Separator for fuel cells

Abstract

The present invention provides a separator for fuel cells that can be produced at a low production cost and has high conductivity of a member that holds a single fuel cell and high adhesiveness to a seal member. An aspect of the present invention relates to a separator for fuel cells comprising a substrate and a membrane layer provided on the surface of the substrate, wherein the membrane layer comprises a power generator holding section that holds a power generator and a seal-adhered section provided on the outer circumference of the power generator holding section to which a seal member that seals the power generator holding section is adhered, the membrane layer comprises a metal layer provided on the surface of the power generator holding section and the surface of the seal-adhered section, and the metal layer comprises an oxide of a metal on the surface. Another aspect of the present invention relates to a method for producing the separator for fuel cells according to an aspect of the present invention comprising: a step of forming a membrane layer comprising forming a membrane layer comprising a power generator holding section and a seal-adhered section on the surface of a substrate; and a step of forming a metal layer comprising forming a metal layer on the surface of the membrane layer formed in the step of forming a membrane layer.

Description

SEPARATOR FOR FUEL CELLS

[0001] The present invention relates to a separator for fuel cells.

[0002] A fuel cell allows hydrogen to electrochemically react with oxygen to generate an electric power. In principle, a by-product from fuel cell power generation is limited to water. Therefore, a fuel cell has drawn attention as a clean power generation system that has substantially no impact on the global environment.

[0003] A fuel cell is configured with a membrane electrode assembly (hereinafter also referred to as "MEA") as a basic unit, in which an electrode catalyst layer is provided on both sides of an electrolyte membrane. During the operation of the fuel cell, fuel gas containing hydrogen is supplied to the electrode catalyst layer on the anode (fuel electrode) side, and an oxidation gas containing oxygen is supplied to the electrode catalyst layer on the cathode (air electrode) side, to thereby generate an electromotive force. An oxidation reaction proceeds at the anode, and a reduction reaction proceeds at the cathode. Accordingly, an electromotive force is supplied to an external circuit.

[0004] In a fuel cell, generally, a gas diffusion layer is provided outside of each electrode catalyst layer of MEA, and a separator is further provided outside the gas diffusion layer, so that a single fuel cell is constituted. In general, fuel cells are used as an assembly of a plurality of fuel cells (hereinafter also referred to as "fuel cell stack") required depending on the electric power of interest.

[0005] A separator not only blocks fuel gas and air supplied to each single fuel cell but also transmits an electric current to the outside. In general, accordingly, a separator comprises a power generator holding section that holds MEA, which is a power generator, and transmits an electric current to the outside and a seal-adhered section to which a seal member that blocks fuel gas and air is adhered.

[0006] For example, Patent Literature 1 discloses a separator for fuel cells comprising: a power generator holding section that holds a power generator; and a seal member-provided section that is provided on the outer circumference of the power generator holding section and is provided with a seal member that seals the power generator holding section, wherein the power generator holding section comprises a metal substrate, a titanium layer formed on the surface of the metal substrate, and a carbon layer formed on the titanium layer, the seal member-provided section comprises a metal substrate and a titanium layer formed on the surface of the metal substrate, and the titanium layer is exposed on the surface of the seal member-provided section.

[0007] Patent Literature 2 discloses a fuel cell comprising a separator, wherein the separator comprises an NC-treated surface, a peripheral section of the separator comprises carbon black in an amount larger than that inside the separator, and at least a part of the peripheral section is adhered to resin having a polar group.

[0008] JP 2023-037254 AJP 2019-192507 A

[0009] As described above, a separator for fuel cells not only blocks fuel gas and air supplied to each single fuel cell but also transmits an electric current to the outside. Accordingly, airtightness and adhesiveness of the seal-adhered section to which a seal member is adhered and conductivity and corrosion resistance of the power generator holding section that holds MEA are important performance of the separator for fuel cells. In the past, separators for fuel cells that have achieved improvement in airtightness and adhesiveness of the seal-adhered section to which a seal member is adhered and conductivity and corrosion resistance of the power generator holding section that holds MEA were proposed (for example, Patent Literatures 1 and 2).

[0010] A fuel cell often uses an expensive noble metal catalyst in an electrode catalyst layer. Accordingly, it is a critical object to lower the production cost of a fuel cell. In the case of the separator for fuel cells described in Patent Literature 1, for example, only the power generator holding section comprises a carbon layer on its outermost surface. This may necessitate a complicated surface treatment when producing the separator for fuel cells described in Patent Literature 1. When a carbon layer is formed over the entire surface of the separator for fuel cells in order to lower the production cost, in contrast, adhesiveness of the carbon layer is very low. In the case of the separator for fuel cells comprising a carbon layer formed over the entire surface, accordingly, adhesiveness of the seal member may be lowered. As described above, the separators for fuel cells according to conventional techniques were problematic in terms of lowering in the production cost and improvement in performance.

[0011] Under the above circumstance, the present invention is intended to provide a separator for fuel cells that can be produced at a low production cost and has high conductivity of a member that holds a single fuel cell and high adhesiveness to a seal member.

[0012] The present inventors have conducted concentrated studies in order to dissolve the problems described above. As a result, the present inventors discovered that a separator for fuel cells having high conductivity of a power generator holding section and high adhesiveness to a seal member could be produced at a low production cost by providing a membrane layer comprising a power generator holding section that holds a power generator and a seal-adhered section to which a seal member is adhered on a substrate, and on the surface of the power generator holding section and the seal-adhered section comprised in the membrane layer, providing a metal layer comprising an oxide of a metal on the surface. The present inventors completed the present invention based on the findings described above.

