Carbon-based gradient composite coating for fuel cell metal bipolar plates and method of making same

Abstract

The present application relates to a fuel cell metal bipolar plate carbon-based gradient composite coating and a preparation method thereof, after pretreatment of a metal bipolar plate substrate, surface modification is carried out by using processes such as dipping, dipping-heat treatment, dipping-ultraviolet irradiation, plasma treatment, etc., to obtain a metal bipolar plate with surface hydroxylated or carboxylated modification, then carbon materials and conductive polymers are mixed according to different mass ratios to obtain several conductive polymer-carbon slurries with different carbon contents, and layer-by-layer deposition technology is used to deposit the conductive polymer-carbon slurries with different carbon contents layer by layer to one side of the surface modified metal bipolar plate, forming a conductive polymer-carbon composite coating with gradient change of carbon content. The present application sets up a conductive polymer-carbon composite coating layer by layer through functional group interaction to enhance the bonding force between the coating and the metal bipolar plate and between each film layer, and fully plays the synergistic effect of the conductive polymer and the carbon material to improve the conductive capacity, and gives consideration to good conductivity and corrosion resistance.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of fuel cells, in particular to a carbon-based gradient composite coating of a fuel cell metal bipolar plate and a preparation method thereof. BACKGROUND

[0002] Proton exchange membrane fuel cells (PEMFC) are considered as ideal clean energy conversion devices due to their great potential in high efficiency, high power density, low operating temperature, strong durability and zero pollution, and have been applied in transportation, spacecraft, mobile devices and other fields. Among them, the metal bipolar plate as the core component of PEMFC has become a research hotspot due to its excellent electrical and thermal conductivity, good corrosion resistance and mechanical properties, easy processing and manufacturing, etc. However, the metal bipolar plate is easily corroded and oxidized in the working environment of PEMFC high temperature, strong acid and high potential, which reduces the electrical conductivity and increases the interface contact resistance, thereby causing the working efficiency and service life of PEMFC to decay. Therefore, PEMFC puts forward higher requirements on the electrical conductivity and corrosion resistance of the metal bipolar plate.

[0003] In view of the above problems, research shows that setting a metal-based coating and a carbon coating on the surface of the metal bipolar plate is an economical and effective method to improve the performance of the bipolar plate. However, the metal coating is expensive, has low production efficiency and generally has low corrosion resistance, and the carbon coating has poor thermal conductivity and a fragile surface that is easily damaged. In addition, these coatings generally have pinhole defects on the surface, which limits the application effect of the metal bipolar plate. SUMMARY

[0004] In order to optimize the high electrical conductivity and corrosion resistance of the metal bipolar plate, the present application provides a carbon-based multi-gradient composite coating of a metal bipolar plate, which is prepared by depositing conductive polymer-carbon thin films on the surface of the metal bipolar plate layer by layer, and a preparation method thereof, which provides a basis for the industrial development of the surface modification of the metal bipolar plate.

[0005] To achieve the above-mentioned purpose of the present application, in a first aspect, the present application provides a preparation method of a carbon-based gradient composite coating of a fuel cell metal bipolar plate, which comprises:

[0006] S1, the metal bipolar plate substrate is sequentially ultrasonically cleaned in acetone, anhydrous ethanol and deionized water and dried, and then is surface modified by one or more processes of immersion, immersion-heat treatment, immersion-ultraviolet irradiation and plasma treatment, to obtain a metal bipolar plate with surface hydroxylated or carboxylated modification;

[0007] S2, carbon materials and conductive polymers are mixed in different mass ratios by a direct physical blending method or an in-situ polymerization method to obtain a plurality of conductive polymer-carbon slurries with different carbon contents;

[0008] S3, using layer-by-layer deposition technique to deposit conductive polymer-carbon paste with different carbon content to the side of the metal bipolar plate obtained from S1 which has been surface modified, and then dried to form conductive polymer-carbon composite coating with gradient change of carbon content.

