Mn-Co coating of SOEC metal connector and preparation method and application of Mn-Co coating

Abstract

The invention relates to an SOEC metal connector Mn-Co coating and a preparation method and application thereof, and belongs to the technical field of solid oxide electrolytic cells. According to the method, firstly, a matrix is pretreated, and the Mn-Co spinel coating is constructed on the surface of a metal connector in situ by adopting an in-situ preparation process combining step-by-step electroplating and subsequent heat treatment. The coating has good oxidation resistance and low surface specific resistance, and the high-temperature service life of the connector can be remarkably prolonged.

Description

Technical Field

[0001] This invention relates to a SOEC metal interconnect Mn-Co coating, its preparation method and application, belonging to the field of solid oxide electrolytic cell technology. Background Technology

[0002] Solid oxide electrolyzers (SOECs) are highly efficient and environmentally friendly all-solid-state electrochemical devices that can produce green hydrogen or green syngas through water electrolysis. Connectors are key components in SOEC stacks, serving to connect individual cells, separate oxidant and fuel gases, and conduct current. To meet the requirements of the operating environment (high temperature, oxidizing and reducing atmospheres), ferritic stainless steel is the preferred material for metal connectors due to its matching coefficient of thermal expansion with the battery components, low cost, and ease of processing.

[0003] However, ferritic stainless steel faces two major challenges in the high-temperature (600-800°C) environment of SOEC long-term operation: 1) An oxide layer (mainly Cr2O3) will form on the surface, which will lead to a sharp increase in contact resistance and reduce battery performance; 2) Cr2O3 will react with water and oxygen to generate gaseous CrO2(OH)2, which will migrate to the cathode and deposit, resulting in "chromium poisoning" of the cathode and severely reducing the electrochemical performance of the battery.

[0004] To address the aforementioned issues, applying a protective coating to the surface of the metal connector is currently the most effective method. Among these, Mn-Co spinel coatings have been extensively studied due to their excellent high-temperature conductivity, thermal expansion coefficient matching the substrate, and good chromium-blocking properties. Existing coating preparation methods, such as physical vapor deposition (PVD), plasma spraying, and screen printing, are limited by the high equipment costs and complex processes of PVD and plasma spraying, the difficulty in fabricating complex-shaped workpieces using screen printing, and the poor coating density, thus restricting their large-scale industrial application.

[0005] Electroplating, as a mature liquid phase deposition technology, has outstanding advantages such as low cost, simple equipment, fast deposition rate, and the ability to obtain uniform coatings on complex-shaped substrates. However, due to the difference in electrode potentials between Mn and Co, the one-step preparation of MnCo alloy coatings is relatively difficult, and the adhesion between the coating and the substrate, as well as the density of the coating, still need to be optimized. Summary of the Invention

[0006] The purpose of this invention is to overcome the aforementioned defects and shortcomings of the prior art and provide a method for preparing a Mn-Co spinel coating for SOEC metal interconnects in situ using electroplating. This process employs an in-situ preparation technique combining stepwise electroplating with subsequent heat treatment to construct a Mn-Co coating on the surface of the metal interconnect with a gradient in composition, structure, and function from the inside out. This coating not only forms a strong bond with the substrate but also effectively inhibits the internal diffusion of oxygen ions and the external volatilization of chromium, ultimately significantly reducing the surface resistivity of the interconnect.

[0007] Another objective of this invention is to provide a high-performance, low-cost, long-life SOEC metal interconnect Mn-Co coating prepared by the above process.

