Titanium plate for fuel cell separator having excellent surface conductivity and durability, and method for manufacturing same

Abstract

Disclosed is a titanium plate for a fuel cell separator, which has excellent surface conductivity and durability. The titanium plate for a fuel cell separator according to the present invention comprises a base metal and a surface oxide layer, the base metal comprising, by weight%, 0.001-0.09% of Si, 0.065% or less of Fe, and the balance of Ti and unavoidable impurities; the surface oxide layer contains, by weight%, 0.20% or less of Si, 0.20% or less of O, and the balance of Ti and unavoidable impurities. Wherein the surface oxide layer may satisfy formula (1) at a point where the weight% of O is a maximum value. Formula (1): 0.05 < = Si / (Ti + O) < = 0.4 wherein Si, Ti, and O represent the content (wt%) of each element.

Description

Technical Field

[0001] This invention relates to a separator material with excellent surface conductivity and durability, and more specifically, to a titanium (Ti) plate for a fuel cell separator that does not require a coating process and exhibits excellent durability and surface conductivity even in the high-potential operating environment of a fuel cell. Background Technology

[0002] Titanium's excellent corrosion resistance makes it a potential material for fuel cell separators. However, while the passivation film formed on the surface layer ensures corrosion resistance, its semiconductor properties mean it cannot guarantee low contact resistance.

[0003] To address this issue, Patent Document 1 discloses a technique for coating graphite powder onto a titanium surface. However, the manufacturing process is complex and suffers from conductivity impairment due to peeling.

[0004] On the other hand, Patent Document 2 discloses a technique for forming a noble metal thin film layer on the surface of a metal component; however, the high manufacturing cost is a problem.

[0005] In addition, Patent Document 3 discloses a technique for forming a phase containing Ti2O3 on the surface of titanium, but the manufacturing process requires a carbon reduction process and has limitations in ensuring conductivity.

[0006] Furthermore, Patent Document 4 discloses a method for coating carbon black onto the surface of a titanium substrate and then performing heat treatment. However, coating with carbon black requires additional steps, leading to increased manufacturing costs.

[0007] (Existing technical literature) Patent Document 1: Japanese Patent No. 5342462 (Publication Date: April 14, 2011) Patent Document 2: Japanese Patent Application Publication No. 2003-105523 (Publication Date: April 9, 2003).

[0008] Patent Document 3: Korean Patent Application Publication No. 10-2019-0095472 (Publication Date: August 14, 2019) Patent Document 4: Japanese Patent Application Publication No. 2019-133863 (Publication Date: August 8, 2019) Summary of the Invention

[0009] [Technical Issues] To address the aforementioned issues, this invention provides a fuel cell separator material that requires no additional coating. By controlling the composition of the titanium (Ti) matrix metal, a conductive oxide layer is easily formed on the surface oxide layer, thereby simultaneously ensuring manufacturing cost, conductivity, and durability.

[0010] [Technical Solution] A titanium plate for use as a fuel cell separator, the titanium plate comprising a base metal and a surface oxide layer, wherein the base metal comprises, by weight %: Si: 0.001% to 0.09%, Fe: less than 0.065%, with the balance being Ti and unavoidable impurities; wherein the surface oxide layer comprises, by weight %: Si: less than 0.20%, O: less than 0.20%, with the balance being Ti and unavoidable impurities; The surface oxide layer satisfies the following equation (1) at the point where the weight % of O is at its maximum.

[0011] Formula (1): 0.05≤Si / (Ti+O)≤0.4 Where Si, Ti, and O represent the content (by weight %) of each element.

[0012] Furthermore, according to one embodiment of the present invention, the thickness of the surface oxide layer of the titanium plate used for the fuel cell separator is from 1.5 nm to 300 nm.

[0013] Furthermore, according to one embodiment of the present invention, the initial surface contact resistance of the titanium plate used for the fuel cell separator can be 10 mΩcm. 2 the following.

[0014] Furthermore, according to one embodiment of the present invention, the surface contact resistance of the titanium plate used for the fuel cell separator is 10 mΩcm after a durability test. 2 the following.