[0009] Preferably, in S1:

[0010] The metal bipolar plate substrate material is selected from one of magnesium, aluminum, titanium, chromium, nickel, copper, zinc, zirconium, niobium, molybdenum, tungsten and alloys thereof and stainless steel;

[0011] The impregnation includes acid solution impregnation and alkali solution impregnation.

[0012] Preferably, in S2:

[0013] The direct physical blending method is to mix the carbon material dispersion liquid and the conductive polymer dispersion liquid directly to prepare the paste by using one or more of stirring, ultrasonic, oscillation, and ball milling;

[0014] The in-situ polymerization method is to polymerize the conductive polymer monomer on the surface of the carbon material in-situ and then prepare the paste.

[0015] Preferably, in S2:

[0016] The carbon material is selected from one or more of graphite or its modified material, carbon nanoribbon or its modified material, carbon nanofiber or its modified material, carbon nanotube or its modified material, graphene or its modified material, carbon black or its modified material, hard carbon or its modified material;

[0017] The conductive polymer material is selected from one or more of polyaniline, polypyrrole, polythiophene, polycarbazole, polyacetylene, polyphenylacetylene, polycyanoethylene, polycarbonate-polyaniline.

[0018] Preferably, in S3, the layer-by-layer deposition technique includes one or more of impregnation, spraying, spin coating, shower coating, and roller coating;

[0019] The impregnation technique includes one of conventional impregnation, vacuum impregnation, pressure impregnation, ultrasonic impregnation, and hot impregnation;

[0020] The spraying technique includes one of air spraying, airless spraying, electrostatic spraying, and thermal spraying;

[0021] The spin coating technique includes one of conventional spin coating and vacuum spin coating;

[0022] The shower coating technique includes one of spray shower coating and curtain shower coating;

[0023] The roller coating technique includes one of co-rotating roller coating, counter-rotating roller coating, rotating roller coating, and impregnated roller coating.

[0024] Preferably, in the S2 and the S3, the carbon materials in the conductive polymer-carbon slurries with different carbon contents are at least one same; the conductive polymer materials in the conductive polymer-carbon slurries with different carbon contents are at least one same.

[0025] In a second aspect, the embodiments of the present application also provide a metal bipolar plate coating, which is a carbon-based gradient composite coating coated on the surface of a metal bipolar plate substrate, and the carbon-based gradient composite coating comprises a plurality of conductive polymer-carbon coatings with different carbon contents arranged in a direction away from the metal bipolar plate substrate.

[0026] Preferably, the thickness of each of the conductive polymer-carbon coatings is 50 nm to 900 nm.

[0027] Preferably, the proportion of the carbon material in each of the conductive polymer-carbon coatings grown upward from the surface of the metal bipolar plate substrate to the total mass of the carbon material and the conductive polymer in the layer gradually decreases, and the proportion of the carbon material in the first layer to the last layer gradually decreases from 90 wt% to 70 wt% to 50 wt% to 10 wt%.

[0028] Preferably, the total number of layers of the carbon-based gradient composite coating is 2 to 40, and the total thickness is 100 nm to 36 μm.

[0029] In summary, the embodiments of the present application provide a carbon-based gradient composite coating for a fuel cell metal bipolar plate, which effectively combines conductive polymers and carbon materials to lay a foundation for assembling a high-performance composite coating. The functional group interaction is used to arrange the conductive polymer-carbon composite coating layer by layer to enhance the bonding force between the coating and the metal bipolar plate and between the film layers, and the synergistic effect of the conductive polymer and the carbon material is fully utilized to further improve the conductive capacity. A dense protective layer is formed on the surface of the metal bipolar plate to block pinhole defects and inhibit the invasion of corrosion sources, thereby obtaining good conductivity and excellent corrosion resistance. Compared with the prior art, the present application has the following advantages:

[0030] (1) The embodiments of the present application provide a metal bipolar plate carbon-based gradient composite coating preparation technology deposited layer by layer, which uses processes such as immersion, spraying, spin coating, shower coating, and roller coating to prepare a uniform, flat, and dense composite coating on the surface of the metal bipolar plate through the functional group interaction and close entanglement between adjacent films. The present application has low cost, simple and efficient method, and wide process conditions, and is easy to scale up.

