FUEL CELL SEPARATOR

Abstract

Separator (3) for a fuel cell (1), wherein the separator (3) is adapted to be in contact with a power generation part (2) comprising a membrane electrode arrangement of the fuel cell (1) in order to separate the power generation part (2) from a power generation part of an adjacent fuel cell, wherein the separator (3) comprises: a metal substrate (31) made of metal; and a tin oxide coating (32) covering at least one surface of the metal substrate (31) on one side of the power generation part (2), characterized by the fact that the tin oxide coating (32) is made of tin oxide containing 1 to 10 atomic percent aluminum, and where a half-width at the half-value maximum of a diffraction vertex on a (110) plane of the tin oxide of the tin oxide coating (32) at approximately 2θ = 26.6°, determined by X-ray diffraction using CuKα rays, is less than or equal to 1°.

Description

BACKGROUND Technical area

[0001] The present disclosure relates to a separator for a fuel cell, wherein the separator is adapted to be in contact with a power generation part of the fuel cell, which includes a membrane electrode arrangement to separate the power generation part from a power generation part of an adjacent fuel cell. State of the art

[0002] A polymer electrolyte fuel cell features a membrane electrode assembly (MEA) comprising an electrolyte membrane with an ion permeability and anode-side and cathode-side catalyst layers (electrode layers) enclosing the electrolyte membrane. The MEA also includes gas diffusion layers (GDLs) on opposite sides for supplying fuel gas or oxidation gas to the MEA and for receiving electricity generated by electrochemical reactions. Such a membrane electrode assembly with GDLs on opposite sides is called a MEGA (membrane electrode and gas diffusion layer assembly), and the MEGA is enclosed between a pair of separators. In this configuration, the MEGA is the power-generating part of the fuel cell. If no gas diffusion layers are included, the MEA itself is the power-generating part of the fuel cell.

[0003] As an example of such a separator for a fuel cell, JP H08-185 870 A proposes the following separator. Specifically, the separator includes a cermet substrate composed of a durable metal containing chromium and a ceramic; and a protective metal oxide layer covering a surface of the substrate on the side facing the cathode gas to prevent contact between the surface and the cathode gas. Furthermore, JP H08-185 870 A illustrates antimony-doped tin oxide as an example of such a metal oxide.

[0004] DE 10 2004 050 921 A1 describes an electrochemical cell with an electrode and an electrically conductive contact element that points towards the electrode to conduct electric current, wherein the electrically conductive contact element has an electrically conductive coating on at least one side of the element, wherein this coating comprises a metal oxide composition that is electrically conductive, and wherein the coating comprises tin oxide doped with fluorine.

[0005] DE 10 2007 029 431 A1 describes a method for applying an electrically conductive and hydrophilic layer to a bipolar plate substrate for a fuel cell, wherein the method comprises providing a film of electrically conductive and hydrophilic particles, wherein the particles may be selected from the group consisting of fluorine-doped tin oxide, antimony-doped tin oxide, indium-doped tin oxide, tantalum-doped titanium oxide and niobium-doped titanium oxide.

[0006] US 2013 / 0 022 893 A1 describes a composite membrane which may include doped tin phosphate.

[0007] WO 2003 / 092 139 A2 describes a fuel cell with one or more metallic bipolar plates coated with a corrosion-resistant metal and then with electrically conductive polycrystalline tin oxide, wherein the conductive tin oxide is fluorinated or antimony-doped tin oxide. SUMMARY

[0008] According to the separator for a fuel cell described in JP H08-185870 A, the diffusion of chromium to the cathode electrode is suppressed, thus preventing a decrease in the fuel cell's power generation. However, even with such a protective coating, it would be difficult to suppress a decrease in the fuel cell's power generation unless the electrical contact resistance on a surface of the fuel cell separator in contact with a power generation component, including a membrane electrode assembly, could be reduced. Furthermore, it has been found that a separator with a tin oxide coating containing antimony, such as the one described in JP H08-185870 A, would exhibit increased contact resistance in a corrosive environment where moisture is generated during electricity production.

[0009] The present disclosure was made with regard to the foregoing, and exemplary embodiments relate to the provision of a separator for a fuel cell which, even in a corrosive environment, can suppress a decrease in the power generation output of the fuel cell by reducing the contact resistance between at least the separator and a power generation part.

