Method for preparing Co3O4-MnCo2O4 composite spinel coating on surface of metal connector matrix

Abstract

The invention relates to a method for preparing a Co3O4-MnCo2O4 composite spinel coating on the surface of a metal connector matrix, belongs to the technical field of surface coatings, solves the technical problem of high resistivity of a MnCo2O4 single-layer spinel coating, and comprises the following steps: S1, preparing a manganese-cobalt spinel powder material by adopting a sol-gel process; s2, preparing a Co3O4 layer on the surface of the substrate by adopting an electrolytic deposition process; s3, taking the manganese-cobalt spinel powder material as a raw material, and further depositing a manganese-cobalt spinel coating by adopting an electrophoretic deposition process; and S4, the metal connector blank prepared in the step S3 is dried and then subjected to sintering treatment, and the Co3O4-MnCo2O4 composite spinel coating modified metal connector is prepared. The preparation method is low in cost and simple in process, the oxidation resistance and the conductivity of the metal connector can be effectively improved through the composite spinel coating, and the composite spinel coating has the good capacity of preventing Cr from volatilizing.

Description

Technical Field

[0001] The invention belongs to the technical field of surface coatings, and specifically relates to a method for preparing a Co3O4-MnCo2O4 composite spinel coating on the surface of a metal connector substrate. Background Art

[0002] Solid Oxide Fuel Cell (SOFC) is a third-generation fuel cell. It is an all-solid-state chemical power generation device that directly converts the chemical energy stored in fuel and oxidant into electrical energy in an efficient and environmentally friendly manner at medium and high temperatures. It is generally believed that it will be a type of fuel cell that will be widely used in the future like proton exchange membrane fuel cells.

[0003] The operating temperature of SOFC is usually a medium-low temperature of 600℃~800℃, and metal materials can generally be used as SOFC connectors. Through comparisons of oxidation resistance, conductivity, mechanical strength, thermal stability and cost, ferritic stainless steel (FSS) is currently the most ideal material for SOFC connectors. However, FSS as a connector material has the problems of weak oxidation resistance and reduced conductivity after long-term oxidation. At the same time, the Cr2O3 produced by the Cr element in FSS will cause Cr "poisoning" at the cathode, thereby affecting battery performance.

[0004] In the prior art, the method used to solve the above problem is to prepare a protective layer on the surface of the connector. The traditional single-layer coating still has a high resistivity during the oxidation process and cannot completely prevent the overflow of Cr elements. Therefore, the preparation of composite coatings has become a new research hotspot. At present, composite coatings on the surface of connectors can be mainly divided into rare earth oxide-spinel composite coatings, metal oxide-spinel composite coatings and double spinel composite coatings. Among the many spinel coatings on the surface of stainless steel, MnCo2O4 spinel exhibits excellent performance in inhibiting the formation of oxidation layer and preventing cathode Cr poisoning, but MnCo2O4 single-layer spinel coatings have the problem of high resistivity. Summary of the invention

[0005] The main purpose of the present invention is to overcome the deficiencies in the prior art and solve the technical problem of high resistivity of MnCo2O4 single-layer spinel coating. The present invention provides a method for preparing a Co3O4-MnCo2O4 composite spinel coating on the surface of a metal connector substrate.

[0006] The design concept of the present invention is: on the one hand, Co3O4 is a transition metal oxide with a spinel structure. Under high temperature conditions, the Co3O4 spinel coating can effectively block the oxidizing medium and slow down the cathode Cr poisoning rate; on the other hand, the excellent conductivity of Co3O4 can also improve the charge transfer characteristics of the stainless steel surface; on this basis, the thermal expansion coefficients of Co3O4 and MnCo2O4 match each other and have good bonding with each other. In summary, based on the physical properties of Co3O4 and MnCo2O4, the present invention uses Co3O4 as the inner layer and MnCo2O4 spinel as the outer layer, and uses electrolytic deposition-electrophoretic deposition to prepare a Co3O4-MnCo2O4 composite spinel coating, and its performance is significantly improved compared with the MnCo2O4 single-layer spinel coating.

