A high potential corrosion resistant metal bipolar plate coating and preparation method thereof

Abstract

The present invention relates to a metal bipolar plate coating resistant to high potential corrosion and a preparation method thereof. The prepared carbon film includes a first carbon layer located inside and a second carbon layer located on the surface. Among them: the first carbon layer uses an arc bend tube magnetic filter coil to emit carbon cations, and the carbon cations are accelerated with a DC bias under preset conditions to strengthen the role of chemical bonds in interface bonding. Ti metal and carbon cations are synthesized into TiC. At the same time, by adjusting the current density applied to the metal bipolar plate, excessive graphitization transformation of the first carbon layer is avoided, so that the TiC phase and sp3 phase at the interface are significantly more than the sp2 phase, thereby improving the high potential corrosion resistance of the first carbon layer and the Ti-C interface. The second carbon layer is a conductive layer, and a low duty cycle and a high pulse bias are used to achieve a low resistance effect. Finally, a metal bipolar plate carbon-based coating that can withstand long-term high potential corrosion and has excellent contact resistance characteristics is obtained.

Description

Technical Field

[0001] The present invention relates to the technical field of surface protection of metal bipolar plates for batteries, and in particular to a metal bipolar plate coating resistant to high potential corrosion and a preparation method thereof. Background Art

[0002] As an efficient and clean energy conversion device, hydrogen fuel cells have received extensive attention in recent years. In hydrogen fuel cells, bipolar plates are one of the key components, and their performance directly affects the overall efficiency and life of the fuel cell. Bipolar plates not only need to have good conductivity to reduce internal resistance, but also need to have excellent electrochemical corrosion resistance to ensure long-term stable operation.

[0003] At present, carbon film is widely used as a bipolar plate coating material due to its good electrical conductivity and corrosion resistance. Common carbon films include sputtered carbon, element / alloy doped sputtered carbon, arc carbon, hydrogen-containing amorphous carbon, etc. These carbon films meet the requirements of bipolar plates for contact resistance and electrochemical corrosion resistance to a certain extent. In bipolar plate coating technology, the performance requirements for carbon films are mainly concentrated in two aspects: one is contact resistance, which is generally required to be less than 10mΩ·cm² to ensure efficient operation of the battery; the other is electrochemical corrosion resistance, especially the potential electrochemical corrosion current density must be less than 1μA / cm² (measurement method reference GB / T 20042.6-2011). However, with the continuous improvement of the service life and durability requirements for hydrogen fuel cell bipolar plates, researchers have found that simple potential electrochemical corrosion tests are no longer sufficient to fully characterize the durability of the coating.

[0004] High potential corrosion is an important problem faced by hydrogen fuel cell bipolar plates. Although this high potential state usually only exists in the instantaneous stages of battery gas shortage, start-up and shutdown, when the battery stack life is required to reach tens of thousands of hours, the accumulated time of these instantaneous high potential states is also considerable. Therefore, improving the coating's resistance to high potential corrosion is crucial to extending battery life. Summary of the invention

[0005] In order to solve the problem that the carbon film of the bipolar plate has poor constant voltage corrosion resistance under high potential, the present application provides a method for preparing a metal bipolar plate coating resistant to high potential corrosion.

[0006] To achieve the above objectives, this application is implemented through the following technical solutions:

[0007] The present application provides a method for preparing a metal bipolar plate coating, comprising the following steps:

[0008] S1. Place the cleaned metal bipolar plate in a single furnace coating machine with an arc elbow magnetic filter coil, an arc cathode and a sputtering cathode, wherein the sputtering cathode is a metal Ti target and the arc cathode is a graphite target, evacuate the plate, and use plasma to clean the surface of the metal bipolar plate;

[0009] S2, applying a preset bias voltage to the metal bipolar plate, wherein the preset bias voltage is 50V to 300V, turning on the sputtering cathode to deposit a metal base layer, and the thickness of the deposited metal base layer is 100nm to 500nm;