[0010] Accordingly, the separator for a fuel cell, as described in the present disclosure, is a separator for a fuel cell, wherein the separator is adapted to be in contact with a power-generating part, including a membrane electrode arrangement of the fuel cell, in order to separate the power-generating part from a power-generating part of an adjacent fuel cell, the separator comprising a metal substrate; and a tin oxide coating covering at least one surface of the metal substrate on the side of the power-generating part. The tin oxide coating is made of tin oxide containing 1 to 10 atomic percent aluminum, and wherein a half-width at the half-power maximum of a diffraction peak on a plane (110) of the tin oxide of the tin oxide coating (32) at about 2θ = 26.6°, determined by X-ray diffraction using CuKα rays, is less than or equal to 1°.

[0011] According to the present disclosure, the tin oxide of the tin oxide coating is produced to contain the aforementioned amount of aluminum, which increases the conductivity of the tin oxide coating and thereby reduces the contact resistance between at least the separator for the fuel cell and the power generation part. BRIEF DESCRIPTION OF THE DRAWINGS The Fig. Figure 1 is a cross-sectional view of the primary part of the fuel cell stack including separators and for fuel cells in accordance with an embodiment of the present disclosure; the Fig. Figure 2 is an enlarged cross-sectional view of an area around a surface of the separator for the fuel cell in accordance with this embodiment; the Fig.Figure 3 is a diagram illustrating the half-value at a half-value maximum of a diffraction vertex on the (110) plane of tin oxide of a tin oxide coating at about 2θ = 26.6°, as measured by X-ray diffraction using CuKα rays; and the Fig. Figure 4 is a graphical representation showing the relationship between the content of aluminium added to the tin oxide coating of a test piece from each of examples 1 to 5 and comparison example 2 and the contact resistance of the test piece after a corrosion test. DETAILED DESCRIPTION

[0012] The structure of the present disclosure is then described in detail based on embodiments shown in the drawings. Although the following embodiments illustrate by way of example a case in which the present disclosure is applied to fuel cells mounted on a fuel cell vehicle or to a fuel cell system containing such fuel cells, the scope of the present disclosure is not limited thereto.

[0013] The Fig. Figure 1 is a cross-sectional view of the primary part of a fuel stack (fuel cells). 10. As in the Fig.As shown in Figure 1, the fuel cell stack 10 comprises a plurality of stacked cell units 1. Each cell 1 is a polymer electrolyte fuel cell that generates an electromotive force when an electrochemical reaction occurs between oxidizer gas (e.g., air) and fuel gas (e.g., hydrogen). The cell 1 includes a MEGA 2 and separators (fuel cell separators) 3 adapted to be in contact with the MEGA 2 in order to separate the MEGA 2 from the MEGAs 2 of the adjacent fuel cells. It should be noted that in this embodiment, the MEGA 2 is inserted between a pair of separators 3, 3.

[0014] The MEGA 2 is an integral body comprising a membrane electrode assembly (MEA) 4 and gas diffusion layers 7, 7 arranged on opposite sides thereof. The membrane electrode assembly 4 includes an electrolyte membrane 5 and a pair of electrodes 6 and 6 connected to insert the electrolyte membrane 5 between them. The electrolyte membrane 5 is a proton-conducting ion-exchange membrane formed from a solid polymer material, and each electrode 6 is formed from a porous carbon material with a catalyst, such as platinum, deposited on it. The electrode 6 located on one side of the electrolyte membrane 5 serves as an anode, and the electrode 6 on the other side serves as a cathode.Each gas diffusion layer 7 is formed from a gas-permeable conductive element, such as a porous carbon body, like carbon paper or carbon fabric, or a porous metal body, such as with a metallic mesh or foamed metal.

[0015] In this embodiment, the MEGA 2 is the power generation part of the fuel cell 10, and the separators 3 are in contact with the gas diffusion layers 7 of the MEGA 2. If the gas diffusion layers 7 are omitted, the membrane electrode assembly 4 is the power generation part, and in such a case, the separators 3 are in contact with the membrane electrode assembly 4. Therefore, the power generation part of the fuel cell 10 includes the membrane electrode assembly 4 and is in contact with the separators 3. Each separator 3 is a plate-like element containing a metal with excellent conductivity and gas impermeability as a substrate, and the gas diffusion layer 7 of the MEGA 2 abuts one side of the separator 3, and the other side of an adjacent separator 3 abuts the separator 3.

