Copper-manganese-iron spinel protective layer prepared by co-deposition electroplating and in-situ oxidation method, its preparation method, application and SOFC connector

Abstract

The present invention discloses a copper-manganese-iron spinel protective layer prepared by co-deposition electroplating and in-situ oxidation method, its preparation method and application, and a SOFC connector, which relates to the field of electrochemical technology. The method includes: S1. Conducting copper-manganese-iron co-deposition electroplating on a substrate in an electroplating solution to deposit an alloy coating on the surface of the substrate; S2. Conducting oxidation treatment on the substrate obtained in step S1 to convert the alloy coating into a copper-manganese-iron spinel protective layer. The present invention co-deposits and electroplates a uniform and dense copper-iron-manganese coating on the surface of stainless steel at a low current density, and prepares a uniform and dense (CuMnFe)3O4 spinel protective layer on the surface of stainless steel by oxidizing the alloy coating, preventing the oxidation of the stainless steel connector and preventing the volatilization of Cr from the stainless steel connector during high-temperature operation.

Description

Technical Field:

[0001] The present invention relates to the field of electrochemical technologies, and particularly to a copper-manganese-iron spinel protective layer prepared by co-deposition electroplating and in-situ oxidation method, a preparation method and application thereof, and a SOFC connector. Background Art:

[0002] With the development of industrialization, the energy crisis has become increasingly severe, and at the same time, the greenhouse effect caused by fossil fuels has also become increasingly serious. In order to get out of this dilemma, clean energy and renewable energy have become the focus of human research. A solid oxide fuel cell (SOFC) is an energy conversion device that directly converts chemical energy into electrical energy and is one of the most effective technologies to solve the environmental pollution problems caused by fossil fuels. At present, the single cell voltage developed is only about 0.7V, which is far from enough for the application of SOFC. The connector is used to connect battery units to isolate fuel gas from oxidizing gas. At present, ceramic materials are generally used as high-temperature connector materials. However, with the development of SOFC towards lower temperatures, the use of metal connectors has become possible. Compared with ceramic connectors, metal connectors have the advantages of low cost, easy processing, good thermoelectric performance, etc.

[0003] As one of the most commonly used metal connectors, stainless steel has the characteristics of strong corrosion resistance, high electrical conductivity and thermal conductivity. However, stainless steel is prone to oxidation during long-term operation at 600 - 800°C, resulting in an increase in interfacial resistance; moreover, the chromium element contained in stainless steel will also diffuse into the SOFC, leading to cathode chromium poisoning. Therefore, it is very necessary to prepare a protective layer on the surface of stainless steel to prevent its oxidation and the diffusion of chromium elements.

[0004] At present, the spinel protective layer commonly used for stainless steel connectors is mainly a binary metal spinel protective layer. For example, Li Yaohua et al. from Northeastern University prepared a (CuMn)3O4 spinel protective layer on the surface of SUS430 stainless steel by magnetron sputtering. After 168h of air oxidation at 800°C, it can be seen from the elemental line scan results of the cross-section that the volatilized Cr layer is about 5μm, and the area specific resistance is about 45mΩ·cm 2 ; Zhao Yongtao et al. from the University of Science and Technology of China prepared a CuFe2O4 spinel protective layer on the surface of SUS430 stainless steel by electroplating. After 1000h of air oxidation at 800°C, the Cr layer is about 2μm, and the area specific resistance is about 16mΩ·cm 2 . Therefore, the long-term thermal stability of traditional binary spinel protective layers needs to be improved.

[0005] In addition, since manganese is inexpensive, adding a certain amount of manganese to the protective layer can reduce the cost of the protective layer. However, since manganese is the metal with the most negative potential that can be electrolytically reduced from an aqueous solution, with a reduction potential of -1.42 V, it is very difficult to electroplate a manganese coating, and a large amount of hydrogen gas will be evolved at the cathode. Therefore, the electroplating conditions must be strictly controlled. The research on electroplating manganese and its alloy coatings mainly focuses on how to obtain a uniform and dense coating. In the prior art, a large current density (10 A / dm 2 or more) is generally used for electroplating to prepare a manganese alloy coating. However, too large a current density will cause problems such as edge burning, uneven electroplating, high porosity in the coating, and low manganese content.

