Fuel cell separator

Abstract

To provide a separator for a fuel cell capable of sufficiently securing conductivity.SOLUTION: A fuel cell separator of the present invention includes: a metal substrate; a titanium layer provided on the metal substrate; and a carbon layer provided on the titanium layer, wherein a TiC component ratio in a boundary region between the titanium layer and the carbon layer is 70% or less.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a separator for a fuel cell. [Background technology]

[0002] In recent years, fuel cells have been adopted as a power source for vehicles, etc. They have a stack structure in which unit cells are stacked. A unit cell has a membrane electrode assembly with anode and cathode electrode layers (catalyst layer and gas diffusion layer) on both sides of an electrolyte membrane, and separators arranged on both sides of the membrane electrode assembly. Fuel cell separators (hereinafter sometimes abbreviated as "separators") have the function of electrically connecting unit cells in series and functioning as partition walls that block fluids such as fuel gas from passing through each other. Various research projects are being conducted on separators.

[0003] For example, Patent Document 1 discloses a conductive member having a metal substrate layer and a conductive carbon layer containing conductive carbon located on at least one main surface of the metal substrate layer, in which the D-band peak intensity (I D ) and G-band peak intensity (I G ) intensity ratio I D / I G Patent Document 2 discloses a conductive member having a metal substrate, a corrosion-resistant metal intermediate layer formed on the metal substrate, and a carbon layer formed on the corrosion-resistant metal intermediate layer, and D / I GFurthermore, Patent Document 3 discloses a separator for a fuel cell in which a titanium layer containing titanium is formed on a metal substrate, and in which the ratio of the (100) plane to the total value obtained by dividing the peak intensities of the titanium-derived (100), (002), and (101) planes by their relative intensities in an X-ray diffraction analysis of the separator surface, expressed by the following formula: {(peak intensity of the (100) plane / relative intensity of the (100) plane) / [(peak intensity of the (100) plane / relative intensity of the (100) plane)+(peak intensity of the (002) plane / relative intensity of the (002) plane)+(peak intensity of the (101) plane / relative intensity of the (101) plane)]} × 100 is 16.9% or more. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2010-153353 [Patent Document 2] Japanese Patent Publication No. 2022-45138 [Patent Document 3] Patent No. 7375723 Summary of the Invention [Problem to be solved by the invention]

[0005] Separators are required to have low contact resistance to ensure electrical conductivity. However, it is difficult to reduce contact resistance so as to ensure electrical conductivity over a long period of time in the environment inside the fuel cell in which the separator is used. Furthermore, in recent years, there has been an increasing need for fuel cells for commercial vehicles, which require a longer service life than passenger cars. For this reason, there is a demand for fuel cells that can maintain electrical conductivity for a longer period of time than before.

[0006] The present invention has been made in view of the above points, and an object of the present invention is to provide a fuel cell separator that can ensure sufficient electrical conductivity. [Means for solving the problem]

[0007] In order to solve the above problems, the fuel cell separator of the present invention comprises a metal substrate, a titanium layer provided on the metal substrate, and a carbon layer provided on the titanium layer, and is characterized in that the TiC component ratio in the boundary region between the titanium layer and the carbon layer is 70% or less. [Effects of the Invention]

[0008] According to the present invention, sufficient conductivity can be ensured. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 2(a) is a schematic perspective view showing a separator according to one embodiment, and FIG. 2(b) is a schematic cross-sectional view showing a cross section parallel to the thickness direction of the layer of a convex portion of the separator according to one embodiment. [Figure 2] (a) is a graph showing the photoelectron spectrum (PT) of the sum of the Ti 2p orbitals obtained by HAXPES analysis of one sample separator, and the spectra (1 to 8) of each component obtained by separating the spectrum. (b) is a table showing a reference calculation example of the orientation ratio of each crystal lattice plane of the titanium layer. [Figure 3] Graph (a) shows the change in the TiC component ratio of the separator of samples 1-1 to 1-9 versus the negative bias voltage of the substrate during deposition of the carbon layer, and graph (b) shows the change in the initial contact resistance and the contact resistance after durability testing versus the TiC component ratio of the separator of samples 1-1 to 1-9. [Figure 4] (a) is a graph showing the change in ID / IG versus the negative bias voltage of the substrate during deposition of the carbon layer of the separator of samples 1-1 to 1-9, and (b) is a graph showing the change in initial contact resistance versus ID / IG of the separator of samples 1-1 to 1-9. [Figure 5](a) is a photograph showing a TEM observation image and an EELS mapping image of the cross section of the titanium layer and carbon layer in the convex portion of the flow channel shape for the separators of Samples 2-1 to 2-3. (b) is a graph showing the change in initial contact resistance versus the thickness of the titanium oxide layer for the separators of Samples 2-1 to 2-3. (c) is an AES depth profile for the separator of Sample 2-1, and (d) is an AES depth profile for the separator of Sample 2-2. [Figure 6] Graph (a) shows the relationship between the orientation ratio of the (100) plane of the titanium layer of each separator of Samples 3-1 to 3-10 and the Fe dissolution rate of multiple samples of each separator. Graph (b) shows the relationship between the orientation ratio of the (002) plane of the titanium layer of each separator of Samples 3-1 to 3-10 and the Fe dissolution rate of multiple samples of each separator. Graphs (c) and (d) are SEM images of the cross sections of a sample with an orientation ratio of the (100) plane of the titanium layer of less than 16.9% and a sample with an orientation ratio of the (100) plane of 16.9% or more, respectively. DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, an embodiment of the fuel cell separator of the present invention will be described. FIG. 1(a) is a schematic perspective view showing a separator according to one embodiment, and FIG. 1(b) is a schematic cross-sectional view showing a cross section parallel to the thickness direction of the layer of a convex portion of the separator according to one embodiment.