[0016] In this embodiment, each separator 3 is formed in a wave shape. Specifically, the separator 3 has a shape such that the wave forms trapezoids with equal sides, the tip region of each wave is flat, and opposite ends of the tip region are angled at equal angles. The shape of each separator 3, viewed from the front and back, is nearly identical. The upper portions of the separator 3 are in surface contact with one of the gas diffusion layers 7 of the MEGA 2, and the upper portions of the other separator 3 are in surface contact with the other gas diffusion layer 7 of the MEGA 2.

[0017] A gas flow channel 21, defined between the gas diffusion layer 7 on the side of one electrode (i.e., the anode) 6 and the separator 3, is a channel through which fuel gas circulates, and a gas flow channel 22, defined between the gas diffusion layer 7 on the side of the other electrode (i.e., the cathode) 6 and the separator 3, is a channel through which oxidation gas circulates. When fuel gas is supplied to one of the gas flow channels 21, and oxidation gas is supplied to the gas flow channel 22, which is opposite the gas flow channel 21 with the cell 1 inserted between them, an electrochemical reaction occurs within the cell 1, generating an electromotive force.

[0018] Furthermore, a given cell 1 and another adjacent cell 1 are arranged such that an electrode 6 serving as an anode and an anode 6 serving as a cathode are positioned opposite each other. Additionally, the upper parts of the rear surface of a separator 3, which is arranged along an electrode 6 serving as an anode of a given cell 1, and the upper parts of a rear surface of a separator 3, which is arranged along an electrode 6 to serve as a cathode of a given cell 1, are in surface contact with each other. Water, as a coolant for cooling the cells, circulates through spaces 23, which are delimited between the separators 3 and 3, which are in surface contact with each other and with the two adjacent cells 1.

[0019] In this embodiment, as in the Fig.As shown in Figure 2, each separator 3 is a metal substrate 31. Examples of the metal substrate 31 material include titanium and stainless steel. Furthermore, opposite surfaces of the separator 3 (that is, a surface on the side of the gas diffusion layer 7 and a surface on the side of the adjacent separator 3) are each covered with a tin oxide coating 32.

[0020] The thickness of the tin oxide coating 32 is preferably in the range of 10 to 300 nm. If the thickness of the tin oxide coating 32 is less than 10 nm, the beneficial effects of the tin oxide coating 32 cannot be fully realized. On the other hand, if the thickness of the tin oxide coating 32 is greater than 300 nm, the internal stress of the tin oxide coating 32 becomes high. Therefore, the tin oxide coating 32 is likely to detach from the metal substrate 31.

[0021] Although in this embodiment the tin oxide coating 32 is formed on every surface of the separator 3, it is acceptable as long as the tin oxide coating 32 is formed on at least one surface of the metal substrate 31 on the side of the gas diffusion layer 7, because a part where the gas diffusion layer 7 and the separator 3 contact each other has a high resistance.

[0022] The tin oxide coating 32 contains aluminum (Al). Accordingly, the tin oxide coating 32 is a semiconductor. Specifically, the tin oxide coating 32 is produced from a tin oxide containing 1 to 10 atomic percent aluminum. In such a tin oxide coating 32, tetravalent tin sites in the crystal lattice of the tin oxide are substituted with trivalent aluminum. Therefore, the tin oxide coating 32, which contains aluminum-doped tin oxide, acts as a p-type semiconductor with supports (holes) within it. Accordingly, the concentration of supports in the tin oxide coating 32 is increased, thereby improving the conductivity of the tin oxide coating 32.

[0023] Consequently, even if the tin oxide coating 32 of the fuel cell stack 10 is exposed to a corrosive environment for a long time and the oxidized state of the tin oxide coating 32 has changed, the carrier concentration does not change because the carriers are holes, not electrons. Accordingly, in this embodiment, the contact resistance of the separator 3 with the tin oxide coating 32 formed on it can be reduced even in a corrosive environment, and consequently, the internal resistance of the fuel cell stack 10 can be reduced.

