Separator and method for manufacturing separator

Abstract

The invention relates to a separator and a method for manufacturing the separator. A stainless steel separator for a fuel cell comprises a coolant contact surface configured so as to be in contact with a coolant, and a gas contact surface configured so as to be in contact with a gas. The coolant contact surface has a conductive passivation film. The gas contact surface has a corrosion resistant metal intermediate layer on a substrate and a conductive layer on the corrosion resistant metal intermediate layer.

Description

Technical Field

[0001] The present disclosure relates to a separator and a method for manufacturing the separator, and in particular, to a separator for a fuel cell and a method for manufacturing the separator for a fuel cell. Background Art

[0002] Fuel cells have a stacked structure consisting of a predetermined number of unit cells that generate an electromotive force through the reaction of fuel gas (hydrogen) and oxidant gas (oxygen). Each unit cell comprises a membrane electrode assembly (MEA) with anode and cathode electrode layers (catalyst layer and gas diffusion layer) on both sides of an electrolyte membrane, and separators placed on each side of the MEA.

[0003] A separator for a fuel cell has the function of electrically connecting unit cells in series and also functions as a partition wall that separates fuel gas, oxidant gas, and coolant from each other.

[0004] Various studies have been conducted on such fuel cell separators.

[0005] For example, Japanese Patent Application Laid-Open No. 2010-86897 discloses a fuel cell separator characterized by comprising: a base layer formed using a separator substrate, a metal layer formed on the base layer and provided continuously with the surface of the base layer, and a metal nitride layer formed on the metal layer.

[0006] Japanese Patent Application Laid-Open No. 2010-140886 discloses a stainless steel material for a separator of a solid polymer fuel cell, characterized in that it includes: a stainless steel base material; an oxide film provided on the surface of the stainless steel base material; a conductive layer provided on the surface of the oxide film and containing a non-metallic conductive substance; and a conductive substance provided in a manner penetrating the oxide film and electrically connected to the stainless steel base material and the conductive layer, wherein the non-metallic conductive substance provided on the surface of the oxide film contains graphitic carbon, and when the peak intensities of the diffraction lines of the atomic planes obtained by wide-angle X-ray diffraction measurement of the graphitic carbon crystals are compared, the ratio of the peak intensity of the diffraction line of the (110) atomic plane to the peak intensity of the diffraction line of the (004) atomic plane is less than 0.1.

[0007] Japanese Patent Application Laid-Open No. 2022-45138 discloses a fuel cell separator comprising a metal substrate, a corrosion-resistant metal intermediate layer formed on the metal substrate, and a carbon layer formed on the corrosion-resistant metal intermediate layer, wherein the D band peak intensity (I D ) and G band peak intensity (I G ) intensity ratio (I D / I G ) is greater than 0.70 and less than 0.95. Summary of the Invention

[0008] Fuel cell separators (hereinafter referred to as "separators") also have the function of transferring generated current to adjacent cells. Therefore, the base material that constitutes the separators must have high electrical conductivity and sufficient corrosion resistance to maintain this high conductivity over long periods of time, even in the high-temperature, acidic atmosphere within the fuel cell. High electrical conductivity refers to low contact resistance. Contact resistance refers to the voltage drop between the electrode and the separator surface due to interfacial phenomena.

[0009] Therefore, pure titanium or titanium alloys having excellent electrical conductivity and corrosion resistance are often used as the base material constituting the separator, which is one of the main factors causing the cost increase in separator production.

[0010] Therefore, in order to reduce costs, attempts have been made to use an inexpensive base material such as stainless steel as a base material, and to form a layer imparting conductivity and corrosion resistance on the surface of the base material to produce a separator having conductivity and corrosion resistance.

[0011] The layer that imparts electrical conductivity and corrosion resistance to stainless steel is formed by, for example, physical vapor deposition (PVD).

[0012] However, this PVD process requires vacuum processing and multiple film-forming steps. Furthermore, in related art, this PVD process is performed on both the separator's surface that contacts the coolant (e.g., cooling water) (the coolant contact surface) and the surface that contacts the supplied gas (fuel gas and / or oxidant gas) (the gas contact surface), potentially leaving areas of the separator with excess performance.

[0013] Therefore, the present disclosure provides a separator for a fuel cell having sufficient corrosion resistance and low contact resistance and a method for producing the separator at low cost.

