Double-layer protective coating for metal connector of flat tube type solid oxide fuel cell as well as preparation method and application of double-layer protective coating

Abstract

The invention discloses a double-layer protective coating for a metal connector of a flat tube type solid oxide fuel cell as well as a preparation method and application of the double-layer protective coating, and relates to the technical field of protective coatings. The double-layer protective coating comprises a first protective coating and a second protective coating which are sequentially laminated on the base body; the first protective coating is made of spinel oxide; and the second protective coating is made of perovskite oxides. Through the double-layer protective coating, the conductivity of the protective coating can be effectively improved, and the protective coating can keep good contact and high compactness with the metal connector, so that a better protective effect is achieved, and volatilization of Cr in the metal connector under the high-temperature condition is effectively inhibited.

Description

Technical Field

[0001] The present invention relates to the technical field of protective coatings, and in particular to a double-layer protective coating for a flat tube solid oxide fuel cell metal connector, a preparation method thereof, and applications thereof. Background Art

[0002] Energy supply is a major issue facing society. Currently, energy is primarily derived from the combustion of fossil fuels, which has irreversible environmental impacts. Solid oxide fuel cells (SOFCs) are power generation devices that directly convert the chemical energy of fuel and oxidant into electrical energy. They offer clean, pollution-free operation, high energy conversion efficiency, and strong fuel adaptability, making them a promising new technology for achieving this energy supply transformation.

[0003] Solid oxide fuel cells (SOFCs) primarily consist of four components: cathode, anode, electrolyte, and interconnect. As fuel cell operating temperatures decrease, metal materials become feasible for use as interconnects. Metal interconnects effectively block the fuel gas from the anode and the oxidizing gas from the cathode, supporting the cell and stack structure. Furthermore, by connecting individual cells, they increase output voltage and current, thereby boosting battery power.

[0004] Currently, Fe-Cr alloys are widely used as interconnects in flat tubular solid oxide fuel cell stacks. However, in the operating environment of SOFCs (600°C-800°C), metal interconnects are susceptible to high-temperature oxidation, which intensifies the volatilization of Cr, leading to adverse consequences such as Cr poisoning of the electrodes and reduced battery performance. Therefore, a protective coating is required on the surface of the metal interconnect to inhibit oxidation, reduce the interfacial contact resistance between the metal interconnect and the electrode, and prevent the volatilization and deposition of Cr on the electrode surface.

[0005] Spinel oxides are widely used in interconnect coatings due to their excellent electrical conductivity, high oxidation resistance, and good thermal expansion compatibility with metal interconnects. However, most spinel oxides, such as Mn-Co spinel, suffer from low electrical conductivity. The electrical conductivity of spinel materials can be improved through element doping, but this increases the cost of coating preparation. Perovskite oxides, on the other hand, possess high high-temperature electrical conductivity and excellent thermal expansion compatibility with the interconnect alloy substrate and spinel oxides. In particular, they exhibit excellent chemical compatibility with adjacent SOFC electrode materials. Therefore, perovskite oxides are used as a second protective coating layer for metal interconnects, effectively improving the conductivity of the protective coating while maintaining good contact and high density with the metal interconnect. Furthermore, since perovskite oxides are often used as current collectors in flat tubular solid oxide fuel cell electrode materials, a dual protective coating can optimize the interfacial contact between the metal interconnect and the battery electrode, inhibit the toxicity of chromium volatilization to the electrode at high temperatures, and thus improve battery power, stability, and durability.

