Preparation method of zinc phthalocyanine-doped PANI coating on surface of metal bipolar plate

Abstract

The present invention discloses a preparation method for a zinc phthalocyanine-doped PANI coating on the surface of a metal bipolar plate, comprising the following steps: surface pretreatment of the bipolar plate, preparation of the electroplating solution, electrodeposition process, and post-treatment process. The preparation method for the zinc phthalocyanine-doped PANI coating on the surface of the metal bipolar plate of the present invention prepares a functional composite coating with a dense structure, excellent conductivity, and outstanding corrosion resistance by precisely controlling the doping concentration of zinc phthalocyanine and the electrodeposition process parameters in the electroplating solution, thereby improving the energy efficiency and service life of the electrolytic water hydrogen production device and the fuel cell system.

Description

Technical Field

[0001] The present invention relates to the technical field of surface treatment of energy conversion devices, and particularly to a preparation method of a zinc phthalocyanine-doped PANI coating on the surface of a metal bipolar plate. Background Art

[0002] As a key functional component in electrolytic water hydrogen production devices and fuel cell systems, the bipolar plate undertakes multiple technical functions simultaneously: on the one hand, it needs to efficiently conduct current to ensure the energy conversion efficiency of the system; on the other hand, it also needs to distribute reaction gases or liquids and maintain structural stability in a harsh electrochemical environment. Especially in the working environments of electrolytic water and fuel cells, the bipolar plate is long-term exposed to strong acidic or alkaline electrolytes, and at the same time is affected by the electric field and temperature fluctuations, facing severe corrosion challenges.

[0003] Due to its advantages such as high mechanical strength, good processing performance, and moderate cost, stainless steel has become the mainstream material choice for bipolar plate manufacturing. However, in practical applications, stainless steel bipolar plates still face two core technical problems: one is the relatively high surface contact resistance, which affects the overall energy efficiency of the system; the other is that it is vulnerable to corrosion in the electrochemical working environment, which not only shortens the equipment life, but also may cause metal ion dissolution to pollute the electrolyte or catalyst. These two problems have become important bottlenecks restricting the large-scale commercial application of electrolytic water and fuel cell technologies.

[0004] In the prior art, surface coatings have been proven to be an effective way to improve the performance of bipolar plates. Especially conductive polymer coatings have received extensive attention due to their combined conductivity and anti-corrosion properties. As a typical conductive polymer, polyaniline (PANI) has the advantages of simple synthesis process, good environmental stability, and adjustable conductivity, and has been explored for surface modification of bipolar plates. Research shows that the PANI coating can form a protective passivation film on the surface of stainless steel, and at the same time provide an electron conduction channel, effectively reducing the contact resistance.

[0005] However, the single PANI coating has obvious limitations in practical applications: although PANI has certain conductivity, its conductivity is difficult to meet the strict requirements of electrolytic water and fuel cells under high current density working conditions, restricting the energy conversion efficiency; the traditional PANI coating has micropores and structural defects, providing a penetration channel for corrosion media.

[0006] To overcome the above technical bottlenecks, it is of great practical significance to develop a composite functional coating with both high electrical conductivity and excellent corrosion resistance. As a metal-organic complex with a large π-conjugated system, zinc phthalocyanine has excellent electron transport properties, chemical stability, and special molecular recognition ability. Introducing zinc phthalocyanine molecules into the PANI network structure is expected to significantly improve the overall performance of the coating through synergistic effects: on the one hand, enhancing the electron conduction ability and reducing the contact resistance; on the other hand, optimizing the molecular arrangement structure of the coating, improving the density and corrosion resistance. Summary of the Invention

[0007] Aiming at some deficiencies in the current electrolyzed water technology, the main purpose of the present invention is to provide a preparation method for a zinc phthalocyanine-doped PANI coating on the surface of a metal bipolar plate. By precisely controlling the doping concentration of zinc phthalocyanine and the electrodeposition process parameters in the electroplating solution, a functional composite coating with a dense structure, excellent electrical conductivity, and outstanding corrosion resistance is prepared, improving the energy efficiency and service life of the electrolyzed water hydrogen production device and the fuel cell system.