[0010] S3, turn off the sputtering cathode, adjust the preset bias voltage applied to the metal bipolar plate to a DC bias voltage, the DC bias voltage is adjusted to 600V-800V, turn on the arc bend magnetic filter coil, and at the same time, adjust the current density applied to the metal bipolar plate to not more than 0.005A / cm 2 , turning on the arc cathode to deposit a first carbon layer, wherein the thickness of the deposited first carbon layer is 10 nm to 50 nm;

[0011] S4. Maintain the parameters of the arc bend tube magnetic filtration coil and the arc cathode unchanged, adjust the preset bias voltage applied to the metal bipolar plate to a high pulse bias voltage with a low duty cycle, the bias voltage of the high pulse bias voltage with a low duty cycle is 1800V to 2200V, and the duty cycle of the high pulse bias voltage with a low duty cycle is 2% to 5%, turn on the arc bend tube magnetic filtration coil, and deposit a second carbon layer, the thickness of the second carbon layer is 50nm to 500nm.

[0012] As a further improvement of the present application, in step S3, the contact resistance of the first carbon layer is 50 mΩ·cm 2 ~200mΩ·cm 2 The corrosion current density of the first carbon layer in a constant potential test at 1.6 V for 5 hours is ≤50 μA / cm 2 , there is no obvious change on the surface of the first carbon layer after corrosion.

[0013] As a further improvement of the present application, in step S4, the contact resistance of the second carbon layer is 2 mΩ·cm 2 ~10mΩ·cm 2 The corrosion current density of the second carbon layer in a constant potential test at 1.6 V for 5 hours is ≤100 μA / cm 2 .

[0014] As a further improvement of the present application, in step S1, the metal bipolar plate is a stainless steel bipolar plate or a titanium-based bipolar plate.

[0015] As a further improvement of the present application, in step S2, the power applied to the cathode sputtering target is 4KW to 10KW.

[0016] As a further improvement of the present application, in step S3, the arc bend tube magnetic filtration coil adopts a 90° bend tube design.

[0017] As a further improvement of the present application, in step S3, the current applied to the arc bending tube magnetic filter coil is 5A to 15A.

[0018] As a further improvement of the present application, in step S3, the distance between the bend outlet of the arc bend magnetic filtration coil and the metal bipolar plate is 10 cm to 30 cm.

[0019] As a further improvement of the present application, in step S3, the current of the arc cathode is 50A to 150A.

[0020] To achieve the above objectives, the present application also provides a high-potential corrosion-resistant metal bipolar plate coating prepared according to the above-mentioned method for preparing a high-potential corrosion-resistant metal bipolar plate coating.

[0021] The beneficial effect of the present application is that the present application provides a method for preparing a metal bipolar plate coating resistant to high potential corrosion, and prepares a carbon film, wherein the carbon film includes a first carbon layer located inside and a second carbon layer located on the surface. The first carbon layer uses an arc bend tube magnetic filter coil to eject carbon cations, and the carbon cations are accelerated with a DC bias under preset conditions to strengthen the role of chemical bonds in the interface bonding, and Ti metal and carbon cations are synthesized into TiC. At the same time, by adjusting the current density applied to the metal bipolar plate, excessive graphitization transformation of the first carbon layer is avoided, so that the TiC phase and sp3 phase at the interface are significantly more than the sp2 phase, thereby improving the high potential corrosion resistance of the first carbon layer and the Ti-C interface. The second carbon layer is a conductive layer, and a low duty cycle and a high pulse bias are used to achieve a low resistance effect. Finally, a metal bipolar plate carbon-based coating that can withstand long-term high potential corrosion and has excellent contact resistance characteristics is obtained. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 This is a schematic diagram of the structure of the coating equipment of Example 4.

[0023] In the figure: 1. Metal bipolar plate; 2. Bias device; 3. Sputtering cathode; 4. Arc bend magnetic filter coil; 5. Arc cathode. DETAILED DESCRIPTION

[0024] The following will be combined with the embodiments of the present application to clearly and completely describe the technical solution of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0025] In order to make the above-mentioned objects, features and advantages of the present application more obvious and easy to understand, the present application is further described in detail below in conjunction with specific implementation methods.

