A composite coating for medium and low temperature SOFC connector and its preparation method

Abstract

The present invention discloses a composite coating for medium- and low-temperature SOFC connectors and its preparation method. The method comprises the following steps: first, mechanically mixing manganese powder, cobalt powder, and iron powder; then, pretreating the substrate surface, cold spraying, and low-temperature oxidation to obtain the composite coating. The Mn and Co in the coating are oxidized to form MnCo2O4, an effective high-temperature oxidation-resistant coating. The Fe element can regulate the thermal expansion coefficient of the composite coating to match that of the YSZ ceramic electrode. The coating exhibits excellent electrical and thermal conductivity, is easy to manufacture, and is low-cost.

Description

Technical Field

[0001] The present invention relates to the preparation of a protective coating, and more particularly to a composite coating for a medium- and low-temperature SOFC connector and a preparation method thereof. Background Art

[0002] With the development of social civilization and the rapid growth of the world's population, human demand for energy is also growing continuously. The excessive consumption of fossil fuels has produced a large amount of pollutants such as carbon dioxide, causing people to worry about environmental pollution and climate change.

[0003] Solid oxide fuel cells (SOFCs), using solid ion-conducting ceramics as their electrolyte, boast conversion efficiencies as high as 85%. They also offer advantages such as high fuel flexibility, low cost, safety and stability, and significantly reduced carbon emissions, holding great promise for development in energy conversion and storage. SOFCs exhibit slower material degradation at low to medium temperatures (500-800°C), resulting in lower operating costs and faster system switching speeds compared to high temperatures. Consequently, SOFC development is primarily targeting lower temperatures.

[0004] As an important component of SOFC, the interconnect not only connects the anodes and cathodes of adjacent cells and acts as a current collector, but also provides a channel for reactants and products, avoids direct contact between fuel gas and oxidant gas, and plays a supporting role. In order for SOFC to operate normally, the interconnect material must have both physical and electrical properties, excellent chemical stability and economy, and a thermal expansion coefficient that matches that of other battery components. Stainless steel has excellent electrical and thermal conductivity, a dense structure, low price, easy processing, excellent mechanical properties, and a thermal expansion coefficient that matches that of commonly used electrodes and electrolytes. However, under high-temperature operating conditions of 500-800°C, the alloy material will inevitably suffer from high-temperature oxidation and other problems, resulting in serious degradation of the battery stack performance.

[0005] Therefore, providing a composite coating for medium and low temperature SOFC connectors is an urgent problem to be solved by those skilled in the art. Summary of the Invention

[0006] In light of this, the present invention provides a composite coating for low- and medium-temperature SOFC connectors and a method for its preparation. The composite coating prepared by the present invention features high electrical and thermal conductivity, ease of manufacture, and low cost. It also exhibits excellent high-temperature oxidation resistance, and its thermal expansion coefficient matches that of the YSZ ceramic electrodes commonly used in low- and medium-temperature SOFCs.

[0007] In order to achieve the above object, the present invention adopts the following technical solutions:

[0008] A composite coating for a medium- and low-temperature SOFC connector contains manganese, cobalt, and iron.

[0009] Preferably, the coating contains 20-50% manganese, 40-60% cobalt, and 10-30% iron in atomic percentage.

[0010] The beneficial effects of the above technical solution are: the coating contains a variety of spinel oxides, and the thermal expansion coefficient of spinel MnCo2O4 at 800℃ is 9.7×10 -6 ℃ -1 The thermal expansion coefficient of spinel CoFe2O4 is 12.1×10 -6 ℃ -1 The thermal expansion coefficient of spinel MnFe2O4 is 12.5×10 -6 ℃ -1 , metal Fe is 12×10 -6 ℃ -1 The thermal expansion coefficient of the ceramic electrode YSZ is 10-12×10 -6 ℃ -1 The present invention contains no more than 30% Fe, utilizes the deformation of Fe to obtain a dense Fe-Mn-Co based composite coating, and simultaneously regulates the overall thermal expansion coefficient of the coating so that the thermal expansion coefficient of the coating matches that of the ceramic electrode YSZ.

[0011] Preferably, the atomic molar ratio of manganese to cobalt in the coating is 0.3-1:1.

