Protective coating slurry, bipolar plate and method of making same and fuel cell

Abstract

The application relates to a protective coating slurry, a bipolar plate and a preparation method thereof and a fuel cell. The protective coating slurry comprises the following components in parts by mass: polyisocyanate grafted hydroxylated graphene 60-70 parts, polyurethane 18-30 parts and carbon black 8-22 parts. The protective coating slurry can be applied to the bipolar plate to form a protective coating, and can improve the corrosion resistance, conductivity and bonding force of the bipolar plate.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of fuel cells, in particular to a protective coating slurry, a bipolar plate, a preparation method thereof and a fuel cell. BACKGROUND

[0002] On the road of global commitment to clean energy development, the automobile industry has also made great progress. In addition to pure electric and hybrid models, fuel cell vehicles are considered the ultimate goal of new energy vehicle development due to their environmental advantages such as low emissions or even zero emissions.

[0003] Fuel cells are divided into five types according to the type of fuel electrolyte. Proton exchange membrane fuel cells (PEMFC) are considered one of the most promising energy sources for fuel cell vehicles due to their low operating temperature, high specific power, and fast start-up. As one of the core components of PEMFC, the bipolar plate not only conducts electrons, but also distributes fuel and oxidant, while managing heat. Its performance directly affects the energy conversion efficiency, stability and even the life of the fuel cell.

[0004] Currently, the manufacturing materials of bipolar plates mainly include graphite, metal and composite materials. Although traditional graphite plates have good chemical stability, they lack mechanical strength and are difficult to compress in thickness, limiting their application in compact and impact-resistant scenarios. Composite bipolar plates are currently in the laboratory research stage due to processing difficulties and high costs. In comparison, metal materials stand out with their excellent electrical conductivity and mechanical strength. However, metal bipolar plates face challenges such as acidic environment, high humidity, high potential, and uneven temperature distribution in the harsh working environment of proton exchange membrane fuel cells. Corrosion or passivation becomes the main failure mode. Once corrosion or passivation occurs, it may increase the contact resistance between the bipolar plate and the carbon paper, reducing the output performance of the battery, or even cause corrosion perforation, causing the oxidant and fuel on both sides of the bipolar plate to mix and pose an explosion risk.

[0005] In order to improve the corrosion resistance of metal bipolar plates and prolong their service life, a protective coating is usually applied to their surface. However, traditional coating techniques mainly include noble metal coatings, conductive polymer coatings or carbon-based coatings, which can enhance the corrosion resistance of bipolar plates to some extent, but still have problems such as high cost and complex preparation process. These factors have hindered the large-scale commercial application of fuel cells. SUMMARY

[0006] Therefore, it is necessary to provide a protective coating slurry that can improve the corrosion resistance of bipolar plates, has low cost and simple preparation process, a bipolar plate, a preparation method thereof and a fuel cell.

[0007] In a first aspect, the present application provides a protective coating slurry, comprising, in parts by mass, polyisocyanate grafted hydroxylated graphene 60-70 parts, polyurethane 18-30 parts, and carbon black 8-22 parts.

[0008] In some embodiments, the polyisocyanate grafted hydroxylated graphene is 60-68 parts, the polyurethane is 20-30 parts, and the carbon black is 8-12 parts, in parts by mass, in the protective coating slurry.

[0009] In some embodiments, the components of the protective coating slurry further comprise a solvent; wherein,

[0010] The solvent comprises propylene carbonate; and / or,

[0011] The mass-to-volume ratio of the polyisocyanate grafted hydroxylated graphene to the solvent is 20 mg / mL-30 mg / mL.

[0012] In a second aspect, the present application provides a bipolar plate comprising a bipolar plate substrate and a protective coating disposed on at least part of the surface of the bipolar plate substrate, the components of the protective coating comprising, in parts by mass, polyisocyanate grafted hydroxylated graphene 60-70 parts, polyurethane 18-30 parts, and carbon black 8-22 parts; or,

[0013] The protective coating is prepared using any of the protective coating slurries described above.

