A fuel cell composite metal bipolar plate and a method of manufacturing the same

Abstract

The present application relates to the technical field of fuel cell, and especially relates to a kind of fuel cell composite metal bipolar plate and its preparation method.First, the metal matrix material is pretreated, then conductive coating is deposited on its surface;The preparation method of conductive coating is as follows: S1, preparation of precursor solution: polyaniline is dissolved in N-methyl pyrrolidone, then modified p-toluenesulfonic acid, multi-walled carbon nanotube, reduced graphene oxide, short carbon fiber are added, and ultrasonic treatment is carried out to obtain the precursor solution;S2, electrophoretic deposition: the precursor solution is poured into the deposition tank, the electrode is inserted, and the voltage is applied for electrophoretic deposition;S3, post-treatment: drying at 60-100 DEG C for 0.5-1.5h, and curing at 120-160 DEG C for 2-4h, and the bipolar plate is obtained.The preparation method of the present application significantly improves the corrosion resistance, mechanical strength, conductivity and service life of the bipolar plate.

Description

TECHNICAL FIELD

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

[0002] With the intensification of energy crisis and the increasing environmental pollution problems, fuel cells have attracted widespread attention as a clean and efficient energy conversion device. In fuel cells, bipolar plates, as one of the core components, bear the important functions of separating reaction gases, collecting current, and distributing reaction gases. Although traditional graphite bipolar plates have good corrosion resistance, they have low mechanical strength and high processing cost. While metal bipolar plates have high mechanical strength and good electrical conductivity, their poor corrosion resistance limits their application in fuel cells. In order to solve the above problems, researchers have begun to explore surface modification techniques for metal bipolar plates to improve their corrosion resistance and electrical conductivity.

[0003] A Chinese invention patent with application number CN202311321161.6 discloses a surface treatment method for fuel cell bipolar plates, which includes the following steps: providing a bipolar plate to be treated, placing the bipolar plate in a sealed chamber; vacuumizing the chamber; filling the chamber with diffusion gas, which contains nitrogen and at least one of unsaturated organic gas and oxygen; heating to make the temperature of the bipolar plate reach the preset temperature of the gas diffusion reaction and maintaining for a preset time to form a diffusion reaction layer inside the bipolar plate extending inward from the surface of the bipolar plate. The bipolar plate obtained by the invention patent has improved performance in a short period of time, but the stability and durability of the diffusion reaction layer are still insufficient during long-term use, and further improvement is needed.

[0004] A Chinese invention with application number CN202410343289.0 discloses a gold plating method for hydrogen fuel cell metal bipolar plate and fuel cell. By implementing the process of primer layer-high resistance buffer layer-gold plating layer on the metal bipolar plate, high conductivity and high durability of the metal bipolar plate plating layer are achieved. The invention is obtained by implementing the plating film method of primer layer-high resistance buffer layer-gold plating layer. By increasing the high resistance buffer layer, the secondary protection of the coating layer from the corrosion liquid infiltrated by local area dense defects of the gold plating layer can be increased, thereby achieving the purpose of increasing the durability of the entire plating layer. However, the multi-step electroplating process in the invention requires precise control of the thickness and electroplating conditions of each layer, increasing the complexity and difficulty of the production process, and has higher requirements for production equipment and operating personnel. In the multi-layer electroplating process, it is difficult to ensure that each layer has uniform thickness and performance distribution on the complex shape and surface of the bipolar plate. If the plating layer is not uniform, it may affect the performance and service life of the bipolar plate, and the multi-layer structure may have insufficient interlayer adhesion due to factors such as thermal expansion coefficient difference and lattice matching degree, which may cause the risk of plating layer peeling in long-term use or complex working conditions.

[0005] Therefore, it is still a technical challenge to further improve the conductivity, mechanical strength and corrosion resistance of the bipolar plate. SUMMARY

[0006] To solve the above problems, the purpose of the present invention is to provide a fuel cell composite metal bipolar plate and a preparation method thereof. The preparation method of the present invention significantly improves the corrosion resistance, mechanical strength, conductivity and service life of the bipolar plate, and the bipolar plate is suitable for proton exchange membrane fuel cells and has a wide application prospect.

[0007] The technical solution adopted by the present invention to achieve the above purpose is:

[0008] A preparation method of a fuel cell composite metal bipolar plate, first pretreats the metal substrate material to remove surface impurities, and then deposits a conductive coating on the surface of the metal substrate by electrophoretic deposition method;

[0009] The specific steps of the electrophoretic deposition conductive coating are:

[0010] S1, preparation of precursor solution: dissolve polyaniline in N-methyl pyrrolidone, stir until completely dissolved, then add modified p-toluenesulfonic acid as a dopant, continue stirring for 20-40 min, then add multi-walled carbon nanotubes and reduced graphene oxide, ultrasonic treatment for uniform dispersion, then add chopped carbon fibers, continue ultrasonic treatment, and obtain the precursor solution;

[0011] S2, electrophoretic deposition: pour the precursor solution into the deposition tank, insert the electrodes, apply voltage, and perform electrophoretic deposition on the surface of the metal substrate;

[0012] S3, post-processing: dry at 60-100℃ for 0.5-1.5h, and cure at 120-160℃ for 2-4h.