[0006] Prior art discloses electrophoretic deposition methods for metal interconnect coatings, which use acetylacetone as the electrophoretic suspension base, resulting in high costs and unsuitable for large-scale production. Prior art also discloses electrophoretic fluids for preparing manganese tetraoxide coatings, whose main components are one or more of methanol, ethanol, isopropanol, acetone, or acetylacetone. These organic solvents are relatively expensive and have the disadvantage of easily settling nanoparticles. Therefore, there is a need to develop a method that avoids the use of alcohol-ketone organic solvents as electrophoretic fluids, is low-cost, and is suitable for preparing metal interconnect coatings for flat tubular solid oxide fuel cells. Summary of the Invention

[0007] To address the shortcomings of the aforementioned background technology, the present invention provides a double-layer protective coating for the metal interconnects of flat tubular solid oxide fuel cells, as well as its preparation method and application. This coating is dense and uniform, effectively inhibiting the poisoning of electrodes by chromium volatilization at high temperatures, thereby increasing battery power and enhancing battery stability and durability. Furthermore, the coating preparation method is easy to implement, unconstrained by the complex structure of the interconnect, and is low-cost, amenable to large-scale production.

[0008] The first object of the present invention is to provide a double-layer protective coating for a flat tube solid oxide fuel cell metal connector, wherein the double-layer protective coating includes a first protective coating and a second protective coating stacked in sequence on a substrate; the material of the first protective coating is a spinel oxide; the material of the second protective coating is a perovskite oxide.

[0009] Preferably, the spinel oxide is one or more of Co-Mn, Cu-Mn, Ni-Mn and Ni-Fe. The perovskite oxide is one or more of lanthanum strontium iron, lanthanum strontium manganese, lanthanum strontium cobalt iron, lanthanum nickel iron, and lanthanum cobaltate series.

[0010] Preferably, the thickness of the double-layer protective coating is 10-30 μm.

[0011] Preferably, the substrate is a metal connector of a flat tube solid oxide fuel cell.

[0012] A second object of the present invention is to provide a method for preparing a double-layer protective coating for a metal interconnect of a flat tubular solid oxide fuel cell, comprising the following steps: Removing the oxide layer from the substrate; A first electrophoretic suspension is prepared using spinel oxides; A second electrophoretic suspension is prepared using perovskite oxides; Using the substrate with the oxide layer removed as the anode and the stainless steel plate as the cathode, electrophoretic deposition is performed in a first electrophoretic suspension to obtain a first protective coating on the substrate; The substrate containing the first protective coating is used as the anode and the stainless steel plate is used as the cathode. Electrophoretic deposition is carried out in the second electrophoretic suspension to prepare the second protective coating on the first protective coating. Subsequently, the second protective coating is calcined in air at 600-800°C for 2-5h to obtain a double protective coating on the substrate.

[0013] Preferably, the first electrophoretic suspension is prepared by dispersing spinel oxides in an electrophoretic base liquid; the second electrophoretic suspension is prepared by dispersing perovskite oxides in an electrophoretic base liquid; wherein the weight ratio of the spinel oxides in the first electrophoretic suspension is 2%-5%; the weight ratio of the perovskite oxides in the second electrophoretic suspension is 2%-5%. The electrophoresis base liquid is acrylic resin or epoxy resin, and the solid content is 65%-75%.

[0014] Preferably, when preparing the first protective coating or the second protective coating, the electrophoretic deposition voltage is 30V-50V, and the electrophoretic deposition time is 30s-60s.

[0015] Preferably, when preparing the first protective coating, after electrophoretic deposition, the coating is reduced in a 5%-10% H2 atmosphere at 600-800°C for 2-5 hours; when preparing the second protective coating, after electrophoretic deposition, the coating is reduced in a 5%-10% H2 atmosphere at 600-800°C for 2-5 hours.

[0016] Preferably, the substrate is a metal connector of a flat tube solid oxide fuel cell; The process of removing the oxide layer from metal interconnects includes: One or more of sodium hydroxide, sodium carbonate and sodium bicarbonate are compounded to prepare an electrolyte; One or more strong acids selected from hydrochloric acid, sulfuric acid, and nitric acid are compounded to prepare an acid solution; Place the metal connector in the electrolyte and electrolyze it at a current of 3-5A / dm -2 The metal connector surface is degreased for 1-2 minutes under the conditions of ; then immersed in acid solution and roughened at 30-50°C for 5-10 minutes.

