Coating material for solid oxide fuel cell separator and manufacturing method thereof

Abstract

The present invention relates to a coating material for a solid oxide fuel cell separator and a method for manufacturing the same. In one embodiment, the coating material for a solid oxide fuel cell separator comprises a composite oxide comprising a matrix comprising a manganese (Mn)-cobalt (Co) spinel oxide; and a dopant doped into the matrix, wherein the dopant comprises copper (Cu) and a lanthanide group element.

Description

Technology Field

[0001] The present invention relates to a coating material for a solid oxide fuel cell separator and a method for manufacturing the same. Background Technology

[0003] A solid oxide fuel cell (SOFC) stack has a structure in which unit cells are stacked in multiple layers. The separator of the SOFC stack is one of the core components, serving to electrically connect the unit cells and block air from the anode from hydrogen gas from the cathode.

[0004] The separator materials for solid oxide fuel cells require excellent electrical conductivity and chemical stability. Among the aforementioned separator materials, metal materials are suitable for separator applications due to their higher mechanical strength, lower cost, and ease of manufacturing compared to ceramic materials; therefore, stainless steel and alloys such as Cr-Fe-Y are primarily used depending on the operating temperature.

[0005] However, metal separators oxidize at the operating temperature of solid oxide fuel cells (typically 600 to 1000°C), causing an increase in electrical resistance. Additionally, oxide films containing mainly chromium (Cr) volatilize, blocking the three-phase boundary where electrochemical reactions occur at the anode, which is disadvantageous for long-term operation. In this case, the performance and lifespan of the solid oxide fuel cell stack are significantly reduced. Therefore, suppressing the formation of an oxide film with low electrical conductivity due to oxidation of the metal separator for solid oxide fuel cells and inhibiting the evaporation of chromium (Cr) from said oxide film can be considered a key technology for solid oxide fuel cell metal separators.

[0006] Meanwhile, in the operating environment of a solid oxide fuel cell, the volatilization of chromium (Cr) occurs as shown in the following reaction equations (1) to (3):

[0007] [Reaction Equation]

[0008] 2Cr2O3(s) + 3O2(g) ↔ 4CrO3(g) … (1)

[0009] 2Cr2O3(s) + 3O2(g) + 4H2O(g) ↔ 4CrO2(OH)2(g) … (2)

[0010] Cr2O3(s) + O2(g) + H2O(g) ↔ 2CrO2(OH)(g) … (3).

[0011] Conventionally, to prevent chromium volatilization on solid oxide fuel cell separators, a method has been proposed to form an oxide film with low electrical conductivity on the surface of a metal separator and to suppress the volatilization of Cr components as much as possible by coating ceramics with high electrical conductivity such as perovskite, spinel structure such as (La,Sr)MnO3, (La,Ca)CrO3, and (Mn,Co)3O4, or reactive element oxides such as yttrium (Y), lanthanum (La), and cerium (Ce).

[0012] Conventional spinel materials allow for dense coating through reoxidation following reduction heat treatment, but they had the problem of low chromium retention. Additionally, perovskite and reactive elemental oxide materials were difficult to coat densely on metal separator plates, making it difficult to prevent chromium from volatilizing and diffusing from the surface of the chromium oxide film.

[0013] The background technology related to the present invention is disclosed in Korean Published Patent Application No. 2010-0120432 (published Nov. 16, 2010; Title of Invention: Separator for Solid Oxide Fuel Cell and Method for Manufacturing the Same). The problem to be solved

[0015] One objective of the present invention is to provide a coating material for a solid oxide fuel cell separator that has an excellent effect of preventing degradation caused by the formation of an oxide film on the solid oxide fuel cell separator and prevents degradation of the fuel cell stack.

[0016] Another objective of the present invention is to provide a coating material for a solid oxide fuel cell separator plate having high electrical conductivity and excellent durability and oxidation resistance.

[0017] Another objective of the present invention is to provide a coating material for a solid oxide fuel cell separator that has excellent adhesion by preventing delamination, having a coefficient of thermal expansion similar to that of the separator.

[0018] Another objective of the present invention is to provide a coating material for a solid oxide fuel cell separator that has excellent structural density during sintering, thereby providing an excellent effect of suppressing continuous oxygen inflow and an excellent effect of suppressing the exposure of a chromium (Cr)-containing oxide film.

[0019] Another objective of the present invention is to provide a coating material for solid oxide fuel cell separators that offers excellent productivity and economic efficiency.

[0020] Another objective of the present invention is to provide a method for manufacturing a coating material for a solid oxide fuel cell separator.

[0021] Another objective of the present invention is to provide a solid oxide fuel cell separator comprising the coating material for the solid oxide fuel cell separator.

[0022] Another objective of the present invention is to provide a method for manufacturing the solid oxide fuel cell separator plate.

