FUEL CELL SEPARATOR

Abstract

Separator (3) for a fuel cell (1, 10), wherein the separator (3) is suitable to be in contact with a power generation section (2) including a membrane electrode assembly (4) of a fuel cell (1) in order to separate the power generation section (2) from a power generation section (2) of an adjacent fuel cell (1), wherein the separator (3) comprises: a metal substrate (31) made of metal; and a tin oxide film (32) covering at least one surface of the metal substrate (31) on one side of the power generation section (2), where: the tin oxide film (32) is made of tin oxide which contains 0.2 to 10 atomic% antimony and the tin oxide film (32) made of tin oxide with a structure formed by SnO 2-X (0.1 ≤ X ≤ 0.4) represents the oxygen deficiency shown.

Description

BACKGROUND Technical area

[0001] The present invention relates to a separator for a fuel cell, wherein the separator is suitable for being in contact with a power generation section including a membrane electrode assembly of the fuel cell in order to separate the power generation section from a power generation section of an adjacent fuel cell. State of the art

[0002] A polymer electrolyte fuel cell comprises a membrane electrode assembly (MEA) which includes an electrolyte membrane with ion permeability and anode-side and cathode-side catalyst layers (electrode layers), with the electrolyte membrane positioned between them. The MEA also has gas diffusion layers (GDLs) on opposite sides to supply fuel gas or oxidation gas to the MEA and to collect current or electricity generated by electrochemical reactions. Such a membrane electrode assembly, which has GDLs on opposite sides, is called a MEGA (membrane electrode and gas diffusion layer assembly), and the MEGA is positioned between a pair of separators. In this context, the MEGA is the power generation section of the fuel cell. If no gas diffusion layers are present, the MEA itself is the power generation section of the fuel cell.

[0003] For such a separator for a fuel cell, JP H08-185 870 A, for example, proposes the separator described below. Specifically, the separator comprises a cermet substrate, which consists of a heat-resistant, durable, or high-melting-point metal containing chromium and ceramic, and a protective metal oxide film covering a surface of the substrate on the cathode gas side to protect the surface from contact with the cathode gas. Furthermore, JP H08-185 870 A presents antimony-doped tin oxide as an example of such a metal oxide.

[0004] Furthermore, the published patent applications or patent specifications DE 601 18 164 T2, DE 10 2007 029 431 A1, WO 2003 / 092 139 A2 and DE 11 2010 004 954 T5 disclose conductive components or separators for fuel cells according to the prior art. SUMMARY

[0005] According to the separator for a fuel cell from JP H08 - 185 870 A, the diffusion of chromium to the cathode electrode is suppressed to such an extent that a reduction in the power generation output of the fuel cell can be prevented. However, even if such a protective film is provided, it would be difficult to suppress a reduction in the power generation output of the fuel cell unless an electrical contact resistance or transition resistance on a surface of the separator for the fuel cell, which is in contact with a power generation section including a membrane electrode assembly, can be suppressed.

[0006] The present invention has been made with regard to the foregoing, and exemplary embodiments relate to the provision of a separator for a fuel cell which can suppress a reduction in the power generation output of the fuel cell by reducing the contact resistance at least between the separator and a power generation section.

[0007] Accordingly, the separator for a fuel cell according to the present invention is a separator for a fuel cell, wherein the separator is adapted to be in contact with a power generation section, including a membrane electrode assembly of the fuel cell, in order to separate the power generation section from a power generation section of an adjacent fuel cell, wherein the separator comprises a metal substrate and a tin oxide film covering at least one surface of the metal substrate on the side of the power generation section. The tin oxide film is made of tin oxide containing 0.2 to 10 atomic percent antimony. Furthermore, the tin oxide film is made of tin oxide with a coating of SnO₂. 2-X (0.1 ≤ X ≤ 0.4) represented oxygen deficiency.