[0013] Preferably, in step S1, the weight-volume ratio of polyaniline to N-methyl pyrrolidone is 0.5-1.5g:40-60ml, and the weight ratio of polyaniline to modified p-toluenesulfonic acid, multi-walled carbon nanotubes, and reduced graphene oxide is 0.5-1.5:0.05-0.15:0.03-0.07:0.03-0.07.

[0014] Preferably, in step S2, stainless steel is used as the anode and the metal substrate as the cathode, with an electrode spacing of 2-4cm; the electrophoretic deposition parameters are: voltage 20-40V, deposition time 3-7min, and current density 1-3mA / cm 2 .

[0015] In the precursor solution, polyaniline, modified p-toluenesulfonic acid, multi-walled carbon nanotubes, reduced graphene oxide and short carbon fibers improve the conductivity and other key properties such as mechanical strength, corrosion resistance and stability through various interactions and synergies. Polyaniline is an important conductive polymer, and its conductivity can be significantly improved by doping with p-toluenesulfonic acid. As a dopant, p-toluenesulfonic acid can effectively dope the quinone nitrogen atoms in polyaniline, thereby increasing its electrical conductivity. Modified p-toluenesulfonic acid enters the polyaniline molecular chain through doping to form a charge transfer complex. This doping can increase the carrier concentration in the polyaniline molecular chain, thereby significantly improving the electrical conductivity of polyaniline. Multi-walled carbon nanotubes and reduced graphene oxide have excellent electrical conductivity and high specific surface area, and can form efficient electron transport channels in the polyaniline matrix. In addition, there is an electrostatic interaction between sulfonated polyaniline and multi-walled carbon nanotubes, which enhances the conjugation length and improves the electron mobility. The addition of multi-walled carbon nanotubes and reduced graphene oxide significantly increases the density of the conductive network, thereby improving the overall conductivity. There is a π-π conjugation and van der Waals force between multi-walled carbon nanotubes, reduced graphene oxide and polyaniline. These interactions make multi-walled carbon nanotubes, reduced graphene oxide and polyaniline combine to form a stable network structure, further enhancing the stability of the conductive network and promoting the rapid transmission of electrons, thereby improving the electrical conductivity and mechanical properties of the overall material. The good electrical conductivity of short carbon fibers makes it an effective conductive filler, and short carbon fibers form a three-dimensional conductive network in the conductive coating, providing additional electron transport paths. At the same time, as a reinforcing material, carbon fibers are uniformly dispersed in the conductive coating to form a physical support structure, not only improving the mechanical strength of the coating, but also supporting the entire conductive network through its three-dimensional structure, ensuring the continuity of the electron transport path, and further improving the electrical conductivity of the coating.

[0016] In addition, polyaniline itself has multiple functions such as shielding, passivation and corrosion inhibition. It can form a protective layer on the metal surface to prevent the penetration of corrosive media such as water and oxygen. The doping mechanism of polyaniline allows it to maintain a stable chemical structure in a corrosive environment, thereby improving the durability of the coating. Modified p-toluenesulfonic acid as a dopant can improve the water solubility and electrochemical properties of polyaniline. Through doping, the corrosion resistance of polyaniline is further enhanced, allowing it to be uniformly dispersed in the coating and form a dense protective layer. Multi-walled carbon nanotubes have excellent mechanical strength and can increase the density and impermeability of the coating when combined with polyaniline, thereby improving its corrosion resistance. Reduced graphene oxide has a high specific surface area and good dispersibility, which can effectively isolate the contact between corrosive media and the metal substrate. The combination of reduced graphene oxide and polyaniline can significantly improve the barrier performance and corrosion inhibition efficiency of the coating.

[0017] Preferably, after the deposition is completed in step S2, the coating substrate is cleaned with N-methyl pyrrolidone to remove the un-deposited particles and residues.

[0018] Preferably, the preparation method of the modified p-toluenesulfonic acid comprises the following steps:

[0019] Step 1, p-toluenesulfonic acid is added to concentrated sulfuric acid and stirred uniformly; under ice bath conditions, concentrated nitric acid is added dropwise, the dropwise addition time is 30-45 min, the reaction temperature is maintained at 0-5℃, and the stirring reaction is performed for 2.5-3.5 h; after the reaction is completed, the reaction liquid is poured into ice water, and after standing for 30-60 min, filtration is performed to obtain a nitration product;

[0020] Step 2, the nitration product is dissolved in anhydrous ethanol, hydrochloric acid and iron powder are added, and the reaction is performed under reflux for 3-5 h at a heating temperature of 80-84℃; the iron powder is removed by filtration, and the ethanol is removed by distillation under reduced pressure to obtain an amination product;

[0021] Step 3, the amination product is dissolved in distilled water and stirred uniformly, potassium permanganate is added, the reaction temperature is 60-70℃, the reaction is performed for 4-6 h, sodium hydroxide solution is added to neutralize to pH 9-10, the precipitate is removed by filtration, and then the filtrate is acidified with hydrochloric acid to pH 2-3 to precipitate the product;

[0022] Step 4, the filtrate after acidification in step 3 is filtered to obtain the precipitated solid product, which is washed with distilled water until neutral and dried to obtain the modified p-toluenesulfonic acid.

