Preparation method of fuel cell metal pole plate composite coating

Abstract

The invention discloses a preparation method of a composite coating of a metal pole plate of a fuel cell. The preparation method comprises the following steps: S1, pretreating a metal base material; s2, carrying out plasma cleaning on the metal base material; and S3, cathode arc ion plating is adopted in vacuum coating equipment, a transition layer, a middle layer and an outer coating are sequentially deposited on the surface of the metal base material from inside to outside, the transition layer is a pure metal coating, the middle layer is a metal nitride coating, and the outer coating is a circulation layer formed by periodically and alternately depositing a metal coating and a ternary coating. Wherein the thickness of the transition layer is 10 to 200 nm; the thickness of the middle layer ranges from 100 nm to 500 nm. The thickness of the outer layer coating ranges from 200 nm to 1000 nm.

Description

Technical Field

[0001] The present invention relates to the technical field of fuel cells, and particularly to a method for preparing a composite coating for a metal bipolar plate of a fuel cell. Background Art

[0002] A proton exchange membrane fuel cell (PEMFC) is an electrochemical power generation device that converts chemical energy into electrical energy through a hydrogen-oxygen reaction, is not limited by the Carnot cycle, and has a high energy conversion efficiency. In addition, when the PEMFC is operating, the only product is water and there are no other pollutants, which is extremely friendly to the environment. The bipolar plate is a core component in the PEMFC, and plays roles such as strength support, fluid distribution, and charge transfer. Relevant research shows that when the PEMFC is operating, the inside is acidic, with a pH value of about 3-5, and anions such as F - , Cl - et al. etch the bipolar plate, which puts higher requirements on the conductivity and corrosion resistance of the surface of the bipolar plate.

[0003] Currently, bipolar plates can be classified into metal plates and graphite plates according to materials. Graphite bipolar plates have good conductivity and chemical stability in the acidic environment of fuel cells and are the earliest applied bipolar plate materials. However, graphite bipolar plates have the disadvantages of poor gas barrier property, high brittleness, low mechanical strength, and are difficult to be further thinned, which is not conducive to the further improvement of the performance and lightweight of the fuel cell stack. In recent years, metal materials, especially stainless steel materials, have the advantages of good electrical and thermal conductivity, high mechanical strength, and easy processing and forming, and have increasingly become the main research object of bipolar plates. However, a single stainless steel material is easily corroded in the acidic environment of fuel cells. In addition, after long-term operation, the surface passivation phenomenon intensifies, resulting in an increase in the contact resistance with the gas diffusion layer. Therefore, it is necessary to modify the surface of the metal material to enhance the conductivity and corrosion resistance, thereby improving the performance and lifespan of the fuel cell.

[0004] The invention patent with the publication number of CN116487623A discloses a preparation process for a self-healing coating of a metal bipolar plate. This process first pre-treats the SS316L stainless steel substrate, and then forms a Cr metal layer, a CrC layer, and a graphite carbon layer on the surface of the substrate from the inside out by sputtering. The coating prepared by this method can show a certain self-healing ability during operation, thereby improving the anti-corrosion performance. However, the compactness of this single-metal corrosion-resistant transition layer is relatively poor and cannot completely isolate the corrosive liquid from eroding the substrate. In addition, the toughness of the coating also needs to be improved.

