Fuel cell metal bipolar plate composite coating and preparation method thereof

Abstract

The present invention relates to a fuel cell metal bipolar plate composite coating and a preparation method thereof. The fuel cell metal bipolar plate composite coating comprises: a metal transition layer (2), a metal nitride intermediate gradient layer (3) and a metal passivation surface layer (4) sequentially formed on the surface of a metal bipolar plate substrate (1) along the coating deposition direction. The fuel cell metal bipolar plate composite coating obtained by the preparation method of the present invention can effectively block the continuous growth of pinhole defects in the coating deposition direction, can significantly improve the surface integrity of the coating, and significantly improve the corrosion resistance of the coating.

Description

Technical Field

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

[0002] Proton exchange membrane fuel cells (PEMFCs) are not limited by the Carnot cycle, have high energy conversion efficiency, and have the characteristics of high power density, fast start-up, low temperature operation and zero emissions during operation. They are considered to be one of the most promising power sources for automobiles, portable power sources and future space fuel cell technology.

[0003] Bipolar plates are the core components of PEMFC and need to meet the requirements of excellent chemical stability, good corrosion resistance, and high conductivity. Compared with graphite bipolar plates, metal plates have better mechanical strength, better conductivity, and lower manufacturing costs. However, metal plates are easily corroded and / or passivated in the weakly acidic environment of PEMFC, forming a passivation film or dissolving. The formation of the passivation film leads to an increase in contact resistance, and the dissolved metal contaminates the membrane electrode of the PEMFC and may cause catalyst poisoning.

[0004] In order to solve the above problems, physical vapor deposition technology is often used to prepare a highly conductive coating on the surface of a metal bipolar plate, thereby improving its corrosion resistance and reducing contact resistance. Chinese patent CN112803033A discloses a method for preparing an oxide-doped nitride coating using a magnetron sputtering technology using an oxide target and a nitride target, wherein the oxide is a mixture of one or more of Al2O3, TiO2, ZrO2, and SiO2, and the nitride is one of CrN, TiN, NbN, and ZrN. Chinese patent CN104617316B discloses a method for preparing a nanocrystalline ZrBN / Zr composite coating suitable for a PEMFC metal bipolar plate, wherein a dual cathode plasma sputtering technology is used to sequentially deposit a Zr diffusion layer, a Zr deposition layer, and a ZrB layer on the surface of the bipolar plate, and finally ion nitridation is performed to form a ZrBN / Zr composite coating.

[0005] However, the coating surface prepared by the above prior art has defects such as pores and pinholes, which become channels for corrosive media to enter the metal substrate, which will reduce the protective effect of the coating to a certain extent, thereby aggravating the corrosion of the bipolar plate. Therefore, in order to further slow down the performance degradation of PEMFC and increase the service life of PEMFC, it is urgent to develop a new surface coating and its preparation process. Summary of the invention

[0006] In order to solve the technical problems existing in the above-mentioned prior art, the present invention provides a fuel cell metal bipolar plate composite coating and a preparation method thereof, which can effectively block the continuous growth of pinhole defects in the coating deposition direction, significantly improve the surface integrity of the coating, and significantly improve the corrosion resistance of the coating.

[0007] In order to achieve the above-mentioned object of the invention, the technical solution of the present invention is:

[0008] The present invention provides a fuel cell metal bipolar plate composite coating, comprising: a metal transition layer, a metal nitride intermediate gradient layer and a metal passivation surface layer sequentially formed on the surface of the metal bipolar plate substrate along the coating deposition direction.

[0009] According to one aspect of the present invention, the material of the metal bipolar plate substrate is titanium, tungsten, chromium, aluminum, nickel, copper, zirconium, molybdenum, niobium or stainless steel;

[0010] The thickness of the metal bipolar plate substrate is 0.05 to 2 mm.

[0011] According to one aspect of the present invention, the metal material in the metal transition layer is at least one of titanium, tungsten, chromium, aluminum, nickel, copper, zirconium, molybdenum, niobium and alloys thereof;

[0012] The thickness of the metal transition layer is 30-650 nm.