[0006] CN117026320A discloses a method for preparing a (CuFeMn)3O4 spinel protective layer by separate electroplating and then oxidation, that is, first electroplating a copper coating, then preparing an iron-manganese coating on the copper coating, and then oxidizing to obtain a (CuFeMn)3O4 spinel protective layer. However, since copper and iron-manganese are in different coatings, during the oxidation process, the copper element in the copper coating cannot completely diffuse into the iron-manganese coating, resulting in a large amount of copper in the copper coating that may be in-situ oxidized to form copper oxide and cannot completely form a (CuFeMn)3O4 spinel phase, that is, the obtained (CuFeMn)3O4 spinel is not uniform enough.

[0007] Therefore, it is very necessary to find a spinel protective layer with long-term thermal stability and uniformity. Summary of the Invention:

[0008] In order to solve the problems in the prior art that the SOFC metal interconnect is prone to high-temperature oxidation and the Cr element diffuses to poison the cathode, the present invention uses a co-deposition electroplating method and an in-situ oxidation treatment method at a low current density to obtain a uniform, dense and strongly adherent copper-manganese-iron spinel protective layer on the SOFC metal interconnect, improving the service life of the SOFC and being suitable for industrial production and application.

[0009] The inventor of the present invention found that, compared with traditional binary spinels, (CuFeMn)3O4, as a new ternary composite metal oxide, has good electrothermal properties and better adhesion to the metal interconnect. Compared with Cu-Mn spinels, the doping of Fe can make the thermal expansion coefficients of the protective layer and the metal matrix more compatible to a large extent, increasing the stability of the protective layer; compared with Fe-Mn spinels, the incorporation of Cu improves the conductivity and corrosion resistance of the protective layer.

[0010] The technical problems to be solved by the present invention are realized by the following technical solutions:

[0011] One of the objects of the present invention is to provide a method for preparing a copper-manganese-iron spinel protective layer by co-deposition electroplating and in-situ oxidation method, the method comprising:

[0012] S1. Co - deposit electroplate copper, manganese and iron on the substrate in the electroplating solution to deposit an alloy coating on the surface of the substrate;

[0013] S2. Oxidize the substrate obtained in step S1 to convert the alloy coating into a copper - manganese - iron spinel protective layer.

[0014] The second object of the present invention is to provide a copper - manganese - iron spinel protective layer obtained by the above - mentioned method.

[0015] The third object of the present invention is to provide the application of the copper - manganese - iron spinel protective layer in an SOFC connector.

[0016] The fourth object of the present invention is to provide an SOFC connector, comprising a metal substrate and a protective layer coated on the surface of the metal substrate, and the protective layer is the above - mentioned copper - manganese - iron spinel protective layer.

[0017] The beneficial effects of the present invention are as follows:

[0018] 1. Under low current density, the present invention co - deposits and electroplates a uniform and dense copper - iron - manganese coating on the surface of stainless steel, with simple operation, and the coating thickness and purity are easy to control.

[0019] 2. By oxidizing the alloy coating, the present invention prepares a uniform and dense (CuMnFe)3O4 spinel protective layer on the surface of stainless steel.

[0020] 3. The present invention applies the (CuMnFe)3O4 spinel protective layer on the surface of a stainless - steel connector to prevent the stainless - steel connector from oxidation and prevent the Cr volatilization of the stainless - steel connector during high - temperature operation. Description of the drawings:

[0021] Figure 1 The surface SEM image and EDS image of the SOFC metal connector prepared for Comparative Example 5;

[0022] Figure 2 The surface SEM image and EDS image of the SOFC metal connector prepared for Example 3;

[0023] Figure 3 The surface SEM image and EDS image of the SOFC metal connector prepared for Example 1;

[0024] Figure 4 The optical photograph of the SOFC metal connector prepared for Comparative Example 6;

[0025] Figure 5 The cross - section SEM image of the SOFC metal connector prepared for Example 1;

[0026] Figure 6 SEM cross-sectional view of the SOFC metal connector prepared in Example 13;

[0027] Figure 7 SEM cross-sectional view of the SOFC metal connector prepared in Example 14;

[0028] Figure 8 XRD patterns of bare steel and the coated stainless steel prepared in Example 1 after being treated in air atmosphere at 800 °C for 100 h and 1000 h;

[0029] Figure 9 EDS line scan of the cross-section of bare steel after being treated in air atmosphere at 800 °C for 200 h;