[0015] According to an example of the present invention, a method for manufacturing a titanium plate for a fuel cell separator includes the step of preparing a titanium ingot by melting a raw material, wherein the raw material comprises, by weight %: Si: 0.001% to 0.09%, Fe: less than 0.065%, and the balance being Ti and unavoidable impurities; The step of manufacturing titanium slabs by heating titanium ingots; The steps of hot rolling titanium slabs; The steps of providing titanium sheets by cold rolling and annealing titanium slabs; and the ... -30 Ba to 10 -8 The step of heating a titanium plate at a temperature of 500°C to 900°C for 10 to 3000 seconds in an oxygen partial pressure atmosphere to form a surface oxide layer.

[0016] Furthermore, in one embodiment of the present invention, in the step of forming the surface oxide layer in the method for manufacturing a titanium plate for a fuel cell separator, the oxygen partial pressure atmosphere is 2.1 x 10⁻⁶. -20 Ba to 6x10 -9 bar.

[0017] Furthermore, according to one embodiment of the present invention, in the step of forming a surface oxide layer in the method for manufacturing a titanium plate for a fuel cell separator, the heating temperature is 650°C to 850°C.

[0018] According to the method of claim 5, the heating time in the step of forming the surface oxide layer is from 30 seconds to 3000 seconds.

[0019] Furthermore, according to an embodiment of the present invention, a method for manufacturing a titanium plate for a fuel cell separator can produce a surface oxide layer that satisfies the following equation (1) at a point where the weight % of O is at its maximum value.

[0020] Formula (1): 0.05≤Si / (Ti+O)≤0.4 Where Si, Ti, and O represent the content (by weight %) of each element.

[0021] Furthermore, according to one embodiment of the present invention, in the method for manufacturing a titanium plate for a fuel cell separator, the thickness of the surface oxide layer can be from 1.5 nm to 300 nm.

[0022] Furthermore, according to one embodiment of the present invention, a method for manufacturing a titanium plate for a fuel cell separator, wherein the initial surface contact resistance of the titanium plate can be 10 mΩcm. 2 the following.

[0023] The method according to claim 5, wherein the surface contact resistance after the durability test is 10 mΩcm. 2 the following.

[0024] [Beneficial Effects] The present invention provides a titanium plate for use as a fuel cell separator, which has excellent surface conductivity and durability. Attached Figure Description

[0025] Figure 1 Images showing the composition of the surface layer and the base metal were obtained by measuring these components using surface analysis of Example 1 using transmission electron microscopy and energy-dispersive X-ray spectroscopy.

[0026] Figure 2 This image shows a surface analysis of Comparative Example 1 performed using transmission electron microscopy energy-dispersive X-ray spectroscopy (which measures the composition of the surface layer and the base metal). Detailed Implementation

[0027] Preferred embodiments of the present invention are described below. However, various modifications can be made to the embodiments of the present invention, and the technical spirit of the present invention is not limited to the embodiments described below. Furthermore, the embodiments of the present invention are provided to describe the present invention more completely to those skilled in the art.

[0028] The terminology used in this invention is for the purpose of describing specific embodiments only. Therefore, singular expressions include plural expressions, and there is no explicit requirement for a singular context. Furthermore, terms such as "comprising" or "including" as used in this invention are used to explicitly indicate the presence of features, steps, functions, ingredients, or combinations thereof described in the specification, rather than to pre-exclude the presence of other features, steps, functions, ingredients, or combinations thereof.

[0029] A description of the accompanying drawings is provided before the following description of the titanium plate.

[0030] Figure 1 The images were obtained by surface analysis of Example 1 using transmission electron microscopy with energy-dispersive X-ray spectroscopy (which measures the composition of the surface layer and the base metal). (Refer to...) Figure 1 In the case of the titanium plate according to Embodiment 1 of the present invention, it can be confirmed that the surface oxide layer is composed of (Ti,Si)xOy oxide.

[0031] Figure 2 Images of the composition of the surface layer and the base metal were obtained by performing surface analysis of Comparative Example 1 using transmission electron microscopy and energy-dispersive X-ray spectroscopy. (Refer to...) Figure 2 It can be confirmed that the surface oxide layer of the titanium plate in Comparative Example 1 is composed of TiO2 oxide.

[0032] The accompanying drawings have been described above. The following will describe a titanium plate for a fuel cell separator according to an embodiment of the present invention.

