A multilayer gradient coating v / vn / (v,w)2alc for proton exchange membrane fuel cell metal bipolar plates and a method of making the same

Abstract

The application belongs to the field of proton exchange membrane fuel cells, and particularly relates to a V / VN / (V,W)2AlC multilayer gradient coating for a metal bipolar plate of a proton exchange membrane fuel cell and a preparation method thereof. The metal bipolar plate comprises a metal substrate, a V transition layer, a VN connecting layer and a (V,W)2AlC outer layer coating. The V coating is first deposited on the metal bipolar plate by using arc ion plating technology with a high deposition rate, so as to improve the adhesion between the substrate and the outer layer. Then, the VN connecting layer is deposited by heating and filling N2 gas during the deposition of V, so as to improve the microstructure of the V coating, reduce the columnar crystals and improve the compactness of the coating. Finally, the (V,W)2AlC coating is deposited by using magnetron sputtering technology, so as to modulate the structure of the multilayer gradient coating and obtain a coating with uniformity, compactness and high adhesion, which can effectively improve the corrosion resistance and the conductive performance after corrosion of the metal substrate. The preparation rate of the overall coating is fast, the process is easy to control, the performance of the bipolar plate can be greatly improved, and the service life of the fuel cell is further improved.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of proton exchange membrane fuel cell, and particularly relates to a modified V / VN / (V, W)2AlC multilayer gradient coating for proton exchange membrane fuel cell metal bipolar plate and a preparation method thereof. BACKGROUND

[0002] Proton exchange membrane fuel cell has the advantages of compact structure, small volume, high energy density, high efficiency, fast start, low temperature operation and zero emission, and is considered as an ideal clean power generation energy at present. As one of the most important components of PEMFC, bipolar plate connects single cells in series, parallel or mixed connection to form a cell stack, plays a supporting role, can isolate the cathode and anode reaction gas, discharge the heat and water generated by the cell stack reaction, and is crucial to the performance of PEMFC cell stack. At present, bipolar plates mainly include graphite bipolar plate, metal bipolar plate and composite bipolar plate. The metal bipolar plate has high strength, is easy to process, and the ultra-thin bipolar plate is easy to obtain large-scale production, which can improve the specific power of fuel cell. However, the bipolar plate working environment has various corrosive ions such as SO4 2- , F - , etc., and the metal bipolar plate material is easily corroded to form a passivation layer, which increases the contact resistance between the bipolar plate and the diffusion layer, greatly affects the output power and durability of the fuel cell stack. Therefore, through surface coating modification, reducing the surface contact resistance of the metal bipolar plate, improving its conductivity and corrosion resistance is the key to its commercial application. The current bipolar plate coating mainly includes carbon-based coating, noble metal coating, conductive polymer coating, hydrophobic coating and transition metal ceramic compound. The carbon-based coating has excellent corrosion resistance, and excellent conductivity and thermal conductivity, and also has low production cost, which has been widely studied. However, the deposition efficiency of carbon-based coating is low, which affects its large-scale application. The noble metal coating has excellent corrosion resistance and conductivity, but the cost is too high. The conductive polymer coating can provide good protection for the bipolar plate, has good corrosion resistance and conductivity, and the most studied ones are polyaniline (PANI) and polypyrrole (PPy), but the adhesion between the coating and the substrate is weak. The hydrophobic performance of the hydrophobic coating can greatly affect the corrosion rate of the bipolar plate, but it is difficult to maintain long-term stability. The transition metal ceramic compound has excellent physical, chemical and mechanical properties, has excellent corrosion resistance and stability in the working environment of the bipolar plate, and can also maintain high conductivity, which is one of the ideal coating materials for PEMFC bipolar plate and has good development prospect. However, the current transition metal ceramic compound coating generally has high preparation cost, low efficiency, pinholes, large particles or columnar crystals in the coating, which seriously affects its long-term stability, and the peeling problem caused by poor adhesion or poor long-term stability of the coating will have a bad impact on the cell stack and accelerate the aging process of the cell stack. SUMMARY

[0003] In order to solve the above problems, the present application provides a multilayer gradient coating for a proton exchange membrane fuel cell metal bipolar plate and a preparation method thereof, which can obtain a coating with uniformity, compactness and high adhesion, reduce defects such as columnar crystals, pinholes and large particles, and effectively improve the corrosion resistance and corrosion resistance of the metal substrate. The preparation rate of the overall coating is fast, the process is easy to control, and the performance of the bipolar plate can be greatly improved, thereby improving the service life of the fuel cell.

