Conductive corrosion-resistant coating of bipolar plate and preparation method of conductive corrosion-resistant coating

Abstract

The invention provides a bipolar plate conductive corrosion-resistant coating and a preparation method thereof.The preparation method comprises the following steps that a high-power pulse magnetron sputtering method is adopted, a FeCoNiCr target material serves as a sputtering target material, negative bias voltage is applied to a stainless steel base body subjected to surface cleaning treatment, target voltage is applied to the FeCoNiCr target material, and the stainless steel base body is subjected to surface cleaning treatment; the method comprises the following steps of: 1) sputtering and depositing a FeCoNiCr layer on the surface of the stainless steel substrate by taking Ar as working gas; and (2) in the mixed atmosphere of Ar and C2H2, deposition continues to be conducted, and the FeCoNiCrCx layer is obtained. The bottom layer close to the base body is designed to be a FeCoNiCr solid solution mainly comprising metallic bonds, it is ensured that tough metallurgical bonding is formed between the coating and the base body, and crucial plasticity and toughness support is provided for follow-up punch forming. The final surface of the coating is a high-carbon-content area, so that the corrosion resistance of the coating in an acid environment is remarkably improved, extremely low interface contact resistance is ensured, and high hardness also brings good wear resistance. The coating can avoid cracks or peeling in the high-strain punch forming process, and the industrial efficient production requirement is met.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of surface modification of proton exchange membrane fuel cell (PEMFC) bipolar plates, and particularly relates to a bipolar plate conductive corrosion-resistant coating and a preparation method. BACKGROUND

[0002] Proton exchange membrane fuel cell (PEMFC) can efficiently convert chemical energy into electrical energy, and has the advantages of high energy density, low working temperature, small noise and zero emission. As a key technology for promoting green economic transformation, PEMFC will play an important role in electric vehicles, portable power systems and other applications. In a PEMFC stack, the bipolar plate (BP) is a multifunctional core component, which is responsible for distributing reaction gases, collecting current, providing mechanical support and integrating single cells. In order to continuously operate in a highly acidic (H + , SO4 2- , F - ion), humid and high temperature (60-80℃) working environment, the bipolar plate must have excellent corrosion resistance, interfacial conductivity, thermal conductivity and mechanical strength. Stainless steel has become the preferred material for bipolar plates (BPs) due to its excellent corrosion resistance, mechanical properties and cost-effectiveness. However, aggressive ions (such as SO4 2- and F - ) can cause localized corrosion, and the leaching of metal ions during the corrosion process can poison the membrane electrode assembly, and the generated metal oxides significantly increase the interfacial contact resistance (ICR) between the bipolar plate and the gas diffusion layer (GDL). These phenomena will reduce the service life and efficiency of PEMFC. To solve the above problems, surface coating modification of stainless steel bipolar plates has become a key link in the development of PEMFC technology. In the physical vapor deposition (PVD) technology, magnetron sputtering technology provides an economical and efficient solution for large-scale production of stainless steel bipolar plate coatings due to its mature industrial application characteristics.

[0003] Currently, PVD modified bipolar plates (BPs) coating includes noble metals (such as Au, Pt, Ag), transition metal nitrides / carbonides (such as TiN, ZrN, CrN), and carbon-based coatings. Although noble metal coatings exhibit excellent corrosion resistance, their high cost limits industrial-scale applications. Ceramic and carbon-based coatings can achieve lower interfacial contact resistance and effectively suppress corrosion, but the coating has the problem of poor adhesion to the substrate. Especially in the industrial production mode of coating first and then forming, the coating is prone to peeling, resulting in shortened battery life and reduced performance. In industrial production, the production mode of coating first and then forming of stainless steel bipolar plates can achieve efficient mass production and improve overall production efficiency, which is more economically beneficial. This production mode puts higher requirements on the performance of the coating, which needs to meet the performance indicators of corrosion resistance, electrical conductivity, toughness, and good film-substrate adhesion.

[0004] FeCoNiCr-based high-entropy alloy as an emerging coating material has excellent corrosion resistance and toughness, but in the acidic environment of the battery, a dense passivation film (such as Cr2O3, F2O3, etc.) will be generated on its surface. These passivation films have semiconductor properties, which cause the surface electrical conductivity to decrease and the interfacial contact resistance to increase, limiting their application in bipolar plates. This key technical bottleneck needs to be solved through material innovation and surface engineering strategies. SUMMARY

[0005] Based on the above background, the present application aims to provide a high-entropy alloy coating suitable for the stainless steel bipolar plate coating first and then stamping process and a preparation method thereof. Using high-power pulsed magnetron sputtering (HiPIMS) technology, a coating with excellent corrosion resistance, low interfacial contact resistance, and good mechanical toughness is prepared, and cracks or peeling during high-strain stamping forming can be avoided, thereby meeting the needs of industrial high-efficiency production.

[0006] The application adopts the following technical solutions: A preparation method of a bipolar plate conductive corrosion-resistant coating, comprising the following steps: A high-power pulsed magnetron sputtering method is used, FeCoNiCr target material is used as the sputtering target, negative bias is applied to the stainless steel substrate after surface cleaning treatment, target voltage is applied to the FeCoNiCr target, and coating deposition is carried out: (1) First, Ar is used as the working gas to sputter deposit a FeCoNiCr layer on the surface of the stainless steel substrate; (2) Then, in an Ar and C2H2 mixed atmosphere, continue to deposit to obtain a FeCoNiCrC x layer.

