Preparation method of manganese-cobalt spinel coating for SOFC interconnect and coating

Abstract

The present application relates to the technical field of solid oxide fuel cell, in particular to a preparation method of manganese cobalt spinel coating for SOFC interconnector and the coating. It comprises substrate treatment, target cleaning, high power pulse magnetron sputtering deposition of MnCo alloy coating and thermal conversion to form (Mn, Co)3O4 spinel coating. The present application significantly improves the uniformity, compactness and high temperature oxidation resistance of the coating by optimizing the process parameters, and solves the problems of shadow effect and coating defects existing in traditional direct current magnetron sputtering. The obtained coating has a thickness of 4.8-5.3 μm, a surface roughness of less than 1 μm, and can effectively inhibit the outward diffusion of Cr element after long-term service at 800℃ for 840 hours, with an ASR value of less than 30 mΩ·cm². The preparation process of the present application is simple, suitable for industrial production, and has high practical value and popularization prospect.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of solid oxide fuel cells, and particularly relates to a preparation method of a (Mn,Co)3O4 spinel coating for a SOFC interconnect and the coating. BACKGROUND

[0002] A solid oxide fuel cell (SOFC) is a power generation device that converts chemical energy in fuel into electrical energy through an electrochemical reaction, has the characteristics of high energy utilization and clean pollution, and is an important part of a new generation of clean energy. The interconnect is an important component of the SOFC, which connects the cathode and the anode and separates the cathode and the anode atmosphere, and its performance affects the overall performance of the cell stack. The current SOFC operating temperature is 600-800 o C, which makes it possible for metal materials to become interconnect materials. Ferritic stainless steel has a similar thermal expansion coefficient to other components of the cell stack, good high-temperature oxidation resistance, and low cost, and is widely used as an SOFC interconnect material.

[0003] Although the ferritic stainless steel has the above advantages, because the Cr element content of the ferritic stainless steel is 16-20wt.%, the ferritic stainless steel will face the following problems during long-term service at high temperature and long-term operation at high temperature:

[0004] Cr2O3 generation problem: Cr2O3 oxide layer will be generated on the surface of the stainless steel, which has a certain protective effect, but its growth will consume chromium in the matrix and affect the long-term performance of the material;

[0005] Cr(Ⅵ) volatilization problem: at high temperature, Cr2O3 will volatilize to form toxic Cr(Ⅵ) gas, causing environmental pollution and safety hazards;

[0006] Cathode poisoning problem: the volatilized Cr(Ⅵ) will migrate to the cathode and react with the cathode material, causing the cathode performance to decrease and even fail.

[0007] In order to solve the above problems, the prior art mainly adopts the method of applying a high-conductivity high-temperature protective coating on the surface of the ferritic stainless steel to reduce the outward diffusion of Cr elements. Common coating types include active element oxide coatings, rare earth perovskite coatings, and spinel coatings. Among them, the (Mn,Co)3O4 spinel coating has been widely studied and applied due to its excellent electrical conductivity and suitable thermal expansion coefficient.

[0008] Currently, the main method for preparing spinel coatings is to prepare a metal alloy coating on the surface of ferritic stainless steel and then convert it into a spinel coating through heat treatment. Direct current magnetron sputtering is a common method for depositing metal coatings. However, traditional direct current magnetron sputtering has the following defects:

[0009] Low ionization rate: The ionization rate of target atoms is low, resulting in a coating with low density.

[0010] Shadow effect: Due to the low ionization rate, ions are easily blocked during deposition, resulting in uneven coating thickness, especially on the surface of complex-shaped substrates.

[0011] Inhomogeneous performance: Microstructure may have holes or columnar crystal defects, and uneven coating thickness can lead to uneven performance, affecting the protective effect of the coating.

