Titanuim plate for bipolar plate with excellent surface electrical conductivity and durability and manufacturing method thereof

Abstract

The present specification discloses a titanium plate for a bipolar plate, having excellent surface conductivity and excellent durability. The titanium plate for a bipolar plate, according to the present invention, comprises, by wt%: a base material including 0.001-0.09% of Si, 0.065% or less of Al, and the remainder of Ti and inevitable impurities; and a surface film layer including 0.20% or less of Si, 0.20% or less of O, and the remainder of Ti and inevitable impurities, wherein the surface film layer having the maximum wt% of O can satisfy expression (1). Expression (1): 0.05 ≤ Si / (Ti+O) ≤ 0.4 (wherein Si, Ti, and O indicate wt% of the respective elements.)

Description

Titanium plate for fuel cell separator with excellent surface conductivity and durability and method for manufacturing the same

[0001] The present invention relates to a separator material having excellent surface conductivity and durability, and more specifically, to a titanium (Ti) plate for a separator that enables the omission of a coating process and has excellent durability and surface conductivity even in a high potential operating environment of a fuel cell.

[0002] Titanium is being considered as a fuel cell separator material due to its excellent corrosion resistance. However, although corrosion resistance is secured by the passive film formed on the surface, its semiconductor properties hinder low contact resistance.

[0003] To solve this problem, Patent Document 1 discloses a technique for applying graphite powder to a titanium surface, but the manufacturing process is complicated and there is a problem that it may hinder conductivity due to peeling, etc.

[0004] Meanwhile, Patent Document 2 discloses a technology for forming a precious metal thin film layer on the surface of a metal member, but has the problem of high manufacturing costs.

[0005] In addition, Patent Document 3 discloses a technology for forming a phase including a Ti2O3 phase on a titanium surface, but it requires a reduction treatment process using carbon during the manufacturing process, and there is a limitation in securing conductivity.

[0006] Furthermore, Patent Document 4 discloses a process of applying carbon black to the surface of a titanium substrate and performing heat treatment, but this requires an additional process of applying carbon black, which has the problem of increased manufacturing costs.

[0007] (Prior art literature)

[0008] Patent Document 1: Japanese Patent Publication No. 5342462 (Publication Date: April 14, 2011)

[0009] Patent Document 2: Japanese Patent Application Laid-Open No. 2003-105523 (Publication Date: April 9, 2003)

[0010] Patent Document 3: Korean Patent Publication No. 10-2019-0095472 (Publication Date: August 14, 2019)

[0011] Patent Document 4: Japanese Patent Application Laid-Open No. 2019-133863 (Publication Date: August 8, 2019)

[0012] In order to solve the above-described problems, the present invention aims to provide a fuel cell separator material that does not require additional coating by simultaneously securing manufacturing cost, conductivity, and durability by controlling the components of a titanium (Ti) base material and easily forming a conductive oxide layer on a surface film layer.

[0013] According to one embodiment of the present invention, a titanium plate for a fuel cell separator comprises a base material including, in wt%, Si: 0.001% or more and 0.09% or less, Fe: 0.065% or less, the remainder Ti and unavoidable impurities, and a surface film layer including Si: 0.20% or less, O: 0.20% or less, the remainder Ti and unavoidable impurities,

[0014] The following equation (1) is satisfied in the surface film layer with the maximum weight % of O.

[0015] Equation (1) 0.05 ≤ Si / (Ti+O) ≤ 0.4

[0016] (Here, Si, Ti and O represent the weight percent of each element.)

[0017] Additionally, according to one embodiment of the present invention, the thickness of the surface film layer of the titanium plate for a fuel cell separator may be 1.5 nm or more and 300 nm or less.

[0018] In addition, according to one embodiment of the present invention, the titanium plate for the fuel cell separator has an initial surface contact resistance of 10 mΩcm. 2 It could be as follows:

[0019] In addition, according to one embodiment of the present invention, the titanium plate for the fuel cell separator has a surface contact resistance of 10 mΩcm after the endurance test. 2 It could be as follows:

[0020] According to one embodiment of the present invention, a method for manufacturing a titanium plate for a fuel cell separator comprises the steps of preparing a titanium ingot by melting a raw material including, in wt%, Si: 0.001% or more and 0.09% or less, Fe: 0.065% or less, the remainder Ti, and unavoidable impurities;

[0021] A step of manufacturing a titanium slab by heating the above titanium ingot;

[0022] A step of hot rolling the above titanium slab;

[0023] A step of cold rolling and annealing the above titanium slab to prepare a titanium plate; and 10 -30 bar or more 10 -8 It may include a step of forming a surface film layer by heating at a temperature of 500°C or higher and 900°C or lower in an oxygen partial pressure atmosphere of less than bar for 10 seconds or longer and 3000 seconds or shorter.