[0026] In order to more accurately evaluate the durability of the bipolar plate coating, the researchers added constant potential tests, such as 72 hours at 0.6V, 5 hours at 1.1V, and 1 hour at 1.6V. For example, taking 1.6V as an example, the coating is corroded at a constant voltage of 1.6V. After a certain period of time (1h, 2h, 3h, 4h, 5h, etc.), the corrosion current is compared, the corrosion phenomenon is observed, and the change in resistance after corrosion is measured. Among them: the higher the voltage of the constant potential test, the higher the corrosion resistance requirements for the bipolar plate coating. This application is mainly proposed to improve the corrosion resistance of the bipolar plate coating in the constant potential test at 1.6V.

[0027] The applicant adopted a variety of schemes to prepare carbon film bipolar plate coatings to improve the corrosion resistance of the bipolar plate coatings, such as: magnetron sputtering process, arc ion plating, plasma enhanced chemical vapor deposition, arc magnetic filtration, etc. The carbon films prepared under most process conditions corroded at a constant potential of 1.6V for 0.5 to 2 hours, and all showed severe corrosion phenomena.

[0028] According to the applicant's research, there are at least two factors that affect the corrosion of carbon film at high potential: one is the slow corrosion of the surface of the carbon film, and the other is the electron channel and defects in the carbon film coating entering the interior of the coating, corroding the interface between the metal base layer and the carbon layer, especially the sp2 phase that is more easily corroded at the interface, and the liquid quickly invades, causing the interlayer bonding to fail, and ultimately leading to the collapse of the carbon film at high potential. The test found that the second method is the main factor affecting the corrosion resistance of the carbon film at a constant potential of 1.6V.

[0029] The carbon film bipolar plate coating prepared by current technology can only meet relatively basic technical requirements. When encountering high-potential corrosion, the coating will fail quickly, and the surface carbon film of the bipolar plate coating will be dissolved or peeled off, thereby increasing the contact resistance and affecting the output efficiency and life of the battery. In more serious corrosion situations, when the coating loses its surface carbon film, the acidic corrosive liquid will penetrate into the stainless steel substrate, causing the precipitation of Fe and Cr ions, resulting in the failure of the membrane electrode and the premature scrapping of the entire battery stack.

[0030] In order to solve the problem of poor constant voltage corrosion resistance of bipolar plate carbon film at high potential, the following technical solutions are provided:

[0031] The present application provides a method for preparing a metal bipolar plate coating, comprising the following steps:

[0032] S1. Place the cleaned metal bipolar plate in a single furnace coating machine with an arc elbow magnetic filter coil, an arc cathode and a sputtering cathode, wherein the sputtering cathode is a metal Ti target and the arc cathode is a graphite target, evacuate the plate, and use plasma to clean the surface of the metal bipolar plate;

[0033] S2, applying a preset bias voltage to the metal bipolar plate, wherein the preset bias voltage is 50V to 300V, turning on the sputtering cathode to deposit a metal base layer, and the thickness of the deposited metal base layer is 100nm to 500nm;

[0034] S3, turn off the sputtering cathode, adjust the preset bias voltage applied to the metal bipolar plate to a DC bias voltage, the DC bias voltage is adjusted to 600V-800V, turn on the arc bend magnetic filter coil, the current of the arc bend magnetic filter coil is 5A-15A, and at the same time, adjust the current density applied to the metal bipolar plate to not exceed 0.005A / cm 2 , turning on the arc cathode to deposit a first carbon layer, wherein the thickness of the deposited first carbon layer is 10 nm to 50 nm;

[0035] S4. Maintain the parameters of the arc bend magnetic filter coil and the arc cathode unchanged, adjust the preset bias applied to the metal bipolar plate to a high pulse bias with a low duty cycle, the bias of the high pulse bias with a low duty cycle is 1800V to 2200V, the duty cycle of the high pulse bias with a low duty cycle is 2% to 5%, deposit a second carbon layer, and the thickness of the second carbon layer is 50nm to 500nm.

