A method for preparing a multilayer coated stainless steel bipolar plate and its use in a proton exchange membrane fuel cell

Abstract

The application relates to the technical field of fuel cells and discloses a preparation method of a multilayer coating stainless steel bipolar plate and application of the multilayer coating stainless steel bipolar plate in a proton exchange membrane fuel cell. a Cr 1‑a / Ti b Cr 1‑b N x O y The multilayer coating is composed of Ti, Cr, N, O and a multilayer plating layer; wherein 0.10<=a<=0.24, 0.17<=b<=0.36, 1.02<=x<=1.08 and 0.17<=y<=0.21. The corrosion resistance of the modified stainless steel bipolar plate is remarkably improved, and the interface contact resistance between the bipolar plate and the gas diffusion layer is obviously reduced, so that the problems of the corrosion resistance and the electric conductivity of the existing coating bipolar plate are solved. The surface-modified stainless steel bipolar plate can be applied to the proton exchange membrane fuel cell, the performance of the device is improved, the batch production is suitable, and a large amount of cost is saved.

Description

Technical Field

[0001] This invention relates to the field of fuel cell technology, specifically to a method for preparing a multilayer coated stainless steel bipolar plate and its application in proton exchange membrane fuel cells. Background Technology

[0002] Proton exchange membrane fuel cells (PEMFCs) have garnered global attention due to their outstanding advantages, including high power density, low operating temperature, low noise, and especially zero emissions. They are expected to play a crucial role in future social development and energy consumption reduction, with significant application prospects in electric vehicles, portable generators, micro-aircraft, and various energy storage systems. Bipolar plates, as a key component of PEMFCs, play an irreplaceable role in separating individual cells, distributing reactant gases, conducting current, and removing heat and moisture. Furthermore, bipolar plates typically account for at least 70% of the total weight and volume of the fuel cell stack, and approximately 20% of the total cost. Therefore, developing low-cost, lightweight, and highly reliable bipolar plates is crucial for promoting the commercialization of PEMFCs. An ideal bipolar plate must possess good machinability, strong mechanical properties, and excellent corrosion resistance and electrical conductivity.

[0003] Graphite-based bipolar plates possess excellent electrical conductivity and corrosion resistance, but their mechanical strength, permeability, and manufacturing cost are insufficient, limiting their large-scale industrial production. Metals and their alloys, with their high specific strength, good processing performance, strong thermal and electrical conductivity, and low manufacturing cost, are relatively ideal bipolar plate matrix materials. However, in the high-temperature, humid, and slightly acidic operating environment of proton exchange membrane fuel cells (such as low pH, high humidity, and an operating temperature of approximately 80°C), low-cost metal bipolar plates such as stainless steel and titanium are exposed to both oxidizing and reducing media. On the anode side, the metal bipolar plate may slowly undergo electrochemical corrosion, and the polyvalent cations generated by corrosion may diffuse into the proton exchange membrane, causing a decrease in the membrane's proton conductivity. On the cathode side, the bipolar plate may undergo surface passivation in an oxygen-rich environment, leading to an increase in surface contact resistance. Therefore, the application of metal bipolar plates requires addressing two main issues: first, the electrochemical corrosion problem in the acidic system of proton exchange membrane fuel cells; and second, the problem of reduced conductivity caused by metal surface passivation. To address the above issues, it is crucial to develop protective coatings that combine corrosion resistance and high conductivity, as well as their preparation methods, which are key to the application of metal bipolar plates in fuel cells.

[0004] In practice, preparing a coating on the surface of a metal bipolar plate can effectively improve its corrosion resistance and electrical conductivity. Compared with a single-layer coating, a multi-layer coating is more beneficial to improving the performance of the bipolar plate, reducing the presence of pinholes, large particles, or columnar crystals in the coating, thereby enhancing the coating's stability. Wang Yanli et al. prepared an organic carbon layer on stainless steel using a segmented annealing process, and then prepared a TiC coating in molten salt using a disproportionation reaction, ultimately obtaining a continuous and dense TiC coating. (Application Publication No.: CN115491675 Multi-layer gradient coating Cr / CrN / (Ti,W)3AlC2 for metal bipolar plates of hydrogen fuel cells and its construction method). Although the obtained TiC coating is complete and dense, its corrosion resistance and electrical conductivity under fuel cell operating conditions have not been reported. Zheng Lili et al. prepared a multilayer gradient coating on a stainless steel substrate using magnetron sputtering and arc particle technology. Cr served as the transition layer, CrN as the connecting layer, and (Ti,W)AlC2 as the outer layer (Application Publication No.: CN116536626 A Surface Modification Method for Thin Titanium Bipolar Plates in Proton Exchange Membrane Fuel Cells). This coating preparation process is relatively complex. Although a multilayer coating was successfully obtained, its corrosion resistance and electrical conductivity are not ideal. Under simulated fuel cell operating conditions (80℃, 0.5 mol / L H2SO4 + 2 ppm HF), the corrosion current density after coating reached 0.78 μA / cm. 2 The contact resistance reached 8.25 mΩ·cm. 2 .