[0005] The invention patent with the publication number CN104310991A discloses a method for preparing a rare earth-doped nano titanium-niobium coating. This method uses plasma spraying technology and can greatly improve the toughness of the coating by adjusting the proportions of various metal oxides and nano titanium and niobium. However, it cannot guarantee the conductivity of the niobium coating. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to provide a method for preparing a composite coating for a fuel cell metal plate. The technical solution adopted is as follows: A method for preparing a composite coating for a fuel cell metal plate includes the following steps S1. Pretreatment of the metal substrate: Place the metal substrate in a cleaning agent for cleaning, and then place it in a vacuum oven for drying to remove the grease and oxide layer on the substrate surface; S2. Plasma cleaning of the metal substrate: Fix the cleaned metal substrate on the sample frame of the vacuum coating equipment. Keep a horizontal distance of 5-20 cm between the metal substrate and the target. First, heat and evacuate the chamber of the vacuum coating equipment, and then introduce argon gas. Use ion beam etching to further remove the oxide layer and other contaminants on the metal substrate surface; S3. Use cathode arc ion plating in the vacuum coating equipment to deposit a transition layer, an intermediate layer, and an outer layer coating on the metal substrate surface from the inside out. The transition layer is a pure metal coating, the intermediate layer is a metal nitride coating, and the outer layer coating is a cyclic layer formed by periodically alternating deposition of a metal coating and a ternary coating. The thickness of the transition layer is 10-200 nm; the thickness of the intermediate layer is 100-500 nm; the thickness of the outer layer coating is 200-1000 nm.

[0007] A further technical feature of the present invention is: When depositing the transition layer in step S3, introduce argon gas and turn on the pure metal target to deposit a metal coating on the metal substrate surface to enhance the bonding between the substrate and the coating; when depositing the intermediate layer, while continuously introducing argon gas and keeping the pure metal target on, introduce nitrogen gas into the chamber to deposit a metal nitride coating on the substrate surface to improve the film-substrate bonding force; when depositing the outer layer coating, turn off the nitrogen gas, continue to keep the pure metal target on, deposit a metal layer on the substrate surface, then turn on the composite target and reintroduce nitrogen gas to deposit a ternary coating on the substrate surface, and then turn off the nitrogen gas and the composite target, only turn on the pure metal target, deposit a metal coating on the substrate surface, repeat the above operations, and periodically deposit a metal coating and a ternary coating on the substrate surface to obtain an outer cyclic layer.

[0008] In step S3, the temperature of the vacuum coating equipment chamber is 200~400°C; the pure metal target in step S3 is Ni, Zr, Ti, Cr, Cu, Ag or Au; in step S3, the substrate bias voltage is -50~-500V, the argon gas flow rate is 10~400 sccm, the nitrogen gas flow rate is 100~1000 sccm, and the target current is 10~200A; the deposition time for both the deposition of the transition layer and the deposition of the intermediate layer is 5~15 min; when depositing the outer coating, the number of cyclic depositions of the metal coating and the ternary coating is 2~5 times, and the deposition time is 2~10 min.

[0009] The composite target in step S3 is an MAl target or an MSi target (M is one of Ni, Zr, Ti, Cr, Cu, Ag or Au), and the atomic number ratio of the two elements is 0.2~1:1.

[0010] In step S1, the thickness of the metal substrate is 0.05~1 mm, and the material is stainless steel, aluminum, titanium or titanium alloy.

[0011] The cleaning agent in step S1 is a water-based cleaning agent, a semi-aqueous cleaning agent and a solvent cleaning agent.

[0012] In step S1, the cleaning method is ultrasonic, bubbling, or spraying, the cleaning time is 10~30 min, the drying time in the vacuum oven is 1~3 h, and the drying temperature is 60~80°C.

[0013] In step S2, the temperature of the vacuum coating equipment chamber is 200~400°C, the vacuum degree is 1×10 -3 ~1×10 - 5 Pa, the argon gas flow rate is 10~400 sccm, the substrate bias voltage is -200~-1000V, and the plasma cleaning time is 5~15 min.

[0014] The beneficial effects of the present invention are: Since in step S3 of the present invention, cathodic arc ion plating is used in the vacuum coating equipment, a transition layer, an intermediate layer, and an outer coating are sequentially deposited from the inside out on the surface of the metal substrate, wherein the transition layer is a pure metal coating, the intermediate layer is a metal nitride coating, and the outer coating is a cyclic layer of periodically alternately deposited metal coatings and ternary coatings, wherein the thickness of the transition layer is 10~200 nm; the thickness of the intermediate layer is 100~500 nm; and the thickness of the outer coating is 200~1000 nm.

