A multilayer gradient coating Cr / CrN / (Cr,Ti)2AlC for proton exchange membrane fuel cell metal bipolar plates and a method of constructing the same

Abstract

The application belongs to the field of proton exchange membrane fuel cells, and particularly relates to a Cr / CrN / (Cr, Ti)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 Cr transition layer, a CrN connecting layer and a (Cr, Ti)2AlC outer layer coating. Firstly, the Cr coating is deposited on the metal bipolar plate by using the arc ion plating technology with high deposition rate, so as to improve the adhesion between the substrate and the outer layer. Then, the N2 gas is filled in the process of depositing the Cr, so as to deposit the CrN connecting layer, improve the microstructure of the Cr coating, reduce the columnar crystal and improve the compactness of the coating. Finally, the (Cr, Ti)2AlC coating is deposited by using the magnetron sputtering technology, so as to modulate the structure of the multilayer gradient coating and obtain the 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 Cr / CrN / (Cr, Ti)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. Bipolar plate, as one of the most important components of PEMFC, 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, and 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 the 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, and has good corrosion resistance and conductivity, among which polyaniline (PANI) and polypyrrole (PPy) are studied more. However, 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 coating adhesion or poor long-term stability 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 uniform, dense and high adhesion coating, 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 as follows:

[0005] A multilayer gradient coating for a proton exchange membrane fuel cell metal bipolar plate, comprising a metal substrate, a Cr transition layer, a CrN connecting layer and a (Cr, Ti) 2AlC outer coating. The coating material is a Cr / CrN / (Cr, Ti) 2AlC multilayer gradient coating, the Cr layer is a transition layer, which can reduce the thermal expansion mismatch between 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 Cr / CrN / (Cr, Ti) 2AlC multilayer gradient coating, the CrN layer is a connecting layer, which can effectively improve the microstructure of the Cr coating, reduce columnar crystals and improve the density of the coating.

[0007] Further, the multilayer gradient coating for a proton exchange membrane fuel cell metal bipolar plate, wherein the outer coating is a chromium aluminum carbon with Ti element solid solution doped in Cr position, the proportion of the doped element is 1-40 at.%, and after doping, the corrosion resistance and conductivity of the chromium aluminum carbon are significantly improved, the corrosion current density is reduced by 85-95%, the self-corrosion potential is increased by 0.06-0.13V, and the contact resistance is reduced by 39-86%. As the outer layer, it mainly improves the corrosion resistance and conductivity of the substrate, and its performance is significantly better than that of chromium aluminum carbon.

[0008] Further, the multilayer gradient coating for a proton exchange membrane fuel cell metal bipolar plate, wherein the thickness of the Cr transition layer is 100-200 nm, the thickness of the CrN connecting layer is 100-200 nm, and the thickness of the (Cr, Ti) 2AlC layer is 200-300 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 is a (Cr, Ti) 2 AlC single-phase target material, the original powder for preparation includes Cr powder, Ti 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 1200-1700 ℃, the holding time is 40-90 minutes, the hot-pressing pressure is 30-70 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 Cr transition layer and the CrN connecting layer are deposited by using an arc ion plating device, the Cr transition layer is prepared by using a Cr metal target material, the CrN layer is obtained by heating and filling N 2 gas after the deposition of the Cr coating, and the CrN 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 Cr transition layer and the CrN 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 4 x 10 -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 100-300℃. The Cr target direct current source is turned on, the arc current is 40-70 A, the bias is -100 to -300 V, and the sputtering time is 3-10 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 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 150-300℃, and the temperature is maintained for 15 min. Then, the Cr target direct current source is turned on again, the arc current is 40-70 A, the bias is -100 to -400 V, and the sputtering time is 5-15 min. Then, the sputtering is stopped and the temperature is lowered.

[0014] Further, the multilayer gradient coating for a proton exchange membrane fuel cell metal bipolar plate,

[0015] characterized in that the (Cr, Ti) 2 AlC outer layer coating is deposited by a 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 150-300℃, and the temperature is maintained for 15 min. Then, the Cr target direct current source is turned on again, the arc current is 40-70 A, the bias is -100 to -400 V, and the sputtering time is 5-15 min. Then, the sputtering is stopped and the temperature is lowered.