[0007] The present invention is implemented by the following technical scheme: A method for preparing a Co3O4-MnCo2O4 composite spinel coating on the surface of a metal connector substrate comprises the following steps: S1. Preparation of MnCo2O4 spinel powder material by sol-gel process: S1-1, adding manganese nitrate tetrahydrate, cobalt nitrate hexahydrate and citric acid to deionized water to prepare a mixed solution, wherein citric acid is used as a complexing agent, the molar ratio of metal element Mn ions and Co ions in the mixed solution is 1:2, and the molar ratio of metal element ions to citric acid is 1:1.25; after the mixed solution is heated to 80° C., it is stirred at a stirring rate of 600 r / min to obtain a complex solution; S1-2, slowly drop ammonia water into the complex solution to adjust the pH value of the complex solution to 7-8 to obtain a precursor solution, and then continue heating and stirring for 4 hours while maintaining the heating temperature and stirring rate in step S1-1 to obtain a wet sol; S1-3, drying the wet sol prepared in step S1-2 at a drying temperature of 135°C and a drying time of 2h; after drying, sintering is performed at a sintering temperature of 800°C, a heating rate of 5°C / min, and a sintering time of 2h to obtain a MnCo2O4 spinel powder material for use in the subsequent step; S2. Preparing a Co3O4 layer on the surface of a metal interconnect substrate in a solid oxide fuel cell by an electrolytic deposition process, comprising the following steps: S2-1, substrate pretreatment: First, ferritic stainless steel is selected as the substrate of the metal connector, and a hole is drilled at the upper position of the substrate; then, the surface of the substrate is ground and polished; finally, the substrate is ultrasonically cleaned in acetone and anhydrous ethanol for 20 minutes in turn, and after the ultrasonic cleaning is completed, the substrate is immersed in alcohol for storage; S2-2. First, prepare a Co deposition electrolyte according to the following composition and its concentration ratio: CoCl2·6H2O: 40g / L, CoSO4·7H2O: 300g / L, H3BO3: 30g / L, sodium dodecyl sulfate: 0.03g / L; secondly, use boric acid and sodium bicarbonate to adjust the pH value of the Co deposition electrolyte to 4-5; thirdly, take out the substrate stored in the alcohol in step S2-1, immerse it in a 10% H2SO4 solution for acid immersion activation, reduce the generation of bubbles and pits during electroplating, and ensure that the substrate and the coating have strong adhesion; finally, take out the substrate after acid immersion activation and place it in the Co deposition electrolyte for electroplating. The temperature of the Co deposition electrolyte is 25°C and the current density is 15mA·cm 2 , the electroplating time is 10min, and a pure Co layer is electroplated on the substrate surface; S2-3, after the electroplating in step S2-2 is completed, the sample is rinsed with deionized water and anhydrous ethanol in turn and blown dry, and then heated to 800°C, with a heating rate of 5°C / min and a holding time of 1h, so that the pure Co layer electroplated on the surface of the substrate is oxidized to a Co3O4 layer, thereby obtaining a substrate with a Co3O4 layer deposited on the surface; S3, using the MnCo2O4 spinel powder material obtained in step S1 as a raw material, further depositing a manganese-cobalt spinel coating on the substrate on which the Co3O4 layer is deposited by an electrophoretic deposition process, comprising the following steps: S3-1, preparing an electrophoretic suspension: mixing equal volumes of acetylacetone and ethanol as an electrophoretic suspension base liquid, using elemental iodine as a nuclear power regulator, adding the nuclear power regulator and the MnCo2O4 spinel powder material prepared in step S1 to the electrophoretic suspension base liquid, the mass volume ratio of the electrophoretic suspension base liquid, the nuclear power regulator and the spinel powder material being: 100 mL: 0.2 g: 1.5 g, to obtain an electrophoretic suspension; S3-2, electrophoretic suspension dispersion treatment: stirring the electrophoretic suspension prepared in step S3-1, maintaining the heating temperature of the electrophoretic suspension at 25° C. during stirring, the stirring rate at 500 r / min, and the stirring time at 15 min; after the stirring, the electrophoretic suspension is placed in an ultrasonic water bath for ultrasonic dispersion, and the ultrasonic dispersion time at 15 min; S3-3, using the substrate with the surface deposited Co3O4 layer prepared in step S2-3 as the cathode, using the ferritic stainless steel with a clean surface polished as the anode, using copper wire to suspend the cathode and the anode respectively and immerse them in the electrophoretic suspension after the ultrasonic dispersion treatment in step S3-2 for electrophoretic deposition, the voltage of the electrophoretic deposition is 75V~100V, the deposition time is 1min~2min, and further electrophoretically depositing a manganese-cobalt spinel coating on the surface of the substrate on which the Co3O4 layer has been deposited, to obtain a metal connector blank; S4. First, the metal connector blank obtained in step S3-3 is dried at a drying temperature of 80°C for 24 hours; then, it is sintered in an argon atmosphere at a sintering temperature of 950°C, a heating rate of 5°C / min, and a sintering time of 1 hour; finally, it is cooled to room temperature in the furnace to obtain a metal connector with a Co3O4-MnCo2O4 composite spinel coating on the surface.

