Protective coating slurry, bipolar plate, preparation method of bipolar plate and fuel cell

Abstract

The invention relates to protective coating slurry, a bipolar plate, a preparation method of the bipolar plate and a fuel cell. The protective coating slurry is prepared from the following components in parts by mass: 60 to 70 parts of polyisocyanate grafted hydroxylated graphene, 18 to 30 parts of polyurethane and 8 to 22 parts of carbon black. The protective coating slurry can be applied to the bipolar plate to form a protective coating, and the corrosion resistance, the conductivity and the binding force of the bipolar plate can be improved.

Description

Technical Field

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

[0002] As the world works together to develop clean energy, the automotive 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. Among them, 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 startup. As one of the core components of PEMFC, bipolar plates are not only responsible for conducting electrons, but also for distributing fuel and oxidants and managing heat. Their performance directly affects the energy conversion efficiency, stability, and even life of the fuel cell.

[0004] At present, 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, which limits their application in compact and impact-resistant scenarios; composite bipolar plates are difficult to process and are expensive, and are currently still in the laboratory research stage. Relatively speaking, metal materials stand out with their excellent conductivity and mechanical strength. However, in the harsh working environment of proton exchange membrane fuel cells, metal bipolar plates face challenges such as acidic environment, high humidity, high potential and uneven temperature distribution, and corrosion or passivation becomes their main failure mode. Once corrosion and passivation occur, the contact resistance between the bipolar plate and the carbon paper is increased at the least, reducing the battery output performance; in severe cases, corrosion perforation occurs, causing the oxidant and fuel on both sides of the bipolar plate to mix, causing the risk of explosion.

[0005] In order to improve the corrosion resistance of metal bipolar plates and extend their service life, it is usually necessary to apply a protective coating on their surface. However, traditional coating technologies mainly include precious metal coatings, conductive polymer coatings or carbon-based coatings, which can enhance the corrosion resistance of bipolar plates to a certain extent, but still have problems such as high cost and complex preparation process. These factors have restricted the large-scale commercial application of fuel cells. Summary of the invention

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

[0007] In a first aspect of the present application, a protective coating slurry is provided, comprising the following components, measured by weight: 60 to 70 parts of polyisocyanate-grafted hydroxylated graphene, 18 to 30 parts of polyurethane, and 8 to 22 parts of carbon black.

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

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

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

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

[0012] In a second aspect of the present application, a bipolar plate is provided, comprising a bipolar plate substrate and a protective coating disposed on at least a portion of the surface of the bipolar plate substrate, wherein the components of the protective coating include, by weight, 60 to 70 parts of polyisocyanate-grafted hydroxylated graphene, 18 to 30 parts of polyurethane, and 8 to 22 parts of carbon black; or,

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

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

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

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

[0017] In a third aspect of the present application, a method for preparing the above-mentioned bipolar plate is provided, comprising the following steps:

[0018] A protective coating slurry is coated on at least a portion of the surface of the bipolar plate substrate, and cured to form the protective coating, thereby obtaining the bipolar plate.

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

[0020] In the raw material for preparing the polyisocyanate-grafted hydroxylated graphene, the mass ratio of the polyisocyanate to the hydroxylated graphene is 2-4:1.

[0021] In a fourth aspect of the present application, a fuel cell is provided, comprising at least two bipolar plates stacked together and a membrane electrode disposed between two adjacent bipolar plates, wherein at least one bipolar plate is a bipolar plate as described in any one of the above items.

[0022] The protective coating slurry of the present invention adopts polyisocyanate-grafted hydroxylated graphene as the main body, and adds carbon black as a conductive bridging agent, and cooperates with carbon black as a conductive component. It not only has good conductivity, but also because the polyisocyanate-grafted hydroxylated graphene contains polyisocyanate, it can chemically react with polyurethane as a binder to form a cross-linked network, thereby increasing the compatibility between graphene and the binder, effectively solving the dispersion problem of graphene in the composite material, avoiding its agglomeration phenomenon, and also enhancing the adhesion strength of the coating to the substrate, improving the bonding force, while optimizing the conductive path of the material, and also having good conductivity.