[0008] According to the present invention, the tin oxide of the tin oxide film is produced to contain the aforementioned amount of antimony, whereby the conductivity of the tin oxide film can be increased and thus the contact resistance can be reduced, at least between the separator for the fuel cell and the power generation section. BRIEF DESCRIPTION OF THE DRAWING Fig. Figure 1 is a cross-sectional view of the primary or main section of a fuel cell stack, which includes separators for fuel cells in accordance with an embodiment of the present invention; Fig. Figure 2 is an enlarged cross-sectional view of an area around a surface of the separator for a fuel cell in accordance with this embodiment; Fig.Figure 3 is a diagram or graph showing the half width at half maximum of a diffraction reflection on the (110) plane of tin oxide of a tin oxide film at approximately 2θ = 26.6°, as measured by X-ray diffractometry using CuKα rays. Fig. Figure 4 is a graph showing the relationship between the antimony content added to a tin oxide film of a test piece from each of Examples 1 to 5 and Comparison Example 2, and the contact resistance of the test piece; and Fig. Figure 5 is a graph showing the ratio of oxygen to tin in a region from the surface to the interior of a tin oxide film of a test piece from Example 7. DETAILED DESCRIPTION

[0009] The arrangement and configuration of the present invention, based on embodiments shown in the drawing, are described in detail below. Although the following embodiments represent an exemplary case in which the present invention is applied to fuel cells mounted on a fuel cell vehicle or a fuel cell system comprising such fuel cells, the applicable scope of the present invention is not limited thereto.

[0010] Fig. Figure 1 is a cross-sectional view of the primary section of a fuel cell stack (fuel cells) 10. As in Fig.As shown in Figure 1, the fuel cell stack 10 comprises a plurality of stacked unit cells 1. Each cell 1 is a polymer electrolyte fuel cell that generates an electromotive force when an electrochemical reaction occurs between an oxidizing gas (for example, air) and a fuel gas (for example, hydrogen). The cell 1 includes a MEGA 2 and separators (fuel cell separators) 3, which are suitable for contact with the MEGA 2 in order to separate the MEGA 2 from the MEGA 2 of the adjacent fuel cells. It should be noted that in this embodiment, the MEGA 2 is arranged between a pair of separators 3, 3.

[0011] The MEGA 2 is an integral part of a membrane electrode assembly (MEA) 4 and the gas diffusion layers 7, 7, which are arranged on opposite sides of the same. The membrane electrode assembly 4 comprises an electrolyte membrane 5 and a pair of electrodes 6 and 6, which are connected to insert or surround the electrolyte membrane 5. The electrolyte membrane 5 is a proton-conducting ion-exchange membrane made of a solid polymer material, and each electrode 6 is made of a porous carbon material with a catalyst, such as platinum, applied to 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 consists of a gas-permeable, conductive element, such as a porous carbon body, like carbon paper or carbon cloth, or a porous metal body, such as a metal fabric or foam metal.

[0012] In this embodiment, the MEGA 2 is the power generation section 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 section, and in such a case, the separators 3 are in contact with the membrane electrode assembly 4. Therefore, the power generation section of the fuel cell 10 comprises the membrane electrode assembly 4 and is in contact with the separators 3.

[0013] Each separator 3 is a plate-like element containing a metal with excellent conductivity and gas impermeability as a substrate, and one side of the separator 3 borders the gas diffusion layer 7 of the MEGA 2, and the other side of the same borders a side of an adjacent separator 3.

[0014] In this embodiment, each separator 3 is formed in a wave shape. In particular, the separator 3 has a shape such that the wave shapes form trapezoids with equal sides, the upper section of each wave is flat, and opposite ends of the upper section are angular with equal angles. The shape of each separator 3 is nearly identical from the front and rear views. The upper sections of the separator 3 are in surface contact with one of the gas diffusion layers 7 of the MEGA 2, and the upper sections of the other separator 3 are in surface contact with the other gas diffusion layers 7 of the MEGA 2.

[0015] A gas flow channel 21 defined between the gas diffusion layer 7 on one electrode side (i.e., 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 other electrode side (i.e., 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 located opposite the gas flow channel 21 with the cell 1 arranged between them, an electrochemical reaction occurs within the cell 1, generating an electromotive force.