[0008] Technical solution A method for in-situ preparation of SOEC metal linker Mn-Co coating includes the following steps: S1: Matrix pretreatment: Ferritic stainless steel was selected as the matrix material (sample) for the metal connector, and the sample was mechanically ground and polished in sequence. Preferably, SiC sandpaper of 400#, 600#, 800#, 1200#, 1500# to 2000# was used to grind and polish the sample. The treated sample is placed in an alkaline solution or acetone solution for 10-20 minutes of ultrasonic cleaning to thoroughly remove surface oil and impurities. The alkaline solution is preferably an aqueous solution containing 50-80 g / L sodium hydroxide (NaOH), and the operating temperature is maintained at 30-50°C. Then, perform multiple ultrasonic cleanings with deionized water and anhydrous ethanol, each lasting 5-10 minutes, to ensure thorough removal of any residual alkali on the surface. Finally, place the product in a dry environment to prevent secondary oxidation.

[0009] Finally, the sample is immersed in an acidic solution for 1-3 minutes to activate it, remove the very thin oxide film on the surface and activate it. The acidic solution is a hydrochloric acid solution of 90% concentrated hydrochloric acid and deionized water in a volume ratio of (10-20):100 or a sulfuric acid solution of 98% concentrated sulfuric acid and deionized water in a volume ratio of (10-15):100, to obtain the pretreated metal linker matrix. S2: Electroplated cobalt transition layer: The metal connector substrate pretreated in step S1 is used as the cathode and suspended in the cobalt electroplating solution. The basic composition and concentration range of the cobalt electroplating solution are: cobalt sulfate (CoSO4·7H2O) 200-400 g / L and cobalt chloride (CoCl2·6H2O) 30-60 g / L, with boric acid (H3BO3) as a pH buffer 25-40 g / L. The pH of the electroplating solution is maintained within the range of 3.5-4.5 using dilute sulfuric acid (H2SO4); the working temperature of the electroplating solution is 50-60°C. A graphite plate is used as the anode, and a dual-anode system is adopted. During the electroplating process, the cathode current density is controlled within the range of 1-5 A / dm² by a DC power supply. The electroplating duration is 2-8 minutes. Under these process conditions, a dense, uniform, and well-adhesive cobalt metal layer is obtained on the substrate surface, with the preferred thickness of the cobalt metal layer being approximately 4 μm.

[0010] S3: Intermediate cleaning and activation: The cobalt-plated substrate is removed from the cobalt electroplating solution and thoroughly rinsed with running deionized water to remove any residual cobalt plating solution adhering to the surface. Then, it is immersed in an H2SO4 solution of 98% concentrated sulfuric acid and deionized water at a volume ratio of 5:100 for 10-30 seconds to remove the extremely thin passivation film on the surface of the cobalt layer, keeping it in an activated state to facilitate the subsequent deposition of the manganese layer. After rinsing lightly with deionized water again, it is quickly transferred to the manganese electroplating tank.

[0011] S4: Electroplated manganese functional layer: A substrate with a cobalt layer on its surface, which has undergone intermediate activation treatment, is used as the cathode and suspended in a manganese electroplating solution. The manganese electroplating solution is preferably a sulfate system with good stability and high deposition efficiency, and its basic composition and concentration range are: manganese sulfate (MnSO4·H2O) 100-150 g / L, ammonium sulfate ((NH4)2SO4) 100-200 g / L, selenium dioxide (SeO2) 0.15-0.3 g / L, and saccharin (C7H5NO3S) 7.2-7.5 g / L. The pH of the electroplating solution is maintained at 5.0-7.0 using dilute sulfuric acid; the operating temperature of the electroplating solution is controlled at a relatively low temperature of 25-35°C to reduce Mn content. 2+ Oxidation; high-purity manganese metal plate is used as a soluble anode; During the electroplating process, the cathode current density is controlled within the range of 1-6 A / dm² by a DC power supply; the electroplating duration is set to 3-10 minutes according to the required manganese layer thickness; under these process conditions, a uniform and dense metallic manganese layer is obtained on the surface of the cobalt layer, with the preferred thickness of the metallic manganese layer being approximately 5 μm.

