. The bonding force between the self-healing coating and the substrate is enhanced by the metal sub-layer, which can prevent the coating from peeling off when stress deformation occurs. The metal two-phase healing layer has certain self-healing performance under corrosion environment conditions and can be used as a healing agent for the coating. When cracks and holes are generated in the coating, the formed oxides can promote the healing of through-cracks in the coating and reduce the porosity of the coating, promote the healing of coating cracks and prevent coating cracking, so as to avoid problems such as stress cracking. And by introducing Al into the metal two-phase healing layer, the bonding force between the metal two-phase healing layer and the dense corrosion-resistant triple-phase ceramic layer is improved, further preventing the peeling off or cracking of the dense corrosion-resistant triple-phase ceramic layer, and thus avoiding the peeling off or cracking of the coating. Moreover, the preparation process of the metal bipolar plate in the present invention is simple and the raw material cost is low. The results of the examples show that the cross-section of the self-healing coating in the metal bipolar plate prepared by the present invention is complete without obvious cracks and micropores and other defects, the surface is dense and complete without cracks and micropores and other defects, the high-potential corrosion resistance ability is excellent, and it can withstand high-potential corrosion for more than 10 hours. Seven days after cracks are generated by external force, it can promote the healing of microcracks and has a repair effect. The coating has strong extensibility, so that the corrosion resistance of the coating is repaired and improved, and the corrosion of the corrosion solution to the matrix material is prevented. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 FIG. 6 is a cross-sectional SEM image of the MAX phase multi-layer composite coating in the metal bipolar plate prepared in Preparation Example 1 of the present invention;

[0025] Figure 2 FIG. 10 is a surface SEM image of the MAX phase multi-layer composite coating in the metal bipolar plate prepared in Preparation Example 1 of the present invention;

[0026] Figure 3 This is the high - potential test result graph of the MAX - phase multi - layer composite coating on the metal bipolar plate prepared in Preparation Example 1 of the present invention;

[0027] Figure 4 This is the surface SEM graph of the MAX - phase multi - layer composite coating on the metal bipolar plate prepared in Preparation Example 1 of the present invention after crack healing. Detailed implementation manners

[0028] The present invention provides a self - healing coating for a metal bipolar plate, comprising a substrate and a self - healing coating. The self - healing coating includes a metal sub - layer, a metal two - phase healing layer, and a dense corrosion - resistant three - phase ceramic layer, which are sequentially arranged from the inside to the outside on the surface of the substrate;

[0029] The material of the metal sub - layer is Ti, Cr, Zr or Nb; the metal two - phase healing layer is composed of Al and alloying elements, and the alloying elements are Ti, Cr, Zr or Nb;

[0030] The dense corrosion - resistant three - phase ceramic layer is a MAX phase.

[0031] In the present invention, the thickness of the metal sub - layer is preferably 15 - 60 nm, more preferably 20 - 50 nm. The present invention controls the thickness of the metal sub - layer within the above range to enhance the bonding strength and extensibility of the self - healing coating.

[0032] In the present invention, the thickness of the metal two - phase healing layer is preferably 80 - 600 nm, more preferably 100 - 500 nm. The present invention controls the thickness of the metal two - phase healing layer within the above range to form a metal two - phase healing layer with stable structural characteristics, so as to ensure that the metal two - phase healing layer can heal cracks to a certain extent and facilitate the attachment and synthesis of the dense corrosion - resistant three - phase ceramic layer.

[0033] In the present invention, the thickness of the dense corrosion - resistant three - phase ceramic layer is preferably 40 - 300 nm, more preferably 50 - 290 nm. The present invention controls the thickness of the dense corrosion - resistant three - phase ceramic layer within the above range so that the formed dense corrosion - resistant three - phase ceramic layer has a long service life and excellent corrosion resistance.

[0034] In the present invention, the MAX phase is preferably a nanocrystalline structure; the crystallinity of the MAX phase is preferably > 80%. The present invention controls the crystallinity of the MAX phase within the above range to form a dense corrosion - resistant three - phase ceramic layer with a dense structure and stable performance on the surface. In the present invention, the MAX phase is preferably Ti2AlC, Cr2AlN and Nb2AlN.