[0005] Li Huanming et al. prepared a multilayer coating on stainless steel surface consisting of an inner metal layer (Au, Ag, Pt), a transition layer (one or more of Ti, Cr, Nb, Ta, W, Mo, C, N, Si), an interfacial diffusion layer (carbides or nitrides of Ti, Cr, Nb, Ta, W, Mo, or non-metallic C, Si), and a surface conductive layer (Au, Ag, Pt) (Application Publication No.: CN 112795886 A A Conductive and Corrosion-Resistant Pre-Coating for Metal Bipolar Plate Forming and its Preparation Method). The corrosion current density of the prepared Ti / TiN / C coating was 4.5 × 10⁻⁶. -5 A / cm 2 (1.6V vs. SCE, 10h), under a clamping force of 0.6MPa, the interfacial contact resistance between the coating and the carbon paper is 3.8mΩ·cm. 2 Although this coating has good electrical conductivity, its corrosion resistance does not meet the DOE standard (corrosion current density <1.0 μA / cm). 2Hou Ming et al. prepared a transition layer (one or more of Cr, Ti, Ni, Cu, Al, V, Co, Ag, and Au) / outermost layer (one or more of Cr, Ti, Ni, Al, and V metal nitrides) coating on stainless steel surfaces using ion plating. The modified coating exhibited a corrosion current density of 0.12 μA / cm². 2 Under a compressive force of 1.4 MPa, the interfacial contact resistance between the coating and the carbon paper is 5.17 mΩ·cm. 2 (Application Publication No.: CN 106684394 A A method for surface modification of stainless steel bipolar plates for proton exchange membrane fuel cells); however, the prepared coating surface has cracks, which reduces the stability of the coating under service conditions.

[0006] As can be seen from the above, existing multilayer coating preparation technologies still have drawbacks such as complex preparation processes, insufficient coating density, low corrosion resistance or conductivity, or insufficient stability. Summary of the Invention

[0007] This invention aims to provide a method for preparing multilayer coated stainless steel bipolar plates and their application in proton exchange membrane fuel cells, thereby solving the technical problems of unsatisfactory corrosion resistance and electrical conductivity of bipolar plates.

[0008] To achieve the above objectives, the present invention adopts the following technical solution: a multilayer coated stainless steel bipolar plate, comprising a stainless steel substrate and Ti deposited on the surface of the stainless steel substrate. a Cr 1-a / Ti b Cr 1-b N x O y The multilayer coating; where 0.10≤a≤0.24, 0.17≤b≤0.36, 1.02≤x≤1.08, 0.17≤y≤0.21.

[0009] Preferably, as an improvement, multilayer Ti a Cr 1-a / Ti b Cr 1-b N x O y The overall thickness of the coating is 2.95-4.59μm.

[0010] In this technical solution, the prepared multilayer Ti a Cr 1-a / Ti b Cr 1-b N x O y The coating thickness is between 2.95 and 4.59 μm, which can achieve a relatively ideal anti-corrosion effect.

[0011] Preferably, 316L stainless steel sheet is used as an improved stainless steel matrix.

[0012] In this technical specification, among various metallic materials, stainless steel, especially 316L stainless steel, is widely used due to its excellent mechanical properties and low cost. Furthermore, 316L stainless steel contains approximately 2 at% molybdenum, which gives it better corrosion resistance than other austenitic or ferritic stainless steels.

[0013] Preferably, as an improvement, a method for preparing a multilayer coated stainless steel bipolar plate includes the following steps:

[0014] S1: Ultrasonic cleaning is performed on the stainless steel substrate to obtain a pretreated stainless steel substrate.

[0015] S2: Sputter cleaning is performed on the pretreated stainless steel substrate to obtain the stainless steel substrate to be coated;

[0016] S3: Multilayer TiCr / Ti is deposited on the surface of the stainless steel substrate to be coated using multi-arc ion plating technology. a Cr 1-a N x O y Coating.

[0017] Preferably, as an improvement, in S1, the specific operation of ultrasonic cleaning is as follows: the stainless steel substrate is ultrasonically cleaned with acetone and anhydrous ethanol for 30 minutes each.

[0018] In this technical solution, ultrasonic cleaning can remove impurities, especially oil impurities, from the surface of the stainless steel substrate; in addition, the sequential cleaning with acetone and anhydrous ethanol can ensure the cleaning effect.

[0019] Preferably, as an improvement, in S1, after ultrasonic cleaning, a drying process is performed, and the drying conditions are vacuum drying at 80°C.

[0020] In this technical solution, vacuum drying is used, which can achieve high drying efficiency at a lower temperature. It can effectively reduce stress concentration caused by temperature gradient inside the material, avoid deformation or cracks in the material during the drying process, and thus reduce thermal damage to the material. Moreover, vacuum drying can reduce the contamination of the material by dust and particulate impurities in the outside air.

