Layer-by-layer assembly of fuel cell metal bipolar plate coatings and methods of making the same

Abstract

The application discloses a layer-by-layer assembled fuel cell metal bipolar plate coating and a preparation method thereof, relates to a metal bipolar plate coating preparation method and a metal bipolar plate, and comprises the following steps: sequentially ultrasonic cleaning a metal bipolar plate base body in acetone, anhydrous ethanol and deionized water, and performing surface hydroxylation modification; then, preparing a conductive polymer dispersion liquid and a polyelectrolyte-carbon material dispersion liquid; sequentially and alternately depositing the positively charged conductive polymer dispersion liquid and the negatively charged polyelectrolyte-carbon material dispersion liquid on the surface of the hydroxylated metal bipolar plate by using a wet deposition method to form a film layer structure in which a plurality of conductive polymer film layers and carbon film layers are sequentially and alternately deposited; the electrostatic attraction of positive and negative charges can improve the attraction force between the film layers; and performing drying treatment; then, performing low-temperature heat treatment in a vacuum environment or under inert gas; finally, depositing a conductive polymer thin film and / or sputtering a carbon thin film by using a magnetron to form a post-treatment layer for plugging pinhole defects, so that the metal bipolar plate has both conductivity and corrosion resistance.

Description

Technical Field

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

[0002] Proton exchange membrane fuel cells (PEMFCs), as an environmentally friendly, efficient, high-power-density, low-operating-temperature, and durable energy production device, have been applied in transportation, spacecraft, mobile equipment, and other fields. Among these applications, metal bipolar plates are considered a core component of PEMFCs due to their low resistivity, high thermal conductivity, good corrosion resistance and mechanical properties, and ease of manufacturing. However, metal bipolar plates are highly susceptible to surface oxidation and corrosion in the high-temperature, strong-acid environment of PEMFCs, leading to reduced conductivity and increased interfacial contact resistance. This severely impacts the durability and stability of PEMFCs, limiting their large-scale application.

[0003] Currently, modifying metal bipolar plates with coatings that exhibit good corrosion resistance and conductivity is an important approach to solving the aforementioned problems. Extensive research has been conducted on preparing protective coatings for bipolar plates using methods such as physical vapor deposition, chemical vapor deposition, electroless plating, and electroplating, with positive results. However, these methods generally suffer from high costs (e.g., due to the introduction of precious metals), high equipment investment, demanding production processes, complex preparation procedures, and limitations on product size.

[0004] For fuel cells aimed at commercialization, finding simple, inexpensive, and effective surface coating modification methods is of great significance. Summary of the Invention

[0005] To address the contradiction between high conductivity and corrosion resistance in metal bipolar plates, this invention provides a multi-structured composite coating consisting of a layered nanoscale conductive polymer coating and a carbon coating on a metal bipolar plate, along with its preparation method. This provides a foundation for the industrial development of surface modification of metal bipolar plates.

[0006] To achieve the above-mentioned objectives of the present invention, in a first aspect, embodiments of the present invention provide a method for preparing a layer-by-layer assembled metal bipolar plate coating for a fuel cell, comprising:

[0007] S1. The metal bipolar plate substrate is ultrasonically cleaned in acetone, anhydrous ethanol and deionized water for a predetermined time to obtain a pretreated metal bipolar plate.

[0008] S2, using one or more of the following methods, pickling, impregnation, alkaline heat treatment and plasma treatment, to perform surface hydroxylation modification on the pretreated metal bipolar plate to obtain a hydroxylated metal bipolar plate;

[0009] S3, uniformly mix the conductive polymer into the solvent to obtain a positively charged conductive polymer dispersion, and uniformly disperse the negatively charged carbon material into a polyelectrolyte solution with the same charge to obtain a negatively charged polyelectrolyte-carbon material dispersion.

[0010] S4. Using wet deposition technology, a conductive polymer dispersion is deposited on the surface of a hydroxylated metal bipolar plate to obtain a conductive polymer film. Then, using wet deposition technology, a polyelectrolyte-carbon material dispersion is deposited on the surface of the conductive polymer film to obtain a carbon film.

[0011] S5, following the method described in S4, conductive polymer film and carbon film are deposited alternately to a predetermined number of layers, followed by drying.

[0012] S6, subjected to low-temperature heat treatment in a vacuum environment or under an inert gas.

