A conductive corrosion-resistant composite coating and a preparation method and application thereof

Abstract

The application discloses a conductive and corrosion-resistant composite coating and a preparation method and application thereof, and belongs to the technical field of materials. The composite coating comprises, from inside to outside on the surface of a substrate, a first Ti-containing coating, a Ti-C coating and a functional surface layer; the functional surface layer comprises alternately arranged second Ti-containing coatings and ta-C coatings. The second Ti-containing coating can form a stable passivation layer in an acidic high-potential environment, the ta-C coating has a high sp3 content, a high density and graphite particles, which are beneficial to improving the corrosion resistance of the coating while ensuring the conductivity of the coating. The primer layer and the transition layer serve as a buffer layer for buffering residual internal stress, can effectively combine the functional surface layer on the surface of the substrate, and improve the bonding strength of the coating and the substrate. The coating material is used on the surface of a fuel cell metal bipolar plate, can effectively prevent the metal bipolar plate from contacting a corrosive liquid, and improves the service life of the metal bipolar plate in the fuel cell.

Description

Technical Field

[0001] The present invention relates to the field of material technology, and in particular to a conductive and corrosion-resistant composite coating and a preparation method and application thereof. Background Art

[0002] Proton exchange membrane fuel cells (PEMFCs) are considered one of the most promising new energy vehicle power generation devices due to their low operating temperature, fast startup, and zero emissions. As a key component of PEMFCs, bipolar plates account for the vast majority of the battery's cost and weight. They perform multiple functions, including distributing reactant gases, conducting electrons, supporting the membrane electrode assembly, and removing reaction product water.

[0003] In recent years, metal bipolar plates have become an ideal material for bipolar plates due to their excellent mechanical strength, formability, high thermal and electrical conductivity, and the ability to be made into bipolar plates with a thickness of less than 1mm. These characteristics significantly reduce the volume and weight of fuel cell stacks and improve the specific power of the stack. However, the high potential generated during the start-stop operation of on-board fuel cells can cause severe corrosion of the metal bipolar plates, increasing the contact resistance at the metal bipolar plate interface. Furthermore, metal ions leached from the metal bipolar plates can contaminate the proton exchange membrane and catalyst, thereby reducing the output performance and durability of the proton exchange membrane fuel cell.

[0004] In view of this, the present invention is proposed. Summary of the Invention

[0005] The purpose of the present invention is to provide a conductive and corrosion-resistant composite coating and its preparation method and application to solve or improve the above technical problems. The composite coating not only has low interface contact resistance but also can resist high potential corrosion.

[0006] This application can be implemented as follows:

[0007] In a first aspect, the present application provides a conductive and corrosion-resistant composite coating, which includes a primer layer, a transition layer, and a functional surface layer sequentially arranged on the surface of a substrate from the inside to the outside;

[0008] Among them, the base layer is a first Ti-containing coating formed by metallic Ti; the transition layer is a Ti-C coating formed by Ti and C; the functional surface layer includes at least one second Ti-containing coating formed by metallic Ti and at least one ta-C coating, and the second Ti-containing coating and the ta-C coating are arranged alternately.

[0009] In an optional embodiment, the thickness of the primer layer is 20-600 nm; and / or the thickness of the transition layer is 20-600 nm; and / or the thickness of the functional surface layer is 20-1200 nm.

[0010] In an optional embodiment, in the functional surface layer, the total thickness of the second Ti-containing coating layer is 10-600 nm, and the total thickness of the ta-C coating layer is 10-600 nm.

[0011] In an optional embodiment, in the functional surface layer, a ratio of the total thickness of the second Ti-containing coating layer to the total thickness of the ta-C coating layer is 3:1 to 1:3.

[0012] In an optional embodiment, the composite coating has at least one of the following characteristics:

[0013] Feature 1: The contact resistance of the composite coating is 2.65-3.95mΩ / cm 2 ;

[0014] Feature 2: The contact resistance of the composite coating after corrosion is 7.53-9.2mΩ / cm 2 ;

[0015] Feature 3: The low-potential corrosion current density of the composite coating is 0.50-0.71μA / cm 2 ;

[0016] Feature 4: The high potential corrosion current density of the composite coating is 23-55μA / cm 2 ;

[0017] Feature 5: The contact angle of the composite coating is 94-108°.

[0018] In a second aspect, the present application provides a method for preparing a composite coating as described in any one of the aforementioned embodiments, comprising the following steps: preparing a first Ti-containing coating, a Ti-C coating and a second Ti-containing coating by magnetron sputtering according to preset positions, and preparing a ta-C coating by vacuum cathode arc ion plating.

[0019] In an optional embodiment, the preparation process of the composite coating is carried out in an inert atmosphere.

[0020] In an alternative embodiment, the flow rate of the inert gas is 80-200 sccm.

[0021] In an optional embodiment, during the preparation of the composite coating, the vacuum degree of the vacuum coating chamber is controlled to be 3×10 -3 Pa to 5×10 -3 Below Pa.

[0022] In an optional embodiment, before preparing the first Ti-containing coating, the substrate is further subjected to the following pretreatment: the surface of the substrate is polished and cleaned, and after drying, the substrate is placed on a workpiece turntable in a vacuum coating chamber so that the distance between the substrate and each target material is maintained at 2-50 cm; the vacuum coating chamber is evacuated to a vacuum degree of at least 10 -3Pa, introduce inert gas into the vacuum coating chamber, adjust the negative bias voltage of the workpiece holder to 200-1000V, and clean and etch the substrate and target material.

[0023] In an optional embodiment, the preparation conditions of the first Ti-containing coating include: the target material is a Ti metal target, 2000-6000 W, the bias voltage is 200-400 V, the deposition temperature is 80-300° C., and the deposition time is 1-15 min.