[0014] The inventors have studied various means for solving the above-mentioned problems and found that: for two substrates made of stainless steel with a conductive film (conductive passivation film) formed on the surface, after overlapping the coolant contact surfaces with the coolant facing inward, PVD treatment is performed on the gas contact surfaces exposed on the surface to form a corrosion-resistant metal intermediate layer as an intermediate layer on the substrate, and then, a conductive layer is formed as an upper layer on the corrosion-resistant metal intermediate layer. This allows two fuel cell separators with sufficient corrosion resistance and low contact resistance (i.e., high conductivity) for each contact surface to be manufactured simultaneously, thus completing the present disclosure.

[0015] A first embodiment of the present disclosure discloses a stainless steel fuel cell separator comprising: a coolant contact surface configured to contact a coolant; and a gas contact surface configured to contact a gas. The coolant contact surface comprises a conductive passivation film. The gas contact surface comprises a corrosion-resistant metal intermediate layer on a substrate and a conductive layer on the corrosion-resistant metal intermediate layer.

[0016] In the separator according to the first aspect of the present disclosure, the Cr / Fe ratio, which correlates with the atomic % in the conductive passivation film as determined by surface X-ray photoelectron spectroscopy, may be 2 or greater. The F concentration in the conductive passivation film as determined by surface X-ray photoelectron spectroscopy may be 0.1 atomic % or greater. The Li concentration in the conductive passivation film as determined by glow discharge optical emission spectroscopy may be 0.05 atomic % or greater.

[0017] The second embodiment of the present disclosure relates to a method for manufacturing a fuel cell separator, comprising: (i) imparting a conductive passivation film to a stainless steel substrate to prepare a conductive substrate; (ii) superimposing two or more conductive substrates obtained by the preparation so that the gas contact surface of each of the two or more conductive substrates is entirely exposed; and (iii) performing a physical vapor deposition treatment on the gas contact surfaces of the two or more conductive substrates superimposed by the superposition to form a corrosion-resistant metal intermediate layer on the substrate and a conductive layer on the corrosion-resistant metal intermediate layer. The entire gas contact surface is in contact with gas. The gas contact surfaces of the two or more conductive substrates are exposed.

[0018] In the method for producing a fuel cell separator according to the second aspect of the present disclosure, the preparation may include: (A) injecting fluorine into the passivation film; (B) injecting lithium into the passivation film; and (C) dissolving iron in the passivation film.

[0019] According to the present disclosure, a fuel cell separator having sufficient corrosion resistance and low contact resistance and a method for producing the separator at low cost are provided. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Features, advantages, and technical and industrial significance of exemplary embodiments of the present invention will be described below with reference to the accompanying drawings, wherein like reference numerals represent like elements, and wherein:

[0021] Figure 1 Schematic cross-sectional views comparing a battery cell including one embodiment of the fuel cell separator disclosed herein and a battery cell including a fuel cell separator of the related art.

[0022] Figure 2A This is a schematic diagram of one embodiment of a method for producing a fuel cell separator disclosed herein.

[0023] Figure 2B Schematic diagram of a method for manufacturing a separator for a fuel cell in the related art.

[0024] Figure 3A The figure specifically shows the surface treatment process in the manufacturing method of the related art.

[0025] Figure 3B This is a schematic diagram illustrating one embodiment of the method for producing a fuel cell separator disclosed herein in more detail.

[0026] Figure 3C A diagram comparing the method disclosed in the present invention with the method of the related art.

[0027] Figure 4 Graph showing the contact resistance results of Comparative Example 1, Reference Example 1, and Example 1.

[0028] Figure 5 This is a graph showing the results of XPS analysis of the coolant contact surface of Example 1.

[0029] Figure 6A This is a graph showing the results of TOF-SIMS depth analysis of the coolant contact surface in Example 1.

[0030] Figure 6B This is a graph showing the results of TOF-SIMS depth analysis of the coolant contact surface in Example 1.

[0031] Figure 6C This is a graph showing the results of TOF-SIMS depth analysis of the coolant contact surface in Example 1.

[0032] Figure 6D This is a graph showing the results of TOF-SIMS depth analysis of the coolant contact surface in Example 1.

[0033] Figure 7 Graph showing the results of GD-OES depth analysis of the coolant contact surfaces of Example 1 and Comparative Example 1.

[0034] Figure 8 Graph showing the results of TEM-EDX elemental mapping analysis of the coolant contact surface of Example 1. DETAILED DESCRIPTION

[0035] Preferred embodiments of the present disclosure are described in detail below.