[0031] (2) The embodiments of the present application provide a composite coating without continuous structural changes, which is constructed by the conductive polymer-carbon coatings with gradient structures deposited layer by layer, realizes good transition between the film layers and fine and effective regulation of the composition and structure of the film layers, and has high conductivity and corrosion resistance through process optimization.

[0032] (3) The embodiment of the present application provides a multilayer structure synergistic conductive polymer-carbon composite coating. In the coating, the carbon material fills the pinhole type defects in the conductive polymer-carbon coating as a nano additive, perfects the structural compactness of the coating, and blocks the diffusion path of corrosive ions; meanwhile, the carbon material also realizes a substantial improvement of the conductivity of the composite coating through the doping effect and the adhesive effect on the conductive polymer. In addition, the effective combination of the composite coating with the metal bipolar plate is strengthened through chemical combination. Therefore, the carbon-based gradient composite coating is beneficial to balancing high conductivity and strong corrosion resistance, thereby realizing effective protection of the metal bipolar plate. BRIEF DESCRIPTION OF DRAWINGS

[0033] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the drawings needed to be used in the embodiments will be briefly introduced as follows. Obviously, the drawings in the following description only constitute some embodiments of the present application, and for those skilled in the art, other drawings can also be obtained without creative labor on the basis of these drawings.

[0034] Figure 1 The structure of the metal bipolar plate in the embodiment of the present application is shown in the figure.

[0035] Figure 2 The flowchart of the preparation method of the carbon-based gradient composite coating of the metal bipolar plate in the embodiment of the present application is shown in the figure. DETAILED DESCRIPTION

[0036] The description of the embodiments of the present application should be combined with the corresponding drawings, and the drawings should be regarded as a part of the complete description. In the drawings, the shape or thickness of the embodiments can be enlarged, and the structures can be simplified or facilitated. In addition, the parts of the structures in the drawings will be described separately, and it should be noted that the elements not shown in the drawings or not described by words are in the form known by those skilled in the art.

[0037] The description of the embodiments herein, any reference to the direction and the orientation, is only for the convenience of description, and cannot be understood as any limitation on the protection scope of the present application. The following description of the preferred embodiments will involve the combination of features, which can exist independently or in combination, and the present application is not particularly limited to the preferred embodiments. The scope of the present application is defined by the claims.

[0038] As Figure 1As shown, the embodiment of the present application provides a metal bipolar plate, which comprises a metal bipolar plate base body 0 and a carbon-based gradient composite coating 1, 2, 3…n coated on the surface of the metal bipolar plate base body 0. The carbon-based gradient composite coating comprises a plurality of layers of conductive polymer-carbon coatings 1, 2, 3…n with different carbon contents arranged in a direction away from the metal bipolar plate base body 0. Through the effective combination of conductive polymers and carbon materials, a foundation is laid for assembling a high-performance composite coating. Among them, the conductive polymer-carbon composite coating is arranged layer by layer through functional group interaction to enhance the bonding force between the coating and the metal bipolar plate and between the film layers, and the synergistic effect of the conductive polymer and the carbon material is fully played to further improve the conductive capacity. By forming a dense protective layer on the surface of the metal bipolar plate and plugging pinhole defects to inhibit the invasion of corrosion sources, good conductivity and excellent corrosion resistance are obtained.