[0021] Preferably, as an improvement, in S2, the specific operation of sputter cleaning is as follows: the stainless steel substrate is placed in the reaction chamber, and the vacuum degree of the reaction chamber is adjusted to 4.0~9.0×10⁻⁶. -3Pa; then argon gas is introduced into the reaction chamber and the pressure in the reaction chamber is maintained at 1 Pa; the DC bias voltage of the substrate for sputter cleaning is -300 to -200 V, the time is 20 to 30 min, and the target arc current is 80 A to 100 A.

[0022] In this technical solution, the substrate surface is sputtered and cleaned before coating to remove the oxide film on the stainless steel substrate surface, while increasing the surface roughness of the titanium substrate to improve the adhesion with the coating.

[0023] Preferably, as an improvement, in S3, a multilayer Ti is deposited on the surface of the stainless steel substrate to be coated. a Cr 1-a / Ti b Cr 1-b N x O y The coating method is as follows: Nitrogen gas is introduced into the reaction chamber to maintain the pressure in the reaction chamber at 3 Pa; a titanium target and / or a chromium target are used as the target material; the arc current is controlled at 120 A, the DC bias voltage of the substrate is -90 V to -130 V, and the sputtering time of the TiCr transition layer is 1 to 8 min; Ti is then sputtered. a Cr 1-a / Ti b Cr 1-b N x O y The total energy of the multi-layer system is 300Ah, with different cycles alternating sequentially, in the order of 4 cycles and 8 cycles.

[0024] In this technical solution, the increase of the alternation period, Ti a Cr 1-a / Ti b Cr 1-b N x O y In multi-layer coatings, there are more interfaces and thinner intermediate layers. The diameter of columnar structures in the coating decreases as the coating thickness decreases. Furthermore, the increased number of interfaces helps to block pinholes or columnar structures, significantly reducing the number of penetration corrosion channels and effectively improving the corrosion resistance of the bipolar plate. In corrosion resistance tests conducted under the conditions of 0.5M H₂SO₄ + 2ppm HF and 80℃, the bipolar plate exhibiting the most ideal corrosion resistance was obtained using an alternating cycle of 8 cycles.

[0025] Preferably, as an improvement, in S3, the lattice mismatch between the TiCr transition layer and the stainless steel substrate is <6%.

[0026] In this technical solution, Ti is controlled a Cr 1-a The lattice mismatch degree of stainless steel, and the use of alternating energy bombardment, are beneficial for suppressing Ti. aCr 1-a / Ti b Cr 1-b N x O y The porosity of the outer layer makes multilayer Ti a Cr 1-a / Ti b Cr 1-b N x O y The coating is more compact. Through extensive experimentation, the inventors discovered that controlling Ti... a Cr 1-a When the lattice mismatch with stainless steel is less than 6%, the corrosion resistance of the coating is effectively improved.

[0027] Preferably, as an improvement, the application of a multilayer coated stainless steel bipolar plate in the preparation of a proton exchange membrane fuel cell.

[0028] In this technical solution, a multi-arc ion plating technique with a high deposition rate is used to deposit a TiCr transition layer and TiCrN on a stainless steel bipolar plate. x O y The coating is prepared by alternating cycles, which modulates the structure of the multilayer coating to obtain a uniform, dense coating with high adhesion. Reducing the thickness between layers suppresses the formation of columnar structures. Furthermore, the dense surface structure of the multilayer coating reduces the probability of defect formation, the transition layer forms a stable interface barrier, and the multilayer structure blocks grain boundaries in columnar structures, eliminating porosity and effectively improving the corrosion resistance and post-corrosion conductivity of the stainless steel substrate. Optimization of alternating cycles significantly improves the stability of the coating, including a significant reduction in corrosion current density, a reduction in long-term corrosion current density under constant potential, and a significant reduction in surface contact resistance decay. The overall coating preparation rate is fast, the process is easy to control, and it can significantly improve the performance of bipolar plates, thereby extending the service life of fuel cells.

[0029] In summary, the principle and advantages of this solution are: This technical solution adopts multi-arc ion plating technology, which sputters multiple layers of Ti onto the surface of a stainless steel substrate through DC reaction. a Cr 1-a / Ti b Cr 1-b N x O y Coating (TiCr transition layer and TiCrN) x O y(Layer). Compared to stainless steel bipolar plates, the modified bipolar plate in this technical solution has a stable interface barrier formed by the transition layer. The multilayer structure can block the grain boundaries in the columnar structure, eliminating the formation of pores and effectively improving corrosion resistance and post-corrosion conductivity. Characterization of the surface morphology, corrosion resistance, and conductivity of the prepared coating revealed that the prepared coating surface forms a continuous and uniform structure. In a 0.5 mol / L H2SO4 + 2 ppm HF solution at 80℃, air was introduced to simulate the working environment of PEMFC. Potentiodynamic polarization testing showed that the corrosion current density decreased to Ti. a Cr 1-a / Ti b Cr 1-b N x O y The coating has a capacity of 0.047 μA / cm. 2 Meanwhile, after long-term constant potential (0.85V vs. SHE) polarization curve testing, Ti a Cr 1-a / Ti b Cr 1-b N x O y The corrosion current density of the coating is as low as 0.055 μA / cm. 2 At 140 N / cm 2 Under the clamping force, the interfacial contact resistance between the bipolar plate and the gas diffusion layer is as low as 4.8 mΩ·cm. 2 .