[0023] Preferably, in step 1, the weight-volume ratio of the p-toluenesulfonic acid, concentrated sulfuric acid, and concentrated nitric acid is 5-15 g: 20-40 ml: 10-20 ml.

[0024] Preferably, in step 2, the weight-volume ratio of the iron powder, anhydrous ethanol, and hydrochloric acid is 15-25 g: 80-120 ml: 3-7 ml, and the weight ratio of the obtained nitration product to iron powder is 10-13: 15-25.

[0025] Preferably, in step 3, the weight-volume ratio of the potassium permanganate and distilled water is 5-10 g: 120-180 ml, and the weight ratio of the obtained amination product to potassium permanganate is 1-1.2: 1.

[0026] The introduction of amino groups (-NH2) and carboxyl groups (-COOH) through the modification of p-toluenesulfonic acid. Amino groups (-NH2) are highly active functional groups that can interact with other molecules through hydrogen bonds. In polyaniline, amino groups can form hydrogen bonds with dopants or other molecules through N-H bonds. The formation of hydrogen bonds can enhance the binding force between the dopant and polyaniline, thereby improving the stability of the doped polyaniline. The presence of hydrogen bonds has a certain influence on the microstructure of polyaniline, changing the arrangement of polyaniline chains and intermolecular interactions, thereby improving its electrical conductivity. Carboxyl groups (-COOH) can dissociate into hydrogen ions under certain conditions, forming negatively charged carboxylate ions, which can form ionic interactions with the positively charged parts of the polyaniline molecular chain. In addition, the oxygen atoms in the carboxyl group can also form hydrogen bonds with the hydrogen atoms on the polyaniline molecular chain. This multiple interaction improves the binding force between the dopant and polyaniline, forming a more stable doping structure, improving the doping efficiency, and ensuring the stability and durability of the conductive network. The modified p-toluenesulfonic acid makes the arrangement of polyaniline molecular chains more regular through multiple interactions, increases the carrier concentration in the polyaniline molecular chain, and forms a more conducive channel for charge transport, thereby improving the conductivity of the coating. Hydrogen bonds and ionic interactions make the binding between polyaniline molecular chains more compact and stable, capable of resisting external environmental factors (such as temperature, humidity, chemicals, etc.), improving the stability of the coating during use. Enhanced intermolecular interactions help improve the mechanical strength and toughness of the polyaniline coating, making it better able to withstand external mechanical stress and deformation, reducing the likelihood of coating cracking and damage. Stable molecular structure can better resist the erosion of corrosive media, protecting the coating and substrate, and extending the service life of the polyaniline conductive coating.

[0027] Preferably, it also includes coating a chromium or nickel coating on the surface of the metal substrate using electroplating method before pre-treatment and electrophoretic deposition of the conductive coating

[0028] The electroplated chromium or nickel coating has excellent corrosion resistance, which can significantly improve the corrosion resistance of the metal substrate. By depositing a polyaniline conductive coating on these metal coatings, the corrosion protection effect can be further enhanced. The polyaniline coating can form a protective layer on the metal surface through redox reaction, thereby effectively blocking the intrusion of corrosive media. The chromium or nickel coating can fill the small defects and pores on the surface of the metal substrate, making the surface more smooth and uniform, improving the roughness and chemical properties of the metal substrate surface, creating good conditions for the uniform deposition of the subsequent polyaniline coating, increasing the binding force between the polyaniline conductive coating, reducing the risk of coating delamination and peeling, and improving the stability and reliability of the coating.

[0029] The fuel cell composite metal bipolar plate prepared by the above method.

[0030] A fuel cell comprising the composite metal bipolar plate.

[0031] The present application has the following advantages:

[0032] The present application adopts electrophoretic deposition method to deposit conductive coating on the surface of metal substrate. In the precursor solution, polyaniline serves as the main conductive polymer, and its molecular chain structure can provide certain conductive path. p-Toluene sulfonic acid, as a dopant, can insert between the molecular chains of polyaniline, change the electronic structure of polyaniline, increase the carrier concentration, and thus improve the conductivity of polyaniline. Multi-walled carbon nanotubes have extremely high conductivity and long-range electron transport capability. They can intertwine and contact with polyaniline in solution to form a continuous conductive network, providing an efficient transmission channel for electrons and significantly enhancing the overall conductivity. Reduced graphene oxide has a large specific surface area and good conductivity. It can fully contact with polyaniline to increase the conductive contact points and further expand the conductive path. At the same time, its sheet structure can also play a barrier and protection role to improve the corrosion resistance of the coating. Short carbon fibers mainly serve to enhance the stability of the solution and the mechanical properties of the coating. During the formation of the coating, short carbon fibers can bridge and interweave between other components to improve the structural integrity and strength of the coating, reduce the generation of cracks and defects, and thus enhance the stability and durability of the coating. The synergistic effect of these components in the precursor solution enables the formation of a coating with excellent conductivity, good corrosion resistance, and mechanical strength in the subsequent processing process, meeting the performance requirements of the fuel cell composite metal bipolar plate.