[0024] In an optional embodiment, the preparation conditions of the Ti-C coating include: the target materials are a C target and a Ti metal target, the sputtering power of the Ti metal target is reduced from 5000W to 500W, the sputtering power of the C target is increased from 500W to 5000W, the deposition temperature is 80-300°C, and the deposition time is 1-15min.

[0025] In an optional embodiment, the preparation conditions of the second Ti-containing coating include: the target material is a Ti target; the sputtering target power is 100-5000W, the bias voltage is 0-400V, the deposition temperature is 80-300°C, and the deposition time is 1-15min.

[0026] In an optional embodiment, the preparation conditions of the ta-C coating include: the target material is a graphite target, the C target arc current is 30-100A, the working pressure is 0.1-0.5Pa, the deposition temperature is 80-300°C, and the deposition time is 1-20min.

[0027] In a third aspect, the present application provides a fuel cell metal bipolar plate, the substrate surface of which has a composite coating according to any one of the aforementioned embodiments.

[0028] The beneficial effects of this application include:

[0029] In the multi-layer composite coating provided by the present application, the second Ti-containing coating in the functional surface layer can form a stable passivation layer in an acidic high-potential environment, and the ta-C coating has a high sp3 content, high density, and graphite particles, which are beneficial to improving the corrosion resistance of the coating while ensuring the electrical conductivity of the coating. The first Ti-containing coating and the Ti-C coating act as buffer layers for buffering residual internal stress, enabling the functional surface layer to be effectively bonded to the surface of the substrate, which is beneficial to overcoming the problem of performance mismatch between the coating and the substrate, maximally weakening the stress in the coating, reducing the generation of cracks, and improving the bonding strength between the coating and the substrate. When this coating material is used on the surface of the metal bipolar plate of a fuel cell, it can effectively block the contact between the metal bipolar plate and the corrosive liquid, thereby increasing the service life of the metal bipolar plate in the fuel cell. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for use in the embodiments. It should be understood that the following drawings only illustrate certain embodiments of the present invention and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other relevant drawings can be obtained based on these drawings without paying any creative work.

[0031] Figure 1 This is a SEM image of the structure of the conductive and corrosion-resistant multi-layer composite coating provided in Example 11 of the present application;

[0032] Figure 2 A graph showing the test results of the electrical conductivity and contact resistance of a fuel cell metal bipolar plate having a multi-layer composite coating provided in Example 11 of the present application;

[0033] Figure 3 This is a graph showing the hydrophobicity test results of a fuel cell metal bipolar plate with a multi-layer composite coating provided in Example 11 of the present application. DETAILED DESCRIPTION

[0034] To make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention are described clearly and completely below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer are used. Where the manufacturer of the reagents or instruments is not specified, all are conventional products that can be purchased commercially.

[0035] The conductive and corrosion-resistant composite coating provided in this application, as well as its preparation method and application are described in detail below.

[0036] The conductive and corrosion-resistant composite coating proposed in the present application includes a primer layer, a transition layer and a functional surface layer arranged in sequence from the inside to the outside on the surface of the substrate.

[0037] The substrate is titanium alloy or stainless steel; the base layer is a first Ti-containing coating formed by metal Ti; the transition layer is a Ti-C coating formed by Ti and C; the functional surface layer includes at least one second Ti-containing coating formed by metal Ti and at least one ta-C coating, and the second Ti-containing coating and the ta-C coating are arranged alternately.

[0038] The second Ti-containing coating is a material that satisfies passivation or stable conditions in an acidic, high-potential environment. The ta-C coating (hydrogen-free carbon coating) has the advantages of corrosion resistance and electrical conductivity.

[0039] In this application, the number of layers of the second Ti-containing coating contained in the functional surface layer is the same as the number of layers of the ta-C coating. In other words, the functional surface layer under this condition is a multi-periodic composite layer, each period includes a second Ti-containing coating layer and a corrosion-resistant and conductive ta-C coating layer, and all the second Ti-containing coating layers and ta-C coating layers in the multi-periodic composite layer are alternately arranged. In the functional surface layer, the outermost layer away from the substrate is the ta-C coating. For ease of understanding, the functional surface layer can be (Ti / ta-C) n Represents, where n≥1.

[0040] For reference, in this application, the thickness of the base layer can be 20-600nm, such as 20nm, 50nm, 100nm, 150nm, 200nm, 250nm, 300nm, 350nm, 400nm, 450nm, 500nm, 550nm or 600nm, etc., or it can be any other value within the range of 20-600nm.

[0041] If the thickness of the primer layer is less than 20 nm, it is not conducive to buffering the internal stress of the coating; if the thickness of the primer layer is greater than 600 nm, it is not conducive to supporting the functional surface layer.

[0042] The thickness of the transition layer can be 20-600 nm, such as 20 nm, 50 nm, 100 nm, 150 nm, 200 nm, 250 nm, 300 nm, 350 nm, 400 nm, 450 nm, 500 nm, 550 nm or 600 nm, or any other value within the range of 20-600 nm.

[0043] If the thickness of the transition layer is less than 20 nm, it is not conducive to buffering the internal stress of the coating; if the thickness of the transition layer is greater than 600 nm, it is not conducive to supporting the functional surface layer.

[0044] The thickness of the functional surface layer can be 20-1200 nm, such as 20 nm, 50 nm, 100 nm, 200 nm, 500 nm, 800 nm, 1000 nm, or 1200 nm, or any other value within the range of 20-1200 nm. In the functional surface layer, the total thickness of the second Ti-containing coating layer can be 10-600 nm, and the total thickness of the ta-C coating layer can be 10-600 nm. In some typical embodiments, the ratio of the total thickness of the second Ti-containing coating layer to the total thickness of the ta-C coating layer in the functional surface layer can be 3:1 to 1:3.

[0045] If the thickness of the functional surface layer is less than 20 nm, it is not conducive to the durability of the coating; if the thickness of the functional surface layer is greater than 1200 nm, it is not conducive to the bonding strength between the coating and the substrate.