[0039] Preferably, the thickness of each layer of conductive polymer-carbon coating 1, 2, 3…n is 50 nm to 900 nm. More preferably, the thickness of each layer of conductive polymer-carbon coating 1, 2, 3…n is 100 nm to 350 nm. For the thickness selection of the coating, when the coating is too thin or too thick, it is easy to cause the surface flatness and density of the prepared coating to be poor, resulting in relatively large internal defects of the coating, which cannot inhibit the invasion of corrosion ions and reduce internal corrosion. When the coating layers are arranged within the above range, the function and quality of the coating can be better guaranteed.

[0040] Preferably, the proportion of the carbon material in each layer of conductive polymer-carbon coating 1, 2, 3…n grown upward from the surface of the metal bipolar plate base body 0 gradually decreases in the total mass of the carbon material and the conductive polymer in the layer. The carbon material proportion of the first layer to the last layer gradually decreases from 90wt% to 70wt% to 50wt% to 10wt%, and at the same time, the content of the conductive polymer in the first layer to the last layer gradually increases from 10wt% to 30wt% to 50wt% to 90wt% in the total mass of the carbon material and the conductive polymer in the layer. More preferably, the carbon material proportion of the first layer to the last layer gradually decreases from 80wt% to 70wt% to 45wt% to 25wt%, and at the same time, the content of the conductive polymer gradually increases from 20wt% to 30wt% to 55wt% to 75wt% in the total mass of the carbon material and the conductive polymer in the layer.

[0041] Preferably, the total number of layers of the carbon-based gradient composite coating is 2 to 40, and the total thickness is 100 nm to 36 μm. More preferably, the total number of layers of the carbon-based gradient composite coating is 4 to 10, and the total thickness is 400 nm to 3500 nm.

[0042] The embodiment of the present application also provides a preparation method of a carbon-based gradient composite coating of a fuel cell metal bipolar plate, which comprises:

[0043] S1, sequentially ultrasonic cleaning the metal bipolar plate substrate in acetone, anhydrous ethanol, deionized water and drying, then surface modification by one or more of the following processes: immersion, immersion-heat treatment, immersion-ultraviolet irradiation, plasma treatment, to obtain a metal bipolar plate with surface hydroxylated or carboxylated modification.

[0044] S2, mixing carbon materials and conductive polymers according to different mass ratios by direct physical blending method or in-situ polymerization method to obtain several conductive polymer-carbon slurries with different carbon contents.

[0045] S3, using layer-by-layer deposition technology to deposit conductive polymer-carbon slurries with different carbon contents on one side of the metal bipolar plate obtained in S1 after surface modification, and then drying to form a conductive polymer-carbon composite coating with gradient change in carbon content.

[0046] Preferably, in S1, the metal bipolar plate substrate material is selected from one of magnesium, aluminum, titanium, chromium, nickel, copper, zinc, zirconium, niobium, molybdenum, tungsten, alloys thereof and stainless steel. Immersion includes acid solution immersion and alkali solution immersion.

[0047] Preferably, in S2, the direct physical blending method is to mix carbon material dispersion liquid and conductive polymer dispersion liquid directly by one or more of stirring, ultrasonic, oscillation, ball milling to prepare a slurry. The in-situ polymerization method is to carry out in-situ polymerization of conductive polymer monomers on the surface of carbon materials and then prepare a slurry.

[0048] Preferably, in S2, the carbon material is selected from one or more of graphite or its modified material, carbon nanoribbon or its modified material, carbon nanofiber or its modified material, carbon nanotube or its modified material, graphene or its modified material, carbon black or its modified material, hard carbon or its modified material. The conductive polymer material is selected from one or more of polyaniline, polypyrrole, polythiophene, polycarbazole, polyacetylene, polyphenylacetylene, polycyanoethylene, polycarbonate-polyaniline.

[0049] Preferably, in S3, the layer-by-layer deposition technology includes one or more of immersion, spraying, spin coating, shower coating, and roller coating. The immersion technology includes one of conventional immersion, vacuum immersion, pressure immersion, ultrasonic immersion, and hot immersion. The spraying technology includes one of air spraying, airless spraying, electrostatic spraying, and thermal spraying. The spin coating technology includes one of conventional spin coating and vacuum spin coating. The shower coating technology includes one of spray shower coating and curtain shower coating. The roller coating technology includes one of co-rotating roller coating, counter-rotating roller coating, rotating roller coating, and immersion roller coating.