[0011] As shown in FIG. 1(a), a separator S according to one embodiment has a flow path shape consisting of recessed portions SB and protruding portions ST extending along the fluid flow path direction, with oblique portions SG between them. A cross section Sc of the separator S perpendicular to the flow path direction has a curved shape corresponding to the flow path shape. As shown in FIG. 1(b), the separator S includes a metal substrate 2 made of stainless steel, a titanium layer 4 provided on the metal substrate 2, and a carbon layer 8 provided on the titanium layer 4. The titanium layer 4 contains metal Ti (titanium), and the carbon layer 8 contains conductive C (carbon).

[0012] The titanium layer 4 and the carbon layer 8 are formed by depositing them in this order on the metal substrate 2 by, for example, a PVD method. Contamination during the process of forming the titanium layer 4 and the carbon layer 8 can cause TiO x Titanium oxide components such as (x<2) components and TiO2 components may be generated and disposed in the boundary region 5 between the titanium layer 4 and the carbon layer 8. In some cases, the titanium oxide layer (TiO x In the process of forming the carbon layer 8, a TiC component (titanium carbide component) may be generated and disposed in the boundary region 5. In some cases, a TiC layer 7 containing the TiC component may be formed in the boundary region 5.

[0013] In the separator S, the TiC component ratio of the boundary region 5 is 70% or less in all of the recessed portion SB, the protruding portion ST, and the oblique portion SG, and the D band peak intensity (I D ) and G-band peak intensity (I G ) intensity ratio (I D / I G ) is 0.7 or more. Furthermore, in all of the recessed portions SB, raised portions ST, and oblique portions SG, the thickness of the titanium oxide layer 6 in the boundary region 5 is 47 nm or less, or the maximum value of the O (oxygen) element ratio in the boundary region 5 is 88 atomic % or less. Furthermore, in all of the recessed portions SB, raised portions ST, and oblique portions SG, the orientation ratio of the (100) plane of the titanium layer 4 is 16.9% or more, and the orientation ratio of the (002) plane of the titanium layer 4 is 61.0% or less.

[0014] Conventionally, it has been difficult for separators using a metal substrate such as a stainless steel substrate to ensure sufficient durability and corrosion resistance as well as electrical conductivity in the environment inside a fuel cell in which the separator is used. For this reason, separators formed by depositing a titanium layer for improving durability and corrosion resistance and a carbon layer for improving electrical conductivity on a metal substrate in this order by a PVD method or the like, such as separator S according to one embodiment, have come to be used. However, even when such a separator is used in a fuel cell, the application of a potential load generated during operation to the separator, Cl, and the like in the environment inside the fuel cell can cause problems. - ions and Fe - If the separator is exposed to low-pH water containing ions and a high-temperature atmosphere (for example, below 100°C), the TiC component at the boundary between the titanium layer and the carbon layer of the separator may oxidize, resulting in the formation of titanium oxide. This can result in peeling of the carbon layer. This can lead to an increase in the contact resistance of the separator after endurance testing.

[0015] In contrast, in the separator S according to one embodiment, the TiC component ratio in the boundary region 5 between the titanium layer 4 and the carbon layer 8 is 70% or less in all of the recessed portions SB, the protruding portions ST, and the oblique portions SG, and the amount of TiC component in the boundary region 5 is suppressed. Therefore, when the separator S is used in the environment inside a fuel cell, the TiC component in the boundary region 5 is prevented from being oxidized to form titanium oxide components. This prevents the contact resistance of the separator S from increasing after endurance testing. Therefore, the conductivity of the separator S can be sufficiently ensured. In addition, I D / I G By making the ratio σ 0.7 or more, the degree of disorder (amount and size of graphite clusters) of the polycrystalline graphite structure of the carbon layer 8 is ensured to be appropriate, and a conductive path from one surface to the other surface of the carbon layer 8 can be ensured. This reduces the initial contact resistance of the separator S, and also reduces the contact resistance of the separator S after endurance testing. This makes it possible to further ensure the conductivity of the separator S. The configuration of the fuel cell separator according to this embodiment will be described in more detail below.