[0033] Further, the modified p-toluene sulfonic acid is used as a dopant. Compared with the unmodified p-toluene sulfonic acid, the introduction of amino (-NH2) and carboxyl (-COOH) enables the modified p-toluene sulfonic acid to form more complex interactions with the polyaniline molecular chain, including hydrogen bonding and ionic interaction. These interactions significantly enhance the binding force between the dopant and polyaniline, thereby significantly improving the conductivity, mechanical strength, corrosion resistance, and other properties of the electrophoretically deposited polyaniline conductive coating, providing more reliable support for its application in fuel cells and other fields.

[0034] The present application adopts electrophoretic deposition method to ensure that the materials in the precursor solution are uniformly deposited on the surface of the metal substrate, forming a dense and uniform conductive coating. This process not only improves the conductivity and corrosion resistance of the coating, but also simplifies the preparation process and reduces production costs. DETAILED DESCRIPTION

[0035] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative work fall within the protection scope of the present application.

[0036] The raw materials used in the following examples are all ordinary commercially available products. Polyaniline, molecular weight 726.87, Wuhan Kemik Biomedical Technology Co., Ltd.; multi-walled carbon nanotubes, diameter 10-30 nm, length 1-2 um, Guangzhou Hongwu Material Technology Co., Ltd.; reduced graphene oxide, model TG1600, Dongguan Keluode New Energy Technology Co., Ltd.; chopped carbon fibers, length 5 mm, manufacturer Jiangxi Suobang New Material Technology Co., Ltd.; concentrated sulfuric acid, concentration 98%, concentrated nitric acid concentration 65%, hydrochloric acid concentration 37%.

[0037] Example 1

[0038] A method for preparing a fuel cell composite metal bipolar plate, comprising the following steps:

[0039] (1) First, the metal substrate material is pretreated, including grinding, polishing and cleaning, to remove the oxides and impurities on the surface;

[0040] (2) A nickel coating is coated on the surface of the pretreated metal substrate by electroplating with nickel sulfate, and the electroplating uses conventional process operation;

[0041] (3) A conductive coating is deposited on the surface of the nickel coating of step (2) by electrophoretic deposition, and the specific steps of the electrophoretic deposition of the conductive coating are:

[0042] S1, preparation of a precursor solution: 1.0 g of polyaniline is dissolved in 55 ml of N-methyl pyrrolidone, stirred for 30 min until completely dissolved, 0.1 g of modified p-toluenesulfonic acid is added as a dopant, and stirring is continued for 30 min, then 0.04 g of multi-walled carbon nanotubes and 0.05 g of reduced graphene oxide are added, and ultrasonic treatment is carried out for 1 h for uniform dispersion; finally, 0.10 g of chopped carbon fibers is added, and ultrasonic treatment is continued for 1 h, and the ultrasonic power is 400 W;

[0043] S2, electrophoretic deposition: stainless steel is selected as the anode, and the metal substrate is selected as the cathode, the electrode spacing is 3 cm, and the electrophoretic deposition parameters are controlled as follows: voltage 30 V, deposition time 5 min, and current density 2.5 mA / cm 2 The precursor solution is poured into the deposition tank, the electrodes are inserted, and the voltage is applied to perform electrophoretic deposition on the surface of the metal substrate; after deposition is completed, the coating substrate is cleaned with NMP (N-methyl pyrrolidone) to remove un-deposited particles and residues;

[0044] S3, post-treatment: drying at 80℃ for 1h; curing at 140℃ for 3h to improve the adhesion and mechanical strength of the coating;

[0045] (4) The composite metal substrate obtained in step (3) is punched and cut to form a composite metal bipolar plate.