[0013] Specifically, the present invention encompasses the aspects and the embodiments described below. (Embodiment 1) A separator for fuel cells comprising a substrate and a membrane layer provided on the surface of the substrate, wherein the membrane layer comprises a power generator holding section that holds a power generator and a seal-adhered section provided on the outer circumference of the power generator holding section to which a seal member that seals the power generator holding section is adhered, the membrane layer comprises a metal layer provided on the surface of the power generator holding section and the surface of the seal-adhered section, and the metal layer comprises an oxide of a metal on the surface. (Embodiment 2) The separator for fuel cells according to Embodiment 1, wherein the metal layer comprises at least one metal selected from the group consisting of silver, gold, platinum, palladium, rhodium, iridium, ruthenium, and osmium or an oxide thereof. (Embodiment 3) The separator for fuel cells according to Embodiment 2, which comprises an oxide of silver on the surface of the metal layer and the metal layer is provided to form a plurality of islands on the surface of the membrane layer. (Embodiment 4) The separator for fuel cells according to Embodiment 2 or 3, which comprises an oxide of silver on the surface of the metal layer and a coverage rate of the metal layer is 3 area% or more, relative to the total surface area of the membrane layer. (Embodiment 5) The separator for fuel cells according to any of Embodiments 2 to 4, which comprises an oxide of silver on the surface of the metal layer and the metal layer has a thickness of 10 nm or less. (Embodiment 6) The separator for fuel cells according to Embodiment 2, which comprises an oxide of at least one metal selected from the group consisting of gold, platinum, palladium, rhodium, iridium, ruthenium, and osmium on the surface of the metal layer, and a coverage rate of the metal layer is 50 area% or more, relative to the total surface area of the membrane layer. (Embodiment 7) The separator for fuel cells according to Embodiment 6, wherein the metal layer has the thickness of 0.5 nm or more. (Embodiment 8) A method for producing the separator for fuel cells according to any of Embodiments 1 to 7 comprising: a step of forming a membrane layer comprising forming a membrane layer comprising a power generator holding section and a seal-adhered section on the surface of a substrate; and a step of forming a metal layer comprising forming a metal layer on the surface of the membrane layer formed in the step of forming a membrane layer. (Embodiment 9) The method according to Embodiment 8, which further comprises a step of oxidizing a metal comprising oxidizing a metal comprised in the metal layer after the metal layer is formed in the step of forming a metal layer.

[0014] The present invention can provide a separator for fuel cells that can be produced at a low production cost and has high conductivity of a member that holds a single fuel cell and high adhesiveness to a seal member. The present specification encompasses the contents described in the specifications and / or drawings of Japanese Patent Application No. 2025-19305 and Japanese Patent Application No. 2025-121935 on which the priority of the present application is based.

[0015] Figure 1 schematically shows a separator for fuel cells according to a conventional technique and an embodiment of the separator for fuel cells according to an aspect of the present invention. In the figure, A schematically shows a separator for fuel cells according to a conventional technique, and B schematically shows an embodiment of the separator for fuel cells according to an aspect of the present invention.Figure 2 schematically shows a preferable embodiment of the separator for fuel cells according to an aspect of the present invention.Figure 3 shows a cross-sectional view of another preferable embodiment of the separator for fuel cells according to an aspect of the present invention.Figure 4 shows the results of surface elemental analysis of the test sample obtained in accordance with the procedure of Example I by Auger electron spectroscopy. In the figure, the horizontal axis indicates the sputtering time (min) in Auger electron spectroscopy and the vertical axis indicates the atomic density (at%).Figure 5 shows the scanning electron microscopy (SEM) image of the surface of the separator test material obtained in accordance with the procedure of Example I observed by SEM.Figure 6 shows the relationship between the surface coverage rate of the metal layer and the adhesion strength of the test sample obtained in accordance with the procedure of Example I. In the figure, the horizontal axis indicates the surface coverage rate (area%) of the metal layer and the vertical axis indicates the adhesion strength (N / mm).Figure 7 shows the relationship between the thickness and the surface coverage rate of the metal layer of the test sample obtained in accordance with the procedure of Example I. In the figure, the horizontal axis indicates the thickness (nm) of the metal layer and the vertical axis indicates the surface coverage rate (area%) of the metal layer. Panel A shows a chart of the whole measurement range and Panel B shows an enlarged diagram of the region surrounded by a dotted line in Panel A.Figure 8 shows the relationship between the surface coverage rate or thickness of the metal layer and the contact resistance of the test sample obtained in accordance with the procedure of Example I. In the figure, Panel A shows a chart demonstrating the relationship between the surface coverage rate of the metal layer and the contact resistance of the test sample. The horizontal axis indicates the surface coverage rate (area%) of the metal layer and the vertical axis indicates the contact resistance (milliohm-square centimeters). Panel B shows a chart demonstrating the relationship between the thickness of the metal layer and the contact resistance of the test sample. The horizontal axis indicates the thickness (nm) of the metal layer and the vertical axis indicates the contact resistance (milliohm-square centimeters).Figure 9 shows the results of surface elemental analysis of the test sample obtained in accordance with the procedure of Example III by Auger electron spectroscopy. In the figure, the horizontal axis indicates the sputtering time (min) in Auger electron spectroscopy and the vertical axis indicates the atomic density (at%).Figure 10 shows the SEM image of the surface of the separator test material obtained in accordance with the procedure of Example III observed by SEM.Figure 11 shows the relationship between the thickness of the metal layer and the adhesion strength of the test sample obtained in accordance with the procedure of Example III. In the figure, the horizontal axis indicates the thickness (nm) of the metal layer and the vertical axis indicates the adhesion strength (N / mm).Figure 12 shows comparison of the adhesion strength of the substrate of the test sample (SUS304), the test sample without a metal layer (i.e., metal layer thickness: 0 nm) (C / Ti), and test material comprising a 0.5-nm-thick metal layer comprising platinum or an oxide of platinum (PtO2 / Pt / C / Ti). In the figure, the horizontal axis indicates the test materials and the vertical axis indicates the adhesion strength (N / mm).Figure 13 shows the relationship between the thickness of the metal layer and the contact resistance of the test sample obtained in accordance with the procedure of Example III. In the figure, the horizontal axis indicates the thickness (nm) of the metal layer and the vertical axis indicates the contact resistance (milliohm-square centimeters).Figure 14 shows the results of surface elemental analysis of the test sample obtained in accordance with the procedure of Example V by Auger electron spectroscopy. In the figure, the horizontal axis indicates the sputtering time (min) in Auger electron spectroscopy and the vertical axis indicates the atomic density (at%).Figure 15 shows the relationship between the thickness of the metal layer and the adhesion strength of the test sample obtained in accordance with the procedure of Example V. In the figure, the horizontal axis indicates the thickness (nm) of the metal layer and the vertical axis indicates the adhesion strength (N / mm).Figure 16 shows comparison of adhesion strength of the substrate of the test sample (SUS304), the test sample without a metal layer (i.e., metal layer thickness: 0 nm) (C / Ti), and a test material comprised of a 2.0-nm-thick metal layer comprising ruthenium or an oxide of ruthenium (RuO2 / Ru / C / Ti). In the figure, the horizontal axis indicates the test materials and the vertical axis indicates the adhesion strength (N / mm).Figure 17 shows the relationship between the thickness of the metal layer and the contact resistance of the test sample obtained in accordance with the procedure of Example V. In the figure, the horizontal axis indicates the thickness (nm) of the metal layer and the vertical axis indicates the contact resistance (milliohm-square centimeters).