[0008] To solve the above technical problems, a technical solution adopted by the present invention is: a preparation method for a zinc phthalocyanine-doped PANI coating on the surface of a metal bipolar plate, comprising the following steps:

[0009] S1. Surface pretreatment of the bipolar plate: Mechanically polish the surface of the stainless steel bipolar plate with sandpaper in sequence until the surface presents a mirror effect, wash and dry it with deionized water, then conduct chemical cleaning on the polished stainless steel bipolar plate in sequence, and after electrochemical activation of the chemically cleaned stainless steel bipolar plate, rinse it with deionized water and prepare for subsequent electrodeposition treatment;

[0010] S2. Preparation of the electroplating solution: Prepare a basic electrolyte solution, dissolve zinc phthalocyanine powder in a small amount of N,N-dimethylformamide, slowly drop the dissolved zinc phthalocyanine solution into the above basic electrolyte solution while continuously stirring, and perform ultrasonic treatment for 30 - 60 minutes to ensure the full dispersion of zinc phthalocyanine in the electroplating solution. Adjust the pH value of the electroplating solution to 0.8 - 1.5, and deoxygenate the prepared electroplating solution under nitrogen protection for 30 minutes before electroplating;

[0011] S3. Electrodeposition process:

[0012] S3.1 Setup of the electrolytic cell: The pretreated stainless steel bipolar plate is used as the working electrode, a platinum sheet is used as the auxiliary electrode, and a saturated calomel electrode is used as the reference electrode. The electrolytic cell is made of acid- and alkali-resistant polytetrafluoroethylene with a working volume of 200 - 500 mL;

[0013] S3.2 Selection of the electrodeposition method: Select the potentiostatic electrodeposition method or the pulse electrodeposition method;

[0014] S3.3 Electroplating process control: During electroplating, stir the electroplating solution to ensure uniform dispersion of zinc phthalocyanine. Monitor the current-time or potential-time curve in real time to ensure a stable electrodeposition process. End the electrodeposition process when the deposition current or charge reaches the preset value.

[0015] S3.4 Preparation of multi-layer composite coating: First, electrodeposit the first pure PANI base layer, then switch to the electroplating solution containing zinc phthalocyanine to deposit the second composite coating layer, and finally electrodeposit the third pure PANI protective layer. Gently rinse between each layer with deionized water, and proceed to the next layer deposition without complete drying.

[0016] S4. Post-treatment process: After deposition, gently rinse the sample with deionized water to remove the residual electrolyte on the surface. Immerse it in dilute sulfuric acid solution and let it stand to stabilize the doping state of polyaniline. Rinse it with deionized water again until neutral, and finally dry and heat-treat the coating.

[0017] In the embodiment of the present invention, the chemical cleaning in S1 includes the following steps: Immerse the polished stainless steel bipolar plate successively in a NaOH solution with a mass concentration of 10 - 30 g / L for cleaning, keep the temperature at 60 - 80 °C for 5 - 10 minutes to remove the oil stain on the surface of the stainless steel bipolar plate, then immerse it in an H2SO4 solution with a volume concentration of 5 - 15%, and treat it at room temperature for 2 - 5 minutes to remove the oxide on the surface of the stainless steel bipolar plate. After the cleaning step, ultrasonically clean it with deionized water for 3 - 5 minutes.

[0018] In the embodiment of the present invention, the electrochemical activation in S1 includes the following steps: Place the chemically cleaned stainless steel bipolar plate in an H2SO4 solution containing 0.1 - 0.5 mol / L for electrochemical activation. Use cyclic voltammetry to scan within the potential range of -0.2 V to +1.0 V for 3 - 5 cycles, with a scan rate of 10 - 200 mV / s. After activation, rinse it with deionized water and immediately proceed with the subsequent electrodeposition treatment.

[0019] In the embodiment of the present invention, the preparation of the basic electrolyte in S2 includes the following steps: Dissolve 0.1 - 0.3 mol / L of aniline monomer in 0.3 - 0.5 mol / L of H2SO4 solution, continuously stir and add 0.05 - 0.15 mol / L of p-toluenesulfonic acid as a dopant, and continue to stir for 15 - 30 minutes to ensure the solution is uniform, obtaining the basic electrolyte.

[0020] In the embodiment of the present invention, in S2, it also includes the step of filtering the obtained electroplating solution with a 0.22 μm microporous filter membrane to remove undispersed particles.

[0021] In the embodiment of the present invention, in S2, the electroplating solution is stored in a brown bottle and protected from light. Ultrasonically disperse it again for 10 minutes before use.

[0022] In an embodiment of the present invention, in the preparation of the S3.4 multi-layer composite coating, the electrodeposition time of the first layer of PANI base layer is 5 - 10 minutes, the electrodeposition time of the second layer of composite coating is 15 - 30 minutes, and the electrodeposition time of the third layer of pure PANI protective layer is 3 - 5 minutes.

