A method for preparing CeO2 / NiO coating by electrochemical deposition and its application

Abstract

The present invention relates to the field of preparation of CeO2 / NiO coatings, and specifically to a method for preparing CeO2 / NiO coatings by electrochemical deposition and its application. The specific preparation steps are as follows: (1) step-by-step electrochemical deposition to obtain a CeO2 / Ni composite coating; and (2) thermal conversion to obtain a CeO2 / NiO coating. The method has the advantages of a simple and easy preparation process and is suitable for stainless steel connector substrates with complex shapes. The prepared CeO2 and NiO have the effect of synergistically improving the high-temperature oxidation resistance and electrical conductivity of the stainless steel connector. The CeO2 layer has a multi-level nanostructure, which can increase Cr2O3 nucleation sites and effectively inhibit interdiffusion.

Description

Technical Field

[0001] The present invention relates to the field of coating preparation, and in particular to a method for preparing a CeO2 / NiO coating by electrochemical deposition and application thereof. Background Art

[0002] Stainless steel interconnects serve the dual purpose of connecting solid oxide fuel cell (SOFC) cells and separating the anode fuel gas and cathode air. They are one of the most critical components in flat-plate SOFCs. Ferritic stainless steel has the advantages of a coefficient of thermal expansion (CTE) very close to that of other SOFC components, low cost, and simple processing, making it a promising interconnect material. However, after prolonged service in SOFC operating environments, the Cr2O3 film that grows on the surface of ferritic stainless steel can reach thicknesses of several microns or even tens of microns. This continuous oxide film growth can lead to undesirable consequences, such as increased sheet resistance and decreased cell stack performance. Furthermore, volatilization of chromium from the interconnect can severely degrade SOFC performance.

[0003] The simplest and most effective way to solve the above problems is to apply a high-temperature oxidation-resistant and conductive protective coating on the surface of ferritic stainless steel connectors. The active element oxide coating can significantly enhance the adhesion of the oxide film and reduce the oxidation rate of stainless steel. However, it is usually too thin and porous to effectively prevent the outward diffusion of Cr during long-term oxidation. The NiO coating formed by thermal conversion of metallic Ni is a conductive barrier that prevents Cr volatilization. Currently, the composite electroplating method is used to embed CeO2 in Ni-based composite materials to enhance the oxidation resistance of stainless steel, which is a more common deposition method. However, Ni and the stainless steel matrix will diffuse into each other, forming an austenite region under the oxide film, which reduces the high-temperature oxidation resistance of stainless steel. Summary of the Invention

[0004] To solve the above technical problems, the present invention provides a method for step-by-step electrochemical deposition of CeO2 / NiO coating and its application. The CeO2 layer with active element effect not only effectively inhibits the diffusion of Ni into the substrate and the outward diffusion of Cr in the substrate by promoting the formation of Cr2O3 diffusion barrier and its own diffusion barrier effect, but also cooperates with NiO to prevent the outward migration of Cr and reduce the thickness of Cr2O3, thereby improving the high-temperature oxidation resistance and conductivity of the substrate.

[0005] The specific technical solutions are as follows:

[0006] (1) Preparation of CeO2 / Ni composite coating by electrochemical deposition: CeO2 electrolyte solution was prepared with the following composition: cerium nitrate 20-25 g / L, ammonium chloride 5-7 g / L, potassium chloride 3-5 g / L. Deposition parameters were: deposition time 8-10 min, bath temperature 40-50 °C, deposition current density 2.5 mA / cm2 Using graphite as the anode and the polished and cleaned substrate as the cathode, multi-level nanostructured CeO2 was electrochemically deposited, and then metallic Ni was electrodeposited for 5 minutes to obtain a nanocomposite coating of Ni embedded in CeO2.

[0007] (2) Thermal conversion: The deposited sample was heated to 800°C in a resistance furnace, kept at this temperature for 1 week, cooled to room temperature in the furnace, and weighed. The cumulative oxidation time was 10 weeks. A CeO2 / NiO coating with a thickness of about 2 μm was obtained, and the oxidation rate constant of the coated stainless steel was (4-5)×10 -14 g 2 cm -4 s -1 The overall surface resistivity of the surface oxide film is 20-25 mΩcm 2 .

[0008] Compared with the prior art, the technical solution of the present invention has the following beneficial effects:

[0009] (1) The preparation process is simple and easy to operate, and is suitable for stainless steel connector substrates with complex shapes;

[0010] (2) The CeO2 layer prepared by the present invention is a multi-level nanostructure, which can increase the Cr2O3 nucleation sites, accelerate the formation of the Cr2O3 diffusion barrier, and inhibit the occurrence of interdiffusion in the early stage of oxidation;

[0011] (3) The CeO2 and NiO coatings of the present invention synergistically improve the high-temperature oxidation resistance and electrical conductivity of the SOFC connector, and are suitable as coating materials for solid oxide fuel cell connectors. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 This is the surface morphology of the CeO2 / Ni coated stainless steel prepared in Example 1.

[0013] Figure 2 This is a cross-sectional morphology of the CeO2 / Ni coated stainless steel prepared in Example 1 after oxidation in air at 800°C for 10 weeks.

[0014] Figure 3 This is a cross-sectional element line scan of the CeO2 / Ni coated stainless steel prepared in Example 1 after oxidation in air at 800°C for 10 weeks. DETAILED DESCRIPTION

[0015] Example 1

[0016] (1) Preparation of CeO2 / Ni composite coating by electrochemical deposition: CeO2 electrolyte solution was prepared with the following composition: cerium nitrate 22 g / L, ammonium chloride 5 g / L, potassium chloride 4 g / L. Deposition parameters were: deposition time 10 min, bath temperature 40°C, deposition current density 2.5 mA / cm 2 Using graphite as the anode and the polished and cleaned substrate as the cathode, multi-level nanostructured CeO2 was electrochemically deposited, and then metallic Ni was electrochemically deposited in the gaps between the CeO2 for 5 minutes to obtain a nanocomposite coating of Ni embedded in CeO2.