[0016] Hereafter, preferable embodiments of the present invention are described in detail.

[0017] <1: Fuel cell separator> An aspect of the present invention relates to a separator for fuel cells. The separator for fuel cells according to the present aspect comprises a substrate and a membrane layer provided on the surface of the substrate. The membrane layer comprises a power generator holding section that holds a power generator and a seal-adhered section provided on the outer circumference of the power generator holding section to which a seal member that seals the power generator holding section is adhered. The membrane layer comprises a metal layer provided on the surface of the power generator holding section and the surface of the seal-adhered section.

[0018] Figure 1 schematically shows a separator for fuel cells according to a conventional technique and an embodiment of the separator for fuel cells according to the present aspect. In the figure, A schematically shows a separator for fuel cells according to a conventional technique, and B schematically shows an embodiment of the separator for fuel cells according to the present aspect. As shown in Figure 1 A, a separator for fuel cells according to a conventional technique comprises a carbon layer on the outermost surface of the power generator holding section exclusively, so as to achieve the conductivity of the power generator holding section and the adhesiveness of the seal-adhered section (Patent Literature 1). When producing a separator for fuel cells having such constitution, a complicated surface treatment may be necessary to form a carbon layer exclusively in the power generator holding section. In the case of the separator for fuel cells according to the present aspect, in contrast, a metal layer comprising an oxide of a metal on the surface is provided on the surfaces of both the power generator holding section and the seal-adhered section comprised in the membrane layer. The separator for fuel cells according to the present aspect having such constitution can be produced by uniformly forming the membrane layer and the metal layer over the entire separator. In the separator for fuel cells according to the present aspect having such constitution, in addition, the power generator holding section has high conductivity and the seal-adhered section has high adhesiveness to the seal member. Accordingly, the separator for fuel cells according to the present aspect having such constitution can achieve high conductivity of the power generator holding section and high adhesiveness to the seal member. More specifically, the adhesion strength between the membrane layer and the seal member can be enhanced while maintaining high conductivity of the power generator holding section.

[0019] Figure 2 schematically shows a preferable embodiment of the separator for fuel cells according to the present aspect. In the figure, the upper diagram shows a top view of the separator for fuel cells according to the present aspect and the lower diagram shows a cross-sectional diagram of the separator for fuel cells according to the present aspect. Hereafter, the separator for fuel cells according to the present aspect is described with reference to the figures.

[0020] As shown in Figure 2, the separator for fuel cells 100 according to the present aspect comprises the substrate 11 and the membrane layer 14 provided on the surface of the substrate 11. The membrane layer 14 comprises the power generator holding section 12 that holds a power generator and the seal-adhered section 13 provided on the outer circumference of the power generator holding section 12 to which a seal member that seals the power generator holding section 12 is adhered. Specifically, the membrane layer comprises the power generator holding section in a region where MEA, which is a power generator, is located. The membrane layer 14 comprises the metal layer 15 provided on the surface of the power generator holding section 12 and of the seal-adhered section 13. The membrane layer 14 may be comprised of a single-layer membrane or a multi-layer membrane. For example, a membrane layer comprises a metal layer provided on the surface on which MEA, which is a power generator, is held.

[0021] In the separator for fuel cells according to the present aspect, a material constituting a substrate is preferably stainless steel, a titanium alloy, or an aluminum alloy, more preferably stainless steel such as SUS (an alloy of iron, chromium, and nickel) or a titanium alloy, and further preferably SUS304. The materials indicated above are relatively inexpensive and have sufficient strength and processability. Thus, such materials are suitable for the substrate of the separator. With the use of the substrate comprised of the materials indicated above, accordingly, the production cost of the separator for fuel cells according to the present aspect can be lowered.

[0022] The thickness of a substrate is not particularly limited. In general, it is in a range of 0.05 mm to 0.2 mm, and it is specifically in a range of 0.08 mm to 0.12 mm. When the thickness of a substrate is within the range indicated above, the production cost of the separator for fuel cells according to the present aspect can be lowered.

[0023] A substrate may comprise a concave-convex flow channel to transport fuel gas and air that are necessary to operate a fuel cell and a fluid such as cooling water.

[0024] In the separator for fuel cells according to the present aspect, a material constituting the membrane layer is preferably titanium, carbon, nitrogen, hydrogen, oxygen, silver, molybdenum, rhodium, palladium, platinum, lead, rubidium, aluminum, nickel, and cobalt, or a combination of at least one material thereof, with titanium or carbon being more preferable. Titanium has high corrosion resistance. Carbon has high conductivity. Accordingly, the separator for fuel cells according to the present aspect having a membrane layer comprised of the materials indicated above can have high corrosion resistance and / or high conductivity.

[0025] In the separator for fuel cells according to the present aspect, the membrane layer may be comprised of a single-layer membrane or a multi-layer membrane. As shown in Figure 2, for example, the membrane layer 14 may be comprised of a bilayer membrane. When a material constituting the substrate is stainless steel, for example, the membrane layer is preferably comprised of a multi-layer membrane, and more preferably a bilayer membrane. In the present embodiment, it is preferable that a titanium layer be provided on the surface of the substrate and a carbon layer be provided on the surface of the titanium layer. When a material constituting the substrate is a titanium alloy, alternatively, the membrane layer is preferably comprised of a single-layer membrane. In the present embodiment, it is preferable that a carbon layer be provided on the surface of the substrate. The separator for fuel cells according to the present aspect having a membrane layer having the constitution indicated above can have high corrosion resistance and / or high conductivity.

[0026] In the separator for fuel cells according to the present aspect, the thickness of the membrane layer is preferably in a range of 10 nm to 300 nm, and more preferably in a range of 10 nm to 150 nm. When the membrane layer is comprised of a multi-layer membrane, the thickness of each membrane is preferably within the range indicated above. When the thickness of the membrane layer is lower than the lower limit indicated above, the separator for fuel cells may not be able to exert performance of interest, such as corrosion resistance and conductivity. When the thickness of the membrane layer is higher than the upper limit indicated above, the production cost may be increased. Accordingly, the separator for fuel cells according to the present aspect comprising the membrane layer with the thickness indicated above can acquire performance of interest while lowering the production cost thereof.

[0027] In each aspect of the present invention, a material constituting a membrane layer can be determined by performing elemental analysis of the membrane layer by, for example, X-ray photoelectron spectroscopy (XPS). Also, the thickness of a membrane layer can be determined by observing a cross section of the membrane layer by, for example, transmission electron microscopy (TEM) and measuring the thickness. The thickness of a membrane layer is generally expressed as an average of the measured values obtained by measuring the thickness of the cross section of the membrane layer at a plurality of sites in accordance with the procedure described above.