[0036] In this specification, the features of the present disclosure are described with reference to the accompanying drawings as appropriate. In the accompanying drawings, the sizes and shapes of the various parts are exaggerated for clarity, and the actual sizes and shapes are not accurately depicted. Therefore, the technical scope of the present disclosure is not limited to the sizes and shapes of the various parts shown in these drawings. Furthermore, the partition of the present disclosure and the method for manufacturing the same are not limited to the following embodiments, and can be implemented in various ways that implement changes, improvements, etc. that can be made by those skilled in the art without departing from the scope of the main purpose of the present disclosure.

[0037] The present disclosure relates to a separator for a fuel cell made of stainless steel having a coolant contact surface for contacting a coolant and a gas contact surface for contacting a gas, wherein the coolant contact surface and the gas contact surface have specific films or layers.

[0038] In the present disclosure, the base material of the separator is not limited as long as it is stainless steel. Examples of stainless steel include austenitic, ferritic, martensitic, austenitic-ferritic (two-phase), and precipitation-hardened stainless steels. Specific examples include SUS301, SUS304, SUS304L, SUS316, SUS316L, SUS430, SUS430J1L, SUS434, SUS444, SUS447, and SUS631. Surface finishing processes include bright annealing (BA), pickling (2D), pickling followed by light rolling (2B), and temper rolling.

[0039] By selecting stainless steel as the base material of the separator, the raw material cost can be suppressed.

[0040] The thickness of the substrate is not limited, but is generally 0.05 mm to 0.2 mm, and in one embodiment, 0.08 mm to 0.12 mm.

[0041] When the thickness of the substrate is within the above range, the raw material cost can be suppressed.

[0042] The coolant-contacting surface of the separator disclosed herein, which is in contact with the coolant, has a conductive passivation film. The term "coolant-contacting surface" refers to the surface of the separator that contacts the coolant. In the case of a substrate, this refers to the surface that contacts the coolant when the separator is finished.

[0043] The conductive passive film is a film obtained by injecting fluorine and lithium into a passive film generally formed on the surface of stainless steel as a base material and increasing the Cr ratio to impart conductivity and corrosion resistance to the passive film.

[0044] The Cr / Fe ratio, which is related to the atomic % in the conductive passivation film, obtained by surface X-ray photoelectron spectroscopy (XPS) analysis, is generally greater than 2, and in one embodiment, greater than 2.5. As described above, increasing the Cr ratio and reducing the Fe ratio on the surface of the conductive passivation film improves film properties, so there is no upper limit to the Cr / Fe ratio.

[0045] The F concentration in the conductive passivation film obtained by surface X-ray photoelectron spectroscopy (XPS) analysis is generally 0.1 atomic % or more, and in one embodiment is 1.0 atomic % or more. There is no limit to the upper limit of the F concentration. The F concentration is generally 20 atomic % or less. Furthermore, the concentrations of various elements in the conductive passivation film obtained by XPS (Cr / Fe ratio (atomic %), F concentration, etc.) can be measured using the following conditions: X-ray photoelectron spectrometer: PHI5000 VersaProbeII (manufactured by ULVAC-PHI), X-ray source: Al-Kα (1486.6 eV), X-ray source condition: 15 kV (25 W), displacement correction: make the bond energy of CC and CH of C1s 284.8 eV, beam diameter: 100 μm Φ, measurement range: about 200 μm × 1000 μm measurement.

[0046] The Li concentration in the conductive passivation film obtained by glow discharge optical emission spectroscopy (GD-OES) analysis is generally 0.05 atomic % or more, and in one embodiment is 0.1 atomic % or more. There is no limit to the upper limit of the Li concentration. The Li concentration is generally 5 atomic % or less. Furthermore, the Li concentration in the conductive passivation film using GD-OES can be measured using the following conditions: glow discharge optical emission spectrometer: GD-Profiler2 (manufactured by Horiba, Ltd.), discharge gas: Ar gas, gas pressure: 600 Pa, electrode: 4 mm electrode measurement.

[0047] By injecting Li and F, which serve as electron carriers, into the passivation film, the electrical conductivity of the passivation film is improved, significantly improving the contact resistance of the resulting passivation film. Furthermore, by modifying the passivation film to a composition primarily composed of Cr oxide and Cr hydroxide, corrosion resistance is improved. Even after prolonged exposure to the atmosphere, the film remains stable, preventing or even suppressing the degradation of surface contact resistance over time.