[0016] Furthermore, a given cell 1 and an adjacent cell 1 are arranged such that an electrode 6, serving as an anode, and an electrode 6, serving as a cathode, are positioned opposite each other. Additionally, the upper sections on the rear surface of a separator 3, which is arranged along an electrode 6 to serve as an anode of a given cell 1, and the upper sections on the rear surface of a separator 3, which is arranged along an electrode 6 to serve as a cathode of another cell 1, are in surface contact with each other. Water, as a coolant for cooling the cells 1, circulates through the spaces 23 defined between the separators 3 and 3, which are in surface contact with each other between the two adjacent cells 1.

[0017] In this embodiment, as in Fig.As shown in Figure 2, each separator 3 comprises a metal substrate 31. Examples of the metal substrate 31 material include titanium and stainless steel. Furthermore, the opposing surfaces of the separator 3 (i.e., 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 film 32.

[0018] The thickness of the tin oxide film 32 is preferably in the range of 10 to 300 nm. If the thickness of the tin oxide film 32 is less than 10 nm, the beneficial effects of the tin oxide film 32 cannot be fully realized. Conversely, if the thickness of the tin oxide film 32 is greater than 300 nm, the residual stress of the tin oxide film 32 becomes high. Therefore, the tin oxide film 32 is likely to flake off the metal substrate 31.

[0019] Although the tin oxide film 32 is formed on every surface of the separator 3 in this embodiment, it is acceptable as long as the tin oxide film 32 is formed on at least one surface of the metal substrate 31 on the side of the gas diffusion layer 7, since a section in which the gas diffusion layer 7 and the separator 3 are in contact with each other has a high resistance.

[0020] The tin oxide film 32 contains antimony (Sb). Accordingly, the tin oxide film 32 becomes a semiconductor. Specifically, the tin oxide film 32 is made of tin oxide containing 0.2 to 10 atomic percent antimony. In such a tin oxide film 32, tetravalent tin sites in the crystal lattice of the tin oxide are substituted with pentavalent antimony. Therefore, the concentration of the carriers in the tin oxide film 32 is increased, and thus the conductivity of the tin oxide film is improved. Consequently, the contact resistance of the separator 3 with the tin oxide film 32 formed on it can be reduced, and thus the internal resistance of the fuel cell stack 10 can be reduced.

[0021] If the antimony content is less than 0.2 atomic percent, increasing the concentration of the carriers by substitution with antimony would be insufficient. Therefore, it is difficult to improve the conductivity of the tin oxide film, and consequently, the contact resistance of separator 3 cannot be sufficiently reduced.

[0022] Meanwhile, even if the antimony content is greater than 10 atomic percent, a further reduction of the contact resistance of the separator 3 by antimony cannot be expected. This is because even if the concentration of the carriers with an increased antimony content is increased, the increased antimony content would interfere with the movement of the carriers. Preferably, the tin oxide film 32 is prepared from tin oxide containing 0.5 to 10 atomic percent antimony.

[0023] When tin oxide containing 0.2 to 10 atomic percent antimony is measured here by X-ray diffractometry using CuKα radiation, a diffraction reflection is measured on the (110) plane of the tetragonal tin oxide at approximately a Bragg angle of 2θ = 26.6° (especially in the range of 26.6° ± 0.5°), as in Fig. 3 shown.

[0024] In this embodiment, the half-width at half the maximum W of a diffraction reflection on the (110) plane of tin oxide of the tin oxide film 32 at approximately 2θ = 26.6°, measured by X-ray diffractometry using CuKα rays, is preferably less than or equal to 1°. The half-width at half the maximum W is the width of a diffraction reflection at half the value (P / 2) of the maximum value P of the diffraction intensity of the diffraction reflection. In this embodiment, the half-width at half the maximum of a diffraction reflection satisfies a condition of less than or equal to 1°, so that the crystallinity of the tin oxide forming the tin oxide film 32 is improved, and thus the conductivity of the tin oxide film 32 can be increased. Consequently, the contact resistance of the separator 3 can be further reduced.

[0025] If the half width at half maximum of the tin oxide film 32 is greater than 1°, the crystallinity of the tin oxide forming the tin oxide film 32 will be low.

[0026] Therefore, the conductivity of the tin oxide film 32 would decrease, and thus the contact resistance of the separator 3 cannot be reduced sufficiently. As can be seen from the examples described below, if the half-width at half the maximum of a diffraction reflection on the (110) plane of tin oxide is less than or equal to 0.5°, the contact resistance of the separator 3 can be reduced further.

