Bipolar plate composite coating, preparation method thereof and bipolar plate

Abstract

The invention provides a bipolar plate composite coating, a preparation method thereof and a bipolar plate, and relates to the technical field of coating materials, the bipolar plate composite coating comprises a base layer, a middle layer and a surface layer which are sequentially deposited on the surface of the bipolar plate; the base layer is made of nickel; the middle layer comprises a nickel element and a sulfur element, and the mass fraction of the sulfur element in the middle layer is 22 ppm to 69 ppm; the surface layer comprises a nickel element and a sulfur element, and the mass fraction of the sulfur element in the surface layer is 415 ppm to 607 ppm. The bipolar plate composite coating provided by the invention not only is relatively small in thickness, but also has relatively strong corrosion resistance, relatively low interface contact resistance and relatively high hardness.

Description

Technical Field

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

[0002] The bipolar plate is an important component of the anion exchange membrane electrolyzer (AEM electrolyzer) and plays multiple roles. The bipolar plate can provide good support for the membrane electrode and withstand a large preload. When the electrolyzer is in operation, the anode loses electrons to produce oxygen evolution reaction, producing O2; the cathode gains electrons to produce hydrogen evolution reaction, producing H2. The bipolar plate conducts electrons for the electrochemical reaction and transfers heat to the electrolyzer, while promoting the uniform distribution of water and the effective discharge of O2 and H2. In addition, the bipolar plate can separate the anode and cathode to prevent hydrogen and oxygen from mixing. In order to improve the electrolysis efficiency and ensure the long-term stable operation of the electrolyzer, the bipolar plate should have strong corrosion resistance, low interface contact resistance and high hardness.

[0003] Currently, there are two main types of bipolar plate materials in the industry: the first option is to use pure nickel plates as bipolar plates, and the second option is to plate a nickel coating on carbon steel or stainless steel as bipolar plates. Pure nickel plates have strong corrosion resistance, but the cost is high, about 8 times that of 316 stainless steel and 53 times that of carbon steel, so the first option is too expensive. The second option uses low-cost stainless steel or carbon steel. Since stainless steel or carbon steel has poor corrosion resistance, a protective coating needs to be plated on the surface of the material. This reduces costs while taking into account corrosion resistance, so the second option is better than the first option. In the second option, there are two ways to plate the protective coating: chemical plating and electroplating. Chemical plating is expensive and has a long production cycle. Compared with chemical plating, electroplating has lower costs and a shorter production cycle, but it has the problem of high thickness and low hardness of the protective coating. In order to further reduce the cost of the protective coating, the thickness of the protective coating must be reduced, while ensuring that the protective coating has strong corrosion resistance, low interface contact resistance, and high hardness. Summary of the Invention

[0004] The problem solved by the present invention is: how to obtain a bipolar plate coating with a smaller thickness, stronger corrosion resistance, lower interface contact resistance and higher hardness.

[0005] To solve the above problems, the present invention provides a bipolar plate composite coating, comprising a base layer, an intermediate layer and a surface layer sequentially deposited on the surface of the bipolar plate; the base layer is made of nickel; the intermediate layer comprises nickel and sulfur, and the mass fraction of the sulfur in the intermediate layer is 22 ppm to 69 ppm; the surface layer comprises nickel and sulfur, and the mass fraction of the sulfur in the surface layer is 415 ppm to 607 ppm.

[0006] Optionally, the thickness of the base layer is less than 5 μm, the thickness of the intermediate layer is less than 10 μm, and the thickness of the surface layer is less than 30 μm.

[0007] Optionally, the sum of the thicknesses of the base layer, the intermediate layer, and the surface layer is less than 40 μm.

[0008] Optionally, the base layer, the intermediate layer, and the surface layer are sequentially deposited on the surface of the bipolar plate by electroplating.