[0023] In an embodiment of the present invention, in the post-treatment process, after deposition is completed, the sample is gently rinsed with deionized water 3 - 5 times, and then immersed in a dilute sulfuric acid solution with pH = 4 and allowed to stand for 5 - 10 minutes.

[0024] In an embodiment of the present invention, in S4, the coating is dried: naturally air-dried at room temperature for 1 - 2 hours or dried at 40 °C for 30 - 60 minutes.

[0025] In an embodiment of the present invention, in S4, the coating is heat-treated: under nitrogen protection, heat-treated at 80 - 120 °C for 1 - 2 hours to enhance the mechanical stability of the coating.

[0026] The beneficial effects of the present invention are as follows: The preparation method of the zinc phthalocyanine-doped PANI coating on the surface of the metal bipolar plate of the present invention prepares a functional composite coating with a dense structure, excellent conductivity, and outstanding corrosion resistance by precisely controlling the doping concentration of zinc phthalocyanine and the electrodeposition process parameters in the electroplating solution, improving the energy efficiency and service life of the electrolytic water hydrogen production device and fuel cell system, and solving the problems of high contact resistance and corrosion faced by stainless steel bipolar plates in devices such as electrolytic water hydrogen production and fuel cells. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following will briefly introduce the drawings required for the description of the embodiments. Obviously, the following drawings are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings, where:

[0028] Figure 1 It is a schematic diagram of the electrodeposition of the metal bipolar plate of the present invention;

[0029] Figure 2 It is a polarization resistance test chart of the simulated fuel cell electrolyte environment of the present invention;

[0030] Figure 3 It is a polarization resistance test chart of the simulated alkaline electrolyzer electrolyte environment of the present invention;

[0031] Figure 4 It is an EIS impedance test chart of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0032] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0033] Please refer to Figures 1-4 , the embodiments of the present invention include: a preparation method for a zinc phthalocyanine-doped PANI coating on the surface of a metal bipolar plate, comprising the following steps:

[0034] S1. Surface pretreatment of the bipolar plate: Mechanically polish the surface of the stainless steel bipolar plate successively with 400 - 2000 mesh sandpaper until the surface presents a mirror effect, wash with deionized water and dry. Then, perform chemical cleaning on the polished stainless steel bipolar plate successively. Immerse the polished stainless steel bipolar plate in a NaOH solution with a mass concentration of 10 - 30 g / L for cleaning at a temperature of 60 - 80 °C for 5 - 10 minutes to remove surface oil stains. Immerse it in an H2SO4 solution with a volume concentration of 5 - 15% and treat it at room temperature for 2 - 5 minutes to remove surface oxides. After the washing steps, ultrasonically clean with deionized water for 3 - 5 minutes. Place the chemically cleaned stainless steel bipolar plate in an H2SO4 solution containing 0.1 - 0.5 mol / L for electrochemical activation. Use cyclic voltammetry to scan within a potential range of -0.2 V to +1.0 V (relative to the saturated calomel electrode) for 3 - 5 cycles at a scanning rate of 10 - 200 mV / s. After activation, rinse with deionized water and immediately perform the subsequent electrodeposition treatment;

[0035] S2. Preparation of the electroplating solution: Dissolve 0.1 - 0.3 mol / L of aniline monomer in 0.3 - 0.5 mol / L of H2SO4 solution. Under continuous stirring, add 0.05 - 0.15 mol / L of p-toluenesulfonic acid as a dopant and continue stirring for 15 - 30 minutes to ensure the solution is uniform, thus preparing a basic electrolyte solution. Weigh an appropriate amount of zinc phthalocyanine powder according to the set concentration (0.5 - 5 mmol / L). Dissolve the zinc phthalocyanine powder in a small amount of N,N-dimethylformamide. Slowly drip the dissolved zinc phthalocyanine solution into the above basic electrolyte solution while continuously stirring, and perform ultrasonic treatment for 30 - 60 minutes to ensure that zinc phthalocyanine is fully dispersed in the electroplating solution. Filter with a 0.22 μm microporous filter membrane to remove undispersed particles. Adjust the pH value of the electroplating solution to 0.8 - 1.5 with 1 mol / L H2SO4 or NaOH. Deoxygenate the prepared electroplating solution under nitrogen protection for 30 minutes before electroplating;

[0036] S3. Electrodeposition process:

[0037] S3.1 Electrolytic cell setup: The pre-treated stainless steel bipolar plate is used as the working electrode, the platinum sheet as the auxiliary electrode, and the saturated calomel electrode as the reference electrode. The electrolytic cell is made of acid- and alkali-resistant polytetrafluoroethylene with a working volume of 200 - 500 mL;

[0038] S3.2 Selection of electrodeposition method: The potentiostatic electrodeposition method or the pulse electrodeposition method is selected;

[0039] 3.2.1 Potentiostatic electrodeposition:

[0040] Potential range: +0.7V to +1.2V (vs. SCE), deposition time: 10 - 30 minutes, temperature control: 20 ± 2°C;

[0041] 3.2.2 Pulse electrodeposition:

[0042] On - potential: +0.9V to +1.2V (vs. SCE), off - potential: +0.3V to +0.5V (vs. SCE);

[0043] Pulse frequency: 1 - 10Hz, duty cycle: 30 - 70%; total deposition time: 20 - 45 minutes; temperature control: 20 ± 2°C;

[0044] S3.3 Electroplating process control: During electroplating, the electroplating solution is stirred to ensure uniform dispersion of zinc phthalocyanine. The current - time or potential - time curve is monitored in real - time to ensure a stable electrodeposition process. When the deposition current or charge reaches the preset value, the electrodeposition process ends;

[0045] S3.4 Preparation of multi - layer composite coatings: First, deposit the first pure PANI base layer by electrodeposition, then switch to the electroplating solution containing zinc phthalocyanine for the deposition of the second composite coating, and finally deposit the third pure PANI protective layer by electrodeposition. Each layer is gently rinsed with deionized water, and the next layer can be deposited without complete drying;

[0046] S4. Post - treatment process: After deposition, immediately rinse the sample gently with deionized water 3 - 5 times to remove the residual electrolyte on the surface; immerse it in a dilute sulfuric acid solution with pH = 4 and let it stand for 5 - 10 minutes to stabilize the doping state of polyaniline, then rinse it with deionized water again until neutral. Coating drying: Air - dry naturally at room temperature for 1 - 2 hours, or dry at 40°C for 30 - 60 minutes; Heat treatment: Under nitrogen protection, heat - treat at 80 - 120°C for 1 - 2 hours to enhance the mechanical stability of the coating.

[0047] Measurement of corrosion voltage and corrosion current: A three - electrode system is selected. First, measure the open - circuit potential (OCP) until it is stable, then start potential scanning from the OCP (usually within ±250mV range), record the potential - current data and plot the polarization curve, and determine the corrosion current and corrosion potential by Tafel extrapolation method.

[0048]

[0049] Polarization resistance test: Prepare the following two solutions respectively: (1) a mixed solution with a concentration of 0.5 mol / L of sulfuric acid (H2SO4) and a concentration of 2 ppm of fluoride ions (F-), and heat the prepared mixed solution to 60 °C by water bath heating; (2) a 30% mass fraction KOH solution and heat it to 80 °C. Conduct tests in these two different solutions with a potential range of -0.6 V to +1.2 V and a scanning rate of 1 mV / s. After fitting by the Tafel extrapolation method, calculate the polarization resistance (ohm, Ω) of the coatings of different preferred embodiments and comparative examples. Example 1

[0050] Standard electroplating process: Polish the surface of the stainless steel (304) bipolar plate 1 successively with 600, 800, 1200, 1500, and 2000-mesh sandpapers and perform ultrasonic cleaning; soak and clean it successively in a 20 g / L NaOH solution (70 °C, 7 minutes) and a 10% H2SO4 solution (room temperature, 3 minutes), and conduct electrochemical activation in 0.3 mol / L H2SO4 (-0.2 V to +1.0 V, 4 cycles). Prepare the electroplating solution: 0.2 mol / L aniline + 0.4 mol / L H2SO4 + 0.1 mol / L p-toluenesulfonic acid + 2 mmol / L zinc phthalocyanine; perform electroplating at +0.9 V (vs. SCE) for 20 minutes by the potentiostatic method, and conduct post-treatment according to step S4 to obtain a polyaniline / zinc phthalocyanine composite coating with a thickness of 2 - 3 μm. Example 2

[0051] Pulse electroplating process: Prepare the sample and electroplating solution according to the steps in the first preferred embodiment. Use the pulse electroplating method: the on-potential is +1.0 V, the off-potential is +0.4 V, the frequency is 5 Hz, the duty cycle is 50%, and the total time is 30 minutes; the post-treatment is the same as that in Example 1, and add heat treatment under nitrogen protection at 100 °C for 1 hour to obtain a dense and uniform polyaniline-zinc phthalocyanine composite coating with a thickness of 3 - 4 μm. Example 3