[0016] The effective benefits of the present application: the Cr / CrN / (Cr,Ti)2AlC multilayer gradient coating of the metal bipolar plate has the advantages of uniformity, compactness and high adhesion. The arc ion plating technology with high deposition rate is used to deposit the Cr transition layer and the CrN connecting layer on the metal bipolar plate, and the same target can be used to obtain the Cr transition layer and the CrN connecting layer 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 Cr 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 CrN connecting layer is deposited on the Cr transition layer, which can effectively improve the microstructure of the Cr coating, reduce the columnar crystal and the pinhole structure in the coating, and improve the compactness of the coating. The outer coating is a chromium aluminum carbide with Ti element doped in Cr position, and the proportion of the doped element is 1-40 at.%. After doping, the corrosion resistance and conductivity of the chromium aluminum carbide are significantly improved, the corrosion current density is reduced by 85-95%, the self-corrosion potential is increased by 0.06-0.13V, and the contact resistance is reduced by 39-86%. 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

[0017] In order to more clearly illustrate the embodiments of the present application, the figures in the embodiments are briefly 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.

[0018] Figure 1 The scanning electron microscope surface image of the coating prepared in Example 1;

[0019] Figure 2 The scanning electron microscope surface image of the coating prepared in Example 2. DETAILED DESCRIPTION

[0020] 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.

[0021] The metal substrate used in the following examples is a metal bipolar plate. The preparation method of the (Cr,Ti)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 Cr powder, Ti powder, Al powder and graphite powder, and the ratio used is determined by the doping content of Ti, (Cr 1-x Ti xIn 2AlC, the ratio of Cr:Ti: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 24-48 hours by a wet mixing method. After that, it is taken out and naturally air-dried, and then sieved for use. The sintering temperature is 1200-1700°C, the holding time is 40-90 minutes, the hot pressing pressure is 30-70 MPa, and flowing argon gas is used as the protective gas.

[0022] Example 1

[0023] First, prepare the (Cr 0.95 Ti 0.05 )2AlC bulk target, and prepare a commercial Cr target and an SS316L stainless steel bipolar plate. That is, the metal bipolar plate sample is polished with 400#, 600#, 800#, 1000#, and 2000# metallographic sandpaper 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.

[0024] The Cr and CrN layers are deposited by arc ion plating method. Before coating preparation, the vacuum chamber is pre-evacuated to a background vacuum of 4x10 -3 Pa, and a 500V negative pulse bias is applied to the substrate to perform reverse sputtering cleaning for 6 minutes to remove contaminants and oxide layers 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 100°C. The Cr target direct current power supply is turned on, the arc current is 45A, the bias is -200V, and the sputtering time is 7 minutes. Then stop sputtering and cool down. Then the vacuum chamber is pre-evacuated to a background vacuum of 4x10 -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 150°C, and the temperature is maintained for 15 minutes. Then the Cr target direct current power supply is turned on again, the arc current is 45A, the bias is -200V, and the sputtering time is 5 minutes. Then stop sputtering and cool down.

[0025] Then the (Cr 0.95 Ti 0.05 )2AlC outer layer coating is deposited by magnetron sputtering method. After the vacuum chamber is pre-evacuated to a background vacuum of 4x10 -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 200°C, and the temperature is maintained for 15 minutes. Then the (Cr 0.95 Ti 0.05)2AlC target DC power supply, sputtering power is 0.3kW, sputtering time is 30min. 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.

[0026] 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 0.37μA / cm 2 [Self-corrosion potential 0.09V (Vs.SCE)], the contact resistance is 7.67mΩ·cm 2 under the condition of assembly force of 150N / cm 2 .

[0027] Example 2

[0028] First, prepare the (Cr 0.8 Ti 0.2 )2AlC bulk target, and prepare the commercial Cr 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 15min, and then dried in air for standby.

[0029] The Cr and CrN 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 subjected to reverse sputtering cleaning for 7min by applying a negative pulse bias of 500V to 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, and 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 200℃. Open the Cr target DC power supply, the arc current is 55A, the bias is -300V, and the sputtering time is 8min. Then stop sputtering and cool down. Then pre-vacuumize the vacuum chamber to a background vacuum of 4×10 -3 Pa, open the N2 gas flow valve, the N2 gas flow rate is 30ml / min, and 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, and the chamber heating temperature is 250℃, and after holding for 15min. Then open the Cr target DC power supply again, the arc current is 55A, the bias is -300V, and the sputtering time is 10min. Then stop sputtering and cool down.