[0023] The protective coating slurry is applied to the bipolar plate to form a protective coating, which can improve the corrosion resistance of the bipolar plate.

[0024] The protective coating slurry can form a protective coating on the bipolar plate substrate through a low-cost coating process, which reduces process costs, simplifies the preparation process, and significantly reduces costs. Moreover, compared with traditional technologies, through the optimization of coating components and scientific adjustment of the ratio, the bipolar plate has both good conductivity and mechanical strength, and also improves the corrosion resistance and service life of the bipolar plate. DETAILED DESCRIPTION

[0025] In order to facilitate the understanding of the present invention, the present invention will be described more comprehensively below, and preferred embodiments of the present invention are given. However, the present invention can be implemented 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 understanding of the disclosure of the present invention more thorough and comprehensive.

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

[0027] "Scope" disclosed in the present application can be limited in the form of lower limit and upper limit, and a given range is limited by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundary of a special range. The scope limited in this way can be including end values ​​or excluding end values, and any end value can be included or not included independently, and can be combined arbitrarily, that is, any lower limit can be combined with any upper limit to form a scope. For example, if the scope of 60-120 and 80-110 is listed for a specific parameter, it is understood that the scope of 60-110 and 80-120 is also expected. In addition, if the minimum range values ​​1 and 2 listed, and if the maximum range values ​​3,4 and 5 are also listed, the following scope can all be expected: 1-3, 1-4, 1-5, 2-3, 2-4 and 2-5. In the present application, unless otherwise specified, the numerical range "ab" represents the abbreviation of any real number combination between a and b, wherein a and b are real numbers. For example, the numerical range "0-5" means that all real numbers between "0-5" are listed in this document, and "0-5" is just an abbreviation of these numerical combinations. In addition, when a parameter is expressed as an integer ≥ 2, it is equivalent to disclosing that the parameter is, for example, an integer 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc. For example, when a parameter is expressed as an integer selected from "2-10", it is equivalent to listing the integers 2, 3, 4, 5, 6, 7, 8, 9 and 10.

[0028] In addition, the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" and "second" may explicitly or implicitly include at least one of the features. In the description of the present invention, the meaning of "plurality" is at least two, such as two, three, etc., unless otherwise clearly and specifically defined.

[0029] In the present application, "plurality", "multiple" and the like, unless otherwise specified, refer to a number greater than or equal to 2. For example, "one or more" means one or greater than or equal to two.

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

[0031] Reference to "embodiments" herein means that a particular feature, structure, or characteristic described in conjunction with the embodiments may be included in at least one embodiment or implementation of the present application. The appearance of the phrase in various locations in the specification does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment that is mutually exclusive with other embodiments. It is explicitly and implicitly understood by those skilled in the art that the embodiments described herein may be combined with other embodiments. The "implementation methods" mentioned herein have a similar understanding.

[0032] Those skilled in the art will appreciate that, in the methods of each embodiment or example, the order in which each step is written does not mean a strict order of execution and does not constitute any limitation on the implementation process, and the detailed order of execution of each step should be determined by its function and possible internal logic. If there is no special explanation, all steps of the present application can be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or steps (b) and (a) performed sequentially. For example, the method may also include step (c), indicating that step (c) can be added to the method in any order, for example, the method may include steps (a), (b) and (c), or steps (a), (c) and (b), or steps (c), (a) and (b), etc.

[0033] In this application, unless otherwise specified, A (such as B) means that B is a non-limiting example of A, and it can be understood that A is not limited to B.

[0034] In this application, "optionally", "optional", and "optional" mean optional, that is, any one of the two parallel schemes of "yes" or "no". If there are multiple "options" in a technical solution, unless otherwise specified and there is no contradiction or mutual restriction, each "option" is independent.

