Preparation method of solid oxide fuel cell connector with coating

Abstract

The invention relates to a preparation method of a solid oxide fuel cell connector with a coating. The preparation method comprises the following steps: 1) performing compression molding on connector material powder to obtain a connector green body; (2) the connector green body is coated with the coating slurry, and the connector green body with a middle coating is obtained; the coating slurry contains manganese powder and cobalt powder; thirdly, the connector green body with the middle coating is sintered in vacuum or reducing atmosphere, and a sintered connector is obtained; and 4) carrying out oxidation treatment on the sintered connector in an oxidizing atmosphere to obtain the solid oxide fuel cell connector with the coating. The connector prepared by the preparation method disclosed by the invention has good mechanical properties, oxidation resistance and conductivity, and a coating is uniform in distribution, smooth in surface and free of cracks; and the preparation process is short, the production efficiency is high, and large-scale production is facilitated.

Description

Technical Field

[0001] The present invention relates to the field of solid oxide fuel cells, and particularly to a method for preparing a solid oxide fuel cell interconnect with a coating. Background Art

[0002] Fossil energy dominates China's energy structure and energy consumption, becoming a key issue affecting China's energy security and ecological environment. Therefore, seeking and developing efficient and clean new energy is of great significance for improving the energy structure, promoting green and low-carbon development, and driving the diversification of energy.

[0003] A solid oxide fuel cell (SOFC) is an energy conversion device that can directly convert fuel into electrical energy without combustion. The interconnect is one of the key components of a solid oxide fuel cell, and its functions are to separate fuel and oxidizing gas, provide electrical connection between cells, and distribute reaction gases to the electrodes. At the same time, the interconnect is in a high-temperature (600°C - 1000°C) and redox atmosphere for a long time, and the harsh working environment determines that the requirements for the material of the interconnect are extremely strict. Among many interconnect materials, ferritic stainless steel has become one of the most promising candidate materials for SOFC metal interconnects among all metal interconnects.

[0004] The preparation of ferritic stainless steel interconnects usually adopts a casting and rolling process. This process cannot form a complex airway on the end face in one step, and the subsequent machining process for the end face airway has disadvantages such as large processing difficulty and long production cycle, resulting in problems such as increased production cycle and low efficiency. In addition, the ferritic stainless steel interconnect will inevitably have problems such as thickening of the surface oxide film and increased battery internal resistance, as well as the problem of Cr element diffusion outside the interconnect and poisoning of the cathode under the actual operating conditions of the solid oxide fuel cell. In the face of the above problems, preparing ferritic stainless steel interconnects by powder metallurgy process and surface modification of the substrate by a protective coating is an effective method to solve the above problems.

[0005] There are currently several methods for preparing protective coatings: One is a method for preparing a metal connector of a solid oxide fuel cell. It obtains a steel plate raw material through rolling, processes it by wire cutting to obtain the shape required for the connector, then seals and splices it to obtain the metal connector, and finally needs to be machined to design the flow channel. However, the connector preparation method of this method has many processing steps, a cumbersome implementation operation process, and a low material utilization rate. Another is an electroplating preparation method for a copper-iron alloy coating of a solid oxide fuel cell connector. After plating the metal to be plated on the substrate material, it also needs to go through high-temperature reduction and oxidation processes, and finally a copper-iron alloy coating is obtained on the surface of the connector. The connector of this method needs to go through multiple high-temperature treatments, which undoubtedly increases the production cost, and the relevant properties of the substrate material will also deteriorate. There is also a method for preparing a connector material for a medium-temperature solid oxide fuel cell. It uses a method of coating with a coating slurry and then co-firing with the green body of the connector. However, this method uses screen printing technology. This method can improve the efficiency well for products with a flat surface, while the connector end face has a complex flow channel, and the screen printing process is prone to unevenness, resulting in uneven distribution of the coating in different regions, which will lead to poor coating performance and coating peeling.

[0006] Therefore, in view of a series of problems caused by the high-temperature oxidation reaction of ferritic stainless steel and some drawbacks of the existing connector and surface coating preparation processes, it is very necessary and urgent to research and develop a coating production process that can not only ensure good coating effects to obtain good performance, but also not significantly increase the production cost and is suitable for mass production. Summary of the Invention

[0007] In order to solve the problems of insufficient performance and complex preparation process of the connector of a solid oxide fuel cell with a coating in the existing technology, the present invention provides a method for preparing a connector of a solid oxide fuel cell with a coating. The preparation method has the advantages of simple preparation process, high efficiency and easy operation, can generate a spinel coating with uniform texture and density, and thereby improves the high-temperature oxidation resistance and mechanical properties of the connector. This method realizes one-time forming and inorganic processing of the connector, greatly improving the operation efficiency. The specific technical solutions are as follows:

[0008] A method for preparing a connector of a solid oxide fuel cell with a coating includes the following steps:

[0009] Step 1) Press the connector material powder into a mold to obtain a green body of the connector;

[0010] Step 2) Spray a coating slurry on the green body of the connector to obtain a green body of the connector with an intermediate coating; the coating slurry contains manganese powder and cobalt powder;

[0011] Step 3) Sinter the green body of the connector with the intermediate coating in a vacuum or reducing atmosphere to obtain a sintered connector;

[0012] Step 4) Heat and oxidize the sintered connector in an oxidizing atmosphere to obtain the solid oxide fuel cell connector with the coating.

[0013] Optionally, the connector material powder includes ferritic stainless steel pre-alloy powder;

[0014] Optionally, the connector material powder further includes paraffin wax; the mass fraction of paraffin wax in the connector material powder is 0.5-1%;

[0015] Optionally, in step 1), the connector powder is compacted at a pressure of 600-800 MPa;

[0016] Optionally, the ferritic stainless steel pre-alloy powder is prepared by a water atomization method;

[0017] Optionally, the density of the green body of the connector is 6.0 g / cm 3 -6.3 g / cm 3 .