[0007] In the technical solution, the bottom layer (FeCoNiCr layer) close to the stainless steel substrate is designed to form a FeCoNiCr solid solution mainly with metal bonds, which can ensure a strong and tough metallurgical bonding between the coating and the substrate and provide important plasticity and toughness support for subsequent stamping forming. The final surface of the coating is a high-carbon content region rich in metal carbides and sp 2 The carbon cluster mainly functions to significantly improve the corrosion resistance of the coating in the acidic environment of the PEMFC and ensure extremely low interface contact resistance, and its high hardness also brings good wear resistance.

[0008] Optionally, before sputter deposition, the stainless steel substrate is sequentially cleaned with acetone and anhydrous ethanol to remove surface impurities; the cleaned and dried stainless steel substrate is placed on a sample table in a vacuum furnace cavity of a magnetron sputtering device, and the vacuum degree in the furnace cavity is maintained to be less than 2x10 -3 Pa for reverse sputtering plasma cleaning; and the FeCoNiCr target is pre-sputtered in an Ar gas atmosphere to remove impurities and oxides adsorbed on the surface of the target.

[0009] Optionally, the reverse sputtering plasma cleaning conditions are as follows: the sputtering gas is Ar, the sputtering gas pressure is 3.0 Pa, the sputtering bias is -1500 V, and the sputtering time is 15 min.

[0010] Optionally, after the reverse sputtering plasma cleaning of the stainless steel, the FeCoNiCr target is rapidly ignited by using a direct current power supply, and the FeCoNiCr target is pre-sputtered to remove oxides and adsorbed impurities on the surface of the target. The pre-sputtering conditions are as follows: an Ar gas atmosphere with a pressure of 0.5-0.6 Pa, a target power of 400-450 W, and a cleaning time of 20 min.

[0011] Optionally, the stainless steel substrate is a 316 austenitic stainless steel substrate.

[0012] As one of the embodiments, further, the atomic percentages of the metal elements Fe, Co, Ni, and Cr in the FeCoNiCr target are 1:1:1:1.

[0013] Optionally, the FeCoNiCr target is an alloy target.

[0014] As one of the embodiments, further, the bias voltage of the stainless steel substrate is -100 V to -50 V; the distance between the target and the stainless steel substrate is 70-90 mm, and the total sputtering time is 18-25 min.

[0015] As one of the embodiments, further, the gas pressure in the cavity is maintained to be 0.8-0.9 Pa during the sputtering process; and the Ar gas flow rate is controlled to be 40-50 sccm.

[0016] As one of the embodiments, further, the voltage 800V, frequency 200Hz, pulse width 150us, duty cycle 3% are adopted by using the HiPIMS power supply to apply voltage.

[0017] As one of the embodiments, further, the conductive corrosion-resistant coating of the bipolar plate is a double-layer structure or a gradient structure. When it is a double-layer structure, the FeCoNiCrC x layer deposition time is less than or equal to the deposition time of the FeCoNiCr layer; when depositing the FeCoNiCrC x layer, by controlling the C2H2 flow, the carbon content is gradually increased from bottom to top or the C2H2 flow is a fixed value to form a clear double-layer structure of the FeCoNiCrCx high-entropy alloy coating. When it is a gradient structure, the FeCoNiCrC x layer deposition time is significantly greater than the deposition time of the FeCoNiCr layer; when depositing the FeCoNiCrC x layer, by controlling the C2H2 flow, the carbon content is gradually increased from 0sccm linearly or according to a specific curve to a preset value during the deposition process to achieve a continuous gradient change.

[0018] As one of the embodiments, further, when the conductive corrosion-resistant coating of the bipolar plate is a double-layer structure, the FeCoNiCrC x layer is deposited, the C2H2 flow is a fixed value of 5sccm or the C2H2 flow is gradually increased by 1-4sccm, and the last deposited surface layer is a fixed value of 5sccm.

[0019] Further, when the C2H2 flow is gradually increased by 1-4sccm and the last deposited surface layer is a fixed value of 5sccm, the time of the last deposited surface layer is greater than any time of the 1-4sccm gradient.

[0020] As one of the embodiments, further, when the conductive corrosion-resistant coating of the bipolar plate is a gradient structure, the C2H2 flow is gradually increased by 0-5sccm.