[0050] Preferably, in S2 and S3, at least one of the carbon materials in the several conductive polymer-carbon slurries with different carbon contents is the same. At least one of the conductive polymer materials in the several conductive polymer-carbon slurries with different carbon contents is the same.

[0051] In summary, the present application has the following advantages:

[0052] (1) The present application provides a preparation technology of a carbon-based gradient composite coating of a layer-by-layer deposited metal bipolar plate, which uses processes such as immersion, spraying, spin coating, shower coating, and roller coating to prepare a uniform, smooth, and dense composite coating on the surface of a metal bipolar plate through the functional group interaction and close entanglement between adjacent films. The present application has low cost, simple and efficient method, and wide process conditions, and is easy to scale up.

[0053] (2) The present application provides a composite coating without continuous structural changes, which is constructed by a layer-by-layer deposited gradient structure of a conductive polymer-carbon coating, realizes good transition between film layers and fine and effective regulation of film layer composition and structure, and has high conductivity and corrosion resistance through process optimization.

[0054] (3) The present application provides a conductive polymer-carbon composite coating with a synergistic effect of a multi-layer structure. Among them, the carbon material fills in the pinhole-like defects in the conductive polymer-carbon coating as a nano additive, perfects the structural density of the coating, and blocks the diffusion path of corrosion ions. At the same time, the carbon material also realizes a substantial improvement in the conductivity of the composite coating through the doping effect and adhesion effect on the conductive polymer. In addition, the chemical combination strengthens the effective combination of the composite coating with the metal bipolar plate. Therefore, the carbon-based gradient composite coating is conducive to balancing high conductivity and strong corrosion resistance, thereby realizing effective protection of the metal bipolar plate.

[0055] Example 1

[0056] In this embodiment, the metal bipolar plate material is a pure titanium metal bipolar plate.

[0057] Amino-functionalized carbon nanotubes (CNT-NH2) and carboxyl-functionalized carbon nanotubes (CNT-COOH) are mixed with polyaniline by a physical blending method to obtain polyaniline-amino-functionalized carbon nanotube (PANI-CNT-NH2) slurry and polyaniline-carboxyl-functionalized carbon nanotube (PANI-CNT-COOH) slurry, respectively. Subsequently, a PANI-CNT-NH2 layer and a PANI-CNT-COOH layer are sequentially deposited on the surface of a pure titanium metal bipolar plate substrate and dried.

[0058] S1. Surface modification of the metal bipolar plate: The pure titanium metal bipolar plate substrate is sequentially ultrasonically cleaned in acetone, anhydrous ethanol, and ultrapure water to remove surface impurities and oxides, and then dried. Concentrated sulfuric acid with a concentration of 98% is mixed with hydrogen peroxide at a volume ratio of 70:30 and kept in a 90°C constant temperature water bath, and then the pure titanium bipolar plate is immersed in the above solution for treatment to obtain a surface-hydroxylated pure titanium bipolar plate.

[0059] S2. Slurry preparation: (1) A certain amount of phytic acid was dissolved in ultrapure water, and aniline was added dropwise, and stirred for 1 h to form 10 mg / ml of ammonium phytate. Then a certain amount of ammonium persulfate (APS) was dissolved in ultrapure water and added dropwise to the ammonium phytate, and the mixture was stirred vigorously at -18℃ for 12 h to form PANI particles. The PANI particles were suction filtered, washed and dried, and then uniformly dispersed in ultrapure water to form a PANI dispersion.

[0060] (2) CNT-NH2 was added to an aqueous solution to prepare a dispersion, and then added to the PANI dispersion at a mass ratio of CNT-NH2 to PANI of 80:20, 70:30, and 50:50, respectively, and ultrasonically stirred and stirred for 1 h to obtain uniformly dispersed slurries A1-1, A3-1, and A5-1.