[0024] In this case, if the aluminum content is less than 1 atomic percent, an increase in the carrier concentration through substitution with aluminum would be insufficient. Therefore, it is difficult to improve the conductivity of the tin oxide coating, and consequently, the contact resistance of separator 3 cannot be sufficiently reduced.

[0025] Meanwhile, even if the aluminum content is greater than 10 atomic percent, a further reduction in the contact resistance of the separator 3 due to aluminum cannot be expected. This is because even if the concentration of supports with an increased aluminum content is increased, the increased aluminum content would interfere with the movement of the supports. Preferably, the tin oxide coating 32 is prepared from tin oxide containing 2 to 10 atomic percent aluminum.

[0026] In this case, when tin oxide containing 1 to 10 atomic percent aluminum is measured by X-ray diffraction using CuKα radiation, as in the Fig. Figure 2 shows a diffraction peak on the (110) plane of the tetragonal tin oxide at approximately a Bragg angle of 2θ = 26.6° (specifically in the range of 26.6° ± 0.5°).

[0027] In this embodiment, the half-power width at the half-value maximum W of a diffraction peak on the (110) plane of tin oxide of the tin oxide coating 32 at approximately 2θ = 26.6°, as measured by X-ray diffraction using CuKα radiation, is less than or equal to 1°. The half-power width at the half-value maximum W is the width of a diffraction peak at one half (P / 2) of the maximum value P of the diffraction intensity of the diffraction peak. In this embodiment, the half-power width at the half-value maximum of a diffraction peak satisfies a condition of less than or equal to 1°, so that the crystallinity of the tin oxide forming the tin oxide coating 32 is increased, and consequently, the conductivity of the tin oxide coating 32 can be increased. As a result, the contact resistance of the separator 3 can be further reduced.

[0028] If the half-width at the half-power maximum of the tin oxide coating 32 is greater than 1°, the crystallinity of the tin oxide forming the tin oxide coating 32 becomes low. Therefore, the conductivity of the tin oxide coating 32 would decrease, and consequently, the contact resistance of the separator 3 cannot be sufficiently reduced. As can be seen from Reference Example 2 described below, if the half-power maximum of a diffraction peak on the (110) plane of tin oxide is less than or equal to 0.5°, the contact resistance of the separator 3 can be further reduced.

[0029] A method for forming the tin oxide coating 32 on the metal substrate 31 of the separator 3 is not particularly limited. For example, the coating can be deposited using physical vapor deposition (PVD), such as sputtering, vacuum deposition, ionized vapor deposition, or ion plating. Specifically, for example, the tin oxide coating 32 can be deposited by sputtering a sintered body, which is obtained by mixing tin oxide particles and aluminum oxide particles and sintering this as a target onto the surface of the metal substrate 31 using plasma or similar processes.In such a case, during the deposition of the tin oxide coating 32, the substrate temperature during the deposition of the coating (coating deposition temperature), an applied voltage and similar parameters are set so that the tin oxide coating 32, which is produced from tin oxide, can be obtained with a half-width at the half-value maximum in the previously mentioned range. Examples

[0030] The present revelation will then be described with reference to examples. [Example 1]

[0031] A test piece corresponding to a separator was manufactured as described below. First, a 0.1 mm thick plate of pure titanium was prepared as the metal substrate for the separator. Next, the metal substrate was placed in a vacuum chamber, and while the chamber was under vacuum, argon gas was introduced. A voltage was then applied to generate argon ions. These argon ions removed an oxide coating from the surface of the metal substrate.

[0032] Next, a sintered body, obtained by mixing and sintering tin oxide and aluminum oxide particles, was positioned as a target in the vacuum chamber. Using this sintered body as the target, sputtering was performed to form a tin oxide coating on the surface of the metal substrate. Specifically, a metal substrate was positioned opposite the target, and then the vacuum chamber was evacuated to create a vacuum atmosphere (a reduced-pressure atmosphere). Argon gas was then introduced into the vacuum chamber as the sputtering gas, and a voltage was applied to the metal substrate, which had been heated to 450°C. This caused the generated argon ions to collide with the target, subsequently depositing the target material onto the metal substrate. It should be noted that a preload was applied across both the target and the metal substrate.In this way, a tin oxide coating with a thickness of 100 nm was deposited on the surface of the metal substrate.