[0004] To achieve the above object, the technical scheme adopted by the present application is:

[0005] A multilayer gradient coating for a proton exchange membrane fuel cell metal bipolar plate, comprising a metal substrate, a V transition layer, a VN connecting layer and a (V, W)2AlC outer layer coating. The coating material is a V / VN / (V, W)2AlC multilayer gradient coating, the V layer is a transition layer, which can reduce the thermal expansion mismatch between the layers and improve the element compatibility of each layer, thereby improving the adhesion of the coating.

[0006] Further, the multilayer gradient coating for a proton exchange membrane fuel cell metal bipolar plate and the preparation method thereof, wherein the coating material is a V / VN / (V, W)2AlC multilayer gradient coating, the VN layer is a connecting layer, which can effectively improve the microstructure of the V coating, reduce columnar crystals and improve the compactness of the coating.

[0007] Further, the multilayer gradient coating for a proton exchange membrane fuel cell metal bipolar plate, wherein the outer layer coating is vanadium aluminum carbon doped with W element at V position, the proportion of the doped element is 0.1-20 at.%, and after doping, the corrosion resistance and conductivity of vanadium aluminum carbon are significantly improved, the corrosion current density is reduced by 93-97%, the self-corrosion potential is increased by 0.11-0.17V, and the contact resistance is reduced by 69-86%. As the outer layer, it mainly improves the corrosion resistance and conductivity of the substrate, and its performance is significantly better than that of vanadium aluminum carbon.

[0008] Further, the multilayer gradient coating for a proton exchange membrane fuel cell metal bipolar plate, wherein the thickness of the V transition layer is 100-200 nm, the thickness of the VN connecting layer is 50-150 nm, and the thickness of the (V, W)2AlC layer is 100-300 nm.

[0009] Further, the multilayer gradient coating for the metal bipolar plate of the proton exchange membrane fuel cell is characterized in that the outer coating target material used is a (V, W) 2 AlC single-phase target material, the original powder used in the preparation includes V powder, W powder, Al powder and graphite powder, and the sintering is prepared in a hot-pressing furnace by using a hot-pressing / solid-liquid phase reaction method, the sintering temperature is 1300-1650°C, the holding time is 20-70 minutes, the hot-pressing pressure is 25-75 MPa, and flowing argon is used as the protective gas.

[0010] Further, the multilayer gradient coating for the metal bipolar plate of the proton exchange membrane fuel cell is characterized in that the V transition layer and the VN connecting layer are deposited by using an arc ion plating device, the V transition layer uses a V metal target material, the VN layer is obtained by heating and filling N 2 gas after depositing the V coating, and the VN connecting layer is deposited.

[0011] Further, the multilayer gradient coating for the metal bipolar plate of the proton exchange membrane fuel cell is characterized in that if the metal bipolar plate is a thin plate (less than 200 μm), the pretreatment method is that the plate is ultrasonically cleaned in acetone, alcohol and deionized water for 10-20 minutes and then dried in air for standby use.

[0012] Further, the multilayer gradient coating for the metal bipolar plate of the proton exchange membrane fuel cell is characterized in that the metal substrate includes but is not limited to SS304, 316L, Ti plate or SS316L bipolar plate metal.