[0061] (3) CNT-COOH was added to an aqueous solution to prepare a dispersion, and then added to the PANI dispersion at a mass ratio of CNT-COOH to PANI of 75:25, 60:40, and 45:55, respectively, and ultrasonically stirred and stirred for 1 h to obtain uniformly dispersed slurries A2-1, A4-1, and A6-1.

[0062] S3. Composite coating preparation: The slurries A1-1, A2-1, A3-1, A4-1, A5-1, and A6-1 were sequentially sprayed onto the surface of the hydroxylated pure titanium bipolar plate of step S1 at a spraying distance of 30 cm, a spraying pressure of 0.3 MPa, and a spraying speed of 1 ml / min at room temperature and atmospheric pressure. Then, it was placed in a vacuum drying oven at a temperature of 80℃ for drying, to obtain a multi-gradient PANI-CNT composite coating with a total number of layers of 6 and a thickness of 1.2 μm.

[0063] Example 2

[0064] In this embodiment, the metal bipolar plate material is a pure titanium metal bipolar plate.

[0065] Amino-functionalized carbon nanotubes (CNT-NH2) and carboxyl-functionalized carbon nanotubes (CNT-COOH) were mixed with polyaniline by physical blending to obtain polyaniline-amino-functionalized carbon nanotube (PANI-CNT-NH2) slurry and polyaniline-carboxyl-functionalized carbon nanotube (PANI-CNT-COOH) slurry, respectively. Subsequently, a PANI-CNT-NH2 layer and a PANI-CNT-COOH layer were sequentially deposited on the surface of a pure titanium metal bipolar plate substrate and dried.

[0066] S1. Surface modification of metal bipolar plate: The pure titanium metal bipolar plate substrate was sequentially cleaned in acetone, anhydrous ethanol, and ultrapure water by ultrasonic cleaning to remove surface impurities and oxides, and then dried. The pure titanium bipolar plate was immersed in a 10 g / L NaOH solution at 60°C to obtain a surface-hydroxylated pure titanium bipolar plate.

[0067] S2. Preparation of slurry: (1) A certain amount of phytic acid was dissolved in ultrapure water, and aniline was added dropwise, and stirred for 1 h to form 10 mg / ml of ammonium phytate, and then a certain amount of ammonium persulfate (APS) was dissolved in ultrapure water and added dropwise to the ammonium phytate, and the mixture was stirred vigorously at -18°C for 12 h to form PANI particles. The PANI particles were suction filtered, washed and dried, and then uniformly dispersed in ultrapure water to form a PANI dispersion.

[0068] (2) CNT-NH2 was added to an aqueous solution to prepare a dispersion, and then added to the PANI dispersion at a mass ratio of CNT-NH2 to PANI of 75:25, 65:35, and 50:50, respectively, and ultrasonically stirred and stirred for 1 h to obtain uniformly dispersed slurries A1-2, A3-2, and A5-2.

[0069] (3) CNT-COOH was added to an aqueous solution to prepare a dispersion, and then added to the PANI dispersion at a mass ratio of CNT-COOH to PANI of 70:30, 60:40, and 40:60, respectively, and ultrasonically stirred and stirred for 1 h to obtain uniformly dispersed slurries A2-2, A4-2, and A6-2.

[0070] S3. Preparation of composite coating: The slurries A1-2, A2-2, A3-2, A4-2, A5-2, and A6-2 were sequentially spin-coated onto the surface of the hydroxylated pure titanium bipolar plate of step S1 at room temperature and atmospheric pressure at a spin-coating speed of 2600 rpm and a spin-coating time of 1 min. Then, it was placed in a vacuum drying oven at a temperature of 90°C to dry, obtaining a multi-gradient PANI-CNT composite coating with a total of 6 layers and a thickness of 1.8 μm.