[0027] Furthermore, the tin oxide film 32 is made of tin oxide with a coating formed by SnO 2-XThe oxygen deficiency shown (0.1 ≤ X ≤ 0.4) is produced. Using oxygen-deficient tin oxide, the concentration of the carriers in the tin oxide film 32 is increased, thus improving the conductivity of the tin oxide film 32. Consequently, the contact resistance of the separator 3 is reduced, and thus the internal resistance of the fuel cell stack 10 can be reduced. It should be noted that "oxygen-deficient tin oxide," as referred to here, is tin oxide with a partial lack of oxygen, based on the tetragonal crystal structure of SnO2.

[0028] A tin oxide with oxygen deficiency, which satisfies X in the aforementioned range, can be obtained, for example, by adjusting the partial pressure of oxygen gas during the deposition or deposition of a film and by applying a voltage during the atomization process described below. If X < 0.1, the oxygen deficiency of the tin oxide becomes small. Therefore, the effect of reducing the contact resistance of the separator 3 cannot be fully realized. Meanwhile, it would be difficult to form the tin oxide film 32, which satisfies X > 0.4.

[0029] A method for forming the tin oxide film 32 on the metal substrate 31 of the separator 3 is not particularly limited. For example, the film can be deposited using physical vapor deposition (PVD), such as sputtering, vacuum deposition, ionized evaporation, or ion plating. In particular, the tin oxide film 32 can be deposited, for example, by sputtering a sintered body, obtained by mixing tin oxide particles and antimony oxide particles and sintering them, 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 film 32, the substrate temperature during the deposition of the film (film deposition temperature), an applied voltage, and similar parameters are adjusted such that the tin oxide film 32 can be obtained from tin oxide with half the width at half the maximum in the aforementioned range.

[0030] When the tin oxide film 32 is deposited using atomization, the atomization is carried out under an oxygen gas atmosphere, an inert gas atmosphere, or a vacuum atmosphere (low-pressure atmosphere). In particular, when the tin oxide film is deposited under an inert gas atmosphere or a vacuum atmosphere (low-pressure atmosphere), an oxygen-deficient tin oxide film can be obtained. [Examples]

[0031] The present invention is described below with reference to the examples. [Example 1]

[0032] A test piece, corresponding to a separator, was fabricated as described below. First, a pure titanium plate with a thickness of 0.1 mm was produced as the metal substrate of the separator. Next, the metal substrate was placed in a vacuum chamber, and argon gas was introduced into the chamber under vacuum conditions. Subsequently, a voltage was applied to generate argon ions. The argon ions were used to remove an oxide film from the surface of the metal substrate.

[0033] Next, a sintered body, obtained by mixing and sintering tin oxide and antimony oxide particles, was placed in the vacuum chamber as a target. Using this sintered body as a target, atomization was performed to form a tin oxide film on the surface of the metal substrate. Specifically, a metal substrate was first placed opposite the target, and then the vacuum chamber was evacuated to create a vacuum (low-pressure) atmosphere. Argon gas was then introduced into the vacuum chamber as the atomizing 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, resulting in the deposition of 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 film with a thickness of 100 nm was deposited on the surface of the metal substrate.

[0034] Next, the antimony (Sb) content in the tin oxide film was measured using an X-ray spectrometer (Quantera SXM manufactured by ULVAC-PHI, Inc.) based on the detection intensity at an antimony binding energy of 540 eV. Consequently, the antimony content in the tin oxide film was determined to be 0.2 atomic% (see Table 1). [Examples 2 to 5]

[0035] The test pieces were prepared as in Example 1. Examples 2 to 5 differ from Example 1 in that the tin oxide films of Examples 2 to 5 were deposited by varying the antimony oxide content in a sintered body as a target, such that the resulting tin oxide films contained 0.5 atomic percent, 3.0 atomic percent, 5.0 atomic percent, and 10.0 atomic percent antimony, respectively. The antimony content in each of the tin oxide films of Examples 2 to 5 was measured as in Example 1. Table 1 shows the results. [Comparison example 1]