[0046] The preparation method of the modified p-toluenesulfonic acid comprises the following steps:

[0047] Step 1, in a fume hood, 10g of p-toluenesulfonic acid is slowly added to 30ml of concentrated sulfuric acid and stirred evenly; under ice bath conditions, 15ml of concentrated nitric acid is slowly added dropwise, the dropping speed is controlled, the dropping time is 30min, the reaction temperature is kept at 0-5℃, and the stirring reaction is carried out for 3h; after the reaction is completed, the reaction liquid is slowly poured into a large amount of ice water, and after standing for 40min, filtration is carried out to obtain a nitration product;

[0048] Step 2, the nitration product is dissolved in 100ml of anhydrous ethanol, 20g of iron powder and 4ml of hydrochloric acid are added, and the reaction is carried out under reflux for 4h at a heating temperature of 81℃, so that the nitro group is reduced to an amino group, and the weight ratio of the obtained nitration product to iron powder is 11.5:20; after the reaction is completed, the remaining iron powder is removed by filtration, and the ethanol is removed by distillation under reduced pressure to obtain an amination product;

[0049] Step 3, the amination product is dissolved in 150ml of distilled water and stirred evenly; 7g of potassium permanganate is slowly added, the reaction temperature is controlled at 65℃, and the reaction is carried out for 5.5h, and the weight ratio of the obtained amination product to potassium permanganate is 1.18:1; after the reaction is completed, sodium hydroxide solution is added to neutralize to pH 9-10, the precipitate is removed by filtration, and then the filtrate is acidified with hydrochloric acid to pH 2-3 to precipitate the product;

[0050] Step 4, the filtrate after acidification in step 3 is filtered to obtain the precipitated solid product, which is washed with distilled water several times until the washing liquid is neutral; the product is dried in a vacuum drying oven at 60℃ to obtain modified p-toluenesulfonic acid.

[0051] Example 2

[0052] A method for preparing a fuel cell composite metal bipolar plate comprises the following steps:

[0053] (1) First, the metal substrate material is pretreated, including grinding, polishing and cleaning, to remove oxides and impurities on the surface;

[0054] (2) A nickel coating is coated on the surface of the pretreated metal substrate by electroplating with nickel sulfate;

[0055] (3) Depositing the conductive coating on the surface of the metal substrate by electrophoretic deposition, the specific steps of the electrophoretic deposition of the conductive coating being:

[0056] S1, preparation of a precursor solution: 1.5 g of polyaniline is dissolved in 60 ml of N-methylpyrrolidone, stirred for 20 min until completely dissolved, 0.05 g of modified p-toluenesulfonic acid is added as a dopant, and stirring is continued for 20 min, then 0.03 g of multi-walled carbon nanotubes and 0.07 g of reduced graphene oxide are added, and ultrasonic treatment is performed for 0.5 h for uniform dispersion; finally, 0.15 g of short carbon fibers is added, and ultrasonic treatment is continued for 1.2 h, and the ultrasonic power is 350 W;

[0057] S2, electrophoretic deposition: stainless steel is selected as the anode, and the metal substrate is selected as the cathode, the electrode spacing is 2 cm, the electrophoretic deposition parameters are controlled as follows: the voltage is 25 V, the deposition time is 3 min, and the current density is 1 mA / cm 2 The precursor solution is poured into the deposition tank, the electrodes are inserted, the voltage is applied, and electrophoretic deposition is performed on the surface of the metal substrate; after the deposition is completed, the coating substrate is cleaned with NMP to remove un-deposited particles and residues;

[0058] S3, post-treatment: drying at 100℃ for 0.5 h; curing at 120℃ for 4 h to improve the adhesion and mechanical strength of the coating;

[0059] (4) The composite metal substrate obtained in step (3) is subjected to stamping and cutting to form a composite metal bipolar plate.

[0060] The preparation method of the modified p-toluenesulfonic acid comprises the following steps:

[0061] Step 1: In a fume hood, 5 g of p-toluenesulfonic acid is slowly added to 20 ml of concentrated sulfuric acid and stirred uniformly; under ice bath conditions, 10 ml of concentrated nitric acid is slowly added dropwise, the dropwise addition speed is controlled, and the reaction temperature is maintained at 0-5℃ during the dropwise addition, and the stirring reaction is performed for 2.5 h; after the reaction is completed, the reaction liquid is slowly poured into a large amount of ice water, and after standing for 30 min, filtration is performed to obtain a nitration product;

[0062] Step 2: The nitration product is dissolved in 80 ml of anhydrous ethanol, 15 g of iron powder and 3 ml of hydrochloric acid are added, and the reaction is performed under reflux for 3 h at a heating temperature of 82℃, so that the nitro group is reduced to an amino group, and the weight ratio of the obtained nitration product to the iron powder is 10:25; after the reaction is completed, the remaining iron powder is removed by filtration, and ethanol is removed by distillation under reduced pressure to obtain an amination product;

[0063] Step 3, the above amination product is dissolved in 140 ml distilled water, stirred evenly; slowly add 5 g of potassium permanganate, control the reaction temperature at 60℃, reaction for 4h, the weight ratio of the obtained amination product and potassium permanganate is 1:1, after the reaction is completed, add sodium hydroxide solution to neutralize to pH 9-10, filter to remove the precipitate, then acidify the filtrate with hydrochloric acid to pH 2-3 to precipitate the product;

[0064] Step 4, filter the filtrate after acidification in step 3 to obtain the precipitated solid product, wash with distilled water for several times until the washing liquid is neutral; dry the product in a vacuum drying oven at 65℃ to obtain the modified p-toluenesulfonic acid.