[0023] Another objective of the present invention is to provide a solid oxide fuel cell comprising the separator plate. means of solving the problem

[0025] One aspect of the present invention relates to a coating material for a solid oxide fuel cell separator. In one embodiment, the coating material for a solid oxide fuel cell separator comprises a composite oxide comprising a matrix comprising a manganese (Mn)-cobalt (Co) spinel oxide; and a dopant doped into the matrix, wherein the dopant comprises copper (Cu) and a lanthanide group element.

[0026] In one embodiment, the manganese-cobalt spinel oxide may include one or more of MnCo2O4 and CoMn2O4.

[0027] In one embodiment, the lanthanide group elements may include one or more of lanthanum (La), cerium (Ce), and samarium (Sm).

[0028] In one embodiment, the coating material may be doped with copper greater than 0 and less than 20 mol% and lanthanide elements greater than 0 and less than 10 mol%.

[0029] In one embodiment, the coating material may further include lanthanide (Ln)-manganese (Mn) perovskite oxide.

[0030] Another aspect of the present invention relates to a method for manufacturing a coating material for a solid oxide fuel cell separator. In one embodiment, the method for manufacturing a coating material for a solid oxide fuel cell separator comprises the steps of: preparing a mixed composition solution by dissolving a precursor mixture comprising a manganese precursor, a cobalt precursor, a copper precursor, and a lanthanide precursor, an acid, and ethylenediaminetetraacetic acid (EDTA) in a solvent; preparing a gel mixture by adjusting the pH of the mixed composition solution and heat-treating it; and calcining the gel mixture; wherein the coating material comprises a composite oxide comprising a matrix comprising a manganese (Mn)-cobalt (Co) spinel oxide and a dopant doped into the matrix, and the dopant comprises copper (Cu) and a lanthanide group element.

[0031] In one embodiment, the gel mixture can be prepared by adjusting the pH of the mixture composition solution to 8.0 or higher and heat-treating it at 150 to 200°C.

[0032] In one embodiment, before calcining the gel mixture, the method may further include a step of heat-treating the gel mixture at 350 to 450°C.

[0033] In one specific example, the above calcination can be carried out at 700 to 900°C.

[0034] In one embodiment, the coating material may be doped with copper greater than 0 and less than 20 mol% and lanthanide elements greater than 0 and less than 10 mol%.

[0035] In one embodiment, the coating material may further include lanthanide (Ln)-manganese (Mn) perovskite oxide.

[0036] Another aspect of the present invention relates to a solid oxide fuel cell separator comprising the coating material for the solid oxide fuel cell separator. In one embodiment, the solid oxide fuel cell separator comprises a metal substrate; and a coating layer formed on at least one surface of the metal substrate; wherein the coating layer is formed from the coating material.

[0037] In one embodiment, the metal substrate may include an Fe-Cr alloy.

[0038] Another aspect of the present invention relates to a method for manufacturing a solid oxide fuel cell separator. In one embodiment, the method for manufacturing a solid oxide fuel cell separator comprises the steps of: coating a coating material on at least one surface of a metal substrate; and heat-treating the metal substrate coated with the coating material.

[0039] In one embodiment, the heat treatment may be carried out by including the step of first heat treating a metal substrate coated with the coating material at 900 to 1100°C in a reducing atmosphere; and the step of second heat treating the metal substrate that has undergone the first heat treatment at 700 to 900°C in the atmosphere. Effects of the invention

[0041] The coating material for a solid oxide fuel cell separator according to the present invention has an excellent effect of preventing degradation caused by the formation of an oxide film on the solid oxide fuel cell separator, prevents degradation of the fuel cell stack, and has high electrical conductivity and excellent durability and oxidation resistance to prevent an increase in current collection resistance during operation; it has excellent adhesion by preventing delamination due to the similar coefficient of thermal expansion between the separator and the coating material; it has excellent structural density during sintering, which provides an excellent effect of suppressing continuous oxygen inflow; it has an excellent effect of suppressing the exposure of a chromium (Cr)-containing oxide film; and it can have excellent productivity and economic efficiency. Brief explanation of the drawing

[0043] Figure 1 is a graph showing the X-ray diffraction analysis results of Example 1. Figure 2 is a scanning electron microscope (SEM) image of Example 1. Figure 3 schematically illustrates the method for measuring the surface resistance of the coating materials of the example and comparative example. Figure 4 is a graph showing the results of measuring the initial sheet resistance (ASR) of the coating layers of the example and comparative example. Figure 5 is a graph of the high-temperature durability evaluation results of the examples and comparative examples. Specific details for implementing the invention

[0044] In describing the present invention, if it is determined that a detailed description of related known technologies or configurations could unnecessarily obscure the essence of the invention, such detailed description will be omitted.

[0045] Furthermore, the terms described below are defined in consideration of their functions in the present invention; since these may vary depending on the intentions or practices of the user or operator, their definitions should be based on the content throughout this specification describing the present invention.