[0048] The thickness of the conductive passivation film is not limited. The thickness of the conductive passivation film is expressed as an average thickness, which is usually 1 nm to 10 nm, and in one embodiment, 2 nm to 6 nm. The average thickness of the conductive passivation film can be measured by, for example, cross-sectional TEM observation.

[0049] When the thickness of the conductive passivation film is within the above range, sufficient conductivity and corrosion resistance as a coolant contact surface can be ensured.

[0050] The gas contact surface of the separator disclosed herein, which contacts gas (fuel gas and / or oxidant gas), comprises a corrosion-resistant metal intermediate layer on a substrate and a conductive layer on the corrosion-resistant metal intermediate layer. The term "gas contact surface" refers to the surface of the separator that contacts gas. In the case of a substrate, this refers to the surface that contacts gas when the separator is formed as a finished product.

[0051] The corrosion-resistant metal intermediate layer is a layer for imparting corrosion resistance to the separator and is not limited thereto. Examples of the corrosion-resistant metal intermediate layer include a titanium layer.

[0052] Since the separator of the present disclosure has the corrosion-resistant metal intermediate layer, the corrosion resistance of the separator can be ensured.

[0053] The conductive layer is a layer for imparting conductivity to the separator and is not limited thereto. Examples of the conductive layer include a carbon layer.

[0054] Since the separator of the present disclosure has a conductive layer, low contact resistance of the separator can be ensured.

[0055] exist Figure 1 Schematic cross-sectional views comparing one embodiment of a fuel cell separator disclosed herein with a fuel cell separator of related art are shown in FIG. Figure 1 In the text, "FCC" is the abbreviation of Fuel Cellstuck Coolant, which means a coolant for fuel cells, "AN separator" means a separator for anodes, "CA separator" means a separator for cathodes, and "MEGA sheet assembly" means a membrane electrode gas diffusion layer assembly sheet assembly. In the AN separator and the CA separator, the raw materials constituting the separator including the surface treatment layer are the same. On the other hand, in order to exhibit the characteristics as a fuel cell, the AN separator and the CA separator have different flow path shapes suitable for each. Since the flow path shape is different from the essence of the present disclosure (does not affect the essence of the present disclosure), in the inclusion of Figure 1 In the accompanying drawings, for simplicity, the AN separator and the CA separator are described as having the same structure.

[0056] according to Figure 1 In the fuel cell separator disclosed herein, a conductive passivation film is formed on the coolant contact surface, which contacts the coolant, and a surface treatment layer is formed on the gas contact surface, which contacts the gas. In related-art fuel cell separators, surface treatment layers are formed on both the coolant contact surface and the gas contact surface. Surface treatment layers typically include a corrosion-resistant metal intermediate layer and a conductive layer. Therefore, related-art fuel cell separators with surface treatment layers on both surfaces are expensive and have excessive performance for the coolant contact surface.

[0057] The present disclosure also relates to a method of manufacturing the separator for a fuel cell of the present disclosure.

[0058] The method for manufacturing a fuel cell separator disclosed herein comprises: (i) a step of forming a conductive passivation film on a conductive substrate; (ii) a step of laminating two or more conductive substrates; and (iii) a surface treatment step of forming a corrosion-resistant metal intermediate layer and a conductive layer on the exposed gas contact surfaces of the two or more conductive substrates. The conductive substrate is stainless steel having a conductive passivation film.

[0059] The step (i) includes: (A) a step of implanting fluorine into the passivation film; (B) a step of implanting lithium into the passivation film; and (C) a step of dissolving iron in the passivation film.

[0060] In the step (i), the substrate used is as described above.

[0061] The thickness of the substrate is not limited, but is generally 0.05 mm to 0.2 mm, and in one embodiment, 0.08 mm to 0.12 mm.

[0062] When the thickness of the substrate is within the above range, the raw material cost can be suppressed.

[0063] As the substrate, a substrate previously pressed into the shape of the final separator can be used.

[0064] By using a pre-pressed substrate as the substrate, a separator can be obtained without further pressing after the titanium layer and the conductive metal oxide layer are formed.

[0065] In step (A), as a method of injecting fluorine into the passivation film, there are methods of immersing the stainless steel in an aqueous solution containing fluoride ions (fluoride ions) (chemical treatment) or electrolyzing the stainless steel (electrochemical treatment).