[0017] The third object of the present invention is to provide an application of a double-layer protective coating in the protection of metal connectors of flat tube solid oxide fuel cells.

[0018] Compared with the prior art, the present invention has the following beneficial effects: The present invention provides a double-layer protective coating for a metal connector of a flat tube solid oxide fuel cell, and its preparation method and application. The double-layer protective coating for the metal connector in a flat tube solid oxide fuel cell prepared by the present invention does not use a traditional organic solvent as the electrophoretic suspension base liquid, but selects a low-cost aqueous polymer resin electrophoretic liquid, thereby reducing production costs and being suitable for large-scale production. In response to the problem of low electrical conductivity of spinel oxides, the present invention selects perovskite oxides with higher electrical conductivity as the second layer of protective material for the metal connector, which can not only effectively improve the electrical conductivity of the protective coating, but also maintain good contact and high density with the metal connector. At the same time, since perovskite oxides are often used as current collecting materials for flat tube solid oxide fuel cell electrode materials, the double-layer protective coating can optimize the interface contact effect between the metal connector and the battery electrode, inhibit the poisoning of the electrode by Cr volatilization at high temperature, improve battery power, and enhance the stability and durability of the battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 This is a surface SEM image of the double-layer protective coating of the metal connector in Example 1; Figure 2 The double-layer protective coating and cross-sectional SEM image of the metal connector in Example 1; Figure 3 The curves of the deposition amount and coating thickness of the metal interconnect under different deposition voltages during the electrophoretic deposition process in Example 3 are as follows; Figure 4 3 is the current variation curve of the metal interconnect under different deposition voltages during the electrophoretic deposition process in Example 3; Figure 5 The graph shows the change of the surface resistivity over time of the SUS 430 alloy substrate with a single MnCo2O4 spinel coating and the SUS 430 protected by a double-layer protective coating in Example 1 in an air atmosphere at 700°C. DETAILED DESCRIPTION

[0020] In order to enable those skilled in the art to better understand and implement the technical solution of the present invention, the present invention is further described below with reference to specific embodiments and drawings, but the embodiments are not intended to limit the present invention.

[0021] The present invention aims to provide a method for preparing a double-layer protective coating for a metal interconnect in a flat tube solid oxide fuel cell, comprising: applying an electrophoretic deposition method to prepare the double-layer protective coating for the metal interconnect, wherein the electrophoretic suspension is primarily composed of an aqueous polymer resin electrophoretic liquid, to which a coating protective material is added to obtain an electrophoretic deposition liquid; wherein the double protective coating comprises a first layer of a spinel oxide and a second layer of a perovskite oxide, and wherein the metal interconnect and the protective material are tightly bonded by step-by-step reduction-oxidation sintering. The present invention utilizes an electrophoretic deposition method to prepare the protective coating, which is not limited by the shape or structural strength of the metal interconnect. The double-layer protective coating can effectively improve the contact matching and electronic conductivity between the protective material and the metal interconnect, optimize the interfacial contact between the metal interconnect and the battery electrode, inhibit the poisoning of the electrode by Cr volatilization at high temperatures, increase battery power, and enhance battery stability and durability.

[0022] In order to achieve the above-mentioned objectives, the first aspect of the present invention provides a double-layer protective coating for a flat tube solid oxide fuel cell metal connector, wherein the double-layer protective coating includes a first protective coating and a second protective coating stacked in sequence on a substrate; the material of the first protective coating is a spinel oxide; the material of the second protective coating is a perovskite oxide.

