Protective coating for stainless steel bipolar plate of hydrogen fuel cell and preparation method of protective coating

Abstract

The invention discloses a hydrogen fuel cell stainless steel bipolar plate protective coating and a preparation method thereof, and relates to the field of fuel cells. According to the protective coating for the stainless steel bipolar plate of the hydrogen fuel cell and the preparation method of the protective coating, the problems that a traditional protective coating is high in preparation time cost, complex in process, low in production efficiency and high in manufacturing cost are systematically solved by arranging the multiple layers of CrN / Cr coatings, and corrosive media are effectively blocked through the characteristics of high hardness and high chemical stability of the CrN coatings; external corrosive substances are prevented from being in contact with the stainless steel substrate; the Cr layer is introduced to construct a multi-layer CrN / Cr structure, a conductive network is optimized, and the structure of the multi-layer CrN / Cr coating is regulated and controlled, so that the interface contact resistance can be reduced while metal ion precipitation is inhibited, and the balance between the protection performance and the conductive performance is realized; the performance requirements of the hydrogen fuel cell on the stainless steel bipolar plate in complex and harsh working environments with strong acidity, high humidity, impurities and the like are met, the performance of the hydrogen fuel cell can be remarkably improved, and the service life of the hydrogen fuel cell can be remarkably prolonged.

Description

TECHNICAL FIELD

[0001] The present application relates to fuel cell technology, in particular to a hydrogen fuel cell stainless steel bipolar plate protective coating and a preparation method thereof. BACKGROUND

[0002] Under the background of the global energy structure accelerating towards low carbonization and cleanization, hydrogen fuel cells have become the next generation of energy technology with great potential in the fields of transportation and distributed power generation, due to their zero emissions, high efficiency and sustainability. As the core component of hydrogen fuel cells, bipolar plates bear the key functions of separating reaction gases, conducting current, supporting electrode structures and leading out reaction water, and their performance directly affects the efficiency and service life of the battery. Currently, bipolar plates are mainly divided into three categories: graphite bipolar plates, composite bipolar plates and metal bipolar plates. Graphite bipolar plates, with excellent chemical stability and electrical conductivity, were widely used in early fuel cells, but their high cost, low density and difficult processing limited large-scale commercialization. Composite bipolar plates are composed of polymers and conductive fillers, which can reduce costs, but have the defects of insufficient mechanical strength and poor aging resistance. Metal bipolar plates, especially stainless steel bipolar plates, have unique competitiveness in the commercialization process due to their low cost, high mechanical strength, scalability, mature forming process (such as stamping and rolling), and strong recyclability, and have become the focus of industry research and application in recent years. However, stainless steel is prone to corrosion and release of metal ions in the harsh working environment of fuel cells with strong acidity, high humidity and chlorine and sulfur impurities, which not only causes poisoning of the proton exchange membrane, reduces the performance of the battery, but also increases the interface contact resistance, seriously affecting the output power and service life of the battery. Therefore, developing an efficient and stable protective coating has become a key technical path to break through the application bottleneck of stainless steel bipolar plates.

[0003] Some existing protective coatings, such as traditional carbon coatings, suffer from low deposition efficiency and poor conductivity. Although some research teams have improved these coatings using catalytic reaction magnetron sputtering, employing bridging nano-copper clusters and graphene-like carbon structures to form a spatial network in the bulk phase, imparting some conductivity to the samples, the overall protective effect still falls short of practical requirements. Furthermore, while isolating the nano-copper clusters by graphene-like carbon structures and amorphous carbon clusters improves corrosion resistance, it also increases the complexity and cost of the preparation process. Cr-based coatings, due to their excellent corrosion resistance, good conductivity, and strong adhesion to stainless steel substrates, are considered ideal materials for bipolar plate protection. CrN coatings possess high hardness and chemical stability, effectively blocking corrosive media; while Cr coatings can further enhance corrosion resistance by forming a dense Cr2O3 passivation layer. Through the synergistic design of multilayer CrN / Cr coatings, it is hoped that a composite coating system with both physical barrier and chemical passivation mechanisms can be constructed, suppressing metal ion precipitation while reducing interfacial contact resistance, achieving a balance between protective and conductive properties.