[0030] Figure 10 EDS line scan of the cross-section of the coated stainless steel prepared in Example 1 after being treated in air atmosphere at 800 °C for 200 h and 1000 h;

[0031] Figure 11 Oxidation weight gain of the coated stainless steel prepared in Example 1 and bare steel after being treated in air atmosphere at 800 °C for 1000 h;

[0032] Figure 12 Variation relationship diagram of the area specific resistance with time of the coated stainless steel prepared in Example 1 and bare steel after being treated in air atmosphere at 800 °C for 1000 h;

[0033] Figure 13 SEM cross-sectional view of the SOFC metal connector prepared in Comparative Example 10;

[0034] Figure 14 SEM cross-sectional view and its line scan EDS diagram of the SOFC metal connector prepared in Comparative Example 11;

[0035] Among them, Figure 6 、 7 The coatings in 8, 11, 12, 14 are the protective layers, the substrates are 430 stainless steels, and the CuMnFeO4 coating is the (CuMnFe)3O4 spinel protective layer. Specific implementation mode:

[0036] In order to make the technical means, creative features, achieved purposes and effects of the present invention easy to understand, the present invention will be further elaborated below in conjunction with specific embodiments and diagrams.

[0037] The present invention provides a method for preparing a copper-manganese-iron spinel protective layer by co-deposition electroplating and in-situ oxidation method, and the method includes:

[0038] S1. Conduct copper-manganese-iron co-deposition electroplating on the substrate in the electroplating solution to deposit an alloy coating on the surface of the substrate;

[0039] S2. Oxidize the substrate obtained in step S1 to convert the alloy coating into a copper-manganese-iron spinel protective layer.

[0040] According to the present invention, the electroplating solution contains components with the following concentrations:

[0041]

[0042] The present invention has strict requirements for the content ratio of Cu 2+ in the electroplating solution. A slight adjustment of the concentration of Cu 2+ in the electroplating solution may cause a significant change in the copper content in the coating. For example, when the concentration of Cu 2+ increases, it will cause a significant increase in the copper content in the electroplated coating, and the manganese and iron contents in the corresponding coating will decrease significantly; this will further lead to: 1) Since the contents of iron and manganese decrease significantly, the content of copper oxide in the finally sintered coating is very high, while the content of spinel is very low; 2) The increase in the copper content also increases the cost of the coating.

[0043] Although the contents of Fe 2+ and Mn 2+ in the electroplating solution are excessive, the electroplating solution can be recycled, and only a certain amount of Cu 2+ needs to be supplemented during the next electroplating to achieve the recycling of the electroplating solution.

[0044] Preferably, the pH value of the electroplating solution is 3.5 - 5.5.

[0045] Preferably, the chelating agent is selected from at least one of sodium citrate, disodium ethylenediaminetetraacetate, and sodium tartrate.

[0046] Preferably, the buffer is selected from at least one of boric acid, phthalic acid, and sodium acetate.

[0047] Preferably, the activating agent is selected from at least one of ammonium chloride, hydroxylamine hydrochloride, and stannous chloride.

[0048] Preferably, the substrate is a metal substrate. It can be a stainless steel substrate or other types of metal substrates.

[0049] According to the present invention, the conditions for the co-deposition electroplating include: the current density is 1 - 10 A / dm 2 , and the electroplating time is 400 - 600 s.

[0050] In the present invention, if the current density of co - deposition electroplating is too high, the density of the alloy coating will become poor. Under preferred conditions, the current density of the co - deposition electroplating is 1 - 10 A / dm 2 , for example, it can be 1 A / dm, 2 A / dm 2 , 3 A / dm 2 , 4 A / dm 2 , 5 A / dm 2 , 6 A / dm 2 , 7 A / dm 2 , 8 A / dm 2 , 9 A / dm 2 , 10 A / dm 2 or any value within the range formed by any two of the above values. If the co - deposition electroplating time is too short, the thickness of the alloy coating will be small, and the copper - manganese - iron spinel coating formed after high - temperature oxidation cannot effectively prevent the escape of Cr in the connector; while if the electroplating time is too long, the thickness of the alloy coating will be too large, reducing the adhesion between the alloy coating and the connector, and the copper - manganese - iron spinel coating formed after high - temperature oxidation is likely to peel off from the connector. Under preferred conditions, the co - deposition electroplating time is 400 - 600 s, for example, it can be 400 s, 500 s, 600 s or any value within the range formed by any two of the above values.