[0065] Example 3

[0066] A method for preparing a fuel cell composite metal bipolar plate, comprising the following steps:

[0067] (1) First, the metal substrate material is pretreated, including grinding, polishing and cleaning, to remove the surface oxides and impurities;

[0068] (2) A nickel coating layer is coated on the surface of the pretreated metal substrate by electroplating method using nickel sulfate;

[0069] (3) An electrically conductive coating layer is deposited on the surface of the metal substrate by electrophoretic deposition method, and the specific steps of the electrophoretic deposition of the electrically conductive coating layer are as follows:

[0070] S1, preparation of precursor solution: 0.5 g of polyaniline is dissolved in 40 ml of N-methyl pyrrolidone, stirred for 40 min until completely dissolved, 0.15 g of modified p-toluenesulfonic acid is added as a dopant, and stirring is continued for 40 min, then 0.07 g of multi-walled carbon nanotubes and 0.03 g of reduced graphene oxide are added, and ultrasonic treatment is carried out for 1.5 h for uniform dispersion; finally, 0.05 g of short carbon fibers is added, and ultrasonic treatment is continued for 0.5 h, and the ultrasonic power is 450 W;

[0071] S2, electrophoretic deposition: stainless steel is selected as the anode and the metal substrate as the cathode, the electrode distance is 4 cm, the electrophoretic deposition parameters are controlled as follows: voltage is 40 V, deposition time is 7 min, and current density is 3 mA / cm 2 The precursor solution is poured into the deposition tank, the electrodes are inserted, and the voltage is applied to perform electrophoretic deposition on the surface of the metal substrate; after the deposition is completed, the coating substrate is cleaned with NMP to remove the un-deposited particles and residues;

[0072] S3, post-treatment: drying at 60℃ for 1.5h; curing at 160℃ for 2h to improve the adhesion and mechanical strength of the coating layer;

[0073] (4) The composite metal substrate obtained in step (3) is punched and cut to form a composite metal bipolar plate.

[0074] The preparation method of the modified p-toluenesulfonic acid comprises the following steps:

[0075] Step 1, in a fume hood, 15 g of p-toluenesulfonic acid is slowly added to 40 ml of concentrated sulfuric acid and stirred uniformly; under ice bath conditions, 20 ml of concentrated nitric acid is slowly added dropwise, the dropping speed is controlled, the dropping time is 35 min, the reaction temperature is maintained at 0-5℃, and the stirring reaction is carried out for 3.5 h; after the reaction is completed, the reaction liquid is slowly poured into a large amount of ice water, and after standing for 60 min, filtration is carried out to obtain a nitration product;

[0076] Step 2, the nitration product is dissolved in 120 ml of anhydrous ethanol, 25 g of iron powder and 7 ml of hydrochloric acid are added, and a reflux reaction is carried out at a heating temperature of 80℃ for 5 h, so that the nitro group is reduced to an amino group, and the weight ratio of the obtained nitration product to iron powder is 13:15; after the reaction is completed, the remaining iron powder is removed by filtration, and ethanol is removed by reduced pressure distillation to obtain an amination product;

[0077] Step 3, the amination product is dissolved in 120 ml of distilled water and stirred uniformly; 10 g of potassium permanganate is slowly added, the reaction temperature is controlled at 70℃, and the reaction is carried out for 6 h, and the weight ratio of the obtained amination product to potassium permanganate is 1.2:1; after the reaction is completed, sodium hydroxide solution is added to neutralize to pH 9-10, the precipitate is removed by filtration, and then the filtrate is acidified with hydrochloric acid to pH 2-3 to precipitate the product;

[0078] Step 4, the filtrate after acidification in step 3 is filtered to obtain the precipitated solid product, which is washed with distilled water for multiple times until the washing liquid is neutral; the product is dried in a vacuum drying oven at 55℃ to obtain modified p-toluenesulfonic acid.

[0079] Example 4

[0080] A preparation method of a fuel cell composite metal bipolar plate comprises the following steps:

[0081] (1) First, the metal substrate material is pretreated, including grinding, polishing and cleaning, to remove the oxides and impurities on the surface;

[0082] (2) A nickel coating layer is coated on the surface of the pretreated metal substrate by electroplating with nickel sulfate;

[0083] (3) An electrically conductive coating layer is deposited on the surface of the metal substrate by electrophoretic deposition, and the specific steps of the electrophoretic deposition of the electrically conductive coating layer are as follows:

[0084] S1, preparation of precursor solution: 1.2 g of polyaniline was dissolved in 50 ml of N-methylpyrrolidone, stirred for 25 min until completely dissolved, 0.12 g of modified p-toluenesulfonic acid was added as a dopant, and stirring was continued for 25 min, then 0.05 g of multi-walled carbon nanotubes and 0.04 g of reduced graphene oxide were added, and ultrasonic treatment was carried out for 0.5 h to achieve uniform dispersion; finally, 0.12 g of short carbon fibers was added, and ultrasonic treatment was continued for 1.5 h, with an ultrasonic power of 420 W;