[0016] A fuel cell separator includes a metal substrate, a titanium layer provided on the metal substrate, and a carbon layer provided on the titanium layer. Separators, like the separator S according to one embodiment, typically have flow channels formed therein for delivering fluids such as fuel gas (H2 (hydrogen)), oxidant gas (O2 (oxygen)), and coolant. The separator's flow channel shape is, for example, a shape consisting of a recessed portion (bottom portion) and a protruding portion (top portion) extending along the fluid flow direction, with an oblique portion between them.

[0017] The metal substrate is not particularly limited, but may be made of a metal cheaper than Ti (titanium), specifically, Fe (iron), Al (aluminum), or an alloy thereof. Among these, a stainless steel substrate is preferred. This is because sufficient electrical conductivity can be ensured at the contact surface. The stainless steel substrate is not particularly limited, but examples thereof include austenitic and ferritic substrates. The thickness of the metal substrate is, for example, 0.05 mm to 1 mm. A thickness within this range easily satisfies the requirements for light weight, thinness, strength, and ease of processing. The metal substrate typically has a flow path shape formed in the separator for delivering fluids such as fuel gas, oxidizer gas, and coolant. The flow path shape of the metal substrate corresponds to the flow path shape of the separator, and is, for example, a shape consisting of recessed and protruding portions extending along the fluid flow path direction and oblique portions between them. The height difference between the recessed and protruding portions in the flow path shape of the metal substrate is, for example, 10 μm to 500 μm, excluding the thickness of the metal substrate. In the separator, the thickness of the titanium layer and the carbon layer is smaller than the thickness of the metal substrate, and therefore the shape of the flow channels in the separator depends on the shape of the flow channels in the metal substrate.

[0018] The titanium layer is not particularly limited as long as it contains Ti (titanium). For example, in an X-ray diffraction analysis of the separator surface, the ratio of the peak intensity of the (100) plane, (002) plane, and (101) planes derived from Ti divided by their relative intensities (theoretical diffraction intensities) to the sum of the peak intensities of the (100) plane divided by the relative intensity of the peak (100) plane (orientation ratio of the (100) plane of the titanium layer) is 16.9% or more, and the ratio of the peak intensity of the (002) plane divided by the relative intensity of the peak (orientation ratio of the (002) plane of the titanium layer) to the sum of the peak intensities of the (100) plane divided by the relative intensity of the peak (orientation ratio of the (002) plane of the titanium layer) is 61.0% or less. Among these, a titanium layer having an orientation ratio of the (100) plane of 20.0% or more and an orientation ratio of the (002) plane of 40.0% or less is preferred. This is because the titanium layer has a dense, flat structure with few defects, thereby improving the corrosion resistance of the separator. Specifically, this is because the generated water can penetrate through defects in the titanium layer to the metal substrate, causing corrosion and preventing the elution of Fe, thereby preventing the poisoning of the electrolyte membrane due to the elution of Fe. It is sufficient for at least a portion of the separator to satisfy the above orientation ratio condition, but it is particularly preferable for the convex portions of the flow channel shape to satisfy the above orientation ratio condition. This is because the convex portions have a significant effect on contact resistance, etc.

[0019] The titanium layer may be a layer containing metallic Ti or a Ti alloy. In addition to Ti, the titanium layer may contain, for example, N (nitrogen), C (carbon), H (hydrogen), O (oxygen), Fe (iron), Al (aluminum), V (vanadium), etc. The thickness of the titanium layer is not particularly limited, but is, for example, 10 nm to 800 nm, and can be calculated, for example, as an average value obtained by observing a cross section with a scanning electron microscope (SEM).

[0020] The carbon layer is not particularly limited as long as it is a conductive carbon layer containing conductive C (carbon). However, as in the carbon layer 8 according to one embodiment, it is preferable that the D band peak intensity (I D ) and G-band peak intensity (I G ) intensity ratio (I D / I G ) is preferably 0.7 or more, and particularly preferably ID / I G is preferably 0.94 or more and 1.00 or less. D / I G When the value is equal to or greater than the lower limit of these ranges, the initial contact resistance of the separator can be reduced, and I D / I G When the value is equal to or less than the upper limit of this range, an increase in the contact resistance of the separator in the environment inside the fuel cell can be suppressed.