[0066] The fluoride ion source used in fluorine implantation is not limited to any compound as long as it is hydrofluoric acid or a fluorine compound that dissolves in water to generate fluoride ions. Examples include alkali metal fluorides (e.g., sodium fluoride, potassium fluoride, etc.), ammonium fluoride, antimony trifluoride, copper fluoride, sodium dihydrogen fluoride, potassium dihydrogen fluoride, etc. In one embodiment, the fluoride ion source is an alkali metal fluoride, such as sodium fluoride or potassium fluoride.

[0067] In order to electrochemically inject fluoride, the stainless steel is subjected to direct current or pulse electrolysis (polarity is anodic and cathodic) in an aqueous solution of hydrogen fluoride or in an acidic aqueous solution to which nitric acid, sulfuric acid, phosphoric acid, etc. is added to the fluoride ion source. The pH of the treatment solution is generally 0 to 3, and in one embodiment, 0 to 2. The fluoride concentration can generally be set to 0.001 kmol / m 3 The aqueous solution does not need to be heated, for example, it can be used at 10°C to 30°C, and in one embodiment at room temperature (for example, 20°C). The direct current or pulse electrolysis conditions (both anode and cathode) are 0.001A / dm 2 ~50A / dm 2 , in one embodiment 0.1 A / dm 2 ~10A / dm 2 The electrolysis time is generally 5 to 600 seconds, and in one embodiment, 10 to 180 seconds.

[0068] In order to chemically inject fluorine, the fluoride ion source is immersed in hydrofluoric acid or a solution in which an oxidizing agent is added to the fluoride ion source. The fluoride concentration can usually be set to 0.001 kmol / m -3 ~Wide range of saturation concentration.

[0069] Examples of the oxidizing agent include nitric acid, potassium permanganate, and hydrogen peroxide. The concentration of the oxidizing agent is usually 0.1 kmol / m 3 ~10kmol / m 3 In one embodiment, it is 1 kmol / m 3 ~5kmol / m 3 The temperature of the aqueous solution is usually 20° C. to 80° C., and in one embodiment, 30° C. to 60° C. The immersion time is usually 10 seconds to 10 minutes, and in one embodiment, 1 minute to 10 minutes.

[0070] In step (B), as a method for implanting lithium into the passivation film, there are methods of immersing the stainless steel in an aqueous solution or non-aqueous solution containing lithium ions (chemical treatment) or electrolyzing the stainless steel (electrochemical treatment).

[0071] As the lithium ion source for lithium injection, there is no limitation as long as it is a lithium compound that dissolves in water or a non-aqueous solvent to generate lithium ions, and any compound can be used. For example, as oxygen-containing compounds, lithium hydroxide, lithium oxide, etc. can be listed, as halides, lithium chloride, lithium bromide, lithium iodide, etc. can be listed, and as oxygen-containing acid salts, lithium nitrate, lithium sulfate, etc. can be listed. As non-aqueous solvents, ethanol, methanol, dimethyl ether, diethyl ether, methyl ethyl ether, etc. can be listed. A mixture of water and a water-miscible non-aqueous solvent can be used.

[0072] The concentration of the lithium compound in the aqueous solution or non-aqueous solution containing the lithium ion source can generally be set to 0.1 kmol / m 3 The solution does not need to be heated, and is usually 10°C to 30°C, and in one embodiment is room temperature (e.g., 20°C). In the case of immersion treatment, the treatment time is usually 10 seconds to 10 minutes, and in one embodiment is about 30 seconds to 5 minutes. In the case of DC or pulse electrolysis (polarity is anode and cathode), the DC or pulse electrolysis density is (both anode and cathode) 0.001A / dm 2 ~10A / dm 2 , in one embodiment 0.1 A / dm 2 ~5A / dm 2 The electrolysis time is generally 10 seconds to 10 minutes, and in one embodiment, about 20 seconds to 5 minutes.

[0073] Regarding the method for effectively injecting fluoride ions and lithium ions into the passivation film, the above-mentioned steps (A) and (B) can be repeated. Regarding the order of step (A) and step (B), either step (A) or (B) can be performed first. In one embodiment, step (A) is performed first, followed by step (B).

[0074] In the process of (C), as a method for preferentially dissolving the iron in the passivation film, a method for immersing the iron in an aqueous solution containing fluoride ions can be cited. Furthermore, before this treatment, it is effective to heat-treat the iron in the atmosphere or in an inert gas atmosphere such as nitrogen or Ar gas. This is because, by heat-treating, the Fe concentrated in the outermost layer of the passivation film easily forms a complex with the fluoride ions by the subsequent immersion treatment in an aqueous solution containing fluoride ions, and is dissolved from the passivation film. By preferentially dissolving Fe from the passivation film, the film is modified to the composition of Cr oxide and Cr hydroxide main body.