[0018] Optionally, the coating slurry is prepared by the following method:

[0019] Mix manganese powder, cobalt powder with a solvent and grind them, then evaporate the solvent to obtain a manganese-cobalt mixed powder; then mix the manganese-cobalt mixed powder with an organic solution to obtain the coating slurry;

[0020] Optionally, the mass ratio of manganese powder to cobalt powder is 1:1-2;

[0021] Optionally, the solvent is ethanol, and the weight ratio of ethanol to the total weight of manganese powder and cobalt powder is 1-3:1;

[0022] Optionally, the grinding method is: mix manganese powder, cobalt powder with ethanol and perform ball milling, the ball milling speed is 100-300 r / min, and the time is 12-48 h.

[0023] Optionally,, the organic solution includes ethyl cellulose and terpineol; the mass ratio of ethyl cellulose to terpineol is 2-4:8-6;

[0024] Optionally, the mass ratio of ethyl cellulose to terpineol is 4:6.

[0025] Optionally, the spraying method is ultrasonic spraying;

[0026] Optionally, the ultrasonic spraying includes: conveying the coating slurry into an ultrasonic disperser, setting the distance between the spray port of the ultrasonic disperser and the surface of the green body of the connector to 35-45 mm, and spraying the atomized coating slurry dispersed well onto the surface of the green body of the connector by using the air flow generated by a gas pressure of 3.5-4.5 MPa.

[0027] Optionally, the thickness of the coating is 20 μm - 100 μm.

[0028] Optionally, in step (ii), after spraying the coating slurry on the green body of the connector, drying is carried out. The drying temperature is 70 - 100 °C, and the drying time is 20 - 60 min.

[0029] Optionally, the sintering in step (iii) is carried out in a reducing atmosphere. The sintering temperature is 1100 - 1200 °C, and the sintering time is 3 - 5 h.

[0030] Optionally, the reducing atmosphere is a mixed atmosphere of hydrogen and nitrogen, and the volume ratio of hydrogen to nitrogen is 1 - 5:99 - 95.

[0031] Optionally, in step (iv), the sintered connector is subjected to a heat oxidation treatment in air. The heat oxidation treatment temperature is 600 °C - 800 °C, and the time is 1 - 3 h.

[0032] Optionally, the density of the solid oxide fuel cell connector with a coating is 6.9 g / cm 3 - 7.1 g / cm 3 。

[0033] The present invention also provides a solid oxide fuel cell connector with a coating prepared by the above preparation method.

[0034] Compared with the prior art, the present invention has the following advantages:

[0035] The present invention provides a method for preparing a solid oxide fuel cell connector with a coating. In the method of the present invention, preparing a green body by powder metallurgy process can improve material utilization rate, reduce subsequent machining, solve the problems of difficult processing and long preparation cycle of the connector material prepared by casting and rolling processes, and at the same time, the powder metallurgy process is more efficient. The present invention uses spraying technology to coat the coating, which has the advantages of low energy consumption, high material utilization rate, environmental friendliness, uniform coating and not easy to fall off for preparing a protective coating on the complex end-face air channels on the surface of the solid oxide fuel cell connector. The method of the present invention adopts a synchronous sintering process for the green body and the coating. Synchronous sintering can make the interface between the coating and the connector matrix more tightly combined, reducing defects and voids at the interface. This enhanced bonding force helps to improve the adhesion and stability of the coating, preventing the coating from peeling or cracking during use. Moreover, the synchronous sintering process can reduce the number of sintering times of the connector matrix, so that the thermal shock and mechanical stress suffered by the connector during preparation are reduced, which helps to reduce the formation of internal defects and microcracks. Therefore, the mechanical strength of the connector is improved, and it can better withstand the mechanical load during operation. Finally, reducing the number of sintering times means simplifying the preparation process flow, which not only improves production efficiency but also reduces production costs. At the same time, the simplified preparation process helps to reduce variables and uncertainties during production, making the performance of the connector more stable and reliable.

[0036] The connector and coating prepared by the preparation method of the present invention are uniformly distributed, the surface is flat, without cracks, and have good mechanical properties, oxidation properties and electrical conductivity; moreover, the process flow is short, the production efficiency is high, which is conducive to large-scale production. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] In order to more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following will briefly introduce the drawings required for use in the description of the specific embodiments or the prior art. Obviously, the drawings in the following description are some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0038] Figure 1 It is the metallographic morphology diagram of the stainless steel connector in Example 5;

[0039] Figure 2 It is the tensile fracture morphology diagram of the stainless steel connector in Example 5;

[0040] Figure 3 It is the surface morphology diagram of the green body of the connector with an intermediate coating on the surface after ultrasonic spraying in Example 5;

[0041] Figure 4Surface morphology diagram of the manganese-cobalt spinel coating after oxidation at high temperature by introducing air in Example 5.

[0042] Figure 5 XRD spectrum of the surface of the prepared solid oxide fuel cell connector with a coating. Detailed implementation manners

[0043] To make the objectives, technical solutions and advantages of the present invention clearer, the embodiments of the present invention will be further described in detail below in conjunction with the accompanying drawings. Examples of the embodiments are shown in the drawings. The embodiments described below by referring to the drawings are exemplary and are only used to explain the present invention, and cannot be construed as limiting the present invention.

[0044] Example 1:

[0045] Step 1) Mix ferritic stainless steel powder and paraffin lubricant, with the addition ratio of the lubricant being 0.8%, and fully mix in a double-cone mixer for 45 min to obtain a uniformly mixed pre-alloy powder; the ferritic stainless steel powder used is prepared by a water atomization process; the main element composition of the ferritic stainless steel powder is: Cr: 22%, Ti: 0.3%, Nb: 0.5%, V: 0.05%, and the balance is Fe.