[0024] In addition, according to one embodiment of the present invention, the method for manufacturing a titanium plate for a fuel cell separator is such that the oxygen partial pressure atmosphere in the step of forming a surface film layer is 2.1x10 -20 bar 6x10 or more -9 It may be less than bar.

[0025] In addition, according to one embodiment of the present invention, in the method for manufacturing a titanium plate for a fuel cell separator, the heating temperature in the step of forming a surface film layer may be 650°C or more and 850°C or less.

[0026] In addition, according to one embodiment of the present invention, in the method for manufacturing a titanium plate for a fuel cell separator, the heating time in the step of forming a surface film layer may be 30 seconds or more and 3000 seconds or less.

[0027] In addition, according to one embodiment of the present invention, a method for manufacturing a titanium plate for a fuel cell separator can satisfy the following equation (1) in a surface film layer having a maximum weight % of O.

[0028] Equation (1) 0.05 ≤ Si / (Ti+O) ≤ 0.4

[0029] (Here, Si, Ti and O represent the weight percent of each element.)

[0030] In addition, according to one embodiment of the present invention, the method for manufacturing a titanium plate for a fuel cell separator may have a surface film layer having a thickness of 1.5 nm or more and 300 nm or less.

[0031] In addition, according to one embodiment of the present invention, the method for manufacturing a titanium plate for a fuel cell separator has an initial surface contact resistance of 10 mΩcm. 2 It could be as follows:

[0032] In addition, according to one embodiment of the present invention, the method for manufacturing a titanium plate for a fuel cell separator has a surface contact resistance of 10 mΩcm after an endurance test. 2 It could be as follows:

[0033] According to the present invention, a titanium plate for a fuel cell separator having excellent surface conductivity and durability for use as a fuel cell separator can be provided.

[0034] Figure 1 is a photograph showing the components of the surface layer and the base material measured by performing surface analysis using transmission electron microscope energy dispersive X-ray spectroscopy for Example 1.

[0035] Figure 2 is a photograph showing the components of the surface layer and the base material measured by performing surface analysis using transmission electron microscope energy dispersive X-ray spectroscopy for comparative example 1.

[0036] Preferred embodiments of the present invention are described below. However, the embodiments of the present invention may be modified in various ways, and the technical concept of the present invention is not limited to the embodiments described below. Furthermore, the embodiments of the present invention are provided to more fully explain the present invention to those of ordinary skill in the art.

[0037] The terminology used in this application is solely for the purpose of describing specific examples. Therefore, for example, singular expressions include plural expressions unless the context clearly dictates otherwise. Additionally, it should be noted that terms such as "comprise" or "have" used in this application are used to clearly indicate the presence of features, steps, functions, components, or combinations thereof described in the specification, and are not used to preliminarily exclude the presence of other features, steps, functions, components, or combinations thereof.

[0038] Before explaining the titanium plate below, let's explain the drawing.

[0039] Figure 1 is a photograph of the components of the surface layer and the base material portion measured by performing surface analysis using transmission electron microscope energy dispersive X-ray spectroscopy for Example 1. Referring to Figure 1, in the case of the titanium plate according to Example 1 of the present invention, the surface film layer is (Ti, Si). x O y You can see that it is composed of oxides.

[0040] Fig. 2 is a photograph showing the components of the surface layer and the base material measured by performing surface analysis using transmission electron microscope energy dispersive X-ray spectroscopy for Comparative Example 1. Referring to Fig. 2, it can be confirmed that the surface film layer of the titanium plate of Comparative Example 1 is composed of TiO2 oxide.

[0041] The above drawing has been described. Below, a titanium plate for a fuel cell separator according to one embodiment of the present invention will be described.

[0042] A titanium plate for a fuel cell separator according to one embodiment of the present invention comprises a base material including, in wt%, Si: 0.001% or more and 0.09% or less, Fe: 0.065% or less, the remainder Ti and unavoidable impurities, and a surface film layer including Si: 0.20% or less, O: 0.20% or less, the remainder Ti and unavoidable impurities, and when surface analysis is performed using transmission electron microscope energy dispersive X-ray spectroscopy, the outermost surface layer contains Ti, Si, and O as essential elements, and the surface film layer having the largest wt% of O can satisfy the following equation (1).

[0043] Equation (1) 0.05 ≤ Si / (Ti+O) ≤ 0.4

[0044] (Here, Si, Ti and O represent the weight percent of each element.)