[0047] Coating material for solid oxide fuel cell separators

[0048] One aspect of the present invention relates to a coating material for a solid oxide fuel cell separator. In one embodiment, the coating material for a solid oxide fuel cell separator (or coating material) comprises a composite oxide comprising a matrix comprising a manganese (Mn)-cobalt (Co) spinel oxide; and a dopant doped into the matrix, wherein the dopant comprises copper (Cu) and a lanthanide group element.

[0049] In one embodiment, the coating material can be represented by the following chemical formula 1:

[0050] [Chemical Formula 1]

[0051] Ln x Cu y Mn z Co q O4

[0052] (In the above chemical formula 1, Ln is a lanthanide element, Cu is copper, Mn is manganese, Co is cobalt, and O is oxygen, 0 < x ≤ 0.3, 0 < y ≤ 0.6, 0 < z < 3 and 0 < q < 3, and x + y + z + q = 3).

[0053] When a coating material of the condition of Chemical Formula 1 above is included, the adhesion between the coating layer and the metal substrate is excellent, and durability, electrical conductivity, chemical resistance, and high-temperature corrosion resistance (heat resistance) may be excellent. For example, in Chemical Formula 1 above, 0 < x ≤ 0.2, 0 < y ≤ 0.5, 0.5 ≤ z ≤ 3, and 0.5 ≤ q ≤ 2, and x + y + z + q = 3. As another example, Chemical Formula 1 above is Ln 0.1 Cu 0.2 Mn 1.35 Co 1.35 It could be O4.

[0054] The above matrix comprises manganese (Mn)-cobalt (Co) spinel oxide ((Mn,Co)3O4). Since the manganese-cobalt spinel oxide has excellent oxidation resistance and a coefficient of thermal expansion similar to that of the ferritic stainless steel material (Fe-Cr alloy) used as the metal substrate for the separator, it exhibits excellent adhesion between the coating layer and the metal substrate and can stably perform the function of the coating layer under high-temperature operating conditions.

[0055] In one embodiment, the manganese-cobalt spinel oxide may include one or more of MnCo2O4 having a cubic structure and CoMn2O4 having a tetragonal structure.

[0056] The above copper (Cu) provides high electrical conductivity and can effectively suppress the influx of oxygen by improving the sinterability of the material when doped into Mn-Co-based oxides.

[0057] The above lanthanide group element is one of the reactive elements, and lanthanide-based oxides have excellent oxidation resistance, so when doped into the matrix of the coating material, the oxidation resistance of the material can be increased.

[0058] In one embodiment, the lanthanide group element may include one or more of lanthanum (La), cerium (Ce), and samarium (Sm). When the lanthanide group element is included, the oxidation resistance of the coating material may be excellent. For example, lanthanum (La) may be included.

[0059] In one embodiment, the copper (Cu) in the coating material may be doped in an amount greater than 0 and less than or equal to 20 mol%. When doped under these conditions, the adhesion between the coating layer and the metal substrate is excellent, and the durability and oxidation resistance of the coating material may be excellent. For example, the copper may be doped in an amount of 1 to 20 mol%, 1 to 10 mol%, or 2 to 5 mol%.

[0060] In one embodiment, the lanthanide group element may be doped into the coating material in an amount greater than 0 and less than or equal to 10 mol%. When doped under these conditions, the adhesion between the coating layer and the metal substrate is excellent, and the structural density and electrical conductivity of the coating material may be excellent. For example, the lanthanide group element may be doped in an amount of 1 to 20 mol%, 1 to 10 mol%, or 2 to 5 mol%.

[0061] In one embodiment, the dopant may contain the lanthanide group element and copper in a molar ratio of 1:0.5 to 1:4. When included under these conditions, the adhesion between the coating layer and the metal substrate is excellent, and the durability, oxidation resistance, structural density, and electrical conductivity of the coating material may be excellent. For example, the lanthanide group element and copper may be contained in a molar ratio of 1:1 to 1:2.5.

[0062] In one embodiment, the coating material may further include lanthanide (Ln)-manganese (Mn) perovskite oxide (or perovskite oxide). When the perovskite oxide is included, the durability, corrosion resistance, and adhesion to the metal substrate of the coating layer may be excellent.

[0063] For example, the above perovskite oxide may include LnMnO3 (where Ln is a lanthanide group element).

[0064] In one embodiment, the lanthanide group element may include one or more of lanthanum (La), cerium (Ce), and samarium (Sm). When the lanthanide group element is included, the oxidation resistance of the coating material may be excellent. For example, lanthanum (La) may be included.

[0065] In one embodiment, the complex oxide and the lanthanide-manganese perovskite oxide each have a specific surface area (BET) of 5 to 30 m² 2 / g. Under the above specific surface area conditions, mixability and moldability are excellent, and the coating material may have excellent high-temperature corrosion resistance, oxidation resistance, structural density, and electrical conductivity.