[0033] Next, the aluminum (Al) content in the tin oxide coating was measured from the detection intensity at an aluminum binding energy of 73 eV using an X-ray spectrometer (Quantera SXM, manufactured by ULVAC-PHI, Inc.). The aluminum content in the tin oxide coating was found to be 1 atomic percent (see Table 1). [Examples 2 to 5]

[0034] Test pieces were prepared as in Example 1. Examples 2 to 5 differ from Example 1 in that the tin oxide coatings of Examples 2 to 5 were modified by changing the content of aluminum oxide in the sintered body as a target, such that the resulting tin oxide coatings would contain 2 atomic percent, 3 atomic percent, 5 atomic percent, and 10 atomic percent of aluminum, respectively. The aluminum content in each of the tin oxide coatings of Examples 2 to 5 was measured as in Example 1. Table 1 shows the results. [Comparison example 1]

[0035] A test piece was produced as in Example 1. Comparison Example 1 differs from Example 1 in that a tin oxide coating was deposited by omitting aluminum oxide as a target in a sintered body, so that the resulting tin oxide coating would contain 0 atomic percent of aluminum (contains no aluminum). The aluminum content in the tin oxide coating of Comparison Example 1 was measured as in Example 1. Table 1 shows the results. [Comparative example 2]

[0036] A test piece was produced as in Example 1. Comparison Example 2 differs from Example 1 in that a tin oxide coating was modified by changing the aluminum oxide content in a sintered body as a target, such that the resulting tin oxide coating would contain 0.5 atomic percent aluminum. The aluminum content in the tin oxide coating of Comparison Example 2 was measured as in Example 1. Table 1 shows the results. [Comparative example 3]

[0037] A test piece was prepared as in Example 1. Comparison Example 3 differs from Example 1 in that a tin oxide coating containing antimony (Sb) was deposited using a sintered body obtained by mixing tin oxide particles and antimony oxide particles and sintering them as a target. The antimony content in the tin oxide of Comparison Example 3 was measured as in Example 1. Table 1 shows the results. < Contact resistance test>

[0038] Carbon paper (TGP-H120, 0.5 mm thick, manufactured by TORAY INDUSTRIES, INC.), corresponding to a diffusion layer of the power-generating part of the fuel cell, was placed on one surface of each of the tin oxide coatings of the test specimens in Examples 1 to 5 and Comparison Examples 1 to 3. A gold-plated copper plate was then placed on top, sandwiching the carbon paper between the test specimen and the copper plate. It should be noted that, in order to measure only the contact resistance between the tin oxide coating and the carbon paper, another gold-plated copper plate was also placed in contact with the other surface (which has no coating) of the test specimen to prevent the formation of contact resistance between such elements.Next, a pressure of 0.98 MPa was applied to the surface of the test piece using a measuring device. Under these conditions, current flowed through the test piece from a power supply, adjusted with an ammeter to ensure a constant current flow. A voltage applied to the test piece was then measured with a voltmeter to determine the contact resistance (pre-corrosion contact resistance) between the tin oxide coating of the test piece and the carbon paper. Table 1 shows the results. < Corrosion test>

[0039] A corrosion test (constant potential corrosion test) in accordance with the procedure for an electrochemical high-temperature corrosion test of metallic materials in molten salts of the Japanese Industrial Standard (JIS Z2294) was performed on each of the test pieces of Examples 1 to 3 and the comparison examples 1 to 3. Specifically, each test piece was immersed in a sulfuric acid solution at a temperature set to 80°C in an open atmospheric air system. In this condition, a counter electrode consisting of a platinum plate and the test piece (sample electrode) were electrically connected, creating a potential difference of 0.9 V between the counter electrode and the sample electrode, thus corroding the test piece. It should be noted that the potential of the test piece was kept constant using a reference electrode. The test was also performed for 100 hours.The contact resistance of each test piece after the corrosion test was measured using the same procedure as for the previously mentioned contact resistance test. Table 1 and . Fig. Figure 4 shows the results. [Table 1] Aluminum content (atomic %) Contact resistance (Ω·cm) 2 ) Before corrosion test After corrosion test Comparative example 1 0 There was no current. There was no current. Comparative example 2 0,5 64 67 Example 1 1 24 26 Example 2 2 16 17 Example 3 3 13 14 Example 4 5 13 14 Example 5 10 13 14 Comparative example 3 Antimony (0.5 atomic %) 16 95 <Ergebnis 1>

[0040] As shown in Table 1, the contact resistance of the test piece was found to be high, consistent with Comparative Example 1, and it was not possible for current to flow between the test piece and the carbon paper. Accordingly, it was found that a tin oxide coating containing no aluminum, as in Comparative Example 1, exhibits strong insulating properties (low conductivity).