[0036] A test piece was produced as in Example 1. Comparison Example 1 differs from Example 1 in that a tin oxide film was deposited through a sintered body without antimony oxide as a target, so that the resulting tin oxide film contained 0 atomic percent antimony (no antimony). The antimony content in the tin oxide film of Comparison Example 1 was measured as in Example 1. Table 1 shows the results. [Comparative example 2]

[0037] A test piece was produced as in Example 1. Comparison Example 2 differs from Example 1 in that a tin oxide film was deposited as a target by modifying the antimony oxide content in a sintered body, resulting in a tin oxide film containing 0.1 atomic percent antimony. The antimony content in the tin oxide film of Comparison Example 2 was measured as in Example 1. Table 1 shows the results. <kontaktwiderstandstest>

[0038] Carbon paper (TGP-H120, 0.5 mm thick, manufactured by TORAY INDUSTRIES, INC.), corresponding to a diffusion layer of the power generation section of the fuel cell, was applied to the surface of each tin oxide film of the test specimens in Examples 1 to 5 and Comparison Examples 1 and 2. A gold-plated copper plate was then placed on top of the carbon paper such that the carbon paper was positioned between the test specimen and the copper plate. It should be noted that, for the sole purpose of measuring the contact resistance between the tin oxide film and the carbon paper, another gold-plated copper plate was also placed in contact with the other surface (which does not have a deposited film) of the test specimen to prevent the contact resistance generated between such units.Next, pressure of a given load (0.98 MPa) was applied to the surface of the test piece using a gauge. With this pressure applied, a current from a power supply was passed through the test piece, adjusted with an ammeter to maintain a constant current flow. Subsequently, a voltage applied to the test piece was measured with a voltmeter to calculate the contact resistance between the tin oxide film of the test piece and the carbon paper. Table 1 and . Fig. Figure 4 shows the results. [Table 1] Antimony content (atomic %) Contact resistance (mΩ·cm 2 ) Comparison example 1 0 There was no current. Comparison example 2 0,1 53 Example 1 0,2 25 Example 2 0,5 16 Example 3 3 11 Example 4 5 10 Example 5 10 10 <Ergebnis 1>

[0039] As shown in Table 1, the contact resistance of the test piece was found to be high, consistent with Comparative Example 1, and no current could flow between the test piece and the carbon paper. Accordingly, it was found that a tin oxide film, which does not contain antimony, as in Comparative Example 1, exhibits high insulating properties (low conductivity).

[0040] Additionally, it was found that, as shown in Table 1 and Fig. Figure 4 shows that the contact resistance of Example 1 decreases sharply or significantly with an increased antimony content compared to those of Comparison Examples 1 and 2, and that the contact resistance of each of Examples 2 to 5 remains essentially constant with successive, increasing antimony content. Accordingly, it can be said that an antimony content of 0.2 atomic percent in a tin oxide film has a significant impact on reducing the contact resistance.

[0041] It is assumed that when tin oxide was produced to contain 0.2 to 10 atomic percent antimony, as in Examples 1 to 5, tetravalent or quadrivalent tin sites in the tin oxide crystal lattice were substituted with pentavalent or pentavalent antimony, thus improving the conductivity of the resulting tin oxide film. In particular, when tin oxide is produced to contain 0.5 to 10 atomic percent antimony, it is assumed that the conductivity of the resulting tin oxide film is further improved.

[0042] If the antimony content in the tin oxide is less than 0.2 atomic percent (especially 0.1 atomic percent), as in comparative example 2, increasing the concentration of the carriers by substitution with antimony would not be sufficient. Therefore, it is considered that the conductivity of the resulting tin oxide film is difficult to improve.