[0009] The present invention also provides a method for preparing the bipolar plate composite coating as described above, which is characterized by including:

[0010] Step S1: Pretreat the bipolar plate to obtain a pretreated bipolar plate;

[0011] Step S2: Electroplate a base layer on the surface of the pretreated bipolar plate; wherein, during the electroplating of the base layer, the electrolyte used is selected from at least one of nickel sulfate solution and nickel sulfamate solution;

[0012] Step S3: Electroplate an intermediate layer on the surface of the base layer; wherein, during the electroplating of the intermediate layer, the electrolyte used includes a first electrolyte and a first additive; the first electrolyte is selected from at least one of nickel sulfate solution and nickel sulfamate solution, and the first additive is selected from at least one of chloral hydrate, 2,5 - dimethyl - 3 - hexyn - 2 - ol, sulfosalicylic acid, sodium 2 - ethylhexyl sulfate, and sodium dihexyl sulfosuccinate;

[0013] Step S4: Electroplate a surface layer on the surface of the intermediate layer; wherein, during the electroplating of the surface layer, the electrolyte used includes a second electrolyte and a second additive; the second electrolyte is selected from at least one of nickel sulfate solution and nickel sulfamate solution, and the second additive is selected from at least one of benzenesulfonamide, sodium salicylate, sodium benzoate, polyethylene glycol, 1,4 - butynediol, and 2 - methyl - 3 - butyn - 2 - amine.

[0014] Optionally, in step S3, during the electroplating of the intermediate layer, the mass fraction of the first additive in the electrolyte used is 0.35% to 0.45%.

[0015] Optionally, in step S4, during the electroplating of the surface layer, the mass fraction of the second additive in the electrolyte used is 0.55% to 0.65%.

[0016] Optionally, in step S1, the material of the bipolar plate is selected from one of carbon steel and stainless steel.

[0017] Optionally, in the step S1, the pretreatment of the bipolar plate includes: successively performing chemical degreasing, electro-chemical degreasing, and chemical derusting on the bipolar plate.

[0018] The present invention also provides a bipolar plate, including the bipolar plate composite coating as described above.

[0019] Compared with the related art, the bipolar plate composite coating provided by the present invention is successively deposited with a primer layer, an intermediate layer, and a surface layer on the surface of the bipolar plate. Among them, the material of the primer layer is pure nickel; the composition of the intermediate layer includes nickel element and sulfur element, and the mass fraction of sulfur element in the intermediate layer is 22 ppm to 69 ppm; the composition of the surface layer includes nickel element and sulfur element, and the mass fraction of sulfur element in the surface layer is 415 ppm to 607 ppm. That is to say, the bipolar plate composite coating is, from the inside to the outside, a nickel primer layer (without sulfur), a nickel intermediate layer (sulfur content is 22 ppm to 69 ppm), and a nickel surface layer (sulfur content is 415 ppm to 607 ppm). The main component nickel in the primer layer, the intermediate layer, and the surface layer is the basis for the bipolar plate composite coating to have strong corrosion resistance, low interfacial contact resistance, and high hardness; in addition, since the sulfur content in the primer layer, the intermediate layer, and the surface layer increases in sequence, the potentials of the primer layer, the intermediate layer, and the surface layer decrease in sequence. Among them, the potential of the intermediate layer is higher than that of the surface layer, which makes the original longitudinal (from the outside to the inside) corrosion become transverse corrosion, protecting the intermediate layer, the primer layer, and the bipolar plate, and greatly delaying the corrosion rate. Therefore, the bipolar plate composite coating provided by the present invention still has strong corrosion resistance under the condition of a relatively small thickness. In addition, it is found through experiments that the bipolar plate composite coating provided by the present invention has low interfacial contact resistance and high hardness under the condition of a relatively small thickness. In summary, the bipolar plate composite coating provided by the present invention not only has a small thickness, but also has strong corrosion resistance, low interfacial contact resistance, and high hardness. Description of the Drawings

[0020] Figure 1 It is a schematic structural diagram of a bipolar plate with a bipolar plate composite coating formed on its surface in an embodiment of the present invention.