[0046] As above, in the composite coating provided by the present application, the second Ti-containing coating contained in the functional surface layer can form a stable passivation layer in an acidic high potential environment, and the ta-C coating has a high sp3 content, high density and graphite particles, which is beneficial to improving the corrosion resistance of the coating while ensuring the electrical conductivity of the coating. The first Ti-containing coating and the Ti-C coating can serve as a buffer layer for buffering residual internal stress, enabling the functional surface layer to be effectively bonded to the substrate surface, which is beneficial to overcoming the problem of performance mismatch between the coating and the substrate, maximally weakening the stress in the coating, reducing the generation of cracks, and improving the bonding strength between the coating and the substrate. That is, the base layer focuses on enhancing the film-base bonding and compatibility regulation, the transition layer focuses on the connecting function, and the functional surface layer focuses on conductive corrosion resistance (the second Ti-containing coating focuses on high potential corrosion passivation performance, and the ta-C coating focuses on low potential corrosion resistance and electrical conductivity). The resulting multilayer composite coating has the advantages of high corrosion resistance, good electrical conductivity, and high hydrophobicity, avoiding problems such as intergranular corrosion, large resistance caused by surface oxides, and poor wetting properties.

[0047] In some embodiments, the contact resistance of the composite coating is 2.65-3.95 mΩ / cm 2 In some embodiments, the composite coating has a post-corrosion contact resistance of 7.53-9.2 mΩ / cm 2 In some embodiments, the composite coating has a low potential corrosion current density of 0.50-0.71 μA / cm 2 In some embodiments, the high potential corrosion current density of the composite coating is 23-55 μA / cm 2 In some embodiments, the composite coating has a contact angle of 94-108°.

[0048] Correspondingly, the present application also provides a method for preparing the above-mentioned composite coating, comprising the following steps: preparing a first Ti-containing coating, a Ti-C coating and a second Ti-containing coating by magnetron sputtering according to preset positions, and preparing a Ta-C coating by vacuum cathode arc ion plating.

[0049] The preparation process of the composite coating is carried out in an inert atmosphere. The flow rate of the inert gas can be, for example, 80-200 sccm (such as 80 sccm, 100 sccm, 150 sccm or 200 sccm). In addition, during the preparation process of the composite coating, the vacuum degree of the vacuum coating chamber is controlled to be 3×10 -3 Pa to 5×10 -3 Below Pa.

[0050] For reference, before preparing the first Ti-containing coating, the substrate is also subjected to the following pre-treatment:

[0051] A. Grind the surface of the substrate to remove the oxide film on the surface of the substrate;

[0052] B. Clean the polished substrate, such as by ultrasonic cleaning with acetone, ethanol, and deionized water in sequence to remove grease and contaminants on the substrate surface, and then blow dry to make the substrate surface smooth;

[0053] C. After drying, place the workpiece on the workpiece turntable of the vacuum coating chamber, and keep the distance between the substrate and each target material at 2-50cm (such as 2cm, 5cm, 8cm, 10cm, 15cm, 20cm, 25cm, 30cm, 35cm, 40cm, 45cm or 50cm, etc.);

[0054] D. Evacuate the vacuum coating chamber until the vacuum degree reaches at least 10 -3 Pa, introduce inert gas (such as high-purity argon, etc.) into the vacuum coating chamber, adjust the negative bias voltage of the workpiece holder to 200-1000V (such as 200V, 400V, 600V, 800V or 1000V, etc.), clean and etch the substrate and target material to remove surface contaminants, which is beneficial to improve the bonding strength between the substrate and the coating.

[0055] In the present application, the preparation conditions of the first Ti-containing coating may include: the target material is a Ti metal target, the sputtering target power is 2000-6000W (such as 2000, 3000W, 4000W, 5000W or 6000W, etc.), the bias voltage is 200-400V (such as 200V, 300V or 400V, etc.), the deposition temperature is 80-300℃ (such as 80℃, 100℃, 150℃, 200℃, 250℃ or 300℃, etc.), and the deposition time is 1-15min (such as 1min, 5min, 10min or 15min, etc.).

[0056] The preparation conditions of the Ti-C coating may include: the target materials are a C target and a Ti metal target, the sputtering power of the Ti metal target is reduced from 5000 W to 500 W, the sputtering power of the C target is increased from 500 W to 5000 W, the deposition temperature is 80-300°C (such as 80°C, 100°C, 150°C, 200°C, 250°C or 300°C, etc.), and the deposition time is 1-15 min (such as 1 min, 5 min, 10 min or 15 min, etc.).

[0057] Preparation conditions of the second Ti-containing coating may include: the target material is a Ti target; the sputtering target power is 100-5000W (such as 100W, 500W, 1000W, 1500W, 2000W, 2500W, 3000W, 3500W, 4000W, 4500W or 5000W, etc.), the bias voltage is 0-400V (such as 0V, 10V, 50V, 100V, 150V, 200V, 250V, 300V, 350V or 400V, etc.), the deposition temperature is 80-300℃ (such as 80℃, 100℃, 150℃, 200℃, 250℃ or 300℃, etc.), and the deposition time is 1-15min (such as 1min, 5min, 10min or 15min, etc.).

[0058] The preparation conditions of the ta-C coating may include: the target material is a graphite target, the C target arc current is 30-100A (such as 30A, 40A, 50A, 60A, 70A, 80A, 90A or 100A, etc.), the working pressure is 0.1-0.5Pa (such as 0.1Pa, 0.2Pa, 0.3Pa, 0.4Pa or 0.5Pa, etc.), the deposition temperature is 80-300℃ (such as 80℃, 100℃, 150℃, 200℃, 250℃ or 300℃, etc.), and the deposition time is 1-20min (such as 1min, 5min, 10min, 15min or 20min, etc.).