[0035] The present invention also provides a preparation method for the metal bipolar plate according to the above - mentioned technical solution, comprising the following steps:

[0036] (1) Ultrasonically clean the stainless steel and dry it with nitrogen gas to obtain a substrate;

[0037] (2) Perform a first deposition on the surface of the substrate obtained in step (1) to form a metal sub-layer, obtaining a substrate after the first deposition;

[0038] (3) Perform a second deposition on the surface of the metal sub-layer of the substrate after the first deposition obtained in step (2) to form a metal two-phase healing layer, obtaining a substrate after the second deposition;

[0039] (4) Perform a third deposition on the surface of the metal two-phase healing layer of the substrate after the second deposition obtained in step (3) to form a three-phase ceramic layer;

[0040] Subject the three-phase ceramic layer to vacuum heat treatment to form a dense corrosion-resistant three-phase ceramic layer with a composition of MAX phase, realizing the preparation of a self-healing coating on the surface of the substrate and obtaining a metal bipolar plate.

[0041] In the present invention, unless otherwise specified, the raw materials used are all conventional commercially available products in the art.

[0042] The present invention ultrasonically cleans the stainless steel and dries it with nitrogen gas to obtain a substrate.

[0043] In the present invention, the ultrasonic cleaning includes sequentially performing ultrasonic cleaning with anhydrous ethanol and ultrasonic cleaning with deionized water. The present invention has no special limitation on the time of the ultrasonic cleaning with anhydrous ethanol and the ultrasonic cleaning with deionized water, and it is only necessary to achieve the cleaning and removal of surface impurities. The present invention has no special limitation on the method of drying with nitrogen gas, and it is only necessary to achieve the removal of surface solvents.

[0044] After obtaining the substrate, the present invention performs a first deposition on the surface of the substrate to form a metal sub-layer, obtaining a substrate after the first deposition.

[0045] In the present invention, the method of the first deposition is preferably multi-arc ion plating, high-power pulsed magnetron sputtering or vacuum cathodic arc ion plating. The present invention preferably pre-treats the substrate before the first deposition. In the present invention, the pre-treatment preferably includes plasma cleaning and activation of the substrate for 0 to 20 minutes at a substrate bias voltage of 0 to 100 V.

[0046] In the present invention, the temperature of the first deposition is preferably 180 to 700 °C, more preferably 200 to 600 °C. The present invention controls the temperature of the first deposition within the above range so that the coating elements have sufficient kinetic energy and activity for deposition to form a metal sub-layer with excellent performance.

[0047] After obtaining the substrate after the first deposition, the present invention performs a second deposition on the surface of the metal sub-layer of the substrate after the first deposition to form a metal two-phase healing layer, obtaining a substrate after the second deposition.

[0048] In the present invention, the method of the second deposition is preferably multi-arc ion plating, high-power pulsed magnetron sputtering or vacuum cathodic arc ion plating. In the present invention, the second deposition preferably uses an Al metal target and an alloy element metal target. In the present invention, the ratio of the deposition current of the alloy element metal target to the Al metal target is preferably (1-5):(1-5). The present invention controls the ratio of the deposition current of the alloy element metal target to the Al metal target within the above range so as to adjust a suitable ratio and form a metal two-phase layer with excellent properties.

[0049] After obtaining the substrate after the second deposition, the present invention performs a third deposition on the surface of the metal two-phase healing layer of the substrate after the second deposition to form a three-phase ceramic layer.

[0050] In the present invention, the method of the third deposition is preferably high-power pulsed magnetron sputtering. In the present invention, the temperature of the third deposition is preferably 150-700 °C, more preferably 200-600 °C. The present invention controls the temperature of the third deposition within the above range, which is beneficial to subsequently form a dense anti-corrosion three-phase ceramic layer with sufficient crystallinity and a composition of MAX phase.