[0051] According to the present invention, the conditions of the oxidation treatment include: the temperature is 700 - 900 °C and the time is 2 - 10 h. The alloy coating is transformed into a copper - manganese - iron spinel protective layer through the oxidation treatment.

[0052] The present invention also provides a copper - manganese - iron spinel protective layer obtained by the above - mentioned method.

[0053] The present invention also provides the application of the described copper - manganese - iron spinel protective layer in the SOFC connector.

[0054] The present invention also provides an SOFC connector, including a stainless - steel substrate and a protective layer coated on the surface of the stainless - steel substrate, and the protective layer is the above - mentioned copper - manganese - iron spinel protective layer. The type of the stainless - steel substrate can be known to those skilled in the art, including but not limited to 430 stainless steel.

[0055] The present invention will be described in detail below through specific examples.

[0056] In the following examples, the surface specific resistance (ASR) of the oxide film of the sample was measured using the "four-point method" (also known as the DC four-probe method). The upper and lower surfaces of the oxidized sample were coated with Ag paste, and after drying, an Ag film was formed to improve the electrical contact between the sample and the measuring device. The sample was clamped between two Ag meshes with two corundum rods and springs, and two Ag wires were led out from each Ag mesh and connected to a DC power supply and a voltmeter respectively. According to Ohm's law, the resistance is equal to the ratio of voltage to current. Since there is an oxide film layer on both the upper and lower surfaces of the sample, the resistance of a single-layer oxide film is:

[0057]

[0058] The calculation formula for ASR is:

[0059]

[0060] where U is the voltage of the oxide film, I is the current of the oxide film, and S is the contact area.

[0061] In the following examples, the oxidation weight gain parameter was measured by calculating the square of the oxidation weight gain per unit area based on the weight difference of samples oxidized at high temperature for different times. The specific method is as follows:

[0062] The dried stainless-steel connector was accurately weighed, and its mass m0 was recorded; then the stainless-steel connector was placed into a pre-heated crucible, and then the crucible was placed into a high-temperature muffle furnace for oxidation treatment in air at 800 °C for a certain period of time. After the oxidation treatment, the sample was placed in a desiccator and cooled to room temperature, and then accurately weighed again, and its mass m1 was recorded. The square of the oxidation weight gain was calculated according to Equation ①:

[0063]

[0064] In Equation ①, S is the area of the stainless-steel connector.

[0065] In the electroplating of the following examples, platinum electrodes (20 mm × 20 mm × 1 mm) were used as anodes, and 430 stainless steel (10 mm × 10 mm × 2 mm) was used as cathodes.

[0066] Before electroplating, 430 stainless steel was pretreated. The pretreatment process was: the 430 stainless steel was polished successively with 400-mesh, 600-mesh, 1000-mesh, and 2000-mesh sandpapers, and then placed in an alkaline solution for degreasing and pickling to remove the oxide film in turn; then ultrasonically cleaned successively with deionized water and absolute ethanol, and finally dried.

[0067] Example 1

[0068] S1. Co-deposit an electroplated alloy coating on the surface of 430 stainless steel, with a current density of 2 A / dm 2, the electroplating time was 600 s, and the composition of the electroplating solution was as follows:

[0069]

[0070] The pH value of the electroplating solution was adjusted to 5 with ammonia water / hydrochloric acid;

[0071] S2. Place the substrate obtained in step S1 in a muffle furnace, perform oxidation treatment at 800 °C for 10 h, and form a copper-manganese-iron spinel protective layer on the surface of 430 stainless steel, thus obtaining the SOFC metal connector.

[0072] Example 2 and Comparative Examples 1 to 4

[0073] Electroplating was carried out using the electroplating solution of Example 1, except for the Mn 2+ , Fe 2+ , Cu 2+ concentrations, as specifically shown in Table 1.

[0074] Take 3 pieces each of the plated stainless steels prepared in Example 2 and Comparative Examples 1 to 4 above, dissolve the plating layer with a 30% by volume aqueous nitric acid solution (note: 430 stainless steel does not dissolve in a 30% aqueous nitric acid solution), and perform elemental analysis on the obtained solution (excluding extreme values and taking the average); place the SOFC metal connectors obtained in Example 2 and Comparative Examples 1 to 4 in air at 800 °C for 1000 h (taking 3 samples for each example), and measure the area specific resistance respectively (excluding extreme values and taking the average), and the results are shown in Table 1.