[0012] S5: In-situ coating preparation: The prepared coating samples were placed in a sintering furnace for heat treatment. The temperature was increased from room temperature to 900-1000°C at a rate of 3°C / min and held at the corresponding temperature for 5-20 hours to eliminate the internal stress generated during electroplating and promote the interdiffusion between the cobalt and manganese layers. Through solid-state reaction sintering, a continuous and dense oxide Mn-Co coating was finally formed, which formed a strong and tight bond with the substrate through diffusion.

[0013] S6: High-temperature oxidation treatment: The samples were subjected to isothermal oxidation treatment at 750-850°C in air for 20-168 hours, and the surface resistivity of the samples was tested.

[0014] The advantages of this invention compared to the prior art are as follows: This invention utilizes separate electroplating of Co and Mn followed by a heat treatment process. By precisely controlling the thickness ratio of the two electroplating steps and the subsequent heat treatment regime, the prepared double Mn-Co coating exhibits superior performance: a) high density with virtually no pores or cracks; b) strong adhesion to the substrate, capable of withstanding harsh thermal cycling; c) low high-temperature surface resistivity, with an ASR consistently below 20 mΩ·cm² after oxidation at 800°C for 168 hours.

[0015] The investment required for this invention is far lower than that for vacuum processes such as PVD and magnetron sputtering. It has a fast deposition rate and low energy consumption, making it particularly suitable for large-scale, low-cost industrial production of complex geometric connectors. It has huge market application potential and economic value. Attached Figure Description

[0016] Figure 1 The XRD patterns of the coatings obtained in Examples 1-4 and Comparative Example 1 are shown.

[0017] Figure 2 The image shows the ASR of the coated sample from Example 1 after 168 hours of oxidation.

[0018] Figure 3 This is a SEM image of the coating obtained in Example 1. Detailed Implementation

[0019] The technical solution of the present invention will be described in detail below through specific embodiments. It should be understood that the following specific embodiments are merely exemplary, and any modifications or changes that do not depart from the technical solution design of the present invention should be within the scope of protection of the claims of the present invention. The present invention will be described in detail below with reference to embodiments.

[0020] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments, but the implementation of the present invention is not limited thereto.

[0021] Example 1: A Mn-Co coating for SOEC metal interconnects and its in-situ preparation method The steps are as follows: S1: Matrix pretreatment: High-performance ferritic stainless steel SUS430 was selected as the base material for the metal connector and cut into 12mm circular pieces. The samples were mechanically ground and polished in sequence. The SiC sandpaper used for mechanical grinding ranged from coarse to fine (from 400#, 600#, 800#, 1200#, 1500# to 2000#). The treated sample was placed in an alkaline solution for 15 minutes of ultrasonic cleaning to thoroughly remove surface oil and impurities. The alkaline solution was an aqueous solution containing 80 g / L sodium hydroxide (NaOH), and the operating temperature was maintained at 35°C. Then, it is ultrasonically cleaned three times in sequence with deionized water and anhydrous ethanol, each time for 10 minutes, to ensure that the residual acid and alkali on the surface are completely removed. Then it is placed in a dry environment for later use to prevent secondary oxidation.

[0022] Finally, the sample was immersed in an acidic solution for 2 minutes to activate it, remove the very thin natural oxide film on the surface and activate the surface. The acidic solution was a sulfuric acid solution made by mixing 98% concentrated sulfuric acid and deionized water in a volume ratio of 10:100. S2: Electroplated cobalt transition layer: The metal connector substrate, which has undergone the above pretreatment and obtained a clean and activated surface, is used as the cathode and suspended in the cobalt electroplating solution. The basic composition and concentration range of the cobalt electroplating solution are: cobalt sulfate (CoSO4·7H2O) 200 g / L, cobalt chloride (CoCl2·6H2O) 30 g / L, and boric acid (H3BO3) 25 g / L (as a pH buffer). The pH of the electroplating solution using dilute sulfuric acid (H2SO4) is maintained at 4; the working temperature of the electroplating solution is controlled at 55°C by heating. Using graphite plates as dual anodes, the cathode current density is controlled to be 3 A / dm³ during the electroplating process via a DC power supply. 2 The electroplating process lasted for 8 minutes, resulting in a dense, uniform, and well-adhered cobalt metal layer with a thickness of approximately 4 μm on the substrate surface.