[0051] In the present invention, the third deposition uses a gaseous carbon source as the working gas. In the present invention, the gaseous carbon source is preferably CH 4 or CH 2 . In the present invention, the volume content of the gaseous carbon source in the working gas is preferably 10%-50%. The present invention controls the volume content of the gaseous carbon source in the working gas within the above range so as to ensure that while providing sufficient carbon source gas to form a coating, the kinetic energy of the deposited elemental particles is not affected, and continuous and stable deposition is carried out to form a three-phase ceramic layer with excellent properties.

[0052] After obtaining the three-phase ceramic layer, the present invention performs vacuum heat treatment on the three-phase ceramic layer to form a dense anti-corrosion three-phase ceramic layer with a composition of MAX phase, realizing the preparation of a self-healing coating on the surface of the substrate and obtaining a metal bipolar plate.

[0053] In the present invention, the temperature of the vacuum heat treatment is preferably 150-900 °C, more preferably 200-800 °C. In the present invention, the heating rate of the vacuum heat treatment is preferably 0.5-12 °C / min, more preferably 1-10 °C / min. In the present invention, the time of the vacuum heat treatment is preferably 20-50 min, more preferably 25-40 min. The present invention controls the temperature, heating rate and time of the vacuum heat treatment within the above range to improve the crystallinity and form a dense anti-corrosion three-phase ceramic layer with stable properties and a high corrosion resistance and a composition of MAX phase.

[0054] The preparation method of the metal bipolar plate provided by the present invention is simple in operation, low in cost, and suitable for large-scale production.

[0055] The present invention also provides an application of the metal bipolar plate described in the above technical solution or the metal bipolar plate prepared by the preparation method in a fuel cell bipolar plate.

[0056] In the present invention, the fuel cell metal bipolar plate is preferably a fuel cell bipolar plate with both anti-corrosion property and mechanical properties.

[0057] Next, the technical solutions in the present invention will be clearly and completely described in conjunction with the embodiments in the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments in the present invention without creative efforts shall fall within the protection scope of the present invention.

[0058] Example 1

[0059] The battery metal bipolar plate is composed of a substrate and a self-healing coating, and the self-healing coating is composed of a metal sub-layer, a metal two-phase healing layer, and a dense anti-corrosion three-phase ceramic layer sequentially arranged from the inside to the outside on the surface of the substrate;

[0060] The material of the metal sub-layer is Ti; the metal two-phase healing layer is composed of Al and alloy element Ti; the dense anti-corrosion three-phase ceramic layer is a MAX phase;

[0061] The thickness of the metal sub-layer is 30 nm, the thickness of the metal two-phase healing layer is 100 nm, and the thickness of the dense anti-corrosion three-phase ceramic layer is 200 nm;

[0062] The MAX phase is Ti2AlC with a nanocrystalline structure and a crystallinity > 80%.

[0063] Preparation Example 1

[0064] The preparation method of the metal bipolar plate described in Example 1 is as follows:

[0065] (1) Take a 5×5 cm stainless steel, perform ultrasonic cleaning with absolute ethanol and ultrasonic cleaning with deionized water in sequence, and then dry it with nitrogen to obtain a substrate;

[0066] (2) Put the substrate obtained in step (1) into a high-power pulsed magnetron sputtering chamber, set the substrate bias voltage to 100 V, perform plasma cleaning and activation on the substrate for 20 min to obtain a pretreated substrate; then turn on the Ti target, set the current to 30 A, set the temperature of the first deposition to 600 °C, and the time of the first deposition to 20 min, and perform the first deposition on the surface of the pretreated substrate to form a metal sub-layer with a thickness of 30 nm, and obtain the substrate after the first deposition;

[0067] (3) Continuously place the first deposited substrate obtained in step (2) in the high-power pulsed magnetron sputtering chamber, and at the same time, turn on the alloy element Ti metal target and Al metal target for the second deposition. Control the deposition current ratio of the two metal targets to be 1:3, control the temperature of the first deposited substrate to be maintained at 500 - 600 °C, and the second deposition time to be 30 min. Perform the second deposition on the surface of the metal sublayer of the first deposited substrate to form a metal two-phase healing layer with a thickness of 100 nm, namely the TiAl3 healing layer, to obtain the second deposited substrate;