[0071] Example 3

[0072] In this example, the metal bipolar plate material was a pure titanium metal bipolar plate.

[0073] Amino-functionalized carbon nanofibers (CNF-NH2) and carboxyl-functionalized carbon nanofibers (CNF-COOH) were mixed with polyaniline by physical blending to obtain polyaniline-amino-functionalized carbon nanofiber (PANI-CNF-NH2) slurry and polyaniline-carboxyl-functionalized carbon nanofiber (PANI-CNF-COOH) slurry, respectively. Subsequently, a positively charged PANI-CNF-NH2 layer and a PANI-CNF-COOH layer were sequentially deposited on the surface of a pure titanium metal bipolar plate substrate and dried.

[0074] S1. Surface modification of metal bipolar plate: The pure titanium metal bipolar plate substrate was sequentially ultrasonically cleaned in acetone, anhydrous ethanol, and ultrapure water to remove surface impurities and oxides, and then dried. Concentrated sulfuric acid with a concentration of 98% was mixed with hydrogen peroxide at a volume ratio of 70:30 and kept in a 90°C constant temperature water bath. Then, the pure titanium bipolar plate was immersed in the above solution for treatment, obtaining a surface-hydroxylated pure titanium bipolar plate.

[0075] S2. Preparation of slurry: (1) A certain amount of phytic acid was dissolved in ultrapure water, and aniline was added dropwise. After stirring for 1 h, 10 mg / ml of ammonium phytate was formed. Then, a certain amount of ammonium persulfate (APS) was dissolved in ultrapure water and added dropwise to the ammonium phytate. After stirring at -18°C for 12 h, PANI particles were formed. The PANI particles were filtered, washed, and dried, and then uniformly dispersed in ultrapure water to form a PANI dispersion.

[0076] (2) CNT-NH2 was added to an aqueous solution to prepare a dispersion, and then added to the PANI dispersion at a mass ratio of CNT-NH2 to PANI of 80:20, 70:30, 60:40, and 50:50, respectively. After ultrasonic stirring and stirring for 1 h, uniformly dispersed slurries A1-3, A3-3, A5-3, and A7-3 were obtained.

[0077] (3) CNT-COOH was added to an aqueous solution to prepare a dispersion, and then added to the PANI dispersion at a mass ratio of CNT-COOH to PANI of 75:25, 65:35, 55:45, and 40:60, respectively. After ultrasonic stirring and stirring for 1 h, uniformly dispersed slurries A2-3, A4-3, A6-3, and A8-3 were obtained.

[0078] S3. Preparation of composite coating: At room temperature and atmospheric pressure, slurries A1-3, A2-3, A3-3, A4-3, A5-3, A6-3, A7-3, and A8-3 were sequentially sprayed onto the surface of the hydroxylated pure titanium bipolar plate of step S1 at a spraying distance of 30 cm, a spraying pressure of 0.3 MPa, and a spraying speed of 1 ml / min. Then, it was placed in a vacuum drying oven at a temperature of 100°C for drying, obtaining a multi-gradient PANI-CNF composite coating with a total of 8 layers and a thickness of 2.5 μm.

[0079] The above descriptions are only the preferred embodiment of the application, not intended to limit the application and any modification, equivalent replacement and improvement made within the principle and technical scope of the application should be included in the protection scope of the application.

