Method for preparing polar plate coating by using cold spraying method

Abstract

The invention provides a method for preparing a polar plate coating by using a cold spraying method. The method comprises the following steps: s1, pretreating a polar plate; s2, carrying out cold spraying coating on the polar plate; and s3, carrying out post-treatment on the polar plate, wherein the post-treatment comprises heat treatment, polishing and cleaning. A film can be formed in the atmospheric environment, the deposition temperature of the coating is low, the coating can be prepared at the room temperature, sprayed particles are not subjected to the high-temperature melting process, the phase structure and the element composition of the coating are kept consistent with powder, and the coating prepared through the method is wide in designable range and good in compatibility.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of hydrogen fuel cells and electrolytic cells, and particularly relates to a method for preparing an electrode plate coating layer by using a cold spraying method. BACKGROUND

[0002] The electrode plate is an important component of a fuel cell and an electrolytic cell, and has the functions of supporting electrode materials, distributing fluids, collecting and conducting electrons, and separating cathode and anode cavities. Currently, the electrode plate materials include graphite materials, composite materials and metal materials. In a proton exchange membrane fuel cell (PEMFC), the metal electrode plate has a lower price and excellent mechanical properties, and thus has a higher proportion in the electrode plate materials. However, in an electrolytic cell (such as a PEM electrolytic cell), due to a high working potential and a large stress (greater than 2 MPa) on the electrode plate, only a metal material with excellent corrosion resistance can be used as the electrode plate material. Hereinafter, the fuel cell and the electrolytic cell are described by taking the PEMFC and the PEM electrolytic cell as examples. Since the working environments of the PEMFC and the PEM electrolytic cell are acidic (pH 2-5), have strong corrosive medium (F-) and a certain potential (fuel cell potential < 1 V, electrolytic cell potential < 2 V), the metal electrode plate usually needs to be surface treated to improve the corrosion resistance and conductivity of the electrode plate. The electrode plate coating layer materials of the PEMFC usually include carbon-based coating layers, metal-based coating layers and polymer coating layers, and the electrode plate coating layer materials of the PEM electrolytic cell usually include noble metal Pt coating layers.

[0003] The cold spraying is a method of accelerating solid particles by using compressed gas, and forming a film by collision with a substrate. In the cold spraying process, plastic deformation and adiabatic shear instability of the particles occur, metal bonds are formed between the particle-substrate and particle-particle interfaces, and finally the coating layer is prepared by mechanical interlocking and metallurgical bonding. The cold spraying technology is a very promising coating preparation method. SUMMARY

[0004] The present application provides a novel method for preparing a metal electrode plate coating layer of a fuel cell and an electrolytic cell. The method can form a film in an atmospheric environment, has a fast film forming speed, can prepare a coating layer at room temperature, and has a wide design range and good compatibility.

[0005] To achieve the above-mentioned application purposes, the present application provides a method for preparing an electrode plate coating layer by using a cold spraying method, which includes the following steps:

[0006] s1: pretreating the electrode plate;

[0007] Using a roughness tester, it is determined whether the roughness of the electrode plate meets the cold spraying surface roughness requirement;

[0008] Cleaning the electrode plate: first, clean the surface of the electrode plate with deionized water, then remove the surface oil with a degreasing agent, then clean the small contaminants with ultrasonic waves, and finally clean the electrode plate with deionized water and dry it;

[0009] s2: cold spraying coating on the electrode plate;

[0010] Before cold spraying, place the electrode plate in the designed tooling to ensure that the electrode plate does not deform during cold spraying;

[0011] Preheat the electrode plate, and after setting the cold spraying process parameters, spray it with metal powder;

[0012] The coating of cold spraying is divided into three layers, from the electrode plate outwardly in turn, transition layer, main layer and conductive layer;

[0013] s3: post-treatment of the electrode plate, including heat treatment, polishing and cleaning.

[0014] Further, the selection of the degreasing agent: the degreasing agent is selected according to the surface roughness of the electrode plate, the surface roughness of the electrode plate meets the requirements, and the alkaline degreasing agent is used to clean the electrode plate; when the surface roughness of the electrode plate is too small, an acidic degreasing agent is used to increase the surface roughness of the electrode plate.

[0015] Further, the transition layer is preferably made of Cu, Ni and a metal close to the composition of the base material, and the thickness of the transition layer is 0.5-2um.

[0016] Further, the main layer is made of high corrosion-resistant metals, preferably Ti, Mo, Ta, Cr, Zr, W, V, Hf, Ru and their alloys, and the thickness of the main layer is 0.5-5um.

[0017] Further, the particle size of the cold spraying metal powder is 0.1-10um, and the preheating temperature of the powder is 25-700℃.