[0030] During the technology research and development phase, controlling the lattice mismatch between the TiCr layer and the stainless steel substrate is one of the key factors affecting coating performance. The inventors discovered during the research and development stage that the lower the lattice mismatch between TiCr and stainless steel, the better the resulting Ti... a Cr 1-a / Ti b Cr 1-b N x O y The lower the corrosion current density of the coating, the better its corrosion resistance. However, the lattice mismatch between TiCr and stainless steel is greatly affected by the composition and sputtering process. This technical solution, through extensive research and development to control the distance between the sample and the target and the composition of TiCr, found that when the lattice mismatch between the TiCr layer and stainless steel is <6%, the coating can simultaneously achieve excellent corrosion resistance. When the lattice mismatch between TiCr and stainless steel is 8.64% to 15.71%, it is difficult for the coating to simultaneously achieve excellent corrosion resistance.

[0031] In addition, the number of coating layers and Ti b Cr 1-b N x O yControlling the layer thickness is another key technology affecting coating performance. This technical solution designs a TiCr / Ti... b Cr 1-b N x O y In multilayer coatings, to ensure coating preparation efficiency, the total sputtering energy was set to 300 Ah, and the total coating thickness was 2.95-4.59 μm. The TiCr sputtering time was 1 min, and the thickness was controlled at approximately 0.03 μm. Furthermore, the study found that the number of sputtering cycles has a crucial influence on coating thickness, corrosion current density, and corrosion resistance stability, and this influence is non-linear. When the number of sputtering cycles is 1, although Ti... b Cr 1-b N x O y The layer thickness is relatively thick, reaching 2.92 μm, and the corrosion current density is relatively high, reaching 0.185 μA / cm. 2 However, its long-term corrosion resistance is poor, and obvious corrosion pits appear on the surface after corrosion. Figure 8 However, more alternations are not necessarily better. When the number of alternations is high (16 times), although the corrosion resistance current is significantly increased, the corrosion density is significantly reduced to 0.072 μA / cm³. 2 It exhibits good long-term corrosion resistance and stability, with no obvious corrosion pits appearing on the surface after corrosion. Figure 8 However, each Ti layer b Cr 1-b N x O y The thickness is relatively thin, only 0.26 μm. When the number of alternations is 8, Ti b Cr 1- b N x O y With moderate thickness, the corrosion current density was significantly reduced to 0.047 μA / cm. 2 It exhibits good long-term corrosion resistance and stability, with no obvious corrosion pits appearing on the surface after corrosion. Figure 8 ).

[0032] This technical solution directly deposits multiple layers of Ti on a stainless steel substrate. a Cr 1-a / Ti b Cr 1-b N x O y The coating is applied, and the transition layer composition is controlled to be 0.10≤a≤0.24, Ti b Cr 1-b N x O yWith a composition of 0.17≤b≤0.36, 1.02≤x≤1.08, and 0.17≤y≤0.21, and an alternation cycle of 4 to 8 cycles, excellent corrosion resistance and electrical conductivity can be obtained simultaneously. Attached Figure Description

[0033] Figure 1 These are XPS full spectra of Examples 1-2 and Comparative Examples 1-3 of the present invention.

[0034] Figure 2 The XRD spectra are those of Examples 1-2 and Comparative Examples 1-3 of the present invention.

[0035] Figure 3 The images are SEM images of the surface-modified bipolar plates of Examples 1-2 and Comparative Examples 1-3 of this invention.

[0036] Figure 4 The images shown are cross-sectional SEM images of the bipolar plates after surface modification in Examples 1-2 and Comparative Examples 1-3 of this invention.

[0037] Figure 5 The figures are potentiodynamic polarization curves of Examples 1-2 and Comparative Examples 1-3 of the present invention under a simulated 80℃ PEMFC cathode working environment.

[0038] Figure 6 The above are the potentiodynamic polarization curves of Embodiment 3 and Comparative Examples 4-7 of the present invention under a simulated 80℃ PEMFC cathode working environment.

[0039] Figure 7 The graphs are constant potential polarization curves of Embodiment 2 and Comparative Example 1 of the present invention under a simulated 80℃ PEMFC cathode working environment.