[0004] While CrN coatings possess excellent corrosion resistance, electrical conductivity, and low cost, their preparation window is extremely narrow. Even slight deviations in process parameters, such as temperature fluctuations of a few degrees Celsius or minute percentage changes in gas flow rate, can significantly alter key properties of the coating, including its crystal structure, chemical composition, and density, ultimately failing to meet expected performance standards. Even CrN films deposited using high-power micro-pulse magnetron sputtering (HiPIMS) under wide N2 / Ar ratio (4%–10%) conditions show some improvement in conductivity and corrosion resistance, but they still struggle to maintain stable performance over long periods under complex operating conditions.

[0005] As can be seen from the above, although Cr-based coatings have shown certain application potential, there are still insufficient studies on the composition control, microstructure optimization and failure mechanism of multilayer CrN / Cr coatings under complex working conditions. It is necessary to provide theoretical basis and technical support for improving the reliability of stainless steel bipolar plates for hydrogen fuel cells through systematic material design and process innovation. Summary of the Invention

[0006] The purpose of this invention is to provide a protective coating for stainless steel bipolar plates of hydrogen fuel cells and its preparation method, so as to solve the problem that the existing CrN / Cr protective coating is still difficult to maintain its performance stably for a long time under complex working conditions.

[0007] To achieve the above objectives, the present invention provides the following technical solution: a protective coating for a stainless steel bipolar plate of a hydrogen fuel cell, comprising multiple layers of Cr and CrN layers interleaved and deposited on the surface of the stainless steel bipolar plate, wherein the bottom layer is a Cr layer and the top layer is a CrN layer.

[0008] A method for preparing a protective coating for a stainless steel bipolar plate in a hydrogen fuel cell, comprising the following steps:

[0009] The stainless steel plate used as the bipolar plate is ground and polished.

[0010] After the stainless steel plate has been polished, it is cleaned and dried, then placed on the stainless steel turntable of the deposition furnace to preheat the stainless steel plate and perform plasma cleaning.

[0011] The deposition furnace temperature and gas atmosphere are set, and the stainless steel plate is rotated by a stainless steel turntable. The DC magnetron sputtering instrument is controlled to form a Cr layer on the surface of the stainless steel plate. The deposition furnace temperature, gas atmosphere and DC reactive sputtering power are adjusted to form a CrN layer outside the Cr layer.

[0012] After sputtering, the stainless steel plate is kept at a certain temperature for a set time, and then cooled down. After cooling down, the stainless steel plate is removed from the furnace, thus completing the preparation of the protective coating on the surface of the stainless steel plate.

[0013] Preferably, in the grinding and polishing process, the stainless steel plate is ground step by step on a manual grinding and polishing machine using silicon carbide abrasive discs with meshes of 280, 500, 1200, and 2000. After the sample surface is flattened, the stainless steel plate is polished with diamond polishing liquid with particle sizes of 3µm, 1µm, and 0.05µm in sequence to obtain a stainless steel sample with a smooth surface and no coarse scratches.

[0014] Preferably, after grinding and polishing, the stainless steel plate is ultrasonically cleaned in acetone, anhydrous ethanol, and deionized water for 20 minutes in sequence. Then, the stainless steel plate is taken out, the surface moisture is quickly removed and dried. The dried stainless steel plate is placed on a stainless steel turntable in the furnace, and the distance between the stainless steel plate and the Cr target is controlled to be 15 cm. The vacuum is drawn to below 3 mTorr, the stainless steel plate is heated to 300°C, and the substrate sample is plasma cleaned for 5 minutes at 100 sssm Ar and RF: 100 W.

[0015] Preferably, the steps for generating two Cr layers and CrN layers include:

[0016] The Cr layer was deposited for 24 min at a temperature of 300 °C, with an Ar atmosphere of 15 sccm. The DC magnetron sputtering power of the magnetron sputtering instrument was controlled at 300 W, and the rotation speed of the stainless steel turntable was 3 RPM.

[0017] The CrN layer was deposited for 1 h at a temperature of 300 °C. The gas atmosphere was Ar:N2 = 15:7 sccm. The DC reactive sputtering power of the magnetron sputtering instrument was controlled at 300 W and the rotation speed of the stainless steel turntable was 3 RPM.

[0018] After sputtering, the temperature is maintained for 30 minutes, then cooled to 80 ℃. The furnace chamber is opened, and the stainless steel plate is removed. The resulting protective coating has a Cr base layer and a CrN surface layer, with a total of 2 layers.