[0021] The gradient structure of the conductive corrosion-resistant coating of the bipolar plate is that the carbon content in the coating continuously changes from bottom to top. The bottom layer close to the stainless steel substrate is designed as a low-carbon content region (close to 0 at %), mainly forming a FeCoNiCr solid solution dominated by metallic bonds, which can ensure that the coating and the substrate form a strong and tough metallurgical bond, and provide important plasticity and toughness support for subsequent stamping forming. From the bottom layer to the surface layer, the carbon content continuously increases in a gradient manner, forming an intermediate layer with smooth performance transition. In this region, non-carbide forming elements (such as Co and Ni) maintain the conductive and thermal conductive network of metallic bonds, while carbide forming elements (such as Cr and Fe) gradually form Me-C covalent bonds with carbon, gradually increasing the hardness of the coating, and also begin to generate beneficial sp 2 The carbon clusters preliminarily enhance the electrical conductivity. This design can effectively avoid interface failure caused by performance mutation. The final surface of the coating is a high-carbon content region rich in metallic carbides and sp 2 The carbon clusters mainly function to significantly improve the corrosion resistance of the coating in the acidic environment of the PEMFC and ensure extremely low interface contact resistance, and the high hardness also brings good wear resistance. The continuous gradient change of the composition and structure can alleviate the internal stress caused by the difference in material properties, thereby improving the bonding strength and service life of the coating.

[0022] Another object of the present application is to provide a conductive corrosion-resistant high-entropy alloy coating prepared by any one of the above-mentioned methods.

[0023] As one of the embodiments, further, the bipolar plate is an electrolytic water hydrogen production bipolar plate or a proton exchange membrane fuel cell bipolar plate.

[0024] The present application successfully solves the key technical problems in the "coating first and forming later" process, and brings many significant beneficial effects: (1) Significantly improving the comprehensive performance of the coating to meet the needs of severe applications Excellent electrical conductivity: a large number of metallic carbide nanocrystals and conductive sp carbon clusters are formed in the high-carbon content region on the surface of the coating. At the same time, the addition of carbon consumes easily passivated metal elements (such as Cr), effectively inhibiting the excessive growth of thick passivation films (such as Cr2O3) with poor electrical conductivity. The synergistic effect of the two ensures that the coating has extremely low interface contact resistance (ICR).

[0025] Excellent corrosion resistance: the doping of carbon promotes the formation of a dense amorphous structure in the coating, which has excellent thermodynamic stability and chemical inertness. In addition, a small amount of dense oxides such as Cr2O3 are generated, which together form an effective corrosion barrier, enabling the coating to exhibit strong corrosion resistance in the acidic environment of the PEMFC.

[0026] Good mechanical properties: the bottom layer is mainly composed of high-entropy alloy with face-centered cubic structure, which is a ductile phase that can effectively inhibit the generation and propagation of cracks. The high-carbon layer of the surface layer is usually thin, and when subjected to external force, the deformation is mainly absorbed by the ductile bottom layer, thereby ensuring that the overall coating is not easily broken or peeled off during subsequent stamping forming.

[0027] (2) Adapt to efficient "coating first and then forming" industrial production process The coating prepared by the application forms a firm metallurgical bond with the substrate through the design of the tough bottom layer, solving the pain points of poor adhesion and easy failure of traditional coatings under this process. This enables the bipolar plate to be coated with a large area and high efficiency first, and then stamped and formed, greatly improving the production efficiency and economic benefits.

[0028] (3) Using the mature and scalable industrial technology of HiPIMS, the preparation of high-performance coatings is realized through the design of composition and structure rather than the addition of expensive elements such as Au and Pt. This technical solution not only has reliable performance, but also has significant cost advantages and application potential, providing strong technical support for the industrialization development of PEMFC. BRIEF DESCRIPTION OF DRAWINGS

[0029] Figure 1 The surface and cross-sectional morphology diagrams of the coating prepared in the present application Comparative Example 1 and Example 2 are shown.

[0030] Figure 2 The Vickers indentation morphology diagram of the coating prepared in the present application Comparative Example 1 and Examples 1-3 is shown. DETAILED DESCRIPTION

[0031] The present application will be specifically illustrated below in conjunction with the drawings: Comparative Example 1 In this comparative example, FeCoNiCrC high-entropy alloy coating was deposited on the surface of 316 austenitic stainless steel substrate material using HiPIMS technology. x The high-entropy alloy coating was prepared using a FeCoNiCr sputtering target with a purity of 99.9%, and the working gas Ar had a purity of 99.999%. The specific preparation process included the following steps: (1) Pretreatment of the substrate material: The 316 austenitic stainless steel was processed into a round sheet with a size of 16 mm x 16 mm x 0.5 mm. After polishing and smoothing, it was ultrasonically cleaned with acetone and anhydrous ethanol for 15 min, and then dried for use.

[0032] (2) Reverse sputtering cleaning of the substrate material: The pretreated 316 austenitic stainless steel substrate material was placed on the sample table in the vacuum furnace cavity of the magnetron sputtering equipment, and the vacuum degree in the furnace cavity was maintained at less than 2 x 10 -3Pa, the baffle is adjusted between the target and the substrate, then Ar gas is introduced, the sputtering pressure is kept at 3.0 Pa, the bias voltage is controlled at -1500 V, and the 316 austenitic stainless steel substrate is subjected to reverse sputtering cleaning for 15 min.

[0033] (3) Target pre-sputtering cleaning: Ar gas is continuously used as the working gas, the sputtering pressure is adjusted to 0.45 Pa, the FeCoNiCr target is rapidly ignited at a power of 450 W, and then pre-sputtering is performed for 20 min.