[0013] S7. After low-temperature heat treatment, a conductive polymer film and / or a carbon film are wet-deposited and / or sputtered by magnetron sputtering to form a post-treatment layer, resulting in a composite coating formed by alternating conductive polymer film layers and carbon film layers and a post-treatment layer.

[0014] 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 and their alloys and stainless steel.

[0015] Preferably, in S4 and S7, the conductive polymer material is selected from at least one of polyaniline, polypyrrole, polythiophene, polyacetylene, polyphenylacetylene, and polycarbazole.

[0016] Preferably, in S4 and S7, the conductive polymer material is the same material.

[0017] Preferably, in S3, the polyelectrolyte material is selected from one of polyetherimide, polyvinyl alcohol, polyethylene oxide, polydiallyldimethylammonium chloride, polytetrafluoroethylene, polyvinylidene fluoride, polyacrylic acid, polyvinyl butyral, polystyrene sulfonic acid, and polyimide.

[0018] Preferably, in S3, the carbon material is selected from one or more of graphite or its modified form, carbon nanoribbons or their modified form, carbon nanofibers or their modified form, carbon nanotubes or their modified form, graphene or its modified form, fullerene or its modified form, carbon black or its modified form, and porous carbon or its modified form.

[0019] Preferably, in S4 and S7, the wet deposition technology includes impregnation, spraying, and spin coating;

[0020] Impregnation deposition includes conventional impregnation, vacuum impregnation, pressure impregnation, and ultrasonic impregnation;

[0021] Spray coating deposition includes air spraying, airless spraying, electrostatic spraying, thermal spraying, and low-pressure atomization spraying;

[0022] Spin coating deposition includes spin coating and mechanical spin coating.

[0023] Preferably, in step S6, the inert gas is argon, and the low-temperature heat treatment involves gradually increasing the temperature from room temperature to 30–350°C at a rate of 2–5°C / min, and then maintaining the highest temperature for 0–360 min before natural cooling.

[0024] Preferably, in S7, the magnetron sputtering technology includes DC magnetron sputtering, radio frequency magnetron sputtering, laser magnetron sputtering, high-power pulsed magnetron sputtering, and ion beam enhanced magnetron sputtering.

[0025] Secondly, embodiments of the present invention provide a metal bipolar plate coating, which is a composite coating applied to the surface of a metal bipolar plate. The composite coating includes a conductive polymer film layer and a carbon film layer alternately arranged in sequence along a direction away from the metal bipolar plate substrate, and a post-treatment layer located on the outermost layer.

[0026] Preferably, the thickness of each conductive polymer film layer is 20 nm to 900 nm.

[0027] Preferably, the thickness of each carbon film layer is 20 nm to 900 nm.

[0028] Preferably, each carbon film layer has the same carbon material content, and the carbon material in the composite coating accounts for 50 wt% to 90 wt% of the total mass of the polyelectrolyte and carbon material.

[0029] Preferably, the total number of layers in the composite coating is 2 to 50.

[0030] Preferably, the conductive polymer film and the carbon film are deposited alternately in a direction away from the surface of the metal bipolar plate substrate, forming a group, and the conductive polymer film and the carbon film in each group have the same thickness.

[0031] Preferably, the thickness of the post-processing layer is 20nm to 500nm.

[0032] This invention proposes a method for preparing a coating for the metal bipolar plate of a layer-by-layer self-assembled fuel cell. A conductive polymer and a polyelectrolyte-carbon material are uniformly mixed to form a conductive polymer dispersion and a polyelectrolyte-carbon material dispersion with opposite charges. Nanoscale conductive polymer films and carbon films are sequentially and alternately deposited along the surface of the metal bipolar plate using one or more wet deposition techniques such as dipping, spraying, or spin coating. Post-treatment is then performed to deposit a conductive polymer film or (and) a carbon film on the outer layer. This provides a composite coating with a controllable and ordered structure and high adhesion between film layers for modifying and optimizing the metal bipolar plate, giving it both excellent conductivity and corrosion resistance. Specifically, it has the following advantages:

[0033] (1) This invention provides a composite coating preparation technology for metal bipolar plates. It employs wet deposition processes such as immersion, spraying, and spin coating to efficiently and rapidly construct layered nano-coatings on the surface of metal bipolar plates. The chemical bonding and mechanical interlocking between adjacent layers due to electrostatic attraction of positive and negative charges improve the density and compatibility of the composite coating. A post-treatment protective layer is formed using wet deposition or magnetron sputtering techniques to compensate for defects in the nano-coating. Furthermore, the raw materials used in this invention are widely available, the methods are simple and easy to implement, and the process conditions are mild, making it suitable for large-scale promotion.