[0067] Method for manufacturing a coating material for solid oxide fuel cell separators

[0068] Another aspect of the present invention relates to a method for manufacturing a coating material for a solid oxide fuel cell separator. In one embodiment, the method for manufacturing a coating material for a solid oxide fuel cell separator comprises: (S10) a step of preparing a mixed composition solution by dissolving a precursor mixture comprising a manganese precursor, a cobalt precursor, a copper precursor, and a lanthanide precursor, an acid, and ethylenediaminetetraacetic acid (EDTA) in a solvent; (S20) a step of preparing a gel mixture by adjusting the pH of the mixed composition solution and heat-treating it; and (S30) a step of calcining the gel mixture; wherein the coating material comprises a composite oxide comprising a matrix comprising a manganese (Mn)-cobalt (Co) spinel oxide and a dopant doped into the matrix, and the dopant comprises copper (Cu) and a lanthanide group element.

[0070] (S10) Preparation step of the mixed composition solution

[0071] The above step is to prepare a mixed composition solution by dissolving a precursor mixture comprising a manganese precursor, a cobalt precursor, a copper precursor, and a lanthanide precursor, an acid, and ethylenediaminetetraacetic acid (EDTA) in a solvent.

[0072] The above manganese precursor may include one or more of manganese acetate and manganese nitrate. For example, it may include manganese acetate tetrahydrate (Mn(CH3COO)2·4H2O).

[0073] The above cobalt precursor may include one or more of cobalt acetate and cobalt nitrate. For example, it may include cobalt nitrate hexahydrate (Co(NO3)2·6H2O).

[0074] The copper precursor may include one or more of copper acetate and copper nitrate. For example, it may include copper nitrate 2.5-hydrate (Cu(NO3)2·2.5H2O).

[0075] The above lanthanide precursor may include one or more of lanthanide acetate and lanthanide nitrate. The above lanthanide may include lanthanide group elements. For example, it may include lanthanide nitrate hexahydrate (La(NO3)3·6H2O).

[0076] For example, the above manganese, cobalt, copper, and lanthanide precursors can each be dissolved in water to be prepared in the form of a precursor solution.

[0077] The above Acid and ethylenediaminetetraacetic acid (EDTA) may be included for the purpose of chelating the above precursor mixture.

[0078] The above acid may include organic acids. For example, the above acid may include one or more of phosphoric acid, fumaric acid, lactic acid, citric acid, malic acid, butyric acid, formic acid, and acetic acid. When the above acid is included, the chelating effect of the precursor mixture may be excellent.

[0079] The above solvent may include water. For example, the above solvent may include ultrapure water.

[0080] In one embodiment, the above-mentioned mixed composition solution can be prepared by dissolving a precursor mixture comprising a manganese precursor, a cobalt precursor, a copper precursor, and a lanthanide precursor in water (ultrapure water), and then adding an acid and ethylenediaminetetraacetic acid (EDTA) to dissolve it.

[0082] (S20) Gel mixture preparation step

[0083] The above step is to prepare a gel mixture by adjusting the pH of the above-mentioned mixed composition solution and heat treating (or primary heat treatment).

[0084] In one embodiment, the gel mixture can be prepared by adjusting the pH of the mixed composition solution to 8.0 or higher and heat-treating at 150 to 200°C. When the pH of the mixed composition solution is adjusted to 8.0 or higher, a sol can be easily formed from the mixed composition solution. For example, the pH of the mixed composition solution can be adjusted to 8 to 13, 8 to 11, or 8 to 10. Additionally, when heat-treated under the above temperature conditions, the sol gels, and the gel mixture can be easily formed.

[0085] For example, the heat treatment can be performed for 1 to 60 hours at 150 to 200°C with a rotation speed of 100 to 300 rpm after adjusting the pH of the mixed composition solution to 8.0 or higher. As another example, the heat treatment can be performed for 25 to 40 hours at 170 to 190°C with a rotation speed of 150 to 250 rpm after adjusting the pH of the mixed composition solution to 8.0 or higher.

[0087] (S30) Calcination stage

[0088] The above step is the step of calcining the gel mixture.

[0089] In one embodiment, before calcining the gel mixture, the method may further include a step of heat-treating (or performing a secondary heat treatment) the gel mixture at 350 to 450°C. Under these conditions, the electrical conductivity, structural density, durability, high-temperature corrosion resistance, and chemical resistance of the composite oxide may be excellent. For example, the heat treatment may involve heat-treating the gel mixture at 350 to 450°C for 1 to 10 hours. As another example, the heat treatment may involve heat-treating the gel mixture at 370 to 420°C for 2 to 5 hours.

[0090] In one embodiment, the calcination can be carried out at 700 to 900°C. When the gel mixture is calcined under these conditions, a coating material containing a composite oxide is easily formed, and the adhesion between the coating material and the metal substrate of the separator is excellent, and the microstructure density, electrical conductivity, durability, high-temperature corrosion resistance, and chemical resistance of the coating material may be excellent.