[0021] When carbon materials are analyzed by Raman spectroscopy, generally, the wavelength of 1350 cm -1 Around 1550cm -1 Highly crystalline graphite has a peak at a wavelength of 1550 cm -1 This peak is usually called the "G-band peak." On the other hand, as the crystallinity decreases (the number of crystal structure defects increases), the wavelength of the peak increases. -1 A peak around this point appears. This peak is generally called the "D band peak." The D band peak intensity (I) is used as an index of the proportion of sp2 bonds and sp3 bonds in the carbon layer. D ) and G-band peak intensity (I G ) intensity ratio (I D / I G ) is used as an index of the degree of disorder in the polycrystalline graphite structure of carbon materials (crystal structure defects), sp2 bond ratio, etc. D / I G is used as an index of the contact resistance of the carbon layer and a film quality parameter that controls the conductivity of the carbon layer. D / I G is calculated by using a Raman spectrometer to obtain the Raman spectrum of the carbon material. Specifically, the Raman spectrum is measured at a wavelength of 1300 cm, known as the "D band." -1 ~1400cm -1 D band peak intensity (I D ) and the "G band" with a wavelength of 1500 cm -1 ~1600cm -1 G-band peak intensity (I G ) and the relative intensity ratio (peak intensity ratio (I D / IG )) can be calculated by the following formula. D / I G is 0.7 or more, but especially in the convex part of the flow path shape, I D / I G It is preferable that the value is 0.7 or more, because the convex portions have a large effect on the contact resistance, etc. The thickness of the carbon layer is not particularly limited, but is, for example, 10 nm to 500 nm, and can be calculated, for example, as an average value by SEM observation of the cross section.

[0022] The separator has a TiC component ratio (hereinafter sometimes abbreviated as "TiC component ratio") in the boundary region between the titanium layer and the carbon layer of 70% or less. For example, as described in the examples below, the TiC component ratio can be calculated by separating the photoelectron spectrum (PT) of the sum of Ti 2p orbitals obtained by HAXPES analysis of the separator into spectra for each component, and then calculating the ratio [%] of the integrated area of ​​the separated TiC spectrum to the total integrated area of ​​the spectra for all separated components. It is preferable that the separator has a TiC component ratio of 70% or less in at least a portion of the separator, and particularly, it is preferable that the TiC component ratio is 70% or less in the convex portions of the flow channel shape. This is because the convex portions have a significant effect on contact resistance, etc.

[0023] The separator is not particularly limited, but as in the separator S according to one embodiment, the thickness of the titanium oxide layer (TiO xThe total thickness of the titanium layer and the TiO2 layer (hereinafter, sometimes abbreviated as "titanium oxide layer thickness"). ) is preferably 47 nm or less, or the maximum value of the O (oxygen) element ratio in the boundary region between the titanium layer and the carbon layer (hereinafter, sometimes abbreviated as "maximum O element ratio") is 88 atomic % or less. This is because the reduction of the titanium oxide component in the boundary region between the titanium layer and the carbon layer ensures a sufficient conduction path between the titanium layer and the carbon layer, thereby further improving the conductivity of the separator. The thickness of the titanium oxide layer can be determined, for example, by obtaining TEM observation images and EELS mapping images of the cross sections (cross sections parallel to the layer thickness direction) of the titanium layer and the carbon layer of the separator and then calculating the TiO x The maximum O element ratio can be calculated as the average value of the total thickness of the TiO layer and the TiO layer. Furthermore, as described in the Examples below, for example, AES depth profile analysis (layer thickness direction) is performed from the surface of the carbon layer of the separator to create an AES depth profile, and the maximum O element ratio [atomic %] in the thickness direction at the boundary region can be calculated from the AES depth profile. A separator preferably has a titanium oxide layer thickness of 47 nm or less in at least a portion of the separator, and more preferably has a titanium oxide layer thickness of 47 nm or less in the convex portions of the flow channel shape. This is because the convex portions have a significant effect on contact resistance, etc. A separator preferably has a maximum O element ratio of 88 atomic % or less in at least a portion of the separator, and more preferably has a maximum O element ratio of 88 atomic % or less in the convex portions of the flow channel shape. This is for the same reason.

[0024] The separator is a component of a single cell of a fuel cell, and is disposed on both sides of a membrane electrode assembly (electrode layers of an electrolyte membrane and anode and cathode disposed on both sides of the electrolyte membrane). Examples of methods for manufacturing a separator include a process for forming a titanium layer on a metal substrate by a PVD method (physical vapor deposition) such as UBMS (unbalanced magnetron sputtering), and a process for forming a carbon layer on the titanium layer by a PVD method such as AIP (arc ion plating). The method for adjusting the TiC component ratio in the boundary region to 70% or less and the method for forming the carbon layer by a PVD method such as AIP (arc ion plating) are also available. D / I G Examples of methods for adjusting the orientation ratio of the (100) plane of the titanium layer to 16.9% or more and the (002) plane of the titanium layer to 61.0% or less include adjusting the negative bias voltage of the metal substrate (titanium layer) within a predetermined range when depositing a carbon layer on the titanium layer by AIP. Examples of methods for adjusting the thickness of the titanium oxide layer in the boundary region to 47 nm or less and the maximum O element ratio in the boundary region to 88 atomic % or less include, for example, preheating the reactor before depositing the titanium layer to sufficiently remove adsorbed and residual moisture, while increasing the degree of vacuum in the reactor during deposition of the titanium layer, thereby suppressing contamination by oxygen atoms in the boundary region. Examples of methods for adjusting the orientation ratio of the (100) plane of the titanium layer to 16.9% or more and the orientation ratio of the (002) plane of the titanium layer to 61.0% or less include, for example, adjusting the UBM coil current value, which controls the plasma intensity, and the negative bias voltage of the metal substrate within predetermined ranges when depositing a titanium layer on a metal substrate by UBMS. [Example]

[0025] The fuel cell separator according to the embodiment will be described in more detail below with reference to examples, comparative examples, and reference examples.