[0046] Step 2) Press the mixed pre-alloy powder at room temperature in a pressing die, with the applied pressing pressure being 800 MPa; after pressing, a green body of the connector is obtained, and the density of the green body is measured to be 6.1 g / cm 3 ;

[0047] Step 3) Mix manganese powder and cobalt powder in a mass ratio of 1:2, then add ethanol twice the mass of the mixed powder for mixing to obtain a manganese-cobalt mixed solution; then ball-mill the manganese-cobalt mixed solution in a ball mill at a rate of 200 r / min for 24 h to prepare a uniformly mixed manganese-cobalt powder ball-milling solution; after ball-milling is completed, take out the ball-milling solution and place it at 90 °C for 24 h to evaporate to remove the ethanol in the ball-milling solution to obtain a dried and uniformly mixed manganese-cobalt mixed powder; then compound ethyl cellulose and terpineol in a mass ratio of 4:6 to obtain a mixed solution; then mix the manganese-cobalt mixed powder with the above solution in a mass ratio of 1:1 uniformly to obtain a mixed slurry;

[0048] Step 4) Then use an injection pump to transport the manganese-cobalt mixed slurry to an ultrasonic disperser at a rate of 1.0 ml / min, set the distance between the spray nozzle and the surface of the green body to 40 mm, and use the airflow generated by a gas pressure of 4.0 MPa to spray the dispersed slurry mist onto the surface of the connector green body; during the spraying process, the high-pressure nozzle moves in a zigzag pattern, with a movement speed of 1 m / s and a width of 2.0 mm, and after spraying, it is fully dried at 90 °C for 30 min to obtain a green body of the connector with an intermediate coating;

[0049] Step 5) Place the green body of the connector with an intermediate coating on its surface into a high-temperature sintering furnace with an atmosphere of 5% hydrogen + 95% nitrogen. First, heat it from room temperature to 900°C at a heating rate of 5°C / min, then heat it from 900°C to 1100°C at a heating rate of 3°C / min, and sinter it at a constant temperature of 1100°C for 5 h.

[0050] Step 6) Subsequently, cool the high-temperature furnace to 600°C at a cooling rate of 3°C / min and keep it at a constant temperature for 3 h. Introduce air for oxidation at the beginning stage of the constant temperature. After the oxidation is completed, cool it to room temperature at a cooling rate of 3°C / min, and thus obtain the connector with a manganese cobalt spinel coating.

[0051] Perform performance tests on the solid oxide fuel cell connector and its coating prepared in this example. The test results are as follows: the density after sintering is 6.9 g / cm 3 ; the yield strength is 272 MPa; the tensile strength is 385 MPa; the oxidation temperature is 800°C, the oxidation duration is 300 h, and the oxidation weight gain is 4.6 mg / cm 2 when the oxidation atmosphere is air; the ASR data measured after 300 h is 25.58 mΩ·cm 2 .

[0052] Example 2:

[0053] Step 1) The same as Example 1;

[0054] Step 2) Press the mixed pre-alloy powder at room temperature in a pressing die, and the applied pressing pressure is 800 MPa; after pressing, obtain the green body of the connector, and the measured density of the green body is 6.1 g / cm 3 ;

[0055] Step 3) The same as Example 1;

[0056] Step 4) The same as Example 1;

[0057] Step 5) The same as Example 1;

[0058] Step 6) Subsequently, cool the high-temperature furnace to 800°C at a cooling rate of 3°C / min and keep it at a constant temperature for 3 h. Introduce air for oxidation at the beginning stage of the constant temperature. After the oxidation is completed, cool it to room temperature at a cooling rate of 3°C / min, and thus obtain the connector with a manganese cobalt spinel coating.

[0059] Perform performance tests on the solid oxide fuel cell connector prepared in this example. The test results are as follows: the density after sintering is 6.9 g / cm 3; The yield strength is 269 MPa; the tensile strength is 373 MPa; the oxidation temperature is 800 °C, the oxidation duration is 300 h, and the oxidation weight gain is 4.2 mg / cm when the oxidation atmosphere is air 2 ; The ASR data measured after 300 h is 21.26 mΩ·cm 2 .

[0060] Example 3:

[0061] Step 1) is the same as in Example 1;

[0062] Step 2) The mixed pre-alloyed powder is cold-pressed at room temperature in a pressing die, and the applied pressing pressure is 800 MPa; after pressing, a green body of the connector is obtained, and the green body density is measured to be 6.1 g / cm 3 ;

[0063] Step 3) is the same as in Example 1;

[0064] Step 4) is the same as in Example 1;

[0065] Step 5) is the same as in Example 1;

[0066] Step 6) Subsequently, the high-temperature furnace is cooled to 750 °C at a cooling rate of 3 °C / min and held at a constant temperature for 3 h. Air is introduced for oxidation at the beginning stage of the constant temperature. After the oxidation is completed, it is cooled to room temperature at a cooling rate of 3 °C / min, and a connector with a manganese cobalt spinel coating is obtained.

[0067] The performance of the solid oxide fuel cell connector prepared in this example is tested, and the test results are: the density after sintering is 7.0 g / cm 3 ; The yield strength is 255 MPa; the tensile strength is 386 MPa; the oxidation temperature is 800 °C, the oxidation duration is 300 h, and the oxidation weight gain is 3.5 mg / cm when the oxidation atmosphere is air 2 ; The ASR data measured after 300 h is 17.38 mΩ·cm 2 .