[0023] The present invention involves the preparation of a double-layer protective coating for metal interconnects. Specifically, the coating comprises two layers: a first layer of spinel oxide and a second layer of perovskite oxide. First, the spinel oxide bonds with the metal interconnect under high-temperature conditions to form the first protective coating. This layer not only provides protection but also increases surface roughness, improving the adhesion of the second coating layer. Next, the perovskite oxide is applied over the first coating layer via an electrophoretic deposition process. Because the spinel oxide and the perovskite oxide form a strong bond during high-temperature sintering, the adhesion between the two coating layers is significantly enhanced. The spinel oxide has good thermal expansion compatibility with the metal interconnect, while the perovskite oxide exhibits high high-temperature electrical conductivity. Therefore, the double-layer protective coating effectively enhances the electrical conductivity of the protective coating while maintaining good contact and high density with the metal interconnect, thereby providing enhanced protection and effectively inhibiting the volatilization of chromium from the metal interconnect under high-temperature conditions.

[0024] Wherein, the spinel oxide is one or more of Co-Mn system, Cu-Mn system, Ni-Mn system, and Ni-Fe system; The perovskite oxide is one or more of lanthanum strontium iron, lanthanum strontium manganese, lanthanum strontium cobalt iron, lanthanum nickel iron, and lanthanum cobaltate series.

[0025] The thickness of the double-layer protective coating is 10-30 μm.

[0026] The matrix is ​​a metal connector of a flat tube solid oxide fuel cell.

[0027] A second aspect of the present invention provides a method for preparing a double-layer protective coating for a metal interconnect of a flat tubular solid oxide fuel cell, comprising the following steps: Removing the oxide layer from the substrate; A first electrophoretic suspension is prepared using spinel oxides; A second electrophoretic suspension is prepared using perovskite oxides; Using the substrate with the oxide layer removed as the anode and the stainless steel plate as the cathode, electrophoretic deposition is performed in a first electrophoretic suspension to obtain a first protective coating on the substrate; The substrate containing the first protective coating is used as the anode and the stainless steel plate is used as the cathode. Electrophoretic deposition is carried out in the second electrophoretic suspension to prepare the second protective coating on the first protective coating. Subsequently, the second protective coating is calcined in air at 600-800°C for 2-5h to obtain a double protective coating on the substrate.

[0028] The present invention uses an electrophoretic deposition method to prepare a double-layer protective coating for a metal connector. The main component of the electrophoretic suspension is an aqueous polymer resin electrophoretic liquid, to which a coating protective material is added to obtain an electrophoretic deposition liquid. The double protective coating comprises a first layer of a spinel oxide and a second layer of a perovskite oxide. The metal connector and the protective material are tightly bonded by step-by-step reduction-oxidation sintering. The present invention uses an electrophoretic deposition method to prepare the protective coating, which is not limited by the shape and structural strength of the metal connector. The double-layer protective coating can effectively improve the contact matching and electronic conductivity between the protective material and the metal connector, optimize the interface contact effect between the metal connector and the battery electrode, inhibit the poisoning of the electrode by Cr volatilization at high temperature, increase battery power, and enhance the stability and durability of the battery.

[0029] The present invention does not use traditional organic solvents (alcohols, ketones) as the main component of the electrophoretic suspension, but uses water-based polymer resin electrophoretic paint, which reduces production costs and is suitable for large-scale production.

[0030] The first electrophoretic suspension is prepared by dispersing spinel oxides in an electrophoretic base liquid; the second electrophoretic suspension is prepared by dispersing perovskite oxides in an electrophoretic base liquid; the weight ratio of the spinel oxides in the first electrophoretic suspension is 2%-5%; the weight ratio of the perovskite oxides in the second electrophoretic suspension is 2%-5%. The electrophoresis base liquid is acrylic resin or epoxy resin, and the solid content is 65%-75%.

[0031] When preparing the first protective coating or the second protective coating, the electrophoretic deposition voltage is 30V-50V, and the electrophoretic deposition time is 30s-60s.

[0032] When preparing the first protective coating, after electrophoretic deposition, the coating is reduced at 600-800°C and 5-10% H2 atmosphere by volume for 2-5 hours; when preparing the second protective coating, after electrophoretic deposition, the coating is reduced at 600-800°C and 5-10% H2 atmosphere by volume for 2-5 hours.