[0034] (4) Sputtering FeCoNiCrC x coating: Ar gas is continuously used as the working gas, the Ar gas flow is 40 sccm, a bias voltage of -50 V is applied, the 316 austenitic stainless steel substrate is not heated, the target-substrate distance is 80 mm, the sputtering pressure is adjusted to 0.8-0.9 Pa, the HiPIMS power supply applies a voltage of 800 V, a frequency of 200 Hz, a pulse width of 150 μs, and a duty cycle of 3%, a FeCoNiCr alloy transition layer is first deposited for 2 min, then C2H2 is introduced, the flow rate is 5 sccm, and the sputtering time is 20 min, i.e. a single-layer FeCoNiCrC x high-entropy alloy coating.

[0035] Comparative Example 2: In this comparative example, a FeCoNiCrC x high-entropy alloy coating is deposited on the surface of a 316 austenitic stainless steel substrate material using HiPIMS technology, a FeCoNiCr sputtering target with a purity of 99.9% is used, and the purity of the working gas Ar is 99.999%, and the specific preparation process includes the following steps: (1) Substrate material pretreatment: The same as Comparative Example 1.

[0036] (2) Reverse sputtering cleaning of the substrate material: The same as Comparative Example 1.

[0037] (3) Target pre-sputtering cleaning: The same as Comparative Example 1.

[0038] (4) Sputtering FeCoNiCrC x coating: The Ar gas is continuously used as the working gas, the Ar gas flow is 40 sccm, a bias voltage of-50 V is applied, the 316 austenitic stainless steel substrate is not heated, the target-substrate distance is 80 mm, the sputtering pressure is adjusted to 0.8-0.9 Pa, the HiPIMS power supply applies a voltage of 800 V, a frequency of 200 Hz, a pulse width of 150 μs, and a duty cycle of 3%, a FeCoNiCr alloy transition layer is first deposited for 2 min, then C2H2 is introduced at a flow rate of 4 sccm, and the sputtering time is 20 min, that is, a single-layer FeCoNiCrC x high-entropy alloy coating.

[0039] Comparative Example 3: In this comparative example, a FeCoNiCrC x high-entropy alloy coating is deposited on the surface of a 316 austenitic stainless steel substrate material by using a HiPIMS technique, wherein an FeCoNiCr sputtering target is used, the purity is 99.9%, and the purity of the working gas Ar is 99.999%, and the specific preparation process includes the following steps: (1) Pretreatment of the substrate material: The same as in Comparative Example 1.

[0040] (2) Reverse sputtering cleaning of the substrate material: The same as in Comparative Example 1.

[0041] (3) Pre-sputtering cleaning of the target material: The same as in Comparative Example 1.

[0042] (4) Sputtering of FeCoNiCrC x coating: The Ar gas is continuously used as the working gas, the Ar gas flow is 40 sccm, a bias voltage of-50 V is applied, the 316 austenitic stainless steel substrate is not heated, the target-substrate distance is 80 mm, the sputtering pressure is adjusted to 0.8-0.9 Pa, the HiPIMS power supply applies a voltage of 800 V, a frequency of 200 Hz, a pulse width of 150 μs, and a duty cycle of 3%, a FeCoNiCr alloy transition layer is first deposited for 2 min, then C2H2 is introduced at a flow rate of 4 sccm, and the sputtering time is 20 min, that is, a single-layer FeCoNiCrC x high-entropy alloy coating.

[0043] Example 1 (gradient structure): In this example, a FeCoNiCrC x high-entropy alloy coating with a gradient distribution of carbon content is deposited on the surface of a 316 austenitic stainless steel substrate material by using a HiPIMS technique, wherein an FeCoNiCr sputtering target is used, the purity is 99.9%, and the purity of the working gas Ar is 99.999%, and the specific preparation process includes the following steps: (1) Substrate pre-treatment: The same as Comparative Example 1.

[0044] (2) Substrate reverse sputter cleaning: The same as Comparative Example 1.

[0045] (3) Target pre-sputter cleaning: The same as Comparative Example 1.

[0046] (4) Sputtering FeCoNiCrC x high-entropy alloy coating: The FeCoNiCr alloy transition layer was deposited for 2 min using Ar gas as the working gas at a flow rate of 40 sccm, and then the reaction gas C2H2 was introduced, with the C2H2 flow rate increasing in a gradient (1, 2, 3, 4, and 5 sccm for 4 min each), the bias voltage was -50 V, the substrate was not heated, the target-substrate distance was 80 mm, the sputtering pressure was adjusted to 0.8-0.9 Pa, the high-power pulse power supply was applied at a voltage of 800 V, a frequency of 200 Hz, a pulse width of 150 μs, a duty cycle of 3%, and the sputtering time was 20 min, i.e., a FeCoNiCrC x high-entropy alloy coating with a gradient distribution of carbon content from low to high from bottom to top was obtained on the surface of the 316 austenitic stainless steel.

[0047] Example 2 (double-layer structure, C2H2 flow rate is a fixed value when depositing FeCoNiCrC x layer): In this example, the HiPIMS technology was used to deposit a double-layer FeCoNiCrC x high-entropy alloy coating on the surface of a 316 austenitic stainless steel substrate, and the target material and working gas were the same as in Example 1. The specific preparation process included the following steps: (1) Substrate pre-treatment: The same as Example 1.