[0036] In an optional embodiment, in step S3, the contact resistance of the first carbon layer is 50 mΩ·cm 2 ~ 200mΩ·cm 2 The corrosion current density of the first carbon layer in a constant potential test at 1.6 V for 5 hours is ≤50 μA / cm 2 .

[0037] In an optional embodiment, in step S4, the contact resistance of the second carbon layer is 2 mΩ·cm 2 ~10mΩ·cm 2 The corrosion current density of the second carbon layer in a constant potential test at 1.6 V for 5 hours is ≤100 μA / cm 2 .

[0038] In an optional embodiment, in step S1, the metal bipolar plate is a stainless steel bipolar plate or a titanium-based bipolar plate.

[0039] In an optional embodiment, in step S2, the power applied to the cathode sputtering target is 4KW to 10KW.

[0040] In an optional implementation scheme, in step S3, the arc bend tube magnetic filtration coil adopts a 90° bend tube design.

[0041] In an optional implementation scheme, in step S3, the current applied to the arc bend magnetic filtration coil is 5A to 15A.

[0042] In an optional implementation scheme, in step S3, the distance between the bend outlet of the arc bend magnetic filtration coil and the metal bipolar plate is 10 cm to 30 cm.

[0043] In an optional implementation, in step S3, the current of the arc cathode is 50A to 150A.

[0044] To support the above technical solution, the following embodiments are also provided.

[0045] Example 1

[0046] This embodiment provides a method for preparing a metal bipolar plate coating, comprising the following steps:

[0047] S1. Place the cleaned metal bipolar plate in a single furnace coating machine with a 90° arc elbow magnetic filter coil, an arc cathode and a sputtering cathode, wherein the metal bipolar plate is a SUS316 bipolar plate, the sputtering cathode is a metal Ti target, and the arc cathode is a graphite target. Vacuum the plate to 4 mPa and use Ar plasma to clean the surface of the metal bipolar plate.

[0048] S2, applying a preset bias voltage to the metal bipolar plate, the preset bias voltage is 100V, turning on the sputtering cathode to deposit a metal base layer, the power applied to the sputtering cathode is 10KW, and the thickness of the deposited metal base layer is 200nm;

[0049] S3, turn off the sputtering cathode, adjust the preset bias voltage applied to the metal bipolar plate to a DC bias voltage of 600V, turn on the arc bend magnetic filter coil, the current of the arc bend magnetic filter coil is 15A, and at the same time, adjust the current density applied to the metal bipolar plate to 0.005A / cm 2 , turning on the arc cathode to deposit a first carbon layer, wherein the thickness of the deposited first carbon layer is 10 nm;

[0050] S4. Maintain the parameters of the arc bend magnetic filter coil and the arc cathode unchanged, adjust the preset bias voltage applied to the metal bipolar plate to a high pulse bias voltage with a low duty cycle, and the bias voltage of the high pulse bias voltage with a low duty cycle is 1800V. At the same time, adjust the duty cycle of the high pulse bias voltage with a low duty cycle to 4%, and deposit a second carbon layer, and the thickness of the second carbon layer is 300nm.

[0051] The performance of the above coating was characterized: the above coating was placed at a constant potential of 1.6V for 5 hours, and there was no obvious change on the coating surface, and the corrosion current density was 82μA / cm 2 Before corrosion, the surface contact resistance of the coating was (1.0MPa) 4.6 mΩ•cm 2 After corrosion, the surface contact resistance of the coating is 6.5 mΩ•cm 2 .