[0019] Preferably, the steps for generating four Cr layers and CrN layers include:

[0020] The Cr layer was deposited for 12 min at a temperature of 300 °C, the gas atmosphere was Ar 15 sccm, the DC magnetron sputtering power of the magnetron sputtering instrument was controlled at 300 W, and the rotation speed of the stainless steel turntable was 3 RPM.

[0021] The CrN layer was deposited for 30 min at a temperature of 300 ℃, the gas atmosphere was Ar:N2=15:7 sccm, the DC reactive sputtering power of the magnetron sputtering instrument was controlled at 300 W, and the rotation speed of the stainless steel turntable was 3 RPM.

[0022] Repeat the above deposition steps once;

[0023] After sputtering, the temperature was maintained for 30 minutes, then cooled to 80 ℃. The furnace chamber was opened, and the stainless steel plate was removed. The resulting protective coating had a Cr base layer and a CrN surface layer, with a total of 4 layers.

[0024] Preferably, the steps for generating the six-layer Cr and CrN layers include:

[0025] The Cr layer was deposited for 8 min at a temperature of 300 °C, the gas atmosphere was Ar 15 sccm, the DC magnetron sputtering power of the magnetron sputtering instrument was controlled at 300 W, and the rotation speed of the stainless steel turntable was 3 RPM.

[0026] The CrN layer was deposited for 20 min at a temperature of 300 °C. The gas atmosphere was Ar:N2 = 15:7 sccm. The DC reactive sputtering power of the magnetron sputtering instrument was controlled at 300 W, and the rotation speed of the stainless steel turntable was 3 RPM.

[0027] Repeat the above deposition steps twice;

[0028] After sputtering, the temperature was maintained for 30 minutes, then cooled to 80 ℃. The furnace chamber was opened, and the stainless steel plate was removed. The resulting protective coating had a Cr base layer and a CrN surface layer, with a total of 6 layers.

[0029] Preferably, the steps for generating eight Cr layers and CrN layers include:

[0030] The Cr layer was deposited for 6 min at a temperature of 300 °C, the gas atmosphere was Ar 15 sccm, the DC magnetron sputtering power of the magnetron sputtering instrument was controlled at 300 W, and the rotation speed of the stainless steel turntable was 3 RPM.

[0031] The CrN layer was deposited for 20 min at a temperature of 300 °C. The gas atmosphere was Ar:N2 = 15:7 sccm. The DC reactive sputtering power of the magnetron sputtering instrument was controlled at 300 W, and the rotation speed of the stainless steel turntable was 3 RPM.

[0032] Repeat the above deposition steps three times;

[0033] After sputtering, the temperature was maintained for 30 minutes, then cooled to 80 ℃. The furnace chamber was opened, and the stainless steel plate was removed. The resulting protective coating had a Cr base layer and a CrN surface layer, with a total of 8 layers.

[0034] Compared with existing technologies, the present invention provides a protective coating for stainless steel bipolar plates of hydrogen fuel cells and its preparation method. By setting up a multi-layer CrN / Cr coating system, it systematically solves the problems of high time and cost, complex process, low production efficiency and high manufacturing cost of traditional protective coatings. Through the high hardness and high chemical stability of the CrN coating, it effectively blocks corrosive media and prevents external corrosive substances from contacting the stainless steel substrate.

[0035] Introducing a Cr layer to construct a multilayer CrN / Cr structure optimizes the conductive network, significantly reducing interfacial corrosion resistance (ICR). Simultaneously, the multilayer interface blocks corrosion diffusion, improving acid resistance, and the Cr layer enhances the bonding force between layers. Structural control of the multilayer CrN / Cr coating can suppress metal ion deposition while reducing interfacial contact resistance, achieving a balance between protective and conductive properties. This meets the performance requirements of stainless steel bipolar plates for hydrogen fuel cells operating in complex and harsh environments with strong acidity, high humidity, and impurities, significantly improving the performance and lifespan of hydrogen fuel cells. Furthermore, the preparation method is simple and controllable, greatly saving on preparation costs and time. Attached Figure Description

[0036] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in this invention. For those skilled in the art, other drawings can be obtained based on these drawings.