[0091] In one embodiment, the coating material can be represented by the following chemical formula 1:

[0092] [Chemical Formula 1]

[0093] Ln x Cu y Mn z Co q O4

[0094] (In the above chemical formula 1, Ln is a lanthanide element, Cu is copper, Mn is manganese, Co is cobalt, and O is oxygen, 0 < x ≤ 0.3, 0 < y ≤ 0.6, 0 < z < 3 and 0 < q < 3, and x + y + z + q = 3).

[0095] When a coating material of the condition of Chemical Formula 1 above is included, the adhesion between the coating layer and the metal substrate is excellent, and durability, electrical conductivity, chemical resistance, and high-temperature corrosion resistance (heat resistance) may be excellent. For example, in Chemical Formula 1 above, 0 < x ≤ 0.2, 0 < y ≤ 0.5, 0.5 ≤ z ≤ 3, and 0.5 ≤ q ≤ 2, and x + y + z + q = 3. As another example, Chemical Formula 1 above is Ln 0.1 Cu 0.2 Mn 1.35 Co 1.35 It could be O4.

[0096] In one embodiment, the lanthanide group element may include one or more of lanthanum (La), cerium (Ce), and samarium (Sm). When the lanthanide group element is included, the oxidation resistance of the coating material may be excellent. For example, lanthanum (La) may be included.

[0097] In one embodiment, the copper (Cu) in the coating material may be doped in an amount greater than 0 and less than or equal to 20 mol%. When doped under these conditions, the adhesion between the coating layer and the metal substrate is excellent, and the durability and oxidation resistance of the coating material may be excellent. For example, the copper may be doped in an amount of 1 to 20 mol%, 1 to 10 mol%, or 2 to 5 mol%.

[0098] In one embodiment, the lanthanide group element may be doped into the coating material in an amount greater than 0 and less than or equal to 10 mol%. When doped under these conditions, the adhesion between the coating layer and the metal substrate is excellent, and the structural density and electrical conductivity of the coating material may be excellent. For example, the lanthanide group element may be doped in an amount of 1 to 20 mol%, 1 to 10 mol%, or 2 to 5 mol%.

[0099] In one embodiment, the dopant may contain the lanthanide group element and copper in a molar ratio of 1:0.5 to 1:4. When included under these conditions, the adhesion between the coating layer and the metal substrate is excellent, and the durability, oxidation resistance, structural density, and electrical conductivity of the coating material may be excellent. For example, the lanthanide group element and copper may be contained in a molar ratio of 1:1 to 1:2.5.

[0100] In one embodiment, the coating material may further include a lanthanide-manganese (Mn) perovskite oxide (or perovskite oxide). For example, during the formation process of the coating layer, the composite oxide and the lanthanide group dopant may react to form a secondary phase of a perovskite structure. When the perovskite oxide is included, the durability, corrosion resistance, and adhesion to the metal substrate of the coating layer may be excellent.

[0101] For example, the above perovskite oxide may include LnMnO3 (where Ln is a lanthanide group element).

[0102] In one embodiment, the lanthanide group element may include one or more of lanthanum (La), cerium (Ce), and samarium (Sm). When the lanthanide group element is included, the oxidation resistance of the coating material may be excellent. For example, lanthanum (La) may be included.

[0103] In one embodiment, the complex oxide and the lanthanide-manganese perovskite oxide each have a specific surface area (BET) of 5 to 30 m² 2 / g. Under the above specific surface area conditions, mixability and moldability are excellent, and the coating material may have excellent high-temperature corrosion resistance, oxidation resistance, structural density, and electrical conductivity.

[0105] Solid oxide fuel cell separator comprising a coating material for solid oxide fuel cell separator

[0106] Another aspect of the present invention relates to a solid oxide fuel cell separator comprising the coating material for the solid oxide fuel cell separator. In one embodiment, the solid oxide fuel cell separator comprises a metal substrate; and a coating layer formed on at least one surface of the metal substrate; wherein the coating layer is formed from the coating material.

[0107] In one embodiment, the metal substrate may include an Fe-Cr alloy. When the metal substrate is included, the thermal expansion coefficient is similar to that of the coating layer, so excellent adhesion may be achieved. For example, the metal substrate may include ferritic stainless steel.

[0108] In one embodiment, the coating layer may have a thickness of 0.1 μm to 1 mm. Under these conditions, the adhesion may be excellent, and the durability, high-temperature corrosion resistance and oxidation resistance may be excellent, and the electrical conductivity may be excellent.

[0109] The above coating material may be the same as that described above.

[0110] In one embodiment, the separator has a surface resistance of the coating layer of 5.0 mΩ·cm measured at 800°C. 2It may be less than or equal to. Under the above conditions, the effect of preventing an increase in current collection resistance at high temperatures may be excellent. For example, the sheet resistance of the coating layer of the separator measured at 800℃ is 1.5~2.5 mΩ·cm 2 It could be.

[0112] Method for manufacturing a solid oxide fuel cell separator

[0113] Another aspect of the present invention relates to a method for manufacturing a solid oxide fuel cell separator. In one embodiment, the method for manufacturing a solid oxide fuel cell separator comprises the steps of: coating a coating material on at least one surface of a metal substrate; and heat-treating the metal substrate coated with the coating material.