[0034] (2) The present invention provides a composite coating with ordered structural changes through layer-by-layer assembly. It is constructed by alternating deposition of nanoscale conductive polymer film, carbon film and post-processing film deposited on the surface. It has the significant advantage of precise control of film composition, structure and thickness, and effectively improves the bonding strength of the coating to the metal bipolar plate.

[0035] (3) This invention provides a high-precision, multi-layered synergistic composite coating. The conductive polymer embedded in the metal bipolar plate through electrostatic attraction maintains good adhesion, while the resulting conductive polymer increases coating stability and reduces contact resistance. Meanwhile, the carbon film layer, through the cross-linked polyelectrolyte and carbon materials, forms an excellent conductive network and a corrosion-resistant protective layer. Heat treatment converts the polyelectrolyte portion into amorphous carbon to further improve the electrical contact between the film layers. Furthermore, post-treatment films seal pinhole defects and create a physical barrier on the surface, preventing electrolyte penetration and corrosion of the bipolar plate. Therefore, combining this polymer-inorganic composite coating, which possesses both high conductivity and corrosion resistance, with a metal bipolar plate exhibiting high volumetric conductivity and high mechanical strength is beneficial for improving the stability and durability of the metal bipolar plate, thus providing technical support for the larger-scale application of metal bipolar plates. Attached Figure Description

[0036] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0037] Figure 1 This is a schematic diagram of the structure of a metal bipolar plate according to an embodiment of the present invention;

[0038] Figure 2 This is a schematic flowchart of the metal bipolar plate coating preparation method according to an embodiment of the present invention. Detailed Implementation

[0039] The description of the embodiments in this specification should be taken in conjunction with the accompanying drawings, which should form part of the complete specification. In the drawings, the shape or thickness of the embodiments may be exaggerated and may be indicated in a simplified or convenient manner. Furthermore, parts of the various structures in the drawings will be described separately; it is worth noting that elements not shown in the figures or not described in words are in a form known to those skilled in the art.

[0040] The descriptions of the embodiments herein, including any references to directions and orientations, are for ease of description only and should not be construed as limiting the scope of the invention. The following description of preferred embodiments involves combinations of features, which may exist independently or in combination; the invention is not particularly limited to the preferred embodiments. The scope of the invention is defined by the claims.

[0041] like Figure 1 As shown, this invention provides a metal bipolar plate, comprising a metal bipolar plate substrate 0 and a composite coating applied to the surface of the metal bipolar plate substrate 0. The composite coating includes a conductive polymer film layer 1 and a carbon film layer 2 alternately arranged in a direction away from the metal bipolar plate substrate 0, and a post-treatment layer 3 located on the outermost layer. The nanoscale conductive polymer film layer 1 primarily enhances the adhesion between the coating and the metal bipolar plate and improves conductivity through electrostatic attraction with the hydroxylated metal bipolar plate. The nanoscale carbon film layer 2 utilizes the excellent conductivity and chemical stability of carbon materials to reduce contact resistance. Furthermore, the post-treatment layer 3, formed on the surface of the metal bipolar plate, seals pinhole-like defects to inhibit the penetration corrosion of corrosive ions, ultimately achieving the dual functions of high conductivity and high corrosion resistance in the metal bipolar plate.

[0042] Preferably, the thickness of each conductive polymer film layer 1 is 20 nm to 900 nm; more preferably, the thickness of each conductive polymer film layer 1 is 100 nm to 300 nm. Preferably, the thickness of each carbon film layer 2 is 20 nm to 900 nm; more preferably, the thickness of each carbon film layer 2 is 100 nm to 300 nm. Preferably, the thickness of the post-treatment layer 3 is 20 nm to 500 nm; more preferably, the thickness of the post-treatment layer 3 is 100 nm to 200 nm. Regarding the selection of coating thickness, when the coating is too thin or too thick, it is easy to lead to poor surface smoothness and density of the prepared coating, resulting in relatively large internal defects in the coating, which in turn cannot suppress the invasion of corrosion ions and reduce internal corrosion. When the coatings are set within the above-mentioned ranges, the function and quality of the coating can be better guaranteed.