[0026] 1. Sample Preparation [Sample 1-1] The separator of Sample 1-1 was fabricated by the following method. First, a 0.1 mm thick stainless steel substrate (SUS304) with the separator flow path shape formed thereon was prepared as the metal substrate. Next, a titanium layer and a carbon layer were formed in this order on the surface of the metal substrate using a PVD coating device.

[0027] In this case, first, the metal substrate was placed in the reaction vessel of the apparatus, and the reaction vessel was evacuated. Subsequently, to deposit a titanium layer, the temperature inside the reaction vessel was raised to the processing temperature using an internal heater. Next, the pure Ti cathode target used for sputtering was etched (cleaned) with plasmatized Ar gas. Furthermore, the surface of the metal substrate was etched with plasmatized Ar gas to remove the passivation present on the surface. Next, a titanium layer was deposited on the surface of the metal substrate by UBMS using the pure Ti cathode target. The deposition conditions were as follows:

[0028] Target thickness: 220 nm Film formation time: 41 minutes Processing temperature: 150℃ Vacuum level: 2E-03mbar Input gas: Ar Gas flow rate: 250sccm Substrate bias type: PLS (pulse) Negative substrate bias voltage: 150V Frequency: 40kHz Off time during frequency: 5µS Target bias type: DC Ti cathode output: 8kW / A / V UBM coil current: 2A Orbital speed: 3 rpm

[0029] Next, to form a carbon layer, the temperature inside the reactor was adjusted to the processing temperature using an internal heater. Next, a carbon layer was formed on the surface of the titanium layer by AIP using high-purity ta-C raw material. The film formation conditions were as follows:

[0030] Target thickness: 25 nm Film formation time: 1 minute Processing temperature: 180℃ Vacuum level: 2E-03mbar Input gas: Ar Gas flow rate: 250sccm Substrate bias type: PLS (pulse) Negative bias voltage of the substrate: 0V Frequency: 40kHz Off time during frequency: 5µS Target bias type: DC C cathode output: 60kW / A / V Orbital speed: 4 rpm

[0031] In this way, a separator of Sample 1-1 was produced.

[0032] [Samples 1-2 to 1-9] Separators of samples 1-2 to 1-9 were produced by the same production method as separator of sample 1-1, except that the negative bias voltage of the substrate during the deposition of the carbon layer was changed as shown in Table 1 below.

[0033] [Sample 2-1] The separator of Sample 2-1 was produced by the same production method as the separator of Sample 1-1, except that the negative bias voltage of the substrate during the formation of the carbon layer and the processing temperature in the reaction vessel during the formation of the titanium layer were changed as shown in Table 1 below.

[0034] [Samples 2-2 and 2-3] The separators of Samples 2-2 and 2-3 were produced by the same production method as the separator of Sample 2-1, except that the treatment temperature in the reaction vessel during the formation of the titanium layer was changed.

[0035] [Sample 3-1] The separator of sample 3-1 was produced by the same production method as the separator of sample 1-1, except that the negative bias voltage of the substrate during the deposition of the titanium layer and the negative bias voltage of the substrate during the deposition of the carbon layer were changed as shown in Table 1 below.

[0036] [Samples 3-2 to 3-10] Separators of Samples 3-2 to 3-10 were produced by the same production method as separator of Sample 3-1, except that the negative bias voltage of the substrate during the deposition of the titanium layer was changed as shown in Table 1 below.

[0037] 2. Evaluation The thicknesses of the titanium layer and carbon layer (average values ​​obtained by SEM observation of the cross section) were measured for the separators of Samples 1-1 to 1-9, 2-1 to 2-3, and 3-1 to 3-10. The results are shown in Table 1 below. Furthermore, evaluations were carried out as follows.

[0038] [TiC component ratio in the boundary region between the titanium layer and the carbon layer] The TiC content [%] of the boundary region between the titanium layer and the carbon layer in the convex portion (top portion) of the flow channel shape of each separator (Samples 1-1 to 1-9, 2-1 to 2-3, and 3-1 to 3-10) was determined. First, the separators were analyzed by hard X-ray photoelectron spectroscopy (HAXPES). The analysis was performed at the beamline BL16XU of the SPring-8 synchrotron radiation facility. Monochromatization was performed using a Si(111)2 crystal monochromator and a Si(444) channel-cut crystal monochromator. For the analysis, hard X-rays were irradiated onto the carbon layer side. After adjusting the carbon layer thickness to a predetermined thickness, the X-ray energy was set to 8 keV and the takeoff angle was set to 80°, and the boundary region between the titanium layer and the carbon layer was used as the measurement region. The analysis conditions were as follows:

[0039] X-ray energy: 8 keV Energy width: 250 meV Pass energy: 200 eV Beam size: Approximately 150 μm x 35 μm (using a bent cylindrical mirror (horizontal focusing + vertical focusing)) Measurement time: 200 ms per point Measurement interval: 50 meV Measured spectrum: Ti (titanium) 2p Take-out angle: 80° Analyzer: VG Scienta R4000

[0040] Figure 2(a) is a graph showing the photoelectron spectrum (PT) of the sum of Ti 2p orbitals obtained by HAXPES analysis of one sample separator, and the spectra (1-8) of each component obtained by separating that spectrum. The horizontal and vertical axes of the graph represent binding energy and normalized photoelectron intensity, respectively. The photoelectron spectrum (PT) of the sum of Ti 2p orbitals of each sample was obtained by HAXPES analysis, as shown in Figure 2(a). Next, using the software PHI MultiPak (manufactured by ULVAC-PHI, Inc.), the background of the photoelectron spectrum (PT) of the sum of Ti 2p orbitals was subtracted based on the Shirley method, as shown in Figure 2(a), and the spectra of metallic Ti (1,5), TiC (2,6), and TiO (7,8). x The spectra were separated into the spectrum (3,7) of TiC and the spectrum (4,8) of TiO2. The integrated areas of the spectra of all these separated components were then calculated. The ratio [%] of the integrated area of ​​the spectrum (2,6) of TiC to the total integrated area of ​​the spectra of all components was calculated as the TiC component ratio. The results are shown in Table 1 below.

[0041] [I in the Raman spectrum of the carbon layer D / I G ] For the separators of Samples 1-1 to 1-9, Samples 2-1 to 2-3, and Samples 3-1 to 3-10, the D band peak intensity (I D ) and G-band peak intensity (I G ) intensity ratio (I D / I G ) was obtained. First, the carbon layer was analyzed using a Raman spectrometer Xplola plus manufactured by HORIBA Corporation, and a Raman spectrum was obtained. Next, baseline correction was performed on the Raman spectrum, and smoothing was performed by taking a moving average of five peak intensity data points. Next, I D As a result, the wavelength is 1350 cm -1 Obtain the simple peak intensity of I GAs a result, the wavelength is 1500 cm -1 ~1600cm -1 The maximum simple peak intensity in the region was obtained. Then, I D and I G From, I D / I G The results are shown in Table 1 below.

[0042] [Maximum thickness and O element ratio of titanium oxide layer at the boundary region between the titanium layer and the carbon layer] For the separators of each of Samples 2-1 to 2-3, the cross sections (cross sections parallel to the thickness direction of the layers) of the titanium layer and carbon layer in the convex portion of the flow channel shape were observed by TEM (transmission electron microscope), and the TEM observation images were mapped by composition analysis using EELS (electron energy loss spectroscopy) to obtain TEM observation images and EELS mapping images of the cross sections. From the EELS mapping images, it was found that the titanium oxide layer, TiO x The average value of the total thickness of the carbon layer and the TiO2 layer (thickness of the titanium oxide layer) was calculated. The results are shown in Table 1 below. Furthermore, for each sample separator, an AES (Auger electron spectroscopy) depth profile was created by performing depth analysis (layer thickness direction) from the surface of the carbon layer at the convex portion of the flow channel shape. From the AES depth profile, the maximum value of the O (oxygen) element ratio [atomic %] in the thickness direction at the boundary region was obtained. The results are shown in Table 1 below.

[0043] [Orientation ratio of the crystal lattice plane of the titanium layer] For the separators of samples 1-1 to 1-9 and 3-1 to 3-10, the orientation ratios [%] of the (100), (002), and (101) crystal lattice planes of the titanium layer in the convex portions of the flow channel shape were calculated using the following procedure. Figure 2(b) is a table showing a reference example of the calculation of the orientation ratio of each crystal lattice plane of the titanium layer.

[0044] (1) The separator was analyzed by XRD (X-ray diffraction) using an X-ray diffraction analyzer SmartLab (X-ray: CuKα) manufactured by Rigaku Corporation. (2) The main diffraction peaks of the titanium layer detected by XRD analysis, namely the (100), (002), and (101) planes, were fitted by the instrument, and the peak intensity (experimental intensity) of each crystal lattice plane of the titanium layer was calculated. (3) Since peak intensities differ depending on the crystal lattice plane and relative intensities exist, the peak intensity of each crystal lattice plane of the titanium layer was divided by the relative intensity (theoretical diffraction intensity) of the peak of that crystal lattice plane. (4) The (peak intensity / relative intensity) of each crystal lattice plane of the titanium layer obtained in (3) was further divided by the sum of the (peak intensity / relative intensity) of all the above crystal lattice planes of the titanium layer, and expressed as a percentage to calculate the orientation ratio [%] of each crystal lattice plane of the titanium layer.