[0012] These problems limit the long-term stability and reliability of the coating in high-temperature environments. In addition, the coating preparation process in the prior art also faces problems such as target surface oxide contamination, incomplete substrate pretreatment, and sputtering source impurities, which further affect the quality and performance of the coating. In particular, under high-temperature service conditions, the uniformity, density, and adhesion of the coating directly determine its barrier performance and long-term stability. Therefore, developing a preparation method that can effectively improve the uniformity, density, and high-temperature oxidation resistance of the coating is of great significance for improving the service performance of SOFC connectors. SUMMARY

[0013] In view of the problems of uneven coating thickness and uneven performance of the manganese-cobalt spinel coating for SOFC connectors prepared by direct current magnetron sputtering in the prior art, the present invention aims to provide a new preparation method for a manganese-cobalt spinel coating for SOFC connectors and a coating. High-power pulsed magnetron sputtering technology is used, which has a very high target atom ionization rate and substrate bias, ensuring the uniformity and consistency of the coating, obtaining a uniform, dense, and excellent performance spinel coating, thereby improving the service performance of SOFC connectors.

[0014] The technical solution of the present invention is:

[0015] A preparation method for a manganese-cobalt spinel coating for SOFC connectors, comprising the following steps:

[0016] (1) Substrate treatment: polish and polish the surface of ferritic stainless steel in sequence, and then ultrasonic clean in a mixture of acetone and ethanol, and dry;

[0017] (2) Target cleaning: In the absence of substrate, the target is cleaned by a combination of DC and pulsed magnetron sputtering to remove surface oxides and impurities. The sputtering time is 45-60 min, the sputtering temperature is 180-220℃, and the vacuum degree is 0.4 Pa. The DC target cleaning parameters include voltage 350-400V, current 1.0-1.5A, and power 400-600W. The pulse target cleaning parameters include voltage 610-680V, ​​frequency 120-150Hz, pulse width 150-170μs, and power 450-550W.

[0018] (3) Coating deposition: MnCo alloy coating was deposited using high-power pulsed magnetron sputtering technology. The specific process parameters are as follows: the parameters for bias cleaning samples include temperature 180-220℃, vacuum degree 1.0-2.0Pa, bias voltage 650-750V, and time 30-60min; the parameters for high-power pulsed sputtering include temperature 180-220℃, vacuum degree 0.38-0.42Pa, voltage 500-700V, pulse width 140-150μs, frequency 140-510Hz, duty cycle 2.1-7.7%, corresponding peak current 50-150A, average power 1960-2040W, and substrate bias voltage of -30 to -80V.

[0019] (4) Thermal conversion: The deposited substrate is oxidized at 800℃ to form a (Mn,Co)3O4 spinel coating.

[0020] Furthermore, in the above-mentioned method for preparing a manganese cobalt spinel coating for an SOFC connector, the volume ratio of acetone to ethanol mixture is 1:3, and the ultrasonic cleaning time is 15-30 min.

[0021] Furthermore, in the above-mentioned method for preparing a manganese cobalt spinel coating for an SOFC connector, in step (3), the distance between the target and the substrate is 15cm, the vacuum degree of the chamber is controlled at 0.4Pa, and Ar gas is introduced during the sputtering process to maintain the vacuum degree at 1.0-2.0Pa.

[0022] Furthermore, in the above-mentioned method for preparing a manganese cobalt spinel coating for an SOFC connector, the thickness of the MnCo alloy coating is 4.8-5.3 μm, the coating has a columnar structure, and the surface roughness of the coating is less than 25 nm.

[0023] Furthermore, in the above-mentioned method for preparing a manganese cobalt spinel coating for an SOFC connector, the plasma density is controlled by adjusting the pulse frequency and duty cycle during the coating deposition process to ensure that the target atom ionization rate reaches more than 80%.

[0024] The manganese cobalt spinel coating prepared by the preparation method has a composition of (Mn, Co)3O4, a compact structure, high-temperature oxidation resistance, and can effectively inhibit the outward diffusion of Cr elements after long-term service at 800 DEG C for 840 hours, and the surface roughness of the spinel coating formed after thermal conversion is less than 1 mu m.