[0015] The deposition transition layer deposits a metal coating on the surface of the metal substrate to enhance the bonding between the substrate and the coating, that is, to enhance the bonding between the substrate and the subsequent intermediate layer; the deposition of the intermediate layer deposits a metal nitride coating on the surface of the transition layer to improve the film-substrate bonding force, that is, to improve the bonding force between the transition layer and the subsequent outer layer coating; the deposition of the outer layer periodically alternates the deposition of a metal coating and a ternary coating on the surface of the intermediate layer to obtain an outer circulation layer. The ternary material coating in the outer layer introduces Al (or Si) elements into the metal nitride to form a ternary material coating. On the one hand, the ternary material can effectively increase the hardness of the coating, thereby improving the erosion resistance of the coating; on the other hand, by introducing a metal layer in the middle of the ternary material coating, not only can the deformation between the substrate and the ternary material coating be coordinated and the energy generated due to the deformation be absorbed, but also the diffusion of cracks in the ternary coating can be hindered, enhancing the bonding strength between the coatings and between the coating and the substrate, thereby endowing the coating with sufficient toughness and improving the corrosion resistance of the coating. At the same time, the electrical conductivity of the coating will not be affected. The plate coating of the present invention is easy to control in process and has a fast overall preparation rate. On the basis of greatly improving the corrosion resistance and electrical conductivity, it can also ensure the production efficiency, which has a great promoting effect on the development of the fuel cell industry. Specific Embodiments

[0016] The following further describes the present invention in detail with specific embodiments: Example 1

[0017] A method for preparing a composite coating for a fuel cell metal plate includes the following steps S1. Use a 316L stainless steel plate with a thickness of 0.1 mm as the substrate, put it into ethanol and ultrasonically clean it for 10 min, and then dry it in a vacuum oven at 60 °C for 2 h to remove the grease and impurity debris on the surface; S2. Place the substrate on the sample frame in the vacuum coating equipment, the horizontal distance between the substrate and the target is 10 cm, then heat the cavity to 300 °C and evacuate the cavity until the cavity vacuum reaches 5×10 -5 Pa, control the substrate bias to -1000 V, and introduce argon with a flow rate of 200 sccm to perform plasma cleaning on the surface of the substrate for 5 min to further remove the oxide layer and other contaminants on the metal surface; S3. In the vacuum coating equipment, cathodic arc ion plating is adopted. A transition layer, an intermediate layer, and an outer coating are sequentially deposited on the surface of the substrate from the inside to the outside. The substrate bias voltage is controlled at -150 V, the argon gas flow rate is controlled at 50 sccm, and the chamber temperature is controlled at 300 °C. First, the Ti target is turned on, the Ti target current is set at 30 A, and it is maintained for 5 min to deposit a transition layer of metal Ti coating on the surface of the substrate. Then, with the process parameters unchanged, nitrogen gas is introduced, the flow rate is controlled at 100 sccm, the Ti target is continuously turned on, and it is maintained for 5 min to deposit an intermediate layer of TiN coating on the surface of the transition layer. Subsequently, with other conditions unchanged, the nitrogen gas is turned off and maintained for 2 min to deposit a metal Ti coating on the intermediate layer of the substrate. Then, the Ti target is turned off, the TiAl composite target is turned on, the atomic ratio of Ti to Al in the composite target is 0.5:1, the TiAl composite target current is set at 30 A, nitrogen gas is introduced, the flow rate is controlled at 100 sccm and maintained for 2 min to deposit a TiAlN ternary coating on the surface of the metal Ti coating. A metal Ti coating is deposited on the surface of the TiAlN ternary coating, and a TiAlN ternary coating is deposited on the surface of the metal Ti to obtain an outer circulation layer with two layers of Ti metal layers and two layers of TiAlN ternary coatings deposited alternately. Example 2