[0048] (2) Substrate reverse sputter cleaning: The same as Example 1.

[0049] (3) Target pre-sputter cleaning: The same as Example 1.

[0050] (4) Sputtering double-layer FeCoNiCrC x high-entropy alloy coating: The Ar gas was continuously used as the working gas, the Ar gas flow was 40 sccm, the 316 austenitic stainless steel substrate was not heated, the target-substrate distance was 80 mm, the FeCoNiCr alloy layer was first deposited for 12 min, then the reaction gas C2H2 was introduced, the C2H2 flow was fixed at 5 sccm, the bias voltage was -50 V, the sputtering pressure was adjusted to 0.8-0.9 Pa, the high-power pulse power voltage was 800 V, the frequency was 200 Hz, the pulse width was 150 μs, the duty cycle was 3%, and the FeCoNiCrC x layer was prepared for 10 min, that is, the FeCoNiCr / FeCoNiCrC x bilateral high-entropy alloy coating was obtained on the surface of the 316 austenitic stainless steel.

[0051] Example 3 (bilateral structure, the C2H2 flow was gradually increased from 1 sccm when the FeCoNiCrC x layer was deposited): In this example, the HiPIMS technology was used to deposit the bilateral FeCoNiCrC x high-entropy alloy coating on the surface of the 316 austenitic stainless steel substrate material, the target material and the working gas were the same as in Example 1, and the specific preparation process included the following steps: (1) Pretreatment of the substrate material: The same as in Example 1.

[0052] (2) Reverse sputtering cleaning of the substrate material: The same as in Example 1.

[0053] (3) Pre-sputtering cleaning of the target material: The same as in Example 1.

[0054] (4) Sputtering of the bilateral FeCoNiCrC x high-entropy alloy coating: The Ar gas was continuously used as the working gas, the Ar gas flow was 40 sccm, the 316 austenitic stainless steel substrate was not heated, the target-substrate distance was 80 mm, the FeCoNiCr alloy layer was first deposited for 12 min, then the reaction gas C2H2 was introduced, the C2H2 flow was gradually increased (1, 2, 3 and 4 sccm were sequentially deposited for 1.5 min, and 5 sccm was deposited for 4 min), the bias voltage was -50 V, the sputtering pressure was 0.8-0.9 Pa, the high-power pulse power voltage was 800 V, the frequency was 200 Hz, the pulse width was 150 μs, the duty cycle was 3%, and the FeCoNiCrC x layer with gradually increased carbon content was deposited for 10 min, that is, the FeCoNiCr / gradient FeCoNiCrC x bilateral high-entropy alloy coating was obtained on the surface of the 316 austenitic stainless steel.

[0055] FeCoNiCrCx High-entropy alloy coating, mechanical properties, corrosion resistance and interface conductive performance characterization: (1) Structure, morphology characterization: The coating of the comparative example 1 and the examples was analyzed by scanning electron microscopy, and the results are shown in Figure 1 Fig. 1. It can be seen from the figure that the coating prepared in Example 2 has no defects, the surface is smooth and dense, and the coating thickness is uniform, about 900 nm. The comparative example 1 has a longer acetylene inlet time than Example 2, resulting in a "target poisoning" phenomenon, which reduces the deposition rate, and the final coating thickness is thinner.

[0056] (2) Indentation toughness: The coating was tested by Vickers hardness tester with a load of 10 N to evaluate its toughness and anti-cracking performance, and the results are shown in Figure 2 Fig. 2. The coating of the comparative example 1 has a high overall carbon content, generating a large amount of hard and brittle carbide, and after indentation, it appears serious fragmentation and serious failure; Example 1 (gradient structure) only produces circumferential microcracks; while Examples 2 and 3 (double-layer structure) only appear radial cracks, the indentation morphology is complete, and no macroscopic cracking is observed. This difference is attributed to the following mechanisms: a. Toughness bottom layer design: In the gradient or double-layer structure of the examples, the lower layer is a low-carbon metal phase (mainly FCC structure), which has good plastic deformation ability and can effectively absorb and disperse indentation stress.

[0057] b. Crack suppression effect: When the crack propagates to the interface between the upper high-carbon layer and the lower metal layer, the metal phase with better toughness can play a role in blocking the crack, changing the crack propagation path or making it stop. The results show that by adjusting the thickness and distribution of the carbon-containing layer (such as using a double-layer or gradient structure), the contradiction between high hardness and high toughness of the coating can be effectively coordinated, which is the key to realizing the "coating first and stamping later" process.