[0075] To dissolve the iron in the passivation film, it is sufficient to immerse the stainless steel in an aqueous solution containing fluoride ions. As the aqueous solution, hydrofluoric acid can be cited, or an acid can be added to the fluoride ion source to prepare an acidic aqueous solution. The pH is generally 0 to 3, and in one embodiment, 0 to 2. The fluoride concentration can generally be set to 0.001 kmol / m 3 Acids used for pH adjustment include nitric acid, sulfuric acid, phosphoric acid, etc. The concentration is usually 0.01 kmol / m 3 ~10kmol / m 3 In one embodiment, it is 0.1 kmol / m 3 ~5kmol / m 3The temperature of the aqueous solution is usually 10° C. to 80° C., and in one embodiment, 20° C. to 60° C. The immersion time is usually 5 seconds to 20 minutes, and in one embodiment, 5 seconds to 10 minutes.

[0076] Furthermore, in order to effectively dissolve the iron in the passivation film, it is preferred to perform a heat treatment in air or in an inert gas atmosphere such as nitrogen or Ar before the immersion treatment in the aqueous solution containing fluoride ions in step (C). The heat treatment temperature is generally 100°C to 600°C, and in one embodiment, 140°C to 500°C. The treatment time is generally 1 second to 30 minutes, and in one embodiment, 10 seconds to 20 minutes.

[0077] This heat treatment forms an iron-concentrated layer on the outermost surface of the passivation film. Subsequent immersion in an aqueous solution containing fluoride ions facilitates the formation of complexes between Fe and fluoride ions, which are then eluted into the solution. This treatment is believed to transform the passivation film into a primarily Cr composition, improving corrosion resistance. Even after prolonged exposure to the atmosphere, the film remains stable, minimizing the degradation of surface contact resistance over time.

[0078] As described above, by injecting Li and F, which serve as electron carriers, into the passivation film, the electrical conductivity of the passivation film is improved, significantly improving the contact resistance of the resulting passivation film. Furthermore, by modifying the passivation film to a composition primarily composed of Cr oxides and hydroxides, the corrosion resistance is improved, and the film does not deteriorate even when exposed to the atmosphere for long periods of time, preventing or even suppressing the degradation of the surface contact resistance over time.

[0079] As a method for forming a conductive passivation film on a stainless steel surface, for example, reference can be made to Japanese Patent Application Laid-Open No. 2008-277146.

[0080] Furthermore, step (i) may be performed on both sides of the substrate or only on the coolant contact surface of the substrate.

[0081] In step (ii), two or more conductive substrates obtained in step (i) are stacked so that one of the two surfaces of each conductive substrate, ie, the gas contact surface, is exposed and the coolant contact surface is not exposed.

[0082] There are no limitations on the method for overlapping two or more conductive substrates, as long as the two or more conductive substrates can be overlapped in such a way that the entire gas contact surface (the entire gas contact surface) of the two or more conductive substrates can be surface-treated in the process (iii) described in detail below. Regarding the method for overlapping two or more conductive substrates, for example, the two conductive substrates can be overlapped with their respective coolant contact surfaces facing inward, fixed with a frame (clamp) as needed, and overlapped in such a way that their respective gas contact surfaces are fully exposed. Regarding the method for overlapping two or more conductive substrates, for example, a plate-like or film-like material can be clamped, and the two or more conductive substrates can be attached and overlapped on both sides of the material in such a way that the gas contact surfaces are exposed. Furthermore, since the coolant contact surface is not exposed, no surface treatment is performed in the process (iii). As needed, the entire surface or a portion of the coolant contact surface can be masked so as not to damage the conductive passivation film.

[0083] By overlapping two or more conductive substrates in step (ii), in step (iii), only the entire surface of the gas contact surface where corrosion resistance and conductivity are particularly required can be surface treated simultaneously on the two or more conductive substrates.

[0084] In the surface treatment step (iii), the gas contact surfaces of two or more conductive substrates exposed in the step (ii) are subjected to surface treatment, i.e., PVD treatment, to form a corrosion-resistant metal intermediate layer and a conductive layer on the corrosion-resistant metal intermediate layer on the substrate.

[0085] The method for forming the corrosion-resistant metal intermediate layer on the substrate and the conductive layer on the corrosion-resistant metal intermediate layer may be any method known in the art and is not limited thereto.