[0040] Figure 8 These are surface SEM images after constant potential polarization tests in Embodiment 2, Comparative Example 1, and Comparative Example 3 of the present invention. Detailed Implementation

[0041] The following detailed description provides further details on specific embodiments, but the embodiments of the present invention are not limited thereto. Unless otherwise specified, the technical means used in the following embodiments are conventional means well known to those skilled in the art; the experimental methods used are all conventional methods; and the materials and reagents used are all commercially available.

[0042] Overview of the plan:

[0043] A multilayer coated stainless steel bipolar plate includes a stainless steel substrate and a Ti layer disposed on the surface of the stainless steel substrate. a Cr 1-a / Ti b Cr 1-b N x Oy The coating consists of multiple layers; where 0.10≤a≤0.24, 0.17≤b≤0.36, 1.02≤x≤1.08, and 0.17≤y≤0.21. The stainless steel substrate is a 27×27×0.1mm 316L stainless steel sheet; multiple layers of Ti... a Cr 1-a / Ti b Cr 1-b N x O y The overall thickness of the coating is 2.95-4.59μm.

[0044] A method for preparing a multilayer coated stainless steel bipolar plate includes the following steps:

[0045] S1: The stainless steel substrate was ultrasonically cleaned with acetone and anhydrous ethanol for 30 minutes each to remove the grease on the surface of the stainless steel sheet. Then it was dried in an 80℃ vacuum drying oven for later use to obtain the pretreated stainless steel substrate.

[0046] S2: Sputter cleaning is performed on the pretreated stainless steel substrate to obtain the stainless steel substrate to be coated; the specific operation of sputter cleaning is as follows: the pretreated stainless steel substrate is placed in the reaction chamber, and the vacuum degree of the reaction chamber is adjusted to 4.0×10 -3 Pa; then argon gas is introduced into the reaction chamber and the pressure inside the reaction chamber is maintained at 1 Pa; the DC bias voltage of the substrate for sputter cleaning is -250V, the time is 30min, and the target arc current is 80A;

[0047] S3: Multilayer TiCr / Ti is deposited on the surface of the stainless steel substrate to be coated using multi-arc ion plating technology. a Cr 1-a N x O y The coating process is as follows: Nitrogen gas is introduced into the reaction chamber to maintain a pressure of 3 Pa; a titanium and / or chromium target is used as the target material; the arc current is controlled at 120 A, the DC bias voltage of the substrate is -100 V, and the sputtering time of the TiCr transition layer is 1 min; Ti is then sputtered. a Cr 1-a / Ti b Cr 1-b N x O y The total energy of the multilayer is 300 Ah, with different cycles alternating sequentially (4 cycles and 8 cycles in sequence), and the lattice mismatch between the TiCr transition layer and the stainless steel substrate is <6%.

[0048] A surface-modified stainless steel bipolar plate is used in a proton exchange membrane fuel cell.

[0049] Example 1

[0050] A method for preparing a multilayer coated stainless steel bipolar plate includes the following steps:

[0051] S1: Clean the 316L stainless steel sheet (27×27×0.1mm) with acetone and anhydrous ethanol for 30 minutes each to remove the grease from the surface of the stainless steel sheet, and then dry it in an 80℃ vacuum drying oven for later use.

[0052] S2: Place the dried stainless steel sheet into the chamber of the multi-arc ion plating instrument, and simultaneously install a titanium target and a chromium target onto the chamber. Close the chamber door. Then, evacuate the vacuum to 4.0 × 10⁻⁶. -3 Argon gas was introduced and the pressure inside the chamber was maintained at 1 Pa for sputter cleaning of the stainless steel substrate surface (i.e., the surface of the stainless steel sheet). The sputter cleaning process was performed with a target arc current of 80 A and a substrate DC bias of -250 V. Ti was then prepared. a Cr 1-a When preparing the transition layer thin film, the sputtering time is 1 minute to prepare Ti. b Cr 1-b N x O y When sputtering thin films, the total sputtering energy is 300 Ah, alternating 4 times. The ion concentration in the cavity is uniform, and the prepared thin film has uniform content. There are no requirements for the target-substrate distance.

[0053] S3: Using titanium and chromium targets as raw materials, a transition TiCr coating is deposited via DC reactive sputtering. The target arc current is set to 120A, the substrate DC bias voltage to -100V, and the sputtering time to 1 minute. Nitrogen gas is introduced, and TiCr is deposited via DC reactive sputtering using titanium and chromium targets, nitrogen gas, and residual oxygen in the chamber as raw materials. b Cr 1-b N x O y For the coating deposition process, the nitrogen pressure was maintained at 3 Pa, the target arc current was set to 120 A, the substrate DC bias voltage was set to -100 V, the total sputtering energy was 300 Ah, and the deposition was carried out alternately 4 times.

[0054] Surface-modified stainless steel bipolar plates were obtained through S1 to S3 treatments, with TiCr / Ti modified onto the upper and lower surfaces of the stainless steel substrate. a Cr 1-a N x O y Coating.