[0018] The difference from Example 1 is only that in step S3, the atomic ratio of Ti to Al in the composite target is 0.75:1; the outer coating is circulated 3 times to obtain an outer circulation layer with three layers of Ti metal layers and three layers of TiAlN ternary coatings deposited alternately. Example 3

[0019] The difference from Example 1 is that in step S3, the metal target is a Cr target; the composite target is a CrAl target. Example 4

[0020] The difference from Example 3 is that in step S3, the atomic ratio of Cr to Al in the composite target is 0.75:1; in step S3, the outer coating is circulated 3 times to obtain an outer circulation layer with three layers of Cr metal layers and three layers of CrAlN ternary coatings deposited alternately.

[0021] In practical applications, the temperature of the chamber of the vacuum coating equipment in step S3 is 200 °C or 300 °C or 400 °C; the thickness of the transition layer in step S3 is 10 nm or 50 nm or 100 nm or 200 nm; the thickness of the intermediate layer is 100 nm or 200 nm or 300 nm or 500 nm; the thickness of the outer coating layer is 200 nm or 400 nm or 600 nm or 800 nm or 1000 nm; the substrate bias voltage in step S3 is -50 V or -100 V or -200 V or -300 or -500 V, the argon gas flow rate is 10 sccm or 60 sccm or 100 sccm or 200 sccm or 400 sccm, the nitrogen gas flow rate is 100 sccm or 200 sccm or 300 sccm or 500 sccm or 800 sccm or 1000 sccm, and the target current is 10 or 50 A or 80 A or 100 A or 150 A or 200 A; the deposition time for depositing the transition layer and the intermediate layer is 5 min or 8 min or 10 min or 15 min; the number of cycle depositions of the metal coating and the ternary coating during the deposition of the outer coating layer is 2 or 3 or 5 times, and the deposition time is 2 min or 5 min or 8 min or 10 min; the composite target in step S3 is an MAl target or an MSi target (M is one of Ni, Zr, Ti, Cr, Cu, Ag or Au), and the atomic number ratio of the two elements is 0.2:1 or 0.5:1 or 0.8:1 or 1:1. The cleaning method in step S1 is ultrasonic or bubbling or spraying, the cleaning time is 10 min or 15 min or 20 min or 30 min, the drying time in the vacuum oven is 1 h or 2 h or 3 h, the drying temperature is 60 °C or 70 °C or 80 °C, and the higher the drying temperature, the shorter the time; the temperature of the chamber of the vacuum coating equipment in step S2 is 200 °C or 300 °C or 400 °C, the vacuum degree is 1×10 -3 Pa or 1×10 -4 or 1×10 -5 Pa, the argon gas flow rate is 10 sccm or 60 sccm or 100 sccm or 200 sccm or 400 sccm, the substrate bias voltage is -200 V or -300 V or -500 V or -800 or -1000 V, and the plasma cleaning time is 5 min or 8 min or 10 min or 15 min.

[0022] Since in step S3 of the present invention, cathodic arc ion plating is used in a vacuum coating equipment, a transition layer, an intermediate layer, and an outer coating layer are sequentially deposited from the inside to the outside on the surface of a metal substrate, wherein the transition layer is a pure metal coating layer, the intermediate layer is a metal nitride coating layer, and the outer coating layer is a cyclic layer of periodically alternately deposited metal coating layers and ternary coating layers. The thickness of the transition layer is 10 - 200 nm; the thickness of the intermediate layer is 100 - 500 nm; and the thickness of the outer coating layer is 200 - 1000 nm.