[0075] Table 1

[0076]

[0077]

[0078] As can be seen from Table 1, the change in the molar ratio of Mn, Fe, and Cu fed in the electroplating solution will directly affect the contents of Mn, Fe, and Cu in the plating layer, thereby affecting the area specific resistance of the sample. The area specific resistance of the sample shows a trend of first decreasing and then increasing with the increase in Mn content. This may be because when the Mn content is too high, the content of manganese oxide in the protective layer increases, while when the Mn content is too low, the content of CuO in the protective layer increases, that is, the content of the ternary (CuFeMn)3O4 spinel phase in the protective layer decreases, resulting in a decrease in the long-term oxidation resistance of the protective layer and further leading to an increase in the area specific resistance of the protective layer.

[0079] When the molar ratio of Mn, Fe, and Cu in the plating layer is 1:1:1, the area specific resistance of the obtained spinel protective layer after oxidation at 800 °C for 1000 h is the smallest, that is, the connector obtained in Example 1 has excellent electrical conductivity.

[0080] Example 3 and Comparative Examples 5 - 6

[0081] Electroplating was carried out using the electroplating solution of Example 1, except for the electroplating time, as shown in Table 2 specifically.

[0082] Table 2

[0083] Electroplating time (s) Coating thickness (μm) SEM and EDS diagrams Example 1 600 14.2 Figure 3 Example 3 400 8.7 Figure 2 Comparative Example 5 200 4.1 Figure 1 Comparative Example 6 1800 21.3 Figure 4

[0084] It can be seen from Table 2 that the longer the electroplating time, the thicker the coating. Comparing Figures 1 - 4 It can be seen that under the condition of constant current density, with the prolongation of the electroplating time, the inhibitory effect of the spinel protective layer formed after the oxidation treatment of the coating on the volatilization of chromium elements in the matrix is enhanced. The effect is the best when the electroplating time is 600 seconds, and the protective layer shows peeling phenomenon when the electroplating time is 1800 seconds. Therefore, it is necessary to control the coating thickness by controlling the electroplating time, and then control the thickness of the protective layer. If the coating is too thin, it cannot effectively inhibit the volatilization of chromium elements; if the coating is too thick, it will increase the interfacial specific resistance, waste resources and increase energy consumption.

[0085] Examples 4 - 6 and Comparative Examples 7 - 9

[0086] Electroplating was carried out using the electroplating solution of Example 1, except for the current density, as shown in Table 3 specifically.

[0087] Table 3

[0088]

[0089] "-" in the table means not measured.

[0090] It can be seen from Table 3 that when the current density is lower than 1 A / dm 2 , the Mn content in the obtained coating is very low; when the current density is 2 A / dm 2 , the molar ratio of Mn, Fe, and Cu in the coating is 1:1:1 and the compactness of the protective layer is good ( Figure 5 ); when the current density is 5 A / dm 2 and 10 A / dm 2 , the compactness of the protective layer decreases significantly ( Figure 6 and Figure 7 ); when the current density is 20 A / dm 2 , the protective layer is prone to peeling. Therefore, the compactness of the coatings obtained when the current density is 1 - 10 A / dm 2 can all meet the use requirements, and the optimal current density is 2 A / dm 2 .

[0091] The stainless steel with coating prepared in Example 1 was treated in air atmosphere at 800 °C for 100 h and 1000 h, and then XRD measurement was carried out. It was compared with the XRD pattern of the stainless steel without coating (referred to as bare steel). The results are as Figure 8 shown.

[0092] From Figure 8 it can be seen that after the stainless steel with coating was treated in air atmosphere at 800 °C for 1000 h, Cr did not volatilize to the surface and remained as a pure copper-manganese-iron spinel protective layer with almost no impurity phase. This shows that the spinel protective layer formed after the coating is oxidized can effectively prevent the volatilization of Cr in the stainless steel.

[0093] The cross-section of the bare steel was subjected to EDS line scanning after being treated in air atmosphere at 800 °C for 200 h. The results are as Figure 9 shown. And the cross-section of the stainless steel with coating prepared in Example 1 was subjected to EDS line scanning after being treated in air atmosphere at 800 °C for 200 h and 1000 h. The results are as Figure 10 shown.

