A fuel cell metal bipolar plate conductive corrosion resistant coating

Abstract

The application relates to a fuel cell metal bipolar plate conductive corrosion-resistant coating and a preparation method thereof, and relates to the technical field of fuel cells. The fuel cell metal bipolar plate conductive corrosion-resistant coating comprises a metal substrate, a metal transition layer and a conductive corrosion-resistant composite layer. The metal transition layer is deposited on the metal substrate to improve the bonding force between the coating and the substrate. The conductive corrosion-resistant composite layer is deposited on the metal transition layer and is composed of a low-chromium-target-current chromium-doped amorphous carbon layer and a high-chromium-target-current chromium-doped amorphous carbon layer to form a composite multi-layer structure. The coating is arranged in a staggered manner through special coating preparation technology and a periodic composite structure, the "pinhole"-shaped defects generated in the deposition process of the coating are staggered, the corrosion liquid is prevented from eroding the substrate through the defect channels, the risk of coating failure is reduced, the stress in the coating is relieved, excellent conductive performance and corrosion resistance are achieved, and the service life of the metal bipolar plate is prolonged.

Description

Technical Field

[0001] This invention relates to the field of fuel cell technology, specifically to a conductive and corrosion-resistant coating for a fuel cell metal bipolar plate and its preparation method. Background Technology

[0002] A proton exchange membrane fuel cell (PEMFC) is an electrochemical device that generates electricity through an electrochemical reaction. As an emerging and prominent clean power source, PEMFC has advantages such as low temperature, low pressure, short start-up and shutdown time, low noise, and high efficiency. It is an important driver for building a green and low-carbon society and for the green transformation of society, and has great development prospects in the field of new energy.

[0003] Bipolar plates are crucial multifunctional components in PEMFCs, accounting for approximately 80% of the battery stack volume, 70% of the weight, and 30% of the cost. Their function includes separating reactant gases, collecting electrons generated during electrochemical reactions, and dissipating heat and waste gases. Based on the material, bipolar plates are mainly classified into graphite bipolar plates, metal bipolar plates, and composite bipolar plates. Metal bipolar plates offer advantages such as high mechanical strength, high conductivity, low airtightness, low cost, and ease of processing, making them widely used by new energy vehicle manufacturers. However, in operating environments with strong acids (pH 2-5), high temperatures (70℃), and high humidity, metal bipolar plates are highly susceptible to corrosion, and dissolved metal ions can poison the catalyst. Simultaneously, the corrosion of the passivation film on the surface increases the interfacial contact resistance (ICR) between the gas diffusion layer (GDL) and the bipolar plate, reducing the stack's output power.

[0004] To address the aforementioned problems with metal bipolar plates, surface modification is necessary. Commonly used methods for preparing modified coatings include magnetron sputtering, arc ion plating, electroplating, electroless plating, and vapor deposition. Magnetron sputtering is the most commonly used and relatively mature method, offering advantages such as low cost, fast deposition speed, and ease of mass production. However, during the deposition process, magnetron sputtering coatings inevitably exhibit penetrating pinholes, which act as channels connecting the etchant to the substrate. Simultaneously, the high internal stress between the substrate and the coating leads to low adhesion, significantly impacting the coating's performance and lifespan. Summary of the Invention

[0005] Therefore, it is necessary to propose a conductive and corrosion-resistant coating for fuel cell metal bipolar plates and its preparation method to address the above problems.

[0006] This invention provides a conductive and corrosion-resistant coating for a fuel cell metal bipolar plate. The metal bipolar plate includes a metal substrate, a metal transition layer, and a conductive and corrosion-resistant composite layer. The conductive and corrosion-resistant composite layer exhibits an n-period structure, with one cycle consisting of depositing a low-chromium target current chromium-doped amorphous carbon layer and a high-chromium target current chromium-doped amorphous carbon layer.

[0007] Furthermore, the period n has a value of 1 to 5.

[0008] Furthermore, the metal substrate is one or more of stainless steel, titanium, and aluminum.

[0009] Furthermore, the metal material in the metal transition layer is one or more of chromium, titanium, zinc, copper, and aluminum, and its function is to enhance the adhesion between the coating and the metal substrate.

