Preparation method of metal bipolar plate surface doped cobalt phthalocyanine PANI composite coating

Abstract

The invention discloses a preparation method of a cobalt phthalocyanine PANI doped composite coating on the surface of a metal bipolar plate. The method comprises the following steps: carrying out surface roughening and acid activation pretreatment on the metal bipolar plate; the preparation method comprises the following steps: preparing precursor slurry from cobalt phthalocyanine and an aniline monomer in an acid environment through in-situ oxidative polymerization; the preparation method comprises the following key steps: introducing an independently designed and synthesized sulfonyl-bis-imidazoline-containing electron bridging aromatic ring as a multifunctional dopant, and effectively bridging a polyaniline chain and cobalt phthalocyanine molecules through the strong electron withdrawing effect of sulfonyl and the coordination synergistic effect of a bis-imidazoline ring to construct a stable three-dimensional conductive network; and finally, coating an activated substrate with the obtained composite slurry, and carrying out heat treatment to form a compact coating. The contact resistance of the composite coating is lower than 8.5 m omega.cm, the corrosion current density is lower than 0.1 mu A / cm, the binding force of the coating reaches the 5B grade, and the composite coating has high conductivity, high corrosion resistance and excellent interface stability.

Description

Technical Field

[0001] This invention relates to the field of surface treatment technology for energy conversion devices, and in particular to a method for preparing a cobalt phthalocyanine (PANI) composite coating on the surface of a metal bipolar plate. Background Technology

[0002] Metal bipolar plates are key components in proton exchange membrane fuel cells and direct methanol fuel cells, requiring low contact resistance, high conductivity, and long-term corrosion resistance. Currently widely used stainless steel bipolar plates are prone to pitting corrosion, intergranular corrosion, and passivation film rupture in high humidity, high acid, and oxygen-rich environments, leading to increased interfacial resistance and decreased durability. Therefore, conductive protective coatings are often applied to the surface to improve performance.

[0003] In existing research, conductive polymers such as polyaniline (PANI) have attracted widespread attention due to their good conductivity, protonation capability, and high chemical stability. However, pure PANI coatings suffer from problems such as disordered chain segment arrangement, loss of dopant ions, and attenuation of the conductive network, making it difficult to maintain stable conductivity and corrosion resistance under long-term operating conditions. To enhance the coating structure, researchers often introduce metal phthalocyanines, carbon materials, or inorganic fillers. Cobalt phthalocyanine can improve electron migration ability, but its dispersion and binding stability in the polyaniline backbone are still insufficient, leading to performance degradation of composite coatings under humid heat cycling and acidic media.

[0004] Meanwhile, existing coating systems generally lack effective interface enhancement mechanisms, resulting in insufficient adhesion between the coating and the metal substrate. This makes them susceptible to microcracks and localized delamination under potential shocks, thermal cycling, or corrosive media, thus accelerating substrate corrosion. Currently, there is a lack of a multifunctional molecular dopant capable of simultaneously achieving "electronic structure regulation, polymer chain segment ordering, and interface adhesion enhancement," making it difficult to comprehensively improve the durability of conductive polymer coatings.

[0005] In summary, current metal bipolar plate coatings still have significant shortcomings in terms of conductivity, corrosion resistance, interfacial adhesion, and cycle stability. There is an urgent need for a novel doping system designed at the molecular level to strengthen the conductive network, improve coating density, and enhance interfacial protection performance. Summary of the Invention

[0006] To address the aforementioned problems, this invention proposes a method for preparing a cobalt phthalocyanine (PANI) composite coating on the surface of a metal bipolar plate. In this invention, cobalt phthalocyanine effectively enhances electron mobility, while S-BIAR, as a multifunctional molecular dopant, not only enhances the orderliness of polymer chains but also strengthens the interfacial bonding strength between the coating and the metal substrate. Substrate activation provides an active surface for robust coating adhesion. These three factors work together to construct a high-performance composite coating that combines high conductivity, strong corrosion resistance, and excellent interfacial stability. This solves the problems of easy attenuation of the conductive network, insufficient corrosion resistance, and poor adhesion of traditional conductive polymer coatings under the harsh operating conditions of fuel cells.