[0114] The metal substrate and coating material mentioned above may be the same as those described above.

[0115] In one embodiment, the heat treatment may be carried out by including: a step of first heat treating a metal substrate coated with the coating material at 900 to 1100°C in a reducing atmosphere; and a step of second heat treating the metal substrate that has undergone the first heat treatment at 700 to 900°C in the atmosphere. Under the above conditions, the structural density of the coating layer is excellent, thereby preventing the phenomenon of volatilization and diffusion of chromium by exposing an oxide film such as chromium (Cr), thus preventing performance degradation of the solid oxide fuel cell, and the electrical conductivity and durability are excellent, and the adhesion between the metal substrate and the coating layer may be excellent.

[0116] In one embodiment, the coating can be carried out using conventional methods. For example, the coating material may be applied to at least one surface of the metal substrate, and then the coating may be carried out using one or more of slot coating, bar coating, roll coating, gravure coating, and spin coating.

[0117] For example, the above first heat treatment may be performed on a metal substrate coated with a coating material in a reducing atmosphere at 900 to 1100°C for 1 to 30 hours. Under these conditions, the durability and structural density of the coating layer are excellent, the adhesion between the metal substrate and the coating layer is excellent, and the electrical conductivity and durability may be excellent. As another example, the above first heat treatment may be performed on a metal substrate coated with a coating material in a reducing atmosphere at 950 to 1050°C for 5 to 15 hours. The above reducing atmosphere may be formed by including one or more of hydrogen (H2), argon (Ar), and nitrogen (N2) gases.

[0118] For example, the above second heat treatment may be performed on the metal substrate that has undergone the first heat treatment in the atmosphere at 700 to 900°C for 1 to 30 hours. Under these conditions, the durability and structural density of the coating layer are excellent, the adhesion between the metal substrate and the coating layer is excellent, and the electrical conductivity and durability may be excellent. As another example, the above second heat treatment may be performed on the metal substrate that has undergone the first heat treatment in the atmosphere at 750 to 850°C for 5 to 15 hours.

[0120] Solid oxide fuel cell including a separator

[0121] Another aspect of the present invention relates to a solid oxide fuel cell comprising the separator plate. In one embodiment, the solid oxide fuel cell (or solid oxide fuel cell stack) may have a tubular, flat tubular, and planar structure.

[0122] In one embodiment, the solid oxide fuel cell comprises one or more unit cells in which a fuel electrode, an electrolyte, and an air electrode are sequentially formed, and a separator plate provided between the unit cells, wherein the separator plate may be the same as that described above.

[0123] The above separator can electrically connect the unit cells and block the air of the positive electrode (air electrode) and the hydrogen gas of the negative electrode (fuel electrode).

[0124] For example, the solid oxide fuel cell may further include a sealing material that seals the outer surface of the unit cell and first and second end plates that contact each of the two ends of the one or more unit cells.

[0126] The present invention can contribute to the development of a high-efficiency power generation system by developing a high-temperature corrosion-resistant separator that plays a pivotal role in improving the durability of a solid oxide fuel cell stack, thereby overcoming the problem of stack degradation caused by chromium poisoning and ensuring stability.

[0127] Furthermore, the present invention can resolve the problem of power supply imbalance, which is one of the disadvantages of renewable energy, by improving the performance of the fuel cell system to solve the load fluctuation problem of renewable energy and realize a stable power supply. Additionally, by applying a self-developed separator protective coating material, high-temperature corrosion resistance of the stainless steel separator is secured, thereby ensuring the long-term durability of the stack and enabling improved economic efficiency.

[0128] The present invention can contribute to the advancement of elemental technologies related to separator coating materials with excellent electrochemical activity, efficient stack design, large-area fabrication, and mass production processes, and by developing separator coating materials with excellent conductivity and oxidation resistance, it can be applied not only to solid oxide fuel cells but also to various industrial fields.

[0129] Furthermore, the present invention is considered the most efficient method for reducing greenhouse gases under the climate change regime by improving the durability and performance of a power generation system that does not generate greenhouse gases or pollutants.

[0131] Hereinafter, the structure and operation of the present invention will be explained in more detail through preferred embodiments. However, these are presented as preferred examples of the present invention and should not be interpreted in any way as limiting the present invention. Details not described herein can be sufficiently technically inferred by those skilled in the art, so such descriptions will be omitted.

[0133] Examples and Comparative Examples

[0134] Example 1

[0135] (1) Preparation of mixed composition solution: A precursor mixture containing manganese acetate tetrahydrate (Mn(CH3COO)2·4H2O), cobalt nitrate hexahydrate (Co(NO3)2·6H2O), copper nitrate 2.5-hydrate (Cu(NO3)2·2.5H2O) and lanthanide nitrate hexahydrate (La(NO3)3·6H2O) (where La is lanthanum (La)) was dissolved in ultrapure water, and acetic acid and ethylenediaminetetraacetic acid (EDTA) were added and mixed to prepare a mixed composition solution in which the precursor mixture was chelated.