[0045] In the case of conventional titanium plates, it can be seen from Figure 2 that the composition of the surface layer is composed of oxides containing Ti and O. That is, Ti can easily form a stable TiO2 oxide of several to several tens of nm in size in the air or during the titanium plate manufacturing process by combining with O.

[0046] According to one embodiment of the present invention, a titanium plate can optimize the composition of a titanium (Ti) base material and the component elements that implement conductivity in the surface film layer to secure conductivity in the film layer formed on the surface without a separate coating process. Specifically, a titanium plate containing Si: 0.001 to 0.09% in the base material can be formed by concentrating the Si component on the surface layer under temperature conditions of low oxygen partial pressure, thereby forming TiSi. x O y It can be formed in the form of oxide, TiSi x O yIt can have conductivity due to oxide. Here, the surface film layer means a region containing a maximum oxygen content of 10 wt% or more in the thickness direction of the titanium plate from the surface, and the base material means a region containing a maximum oxygen content of less than 10 wt% in the thickness direction of the titanium plate from the surface.

[0047] A titanium plate according to one embodiment of the present invention can have conductivity, which is because the band gap energy is lowered by the doping effect of Si, thereby changing to a conductive property.

[0048] In addition, the titanium plate according to one embodiment of the present invention may limit the lower limit of the Si content of the base material to 0.001% or more in weight %. This is because this is the minimum content value that can exhibit the Si doping effect indicating the conductivity of the surface layer. In addition, the lower limit of the Si content of the base material may be limited to 0.09%, because when it exceeds 0.09%, it may adversely affect the formability of the material.

[0049] In addition, the titanium plate according to one embodiment of the present invention can have a surface film layer composition ratio at a point where the O content is at its maximum with an optimal surface layer composition, which satisfies the following equation (1).

[0050] Equation (1) 0.05 ≤ Si / (Ti+O) ≤ 0.4

[0051] (Here, Si, Ti and O represent the weight percent of each element.)

[0052] The reason why the composition ratio of the surface film layer at the point where the O content is maximum is limited as above is as follows. In order to secure the conductive properties by Si doping, the lower limit of equation (1) can be set to 0.05 or more, and when it exceeds 0.4, the conductive properties are changed to semiconductor properties due to the concentration of Si, which deteriorates the conductivity, so the upper limit can be limited to 0.4 or less.

[0053] In addition, the titanium plate for a fuel cell separator according to one embodiment of the present invention may have a surface film layer thickness of 1.5 nm or more and 300 nm or less. In order to secure a minimum film thickness for maintaining conductivity in a fuel cell environment and prevent performance degradation due to restoration of the TiO2 film layer due to destruction of the film layer, the lower limit of the film thickness may be 1.5 nm or more, and in order to prevent defects such as cracks from occurring when a separator forming process is applied after manufacturing the titanium plate, the upper limit may be limited to 300 nm.

[0054] In addition, a titanium plate for a fuel cell separator according to one embodiment of the present invention may be composed of a titanium base material made of pure titanium material or a titanium alloy, and may contain Si in an amount of 0.001% or more and 0.09% or less by weight.

[0055] In addition, the titanium plate for a fuel cell separator according to one embodiment of the present invention has an initial surface contact resistance of 10 mΩcm. 2 It may be less than 10 mΩcm, and the surface contact resistance after the endurance test 2 It could be as follows:

[0056] In addition, a titanium plate for a fuel cell separator according to one embodiment of the present invention may include at least one of C, N, Mg, Al, and V as impurities in addition to Ti, Si, and O as essential elements in the outermost surface layer.

[0057] In addition, a method for manufacturing a titanium plate for a fuel cell separator according to an embodiment of the present invention comprises the steps of preparing a titanium ingot by melting a raw material including, in wt%, Si: 0.001% or more and 0.09% or less, Fe: 0.065% or less, the remainder Ti, and unavoidable impurities, the step of heating the titanium ingot to manufacture a titanium slab, the step of hot-rolling the titanium slab, the step of cold-rolling and annealing the titanium slab to prepare a titanium plate, and the step of annealing the titanium plate at a temperature of 10° C. -30 bar or more 10-8 It may include a step of forming a surface film layer by heating at a temperature of 500°C or higher and 900°C or lower in an oxygen partial pressure atmosphere of less than bar for 10 seconds or longer and 3000 seconds or shorter.