[0068] (4) Continuously place the second deposited substrate obtained in step (2) in the high-power pulsed magnetron sputtering chamber, and at the same time, turn on the Ti metal target and Al metal target. Then, introduce a working gas with a content of 40% CH 4 and control the temperature of the third deposition to be 400 °C. Perform the third deposition on the surface of the metal two-phase healing layer of the second deposited substrate to form a three-phase ceramic layer with a thickness of 200 nm;

[0069] Heat the three-phase ceramic layer at a heating rate of 10 °C / min to 800 °C, and then perform vacuum heat treatment at 800 °C for 30 min to form a dense corrosion-resistant three-phase ceramic layer with a thickness of 200 nm and a composition of Ti2AlC, thereby realizing the preparation of a self-healing coating on the surface of the substrate to obtain a metal bipolar plate.

[0070] Use a scanning electron microscope to observe the cross-sectional morphology and surface morphology of the MAX-phase multi-layer composite coating in the metal bipolar plate prepared in Preparation Example 1 of the present invention. The cross-sectional SEM image of the MAX-phase multi-layer composite coating in the metal bipolar plate prepared in Preparation Example 1 of the present invention is as shown in Figure 1 and the surface SEM image is as shown in Figure 2 . It can be seen from Figure 1 and Figure 2 that the MAX-phase multi-layer composite coating in the metal bipolar plate prepared in Example 1 of the present invention is composed of a metal sublayer (i.e., Ti sublayer), a metal two-phase healing layer (i.e., TiAl3 healing layer, also known as TiAl 3 precursor), and a dense corrosion-resistant three-phase ceramic layer (i.e., Ti 2 AlC coating) that are sequentially arranged from the inside to the outside on the surface of the stainless steel substrate. The cross-section of the MAX-phase multi-layer composite coating prepared in Example 1 is complete without obvious cracks and micropores and other defects, and the surface is dense and complete without cracks and micropores and other defects.

[0071] The MAX-phase multi-layer composite coating in the metal bipolar plate prepared in Preparation Example 1 of the present invention was used as Sample S1, and a high-potential test was carried out by means of an electrochemical test method. The potentiostatic test of an electrochemical workstation was used, and a high potential of 1.6 V was set, and the test time was 10 h. The corrosion current density curve of Sample S1 was obtained, that is, the high-potential test result diagram of the MAX-phase multi-layer composite coating prepared in Preparation Example 1 of the present invention was obtained as Figure 3 shown. From Figure 3 it can be seen that the corrosion current density value of the MAX-phase multi-layer composite coating in the metal bipolar plate prepared in Preparation Example 1 of the present invention < 1E-5, indicating that it has strong corrosion resistance, excellent potential corrosion resistance, and can withstand high-potential corrosion for more than 10 h.

[0072] Cracks were generated in the MAX-phase multi-layer composite coating in the metal bipolar plate prepared in Preparation Example 1 of the present invention by mechanical methods such as bending and stretching. After 7 days, the surface morphology of the MAX-phase multi-layer composite coating after the surface cracks healed was observed by a scanning electron microscope, and the surface SEM diagram was obtained as Figure 4 shown. From Figure 4 it can be seen that the MAX-phase multi-layer composite coating in the metal bipolar plate prepared in Preparation Example 1 of the present invention can promote the healing of microcracks to a certain extent, repair and improve the corrosion resistance of the coating, and prevent the corrosion solution from corroding the matrix material.