[0035] For the formation process of protective coatings on metal bipolar plates, physical vapor deposition (PVD) technology is currently the mainstream method for manufacturing metal bipolar plates. Although the coatings prepared by PVD have excellent performance and high uniformity, this technology still has some defects that are difficult to ignore. 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 high maintenance costs. At the same time, the large amount of electricity consumption required to maintain the vacuum environment and plasma during the deposition process makes the cost of coating preparation high. In addition, PVD's strict requirements for pre-processing and the precision requirements for 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 invention provides a protective coating slurry, a bipolar plate and a method for preparing the same, and a fuel cell. The protective coating slurry can be formed on the bipolar plate substrate through a low-cost coating process, which reduces the process cost, simplifies the preparation process, and significantly reduces the cost. Moreover, compared with traditional technologies, through the optimization of coating components and the scientific adjustment of the ratio, the bipolar plate has both good conductivity and mechanical strength, and also improves the corrosion resistance and service life of the bipolar plate.

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

[0038] In a first aspect of the present application, a protective coating slurry is provided, comprising the following components, measured by weight: 60 to 70 parts of polyisocyanate-grafted hydroxylated graphene, 18 to 30 parts of polyurethane, and 8 to 22 parts of carbon black.

[0039] The protective coating slurry of the present invention adopts polyisocyanate-grafted hydroxylated graphene as the main body, and adds carbon black as a conductive bridging agent, and cooperates with carbon black as a conductive component. It not only has good conductivity, but also because the polyisocyanate-grafted hydroxylated graphene contains polyisocyanate, it can chemically react with polyurethane as a binder to form a cross-linked network, thereby increasing the compatibility between graphene and the binder, effectively solving the dispersion problem of graphene in the composite material, avoiding its agglomeration phenomenon, and also enhancing the adhesion strength of the coating to the substrate, improving the bonding force, and optimizing the conductive path of the material, and also having good conductivity.

[0040] The protective coating slurry is 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 form a protective coating on the bipolar plate substrate through a low-cost coating process, which reduces process costs, simplifies the preparation process, and significantly reduces costs. Moreover, compared with traditional technologies, through the optimization of coating components and scientific adjustment of the ratio, the bipolar plate has both good conductivity and mechanical strength, and also improves the corrosion resistance and service life of the bipolar plate.

[0042] It is understandable that the polyisocyanate-grafted hydroxylated graphene can be purchased commercially or prepared in-house. The polyisocyanate-grafted hydroxylated graphene can be prepared by the following method: polyisocyanate and hydroxylated graphene are mixed and reacted to obtain polyisocyanate-grafted hydroxylated graphene. Further, the mixed reaction is reacted at 60-80° C. for 3 h to 12 h.

[0043] Furthermore, in the raw material for preparing the polyisocyanate-grafted hydroxylated graphene, the mass ratio of the polyisocyanate to the hydroxylated graphene is 2 to 4: 1. As an example, the mass ratio may be 2: 1, 2.5: 1, 3: 1, 3.5: 1, 4: 1, or within the range of any two of the above values.

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

[0045] Furthermore, the hydroxyl functionalization treatment of graphene includes the following steps: oxidizing the multilayer graphene dispersion with hydrogen peroxide and copper sulfate; specifically including the following steps:

[0046] S11: Dispersing the multilayer graphene in water by using an ultrasonic homogenizer or the like, adding sodium dodecyl sulfate, mixing and dispersing, and obtaining a graphene dispersion.

[0047] Furthermore, the mixing and dispersion time is 30 to 60 minutes.

[0048] Furthermore, the mass proportions of multilayer graphene, water and sodium dodecyl sulfate are 50-100 parts, 100-200 parts and 8-12 parts respectively.

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

[0050] S12: H2SO4 solution is added dropwise to adjust the pH value of the graphene dispersion to ensure the stability of the graphene dispersion.