[0037] Figure 1 This is a flowchart of the protective coating preparation method provided in an embodiment of the present invention;

[0038] Figure 2 The dynamic point polarization diagram provided as a verification example of the present invention;

[0039] Figure 3 The constant potential polarization diagram provided as a verification example of the present invention;

[0040] Figure 4 ICR diagrams provided for verification examples of this invention;

[0041] Figure 5 STEM image provided for verification examples of the present invention;

[0042] Figure 6 The following are scanning electron microscope images of stainless steel plates with different numbers of protective layers provided as verification examples of the present invention. a, b, c, and d correspond to stainless steel plates with two, four, six, and eight protective layers, respectively. Detailed Implementation

[0043] To enable those skilled in the art to better understand the technical solution of the present invention, the present invention will be further described in detail below with reference to the accompanying drawings.

[0044] As attached Figure 1 To be continued Figure 6 As shown:

[0045] Example:

[0046] The present invention provides a protective coating for a stainless steel bipolar plate for a hydrogen fuel cell, comprising multiple layers of Cr and CrN layers interleaved on the surface of the stainless steel bipolar plate, wherein the bottom layer is a Cr layer and the top layer is a CrN layer.

[0047] A method for preparing a protective coating for a stainless steel bipolar plate in a hydrogen fuel cell, comprising the following steps:

[0048] The stainless steel plate used as the bipolar plate is ground and polished.

[0049] After the stainless steel plate has been polished, it is cleaned and dried, then placed on the stainless steel turntable of the deposition furnace to preheat the stainless steel plate and perform plasma cleaning.

[0050] The deposition furnace temperature and gas atmosphere are set, and the stainless steel plate is rotated by a stainless steel turntable. The DC magnetron sputtering instrument is controlled to form a Cr layer on the surface of the stainless steel plate. The deposition furnace temperature, gas atmosphere and DC reactive sputtering power are adjusted to form a CrN layer outside the Cr layer.

[0051] After sputtering, the stainless steel plate is kept at a certain temperature for a set time, and then cooled down. After cooling down, the stainless steel plate is removed from the furnace, thus completing the preparation of the protective coating on the surface of the stainless steel plate.

[0052] As can be seen from the above, the problems of high time and cost, complex process, low production efficiency and high manufacturing cost of traditional protective coatings can be solved by setting up a multi-layer CrN / Cr coating system. The high hardness and high chemical stability of the CrN coating can effectively block corrosive media and prevent external corrosive substances from contacting the stainless steel substrate.

[0053] Introducing a Cr layer to construct a multilayer CrN / Cr structure optimizes the conductive network, significantly reducing interfacial corrosion resistance (ICR). Simultaneously, the multilayer interface blocks corrosion diffusion, improving acid resistance, and the Cr layer enhances the bonding force between layers. Structural control of the multilayer CrN / Cr coating can suppress metal ion deposition while reducing interfacial contact resistance, achieving a balance between protective and conductive properties. This meets the performance requirements of stainless steel bipolar plates for hydrogen fuel cells operating in complex and harsh environments with strong acidity, high humidity, and impurities, significantly improving the performance and lifespan of hydrogen fuel cells. Furthermore, the preparation method is simple and controllable, greatly saving on preparation costs and time.

[0054] In the grinding and polishing process, the stainless steel plate was ground step by step on a manual grinding and polishing machine using silicon carbide abrasive discs with mesh sizes of 280, 500, 1200, and 2000. After the sample surface was smoothed, the stainless steel plate was polished with diamond polishing liquid with particle sizes of 3um, 1um, and 0.05um in sequence to obtain a stainless steel sample with a smooth surface and no coarse scratches.

[0055] After grinding and polishing, the stainless steel plate was ultrasonically cleaned in acetone, anhydrous ethanol, and deionized water for 20 minutes in sequence. The stainless steel plate was then removed, surface moisture was quickly removed, and the plate was dried. The dried stainless steel plate was placed on a stainless steel turntable in the furnace, and the distance between the stainless steel plate and the Cr target was controlled to be 15 cm. The vacuum was evacuated to below 3 mTorr, and the stainless steel plate was heated to 300°C. The substrate sample was then plasma cleaned for 5 minutes at 100 sssmAr and RF: 100 W.

[0056] The steps for generating two Cr layers and a CrN layer include:

[0057] The Cr layer was deposited for 24 min at a temperature of 300 °C, with an Ar atmosphere of 15 sccm. The DC magnetron sputtering power of the magnetron sputtering instrument was controlled at 300 W, and the rotation speed of the stainless steel turntable was 3 RPM.