[0013] According to one aspect of the present invention, the metal material in the metal nitride intermediate gradient layer is at least one of titanium, tungsten, chromium, aluminum, nickel, copper, zirconium, molybdenum, and niobium, wherein the metal nitride is MNx, 0≤x<1.5;

[0014] The thickness of the metal nitride intermediate gradient layer is 1-4.2 μm.

[0015] According to one aspect of the present invention, the metal nitride intermediate gradient layer is a gradient structure, and the metal component in the coating gradually decreases from 95wt% to 15-30wt% along the coating deposition direction, and the metal nitride component gradually increases from 5wt% to 70-85wt%.

[0016] According to one aspect of the present invention, the metal material in the surface layer of the metal passivation is at least one of titanium, tungsten, chromium, aluminum, nickel, copper, zirconium, molybdenum and niobium, wherein the metal passivation is MOy, 0<y<4.

[0017] The present invention also provides a method for preparing the fuel cell metal bipolar plate composite coating, comprising the steps of:

[0018] S1. Degreasing, ultrasonic cleaning and drying of the metal bipolar plate substrate;

[0019] S2. placing the treated metal bipolar plate substrate into the arc ion plating equipment cavity, and etching the metal bipolar plate substrate using ionized argon ions;

[0020] S3. Depositing a metal transition layer on the surface of the metal bipolar plate substrate using arc ion plating technology;

[0021] S4. Depositing a metal nitride intermediate gradient layer on the metal transition layer using arc ion plating technology;

[0022] S5. Preparing a metal passivation surface layer on the metal nitride intermediate gradient layer.

[0023] According to another aspect of the present invention, step S2 includes: setting the temperature of the metal bipolar plate substrate to 50 to 350°C, setting the vacuum degree to 9×10-4Pa to 7×10-3Pa, introducing an argon gas flow rate of 5 to 250sccm, setting the ion source voltage to 500 to 3000V, and using ionized argon ions to etch the metal bipolar plate substrate for 10 to 50 minutes.

[0024] According to another aspect of the present invention, step S3 includes: setting the target substrate distance to 10 to 45 cm, setting the metal bipolar plate substrate temperature to 50 to 350° C., introducing an argon gas flow rate of 5 to 180 sccm, setting the working gas pressure to 0.1 to 2.0 Pa, setting the metal bipolar plate substrate bias to -50 to -200 V, setting the target arc flow to 30 to 150 A, and depositing for 2 to 50 minutes.

[0025] According to another aspect of the present invention, step S4 includes: setting the substrate temperature of the metal bipolar plate to 50-350°C, introducing a nitrogen flow rate of 5-200 sccm, setting the substrate bias of the metal bipolar plate to -30--200 V, setting the arc target arc current to 30-150 A, and depositing for 5-110 min.

[0026] According to another aspect of the present invention, step S5 includes: introducing 5 to 50 sccm of argon and 1 to 35 sccm of oxygen into the vacuum chamber, setting the substrate temperature of the metal bipolar plate to 50 to 350° C., setting the bias voltage to -250 to -950 V, and performing oxygen plasma sputtering for 1 to 15 minutes.

[0027] Compared with the prior art, the present invention has the following advantages:

[0028] According to the solution of the present invention, the metal nitride-based composite coating on the surface of the metal bipolar plate has a conductive and corrosion-resistant function. In the direction of its deposition, it is composed of a metal transition layer, a metal nitride intermediate gradient layer and a metal passivation conductive and corrosion-resistant surface layer in sequence. The metal nitride intermediate gradient layer with a gradient component can optimize the internal structure of the coating and effectively block the continuous growth of pinhole defects in the deposition direction of the coating. The metal nitride-based composite coating has a metal passivation layer deposited on the outermost surface, which can significantly improve the surface integrity of the coating and significantly improve the corrosion resistance of the coating. The difference in thermal expansion coefficients between different coatings of the composite coating is small, and the internal stress between the coating and the substrate is small, which can greatly improve the bonding strength between the membrane and the substrate and significantly reduce the contact resistance of the coating. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments are briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention, and for ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0030] Figure 1 A schematic diagram showing the structure of a fuel cell metal bipolar plate composite coating disclosed in an embodiment of the present invention;

[0031] Figure 2 The flowchart schematically shows a method for preparing a composite coating of a fuel cell metal bipolar plate disclosed in an embodiment of the present invention.