[0059] After the coating is prepared, turn off the power supply and bias, turn off the gas, wait for the substrate to cool to 150°C, open the vacuum coating chamber and take out the substrate with the composite coating deposited.

[0060] Continuing from the above, the above-mentioned composite coating is prepared by a composite physical vapor deposition method of magnetron sputtering and vacuum arc ion plating deposition. The bonding force between the metal bipolar plate substrate and the composite coating is extremely high, realizing the preparation of a coating with multi-layer composite functional integration and strong membrane-base bonding. It can improve the high-potential corrosion resistance and long-term corrosion resistance of the metal bipolar plate while ensuring the conductivity of the fuel cell metal bipolar plate coating, and realize the requirements of good hydrophobicity, conductive and corrosion-resistant synergistic integration of the fuel cell metal bipolar plate.

[0061] In addition, the present application also provides a fuel cell metal bipolar plate, the substrate surface of which has the above-mentioned composite coating.

[0062] By depositing the composite coating provided in this application with the characteristics of low contact resistance, high hydrophobicity and resistance to high potential corrosion on the surface of the metal bipolar plate of the fuel cell, the contact between the metal bipolar plate and the corrosive liquid can be effectively blocked, thereby improving the service life of the metal bipolar plate in the fuel cell.

[0063] The features and performance of the present invention are further described in detail below with reference to the embodiments.

[0064] Example 1

[0065] This embodiment provides a conductive and corrosion-resistant multilayer composite coating, which includes a first Ti-containing coating, a Ti-C coating and a functional surface layer arranged in sequence from the inside to the outside on the surface of the substrate, and the functional surface layer includes a second Ti-containing coating and a ta-C coating arranged alternately.

[0066] The total thickness of the multilayer composite coating is 800 nm, wherein the thickness of the first Ti-containing coating is 100 nm, the thickness of the Ti-C coating is 100 nm, the total thickness of the functional surface layer is 600 nm, and the ratio of the thickness of the second Ti-containing coating to the thickness of the ta-C coating is 1:3 (i.e., the thickness of the second Ti-containing coating is 150 nm, and the thickness of the ta-C coating is 450 nm).

[0067] The preparation method of the multi-layer composite coating comprises:

[0068] Step (1): Pre-treating the base material.

[0069] A. Grind the surface of the metal bipolar plate substrate (made of SS-316L) to remove the surface oxide film;

[0070] B. Surface cleaning of the substrate material: ultrasonically clean the metal bipolar plate substrate with acetone, ethanol, and deionized water in sequence to remove grease and contaminants on the substrate surface, and then blow dry to make the surface of the metal bipolar plate substrate smooth;

[0071] C. After air drying, place the sample on the workpiece rotating rack of the vacuum coating chamber so that the distance between the metal bipolar plate substrate sample and each target material is 35 cm;

[0072] D. Evacuate the vacuum coating chamber until the vacuum degree reaches 10 -3 Pa, high-purity argon gas is introduced into the vacuum coating chamber, the negative bias voltage of the workpiece holder is adjusted to 300 V, and the substrate and target material are cleaned and etched to remove surface contaminants, thereby improving the bonding strength between the substrate and the coating.

[0073] Step (2): preparing a first Ti-containing coating.

[0074] The magnetron sputtering coating device was used to pump the vacuum degree of the vacuum coating chamber to 3×10 -3 Pa, argon gas was introduced at a flow rate of 100 sccm, Ti target was used as target material, the sputtering target power was adjusted to 5000 W, the bias voltage was 300 V, and the first Ti-containing coating was deposited on the surface of the metal bipolar plate substrate as a base layer. The deposition temperature was 280 ° C, the deposition time was 5 min, and the deposition thickness was 100 nm.

[0075] Step (3): Prepare Ti-C coating.

[0076] Maintaining the argon flow rate, using C target and Ti metal target as target materials, the C target power was adjusted from 500W to 5000W, the Ti target power was adjusted from 5000W to 500W, the bias voltage was 100V, and Ti-C coating was deposited on the surface of the base layer as a transition layer. The deposition temperature was 280℃, the deposition time was 5min, and the deposition thickness was 100nm.

[0077] Step (4): Prepare the functional surface layer.

[0078] A. Preparation of a second Ti-containing coating: Maintaining the argon flow rate, using a Ti target as the target material, adjusting the sputtering target power to 5000 W and the bias voltage to 360 V, deposit a layer of the second Ti-containing coating on the surface of the Ti-C coating at a deposition temperature of 280°C, a deposition time of 8 min, and a deposition thickness of 150 nm.

[0079] B. Preparation of ta-C coating: Maintaining the argon flow rate, using a graphite target as the target material, a layer of ta-C coating was deposited on the surface of the second Ti-containing coating by cathode arc ion plating technology. The C target arc current was adjusted to 60 A, the working pressure was 0.3 Pa, the deposition temperature was 280 ° C, the deposition time was 20 min, and the deposition thickness was 450 nm.

[0080] Step (5): Post-processing.

[0081] After the coating is prepared, the power supply and bias are turned off, the gas is turned off, and after the metal bipolar plate substrate cools to 150°C, the vacuum coating chamber is opened and the metal bipolar plate substrate is taken out to obtain a metal bipolar plate with a multi-layer composite coating.

[0082] Example 2

[0083] The difference between this embodiment and embodiment 1 is that the ratio of the thickness of the second Ti-containing coating to the thickness of the ta-C coating is 1:2 (ie, the thickness of the second Ti-containing coating is 200 nm, and the thickness of the ta-C coating is 400 nm).

[0084] Example 3

[0085] The difference between this embodiment and embodiment 1 is that the ratio of the thickness of the second Ti-containing coating to the thickness of the ta-C coating is 1:1 (ie, the thickness of the second Ti-containing coating is 300 nm, and the thickness of the ta-C coating is 300 nm).