[0013] Further, the multilayer gradient coating for the metal bipolar plate of the proton exchange membrane fuel cell is characterized in that the V transition layer and the VN connecting layer are deposited by using an arc ion plating method, and before the coating preparation, the vacuum chamber is pre-evacuated to a background vacuum of 4x10 -3After 500 Pa, the substrate is subjected to reverse sputtering cleaning for 5-10 min by applying a negative pulse bias of 500 V to the substrate to remove contaminants and oxide layers on the surface of the substrate. Then the Ar flow valve is opened, the Ar flow rate is 50 ml / min, the working pressure in the vacuum chamber is controlled by adjusting the pumping speed of the molecular pump to maintain at about 0.4 Pa, and the chamber heating temperature is 50-150℃. The V target DC power supply is turned on, the arc current is 30-65 A, the bias is -100 to -400 V, and the sputtering time is 1-5 min. Then stop sputtering and cool down. Then the vacuum chamber is pre-evacuated to a background vacuum of 4x10 -3 After 500 Pa, the Ar flow valve is opened, the Ar flow rate is 50 ml / min, the working pressure in the vacuum chamber is controlled by adjusting the pumping speed of the molecular pump to maintain at about 0.45 Pa, the chamber heating temperature is 50-150℃, and the temperature is maintained for 15 min. Then the V target DC power supply is turned on again, the arc current is 30-65 A, the bias is -100 to -400 V, and the sputtering time is 1-5 min. Then stop sputtering and cool down.

[0014] Further, the multilayer gradient coating for the metal bipolar plate of the proton exchange membrane fuel cell is characterized in that the (V,W)2AlC outer coating is deposited by the magnetron sputtering method, the vacuum chamber is pre-evacuated to a background vacuum of 4x10 -3 After 500 Pa, the Ar flow valve is opened, the Ar flow rate is 50 ml / min, the working pressure in the vacuum chamber is controlled by adjusting the pumping speed of the molecular pump to maintain at about 0.45 Pa, the chamber heating temperature is 50-150℃, and the temperature is maintained for 15 min. Then the V target DC power supply is turned on again, the arc current is 30-65 A, the bias is -100 to -400 V, and the sputtering time is 1-5 min. Then stop sputtering and cool down.

[0015] The effective benefits of the present application: the V / VN / (V,W)2AlC multilayer gradient coating of the metal bipolar plate of the present application has the advantages of uniformity, compactness and high adhesion. The V transition layer and the VN connecting layer are deposited on the metal bipolar plate by using the arc ion plating technology with high deposition rate, and the V transition layer and the VN connecting layer can be obtained by introducing different gases into the cavity during the deposition process, which is efficient, low in cost and easy to operate. At the same time, the V transition layer is deposited in the inner layer, which can reduce the thermal expansion mismatch degree between layers and improve the adhesion of the coating. The VN connecting layer is deposited on the V transition layer, which can effectively improve the microstructure of the V coating, reduce the columnar crystal and the pinhole structure in the coating, and improve the compactness of the coating. The outer coating is vanadium aluminum carbon with W element doped in V position, and the proportion of the doped element is 0.1-20at.%. After doping, the corrosion resistance and conductivity of vanadium aluminum carbon are significantly improved, the corrosion current density is reduced by 93-97%, the self-corrosion potential is increased by 0.11-0.17V, and the contact resistance is reduced by 69-86%. At the same time, the preparation method of the coating is easy to control and efficient, and the gradient coating with compactness, flatness and uniform composition structure can be obtained, which can greatly improve the performance of the bipolar plate and the service life of the fuel cell, and is easy to be popularized in industry. BRIEF DESCRIPTION OF DRAWINGS

[0016] In order to more clearly illustrate the embodiments of the present application, the figures in the embodiments are simply introduced. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art or researchers without creative labor on the basis of these drawings.

[0017] Figure 1 The scanning electron microscope surface image of the coating prepared in Example 1 is shown in Figure 1.

[0018] Figure 2 The scanning electron microscope surface image of the coating prepared in Example 2 is shown in Figure 2. DETAILED DESCRIPTION

[0019] The present application will be further described in detail below in combination with specific embodiments and drawings, but the present application is not limited in any way by the embodiments.