[0032] Reference numerals:

[0033] 1-metal bipolar plate substrate; 2-metal transition layer; 3-metal nitride intermediate gradient layer; 4-metal passivation surface layer. DETAILED DESCRIPTION

[0034] The description of the embodiments of this specification should be combined with the corresponding drawings, which should be considered as part of the complete specification. In the drawings, the shape or thickness of the embodiments may be enlarged and indicated for simplification or convenience. Furthermore, the parts of each structure in the drawings will be described separately. It is worth noting that the elements not shown in the drawings or not described in words are in a form known to ordinary technicians in the relevant technical field.

[0035] The description of the embodiments herein and any reference to directions and orientations are only for the convenience of description and are not to be construed as any limitation on the scope of protection of the present invention. The following description of the preferred embodiments may involve combinations of features, which may exist independently or in combination, and the present invention is not particularly limited to the preferred embodiments. The scope of the present invention is defined by the claims.

[0036] The embodiment of the present invention provides a fuel cell metal bipolar plate composite coating, such as Figure 1 As shown, the composite coating includes: a metal transition layer 2, a metal nitride intermediate gradient layer 3 and a metal passivation surface layer 4 which are sequentially formed on the surface of a metal bipolar plate substrate 1 along a coating deposition direction.

[0037] The material of the metal bipolar plate substrate 1 is titanium, tungsten, chromium, aluminum, nickel, copper, zirconium, molybdenum, niobium or stainless steel, and the thickness of the metal bipolar plate substrate 1 is 0.05 to 2 mm, preferably 0.1 to 0.15 mm.

[0038] The metal material in the metal transition layer 2 is at least one of titanium, tungsten, chromium, aluminum, nickel, copper, zirconium, molybdenum, niobium and alloys thereof (one or a combination of several), preferably titanium, chromium, zirconium, niobium, titanium-chromium alloy, titanium-niobium alloy, titanium-chromium-niobium alloy. The thickness of the metal transition layer 2 is 30 to 650 nm, preferably 50 to 550 nm.

[0039] The metal material in the metal nitride intermediate gradient layer 3 is at least one (one or a combination of several) of titanium, tungsten, chromium, aluminum, nickel, copper, zirconium, molybdenum, and niobium, preferably titanium, chromium, zirconium, and niobium. The metal nitride is MNx, 0≤x<1.5, including nitrides formed by one or several of titanium, tungsten, chromium, aluminum, nickel, copper, zirconium, molybdenum, and niobium, preferably one or several combinations of TiN, CrN, NbN, ZrN, TiCrN, TiNbN, TiZrN, CrNbN, CrZrN, and NbZrN, and the mass fraction of the metal nitride is 70-85%, preferably 75-80%. The thickness of the metal nitride intermediate gradient layer is 1-4.2 μm, preferably 1.5-3.8 μm.

[0040] The metal nitride intermediate gradient layer 3 is a gradient structure, and the metal component in the coating gradually decreases from 95wt% to 15-30wt% along the coating deposition direction, and the metal nitride component gradually increases from 5wt% to 70-85wt%. In this embodiment, the metal nitride intermediate gradient layer 3 is provided with 3 to 7 component gradients, preferably 5 component gradients.

[0041] The metal material in the metal passivation surface layer 4 is at least one (one or a combination of several) of titanium, tungsten, chromium, aluminum, nickel, copper, zirconium, molybdenum, and niobium, preferably titanium, chromium, niobium, and zirconium. The metal passivation is an oxide MOy, 0<y<4.