[0028] In the separator for fuel cells according to the present aspect, the metal layer comprises an oxide of a metal on the surface. Specifically, the metal layer comprises an oxide of a metal on the surface on which MEA, which is a power generator, is held. Metal materials constituting the metal layer are not particularly limited, and preferably noble metals. A metal layer preferably comprises at least one metal selected from the group consisting of silver, gold, platinum, palladium, rhodium, iridium, ruthenium, and osmium or an oxide thereof. In an embodiment, a metal layer preferably comprises silver or an oxide thereof. In another embodiment, a metal layer preferably comprises at least one metal selected from the group consisting of platinum, gold, palladium, rhodium, iridium, ruthenium, and osmium or an oxide thereof, and it more preferably comprises platinum or an oxide thereof or ruthenium or an oxide thereof. The metals and oxides thereof indicated above have low contact resistance. In addition, such metals and oxides thereof have high adhesiveness to a seal member. Among the noble metals indicated above, silver is relatively inexpensive. Accordingly, the separator for fuel cells according to the present aspect comprising the metal layer comprising the metal indicated above or an oxide thereof can achieve high conductivity of the power generator holding section and high adhesiveness to the seal member. By constituting the metal layer with the metal material indicated above, in addition, the production cost can be lowered.

[0029] In the separator for fuel cells according to the present aspect, the metal layer comprises an oxide of a metal on the surface. The oxide of the metal comprised in the metal layer may be distributed substantially uniformly over the entire metal layer or localized in a part of the metal layer. It is preferable that at least some of the oxide of the metal comprised in the metal layer be present on the surface of the metal layer. Oxygen atoms comprised in the oxide of the metal can contribute to the improvement of the adhesion strength between the metal layer and the seal member. Accordingly, the separator for fuel cells according to the present aspect comprising the metal layer having the features described above can have high adhesiveness to the seal member.

[0030] In each aspect of the present invention, a material constituting a metal layer can be determined by performing elemental analysis of the metal layer by, for example, XPS. Also, distribution of an oxide of a metal comprised in the metal layer can be determined by performing elemental analysis in the depth direction from the surface of the metal layer by, for example, Auger electron spectroscopy (AES).

[0031] In the separator for fuel cells according to the present aspect, the metal layer may be provided to cover the entire surface of the membrane layer, or it may be provided to cover a part of the surface of the membrane layer. In an embodiment in which a metal layer comprises silver or an oxide thereof, for example, a coverage rate of the metal layer is preferably 3 area% or more, more preferably 5 area% or more, and further preferably 10 area% or more, relative to the total surface area of the membrane layer. In this embodiment, a coverage rate of the metal layer is preferably 100 area% or less, more preferably 80 area% or less, and further preferably 50 area% or less, relative to the total surface area of the membrane layer. In an embodiment in which a metal layer comprises at least one metal selected from the group consisting of platinum, gold, palladium, rhodium, iridium, ruthenium, and osmium or an oxide thereof, alternatively, a coverage rate of the metal layer is preferably 50 area% or more, more preferably 55 area% or more, and further preferably 59 area% or more, relative to the total surface area of the membrane layer. In this embodiment, a coverage rate of the metal layer is preferably 100 area% or less, more preferably 80 area% or less, and further preferably 60 area% or less, relative to the total surface area of the membrane layer. When a coverage rate of the metal layer is lower than the lower limit indicated above, the separator for fuel cells may not be able to exert sufficient adhesiveness to the seal member. When a coverage rate of the metal layer is higher than the upper limit indicated above, the production cost of the separator for fuel cells according to the present aspect may be increased. Accordingly, the separator for fuel cells according to the present aspect comprising the metal layer provided as described above at the coverage rate as indicated above can have high adhesiveness to the seal member. By constituting the metal layer provided as described above at the coverage rate indicated above, the production cost can be lowered.

[0032] In the separator for fuel cells according to the present aspect, the thickness of the metal layer is generally 20 nm or less, preferably 10 nm or less, more preferably 8 nm or less, and further preferably 5 nm or less. Also, the thickness of the metal layer is preferably 0.2 nm or more, more preferably 0.5 nm or more, further preferably 1 nm or more, and particularly preferably 2 nm or more. In an embodiment in which a metal layer comprises silver or an oxide thereof, for example, the thickness of the metal layer is preferably in a range of 0.5 nm to 10 nm, and more preferably in a range of 0.5 nm to 5 nm. In an embodiment in which a metal layer comprises at least one metal selected from the group consisting of platinum, gold, palladium, rhodium, iridium, ruthenium, and osmium or an oxide thereof, alternatively, the thickness of a metal layer is preferably in a range of 0.2 nm to 10 nm, more preferably in a range of 0.2 nm to 5 nm, and further preferably in a range of 0.5 nm to 5 nm. When the thickness of the membrane layer is higher than the upper limit indicated above, the production cost of the separator for fuel cells according to the present aspect may be increased. When the thickness of the membrane layer is lower than the lower limit indicated above, the separator for fuel cells may not be able to exert sufficient adhesiveness to the seal member. Accordingly, the separator for fuel cells according to the present aspect comprising the metal layer with the thickness in the range indicated above can have high adhesiveness to the seal member. By constituting the membrane layer with the metal layer having the thickness within the range indicated above, the production cost can be lowered.

[0033] In the separator for fuel cells according to the present aspect, the metal layer can be in any form. As shown in Figure 2, for example, the metal layer 15 may form a membrane that covers the entire surface of the membrane layer 14. As shown in Figure 3, alternatively, the metal layer 25 may form a plurality of islands on the surface of the membrane layer 24. In an embodiment in which the metal layer comprises silver or an oxide thereof, for example, the metal layer is preferably provided to form a plurality of islands on the surface of the membrane layer. In this embodiment, a small quantity of a metal layer can have substantially equivalent adhesiveness to a seal member over the entire surface of the membrane layer. In an embodiment in which the metal layer comprises at least one metal selected from the group consisting of platinum, gold, palladium, rhodium, iridium, ruthenium, and osmium or an oxide thereof, alternatively, the metal layer is preferably provided to form a membrane that covers the entire surface of the membrane layer. Accordingly, the separator for fuel cells according to the present aspect comprising the metal layer as described above can have high adhesiveness to the seal member. By constituting the metal layer to have the features described above, the production cost can be lowered.