[0045] The calculation results are shown in Table 1. For the separator samples with an orientation ratio of the (100) plane of the titanium layer of less than 16.9% and the separator samples with an orientation ratio of the (100) plane of the titanium layer of 16.9% or more, the cross sections of the convex portions (cross sections parallel to the thickness direction of the layer) were observed using a scanning electron microscope (SEM).

[0046] [Initial contact resistance] The initial contact resistance was determined for the separators of each of Samples 1-1 to 1-9, Samples 2-1 to 2-3, and Samples 3-1 to 3-10. First, a carbon sheet (TGP-H-060 manufactured by Toray Industries, Inc.) used as a GDL (gas diffusion layer) was placed on the surface of the carbon layer of the separator. A constant load (1 MPa) was applied using a measuring jig. Current from a power source was adjusted so that the current flowing through the separator was 1 A, as measured by an ammeter. The voltage applied between the separator and the carbon sheet was measured using a voltmeter. Next, the voltage value was converted to a resistance value and multiplied by the evaluation area to determine the initial contact resistance [mΩ cm 2 The results are shown in Table 1 below.

[0047] [Fe elution rate] For each of the separators of samples 1-1 to 1-9 and samples 3-1 to 3-10, one or more samples of a predetermined shape were cut out in plan view. A leaching test simulating a corrosive environment was conducted on each sample, and the Fe leaching rate of each sample was determined. One sample (n1) was cut out from the separators of samples 1-1 to 1-9, and the Fe leaching rate of the single sample was determined. Three samples (n1 to n3) were cut out from the separators of samples 3-1, 3-2, 3-4, and 3-6 to 3-10, and the Fe leaching rate of the three samples was determined. Thirteen samples (n1 to n13) were cut out from the separator of sample 3-3, and the Fe leaching rate of the 13 samples was determined. Four samples (n1 to n4) were cut out from the separator of sample 3-5, and the Fe leaching rate of the four samples was determined. First, a constant potential corrosion test was conducted in accordance with JIS Z2294 as a leaching test. Specifically, each sample was immersed in a sulfuric acid aqueous solution adjusted to a temperature of 80°C, and the test was conducted by maintaining a constant potential of 0.9 V vs. SHE for 60 hours. In the test, the sulfuric acid aqueous solution used had NaF dissolved therein so that the fluoride ion concentration was 3 ppm. The amount of Fe (weight) in the sulfuric acid aqueous solution before and after the test was measured using an ICP analyzer. Next, the difference in the amount of Fe in the sulfuric acid aqueous solution before and after the test was calculated, and the difference in the amount of Fe was converted to the amount of substance and divided by the test time and evaluation area to determine the Fe leaching rate [10 -10 mol / cm 2 / hr] was calculated. The results are shown in Table 1 below, and the details will be described later.

[0048] [Contact resistance after durability] The contact resistance after durability testing was determined for the separators of Samples 1-1 to 1-9. First, a durability test was conducted on the separators, similar to the elution test used to determine the Fe elution rate. Then, for the separators 240 hours after the test, the contact resistance after durability testing (mΩ cm) was measured using the same method as for the initial contact resistance. 2 The results are shown in Table 1 below.

[0049] [Table 1]

[0050] 3. Discussion of evaluation results Based on the evaluation results, the relationship between the separator configuration and the contact resistance and Fe elution rate was considered as follows.

[0051] [Relationship between TiC component ratio and contact resistance] FIG. 3(a) is a graph showing the change in the TiC component ratio with respect to the negative bias voltage of the substrate during the deposition of the carbon layer of the separator of Samples 1-1 to 1-9, and FIG. 3(b) is a graph showing the change in the initial contact resistance and the contact resistance after the endurance test with respect to the TiC component ratio of the separator of Samples 1-1 to 1-9. As shown in FIG. 3(a) and Table 1, the TiC component ratio increased as the negative bias voltage of the substrate during the deposition of the carbon layer increased. As shown in FIG. 3(b) and Table 1, when the TiC component ratio exceeded 70%, the contact resistance after the endurance test increased significantly and fell below the standard value (≦10 mΩ cm 2 ) was exceeded. From this, it is considered that a TiC composition ratio of 70% or less is preferable. As shown in Figure 3(b) and Table 1, in sample 1-3, the initial contact resistance was 17.4 mΩ cm despite the TiC composition ratio being 43.5%, which is below 70%. 2 and the standard value (≦3mΩ·cm 2 ) was exceeded. As will be explained later, D / I G This is thought to be due to the fact that the value is less than 0.7.