[0052] Example 2

[0053] This embodiment provides a method for preparing a metal bipolar plate coating, comprising the following steps:

[0054] S1. Place the cleaned metal bipolar plate in a single furnace coating machine with a 90° arc elbow magnetic filter coil, an arc cathode and a sputtering cathode, wherein the metal bipolar plate is a SUS316 bipolar plate, the sputtering cathode is a metal Ti target, and the arc cathode is a graphite target. Vacuum the plate to 4 mPa and use Ar plasma to clean the surface of the metal bipolar plate.

[0055] S2, applying a preset bias voltage to the metal bipolar plate, the preset bias voltage is 80V, turning on the sputtering cathode to deposit a metal base layer, the power applied to the sputtering cathode is 8KW, and the thickness of the deposited metal base layer is 150nm;

[0056] S3, turn off the sputtering cathode, adjust the preset bias voltage applied to the metal bipolar plate to a DC bias voltage of 700V, turn on the arc bend magnetic filter coil, the current of the arc bend magnetic filter coil is 10A, and at the same time, adjust the current density applied to the metal bipolar plate to 0.003A / cm 2 , turning on the arc cathode to deposit a first carbon layer, wherein the thickness of the deposited first carbon layer is 20 nm;

[0057] S4. Maintain the parameters of the arc bend magnetic filter coil and the arc cathode unchanged, adjust the preset bias applied to the metal bipolar plate to a high pulse bias with a low duty cycle, the bias voltage of the high pulse bias with a low duty cycle is 2000V, and the duty cycle of the high pulse bias with a low duty cycle is 2%, and deposit a second carbon layer with a thickness of 200nm.

[0058] The performance of the above coating was characterized: the above coating was placed at a constant potential of 1.6V for 5 hours, and there was no obvious change on the coating surface, and the corrosion current density was 88μA / cm 2 Before corrosion, the surface contact resistance of the coating was (1.0MPa) 5.9 mΩ•cm 2 After corrosion, the surface contact resistance of the coating is 6.9 mΩ•cm 2 .

[0059] Example 3

[0060] This embodiment provides a method for preparing a metal bipolar plate coating, comprising the following steps:

[0061] S1. Place the cleaned metal bipolar plate in a single furnace coating machine with a 90° arc elbow magnetic filter coil, an arc cathode and a sputtering cathode, wherein the metal bipolar plate is a SUS316 bipolar plate, the sputtering cathode is a metal Ti target, and the arc cathode is a graphite target. Vacuum the plate to 4 mPa and use Ar plasma to clean the surface of the metal bipolar plate.

[0062] S2, applying a preset bias voltage to the metal bipolar plate, the preset bias voltage is 80V, turning on the sputtering cathode to deposit a metal base layer, the power applied to the sputtering cathode is 8KW, and the thickness of the deposited metal base layer is 150nm;

[0063] S3, turn off the sputtering cathode, adjust the preset bias voltage applied to the metal bipolar plate to a DC bias voltage of 800V, turn on the arc bend magnetic filter coil, the current of the arc bend magnetic filter coil is 5A, and at the same time, adjust the current density applied to the metal bipolar plate to 0.004A / cm 2 , turning on the arc cathode to deposit a first carbon layer, wherein the thickness of the deposited first carbon layer is 30 nm;

[0064] S4. Maintain the parameters of the arc bend magnetic filter coil and the arc cathode unchanged, adjust the preset bias voltage applied to the metal bipolar plate to a high pulse bias voltage with a low duty cycle, the bias voltage of the high pulse bias voltage with a low duty cycle is 2200V, and the duty cycle is 5%, and deposit a second carbon layer with a thickness of 200nm.

[0065] The performance of the above coating was characterized: the above coating was placed at a constant potential of 1.6V for 5 hours, and there was no obvious change on the coating surface, and the corrosion current density was 82μA / cm 2 Before corrosion, the surface contact resistance of the coating was (1.0MPa) 4.5 mΩ•cm 2 After corrosion, the surface contact resistance of the coating is 6.1 mΩ•cm 2 .