[0008] Furthermore, in the step S2-1, the ferritic stainless steel is SUS430 ferritic stainless steel.

[0009] Furthermore, in the step S4, the thickness of the Co3O4-MnCo2O4 composite spinel coating on the surface of the metal interconnect is 50um~60μm.

[0010] The beneficial effects of the present invention are: 1. The present invention adopts an electrolytic deposition-electrophoretic deposition process to prepare a Co3O4-MnCo2O4 composite spinel coating on the surface of a substrate. By comparing the oxidation performance and conductivity of a SUS430 substrate, a single-layer MnCo2O4 spinel coating and a Co3O4-MnCo2O4 composite spinel coating, the Co3O4-MnCo2O4 composite spinel coating significantly improves the oxidation resistance and conductivity of the MnCo2O4 single-layer spinel coating, and improves the performance of preventing the volatilization of the Cr element; 2. In the Co3O4-MnCo2O4 composite spinel coating, Co3O4 is used as the inner layer and MnCo2O4 spinel is used as the outer layer to form a double-layer composite coating, which has the advantages of simple preparation method, reduced production cost, and easy large-scale industrialization. It also enriches the types of metal oxide-spinel composite coatings and has important practical significance for promoting the large-scale production and application of composite spinel coatings on the surface of connectors. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Figure 1 This is a microscopic morphology of the Co3O4-MnCo2O4 composite spinel coating prepared by the present invention; Figure 2 The XRD phase analysis comparison diagram of Co3O4-MnCo2O4 composite spinel coating after different oxidation times; Figure 3 The comparison diagram of oxidation kinetic curves of substrate SUS430 and different spinel coating samples after cyclic oxidation at 800℃ in air for 200h; Figure 4 The ASR curves of the substrate SUS430 and different spinel coating samples after cyclic oxidation at 800℃ in air for 200h are compared with time. Figure 5A comparison of the relative contents of Cr2p atoms on the surfaces of different spinel coating samples after different oxidation times. DETAILED DESCRIPTION

[0012] The present invention is further described in detail below in conjunction with the accompanying drawings and embodiments.