[0068] Example 4

[0069] Step 1) is the same as in Example 1;

[0070] Step 2) is the same as in Example 1;

[0071] Step 3) Mix manganese powder and cobalt powder in a mass ratio of 1:2, and then add ethanol twice the mass of the mixed powder for mixing to obtain a manganese-cobalt mixed solution; subsequently, ball-mill the manganese-cobalt mixed solution in a ball mill at a rate of 200 r / min for 24 h to prepare a uniformly mixed manganese-cobalt powder ball-milling solution; after the ball milling is completed, take out the ball-milling solution and place it at 60 °C for 24 h to evaporate to remove the ethanol in the ball-milling solution, obtaining a dried and uniformly mixed manganese-cobalt mixed powder; then compound ethyl cellulose and terpineol in a mass ratio of 2:8 to obtain a mixed solution; subsequently, mix the manganese-cobalt mixed powder and the above solution evenly in a mass ratio of 1:1 to obtain a mixed slurry; comparing the mixed slurry obtained when the mass ratio of ethyl cellulose to terpineol is controlled at 4:6 (Example 3), when its mass ratio is controlled at 2:8 (Example 4), the proportion of terpineol is too high, resulting in a relatively large overall viscosity of the obtained mixed slurry, which is not conducive to the subsequent spraying process.

[0072] Step 4) Subsequently, use an injection pump to transport the manganese-cobalt mixed slurry to an ultrasonic disperser at a rate of 1.0 ml / min, set the distance between the spray nozzle and the surface of the green body to 40 mm, and use the airflow generated by a gas pressure of 4.0 MPa to spray the dispersed slurry mist onto the surface of the green body of the connector; during the spraying process, the high-pressure nozzle moves in a zigzag pattern, with a movement speed of 1 m / s and a width of 2.0 mm. After spraying, the green body of the connector with an intermediate coating is obtained after sufficient drying at 90 °C for 30 min;

[0073] Step 5) The same as Example 1;

[0074] Step 6) Subsequently, cool the high-temperature furnace to 750 °C at a cooling rate of 3 °C / min and keep it at a constant temperature for 3 h. At the beginning stage of the constant temperature, introduce air for oxidation. After the oxidation is completed, cool it to room temperature at a cooling rate of 3 °C / min, and then a connector with a manganese-cobalt spinel coating is obtained.

[0075] Perform performance tests on the solid oxide fuel cell connector prepared in this example. The test results are as follows: the density after sintering is 6.9 g / cm 3 ; the yield strength is 261 MPa; the tensile strength is 381 MPa; the oxidation temperature is 800 °C, the oxidation duration is 300 h, and the oxidation weight gain is 5.1 mg / cm 2 when the oxidation atmosphere is air; the ASR data measured after 300 h is 28.57 mΩ·cm 2 .

[0076] Comparing Example 3 and Example 4 above, it can be seen that the organic solvent prepared by compounding ethyl cellulose and terpineol in a mass ratio of 4:6 is more conducive to ultrasonic spraying. The manganese-cobalt spinel coating obtained through subsequent steps has relatively better performance. Specifically, see Examples 3 and 4 in Table 2. Because terpineol has a relatively large viscosity, its viscosity at room temperature is about 60 times that of water. When its proportion is controlled at 60%, it can prevent the settlement of manganese and cobalt metal powders with relatively large densities, help the slurry maintain stability, and is conducive to achieving better results in the ultrasonic spraying process. When its proportion is controlled at 80%, too high a content will cause the slurry viscosity to be too large, resulting in uneven discharge and uneven distribution during the spraying process, thus leading to poor coating effects.

[0077] Example 5

[0078] Step 1) is the same as in Example 1;

[0079] Step 2) is the same as in Example 1;

[0080] Step 3) Mix manganese powder and cobalt powder in a mass ratio of 1.5:1.5, then add ethanol twice the mass of the mixed powder for mixing to obtain a manganese-cobalt mixed solution; then ball-mill the manganese-cobalt mixed solution in a ball mill at a rate of 200 r / min for 24 h to prepare a uniformly mixed manganese-cobalt powder ball-milling solution; after ball-milling is completed, take out the ball-milling solution and place it at 90 °C for 24 h to evaporate to remove the ethanol in the ball-milling solution to obtain dry and uniformly mixed manganese-cobalt mixed powder; then compound ethyl cellulose and terpineol in a mass ratio of 4:6 to obtain a mixed solution; then mix the manganese-cobalt mixed powder and the above solution in a mass ratio of 1:1 uniformly to obtain a mixed slurry;

[0081] Step 4) is the same as in Example 1;

[0082] Step 5) is the same as in Example 1;

[0083] Step 6) Then reduce the temperature of the high-temperature furnace to 750 °C at a rate of 3 °C / min and keep it constant for 3 h. At the beginning stage of constant temperature, introduce air for oxidation. After oxidation is completed, reduce the temperature to room temperature at a rate of 3 °C / min to obtain a connector with a manganese-cobalt spinel coating.

[0084] Perform performance tests on the solid oxide fuel cell connector prepared in this example. The test results are as follows: the density after sintering is 6.9 g / cm 3 ; the yield strength is 276 MPa; the tensile strength is 396 MPa; the oxidation temperature is 800 °C, the oxidation duration is 300 h, and the oxidation weight gain is 3.2 mg / cm when the oxidation atmosphere is air 2 ; the ASR data measured after 300 h is 13.35 mΩ·cm 2 .

[0085] Example 6

[0086] Step 1) is the same as that in Example 1;

[0087] Step 2) Press the mixed pre-alloy powder at room temperature in a pressing die, and the applied pressing pressure is 800 MPa; after pressing, a green body of the connector is obtained, and the density of the green body is measured to be 6.0 g / cm 3 ;

[0088] Step 3) Mix manganese powder and cobalt powder in a mass ratio of 1.5:1.5, then add ethanol twice the mass of the mixed powder for mixing to obtain a manganese-cobalt mixed solution; then ball-mill the manganese-cobalt mixed solution in a ball mill at a rate of 200 r / min for 24 h to prepare a uniformly mixed manganese-cobalt powder ball-milling solution; after the ball milling is completed, take out the ball-milling solution and place it at 90 °C for 24 h to evaporate to remove the ethanol in the ball-milling solution to obtain dry and uniformly mixed manganese-cobalt mixed powder; then compound ethyl cellulose and terpineol in a mass ratio of 4:6 to obtain a mixed solution; then mix the manganese-cobalt mixed powder and the above solution in a mass ratio of 1:1 uniformly to obtain a mixed slurry;