[0020] The metal substrate used in the following examples is a metal bipolar plate. The preparation method of the (V,W)2AlC target material used for deposition adopts a hot pressing / solid-liquid phase reaction method to sinter in a hot pressing furnace, and the raw powder used in the preparation includes V powder, W powder, Al powder and graphite powder, and the ratio used is determined by the doping content of W, (V 1-x W xIn 2AlC, the ratio of V:W:Al:C is configured according to the ratio of 2(1-x):2x:1:1 of the raw material powder, and the raw material powder is mixed in a ball mill for 12-48 hours by a wet mixing method. After that, the natural air drying is taken out, and then sieved for use. The sintering temperature is 1300-1650°C, the holding time is 30-70 minutes, the hot pressing pressure is 25-70 MPa, and flowing argon is used as the protective gas.

[0021] Example 1

[0022] First, the (V 0.97 W 0.03 )2AlC bulk target material is prepared, and a commercial V target and an SS316L stainless steel bipolar plate are prepared. That is, the 400#, 600#, 800#, 1000#, and 2000# metallographic sandpaper are polished in sequence, and then the polished metal bipolar plate sample is ultrasonically cleaned with acetone, alcohol, and deionized water for 15 minutes respectively, and then dried in air for standby use.

[0023] The V and VN layers are deposited by arc ion plating method. Before the coating preparation, the vacuum chamber is pre-evacuated to a background vacuum of 4×10 -3 Pa, and a 500V negative pulse bias is applied to the substrate for 8 minutes to remove the contaminants and oxide layer on the surface of the substrate. Then the Ar flow valve is opened, the Ar flow rate is 50ml / min, the working gas pressure in the vacuum chamber is controlled by adjusting the pumping speed of the molecular pump to maintain at about 0.4Pa, and the chamber heating temperature is 70°C. The V target direct current power supply is turned on, the arc current is 35A, the bias is -200V, and the sputtering time is 3 minutes. Then stop sputtering and cool down. Then the vacuum chamber is pre-evacuated to a background vacuum of 4×10 -3 Pa, the N2 flow valve is opened, the N2 flow rate is 30ml / min, the working gas pressure in the vacuum chamber is controlled by adjusting the pumping speed of the molecular pump to maintain at about 0.45Pa, the chamber heating temperature is 100°C, and the holding time is 15 minutes. Then the V target direct current power supply is turned on again, the arc current is 35A, the bias is -200V, and the sputtering time is 3 minutes. Then stop sputtering and cool down.

[0024] Then the (V 0.97 W 0.03 )2AlC outer layer coating is deposited by magnetron sputtering method. After the vacuum chamber is pre-evacuated to a background vacuum of 4×10 -3 Pa, the Ar flow valve is opened, the Ar flow rate is 50ml / min, the working gas pressure in the vacuum chamber is controlled by adjusting the pumping speed of the molecular pump to maintain at about 0.45Pa, the chamber heating temperature is 250°C, and the holding time is 15 minutes. Then the (V 0.97 W 0.03)2AlC target DC power supply, sputtering power is 0.2kW, sputtering time is 20min. After the deposition, in the original vacuum conditions, the temperature is decreased to room temperature at the rate of 10℃ / min, then stop vacuumizing, and the pressure is removed.

[0025] After the experiment, the surface and cross-section micro-morphology of the deposited coating are observed by scanning electron microscope, and it is found that the obtained coating is flat, dense, and well combined with the substrate, and the thickness of each layer of the coating is uniform, as shown in Figure 1 The potentiodynamic test is carried out in the fuel cell simulation environment, i.e. 0.5mol / L H2SO4 and 2ppm HF solution, at the temperature of 80℃, and the corrosion current density is 0.69μA / cm 2 [Self-corrosion potential 0.14V (vs. SCE)], the contact resistance is 4.98mΩ·cm 2 under the assembly force of 150N / cm 2 .

[0026] Example 2

[0027] First, prepare the bulk target of (V 0.9 W 0.1 )2AlC, and prepare the commercial V target and SS316L stainless steel bipolar plate. Select 100μm thick sheet, and the metal bipolar plate sample is ultrasonically cleaned with acetone, alcohol and deionized water for 12min respectively, and then dried in air for standby.