[0086] Example 4

[0087] The difference between this embodiment and embodiment 1 is that the ratio of the thickness of the second Ti-containing coating to the thickness of the ta-C coating is 2:1 (ie, the thickness of the second Ti-containing coating is 400 nm, and the thickness of the ta-C coating is 200 nm).

[0088] Example 5

[0089] The difference between this embodiment and embodiment 1 is that the ratio of the thickness of the second Ti-containing coating to the thickness of the ta-C coating is 3:1 (ie, the thickness of the second Ti-containing coating is 450 nm, and the thickness of the ta-C coating is 150 nm).

[0090] Example 6

[0091] The difference between this embodiment and embodiment 1 is that the second Ti-containing coating and the ta-C coating are both 2 layers, the thickness of each second Ti-containing coating layer is 75 nm, the thickness of each ta-C coating layer is 225 nm, and the second Ti-containing coating and the ta-C coating are arranged alternately, that is, arranged in the manner of second Ti-containing coating → ta-C coating → second Ti-containing coating → ta-C coating.

[0092] Example 7

[0093] The difference between this embodiment and embodiment 1 is that the second Ti-containing coating and the ta-C coating both have three layers, the thickness of each second Ti-containing coating layer is 50 nm, the thickness of each ta-C coating layer is 150 nm, and the second Ti-containing coating and the ta-C coating are arranged alternately, that is, in the order of second Ti-containing coating → ta-C coating → second Ti-containing coating → ta-C coating → second Ti-containing coating → ta-C coating.

[0094] Example 8

[0095] The difference between this embodiment and Example 1 is that the second Ti-containing coating and the ta-C coating both have 4 layers, the thickness of each second Ti-containing coating layer is 37.5 nm, the thickness of each ta-C coating layer is 112.5 nm, and the second Ti-containing coating and the ta-C coating are arranged alternately, that is, in the order of second Ti-containing coating → ta-C coating → second Ti-containing coating → ta-C coating → second Ti-containing coating → ta-C coating → second Ti-containing coating → ta-C coating.

[0096] Example 9

[0097] The difference between this embodiment and embodiment 1 is that the second Ti-containing coating and the ta-C coating are both 2 layers, the thickness of each second Ti-containing coating layer is 225 nm, the thickness of each ta-C coating layer is 75 nm, and the second Ti-containing coating and the ta-C coating are arranged alternately, that is, arranged in the manner of second Ti-containing coating → ta-C coating → second Ti-containing coating → ta-C coating.

[0098] Example 10

[0099] The difference between this embodiment and embodiment 1 is that the second Ti-containing coating and the ta-C coating both have three layers, the thickness of each second Ti-containing coating layer is 150 nm, the thickness of each ta-C coating layer is 50 nm, and the second Ti-containing coating and the ta-C coating are arranged alternately, that is, in the order of second Ti-containing coating → ta-C coating → second Ti-containing coating → ta-C coating → second Ti-containing coating → ta-C coating.

[0100] Example 11

[0101] The difference between this embodiment and Example 1 is that the second Ti-containing coating and the ta-C coating both have 4 layers, the thickness of each second Ti-containing coating layer is 112.5 nm, the thickness of each ta-C coating layer is 37.5 nm, and the second Ti-containing coating and the ta-C coating are arranged alternately, that is, in the order of second Ti-containing coating → ta-C coating → second Ti-containing coating → ta-C coating → second Ti-containing coating → ta-C coating → second Ti-containing coating → ta-C coating.

[0102] The SEM image of the conductive and corrosion-resistant multilayer composite coating obtained in this embodiment is shown in FIG. Figure 1 shown.

[0103] Example 12

[0104] This embodiment provides a conductive and corrosion-resistant multilayer composite coating, which includes a first Ti-containing coating, a Ti-C coating and a functional surface layer arranged in sequence from the inside to the outside on the surface of the substrate, and the functional surface layer includes a second Ti-containing coating and a ta-C coating arranged alternately.

[0105] The total thickness of the multilayer composite coating is 60 nm, wherein the thickness of the first Ti-containing coating is 20 nm, the thickness of the Ti-C coating is 20 nm, the total thickness of the functional surface layer is 20 nm, and the ratio of the thickness of the second Ti-containing coating to the thickness of the ta-C coating is 1:1 (i.e., the thickness of the second Ti-containing coating is 10 nm, and the thickness of the ta-C coating is 10 nm).

[0106] The preparation method of the multi-layer composite coating comprises:

[0107] Step (1): Pre-treating the base material.

[0108] A. Grind the surface of the metal bipolar plate substrate (made of 316L) to remove the surface oxide film;

[0109] B. Surface cleaning of the substrate material: ultrasonically clean the metal bipolar plate substrate with acetone, ethanol, and deionized water in sequence to remove grease and contaminants on the substrate surface, and then blow dry to make the surface of the metal bipolar plate substrate smooth;

[0110] C. After air drying, place the sample on the workpiece rotating rack of the vacuum coating chamber so that the distance between the metal bipolar plate substrate sample and each target material is 2 cm;

[0111] D. Evacuate the vacuum coating chamber until the vacuum degree reaches 10 -3 Pa, high-purity argon gas is introduced into the vacuum coating chamber, the negative bias voltage of the workpiece holder is adjusted to 200 V, and the substrate and target material are cleaned and etched to remove surface contaminants, thereby improving the bonding strength between the substrate and the coating.

[0112] Step (2): preparing a first Ti-containing coating.

[0113] The magnetron sputtering coating device was used to pump the vacuum degree of the vacuum coating chamber to 3×10 -3 Pa, argon gas was introduced at a flow rate of 100 sccm, a Ti target was used as the target material, the sputtering target power was adjusted to 5000 W, the bias voltage was 300 V, and a first Ti-containing coating was deposited on the surface of the metal bipolar plate substrate as a base layer. The deposition temperature was 280° and the deposition time was 1 min.

[0114] Step (3): Prepare Ti-C coating.