[0051] Furthermore, when the mass fraction of the multilayer graphene is 50 to 100 parts, the volume of the H2SO4 solution is 0.5 mL to 1 mL, and the concentration of the H2SO4 solution is 1 mol / L to 2 mol / L.

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

[0053] Furthermore, when the mass fraction of multilayer graphene is 50 to 100 parts, CuSO 4-The mass fraction of 5H2O powder is 0.5~1 part.

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

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

[0056] As an example, the mass fraction of the polyisocyanate-grafted hydroxylated graphene can be 60, 62, 65, 68, 70 parts, or within a range between any two of the above values, such as 60-68 parts.

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

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

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

[0060] Furthermore, the mass fractions of the polyisocyanate-grafted hydroxylated graphene, the polyurethane and the carbon black are 100 parts.

[0061] In some embodiments, the protective coating slurry further comprises a solvent, and the slurry can be formed by mixing the above components and the solvent. Further, the solvent comprises propylene carbonate.

[0062] Furthermore, the mass volume ratio of the polyisocyanate-grafted hydroxylated graphene to the solvent is 20 mg / mL to 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 within the range formed by any two of the above point values.

[0063] In a second aspect of the present application, a bipolar plate is provided, comprising a bipolar plate substrate and a protective coating disposed on at least a portion of the surface of the bipolar plate substrate, wherein the components of the protective coating include, by mass, 60 to 70 parts of polyisocyanate-grafted hydroxylated graphene, 18 to 30 parts of polyurethane, and 8 to 22 parts of carbon black.

[0064] The protective coating is prepared by using any of the protective coating slurries described above. Further, the components of the protective coating are, by weight, 60 to 68 parts of the polyisocyanate-grafted hydroxylated graphene, 20 to 30 parts of the polyurethane, and 8 to 12 parts of the carbon black. It is understandable that the ratio of the polyisocyanate-grafted hydroxylated graphene, polyurethane and carbon black in the protective coating is the same as that in the protective coating slurry, and will not be repeated here.

[0065] In some of the embodiments, the thickness of the protective coating is 0.2 mm to 1 mm; as an example, it can be 0.2 mm, 0.4 mm, 0.5 mm, 0.6 mm, 0.8 mm, 1 mm, or within the range formed by any two of the above point values.

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

[0067] In a third aspect of the present application, a method for preparing the above-mentioned bipolar plate is provided, comprising the following steps:

[0068] The protective coating slurry is coated on at least a portion of the surface of the bipolar plate substrate, and cured to form a protective coating to obtain a bipolar plate.

[0069] It is understandable that the protective coating slurry may be applied to part or all of the surface of the bipolar plate substrate to form a protective coating. For example, the protective coating may be formed on the entire outer surface to enhance its protective effect. Alternatively, the coating may be applied to one outer surface or two opposite outer surfaces of the bipolar plate substrate.

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

[0071] In some of the embodiments, before coating the protective coating slurry, the process further includes polishing and cleaning the surface of the bipolar plate substrate.

[0072] Specifically, the surface of the metal bipolar plate is polished with sandpaper, and then the bipolar plate is wiped with H2SO4 with a molar concentration of 1 mol / L to remove the passivation layer; the metal bipolar plate is placed in acetone for ultrasonic cleaning.

[0073] The coating method may be selected from at least one of spray coating, roller coating, blade coating and brush coating.

[0074] In a fourth aspect of the present application, a fuel cell is provided, comprising at least two bipolar plates stacked together and a membrane electrode disposed between two adjacent bipolar plates, wherein at least one bipolar plate is a bipolar plate as described in any one of the above items.

[0075] In some embodiments, the fuel cell is a hydrogen fuel cell, which is a device that converts chemical energy into electrical energy through a chemical reaction between hydrogen and oxygen in a fuel cell stack.

