Separator for solid oxide fuel cell and manufacturing method therefor

Abstract

The present invention relates to a separator for a solid oxide fuel cell and a manufacturing method therefor, the separator comprising: a metal support layer; and a protective layer surrounding the metal support layer, wherein the metal support layer is an alloy plate containing chromium, the protective layer is a cobalt-nickel alloy thin film, comprises 30 to 70 wt% of cobalt and 70 to 30 wt% of nickel, and has a maximum tensile strength of 1200 MPa to 2300 MPa (both inclusive). The separator for a solid oxide fuel cell and the manufacturing method therefor of the present invention can exhibit improved mechanical properties, excellent suppression of chromium volatilization, and low sheet resistance at high temperatures.

Description

Separator for solid oxide fuel cells and method for manufacturing the same

[0001] The present invention relates to a separator for a solid oxide fuel cell having improved mechanical properties, an excellent chromium volatilization inhibition effect, and low sheet resistance, and a method for manufacturing the same.

[0002] The present invention is derived from research conducted as part of the Materials and Components Package Technology Development Project of the Korea Institute of Industrial Technology Evaluation and Management, funded by the government (Ministry of Trade, Industry and Energy) [Project No.: 2410003844, Research Project Title: Development of Design and Manufacturing Technology for 400 cm² Thick Plate SOFC Separator Based on High-Temperature Plastic Deformation].

[0003] The present invention is derived from research conducted as part of the Future Leading Research Equipment Core Technology Development (R&D) by the Korea Institute of Science and Technology Promotion, funded by the government (Ministry of Science and ICT) [Project No.: 2710069216, Research Project Title: Development of Core Technology for Scanning Electrochemical Microscope for Electrochemistry-based Analysis of Low-Dimensional Nanomaterials].

[0004] The use of fuel cells as clean energy is continuously increasing across all industrial sectors, including automobiles and energy. Accordingly, there is also a growing demand for fuel cells that maintain stable performance even after long-term use.

[0005] Solid oxide fuel cells (SOFCs) are manufactured in planar SOFC stacks and various other shapes. Planar SOFC stacks are manufactured with a structure in which unit cells and metal separators are stacked alternately. The unit cells consist of an oxygen ion-conducting electrolyte and a cathode and anode located on either side thereof. The metal separators are formed with embossed or recessed channels to supply fuel gas or air.

[0006] A plate solid oxide fuel cell is a planar SOFC stack, a plate-type single cell is a unit cell, and a metal separator refers to a metal separator. The metal separator used in conventional planar SOFC stacks, i.e., solid oxide fuel cells, is formed into a plate shape with channels for supplying fuel gas or air molded in intaglio or relief.

[0007] Ferritic stainless steel is used to improve durability and ensure a long lifespan while operating planar SOFC stacks at high temperatures of 650 to 1000°C. Ferritic stainless steel is composed of Fe-Cr alloys with a high Cr content.

[0008] When Fe-Cr alloys are used as metal separators in solid oxide fuel cells, the metal separators oxidize at high temperatures, forming a Cr oxide film (Cr2O3) with insulating properties on the metal surface. The volatilization of this formed Cr oxide film causes problems that degrade the electrical characteristics and long-term operational stability of the solid oxide fuel cell.

[0009] Related prior art includes Korean published patent No. 10-2024-0039471 and Korean published patent No. 10-2176482.

[0010] The objective of the embodiment is to provide a separator for a solid oxide fuel cell having improved mechanical properties, an excellent chromium volatilization inhibition effect, and low sheet resistance at high temperatures, and a method for manufacturing the same.

[0011] To achieve the above objective, a separator for a solid oxide fuel cell according to one embodiment of the present invention comprises a metal support layer and a protective layer surrounding the metal support layer.

[0012] The above metal support layer may be an alloy plate containing chromium.

[0013] The above protective layer is a cobalt-nickel alloy thin film.