[0013] The method for preparing a Co3O4-MnCo2O4 composite spinel coating on the surface of a metal connector substrate comprises the following steps: S1. Preparation of MnCo2O4 spinel powder material by sol-gel process: S1-1, adding manganese nitrate tetrahydrate, cobalt nitrate hexahydrate and citric acid to deionized water to prepare a mixed solution, wherein citric acid is used as a complexing agent, the molar ratio of metal element Mn ions and Co ions in the mixed solution is 1:2, and the molar ratio of metal element ions to citric acid is 1:1.25; after the mixed solution is heated to 80° C., it is stirred at a stirring rate of 600 r / min to obtain a complex solution; S1-2, slowly drop ammonia water into the complex solution to adjust the pH value of the complex solution to 7-8 to obtain a precursor solution, and then continue heating and stirring for 4 hours while maintaining the heating temperature and stirring rate in step S1-1 to obtain a wet sol; S1-3, drying the wet sol prepared in step S1-2 at a drying temperature of 135°C and a drying time of 2h; after drying, sintering is performed at a sintering temperature of 800°C, a heating rate of 5°C / min, and a sintering time of 2h to obtain a MnCo2O4 spinel powder material for use in the subsequent step; S2. Preparing a Co3O4 layer on the surface of a metal interconnect substrate in a solid oxide fuel cell by an electrolytic deposition process, comprising the following steps: S2-1, substrate pretreatment: First, ferritic stainless steel is selected as the substrate of the metal connector. In this embodiment, the ferritic stainless steel is SUS430 ferritic stainless steel. The size of the substrate is: length 15mm×width 15mm×thickness 1mm. A hole is drilled at the upper position of the substrate. Then, the surface of the substrate is ground and polished. Finally, the substrate is ultrasonically cleaned in acetone and anhydrous ethanol for 20 minutes in turn. After the ultrasonic cleaning is completed, the substrate is immersed in alcohol for storage; S2-2. First, prepare a 200 mL Co deposition electrolyte according to the following composition and concentration ratio: CoCl2·6H2O: 40 g / L, CoSO4·7H2O: 300 g / L, H3BO3: 30 g / L, sodium dodecyl sulfate: 0.03 g / L; secondly, use boric acid and sodium bicarbonate to adjust the pH value of the Co deposition electrolyte to 4-5; thirdly, take out the substrate preserved in the alcohol in step S2-1, immerse it in a 10% H2SO4 solution for acid leaching to activate the substrate; finally, take out the substrate after acid leaching and place it in the Co deposition electrolyte for electroplating. The temperature of the Co deposition electrolyte is 25°C and the current density is 15 mA·cm 2 , the electroplating time is 10min, and a pure Co layer is electroplated on the substrate surface; S2-3, after the electroplating in step S2-2 is completed, the sample is rinsed with deionized water and anhydrous ethanol in turn and blown dry, and then heated to 800°C, with a heating rate of 5°C / min and a holding time of 1h, so that the pure Co layer electroplated on the surface of the substrate is oxidized to a Co3O4 layer, thereby obtaining a substrate with a Co3O4 layer deposited on the surface; S3, using the MnCo2O4 spinel powder material obtained in step S1 as a raw material, further depositing a manganese-cobalt spinel coating on the substrate on which the Co3O4 layer is deposited by an electrophoretic deposition process, comprising the following steps: S3-1, preparing an electrophoretic suspension: mixing equal volumes of acetylacetone and ethanol as an electrophoretic suspension base liquid, using elemental iodine as a nuclear power regulator, adding the nuclear power regulator and the MnCo2O4 spinel powder material prepared in step S1 to the electrophoretic suspension base liquid, the mass volume ratio of the electrophoretic suspension base liquid, the nuclear power regulator and the spinel powder material being: 100 mL: 0.2 g: 1.5 g, to obtain an electrophoretic suspension; S3-2, electrophoretic suspension dispersion treatment: stirring the electrophoretic suspension prepared in step S3-1, maintaining the heating temperature of the electrophoretic suspension at 25° C. during stirring, the stirring rate at 500 r / min, and the stirring time at 15 min; after the stirring, the electrophoretic suspension is placed in an ultrasonic water bath for ultrasonic dispersion, and the ultrasonic dispersion time at 15 min; S3-3, using the substrate with the surface deposited Co3O4 layer prepared in step S2-3 as the cathode, using the ferritic stainless steel with a clean surface polished as the anode, using copper wire to suspend the cathode and the anode respectively and immerse them in the electrophoretic suspension after the ultrasonic dispersion treatment in step S3-2 for electrophoretic deposition, the voltage of the electrophoretic deposition is 75V~100V, the deposition time is 1min~2min, and further electrophoretically depositing a manganese-cobalt spinel coating on the surface of the substrate on which the Co3O4 layer has been deposited, to obtain a metal connector blank; S4. First, dry the metal connector blank obtained in step S3-3 at 80°C for 24 hours; then, sinter it in an argon atmosphere at 950°C, at a heating rate of 5°C / min, and for 1 hour; finally, cool it to room temperature with the furnace to obtain a metal connector with a Co3O4-MnCo2O4 composite spinel coating on the surface, and the thickness of the Co3O4-MnCo2O4 composite spinel coating is 50um~60μm. The microscopic morphology of the Co3O4-MnCo2O4 composite spinel coating prepared in this embodiment is as follows: Figure 1 As shown, it is not difficult to see that the Co3O4-MnCo2O4 composite spinel coating presents a uniform, dense and excellent spinel structure, without cracks or peeling, indicating that it has good adhesion.