[0052] Prepare the sample according to the steps in the first preferred embodiment. First, electroplate for 7 minutes in an electroplating solution without zinc phthalocyanine to form the first layer of pure PANI base layer 2, then switch to an electroplating solution containing 3 mmol / L zinc phthalocyanine and perform electroplating at +0.9 V (vs. SCE) for 25 minutes to form the second layer of composite coating 3, and then switch back to the pure PANI electroplating solution and electroplate for 5 minutes to form the third layer of pure PANI protective layer 4. According to the complete post-treatment process of S4, obtain a composite functional coating with a three-layer structure.

[0053] Comparative Example 1:

[0054] For the standard electrodeposited PANI coating, the surface of the stainless steel (304) bipolar plate was polished successively with 600, 800, 1200, 1500, and 2000 - mesh sandpaper and then ultrasonically cleaned; it was successively soaked and cleaned in 20 g / L NaOH solution (70 °C, 7 minutes) and 10% H2SO4 solution (room temperature, 3 minutes), electrochemically activated in 0.3 mol / L H2SO4 (-0.2 V to +1.0 V, 4 cycles). The electroplating solution was prepared: 0.2 mol / L aniline + 0.4 mol / L H2SO4 + 0.1 mol / L p - toluenesulfonic acid. Electrodeposition was carried out at +0.9 V (vs. SCE) for 20 minutes using the potentiostatic method, and post - treatment was carried out according to step S4 to obtain a polyaniline coating with a thickness of 2 - 3 μm.

[0055] The beneficial effects of the preparation method of the zinc phthalocyanine - doped PANI coating on the surface of the metal bipolar plate in the present invention are as follows: By precisely controlling the doping concentration of zinc phthalocyanine and the electrodeposition process parameters in the electroplating solution, a functional composite coating with a dense structure, excellent conductivity, and outstanding corrosion resistance is prepared. It exhibits excellent corrosion resistance in a wide pH range of pH = 2 - 12, and the corrosion current density is reduced by 2 - 3 orders of magnitude compared with bare stainless steel. After long - term immersion testing (>1000 hours), the coating still maintains good structural integrity and anti - corrosion performance, is suitable for long - term working environments, improves the energy efficiency and service life of electrolytic water hydrogen production devices and fuel cell systems, and solves the problems of high contact resistance and corrosion faced by stainless steel bipolar plates in devices such as electrolytic water hydrogen production and fuel cells.

[0056] The above are only the embodiments of the present invention, and do not limit the patent scope of the present invention accordingly. All equivalent structural or equivalent process transformations made using the content of the specification of the present invention, or directly or indirectly applied in other related technical fields, are similarly included in the patent protection scope of the present invention.

Claims

1. A preparation method of a zinc phthalocyanine-doped PANI coating on the surface of a metal bipolar plate, characterized in that, It includes the following steps: S1. Bipolar plate surface pretreatment: Mechanically polish the surface of the stainless-steel bipolar plate with sandpaper in sequence until the surface presents a mirror effect, wash and dry it with deionized water, then conduct chemical cleaning on the polished stainless-steel bipolar plate in sequence, and after electrochemically activating the chemically cleaned stainless-steel bipolar plate, rinse it with deionized water and prepare for subsequent electrodeposition treatment; S2. Electroplating solution preparation: Preparing the basic electrolyte includes the following steps: Dissolve 0.1 - 0.3 mol / L of aniline monomer in 0.3 - 0.5 mol / L of H2SO4 solution, continuously stir and add 0.05 - 0.15 mol / L of p-toluenesulfonic acid as a dopant, continue to stir for 15 - 30 minutes to ensure the solution is uniform to obtain the basic electrolyte, dissolve zinc phthalocyanine powder in a small amount of N,N-dimethylformamide, slowly drip the dissolved zinc phthalocyanine solution into the above basic electrolyte while continuously stirring, perform ultrasonic treatment for 30 - 60 minutes to ensure the full dispersion of zinc phthalocyanine in the electroplating solution, adjust the pH value of the electroplating solution to 0.8 - 1.5, and deoxygenate the prepared electroplating solution for 30 minutes under nitrogen protection before electroplating; S3. Electrodeposition process: S3.1 Electrolytic cell setup: The pretreated stainless-steel bipolar plate serves as the working electrode, a platinum sheet serves as the auxiliary electrode, and a saturated calomel electrode serves as the reference electrode. The electrolytic cell is made of acid- and alkali-resistant polytetrafluoroethylene material with a working volume of 200 - 500 mL; S3.2 Selection of electrodeposition method: Select the potentiostatic electrodeposition method or the pulse electrodeposition method; S3.3 Control of the electroplating process: Keep stirring the electroplating solution during electroplating to ensure the uniform dispersion of zinc phthalocyanine, and monitor the current-time or potential-time curve in real time to ensure the stability of the electrodeposition process. End the electrodeposition process when the deposition current or charge reaches the preset value; S3.4 Preparation of multi-layer composite coating: First, electrodeposit the first pure PANI base layer in the basic electrolyte, then switch to the electroplating solution containing zinc phthalocyanine to deposit the second composite coating layer, and finally electrodeposit the third pure PANI protective layer. Gently rinse between each layer with deionized water, and the next layer deposition can be carried out without complete drying; S4. Post-treatment process: After deposition, gently rinse the sample with deionized water to remove the residual electrolyte on the surface, immerse it in a dilute sulfuric acid solution and let it stand to stabilize the doping state of polyaniline, rinse it with deionized water again until it is neutral, and finally dry and heat-treat the coating.