[0041] Additionally, as shown in Table 1 and Fig.As shown in Figure 4, it was found that the contact resistance of Example 1 with an increased aluminum content decreased significantly compared to those of Comparison Examples 1 and 2, both before and after the corrosion test, and the contact resistance of each of Examples 2 to 5 with progressively increasing aluminum content was found to be essentially constant. Accordingly, it can be said that an aluminum content of 1 atomic percent in a tin oxide coating has critical significance in reducing the contact resistance. It is assumed that when tin oxide contains aluminum, as in Examples 1 to 5 and Comparison Example 2, tetravalent tin sites in the tin oxide crystal lattice are substituted with trivalent aluminum, and consequently, the tin oxide becomes a semiconductor (p-type semiconductor).

[0042] The aluminum content in each of Examples 1 to 5 is higher than that of the comparative example 2. Therefore, the concentration of carriers (holes) in the tin oxide coating (semiconductor) is high, and consequently, the tin oxide coating of each of Examples 1 to 5 is considered to have improved conductivity compared to that of comparative example 2. In particular, if the tin oxide contains 2 to 10 atomic percent aluminum, the conductivity of the resulting tin oxide coating is expected to be further improved.

[0043] In this case, if the aluminum content in tin oxide is less than 1 atomic percent (specifically 0.5 atomic percent), as in comparative example 2, increasing the concentration of the carriers (holes) in the tin oxide coating (semiconductor) by substitution with aluminum would be insufficient. Consequently, it is assumed that the conductivity of the resulting tin oxide coating is difficult to improve.

[0044] Meanwhile, if the aluminum content is greater than 10 atomic percent, the concentration of the carriers in the tin oxide coating (semiconductor) is also increased, and it is assumed that the increased aluminum content in the tin oxide would interfere with the movement of the carriers. Consequently, it is assumed that the conductivity of the resulting tin oxide coating will not improve, and therefore a further reduction in the contact resistance of the separator by means of aluminum cannot be expected.

[0045] Furthermore, in the tin oxide coating of comparison example 3, tetravalent tin sites in the tin oxide crystal lattice were substituted with pentavalent antimony, and consequently, the tin oxide becomes a semiconductor with electrons as carriers (n-type semiconductor). Therefore, the tin oxide coating is assumed to be oxygen-deficient tin oxide. As a result, the contact resistance of the test piece of comparison example 3 before the corrosion test is approximately the same as that of examples 1 to 5.

[0046] However, although the contact resistance of the test piece of each of examples 1 to 5 remained almost the same after the corrosion test as before, the contact resistance of the test piece of comparison example 3 increased dramatically after the corrosion test, unlike those of examples 1 to 5. It is assumed that this is due to the fact that, in the test piece of comparison example 3, the carriers generated by the oxygen deficiency of the tin oxide decreased after the corrosion test as a result of the oxidation of the tin oxide. Meanwhile, when considering the test piece of each of examples 1 to 5, the tin oxide coating functions as a p-type semiconductor, and the carriers in the semiconductor are not electrons but holes. Therefore, the carriers are hardly affected by the oxidation of the tin oxide.Consequently, it is assumed that the contact resistance of the test piece of each of examples 1 to 5 after the corrosion test is unlikely to change significantly from that before the corrosion test. [Reference examples 1 to 3]

[0047] Test pieces were produced as previously described in Comparison Example 3. Reference Examples 1 and 3 differ from Example 1 in that the temperature of a metal substrate during the deposition of a coating (deposition temperature) was set to 350°C and 550°C, respectively. It should be noted that Reference Example 2 is identical to Comparison Example 3. <Röntgenbeugungsmesstest>