[0021] Description of the Reference Numerals:

[0022] 1. Bipolar plate; 2. Primer layer; 3. Intermediate layer; 4. Surface layer. Detailed Embodiments

[0023] To make the above objects, features, and advantages of the present invention more apparent and understandable, the following provides a detailed description of specific embodiments of the present invention in conjunction with the accompanying drawings. Although some embodiments of the present invention are shown in the drawings, it should be understood that the present invention can be implemented in various forms and should not be construed as limited to the embodiments described herein. Instead, these embodiments are provided to more thoroughly and completely understand the present invention. It should be understood that the drawings and embodiments of the present invention are only for exemplary purposes and are not used to limit the protection scope of the present invention.

[0024] Unless otherwise defined, all technical and scientific terms used in the present invention have the same meaning as commonly understood by those skilled in the technical field to which the present invention belongs. The terms used in the present invention in the specification are only for the purpose of describing specific embodiments and are not intended to limit the present invention.

[0025] As used herein, the term "including" and its variants are open-ended, that is, "including but not limited to"; the term "based on" is "at least partially based on"; the term "one embodiment" means "at least one embodiment"; the term "another embodiment" means "at least one additional embodiment"; the term "some embodiments" means "at least some embodiments"; the term "optionally" means "optional embodiment". The relevant definitions of other terms will be given in the following description. It should be noted that the concepts of "first", "second", etc. mentioned in the present invention are used to distinguish different objects and are not used to describe a specific order or primary-secondary relationship. In addition, the terms "first" and "second" are only used for descriptive purposes and cannot be understood as indicating or implying relative importance or implicitly indicating the quantity of the indicated technical features. Thus, the features defined with "first" and "second" may explicitly or implicitly include one or more of such features. In the description of the present invention, unless otherwise specified, the meaning of "a plurality" is two or more. It should be noted that in the present invention, ppm represents one part per million.

[0026] As Figure 1 shown, a bipolar plate composite coating provided by an embodiment of the present invention includes a primer layer 2, an intermediate layer 3, and a surface layer 4 sequentially deposited on the surface of the bipolar plate 1; the material of the primer layer 2 is nickel; the composition of the intermediate layer 3 includes nickel and sulfur elements, and the mass fraction of sulfur element in the intermediate layer 3 is 22 ppm to 69 ppm; the composition of the surface layer 4 includes nickel and sulfur elements, and the mass fraction of sulfur element in the surface layer 4 is 415 ppm to 607 ppm.

[0027] The double - plate composite coating provided by the embodiments of the present invention is successively deposited with a primer layer 2, an intermediate layer 3, and a surface layer 4 on the surface of the bipolar plate 1. Among them, the material of the primer layer 2 is pure nickel; the composition of the intermediate layer 3 includes nickel element and sulfur element, and the mass fraction of sulfur element in the intermediate layer 3 is 22 ppm to 69 ppm; the composition of the surface layer 4 includes nickel element and sulfur element, and the mass fraction of sulfur element in the surface layer 4 is 415 ppm to 607 ppm. That is to say, the double - plate composite coating from the inside to the outside is a nickel primer layer 2 (without sulfur), a nickel intermediate layer 3 (sulfur content is 22 ppm to 69 ppm), and a nickel surface layer 4 (sulfur content is 415 ppm to 607 ppm). The main component nickel in the primer layer 2, the intermediate layer 3, and the surface layer 4 is the basis for the double - plate composite coating to have strong corrosion resistance, low interfacial contact resistance, and high hardness; in addition, since the sulfur content in the primer layer 2, the intermediate layer 3, and the surface layer 4 increases in turn, the potentials of the primer layer 2, the intermediate layer 3, and the surface layer 4 decrease in turn. Among them, the potential of the intermediate layer 3 is higher than that of the surface layer 4, which makes the original longitudinal (from the outside to the inside) corrosion become transverse corrosion, protecting the intermediate layer 3, the primer layer 2, and the bipolar plate 1, and greatly delaying the corrosion rate. Therefore, the double - plate composite coating provided by the present invention still has strong corrosion resistance under the condition of a relatively small thickness. In addition, through experiments, it is found that the double - plate composite coating provided by the embodiments of the present invention has low interfacial contact resistance and high hardness under the condition of a relatively small thickness. In summary, the double - plate composite coating provided by the embodiments of the present invention not only has a small thickness, but also has strong corrosion resistance, low interfacial contact resistance, and high hardness.