[0043] Preferably, each carbon film layer 2 in the composite coating has the same carbon material content, with the carbon material accounting for 50wt% to 90wt% of the total mass of the polyelectrolyte and carbon material; more preferably, each carbon film layer in the composite coating has the same carbon material content, with the carbon material accounting for 65wt% to 80wt% of the total mass of the polyelectrolyte and carbon material. By setting the carbon material content within a certain range, the conductivity and uniformity of the coating can be better balanced.

[0044] Preferably, the total number of layers in the composite coating is 2 to 50; more preferably, the total number of layers in the composite coating is 4 to 10. Preferably, in the composite coating, each conductive polymer film layer 1 and carbon film layer 2 deposited alternately upwards from the metal bipolar plate substrate 0 forms a group, and the conductive polymer film layer 1 and carbon film layer 2 within each group have the same thickness. Since the conductive polymer film layer 1 is positively charged and the carbon film layer 2 is negatively charged, the above arrangement can strengthen the attraction between positive and negative charges between adjacent layers, thereby improving the bonding force between the film layers.

[0045] like Figure 2 As shown, this embodiment of the invention also provides a method for preparing a coating for a layer-by-layer assembled metal bipolar plate of a fuel cell, comprising:

[0046] S1. The metal bipolar plate substrate is ultrasonically cleaned in acetone, anhydrous ethanol and deionized water for a predetermined time (e.g., 5 min) to obtain a pretreated metal bipolar plate.

[0047] S2, using one or more of the following methods, such as pickling, impregnation, alkaline heat treatment and plasma treatment, to perform surface hydroxylation modification on the pretreated metal bipolar plate to obtain a hydroxylated metal bipolar plate; since the hydroxyl group carries a negative charge, it attracts the positive charge in the conductive polymer, which can improve the film-substrate adhesion.

[0048] S3, a positively charged conductive polymer dispersion is obtained by uniformly mixing the conductive polymer into a solvent, and a negatively charged carbon material is uniformly dispersed into a polyelectrolyte solution with the same charge to obtain a negatively charged polyelectrolyte-carbon material dispersion.

[0049] S4. Using wet deposition technology, a conductive polymer dispersion is deposited on the surface of a hydroxylated metal bipolar plate to obtain a conductive polymer film. Then, using wet deposition technology, a polyelectrolyte-carbon material dispersion is deposited on the surface of the conductive polymer film to obtain a carbon film.

[0050] S5. Following the method described in S4, conductive polymer film and carbon film are deposited alternately to a predetermined number of layers, followed by drying.

[0051] S6 is subjected to low-temperature heat treatment in a vacuum or inert gas environment. Low-temperature heat treatment helps to convert the polyelectrolyte portion into amorphous carbon, improving conductivity.

[0052] S7. After low-temperature heat treatment, a conductive polymer film and / or a carbon film are wet-deposited to form a post-treatment layer. The post-treatment layer can seal pinhole defects to inhibit the penetration corrosion of corrosion ions, thereby obtaining a composite coating formed by alternating conductive polymer film layers and carbon film layers and a post-treatment layer.

[0053] Preferably, in step S1, the substrate material of the metal bipolar plate is selected from one of magnesium, aluminum, titanium, chromium, nickel, copper, zinc, zirconium, niobium, molybdenum, tungsten and their alloys and stainless steel.

[0054] Preferably, in steps S4 and S7, the conductive polymer material is selected from at least one of polyaniline, polypyrrole, polythiophene, polyacetylene, polyphenylacetylene, and polycarbazole.

[0055] Preferably, in steps S4 and S7, the conductive polymer material is the same.

[0056] Preferably, in step S3, the polyelectrolyte material is selected from one of polyetherimide, polyvinyl alcohol, polyethylene oxide, polydiallyldimethylammonium chloride, polytetrafluoroethylene, polyvinylidene fluoride, polyacrylic acid, polyvinyl butyral, polystyrene sulfonic acid, and polyimide.

[0057] Preferably, in step S3, the carbon material is selected from one or more of graphite or its modified form, carbon nanoribbons or their modified form, carbon nanofibers or their modified form, carbon nanotubes or their modified form, graphene or its modified form, fullerene or its modified form, carbon black or its modified form, and porous carbon or its modified form.

[0058] Preferably, in steps S4 and S7, the wet deposition technology includes immersion, spraying, and spin coating; immersion deposition includes conventional immersion, vacuum immersion, pressure immersion, and ultrasonic immersion; spraying deposition includes air spraying, airless spraying, electrostatic spraying, thermal spraying, and low-pressure atomization spraying; spin coating deposition includes spin coating and mechanical spin coating.