[0007] This invention can be achieved through the following technical solutions: Step 1: Roughen the metal plate with sandpaper, ultrasonically wash it with deionized water for 10-20 minutes, then immerse it in dilute hydrochloric acid for activation, and dry it to obtain an activated metal bipolar plate. Step 2: Add hydrochloric acid, cobalt phthalocyanine, and aniline monomer to the flask, stir and mix well, and slowly add ammonium persulfate oxidant under ice bath conditions to carry out in-situ oxidative polymerization to obtain cobalt phthalocyanine PANI precursor slurry. Then add sulfonyl-bisimidazolinone electron-bridged aromatic ring (S-BIAR), stir at 25-40℃ for 2-4 h to obtain composite coating slurry. Step 3: The obtained composite coating slurry is uniformly coated on the surface of the activated metal bipolar plate and placed in an oven for heat treatment to form a cobalt phthalocyanine (PANI) composite coating.

[0008] Preferably, the activation temperature of dilute hydrochloric acid in step 1 is 25-40℃, and the time is 3-8 min.

[0009] Preferably, the in-situ oxidative polymerization in step 2 is carried out at a temperature of 0-5°C for 1-3 hours.

[0010] Preferably, in step 2, the ratio of cobalt phthalocyanine, aniline monomer, ammonium persulfate oxidant, and S-BIAR is (0.05-0.2) g : (0.2-0.6) g : (0.4-1.2) g : (0.05-0.15) g.

[0011] Preferably, the preparation method of S-BIAR is as follows: N,N-dimethylformamide, p-phenylenediamine, 2-chloroacetamide, and anhydrous potassium carbonate are added to a flask and stirred in an ice bath at 0–5°C. A nucleophilic substitution reaction is then carried out, followed by cooling to precipitate a solid. The solid is filtered, washed with water, and dried to obtain crude N,N′-bis(2-acetamido)-p-aniline. Anhydrous ethanol and ethylenediamine are added to the obtained crude product, and the mixture is refluxed at 100–120°C for 8–12 h. After cooling and filtration, the mixture is washed with ethanol, and then tetrahydrofuran, chlorosulfonic acid, and triethylamine are added. The mixture is stirred in an ice bath and then sulfonated. After the reaction is complete, the mixture is poured into ice water to crystallize, filtered, washed with deionized water, and dried to finally obtain S-BIAR.

[0012] Preferably, the mass ratio of p-phenylenediamine, 2-chloroacetamide, and anhydrous potassium carbonate is (10-15) g: (15-25) g, (30-60) g.

[0013] Preferably, the nucleophilic substitution reaction is carried out at a temperature of 80-90°C for 6-10 hours.

[0014] Preferably, the sulfonation temperature is 65-85°C and the time is 5-8 h.

[0015] Preferably, the heat treatment temperature in step 3 is 60-120℃ and the time is 0.5-2 h.

[0016] The beneficial effects of this invention are: The cobalt phthalocyanine (PANI) composite coating on the surface of a metal bipolar plate prepared in this invention exhibits excellent comprehensive performance: the interfacial contact resistance is less than 8.5 mΩ·cm² under 1.5 MPa pressure, the corrosion current density is less than 0.1 μA / cm², and the coating adhesion reaches level 5B, significantly better than the unoptimized comparative sample. The beneficial effects of this composite coating are mainly attributed to the designed and synthesized sulfonyl-bisimidazoline electron-bridged aromatic ring (S-BIAR). This S-BIAR molecule organically combines the strong electronic effect of the sulfonyl group, the coordination ability of the bisimidazoline ring, and the rigid planar structure of the aromatic ring, forming a multifunctional bridging unit. It can promote the orderly arrangement of polyaniline segments, construct a continuous three-dimensional conductive network, and form a strong chemical bond with the metal substrate through the active groups at its molecular ends, significantly enhancing the interfacial bonding strength between the coating and the substrate. Simultaneously, the sulfonic acid groups in the S-BIAR provide a good proton conduction channel, while the bisimidazoline structure stabilizes the coating structure through coordination with cobalt phthalocyanine. The introduction of this multifunctional molecular bridging agent fundamentally solves key technical problems such as discontinuous conductive networks, weak interfacial bonding, and poor long-term stability in traditional conductive polymer coatings. Attached Figure Description