[0042] like Figure 2 As shown, the embodiment of the present invention also provides a method for preparing the above-mentioned fuel cell metal bipolar plate composite coating, comprising the steps of:

[0043] S1. Degreasing, ultrasonic cleaning and drying of the metal bipolar plate substrate;

[0044] S2. placing the treated metal bipolar plate substrate into the arc ion plating equipment chamber, and etching the metal bipolar plate substrate using ionized argon ions;

[0045] S3. Depositing a metal transition layer on the surface of the metal bipolar plate substrate using arc ion plating technology;

[0046] S4. Depositing a metal nitride intermediate gradient layer on the metal transition layer using arc ion plating technology;

[0047] S5. Prepare a metal passivation surface layer on the metal nitride intermediate gradient layer.

[0048] Wherein, step S2 comprises: setting the base temperature of the metal bipolar plate to 50-350°C, preferably 100-300°C, and more preferably 150-250°C; setting the vacuum degree to 9×10 -4 Pa~7×10 -3 Pa, preferably 1×10 -3 Pa~6×10 -3 Pa, more preferably 2×10 -3 Pa~4×10 -3 Pa; the argon flow rate is 5 to 250 sccm, preferably 40 to 200 sccm, and more preferably 80 to 120 sccm; the ion source voltage is set to 500 to 3000 V, preferably 1000 to 2300 V, and more preferably 1300 to 2100 V; and the metal bipolar plate substrate is etched using ionized argon ions for 10 to 50 min, preferably 20 to 40 min, and more preferably 25 to 35 min.

[0049] Step S3 includes: selecting a metal M target as the cathode target (wherein M is one or a combination of titanium, chromium, zirconium, niobium, titanium-chromium alloy, titanium-niobium alloy and titanium-chromium-niobium alloy), setting the target-substrate distance to 10-45 cm, preferably 15-30 cm, and more preferably 22-24 cm; setting the base temperature of the metal bipolar plate to 50-350° C., preferably 80-300° C., and more preferably 100-250° C.; introducing an argon gas flow rate of 5-180 sccm, preferably 30-150 sccm, and more preferably 80~120sccm; set the working gas pressure to 0.1~2.0Pa, preferably 0.3~1.8Pa, and further preferably 0.6~1.2Pa; set the metal bipolar plate substrate bias to -50~-250V, preferably -60~-200, and further preferably -70~-130V; set the target arc current to 30~150A, preferably 50~90A, and further preferably 60~80A; and deposit for 2~50min, preferably 3~40min, and further preferably 5~30min.

[0050] Step S4 includes: setting the substrate temperature of the metal bipolar plate to 50-350°C, preferably 80-250°C, and further preferably 100-180°C; introducing a nitrogen flow rate of 5-200sccm, preferably 40-180sccm; further preferably 40-160sccm; setting the substrate bias of the metal bipolar plate to -30--200V, preferably -35--150V, and further preferably -40--90V; setting the arc target arc current to 30-150A, preferably 40-100A, and further preferably 60-80A; and depositing for 5-110min, preferably 10-95min, and further preferably 15-75min.

[0051] Step S5 includes: introducing argon gas into the vacuum chamber at 5 to 50 sccm, preferably 15 to 40 sccm, more preferably 20 to 30 sccm, and oxygen gas at 1 to 35 sccm, preferably 2 to 15 sccm, more preferably 3 to 8 sccm; setting the substrate temperature of the metal bipolar plate to 50 to 350°C, preferably 80 to 250°C, more preferably 150 to 220°C; setting the bias voltage to -250 to -950V, preferably -450 to -850V, more preferably -550 to -750V; oxygen plasma sputtering for 1 to 15 minutes, preferably 2 to 10 minutes, more preferably 3 to 6 minutes. The surface layer of the metal passivation (MOy, where 0 < y < 4) is prepared to achieve the purpose of surface pinhole blocking at a relatively low oxide amount that does not affect the contact resistance and corrosion resistance of the metal nitride coating.

[0052] Example 1

[0053] The gradient metal nitride-based composite coating for a fuel cell bipolar plate provided in this embodiment is as follows: Figure 1 As shown, a metal transition layer 2, a metal nitride intermediate gradient layer 3 and a metal passivation surface layer 4 are sequentially coated on the surface of a metal bipolar plate substrate 1 of the metal bipolar plate. In this embodiment, the metal bipolar plate substrate 1 is a pure titanium bipolar plate for a proton exchange membrane fuel cell, and the preparation method of the composite coating on the substrate surface is as follows:

[0054] (1) The metal bipolar plate substrate 1 after degreasing, ultrasonic cleaning and drying is placed in the arc ion plating equipment chamber, and the metal bipolar plate substrate 1 is heated to 170°C and the vacuum degree reaches 3×10 -3 After the pressure drops below Pa, 100 sccm of argon gas is introduced, the ion source voltage is set to 2000 V, and the metal bipolar plate substrate 1 is etched with ionized argon ions for 30 minutes.