[0025] Further, the manganese cobalt spinel coating prepared by the preparation method has a parabolic oxidation kinetic curve.

[0026] Further, the manganese cobalt spinel coating prepared by the preparation method has an ASR value of less than 25 m Omega cm after long-term service at 800 DEG C for 840 hours. 2 .

[0027] Advantages and beneficial effects of the present application:

[0028] The coating prepared by the method has a compact structure, few defects, high-temperature stability and high-temperature oxidation resistance, can effectively inhibit the outward diffusion of Cr elements, avoid the pollution of Cr(Ⅵ) volatilization to the environment and the toxic effect on the cathode performance. In addition, the coating preparation process is simple and easy to operate, and each process parameter can be accurately controlled, so that the industrial production is suitable, and the coating has high practical value and popularization prospect. Compared with the prior art, the coating also has the following advantages:

[0029] (1) Compared with the existing direct current magnetron sputtering technology, the (Mn, Co)3O4 coating of the present application is prepared by high-power pulse magnetron sputtering process, which greatly improves the adhesion between the coating and the substrate.

[0030] (2) The high-power pulse magnetron sputtering technology effectively reduces the generation of large particles in the deposition process, and the coating surface is smoother and has fewer defects, thereby reducing the surface roughness of the coating.

[0031] (3) The high-power pulse magnetron sputtering technology significantly improves the target atomic ionization rate. Under the action of the substrate bias, the high target atomic ionization rate promotes the migration and diffusion ability of the sputtering ions on the substrate surface, effectively solves the shadow effect problem existing in the direct current magnetron sputtering, and ensures the uniformity and consistency of the coating thickness. BRIEF DESCRIPTION OF DRAWINGS

[0032] Figure 1 The surface and cross-sectional morphology of the coating before thermal conversion under different current conditions, wherein (a) is the surface morphology of the 50A coating before thermal conversion, (b) is the surface morphology of the 100A coating before thermal conversion, (c) is the surface morphology of the 150A coating before thermal conversion, (d) is the cross-sectional morphology of the 50A coating before thermal conversion, (e) is the cross-sectional morphology of the 100A coating before thermal conversion, and (f) is the cross-sectional morphology of the 150A coating before thermal conversion.

[0033] Figure 2 XRD patterns of the coating before thermal conversion under different current conditions; the left graph is the overall pattern of the main phase composition of the coating, and the right graph is the enlarged local pattern to show the peak width change;

[0034] Figure 3 Surface and cross-section morphology of the coating after thermal conversion for 840h under different current conditions, wherein (a) is the surface morphology of the 50A coating after thermal conversion for 840h, (b) is the surface morphology of the 100A coating after thermal conversion for 840h, (c) is the surface morphology of the 150A coating after thermal conversion for 840h, (d) is the cross-section morphology of the 50A coating after thermal conversion for 840h, (e) is the cross-section morphology of the 100A coating after thermal conversion for 840h, and (f) is the cross-section morphology of the 150A coating after thermal conversion for 840h;

[0035] Figure 4 XRD patterns of the coating after thermal conversion under different current conditions, showing the existence of (Mn, Co)3O4 spinel phase;

[0036] Figure 5 ASR values of the coating after thermal conversion under different current conditions, wherein (a) is the ASR value of the 50A coating after thermal conversion for 168h and 840h, (b) is the ASR value of the 100A coating after thermal conversion for 168h and 840h, and (c) is the ASR value of the 150A coating after thermal conversion for 168h and 840h;

[0037] Figure 6 3D images and surface roughness of the 50A coating before and after thermal conversion, wherein (a) is the 3D image and surface roughness (Ra=18.4nm) before thermal conversion, and (b) is the 3D image and surface roughness (Ra=0.422μm) after thermal conversion. DETAILED DESCRIPTION

[0038] The technical solutions in the present application will be clearly and completely described below with reference to the drawings in the present application. Obviously, the described embodiments are only some of the embodiments of the present application, rather than all the embodiments. Based on the embodiments of the present application, all other embodiments obtained by those skilled in the art without creative work fall within the scope of the present application.