[0010] Furthermore, the conductive and corrosion-resistant composite layer is composed of a low-chromium target current chromium-doped amorphous carbon layer and a high-chromium target current chromium-doped amorphous carbon layer.

[0011] Furthermore, in the conductive and corrosion-resistant composite layer, the low-chromium target current and the carbon and chromium elements in the chromium-doped amorphous carbon layer mainly exist in elemental form.

[0012] Furthermore, in the high-chromium target current of the conductive and corrosion-resistant composite layer, the carbon and chromium elements in the chromium-doped amorphous carbon layer mainly exist in the form of metal carbides.

[0013] Furthermore, the conductive and corrosion-resistant coating of the metal bipolar plate is prepared by magnetron sputtering.

[0014] Preferably, the thickness of the metal transition layer is 20–50 nm.

[0015] Preferably, the carbon content in the low-chromium target current chromium-doped amorphous carbon layer is 50%–70%, the chromium content is 20%–40%, and the chromium carbide content is 1%–5%.

[0016] Preferably, the carbon content in the high-chromium target current chromium-doped amorphous carbon layer is 20%–40%, the chromium content is 10%–20%, and the chromium carbide content is 50%–60%.

[0017] Preferably, the thickness of the low-chromium target current chromium-doped amorphous carbon layer in the conductive and corrosion-resistant composite layer is 150nm-300nm.

[0018] Preferably, the thickness of the high-chromium target current chromium-doped amorphous carbon layer in the conductive and corrosion-resistant composite layer is 100nm-300nm.

[0019] This invention also provides a method for preparing a conductive and corrosion-resistant coating for a metal bipolar plate, the specific steps of which are as follows:

[0020] (1) The metal bipolar plate substrate was placed in acetone, ethanol and deionized water for ultrasonic cleaning for 20 minutes each. After drying, it was fixed on the sample holder. After the vacuum reached 6.0×10-4~8.0×10-4Pa, a certain amount of argon gas was introduced. Under the bias voltage of -300~-500V, the substrate was etched by Ar ion glow discharge for 30 minutes.

[0021] (2) Deposit a chromium transition layer on a metal bipolar plate substrate by turning on the metal target current. The metal target current is 0 to 5A, the argon flow rate is 30 to 60 sccm, the bias voltage is -70 to -150V, and the deposition time is 1 to 10 min.

[0022] (3) Turn off the metal target current and turn on the carbon target current and chromium target current. Deposit a low chromium target current chromium-doped amorphous carbon layer on the metal transition layer. The carbon target current is 0-5A and the chromium target current is 0-2A. The chromium target current is always less than the carbon target current. The argon flow rate and bias voltage remain unchanged. The deposition time is 10-30min.

[0023] (4) Keep the carbon target current constant and increase the chromium target current to deposit a high chromium target current chromium doped amorphous carbon layer on the low chromium target current chromium doped amorphous carbon layer. The chromium target current is 2-5A, the argon flow rate and bias voltage are constant, and the deposition time is 10-20min.

[0024] (5) Using (3) and (4) as one process cycle, repeat n cycles to obtain a conductive and corrosion-resistant composite layer.

[0025] Compared with existing technologies, this invention has the following advantages: 1. In magnetron sputtering, by changing the coating process and alternating the magnitude of the chromium target current, chromium-doped amorphous carbon films with different microstructures are obtained, thereby improving the density of the coating while reducing the high internal stress within the coating. 2. By taking the deposition of a low-chromium-target-current chromium-doped amorphous carbon layer and a high-chromium-target-current chromium-doped amorphous carbon layer as one cycle, a multilayer structure of conductive and corrosion-resistant composite layer with multiple cycles is prepared. Through multilayer design, pinhole defects in each layer are effectively misaligned, reducing the probability that the corrosion liquid will affect the substrate through defects and cause coating failure. Attached Figure Description

[0026] Figure 1 This is a schematic diagram of the coating of the present invention;

[0027] Figure 2 This is an enlarged view of the conductive and corrosion-resistant composite layer structure;

[0028] Figure 3 This is a schematic diagram of the n=2 coating of the present invention.