[0028] In some embodiments of the present invention, the thickness of the primer layer 2 is less than 5 μm, the thickness of the intermediate layer 3 is less than 10 μm, and the thickness of the surface layer 4 is less than 30 μm; the sum of the thicknesses of the primer layer 2, the intermediate layer 3, and the surface layer 4 is less than 40 μm. In this embodiment, the double - plate composite coating not only has a small thickness, but also has strong corrosion resistance, low interfacial contact resistance, and high hardness.

[0029] In some embodiments of the present invention, the primer layer 2, the intermediate layer 3, and the surface layer 4 are successively deposited on the surface of the bipolar plate 1 by electroplating.

[0030] The embodiments of the present invention also provide a preparation method of the double - plate composite coating as described above, which is characterized by including:

[0031] Step S1, pretreat the bipolar plate 1 to obtain a pretreated bipolar plate; <……>

[0032] Step S2: Electroplate an underlayer 2 on the surface of the pretreated bipolar plate. Among them, during the electroplating of the underlayer 2, the electrolyte used is selected from at least one of nickel sulfate solution and nickel sulfamate solution;

[0033] Step S3: Electroplate an intermediate layer 3 on the surface of the underlayer 2. Among them, during the electroplating of the intermediate layer 3, the electrolyte used includes a first electrolyte and a first additive; the first electrolyte is selected from at least one of nickel sulfate solution and nickel sulfamate solution, and the first additive is selected from at least one of chloral hydrate, 2,5-dimethylhexynediol, sulfosalicylic acid, sodium 2-ethylhexyl sulfate, and sodium dihexyl sulfosuccinate;

[0034] Step S4: Electroplate a surface layer 4 on the surface of the intermediate layer 3. Among them, during the electroplating of the surface layer 4, the electrolyte used includes a second electrolyte and a second additive; the second electrolyte is selected from at least one of nickel sulfate solution and nickel sulfamate solution, and the second additive is selected from at least one of benzenesulfonamide, sodium salicylate, sodium benzoate, polyethylene glycol, 1,4-butynediol, and 2-methyl-3-butyn-2-amine.

[0035] In some embodiments of the present invention, in step S3, during the electroplating of the intermediate layer 3, the mass fraction of the first additive in the electrolyte used is 0.35% to 0.45%.

[0036] In some embodiments of the present invention, in step S4, during the electroplating of the surface layer 4, the mass fraction of the second additive in the electrolyte used is 0.55% to 0.65%.

[0037] In some embodiments of the present invention, in step S1, the material of the bipolar plate 1 is selected from one of carbon steel and stainless steel; exemplarily, the carbon steel is selected from one of DC01 steel, DC04 steel, and Q235 steel, and the stainless steel is selected from one of 304 steel and 316 steel.

[0038] In some embodiments of the present invention, in step S1, the pretreatment of the bipolar plate 1 includes: sequentially performing chemical degreasing, electro-chemical degreasing, and chemical derusting on the bipolar plate 1.

[0039] The present invention also provides a bipolar plate, including the bipolar plate composite coating as described above.

[0040] The present invention will be further described below in conjunction with specific embodiments. The rust remover used in the embodiments of the present invention is METEX M 629.

[0041] Example 1

[0042] A1. Immerse the bipolar plate in a degreasing agent solution at 85°C for chemical degreasing. Then, using the bipolar plate as the anode, a stainless-steel electrode as the cathode, and an alkaline solution as the electrolyte, apply a current of 8 ASD at 85°C for 4 minutes for electrochemical degreasing. Finally, immerse the bipolar plate in a rust remover solution for 5 minutes for chemical derusting to obtain a pretreated bipolar plate; wherein, the material of the bipolar plate is DC01 steel.