[0012] The beneficial effect of the above technical solution is that the ideal product of the coating is Fe-doped MnCo2O4, and by limiting the atomic molar ratio of cobalt and manganese, it can be ensured that the main component of the oxidized cobalt manganese oxide is MnCo2O4.

[0013] The present invention also provides a method for preparing a composite coating for a medium- and low-temperature SOFC connector, comprising the following steps:

[0014] (1) mechanically mixing manganese powder, cobalt powder and iron powder according to the above ratio to obtain a mixed powder;

[0015] (2) pre-treating the surface of the connector, including polishing, chemical degreasing, ultrasonic cleaning, and drying;

[0016] (3) In a protective atmosphere, the mixed powder is cold sprayed onto the connector, and then low-temperature oxidation is performed to obtain a composite coating.

[0017] Preferably, the particle size distribution range of the manganese powder in step (1) is 10-60 μm, and the average particle size is 20-40 μm; the particle size distribution range of the cobalt powder is 10-60 μm, and the average particle size is 30-50 μm; the particle size distribution range of the iron powder is 10-70 μm, and the average particle size is 15-30 μm.

[0018] The beneficial effects of the above technical solution are: when the particle size of the metal powder is within the above range, it has excellent bonding strength when sprayed onto the connector and can achieve maximum deposition efficiency.

[0019] Preferably, the connector in step (2) is made of stainless steel.

[0020] Preferably, the protective atmosphere in step (3) is nitrogen, helium or a mixture of several thereof.

[0021] Preferably, the process parameters of the cold spraying in step (3) are: temperature of 400-700°C, pressure of 0.1-5MPa, powder feeding rate of 10-100g / min, spraying distance of 5-30mm, and spraying times of 3 times.

[0022] Preferably, the temperature of the low-temperature oxidation in step (3) is 200-300° C., and the time is 8-12 hours.

[0023] The beneficial effect of this technical solution is that the intermixed manganese and cobalt atoms in the coating diffuse into each other in air at 200-300°C and are oxidized by oxygen to form MnCo2O4 oxide, an effective high-temperature resistant coating. Furthermore, the lower temperature prevents the chromium in the substrate from diffusing and oxidizing into a non-conductive oxide.

[0024] As can be seen from the above technical solution, compared with the prior art, the present invention provides a composite coating for a medium- and low-temperature SOFC connector and a preparation method thereof, which has the following advantages:

[0025] (1) The present invention adopts a method of low-temperature oxidation after cold spraying to prepare the connector coating. The process temperature is lower than the 900℃-1100℃ of traditional chemical deposition CVD. The deposition efficiency is higher than that of CVD, the operation is simple, and the processing cost is lower.

[0026] (2) The composite coating of the present invention has the advantages of excellent electrical conductivity, high thermal conductivity, easy manufacturing and low cost, stable chemical composition, and can reduce the raw material purification process, improve efficiency and reduce cost.

[0027] (3) The thermal expansion coefficient of the interconnect and its coating should be similar to that of other battery components. If the thermal expansion coefficients of the interconnect and other battery components do not match, thermal stress will be generated within the medium- and low-temperature SOFC fuel cell during heating, causing the interconnect to warp and ultimately leading to catastrophic failure of the battery stack. The present invention adds 10-30% iron to match the thermal expansion coefficient of the composite coating with the YSZ ceramic electrode commonly used in medium- and low-temperature SOFCs, thereby avoiding the generation and residual thermal stress.

[0028] (4) The composite coating of the present invention has excellent high-temperature oxidation resistance after low-temperature oxidation treatment at 200-300°C. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are merely embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings without paying any creative work.

[0030] Figure 1 Schematic diagram of the cold spraying process of the composite coating of the present invention, wherein 1 is the initial position of the spray gun and 2 is the connector.

[0031] Figure 2 This is a scanning electron microscope microscopic morphology image of the composite coating of Example 1 of the present invention.

[0032] Figure 3 This is the X-ray diffraction pattern of the composite coating of Example 1 of the present invention.

[0033] Figure 4 The weight gain data of the ferritic stainless steel SUS430 joint body with and without coating in the embodiment of the present invention were oxidized in air at 800°C. DETAILED DESCRIPTION

[0034] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0035] Example 1

[0036] A composite coating for medium- and low-temperature SOFC connectors contains, by atomic percentage, 20% manganese, 50% cobalt, and 30% iron. The atomic molar ratio of manganese to cobalt in the coating is 0.4:1.