[0058] (3) Corrosion resistance: Under the conditions of simulated PEMFC acid, humidity, high temperature (H + , F - , SO4 2- , 70-80℃), the corrosion resistance of the coating was evaluated by potentiodynamic polarization test (-0.5V-+1.2V, 1mV / s) and 5 hours of constant potential polarization test. All the data of the test are shown in Table 2. The data after polarization test were subjected to Tafel fitting, respectively, to obtain the corresponding self-corrosion current density. In the potentiodynamic polarization, the i corr of comparative examples 1, 2 and 3 are 4.02E-8, 1.80E-7, 1.0E-7 A / cm 2 , respectively, and the i corr3.60E-8, 4.59E-8, 6.83E-8 A / cm 2 . In the potentiostatic polarization, the ICR of Comparative Examples 1, 2 and 3 were 3.52 mΩ·cm i corr 5.58E-8, 5.80E-7, 2.9E-7 A / cm 2 , respectively. The ICR of Examples 1, 2, 3 were 2.98 mΩ·cm i corr 2.34E-8, 4.07E-8, 4.53E-8 A / cm 2 It can be found that all the examples have lower self-corrosion current density compared to the comparative examples, indicating that the gradient coating and the double-layer coating have significantly better corrosion resistance than the coating with uniform carbon content, which is due to the composition and structural design of the examples, effectively solving the performance defects commonly found in uniform coatings. Although the overall carbon content of the uniform coating is consistent, continuous columnar crystal structures are easily formed during preparation, and micro-pores or cracks may be generated between the grain boundaries. These structural defects provide a direct path for the corrosion medium to reach the substrate, and the interface stress concentration caused by the difference in physical properties between the coating and the substrate also increases the risk of coating peeling. In contrast, the gradient coating achieves a continuous and gradual change in carbon content from the substrate to the surface, not only alleviating the interface stress and avoiding performance mutations, but more importantly, disrupting the directional and continuous growth of columnar crystals. This non-continuous structure can effectively block the penetration path of corrosion ions, making the coating more dense. The double-layer structure achieves a synergistic optimization of performance through clear functional layering, such as the bottom layer providing strong and tough bonding and the surface layer being responsible for corrosion resistance. This design provides a second line of defense even if the surface layer is locally breached, delaying the spread of corrosion to the substrate, thereby providing more durable and stable protection.

[0059] (5) Interfacial conductive properties of the coating: The interfacial conductive properties of the coating under simulated battery assembly force (1.4 MPa) were studied. The comparative examples and examples were placed in the middle of carbon paper using the "sandwich" method, and gold-plated copper electrodes were connected to an ammeter and a voltmeter. By continuously increasing the external load, the voltage and current changes were recorded, and finally the corresponding interfacial contact resistance values were calculated according to Ohm's law.

[0060] Table 2 shows the changes in the interfacial contact resistance (ICR) values between the coating and the carbon paper of the comparative examples and examples under a pressure of 1.4 MPa. The ICR of Comparative Examples 1, 2 and 3 before potentiostatic corrosion were 3.52 mΩ·cm 2 , 93.7 mΩ·cm 2 , 157.90 mΩ·cm 2 , respectively. The ICR of Examples 1, 2, 3 were 2.98 mΩ·cm 2, 2.93 mΩ·cm 2 , 319 mΩ·cm 2 . The ICR of Comparative Example 1, 2 and 3 after potentiostatic polarization were 6.49 mΩ·cm 2 , 110.8 mΩ·cm 2 , 400.30 mΩ·cm 2 ; The ICR of Example 1, 2, 3 were 10.64 mΩ·cm 2 , 4.17 mΩ·cm 2 , 13.1 mΩ·cm 2 . It can be found that the contact resistance values of Comparative Example 2 and 3 were much larger than Comparative Example 1 and Examples, indicating that when the carbon content on the coating surface is low, there are fewer conductive sites in the coating, which cannot provide good interface conductivity for the coating. The contact resistance values of Comparative Example 1 and Examples 1, 2, 3 are low, and high carbon content can form conductive carbides, and the excess carbon will gather to form a large number of sp 2 clusters. These conductive sp 2 clusters will be connected to each other to form a continuous conductive network in the entire amorphous coating, and electrons can preferentially transmit through this low-resistance network, thereby obtaining a low ICR. After potentiostatic test, the ICR of Example 2 increased the least, which was attributed to its high carbon content effectively inhibiting the oxidation of metal elements and reducing the generation of poor-conductive passivation film (such as Cr2O3). While the ICR of Comparative Example 2 increased significantly due to insufficient carbon content. Although the conductivity and corrosion resistance of Comparative Example 1 meet the performance requirements of bipolar plates, its mechanical properties are poor and cannot meet the process requirements of coating after forming; the surface contact resistance of Comparative Examples 2 and 3 is too high to meet the surface conductivity requirements of bipolar plates.

[0061] (6) Corrosion resistance after stamping: The corrosion resistance of the coating after stamping was evaluated by simulating the "coating after stamping" process by rubber pad forming method (75 kN load): the i corr of Example 1 after stamping was 7.52E-7 A / cm 2 , the i corr of Example 2 after stamping was 3.73E-7 A / cm 2 , and the i corr of Example 3 after stamping was 4.57E-7 A / cm 2 . It can be seen that all the coating layers of the examples still maintain excellent corrosion resistance after forming, among which Example 2 has the best performance. It indicates that the double-layer structure with high carbon content on the surface can still maintain close bonding with the substrate after plastic deformation, providing sustained corrosion protection.