[0014] The protective layer may contain 30 to 70 wt% cobalt and 70 to 30 wt% nickel.

[0015] The maximum tensile strength of the above protective layer may be 1200 MPa or more and 2300 MPa or less.

[0016] To achieve the above objective, a method for manufacturing a separator for a solid oxide fuel cell according to another embodiment of the present invention comprises the step of forming a protective layer on a metal support layer through electroplating to obtain a separator for a solid oxide fuel cell, wherein the metal support layer is an alloy plate containing chromium, the protective layer is a cobalt-nickel alloy thin film, and the protective layer has a content range of 30 to 70 wt% of cobalt and 70 to 30 wt% of nickel.

[0017] The separator for a solid oxide fuel cell and the method for manufacturing the same according to the present invention have improved mechanical properties, an excellent effect of suppressing chromium volatilization, and can have low sheet resistance at high temperatures.

[0018] FIG. 1 is a conceptual diagram illustrating an exemplary cross-sectional form of a separator plate according to the present invention.

[0019] FIGS. 2A, 2B, and 2C are graphs and SEM images confirming the composition and plating state of the thin film through an EDS line scan test measured with samples of Example 1, Example 2, and Comparative Example of the manufacturing example, respectively.

[0020] FIGS. 3A, FIGS. 3B, and FIGS. 3C are graphs and SEM images showing the results of Cr volatility evaluation using an EDS line scan test measured with samples of Example 1, Example 2 of the manufacturing example, and the comparative example, respectively.

[0021] Figure 4 is a conceptual diagram explaining the preparation and method of the tensile test specimen applied in Evaluation Example 3.

[0022] Figure 5 is a graph showing the tensile test results of Evaluation Example 3.

[0023] To achieve the above objective, a separator for a solid oxide fuel cell according to one embodiment of the present invention comprises a metal support layer and a protective layer surrounding the metal support layer.

[0024] The above metal support layer may be an alloy plate containing chromium.

[0025] The above protective layer is a cobalt-nickel alloy thin film.

[0026] The protective layer may contain 30 to 70 wt% cobalt and 70 to 30 wt% nickel.

[0027] The maximum tensile strength of the above protective layer may be 1200 MPa or more and 2300 MPa or less.

[0028] To achieve the above objective, a method for manufacturing a separator for a solid oxide fuel cell according to another embodiment of the present invention comprises the step of forming a protective layer on a metal support layer through electroplating to obtain a separator for a solid oxide fuel cell, wherein the metal support layer is an alloy plate containing chromium, the protective layer is a cobalt-nickel alloy thin film, and the protective layer has a content range of 30 to 70 wt% of cobalt and 70 to 30 wt% of nickel.

[0029] Hereinafter, embodiments of the present invention will be described in detail with reference to the attached drawings so that those skilled in the art can easily implement the present invention. However, the present invention may be embodied in various different forms and is not limited to the embodiments described herein. Throughout the specification, similar parts are denoted by the same reference numerals.

[0030]

[0031] FIG. 1 is a conceptual diagram illustrating an exemplary cross-sectional form of a separator plate according to the present invention. With reference to FIG. 1, an embodiment will be described in more detail.

[0032] To achieve the above objective, a separator (1) for a solid oxide fuel cell according to one embodiment includes a metal support layer (100) and a protective layer (200) surrounding the metal support layer (100).

[0033] A separator (1) for a solid oxide fuel cell is placed within the stack structure of the fuel cell, and may have a structure such as that shown in FIG. 1, for example.

[0034] The above separator plate (1) may have a shape in which protrusions (110) and depressions (120) are alternately formed along the longitudinal direction. In this case, the depressions (120) may be utilized as passages for supplying reaction gases (hydrogen, oxygen, or air) generated during the use of the fuel cell or for discharging water. Since the specific stack structure and role of the fuel cell are known, a detailed description is omitted.