[0014] In some embodiments, the polyisocyanate grafted hydroxylated graphene is 60-70 parts, the polyurethane is 18-30 parts, and the carbon black is 8-22 parts, in parts by mass, in the components of the protective coating.

[0015] In some embodiments, the thickness of the protective coating is 0.2 mm-1 mm.

[0016] In some embodiments, the bipolar plate substrate is a metal substrate.

[0017] In a third aspect, the present application provides a method for preparing the bipolar plate described above, comprising the following steps:

[0018] Coating a protective coating slurry on at least part of the surface of the bipolar plate substrate, and curing to form the protective coating, thereby obtaining the bipolar plate.

[0019] In some embodiments, the heating temperature for curing is 130°C-170°C, and the heating time is 20 min-40 min; and / or,

[0020] The mass ratio of the polyisocyanate and the hydroxylated graphene in the raw material for preparing the polyisocyanate-grafted hydroxylated graphene is 2-4:1.

[0021] In a fourth aspect, the application provides a fuel cell, comprising at least two bipolar plates and a membrane electrode arranged in a stack, wherein at least one of the bipolar plates is the bipolar plate according to any one of the preceding aspects.

[0022] The protective coating slurry has the polyisocyanate-grafted hydroxylated graphene as the main body, and the carbon black is added as the conductive bridging agent and the conductive component, so that the protective coating slurry has good conductivity, and the polyisocyanate-grafted hydroxylated graphene can react with the polyurethane as the binder to form a crosslinked network, thereby increasing the compatibility between the graphene and the binder, effectively solving the dispersion problem of the graphene in the composite material, avoiding the agglomeration of the graphene, and further enhancing the adhesion strength of the coating to the substrate, improving the bonding force, optimizing the conductive path of the material, and having good conductivity.

[0023] The protective coating slurry is applied to the bipolar plate to form a protective coating, so that the corrosion resistance of the bipolar plate is improved.

[0024] The protective coating slurry can be used to form a protective coating on the bipolar plate substrate through a low-cost coating process, thereby reducing the process cost, simplifying the preparation process, and significantly reducing the cost. Moreover, compared with the traditional technology, the bipolar plate has good conductivity and mechanical strength, and the corrosion resistance and service life of the bipolar plate are improved by optimizing the components of the coating and scientifically adjusting the ratio of the components. DETAILED DESCRIPTION

[0025] In order to facilitate the understanding of the present application, the present application will be described more fully below, and preferred embodiments of the present application will be given. However, the present application can be realized in many different forms, and is not limited to the embodiments described herein. It should be understood that the purpose of providing these embodiments is to make the disclosure of the present application more thorough and comprehensive.

[0026] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the present application belongs. The terms used in the specification of the present application are only for the purpose of describing the specific embodiments and are not intended to limit the present application. The term "and / or" used herein includes any and all combinations of one or more related listed items.

[0027] "ranges" disclosed herein can be defined, for example, by the use of "between" language. Unless otherwise specifically stated, the use of "about" preceding a value herein is intended to describe or include the value plus or minus ten percent (10%) of the value. For example, "about 90%" includes 81% to 99% and "about 50%" includes 45% to 55%. When particular values or ranges of values are given, it is understood that other values or ranges of values are contemplated, which are reasonably encompassed by the particular values or ranges of values given. For example, if a range of 60-120 and a range of 80-110 are given, it is understood that ranges of 60-110 and 80-120 are contemplated. Furthermore, if a minimum range value of 1 and 2 are given, and if a maximum range value of 3, 4, and 5 are given, then the following ranges are all contemplated: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In this application, unless otherwise specified, a numerical range "a-b" indicates a shorthand way of describing each and every number that is an integer within the given range of a and b, wherein a and b are real numbers. For example, the numerical range "0-5" indicates that all real numbers between 0 and 5 have been listed herein, and "0-5" is merely a shorthand way of describing those numerical combinations. Additionally, when a parameter is stated to be an integer ≥ 2, it is equivalent to disclose that the parameter is, for example, an integer of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc. For example, when a parameter is stated to be an integer selected from "2-10", it is equivalent to list the integers 2, 3, 4, 5, 6, 7, 8, 9, and 10.