[0062] Table 1 ; Table 2 ; Example 4: Deposition of FeCoNiCrC high-entropy alloy coating on 316 austenitic stainless steel substrate using HiPIMS technique x The FeCoNiCr sputtering target had a purity of 99.9%, and the working gas Ar had a purity of 99.999%. The specific preparation process included the following steps: (1) Pretreatment of the substrate material: The 316 austenitic stainless steel was sequentially ultrasonically cleaned with acetone and anhydrous ethanol, and then dried for use.

[0063] (2) Reverse sputtering cleaning of the substrate material: The pretreated 316 austenitic stainless steel substrate material was placed on the sample stage in the vacuum furnace cavity of the magnetron sputtering equipment, and the vacuum degree in the furnace cavity was maintained at less than 2 x 10 -3 Pa. Ar gas was introduced, the sputtering gas pressure was maintained at 3.0 Pa, the bias voltage was controlled at -1500 V, and the 316 austenitic stainless steel substrate was reverse sputtered for 15 min.

[0064] (3) Pre-sputtering cleaning of the target material: Ar gas was continuously used as the working gas, the sputtering gas pressure was adjusted to 0.5 Pa, the FeCoNiCr target was rapidly ignited at a power of 450 W, and then pre-sputtering was performed for 20 min.

[0065] (4) Sputtering of FeCoNiCrC high-entropy alloy coating with gradient change in carbon content: x Ar gas was continuously used as the working gas, the Ar gas flow was 40 sccm, a 2 min FeCoNiCr alloy transition layer was deposited, then the reaction gas C2H2 was introduced, the C2H2 flow gradient was increased (1, 2, 3, 4 sccm were sequentially deposited for 3 min, 5 sccm was deposited for 4 min), the bias voltage was -50 V, the substrate was not heated, the target-substrate distance was 80 mm, the sputtering gas pressure was adjusted to 0.8-0.9 Pa, the high-power pulse power supply applied a voltage of 800 V, a frequency of 200 Hz, a pulse width of 150 μs, a duty cycle of 3%, and the sputtering time was 16 min, thereby obtaining a FeCoNiCrC high-entropy alloy coating with a gradient distribution of carbon content from low to high on the surface of the 316 austenitic stainless steel from bottom to top. x

[0066] Example 5: Deposition of FeCoNiCrC high-entropy alloy coating on 316 austenitic stainless steel substrate using HiPIMS technique​​x A high-entropy alloy coating was prepared using a FeCoNiCr sputtering target with a purity of 99.9% and Ar gas with a purity of 99.999%. The specific preparation process included the following steps: (1) Pretreatment of the base material: The 316 austenitic stainless steel was sequentially cleaned with acetone and anhydrous ethanol by ultrasonic cleaning, and then dried for use.

[0067] (2) Reverse sputtering cleaning of the base material: The pretreated 316 austenitic stainless steel base material was placed on the sample table in the vacuum furnace cavity of the magnetron sputtering equipment, and the vacuum degree in the furnace cavity was maintained at less than 2x10 -3 Pa, the baffle was adjusted between the target and the base, then Ar gas was introduced, the sputtering gas pressure was maintained at 3.0 Pa, the bias voltage was controlled at -1500 V, and the 316 austenitic stainless steel base was reverse sputtered for 15 min.

[0068] (3) Pre-sputtering cleaning of the target: Continue to use Ar gas as the working gas, adjust the sputtering gas pressure to 0.6 Pa, and make the FeCoNiCr target glow rapidly at a power of 400 W, then pre-sputter for 20 min.

[0069] (4) Sputtering of double-layer FeCoNiCrC x High-entropy alloy coating: Continue to use Ar gas as the working gas, the Ar gas flow is 45 sccm, the 316 austenitic stainless steel base is not heated, the target-to-base distance is 80 mm, first deposit a 15 min FeCoNiCr alloy layer, then introduce the reaction gas C2H2, fix the C2H2 flow at 5 sccm, the bias voltage at -50 V, adjust the sputtering gas pressure to 0.8-0.9 Pa, and prepare a 10 min FeCoNiCrC x layer on the surface of the 316 austenitic stainless steel, i.e. FeCoNiCr / FeCoNiCrC x double-layer high-entropy alloy coating.

[0070] Example 6: A FeCoNiCrC x high-entropy alloy coating was deposited on the surface of a 316 austenitic stainless steel base material using HiPIMS technology. The FeCoNiCr sputtering target had a purity of 99.9%, and the Ar gas had a purity of 99.999%. The specific preparation process included the following steps: (1) Pretreatment of the base material: The 316 austenitic stainless steel was sequentially cleaned with acetone and anhydrous ethanol by ultrasonic cleaning, and then dried for use.

[0071] (2) Base material reverse sputtering cleaning: The pretreated 316 austenitic stainless steel base material was placed on the sample table in the vacuum furnace cavity of the magnetron sputtering equipment, and the vacuum degree in the furnace cavity was kept less than 2x10 -3 Pa, the baffle was adjusted between the target material and the base, then Ar gas was introduced, the sputtering gas pressure was kept at 3.0 Pa, the bias voltage was controlled at -1500 V, and the 316 austenitic stainless steel base was reverse sputtered for 15 min.

[0072] (3) Target pre-sputtering cleaning: Ar gas was continuously used as the working gas, the sputtering gas pressure was adjusted to 0.6 Pa, the FeCoNiCr target was rapidly ignited at a power of 450 W, and then pre-sputtering was performed for 20 min.