[0035] The metal support layer (100) above is an alloy plate containing chromium. Iron-based stainless steel may be used as the alloy plate. Examples include SUS430, Crofer 22 APU, FC460, etc., but are not limited thereto.

[0036] Iron-based stainless steel alloy plates are evaluated to have characteristics that are above an appropriate level in various aspects, such as oxidation resistance, electrical conductivity, workability, and cost. However, iron-based stainless steel contains chromium, which causes a problem called Cr Poisoning in fuel cells, leading to performance degradation.

[0037] In solid oxide fuel cells (SOFCs) operating at high temperatures (600°C to 900°C), chromium in the separator can form oxide (Cr2O3) during operation, and this chromium oxide may react with oxygen and water vapor to volatilize in the form of chromium vapor compounds. These chromium vapor compounds are adsorbed or deposited on electrode surfaces, etc., forming insulating chromium compounds and degrading the performance of the fuel cell.

[0038] In order to prevent performance degradation of the fuel cell due to chromium oxide, a protective layer (200) is formed on the separator (1). A cobalt-nickel alloy electroplated layer is proposed as the protective layer (200).

[0039] The protective layer (200) is a cobalt-nickel alloy thin film and contains 30 to 70 wt% cobalt and 70 to 30 wt% nickel. Alternatively, the protective layer (200) contains 50 to 70 wt% cobalt and 50 to 30 wt% nickel. The protective layer (200) may contain 50 wt% or more of cobalt, or 55 wt% or more, and 65 wt% or less. In addition, it may contain 50 wt% or less of nickel, or 45 wt% or less, or 35 wt% or more. When the protective layer (200) is composed within these content ranges, a protective layer with superior long-term durability and mechanical strength can be provided.

[0040] The maximum tensile strength of the protective layer (200) may be 1200 MPa or more, 1300 MPa or more, 1400 MPa or more, or 1500 MPa or more. The maximum tensile strength of the protective layer (200) may be 2300 MPa or less, 2200 MPa or less, 2100 MPa or less, or 2000 MPa or less. The protective layer (200) having such an enhanced maximum tensile strength can protect the metal plate with excellent strength, so that it can reliably protect the alloy plate even when using the fuel cell.

[0041] The elongation rate of the protective layer (200) may be 2% or more, 2.5% or more, or 3% or more. The elongation rate of the protective layer (200) may be 5% or less, or 4.5% or less. A protective layer (200) having such an elongation rate can reliably protect the alloy plate even when using a fuel cell.

[0042] The micro-Vickers hardness on the surface of the protective layer (200) may be 350 HV or higher, or 450 HV or higher. The micro-Vickers hardness on the surface of the protective layer (200) may be 550 HV or lower. A protective layer (200) having such micro-Vickers hardness may be more advantageous for protecting an alloy plate because it is resistant to impacts that are strong on the surface and causes less damage.

[0043] The sheet resistance of the protective layer (200) is the sheet resistance measured by a 4-probe method while maintaining a temperature of 800°C after heat-treating the protective layer at a temperature of 800°C for 500 hours, and this is an experiment conducted to simulate long-term durability.

[0044] The sheet resistance of the protective layer (200) after the above heat treatment is 45 mΩ·cm 2 Below, 40 mΩ·cm 2 Below, 35 mΩ·cm 2 Less than or equal to 30 mΩ·cm 2 It may be less than or equal to. The sheet resistance of the protective layer after the above heat treatment is 16 mΩ·cm 2 Greater than or equal to 19 mΩ·cm 2 It may be above. A protective layer having these characteristics maintains low sheet resistance even during long-term use, which can help improve the performance of the fuel cell.

[0045] The protective layer (200) may have a thickness of 3 μm or more, 5 μm or more, 8 μm or more, or 15 μm or more. The thickness may be 150 μm or less, 100 μm or less, or 75 μm or less.

[0046] In cobalt-nickel alloys, superior physical properties can be obtained when a large amount of cobalt is applied.