[0089] Step 4) is the same as that in Example 1;

[0090] Step 5) Place the green body of the connector with an intermediate coating on the surface into a high-temperature sintering furnace in a vacuum atmosphere, first heat from room temperature to 900 °C at a heating rate of 5 °C / min, then heat from 900 °C to 1200 °C at a heating rate of 3 °C / min, and sinter at 1200 °C for 3 h at a constant temperature;

[0091] Step 6) Then cool the high-temperature furnace to 800 °C at a cooling rate of 3 °C / min and keep it at a constant temperature for 3 h. At the beginning stage of the constant temperature, introduce air for oxidation. After the oxidation is completed, cool to room temperature at a cooling rate of 3 °C / min, and a connector with a manganese-cobalt spinel coating is obtained.

[0092] Perform performance tests on the solid oxide fuel cell connector prepared in this example. The test results are as follows: the density after sintering is 6.6 g / cm 3 ; the yield strength is 249 MPa; the tensile strength is 370 MPa; the oxidation temperature is 800 °C, the oxidation duration is 300 h, and the oxidation weight gain is 3.9 mg / cm when the oxidation atmosphere is air 2 ; the ASR data measured after 300 h is 18.41 mΩ·cm 2 .

[0093] Comparing the above Examples 5 and 6, it can be seen that an atmosphere of 5% hydrogen + 95% nitrogen is more suitable for the sintering of the interconnect, and the density after sintering is relatively higher. Specifically, see Example 5 and Example 6 in Table 1. This is because 5% hydrogen + 95% nitrogen belongs to a reducing gas, which can effectively prevent the oxidation of metal particles and powders in the interconnect. Additionally, under the condition of a reducing atmosphere, the oxides on the surface of metal particles will be reduced to metals, and a clean metal surface will be formed on the surface of metal particles, which helps the progress of atomic diffusion, making the bonding between metal particles more firm, thereby improving the sintering effect of the interconnect.

[0094] Comparative Example 1

[0095] Step 1) is the same as in Example 1;

[0096] Step 2) Press the mixed pre-alloy powder at room temperature in a pressing die, and the applied pressing pressure is 800 MPa; after pressing, a green body of the interconnect is obtained, and the density of the green body is measured to be 6.2 g / cm 3 ;

[0097] Step 3) Place the green body of the interconnect directly into a high-temperature sintering furnace with an atmosphere of 5% hydrogen + 95% nitrogen. First, heat from room temperature to 900 °C at a heating rate of 5 °C / min, then heat from 900 °C to 1200 °C at a heating rate of 3 °C / min, and sinter at 1200 °C for 3 h; after sintering, an interconnect is obtained, and the density of the sintered sample is measured to be 7.1 g / cm 3 ;

[0098] Step 4) Mix manganese powder and cobalt powder in a mass ratio of 1:2, then add ethanol twice the mass of the mixed powder for mixing to obtain a manganese-cobalt mixed solution; subsequently, ball-mill the manganese-cobalt mixed solution in a ball mill at a rate of 200 r / min for 24 h to prepare a uniformly mixed manganese-cobalt powder ball-milling solution; after ball-milling is completed, take out the ball-milling solution and place it at 90 °C for 24 h to evaporate to remove the ethanol in the ball-milling solution, obtaining dried and uniformly mixed manganese-cobalt mixed powder; then compound ethyl cellulose and terpineol in a mass ratio of 4:6 to obtain a mixed solution; subsequently, mix the manganese-cobalt mixed powder and the above solution in a mass ratio of 1:1 uniformly to obtain a mixed slurry;

[0099] Step 5) Subsequently, spray the above coating slurry onto the surface of the interconnect using an ultrasonic spraying process, and after sufficient drying at 90 °C for 30 min, obtain an interconnect with an intermediate coating;

[0100] Step 6) Place the interconnect with an intermediate coating on its surface into a high-temperature sintering furnace with an atmosphere of 5% hydrogen + 95% nitrogen. First, heat from room temperature to 900 °C at a heating rate of 5 °C / min, then heat from 900 °C to 1200 °C at a heating rate of 3 °C / min, and sinter at 1200 °C for 3 h;

[0101] Step 7) Subsequently, the high-temperature furnace was cooled to 750 °C at a cooling rate of 3 °C / min and kept at a constant temperature for 3 h. Air was introduced for oxidation at the beginning stage of constant temperature. After the oxidation was completed, it was cooled to room temperature at a cooling rate of 3 °C / min, and the connector with a manganese cobalt spinel coating was obtained.

[0102] Performance tests were carried out on the solid oxide fuel cell connector and its coating prepared in this comparative example. The test results were as follows: the density after sintering was 7.0 g / cm 3 ; the yield strength was 226 MPa; the tensile strength was 324 MPa; the oxidation temperature was 800 °C, the oxidation duration was 300 h, and the oxidation weight gain was 8.1 mg / cm when the oxidation atmosphere was air. 2 ; the ASR data measured after 300 h was 40.12 mΩ·cm 2 .