[0066] Example 4

[0067] This embodiment provides a coating device for preparing the metal bipolar plate coating of embodiments 1-3, such as Figure 1 As shown, the coating equipment includes a single furnace coating machine, a metal bipolar plate 1 arranged in the cavity of the single furnace coating machine, a bias device 2 for applying a preset bias to the metal bipolar plate 1, a sputtering cathode 3 is also provided in the cavity of the single furnace coating machine, and the sputtering cathode 3 is used to sputter a metal base layer to the metal bipolar plate 1. The cavity of the single furnace coating machine is also connected to the arc cathode 5 through an arc bend magnetic filter coil 4, and the arc cathode 5 is used to deposit a carbon layer on the metal bipolar plate 1, and the specific carbon layer includes a first carbon layer and a second carbon layer.

[0068] Comparative Example 1

[0069] Compared with Example 1, the difference of this comparative example is that the deposition of the first carbon layer is eliminated, and other parameters remain unchanged.

[0070] The performance of the above coating was characterized: the above coating was placed at a constant potential of 1.6V for 5 hours, the color of the coating surface changed, the corrosion current density decreased, and the surface was passivated. Contact resistance before corrosion (1.0MPa) 4.4mΩ•cm 2 After the corrosion is completed, the contact resistance is 25.7 mΩ•cm 2 , the coating falls off and fails during the corrosion resistance process.

[0071] Comparative Example 2

[0072] Compared with Example 1, the difference of this comparative example is that in step S3, when depositing the first carbon layer, the preset bias voltage applied to the metal bipolar plate is adjusted to 50V, and other parameters remain unchanged.

[0073] The performance of the above coating was characterized: the above coating was placed at a constant potential of 1.6V for 5 hours, the color of the coating surface changed, the corrosion current density decreased, and the surface was passivated. Contact resistance before corrosion (1.0MPa) 12.1mΩ•cm 2 After corrosion, the contact resistance is 29.2 mΩ•cm 2 The initial resistance is large, and the coating falls off and fails during the corrosion resistance process.

[0074] Comparative Example 3

[0075] Compared with Example 1, the difference of this comparative example is that in step S3, when depositing the first carbon layer, the preset bias voltage applied to the metal bipolar plate is adjusted to 1200 V, and other parameters remain unchanged.

[0076] The performance of the above coating was characterized: the above coating was placed at a constant potential of 1.6V for 5 hours, the color of the coating surface changed, the corrosion current density decreased, and the surface was passivated. Contact resistance before corrosion (1.0MPa) 2.5mΩ•cm 2 After corrosion, the contact resistance is 26.6 mΩ•cm 2 ,Although the initial resistance is good, the coating falls off and fails during the corrosion resistance process.

[0077] Comparative Example 4

[0078] Compared with Example 1, the difference of this comparative example is that in step S4, when depositing the second carbon layer, the bias voltage of the high pulse bias with a low duty cycle is adjusted to 1300 V, and other parameters remain unchanged.

[0079] The performance of the above coating was characterized: the above coating was placed at a constant potential of 1.6V for 5 hours, and the color of the coating surface did not change significantly, and the corrosion current density was 70μA / cm 2 Contact resistance before corrosion (1.0MPa) 18.4mΩ•cm 2 After corrosion, the contact resistance is 20.1 mΩ•cm 2 , the coating contact resistance is large.

[0080] Comparative Example 5

[0081] Compared with Example 1, the difference of this comparative example is that in step S4, when depositing the second carbon layer, the bias voltage of the high pulse bias with a low duty cycle is adjusted to 2500V, and other parameters remain unchanged.

[0082] The performance of the above coating was characterized: the above coating was placed at a constant potential of 1.6V for 5 hours, the coating surface changed color, and the corrosion current density was 232μA / cm 2 Contact resistance before corrosion (1.0MPa) 3.9mΩ•cm 2 After corrosion, the contact resistance is 10.3 mΩ•cm 2 The corrosion current increases, the contact resistance decreases after coating, and the contact resistance increases significantly after corrosion, and the corrosion resistance deteriorates.