[0047] Cobalt and nickel are adjacent on the periodic table, with atomic numbers 27 and 28, respectively. Although nickel has one more atomic number, cobalt has a slightly larger atomic weight and radius. When nickel and cobalt are alloyed, solid solution strengthening occurs as they form a substitutional solid solution. The crystal structure can vary depending on the cobalt content, and it is possible to form both FCC (Face-Centered Cubic) and a structure in which FCC and HCP (Hexagonal Close-Packed) coexist.

[0048] The above protective layer (200) is preferably composed of nickel and cobalt, with the cobalt content being greater than the nickel content. This is because, when the cobalt content is higher, a mixed phase structure in which FCC and HCP are mixed is exhibited, and solid solution strengthening can occur, which is thought to result in superior physical properties for application in fuel cells.

[0049]

[0050] To achieve the above objective, a method for manufacturing a separator for a solid oxide fuel cell according to another embodiment comprises the step of forming a protective layer on a metal support layer through electroplating to obtain a separator for a solid oxide fuel cell.

[0051] The metal support layer is an alloy plate containing chromium, the protective layer is a cobalt-nickel alloy thin film, and the protective layer has a content range of 30 to 70 wt% of cobalt and 70 to 30 wt% of nickel.

[0052] The above electroplating can be carried out by applying a plating solution to a nickel anode and a stainless steel cathode.

[0053] The plating solution may comprise 10 to 100 parts by weight of nickel sulfate, 10 to 100 parts by weight of nickel chloride, 1 to 100 parts by weight of cobalt sulfate, and 4 to 70 parts by weight of cobalt chloride.

[0054] The formation of the protective layer described above can be carried out, for example, by immersing a substrate and an electrode in a plating solution and applying an electric current to the substrate and the electrode. The electrode may, for example, be a nickel or stainless steel electrode, but is not limited thereto. The current value can be adjusted according to the reaction area between the plating solution and the substrate.

[0055] Cobalt strike plating may be performed first prior to the above electroplating. For example, cobalt strike plating may be performed by applying a platinum mesh anode and a stainless steel cathode to a plating solution containing cobalt chloride and hydrochloric acid.

[0056] The solid oxide fuel cell separator of the embodiment and the method for manufacturing the same can provide a solid oxide fuel cell separator with a protective layer formed thereon, which can improve mechanical strength and long-term performance of the fuel cell by efficiently forming a protective layer on the separator.

[0057]

[0058] The following provides a more detailed explanation through specific embodiments. The following embodiments are merely examples to aid in understanding the present invention and do not limit the scope of the invention.

[0059]

[0060] Fabrication of Co and Co-Ni alloy thin films (electroplating)

[0061] To manufacture a separator, an iron-based stainless steel (SUS430) substrate containing chromium was prepared.

[0062] A cobalt strike plating solution as presented in Table 1 below was prepared, and a first plating was performed according to the plating conditions presented in Table 1.

[0063] Cobalt chloride hydrochloric acid anode cathode temperature flow rate mA / cm 2 Plating time 100 g / L 100 ml / LP t mesh SUS43025 ℃ 200 rpm 300 50 sec

[0064] Afterwards, a plating solution was prepared according to the composition in Table 2 below, and electroplating was performed on the substrate by applying the temperature, current, etc., as described in each.

[0065] Plating Conditions Nickel Sulfate Nickel Chloride Cobalt Sulfate Cobalt Chloride H3BO3C6H8O6C7H5NO3SNa·2H2O Example 1 Co:Ni = 60:40 10~100g / L 10~100 g / L 1~100 g / L 40~70 g / L 1~50 g / L 1~50 g / L 1~50 g / L Example 2 Co:Ni = 40:60 10~100g / L 10~100 g / L 1~100 g / L 5~10 g / L 1~50 g / L 1~50 g / L 1~50 g / L Comparative Example 1 --- 100 g / L 35 g / L -- Plating Conditions Anode Cathode Temperature Flow Rate mA / cm 2 --Example 1 NiSUS43050 ℃ 200 rpm 30--Example 2 NiSUS43050 ℃ 200 rpm 30--Comparative Example 1 Pt meshSUS43025 ℃ 200 rpm 30--

[0066] In Table 2, Example 1 contains about 60 wt% cobalt and about 40 wt% nickel, Example 2 contains about 40 wt% cobalt and about 60 wt% nickel, and Comparative Example contains about 100 wt% cobalt.