[0103] Comparative Example 2

[0104] Step 1) The same as in Example 1;

[0105] Step 2) The mixed pre-alloy powder was cold-pressed into shape at room temperature in a pressing die, and the pressing pressure used was 800 MPa; the green body of the connector was obtained after pressing, and the density of the green body was measured to be 6.2 g / cm 3 ;

[0106] Step 3) The green body of the connector was directly placed into a high-temperature sintering furnace with an atmosphere of 5% hydrogen + 95% nitrogen. It was first heated from room temperature to 900 °C at a heating rate of 5 °C / min, and then heated from 900 °C to 1200 °C at a heating rate of 3 °C / min, and sintered at 1200 °C for 3 h; the connector was obtained after sintering, and the density of the sintered sample was measured to be 6.9 g / cm 3 ;

[0107] Step 4) Manganese powder and cobalt powder were mixed at a mass ratio of 1.5:1.5, and then ethanol twice the mass of the mixed powder was added for mixing to obtain a manganese cobalt mixed solution; subsequently, the manganese cobalt mixed solution was ball-milled in a ball mill at a rate of 200 r / min for 24 h to prepare a uniformly mixed manganese cobalt powder ball-milling solution; after the ball milling was completed, the ball-milling solution was taken out and placed at 90 °C for 24 h to evaporate to remove the ethanol in the ball-milling solution, and a dried and uniformly mixed manganese cobalt mixed powder was obtained; then ethyl cellulose and terpineol were compounded at a mass ratio of 4:6 to obtain a mixed solution; subsequently, the manganese cobalt mixed powder was mixed uniformly with the above solution at a mass ratio of 1:1 to obtain a mixed slurry;

[0108] Step 5) Subsequently, the above coating slurry was sprayed onto the surface of the sintered connector using an ultrasonic spraying process, and then fully dried at 90 °C for 30 min to obtain a connector with an intermediate coating;

[0109] Step 6) Place the connector with an intermediate coating on its surface into a high-temperature sintering furnace with an atmosphere of 5% hydrogen + 95% nitrogen. First, heat it from room temperature to 900°C at a heating rate of 5°C / min, then heat it from 900°C to 1200°C at a heating rate of 3°C / min, and keep it at a constant temperature of 1200°C for 3 h for sintering;

[0110] Step 7) Subsequently, cool the high-temperature furnace to 750°C at a cooling rate of 3°C / min and keep it at a constant temperature for 3 h. Introduce air for oxidation at the beginning stage of the constant temperature. After the oxidation ends, cool it to room temperature at a cooling rate of 3°C / min, and a manganese cobalt spinel coating is obtained on the surface of the connector.

[0111] Perform performance tests on the solid oxide fuel cell connector and its coating prepared in this comparative example. The test results are as follows: the density after sintering is 6.9 g / cm 3 ; the yield strength is 219 MPa; the tensile strength is 333 MPa; the oxidation temperature is 800°C, the oxidation duration is 300 h, and the oxidation weight gain is 6.8 mg / cm when the oxidation atmosphere is air 2 ; the ASR data measurement after 300 h is 35.91 mΩ·cm 2 .

[0112] Combining the experimental data of Comparative Example 1 and Comparative Example 2 above, it can be seen that the preparation method proposed by the present technology can obtain a connector with better mechanical properties, and the electrical performance index ASR during long-term service is also better than that of the above comparative examples. Specifically, see Examples 5 and 6 and Comparative Examples 1 and 2 in Tables 1 and 2. This is because the synchronous sintering process can reduce the number of sintering times of the matrix material, which can reduce the thermal shock and mechanical stress suffered by the connector during the preparation process, helping to reduce the formation of internal defects and microcracks; in addition, synchronous sintering of the green body of the connector and the coating can make the interfacial bonding between the coating and the connector matrix closer, reducing the defects and voids at the interface.

[0113] Comparative Example 3

[0114] Step 1) In this comparative example, the obtained manganese cobalt mixed slurry is placed above the screen printing plate by means of screen printing, and the slurry is scraped with appropriate force and angle so that the slurry leaks through the mesh holes onto the surface of the green body of the connector, and then dried at 90°C for 30 min to obtain a green body of the connector with an intermediate coating;

[0115] Step 2) Place the green body of the connector with an intermediate coating on its surface into a high-temperature sintering furnace with an atmosphere of 5% hydrogen + 95% nitrogen. First, heat it from room temperature to 900°C at a heating rate of 5°C / min, then heat it from 900°C to 1200°C at a heating rate of 3°C / min, and keep it at 1200°C for 3 h for sintering.

[0116] Step 3) Subsequently, cool the high-temperature furnace to 750°C at a cooling rate of 3°C / min and keep it at a constant temperature for 3 h. Introduce air for oxidation at the beginning stage of constant temperature. After the oxidation is completed, cool it to room temperature at a cooling rate of 3°C / min to obtain a manganese cobalt spinel coating.

[0117] It was found that, compared with the ultrasonic spraying process, the coating obtained by this method was unevenly distributed, and full coating of the coating could not be achieved at the complex air passages at the end face. Moreover, there were many cracks on the surface of the coating after sintering. After the oxidation experiment, there was a high oxidation weight gain and poor electrical properties, affecting the overall conductivity of the coating. When the oxidation temperature was 800°C, the oxidation duration was 300 h, and the oxidation atmosphere was air, its oxidation weight gain was 12.38 mg / cm 2 ; The ASR data measured after 300 h was 50.96 mΩ·cm 2 , showing poor conductivity.

[0118] Perform performance tests on the solid oxide fuel cell connector prepared in this comparative example. The test results are as follows: the density after sintering is 7.0 g / cm 3 ; The yield strength is 263 MPa; the tensile strength is 382 MPa.

[0119] Comparative Example 4

[0120] Step 1) In this comparative example, a ferritic stainless steel with the grade SUS430 is selected to manufacture the substrate of the solid oxide fuel cell connector. The substrate size is 25 mm x 25 mm x 1 mm. Grind the surface of the specimen successively with 150#, 400#, 800#, 1000#, and 1200# water sandpapers, and then ultrasonically clean and dry it with acetone and absolute ethanol in turn to remove the oxide layer and stains on the surface of the specimen.