[0023] S3: Intermediate cleaning and activation: The sample coated with cobalt was removed from the cobalt electroplating solution and rinsed thoroughly with running deionized water to remove any residual cobalt plating solution adhering to the surface. Then, it was immersed in a 5% vol. H2SO4 solution for 30 seconds to remove the very thin passivation film on the surface of the cobalt layer, keeping it in an activated state to facilitate the subsequent deposition of the manganese layer. After rinsing lightly with deionized water again, it was quickly transferred to the manganese electroplating tank to minimize the exposure time to air.

[0024] S4: Electroplated manganese functional layer: A substrate sample with a cobalt layer on its surface, which has undergone intermediate activation treatment, is used as the cathode and suspended in a manganese electroplating solution. The manganese electroplating solution is preferably a sulfate system with good stability and high deposition efficiency, and its basic composition and concentration range are: manganese sulfate (MnSO4·H2O) 130 g / L, ammonium sulfate ((NH4)2SO4) 150 g / L, selenium dioxide (SeO2) 0.2 g / L, and saccharin (C7H5NO3S) 7.2 g / L. The pH of the electroplating solution was maintained at 5.0 using dilute sulfuric acid; the operating temperature of the electroplating solution was controlled at 30°C to reduce Mn. 2+ Oxidation; high-purity manganese metal plate is used as a soluble anode; During the electroplating process, the cathode current density was controlled to be 6A / dm² by a DC power supply; the electroplating duration was set to 5 minutes, and a uniform and dense layer of metallic manganese with a thickness of about 5 μm was obtained on the surface of the cobalt layer.

[0025] S5: In-situ coating preparation: The prepared Co / Mn bilayer metal sample was placed in a sintering furnace. The temperature was increased from room temperature to 950°C at a rate of 3°C / min and held at 950°C for 5 hours to eliminate the internal stress generated during electroplating and promote the interdiffusion between the cobalt and manganese layers. Through solid-state reaction sintering, it was finally transformed into a continuous and dense MnCo2O4 oxide Mn-Co coating.

[0026] S6: High-temperature oxidation: The sample was subjected to isothermal oxidation treatment at 800°C and in air atmosphere for 168 hours, and the surface resistivity of the coating was tested.

[0027] Example 2: A Mn-Co coating for SOEC metal interconnects and its in-situ preparation method The steps in Example 2 are similar to those in Example 1, except that during Co electroplating, a graphite plate is used as the dual anode, and the cathode current density is controlled to be 3 A / dm³ using a DC power supply. 2 The electroplating process lasted for 5 minutes, resulting in a dense, uniform, and well-adhesive cobalt metal layer with a thickness of approximately 5.6 μm on the substrate surface.

[0028] Example 3: A Mn-Co coating for SOEC metal interconnects and its in-situ preparation method The steps in Example 3 are similar to those in Example 1, except that during Co electroplating, a graphite plate is used as the dual anode, and the cathode current density is controlled to be 2 A / dm³ using a DC power supply. 2 The electroplating process lasted for 3 minutes, resulting in a dense, uniform, and well-adhesive cobalt metal layer with a thickness of approximately 3 μm on the substrate surface.

[0029] Example 4: A Mn-Co coating for SOEC metal interconnects and its in-situ preparation method The steps in Example 4 are similar to those in Example 1, except that during Co electroplating, a graphite plate is used as the dual anode, and the cathode current density is controlled to be 1 A / dm³ using a DC power supply. 2 The electroplating process lasted for 2 minutes, resulting in a dense, uniform, and well-adhesive cobalt metal layer with a thickness of approximately 1 μm on the substrate surface.