[0059] Preferably, in step S6, the inert gas is argon, and the low-temperature heat treatment involves gradually increasing the temperature from room temperature to 30–350°C at a rate of 2–5°C / min, and then maintaining the highest temperature for 0–360 min before natural cooling.

[0060] Preferably, in step S7, the magnetron sputtering technology includes DC magnetron sputtering, radio frequency magnetron sputtering, laser magnetron sputtering, high-power pulsed magnetron sputtering, and ion beam enhanced magnetron sputtering.

[0061] In summary:

[0062] (1) This invention provides a composite coating preparation technology for metal bipolar plates. It employs wet deposition processes such as immersion, spraying, and spin coating to efficiently and rapidly construct layered nano-coatings on the surface of metal bipolar plates. The chemical bonding and mechanical interlocking between adjacent layers due to electrostatic attraction of positive and negative charges improve the density and compatibility of the composite coating. A post-treatment protective layer is formed using wet deposition or magnetron sputtering techniques to compensate for defects in the nano-coating. Furthermore, the raw materials used in this invention are widely available, the methods are simple and easy to implement, and the process conditions are mild, making it suitable for large-scale promotion.

[0063] (2) The present invention provides a composite coating with ordered structural changes through layer-by-layer assembly. It is constructed by alternating deposition of nanoscale conductive polymer film, carbon film and post-processing film deposited on the surface. It has the significant advantage of precise control of film composition, structure and thickness, and effectively improves the bonding strength of the coating to the metal bipolar plate.

[0064] (3) This invention provides a high-precision, multi-layered synergistic composite coating. The conductive polymer embedded in the metal bipolar plate through electrostatic attraction maintains good adhesion, while the resulting conductive polymer increases coating stability and reduces contact resistance. Meanwhile, the carbon film layer, through the cross-linked polyelectrolyte and carbon materials, forms an excellent conductive network and a corrosion-resistant protective layer. Heat treatment converts the polyelectrolyte portion into amorphous carbon to further improve the electrical contact between the film layers. Furthermore, post-treatment films seal pinhole defects and create a physical barrier on the surface, preventing electrolyte penetration and corrosion of the bipolar plate. Therefore, combining this polymer-inorganic composite coating, which possesses both high conductivity and corrosion resistance, with a metal bipolar plate exhibiting high volumetric conductivity and high mechanical strength is beneficial for improving the stability and durability of the metal bipolar plate, thus providing technical support for the larger-scale application of metal bipolar plates.

[0065] Example 1

[0066] In this embodiment, the metal bipolar plate is a pure titanium metal bipolar plate.

[0067] Polyaniline (PANI) film and carbon (CNT) film are sequentially and alternately deposited on the surface of a pure titanium bipolar plate substrate.

[0068] S1. Surface pretreatment of metal bipolar plates: The pure titanium metal bipolar plate substrate is ultrasonically cleaned for 5 minutes in acetone, anhydrous ethanol and deionized water respectively to remove surface impurities and oxides, and then dried for use.

[0069] S2. Hydroxylation treatment of metal bipolar plate surface: Piranhan solution was prepared by mixing 98% concentrated sulfuric acid and hydrogen peroxide at a volume ratio of 70:30. Then, the pure titanium bipolar plate in S1 was placed in the Piranhan solution in a constant temperature water bath at 90℃ for 2 hours to obtain a surface hydroxylated pure titanium bipolar plate.

[0070] S3. Dispersion Preparation

[0071] (1) A certain amount of phytic acid was dissolved in 30 mL of ultrapure water, and 300 mg of aniline was added dropwise. The mixture was stirred thoroughly for 1 h to form ammonium phytate salt. Subsequently, a certain amount of ammonium persulfate (APS) was dissolved in ultrapure water and added dropwise to the ammonium phytate salt. The mixture was stirred vigorously at -18 °C for 12 h to form easily soluble PANI particles. The PANI particles were filtered, washed, and dried, and then a PANI dispersion was prepared for later use.

[0072] (2) Dissolve 10 mg of sodium polystyrene sulfonate (PSS) in 100 ml of deionized water, then add 30 mg of carboxylated carbon nanotubes (CNT-COOH) to the solution and sonicate for 5 h to obtain a uniform and stable PSS-CNT dispersion. The mass ratio of PSS to CNT-COOH is 25:75.