[0039] In the prior art, the cathode of a solid oxide fuel cell interconnector has long been plagued by the problem of chromium element out-diffusion induced cathode poisoning under high temperature environment. Although the traditional magnetron sputtering technology can prepare protective coatings, it is limited by the insufficient plasma ionization rate, resulting in defects such as uneven thickness and poor compactness of the coating. Especially on the surface of a complex-shaped substrate, the traditional process is difficult to eliminate the shadow effect, and the weak area of the coating is easy to become a diffusion channel for chromium elements, which seriously affects the long-term stability of the cell stack.

[0040] To solve the above problems, the high ionization rate characteristics of high power pulse technology can improve the coating uniformity, but the initial experiment found that the surface oxide contamination of the target material can significantly reduce the deposition efficiency. By analyzing the coating defect formation mechanism, it is found that the incomplete pretreatment of the substrate and the impurities in the sputtering source are the key factors affecting the coating quality. Further research found that the phase change process of metal alloy to spinel structure at a certain oxidation temperature directly affects the barrier performance of the coating, which provides a direction for optimizing the heat treatment parameters.

[0041] Therefore, the application proposes a preparation method including substrate treatment, target cleaning, coating deposition and heat conversion. The substrate treatment includes surface polishing and ultrasonic cleaning with a specific ratio of solvent, the target cleaning uses a composite magnetron sputtering mode, the coating deposition uses high power pulse magnetron sputtering combined with substrate bias control, and the heat conversion stage is completed at a set temperature.

[0042] Example 1

[0043] The embodiment is a preparation method of a manganese-cobalt spinel coating for a SOFC connector, which specifically includes the following steps:

[0044] (1) Substrate treatment: polish the surface of the ferritic stainless steel with 400#, 600#, 1000# and 2000# SiC abrasive paper, and perform edge and corner treatment, and polish with diamond abrasive paste until the surface is bright and scratch-free, so as to ensure that the surface roughness is less than 0.5 μm, thereby improving the adhesion between the coating and the substrate. The polished substrate is ultrasonically cleaned in an acetone and ethanol mixture for 20 min, and then dried in an oven, and the volume ratio of the acetone and ethanol mixture is 1:3.

[0045] (2) Target cleaning: in the absence of a substrate, the target is cleaned by a direct current and pulse magnetron sputtering composite process to remove surface oxides and impurities, and sputtering is performed for 60 min at a sputtering temperature of 180°C and a vacuum degree of 0.4 Pa; the direct current sputtering parameters are: voltage 350 V, current 1.0 A, and power 400 W; the pulse cleaning parameters are: voltage 610 V, frequency 150 Hz, pulse width 150 μs, and power 450 W.

[0046] (3) Coating deposition: MnCo alloy coating is deposited using high power pulse magnetron sputtering technology, the chamber door of the magnetron sputtering instrument is opened, the substrate is placed on the turntable, the chamber door is closed, the distance between the target and the substrate is 15 cm, the mechanical pump and the pre-evacuation valve are first opened, and then the diffusion pump and the front valve are opened when the vacuum is pumped to 5 Pa, and then the vacuum is pumped to 6 x 10 -3Pa, then Ar was introduced, the chamber was vacuumed to 1.0 Pa, bias was set to 650 V, and the sample was cleaned for 60 min. The high-power pulse sputtering parameters were: temperature 180 ℃, vacuum degree 0.42 Pa, substrate bias -80 V, voltage 500 V, pulse width 150 μs, frequency 510 Hz, duty cycle 7.7%, corresponding peak current 50 A, average power 2000 W. Figure 1 (a) indicating that the coating surface is densely packed cauliflower-like, Figure 1 (d) indicating that the coating thickness is uniform and well combined with the substrate. Figure 2 indicating that the composition of the coating before thermal conversion is single γ-Co.