[0033] A titanium plate for use as a fuel cell separator, the titanium plate comprising a base metal and a surface oxide layer, wherein the base metal comprises, by weight %: Si: 0.001% to 0.09%; Fe: less than 0.065%; the balance being Ti and unavoidable impurities; the surface oxide layer comprises, by weight %: Si: less than 0.20%; O: less than 0.20%; the balance being Ti and unavoidable impurities; wherein surface analysis by transmission electron microscopy energy-dispersive X-ray spectroscopy shows that the outermost surface layer comprises Ti, Si and O as basic elements; and wherein the surface oxide layer satisfies the following equation (1) at the point where the weight % of O is at its maximum.

[0034] Formula (1): 0.05≤Si / (Ti+O)≤0.4 Where Si, Ti, and O represent the content (by weight %) of each element.

[0035] Figure 2 The surface layer of a conventional titanium plate is shown to consist of oxides containing Ti and O. That is, Ti can easily form stable TiO2 oxides of several nm to tens of nm in the atmosphere or during the manufacturing process of the titanium plate by bonding with O.

[0036] To ensure the conductivity of the coating formed on the surface layer without requiring a separate coating process, one embodiment of the present invention optimizes the composition of the titanium (Ti) base metal and the constituent elements that enable the surface oxide layer to conduct electricity. Specifically, a titanium plate containing 0.001 wt% to 0.09 wt% Si in the base metal allows the Si component to accumulate in the surface layer and form as TiSixOy oxide under low oxygen partial pressure temperature conditions, and conductivity can be provided by the TiSixOy oxide. Herein, the surface oxide layer is defined as a region extending from the surface of the titanium plate along the thickness direction of the titanium plate containing a maximum oxygen content of 10 wt% or more, and the base metal is defined as a region extending from the surface of the titanium plate along the thickness direction of the titanium plate containing a maximum oxygen content of less than 10 wt%.

[0037] According to one embodiment of the present invention, the titanium plate can be conductive because the band gap energy is reduced by the doping of silicon, thereby changing the property to conductive properties.

[0038] Furthermore, according to one embodiment of the present invention, the silicon content of the base metal in the titanium plate can be limited to a lower limit of 0.001% by weight or more. This is because this is the lowest content value at which the silicon doping effect (indicating the conductivity of the surface layer) can occur. Additionally, the silicon content of the base metal can be limited to below 0.09%, as exceeding 0.09% would adversely affect the formability of the material.

[0039] Furthermore, according to an embodiment of the present invention, the titanium plate comprises an optimal surface oxide layer composition, wherein the surface oxide layer satisfies the following equation (1) at the point where the weight % of O is at its maximum value.

[0040] Formula (1): 0.05≤Si / (Ti+O)≤0.4 Where Si, Ti, and O represent the content (by weight %) of each element.

[0041] As mentioned above, the reason for limiting the composition ratio of the surface oxide layer at the point where the weight % of O is at its maximum is as follows. In order to ensure the conductivity due to silicon doping, the lower limit of equation (1) can be set to 0.05 or higher. Values ​​greater than 0.4 cause the conductivity to change into semiconductor properties due to silicon enrichment, thereby deteriorating the conductivity; therefore, the upper limit can be limited to below 0.4.

[0042] Furthermore, according to one embodiment of the present invention, the thickness of the surface oxide layer of the titanium plate used for the fuel cell separator can be from 1.5 nm to 300 nm. The lower limit of the coating thickness can be 1.5 nm or more to ensure a minimum coating thickness that maintains conductivity in the fuel cell environment and to prevent performance degradation caused by TiO2 coating recovery after coating damage. The upper limit can be limited to 300 nm to prevent defects such as cracks from occurring during the separator forming process after the titanium plate is manufactured.

[0043] Furthermore, according to one embodiment of the present invention, a titanium plate for a fuel cell separator may be provided, wherein the titanium matrix metal may be composed of pure titanium material or titanium alloy, and may contain Si from 0.001% to 0.09% by weight.

[0044] Furthermore, according to one embodiment of the present invention, the initial surface contact resistance of the titanium plate used for the fuel cell separator is 10 mΩcm. 2 The surface contact resistance after the durability test is 10 mΩcm. 2 the following.

[0045] Furthermore, according to one embodiment of the present invention, the outermost surface layer of the titanium plate used for the fuel cell separator may contain Ti, Si and O as basic elements, and one or more of C, N, Mg, Al and V as other impurities.