[0055] (2) Arc ion plating technology is used to deposit a Ti transition layer 2 on a pure titanium bipolar plate substrate 1, wherein a single-element Ti target is selected as a cathode target, the target-substrate distance is set to 23 cm, the arc target current is 70 A, the temperature of the metal bipolar plate substrate 1 is 150°C, the argon gas flow rate is 100 sccm, the working pressure is 0.8 Pa, the metal bipolar plate substrate 1 is biased at -100 V, the deposition time is 12 min, and the deposited Ti transition layer 2 has a thickness of about 400 nm.

[0056] (3) Arc ion plating technology is used to deposit TiCrN intermediate gradient layer 3 on Ti transition layer 2. The cathode target is a single Cr target and a single Ti target, the target-substrate distance is set to 23 cm, the arc target current is 50 A, the temperature of the metal bipolar plate substrate 1 is 150 ° C, the metal bipolar plate substrate 1 is biased at -80 V, if the nitrogen flow rate is 60 sccm, the deposition time is 5 min; if the nitrogen flow rate is 80 sccm, the deposition time is 8 min; if the nitrogen flow rate is 100 sccm, the deposition time is 12 min; if the nitrogen flow rate is 120 sccm, the deposition time is 15 min; if the nitrogen flow rate is 150 sccm, the deposition time is 20 min. The thickness of the TiCrN intermediate gradient layer 3 finally deposited is about 3.2 μm.

[0057] (4) Preparation of metal passivation surface layer 4. The purpose of plugging surface pinholes is achieved at a relatively low oxide content that does not affect the contact resistance and corrosion resistance of the metal nitride coating, including: introducing argon gas 25 sccm and oxygen gas 4 sccm into the vacuum chamber, setting the temperature of the metal bipolar plate substrate 1 to 200°C, setting the bias voltage to -650V, and oxygen plasma sputtering for 5 minutes.

[0058] Example 2

[0059] The gradient metal nitride-based composite coating for a fuel cell bipolar plate provided in this embodiment is as follows: Figure 1 As shown, a metal transition layer 2, a metal nitride intermediate gradient layer 3 and a metal passivation surface layer 4 are sequentially coated on the surface of a metal bipolar plate substrate 1. In this embodiment, the metal bipolar plate substrate 1 is a pure titanium bipolar plate for a proton exchange membrane fuel cell, and the preparation method of the composite coating on the substrate surface is as follows:

[0060] (1) The metal bipolar plate substrate 1 after degreasing, ultrasonic cleaning and drying is placed in the arc ion plating equipment chamber, and the metal bipolar plate substrate 1 is heated to 170°C and the vacuum degree reaches 3×10 -3 After the pressure drops below Pa, 100 sccm of argon gas is introduced, the ion source voltage is set to 1500 V, and the metal bipolar plate substrate 1 is etched with ionized argon ions for 25 min.

[0061] (2) Arc ion plating technology is used to deposit a Ti transition layer 2 on a pure titanium bipolar plate substrate 1, wherein a single-element Ti target is selected as the cathode target, the target-substrate distance is set to 23 cm, the arc target current is 70 A, the temperature of the metal bipolar plate substrate 1 is 150°C, the argon gas flow rate is 100 sccm, the working pressure is 0.8 Pa, the metal bipolar plate substrate 1 is biased at -80 V, the deposition time is 10 min, and the thickness of the deposited Ti transition layer 2 is about 280 nm.