[0017] The accompanying drawings are provided to further illustrate the invention and form part of the specification. They are used in conjunction with embodiments of the invention to explain the invention and do not constitute a limitation thereof. In the drawings:

[0018] Figure 1 The contact resistance and corrosion current density of the composite coating are given. Detailed Implementation

[0019] The following provides a detailed description of the embodiments of the present invention: These embodiments are implemented based on the technical solution of the present invention, and provide detailed implementation methods and processes. However, the scope of protection of the present invention is not limited to the following embodiments. Experimental methods in the following embodiments that do not specify specific conditions are generally performed under conventional conditions.

[0020] Example 1 This embodiment describes a method for preparing a cobalt phthalocyanine (PANI) composite coating on the surface of a metal bipolar plate, comprising the following steps: Step 1: The metal plate is roughened by sandpaper, ultrasonically washed with deionized water for 10 min, then immersed in dilute hydrochloric acid, activated at 25°C for 8 min, and dried to obtain activated metal bipolar plate. Step 2: Add 100 mL of N,N-dimethylformamide, 10 g of p-phenylenediamine, 15 g of 2-chloroacetamide, and 30 g of anhydrous potassium carbonate to a flask. Stir in an ice bath at 0°C, and then carry out a nucleophilic substitution reaction at 80°C for 10 h. Cool to precipitate a solid, filter, wash with water, and dry to obtain crude N,N′-bis(2-acetamido)-p-aniline. Add 150 mL of anhydrous ethanol and 15 mL of ethylenediamine to the crude product, reflux at 100°C for 12 h, cool, filter, wash with ethanol, and then add 120 mL of tetrahydrofuran, 6.5 mL of chlorosulfonic acid, and 20 mL of triethylamine. Stir in an ice bath, and then carry out sulfonation at 65°C for 8 h. After the reaction is complete, pour the mixture into 800 mL of ice water to crystallize, filter, wash with deionized water, and dry to finally obtain S-BIAR. Step 3: Add 0.5 L hydrochloric acid, 0.5 g cobalt phthalocyanine, and 2 g aniline monomer to the flask, stir and mix well, and slowly add 4 g ammonium persulfate oxidant under ice bath conditions. In-situ oxidative polymerization is carried out at 0℃ for 3 h to obtain cobalt phthalocyanine PANI precursor slurry. Then add 0.5 g S-BIAR and stir at 25℃ for 4 h to obtain composite coating slurry. Step 4: The obtained composite coating slurry is uniformly coated on the surface of the activated metal bipolar plate and placed in a 60℃ oven for heat treatment for 2 h to form a cobalt phthalocyanine (PANI) composite coating.

[0021] Example 2 This embodiment describes a method for preparing a cobalt phthalocyanine (PANI) composite coating on the surface of a metal bipolar plate, comprising the following steps: Step 1: The metal plate is roughened by sandpaper, ultrasonically washed with deionized water for 20 min, then immersed in dilute hydrochloric acid, activated at 40℃ for 3 min, and dried to obtain activated metal bipolar plate. Step 2: Add 100 mL of N,N-dimethylformamide, 15 g of p-phenylenediamine, 25 g of 2-chloroacetamide, and 60 g of anhydrous potassium carbonate to a flask. Stir in an ice bath at 5 °C, and then carry out a nucleophilic substitution reaction at 90 °C for 6 h. Cool to precipitate a solid, filter, wash with water, and dry to obtain crude N,N′-bis(2-acetamido)-p-aniline. Add 150 mL of anhydrous ethanol and 15 mL of ethylenediamine to the crude product, reflux at 120 °C for 8 h, cool, filter, wash with ethanol, and then add 120 mL of tetrahydrofuran, 6.5 mL of chlorosulfonic acid, and 20 mL of triethylamine. Stir in an ice bath, and then carry out sulfonation at 85 °C for 5 h. After the reaction is complete, pour the mixture into 800 mL of ice water to crystallize, filter, wash with deionized water, and dry to finally obtain S-BIAR. Step 3: Add 1 L of hydrochloric acid, 2 g of cobalt phthalocyanine, and 6 g of aniline monomer to the flask, stir and mix well, and slowly add 12 g of ammonium persulfate oxidant under ice bath conditions. In-situ oxidative polymerization is carried out at 5°C for 1 h to obtain cobalt phthalocyanine PANI precursor slurry. Then add 1.5 g of S-BIAR and stir at 40°C for 2 h to obtain composite coating slurry. Step 4: The obtained composite coating slurry is uniformly coated on the surface of the activated metal bipolar plate and placed in an oven at 120℃ for heat treatment for 0.5 h to form a cobalt phthalocyanine (PANI) composite coating.