[0073] S4. Layer-by-layer assembly of the composite coating: At room temperature and atmospheric pressure, the PANI dispersion was sprayed onto the surface of the pure titanium bipolar plate from step S2 at a spraying distance of 20 cm, a spraying pressure of 0.2 MPa, and a spraying speed of 1 ml / min to obtain PANI film layer-1A. The PSS-CNT dispersion was then sprayed onto the surface of PANI film layer-1A at a spraying distance of 20 cm, a spraying pressure of 0.2 MPa, and a spraying speed of 1 ml / min to obtain CNT film layer-1A. Subsequently, the above spraying process was repeated four times to obtain PANI film layer-1B, CNT film layer-1B, PANI film layer-1C, and CNT film layer-1C, respectively. Finally, a composite coating with a total of 6 layers and a thickness of 1.6 μm was obtained on the pure titanium bipolar plate.

[0074] S5. Low-temperature heat treatment: The above composite coating is subjected to low-temperature heat treatment in a vacuum environment. The heat treatment conditions are to gradually increase the temperature from room temperature to 200°C at a heating rate of 2°C / min, and then maintain the highest calcination temperature for 120 minutes before naturally cooling down.

[0075] S6. Post-treatment: The PANI dispersion is sprayed onto the surface of the low-temperature heat-treated coating in step S5 at a spraying distance of 20cm, a spraying pressure of 0.2MPa, and a spraying speed of 1.5ml / min to prepare a PANI-1D post-treatment layer with a thickness of 170nm. Finally, a highly conductive and corrosion-resistant composite coating is obtained on the surface of the metal bipolar plate.

[0076] Example 2

[0077] In this embodiment, the metal bipolar plate is a pure titanium metal bipolar plate.

[0078] PANI film and carbon (CNF) film are sequentially and alternately deposited on the surface of a pure titanium bipolar plate substrate.

[0079] S1. Surface pretreatment of metal bipolar plates: The pure titanium metal bipolar plate substrate is ultrasonically cleaned for 5 minutes in acetone, anhydrous ethanol and deionized water respectively to remove surface impurities and oxides, and then dried for use.

[0080] S2. Hydroxylation treatment of metal bipolar plate surface: Piranhan solution was prepared by mixing 98% concentrated sulfuric acid and hydrogen peroxide at a volume ratio of 70:30. Then, the pure titanium bipolar plate in S1 was placed in the Piranhan solution in a constant temperature water bath at 90℃ for 2 hours to obtain a surface hydroxylated pure titanium bipolar plate.

[0081] S3. Dispersion Preparation

[0082] (1) A certain amount of phytic acid was dissolved in 30 mL of ultrapure water, and 300 mg of aniline was added dropwise. The mixture was stirred thoroughly for 1 h to form ammonium phytate. Subsequently, a certain amount of APS was dissolved in ultrapure water and added dropwise to the ammonium phytate. The mixture was stirred vigorously at -18 °C for 12 h to form easily soluble PANI particles. The PANI particles were filtered, washed, and dried, and then a PANI dispersion was prepared for later use.

[0083] (2) Dissolve 10 mg PSS in 100 ml of deionized water, then add 30 mg of carboxylated carbon nanotubes (CNF-COOH) to the solution and sonicate for 5 h to obtain a uniform and stable PSS-CNF dispersion. The mass ratio of PSS to CNF-COOH is 25:75.

[0084] S4. Layer-by-layer assembly of the composite coating: At room temperature and atmospheric pressure, the PANI dispersion was spin-coated onto the surface of the pure titanium bipolar plate from step S2 at a spin-coating speed of 2500 rpm and a spin-coating time of 1 min to obtain PANI film layer-2A. The PSS-CNF dispersion was then spin-coated onto the surface of PANI film layer-2A at a spin-coating speed of 2500 rpm and a spin-coating time of 1 min to obtain CNF film layer-1A. Subsequently, the above spin-coating process was repeated 6 times to obtain PANI film layer-2B, CNF film layer-1B, PANI film layer-2C, CNF film layer-1C, PANI film layer-2D, and CNF film layer-1D, respectively. Finally, a composite coating with a total of 8 layers and a thickness of 2.3 μm was obtained on the pure titanium bipolar plate.

[0085] S5. Low-temperature heat treatment: The above composite coating is subjected to low-temperature heat treatment in a vacuum environment. The heat treatment conditions are to gradually increase the temperature from room temperature to 200°C at a heating rate of 2°C / min, and then maintain the highest calcination temperature for 120 minutes before naturally cooling down.