[0014] The properties of the Co3O4-MnCo2O4 composite spinel coating prepared by the specific implementation are further analyzed below in conjunction with the accompanying drawings, as follows.

[0015] (I) The Co3O4-MnCo2O4 composite spinel coating prepared in this example and the sample after cyclic oxidation were subjected to phase analysis using XRD. Figure 2 As shown, compared with the standard card, it can be seen that the produced phases are all MnCo2O4 spinel phases, proving that the spinel coating completely covers the Co3O4 layer, and after 200h of cyclic oxidation, the diffraction peak is significantly enhanced. No new phase is produced with the extension of oxidation time, and it has good thermal stability.

[0016] (ii) In order to verify the high temperature oxidation resistance, electrical conductivity and Cr resistance of Co3O4 nano-spinel coating, the performance of SUS430 substrate and ALD-Co3O4 nano-spinel coating was compared, which is further explained in the following figures.

[0017] 1. In order to verify that the oxidation resistance of the Co3O4-MnCo2O4 composite spinel coating is better than that of the MnCo2O4 single-layer spinel coating, the composite spinel coating prepared in this embodiment and the prepared MnCo2O4 single-layer spinel coating are heated to 800°C in an air environment, with a cycle process of 10 hours and a cyclic oxidation for 200 hours to simulate the aging process of the connector in the fuel cell under working conditions. The area ratio mass gain of the spinel coating after different aging periods is measured and the results are shown in Table 1.

[0018]

[0019] According to the results measured in Table 1, the oxidation kinetic curves of different spinel coatings and substrates were drawn (such as Figure 3 As shown), it can be found that: 1) In the early stage of oxidation (t<50h), on the one hand, since the oxide layer between the substrate and the coating is in the generation stage, the oxidation rate of the single-layer MnCo2O4 coating is slow; on the other hand, since the composite coating is heat treated with low oxygen partial pressure in Ar atmosphere, the Co3O4 layer is still oxidizing. The establishment of the oxide layer between the substrate and the Co3O4 layer, and between the Co3O4 layer and the spinel coating and the diffusion of elements lead to a faster oxidation rate at this stage and a larger weight gain; 2) With the growth of the oxide layer, the diffusion process of atoms is inhibited and the growth rate of the composite coating slows down. By comparing the SUS430 substrate, MnCo2O4 spinel coating and Co3O4-MnCo2O4 composite coating after cyclic oxidation at 800 ℃ in air atmosphere for 200 h, it is found that the area-to-weight gain curve of the Co3O4-MnCo2O4 composite coating is more stable after the early oxidation stage, and the oxidation weight gain per unit area is less than that of the substrate and the single-layer MnCo2O4 coating, which plays a significant role in improving the antioxidant properties of the substrate.

[0020] 2. In order to verify the strength of the conductive performance of the Co3O4-MnCo2O4 composite spinel coating, the Co3O4-MnCo2O4 composite spinel coating, the MnCo2O4 single-layer spinel coating and the SUS430 stainless steel substrate prepared in this embodiment were respectively tested for surface resistivity. The testing method is as follows: platinum slurry is brushed on both sides of the spinel coating to prepare two electrode contact layers of the same size, the electrodes of the surface resistivity measuring device are tightly fitted to the contact layer, and a current of 20 mA is applied to the device, which is then placed in a tube furnace and heated to the test temperature. According to the formula R=U / 2I; ASR = R·S, the surface resistivity values ​​of different spinel coatings after 200 h of cyclic oxidation are measured and calculated. The results are shown in Table 2.