[0055] Example 2

[0056] The total sputtering energy in this embodiment is 300 Ah, and the TiCr transition layer sputtering time is 1 minute. The difference from Embodiment 1 is that in this embodiment, the deposition is carried out alternately 8 times, and the energy of each alternating sputtering is 37.5 Ah.

[0057] Example 3

[0058] The total sputtering energy in this embodiment is 300 Ah, and the TiCr transition layer sputtering time is 1 minute. The difference from Embodiment 1 is that in this embodiment, the deposition is carried out alternately 4 times, and the energy of each alternating sputtering is 75 Ah.

[0059] Comparative Example 1

[0060] The total sputtering energy of this comparative example is 300 Ah, and the sputtering time of the TiCr transition layer is 1 minute. The difference from Example 1 is that the deposition is alternating once.

[0061] Comparative Example 2

[0062] The total sputtering energy of this comparative example is 300 Ah, and the sputtering time of the TiCr transition layer is 1 minute. The difference from Example 1 is that the deposition is carried out alternately twice.

[0063] Comparative Example 3

[0064] The total sputtering energy of this comparative example is 300 Ah, and the sputtering time of the TiCr transition layer is 1 minute. The difference from Example 1 is that: the alternating deposition is performed 16 times, and the energy of each alternating sputtering is 18.75 Ah.

[0065] Comparative Examples 4-7

[0066] Comparative Examples 4-7 were essentially the same as Example 1, with a total sputtering energy of 300 Ah and a TiCr transition layer sputtering time of 1 minute, alternating deposition four times. The only difference from Example 1 was that the distance between the stainless steel substrate (stainless steel sheet) and the titanium and chromium targets changed during the deposition of the TiCr transition layer. The content of Ti and Cr elements was adjusted by regulating the target distance. The specific settings for Comparative Examples 4-7 are detailed in Table 1.

[0067] Table 1. Elemental contents of the TiCr transition layers in Examples 1-3 and Comparative Examples 1-7

[0068]

[0069]

[0070] The elemental content and composition of the TiCr transition layer prepared in Examples 1-3 and Comparative Examples 1-7, as well as the elemental content and film composition of the outermost layer, are detailed in Table 2. The relative elemental content of the transition layer is calculated as follows: Ti = Ti(at.%) / (Ti(at.%) + Cr(at.%)); Cr = Cr(at.%) / (Ti(at.%) + Cr(at.%)); x = N(at.%) / (Ti(at.%) + Cr(at.%); y = O(at.%) / (Ti(at.%) + Cr(at.%)).

[0071] Table 2. Elemental content and composition of the TiCr transition layers in Examples 1-3 and Comparative Examples 1-7

[0072]

[0073] As shown in Table 1-2, the multilayer Ti prepared in Example 1 a Cr 1-a / Ti b Cr 1-b N x O y The coating, with the inner layer composed of Ti, is a high-performance coating. 0.24 Cr 0.76 outer Ti b Cr 1-b N x O y The contents of Ti, Cr, N, and O elements in the coating are 11.58 at.%, 32.99 at.%, 47.20 at.%, and 8.23 ​​at.%, respectively. The composition of the film is Ti. 0.24 Cr 0.76 / Ti 0.26 Cr 0.74 N 1.05 O 0.18 The eight-layer thin film prepared in Example 2 has a Ti composition. 0.23 Cr 0.77 / Ti 0.17 Cr 0.83 N 1.08 O 0.21 The thin film prepared in Example 3 has a Ti composition. 0.10 Cr 0.90 / Ti 0.18 Cr 0.82 N 1.02 O 0.17 The thin film prepared in Comparative Example 1 has a Ti composition. 0.25 Cr 0.75 / Ti 0.35 Cr 0.65 N 1.02 O 0.17 The thin film prepared in Comparative Example 2 has a Ti composition.0.25 Cr 0.75 / Ti 0.36 Cr 0.64 N 1.02 O 0.17 The thin film prepared in Comparative Example 2 has a Ti composition. 0.24 Cr 0.76 / Ti 0.42 Cr 0.58 N 1.02 O 0.15 The thin film prepared in Comparative Example 4 has a Ti composition. 0.79 Cr 0.21 / Ti 0.75 Cr 0.25 N 1.01 O 0.14 The thin film prepared in Comparative Example 5 has a Ti composition. 0.77 Cr 0.23 / Ti 0.61 Cr 0.39 N 1.02 O 0.12 The thin film prepared in Comparative Example 6 has a Ti composition. 0.66 Cr 0.34 / Ti 0.48 Cr 0.52 N 1.05 O 0.13 The thin film prepared in Comparative Example 7 has a Ti composition. 0.52 Cr 0.48 / Ti 0.36 Cr 0.64 N 1.3 O 0.12 .