[0034] In each aspect of the present invention, the form of the metal layer can be determined by observing the surface of the metal layer by, for example, scanning electron microscopy (SEM). Also, the thickness of a metal layer can be determined by observing a cross section of the metal layer by, for example, TEM and measuring the thickness. The thickness of a metal layer is generally expressed as an average of the measured values obtained by measuring the thickness of the cross section of the metal layer at a plurality of sites in accordance with the procedure described above. The coverage rate of the metal layer can be determined in accordance with the procedure described below. The SEM image of the surface of the separator is binarized, and the area of the white region (the region of the metal layer) and that of the black region (the region of the membrane layer) in the SEM image are measured. The SEM images are obtained and the areas are measured at a plurality of sites. As the percentage of the area average in the region of the metal layer relative to the total surface area of the separator, the average of the coverage rate of the metal layer (area%) on the surface of the separator is determined. In the separator for fuel cells according to the present aspect, the first-order relationship can be established between the thickness of a metal layer comprising a particular metal or an oxide thereof and the coverage rate of the metal layer. Concerning the separator for fuel cells according to the present aspect having a metal layer comprising a particular metal or an oxide thereof, the thickness of the metal layer and the coverage rate of the metal layer of at least 1 test material are measured to obtain the first-order relational expression, so that the coverage rate of the metal layer or the thickness of the metal layer relative to the thickness of a particular metal layer or the coverage rate of the metal layer can be interpolated based on the relational expression.

[0035] In the separator for fuel cells according to the present aspect, the power generator holding section that holds a power generator has high conductivity. The conductivity of the separator for fuel cells according to the present aspect can be evaluated based on, for example, the contact resistance of the separator. The contact resistance of the separator for fuel cells according to the present aspect is generally 2 milliohm-square centimeters or lower, and, in particular, it is in a range of 1 to 2 milliohm-square centimeters. The range of the contact resistance indicated above is equivalent to the range of the contact resistance of a material, such as carbon or titanium, that is generally used for a power generator holding section that holds a power generator in the art. Accordingly, the separator for fuel cells according to the present aspect having the contact resistance in the range indicated above can achieve high conductivity of a power generator holding section that holds a power generator.

[0036] In each aspect of the present invention, the conductivity of the separator for fuel cells can be determined by measuring the contact resistance of the separator in accordance with, for example, the procedure described below. A test piece with given dimensions (e.g., 50 ~ 50 ~ 0.1 mm) is cut from the separator test material. The test piece and the gas diffusion layer (GDL) are superposed on top of another, and the contact resistance (milliohm-square centimeters) between the test piece and GDL is measured with the application of a given load (e.g., 1 MPa).

[0037] The separator for fuel cells according to the present aspect has high adhesiveness to the seal member. The adhesion strength of the separator for fuel cells according to the present aspect can be evaluated based on, for example, the adhesion strength of the separator. The adhesion strength of the separator for fuel cells according to the present aspect is generally 0.5 N / mm or higher, and, in particular, it is in a range of 0.5 to 1.5 N / mm. The separator for fuel cells according to the present aspect having the adhesion strength in the range indicated above can have high adhesiveness to the seal member.

[0038] In each aspect of the present invention, the adhesiveness of the separator for fuel cells to the seal member can be determined by measuring the adhesion strength (N / mm) of the separator in accordance with, for example, the procedure of the peel strength test in hot water described in Patent Literature 1 (JP 2023-037254 A).

[0039] The separator for fuel cells according to the present aspect has high conductivity of a power generator holding section that holds a power generator and high adhesiveness to the seal member. Accordingly, the separator for fuel cells according to the present aspect can be applied to the fuel cell for use in the power to move mobile objects, such as automobiles, marine vessels, aircrafts, or rail vehicles, or the domestic or commercial power source.

[0040] <2: Method for producing a separator for fuel cells> Another aspect of the present invention relates to a method for producing the separator for fuel cells according to an aspect of the present invention. The method according to the present aspect comprises a step of forming a membrane layer and a step of forming a metal layer. The method according to the present aspect may comprise a step of preparation, according to need.

[0041] [2-1:Step of preparation] This step comprises preparing a substrate. This step may comprise preparing additional materials to form a membrane layer and a metal layer, according to need.

[0042] A substrate prepared in this step may be comprised of a material having the features described above.

[0043] In this step, a material having a given features may be produced, or a commercial product may be purchased.

[0044] [2-2: Step of forming a membrane layer] This step comprises forming a membrane layer comprising a power generator holding section and a seal-adhered section on the surface of the substrate.

[0045] In general, this step can be performed by physical vapor deposition (PVD). PVD performed in this step is preferably vacuum deposition, sputtering, or ion plating, and more preferably sputtering or ion plating. A person skilled in the art can adequately determine the PVD conditions based on, for example, materials of a membrane layer and a constitution and dimensions of a membrane. In an embodiment in which a membrane layer is comprised of a multi-layer membrane, it is preferable that a plurality of membranes be successively formed by PVD. In an embodiment in which a membrane layer is comprised of a titanium layer and a carbon layer provided on the surface of the titanium layer, for example, a titanium layer can be first formed on the surface of the substrate by sputtering, and a carbon layer can then be formed on the surface of the titanium layer by ion plating.

[0046] [2-3: Step of forming a metal layer] This step comprises forming a metal layer on the surface of the membrane layer formed in the step of forming a membrane layer.

[0047] In general, this step can be performed by PVD. PVD performed in this step is preferably vacuum deposition, sputtering, or ion plating, and more preferably sputtering. A person skilled in the art can adequately determine the PVD conditions based on, for example, materials, a constitution, and dimensions of a metal layer. In an embodiment in which a metal layer comprises silver or an oxide thereof, for example, a metal layer may be formed by PVD, and preferably by sputtering, to have a thickness of 10 nm or more, and preferably in a range of 10 nm to 20 nm. In such a case, the metal layer is generally provided to form a membrane that covers the entire surface of the membrane layer. When a metal layer is formed by PVD, and preferably by sputtering, to have a thickness of 20 nm or less, preferably 10 nm or less, and more preferably in a range of 0.5 nm to 10 nm, in the present embodiment, a metal layer is generally provided to form a plurality of islands on the surface of the membrane layer. In an embodiment in which a metal layer comprises at least one metal selected from the group consisting of platinum, gold, palladium, rhodium, iridium, ruthenium, and osmium or an oxide thereof, alternatively, a metal layer may be formed by PVD, and preferably by sputtering, to have a thickness of 0.2 nm or more, preferably in a range of 0.2 nm to 10 nm, more preferably in a range of 0.2 nm to 5 nm, and further preferably in a range of 0.5 nm to 5 nm. In such a case, the metal layer is generally provided to form a membrane that covers the entire surface of the membrane layer. This step may be performed to achieve the thickness within the range indicated above, so that a metal layer in a desired form can be formed.