[0028] The V and VN layers are deposited by arc ion plating method. Before the coating preparation, the vacuum chamber is pre-vacuumized to a background vacuum of 4×10 -3 Pa, and the substrate is reverse sputter cleaned for 5min by applying a negative pulse bias of 500V on the substrate to remove the contaminants and oxide layer on the surface of the substrate. Then open the Ar flow valve, the Ar flow rate is 50ml / min, the working gas pressure in the vacuum chamber is controlled by adjusting the pumping speed of the molecular pump to maintain at about 0.4Pa, and the chamber heating temperature is 100℃. Open the V target DC power supply, the arc current is 50A, the bias is -300V, and the sputtering time is 5min. Then stop sputtering and cool down. Then pre-vacuumize the vacuum chamber to a background vacuum of 4×10 -3 Pa, open the N2 flow valve, the N2 flow rate is 30ml / min, the working gas pressure in the vacuum chamber is controlled by adjusting the pumping speed of the molecular pump to maintain at about 0.45Pa, the chamber heating temperature is 120℃, and the temperature is maintained for 15min. Then open the V target DC power supply again, the arc current is 50A, the bias is -300V, and the sputtering time is 2min. Then stop sputtering and cool down.

[0029] Then the (V 0.9 W 0.1)2AlC outer coating, the vacuum chamber is pre-evacuated to a back vacuum of 4×10 -3 After Pa, open the Ar flow valve, set the Ar gas flow rate to 50 ml / min, and control the working pressure inside the vacuum chamber by adjusting the pumping speed of the molecular pump to maintain it at approximately 0.45 Pa. Set the chamber heating temperature to 300℃ and hold for 15 minutes. Then open (V 0.9 W 0.1 The AlC target was powered by a DC power supply with a sputtering power of 1.0 kW and a sputtering time of 30 min. After deposition, the target was cooled to room temperature at a rate of 10 °C / min under the original vacuum conditions, and then the vacuum was stopped and the pressure was released.

[0030] After the experiment, the surface and cross-sectional microstructure of the deposited coating were observed using a scanning electron microscope. The results showed that the coating was smooth, dense, and well-bonded to the substrate, with uniform thickness in all layers. Figure 2 As shown. Potentiodynamic testing was conducted in a fuel cell simulation environment, specifically in a solution with H₂SO₄ concentration of 0.5 mol / L and HF concentration of 2 ppm, at a temperature of 80 °C, with a corrosion current density of 0.42 μA / cm². 2 [Self-corrosion potential 0.18V (vs. SCE)], at an assembly force of 150N / cm 2 Under these conditions, the contact resistance is 3.26 mΩ·cm. 2 .

[0031] Example 3

[0032] First, prepare (V) 0.82 W 0.18 )2AlC bulk target material, and prepare commercial V target material and SS316L stainless steel bipolar plate. Then, polish it step by step with 400#, 600#, 800#, 1000# and 2000# metallographic sandpaper. After polishing, the metal bipolar plate sample is ultrasonically cleaned with acetone, alcohol and deionized water for 20 minutes respectively, and then blown dry in air for later use.

[0033] V and VN layers were deposited using arc ion plating. Before coating preparation, the vacuum chamber was pre-evacuated to a background vacuum of 4 × 10⁻⁶. -3 After Pa, a 500V negative pulse bias voltage was applied to the substrate for backsplash cleaning for 10 min to remove contaminants and oxide layers from the substrate surface. Then, the Ar flow valve was opened, and the Ar gas flow rate was 50 ml / min. The working pressure in the vacuum chamber was controlled by adjusting the pumping speed of the molecular pump to maintain it at approximately 0.4 Pa, and the chamber heating temperature was 150℃. The V target DC power supply was turned on, with an arc current of 60 A, a bias voltage of -400 V, and a sputtering time of 1 min. Sputtering was then stopped, and the chamber was allowed to cool. The vacuum chamber was then pre-evacuated to a background vacuum of 4 × 10⁻⁶. -3After 0.45 Pa, open the N2 flow valve, N2 flow rate 30 ml / min, by adjusting the pumping speed of the molecular pump to control the working gas pressure in the vacuum chamber, so as to maintain at about 0.45 Pa, the chamber heating temperature is 150℃, after 15 minutes of heat preservation. Then open the V target DC power supply again, arc current is 60A, bias-400V, sputtering time is 2min. Then stop sputtering, cooling.