[0076] In order to make the purpose, technical solutions and advantages of the present invention more concise and clear, the present invention is described with the following specific embodiments, but the present invention is by no means limited to these embodiments. The embodiments described below are only preferred embodiments of the present invention, which can be used to describe the present invention and cannot be understood as limiting the scope of the present invention. It should be pointed out that any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

[0077] In order to better illustrate the present invention, the present invention is further described below in conjunction with the embodiments. The following are specific embodiments.

[0078] Embodiment 1:

[0079] This embodiment provides a method for preparing a bipolar plate of a fuel cell with a simple process and low cost:

[0080] (1) Preparation of hydroxylated graphene: 50 mg of multilayer graphene was dispersed in 120 mL of deionized water using an ultrasonic homogenizer, and 10 mg of sodium dodecyl sulfate was added, and the dispersion was continued for 40 min. Then, 0.5 mL of 1 mol / L sulfuric acid solution was dropped to adjust the pH value of the graphene dispersion. Then, 1 g of CuSO4-5H2O was added to the graphene dispersion. Finally, 0.5 mL of H2O2 solution (mass content of 8%) was slowly injected using a micro syringe pump at a speed of 40 mL / h to allow the substances in the graphene dispersion to react fully for 60 min to generate hydroxylated graphene, and the unreacted substances were removed by filtration.

[0081] (2) Mixing polyisocyanate and hydroxylated graphene in a mass ratio of 3:1, stirring at 60°C for 10 hours to obtain a reaction product; dispersing the reaction product in propylene carbonate at a dispersion ratio of 20 mg / mL to obtain a polyisocyanate-grafted hydroxylated graphene solution; mixing the polyisocyanate-grafted hydroxylated graphene, polyurethane and carbon black in the polyisocyanate-grafted hydroxylated graphene solution in a mass ratio of 60%:30%:10% by ultrasonic cleaning to obtain a composite slurry.

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

[0083] Embodiment 2:

[0084] This embodiment provides a method for preparing a bipolar plate of a fuel cell with a simple process and low cost:

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

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

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

[0088] Embodiment 3:

[0089] This embodiment provides a method for preparing a bipolar plate of a fuel cell with a simple process and low cost:

[0090] (1) Preparation of hydroxylated graphene: 100 mg of multilayer 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 dripped into the dispersion to adjust the pH value of the graphene dispersion. Then, 1 g of CuSO4-5H2O was added to the dispersion. Finally, 0.1 mL of H2O2 solution (mass content of 8%) was slowly injected using a micro syringe pump at a speed of 3 mL / h to allow the substances in the graphene dispersion to react fully for 70 min to generate hydroxylated graphene, and the unreacted substances were removed by filtration.

[0091] (2) Polyisocyanate and hydroxylated graphene were mixed in a mass ratio of 3:1, stirred at 65°C for 12 hours 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, polyurethane and 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 is applied by brushing to the surface of a clean metal bipolar plate from which the passivation film has been removed. The coating thickness is 1 mm. The bipolar plate is then placed in a heating furnace and heated to 160°C for 20 minutes to allow the coating to solidify and form a protective coating.

[0093] Example 4

[0094] This embodiment 4 provides a method for preparing a bipolar plate of a fuel cell, which differs from embodiment 3 in that the composition of the composite slurry in step (2) is different. Specifically, polyisocyanate-grafted hydroxylated graphene, polyurethane and carbon black in a polyisocyanate-grafted hydroxylated graphene solution are 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 differs from Example 1 in that polyurethane is not added to the composite slurry in step (2), and other conditions are the same as those in Example 1.

[0097] Comparative Example 2:

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

[0099] Comparative Example 3

[0100] This comparative example 3 provides a method for preparing a bipolar plate of a fuel cell, which is different from the method of Example 1 in that the polyisocyanate-grafted hydroxylated graphene solution is not added to the composite slurry in step (2), but a hydroxylated graphene solution of the same mass is directly used, and other conditions are the same as those of 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 of a fuel cell, which differs from Example 1 in that a larger amount of polyisocyanate-grafted hydroxylated graphene solution is added to the composite slurry in step (2). Specifically, polyisocyanate-grafted hydroxylated graphene, polyurethane and carbon black in the polyisocyanate-grafted hydroxylated graphene solution are mixed in a mass ratio of 80%:10%:10% by ultrasonic cleaning to obtain a composite slurry.