[0030] Then deposit (Cr 0.8 Ti 0.2)2AlC target, the vacuum chamber was pre-evacuated to a background vacuum of 4x10 -3 Pa, then the Ar flow valve was opened, the Ar gas flow was 50ml / min, the working pressure in the vacuum chamber was controlled by adjusting the pumping speed of the molecular pump to maintain at about 0.45Pa, the chamber heating temperature was 300℃, and the temperature was maintained for 15min, then the (Cr 0.8 Ti 0.2 )2AlC target, the direct current power supply was turned on, the sputtering power was 1.0kW, and the sputtering time was 40min. After the deposition was completed, the temperature was lowered to room temperature at a rate of 10℃ / min under the original vacuum condition, and then the evacuation and pressure relief were stopped.

[0031] After the experiment, the surface and cross-section micro-morphology of the deposited coating were observed by scanning electron microscopy, and it was found that the obtained coating was flat, dense, and well combined with the substrate, and the thickness of each layer of the coating was uniform, as shown in Figure 2 The potentiodynamic test was carried out in a fuel cell simulation environment, i.e. a 0.5mol / L H2SO4 and 2ppm HF solution, at a temperature of 80℃, and the corrosion current density was 0.29μA / cm 2 [Self-corrosion potential 0.12V (Vs. SCE)], and the contact resistance was 5.37mΩ·cm 2 under the condition of an assembly force of 150N / cm 2 .

[0032] Example 3

[0033] First, a (Cr 0.65 Ti 0.35 )2AlC bulk target was prepared, and a commercial Cr target and a SS316L stainless steel bipolar plate were prepared. That is, the metal bipolar plate sample was polished by 400#, 600#, 800#, 1000# and 2000# metallographic sandpaper in turn, and then the polished metal bipolar plate sample was ultrasonically cleaned with acetone, alcohol and deionized water for 12min, and then dried in air for standby.

[0034] The Cr and CrN layers were deposited by arc ion plating method. Before the coating was prepared, the vacuum chamber was pre-evacuated to a background vacuum of 4x10 -3 Pa, and a 500V negative pulse bias was applied to the substrate to perform reverse sputtering cleaning for 10min to remove the contaminants and oxide layer on the surface of the substrate. Then the Ar flow valve was opened, the Ar gas flow was 50ml / min, the working pressure in the vacuum chamber was controlled by adjusting the pumping speed of the molecular pump to maintain at about 0.4Pa, and the chamber heating temperature was 300℃. The direct current power supply of the Cr target was turned on, the arc current was 65A, the bias was -400V, and the sputtering time was 5min. Then the sputtering was stopped, and the temperature was lowered. Then the vacuum chamber was pre-evacuated to a background vacuum of 4x10 -3After 0.45 Pa, open N2 gas flow valve, N2 gas flow 30 ml / min, by adjusting the pumping speed to control the working gas pressure in the vacuum chamber, so that it is maintained at about 0.45 Pa, chamber heating temperature is 300℃, heat preservation 15 minutes. Then open the Cr target DC power again, arc current is 65A, bias-400V, sputtering time is 10 min. Then stop sputtering, cooling.

[0035] Then the magnetron sputtering method is used to deposit (Cr 0.65 Ti 0.35 ) outer coating, the vacuum chamber is pre-evacuated to a background vacuum of 4x10 -3 Pa, then open the Ar flow valve, Ar gas flow 50 ml / min, by adjusting the pumping speed to control the working gas pressure in the vacuum chamber, so that it is maintained at about 0.45 Pa, chamber heating temperature 200℃, heat preservation 15 min, then open (Cr 0.65 Ti 0.35 ) target DC power, sputtering power is 1.5kW, sputtering time is 50 min. After deposition, under the original vacuum conditions, the temperature is reduced to room temperature at a rate of 10℃ / min, and then the vacuum is stopped and the pressure is removed.

[0036] 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. In the fuel cell simulation environment, that is, H2SO4 concentration is 0.5mol / L and 2ppm HF solution, temperature is 80℃, potentiodynamic test is carried out, corrosion current density is 0.13μA / cm 2 [Self-corrosion potential 0.16V (Vs.SCE)], under the condition of assembly force 150N / cm 2 , the contact resistance is 1.79mΩ·cm 2 .

[0037] Comparative example

[0038] The comparative example is to prepare a Cr2AlC coating sample on a metal bipolar plate SS316L.

[0039] First, prepare the Cr2AlC bulk target, and prepare the 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 with acetone, alcohol and deionized water for 15 min respectively, and then dry in air for standby.

[0040] Then the Cr2AlC outer coating is deposited by magnetron sputtering method, first, the chamber temperature is adjusted to 250℃, and then the temperature is kept for 15 min, then the DC power of Cr2AlC target is turned on, the sputtering power is 1.5kW, and the sputtering time is 30 min. 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.