[0048] In this step, a metal layer comprising an oxide of a metal may be formed with the use of the oxide of the metal as a vapor-deposited material. In this embodiment, a metal layer comprising an oxide of a metal substantially uniformly distributed over the entire layer can be formed. Alternatively, a metal layer comprising an oxide of a metal may be formed by forming a metal layer and then performing a step of oxidizing a metal comprising oxidizing a metal comprised in the metal layer. The step of oxidizing a metal can be performed by forming a metal layer in accordance with the procedure described above and oxidizing the surface of the metal layer. In this embodiment, a metal layer comprising an oxide of a metal localized in a part thereof, and preferably a metal layer comprising some of an oxide of a metal on the surface thereof, can be formed.

[0049] As described above, the separator for fuel cells according to an aspect of the present invention can be produced by performing the method according to the present aspect.

[0050] As described in detail herein, the separator for fuel cells according to an aspect of the present invention has high conductivity of a power generator holding section that holds a power generator and high adhesiveness to the seal member. According to the method of production according to an aspect of the present invention, therefore, a separator for fuel cells that can be applied to the fuel cell for use in the power to move mobile objects, such as automobiles, marine vessels, aircrafts, or rail vehicles, or the domestic or commercial power source can be provided at a low production cost.

[0051] Hereafter, the present invention is described in greater detail with reference to the examples, although the technical scope of the present invention is not limited to these examples.

[0052] <I: Production of separator (1)> A 0.1-mm-thick plate-like substrate (stainless steel (SUS304)) was prepared. The substrate was introduced into a vacuum coating equipment. While heating the substrate using a heater in the equipment, the inside of the equipment was depressurized. The surface of the substrate was cleaned by argon sputtering. A 100-nm-thick titanium layer was formed on the surface of the cleaned substrate by sputtering. A 25-nm-thick carbon layer was formed on the surface of the titanium layer by ion plating (the step of forming a membrane layer). Subsequently, a silver-containing metal layer with a given thickness (0, 0.5, 1, 2, 4, 5, 8, or 10 nm) was formed by sputtering (the step of forming a metal layer). A substrate comprising a plurality of layers formed thereon was removed from the equipment, and the surface of the metal layer was oxidized to form a metal layer comprising an oxide of silver (the step of oxidizing a metal). The separator test material was obtained in accordance with the procedure described above.

[0053] <II: Evaluation of separator> [II-1: Surface elemental analysis] The outermost surface of the separator test material obtained in accordance with the procedure described in I above was subjected to surface elemental analysis by Auger electron spectroscopy (AES). Figure 4 shows the results of surface elemental analysis of the test sample performed by AES. In the figure, the horizontal axis indicates the sputtering time (min) in AES, and the vertical axis indicates the atomic density (at%). The sputtering time corresponds to the depth from the outermost surface of the test sample.

[0054] As shown in Figure 4, oxygen derived from silver oxide was detected on the outermost surface of the test sample. The results demonstrate that the metal layer on the outermost surface of the test material comprises an oxide of silver.

[0055] [II-2: Measurement of thickness] A plurality of sites on the cross sections of the titanium layer, the carbon layer, and the metal layer of the test sample were observed by transmission electron microscopy (TEM) to measure the thickness at each site. The averages of the measured values were determined as the thickness (nm) of the titanium layer, that of the carbon layer, and that of the metal layer.

[0056] [II-3: Calculation of surface coverage rate] The surface of the separator test material obtained in accordance with the procedure described in I above was observed by scanning electron microscopy (SEM). Figure 5 shows the SEM image of the surface of the test material.

[0057] As shown in Figure 5, the metal layer comprising silver or an oxide of silver was observed as a white region and the carbon layer was observed as a black region in the SEM image of the surface of the test material. The results demonstrate that the metal layer is provided to form a plurality of islands on the surface of the carbon layer.

[0058] The SEM image of the surface of the test material was binarized, and the area of the white region and that of the black region in the SEM image were measured. The SEM images of each test material were obtained and the areas were measured at a plurality of sites. As the percentage of the area average in the metal layer (the white region) comprising silver or an oxide of silver, relative to the total surface area of the test material, the average of the coverage rate of the metal layer comprising silver or an oxide of silver (area%) on the surface of the test material was calculated.

[0059] [II-4: Adhesion strength test] An L-shaped test piece was cut from the separator test material obtained in accordance with the procedure described in I above. In accordance with the procedure of the peel strength test in hot water described in Patent Literature 1 (JP 2023-037254 A), a T-shaped test piece was prepared, and the peel strength (adhesion strength) in hot water of the test piece was measured. In this test, the adhesion strength when the substrate (SUS304) was used as the test piece is 0.99 N / mm, and the targeted adhesion strength is 0.59 N / mm or higher.

[0060] [II-5: Measurement of contact resistance] A test piece with dimensions of 50 ~ 50 ~ 0.1 mm was cut from the separator test material obtained in accordance with the procedure described in I above. The test piece and the gas diffusion layer (GDL, Toray Industries, Inc.) were superposed on top of another, and the contact resistance between the test piece and GDL was measured with the application of a load of 1 MPa.

[0061] [II-6: Results of evaluation] Table 1 shows the results of performance evaluation of the test samples.

[0062]

[0063] Figure 6 shows the relationship between the surface coverage rate of the metal layer and the adhesion strength of the test sample. In the figure, the horizontal axis indicates the surface coverage rate (area%) of the metal layer and the vertical axis indicates the adhesion strength (N / mm).

[0064] As shown in Figure 6, the test material with the surface coverage rate of 3 area% or more exhibited the adhesion strength equivalent to or higher than the targeted adhesion strength, which is 0.59 N / mm.

[0065] Figure 7 shows the relationship between the thickness and the surface coverage rate of the metal layer of the test sample. In the figure, the horizontal axis indicates the thickness (nm) of the metal layer and the vertical axis indicates the surface coverage rate (area%) of the metal layer. Panel A shows a chart of the whole measurement range and Panel B shows an enlarged diagram of the region surrounded by a dotted line in Panel A.

[0066] As shown in Figure 7, the test sample having a metal layer with the thickness of 0.5 nm or more exhibited the surface coverage rate of 3 area% or more.