[0094] Combined with Figure 9 and Figure 10 it can be seen that after the bare steel was treated in air atmosphere at 800 °C for 200 h, the Cr layer volatilized from the surface has exceeded 6 μm, while after the stainless steel with coating was treated in air atmosphere at 800 °C for 1000 h, the Cr layer volatilized from the surface was only 1.6 μm. This further shows that the spinel protective layer formed after the coating is oxidized can effectively inhibit the volatilization of Cr in the stainless steel.

[0095] The oxidation weight gain of the stainless steel with coating prepared in Example 1 and the bare steel was measured after being treated in air atmosphere at 800 °C for 1000 h. The results are as Figure 11 shown.

[0096] From Figure 11 the left figure in it can be seen that within the first 50 h of the thermal cycle, the stainless steel with coating gained weight significantly faster. The reason is that the original coating was an electroplated pure metal phase, and at the beginning of the thermal cycle, it was a process of oxidizing from the pure metal phase to the spinel phase, so the weight gain was significantly more than that of the bare steel; during the thermal cycle from 200 h to 1000 h, the coating was basically completely transformed into a pure spinel phase, which had a good protective effect on the substrate, so the weight gain became much slower than that of the bare steel. In order to more clearly compare the weight gain rates of the bare steel and the stainless steel with protective layer during the thermal cycle from 200 h to 1000 h, the present invention plotted a graph of the square of the oxidation weight gain per unit area and the thermal cycle time, as shown in the right figure of Figure 11 . After fitting, the weight gain square rate K1 of the bare steel = 6.512 * 10 -13 g 2 ·cm -4 ·s-1 , while the square rate of weight gain K2 of the stainless steel with the protective layer is 5.450 * 10 - 14 g 2 ·cm -4 ·s -1 , and the difference in the square rate of weight gain between the two is nearly 12 times. This shows that the copper-manganese-iron spinel protective layer prepared by the present invention on stainless steel has very excellent antioxidant properties.

[0097] The plated stainless steel and the bare steel prepared in Example 1 were treated in an air atmosphere at 800 °C for 1000 h, and the change relationship of the surface specific resistance with time was measured. The results are as Figure 12 shown.

[0098] From Figure 12 it can be seen that for the bare steel under the 800 °C thermal cycle, the surface specific resistance at 100 h is 3.329 mΩ·cm 2 , increasing to 14.885 mΩ·cm at 600 h 2 , and as high as 30.696 mΩ·cm at 1000 h 2 ; while the surface specific resistances of the plated stainless steel at the same time points are 0.713 mΩ·cm 2 , 1.937 mΩ·cm 2 , 4.109 mΩ·cm 2 respectively. This shows that the copper-manganese-iron spinel protective layer prepared by the present invention on stainless steel has a good inhibitory effect on the increase of the surface specific resistance.

[0099] Comparative Example 10

[0100] The (CuFeMn)3O4 spinel protective layer was prepared by the cold spraying method as follows:

[0101] 1) Preparation of (CuFeMn)3O4 powder

[0102] S1. Dissolve 0.01 mol of Fe(NO3)3·9H2O, 0.01 mol of Cu(NO3)2·3H2O, and 0.01 mol of Mn(NO3)2·4H2O in 200 mL of deionized water to obtain Solution 1;

[0103] Dissolve 0.02 mol of citric acid and 0.01 mol of EDTA in 200 mL of deionized water, and adjust the pH to 6.5 with NH3·H2O to obtain Solution 2;

[0104] S2. Under stirring conditions, slowly add Solution 1 drop by drop to Solution 2 while maintaining the solution pH at 6.5. After the addition is complete, react the mixed solution at 25°C for 6 h, then stir it at a constant temperature of 80°C for 12 h to obtain a wet gel. Then, place the wet gel in an oven at 260°C and dry it for 12 h to obtain a dry gel;

[0105] S3. Place the dry gel in a muffle furnace and sinter it at 800°C for 10 h. After ball milling, obtain (CuFeMn)3O4 powder;

[0106] 2) Spray (CuFeMn)3O4 powder on the substrate

[0107] Prepare the (CuFeMn)3O4 powder into a spraying solution and spray it onto a 430 stainless steel (10 mm × 10 mm × 2 mm) sheet by cold spraying. Then, place it in a muffle furnace and treat it at 800°C for 2 h to obtain a 430 stainless steel sheet coated with a (CuFeMn)3O4 spinel protective layer, which is the connector.