[0073] In summary, the self-healing coating in the metal bipolar plate prepared by the present invention has a complete coating cross-section without obvious cracks, micropores and other defects, a dense and complete surface without cracks, micropores and other defects, excellent high-potential corrosion resistance, and can withstand high-potential corrosion for more than 10 h; 7 days after external force generates cracks, it can promote the healing of microcracks and has a repair effect. The coating has strong extensibility, repairs and improves the corrosion resistance of the coating, and prevents the corrosion solution from corroding the matrix material. For the metal bipolar plate provided by the present invention, by providing a metal two-phase healing layer with a certain thickness in the MAX-phase multi-layer composite coating as the healing agent of the MAX-phase multi-layer composite coating, when cracks and holes are generated in the coating, the formed oxides can promote the healing of the through cracks in the coating and reduce the porosity of the coating. A metal sub-layer is further provided on the metal two-phase healing layer to enhance the bonding force between the MAX-phase multi-layer composite coating and the matrix, and prevent the coating from falling off when stress deformation occurs.

[0074] The above are only the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and retouches can be made, and these improvements and retouches should also be regarded as the protection scope of the present invention.

Claims

1. A metal bipolar plate, comprising a substrate and a self-healing coating, wherein the self-healing coating includes a metal sub-layer, a metal two-phase healing layer, and a dense corrosion-resistant three-phase ceramic layer, which are sequentially arranged from the inside to the outside on the surface of the substrate; The material of the metal sub-layer is Ti, Cr, Zr or Nb; the metal two-phase healing layer is composed of Al and alloying elements, and the alloying elements are Ti, Cr, Zr or Nb; The dense corrosion-resistant three-phase ceramic layer is a MAX phase.

2. The metal bipolar plate according to claim 1, wherein, the thickness of the metal sub-layer is 15 - 60 nm, the thickness of the metal two-phase healing layer is 80 - 600 nm, and the thickness of the dense corrosion-resistant three-phase ceramic layer is 40 - 300 nm.

3. The metal bipolar plate according to claim 2, wherein, the thickness of the metal sub-layer is 20 - 50 nm, the thickness of the metal two-phase healing layer is 100 - 500 nm, and the thickness of the dense corrosion-resistant three-phase ceramic layer is 50 - 290 nm.

4. The metal bipolar plate according to claim 1, wherein, the MAX phase is a nanocrystalline structure, and the crystallinity of the MAX phase > 80%.

5. A method for preparing the metal bipolar plate according to any one of claims 1 - 4, comprising the following steps: (1) Ultrasonically clean the stainless steel and dry it with nitrogen to obtain a substrate; (2) Perform a first deposition on the surface of the substrate obtained in step (1) to form a metal sub-layer, and obtain a substrate after the first deposition; (3) Perform a second deposition on the surface of the metal sub-layer of the substrate after the first deposition obtained in step (2) to form a metal two-phase healing layer, and obtain a substrate after the second deposition; (4) Perform a third deposition on the surface of the metal two-phase healing layer of the substrate after the second deposition obtained in step (3) to form a three-phase ceramic layer; Perform vacuum heat treatment on the three-phase ceramic layer to form a dense corrosion-resistant three-phase ceramic layer with a composition of MAX phase, and realize the preparation of a self-healing coating on the surface of the substrate to obtain a metal bipolar plate.

6. The preparation method according to claim 5, wherein, the method of the first deposition in step (1) is multi-arc ion plating, high-power pulsed magnetron sputtering or vacuum cathodic arc ion plating, and the temperature of the first deposition is 180 - 700 °C.

7. The preparation method according to claim 5, wherein, in step (2), an Al metal target and an alloying element metal target are used for the second deposition, and the deposition current ratio of the alloying element metal target to the Al metal target is (1:5) - (5:1).

8. The preparation method according to claim 5, wherein, the method of the third deposition in step (4) is high-power pulsed magnetron sputtering, and the temperature of the third deposition is 150 - 700 °C.

9. The preparation method according to claim 5, wherein, in step (4), a gaseous carbon source is used as the working gas for the third deposition, and the volume content of the gaseous carbon source in the working gas is 10% - 50%.

10. The preparation method according to claim 5, wherein, In the step (4), the temperature of the vacuum heat treatment is 150 to 900 °C, the heating rate of the vacuum heat treatment is 0.5 to 12 °C / min, and the time of the vacuum heat treatment is 20 to 50 min.

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