[0067] Figure 8 shows the relationship between the surface coverage rate or thickness of the metal layer and the contact resistance of the test sample. In the figure, Panel A shows a chart demonstrating the relationship between the surface coverage rate of the metal layer and the contact resistance of the test sample. The horizontal axis indicates the surface coverage rate (area%) of the metal layer and the vertical axis indicates the contact resistance (milliohm-square centimeters). Panel B shows a chart demonstrating the relationship between the thickness of the metal layer and the contact resistance of the test sample. The horizontal axis indicates the thickness (nm) of the metal layer and the vertical axis indicates the contact resistance (milliohm-square centimeters).

[0068] As shown in Figure 8, the contact resistance of the test material was substantially constant, regardless of the surface coverage rate or thickness of the metal layer. On the basis of the results, it is deduced that the contact resistance of the test material would not be influenced by the presence or absence of the metal layer or thickness thereof.

[0069] <III: Production of separator (2)> A 0.1-mm-thick plate-like substrate (stainless steel (SUS304)) was prepared. The substrate was introduced into a vacuum coating equipment. While heating the substrate using a heater in the equipment, the inside of the equipment was depressurized. The surface of the substrate was cleaned by argon sputtering. A 100-nm-thick titanium layer was formed on the surface of the cleaned substrate by sputtering. A 25-nm-thick carbon layer was formed on the surface of the titanium layer by ion plating (the step of forming a membrane layer). Subsequently, a platinum-containing metal layer with a given thickness (0, 0.5, 1, 2, 4, 5, 8, or 10 nm) was formed by sputtering (the step of forming a metal layer). A substrate comprising a plurality of layers formed thereon was removed from the equipment, and the surface of the metal layer was oxidized to form a metal layer comprising an oxide of platinum (the step of oxidizing a metal). The separator test material was obtained in accordance with the procedure described above.

[0070] <IV: Evaluation of separator> [IV-1: Surface elemental analysis] The outermost surface of the separator test material obtained in accordance with the procedure described in III above was subjected to surface elemental analysis by AES in the same manner as in II-1 above. Figure 9 shows the results of surface elemental analysis of the test sample performed by AES. In the figure, the horizontal axis indicates the sputtering time (min) in AES, and the vertical axis indicates the atomic density (at%). The sputtering time corresponds to the depth from the outermost surface of the test sample.

[0071] As shown in Figure 9, oxygen derived from an oxide of platinum was detected on the outermost surface of the test sample. The results demonstrate that the metal layer on the outermost surface of the test material comprises an oxide of platinum.

[0072] [IV-2: Measurement of thickness] The averages of the thickness (nm) of the titanium layer, the carbon layer, and the metal layer of the test sample were calculated in the same manner as in II-2 above.

[0073] [IV-3: Calculation of surface coverage rate] The surface of the separator test material obtained in accordance with the procedure described in III above was observed by SEM in the same manner as in II-3 above. In the same manner as in II-3 above, the average of the coverage rate (area%) of the metal layer comprising platinum or an oxide of platinum on the surface of the test material with a 0.5 nm-thick metal layer was calculated. Figure 10 shows the SEM image of the surface of the test material.

[0074] The SEM image of the surface of the test material shown in Figure 10 demonstrates that a metal layer is provided to form a membrane that covers the entire surface of the carbon layer.

[0075] [IV-4: Adhesion strength test] The peel strength (adhesion strength) in hot water of the L-shaped test piece cut from the separator test material obtained in accordance with the procedure described in III above was measured in the same manner as in II-4 above.

[0076] [IV-5: Measurement of contact resistance] The contact resistance between the test piece cut from the separator test material obtained in accordance with the procedure described in III above and GDL was measured in the same manner as in II-5 above.

[0077] [IV-6: Results of evaluation] Table 2 shows the results of performance evaluation of the test samples obtained in accordance with the procedure described in III above. In the table, the surface coverage rate of the metal layer of the test material with a 0.5 nm-thick metal layer is the measured value, and the surface coverage rates of the metal layers of other test materials are values deduced using the first-order relational expression of the thickness of the metal layer and the coverage rate of the metal layer determined based on the measured value of the surface coverage rate of the metal layer of the test material with a 0.5 nm-thick metal layer.

[0078]

[0079] Figure 11 shows the relationship between the thickness of the metal layer and the adhesion strength of the test sample. In the figure, the horizontal axis indicates the thickness (nm) of the metal layer and the vertical axis indicates the adhesion strength (N / mm). Figure 12 shows comparison of the adhesion strength of the substrate of the test sample (SUS304), the test sample without a metal layer (i.e., metal layer thickness: 0 nm) (C / Ti), and the test material comprising a 0.5-nm-thick metal layer comprising platinum or an oxide of platinum (PtO2 / Pt / C / Ti). In the figure, the horizontal axis indicates the test materials and the vertical axis indicates the adhesion strength (N / mm).

[0080] As shown in Figure 11, the test sample comprising the metal layer with the thickness of 0.5 nm or more exhibited the adhesion strength equivalent to or higher than the targeted adhesion strength, which is 0.59 N / mm. As shown in Figure 12, the test material comprising a 0.5-nm-thick metal layer (PtO2 / Pt / C / Ti) exhibited the adhesion strength significantly higher than that of the test sample (C / Ti) without a metal layer and equivalent to that of the substrate (SUS304).

[0081] Figure 13 shows the relationship between the thickness of the metal layer and the contact resistance of the test sample. In the figure, the horizontal axis indicates the thickness (nm) of the metal layer and the vertical axis indicates the contact resistance (milliohm-square centimeters).

[0082] As shown in Figure 13, the contact resistance of the test material was substantially constant, regardless of the thickness of the metal layer. On the basis of the results, it is deduced that the contact resistance of the test material would not be influenced by the thickness of the metal layer.

[0083] <V: Production of separator (3)> A 0.1-mm-thick plate-like substrate (stainless steel (SUS304)) was prepared. The substrate was introduced into a vacuum coating equipment. While heating the substrate using a heater in the equipment, the inside of the equipment was depressurized. The surface of the substrate was cleaned by argon sputtering. A 100-nm-thick titanium layer was formed on the surface of the cleaned substrate by sputtering. A 25-nm-thick carbon layer was formed on the surface of the titanium layer by ion plating (the step of forming a membrane layer). Subsequently, a ruthenium-containing metal layer with a given thickness (0, 0.5, 1, 2, 4, 5, 8, or 10 nm) was formed by sputtering (the step of forming a metal layer). A substrate comprising a plurality of layers formed thereon was removed from the equipment, and the surface of the metal layer was oxidized to form a metal layer comprising an oxide of ruthenium (the step of oxidizing a metal). The separator test material was obtained in accordance with the procedure described above.