[0030] Comparative Example 1 High-performance ferritic stainless steel SUS430 was selected as the base material for the metal connector and cut into 12mm circular pieces. The samples were subjected to rigorous mechanical grinding and polishing treatment in sequence, with SiC sandpaper being used to grind from coarse to fine (from 400#, 800#, 1200#, 1500# to 2000#). The polished sample was ultrasonically cleaned in an alkaline solution or acetone solution for 20 minutes to thoroughly remove surface oil and impurities. The alkaline solution was preferably an aqueous solution containing 80 g / L sodium hydroxide (NaOH), and the operating temperature was maintained at 40°C. Subsequently, the sample was ultrasonically cleaned multiple times with deionized water and anhydrous ethanol, each time for 10 minutes, to ensure thorough removal of residual acid and alkali solutions and particles from the surface. It was then placed in a dry environment to prevent secondary oxidation. Finally, the sample was immersed in an acidic solution of a specific concentration for a short time (1-3 minutes) to activate it, removing the extremely thin natural oxide film and activating the surface. The acidic solution was preferably a 15% (v / v) sulfuric acid solution. The treated stainless steel was then oxidized at 800℃ for 168 hours, and its surface resistivity was measured. The surface resistivity after oxidation was approximately 210 mΩ·cm. 2 .

[0031] Comparative Example 2 Comparative Example 2 differs from Comparative Example 1 in that commercially available MnCo2O4 spinel material was screen-printed onto the treated SUS430 stainless steel surface to a thickness of approximately 10 μm. The sample was then oxidized at 800 °C for 168 h. The surface resistivity of the oxidized sample at 800 °C was approximately 30 mΩ·cm.2 .

[0032] Experimental Example: The areal resistivity of the coating samples obtained in Examples 1-4 and Comparative Examples 1-2 was tested, and the results are shown in Table 1. Figures 1-3 As shown.

[0033] ; Table 1 shows the coating thickness and surface resistivity of coated steels after different electroplating processes, oxidized at 800℃ for 168 hours. It can be observed that the surface resistivity of uncoated stainless steel (Comparative Example 1) is as high as 210 mΩ·cm. 2 The surface resistivity of samples with electroplated Mn and Co coatings was below 20 mΩ·cm², which was also lower than that of Mn-Co spinel-coated samples prepared by screen printing (30.4 mΩ·cm²). 2 This indicates that the coating formed by this method through double-layer electroplating and in-situ oxidation has good oxidation resistance.

[0034] Figure 1 The XRD patterns of the Mn-Co coatings obtained in Examples 1-4 and Comparative Example 1 are shown. The results show that the Mn-Co coating with a pure cubic phase was obtained after oxidation pretreatment at 950℃ in Example 1. The Mn-Co coatings after oxidation treatment in Examples 2-4 include a cubic Mn-Co oxide main phase and a small amount of tetragonal Mn-Co oxide.

[0035] The sheet resistivity diagram of the coated steel sample obtained in Example 1 after oxidation at 800℃ for 168 hours is shown in the figure between 850-650℃. Figure 2 As shown. Example 1 shows the SEM image of the Mn-Co coating surface. Figure 3 As shown, the results indicate that the surface Mn-Co coating is relatively dense and can effectively prevent the oxidation of steel.