[0058] In the method for manufacturing a titanium plate for a fuel cell separator according to one embodiment of the present invention, the reason why the oxygen partial pressure in the step of forming a surface film layer is limited as described above is as follows. The oxygen partial pressure is 10 -8 If it is below bar, an atmosphere can be formed in which Si can be doped by diffusing into the Ti, O compound layer on the surface, and the maximum oxygen partial pressure condition that allows Si diffusion can be formed, but if the oxygen partial pressure is 10 -30 In the case of less than bar, in order to implement such an atmosphere, not only must an excessive amount of hydrogen, CO, CO2, methane, propane gas, etc. be used, but also expensive manufacturing costs may be required. The step of forming a surface film layer requires an oxygen partial pressure of 10 -30 bar or more 10 -8 It is preferable to have a bar, most preferably 2.1x10 -20 bar 6x10 or more -9 It may be less than bar.

[0059] In addition, in the method for manufacturing a titanium plate for a fuel cell separator according to an embodiment of the present invention, the reason why the temperature and time in the step of forming the surface film layer are limited as described above is as follows. In order to diffuse Si, the lower limit of the heating temperature is limited to 500°C or higher, and in order to prevent deterioration of formability due to excessive grain growth, the lower limit of the heating temperature may be limited to 900°C or lower. In addition, the time for maintaining the heating is set in consideration of the minimum and maximum maintenance times due to Si doping in the surface film layer, and it is preferable that the heating time be 30 seconds or more and 3000 seconds or less at a heating temperature of 650°C or higher and 850°C or lower.

[0060] Hereinafter, the present invention will be described in more detail through preferred embodiments.

[0061] {Example}

[0062] A 30 kg ingot having the composition shown in Table 1 below was vacuum melted, and a 4.5 mm thick material was manufactured through a hot rolling process. Afterwards, a titanium cold-rolled (0.2 mm thick) plate having the composition shown in Table 1 was manufactured through two cold rolling and two annealing processes.

[0063] Ti(wt%)Si(wt%)Fe(wt%)Composition 1bal.0.0010.06Composition 2bal.0.02-Composition 3bal.-0.065

[0064] Table 2 below shows the composition ratio, surface film thickness, initial contact resistance, and contact resistance after durability test in the surface layer with the maximum O content after cold rolling of a titanium plate having the above composition and exposure to heating and oxygen atmosphere under the conditions of Table 2.

[0065] Composition ratio in the surface layer of the maximum O content in the atmosphere of the composition heating maintenance surface film layer initial contact resistance contact resistance after endurance test temperature (℃) time (sec) oxygen partial pressure (bar) Si (wt%) / [Ti (wt%) + O (wt%)] thickness (nm) (mΩcm) 2 ) @1MPa(mΩcm 2 ) @1MPaComparative example 1 Composition 1700301.5x10 -4 0.016.2125270Comparison Example 2 Composition 2800308x10 -5 06578150 Comparative Example 3 Composition 3500303.2x10 -9 012127325 Example 1 Composition 1800302x10 -19 0.246.16.36.8 Example 2 Composition 16506001.7x10 -12 0.05557.27.8 Example 3 Composition 285030002.1x10 -20 0.42805.55.6 Example 4 Composition 2750206x10 -9 0.32366.2

[0066] The cold-rolled plates according to the comparative examples and examples in Table 2 were cut into 10 cm x 10 cm pieces, ultrasonically cleaned in acetone for 1 hour in a laboratory, and then heat-treated in a controlled atmosphere in a low oxygen partial pressure atmosphere. At this time, to control the low oxygen partial pressure atmosphere, argon, hydrogen, carbon monoxide, carbon dioxide, methane, and propane gases were used to control the atmosphere, and the oxygen partial pressure was measured using an oxygen partial pressure meter from Metlor. After heat treatment, the specimens were subjected to surface analysis using transmission electron microscopy energy-dispersive X-ray spectroscopy. Fig. 1 shows the results of analyzing the composition of the surface film layer under the conditions of Example 1 by transmission electron microscope energy dispersive X-ray spectroscopy, and Si, Ti, and O components were detected in the surface layer, and the component ratios and contact resistance values ​​thereof are shown in Table 2. In addition, Fig. 2 shows the results of analyzing the composition of the surface film layer for Comparative Example 1 by transmission electron microscope energy dispersive X-ray spectroscopy, and Ti and O components were detected in the surface layer, and the component ratios and contact resistance values ​​thereof are shown in Table 2.

[0067] For the contact resistance evaluation, the measurement sample was cut into 5 cm x 5 cm, and carbon paper (GDL) / specimen / carbon paper (GDL) / specimen / carbon paper (GDL) was placed inside the upper / lower Cu plates, and after applying current to the Cu plate, the voltage terminal was connected to the specimen to evaluate the initial contact resistance. For the durability evaluation of the initial contact resistance specimen in the fuel cell operating environment, the contact resistance was reevaluated after immersing it in a 0.05 M sulfuric acid + 2 ppm hydrofluoric acid solution for 100 hours to check for changes.