[0058] The CrN layer was deposited for 1 h at a temperature of 300 °C. The gas atmosphere was Ar:N2 = 15:7 sccm. The DC reactive sputtering power of the magnetron sputtering instrument was controlled at 300 W and the rotation speed of the stainless steel turntable was 3 RPM.

[0059] After sputtering, the temperature is maintained for 30 minutes, then cooled to 80 ℃. The furnace chamber is opened, and the stainless steel plate is removed. The resulting protective coating has a Cr base layer and a CrN surface layer, with a total of 2 layers.

[0060] The steps for generating four Cr and CrN layers include:

[0061] The Cr layer was deposited for 12 min at a temperature of 300 °C, the gas atmosphere was Ar 15 sccm, the DC magnetron sputtering power of the magnetron sputtering instrument was controlled at 300 W, and the rotation speed of the stainless steel turntable was 3 RPM.

[0062] The CrN layer was deposited for 30 min at a temperature of 300 ℃, the gas atmosphere was Ar:N2=15:7 sccm, the DC reactive sputtering power of the magnetron sputtering instrument was controlled at 300 W, and the rotation speed of the stainless steel turntable was 3 RPM.

[0063] Repeat the above deposition steps once;

[0064] After sputtering, the temperature was maintained for 30 minutes, then cooled to 80 ℃. The furnace chamber was opened, and the stainless steel plate was removed. The resulting protective coating had a Cr base layer and a CrN surface layer, with a total of 4 layers.

[0065] The steps for generating six Cr and CrN layers include:

[0066] The Cr layer was deposited for 8 min at a temperature of 300 °C, the gas atmosphere was Ar 15 sccm, the DC magnetron sputtering power of the magnetron sputtering instrument was controlled at 300 W, and the rotation speed of the stainless steel turntable was 3 RPM.

[0067] The CrN layer was deposited for 20 min at a temperature of 300 °C. The gas atmosphere was Ar:N2 = 15:7 sccm. The DC reactive sputtering power of the magnetron sputtering instrument was controlled at 300 W, and the rotation speed of the stainless steel turntable was 3 RPM.

[0068] Repeat the above deposition steps twice;

[0069] After sputtering, the temperature was maintained for 30 minutes, then cooled to 80 ℃. The furnace chamber was opened, and the stainless steel plate was removed. The resulting protective coating had a Cr base layer and a CrN surface layer, with a total of 6 layers.

[0070] The steps for generating eight Cr and CrN layers include:

[0071] The Cr layer was deposited for 6 min at a temperature of 300 °C, the gas atmosphere was Ar 15 sccm, the DC magnetron sputtering power of the magnetron sputtering instrument was controlled at 300 W, and the rotation speed of the stainless steel turntable was 3 RPM.

[0072] The CrN layer was deposited for 20 min at a temperature of 300 °C. The gas atmosphere was Ar:N2 = 15:7 sccm. The DC reactive sputtering power of the magnetron sputtering instrument was controlled at 300 W, and the rotation speed of the stainless steel turntable was 3 RPM.

[0073] Repeat the above deposition steps three times;

[0074] After sputtering, the temperature was maintained for 30 minutes, then cooled to 80 ℃. The furnace chamber was opened, and the stainless steel plate was removed. The resulting protective coating had a Cr base layer and a CrN surface layer, with a total of 8 layers.

[0075] Verification example:

[0076] The corrosion resistance of the stainless steel plate with protective coating was evaluated using a Chenhua electrochemical workstation under a simulated PEMFC working environment (0.5M H2SO4, 2 ppm F-, 70 ℃). In the electrochemical experiments, air was injected into the corrosion solution at a constant rate of 20 ml / min. A three-electrode electrochemical testing system was used to test the corrosion behavior of the stainless steel plate sample with protective coating. A platinum sheet and a saturated calomel electrode (SCE) were used as the counter electrode and reference electrode, respectively, and the sample was used as the working electrode. In the potentiodynamic polarization experiment, the potential was set from -0.6 V to 0.8 V (vs SCE), and the scan rate was 2 mV / s. A potentiostatic polarization test was performed at 0.6 V (vs SCE) for 14400 s to evaluate the corrosion stability of the multilayer CrN / Cr coating under PEMFC working conditions. Before each electrochemical corrosion test, the system was kept running for 1 h to stabilize the open circuit potential (OCP). The measured coating potentiodynamics and potentiostatic corrosion current density are shown in the table below.