[0086] S6. Post-processing: High-pulse magnetron sputtering technology was used, with the substrate temperature set to 300℃, substrate bias voltage to -100V, and argon gas flow rate to 700sccm, while maintaining the gas pressure at 0.5Pa. After working at a sputtering power of 6kW for 200s, a carbon post-processing layer with a thickness of 150nm was prepared on the surface of the coating after the low-temperature heat treatment in step S5. Finally, a highly conductive and corrosion-resistant composite coating was obtained on the surface of the metal bipolar plate.

[0087] Example 3

[0088] In this embodiment, the metal bipolar plate is a pure titanium metal bipolar plate.

[0089] Polypyrrole (PPy) film and carbon (CNT) film are sequentially and alternately deposited on the surface of a pure titanium bipolar plate substrate.

[0090] S1. Surface pretreatment of metal bipolar plates: The pure titanium metal bipolar plate substrate is ultrasonically cleaned for 5 minutes in acetone, anhydrous ethanol and deionized water respectively to remove surface impurities and oxides, and then dried for use.

[0091] S2. Hydroxylation treatment of metal bipolar plate surface: Piranhan solution was prepared by mixing 98% concentrated sulfuric acid and hydrogen peroxide at a volume ratio of 70:30. Then, the pure titanium bipolar plate in S1 was placed in the Piranhan solution in a constant temperature water bath at 90℃ for 2 hours to obtain a surface hydroxylated pure titanium bipolar plate.

[0092] S3. Dispersion Preparation

[0093] (1) 2 ml of redistilled pyrrole monomer and 10.45 g of sodium dodecylbenzenesulfonate (SDBS) were added to a 20 wt% methanol solution. Subsequently, a 0.5 mol / L FeCl3·6H2O solution was slowly added to the above solution at 0 °C and magnetically stirred for 6 h to form PPy particles. The PPy particles were washed, filtered, and dried, and then a PPy dispersion was prepared for later use.

[0094] (2) Dissolve 20 mg PSS in 100 ml of deionized water, then add 30 mg CNT-COOH to the solution and sonicate for 5 h to obtain a uniform and stable PSS-CNT dispersion. The mass ratio of PSS to CNT-COOH is 40:60.

[0095] S4. Layer-by-layer assembly of the composite coating: At room temperature and atmospheric pressure, PPy dispersion was sprayed onto the surface of the pure titanium bipolar plate from step S2 at a spraying distance of 20 cm, a spraying pressure of 0.2 MPa, and a spraying speed of 1 ml / min to obtain PPy film layer-1A. PSS-CNT dispersion was then sprayed onto the surface of PPy film layer-1A at a spraying distance of 20 cm, a spraying pressure of 0.2 MPa, and a spraying speed of 1 ml / min to obtain CNT film layer-2A. Subsequently, the above spraying process was repeated 6 times to obtain PPy film layer-1B, CNT film layer-2B, PPy film layer-1C, CNT film layer-2C, PPy film layer-1D, and CNT film layer-2D, respectively. Finally, a composite coating with a total of 8 layers and a thickness of 2.4 μm was obtained on the pure titanium bipolar plate.

[0096] S5. Low-temperature heat treatment: The above composite coating is subjected to low-temperature heat treatment in a vacuum environment. The heat treatment conditions are to gradually increase the temperature from room temperature to 200°C at a heating rate of 2°C / min, and then maintain the highest calcination temperature for 120 minutes before naturally cooling down.

[0097] S6. Post-processing: High-pulse magnetron sputtering technology was used, with the substrate temperature set to 300℃, substrate bias voltage to -100V, and argon gas flow rate to 700sccm, while maintaining the gas pressure at 0.5Pa. After working at a sputtering power of 5kW for 200s, a carbon post-processing layer with a thickness of 110nm was prepared on the surface of the coating obtained in step S5 low-temperature heat treatment. Finally, a highly conductive and corrosion-resistant composite coating was obtained on the surface of the metal bipolar plate.