[0067] The thickness of the plating layer on the specimens prepared by the above method was adjusted to suit each physical property evaluation, and for the tensile test, specimen preparation was carried out using a different method, which will be described later in the relevant method section.

[0068]

[0069] Evaluation Example 1: EDS line scan test

[0070] The samples obtained above were formed by creating a thin film after strike plating on a substrate, with a thickness of approximately 5 to 8 μm. The cross-section of the separator containing this thin film was subjected to elemental analysis based on thickness using EDS analysis (FEI, Inspect F50 + EDAX, Apollo EDS instrument). The results are shown in Table 3 below and in Figures 2a to 2c, along with SEM images of the cross-section.

[0071] Ingredient Content (wt%) Example 1 Cross-section Co 60.83 Ni 39.17 Example 2 Cross-section Co 41.08 Ni 58.92 Comparative Example Co 100.00 Ni -

[0072] Referring to Table 3, it was clearly confirmed that in Example 1, a thin film was formed with approximately 60 wt% cobalt and approximately 40 wt% nickel, and in the case of Example 2, it was also confirmed to be approximately 40 wt% cobalt and approximately 60 wt% nickel.

[0073] Referring to FIGS. 2a to 2c, the samples of Example 1 and Example 2 could confirm the composition of the metal support layer, as well as the cobalt peak of the strike layer and the distribution of Co-Ni within the thin film.

[0074]

[0075] Evaluation Example 2: Evaluation of Cr Volatility Using EDS Line Scan Test

[0076] The samples obtained above were formed by creating a thin film after strike plating on a substrate, and cross-sectional EDS line scan analysis was performed on the samples after heat treatment at 800 °C for 100 hours. This allows for confirmation of whether chromium oxide has diffused. The results are shown in Figures 3a to 3c.

[0077] The thickness of the Cr oxide was shown to be thick in the order of Fig. 3a, Fig. 3b, and Fig. 3c, and it was confirmed that the thickness of the chromium oxide in Example 1 (60Co-40Ni) was reduced to about 55% compared to Comparative Example 1.

[0078]

[0079] Evaluation Example 3: Tensile Test

[0080] The tensile testing process is shown in Fig. 4. Referring to Fig. 4, specimens were prepared in the same manner as in the manufacturing example for the tensile test; however, instead of using an alloy plate as the metal support layer, a thin film was formed by plating a titanium plate to a thickness of approximately 10 μm without applying a strike layer, the specimens were cut to a width of 12.5 mm, and the tensile test was conducted. A Shimadzu AG-1 tensile testing machine equipped with a pneumatic grip system was used, and the flow rate for the tensile test was applied by setting the pump voltage to 160 V. The results of the stress-strain curve are shown in Fig. 5, and the maximum tensile strength and elongation are shown together in Fig. 5 and Table 4 below.

[0081] Maximum Tensile Strength (MPa) Elongation (%) Example 1 183.324.00 Example 2 1593.493.06 Comparative Example 5 47.61.78

[0082] Referring to Figure 5 and Table 4 above, it was confirmed that the mechanical properties of Example 1 and Example 2 were significantly superior to those of the comparative example, and in particular, Example 1 had excellent mechanical properties as both elongation and maximum tensile strength were excellent.