[0043] Meanwhile, if the antimony content is greater than 10 atomic percent, the carrier concentration is also increased, but it is assumed that the increased antimony 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 film will not improve, and thus no further reduction of the separator's contact resistance can be expected by means of antimony. [Examples 6 to 8]

[0044] The test pieces were prepared as in Example 1. Examples 6 and 8 differ from Example 1 in that the temperature of a metal substrate during deposition or film deposition (deposition temperature) was set to 350 °C and 550 °C, respectively. It should be noted that Example 7 is the same as Example 2. <Röntgen-Diffraktometriemessungstest>

[0045] For the tin oxide film of the test piece from each of Examples 6 to 8, a diffraction reflection angle on the (110) plane of the tin oxide was measured from an X-ray diffraction pattern or X-ray diffractogram using an X-ray analyzer employing CuKα radiation (with a wavelength of 0.154 nm) as the X-ray source in a copper tube. The diffraction reflection angle of the tin oxide from each of the test pieces was found around a Bragg angle of 2θ = 26.6°, and half the width at half the maximum of the diffraction reflection was measured. Table 2 shows the results. The contact resistance of the test pieces from each of Examples 6 to 7 was measured as in Example 1. Table 2 shows the results. <Rutherford-Rückstreu-Spektrometrie (RBS)>

[0046] Rutherford backscattering spectrometry was performed on the tin oxide film of the test piece from Example 7, so that the oxygen / tin ratio (atomic ratio) was measured along the direction of thickness from the surface of the tin oxide film. Fig. Figure 5 shows the results. [Table 2] Film deposition temperature (°C) Half the width at half the maximum (°) Contact resistance (mΩ·cm 2 ) Example 6 350 1,1 45 Example 7 450 0,5 16 Example 8 550 0,3 12 <Ergebnis 2>

[0047] As shown in Table 2, the half-width at half the maximum of a diffraction reflection on the (110) plane of tin oxide in the tin oxide film was found to be smaller than that of Example 6 for each of Examples 7 and 8. Therefore, the crystallinity of the tin oxide in the tin oxide film of each of Examples 7 and 8 is considered to be higher than that of Example 6. Furthermore, the contact resistance of the test specimen of Examples 7 and 8 was found to be lower than that of Example 6.

[0048] Accordingly, if the half-width at half the maximum of a diffraction reflection is less than or equal to 1°, or preferably less than or equal to 0.5°, as in the test pieces of each of Examples 7 and 8, the crystallinity of the tin oxide of the tin oxide film is high. Consequently, the conductivity of the tin oxide film is considered to be increased, and thus the contact resistance of the test piece (separator) is reduced.

[0049] Furthermore, as in Fig. Figure 5 shows that, with regard to the test piece from Example 7, the oxygen / tin ratio (atomic ratio) along the thickness direction from the surface of the tin oxide film was found to be 1.78. This is considered to be the reason why, when a film was deposited under a vacuum atmosphere, as in Example 7, some of the oxygen atoms migrating from the target to the metal substrate were desorbed.

[0050] As described above, the tin oxide film of the test piece from Example 7 is replaced by SnO 1,78 The tin oxide shown is produced under oxygen-deficient conditions, and the concentration of the carriers is increased by using oxygen-deficient tin oxide. Therefore, it is assumed that the conductivity of the tin oxide film is increased, and thus the contact resistance of the test piece (separator) is reduced.

[0051] Although the embodiments of the present invention have been described in detail above, specific configurations or arrangements are not limited thereto. DESCRIPTION OF REFERENCE MARKS 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 film< / kontaktwiderstandstest>

Claims

[1] Separator (3) for a fuel cell (1, 10), wherein the separator (3) is suitable to be in contact with a power generation section (2) including a membrane electrode assembly (4) of a fuel cell (1) in order to separate the power generation section (2) from a power generation section (2) of an adjacent fuel cell (1), wherein the separator (3) comprises: a metal substrate (31) made of metal; and a tin oxide film (32) covering at least one surface of the metal substrate (31) on one side of the power generation section (2), where: the tin oxide film (32) is made of tin oxide which contains 0.2 to 10 atomic% antimony and the tin oxide film (32) made of tin oxide with a structure formed by SnO 2-X (0.1 ≤ X ≤ 0.4) represents the oxygen deficiency shown. [2] Separator (3) for a fuel cell (1, 10) according to claim 1, wherein half the width at half the maximum of a diffraction reflection on a (110) plane of the tin oxide of the tin oxide film (32) at approximately 2θ = 26.6°, as determined by X-ray diffraction using CuKα rays, is less than or equal to 1°.

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