[0062] (3) Arc ion plating technology is used to deposit TiCrN intermediate gradient layer 3 on Ti transition layer 2. The cathode target is a single Cr target and a single Ti target, the target-substrate distance is set to 23 cm, the arc target current is 70 A, the temperature of the metal bipolar plate substrate 1 is 150 ° C, the metal bipolar plate substrate 1 is biased at -50 V, if the nitrogen flow rate is 50 sccm, the deposition time is 3 min; if the nitrogen flow rate is 70 sccm, the deposition time is 5 min; if the nitrogen flow rate is 100 sccm, the deposition time is 8 min; if the nitrogen flow rate is 115 sccm, the deposition time is 10 min; if the nitrogen flow rate is changed to 135 sccm, the deposition time is 15 min; the thickness of the TiCrN intermediate gradient layer 3 finally deposited is about 2.4 μm.

[0063] (4) Preparation of a metal passivation surface layer 4 to achieve the purpose of surface pinhole plugging at a relatively low oxide content that does not affect the contact resistance and corrosion resistance of the metal nitride coating, including: introducing 25 sccm of argon and 4 sccm of oxygen into the vacuum chamber, setting the temperature of the metal bipolar plate substrate 1 to 200°C, setting the bias voltage to -650V, and oxygen plasma sputtering for 3 minutes.

[0064] Example 3

[0065] The gradient metal nitride-based composite coating for a fuel cell bipolar plate provided in this embodiment is as follows: Figure 1 As shown, a metal transition layer 2, a metal nitride intermediate gradient layer 3 and a metal passivation surface layer 4 are sequentially coated on the surface of a metal bipolar plate substrate 1. In this embodiment, the metal bipolar plate substrate 1 is a pure titanium bipolar plate for a proton exchange membrane fuel cell, and the preparation method of the composite coating on the substrate surface is as follows:

[0066] (1) The metal bipolar plate substrate 1 after degreasing, ultrasonic cleaning and drying is placed in the arc ion plating equipment chamber, and the metal bipolar plate substrate 1 is heated to 170°C and the vacuum degree reaches 3×10 -3 After the pressure drops below Pa, 100 sccm of argon gas is introduced, the ion source voltage is set to 2000 V, and the metal bipolar plate substrate 1 is etched with ionized argon ions for 30 minutes.

[0067] (2) Arc ion plating technology is used to deposit a Ti transition layer 2 on a pure titanium bipolar plate substrate 1, wherein a single-element Ti target is selected as the cathode target, the target-substrate distance is set to 23 cm, the arc target current is 70 A, the temperature of the metal bipolar plate substrate 1 is 150°C, the argon gas flow rate is 100 sccm, the working pressure is 0.8 Pa, the metal bipolar plate substrate 1 is biased at -100 V, the deposition time is 6 min, and the thickness of the deposited Ti transition layer 2 is about 180 nm.

[0068] (3) Arc ion plating technology is used to deposit a TiN intermediate gradient layer 3 on the Ti transition layer 2. The cathode target is a single-element Ti target, the target-substrate distance is set to 23 cm, the arc target current is 50 A, the metal bipolar plate substrate 1 temperature is 150° C., the metal bipolar plate substrate 1 bias voltage is -80 V, if the nitrogen flow rate is 60 sccm, the deposition time is 3 min; if the nitrogen flow rate is 80 sccm, the deposition time is 5 min; if the nitrogen flow rate is 90 sccm, the deposition time is 8 min; if the nitrogen flow rate is 100 sccm, the deposition time is 12 min; if the nitrogen flow rate is 120 sccm, the deposition time is 15 min; the thickness of the TiN intermediate gradient layer 3 finally deposited is about 1.5 μm.

[0069] (4) Preparation of metal passivation surface layer. The purpose of surface pinhole plugging is achieved at a relatively low oxide content that does not affect the contact resistance and corrosion resistance of the metal nitride coating, including: introducing argon gas 25 sccm and oxygen gas 4 sccm into the vacuum chamber, setting the temperature of the metal bipolar plate substrate 1 to 200°C, setting the bias voltage to -650V, and oxygen plasma sputtering for 5 minutes.

[0070] The serial numbers of the above-mentioned steps involved in the method of the present invention do not mean the order of execution of the method. The execution order of each step should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the implementation mode of the present invention.