[0033] According to the present invention, the substrate is a metal connector of a flat tube solid oxide fuel cell; The process of removing the oxide layer from metal interconnects includes: One or more of sodium hydroxide, sodium carbonate and sodium bicarbonate are compounded to prepare an electrolyte; One or more strong acids selected from hydrochloric acid, sulfuric acid, and nitric acid are compounded to prepare an acid solution; Place the metal connector in the electrolyte and electrolyze it at a current of 3-5A dm -2 The metal connector surface is degreased for 1-2 minutes under the conditions of ; then immersed in acid solution and roughened at 30-50°C for 5-10 minutes.

[0034] Exemplarily, a method for preparing a double-layer protective coating for a metal interconnect of a flat tubular solid oxide fuel cell comprises: The first step is to pre-treat the SUS430 metal connector to remove the oxide layer on the surface of the metal connector; The second step, preparing the first protective coating, involves adding spinel oxides to a water-based electrophoretic base solution and dispersing them evenly to create an electrophoretic suspension. Using the metal connector as the anode and the stainless steel plate as the cathode, electrophoretic deposition is performed in the suspension to create the first protective coating.

[0035] The third step is to perform reduction sintering on the first protective coating to obtain a metal connector with a spinel coating.

[0036] The fourth step involves preparing the second protective coating. A water-based polymer is used as the electrophoretic base liquid, and perovskite oxides are added and evenly dispersed to form an electrophoretic suspension. Using the spinel-coated metal connector as the anode and the stainless steel plate as the cathode, electrophoretic deposition is performed in the suspension to form the second protective coating.

[0037] Finally, the second protective coating is subjected to reduction sintering treatment to obtain a metal interconnect having a double protective coating of spinel and perovskite.

[0038] A third aspect of the present invention provides an application of a double-layer protective coating in protecting metal connectors of a flat tube solid oxide fuel cell.

[0039] It should be noted that the experimental methods used in the present invention are all conventional methods unless otherwise specified; the reagents and materials used are all commercially available unless otherwise specified.

[0040] Example 1 This embodiment provides a method for preparing a double-layer protective coating for a metal interconnect of a flat tubular solid oxide fuel cell, which specifically includes the following steps: The first step is to remove oil from the surface of the metal connector. First, weigh 50g of sodium hydroxide, 50g of sodium carbonate, and 50g of sodium bicarbonate, dissolve them in 1L of deionized water, and electrolyze them in a water bath at 80℃ and a current of 3A·dm -2 The metal connector surface was degreased for 2 minutes under the conditions of , and then completely rinsed with deionized water; 100 ml of hydrochloric acid, 200 ml of sulfuric acid, and 130 ml of nitric acid were dissolved in 1 L of deionized water, and the cleaned metal connector was immersed in the acid solution at 30 ° C for 10 minutes to roughen the surface, and then completely rinsed with deionized water.

[0041] In the second step, epoxy resin electrophoresis liquid with a solid content of 10% was used as the main component of the electrophoresis base liquid, and 50g·L -1 MnCo2O4 spinel oxide was ultrasonically mixed to obtain an electrophoretic suspension. Using the metal connector as the anode and the stainless steel plate as the cathode, electrophoretic deposition was performed in the suspension at a voltage of 40V for 30 seconds to obtain the first protective coating.

[0042] In the third step, the first layer of protective coating is subjected to reduction sintering treatment in an atmosphere of 5% H2 and 800°C to obtain a metal connector with a MnCo2O4 spinel coating.

[0043] In the fourth step, epoxy resin electrophoresis liquid with a solid content of 10% was used as the main component of the electrophoresis base liquid, and 50g·L -1 La 0.8 Sr 0.2 Co 0.2 Fe 0.8 O3 perovskite oxide was ultrasonically mixed to obtain an electrophoretic suspension. Using the spinel-coated metal interconnect as the anode and the stainless steel plate as the cathode, electrophoretic deposition was performed in the suspension at a voltage of 40 V for 30 seconds to obtain a second protective coating.