[0084] <VI: Evaluation of separator> [VI-1: Surface elemental analysis] The outermost surface of the separator test material obtained in accordance with the procedure described in V above was subjected to surface elemental analysis by AES in the same manner as in II-1 above. Figure 14 shows the results of surface elemental analysis of the test sample performed by AES. In the figure, the horizontal axis indicates the sputtering time (min) in AES, and the vertical axis indicates the atomic density (at%). The sputtering time corresponds to the depth from the outermost surface of the test sample.

[0085] As shown in Figure 14, oxygen derived from an oxide of ruthenium was detected on the outermost surface of the test sample. The results demonstrate that the metal layer on the outermost surface of the test material comprises an oxide of ruthenium.

[0086] [VI-2: Measurement of thickness] The averages of the thickness (nm) of the titanium layer, the carbon layer, and the metal layer of the test sample were calculated in the same manner as in II-2 above.

[0087] [VI-3: Calculation of surface coverage rate] The surface of the separator test material obtained in accordance with the procedure described in V above was observed by SEM in the same manner as in II-3 above. In the same manner as in II-3 above, the average of the coverage rate (area%) of the metal layer comprising platinum or an oxide of platinum on the surface of the test material with a 0.5 nm-thick metal layer was calculated.

[0088] [VI-4: Adhesion strength test] The peel strength (adhesion strength) in hot water of the L-shaped test piece cut from the separator test material obtained in accordance with the procedure described in V above was measured in the same manner as in II-4 above.

[0089] [VI-5: Measurement of contact resistance] The contact resistance between the test piece cut from the separator test material obtained in accordance with the procedure described in V above and GDL was measured in the same manner as in II-5 above.

[0090] [VI-6:Results of evaluation] Table 3 shows the results of performance evaluation of the test samples obtained in accordance with the procedure described in V above. In the table, the surface coverage rate of the metal layer of the test material with a 0.5 nm-thick metal layer is the measured value, and the surface coverage rates of the metal layers of other test materials are values deduced using the first-order relational expression of the thickness of the metal layer and the coverage rate of the metal layer determined based on the measured value of the surface coverage rate of the metal layer of the test material with a 0.5 nm-thick metal layer.

[0091]

[0092] Figure 15 shows the relationship between the thickness of the metal layer and the adhesion strength of the test sample. In the figure, the horizontal axis indicates the thickness (nm) of the metal layer and the vertical axis indicates the adhesion strength (N / mm). Also, Figure 16 shows comparison of adhesion strength of the substrate of the test sample (SUS304), the test sample without a metal layer (i.e., metal layer thickness: 0 nm) (C / Ti), and a test material comprised of a 2.0-nm-thick metal layer comprising ruthenium or an oxide of ruthenium (RuO2 / Ru / C / Ti). In the figure, the horizontal axis indicates the test materials and the vertical axis indicates the adhesion strength (N / mm).

[0093] As shown in Figure 15, the test sample comprising the metal layer with the thickness of 0.5 nm or more exhibited the adhesion strength equivalent to or higher than the targeted adhesion strength, which is 0.59 N / mm. As shown in Figure 16, the test material comprising a 0.5-nm-thick metal layer (RuO2 / Ru / C / Ti) exhibited the adhesion strength significantly higher than that of the test sample (C / Ti) without a metal layer and equivalent to that of the substrate (SUS304).

[0094] Figure 17 shows the relationship between the thickness of the metal layer and the contact resistance of the test sample. In the figure, the horizontal axis indicates the thickness (nm) of the metal layer and the vertical axis indicates the contact resistance (milliohm-square centimeters).

[0095] As shown in Figure 17, the contact resistance of the test material was substantially constant, regardless of the thickness of the metal layer. On the basis of the results, it is deduced that the contact resistance of the test material would not be influenced by the thickness of the metal layer.

[0096] The present invention is not limited to the examples described above and includes various modifications. The examples described above have been described in detail to facilitate understanding of the present invention and are not necessarily limited to those having all the described configuration. It is also possible to add, delete, and / or replace part of the configuration of each example with another configuration. All publications, patents, and patent applications cited herein are incorporated herein by reference in their entirety.

[0097] 100, 200: Separator for fuel cells; 11, 21: Substrate; 12: Power generator holding section; 13: Seal-adhered section; 14, 24: Membrane layer; 15, 25: Metal layer

Claims

A separator for fuel cells comprising a substrate and a membrane layer provided on the surface of the substrate,whereinthe membrane layer comprises a power generator holding section that holds a power generator and a seal-adhered section provided on the outer circumference of the power generator holding section to which a seal member that seals the power generator holding section is adhered,the membrane layer comprises a metal layer provided on the surface of the power generator holding section and the surface of the seal-adhered section, andthe metal layer comprises an oxide of a metal on the surface.The separator for fuel cells according to claim 1, wherein the metal layer comprises at least one metal selected from the group consisting of silver, gold, platinum, palladium, rhodium, iridium, ruthenium, and osmium or an oxide thereof.The separator for fuel cells according to claim 2, which comprises an oxide of silver on the surface of the metal layer and the metal layer is provided to form a plurality of islands on the surface of the membrane layer.The separator for fuel cells according to claim 2, which comprises an oxide of silver on the surface of the metal layer and a coverage rate of the metal layer is 3 area% or more, relative to the total surface area of the membrane layer.The separator for fuel cells according to claim 2, which comprises an oxide of silver on the surface of the metal layer and the metal layer has a thickness of 10 nm or less.The separator for fuel cells according to claim 2, which comprises an oxide of at least one metal selected from the group consisting of gold, platinum, palladium, rhodium, iridium, ruthenium, and osmium on the surface of the metal layer and a coverage rate of the metal layer is 50 area% or more, relative to the total surface area of the membrane layer.The separator for fuel cells according to claim 6, wherein the metal layer has the thickness of 0.5 nm or more.A method for producing the separator for fuel cells according to claim 1 comprising:a step of forming a membrane layer comprising forming a membrane layer comprising a power generator holding section and a seal-adhered section on the surface of a substrate; anda step of forming a metal layer comprising forming a metal layer on the surface of the membrane layer formed in the step of forming a membrane layer.The method according to claim 8, which further comprises a step of oxidizing a metal comprising oxidizing a metal comprised in the metal layer after the metal layer is formed in the step of forming a metal layer.

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