[0047] (4) Thermal conversion: the deposited substrate was oxidized in a muffle furnace at 800 ℃ to form a (Mn, Co) 3O4 spinel coating. Figure 4 indicating that the composition of the oxidation film is single MnCo2O4. Figure 5 The ASR result of indicates that the ASR is only 28.728 mΩ·cm 2 after oxidation for 840 hours.

[0048] The thickness of the MnCo alloy coating of the Mn-Co spinel coating for SOFC interconnect obtained in the example is 5.2 μm, and the surface roughness of the spinel coating formed after thermal conversion is 0.422 μm. The coating composition is (Mn, Co) 3O4, has a dense structure, high-temperature oxidation resistance, and can effectively inhibit the outward diffusion of Cr element after long-term service at 800 ℃ for 840 hours.

[0049] Example 2

[0050] The preparation method of the Mn-Co spinel coating for SOFC interconnect in the example specifically includes the following steps:

[0051] (1) Substrate treatment: polish the surface of the ferritic stainless steel successively using 400#, 600#, 1000# and 2000# SiC water abrasive paper, and perform edge and corner treatment, and polish using diamond polishing paste until the surface is bright and scratch-free, and ensure that the surface roughness is less than 0.5 μm. Ultrasonic cleaning in a mixed solution of acetone and ethanol for 15 min, and oven drying for standby. The volume ratio of the acetone and ethanol mixed solution is 1:3.

[0052] (2) Target cleaning: in the absence of a substrate, the target was cleaned using a direct current and pulse magnetron sputtering combined process to remove surface oxides and impurities. Sputtering for 45 min, sputtering temperature 220 ℃, vacuum degree 0.4 Pa; direct current sputtering parameters: voltage 380 V, current 1.5 A, power 570 W; pulse sputtering parameters: voltage 650 V, frequency 120 Hz, pulse width 160 μs, power 520 W.

[0053] (3) Coating deposition: MnCo alloy coating was deposited by high power pulsed magnetron sputtering technology. The chamber door of the magnetron sputtering instrument was opened, and the substrate was placed on the turret. The chamber door was closed, the distance between the target and the substrate was 15 cm, the mechanical pump and the pre-pumping valve were opened first, and the vacuum was pumped to 5 Pa. Then the diffusion pump and the front valve were opened, and the vacuum was pumped to 6 x 10 -3 Pa. Then Ar was introduced to make the chamber vacuum degree 2.0 Pa. The bias voltage was set to 750 V, and the sample was cleaned for 30 min. The high power pulsed sputtering parameters were as follows: temperature 220 ℃, vacuum degree 0.38 Pa, substrate bias -50 V, voltage 600 V, pulse width 145 μs, frequency 230 Hz, duty cycle 3.5%, corresponding peak current 100 A, average power 2040 W. Figure 1 (b) indicating that the coating has no obvious defects, Figure 1 (e) indicating that the coating is tightly combined with the substrate. The XRD spectrum indicates that the coating phase composition is γ-Co.

[0054] (4) Thermal conversion: the deposited substrate was oxidized in a muffle furnace at 800 ℃ to form a (Mn, Co) 3O4 spinel coating. The XRD spectrum indicates that the oxide is only MnCo2O4. The ASR result indicates that the oxidation time is 5 weeks, and the resistance is 28.994 mΩ·cm 2 .

[0055] The thickness of the MnCo alloy coating of the SOFC connecting body with the manganese cobalt spinel coating obtained in the embodiment is 5.3 μm, and the surface roughness of the spinel coating formed after thermal conversion is 0.589 μm. The coating composition is (Mn, Co) 3O4, has a dense structure, high temperature oxidation resistance, and can effectively inhibit the outward diffusion of Cr element after long-term service at 800 ℃ for 840 hours.