[0077] Table 1

[0078] Zeta potential 2 layers 4 layers 6 layers 8 layers E (V) -0.236 -0.200 -0.158 0.001 I (uA / cm 2 )]]> 0.68 0.51 0.33 0.295

[0079] Table 2

[0080] Constant potential 2 layers 4 layers 6 layers 8 layers I (uA / cm 2 )]]> 0.138 0.108 0.084 0.052

[0081] In the modified voltammetry method for testing the surface contact resistance of samples, the carbon paper (TGP-H-060) and SS316L samples were both 20 mm × 20 mm in size, and the resistance values ​​were directly measured using a microresistance meter. Throughout the process, varying clamping forces were applied to both ends of the copper electrodes, uniformly increasing from 0.1 MPa to 2.4 MPa at a rate of 0.5 N s⁻¹. The clamping force was provided by a 1 kN electronic universal testing machine, and the resistance value at 1.5 MPa was recorded.

[0082] Table 3

[0083] ICR (mΩ·cm 2 )]]> 2 layers 4 layers 6 layers 8 layers 1.5 MPa 3 6.2 8.6 10.6

[0084] In summary, constructing a multilayer CrN / Cr structure using magnetron sputtering coating technology significantly reduces the corrosion current density and surface contact resistance of stainless steel bipolar plates. With the increase in the number of layers, the corrosion potential shifts positively, the corrosion current density decreases, and the corrosion resistance is enhanced.

[0085] Surface morphology: As the number of layers increases, the thickness of a single coating layer decreases, the grain size becomes finer, and it becomes denser.

[0086] STEM: The coating is a cross-deposition of Cr and CrN, and the coating is dense.

[0087] The foregoing has only described certain exemplary embodiments of the present invention by way of illustration. Undoubtedly, those skilled in the art can modify the described embodiments in various ways without departing from the spirit and scope of the present invention. Therefore, the foregoing drawings and descriptions are illustrative in nature and should not be construed as limiting the scope of protection of the claims of the present invention.

Claims

1. A protective coating for a stainless steel bipolar plate of a hydrogen fuel cell, characterized in that, It includes multiple layers of Cr and CrN layers deposited alternately on the surface of the stainless steel electrode plate, with the bottom layer being a Cr layer and the top layer being a CrN layer.

2. A method for preparing a protective coating for a stainless steel bipolar plate of a hydrogen fuel cell, characterized in that, The preparation steps include: The stainless steel plate used as the bipolar plate is ground and polished. After the stainless steel plate has been polished, it is cleaned and dried, then placed on the stainless steel turntable of the deposition furnace to preheat the stainless steel plate and perform plasma cleaning. The deposition furnace temperature and gas atmosphere are set, and the stainless steel plate is rotated by a stainless steel turntable. The DC magnetron sputtering instrument is controlled to form a Cr layer on the surface of the stainless steel plate. The deposition furnace temperature, gas atmosphere and DC reactive sputtering power are adjusted to form a CrN layer outside the Cr layer. After sputtering, the stainless steel plate is kept at a certain temperature for a set time, and then cooled down. After cooling down, the stainless steel plate is removed from the furnace, thus completing the preparation of the protective coating on the surface of the stainless steel plate.

3. The method for preparing a protective coating for a stainless steel bipolar plate of a hydrogen fuel cell according to claim 2, characterized in that, In the grinding and polishing process, the stainless steel plate is ground step by step on a manual grinding and polishing machine using silicon carbide abrasive discs with mesh sizes of 280, 500, 1200, and 2000. After the sample surface is flattened, the stainless steel plate is polished with diamond polishing liquid with particle sizes of 3um, 1um, and 0.05um to obtain a stainless steel sample with a smooth surface.