[0028] In addition, the terms "first", "second", etc. are used herein only to describe different instances, and do not imply or suggest relative importance or a number of the technical features indicated. Thus, the features defined with "first", "second", etc. can explicitly or implicitly include at least one of the features. In the description of the present application, the meaning of "a plurality of" is at least two, for example, two, three, etc., unless otherwise specifically limited.

[0029] In the present application, "a plurality of", "a plurality of kinds", etc. are used without specific limitation, and refer to more than two or equal to two in number. For example, "one or more" means one or more than two.

[0030] Unless otherwise specifically stated, all embodiments and optional embodiments of the present application can be combined with each other to form new technical solutions.

[0031] Reference to an "embodiment" in this document means that a particular feature, structure, or characteristic described in connection with the embodiment can be included in at least one embodiment or implementation of the application. The appearances of the phrase in various places in the specification are not necessarily all referring to the same embodiment, nor are they necessarily mutually exclusive of one another. Those skilled in the art will appreciate from the present description that embodiments described herein can be combinable with other embodiments. Reference to an "implementation" herein is understood similarly.

[0032] Those skilled in the art can understand that, in the method of each implementation or embodiment, the writing order of each step does not mean a strict execution order and does not constitute any limitation on the implementation process, and the detailed execution order of each step should be determined according to its function and possible internal logic. If not specifically stated, all steps of the application can be performed in sequence or randomly, and preferably in sequence. For example, the method includes steps (a) and (b), which means that the method can include steps (a) and (b) performed in sequence, or steps (b) and (a) performed in sequence. For example, the method also includes step (c), which means that step (c) can be added to the method in any order, for example, the method can include steps (a), (b) and (c), or steps (a), (c) and (b), or steps (c), (a) and (b), etc.

[0033] In the present application, A (such as B) means that B is one non-limiting example of A, and it can be understood that A is not limited to B.

[0034] In the present application, "optionally", "optional" and "optional" mean that it can or can not exist, that is, it means to select any one from the two parallel schemes of "have" or "have". If there are multiple "options" in a technical solution, if there is no special statement and no contradictory or mutually restrictive relationship, each "option" is independent.

[0035] For the forming process of the protective coating on the metal bipolar plate, the physical vapor deposition (PVD) technology is currently the mainstream method for manufacturing metal bipolar plates. Although the coating prepared by PVD has excellent performance and high uniformity, this technology still has some defects that cannot be ignored. The most prominent problem is that PVD technology is highly dependent on vacuum coating equipment, which not only leads to high equipment costs, but also has high maintenance costs. At the same time, the large amount of power consumption required to maintain the vacuum environment and plasma during the deposition process makes the cost of coating preparation high. In addition, the strict requirements of PVD on the preliminary treatment and the precision requirements of the vacuum state and temperature control further increase the complexity of the coating preparation process.

[0036] In view of the limitations of these technologies, the present application provides a protective coating slurry, a bipolar plate and a preparation method thereof and a fuel cell. The protective coating slurry can be formed on the bipolar plate substrate by a low-cost coating process, the process cost is reduced, the preparation process is simple, and the cost is significantly reduced. Moreover, compared with traditional technologies, through the optimization and scientific adjustment of the composition of the coating, the bipolar plate has good electrical conductivity and mechanical strength, and the corrosion resistance and service life of the bipolar plate are also improved.

[0037] In addition, the present application provides a lower-cost production method, which simplifies the preparation steps and effectively reduces the overall manufacturing cost, providing an economic and efficient and environmentally friendly solution for the fuel cell industry. Through the application of the present technology, it is expected to realize the wide application of fuel cell systems and promote the sustainable development of the global energy industry.

[0038] In the first aspect of the present application, a protective coating slurry is provided, which comprises the following components in terms of mass fraction: polyisocyanate grafted hydroxylated graphene 60-70 parts, polyurethane 18-30 parts and carbon black 8-22 parts.