[0073] (4) Sputtering double-layer FeCoNiCrC x High-entropy alloy coating: Ar gas was continuously used as the working gas, the Ar gas flow was 50 sccm, the 316 austenitic stainless steel base was not heated, the target-to-base distance was 80 mm, the FeCoNiCr alloy layer was first deposited for 12 min, then the reaction gas C2H2 was introduced, the C2H2 flow was increased in gradient (1, 2, 3 and 4 sccm were deposited for 1 min, and 5 sccm was deposited for 6 min), the bias voltage was -50 V, the sputtering gas pressure was 0.8-0.9 Pa, the high-power pulse power voltage was 800 V, the frequency was 200 Hz, the pulse width was 150 μs, the duty cycle was 3%, and the FeCoNiCrC x layer with increasing carbon content was deposited for 10 min, i.e. the FeCoNiCr / gradient FeCoNiCrC x double-layer high-entropy alloy coating was obtained on the surface of the 316 austenitic stainless steel.

[0074] Of course, the above description is not a limitation of the present application, and the present application is not limited to the above examples. Based on the content of the present application, all other embodiments obtained by those skilled in the art without creative labor are within the scope of protection of the present application. Changes, modifications, additions or substitutions made by those skilled in the art within the essential scope of the present application should also be within the protection scope of the present application.

Claims

1. A method for preparing a conductive and corrosion-resistant coating for bipolar plates, characterized in that, Includes the following steps: A high-power pulsed magnetron sputtering method was employed, using FeCoNiCr as the sputtering target. A negative bias was applied to the surface-cleaned stainless steel substrate, and a target voltage was applied to the FeCoNiCr target to deposit the coating. (1) First, using Ar as the working gas, FeCoNiCr layer is sputtered and deposited on the surface of stainless steel substrate; (2) FeCoNiCrC was then deposited in a mixed atmosphere of Ar and C2H2 to obtain FeCoNiCrC. x layer.

2. The method for preparing a bipolar plate conductive and corrosion-resistant coating according to claim 1, characterized in that, The atomic percentages of the metallic elements Fe, Co, Ni, and Cr in the FeCoNiCr target are 1:1:1:

1.

3. The method for preparing a bipolar plate conductive and corrosion-resistant coating according to claim 1, characterized in that, The stainless steel substrate bias voltage is -100V to -50V; the distance between the target and the stainless steel substrate is 70~90mm; and the total sputtering time is 18~25min.

4. The method for preparing a bipolar plate conductive and corrosion-resistant coating according to claim 1, characterized in that, During sputtering, the gas pressure inside the cavity is maintained at 0.8–0.9 Pa; the Ar gas flow rate is controlled at 40–50 sccm.

5. The method for preparing a bipolar plate conductive and corrosion-resistant coating according to claim 1, characterized in that, The HiPIMS power supply was used to apply a voltage of 800V, a frequency of 200Hz, a pulse width of 150μs, and a duty cycle of 3%.

6. The method for preparing a bipolar plate conductive and corrosion-resistant coating according to claim 1, characterized in that, The bipolar plate conductive and corrosion-resistant coating has a double-layer structure or a gradient structure. When it is a double-layer structure, FeCoNiCrC x The deposition time of the FeCoNiCr layer is less than or equal to the deposition time of the FeCoNiCr layer; the deposition time of FeCoNiCrC x During the layering process, by controlling the C2H2 flow rate, the carbon content from the bottom layer to the surface layer can be increased in a gradient from bottom to top, or the C2H2 flow rate can be kept constant to form a clearly layered double-layer structure of FeCoNiCrCx high-entropy alloy coating. When it is a gradient structure, FeCoNiCrC x The deposition time of the FeCoNiCr layer is significantly longer than that of the FeCoNiCr layer, resulting in the deposition of FeCoNiCrC. x During the deposition process, the C2H2 flow rate is controlled to gradually increase from 0 sccm linearly or according to a specific curve to a preset value, thereby achieving a continuous gradient change in carbon content.

7. The method for preparing a bipolar plate conductive and corrosion-resistant coating according to claim 6, characterized in that, When the bipolar plate conductive and corrosion-resistant coating has a double-layer structure, FeCoNiCrC is deposited. x The C2H2 flow rate is either a fixed value of 5 sccm or a C2H2 flow rate that increases gradually from 1 to 4 sccm. The final deposition of the surface layer is at a fixed value of 5 sccm, and the time for the final deposition of the surface layer is greater than any of the 1 to 4 sccm gradients.

8. The method for preparing a bipolar plate conductive and corrosion-resistant coating according to claim 6, characterized in that, When the bipolar plate conductive and corrosion-resistant coating has a gradient structure, the C2H2 flow rate gradually increases from 0 to 5 sccm.

9. A conductive, corrosion-resistant, high-entropy alloy coating, characterized in that, It is prepared according to any one of claims 1-8.

10. The bipolar plate conductive and corrosion-resistant coating according to claim 9, characterized in that, The bipolar plate is either an electrolytic water hydrogen production bipolar plate or a proton exchange membrane fuel cell bipolar plate.

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