[0071] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A fuel cell metal bipolar plate composite coating, characterized in that: include: A metal transition layer (2), a metal nitride intermediate gradient layer (3) and a metal passivation surface layer (4) are sequentially formed on the surface of a metal bipolar plate substrate (1) along a coating deposition direction, wherein the metal transition layer (2) and the metal nitride intermediate gradient layer (3) are prepared by arc ion plating technology; the metal material in the metal nitride intermediate gradient layer (3) is at least one of titanium, tungsten, chromium, aluminum, nickel, copper, zirconium, molybdenum and niobium, wherein the metal nitride is MNx, 0≤x<1.5; The metal material in the metal passivation surface layer (4) is at least one of titanium, tungsten, chromium, aluminum, nickel, copper, zirconium, molybdenum and niobium, wherein the metal passivation is MOy, 0<y<4; The metal nitride intermediate gradient layer (3) is a gradient structure. Along the coating deposition direction, the metal component in the coating gradually decreases from 95wt% to 15-30wt%, and the metal nitride component gradually increases from 5wt% to 70-85wt%. The metal nitride intermediate gradient layer (3) is provided with 3 to 7 component gradients.

2. The fuel cell metal bipolar plate composite coating according to claim 1, characterized in that: The material of the metal bipolar plate substrate (1) is titanium, tungsten, chromium, aluminum, nickel, copper, zirconium, molybdenum, niobium or stainless steel; The thickness of the metal bipolar plate substrate (1) is 0.05 to 2 mm.

3. The fuel cell metal bipolar plate composite coating according to claim 1, characterized in that: The metal material in the metal transition layer (2) is at least one of titanium, tungsten, chromium, aluminum, nickel, copper, zirconium, molybdenum, niobium and alloys thereof; The thickness of the metal transition layer (2) is 30 to 650 nm.

4. The fuel cell metal bipolar plate composite coating according to claim 1, characterized in that: The thickness of the metal nitride intermediate gradient layer (3) is 1 to 4.2 μm.

5. A method for preparing a fuel cell metal bipolar plate composite coating according to any one of claims 1 to 4, comprising the steps of: S1. Degreasing, ultrasonic cleaning and drying of the metal bipolar plate substrate; S2. placing the treated metal bipolar plate substrate into the arc ion plating equipment cavity, and etching the metal bipolar plate substrate using ionized argon ions; S3. Depositing a metal transition layer on the surface of the metal bipolar plate substrate using arc ion plating technology; S4. Depositing a metal nitride intermediate gradient layer on the metal transition layer using arc ion plating technology; S5. Preparing a metal passivation surface layer on the metal nitride intermediate gradient layer.

6. The method according to claim 5, characterized in that The step S2 includes: setting the base temperature of the metal bipolar plate to 50-350°C, setting the vacuum degree to 9×10 -4 Pa~7×10 -3 Pa, the argon flow rate is 5 to 250 sccm, the ion source voltage is set to 500 to 3000 V, and the metal bipolar plate substrate is etched with ionized argon ions for 10 to 50 minutes.

7. The method according to claim 5, characterized in that The step S3 includes: setting the target substrate distance to 10 to 45 cm, setting the metal bipolar plate substrate temperature to 50 to 350° C., introducing an argon gas flow rate of 5 to 180 sccm, setting the working gas pressure to 0.1 to 2.0 Pa, setting the metal bipolar plate substrate bias to -50 to -200 V, setting the target arc flow to 30 to 150 A, and depositing for 2 to 50 minutes.

8. The method according to claim 5, characterized in that The step S4 comprises: setting the substrate temperature of the metal bipolar plate to 50-350° C., introducing a nitrogen flow rate of 5-200 sccm, setting the substrate bias voltage of the metal bipolar plate to -30--200 V, setting the arc target current to 30-150 A, and depositing for 5-110 minutes; The step S5 includes: introducing 5-50 sccm of argon and 1-35 sccm of oxygen into the vacuum chamber, setting the substrate temperature of the metal bipolar plate to 50-350° C., setting the bias voltage to -250--950 V, and performing oxygen plasma sputtering for 1-15 minutes.

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