[0056] Example 3

[0057] The preparation method of the SOFC connecting body with the manganese cobalt spinel coating in the embodiment specifically comprises the following steps:

[0058] (1) Substrate treatment: the surface of the ferritic stainless steel was polished with 400#, 600#, 1000# and 2000# SiC water abrasive paper in sequence, and the edge and corner were treated, and the diamond grinding paste was used for polishing until the surface was bright and scratch-free, and the surface roughness was less than 0.5 μm. Ultrasonic cleaning in acetone and ethanol mixed solution for 30 min, and oven drying, the volume ratio of acetone and ethanol mixed solution was 1:3.

[0059] (2) Target cleaning: The target was cleaned in a direct current and pulse magnetron sputtering combined process without a substrate, and the surface oxides and impurities were removed. The sputtering was performed for 45 min at a temperature of 200°C and a vacuum degree of 0.4 Pa. The direct current sputtering parameters were as follows: a voltage of 400 V, a current of 1.5 A, and a power of 600 W. The pulse sputtering parameters were as follows: a voltage of 680 V, a frequency of 160 Hz, a pulse width of 170 μs, and a power of 550 W.

[0060] (3) Coating deposition: A MnCo alloy coating was deposited by using a high-power pulse magnetron sputtering technology. The chamber door of the magnetron sputtering instrument was opened, and the substrate was placed on a rotating stand. The chamber door was closed, and the distance between the target and the substrate was 15 cm. First, a mechanical pump and a pre-pumping valve were opened, and the vacuum was pumped to 5 Pa. Then, a diffusion pump and a front valve were opened, and the vacuum was pumped to 6 x 10 -3 Pa. Subsequently, Ar was introduced, so that the chamber vacuum degree was 1.5 Pa. The bias voltage was set to 700 V, and the sample was cleaned for 45 min. The high-power pulse sputtering parameters were as follows: a temperature of 200°C, a vacuum degree of 0.4 Pa, a substrate bias voltage of -30 V, a voltage of 700 V, a pulse width of 140 μs, a frequency of 140 Hz, a duty cycle of 2.1%, a corresponding peak current of 150 A, and an average power of 1960 W. The XRD results showed that the phase composition was the same as that of the 50A and 100A coatings, but the half peak width was obviously increased, and the coating grain was obviously refined. Figure 2

[0061] (4) Thermal conversion: The deposited substrate was oxidized in a muffle furnace at 800°C to form a (Mn, Co)3O4 spinel coating. Figure 4 The results showed that the oxidation was the same as that of the previous two. Figure 5 The results showed that the ASR value of the sample after oxidation for 5 weeks was 27.864 mΩ·cm 2 .

[0062] The thickness of the MnCo alloy coating obtained in the example was 4.8 μm, and the surface roughness of the spinel coating formed after thermal conversion was 0.508 μm. The coating composition was (Mn, Co)3O4, had a dense structure, high-temperature oxidation resistance, and could effectively inhibit the outward diffusion of Cr elements after long-term service at 800°C for 840 hours.

[0063] It can be seen from Figure 1 that as the current increases, the coating surface gradually tends to be dense, and is well combined with the substrate.

[0064] Figure 2 The XRD patterns of the coating before thermal conversion under different current conditions are shown. The left graph is the overall pattern of the main phase composition of the coating, and the right graph is the enlarged local pattern to show the peak width change.

[0065] ​Figure 3 The surface and cross-section morphology of the coating after 840 hours of thermal conversion under different current conditions are shown, wherein (a), (b), (c) are the surface morphology of the coating under 50A, 100A, 150A current, respectively, (d), (e), (f) are the corresponding cross-section morphology. Figure 3 It can be seen that after long-term high-temperature oxidation, the coating still maintains a dense structure and is tightly combined with the substrate.

[0066] Figure 4 The XRD pattern of the coating after thermal conversion is shown, which shows that the coating is completely converted into a single-phase MnCo2O4 spinel structure.

[0067] Figure 5 The ASR values of the coating after thermal conversion under different current conditions are shown, wherein (a), (b), (c) are the ASR values of the coating under 50A, 100A, 150A current at 168 hours and 840 hours, respectively. Figure 5 It can be seen that the ASR values of the coating after long-term service at 800℃ for 840 hours are all lower than 25 mΩ·cm², indicating that the coating has excellent electrical conductivity.