[0068] Examples 1 to 4 according to the present invention satisfy composition 1 and composition 2, and the oxygen partial pressure in the atmosphere is 10 -30 10 at the bar -8 It satisfies the temperature of 500℃ or more and 900℃ or less for 10 seconds or more and 3000 seconds, and the equation (1) satisfies 0.05 to 0.4, so that the initial surface contact resistance and the contact resistance after the endurance test are 10 mΩcm. 2It was confirmed that the following was satisfied.

[0069] On the other hand, in the case of comparative example 3, it has composition 3 and the oxygen partial pressure in the atmosphere is 10 -8 bar was exceeded, and equation (1) was less than 0.05, and comparative examples 1 and 2 had an oxygen partial pressure of 10 in the atmosphere. -8 bar was exceeded, and since equation (1) is less than 0.05, the initial surface contact resistance and the contact resistance after the endurance test were 10 mΩcm. 2 It was confirmed that it exceeded .

[0070] A titanium plate according to one embodiment of the present invention can secure conductivity of a film layer formed on a surface without a separate coating process by controlling the components of a titanium (Ti) base material and easily forming a conductive oxide layer on a surface film layer.

[0071] Although exemplary embodiments of the present invention have been described above, the present invention is not limited thereto, and those skilled in the art will understand that various changes and modifications are possible within the scope and spirit of the claims set forth below.

Claims

1. A base material including, by weight%, Si: 0.001% or more and 0.09% or less, Fe: 0.065% or less, the remainder Ti and unavoidable impurities, and a surface film layer including Si: 0.20% or less, O: 0.20% or less, the remainder Ti and unavoidable impurities, A titanium plate for a fuel cell separator, wherein the surface film layer having the maximum weight % of O satisfies the following equation (1). Equation (1) 0.05 ≤ Si / (Ti+O) ≤ 0.4 (Here, Si, Ti and O represent the weight% of each element.) 2. In claim 1, A titanium plate for a fuel cell separator having a thickness of the surface film layer of 1.5 nm to 300 nm.

3. In claim 1, Initial surface contact resistance is 10 mΩcm 2 Titanium plate for fuel cell separator.

4. In claim 1, Surface contact resistance after endurance test is 10 mΩcm 2 Titanium plate for fuel cell separator.

5. A step of preparing a titanium ingot by melting a raw material containing, by weight%, Si: 0.001% or more and 0.09% or less, Fe: 0.065% or less, the remainder Ti, and unavoidable impurities; A step of manufacturing a titanium slab by heating the above titanium ingot; A step of hot rolling the above titanium slab; A step of cold rolling and annealing the above titanium slab to prepare a titanium plate; and The above titanium plate is 10 -30 bar 10 or more -8 A method for manufacturing a titanium plate for a fuel cell separator, comprising the step of forming a surface film layer by heating at a temperature of 500°C or higher and 900°C or lower in an atmosphere with an oxygen partial pressure of less than 1 bar for 10 seconds or longer and 3000 seconds or shorter.

6. In claim 5, The oxygen partial pressure atmosphere in the step of forming the above surface film layer is 2.1x10 -20 bar 6x10 or more -9 A method for manufacturing a titanium plate for a fuel cell separator having a thickness of less than bar.

7. In claim 5, A method for manufacturing a titanium plate for a fuel cell separator, wherein the heating temperature in the step of forming the surface film layer is 650°C or higher and 850°C or lower.

8. In claim 5, A method for manufacturing a titanium plate for a fuel cell separator, wherein the heating time in the step of forming the surface film layer is 30 seconds or more and 3000 seconds or less.

9. In claim 5, A method for manufacturing a titanium plate for a fuel cell separator, wherein the titanium plate satisfies the following equation (1) in a surface film layer having a maximum weight % of O. Equation (1) 0.05 ≤ Si / (Ti+O) ≤ 0.4 (Here, Si, Ti and O represent the weight% of each element.) 10. In claim 5, A method for manufacturing a titanium plate for a fuel cell separator, wherein the thickness of the surface film layer is 1.5 nm or more and 300 nm or less.

11. In claim 5, Initial surface contact resistance is 10 mΩcm 2 A method for manufacturing a titanium plate for a fuel cell separator is disclosed.

12. In claim 5, Surface contact resistance after endurance test is 10 mΩcm 2 A method for manufacturing a titanium plate for a fuel cell separator is disclosed.

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