[0023] Depositing the transition layer is to deposit a metal coating layer on the surface of the metal substrate to enhance the bonding between the substrate and the coating, that is, to enhance the bonding between the substrate and the subsequent intermediate layer; depositing the intermediate layer is to deposit a metal nitride coating layer on the surface of the transition layer to improve the film-substrate bonding force, that is, to improve the bonding force between the transition layer and the subsequent outer coating layer; depositing the outer layer is to periodically alternately deposit a metal coating layer and a ternary coating layer on the surface of the intermediate layer to obtain an outer cyclic layer. The ternary material coating layer in the outer layer introduces Al (or Si) elements into the metal nitride to form a ternary material coating layer. On the one hand, the ternary material can effectively improve the coating hardness, thereby improving the erosion resistance of the coating; on the other hand, by introducing a metal layer between the ternary material coating layers, not only can the deformation between the substrate and the ternary material coating layer be coordinated and the energy generated due to the deformation be absorbed, but also the diffusion of cracks in the ternary coating layer can be hindered, enhancing the bonding strength between the coating layers and between the coating layer and the substrate, thereby endowing the coating with sufficient toughness, improving the corrosion resistance of the coating, and at the same time, the electrical conductivity of the coating will not be affected. The plate coating of the present invention has easy process control and a fast overall preparation rate. On the basis of greatly improving the corrosion resistance and electrical conductivity, it can also ensure the production efficiency, which has a great promoting effect on the development of the fuel cell industry.

[0024] Comparative Example 1 The difference from Example 1 is that in step S3, the deposition of the outer coating layer is cancelled, and only a Ti coating layer and a TiN coating layer are sequentially deposited from the inside to the outside on the surface of the metal substrate. The deposition time of the TiN coating layer is 10 min.

[0025] Comparative Example 2 The difference from Example 1 is that in step S3, a transition layer Ti coating layer is deposited from the inside to the outside on the surface of the metal substrate, an intermediate layer TiN coating layer is deposited, and only a ternary coating layer, that is, a TiAlN coating layer, is deposited for the outer coating layer; wherein, the deposition time of the TiAlN ternary coating layer is 10 min.

[0026] Result Detection The corrosion current was measured using a three - electrode system. First, a linear voltammogram curve was obtained through potentiodynamic scanning, then the curve was subjected to Tafel fitting, and the corrosion current of the sample was determined by extrapolating the Tafel straight line. The corrosion current represents the speed of material corrosion in the corrosive environment. The larger the corrosion current, the faster the corrosion rate. On the contrary, the smaller the corrosion current, the lower the material corrosion rate and the better the corrosion resistance.

[0027] The contact resistance characterizes the conductivity of the coating. The smaller the contact resistance, the better the conductivity. The carbon paper used in this test was Toray carbon paper, and the pressure was 1.4 MPa.

[0028] Table 1 Corrosion current μA / cm2 Contact resistance mΩ.cm2 Example 1 0.08 4.8 Example 2 0.06 4.3 Example 3 0.12 3.8 Example 4 0.14 3.2 Comparative Example 1 0.6 10.5 Comparative Example 2 0.4 11.4 As can be seen from Table 1, for the coatings prepared in Examples 1 - 4, their corrosion currents are much lower than those in Comparative Examples 1 and 2, and their contact resistances are much smaller than those in Comparative Examples 1 and 2. This shows that the coatings prepared by the method provided by the present invention have more excellent corrosion resistance and conductivity.

[0029] The technical content and features of the present invention have been disclosed as above. However, it can be understood that under the spirit and creative idea of the present invention, those skilled in the art can make various changes and improvements to the above - mentioned structure, including combinations of the technical features disclosed or claimed here alone, and other combinations that obviously include these features. These deformations and / or combinations all fall within the technical field involved in the present invention and within the protection scope of the claims of the present invention.