[0039] The protective coating slurry described above uses polyisocyanate grafted hydroxylated graphene as the main body, and carbon black is added as a conductive bridging agent, which cooperates with carbon black as a conductive component. Not only does it have good electrical conductivity, but also because the polyisocyanate grafted hydroxylated graphene contains polyisocyanate, it can chemically react with the polyurethane as the binder to form a crosslinked network, increasing the compatibility between graphene and the binder. This effectively solves the dispersion problem of graphene in composite materials and avoids agglomeration. It also enhances the adhesion strength of the coating to the substrate and improves the bonding force. At the same time, the material's conductive path is optimized, and it also has good electrical conductivity.

[0040] The protective coating slurry can be applied to the bipolar plate to form a protective coating, which can improve the corrosion resistance of the bipolar plate.

[0041] The protective coating slurry can be formed on the bipolar plate substrate by a low-cost coating process, the process cost is reduced, the preparation process is simple, and the cost is significantly reduced. Moreover, compared with traditional technologies, through the optimization and scientific adjustment of the composition of the coating, the bipolar plate has good electrical conductivity and mechanical strength, and the corrosion resistance and service life of the bipolar plate are also improved.

[0042] Understandably, polyisocyanate grafted hydroxylated graphene can be purchased or self-made. The polyisocyanate grafted hydroxylated graphene can be prepared by mixing and reacting polyisocyanate and hydroxylated graphene to obtain polyisocyanate grafted hydroxylated graphene. Further, the mixing reaction is carried out at 60-80℃ for 3h-12h.

[0043] Further, the mass ratio of the polyisocyanate and the hydroxylated graphene in the raw material for preparing the polyisocyanate-grafted hydroxylated graphene is 2-4:1. As an example, the mass ratio can be 2:1, 2.5:1, 3:1, 3.5:1, 4:1, or a range formed by any two of the above point values.

[0044] Further, the hydroxylated graphene can be prepared by hydroxyl functionalization treatment of graphene. It can be understood that the hydroxyl functionalization treatment of graphene can be prepared by using known techniques in the art, for example, by using strong oxidizing agents such as potassium permanganate, concentrated nitric acid, etc., to oxidize the carbon atoms on the surface of graphene into hydroxyl groups.

[0045] Further, the hydroxyl functionalization treatment of graphene includes the following steps: preparing a multi-layer graphene dispersion liquid by using hydrogen peroxide and copper sulfate for oxidation; specifically including the following steps

[0046] S11: Disperse the multi-layer graphene in water using an ultrasonic homogenizer or the like, and add sodium dodecyl sulfonate, mix and disperse to obtain a graphene dispersion liquid.

[0047] Further, the mixing and dispersion is for 30-60 minutes.

[0048] Further, the mass fractions of the multi-layer graphene, water and sodium dodecyl sulfonate are 50-100 parts, 100-200 parts and 8-12 parts, respectively.

[0049] As an example, the mass fraction of the multi-layer graphene can be 50, 60, 70, 80, 90, 100 parts, or a range formed by any two of the above point values. As an example, the mass fraction of the water can be 100, 120, 140, 150, 180, 200 parts, or a range formed by any two of the above point values. As an example, the mass fraction of the sodium dodecyl sulfonate can be 8, 9, 10, 11, 12 parts, or a range formed by any two of the above point values.

[0050] S12: Drop in H2SO4 solution to adjust the pH value of the graphene dispersion liquid to ensure the stability of the graphene dispersion liquid.

[0051] Further, when the mass fraction of the multi-layer graphene is 50-100 parts, the volume of the H2SO4 solution is 0.5 mL-1 mL, and the concentration of the H2SO4 solution is 1 mol / L-2 mol / L.

[0052] S13: Add CuSO 4- 5H2O powder to the graphene dispersion liquid.

[0053] Further, when the mass fraction of the multi-layer graphene is 50-100 parts, the mass fraction of the CuSO 4-The mass fraction of the 5H2O powder is 0.5-1 parts.

[0054] S14: Slowly inject the H2O2 solution using a micro-injection pump or the like, so that the substances in the graphene dispersion solution fully react to form hydroxylated graphene, and the unreacted substances are removed through a filtration step.