[0115] Maintaining the argon flow rate, using C target and Ti metal target as target materials, the C target power was adjusted from 500W to 5000W, the Ti target power was adjusted from 5000W to 500W, the bias voltage was 100V, and Ti-C coating was deposited on the surface of the base layer as a transition layer. The deposition temperature was 280℃ and the deposition time was 1min.

[0116] Step (4): Prepare the functional surface layer.

[0117] A. Preparation of the second Ti-containing coating: maintaining the argon flow rate, using a Ti target as the target material, adjusting the sputtering target power to 100 W, the bias voltage to 0 V, and depositing a layer of the second Ti-containing coating on the surface of the Ti-C coating at a deposition temperature of 80°C for 1 min.

[0118] B. Preparation of ta-C coating: maintaining the argon flow rate, using graphite target as target material, adopt cathode arc ion plating technology to deposit a layer of ta-C coating on the surface of the second Ti-containing coating, the C target arc current is adjusted to 30A, the working pressure is 0.1Pa, and the deposition temperature is 80℃.

[0119] Step (5): Post-processing.

[0120] After the coating is prepared, the power supply and bias are turned off, the gas is turned off, and after the metal bipolar plate substrate cools to 150°C, the vacuum coating chamber is opened and the metal bipolar plate substrate is taken out to obtain a metal bipolar plate with a multi-layer composite coating.

[0121] Example 13

[0122] This embodiment provides a conductive and corrosion-resistant multilayer composite coating, which includes a first Ti-containing coating, a Ti-C coating and a functional surface layer arranged in sequence from the inside to the outside on the surface of the substrate, and the functional surface layer includes a second Ti-containing coating and a ta-C coating arranged alternately.

[0123] The total thickness of the multilayer composite coating is 2400nm, wherein the thickness of the first Ti-containing coating is 600nm, the thickness of the Ti-C coating is 600nm, the total thickness of the functional surface layer is 1200nm, and the ratio of the thickness of the second Ti-containing coating to the thickness of the ta-C coating is 1:1 (that is, the thickness of the second Ti-containing coating is 600nm, and the thickness of the ta-C coating is 600nm).

[0124] The preparation method of the multi-layer composite coating comprises:

[0125] Step (1): Pre-treating the base material.

[0126] A. Grind the surface of the metal bipolar plate substrate (made of SS-316L) to remove the surface oxide film;

[0127] B. Surface cleaning of the substrate material: ultrasonically clean the metal bipolar plate substrate with acetone, ethanol, and deionized water in sequence to remove grease and contaminants on the substrate surface, and then blow dry to make the surface of the metal bipolar plate substrate smooth;

[0128] C. After air drying, place the sample on the workpiece rotating rack of the vacuum coating chamber so that the distance between the metal bipolar plate substrate sample and each target material is 50 cm;

[0129] D. Evacuate the vacuum coating chamber until the vacuum degree reaches 10 -3 Pa, high-purity argon gas is introduced into the vacuum coating chamber, the negative bias voltage of the workpiece holder is adjusted to 1000 V, and the substrate and target material are cleaned and etched to remove surface contaminants, thereby improving the bonding strength between the substrate and the coating.

[0130] Step (2): preparing a first Ti-containing coating.

[0131] The magnetron sputtering coating device was used to pump the vacuum degree of the vacuum coating chamber to 3×10 -3 Pa, argon gas was introduced at a flow rate of 100 sccm, Ti target was used as target material, the sputtering target power was adjusted to 5000 W, the bias voltage was 300 V, and the first Ti-containing coating was deposited on the surface of the metal bipolar plate substrate as a base layer. The deposition temperature was 300 ° C and the deposition time was 8 min.

[0132] Step (3): Prepare Ti-C coating.

[0133] Maintaining the argon flow rate, using C target and Ti metal target as target materials, the C target power was adjusted from 500W to 5000W, the Ti target power was adjusted from 5000W to 500W, the bias voltage was 150V, and Ti-C coating was deposited on the surface of the base layer as a transition layer. The deposition temperature was 300℃ and the deposition time was 5min.

[0134] Step (4): Prepare the functional surface layer.

[0135] A. Preparation of the second Ti-containing coating: maintaining the argon flow rate, using a Ti target as the target material, adjusting the sputtering target power to 3000 W, the bias voltage to 400 V, and depositing a layer of the second Ti-containing coating on the surface of the Ti-C coating at a deposition temperature of 300°C for 15 min.

[0136] B. Preparation of ta-C coating: Maintaining the argon flow rate, using a graphite target as the target material, a layer of ta-C coating was deposited on the surface of the second Ti-containing coating by cathode arc ion plating technology. The C target arc current was adjusted to 100 A, the working pressure was 0.5 Pa, the deposition temperature was 300 ° C, and the deposition time was 20 min.

[0137] Step (5): Post-processing.

[0138] After the coating is prepared, the power supply and bias are turned off, the gas is turned off, and after the metal bipolar plate substrate cools to 150°C, the vacuum coating chamber is opened and the metal bipolar plate substrate is taken out to obtain a metal bipolar plate with a multi-layer composite coating.

[0139] Comparative Example 1

[0140] The only difference between this comparative example and Example 3 is that the functional surface layer is only a 600 nm ta-C coating.

[0141] The Ti / Ti-C / ta-C coating provided in Comparative Example 1 lacks the alternating cycle of the high-potential corrosion-resistant environment stable passivation layer of Ti after deposition, and its corrosion resistance at high potential is significantly reduced compared with that of the embodiment. The ta-C is broken down at high potential, resulting in an increase in contact resistance after corrosion and a decline in conductive performance.

[0142] Comparative Example 2

[0143] The only difference between this comparative example and Example 3 is that the functional surface layer is only the second Ti-containing coating layer with a thickness of 600 nm.