[0086] For example, when forming a corrosion-resistant metal intermediate layer on a substrate, an etching step is first performed to remove the passivation film on the substrate. Then, as an intermediate layer film formation step, a metal layer serving as the intermediate layer is formed using a PVD method. The corrosion-resistant metal intermediate layer is not limited as long as it imparts corrosion resistance to the separator. Examples of the corrosion-resistant metal intermediate layer include titanium layers.

[0087] The PVD method for forming the metal layer is not limited, and examples thereof include a vacuum deposition method, a sputtering method, and an ion plating method.

[0088] For example, the titanium layer can be formed by sputtering, which facilitates mass production management.

[0089] For the sputtering method, for example, the bias voltage of the substrate, the initial vacuum level in the device chamber, the cleaning conditions of the metal substrate surface (such as the conditions of argon bombardment treatment), the conditions of the plasma generation gas, the film formation time, the film formation temperature, etc., the conditions known in the technical field can be used (for example, refer to International Publication No. 2015 / 068776).

[0090] The thickness of the corrosion-resistant metal intermediate layer is not limited, but is generally 50 nm to 1000 nm, and in one embodiment, 50 nm to 300 nm, as expressed in terms of average thickness. The average thickness of the corrosion-resistant metal intermediate layer can be measured, for example, by cross-sectional TEM observation.

[0091] By setting the upper limit of the thickness of the corrosion-resistant metal intermediate layer as described above, the amount of corrosion-resistant metal used can be reduced while preventing excessive increases in film stress caused by forming the corrosion-resistant metal intermediate layer. This can suppress the occurrence of cracks in the corrosion-resistant metal intermediate layer and deformation of the substrate on which the corrosion-resistant metal intermediate layer is laminated. By setting the lower limit of the thickness of the corrosion-resistant metal intermediate layer as described above, sufficient corrosion resistance can be ensured.

[0092] Next, as a conductive layer forming step, a conductive layer is formed on the corrosion-resistant metal intermediate layer by using a PVD method.

[0093] The conductive layer is not limited as long as it has conductivity and thus reduces the contact resistance of the separator. Examples of the conductive layer include a carbon layer.

[0094] The PVD method for forming the conductive layer is not limited, and examples thereof include a vacuum deposition method, a sputtering method, and an ion plating method.

[0095] For example, the carbon layer can be formed by sputtering. The details of the sputtering conditions are the same as those for forming the corrosion-resistant metal intermediate layer.

[0096] For example, the carbon layer can be formed by using an ion plating method.

[0097] As an ion plating method, an arc ion plating (AIP) method is mentioned, for example.

[0098] For the arc ion plating method, conditions known in the technical field (for example, refer to Japanese Patent Application Laid-Open No. 2008-204876) can be used, such as bias voltage, initial vacuum degree in the device chamber, cleaning conditions of the metal substrate surface (for example, conditions of argon bombardment treatment), conditions of the plasma generation gas, film formation time, and film formation temperature.

[0099] The thickness of the conductive layer is not limited, but is generally 5 nm to 500 nm, and in one embodiment, 30 nm to 150 nm, as expressed in terms of average thickness. The average thickness of the conductive layer can be measured, for example, by cross-sectional TEM observation.

[0100] By setting the thickness of the conductive layer to be within the above range, low contact resistance of the separator, that is, high conductivity, can be ensured.

[0101] By adopting the manufacturing method disclosed in the present invention, it is possible to simultaneously manufacture two or more partitions having the required corrosion resistance and conductivity on the coolant contact surface, and the required corrosion resistance on the gas contact surface, sufficient corrosion resistance brought by the metal intermediate layer, and low contact resistance brought by the conductive layer, thereby significantly reducing manufacturing costs and improving manufacturing efficiency.

[0102] use Figure 2A and Figure 2B , a comparison is made between one embodiment of the method for manufacturing a fuel cell separator disclosed herein and a method for manufacturing a fuel cell separator of the related art. Figure 2A and Figure 2B The following can be known. Figure 2A In the process, stainless steel (SUS substrate) having a conductive passivation film on the surface is used. The conductive passivation film is used to fully ensure the corrosion resistance and conductivity of the coolant contact surface. That is, no further surface treatment is required for the coolant contact surface. Therefore, a surface treatment layer with better corrosion resistance and conductivity can be formed only on the gas contact surface. Based on the above, in the surface treatment process of the present invention, for two SUS substrates having a conductive passivation film, the gas contact surfaces of the two partitions can be surface treated at the same time by making the coolant contact surfaces overlap relative to each other so that the gas contact surfaces are exposed. On the other hand, in the related manufacturing method shown in Figure 2B In the process, surface treatment is performed on both sides of the SUS substrate, so only one separator can be manufactured by a single surface treatment.