[0085] S2, electrophoretic deposition: stainless steel was selected as the anode, and a metal substrate was selected as the cathode, with an electrode spacing of 2 cm; the electrophoretic deposition parameters were controlled as follows: voltage of 20 V, deposition time of 4 min, and current density of 2 mA / cm 2 The precursor solution was poured into the deposition tank, the electrodes were inserted, and a voltage was applied to perform electrophoretic deposition on the surface of the metal substrate; after deposition was completed, the coating substrate was cleaned with NMP to remove un-deposited particles and residues;

[0086] S3, post-treatment: drying at 70°C for 1 h; curing at 130°C for 3 h to improve the adhesion and mechanical strength of the coating;

[0087] (4) The composite metal bipolar plate was prepared by stamping and cutting the composite metal substrate obtained in step (3).

[0088] The preparation method of the modified p-toluenesulfonic acid comprises the following steps:

[0089] Step 1: In a fume hood, 8 g of p-toluenesulfonic acid was slowly added to 32 ml of concentrated sulfuric acid and stirred uniformly; under ice bath conditions, 17 ml of concentrated nitric acid was slowly added dropwise, the dropping speed was controlled, the dropping time was 40 min, the reaction temperature was maintained at 0-5°C, and the stirring reaction was carried out for 2.8 h; after the reaction was completed, the reaction liquid was slowly poured into a large amount of ice water, and after standing for 50 min, filtration was performed to obtain a nitration product;

[0090] Step 2: The nitration product was dissolved in 90 ml of anhydrous ethanol, 18 g of iron powder and 6 ml of hydrochloric acid were added; heating reflux reaction was carried out for 4.5 h, the heating temperature was 84°C, the nitro group was reduced to an amino group, and the weight ratio of the obtained nitration product to iron powder was 12:18; after the reaction was completed, the remaining iron powder was removed by filtration, ethanol was removed by distillation under reduced pressure, and an amination product was obtained;

[0091] Step 3: The amination product was dissolved in 180 ml of distilled water and stirred uniformly; 9 g of potassium permanganate was slowly added, the reaction temperature was controlled at 63°C, and the reaction was carried out for 5 h; the weight ratio of the obtained amination product to potassium permanganate was 1.15:1; after the reaction was completed, sodium hydroxide solution was added to neutralize to pH 9-10, the precipitate was removed by filtration, and then the filtrate was acidified with hydrochloric acid to pH 2-3 to precipitate the product;

[0092] Step 4, the filtrate after acidification in step 3 is filtered to obtain the precipitated solid product, which is washed with distilled water for several times until the washing liquid is neutral; the product is dried in a vacuum drying oven at 70℃ to obtain the modified p-toluenesulfonic acid.

[0093] Comparative Example 1

[0094] A method for preparing a fuel cell composite metal bipolar plate, wherein in the conductive polymer, only polyaniline is contained in the precursor solution, and no p-toluenesulfonic acid, multi-walled carbon nanotubes, reduced graphene oxide, or short carbon fibers are added, and the rest is the same as in Example 1.

[0095] Comparative Example 2

[0096] A method for preparing a fuel cell composite metal bipolar plate, wherein in the conductive polymer, the p-toluenesulfonic acid is a common unmodified p-toluenesulfonic acid, and the rest is the same as in Example 1.

[0097] Performance test:

[0098] The composite protective coating containing bipolar plates prepared in Examples 1-4 and Comparative Examples 1-2 are subjected to contact resistance and corrosion current density tests, and the test methods are all in accordance with GB / T20042.6-2011, wherein the corrosion current density is tested by dynamic potential polarization using an electrochemical workstation, and the polarization is carried out at 80℃ in 0.5M H2SO4+1ppm HF solution for 1h at a constant potential (0.6V vs.SCE). The contact resistance and corrosion current density test results are shown in Table 1.

[0099] Table 1, corrosion current density and contact resistance test results

[0100] Item Corrosion current density (pA / cm 2 , 0.6 V) Contact resistance mΩ·cm 2 (pressure 0.6 MPa) Example 1 0.12 3.8 Example 2 0.09 3.4 Example 3 0.08 3.5 Example 4 0.13 3.7 Comparative Example 1 0.86 7.4 Comparative Example 2 0.72 7.1

[0101] As can be seen from Table 1, the contact resistance and corrosion current density of the composite metal bipolar plates of Examples 1-4 are lower than those of Comparative Examples 1-2, which indicates that in Examples 1-4, the modified p-toluenesulfonic acid is added to dope polyaniline, and multi-walled carbon nanotubes, reduced graphene oxide, and short carbon fibers are added for electrophoretic deposition, and the composite metal bipolar plates obtained thereby have better conductivity and corrosion resistance than Comparative Examples 1 and 2.