Claims

1. A method for in-situ preparation of an SOEC metal linker Mn-Co coating, characterized in that, The steps of the method shown are as follows: S1: Matrix pretreatment: Ferritic stainless steel was selected as the matrix material for the metal connector (sample), and the sample was mechanically ground and polished in sequence. The treated sample is placed in an alkaline solution or acetone solution for 10-20 minutes of ultrasonic cleaning to thoroughly remove surface oil and impurities. The alkaline solution is an aqueous solution containing 50-80 g / L sodium hydroxide (NaOH), and the operating temperature is maintained at 30-50°C. Then, it is ultrasonically cleaned repeatedly with deionized water and anhydrous ethanol, each time for 5-10 minutes, and then placed in a dry environment for later use. Finally, the sample is immersed in an acidic solution for 1-3 minutes for activation. The acidic solution is either a hydrochloric acid solution made by mixing 90% concentrated hydrochloric acid and deionized water in a volume ratio of (10-20):100, or a sulfuric acid solution made by mixing 98% concentrated sulfuric acid and deionized water in a volume ratio of (10-15):100, to obtain the pretreated metal linker matrix. S2: Electroplated cobalt transition layer: The metal connector substrate pretreated in step S1 is used as the cathode and suspended in the cobalt electroplating solution. The basic composition and concentration range of the cobalt electroplating solution are: cobalt sulfate (CoSO4·7H2O) 200-400 g / L and cobalt chloride (CoCl2·6H2O) 30-60 g / L, with boric acid (H3BO3) as a pH buffer 25-40 g / L. The pH of the electroplating solution is maintained within the range of 3.5-4.5 using dilute sulfuric acid (H2SO4); the working temperature of the electroplating solution is 50-60°C. Graphite plates are used as anodes, and a dual-anode system is adopted. During the electroplating process, the cathode current density is controlled within the range of 1-5 A / dm² by a DC power supply. The electroplating duration is 1-8 minutes. Under these process conditions, a layer of metallic cobalt is obtained on the substrate surface. S3: Intermediate cleaning and activation: Remove the cobalt-plated substrate from the cobalt electroplating solution and rinse it thoroughly with running deionized water. Then immerse it in an H2SO4 solution made of 98% concentrated sulfuric acid and deionized water at a volume ratio of 5:100 for 10-30 seconds. After rinsing it again with deionized water, quickly transfer it into the manganese electroplating tank. S4: Electroplated manganese functional layer: A substrate with a cobalt layer on its surface, which has undergone intermediate activation treatment, is used as the cathode and suspended in a manganese electroplating solution. The manganese electroplating solution is a sulfate system, which consists of: manganese sulfate (MnSO4·H2O) 100-150 g / L, ammonium sulfate ((NH4)2SO4) 100-200 g / L, selenium dioxide (SeO2) 0.15-0.3 g / L, and saccharin (C7H5NO3S) 7.2-7.5 g / L. The pH of the electroplating solution is maintained at 5.0-7.0 using dilute sulfuric acid; the working temperature of the electroplating solution is controlled at a relatively low temperature of 25-35°C; and a high-purity manganese metal plate is used as the soluble anode. During the electroplating process, the cathode current density is controlled within the range of 1-6 A / dm² by a DC power supply; the electroplating duration is set to 3-10 minutes according to the required manganese layer thickness; under these process conditions, a layer of metallic manganese is obtained on the surface of the cobalt layer. S5: In-situ coating preparation: The prepared coating sample was placed in a sintering furnace for heat treatment. The temperature was increased from room temperature to 900-1000°C at a rate of 3°C / min and held at the corresponding temperature for 5-20 hours to eliminate the internal stress generated during electroplating and promote the interdiffusion between the cobalt and manganese layers. Through solid-state reaction sintering, it was finally transformed into a continuous and dense oxide Mn-Co coating. S6: High-temperature oxidation: The substrate with the Mn-Co coating was subjected to isothermal oxidation treatment at 750-850°C and in air for 20-168 hours. The surface resistivity of the oxidized sample with the coating was then tested.

2. The method according to claim 1, characterized in that, The ferritic stainless steel selected in step S1 is one of SUS430, SUS441, Crofer 22APU, and AMG232. The sample is cut into 12mm round pieces, and SiC sandpaper of grade 400#, 600#, 800#, 1200#, 1500# to 2000# is used to polish the sample.

3. The method according to claim 1, characterized in that, The thickness of the cobalt metal layer in step S2 is 1-8 μm.

4. The method according to claim 1, characterized in that, The thickness of the manganese metal layer in step S4 is 4-5 μm.

5. The SOEC metal interconnect Mn-Co coating obtained by the method of any one of claims 1-4.

6. The application of the SOEC metal connector Mn-Co coating as described in claim 5 in metal connectors.

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