4. The method for preparing a protective coating for a stainless steel bipolar plate of a hydrogen fuel cell according to claim 2, characterized in that, After grinding and polishing, the stainless steel plate was ultrasonically cleaned in acetone, anhydrous ethanol, and deionized water for 20 minutes in sequence. The stainless steel plate was then removed, the surface moisture was quickly removed, and the plate was dried. The dried stainless steel plate was placed on a stainless steel turntable in the furnace, and the distance between the stainless steel plate and the Cr target was controlled to be 15 cm. The vacuum was evacuated to below 3 mTorr, and the stainless steel plate was heated to 300°C. The substrate sample was then plasma cleaned for 5 minutes at 100 sssm Ar and RF: 100 W.

5. The method for preparing a protective coating for a stainless steel bipolar plate of a hydrogen fuel cell according to claim 2, characterized in that, The steps for generating two Cr layers and a CrN layer include: The Cr layer was deposited for 24 min at a temperature of 300 °C, with an Ar atmosphere of 15 sccm. The DC magnetron sputtering power of the magnetron sputtering instrument was controlled at 300 W, and the rotation speed of the stainless steel turntable was 3 RPM. The CrN layer was deposited for 1 h at a temperature of 300 °C. The gas atmosphere was Ar:N2 = 15:7 sccm. The DC reactive sputtering power of the magnetron sputtering instrument was controlled at 300 W and the rotation speed of the stainless steel turntable was 3 RPM. After sputtering, the temperature is maintained for 30 minutes, then cooled to 80 ℃. The furnace chamber is opened, and the stainless steel plate is removed. The resulting protective coating has a Cr base layer and a CrN surface layer, with a total of 2 layers.

6. The method for preparing a protective coating for a stainless steel bipolar plate of a hydrogen fuel cell according to claim 2, characterized in that, The steps for generating four Cr and CrN layers include: The Cr layer was deposited for 12 min at a temperature of 300 °C, the gas atmosphere was Ar 15 sccm, the DC magnetron sputtering power of the magnetron sputtering instrument was controlled at 300 W, and the rotation speed of the stainless steel turntable was 3 RPM. The CrN layer was deposited for 30 min at a temperature of 300 ℃, the gas atmosphere was Ar:N2=15:7 sccm, the DC reactive sputtering power of the magnetron sputtering instrument was controlled at 300 W, and the rotation speed of the stainless steel turntable was 3 RPM. Repeat the above deposition steps once; After sputtering, the temperature was maintained for 30 minutes, then cooled to 80 ℃. The furnace chamber was opened, and the stainless steel plate was removed. The resulting protective coating had a Cr base layer and a CrN surface layer, with a total of 4 layers.

7. The method for preparing a protective coating for a stainless steel bipolar plate of a hydrogen fuel cell according to claim 2, characterized in that, The steps for generating six Cr and CrN layers include: The Cr layer was deposited for 8 min at a temperature of 300 °C, the gas atmosphere was Ar 15 sccm, the DC magnetron sputtering power of the magnetron sputtering instrument was controlled at 300 W, and the rotation speed of the stainless steel turntable was 3 RPM. The CrN layer was deposited for 20 min at a temperature of 300 °C. The gas atmosphere was Ar:N2 = 15:7 sccm. The DC reactive sputtering power of the magnetron sputtering instrument was controlled at 300 W, and the rotation speed of the stainless steel turntable was 3 RPM. Repeat the above deposition steps twice; After sputtering, the temperature was maintained for 30 minutes, then cooled to 80 ℃. The furnace chamber was opened, and the stainless steel plate was removed. The resulting protective coating had a Cr base layer and a CrN surface layer, with a total of 6 layers.

8. The method for preparing a protective coating for a stainless steel bipolar plate of a hydrogen fuel cell according to claim 2, characterized in that, The steps for generating eight Cr and CrN layers include: The Cr layer was deposited for 6 min at a temperature of 300 °C, the gas atmosphere was Ar 15 sccm, the DC magnetron sputtering power of the magnetron sputtering instrument was controlled at 300 W, and the rotation speed of the stainless steel turntable was 3 RPM. The CrN layer was deposited for 20 min at a temperature of 300 °C. The gas atmosphere was Ar:N2 = 15:7 sccm. The DC reactive sputtering power of the magnetron sputtering instrument was controlled at 300 W, and the rotation speed of the stainless steel turntable was 3 RPM. Repeat the above deposition steps three times; After sputtering, the temperature was maintained for 30 minutes, then cooled to 80 ℃. The furnace chamber was opened, and the stainless steel plate was removed. The resulting protective coating had a Cr base layer and a CrN surface layer, with a total of 8 layers.

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