2. The preparation method of the zinc phthalocyanine-doped PANI coating on the surface of the metal bipolar plate according to claim 1, characterized in that, The chemical cleaning in S1 includes the following steps: Immerse the polished stainless-steel bipolar plate in a NaOH solution with a mass concentration of 10 - 30 g / L in sequence for cleaning, keep the temperature at 60 - 80 °C for 5 - 10 minutes to remove the oil stain on the surface of the stainless-steel bipolar plate, immerse it in an H2SO4 solution with a volume concentration of 5 - 15%, and treat it at room temperature for 2 - 5 minutes to remove the oxide on the surface of the stainless-steel bipolar plate. After the cleaning steps, ultrasonically clean it with deionized water for 3 - 5 minutes.

3. The preparation method of the zinc phthalocyanine-doped PANI coating on the surface of the metal bipolar plate according to claim 2, characterized in that, The electrochemical activation in S1 includes the following steps: placing the chemically cleaned stainless steel bipolar plate in a 0.1 - 0.5 mol / L H2SO4 solution for electrochemical activation, scanning 3 - 5 cycles in the potential range of -0.2 V to +1.0 V using cyclic voltammetry, with a scanning rate of 10 - 200 mV / s. After activation, rinse with deionized water and immediately perform the subsequent electrodeposition treatment.

4. The preparation method of the zinc phthalocyanine-doped PANI coating on the surface of the metal bipolar plate according to claim 1, characterized in that In S2, it also includes the step of filtering the obtained electroplating solution with a 0.22 μm microporous filter membrane to remove undispersed particles.

5. The preparation method of the zinc phthalocyanine-doped PANI coating on the surface of the metal bipolar plate according to claim 1, characterized in that In S2, the electroplating solution is stored in a brown bottle in the dark and ultrasonically dispersed again for 10 minutes before use.

6. The preparation method of the zinc phthalocyanine-doped PANI coating on the surface of the metal bipolar plate according to claim 1, wherein, In the preparation of the S3.4 multi-layer composite coating, the electrodeposition time of the first pure PANI base layer is 5 - 10 minutes, the electrodeposition time of the second composite coating is 15 - 30 minutes, and the electrodeposition time of the third pure PANI protective layer is 3 - 5 minutes.

7. The preparation method of the zinc phthalocyanine-doped PANI coating on the surface of the metal bipolar plate according to claim 1, characterized in that, In the post-treatment process, after deposition is completed, gently rinse the sample with deionized water 3 - 5 times, and then immerse it in a dilute sulfuric acid solution with pH = 4 and let it stand for 5 - 10 minutes.

8. The preparation method of the zinc phthalocyanine-doped PANI coating on the surface of the metal bipolar plate according to claim 1, characterized in that, In S4, dry the coating: air dry naturally at room temperature for 1 - 2 hours or dry at 40 °C for 30 - 60 minutes.

9. The preparation method of the zinc phthalocyanine-doped PANI coating on the surface of the metal bipolar plate according to claim 1, characterized in that, In S4, heat-treat the coating: under nitrogen protection, heat-treat at 80 - 120 °C for 1 - 2 hours to enhance the mechanical stability of the coating.

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