[0044] Finally, the double-layer protective coating was subjected to reduction sintering treatment, first sintered in 5% H2, 800℃ atmosphere for 2h, and then oxidized sintered in air atmosphere at 800℃ for 2h to obtain a double-layer protective coating with MnCo2O4 spinel and La 0.8 Sr 0.2 Co 0.2 Fe 0.8 Metal interconnects with O6 perovskite double barrier coating.

[0045] Figure 1 This is an SEM image of the surface of the metal interconnect with a double-layer protective coating prepared in this embodiment. Figure 2 This is the cross-sectional SEM image of the metal connector with double-layer protective coating prepared in this embodiment. Figures 1 and 2 It can be seen that the surface of the protective coating presents a dense structure and is tightly bonded to the metal connector, which is beneficial to improving the oxidation resistance of the metal connector and preventing the outward diffusion of Cr.

[0046] Example 2 This embodiment provides a method for preparing a double-layer protective coating for a metal interconnect of a flat tubular solid oxide fuel cell, which specifically includes the following steps: The first step is to remove oil from the surface of the metal connector. First, weigh 50g of sodium hydroxide, 50g of sodium carbonate, and 50g of sodium bicarbonate, dissolve them in 1L of deionized water, and electrolyze them in a water bath at 80℃ and a current of 3A·dm -2 The metal connector surface was degreased for 2 minutes under the conditions of , and then completely rinsed with deionized water; 100 ml of hydrochloric acid, 200 ml of sulfuric acid, and 130 ml of nitric acid were dissolved in 1 L of deionized water, and the cleaned metal connector was immersed in the acid solution at 30 ° C for 10 minutes to roughen the surface, and then completely rinsed with deionized water.

[0047] In the second step, an acrylic resin electrophoresis liquid with a solid content of 10% was used as the main component of the electrophoresis base liquid, and 50 g·L -1 NiFe2O4 spinel oxide was ultrasonically mixed to obtain an electrophoretic suspension. Using the metal connector as the anode and the stainless steel plate as the cathode, electrophoretic deposition was performed in the suspension at a voltage of 40V for 40 seconds to obtain the first protective coating.

[0048] In the third step, the first layer of protective coating is subjected to reduction sintering treatment in an atmosphere of 5% H2 and 800°C to obtain a metal connector with a NiFe2O4 spinel coating.

[0049] In the fourth step, an acrylic resin electrophoresis liquid with a solid content of 10% was used as the main component of the electrophoresis base liquid, and 50 g·L -1 LaNi 0.6 Fe 0.4O3 perovskite oxide was ultrasonically mixed to obtain an electrophoretic suspension. Using the spinel-coated metal interconnect as the anode and the stainless steel plate as the cathode, electrophoretic deposition was performed in the suspension at a voltage of 40 V for 40 seconds to obtain a second protective coating.

[0050] Finally, the double-layer protective coating was subjected to reduction sintering treatment, first sintered in 5% H2, 800℃ atmosphere for 2h, and then oxidized sintered in air atmosphere at 800℃ for 2h to obtain NiFe2O4 spinel and LaNi 0.6 Fe 0.4 Metal interconnects with O3 perovskite double barrier coating.

[0051] Example 3 This embodiment tests the deposition amount and coating thickness at different deposition voltages, and uses a digital multimeter to record the current changes during the deposition process. Taking the deposition of MnCo2O4 spinel oxide coating as an example, the specific steps include: Step 1: Degreasing the surface of the metal connector: First, weigh 50g of sodium hydroxide, 50g of sodium carbonate, and 50g of sodium bicarbonate, dissolve them in 1L of deionized water, and place them in a water bath at 80℃ and an electrolysis current of 3A dm -2 The metal connector surface was degreased for 2 minutes under the conditions of , and then completely rinsed with deionized water; 100 ml of hydrochloric acid, 200 ml of sulfuric acid, and 130 ml of nitric acid were dissolved in 1 L of deionized water, and the cleaned metal connector was immersed in the acid solution at 30 ° C for 10 minutes to roughen the surface, and then completely rinsed with deionized water.