[0048] For the tin oxide coatings of the test specimen of each of Reference Examples 1 to 3, a diffraction peak angle on the (110) plane of tin oxide was detected from an X-ray diffraction pattern using an X-ray analyzer employing CuKα rays (with a wavelength of 0.154 nm) as the X-ray source, a copper tube. The diffraction peak angle of tin oxide of each test specimen was found to be around a Bragg angle of 2θ = 26.6°, and the full width at half maximum of the diffraction peak was measured. Table 2 shows the results. The contact resistance of the test specimen of each of Reference Examples 1 to 3 was measured in Example 1. Table 2 shows the results. [Table 2] Coating deposition temperature (°C) Half-width at half-power maximum (°) Contact resistance (mΩ· cm 2 ) Reference example 1 350 1,1 45 Reference example 2 450 0,5 16 Reference example 3 550 0,3 12 <Ergebnis 2>

[0049] As shown in Table 2, the half-width of a half-power maximum of a diffraction vertex on the (110) plane of tin oxide in the tin oxide coating of each of reference examples 2 and 3 was found to be smaller than that of reference example 1. Therefore, the crystallinity of the tin oxide in the tin oxide coating of each of reference examples 2 and 3 is considered to be higher than that of reference example 1. Furthermore, the contact resistance of each of reference examples 2 and 3 was found to be lower than that of reference example 1.

[0050] Accordingly, if, as in the test specimen of each of Reference Examples 2 and 3, the half-width at the half-value maximum of an X-ray diffraction peak is less than or equal to 1°, or preferably less than or equal to 0.5°, the crystallinity of the tin oxide of the tin oxide coating is high. Accordingly, it is assumed that the conductivity of the tin oxide coating is increased, and consequently the contact resistance of the test specimen (separator) is reduced.

[0051] With respect to each of Reference Examples 1 to 3, one element contained in the tin oxide coating is antimony. However, if one element contained in the tin oxide coating is aluminum, the relationship between the crystallinity of the tin oxide and the conductivity of the tin oxide coating is considered to be the same. Therefore, even if a tin oxide coating contains aluminum, the full width at half maximum of a diffraction peak is less than or equal to 1°, or preferably less than or equal to 0.5°.

[0052] Although the embodiments of the present disclosure have been described in detail previously, specific configurations are not limited thereto, and all design changes that are within the intellectual scope of the present invention are included in the present disclosure. DESCRIPTION OF SYMBOLS 1 cell 2 MEGA (power generation section) 3 Separator (separator for fuel cell) 4 membrane electrode assembly (MEA) 6 electrode 7 Gas diffusion layer 10 fuel cell stacks (fuel cell) 21, 22 Gas flow channels 31 Metal substrate 32 Tin oxide coating

[0053] A separator for a fuel cell is provided, which can suppress a decrease in the power generation output of the fuel cell by reducing the contact resistance of the separator.

[0054] Specifically, a separator for a fuel cell is provided, wherein the separator is adapted to be in contact with a MEGA (power generation part) including a membrane electrode assembly of the fuel cell in order to separate the MEGA from a MEGA of an adjacent fuel cell, wherein the separator contains a metal substrate; and a tin oxide coating that covers a surface of the metal substrate on the side of the MEGA. The tin oxide coating is made of tin oxide containing 1 to 10 atomic percent aluminum.

Claims

[1] Separator (3) for a fuel cell (1), wherein the separator (3) is adapted to be in contact with a power generation part (2) comprising a membrane electrode arrangement of the fuel cell (1) in order to separate the power generation part (2) from a power generation part of an adjacent fuel cell, wherein the separator (3) comprises: a metal substrate (31) made of metal; and a tin oxide coating (32) covering at least one surface of the metal substrate (31) on one side of the power generation part (2), characterized by , that the tin oxide coating (32) is made of tin oxide containing 1 to 10 atomic percent aluminum, and where a half-width at the half-value maximum of a diffraction vertex on a (110)-plane of the tin oxide of the tin oxide coating (32) at about 2θ = 26.6°, determined by X-ray diffraction using CuKα rays, is less than or equal to 1°. [2] Separator (3) for a fuel cell (1) according to claim 1, wherein the tin oxide coating (32) has a thickness in the range of 10 to 300 nm.

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