[0108] The cross-sectional SEM image of the connector obtained in Comparative Example 10 is as Figure 13 shown, where Figure B is a partial enlarged view of the protective layer in Figure A. It can be seen from Figure 13 that the (CuFeMn)3O4 spinel protective layer prepared by the cold spraying method is porous and has a low density.

[0109] Comparative Example 11

[0110] According to the method disclosed in Example 1 of CN117026320A, a (CuFeMn)3O4 spinel protective layer was prepared on the SOFC metal connector by the method of layered electroplating and then oxidation. The cross-sectional SEM image and the line-scan EDS image of the obtained SOFC metal connector are as Figure 14 shown.

[0111] As Figure 14 shown, there is a copper-rich region in the (CuFeMn)3O4 spinel protective layer prepared by the method of layered electroplating and then oxidation. This may be because during the oxidation process, the copper element in the copper coating obtained by the first electroplating cannot completely diffuse into the iron-manganese composite coating, resulting in an uneven (CuFeMn)3O4 spinel protective layer.

[0112] In summary, the present invention obtains an alloy coating through co-deposition electroplating for the first time. Compared with layer-by-layer electroplating, the coating is denser, more uniform, has stronger adhesion, is green and energy-saving, and subverts the traditional concept that Mn must be electroplated at a high current density. Moreover, it can be seen from a series of test analyses that the copper-manganese-iron ternary spinel protective layer has extremely excellent protective effects on the stainless-steel connectors of solid oxide fuel cells, making it possible to industrialize the preparation of copper-manganese-iron ternary spinel on the surface of stainless-steel connectors through electroplating-oxidation method.

[0113] The foregoing has shown and described the basic principles, main features and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited by the above embodiments. The above embodiments and the descriptions in the specification only illustrate the principles of the present invention. Without departing from the spirit and scope of the present invention, the present invention will have various changes and improvements, and all these changes and improvements fall within the scope of the present invention claimed. The scope of the present invention claimed is defined by the appended claims and their equivalents.

Claims

1. A method for preparing a copper-manganese-iron spinel protective layer by co-deposition electroplating and in-situ oxidation method, characterized in that, The method includes: S1. Conducting co - deposition electroplating of copper, manganese, and iron on the substrate in the electroplating solution to deposit an alloy coating on the surface of the substrate; S2. Conducting oxidation treatment on the substrate obtained in step S1 to convert the alloy coating into a copper - manganese - iron spinel protective layer; The electroplating solution contains components with the following concentrations: Cu 2+ 0.003 to 0.0035 mol / L Fe 2+ 0.03 to 0.05 mol / L Mn 2+ 0.5 to 0.75 mol / L Chelating agent: 0.05 - 0.5 mol / L Buffering agent: 10 - 40 g / L Activator: 0.01 - 0.2 g / L; The conditions of the co-deposition electroplating include: the current density is 1~10 A / dm 2 , and the electroplating time is 400~600 s.

2. The method according to claim 1, wherein The pH value of the electroplating solution is 3.5 - 5.

5.

3. The method according to claim 1, wherein The chelating agent is selected from at least one of sodium citrate, disodium ethylenediaminetetraacetate, and sodium tartrate.

4. The method according to claim 1, wherein The buffering agent is selected from at least one of boric acid, phthalic acid, and sodium acetate.

5. The method according to claim 1, characterized in that, The activator is selected from at least one of ammonium chloride, hydroxylamine hydrochloride, and stannous chloride.

6. The method according to claim 1, wherein The substrate is a metal substrate.

7. The method according to claim 1, wherein The conditions of the oxidation treatment include: temperature of 700 - 900 °C and time of 2 - 10 h.

8. A copper - manganese - iron spinel protective layer obtained by the method according to any one of claims 1 - 7.

9. Application of the copper - manganese - iron spinel protective layer according to claim 8 in an SOFC interconnect.

10. An SOFC interconnect, comprising a metal substrate and a protective layer coated on the surface of the metal substrate, wherein the protective layer is the copper - manganese - iron spinel protective layer according to claim 9.

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