[0055] Further, the speed of injecting the H2O2 solution is 3 mL / h-60 mL / h. Further, when the mass fraction of the multilayer graphene is 50-100 parts, the amount of the H2O2 solution added is 0.5 mL-1 mL; further, the mass content of the H2O2 solution is 5%-10%, for example, it can be 5%, 6%, 7%, 8%, 9%, 10%, or a range formed by any two of the above-mentioned point values.

[0056] As an example, the mass fraction of the polyisocyanate grafted hydroxylated graphene can be 60, 62, 65, 68, 70 parts, or a range formed by any two of the above-mentioned point values, for example, 60-68 parts.

[0057] As an example, the mass fraction of the polyurethane can be 18, 20, 22, 25, 28, 30 parts, or a range formed by any two of the above-mentioned point values, for example, 20-30 parts.

[0058] As an example, the mass fraction of the carbon black can be 8, 10, 12, 15, 18, 20, 22 parts, or a range formed by any two of the above-mentioned point values, for example, 8-15 parts, or 8-12 parts.

[0059] In some embodiments, in the protective coating slurry, the mass fraction of the polyisocyanate grafted hydroxylated graphene is 60-68 parts, the mass fraction of the polyurethane is 20-30 parts, and the mass fraction of the carbon black is 8-12 parts.

[0060] Further, the mass fraction of the polyisocyanate grafted hydroxylated graphene, the polyurethane, and the carbon black is 100 parts.

[0061] In some embodiments, the components of the protective coating slurry further include a solvent, and thus the above-mentioned components and the solvent are mixed to form the slurry. Further, the solvent includes propylene carbonate.

[0062] Further, the mass-volume ratio of the polyisocyanate grafted hydroxylated graphene to the solvent is 20 mg / mL-30 mg / mL; as an example, it can be 20 mg / mL, 22 mg / mL, 25 mg / mL, 26 mg / mL, 28 mg / mL, 30 mg / mL, or a range formed by any two of the above-mentioned point values.

[0063] In a second aspect, the application provides a bipolar plate, comprising a bipolar plate substrate and a protective coating layer disposed on at least part of the surface of the bipolar plate substrate, wherein the protective coating layer comprises, by mass fraction, 60-70 parts of polyisocyanate-grafted hydroxylated graphene, 18-30 parts of polyurethane, and 8-22 parts of carbon black.

[0064] The protective coating layer is prepared using any of the protective coating slurries described above. Further, in the components of the protective coating layer, the polyisocyanate-grafted hydroxylated graphene is 60-68 parts by mass fraction, the polyurethane is 20-30 parts by mass fraction, and the carbon black is 8-12 parts by mass fraction. Understandably, the proportions of the polyisocyanate-grafted hydroxylated graphene, the polyurethane, and the carbon black in the protective coating layer are the same as those in the protective coating slurry, and will not be described here.

[0065] In some embodiments, the thickness of the protective coating layer is 0.2 mm-1 mm; for example, it can be 0.2 mm, 0.4 mm, 0.5 mm, 0.6 mm, 0.8 mm, 1 mm, or a range between any two of the above values.

[0066] In some embodiments, the bipolar plate substrate is a metal substrate, including but not limited to one of aluminum, nickel, titanium, and stainless steel.

[0067] In a third aspect, the application provides a method for preparing the bipolar plate described above, comprising the following steps:

[0068] Coating the protective coating slurry on at least part of the surface of the bipolar plate substrate, and curing to form a protective coating layer, thereby obtaining a bipolar plate.

[0069] Understandably, the protective coating slurry can be coated on part or all of the surface of the bipolar plate substrate to form a protective coating layer. For example, the protective coating layer can be formed on all external surfaces to enhance its protective effect. Alternatively, the protective coating layer can be formed on one external surface or two opposite external surfaces of the bipolar plate substrate.

[0070] In some embodiments, the heating temperature for curing is 130°C-170°C, and the heating time is 20 min-40 min.

[0071] In some embodiments, before coating the protective coating slurry, the surface of the bipolar plate substrate is polished and cleaned.