[0029] 1. Metal substrate; 2. Metal transition layer; 3. Conductive and corrosion-resistant composite layer; 4. High chromium target current chromium-doped amorphous carbon layer; 5. Low chromium target current chromium-doped amorphous carbon layer; 6. One cycle of the conductive and corrosion-resistant composite layer. Detailed Implementation

[0030] To facilitate understanding of the present invention, a more complete description will be given below with reference to the accompanying drawings. Preferred embodiments of the invention are shown in the drawings. However, the invention can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a thorough and complete understanding of the disclosure of the invention.

[0031] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the description of the invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0032] like Figure 1 and Figure 2 As shown, the present invention provides a conductive and corrosion-resistant coating for a fuel cell metal bipolar plate. The metal bipolar plate includes: a metal substrate 1, a metal transition layer 2, and a conductive and corrosion-resistant composite layer 3. The conductive and corrosion-resistant composite layer 3 exhibits an n-period structure, with one cycle consisting of depositing a low-chromium target current chromium-doped amorphous carbon layer 5 and a high-chromium target current chromium-doped amorphous carbon layer 4.

[0033] Furthermore, the period n has a value of 1 to 5.

[0034] Furthermore, the metal substrate is one or more of stainless steel, titanium, and aluminum.

[0035] Furthermore, the metal material in the metal transition layer is one or more of chromium, titanium, zinc, copper, and aluminum, and its function is to enhance the adhesion between the coating and the metal substrate.

[0036] Furthermore, the conductive and corrosion-resistant composite layer is composed of a low-chromium target current chromium-doped amorphous carbon layer and a high-chromium target current chromium-doped amorphous carbon layer.

[0037] Furthermore, in the conductive and corrosion-resistant composite layer, the low-chromium target current and the carbon and chromium elements in the chromium-doped amorphous carbon layer mainly exist in elemental form.

[0038] Furthermore, in the high-chromium target current of the conductive and corrosion-resistant composite layer, the carbon and chromium elements in the chromium-doped amorphous carbon layer mainly exist in the form of metal carbides.

[0039] Furthermore, the conductive and corrosion-resistant coating of the metal bipolar plate is prepared by magnetron sputtering.

[0040] Preferably, the thickness of the metal transition layer is 20–50 nm.

[0041] Preferably, the carbon content in the low-chromium target current chromium-doped amorphous carbon layer is 50%–70%, the chromium content is 20%–40%, and the chromium carbide content is 1%–5%.

[0042] Preferably, the carbon content in the high-chromium target current chromium-doped amorphous carbon layer is 20%–40%, the chromium content is 10%–20%, and the chromium carbide content is 50%–60%.

[0043] Preferably, the thickness of the low-chromium target current chromium-doped amorphous carbon layer in the conductive and corrosion-resistant composite layer is 150nm-300nm.

[0044] Preferably, the thickness of the high-chromium target current chromium-doped amorphous carbon layer in the conductive and corrosion-resistant composite layer is 100nm-300nm.

[0045] Example

[0046] like Figure 3 As shown, a conductive and corrosion-resistant coating for a fuel cell metal bipolar plate includes a metal transition layer and a conductive and corrosion-resistant composite layer deposited sequentially from the inside out. The metal transition layer is a chromium layer with a thickness of 50 nm. The conductive and corrosion-resistant composite layer consists of two cycles of low-chromium target current chromium-doped amorphous carbon layers and high-chromium target current chromium-doped amorphous carbon layers. Each individual low-chromium target current chromium-doped amorphous carbon layer has a thickness of 150 ± 10 nm, and each individual high-chromium target current chromium-doped amorphous carbon layer has a thickness of 150 ± 10 nm.

[0047] The specific preparation method of the highly conductive and corrosion-resistant composite coating for fuel cell metal bipolar plates is as follows:

[0048] S1. Pretreatment: The metal bipolar plate substrate was ultrasonically cleaned in acetone, ethanol and deionized water for 20 minutes each, dried and fixed on the sample holder. After the vacuum degree reached 6.0×10-4~8.0×10-4Pa, a certain amount of argon gas was introduced and the substrate was etched by Ar ion glow discharge for 30 minutes under a bias voltage of -300~-500V.

[0049] S2. Preparation of metal transition layer: Turn on the chromium magnetron target and deposit the chromium layer on the surface of the metal substrate under an argon atmosphere.