[0034] Then the magnetron sputtering method is used to deposit (V 0.82 W 0.18 )2AlC outer coating, the vacuum chamber is pre-evacuated to a background vacuum of 4×10 -3 Pa, then open the Ar flow valve, Ar flow rate 50 ml / min, by adjusting the pumping speed of the molecular pump to control the working gas pressure in the vacuum chamber, so as to maintain at about 0.45 Pa, the chamber heating temperature is 200℃, heat preservation for 15min, then open (V 0.82 W 0.18 )2AlC target DC power supply, sputtering power is 1.5kW, sputtering time is 50min. After deposition, under the original vacuum condition, the temperature is reduced to room temperature at a rate of 10℃ / min, and then the vacuum is stopped and the pressure is removed.

[0035] After the experiment, the surface and cross-section microstructure of the deposited coating is observed by scanning electron microscope, it is found that the obtained coating is flat, dense, and well combined with the substrate, the thickness of each layer of the coating is uniform, as shown in the figure. Figure 2 In the fuel cell simulation environment, that is, in 0.5mol / L H2SO4 and 2ppm HF solution, the temperature is 80℃, the potentiostatic test is carried out, the corrosion current density is 0.27μA / cm 2 [Self-corrosion potential 0.20V (vs. SCE)], under the condition of assembly force 150N / cm 2 , the contact resistance is 2.21mΩ·cm 2 .

[0036] Comparative example

[0037] The comparative example is to prepare V2AlC coating on metal bipolar plate SS316L.

[0038] First, prepare V2AlC bulk target material, and prepare SS316L metal bipolar plate sample. That is, use 400#, 600#, 800#, 1000#, 2000# metallographic sandpaper to polish step by step, then ultrasonic clean the polished metal bipolar plate sample in acetone, alcohol and deionized water for 15min respectively, and then dry in air for standby.

[0039] Then the V2AlC outer coating is deposited by magnetron sputtering method, first, the chamber temperature is adjusted to 250℃, and then the V2AlC target direct current power is turned on, the sputtering power is 1kW, and the sputtering time is 25min. After the deposition, the temperature is decreased to room temperature at a rate of 10℃ / min under the original vacuum condition, and then the vacuum is stopped and the pressure is removed.

[0040] After the experiment, the surface and cross-section micro-morphology of the deposited coating are observed by scanning electron microscope, and it is found that the obtained coating is flat and well combined with the substrate. In the fuel cell simulation environment, i.e. 0.5mol / L H2SO4 and 2ppm HF solution, the temperature is 80℃, and the potentiodynamic test is carried out, the corrosion current density is 9.45μA / cm 2 [0.03V(vs.SCE) from the self-corrosion potential], the contact resistance is 15.9mΩ·cm 2 under the assembly force of 150N / cm 2 .

[0041] Of course, the above description is not a limitation of the present application, and the present application is not limited to the above examples, and the changes, modifications, additions or replacements made by the ordinary skilled in the art within the essential scope of the present application shall belong to the protection scope of the present application.

Claims

1. A multilayer gradient coating for a proton exchange membrane fuel cell metal bipolar plate comprising a substrate and a coating, characterized in that, The coating is a V / VN / (V,W)2AlC multilayer gradient coating, wherein V is a transition layer, VN is a connecting layer, and (V,W)2AlC is a modified and optimized material of ternary layered ceramic vanadium aluminum carbon.

2. A multilayer gradient coating for a proton exchange membrane fuel cell metal bipolar plate according to claim 1, wherein The (V,W)2AlC coating is solid solution doped with W element at V position, and the proportion of the doped element is 0.1-20 at.%.

3. A multilayer gradient coating for a proton exchange membrane fuel cell metal bipolar plate according to claim 1, wherein The thickness of the V transition layer is 100-200 nm, the thickness of the VN connecting layer is 50-150 nm, and the thickness of the (V,W)2AlC layer is 100-300 nm.