[0021]

[0022] According to the results measured in Table 2, the ASR resistance of different spinel coatings after 200h cyclic oxidation is plotted as a function of temperature (e.g. Figure 4As shown in the figure, it can be found that: with the continuous increase of oxidation time, the ASR of the substrate and different spinel coating samples continues to increase. This is because the ASR is mainly related to the formation thickness of the oxide layer, and the oxide layer continues to grow with the increase of oxidation time. The ASR test results show that the resistance of the samples with spinel coating is lower than that of the substrate, and the resistivity of the Co3O4-MnCo2O4 composite coating is significantly lower than that of the MnCo2O4 coating. Ea reflects the energy barrier that the material needs to overcome during the conduction process. The larger the Ea, the larger the barrier, the lower the conductivity of the material, and the worse the conductivity. After 200h of cyclic oxidation, the activation energies of the single-layer MnCo2O4 spinel coating and the Co3O4-MnCo2O4 composite coating are 0.459 and 0.301 eV, respectively. The activation energy and ASR of the Co3O4-MnCo2O4 composite coating are smaller, thereby improving the conductive properties of the material.

[0023] 3. In order to verify the Cr-blocking performance of the Co3O4-MnCo2O4 composite spinel coating, the content of Cr on the 2p orbital of the sample surface was measured by XPS after the oxidation test of this embodiment. Figure 5 As shown, it can be concluded that the Cr content of the Co3O4-MnCo2O4 composite spinel coating after cyclic oxidation is less than that of the substrate and single-layer MnCo2O4 spinel coating, and it has better Cr resistance.

[0024] In summary, the present invention adopts the electrolytic deposition-electrophoretic deposition industry to prepare the Co3O4-MnCo2O4 composite spinel coating on the surface of the SUS430 substrate. Experiments have proved that the Co3O4-MnCo2O4 composite spinel coating has a uniform and dense composition, and is well bonded to the substrate, and can better improve the antioxidant and conductive properties of the connector, and has excellent Cr resistance. It is a good connector surface modification coating.

[0025] The above is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by a person skilled in the art within the technical scope disclosed by the present invention should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention shall be based on the protection scope of the claims.