[0041] 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 simulated environment of fuel cell, i.e. in the solution of 0.5mol / L H2SO4 and 2ppm HF, the temperature is 80℃, and the potentiodynamic test is carried out, the corrosion current density is 2.49μA / cm 2 [The self-corrosion potential is 0.03V (Vs.SCE)], and the contact resistance is 12.6mΩ·cm 2 under the assembling force of 150N / cm 2 .

[0042] 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 material of the coating is Cr / CrN / (Cr,Ti)2AlC multilayer gradient coating, wherein Cr is a transition layer, CrN is a connecting layer, and (Cr,Ti)2AlC is a modified and optimized material of ternary layered ceramic chromium aluminum carbon.

2. A multilayer gradient coating for a proton exchange membrane fuel cell metal bipolar plate according to claim 1, wherein The outer coating is (Cr,Ti)2AlC, which is chromium aluminum carbon solid solution doped with Ti element at Cr position, and the proportion of the doped element is 1-40 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 Cr transition layer is 100-200 nm, the thickness of the CrN connecting layer is 100-200 nm, and the thickness of the (Cr,Ti)2AlC layer is 200-300 nm.

4. A method for the production of a multilayer gradient coating for a metal 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 Cr transition layer and a CrN connecting layer are deposited by using an arc ion plating device, the Cr transition layer uses a Cr metal target; the deposition of the CrN connecting layer is to stop sputtering after the deposition of the Cr transition layer, to cool down, to pre-extract the vacuum chamber to a background vacuum of 4*10 -3 After the background vacuum is 4*10 Pa, the N2 flow valve is opened, the N2 flow is 30ml / min, the working pressure in the vacuum chamber is controlled by adjusting the pumping speed of the molecular pump to be about 0.45Pa, the chamber heating temperature is 150-300℃, and after holding for 15 minutes, the Cr target direct current power is opened again, the arc current is 40-70A, the bias voltage is -100--400V, and the sputtering time is 5-15min; then the sputtering is stopped and the temperature is lowered; the (Cr,Ti)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 the deposition of the coating, the column for hanging the sample can rotate, and meanwhile the rotating column can revolve with the rotating table to obtain uniform plating.

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 (Cr,Ti)2AlC single-phase target material, the original powder of the target material comprises Cr powder, Ti powder, Al powder and graphite powder, and is prepared by hot-pressing sintering in a hot-pressing furnace, the sintering temperature is 1200-1700 DEG C, the holding time is 40-90 minutes, the hot-pressing pressure is 30-70 MPa, and flowing argon is used as a protective gas.

6. 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, When the metal bipolar plate is a thin plate, the pretreatment method is: ultrasonic cleaning with acetone, alcohol and deionized water for 10-20 minutes, and then blowing dry in air for standby; the thickness of the thin plate is less than 200 μm.

7. A method for making a multilayer gradient coating for a proton exchange membrane fuel cell metal bipolar plate according to claim 4, wherein A Cr transition layer and a CrN 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 the background vacuum is 4x10 Pa, a negative pulse bias of 500 V is applied to the substrate to perform reverse sputtering cleaning for 5-10 min, so as to remove contaminants and oxide layers on the surface of the substrate. Then, an 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 a molecular pump to be about 0.4 Pa, the chamber heating temperature is 100-300 DEG C, a Cr target direct current source is opened, the arc current is 40-70 A, the bias voltage is -100 to -300 V, and the sputtering time is 3-10 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 background vacuum is 4x10 Pa, an 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 a molecular pump to be about 0.45 Pa, the chamber heating temperature is 150-300 DEG C, and the temperature is kept for 15 min. Then, the Cr target direct current source is opened again, the arc current is 40-70 A, the bias voltage is -100 to -400 V, and the sputtering time is 5-15 min. Then, the sputtering is stopped and the temperature is lowered.

8. 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, (Cr, Ti)2AlC outer layer coating was deposited by using a magnetron sputtering device, the vacuum chamber was pre-evacuated to a background vacuum of 4x10 -3 After the pressure was stabilized at 0.45 Pa, the chamber was heated to a temperature of 200-400°C for 15 min. Then the direct current power supply for the (Cr, Ti)2AlC target was turned on, and the sputtering power was 0.2-2.0 kW, and the sputtering time was 20-60 min. After the deposition was completed, the temperature was decreased to room temperature at a rate of 10°C / min under the original vacuum condition, and then the evacuation and pressure relief were stopped.

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