[0050] S3. Preparation of a conductive and corrosion-resistant composite layer:

[0051] S3.1. Preparation of high chromium target current chromium-doped amorphous carbon layer: Control the chromium target current to decrease slowly, while simultaneously turning on the carbon target current and increasing it slowly. At this time, the chromium target current is greater than the carbon target current. Under an argon atmosphere, the high chromium target current chromium-doped amorphous carbon layer is deposited on the chromium transition layer.

[0052] S3.2. Preparation of low-chromium target current chromium-doped amorphous carbon layer: Control the chromium target current to decrease slowly, while simultaneously turning on the carbon target current and increasing it slowly. At this time, the chromium target current is less than the carbon target current. Under an argon atmosphere, the low-chromium target current chromium-doped amorphous carbon layer is deposited on the high-chromium target current chromium-doped amorphous carbon layer.

[0053] S3.2. Preparation of the second-cycle high-chromium target current chromium-doped amorphous carbon layer: Control the chromium target current to rise slowly while the carbon target current falls slowly. Under an argon atmosphere, deposit the second-cycle high-chromium target current chromium-doped amorphous carbon layer on the first-cycle low-chromium target current chromium-doped amorphous carbon layer.

[0054] S3.4. Preparation of the second cycle low chromium target current chromium-doped amorphous carbon layer: Control the chromium target current to decrease slowly while the carbon target current increases slowly. Under an argon atmosphere, deposit the second cycle low chromium target current chromium-doped amorphous carbon layer on the second cycle low chromium target current chromium-doped amorphous carbon layer to obtain a conductive and corrosion-resistant composite coating for the fuel cell metal bipolar plate.

[0055] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.

Claims

1. A specific method for preparing a highly conductive and corrosion-resistant composite coating for a fuel cell metal bipolar plate, characterized in that, The metal bipolar plate includes: a metal substrate, a metal transition layer, and a conductive and corrosion-resistant composite layer; the conductive and corrosion-resistant composite layer exhibits an n-period structure with one cycle consisting of depositing a high-chromium target current chromium-doped amorphous carbon layer and a low-chromium target current chromium-doped amorphous carbon layer. The preparation steps include the following: S1. Pre-processing; S2. Preparation of metal transition layer: Turn on the chromium magnetron target and deposit chromium on the surface of the metal substrate under an argon atmosphere; S3. Preparation of a conductive and corrosion-resistant composite layer: S3.

1. Preparation of high chromium target current chromium-doped amorphous carbon layer: control the chromium target current to decrease slowly, while turning on the carbon target current and increasing it slowly. The chromium target current is 0 to 2 A, and the chromium target current is always greater than the carbon target current. Under an argon atmosphere, the high chromium target current chromium-doped amorphous carbon layer is deposited on the chromium transition layer. S3.

2. Preparation of low chromium target current chromium-doped amorphous carbon layer: control the chromium target current to decrease slowly, while turning on the carbon target current and increasing it slowly. The carbon target current is 0-5A and the chromium target current is 0-2A. The chromium target current is always less than the carbon target current. Under an argon atmosphere, the low chromium target current chromium-doped amorphous carbon layer is deposited on the high chromium target current chromium-doped amorphous carbon layer. The low-chromium target current chromium-doped amorphous carbon layer has a carbon content of 50%–70%, a chromium content of 20%–40%, and a chromium carbide content of 1%–5%. The high-chromium target current chromium-doped amorphous carbon layer has a carbon content of 20%–40%, a chromium content of 10%–20%, and a chromium carbide content of 50%–60%.

2. The method according to claim 1, characterized in that, The period n has a value of 1 to 5.

3. The method according to claim 1, characterized in that, The low chromium target current in the conductive and corrosion-resistant composite layer and the carbon and chromium elements in the chromium-doped amorphous carbon layer mainly exist in elemental form.

4. The method according to claim 1, characterized in that, The thickness of the metal transition layer is 20–50 nm.

5. The method according to claim 1, characterized in that, The low-chromium target current chromium-doped amorphous carbon layer in the conductive and corrosion-resistant composite layer has a thickness of 150nm-300nm.

6. The method according to claim 1, characterized in that, The high-chromium target current chromium-doped amorphous carbon layer in the conductive and corrosion-resistant composite layer has a thickness of 100nm-300nm.

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