Claims

1. A method for preparing a Co3O4-MnCo2O4 composite spinel coating on the surface of a metal interconnect substrate, characterized in that: The following steps are involved: S1. Preparation of MnCo2O4 spinel powder material by sol-gel process: S1-1, adding manganese nitrate tetrahydrate, cobalt nitrate hexahydrate and citric acid to deionized water to prepare a mixed solution, wherein citric acid is used as a complexing agent, the molar ratio of metal element Mn ions and Co ions in the mixed solution is 1:2, and the molar ratio of metal element ions to citric acid is 1:1.25; after the mixed solution is heated to 80° C., it is stirred at a stirring rate of 600 r / min to obtain a complex solution; S1-2, slowly drop ammonia water into the complex solution to adjust the pH value of the complex solution to 7-8 to obtain a precursor solution, and then continue heating and stirring for 4 hours while maintaining the heating temperature and stirring rate in step S1-1 to obtain a wet sol; S1-3, drying the wet sol prepared in step S1-2 at a drying temperature of 135°C and a drying time of 2h; after drying, sintering is performed at a sintering temperature of 800°C, a heating rate of 5°C / min, and a sintering time of 2h to obtain a MnCo2O4 spinel powder material for use in the subsequent step; S2. Preparing a Co3O4 layer on the surface of a metal interconnect substrate in a solid oxide fuel cell by an electrolytic deposition process, comprising the following steps: S2-1, substrate pretreatment: First, ferritic stainless steel is selected as the substrate of the metal connector, and a hole is drilled at the upper position of the substrate; then, the surface of the substrate is ground and polished; finally, the substrate is ultrasonically cleaned in acetone and anhydrous ethanol for 20 minutes in turn, and after the ultrasonic cleaning is completed, the substrate is immersed in alcohol for storage; S2-2. First, prepare a Co deposition electrolyte according to the following composition and its concentration ratio: CoCl2·6H2O: 40g / L, CoSO4·7H2O: 300g / L, H3BO3: 30g / L, sodium dodecyl sulfate: 0.03g / L; secondly, use boric acid and sodium bicarbonate to adjust the pH value of the Co deposition electrolyte to 4-5; thirdly, take out the substrate preserved in the alcohol in step S2-1, immerse it in a 10% H2SO4 solution for acid leaching to activate the substrate; finally, take out the substrate after acid leaching and place it in the Co deposition electrolyte for electroplating. The temperature of the Co deposition electrolyte is 25°C and the current density is 15mA·cm 2 , the electroplating time is 10min, and a pure Co layer is electroplated on the substrate surface; S2-3, after the electroplating in step S2-2 is completed, the sample is rinsed with deionized water and anhydrous ethanol in turn and blown dry, and then heated to 800°C, with a heating rate of 5°C / min and a holding time of 1h, so that the pure Co layer electroplated on the surface of the substrate is oxidized to a Co3O4 layer, thereby obtaining a substrate with a Co3O4 layer deposited on the surface; S3, using the MnCo2O4 spinel powder material obtained in step S1 as a raw material, further depositing a manganese-cobalt spinel coating on the substrate on which the Co3O4 layer is deposited by an electrophoretic deposition process, comprising the following steps: S3-1, preparing an electrophoretic suspension: mixing equal volumes of acetylacetone and ethanol as an electrophoretic suspension base liquid, using elemental iodine as a nuclear power regulator, adding the nuclear power regulator and the MnCo2O4 spinel powder material prepared in step S1 to the electrophoretic suspension base liquid, the mass volume ratio of the electrophoretic suspension base liquid, the nuclear power regulator and the spinel powder material being: 100 mL: 0.2 g: 1.5 g, to obtain an electrophoretic suspension; S3-2, electrophoretic suspension dispersion treatment: stirring the electrophoretic suspension prepared in step S3-1, maintaining the heating temperature of the electrophoretic suspension at 25° C. during stirring, the stirring rate at 500 r / min, and the stirring time at 15 min; after the stirring, the electrophoretic suspension is placed in an ultrasonic water bath for ultrasonic dispersion, and the ultrasonic dispersion time at 15 min; S3-3, using the substrate with the surface deposited Co3O4 layer prepared in step S2-3 as the cathode, using the ferritic stainless steel with a clean surface polished as the anode, using copper wire to suspend the cathode and the anode respectively and immerse them in the electrophoretic suspension after the ultrasonic dispersion treatment in step S3-2 for electrophoretic deposition, the voltage of the electrophoretic deposition is 75V~100V, the deposition time is 1min~2min, and further electrophoretically depositing a manganese-cobalt spinel coating on the surface of the substrate on which the Co3O4 layer has been deposited, to obtain a metal connector blank; S4. First, the metal connector blank obtained in step S3-3 is dried at a drying temperature of 80°C for 24 hours; then, it is sintered in an argon atmosphere at a sintering temperature of 950°C, a heating rate of 5°C / min, and a sintering time of 1 hour; finally, it is cooled to room temperature in the furnace to obtain a metal connector with a Co3O4-MnCo2O4 composite spinel coating on the surface.

2. The method for preparing a Co3O4-MnCo2O4 composite spinel coating on the surface of a metal interconnect substrate according to claim 1, characterized in that: In the step S2-1, the ferritic stainless steel is SUS430 ferritic stainless steel.

3. The method for preparing a Co3O4-MnCo2O4 composite spinel coating on the surface of a metal interconnect substrate according to claim 1, characterized in that: In the step S4, the thickness of the Co3O4-MnCo2O4 composite spinel coating on the surface of the metal interconnect is 50um-60μm.

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