[0144] The Ti / Ti-C / Ti coating provided in this comparative example has the characteristic that the Ti element can form a stable passivation layer under acidic high potential, but due to the large contact resistance of the Ti layer, it cannot meet the DOE requirement of 10mΩ / cm 2 Within.

[0145] Comparative Example 3

[0146] The only difference between this comparative example and Example 3 is that the functional surface layer is deposited in the order of ta-C coating → second Ti-containing coating.

[0147] The Ti / Ti-C / ta-C / Ti coating provided in this comparative example has the characteristics of stable passivation of the Ti element at acidic high potentials and good conductivity and corrosion resistance of ta-C. The Ti surface layer has good corrosion resistance during high-potential corrosion, but its own contact resistance is too large, and the ta-C in the inner layer cannot significantly reduce the contact resistance.

[0148] Comparative Example 4

[0149] The only difference between this comparative example and comparative example 1 is that the Ti in the first Ti-containing coating layer and the transition layer is replaced by Cr which also has good electrical conductivity and corrosion resistance.

[0150] Compared with Example 1, the Cr / CrC / ta-C coating provided in this comparative example uses Cr element as a transition layer. Cr element has good electrical conductivity and corrosion resistance.

[0151] The Cr / CrC / ta-C coating provided in this comparative example will undergo internal corrosion and dissolution during the high-potential corrosion process, causing the film layer to fall off and lose its protective effect. The corrosive solution directly corrodes the substrate itself, causing severe corrosion.

[0152] Comparative Example 5

[0153] The difference between this comparative example and comparative example 1 is that the functional surface layer is an aC coating.

[0154] The above-mentioned aC coating is prepared using a magnetron sputtering process. Specifically, the argon flow rate is maintained at 150 sccm, a graphite target is used as the target material, the sputtering target power is adjusted to 5000 W, the bias voltage is 160 V, the deposition temperature is 200°C, the deposition time is 360 min, and a conductive aC coating is deposited on the surface of the transition layer as a functional surface layer with a deposition thickness of 600 nm.

[0155] The Ti / Ti-C / aC coating provided in this comparative example, wherein the aC coating is prepared by a magnetron sputtering process, which reduces the ionization rate, resulting in a lower sp3 content in the coating, and the sputtering rate of this method is low, and the deposition time is increased by 300 minutes compared with the deposition time of comparative example 1.

[0156] Comparative Example 6

[0157] The difference between this comparative example and Example 9 is that the Ti in the first Ti-containing coating, the transition layer and the second Ti-containing coating is replaced by Cr which also has good electrical conductivity and corrosion resistance.

[0158] Comparative Example 7

[0159] The difference between this comparative example and comparative example 1 is that there is no primer layer and transition layer.

[0160] The surface coating of the comparative example sample peeled off when the furnace door was opened, and the corrosion resistance and electrical conductivity of the coating could not be characterized.

[0161] Comparative Example 8

[0162] The difference between this comparative example and comparative example 1 is that the thickness of the base layer is 10 nm, and the thickness of the transition layer is 10 nm.

[0163] After the comparative example sample was taken out of the furnace chamber and placed for 24 hours, the film peeling phenomenon appeared on the surface, and the corrosion resistance and electrical conductivity of the coating could not be characterized.

[0164] Comparative Example 9

[0165] The difference between this comparative example and comparative example 1 is that the thickness of the primer layer is 600 nm, and the thickness of the ta-C coating layer is 800 nm.

[0166] After the comparative example sample was taken out, the film peeling phenomenon appeared on the surface, and the corrosion resistance and electrical conductivity of the coating could not be characterized.

[0167] Comparative Example 10

[0168] The difference between this comparative example and comparative example 1 is that the total thickness of the functional surface layer is 1.5 μm.

[0169] After the comparative example sample was taken out and placed for 24 hours, the film peeling phenomenon appeared on the surface, and the corrosion resistance and electrical conductivity of the coating could not be characterized.

[0170] Test example

[0171] The performance of the metal bipolar plates with multilayer composite coatings prepared in Examples 1-13 and Comparative Examples 1-10 was compared, and the results are shown in Table 1 and Figures 2 to 3 shown.

[0172] Among them, the contact resistance is tested with reference to "GB / T 20042.6-2011", the contact resistance after corrosion is tested with reference to "GB / T20042.6-2011", the low potential corrosion current density is tested with reference to "GB / T 20042.6-2011", the high potential corrosion current density is tested with reference to "GB / T 20042.6-2011", and the hydrophobicity is tested with reference to "ASTMD724-88".

[0173] Table 1 Test results

[0174]

[0175]

[0176] As shown in Table 1, Examples 1-13 can produce composite coatings with advantages over Comparative Examples 1-10, such as high corrosion resistance, good electrical conductivity, and high hydrophobicity. This helps avoid problems such as intergranular corrosion, high resistance caused by surface oxides, and poor wettability. The corresponding preparation method offers a more integrated molding process than other methods, is simple and continuous, has low costs, good safety, and exhibits long lifespan and reliability due to the multi-interface effect.

[0177] In summary, the solution provided in this application has the following features and advantages:

[0178] (1) The conductive and corrosion-resistant multilayer composite coating provided by this application can give full play to the conductive and low-potential corrosion resistance of the ta-C coating and the high-potential corrosion resistance of the Ti layer. In a long-term corrosion environment, because the ta-C coating contains a high sp 3The second Ti-containing coating can improve the density and long-term corrosion resistance of the coating. At the same time, the carbon clusters on the surface ensure electrical conductivity. In a long-term high-potential corrosion environment, the second Ti-containing coating can improve the high-potential corrosion resistance of the coating as a whole. In addition, a first Ti-containing coating and a Ti-C layer are sandwiched between the functional surface layer and the metal bipolar plate substrate as a buffer layer to buffer residual internal stress. This coating structure can connect the upper and lower layers, allowing the functional surface layer to be effectively bonded to the surface of the fuel cell metal bipolar plate substrate, overcoming the performance mismatch between the coating and the fuel cell metal bipolar plate substrate, minimizing the stress in the coating, reducing the generation of cracks, and improving the bonding strength between the coating and the fuel cell metal bipolar plate substrate.