[0074] Experimental Example 1

[0075] The lattice mismatch (lattice mismatch degree) between the TiCr layers prepared in Examples 1-3 and Comparative Examples 1-7 and the stainless steel substrate was tested, and the results are shown in Table 3:

[0076] Table 3. Lattice mismatch between the inner TiCr layer and the stainless steel substrate in Examples 1-3 and Comparative Examples 1-7

[0077] project Lattice mismatch Example 1 5.76％ Example 2 5.25％ Example 3 1.56％ Comparative Example 1 5.85％ Comparative Example 2 5.93％ Comparative Example 3 5.58％ Comparative Example 4 15.71％ Comparative Example 5 12.62％ Comparative Example 6 10.15％ Comparative Example 7 8.64％

[0078] The formula for calculating the crystal mismatch is δ=(|d1–d2|) / d2, where δ is the lattice mismatch, and d1 and d2 are the interplanar spacings of the substrate and coating, respectively. d1 is the (110) interplanar spacing of the stainless steel base layer, and d2 is the (311) interplanar spacing of the TiCr intermediate layer.

[0079] Experimental Example 2

[0080] X-ray photon energy and X-ray diffraction analyses were performed on the thin films prepared in Examples 1-2 and Comparative Examples 1-3, and the results are as follows: Figure 1 , Figure 2 As shown. From Figure 1 , Figure 2 It can be seen that the outermost layer of the coating in Examples 1-3 forms a solid solution, with a preferred orientation along the (111) crystal plane. The outermost layer of the coating in Comparative Examples 1-2 also forms a solid solution, with a preferred orientation along the (111) crystal plane.

[0081] Experimental Example 3

[0082] Scanning electron microscopy analysis was performed on the surface-modified bipolar plates of Examples 1-2 and Comparative Examples 1-3, and the results are as follows: Figure 3 As shown. From Figure 3 It can be seen that the coatings prepared in Examples 1-2 have smooth surfaces, are tightly bonded to the titanium substrate, and have a total thickness of 3.24 μm.

[0083] Experiment Example 4

[0084] Scanning electron microscopy analysis was performed on the cross-sections of the surface-modified bipolar plates of Examples 1-2 and Comparative Examples 1-3. The results are as follows: Figure 4 As shown.

[0085] Experimental Example 5: Corrosion Performance Test

[0086] The bipolar plates prepared in Examples 1-3 and Comparative Examples 1-7 were subjected to potentiodynamic polarization tests in a simulated PEMFC cathode working environment (0.5 MH₂SO₄ + 2 ppm HF, 80 °C, air). Potential dynamic polarization was performed using the TAFEL-Tafel plot. Within a certain voltage range, the test current varied with the potential. The scan rate was set to 0.3 mV / s during the test, and the resulting curve was called the potentiodynamic polarization curve. The corrosion current could be extrapolated from the TAFEL curve using the formula (E... corr The calculation is performed using (a + b Logi). The linear portions (Tafel region) of the cathode and anodic side curves are fitted, and their extensions intersect at a single point. The potential at this intersection is the corrosion potential, and the corresponding current is the corrosion current. The test results are as follows: Figure 5-7 And as shown in Table 4. The results show that the corrosion potential and current density of the coating in Example 1 are 0.61 V (vs. SHE) and 0.058 μA / cm, respectively. 2 Furthermore, the corrosion current density of Examples 1-3 was significantly lower than that of the comparative examples. Moreover, since the lattice mismatch of Comparative Examples 4-7 was >6%, the corrosion potential was significantly reduced and the corrosion current density was significantly increased.

[0087] Table 4 shows the test results of corrosion resistance of Examples 1-3 and Comparative Examples 1-7.

[0088] project Corrosion potential (V vs. SHE) <![CDATA[Corrosion current density (μA / cm 2 )]]> Example 1 0.610 0.058 Example 2 0.615 0.047 Example 3 0.605 0.078 Comparative Example 1 0.715 0.187 Comparative Example 2 0.645 0.153 Comparative Example 3 0.41 0.072 Comparative Example 4 0.045 2.678 Comparative Example 5 -0.26 1.955 Comparative Example 6 0.092 0.947 Comparative Example 7 -0.196 0.812

[0089] Experimental Example 6

[0090] The bipolar plates prepared in Example 2 and Comparative Example 1 were subjected to constant potential polarization tests in a simulated PEMFC cathode working environment (0.5MH₂SO₄ + 2ppm HF, 80℃, air). The constant potential polarization test was performed using an IT program, which measures the change in current over time at a constant potential, primarily to study the stability and durability of the coating. The constant potential polarization test was conducted in a simulated PEMFC cathode working environment for 10 hours. The results are as follows: Figure 7 As shown, Figure 7 It can be seen that the corrosion current density of Comparative Example 1 is significantly higher than that of Example 2.