Claims

1. A method of making a carbon-based gradient composite coating for a fuel cell metal bipolar plate, characterized by, The method comprises: S1, sequentially ultrasonic cleaning the metal bipolar plate substrate in acetone, anhydrous ethanol, deionized water and drying, and then adopting one or more processes of immersion, immersion-heat treatment, immersion-ultraviolet irradiation and plasma treatment for surface modification to obtain a metal bipolar plate with surface hydroxylated or carboxylated modification; S2, mixing carbon materials and conductive polymers according to different mass ratios by direct physical blending method or in-situ polymerization method to obtain several conductive polymer-carbon slurries with different carbon contents; S3, adopting layer-by-layer deposition technology to deposit the conductive polymer-carbon slurries with different carbon contents to one side of the metal bipolar plate obtained in S1 which has been surface modified, and then drying to form a conductive polymer-carbon composite coating with gradient change in carbon content; The fuel cell metal bipolar plate carbon-based gradient composite coating obtained based on the above steps, the proportion of carbon materials in each layer of conductive polymer-carbon coating grown from the surface of the metal bipolar plate substrate to the upper gradually decreases, and the carbon material proportion of the first layer to the last layer gradually decreases from 90wt%-70wt% to 50wt%-10wt%.

2. The method of claim 1, wherein the carbon-based gradient composite coating is prepared by a process comprising: In S1: The metal bipolar plate substrate material is selected from one of magnesium, aluminum, titanium, chromium, nickel, copper, zinc, zirconium, niobium, molybdenum, tungsten, alloys thereof and stainless steel; The immersion includes acid solution immersion and alkali solution immersion.

3. The method of claim 1, wherein the carbon-based gradient composite coating is prepared by a process comprising: In S2: The direct physical blending method is to directly mix carbon material dispersion liquid and conductive polymer dispersion liquid by one or more processes of stirring, ultrasonic, oscillation and ball milling to prepare a slurry; The in-situ polymerization method is to in-situ polymerize conductive polymer monomers on the surface of carbon materials and then prepare a slurry.

4. The method of claim 1, wherein the carbon-based gradient composite coating is prepared by a process comprising: In S2: The carbon material is selected from one or more of graphite or its modified material, carbon nanobelt or its modified material, carbon nanofiber or its modified material, carbon nanotube or its modified material, graphene or its modified material, carbon black or its modified material, hard carbon or its modified material; The conductive polymer material is selected from one or more of polyaniline, polypyrrole, polythiophene, polycarbazole, polyacetylene, polyphenylacetylene, polycyanoethylene, polycarbonate-polyaniline.

5. The method for preparing a carbon-based gradient composite coating for a fuel cell metal bipolar plate according to claim 1, characterized in that, In S3, the layer-by-layer deposition technology includes one or more of immersion, spraying, spin coating, shower coating, and roller coating; The immersion technology includes one of conventional immersion, vacuum immersion, pressure immersion, ultrasonic immersion and hot immersion; The spraying technology includes one of air spraying, airless spraying, electrostatic spraying and thermal spraying; The spin coating technology includes one of conventional spin coating and vacuum spin coating; The shower coating technology includes one of spray shower coating and curtain shower coating; The roller coating technology includes one of co-rotating roller coating, counter-rotating roller coating, rotating roller coating and immersion roller coating.

6. The preparation method of the fuel cell metal bipolar plate carbon-based gradient composite coating according to claim 1, in S2 and S3, at least one of the carbon materials in the several conductive polymer-carbon slurries with different carbon contents is the same; at least one of the conductive polymer materials in the several conductive polymer-carbon slurries with different carbon contents is the same.

7. A metal bipolar plate coating, characterized by For a carbon-based gradient composite coating coated on the surface of a metal bipolar plate substrate, the carbon-based gradient composite coating comprises a plurality of layers of conductive polymer-carbon coatings with different carbon contents arranged in a direction away from the metal bipolar plate substrate. The proportion of carbon material in each layer of the conductive polymer-carbon coating grown upward from the surface of the metal bipolar plate substrate gradually decreases, and the proportion of carbon material in the first layer to the last layer gradually decreases from 90wt% to 70wt% to 50wt% to 10wt%.

8. The metal bipolar plate coating of claim 7, wherein, The thickness of each layer of the conductive polymer-carbon coating is 50nm to 900nm.

9. The metal bipolar plate coating of claim 7, wherein, The total number of layers of the carbon-based gradient composite coating is 2 to 40, and the total thickness is 100nm to 36μm.

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