[0043] A2. Electroplate a primer layer on the surface of the pretreated bipolar plate; wherein, during the electroplating of the primer layer, the electrolyte used is a nickel sulfate solution with a mass fraction of 25%, the anode is a nickel ball, the cathode is the pretreated bipolar plate, the temperature is 55°C, and the current density is 5 ASD; the primer layer is pure nickel and the thickness of the primer layer is 2 μm.

[0044] A3. Electroplate an intermediate layer on the surface of the primer layer; wherein, during the electroplating of the intermediate layer, the anode is a nickel ball, the cathode is the pretreated bipolar plate plated with the primer layer, and the electrolyte used includes a nickel sulfate solution and a first additive. The mass fraction of nickel sulfate in the electrolyte is 25%, and the mass fraction of the first additive is 0.4%. The first additive is chloral hydrate, the temperature is 55°C, and the current density is 5 ASD; the composition of the intermediate layer includes nickel and sulfur elements, the mass fraction of sulfur element in the intermediate layer is 45 ppm, and the thickness of the intermediate layer is 6 μm.

[0045] A4. Electroplate a surface layer on the surface of the intermediate layer to finally obtain a bipolar plate with a protective coating formed on its surface; wherein, during the electroplating of the surface layer, the anode is a nickel ball, the cathode is the pretreated bipolar plate plated with the intermediate layer, and the electrolyte used includes a nickel sulfate solution and a second additive. The mass fraction of nickel sulfate in the electrolyte is 25%, and the mass fraction of the second additive is 0.6%. The second additive is benzenesulfonamide, the temperature is 55°C, and the current density is 5 ASD; the composition of the surface layer includes nickel and sulfur elements, the mass fraction of sulfur element in the surface layer is 500 ppm, and the thickness of the surface layer is 22 μm.

[0046] Example 2

[0047] The difference from Example 1 is that in step A3, the mass fraction of sulfur element in the intermediate layer is 22 ppm.

[0048] Example 3

[0049] The difference from Example 1 is that in step A3, the mass fraction of sulfur element in the intermediate layer is 69 ppm.

[0050] Example 4

[0051] The difference from Example 1 is that in step A4, the mass fraction of sulfur element in the surface layer is 415 ppm.

[0052] Example 5

[0053] The difference from Example 1 is that in step A4, the mass fraction of sulfur element in the surface layer is 607 ppm.

[0054] Comparative Example 1

[0055] B1. Immerse the bipolar plate in a degreasing agent solution at 85 °C for chemical degreasing. Then, using the bipolar plate as the anode, a stainless-steel electrode as the cathode, and an alkaline solution as the electrolyte, apply a current of 8 ASD at 85 °C for 4 min for electrochemical degreasing. Finally, immerse the bipolar plate in a rust remover solution for 5 min for chemical rust removal to obtain a pretreated bipolar plate; wherein the material of the bipolar plate is DC01 steel.

[0056] B2. Electroplate a protective coating on the surface of the pretreated bipolar plate; wherein, during the electroplating of the protective coating, the electrolyte used is a nickel sulfate solution with a mass fraction of 25%, the anode is a nickel ball, the cathode is the pretreated bipolar plate, the temperature is 55 °C, and the current density is 5 ASD; the protective coating is pure nickel with a thickness of 60 μm.

[0057] Comparative Example 2

[0058] Immerse the bipolar plate in a degreasing agent solution at 85 °C for chemical degreasing. Then, using the bipolar plate as the anode, a stainless-steel electrode as the cathode, and an alkaline solution as the electrolyte, apply a current of 8 ASD at 85 °C for 4 min for electrochemical degreasing. Finally, immerse the bipolar plate in a rust remover solution for 5 min for chemical rust removal to obtain a pretreated bipolar plate; wherein the material of the bipolar plate is DC01 steel.