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

[0104] According to the GB / T 8642 standard method, the bonding strength between the protective coating of the bipolar plate and the metal bipolar plate is tested.

[0105] According to the GB / T 20042.6 standard method, the contact resistance and corrosion current of the protective coating of the bipolar plate are tested.

[0106] Table 1

[0107]

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

[0109] Compared with Example 1, no polyurethane is added to the composite slurry of Comparative Example 1, and the bonding force of the coating is greatly reduced; compared with Example 1, no carbon black is added to the composite slurry of Comparative Example 2, and the conductivity and corrosion resistance of the coating are significantly reduced. Compared with Example 1, the graphene used in Comparative Example 3 is hydroxylated graphene, and the bonding force of the coating is greatly reduced, and the contact resistance and corrosion current density are also large, indicating that its conductivity and corrosion resistance are poor. Comparative Example 4 has a different ratio, and its contact resistance and corrosion current density are large, indicating that its conductivity and corrosion resistance are poor.

[0110] The technical features of the above-described embodiments may be arbitrarily combined. To make the description concise, not all possible combinations of the technical features in the above-described 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 above-mentioned embodiments only express several implementation methods of the present invention, and the description is relatively specific and detailed, but it cannot be understood as limiting the scope of the invention patent. It should be pointed out that for ordinary technicians in this field, several modifications and improvements can be made without departing from the concept of the present invention, which all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention shall be based on the attached claims, and the description can be used to interpret the content of the claims.

Claims

1. A protective coating slurry, characterized in that: The invention comprises the following components by weight: 60-70 parts of hydroxylated graphene grafted with polyisocyanate, 18-30 parts of polyurethane and 8-22 parts of carbon black.

2. The protective coating slurry according to claim 1, characterized in that In the protective coating slurry, the polyisocyanate-grafted hydroxylated graphene is 60-68 parts by weight, the polyurethane is 20-30 parts by weight, and the carbon black is 8-12 parts by weight.

3. The protective coating slurry according to claim 1 or 2, characterized in that: The protective coating slurry also includes a solvent; wherein, The solvent comprises propylene carbonate; and / or, The mass volume ratio of the polyisocyanate-grafted hydroxylated graphene to the solvent is 20 mg / mL to 30 mg / mL.

4. A bipolar plate, characterized in that: It comprises a bipolar plate substrate and a protective coating disposed on at least part of the surface of the bipolar plate substrate, wherein the components of the protective coating include 60-70 parts of polyisocyanate-grafted hydroxylated graphene, 18-30 parts of polyurethane and 8-22 parts of carbon black in terms of mass fractions; or, The protective coating is prepared using the protective coating slurry according to any one of claims 1 to 3.

5. The bipolar plate according to claim 4, characterized in that: In the components of the protective coating, the polyisocyanate-grafted hydroxylated graphene accounts for 60 to 68 parts, the polyurethane accounts for 20 to 30 parts, and the carbon black accounts for 8 to 12 parts by mass.

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

7. The bipolar plate according to claim 4 or 5, characterized in that: The bipolar plate substrate is a metal substrate.

8. A method for preparing a bipolar plate according to any one of claims 4 to 7, characterized in that: The steps include: A protective coating slurry is coated on 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°C to 170°C, and the heating time is 20 min to 40 min; and / or, In the raw material for preparing the polyisocyanate-grafted hydroxylated graphene, the mass ratio of the polyisocyanate to the hydroxylated graphene is 2-4:

1.

10. A fuel cell, characterized in that: The invention comprises at least two bipolar plates stacked in layers and a membrane electrode located between two adjacent bipolar plates, wherein at least one bipolar plate is the bipolar plate according to any one of claims 4 to 7.

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