4. A method for the production of a multilayer gradient coating for a metallic bipolar plate of a proton exchange membrane fuel cell according to any one of claims 1 to 3, characterized in that The method comprises the following steps: A V transition layer and a VN connecting layer are deposited by using an arc ion plating device, the V transition layer uses a V metal target; the VN connecting layer is deposited by stopping sputtering after the V transition layer is deposited, cooling, then pre-pumping the vacuum chamber to a background vacuum of 4*10 -3 After the pressure in the vacuum chamber is reduced to 0.45 Pa, the N2 flow valve is opened, the N2 flow is 30 ml / min, the working pressure in the vacuum chamber is controlled by adjusting the pumping speed of the molecular pump, the chamber heating temperature is 50-150 DEG C, and the temperature is maintained for 15 minutes, then the V target direct current power is opened again, the arc current is 30-65 A, the bias voltage is -100--400 V, and the sputtering time is 1-5 min; then the sputtering is stopped, and the temperature is reduced; a (V, W)2AlC coating is deposited on the outer surface by using a magnetron sputtering device, the sample is hung on the sample holder of the device during deposition of the coating, the stand for hanging the sample can rotate, and the rotating stand can revolve, so that uniform coating is obtained.

5. A method for the production of a multilayer gradient coating for a proton exchange membrane fuel cell metal bipolar plate according to claim 4, characterized in that The target material used for the coating is a (V,W)2AlC single-phase target material, the original powder of the target material comprises V powder, W powder, Al powder and graphite powder, and the target material is prepared by sintering in a hot-pressing furnace by using a hot-pressing method, the sintering temperature is 1300-1650 DEG C, the holding time is 30-70 minutes, the hot-pressing pressure is 25-70 MPa, and flowing argon is used as a protective gas.

6. A method for the fabrication of a multilayer gradient coating for a proton exchange membrane fuel cell metal bipolar plate according to claim 4, characterized in that, When the metal bipolar plate is a thin plate, the pretreatment method is: after ultrasonic cleaning for 10-20 minutes respectively by using acetone, alcohol and deionized water, the thin plate is dried in air and is ready for use, and the thickness of the thin plate is less than 200 microns.

7. A method for the fabrication of a multilayer gradient coating for a proton exchange membrane fuel cell metal bipolar plate according to claim 4, characterized in that, The V transition layer and VN connecting layer are deposited by using an arc ion plating device. Before coating preparation, the vacuum chamber is pre-evacuated to a background vacuum of 4x10 -3 After 500 V negative pulse bias is applied to the substrate, the substrate is back sputter cleaned for 5-10 min to remove contaminants and oxide layer on the surface of the substrate; then the Ar flow valve is opened, the Ar flow rate is 50 ml / min, the working pressure in the vacuum chamber is controlled by adjusting the pumping speed of the molecular pump to maintain at about 0.4 Pa, the chamber heating temperature is 50-150 DEG C; the V target direct current source is opened, the arc current is 30-65 A, the bias is -100 to -400 V, and the sputtering time is 1-5 min; then the sputtering is stopped and the temperature is lowered; then the vacuum chamber is pre-evacuated to a background vacuum of 4x10 -3 After the N2 flow valve is opened, the N2 flow rate is 30 ml / min, the working pressure in the vacuum chamber is controlled by adjusting the pumping speed of the molecular pump to maintain at about 0.45 Pa, the chamber heating temperature is 50-150 DEG C, and the temperature is maintained for 15 min; then the V target direct current source is opened again, the arc current is 30-65 A, the bias is -100 to -400 V, and the sputtering time is 1-5 min; then the sputtering is stopped and the temperature is lowered.

8. A method for making a multilayer gradient coating for a proton exchange membrane fuel cell metal bipolar plate according to claim 4, characterized in that, The (V, W)2AlC coating was deposited by using a magnetron sputtering device, the vacuum chamber was pre-evacuated to a background vacuum of 4×10 -3 After the pressure was maintained at 0.45 Pa for 15 min, the (V, W)2AlC target was connected to a direct current power supply, the sputtering power was 0.08-1.8 kW, and the sputtering time was 10-40 min. After the deposition was completed, the temperature was decreased to room temperature at a rate of 10 ℃ / min under the original vacuum condition, and then the evacuation and pressure relief were stopped.

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