[0072] Specifically, the surface of the metal bipolar plate is polished with sandpaper, and then the bipolar plate is wiped with 1 mol / L H2SO4 to remove the passivation layer; the metal bipolar plate is ultrasonically cleaned in acetone.

[0073] The coating method can be selected from at least one of spraying, rolling, scraping, and brushing.

[0074] In a fourth aspect of the present application, a fuel cell is provided, comprising at least two bipolar plates and a membrane electrode arranged in a stack, wherein at least one of the bipolar plates is the bipolar plate according to any one of the preceding aspects.

[0075] In some embodiments, the fuel cell is a hydrogen fuel cell, which is a device that converts chemical energy from hydrogen and oxygen into electricity through a chemical reaction that occurs within the fuel cell stack.

[0076] In order to make the purpose, technical solutions and advantages of the present application more concise and clear, the present application is described by the following specific embodiments, but the present application is not limited to these embodiments. The embodiments described below are only better embodiments of the present application, which can be used to describe the present application, and cannot be understood as limiting the scope of the present application. It should be noted that any modification, equivalent replacement and improvement made within the spirit and principle of the present application shall be included in the protection scope of the present application.

[0077] In order to better illustrate the present application, the content of the present application is further described below in combination with embodiments. The following are specific embodiments.

[0078] Embodiment 1:

[0079] The present embodiment provides a preparation method of a bipolar plate of a fuel cell, which is simple in process and low in cost:

[0080] (1) Preparation of hydroxylated graphene: 50 mg of multi-layer graphene is dispersed in 120 mL of deionized water using an ultrasonic homogenizer, and 10 mg of sodium dodecyl sulfate is added, and the dispersion is continued for 40 min; then 0.5 mL of 1 mol / L sulfuric acid solution is added dropwise to adjust the pH value of the graphene dispersion; then 1 g of CuSO4-5H2O is added to the graphene dispersion; finally, 0.5 mL of H2O2 solution (mass content of 8%) is slowly injected using a micro-injection pump at a speed of 40 mL / h, so that the substances in the graphene dispersion are fully reacted for 60 min to generate hydroxylated graphene, and the unreacted substances are removed by filtration.

[0081] (2) The polyisocyanate and the hydroxylated graphene are mixed in a mass ratio of 3:1, stirred at 60°C for 10 h to obtain a reaction product; and the reaction product is dispersed in propylene carbonate at a dispersion ratio of 20 mg / mL to obtain a polyisocyanate grafted hydroxylated graphene solution; the polyisocyanate grafted hydroxylated graphene, polyurethane and carbon black in the polyisocyanate grafted hydroxylated graphene solution are mixed by ultrasonic cleaning at a mass ratio of 60%:30%:10% to obtain a composite slurry.

[0082] (3) The composite slurry is coated on the entire outer surface of the clean metal bipolar plate from which the passivation film has been removed by brushing to form a coating layer, and the thickness of the coating is 0.5 mm. Then the bipolar plate is placed in a heating furnace and heated to 150°C for 30 minutes to solidify the coating layer and form a protective coating layer.

[0083] Example 2

[0084] The embodiment provides a preparation method of a bipolar plate of a fuel cell, which is simple in process and low in cost.

[0085] (1) Preparation of hydroxylated graphene: 80 mg of multi-layer graphene is dispersed in 180 mL of deionized water using an ultrasonic homogenizer, and 9 mg of sodium dodecyl sulfate is added, and the dispersion is continued for 60 min. Then 1 mL of a sulfuric acid solution with a concentration of 1.5 mol / L is added dropwise to adjust the pH value of the graphene dispersion. Then 0.5 g of CuSO4-5H2O is added to the graphene dispersion. Finally, 0.5 mL of H2O2 solution (mass content of 8%) is slowly injected using a micro-injection pump at a speed of 60 mL / h, so that the substances in the graphene dispersion are fully reacted for 80 min to generate hydroxylated graphene, and the unreacted substances are removed by a filtration step.