[0091] Experimental Example 7

[0092] After performing constant potential polarization tests on the bipolar plates of Example 2, Comparative Example 1, and Comparative Example 3, their surfaces were analyzed by scanning electron microscopy. The results are as follows: Figure 8 As shown. From Figure 8 It can be seen that no obvious corrosion pits appeared on the coating surface after the test in Example 2, while obvious corrosion pits appeared on the coating surface after the test in Comparative Examples 1 and 3.

[0093] Experimental Example 8 Surface Contact Resistance

[0094] The surface contact resistance of the coatings prepared in Examples 1-3 and Comparative Examples 1-7 was tested according to GB / T3048.16. The test results are shown in Table 5. As can be seen from the data in Table 5, the surface contact resistance of the coatings prepared in each example and comparative example was 140 N / cm. 2 Under pressure, the interfacial contact resistance between the coating layer and the carbon paper is 4.21–7.81 mΩ·cm. 2 All meet the DOE2020 standard (ICR < 10 mΩ·cm). 2 ).

[0095] Table 5

[0096] Group <![CDATA[Surface contact resistance (mΩ·cm 2 )]]> Example 1 4.80 Example 2 4.90 Example 3 7.81 Comparative Example 1 4.21 Comparative Example 2 4.53 Comparative Example 3 5.33 Comparative Example 4 4.21 Comparative Example 5 4.62 Comparative Example 6 5.16 Comparative Example 7 5.93

[0097] The above descriptions are merely embodiments of the present invention, and common knowledge such as specific technical solutions and / or characteristics are not described in detail here. It should be noted that those skilled in the art can make various modifications and improvements without departing from the technical solutions of the present invention, and these should also be considered within the scope of protection of the present invention. These modifications and improvements will not affect the effectiveness of the implementation of the present invention or the practicality of the patent. The scope of protection claimed in this application should be determined by the content of its claims, and the specific embodiments described in the specification can be used to interpret the content of the claims.

Claims

1. A multi-layer coated stainless steel bipolar plate, characterized in that: Includes a stainless steel substrate and Ti deposited on the surface of the stainless steel substrate. a Cr 1-a / Ti b Cr 1-b N x O y Multilayer coating; wherein 0.10≤a≤0.24, 0.17≤b≤0.36, 1.02≤x≤1.08, 0.17≤y≤0.21; multilayer Ti a Cr 1-a / Ti b Cr 1-b N x O y The overall thickness of the coating is 2.95-4.59 μm; multiple layers of Ti are deposited on the surface of the stainless steel substrate. a Cr 1-a / Ti b Cr 1-b N x O y The coating method is as follows: nitrogen gas is introduced into the reaction chamber to maintain the pressure in the reaction chamber at 3 Pa; a titanium target and / or a chromium target are used as the target material; the arc current is controlled at 120 A, the DC bias voltage of the substrate is -90 V to -130 V, and the sputtering time of the TiCr transition layer is 1 to 8 min; Ti is sputtered... a Cr 1-a / Ti b Cr 1-b N x O y The total energy of the multilayer is 300Ah, with different cycles alternating sequentially, and the alternation of different cycles is 4 or 8 cycles; the lattice mismatch between the TiCr transition layer and the stainless steel substrate is <6%.

2. The multi-layer coated stainless steel bipolar plate according to claim 1, characterized in that: The stainless steel substrate is a 316L stainless steel sheet.

3. A method for preparing a multilayer coated stainless steel bipolar plate according to any one of claims 1 to 2, characterized in that, Includes the following steps: S1: Ultrasonic cleaning is performed on the stainless steel substrate to obtain a pretreated stainless steel substrate. S2: Sputter cleaning is performed on the pretreated stainless steel substrate to obtain the stainless steel substrate to be coated; S3: Multilayer TiCr / Ti is deposited on the surface of the stainless steel substrate to be coated using multi-arc ion plating technology. a Cr 1-a N x O y Coating.

4. The method for preparing a multilayer coated stainless steel bipolar plate according to claim 3, characterized in that: In S1, the specific operation of ultrasonic cleaning is as follows: the stainless steel substrate is ultrasonically cleaned with acetone and anhydrous ethanol for 30 minutes each.

5. The method for preparing a multilayer coated stainless steel bipolar plate according to claim 4, characterized in that: In S1, after ultrasonic cleaning, the product undergoes drying treatment under vacuum drying conditions at 80°C.

6. A method for preparing a multilayer coated stainless steel bipolar plate according to claim 5, characterized in that: In S2, the specific operation of sputter cleaning is as follows: The stainless steel substrate is placed in the reaction chamber, and the vacuum degree of the reaction chamber is adjusted to 4.0~9.0×10⁻⁻¹. 3 Pa; then argon gas is introduced into the reaction chamber and the pressure inside the reaction chamber is maintained at 1 Pa; the DC bias voltage of the substrate for sputter cleaning is -300~-200V, the time is 20~30min, and the target arc current is 80A~100A.

7. The application of a multilayer coated stainless steel bipolar plate according to any one of claims 1 to 2 in the preparation of a proton exchange membrane fuel cell.

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