[0018] The advantages of the prepared coating are: first, no vacuum environment is needed, the film can be formed in the atmospheric environment, which can greatly reduce the cost of preparing the coating; second, the film forming speed is fast, which can reach 5-2000um / min in the thickness direction; third, the coating deposition temperature is low, the coating can be prepared at room temperature, and the thermal influence on the substrate is small; fourth, the sprayed particles do not undergo high-temperature melting process, and the phase structure and element composition of the coating are consistent with the powder; fifth, the use of this method for preparing the coating has wide design range and good compatibility, and different coatings can be prepared according to different scene requirements. BRIEF DESCRIPTION OF DRAWINGS

[0019] Figure 1 The composition of the electrode plate coating prepared by the cold spraying method is shown in the figure;

[0020] 1. conductive layer; 2. main body layer; 3. transition layer; 4. polar plate. DETAILED DESCRIPTION

[0021] In order to better understand the purpose, structure and function of the present application, the following will be further described in detail in combination with the drawings.

[0022] The present application provides a cold spraying technology for preparing a fuel cell or electrolytic cell polar plate coating method. The coating prepared by using the method mainly comprises three steps: s1: pretreatment of the polar plate 4; s2: cold spraying coating of the polar plate 4, the coating can be designed according to the use scene and performance, and the coating usually has two layers, a corrosion-resistant layer and a conductive layer. S3: post-treatment of the polar plate, the post-treatment includes heat treatment, polishing and cleaning.

[0023] 1. The cold spraying polar plate has the following characteristics: ① The polar plate needs to have a certain strength to resist deformation during spraying; ② The polar plate surface has a certain roughness to ensure mechanical engagement between the coating and the substrate, and the roughness is usually between 1-40 μm; ③ The polar plate surface must be kept clean, free of oil stains, oxides, rust spots, dust or other contaminants; ④ Suitable spraying polar plate materials include iron-based, aluminum-based, titanium-based and nickel-based alloys.

[0024] 2. Polar plate pretreatment: ① First, use a roughness tester to determine whether the roughness of the polar plate meets the requirements, and the roughness is usually between 1-40 μm, and the specific roughness is related to the average particle size of the cold spraying powder of the coating; ② Clean the polar plate: first clean the surface of the polar plate with deionized water, then remove the surface oil with a degreasing agent, then clean the small contaminants with ultrasonic cleaning, and finally clean and dry the polar plate with deionized water.

[0025] 3. Selection of degreasing agent: The degreasing agent is selected according to the surface roughness of the polar plate. If the surface roughness of the polar plate meets the requirements, use an alkaline degreasing agent to clean the polar plate; if the surface roughness of the polar plate is too small, use an acidic degreasing agent to increase the surface roughness of the polar plate.

[0026] 4. Preparation before cold spraying: Before cold spraying, place the polar plate in a designed tooling to ensure that the polar plate does not deform during cold spraying.

[0027] 5. Cold spraying of the polar plate: The cold spraying can prepare carbon-based coatings, metal-based coatings or ceramic-based coatings, which can be single-component coatings or multi-component coatings, and can be designed according to the use scene and performance. The coating usually has two layers, a corrosion-resistant layer and a conductive layer 1, and the coating thickness is 1.5-10 μm.

[0028] 6. Corrosion resistant layer coating design: The corrosion resistant layer can be divided into transition layer 3 and main layer 2. The transition layer 3 is preferably made of Cu, Ni and metals close to the composition of the base material, and the thickness of the transition layer is 0.5-2 um; the main layer 2 can be made of high corrosion resistant metals, preferably Ti, Mo, Ta, Cr, Zr, W, V, Hf, Ru, etc., and the thickness of the main layer 2 is 0.5-5 um;

[0029] 7. Conductive layer coating design: The conductive layer 1 coating can be selected from carbon-based coating, metal-based coating or ceramic-based coating. The conductive layer is preferably made of graphite, Au, Ag, Pt, Ir, CrC(N), TiC(N) and the like, and the thickness of the conductive layer is 0.5-3 um.

[0030] 8. Corrosion resistant layer and conductive layer coating cold spraying: The particle size of the coating cold sprayed metal powder is 0.1-10 um, the powder preheating temperature is 25-700°C, the electrode plate preheating temperature is 25-1000°C, the pressure is 0.5-4 MPa, the spraying distance is 1-30 mm, the powder speed is 100-1200 m / s, the nozzle moving speed is 1-100 mm / s, and the spraying working gas is N2, Ar, He or air, etc.

[0031] 9. Post-processing of the electrode plate mainly includes heat treatment, polishing and cleaning processes.