[0083]

[0084] Evaluation Example 4: Evaluation of Micro-Vickers Hardness of Thin Films

[0085] The micro-Vickers hardness of the thin film was evaluated using a micro-Vickers hardness tester. The Mitutoyo 810-127k model was used.

[0086] Considering that ASTM E384 requires a thin film thickness of at least 10 times the indentation depth and ISO 6507 requires a thin film thickness of at least 1.5 times the indentation diameter, the thin film thickness was set to 150 μm and applied to the hardness test. Hardness tests were conducted on samples of the Comparative Example and Example 1. As a result of the test, the Micro-Vickers hardness (HV) of the Comparative Example was 290.11 HV, and that of Example 1 was 513.47 HV, confirming that the Example had a significantly superior hardness value compared to the Comparative Example.

[0087]

[0088] Evaluation Example 5: Sheet resistance analysis after 500 hours of oxidation

[0089] Area Specific Resistance (ASR) according to the reaction area was measured by applying the same thin film as in Example 1, Example 2 and Comparative Example. For the plating, a sample with 1 μm plating formed on both sides of the specimen was heat-treated at 800°C for 500 hours, and the sheet resistance was measured using the 4-prop method.

[0090] As a result of the measurement, the comparative example is 65.45 mΩ·cm 2 , Example 1 is 21.87 mΩ·cm 2 , and Example 2 is 31.36 mΩ·cm 2 It appeared as.

[0091] Compared to a pure cobalt thin film, the ASR results of the cobalt-nickel alloy thin film were superior, and the result of Example 1 was the best. This demonstrates that it can exhibit excellent performance even when operated for a long period as a fuel cell separator.

[0092]

[0093] Although preferred embodiments of the present invention have been described in detail above, the scope of the present invention is not limited thereto, and various modifications and improvements by those skilled in the art using the basic concept of the present invention as defined in the following claims also fall within the scope of the present invention.

[0094] The present invention relates to a separator for a solid oxide fuel cell having improved mechanical properties, an excellent chromium volatilization inhibition effect, and low sheet resistance, and a method for manufacturing the same.

Claims

1. Includes a metal support layer and a protective layer surrounding the metal support layer, The above metal support layer is an alloy plate containing chromium, and The above protective layer is a cobalt-nickel alloy thin film, and The protective layer comprises 30 to 70 wt% cobalt and 70 to 30 wt% nickel, and A separator for a solid oxide fuel cell, wherein the maximum tensile strength of the protective layer is 1200 MPa or more and 2300 MPa or less.

2. In Paragraph 1, A separator for a solid oxide fuel cell, wherein the micro-Vickers hardness on the surface of the protective layer is 350 HV or more and 550 HV or less.

3. In Paragraph 1, The sheet resistance of the protective layer is the sheet resistance measured using a 4-probe method while maintaining a temperature of 800°C after heat-treating the protective layer at a temperature of 800°C for 500 hours, and The sheet resistance of the above protective layer is 45 mΩ·cm 2 16 mΩ·cm or less 2 Lee Sang-in, separator for solid oxide fuel cells.

4. A step of forming a protective layer on a metal support layer through electroplating; thereby obtaining a separator for a solid oxide fuel cell, The above metal support layer is an alloy plate containing chromium, and The above protective layer is a cobalt-nickel alloy thin film, and The protective layer has a content range of 30 to 70 wt% cobalt and 70 to 30 wt% nickel, and A method for manufacturing a separator for a solid oxide fuel cell, wherein the maximum tensile strength of the protective layer is 1200 MPa or more and 2300 MPa or less.

5. In Paragraph 4, The above electroplating is carried out by applying a plating solution to a nickel anode and a stainless steel cathode, and A method for manufacturing a separator for a solid oxide fuel cell, wherein the plating solution comprises 10 to 100 parts by weight of nickel sulfate, 10 to 100 parts by weight of nickel chloride, 1 to 100 parts by weight of cobalt sulfate, and 4 to 70 parts by weight of cobalt chloride.

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