[0136] (2) Preparation of gel mixture: A sol was formed by adjusting the pH of the above-mentioned mixture solution to 8.0 or higher, and a gel mixture was prepared by heat treatment (first heat treatment) by heat treatment at 180°C at 180 rpm for 30 hours.

[0137] (3) Preparation of coating material for solid oxide fuel cell separator: After the above sol was completely transformed into a gel (gel mixture), heat treatment (secondary heat treatment) was performed at 400°C for 3 hours. Then, the heat-treated gel mixture was calcined at 750°C for 5 hours to prepare a coating material for a solid oxide fuel cell separator.

[0138] The above coating material is [Chemical Formula 1] La 0.1 Cu 0.2 Mn 1.35 Co 1.35It was represented as O4. The coating material included a composite oxide comprising a matrix containing manganese (Mn)-cobalt (Co) spinel oxide; and a dopant doped into the matrix; and a lanthanide (lanthanum (La))-manganese (Mn) perovskite oxide (LaMnO3). In this case, the matrix of the composite oxide was formed as spinel oxides of MnCo2O4 and CoMn2O4, and the composite oxide was doped with copper (Cu) and lanthanum (La) as dopants into the matrix. Additionally, lanthanum (La) formed a perovskite secondary phase with the manganese (Mn). Furthermore, as shown in Chemical Formula 1, the coating material was doped with 6.67 mol% copper and 3.33 mol% lanthanum.

[0140] Comparative Example 1

[0141] A coating material for a solid oxide fuel cell separator was prepared using the same method as in Example 1, except that the above-mentioned lanthanide nitrate was not applied. The coating material is Cu 0.2 Mn 1.4 Co 1.4 A complex oxide represented as O4 was formed.

[0143] Experimental Example

[0144] (1) X-ray diffraction analysis: X-ray diffraction analysis was performed on Example 1 above, and the results are shown in Figure 1 below. In addition, Example 1 above was analyzed using a scanning electron microscope (SEM).

[0145] Figure 1 is a graph showing the X-ray diffraction analysis results of Example 1, and Figure 2 is a scanning electron microscope (SEM) image of Example 1. Referring to Figures 1 and 2, it was found that Example 1 contains a mixture of a composite oxide and a lanthanum-manganese perovskite oxide. In addition, the composite oxide is formed with a cubic structure of MnCo2O4 and a tetragonal structure of CoMn2O4 as the matrix, and it was found that copper and lanthanum were doped into the matrix ((Mn,Co)3O4 lattice) of the composite oxide, and that the lanthanum (La) formed a secondary phase with manganese (Mn).

[0146] (2) Evaluation of surface resistance of coating material: The surface resistance of the coating materials of Example 1 and Comparative Example 1 was evaluated. Specifically, the surface resistance was measured by forming coating layers using the coating materials of Example 1 and Comparative Example 1 on both sides of a metal substrate, VDM Metal’s Crofer 22 APU (Cr-Fe steel). Specifically, the metal substrate (size: 10 x 10 x 2 mm 3 A separator plate was prepared by slurry spin coating the coating materials of Example 1 and Comparative Example 1 on both sides of the metal substrate, respectively, and then performing a first heat treatment at 1000°C for 10 hours in a reducing atmosphere (3.9% / Ar), followed by a second heat treatment at 800°C for 10 hours to form a coating layer (thickness: about 10.6 μm) on the surface of the metal substrate.

[0147] In addition, a measurement system for evaluating surface resistance was constructed using a self-made alumina jig and a small furnace advantageous for maintaining temperature, and the surface resistance (ASR, Area Specific Resistance) of the above examples and comparative examples was precisely calculated through the 4-probe DC conductivity measurement method. Figure 3 below schematically illustrates the surface resistance measurement method of the coating materials of the examples and comparative examples.

[0148] The separator plates of Example 1 and Comparative Example 1 above were subjected to 200 mA / cm² at 50°C intervals within a measurement temperature range of 650–800°C. 2 Sheet resistance was measured by applying a constant current. To stabilize Example 1 and Comparative Example 1 prior to sheet resistance measurement, pre-oxidizing was performed at 800°C for 1 hour. Meanwhile, sheet resistance was also measured for a metal substrate without a coating layer (Crofer 22 APU (Bare), Comparative Example 2) using the same method as in Example 1, and the results are shown in Fig. 4 below.

[0149] Figure 4 is a graph showing the measurement results of the initial sheet resistance (ASR) of the coating layers of the example and comparative example. In Figure 4, Comparative Example 3 shows the initial sheet resistance value of a conventionally known metal substrate (Crofer 22 APU(Bare) ref).