[0083] Comparative Example 6

[0084] Compared with Example 1, the difference of this comparative example is that the deposition order of the first carbon layer and the second carbon layer is adjusted, and other parameters remain unchanged.

[0085] The performance of the above coating was characterized: the above coating was placed at a constant potential of 1.6V for 5 hours, and the coating surface had obvious color changes and surface passivation. Contact resistance before corrosion (1.0MPa) 9.5mΩ•cm 2 After corrosion, the contact resistance is 26.6 mΩ•cm2 . The coating falls off and fails during the corrosion resistance process.

[0086] Comparative Example 7

[0087] Compared with Example 1, the difference of this comparative example is that in step S3, the current density applied to the metal bipolar plate is adjusted to 0.01A / cm 2 .

[0088] The performance of the above coating was characterized: the above coating was placed at a constant potential of 1.6V for 5 hours, and the coating surface had obvious color changes and surface passivation. Contact resistance before corrosion (1.0MPa) 3.8mΩ•cm 2 After corrosion, the contact resistance is 35.5 mΩ•cm 2 . The coating falls off and fails during the corrosion resistance process.

[0089] Comparative Example 8

[0090] Compared with Example 1, the difference of this comparative example is that in step S4, the duty cycle of the high pulse bias with a low duty cycle is adjusted to 10.0%.

[0091] The performance of the above coating was characterized: the above coating was placed at a constant potential of 1.6V for 5 hours, and there was no obvious change on the coating surface, and the corrosion current density was 35μA / cm 2 Before corrosion, the surface contact resistance of the coating was (1.0MPa) 18.4 mΩ•cm 2 After corrosion, the surface contact resistance of the coating is 19.5mΩ•cm 2 . The contact resistance is large and increases slightly after corrosion.

[0092] Comparative Example 9

[0093] Compared with Example 1, the difference of this comparative example is that the 90° arc bend magnetic filtering coil is replaced with a conventional arc cathode, and a non-filtered arc cathode is used to deposit the first carbon layer and the second carbon layer, while keeping the deposition parameters unchanged.

[0094] The performance of the above coating was characterized: the above coating was placed at a constant potential of 1.6V for 5 hours, and the coating surface had obvious color changes, and the corrosion current density increased first and then decreased, and finally stabilized at 5μA / cm 2 , surface passivation. Contact resistance before corrosion (1.0MPa) 3.5mΩ•cm 2 After corrosion, the contact resistance is 28.6 mΩ•cm 2 During the test, the coating was severely corroded, indicating that the electrochemical performance was degraded. Although the resistance was small before corrosion, it became significantly worse after corrosion.

[0095] In summary, the present application discloses a new method for preparing a metal bipolar plate coating resistant to high potential corrosion, wherein the coating is composed of two layers of carbon film: an inner first carbon layer and an outer second carbon layer. In order to form the first carbon layer, the inventors used an arc bend tube magnetic filter coil to emit carbon cations, and accelerated these ions by applying a specific DC bias, thereby enhancing the binding force of chemical bonds between interfaces. In this process, Ti metal reacts chemically with the carbon cations to generate TiC. At the same time, by precisely controlling the current density of the arc bend tube magnetic filter coil, the excessive transformation of the first carbon layer to graphitization is effectively prevented, ensuring that the number of TiC phases and sp3 phases at the interface is significantly better than that of the sp2 phase, which greatly improves the corrosion resistance of the first carbon layer and its interface with Ti and C at high potentials.

[0096] As for the second carbon layer, it mainly exists as a conductive layer. By adopting the process conditions of low duty cycle and high pulse bias, the low resistance effect was successfully achieved. In the end, this metal bipolar plate coating composed of two layers of carbon film not only has excellent high potential corrosion resistance, but also has excellent contact resistance characteristics, which can meet the needs of long-term use.

[0097] Although this specification is described according to implementation modes, not every implementation mode contains only one independent technical solution. This description of the specification is only for the sake of clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each implementation mode may also be appropriately combined to form other implementation modes that can be understood by those skilled in the art.