[0037] A method for preparing a composite coating for a medium- and low-temperature SOFC connector comprises the following steps:

[0038] (1) According to the above proportions, 14.732 g of manganese powder, 41.507 g of cobalt powder, and 21.510 g of iron powder were mechanically mixed for 8 hours to obtain a mixed powder;

[0039] The particle size distribution range of manganese powder is 10μm-50μm, with an average particle size of 32μm; the particle size distribution range of cobalt powder is 20μm-60μm, with an average particle size of 35μm; the particle size distribution range of iron powder is 10μm-30μm, with an average particle size of 19μm;

[0040] (2) A stainless steel connector with a surface size of 15 cm × 15 cm and a thickness of 5 mm was pretreated, including grinding and polishing, chemical degreasing, ultrasonic acetone cleaning, and drying;

[0041] (3) cold spraying the mixed powder onto the connector under a helium protective atmosphere, and then placing it in a muffle furnace for low-temperature oxidation to obtain a composite coating;

[0042] The process parameters of the cold spraying are: temperature of 470°C, pressure of 2.1 MPa, powder feeding rate of 60 g / min, spraying distance of 20 mm, and spraying times of 3 times;

[0043] The temperature of the low-temperature oxidation is 290° C. and the time is 9 hours.

[0044] The microscopic morphology of the composite coating prepared in this embodiment is as follows Figure 2 As shown, the average coating thickness is about 535 μm.

[0045] Figure 3 The XRD spectrum of this embodiment shows that the diffraction peaks of the XRD pattern of this coating (2θ=18.542°, 30.527°, 35.899°, 43.651°, 57.905°, 63.602°) show the diffraction peaks of the (111), (220), (111), (311), (400), (511), and (440) crystal planes of the MnCo2O4 spinel phase, indicating that the main component of this coating is MnCo2O4.

[0046] At high temperatures, the connector reacts with oxygen in the air to produce non-conductive oxides, such as nickel oxide and iron oxide. These oxides adhere to the connector surface, increasing its mass while reducing its electrical conductivity. The coating prepared in this example was oxidized at 800°C for 3600 hours, with an average weight gain of 1.134 mg / cm 2The average weight gain of uncoated ferritic stainless steel SUS430 in the same environment is 2.924 mg / cm 2 The results show that after 3600 hours in air at 800°C, the coating prepared in this embodiment has a much smaller weight gain due to oxidation than the uncoated ferritic stainless steel, and has good high-temperature oxidation resistance.

[0047] Example 2

[0048] A composite coating for SOFC interconnects contains, by atomic percentage, 25% manganese, 55% cobalt, and 20% iron. The atomic ratio of manganese to cobalt in the coating is 0.46:1.

[0049] A method for preparing a composite coating for a SOFC connector comprises the following steps:

[0050] (1) According to the above proportions, 25.715 g of manganese powder, 46.571 g of cobalt powder, and 14.310 g of iron powder were mechanically mixed for 8 hours to obtain a mixed powder;

[0051] The particle size distribution range of manganese powder is 10μm-50μm, with an average particle size of 25μm; the particle size distribution range of cobalt powder is 20μm-60μm, with an average particle size of 46μm; the particle size distribution range of iron powder is 10μm-30μm, with an average particle size of 25μm;

[0052] (2) A stainless steel connector with a surface size of 15 cm × 15 cm and a thickness of 5 mm was pretreated, including grinding and polishing, chemical degreasing, ultrasonic acetone cleaning, and drying;

[0053] (3) cold spraying the mixed powder onto the connector under a helium protective atmosphere, and then placing it in a muffle furnace for low-temperature oxidation to obtain a composite coating;

[0054] The process parameters of the cold spraying are: temperature of 490°C, pressure of 2.7 MPa, powder feeding rate of 65 g / min, spraying distance of 10 mm, and spraying times of 3 times;

[0055] The temperature of the low-temperature oxidation is 260° C. and the time is 10 hours.

[0056] The coating prepared in this example was oxidized at 800°C for 3600 hours, and the average weight gain was 0.765 mg / cm 2 The average weight gain of uncoated ferritic stainless steel SUS430 under the same environment is 2.924 mg / cm 2 The results show that after 3600 hours in air at 800°C, the coating prepared in this embodiment has a much smaller weight gain due to oxidation than the uncoated ferritic stainless steel, and has good high-temperature oxidation resistance.