[0121] Step 2) Mix manganese powder and cobalt powder in a mass ratio of 1.5:1.5, then add ethanol twice the mass of the mixed powder for mixing to obtain a manganese-cobalt mixed solution; subsequently, ball-mill the manganese-cobalt mixed solution in a ball mill at a rate of 200 r / min for 24 h to prepare a uniformly mixed manganese-cobalt powder ball-milling solution; after ball-milling is completed, take out the ball-milling solution and place it at 90 °C for 24 h to evaporate and remove the ethanol in the ball-milling solution to obtain dry and uniformly mixed manganese-cobalt mixed powder; then compound ethyl cellulose and terpineol in a mass ratio of 4:6 to obtain a mixed solution; subsequently, mix the manganese-cobalt mixed powder and the above solution in a mass ratio of 1:1 uniformly to obtain a mixed slurry;

[0122] Step 3) Subsequently, spray the above coating slurry onto the surface of the connector using an ultrasonic spraying process, and after sufficient drying at 90 °C for 30 min, obtain a connector with an intermediate coating;

[0123] Step 4) Place the connector with the intermediate coating on its surface into a high-temperature sintering furnace with an atmosphere of 5% hydrogen + 95% nitrogen, first heat it from room temperature to 900 °C at a heating rate of 5 °C / min, then heat it from 900 °C to 1200 °C at a heating rate of 3 °C / min, and sinter at 1200 °C for 3 h at a constant temperature;

[0124] Step 5) Subsequently, cool the high-temperature furnace to 750 °C at a cooling rate of 3 °C / min and keep it at a constant temperature for 3 h. Introduce air for oxidation at the beginning stage of constant temperature. After the oxidation is completed, cool it to room temperature at a cooling rate of 3 °C / min, and then obtain a connector with a manganese-cobalt spinel coating.

[0125] Perform performance tests on the solid oxide fuel cell connector and its coating prepared in this comparative example. The test results are as follows: the yield strength is 207 MPa; the tensile strength is 325 MPa; when the oxidation temperature is 800 °C, the oxidation duration is 300 h, and the oxidation atmosphere is air, its oxidation weight gain is 8.6 mg / cm 2 ; the ASR data measurement after 300 h is 39.31 mΩ·cm 2 . Comprehensive comparison of Comparative Example 4 and Example 5 shows that the relevant performance of the connector and coating prepared by the powder process through the synchronous sintering process is better than that of the traditional substrate. For specific data on Comparative Example 4 and Example 5, refer to Tables 1 and 2.

[0126] Comparative Example 5

[0127] Step 1) The same as in Example 1;

[0128] Step 2) The same as in Example 1;

[0129] Step 3) The same as in Example 1;

[0130] Step 4) The same as in Example 1;

[0131] Step 5) Place the green body of the connector with an intermediate coating on its surface into a high-temperature sintering furnace under an air atmosphere. First, heat it from room temperature to 900 °C at a heating rate of 5 °C / min, then heat it from 900 °C to 1200 °C at a heating rate of 3 °C / min, and sinter it at a constant temperature of 1200 °C for 3 h.

[0132] Step 6) After the sintering is completed, cool the high-temperature furnace to 600 °C at a cooling rate of 3 °C / min and keep it at a constant temperature for 3 h. After the oxidation is completed, cool it to room temperature at a cooling rate of 3 °C / min, and a connector with a manganese cobalt spinel coating is obtained.

[0133] Perform performance tests on the solid oxide fuel cell and its coating prepared in this comparative example. The results show that the density of the specimen sintered under an air atmosphere is extremely low, only 6.3 g / cm3, and there is serious oxidation on the surface of the specimen, specifically manifested as the specimen turning black after sintering; measure its yield strength to be only 178 MPa; the tensile strength is only 203 MPa. Due to the low density of the specimen, the mechanical properties are poor; when the oxidation temperature is 800 °C, the oxidation duration is 300 h, and the oxidation atmosphere is air, the oxidation weight gain data is very high, reaching 21.75 mg / cm2; the ASR data measured after 300 h is 92.68 mΩ·cm2.

[0134] By comparing the experimental situations and data of Example 1 and Comparative Example 5, it can be seen that sintering under a reducing atmosphere is crucial for the preparation of specimens. Under a reducing atmosphere, it is possible to prevent serious oxidation of the specimens during high-temperature sintering, and ensure the density and stability of the specimens; in addition, it is also verified that the preparation of the manganese cobalt spinel coating should first go through a reducing sintering process to remove metal oxides in the slurry, ensuring that the metal elements: Mn and Co can participate in subsequent oxidation reactions in an ideal state; then through an oxidation process, which is a key step in forming the spinel structure. It can promote the combination of manganese and cobalt in an appropriate oxidation state into the spinel structure, thereby endowing the coating with excellent electrical conductivity and other properties.

[0135] Test Example

[0136] Perform sintering density tests and room temperature tensile tests on the standard tensile specimens of the connectors made of stainless steel prepared in Examples 1, 2, 3, 4, 5, 6 and Comparative Examples 1, 2, 3, 4, 5 of this application. The test results of the properties of the obtained connectors are shown in Table 1:

[0137] Table 1

[0138]

[0139]

[0140] In addition, in order to measure the oxidation resistance and electrical properties of the spinel coating prepared by this solution, high-temperature oxidation experiments were carried out on the connectors prepared in Examples 1, 2, 3, 4, 5, 6 and Comparative Examples 1, 2, 3, 4, 5 of this application for up to 300 h, and the mass gain of each example and comparative example was recorded; two silver electrodes of the same size were prepared on both sides of the oxidized connector using a conductive paste mainly composed of silver, and the four-terminal resistance measurement method was used to measure the resistance value between the two electrodes of the connector after high-temperature oxidation. To evaluate the conductivity of the coating, the area specific resistance (ASR) of the coating at each temperature was calculated using the following formula:

[0141]

[0142] where R is the measured resistance and S is the area of the silver electrode.