[0098] The series of detailed descriptions listed above are only specific descriptions of feasible implementation methods of the present application. They are not intended to limit the scope of protection of the present application. Any equivalent implementation methods or changes that do not deviate from the technical spirit of the present application should be included in the scope of protection of the present application.

Claims

1. A method for preparing a metal bipolar plate coating resistant to high potential corrosion, characterized in that: The steps include: S1. Place the cleaned metal bipolar plate in a single furnace coating machine with an arc elbow magnetic filter coil, an arc cathode and a sputtering cathode, wherein the sputtering cathode is a metal Ti target and the arc cathode is a graphite target, evacuate the plate, and use plasma to clean the surface of the metal bipolar plate; S2, applying a preset bias voltage to the metal bipolar plate, wherein the preset bias voltage is 50V to 300V, turning on the sputtering cathode to deposit a metal base layer, and the thickness of the deposited metal base layer is 100nm to 500nm; S3, turn off the sputtering cathode, adjust the preset bias voltage applied to the metal bipolar plate to a DC bias voltage, the DC bias voltage is adjusted to 600V-800V, turn on the arc bend magnetic filter coil, and at the same time, adjust the current density applied to the metal bipolar plate to not more than 0.005A / cm 2 , turning on the arc cathode to deposit a first carbon layer, wherein the thickness of the deposited first carbon layer is 10 nm to 50 nm; S4. Maintain the parameters of the arc bend magnetic filter coil and the arc cathode unchanged, adjust the preset bias applied to the metal bipolar plate to a high pulse bias with a low duty cycle, the bias of the high pulse bias with a low duty cycle is 1800V to 2200V, the duty cycle of the high pulse bias with a low duty cycle is 2% to 5%, deposit a second carbon layer, and the thickness of the second carbon layer is 50nm to 500nm.

2. The method for preparing a high potential corrosion resistant metal bipolar plate coating according to claim 1, characterized in that: In step S3, the contact resistance of the first carbon layer is 50 mΩ·cm 2 ~ 200mΩ·cm 2 The corrosion current density of the first carbon layer in a constant potential test at 1.6 V for 5 hours is ≤50 μA / cm 2 .

3. The method for preparing a high potential corrosion resistant metal bipolar plate coating according to claim 1, characterized in that: In step S4, the contact resistance of the second carbon layer is 2 mΩ·cm 2 ~10mΩ·cm 2 The corrosion current density of the second carbon layer in a constant potential test at 1.6 V for 5 hours is ≤100 μA / cm 2 .

4. The method for preparing a high potential corrosion resistant metal bipolar plate coating according to claim 1, characterized in that: In step S1, the metal bipolar plate is a stainless steel bipolar plate or a titanium-based bipolar plate.

5. The method for preparing a high potential corrosion resistant metal bipolar plate coating according to claim 1, characterized in that: In step S2, the power applied to the cathode sputtering target is 4KW to 10KW.

6. The method for preparing a high potential corrosion resistant metal bipolar plate coating according to claim 1, characterized in that: In step S3, the arc bend tube magnetic filtration coil adopts a 90° bend tube design.

7. The method for preparing a high potential corrosion resistant metal bipolar plate coating according to claim 1, characterized in that: In step S3, the current applied to the arc bending tube magnetic filtering coil is 5A to 15A.

8. The method for preparing a high potential corrosion resistant metal bipolar plate coating according to claim 1, characterized in that: In step S3, the distance between the bend outlet of the arc bend magnetic filtration coil and the metal bipolar plate is 10 cm to 30 cm.

9. The method for preparing a high potential corrosion resistant metal bipolar plate coating according to claim 1, characterized in that: In step S3, the current of the arc cathode is 50A-150A.

10. A high-potential corrosion-resistant metal bipolar plate coating prepared according to the method for preparing a high-potential corrosion-resistant metal bipolar plate coating according to any one of claims 1 to 9.

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