[0022] Example 3 This embodiment describes a method for preparing a cobalt phthalocyanine (PANI) composite coating on the surface of a metal bipolar plate, comprising the following steps: Step 1: The metal plate is roughened by sandpaper, ultrasonically washed with deionized water for 15 min, then immersed in dilute hydrochloric acid, activated at 35℃ for 5 min, and dried to obtain activated metal bipolar plate. Step 2: Add 100 mL of N,N-dimethylformamide, 13 g of p-phenylenediamine, 20 g of 2-chloroacetamide, and 45 g of anhydrous potassium carbonate to a flask. Stir in an ice bath at 3°C, and then carry out a nucleophilic substitution reaction at 85°C for 8 h. Cool to precipitate a solid, filter, wash with water, and dry to obtain crude N,N′-bis(2-acetamido)-p-aniline. Add 150 mL of anhydrous ethanol and 15 mL of ethylenediamine to the crude product, reflux at 110°C for 10 h, cool, filter, wash with ethanol, and then add 120 mL of tetrahydrofuran, 6.5 mL of chlorosulfonic acid, and 20 mL of triethylamine. Stir in an ice bath, and then carry out sulfonation at 75°C for 6 h. After the reaction is complete, pour the mixture into 800 mL of ice water to crystallize, filter, wash with deionized water, and dry to finally obtain S-BIAR. Step 3: Add 0.75 L hydrochloric acid, 1.25 g cobalt phthalocyanine, and 4 g aniline monomer to the flask, stir and mix well, and slowly add 8 g ammonium persulfate oxidant under ice bath conditions. In-situ oxidative polymerization is carried out at 3°C ​​for 2 h to obtain cobalt phthalocyanine PANI precursor slurry. Then add 1 g S-BIAR and stir at 30°C for 3 h to obtain composite coating slurry. Step 4: The obtained composite coating slurry is uniformly coated on the surface of the activated metal bipolar plate and placed in a 90℃ oven for heat treatment for 1.25 h to form a cobalt phthalocyanine (PANI) composite coating.

[0023] Comparative Example 1: The difference between this comparative example and Example 1 is that S-BIAR is not added.

[0024] This embodiment describes a method for preparing a cobalt phthalocyanine (PANI) composite coating on the surface of a metal bipolar plate, comprising the following steps: Step 1: The metal plate is roughened by sandpaper, ultrasonically washed with deionized water for 10 min, then immersed in dilute hydrochloric acid, activated at 25°C for 8 min, and dried to obtain activated metal bipolar plate. Step 2: Add 0.5 L hydrochloric acid, 0.5 g cobalt phthalocyanine, and 2 g aniline monomer to the flask, stir and mix well, and slowly add 4 g ammonium persulfate oxidant under ice bath conditions. In-situ oxidative polymerization is carried out at 0°C for 3 h to obtain cobalt phthalocyanine PANI precursor slurry. Step 3: The obtained cobalt phthalocyanine (PANI) precursor slurry is uniformly coated on the surface of the activated metal bipolar plate and placed in a 60℃ oven for heat treatment for 2 h to form a cobalt phthalocyanine (PANI) composite coating.

[0025] Comparative Example 2: The difference between this comparative example and Example 1 is that ordinary phthalocyanine is used instead of cobalt phthalocyanine.