[0102] It is to be understood that the terminology used herein such as first and second, and the like, is only used to distinguish one entity or action from another entity or action, and does not necessarily require or imply any such actual relationship or order between such entities or actions. Moreover, the terms "comprises", "comprising", or any other variations thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but can include other elements not expressly listed or inherent to such process, method, article, or apparatus.

[0103] While embodiments of the present application have been shown and described with reference to particular embodiments thereof, it will be understood by those skilled in the art that various changes in form and details can be made therein without departing from the spirit and scope of the application. The scope of the application is thus defined by the appended claims and their equivalents.

Claims

1. A method for preparing a composite metal bipolar plate for a fuel cell, characterized in that, First, the metal substrate material is pretreated to remove surface impurities, and then a conductive coating is deposited on the surface of the metal substrate by electrophoretic deposition. The specific steps for depositing a conductive coating on the surface of a metal substrate by electrophoretic deposition are as follows: S1, Preparation of precursor solution: Polyaniline is dissolved in N-methylpyrrolidone and stirred until completely dissolved. Then, modified p-toluenesulfonic acid is added as a dopant and stirred for 20-40 min. Multi-walled carbon nanotubes and reduced graphene oxide are added and subjected to ultrasonic treatment. After uniform dispersion, short-cut carbon fibers are added and ultrasonic treatment is continued to obtain the precursor solution. S2, Electrophoretic deposition: The precursor solution is poured into the deposition tank, electrodes are inserted, voltage is applied, and electrophoretic deposition is performed on the surface of the metal substrate. S3, Post-treatment: Dry at 60-100℃ for 0.5-1.5h, then cure at 120-160℃ for 2-4h to obtain the product; The method for preparing the modified p-toluenesulfonic acid includes the following steps: Step 1: Add p-toluenesulfonic acid to concentrated sulfuric acid and stir until homogeneous. Under ice bath conditions, add concentrated nitric acid dropwise over 30-45 minutes. Maintain the reaction temperature at 0-5°C and stir for 2.5-3.5 hours. After the reaction is complete, pour the reaction solution into ice water, let it stand for 30-60 minutes, and then filter to obtain the nitrated product. Step 2: Dissolve the above nitrated product in anhydrous ethanol, add hydrochloric acid and iron powder, heat under reflux for 3-5 hours at a temperature of 80-84℃, filter to remove iron powder, and remove ethanol by vacuum distillation to obtain the aminated product. Step 3: Dissolve the above amination product in distilled water, stir well, add potassium permanganate, react at 60-70℃ for 4-6 hours, add sodium hydroxide solution to neutralize to pH 9-10, filter to remove precipitate, and then acidify the filtrate with hydrochloric acid to pH 2-3. Step 4: Filter the filtrate after acidification in Step 3 to obtain the precipitated solid product, wash it with distilled water until neutral, and dry it to obtain modified p-toluenesulfonic acid.

2. The method for preparing the composite metal bipolar plate for a fuel cell according to claim 1, characterized in that, In step S1, the weight-to-volume ratio of polyaniline to N-methylpyrrolidone is 0.5-1.5g:40-60ml, and the weight ratio of polyaniline to modified p-toluenesulfonic acid, multi-walled carbon nanotubes, and reduced graphene oxide is 0.5-1.5:0.05-0.15:0.03-0.07:0.03-0.

07.

3. The method for preparing the composite metal bipolar plate for a fuel cell according to claim 1, characterized in that, In step S2, stainless steel is used as the anode and a metal substrate as the cathode, with an electrode spacing of 2-4 cm. The electrophoretic deposition parameters are: voltage 20-40V, deposition time 3-7 min, and current density 1-3 mA / cm². 2 .

4. The method for preparing the composite metal bipolar plate for a fuel cell according to claim 1, characterized in that, In step 1, the weight-to-volume ratio of p-toluenesulfonic acid to concentrated sulfuric acid and concentrated nitric acid is 5-15g: 20-40ml: 10-20ml.

5. The method for preparing the composite metal bipolar plate for a fuel cell according to claim 1, characterized in that, In step 2, the weight-to-volume ratio of iron powder to anhydrous ethanol and hydrochloric acid is 15-25g: 80-120ml: 3-7ml, and the weight ratio of the resulting nitrated product to iron powder is 10-13: 15-25.

6. The method for preparing the composite metal bipolar plate for a fuel cell according to claim 1, characterized in that, In step 3, the weight-to-volume ratio of potassium permanganate to distilled water is 5-10g:120-180ml, and the weight ratio of the resulting aminated product to potassium permanganate is 1-1.2:

1.

7. The method for preparing a composite metal bipolar plate for a fuel cell according to claim 1, characterized in that, It also includes applying a chromium or nickel coating to the surface of a metal substrate by electroplating after pretreatment and before electrophoretic deposition of a conductive coating.

8. The fuel cell composite metal bipolar plate obtained by the preparation method according to any one of claims 1-7.

9. A fuel cell, characterized in that, Including the composite metal bipolar plate as described in claim 8.