[0032] 10. Heat treatment: Coating heat treatment is not a necessary process, which is determined according to the porosity of the coating or the stress state of the electrode plate after spraying. Only when the porosity of the coating is greater than 2% or the internal stress of the electrode plate after spraying is large, heat treatment will be carried out. The heat treatment temperature is between the tempering temperature and the recrystallization temperature. The stress relief annealing temperature of different materials depends on the type and properties of the material, and it is ensured that there is no adverse effect on the structure and performance of the material.

[0033] 11. Polishing and cleaning: The surface roughness of the electrode plate after cold spraying is large, and polishing treatment is usually required. Polishing can be selected from mechanical polishing, chemical polishing or electrolytic polishing, and the appropriate polishing type and process is selected according to the requirement of the electrode plate on the surface roughness of the material. The cleaning process of the electrode plate after polishing is consistent with the cleaning of the pre-treatment.

[0034] Example 1

[0035] This example describes the preparation of a carbon coating on the surface of a bipolar plate by cold spraying. A 316L stainless steel bipolar plate with dimensions of 50 x 50 x 0.4 mm (length x width x thickness) for a fuel cell stack was selected. The surface roughness of the bipolar plate was measured using a JD520plus split-body surface roughness meter. The Ra of the bipolar plate was 1.85 ± 0.15 μm, which met the requirements of cold spraying for roughness. The bipolar plate was then cleaned. First, it was cleaned with deionized water at room temperature for 2 min, then with an alkaline degreasing agent at 40°C for 5 min, followed by ultrasonic cleaning in deionized water at 40°C for 5 min, and finally cleaned with deionized water and dried. The composition of the degreasing agent was 5-15 wt% NaOH, 5-20 wt% Na2CO3, 5-10 wt% sodium alkylbenzenesulfonate, 2-5 wt% polyoxyethylene ether, 1-3 wt% EDTA, 5-10 wt% ethanol, and the balance deionized water. The cleaned bipolar plate was placed in a cold spraying tool, and the bipolar plate was fixed. Cold spraying was then performed. The bipolar plate was preheated to a temperature of 430°C. The cold sprayed coating was divided into three layers, in order from the bipolar plate outward, a transition layer, a main corrosion-resistant layer, and a conductive layer. The cold spraying process parameters for the three layers are shown in the table below. The transition layer used a nickel-copper alloy (Cu-Ni30) ultra-fine spherical powder with an average particle size of 0.5 μm. The cold spraying process parameters for the transition layer were a powder preheating temperature of 150°C, a gas selected from 99.99% high-purity N2, a gas pressure of 1.5 MPa, a powder velocity of 700 m / s, a spraying distance of 5 mm, a nozzle moving speed of 8 mm / s, a transition layer coating thickness of 1 μm, and spraying of 2 layers. The main corrosion-resistant layer used a TA1 pure titanium ultra-fine spherical powder with an average particle size of 0.8 μm. The cold spraying process parameters for the main corrosion-resistant layer were a powder preheating temperature of 120°C, a gas selected from 99.99% high-purity N2, a gas pressure of 2.5 MPa, a powder velocity of 800 m / s, a spraying distance of 20 mm, a nozzle moving speed of 5 mm / s, a main corrosion-resistant layer coating thickness of 1.6 μm, and spraying of 2 layers. The conductive layer used a graphite ultra-fine spherical powder with an average particle size of 1.4 μm. The cold spraying process parameters for the main corrosion-resistant layer were a powder preheating temperature of 120°C, a gas selected from high-purity Ar, a gas pressure of 1.5 MPa, a powder velocity of 600 m / s, a spraying distance of 10 mm, a nozzle moving speed of 3 mm / s, a main corrosion-resistant layer coating thickness of 1.6 μm, and spraying of 2 layers.

[0036] Cold spraying process parameters for the three layers

[0037]

[0038] The cold sprayed graphite powder can form a compact carbon film on the surface due to the collision energy, which can convert part of the graphite powder into amorphous carbon. The coating has excellent electrical conductivity and good corrosion resistance. When cold spraying graphite powder, the powder speed should be controlled between 500-700 m / s, and the substrate preheating temperature should be controlled between 100-400℃, so as to ensure that the cold sprayed graphite powder can form a better film. Finally, the cold sprayed plate is post-treated. First, the plate is heat treated at 300℃ for 3h in a vacuum heat treatment furnace. Second, the plate is polished using an electrolytic polishing solution of HNO3:H2O=30:70. Finally, the plate is cleaned using a pre-treatment plate process to complete the preparation of the plate coating.