[0179] (2) This application starts from the coating service conditions and technical indicators of the fuel cell metal bipolar plate substrate, and proposes a coating system that integrates multiple periods and multi-layer composite structures through the design of coating composition and organizational structure, that is, it presents from the outside to the inside: the functional surface layer is composed of multiple periods of high-potential corrosion-resistant layers and conductive low-potential corrosion-resistant layers alternately, that is, it is composed of a Ti coating that can form a stable passivation layer at acidic high potential and a corrosion-resistant conductive Ta-C coating; the transition layer is a Ti-C layer with moderate hardness and strength and is a link between the upper and lower layers, and the base layer is a Ti layer that is integrated and matched with the physical and chemical interface of the substrate, forming an integrated multifunctional integrated coating system with conductive and corrosion-resistant synergy.

[0180] (3) This application proposes a method and method for the controlled preparation of a conductive, corrosion-resistant functional coating that integrates multiple periods and multi-layer composite functions by using a composite technology of vacuum arc ion deposition and magnetron sputtering. By using composite technology to finely control the coating composition and structure, the preparation of a coating that integrates multi-layer composite functions and membrane-based composite functions is achieved, meeting the compatibility matching of conductive and corrosion-resistant properties.

[0181] (4) The conductive and corrosion-resistant multilayer composite coating proposed in this application can significantly improve the high-potential corrosion resistance, hydrophobicity and conductivity of the fuel cell bipolar plate coating.

[0182] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations of the present invention are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention shall be included within the scope of protection of the present invention.

Claims

1. A conductive and corrosion-resistant composite coating, characterized in that: The composite coating comprises a primer layer, a transition layer and a functional surface layer arranged in sequence from the inside to the outside on the substrate surface; The primer layer is a first Ti-containing coating formed of metallic Ti; the transition layer is a Ti-C coating formed of Ti and C; the functional surface layer includes at least one second Ti-containing coating formed of metallic Ti and at least one ta-C coating, and the second Ti-containing coating and the ta-C coating are alternately arranged in the order of first the second Ti-containing coating and then the ta-C coating; The thickness of the primer layer is 20-600 nm; the thickness of the transition layer is 20-600 nm; the thickness of the functional surface layer is 20-1200 nm; In the functional surface layer, the total thickness of the second Ti-containing coating is 10-600 nm, and the total thickness of the ta-C coating is 10-600 nm; in the functional surface layer, the ratio of the total thickness of the second Ti-containing coating to the total thickness of the ta-C coating is 3:1 to 1:3; The contact resistance of the composite coating is 2.65-3.95 mΩ / cm 2 , the contact resistance after corrosion is 7.53-9.2mΩ / cm 2 , low potential corrosion current density is 0.50-0.71μA / cm 2 , high potential corrosion current density is 23-55μA / cm 2 , contact angle is 94-108°; The preparation of the conductive and corrosion-resistant composite coating includes the following steps: preparing the first Ti-containing coating, the Ti-C coating and the second Ti-containing coating by magnetron sputtering according to preset positions, and preparing the ta-C coating by vacuum cathode arc ion plating.

2. A method for preparing a composite coating according to claim 1, characterized in that: The method comprises the following steps: preparing the first Ti-containing coating, the Ti-C coating and the second Ti-containing coating by magnetron sputtering at preset positions, and preparing the Ta-C coating by vacuum cathode arc ion plating.

3. The preparation method according to claim 2, characterized in that The preparation process of the composite coating is carried out in an inert atmosphere.

4. The preparation method according to claim 3, characterized in that The flow rate of the inert gas is 80-200 sccm.

5. The preparation method according to claim 2, characterized in that During the preparation of the composite coating, the vacuum degree of the vacuum coating chamber was controlled to be 3×10 -3 Pa to 5×10 -3 Pa.

6. The preparation method according to claim 2, characterized in that Before preparing the first Ti-containing coating, the substrate is subjected to the following pretreatment: the surface of the substrate is polished and cleaned, and after drying, the substrate is placed on a workpiece turntable in a vacuum coating chamber, so that the distance between the substrate and each target material is maintained at 2-50 cm; the vacuum coating chamber is evacuated to a vacuum degree of at least 10 -3 Pa, introduce inert gas into the vacuum coating chamber, adjust the negative bias voltage of the workpiece holder to 200-1000V, and clean and etch the substrate and target material.

7. The preparation method according to claim 6, characterized in that The preparation conditions of the first Ti-containing coating include: the target material is a Ti metal target, the sputtering target power is 2000-6000W, the bias voltage is 200-400V, the deposition temperature is 80-300°C, and the deposition time is 1-15min.

8. The preparation method according to claim 6, characterized in that The preparation conditions of the Ti-C coating include: the targets are C target and Ti metal target, the sputtering power of the Ti metal target is reduced from 5000W to 500W, the sputtering power of the C target is increased from 500W to 5000W, the deposition temperature is 80-300°C, and the deposition time is 1-15 minutes.

9. The preparation method according to claim 6, characterized in that The preparation conditions of the second Ti-containing coating include: the target material is a Ti target; the sputtering target power is 100-5000W, the bias voltage is 0-400V, the deposition temperature is 80-300°C, and the deposition time is 1-15min.

10. The preparation method according to claim 6, characterized in that The preparation conditions of the ta-C coating include: the target material is a graphite target, the C target arc current is 30-100A, the working pressure is 0.1-0.5Pa, the deposition temperature is 80-300°C, and the deposition time is 1-20min.

11. A metal bipolar plate for a fuel cell, characterized in that: The substrate surface of the fuel cell metal bipolar plate has the composite coating according to claim 1.

Images