[0150] Referring to Figure 4 above, it was found that Example 1 had significantly lower initial sheet resistance than Comparative Example 1, which did not apply a lanthanide element as a dopant, and Comparative Examples 2 and 3, which did not apply a coating layer, indicating excellent electrical conductivity. Additionally, it was found that the initial sheet resistance of Comparative Example 2 showed a trend similar to that of a conventionally known metal substrate (Comparative Example 3).

[0152] (3) Durability evaluation: For the above Example 1 and Comparative Examples 1 and 2, a durability evaluation was conducted to evaluate the degradation rate in a high-temperature oxidizing atmosphere. Specifically, for the above Example 1 and Comparative Examples 1 and 2, 200 mA / cm² at 800°C 2 Durability evaluation was conducted by applying a constant current, and the results are shown in Figure 5 below.

[0153] Figure 5 is a graph showing the results of the high-temperature durability evaluation of the Examples and Comparative Examples. Referring to Figure 5, it was found that Example 1 exhibited significantly superior high-temperature durability compared to Comparative Examples 1 and 2. In the case of Comparative Example 1, rapid degradation occurred during the initial 20 hours, while in Comparative Example 2, rapid degradation occurred within the initial 10 hours. In the case of Example 1, 0.8 mΩ·cm was maintained for approximately 140 hours. 2 It was found that it had a degradation rate of / khrs.

[0155] The present invention has been described above with reference to embodiments. Those skilled in the art will understand that the present invention may be embodied in modified forms without departing from the essential characteristics of the invention. Therefore, the disclosed embodiments should be considered in an illustrative rather than a restrictive sense. The scope of the invention is defined by the claims, not by the foregoing description, and all variations within the scope of equivalents should be interpreted as being included in the invention.

Claims

Claim 1 A coating material for a solid oxide fuel cell separator comprising a matrix including a manganese (Mn)-cobalt (Co) spinel oxide; and a dopant doped into the matrix; and a matrix including a lanthanide (Ln)-manganese (Mn) perovskite oxide, wherein the dopant comprises copper (Cu) and lanthanide group elements. Claim 2 In claim 1, the manganese-cobalt spinel oxide is a coating material for solid oxide fuel cell separators comprising one or more of MnCo2O4 and CoMn2O4. Claim 3 A coating material for a solid oxide fuel cell separator according to claim 1, wherein the lanthanide group element comprises one or more of lanthanum (La), cerium (Ce), and samarium (Sm). Claim 4 In claim 1, the coating material is a coating material for a solid oxide fuel cell separator plate doped with more than 0 and less than 20 mol% of copper and more than 0 and less than 10 mol% of a lanthanide group element. Claim 5 delete Claim 6 A method for manufacturing a coating material for a solid oxide fuel cell separator, comprising: a step of preparing a mixed composition solution by dissolving a precursor mixture including a manganese precursor, a cobalt precursor, a copper precursor, and a lanthanide precursor, an acid, and ethylenediaminetetraacetic acid (EDTA) in a solvent; a step of preparing a gel mixture by adjusting the pH of the mixed composition solution and heat-treating it; and a step of calcining the gel mixture; wherein the coating material comprises a composite oxide including a matrix including a manganese (Mn)-cobalt (Co) spinel oxide and a dopant doped to the matrix, and a lanthanide (Ln)-manganese (Mn) perovskite oxide, and wherein the dopant comprises copper (Cu) and lanthanide group elements. Claim 7 In claim 6, the method for manufacturing a coating material for a solid oxide fuel cell separator is prepared by adjusting the pH of the gel mixture to 8.0 or higher and heat-treating it at 150 to 200°C. Claim 8 A method for manufacturing a coating material for a solid oxide fuel cell separator according to claim 6, further comprising the step of heat-treating the gel mixture at 350 to 450°C before calcining the gel mixture. Claim 9 In claim 6, the method for manufacturing a coating material for a solid oxide fuel cell separator plate, wherein the calcination is carried out at 700 to 900°C. Claim 10 A method for manufacturing a coating material for a solid oxide fuel cell separator according to claim 6, wherein the coating material is doped with copper greater than 0 and 20 mol% and lanthanide group elements greater than 0 and 10 mol%. Claim 11 delete Claim 12 A solid oxide fuel cell separator comprising: a metal substrate; and a coating layer formed on at least one surface of the metal substrate; wherein the coating layer is formed from a coating material according to any one of claims 1 to 4. Claim 13 In claim 12, the metal substrate comprises a Fe-Cr alloy, forming a solid oxide fuel cell separator. Claim 14 A method for manufacturing a solid oxide fuel cell separator, comprising: a step of coating a coating material according to any one of claims 1 to 4 on at least one surface of a metal substrate; and a step of heat-treating the metal substrate coated with the coating material. Claim 15 A method for manufacturing a solid oxide fuel cell separator according to claim 14, wherein the heat treatment comprises: a step of first heat treating a metal substrate coated with the coating material at 900 to 1100°C in a reducing atmosphere; and a step of second heat treating the metal substrate that has undergone the first heat treatment at 700 to 900°C in air.

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