[0046] According to one embodiment of the present invention, a method for manufacturing a titanium plate for a fuel cell separator includes: a step of preparing a titanium ingot by melting a raw material, said raw material comprising, by weight %: Si: 0.001% to 0.09%, Fe: less than 0.065%, with the balance being Ti and unavoidable impurities; a step of manufacturing a titanium slab blank by heating the titanium ingot; a step of hot rolling the titanium slab blank; a step of providing a titanium plate by cold rolling and annealing the titanium slab blank; and a step of further manufacturing a titanium plate by 10 -30 Ba to 10 -8 The step of heating a titanium plate at a temperature of 500°C to 900°C for 10 to 3000 seconds in an oxygen partial pressure atmosphere to form a surface oxide layer.

[0047] According to one embodiment of the present invention, the reason for limiting the oxygen partial pressure as described above during the step of forming the surface oxide layer in the method for manufacturing a titanium plate for a fuel cell separator is as follows. 10 -8 Oxygen partial pressures below 10 bar can create an atmosphere that allows silicon to diffuse and be doped into the Ti, O compound layer on the surface, thus forming the maximum oxygen partial pressure conditions for silicon diffusion. However, less than 10 bar... -30 Achieving the required oxygen partial pressure in the atmosphere not only necessitates the use of excessive amounts of hydrogen, CO, CO2, methane, and propane, but also results in higher manufacturing costs. Therefore, the step of forming the surface oxide layer is preferably performed using a 10-step process.-30 Ba to 10 -8 The partial pressure of oxygen in bar. Most preferably, the partial pressure of oxygen can be 2.1 x 10⁻⁶. -20 Ba to 6x10 -9 bar.

[0048] Furthermore, in a method for manufacturing a titanium plate for a fuel cell separator according to one embodiment of the present invention, the temperature and time in the step of forming the surface oxide layer are subject to the above-mentioned limitations for the following reasons. For Si diffusion, the lower limit of the heating temperature is limited to 500°C or higher; to prevent a decrease in formability due to excessive grain growth, the heating temperature can be limited to 900°C or lower; in addition, considering the shortest to the longest retention time of silicon doping in the surface oxide layer, the heating time is set, wherein at a heating temperature of 650°C to 850°C, the heating time is preferably 30 seconds to 3000 seconds.

[0049] The present invention will now be described in more detail through preferred embodiments.

[0050] {Example} A 30 kg ingot with the composition shown in Table 1 was vacuum melted. A material with a thickness of 4.5 mm was manufactured by hot rolling. Subsequently, after two cold rolling processes and two annealing processes, a titanium cold-rolled sheet (0.2 mm thick) with the composition shown in Table 1 was manufactured.

[0051] [Table 1]

[0052] Table 2 below lists the composition ratio at the surface layer with the highest oxygen content, the thickness of the surface oxide layer, the initial surface contact resistance, and the measured values ​​of the surface contact resistance after the durability test. These measurements were obtained by cold rolling a titanium plate with the above composition according to the conditions shown in Table 2, followed by heating and exposure to an oxygen atmosphere.

[0053] [Table 2]

[0054] According to the comparative examples and embodiments in Table 2, cold-rolled steel sheets were cut into 10cm × 10cm pieces. After ultrasonic cleaning in acetone for 1 hour in the laboratory, heat treatment was performed under a controlled atmosphere with low oxygen partial pressure. Argon, hydrogen, carbon monoxide, carbon dioxide, methane, and propane gases were used to control the atmosphere. Oxygen partial pressure was measured using a Mellor oxygen partial pressure meter. After heat treatment, the surface of the samples was analyzed by transmission electron microscopy and energy-dispersive X-ray spectroscopy. Figure 1The composition of the surface oxide layer under the conditions of Example 1 is shown. The composition was analyzed by transmission electron microscopy and energy-dispersive X-ray spectroscopy, revealing the presence of Si, Ti, and O components in the surface layer. The component ratios and contact resistance values ​​are listed in Table 2. Furthermore, Figure 2 The surface oxide layer composition of Comparative Example 1 is shown. The composition was analyzed by transmission electron microscopy and energy-dispersive X-ray spectroscopy, in which Ti and O components were detected in the surface layer. The component ratios and contact resistance values ​​of each component are listed in Table 2.

[0055] Contact resistance evaluation included: cutting the sample into 5cm x 5cm pieces; placing carbon paper (GDL) / sample / carbon paper (GDL) / sample / carbon paper (GDL) between upper and lower Cu plates; and evaluating the initial contact resistance by applying current to the Cu plates and connecting the voltage terminals to the sample. To evaluate durability under fuel cell operating conditions, the initial contact resistance evaluation sample was immersed in a 0.05M sulfuric acid + 2ppm hydrofluoric acid solution for 100 hours. The contact resistance was then re-evaluated to confirm any changes.