[0057] Example 3

[0058] A composite coating for SOFC interconnects contains, by atomic percentage, 35% manganese, 50% cobalt, and 15% iron. The atomic ratio of manganese to cobalt in the coating is 0.7:1.

[0059] A method for preparing a composite coating for a SOFC connector comprises the following steps:

[0060] (1) According to the above proportions, 19.871 g of manganese powder, 42.592 g of cobalt powder, and 10.702 g of iron powder were mechanically mixed for 8 hours to obtain a mixed powder;

[0061] The particle size distribution range of manganese powder is 10μm-50μm, with an average particle size of 35μm; the particle size distribution range of cobalt powder is 20μm-60μm, with an average particle size of 34μm; the particle size distribution range of iron powder is 10μm-30μm, with an average particle size of 21μm;

[0062] (2) A stainless steel connector with a surface size of 15 cm × 15 cm and a thickness of 5 mm was pretreated, including grinding and polishing, chemical degreasing, ultrasonic acetone cleaning, and drying;

[0063] (3) cold spraying the mixed powder onto the connector under a helium protective atmosphere, and then placing it in a muffle furnace for low-temperature oxidation to obtain a composite coating;

[0064] The process parameters of the cold spraying are: temperature of 500°C, pressure of 1.5 MPa, powder feeding rate of 50 g / min, spraying distance of 15 mm, and spraying times of 3 times;

[0065] The temperature of the low-temperature oxidation is 240° C. and the time is 12 hours.

[0066] The coating prepared in this example was oxidized at 800°C for 3600 hours, and the average weight gain was 0.473 mg / cm 2 The average weight gain of uncoated ferritic stainless steel SUS430 under the same environment is 2.924 mg / cm 2 The results show that after 3600 hours in air at 800°C, the coating prepared in this embodiment has a much smaller weight gain due to oxidation than the uncoated ferritic stainless steel, and has good high-temperature oxidation resistance.

[0067] The various embodiments in this specification are described in a progressive manner, and each embodiment focuses on the differences from other embodiments. The same or similar parts between the various embodiments can be referenced to each other.

[0068] The above description of the disclosed embodiments is intended to enable one skilled in the art to implement or use the present invention. Various modifications to these embodiments will be readily apparent to one skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention is not limited to the embodiments shown herein but is intended to conform to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for preparing a composite coating for a medium- and low-temperature SOFC connector, characterized in that: The following steps are involved: (1) The coating contains, in atomic percentage, 20-50% manganese, 40-60% cobalt, and 10-30% iron; the atomic molar ratio of manganese to cobalt in the coating is 0.3-1:1; Mechanically mixing manganese powder, cobalt powder and iron powder according to the above proportions to obtain a mixed powder; (2) pre-treating the surface of the connector, including polishing, chemical degreasing, ultrasonic cleaning, and drying; (3) cold spraying the mixed powder onto the connector under a protective atmosphere, and then performing low-temperature oxidation to obtain a composite coating; The temperature of the low-temperature oxidation in step (3) is 200-300° C., and the time is 8-12 hours.

2. The method for preparing a composite coating for a medium- and low-temperature SOFC interconnect according to claim 1, characterized in that: The particle size distribution range of the manganese powder in step (1) is 10-60 μm, and the average particle size is 20-40 μm; the particle size distribution range of the cobalt powder is 10-60 μm, and the average particle size is 30-50 μm; the particle size distribution range of the iron powder is 10-70 μm, and the average particle size is 15-30 μm.

3. The method for preparing a composite coating for a medium- and low-temperature SOFC interconnect according to claim 1, characterized in that: The material of the connector in step (2) is stainless steel.

4. The method for preparing a composite coating for a medium- and low-temperature SOFC interconnect according to claim 1, characterized in that: The protective atmosphere in step (3) is one or a mixture of nitrogen and helium.

5. The method for preparing a composite coating for a medium- and low-temperature SOFC interconnect according to claim 1, characterized in that: The process parameters of the cold spraying in step (3) are: temperature of 400-700°C, pressure of 0.1-5MPa, powder feeding rate of 10-100g / min, spraying distance of 5-30mm, and spraying times of 3 times.

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