[0039] Example 2

[0040] This example introduces the preparation of a carbon coating on the surface of the plate by cold spraying technology. A pure titanium plate with a size of 50x50x1mm (lengthxwidthxthickness) for electrolytic cell is selected. The surface roughness of the plate is measured using a JD520plus split surface roughness meter. The Ra of the plate is 2.85±0.15μm, which meets the requirements of cold spraying for roughness. Then the plate is cleaned. First, it is cleaned with deionized water at room temperature for 2min, then with an alkaline degreasing agent at 80℃ for 10min, followed by ultrasonic cleaning in deionized water at 40℃ for 5min, and finally cleaned with deionized water and dried. The composition of the degreasing agent is: 5-15wt% NaOH, 5-20wt% Na2CO3, 5-10wt% sodium alkyl benzene sulfonate, 2-5wt% polyoxyethylene ether, 1-3wt% EDTA, 5-10wt% ethanol, and the rest is deionized water. The cleaned plate is placed in the cold spraying tooling, and the plate is fixed. Cold spraying coating is started. The plate is preheated for cold spraying. The preheating temperature is 500℃. The cold sprayed coating is divided into two layers. From the plate outward, they are the main corrosion-resistant layer and the conductive layer. The cold spraying process parameters of the two coatings are shown in the table below. The main corrosion-resistant layer uses TA1 pure titanium and Ta ultra-fine spherical powder with an average particle size of 0.8μm. The main corrosion-resistant layer cold spraying process parameters are: powder preheating temperature 120℃, gas selected high-purity N2 99.99%, gas pressure 2.5MPa, powder speed away from the spray gun 800m / s, spraying distance 20mm, nozzle moving speed 5mm / s, main corrosion-resistant layer coating thickness 1.6μm, and spraying 2 layers. The conductive layer uses Pt ultra-fine spherical powder with an average particle size of 1μm. The main corrosion-resistant layer cold spraying process parameters are: powder preheating temperature 150℃, gas selected high-purity Ar, gas pressure 2MPa, powder speed away from the spray gun 800m / s, spraying distance 10mm, nozzle moving speed 3mm / s, main corrosion-resistant layer coating thickness 1μm, and spraying 1 layer.

[0041] Cold spraying process parameters of two coatings

[0042]

[0043] Finally, the cold sprayed electrode plate is post-processed. Firstly, the electrode plate is heat treated at 400°C for 4h in a vacuum heat treatment furnace. Secondly, the electrode plate is polished using an electrolytic polishing solution of HNO3:H2O=30:70. Finally, the electrode plate is cleaned using a pre-treatment electrode plate process to complete the preparation of the electrode plate coating.

Claims

1. A method for preparing an electrode coating using a cold spraying method, characterized in that, Includes the following steps: s1: Pre-treat the electrode plate (4); Use a roughness tester to determine whether the roughness of the electrode plate (4) meets the surface roughness requirements of cold spraying. Cleaning the plates (4): First, use deionized water to clean the particles on the surface of the plates, then use a degreasing agent to remove surface oil, then use ultrasonic cleaning to clean the tiny contaminants, and finally use deionized water to clean and dry the plates. s2: Apply a cold spray coating to the electrode plate; Before cold spraying, the electrode plate is placed in the designed tooling to ensure that the electrode plate does not deform during cold spraying. The electrode plates are preheated, and after setting the cold spraying process parameters, they are sprayed with metal powder. The cold spray coating consists of three layers, from the electrode plate outwards: a transition layer (3), a main body layer (2), and a conductive layer (1). s3: Post-processing of the electrode plates, which includes heat treatment, polishing and cleaning.

2. The method for preparing an electrode coating using a cold spraying method according to claim 1, characterized in that: The selection of the degreasing agent: The degreasing agent is selected according to the surface roughness of the electrode plate. If the surface roughness of the electrode plate meets the requirements, an alkaline degreasing agent is used to clean the electrode plate; if the surface roughness of the electrode plate is too small, an acidic degreasing agent is used to increase the surface roughness of the electrode plate.

3. The method for preparing an electrode coating using a cold spraying method according to claim 1, characterized in that: The transition layer (3) is preferably made of Cu, Ni, or a metal with a composition similar to that of the substrate, and the thickness of the transition layer is 0.5 to 2 μm.

4. The method for preparing an electrode coating using a cold spraying method according to claim 1, characterized in that: The main body layer (2) is made of highly corrosion-resistant metal, preferably elemental metals such as Ti, Mo, Ta, Cr, Zr, W, V, Hf, Ru, or their combination, and the thickness of the main body layer is 0.5 to 5 μm.

5. A method for preparing an electrode coating using a cold spraying method according to claim 1, characterized in that: The cold-sprayed metal powder has a particle size of 0.1–10 μm and a powder preheating temperature of 25–700 °C.

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