[0056] According to Examples 1 to 4 of the present invention, which satisfy composition 1 and composition 2, the oxygen partial pressure in the atmosphere is 10. -30 Ba to 10 -8 The temperature is 500℃ to 900℃, and the heating time is 10 seconds to 3000 seconds. Equation (1) satisfies 0.05 to 0.4, which confirms that both the initial surface contact resistance and the contact resistance after the durability test meet 10 mΩcm. 2 the following.

[0057] In contrast, Comparative Example 3 has composition 3 and an oxygen partial pressure in the atmosphere greater than 10. -8 The oxygen partial pressure in the atmosphere was greater than 10 bar, and equation (1) was less than 0.05. For Comparative Example 1 and Comparative Example 2, the oxygen partial pressure in the atmosphere was greater than 10 bar. -8 Since the value of bar is less than 0.05, it can be confirmed that both the initial surface contact resistance and the surface contact resistance after the durability test are greater than 10 mΩcm. 2 .

[0058] According to one embodiment of the present invention, the titanium plate can ensure the conductivity of the surface oxide layer formed on the surface by controlling the composition of the titanium (Ti) matrix metal and by easily forming a surface oxide layer as a conductive oxide layer without the need for a separate coating process.

[0059] While various exemplary embodiments of the present invention have been described above, the present invention is not limited thereto. Those skilled in the art should understand that various changes and modifications can be made without departing from the concept and scope of the claims.

Claims

1. A titanium plate for a fuel cell separator, the titanium plate comprising a base metal and a surface oxide layer, wherein the base metal comprises, by weight %: Si: 0.001% to 0.09%, Fe: less than 0.065%, with the balance being Ti and unavoidable impurities; wherein the surface oxide layer comprises, by weight %: Si: less than 0.20%, O: less than 0.20%, with the balance being Ti and unavoidable impurities; The surface oxide layer satisfies the following condition at the point where the weight % of O is at its maximum value. Formula (1): 0.05≤Si / (Ti+O)≤0.4 Where Si, Ti and O represent the content of each element in weight percent.

2. The titanium plate for a fuel cell separator according to claim 1, The thickness of the surface oxide layer is 1.5 nm to 300 nm.

3. The titanium plate for a fuel cell separator according to claim 1, where the initial surface contact resistance is 10 mΩcm 2 The following.

4. The titanium plate for a fuel cell separator according to claim 1, where the surface contact resistance after durability testing is 10 mΩcm 2 The following.

5. A method for manufacturing a titanium plate for a fuel cell separator, the method comprising: The step of preparing titanium ingots by melting raw materials, wherein the raw materials comprise, by weight %: Si: 0.001% to 0.09%, Fe: less than 0.065%, with the balance being Ti and unavoidable impurities; The step of manufacturing titanium slabs by heating the titanium ingot; The step of hot rolling the titanium slab; The steps of providing titanium sheets by cold rolling and annealing the titanium slab; and Through 10 -30 Ba to 10 -8 The step of heating the titanium plate in an oxygen partial pressure atmosphere at a temperature of 500°C to 900°C for 10 seconds to 3000 seconds to form a surface oxide layer.

6. The method according to claim 5, In the step of forming the surface oxide layer, the oxygen partial pressure atmosphere is 2.1 x 10⁻⁶. -20 Ba to 6x10 -9 bar.

7. The method according to claim 5, In the step of forming the surface oxide layer, the heating temperature is 650°C to 850°C.

8. The method according to claim 5, In the step of forming the surface oxide layer, the heating time is from 30 seconds to 3000 seconds.

9. The method according to claim 5, The surface oxide layer satisfies the following equation (1) at the point where the weight % of O is at its maximum: Formula (1): 0.05≤Si / (Ti+O)≤0.4 Where Si, Ti and O represent the content of each element in weight percent.

10. The method of claim 5, wherein the thickness of the surface oxide layer is from 1.5 nm to 300 nm.

11. The method according to claim 5, The initial surface contact resistance is 10 mΩcm. 2 the following.

12. The method according to claim 5, The surface contact resistance after the durability test was 10 mΩcm. 2 the following.

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