[0086] (2) The polyisocyanate and the hydroxylated graphene are mixed in a mass ratio of 3:1, and stirred at 80°C for 6 h to obtain a reaction product. The reaction product is dispersed in propylene carbonate at a dispersion ratio of 30 mg / mL to obtain a polyisocyanate-grafted hydroxylated graphene solution; the polyisocyanate-grafted hydroxylated graphene, the polyurethane and the carbon black in the polyisocyanate-grafted hydroxylated graphene solution are mixed in a mass ratio of 65%:20%:15% by ultrasonic cleaning to obtain a composite slurry.

[0087] (3) The composite slurry is coated on the surface of the clean metal bipolar plate from which the passivation film has been removed by brushing, and the thickness of the coating is 1 mm. Then the bipolar plate is placed in a heating furnace and heated to 130°C for 40 minutes to solidify the coating layer and form a protective coating layer.

[0088] Example 3

[0089] The embodiment provides a preparation method of a bipolar plate of a fuel cell, which is simple in process and low in cost.

[0090] (1) Preparation of hydroxylated graphene: 100 mg of multi-layer graphene was dispersed in 200 mL of deionized water using an ultrasonic homogenizer, and 12 mg of sodium dodecyl sulfate was added, and the dispersion was continued for 60 min; then 0.8 mL of a 2 mol / L sulfuric acid solution was added dropwise to adjust the pH value of the graphene dispersion; 1 g of CuSO4-5H2O was then added to the graphene dispersion; finally, 0.1 mL of H2O2 solution (mass content of 8%) was slowly injected using a micro-injection pump at a speed of 3 mL / h, and the substances in the graphene dispersion were allowed to react fully for 70 min to generate hydroxylated graphene, and unreacted substances were removed by a filtration step;

[0091] (2) The polyisocyanate and the hydroxylated graphene were mixed in a mass ratio of 3:1, stirred at 65°C for 12 h to obtain a reaction product, and the reaction product was dispersed in propylene carbonate at a dispersion ratio of 25 mg / mL to obtain a polyisocyanate grafted hydroxylated graphene solution; the polyisocyanate grafted hydroxylated graphene, the polyurethane and the carbon black in the polyisocyanate grafted hydroxylated graphene solution were mixed in a mass ratio of 68%:22%:10% by ultrasonic cleaning to obtain a composite slurry.

[0092] (3) The composite slurry was coated onto the surface of a clean metal bipolar plate with removed passivation film by brush coating, and the thickness of the coating was 1 mm; then the bipolar plate was placed in a heating furnace and heated to 160°C for 20 min to cure the coating to form a protective coating.

[0093] Example 4

[0094] This example 4 provides a method for preparing a bipolar plate of a fuel cell, which is different from example 3 in that the composition of the composite slurry in step (2) is different, specifically, the polyisocyanate grafted hydroxylated graphene, the polyurethane and the carbon black in the polyisocyanate grafted hydroxylated graphene solution were mixed in a mass ratio of 60%:18%:22% by ultrasonic cleaning to obtain a composite slurry.

[0095] Comparative Example 1

[0096] This comparative example 1 provides a method for preparing a bipolar plate of a fuel cell, which is different from example 1 in that no polyurethane is added to the composite slurry in step (2), and the other conditions are the same as in example 1.

[0097] Comparative Example 2

[0098] This comparative example 2 provides a method for preparing a bipolar plate of a fuel cell, which is different from example 1 in that no carbon black is added to the composite slurry in step (2), and the other conditions are the same as in example 1.

[0099] Comparative Example 3

[0100] Comparative Example 3 provides a method for preparing a bipolar plate for a fuel cell. The difference from Example 1 is that, in step (2), the composite slurry does not contain a polyisocyanate-grafted hydroxylated graphene solution, but instead uses a solution of the same mass of hydroxylated graphene directly. Other conditions are the same as in Example 1. The hydroxylated graphene solution is prepared as follows: the hydroxylated graphene obtained in step (1) is dispersed in propylene carbonate at a dispersion ratio of 20 mg / mL.