[0059] Electroplate a protective coating on the surface of the pretreated bipolar plate to obtain a bipolar plate with a protective coating formed on its surface; wherein, during the electroplating of the protective coating, the anode is a nickel ball, the cathode is the pretreated bipolar plate, the electrolyte used includes a nickel sulfate solution and a first additive, the mass fraction of nickel sulfate in the electrolyte is 25%, the mass fraction of the first additive is 0.4%, the first additive is chloral hydrate, the temperature is 55 °C, and the current density is 5 ASD; the composition of the protective coating includes nickel element and sulfur element, the mass fraction of sulfur element in the protective coating is 45 ppm, and the thickness of the protective coating is 60 μm.

[0060] Comparative Example 3

[0061] The bipolar plate is soaked in a degreasing agent solution at 85 °C for chemical degreasing. Then, with the bipolar plate as the anode, a stainless-steel electrode as the cathode, and an alkaline solution as the electrolyte, a current of 8 ASD is applied at 85 °C for 4 minutes for electrochemical degreasing. Finally, the bipolar plate is soaked in a rust remover solution for 5 minutes for chemical derusting to obtain a pretreated bipolar plate; wherein, the material of the bipolar plate is DC01 steel.

[0062] A protective coating is electroplated on the surface of the pretreated bipolar plate to obtain a bipolar plate with a protective coating formed on its surface; wherein, during the electroplating of the protective coating, the anode is a nickel ball, the cathode is the pretreated bipolar plate, and the electrolyte used includes a nickel sulfate solution and a second additive. The mass fraction of nickel sulfate in the electrolyte is 25%, and the mass fraction of the second additive is 0.6%. The second additive is benzenesulfonamide, the temperature is 55 °C, and the current density is 5 ASD; the composition of the protective coating includes nickel and sulfur elements, and the mass fraction of sulfur element in the protective coating is 500 ppm, and the thickness of the protective coating is 60 μm.

[0063] Experimental examples

[0064] The bipolar plates with protective coatings formed on their surfaces prepared in Examples 1 to 5 and Comparative Examples 1 to 3 are tested for interfacial contact resistance, hardness, and corrosion resistance time. The results are shown in Table 1. It can be seen from Table 1 that compared with Comparative Examples 1 to 3, the thickness of the protective coatings prepared in Examples 1 to 5 is smaller, which is 30 μm, and the thickness of the protective coatings prepared in Comparative Examples 1 to 3 is 60 μm. Moreover, the protective coatings prepared in Examples 1 to 5 have a smaller interfacial contact resistance, a larger hardness, and a longer corrosion resistance time, indicating that the protective coatings prepared in Examples 1 to 5 not only have a smaller thickness but also have strong corrosion resistance, a lower interfacial contact resistance, and a higher hardness.

[0065] Table 1

[0066]

[0067] The protective coatings prepared in Examples 1 to 5 are subjected to blue dot test and cross hatch test. The results are shown in Table 2. As shown in Table 2, no blue dots are shown on the surface of the bipolar plate within 5 minutes for the protective coatings prepared in Examples 1 to 5, indicating that the protective coatings are densely formed and completely cover the bipolar plate substrate; as shown in Table 2, after pulling the protective coatings prepared in Examples 1 to 5 3 times at the same position with 3M 898 tape, no coating peeling is found (cross hatch test), indicating that the protective coatings have excellent adhesion.

[0068] Table 2

[0069] Sample Number Blue Dot Test Result Cross-Cut Test Result Example 1 No blue dot within 5 min Did not fall off after pulling 3 times at the same position Example 2 No blue dot within 5 min Did not fall off after pulling 3 times at the same position Example 3 No blue dot within 5 min Did not fall off after pulling 3 times at the same position Example 4 No blue dot within 5 min Did not fall off after pulling 3 times at the same position Example 5 No blue dot within 5 min Did not fall off after pulling 3 times at the same position

[0070] The test methods involved in the present invention are as follows

[0071] (1) The interfacial contact resistance is tested in accordance with the national standard GB / T 20042.6. The test pressure range is 0.1 - 1.6 MPa, and the test pressure interval is 0.1 MPa.