[0026] The preparation method of a phthalocyanine (PANI) composite coating on the surface of a metal bipolar plate in this comparative example includes the following steps: Step 1: The metal plate is roughened by sandpaper, ultrasonically washed with deionized water for 10 min, then immersed in dilute hydrochloric acid, activated at 25°C for 8 min, and dried to obtain activated metal bipolar plate. Step 2: Add 100 mL of N,N-dimethylformamide, 10 g of p-phenylenediamine, 15 g of 2-chloroacetamide, and 30 g of anhydrous potassium carbonate to a flask. Stir in an ice bath at 0°C, and then carry out a nucleophilic substitution reaction at 80°C for 10 h. Cool to precipitate a solid, filter, wash with water, and dry to obtain crude N,N′-bis(2-acetamido)-p-aniline. Add 150 mL of anhydrous ethanol and 15 mL of ethylenediamine to the crude product, reflux at 100°C for 12 h, cool, filter, wash with ethanol, and then add 120 mL of tetrahydrofuran, 6.5 mL of chlorosulfonic acid, and 20 mL of triethylamine. Stir in an ice bath, and then carry out sulfonation at 65°C for 8 h. After the reaction is complete, pour the mixture into 800 mL of ice water to crystallize, filter, wash with deionized water, and dry to finally obtain S-BIAR. Step 3: Add 0.5 L hydrochloric acid, 0.5 g ordinary phthalocyanine, and 2 g aniline monomer to the flask, stir and mix well, and slowly add 4 g ammonium persulfate oxidant under ice bath conditions. In-situ oxidative polymerization is carried out at 0℃ for 3 h to obtain ordinary phthalocyanine PANI precursor slurry. Then add 0.5 g S-BIAR and stir at 25℃ for 4 h to obtain composite coating slurry. Step 4: The obtained composite coating slurry is uniformly coated on the surface of the activated metal bipolar plate and placed in a 60℃ oven for heat treatment for 2 h to form a phthalocyanine (PANI) composite coating.

[0027] Comparative Example 3: The difference between this comparative example and Example 1 is that it does not undergo dilute hydrochloric acid activation treatment.

[0028] The preparation method of a cobalt phthalocyanine (PANI) composite coating on the surface of a metal bipolar plate in this comparative example includes the following steps: Step 1: The metal plate is roughened by sandpaper, ultrasonically washed with deionized water for 10 minutes, and dried to obtain the treated metal bipolar plate. Step 2: Add 100 mL of N,N-dimethylformamide, 10 g of p-phenylenediamine, 15 g of 2-chloroacetamide, and 30 g of anhydrous potassium carbonate to a flask. Stir in an ice bath at 0°C, and then carry out a nucleophilic substitution reaction at 80°C for 10 h. Cool to precipitate a solid, filter, wash with water, and dry to obtain crude N,N′-bis(2-acetamido)-p-aniline. Add 150 mL of anhydrous ethanol and 15 mL of ethylenediamine to the crude product, reflux at 100°C for 12 h, cool, filter, wash with ethanol, and then add 120 mL of tetrahydrofuran, 6.5 mL of chlorosulfonic acid, and 20 mL of triethylamine. Stir in an ice bath, and then carry out sulfonation at 65°C for 8 h. After the reaction is complete, pour the mixture into 800 mL of ice water to crystallize, filter, wash with deionized water, and dry to finally obtain S-BIAR. Step 3: Add 0.5 L hydrochloric acid, 0.5 g cobalt phthalocyanine, and 2 g aniline monomer to the flask, stir and mix well, and slowly add 4 g ammonium persulfate oxidant under ice bath conditions. In-situ oxidative polymerization is carried out at 0℃ for 3 h to obtain cobalt phthalocyanine PANI precursor slurry. Then add 0.5 g S-BIAR and stir at 25℃ for 4 h to obtain composite coating slurry. Step 4: The obtained composite coating slurry is uniformly coated on the surface of the treated metal bipolar plate and placed in a 60℃ oven for heat treatment for 2 hours to form a cobalt phthalocyanine (PANI) composite coating.