[0098] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing a coating for a layer-by-layer assembled metal bipolar plate of a fuel cell, characterized in that, include: S1. The metal bipolar plate substrate is ultrasonically cleaned in acetone, anhydrous ethanol and deionized water for a predetermined time to obtain a pretreated metal bipolar plate. S2, using one or more of the following methods, pickling, impregnation, alkaline heat treatment and plasma treatment, to perform surface hydroxylation modification on the pretreated metal bipolar plate to obtain a hydroxylated metal bipolar plate; S3, uniformly mix the conductive polymer into the solvent to obtain a positively charged conductive polymer dispersion, and uniformly disperse the negatively charged carbon material into a polyelectrolyte solution with the same charge to obtain a negatively charged polyelectrolyte-carbon material dispersion. The conductive polymer material is the same material, selected from polyaniline, polypyrrole, polythiophene, polyacetylene, polyphenylacetylene, and polycarbazole; S4. Using wet deposition technology, a conductive polymer dispersion is deposited on the surface of a hydroxylated metal bipolar plate to obtain a conductive polymer film. Then, using wet deposition technology, a polyelectrolyte-carbon material dispersion is deposited on the surface of the conductive polymer film to obtain a carbon film. Wet deposition techniques include immersion, spraying, and spin coating; immersion deposition includes conventional immersion, vacuum immersion, pressure immersion, and ultrasonic immersion; spraying deposition includes air spraying, airless spraying, electrostatic spraying, thermal spraying, and low-pressure atomization spraying; spin coating deposition includes spin coating and mechanical spin coating. S5, following the method described in S4, conductive polymer film and carbon film are deposited alternately to a predetermined number of layers, followed by drying. S6, subjected to low-temperature heat treatment in a vacuum environment or under an inert gas. S7. After low-temperature heat treatment, a conductive polymer film and / or a carbon film are wet-deposited and / or sputtered by magnetron sputtering to form a post-treatment layer, resulting in a composite coating formed by alternating conductive polymer film layers and carbon film layers and a post-treatment layer.

2. The method for preparing a layer-by-layer assembled fuel cell metal bipolar plate coating according to claim 1, characterized in that, In S1, the substrate material of the metal bipolar plate is selected from one of magnesium, aluminum, titanium, chromium, nickel, copper, zinc, zirconium, niobium, molybdenum, tungsten and their alloys and stainless steel.

3. The method for preparing a layer-by-layer assembled fuel cell metal bipolar plate coating according to claim 1, characterized in that, In S3: The polyelectrolyte material is selected from polyetherimide, polyvinyl alcohol, polyethylene oxide, polydiallyl dimethyl ammonium chloride, polytetrafluoroethylene, polyvinylidene fluoride, polyacrylic acid, polyvinyl butyral, polystyrene sulfonic acid, and polyimide; The carbon materials are selected from graphite or its modified forms, carbon nanoribbons or their modified forms, carbon nanofibers or their modified forms, carbon nanotubes or their modified forms, graphene or its modified forms, fullerenes or their modified forms, carbon black or its modified forms, and porous carbon or its modified forms.

4. The method for preparing a layer-by-layer assembled fuel cell metal bipolar plate coating according to claim 1, characterized in that, In S7, the magnetron sputtering technology includes DC magnetron sputtering, radio frequency magnetron sputtering, laser magnetron sputtering, high-power pulsed magnetron sputtering, and ion beam enhanced magnetron sputtering.

5. The method for preparing a layer-by-layer assembled fuel cell metal bipolar plate coating according to claim 1, characterized in that, In step S6, the inert gas is argon, and the low-temperature heat treatment involves gradually increasing the temperature from room temperature to 30–350°C at a rate of 2–5°C / min, and then maintaining the temperature at the highest temperature for 0–360 min before natural cooling.

6. A coating for a metal bipolar plate, characterized in that, Obtained based on the preparation method described in claim 5; The composite coating is applied to the surface of a metal bipolar plate substrate. The composite coating includes a conductive polymer film layer (1) and a carbon film layer (2) arranged alternately in a direction away from the metal bipolar plate substrate, and a post-treatment layer (3) located on the outermost layer.

7. The metal bipolar plate coating according to claim 6, characterized in that, The thickness of each conductive polymer film layer (1) is 20 nm to 900 nm; The thickness of each carbon film layer (2) is 20 nm to 900 nm; The thickness of the post-processing layer (3) is 20nm to 500nm.

8. The metal bipolar plate coating according to claim 6, characterized in that, Each carbon film layer (2) has the same carbon material content, and the carbon material in the composite coating accounts for 50 wt% to 90 wt% of the total mass of the polyelectrolyte and carbon material.

9. The metal bipolar plate coating according to claim 6, characterized in that, The total number of layers in the composite coating is 2 to 50. Each layer of conductive polymer film (1) and carbon film (2) is deposited alternately along the direction away from the surface of the metal bipolar plate substrate. The conductive polymer film (1) and carbon film (2) in each group have the same thickness.

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