Claims

1. A method for preparing a composite coating on a fuel cell metal plate, characterized in that It includes the following steps: S1. Pretreatment of the metal substrate: The metal substrate is put into a cleaning agent for cleaning, and then dried in a vacuum oven to remove the grease and oxide layer on the substrate surface; S2. Plasma cleaning of the metal substrate: The cleaned metal substrate is fixed on the sample frame of the vacuum coating equipment. The metal substrate and the target are kept at a horizontal distance of 5 - 20 cm. First, the chamber of the vacuum coating equipment is heated and evacuated, and then argon is introduced. Using ion beam etching, the oxide layer and other contaminants on the metal substrate surface are further removed; S3. Cathodic arc ion plating is adopted in the vacuum coating equipment to deposit a transition layer, an intermediate layer, and an outer coating on the metal substrate surface from the inside outwards. The transition layer is a pure metal coating, the intermediate layer is a metal nitride coating, and the outer coating is a cyclic layer formed by periodically alternating deposition of a metal coating and a ternary coating. The thickness of the transition layer is 10 - 200 nm; the thickness of the intermediate layer is 100 - 500 nm; the thickness of the outer coating is 200 - 1000 nm.

2. The preparation method of the composite coating for the fuel cell metal plate according to claim 1, characterized in that When depositing the transition layer in step S3, argon is introduced and the pure metal target is turned on to deposit a metal coating on the metal substrate surface to enhance the bonding between the substrate and the coating; when depositing the intermediate layer, under the condition of continuously introducing argon and turning on the pure metal target, nitrogen is introduced into the chamber to deposit a metal nitride coating on the substrate surface to improve the film - substrate bonding force; when depositing the outer coating, nitrogen is turned off, the pure metal target is continuously turned on to deposit a metal layer on the substrate surface, then the composite target is turned on and nitrogen is re - introduced to deposit a ternary coating on the substrate surface, and then nitrogen and the composite target are turned off, only the pure metal target is turned on to deposit a metal coating on the substrate surface. Repeat the above operations to periodically deposit the metal coating and the ternary coating on the substrate surface to obtain the outer cyclic layer.

3. The preparation method of the composite coating for the fuel cell metal plate according to claim 2, characterized in that: In step S3, the temperature of the chamber of the vacuum coating equipment is 200 - 400 °C; the pure metal target materials in step S3 are Ni, Zr, Ti, Cr, Cu, Ag, or Au; the substrate bias voltage in step S3 is - 50 - - 500 V, the argon flow rate is 10 - 400 sccm, the nitrogen flow rate is 100 - 1000 sccm, and the target current is 10 - 200 A; the deposition time for both the deposition of the transition layer and the deposition of the intermediate layer is 5 - 15 min; when depositing the outer coating, the number of cycle depositions of the metal coating and the ternary coating is 2 - 5 times, and the deposition time is 2 - 10 min.

4. The preparation method of the composite coating for the fuel cell metal plate according to claim 2, characterized in that: The composite target in step S3 is an MAl target or an MSi target, and the atomic number ratio of the two elements is 0.2 - 1:

1.

5. The method for preparing the composite coating of the fuel cell metal plate according to claim 1 or claim 2 or claim 3 or claim 4, characterized in that: The thickness of the metal substrate in step S1 is 0.05 - 1 mm, and the material is stainless steel, aluminum, titanium, or titanium alloy.

6. The preparation method of the composite coating for the fuel cell metal plate according to claim 1 or claim 2 or claim 3 or claim 4, characterized in that: The cleaning agent in step S1 is a water - based cleaning agent, a semi - water - based cleaning agent, and a solvent cleaning agent.

7. The preparation method of the composite coating for the fuel cell metal plate according to claim 1 or claim 2 or claim 3 or claim 4, characterized in that: The cleaning method in step S1 is ultrasonic, bubbling, or spraying. The cleaning time is 10 - 30 min, the drying time in the vacuum oven is 1 - 3 h, and the drying temperature is 60 - 80 °C.

8. The method for preparing a composite coating for a fuel cell metal plate according to claim 1 or claim 2 or claim 3 or claim 4, characterized in that: In step S2, the temperature of the chamber of the vacuum coating equipment is 200~400°C, the vacuum degree is 1×10 -3 ~1×10 -5 Pa, the argon gas flow rate is 10~400 sccm, the substrate bias voltage is -200~-1000 V, and the plasma cleaning time is 5~15 min.