[0143] According to the measurement results, the mass gain and area specific resistance of the connectors in the above examples and comparative examples are shown in Table 2:

[0144] Table 2

[0145] <![CDATA[Mass gain (mg·cm -2 )]]> <![CDATA[Surface specific resistance (mΩ·cm 2 )]]> Example 1 4.6 25.58 Example 2 4.2 21.26 Example 3 3.5 17.38 Example 4 5.1 28.57 Example 5 3.2 13.35 Example 6 3.9 18.41 Comparative Example 1 8.1 40.12 Comparative Example 2 6.8 35.91 Comparative Example 3 12.38 50.96 Comparative Example 4 8.6 39.31 Comparative Example 5 21.75 92.68

[0146] The morphology of the sample prepared in Example 5 was tested, as Figures 1 to 4 shown:

[0147] Figure 1 is the metallographic structure diagram of the connector specimen of the present invention, and it can be observed that its grains are fine and the structure is uniform;

[0148] Figure 2 is the tensile fracture morphology diagram of the connector specimen, and it can be observed that a large number of cleavage platforms are present, and its fracture mode is brittle fracture, showing good mechanical properties;

[0149] Figure 3 is the surface morphology diagram of the green body of the connector with an intermediate coating on the surface after ultrasonic spraying;

[0150] Figure 4 is the surface morphology diagram of the manganese cobalt spinel coating after oxidation at high temperature by introducing air, and it can be observed that a large number of regular octahedron structures are formed on the surface, that is, the manganese cobalt spinel coating was successfully prepared on the surface of the specimen through the process of first reduction and then oxidation;

[0151] Figure 5 is the XRD spectrum diagram of the surface after oxidation. The XRD spectrum diagram can strongly prove the successful preparation of the manganese cobalt spinel coating.

[0152] Obviously, the above embodiments are merely examples given for clear illustration and are not limitations on the implementation manners. For those of ordinary skill in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to enumerate all implementation manners here. And the obvious changes or modifications derived therefrom still fall within the protection scope of the present invention.

Claims

1. A method for preparing a solid oxide fuel cell interconnector having a coating, characterized in that: The steps include: Step 1) pressing the powder of the connector material into a shape to obtain a connector green body; Step 2) spraying a coating slurry on the connector green body to obtain a connector green body with an intermediate coating; the coating slurry comprises manganese powder and cobalt powder; Step 3) sintering the green body of the interconnector having the intermediate coating in a vacuum or reducing atmosphere to obtain a sintered interconnector; Step 4) heating and oxidizing the sintered interconnect in an oxidizing atmosphere to obtain the solid oxide fuel cell interconnect with the coating.

2. The method for preparing a solid oxide fuel cell interconnector having a coating according to claim 1, characterized in that: The connector material powder includes ferrite stainless steel pre-alloy powder; Preferably, the connector material powder further comprises paraffin wax; the mass fraction of the paraffin wax in the connector material powder is 0.5-1%; Preferably, in the step 1), the interconnect powder is pressed and formed at a pressure of 600 to 800 MPa; Preferably, the ferritic stainless steel pre-alloyed powder is prepared by a water atomization method; Preferably, the green density of the connector is 6.0 g / cm 3 -6.3g / cm 3 .

3. The method for preparing a solid oxide fuel cell interconnector having a coating according to claim 1, characterized in that: The coating slurry is prepared by the following method: Mixing manganese powder, cobalt powder and solvent and grinding them, then evaporating the solvent to obtain manganese-cobalt mixed powder; then mixing the manganese-cobalt mixed powder with an organic solution to obtain a coating slurry; Preferably, the mass ratio of manganese powder to cobalt powder is 1:1-2; Preferably, the solvent is ethanol, and the ratio of the weight of ethanol to the total weight of manganese powder and cobalt powder is 1 to 3:1; Preferably, the grinding method is: mixing manganese powder, cobalt powder and ethanol and performing ball milling, the ball milling speed is 100-300r / min, and the time is 12-48h.

4. The method for preparing a solid oxide fuel cell interconnector having a coating according to claim 1, characterized in that: The organic solution comprises ethyl cellulose and terpineol; the mass ratio of ethyl cellulose to terpineol is 2-4:8-6; preferably, the mass ratio of ethyl cellulose to terpineol is 4:

6.

5. The method for preparing a solid oxide fuel cell interconnector having a coating according to claim 1, characterized in that: The spraying method is ultrasonic spraying; Preferably, the ultrasonic spraying includes: conveying the coating slurry into an ultrasonic disperser, setting the distance between the ultrasonic disperser spray port and the surface of the connector green body to 35-45 mm, and using an air flow generated by an air pressure of 3.5-4.5 MPa to spray the dispersed coating slurry liquid mist onto the surface of the connector green body.

6. The method for preparing a solid oxide fuel cell interconnector having a coating according to claim 1, characterized in that: The thickness of the coating is 20 μm-100 μm.

7. The method for preparing a solid oxide fuel cell interconnector having a coating according to claim 1, characterized in that: In the step 2), the coating slurry is sprayed on the connector green body and then dried. The drying temperature is 70-100° C. and the drying time is 20-60 minutes.

8. The method for preparing a solid oxide fuel cell interconnector having a coating according to claim 1, characterized in that: In the step 3), the sintering is carried out in a reducing atmosphere, the sintering temperature is 1100-1200° C., and the sintering time is 3-5 hours; Preferably, the reducing atmosphere is a mixed atmosphere of hydrogen and nitrogen, and the volume ratio of hydrogen to nitrogen is 1-5:99-95.

9. The method for preparing a solid oxide fuel cell interconnector having a coating according to claim 1, characterized in that: In the step 4), the sintered interconnect is subjected to a heating oxidation treatment in air at a temperature of 600° C. to 800° C. for 1 to 3 hours; Preferably, the density of the solid oxide fuel cell connector with coating is 6.9 g / cm 3 -7.1g / cm 3 .

10. A solid oxide fuel cell interconnector having a coating layer obtained by the preparation method according to any one of claims 1 to 9.

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