[0101] Comparative Example 4

[0102] This comparative example provides a method for preparing a bipolar plate for a fuel cell. The difference from Example 1 is that the amount of polyisocyanate-grafted hydroxyl graphene solution added in the composite slurry in step (2) is larger. Specifically, the polyisocyanate-grafted hydroxyl graphene, polyurethane and carbon black in the polyisocyanate-grafted hydroxyl graphene solution are mixed by ultrasonic cleaning in a mass ratio of 80%:10%:10% to obtain the composite slurry.

[0103] The protective coatings of the bipolar plates prepared in the above embodiments and comparative examples were subjected to relevant performance tests, and the test results are shown in Table 1.

[0104] The adhesion between the protective coating of the bipolar plate and the metal bipolar plate was tested according to the GB / T 8642 standard method.

[0105] The contact resistance and corrosion current of the protective coating of the bipolar plate were tested according to the standard method of GB / T 20042.6.

[0106] Table 1

[0107]

[0108] The results show that the adhesion of the bipolar plate coatings in Examples 1-4 all exceeded 30 MPa, and the contact resistance was less than or equal to 5.2 mΩ·cm. 2 The corrosion current density is less than or equal to 0.56 μA / cm. 2 This indicates that the bipolar plate coating has good adhesion, conductivity, and corrosion resistance.

[0109] Compared to Example 1, the composite slurry in Comparative Example 1, which did not contain polyurethane, showed a significant decrease in coating adhesion. Similarly, the composite slurry in Comparative Example 2, which did not contain carbon black, showed a significant decrease in coating conductivity and corrosion resistance. Compared to Example 1, Comparative Example 3 used hydroxylated graphene, resulting in a significantly reduced coating adhesion, higher contact resistance, and higher corrosion current density, indicating poor conductivity and corrosion resistance. Comparative Example 4, with its different formulation, exhibited higher contact resistance and higher corrosion current density in its coating, indicating poor conductivity and corrosion resistance.

[0110] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0111] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims, and the specification can be used to interpret the content of the claims.

Claims

1. A protective coating slurry, characterized in that, The protective coating slurry comprises the following components by mass: 60-68 parts of polyisocyanate-grafted hydroxylated graphene, 20-30 parts of polyurethane, and 8-18 parts of carbon black. The components of the protective coating slurry also include a solvent, and the mass-volume ratio of the polyisocyanate-grafted hydroxylated graphene to the solvent is 20 mg / mL to 30 mg / mL.

2. The protective coating slurry as described in claim 1, characterized in that, The carbon black comprises 8 to 12 parts by weight in the protective coating slurry.

3. The protective coating slurry as described in claim 1 or 2, characterized in that, The solvent includes propylene carbonate; and / or, The mass-to-volume ratio of the polyisocyanate-grafted hydroxylated graphene to the solvent is 22 mg / mL to 30 mg / mL.

4. A bipolar plate, characterized in that, The invention includes a bipolar plate substrate and a protective coating disposed on at least a portion of the surface of the bipolar plate substrate, the protective coating being prepared using a protective coating slurry as described in any one of claims 1 to 3.

5. The bipolar plate as described in claim 4, characterized in that, The polyurethane comprises 22 to 30 parts by mass of the components of the protective coating.

6. The bipolar plate as described in claim 4 or 5, characterized in that, The thickness of the protective coating is 0.2 mm to 1 mm.

7. The bipolar plate as described in claim 4 or 5, characterized in that, The bipolar plate substrate is a metal substrate.

8. A method for preparing a bipolar plate as described in any one of claims 4 to 7, characterized in that, Includes the following steps: A protective coating slurry is applied to at least a portion of the surface of the bipolar plate substrate and cured to form the protective coating, thereby obtaining the bipolar plate.

9. The preparation method according to claim 8, characterized in that, The curing heating temperature is 130℃~170℃, and the heating time is 20 min~40 min; and / or, In the preparation of the polyisocyanate-grafted hydroxylated graphene, the mass ratio of polyisocyanate to hydroxylated graphene is 2~4:

1.

10. A fuel cell, characterized in that, It includes at least two bipolar plates stacked together and a membrane electrode located between two adjacent bipolar plates, wherein at least one bipolar plate is a bipolar plate as described in any one of claims 4 to 7.

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