[0029] Performance testing 1. Contact Resistance: A 20 mm × 20 mm coated bipolar plate sample was sandwiched between two highly polished copper plates along with a piece of SIGRACET® 22BB commercial carbon paper of the same size, and the entire sample was placed on a material testing machine. Pressures of 0.5–2.5 MPa were applied using the testing machine to simulate the assembly tightness of the battery stack. After stabilizing for 10 s at each specific pressure point, the total resistance was measured using a micro-ohmmeter with a four-point probe method at 10 mA DC. The interfacial contact resistance between the coating and the carbon paper was obtained by subtracting the known resistances of the carbon paper and the metal substrate and calculating the resistance per unit area. The curve showing this resistance change with applied pressure directly reflects the conductivity of the coating; the target is a contact resistance of less than 10 mΩ·cm² at 1.5 MPa pressure.

[0030] 2. Corrosion Current Density: Potentiodynamic polarization was measured using an electrochemical workstation with a classic three-electrode system. The coated sample (exposed area 1 cm²) was used as the working electrode, a platinum electrode as the counter electrode, and a saturated calomel electrode as the reference electrode. The electrolyte was a 0.5 M H₂SO₄ + 2 ppm HF solution simulating the cathode environment of a proton exchange membrane fuel cell, and the temperature was maintained at 70 ± 2 °C. Before testing, the sample was stabilized at the open circuit potential for 30 min, and then the potential was scanned from -0.25 V relative to the open circuit potential to +0.6 V at a scan rate of 1 mV / s. By analyzing the obtained Tafel curves, the cathode and anode branches in the strongly polarized region (typically ranging from ±50 mV to ±250 mV) were extrapolated tangentially, and the current density corresponding to the intersection point was the corrosion current density (I0). corr The smaller the value, the better the corrosion resistance of the coating. Typically, an I value is required. corr Less than 1 μA / cm².

[0031] 3. Coating Adhesion: Using a multi-blade cutter with a blade spacing of 1 mm, prepare a set of 6 parallel cuts on the coating surface, penetrating the entire coating depth to the metal substrate. Then, prepare a set of identical vertical cuts at the same location, forming 25 1 mm × 1 mm grid patterns. After removing debris by lightly brushing along the grid diagonal 5 times with a soft brush, firmly adhere the special 3M #600 pressure-sensitive tape to the grid area, and press back and forth 5 times with a hand-held rubber roller to ensure complete contact. Then, quickly and smoothly peel off the tape at a 60° angle to the surface within 60 ± 5 seconds. Finally, observe the coating peeling in the grid area under an optical microscope and rate it according to the ASTM D3359 standard chart (0B to 5B, 5B being no peeling). A good performance coating should achieve a rating of 4B or higher.

[0032] Table 1 Performance Test Data

[0033] As shown in Table 1, the coatings prepared in Examples 1-3 exhibit excellent performance in terms of conductivity, corrosion resistance (corrosion current density < 0.6 μA / cm²), and adhesion. This is mainly attributed to the fact that cobalt phthalocyanine enhances electron migration ability, S-BIAR strengthens polymer chain segment order and interfacial bonding strength, and substrate activation ensures strong adhesion between the coating and the metal substrate, collectively constructing a high-performance composite coating. In Comparative Example 1, due to the absence of S-BIAR, the composite coating lacks effective electron bridging and chain segment ordering, resulting in discontinuous conductive network and decreased coating density. Consequently, the contact resistance increases (15.2 mΩ·cm²), and corrosion resistance significantly deteriorates. Simultaneously, the interfacial bonding strength between the coating and the substrate is also significantly reduced due to the lack of S-BIAR bridging effect. The ordinary phthalocyanine used in Comparative Example 2 lacks the catalytic and electron migration-promoting capabilities of the cobalt metal center in cobalt phthalocyanine, leading to a decrease in the overall conductivity of the coating and a corresponding weakening of its corrosion protection performance. Comparative Example 3 did not undergo dilute hydrochloric acid activation treatment, resulting in ineffective removal of the oxide layer on the metal substrate surface and insufficient active sites, which severely affected the adhesion between the coating and the substrate. Poor adhesion led to increased interfacial contact resistance and exacerbated the risk of localized corrosion.