[0052] In the second step, an acrylic resin electrophoresis liquid with a solid content of 10% was used as the main component of the electrophoresis base liquid, and 50 g·L -1 The MnCo2O4 spinel oxide was ultrasonically mixed to obtain an electrophoretic suspension. Using the metal connector as the anode and the stainless steel plate as the cathode, electrophoretic deposition was performed in the suspension at a voltage of 10-100V and a deposition time of 60 seconds to obtain a MnCo2O4 spinel protective coating.

[0053] In the third step, the MnCo2O4 spinel protective coating is subjected to reduction sintering treatment in a 5% H2, 800°C atmosphere, and then oxidized and sintered in an air atmosphere at 800°C for 2 hours to obtain a metal connector with a MnCo2O4 spinel coating.

[0054] Figure 3 The deposition amount and coating thickness curves obtained for this example under different deposition voltages are shown in Figure 2. Figure 3As can be seen in the figure, during electrophoresis, when the voltage is low, the particle migration rate between the electrodes is slow, fewer particles reach the substrate, and the resulting coating thickness is small. As the voltage increases, the particles continue to migrate and deposit, and the resulting coating thickness gradually increases. When the deposition voltage exceeds 80V, the deposition weight and coating thickness decrease. This may be because the excessive voltage causes larger charged particles to deposit on the substrate surface, which is prone to agglomeration and shedding.

[0055] Figure 4 The current variation curves under different deposition voltages during electrophoretic deposition obtained in this example are as follows: Figure 4 It can be seen from the figure that at the beginning of the electrophoretic deposition process, the current is large, and as the deposition time increases, the current decreases until it reaches equilibrium.

[0056] Example 4 In this embodiment, a double-layer protective coating for a metal connector of a flat tube solid oxide fuel cell is used, and a "four-probe method" is used to perform surface resistivity testing on stainless steel with the coating.

[0057] The "four-probe method" was used to test the surface resistivity of the metal connector with a double-layer protective coating and the one with only a MnCo2O4 spinel coating in an air atmosphere to show the effect of the prepared double-layer protective coating on the conductive properties of the metal connector during high-temperature oxidation. On the alloy surface of the metal connector, silver paste was used to bond the silver mesh to the upper and lower surfaces of the workpiece, which served as voltage and current leads, respectively. Direct current was passed through both ends of the sample, and the voltage between the two voltage lines was measured by a digital multimeter to obtain the resistance value between the voltage lines at both ends of the sample (i.e., the digital multimeter reading). The surface resistivity of the sample can be calculated by the formula ASR=1 / 2(R*S). The test temperature was 700°C and the test time was 400h.

[0058] Figure 5 The following is a curve showing the change in surface resistivity over time in an air atmosphere at 700°C for a SUS 430 alloy substrate with a single MnCo2O4 spinel coating and the SUS 430 protected by a double-layer protective coating in Example 1. It can be seen from the test results that the surface resistivity of the double-layer protective coating is significantly lower than that of the single-layer coating. This is because the electrical conductivity of perovskite oxide is higher than that of spinel oxide. Therefore, after adding perovskite oxide to the surface, the electrical conductivity of the coating is improved, and its conductive properties are enhanced. In addition, under high temperature conditions, the double-layer coating has better compactness than the single-layer coating, exhibits stronger antioxidant ability, and exhibits excellent stability. This enables the double-layer coating to more effectively maintain its performance during long-term high-temperature use, reduces the rate of oxidation and degradation, thereby extending its service life, and has an important impact on improving the power of flat tube solid oxide fuel cells. While embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions, and variations may be made to these embodiments without departing from the principles and spirit of the invention, and that the scope of the invention is defined by the appended claims and their equivalents.

Claims

1. A double-layer protective coating for a flat tube solid oxide fuel cell metal connector, characterized in that: The double-layer protective coating includes a first protective coating and a second protective coating stacked in sequence on a substrate; the first protective coating is made of spinel oxide; the second protective coating is made of perovskite oxide.