[0072] (2) The corrosion resistance time is tested in accordance with the national standard GB / T 10125 - 2021.

[0073] (3) The blue dot test is carried out according to the standard QB / T 3823 - 1999, and the cross - cut test is carried out according to the standard ISO 2409:2020.

Claims

1. A bipolar plate composite coating, characterized in that, It includes a primer layer (2), an intermediate layer (3), and a surface layer (4) sequentially deposited on the surface of the bipolar plate (1); the material of the primer layer (2) is nickel; The composition of the intermediate layer (3) includes nickel element and sulfur element, and the mass fraction of sulfur element in the intermediate layer (3) is 22 ppm to 69 ppm; the composition of the surface layer (4) includes nickel element and sulfur element, and the mass fraction of sulfur element in the surface layer (4) is 415 ppm to 607 ppm.

2. The bipolar plate composite coating according to claim 1, wherein The thickness of the primer layer (2) is less than 5 μm, the thickness of the intermediate layer (3) is less than 10 μm, and the thickness of the surface layer (4) is less than 30 μm.

3. The bipolar plate composite coating according to claim 1, characterized in that, The sum of the thicknesses of the primer layer (2), the intermediate layer (3), and the surface layer (4) is less than 40 μm.

4. The bipolar plate composite coating according to claim 1, wherein, The primer layer (2), the intermediate layer (3), and the surface layer (4) are all sequentially deposited on the surface of the bipolar plate (1) by electroplating.

5. A method for preparing the bipolar plate composite coating according to any one of claims 1 to 4, characterized in that, It includes: Step S1: Pretreat the bipolar plate (1) to obtain a pretreated bipolar plate; Step S2: Electroplate the primer layer (2) on the surface of the pretreated bipolar plate; wherein, during the electroplating of the primer layer (2), the electrolyte used is selected from at least one of nickel sulfate solution and nickel sulfamate solution; Step S3: Electroplate the intermediate layer (3) on the surface of the primer layer (2); wherein, during the electroplating of the intermediate layer (3), the electrolyte used includes a first electrolyte and a first additive; the first electrolyte is selected from at least one of nickel sulfate solution and nickel sulfamate solution, and the first additive is selected from at least one of chloral hydrate, 2,5-dimethylhexynediol, sulfosalicylic acid, sodium 2-ethylhexyl sulfate, and sodium dihexyl sulfosuccinate; Step S4: Electroplate the surface layer (4) on the surface of the intermediate layer (3); wherein, during the electroplating of the surface layer (4), the electrolyte used includes a second electrolyte and a second additive; the second electrolyte is selected from at least one of nickel sulfate solution and nickel sulfamate solution, and the second additive is selected from at least one of benzenesulfonamide, sodium salicylate, sodium benzoate, polyethylene glycol, 1,4-butynediol, and 2-methyl-3-butyn-2-amine.

6. The preparation method of the bipolar plate composite coating according to claim 5, characterized in that, In the step S3, during the electroplating of the intermediate layer (3), the mass fraction of the first additive in the electrolyte used is 0.35% to 0.45%.

7. The preparation method of the bipolar plate composite coating according to claim 5, wherein In the step S4, during the electroplating of the surface layer (4), the mass fraction of the second additive in the electrolyte used is 0.55% to 0.65%.

8. The preparation method of the bipolar plate composite coating according to claim 5, characterized in that, In the step S1, the material of the bipolar plate (1) is selected from one of carbon steel and stainless steel.

9. The preparation method of the bipolar plate composite coating according to claim 5, characterized in that, In the step S1, the pretreatment of the bipolar plate (1) includes: sequentially performing chemical degreasing, electro-chemical degreasing, and chemical rust removal on the bipolar plate (1).

10. A bipolar plate, characterized in that, It includes the bipolar plate composite coating as described in any one of claims 1 to 4.

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