[0052] [I D / I G and contact resistance] Figure 4(a) shows the relationship between the negative bias voltage of the substrate and the I D / I G 4(b) is a graph showing the change in I of the separators of Samples 1-1 to 1-9. D / I GAs shown in Fig. 4(a) and Table 1, when the negative bias voltage of the substrate during the deposition of the carbon layer is in the range of 50 V or more, the initial contact resistance decreases as the negative bias voltage increases. D / I G As shown in Figure 4(b) and Table 1, I D / I G When I was 0.7 or more, the initial contact resistance was generally within the range of the standard value. D / I G From the above, it is considered that a TiC ratio of 70% or less and I D / I G A separator having a value of 0.7 or more is considered preferable because the initial contact resistance and the contact resistance after endurance testing are within the range of the standard values.

[0053] [Relationship between titanium oxide layer thickness and contact resistance] Figure 5(a) is a photograph showing a TEM observation image and an EELS mapping image of the cross section of the titanium layer and the carbon layer in the convex portion of the flow channel shape for the separators of Samples 2-1 to 2-3. Figure 5(b) is a graph showing the change in initial contact resistance versus the thickness of the titanium oxide layer for the separators of Samples 2-1 to 2-3. Figure 5(c) is an AES depth profile for the separator of Sample 2-1, and Figure 5(d) is an AES depth profile for the separator of Sample 2-2. As shown in Figures 5(a) and (b) and Table 1, the thickness of the titanium oxide layer (TiO x When the total thickness of the titanium oxide layer and the TiO2 layer was 47 nm or less, the initial contact resistance was within the specified range. Furthermore, as shown in Figures 5(c) and (d), when the titanium oxide layer was 47 nm or less, the maximum O (oxygen) element ratio in the thickness direction at the boundary region between the titanium layer and the carbon layer was 88 atomic % or less, which is considered to ensure a sufficient conductive path. Therefore, a titanium oxide layer thickness of 47 nm or less is preferable for the separator, and a titanium oxide layer thickness of 47 nm or less is considered to ensure a sufficient conductive path, thereby sufficiently reducing contact resistance.

[0054] [Relationship between the orientation ratio of the crystal lattice planes of the titanium layer and the Fe dissolution rate] Fig. 6(a) is a graph showing the relationship between the (100) orientation ratio of the titanium layer of each separator sample 3-1 to 3-10 and the Fe dissolution rate of multiple samples of each separator, and Fig. 6(b) is a graph showing the relationship between the (002) orientation ratio of the titanium layer of each separator sample 3-1 to 3-10 and the Fe dissolution rate of multiple samples of each separator. In Fig. 6(a) and (b), when two or more of the multiple samples (3, 13, or 4) of each separator showed substantially the same Fe dissolution rate, only the average dissolution rate is shown. When two or more of the multiple samples of each separator showed different Fe dissolution rates, the average dissolution rate, maximum dissolution rate, and minimum dissolution rate are shown.

[0055] As shown in Figures 6(a) and 6(b), when the orientation ratio of the (100) plane of the titanium layer was 16.9% or higher, the average, maximum, and minimum Fe dissolution rates of the separator were all consistently low. When the orientation ratio of the (002) plane of the titanium layer was 61.0% or lower, the average, maximum, and minimum Fe dissolution rates of the separator were all consistently low. From the perspective of separator corrosion resistance, it is considered that a titanium layer with a (100) plane orientation ratio of 16.9% or higher is favorable, and a titanium layer with a (002) plane orientation ratio of 61.0% or lower is favorable.

[0056] Figures 6(c) and 6(d) are SEM images of the cross sections of a sample with a (100) orientation ratio of less than 16.9% and a sample with a (100) orientation ratio of 16.9% or more, respectively. As shown in Figures 6(c) and 6(d), the sample with a (100) orientation ratio of less than 16.9% had a columnar structure and many defects, whereas the sample with a (100) orientation ratio of 16.9% or more had a flat structure and few defects.

[0057] The above describes in detail the embodiments of the fuel cell separator according to the present invention, but the present invention is not limited to the above-described embodiments, and various design modifications can be made within the scope of the spirit of the present invention as set forth in the claims. [Explanation of symbols]

[0058] S: Fuel cell separator, 2: Metal substrate, 4: Titanium layer, 5: Boundary region, 6: Titanium oxide layer, 8: Carbon layer

Claims

1. A metal substrate; a titanium layer provided on the metal substrate; a carbon layer disposed on the titanium layer; Equipped with A fuel cell separator, wherein the TiC component ratio in the boundary region between the titanium layer and the carbon layer is 70% or less.

2. The D band peak intensity (I Ｄ ) and G band peak intensity (I Ｇ ) intensity ratio (I Ｄ / I Ｇ 2. The fuel cell separator according to claim 1, wherein the value of (a) is 0.7 or more.

3. 3. The fuel cell separator according to claim 1, wherein the thickness of the titanium oxide layer in the boundary region between the titanium layer and the carbon layer is 47 nm or less, or the maximum value of the O element ratio in the boundary region between the titanium layer and the carbon layer is 88 atomic % or less.

4. 3. The fuel cell separator according to claim 1, wherein the orientation ratio of the (100) plane of the titanium layer is 16.9% or more, and the orientation ratio of the (002) plane of the titanium layer is 61.0% or less.

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