[0068] Figure 6 The 3D images and surface roughness of the 50A coating before and after thermal conversion are shown, wherein (a) is the 3D image and surface roughness before thermal conversion (Ra=18.4 nm), (b) is the 3D image and surface roughness after thermal conversion (Ra=0.422 μm). Figure 6 It can be seen that the surface of the coating after thermal conversion is smoother and more uniform, and the roughness is significantly reduced.

Claims

1. A method for producing a manganese-cobalt spinel coating for SOFC interconnects, characterized in that The method comprises the following steps: (1) substrate treatment: the surface of ferritic stainless steel is polished and polished in sequence, and then is ultrasonically cleaned in a mixture of acetone and ethanol and dried; (2) target cleaning: in the state of no substrate, the target is cleaned by a direct current and pulse magnetron sputtering combined process, so as to remove surface oxides and impurities, the sputtering time is 45-60 min, the sputtering temperature is 180-220 DEG C, and the vacuum degree is 0.4 Pa; the direct current cleaning parameters include a voltage of 350-400 V, a current of 1.0-1.5 A, and a power of 400-600 W; the pulse cleaning parameters include a voltage of 610-680 V, a frequency of 120-150 Hz, a pulse width of 150-170 mu s, and a power of 450-550 W; (3) coating deposition: the MnCo alloy coating is deposited by using a high-power pulse magnetron sputtering technology, and the specific process parameters are as follows: the sample bias cleaning parameters include a temperature of 180-220 DEG C, a vacuum degree of 1.0-2.0 Pa, a bias voltage of 650-750 V, and a time of 30-60 min; the high-power pulse sputtering parameters include a temperature of 180-220 DEG C, a vacuum degree of 0.38-0.42 Pa, a voltage of 500-700 V, a pulse width of 140-150 mu s, a frequency of 140-510 Hz, a duty cycle of 2.1-7.7%, a corresponding peak current of 50-150 A, an average power of 1960-2040 W, and a substrate bias of-30 to-80 V; the deposited MnCo alloy coating has a thickness of 4.8-5.3 mu m, is columnar in structure, and has a surface roughness of less than 25 nm; (4) thermal conversion: the deposited substrate is oxidized at 800 DEG C to form a (Mn, Co) 3O4 spinel coating, the coating is completely converted into a single-phase MnCo2O4 spinel structure, has a dense structure and high-temperature oxidation resistance, and can effectively inhibit the outward diffusion of Cr elements after long-term service at 800 DEG C for 840 hours, and the surface roughness of the spinel coating formed after thermal conversion is less than 1 mu m.

2. The method for preparing a manganese-cobalt spinel coating for an SOFC connector according to claim 1, characterized in that, The volume ratio of the acetone and ethanol mixture is 1:3, and the ultrasonic cleaning time is 15-30 min.

3. The method for preparing a manganese-cobalt spinel coating for an SOFC connector according to claim 1, characterized in that, In step (3), the distance between the target and the substrate is 15 cm, the chamber vacuum degree is controlled to be 0.4 Pa, and Ar gas is introduced during the sputtering process to maintain the vacuum degree at 1.0-2.0 Pa.

4. The method for preparing a manganese-cobalt spinel coating for an SOFC connector according to claim 1, characterized in that, During the coating deposition process, the plasma density is controlled by adjusting the pulse frequency and duty cycle to ensure that the target atom ionization rate reaches more than 80%.

5. A manganese-cobalt spinel coating produced by the method of any one of claims 1 to 4, characterized in that The oxidation kinetic curve of the coating is a parabola.

6. A manganese-cobalt spinel coating produced by the method of any one of claims 1 to 4, characterized in that The coating has an ASR value of less than 30 mΩ-cm after 840 hours of long term service at 800°C 2 .

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