2. The double-layer protective coating for the metal interconnect of a flat tube solid oxide fuel cell according to claim 1, characterized in that: The spinel oxide is one or more of Co-Mn, Cu-Mn, Ni-Mn and Ni-Fe; The perovskite oxide is one or more of lanthanum strontium iron, lanthanum strontium manganese, lanthanum strontium cobalt iron, lanthanum nickel iron, and lanthanum cobaltate series.

3. The double-layer protective coating for the metal interconnect of a flat tube solid oxide fuel cell according to claim 1, characterized in that: The thickness of the double-layer protective coating is 10-30 μm.

4. The double-layer protective coating for the metal interconnect of a flat tube solid oxide fuel cell according to claim 1, characterized in that: The matrix is ​​a metal connector of a flat tube solid oxide fuel cell.

5. A method for preparing a double-layer protective coating for a flat tubular solid oxide fuel cell metal interconnect according to any one of claims 1 to 4, characterized in that: The following steps are involved: Removing the oxide layer from the substrate; A first electrophoretic suspension is prepared using spinel oxides; A second electrophoretic suspension is prepared using perovskite oxides; Using the substrate with the oxide layer removed as the anode and the stainless steel plate as the cathode, electrophoretic deposition is performed in a first electrophoretic suspension to obtain a first protective coating on the substrate; The substrate containing the first protective coating is used as the anode and the stainless steel plate is used as the cathode. Electrophoretic deposition is carried out in the second electrophoretic suspension to prepare the second protective coating on the first protective coating. Subsequently, the second protective coating is calcined in air at 600-800°C for 2-5h to obtain a double protective coating on the substrate.

6. The method for preparing a double-layer protective coating for a flat tube solid oxide fuel cell metal interconnect according to claim 5, characterized in that: The first electrophoretic suspension is prepared by dispersing spinel oxides in an electrophoretic base liquid; the second electrophoretic suspension is prepared by dispersing perovskite oxides in an electrophoretic base liquid; wherein the weight ratio of the spinel oxides in the first electrophoretic suspension is 2%-5%; the weight ratio of the perovskite oxides in the second electrophoretic suspension is 2%-5%. The electrophoresis base liquid is acrylic resin or epoxy resin, and the solid content is 65%-75%.

7. The method for preparing a double-layer protective coating for a flat tube solid oxide fuel cell metal interconnect according to claim 5, characterized in that: When preparing the first protective coating or the second protective coating, the electrophoretic deposition voltage is 30V-50V, and the electrophoretic deposition time is 30s-60s.

8. The method for preparing a double-layer protective coating for a flat tube solid oxide fuel cell metal interconnect according to claim 5, characterized in that: When preparing the first protective coating, after electrophoretic deposition, the coating is reduced at 600-800°C and 5%-10% H2 atmosphere for 2-5 hours; when preparing the second protective coating, after electrophoretic deposition, the coating is reduced at 600-800°C and 5%-10% H2 atmosphere for 2-5 hours.

9. The method for preparing a double-layer protective coating for a flat tube solid oxide fuel cell metal interconnect according to claim 5, characterized in that: The substrate is a metal connector of a flat tube solid oxide fuel cell; The process of removing the oxide layer from metal interconnects includes: One or more of sodium hydroxide, sodium carbonate and sodium bicarbonate are compounded to prepare an electrolyte; One or more strong acids selected from hydrochloric acid, sulfuric acid, and nitric acid are compounded to prepare an acid solution; Place the metal connector in the electrolyte and electrolyze it at a current of 3-5A / dm -2 The metal connector surface is degreased for 1-2 minutes under the conditions of ; then immersed in acid solution and roughened at 30-50°C for 5-10 minutes.

10. Use of the double-layer protective coating according to any one of claims 1 to 4 in protecting metal connectors of flat tubular solid oxide fuel cells.

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