[0034] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A method for preparing a cobalt phthalocyanine (PANI) composite coating on the surface of a metal bipolar plate, characterized in that, Includes the following steps: Step 1: Roughen the metal plate with sandpaper, ultrasonically wash it with deionized water for 10-20 minutes, then immerse it in dilute hydrochloric acid for activation, and dry it to obtain an activated metal bipolar plate. Step 2: Add hydrochloric acid, cobalt phthalocyanine, and aniline monomer to the flask, stir and mix well, add ammonium persulfate oxidant under ice bath conditions, and carry out in-situ oxidative polymerization to obtain cobalt phthalocyanine PANI precursor slurry. Then add sulfonyl-bisimidazolinone electron-bridged aromatic ring (S-BIAR), stir at 25-40℃ for 2-4 h to obtain composite coating slurry. Step 3: The obtained composite coating slurry is uniformly coated on the surface of the activated metal bipolar plate and placed in an oven for heat treatment to form a cobalt phthalocyanine (PANI) composite coating.

2. The method for preparing a cobalt phthalocyanine (PANI) composite coating on the surface of a metal bipolar plate according to claim 1, characterized in that, In step 1, the activation temperature of dilute hydrochloric acid is 25-40℃, and the time is 3-8 min.

3. The method for preparing a cobalt phthalocyanine (PANI) composite coating on the surface of a metal bipolar plate according to claim 1, characterized in that, In step 2, the in-situ oxidative polymerization is carried out at a temperature of 0-5℃ for 1-3 hours.

4. The method for preparing a cobalt phthalocyanine (PANI) composite coating on the surface of a metal bipolar plate according to claim 1, characterized in that, In step 2, the ratio of cobalt phthalocyanine, aniline monomer, ammonium persulfate oxidant, and S-BIAR is (0.05-0.2) g : (0.2-0.6) g : (0.4-1.2) g : (0.05-0.15) g.

5. The method for preparing a cobalt phthalocyanine (PANI) composite coating on the surface of a metal bipolar plate according to claim 4, characterized in that, The preparation method of S-BIAR is as follows: N,N-dimethylformamide, p-phenylenediamine, 2-chloroacetamide, and anhydrous potassium carbonate are added to a flask and stirred in an ice bath at 0–5°C. Nucleophilic substitution reaction is then carried out, and the solid is precipitated by cooling. The solid is filtered, washed with water, and dried to obtain crude N,N′-bis(2-acetamido)p-aniline. Anhydrous ethanol and ethylenediamine are added to the obtained crude product, and the mixture is refluxed at 100–120°C for 8–12 h. After cooling, the mixture is filtered, washed with ethanol, and then tetrahydrofuran, chlorosulfonic acid, and 20 mL of triethylamine are added. The mixture is stirred in an ice bath and then sulfonated. After the reaction is completed, the mixture is poured into ice water to crystallize, filtered, washed with deionized water, and dried to finally obtain S-BIAR.

6. The method for preparing a cobalt phthalocyanine (PANI) composite coating on the surface of a metal bipolar plate according to claim 5, characterized in that, The mass ratio of p-phenylenediamine, 2-chloroacetamide, and anhydrous potassium carbonate is (10-15) g: (15-25) g, (30-60) g.

7. The method for preparing a cobalt phthalocyanine (PANI) composite coating on the surface of a metal bipolar plate according to claim 5, characterized in that, The nucleophilic substitution reaction is carried out at a temperature of 80-90℃ for 6-10 h.

8. The method for preparing a cobalt phthalocyanine (PANI) composite coating on the surface of a metal bipolar plate according to claim 5, characterized in that, The sulfonation is carried out at a temperature of 65-85°C for 5-8 hours.

9. The method for preparing a cobalt phthalocyanine (PANI) composite coating on the surface of a metal bipolar plate according to claim 1, characterized in that, In step 3, the heat treatment temperature is 60-120℃ and the time is 0.5-2 h.

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