[0017] (2) Thermal conversion: The deposited sample was heated to 800 °C in a resistance furnace, kept warm for 1 week, cooled to room temperature in the furnace, and then weighed. The cumulative oxidation time was 10 weeks, and a CeO2 / NiO coating was obtained.

[0018] Figure 1 This is the surface morphology of the CeO2 / Ni coated stainless steel prepared in Example 1. After step-by-step electrochemical deposition, a nano-composite coating of Ni embedded in CeO2 was prepared on the surface of the stainless steel substrate. The coating has a dense structure and CeO2 is a multi-level nanostructure.

[0019] Figure 2 、 Figure 3 The following are the cross-sectional morphology and corresponding elemental line scan images of the CeO2 / Ni-coated stainless steel prepared in Example 1 after oxidation at 800°C in air for 10 weeks. The CeO2 / NiO coating formed on the surface of the CeO2 / Ni-coated stainless steel obtained by electrochemical deposition in this invention is no longer detected in the CeO2 / NiO. Furthermore, the Ni content of the stainless steel matrix beneath the oxide film is relatively low, indicating that the CeO2 layer effectively inhibits interdiffusion during the initial oxidation phase and, in conjunction with NiO, prevents the outward migration of Cr. The thermally grown Cr2O3 inner layer is only approximately 1 μm thick, demonstrating that the CeO2 / NiO coating significantly improves the high-temperature oxidation resistance and electrical properties of the stainless steel.

[0020] Example 2

[0021] (1) Preparation of CeO2 / Ni composite coating by electrochemical deposition: CeO2 electrolyte solution was prepared with the following composition: cerium nitrate 25 g / L, ammonium chloride 7 g / L, potassium chloride 5 g / L. Deposition parameters were: deposition time 10 min, bath temperature 50 °C, deposition current density 2.5 mA / cm 2 Using graphite as the anode and the polished and cleaned substrate as the cathode, multi-level nanostructured CeO2 was electrochemically deposited, and then metallic Ni was electrochemically deposited in the gaps between the CeO2 for 5 minutes to obtain a nanocomposite coating of Ni embedded in CeO2.

[0022] (2) Thermal conversion: The deposited sample was heated to 800°C in a resistance furnace, kept at this temperature for 1 week, cooled to room temperature in the furnace, and weighed. The cumulative oxidation time was 10 weeks. CeO2 / NiO coating was obtained.

[0023] Example 3

[0024] (1) Preparation of CeO2 / Ni composite coating by electrochemical deposition: CeO2 electrolyte solution was prepared with the following composition: cerium nitrate 20 g / L, ammonium chloride 5 g / L, potassium chloride 3 g / L. Deposition parameters were: deposition time 10 min, bath temperature 40°C, deposition current density 2.5 mA / cm 2 Using graphite as the anode and the polished and cleaned substrate as the cathode, multi-level nanostructured CeO2 was electrochemically deposited, and then metallic Ni was electrochemically deposited in the gaps between the CeO2 for 5 minutes to obtain a nanocomposite coating of Ni embedded in CeO2.

[0025] (2) Thermal conversion: The deposited sample was heated to 800°C in a resistance furnace, kept at this temperature for 1 week, cooled to room temperature in the furnace, and weighed. The cumulative oxidation time was 10 weeks. CeO2 / NiO coating was obtained.

[0026] The above description is merely an embodiment of the present invention and does not limit the present invention. Any simple modification, change and equivalent change made to the embodiment according to the technical essence of the invention shall fall within the protection scope of the technical solution of the present invention.

Claims

1. A method for preparing a CeO2 / NiO coating by electrochemical deposition, characterized in that: The following steps are involved: (1) Using graphite as the anode and the polished and cleaned substrate as the cathode, electrochemically depositing CeO2, and then electrochemically depositing metal Ni in the gaps between CeO2 to obtain a nanocomposite coating of Ni embedded in CeO2; (2) The deposited sample was placed in an 800 °C resistance furnace for oxidation to obtain a CeO2 / NiO coating.

2. The method according to claim 1, characterized in that The CeO2 in step (1) is a multi-level nanostructure.

3. The method according to claim 1, characterized in that The parameters for the electroplating of CeO2 in step (1) are: deposition time 8-10 minutes, bath temperature 40-50 °C, deposition current density 2.5 mA / cm 2 .

4. The method according to claim 1, wherein The composition of the solution used for electrodeposition in step (1) is as follows: 20-25 g / L of cerium nitrate, 5-7 g / L of ammonium chloride, and 3-5 g / L of potassium chloride.

5. The method according to claim 1, characterized in that The oxidation time in step (2) was 10 weeks.

6. The method according to claim 1, characterized in that The oxidation rate constant of the deposited sample described in step (2) is (4~5)×10 -14 g 2 cm -4 s -1 .

7. The method according to claim 5, characterized in that After 10 weeks of oxidation in step (2), the thermal conversion film is mainly composed of CeO2 / NiO, and the coating thickness is 2~4 μm.

8. The method according to claim 5, characterized in that The substrate in step (1) is stainless steel. The surface oxide film of the coated stainless steel obtained after oxidation for 10 weeks in step (2) has an overall surface resistivity of 20-25 mW cm 2 .

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