[0103] exist Figures 3A to 3C One embodiment of the method for producing a fuel cell separator disclosed herein is described in more detail. Figure 3A This figure specifically illustrates the surface treatment steps in the manufacturing method of the related art. In the surface treatment steps, the passivation film on the surface of the SUS substrate is removed by (1) etching, the corrosion-resistant metal intermediate layer is formed by (2) intermediate layer film formation, and the conductive layer is formed by (3) conductive layer film formation. Figure 3B Specifically illustrating the characteristics of the present disclosure, the diagram schematically shows how two SUS substrates having a conductive passivation film are placed on a frame (jig) with their coolant contact surfaces facing each other and overlapped to expose their gas contact surfaces. Figure 3C is a diagram comparing the method of the present disclosure with the method of the related art. Figure 3A Surface treatment processes of related technologies such as Figure 3BIn this way, the manufacturing method is changed to one in which two or more SUS substrates are provided. That is, in the present disclosure, the manufacturing method of forming a film on both the coolant contact surface and the gas contact surface in the related art is changed to a manufacturing method in which a film is formed only on the gas contact surface (single surface). By forming a film on only one side, it is possible to carry twice as many partitions in the frame (trolley) during film formation, such as Figure 3C As shown, the film forming efficiency on the separator is increased by 2 times.

[0104] The fuel cell separator produced according to the present disclosure is a component of a unit cell in a fuel cell and is disposed on both surfaces of a membrane electrode assembly (electrolyte membrane and anode and cathode electrode layers disposed on both surfaces of the electrolyte membrane).

[0105] The fuel cell separator manufactured according to the present disclosure uses fuel cell components known in the art, such as a membrane electrode assembly and a sealing member, and is bonded together using, for example, an adhesive to manufacture the fuel cell.

[0106] A fuel cell manufactured using the fuel cell separator manufactured according to the present disclosure can be used in various electrochemical devices such as solid polymer fuel cells.

[0107] Example

[0108] Several embodiments related to the present disclosure are described below, but the present disclosure is not intended to be limited to the contents shown in these embodiments.

[0109] I. Manufacturing of separators

[0110] Comparative Example 1

[0111] As the separator of Comparative Example 1, a stainless steel plate with a thickness of 0.1 mm was press-formed to produce a stainless steel substrate having a flow path formed thereon. The material of the stainless steel was SUS304-BA.

[0112] Reference Example 1

[0113] The separator of Reference Example 1 was produced by the method described in Example 1 of Japanese Patent Application Laid-Open No. 2022-45138. Specifically, the method is as follows.

[0114] As a substrate, a stainless steel substrate (SUS304, 0.1 mm thick) having a flow path shape was prepared. Then, a corrosion-resistant metal intermediate layer and a carbon layer were formed on both sides of the stainless steel substrate using a PVD film-forming device (manufactured by Hauzer, FC1200). Specifically, first, after the stainless steel substrate was placed in a reaction vessel of the device, the reaction vessel was vacuumed and heated with an internal heater. Secondly, the pure Ti cathode target used for sputtering was etched (cleaned) with plasma-formed Ar gas. In addition, in order to remove the passivation present on the surface of the stainless steel substrate, the stainless steel substrate was etched with plasma-formed Ar gas. Secondly, using the above-mentioned pure Ti cathode target, unbalanced magnetron sputtering (UBMS) was used to form a titanium layer. The film-forming conditions of the titanium layer are set as described below.

[0115] Target film thickness: 250nm

[0116] Processing temperature: 150℃

[0117] Vacuum degree: 2E-03mbar

[0118] Input gas: Ar

[0119] Gas flow rate: 250sccm

[0120] Bias: PLS

[0121] Voltage: -75V

[0122] Frequency: 40kHz

[0123] Off time in frequency: 5μS

[0124] Ti cathode output: 8kW / A / V

[0125] UBM coil current: 2A

[0126] Revolution speed: 3rpm

[0127] Next, a carbon layer was formed by arc ion plating (AIP) using a high-purity ta-C raw material. The carbon layer formation conditions were set as follows.

[0128] Target film thickness: 50nm

[0129] Processing temperature: 180℃

[0130] Vacuum degree: 2E-03mbar

[0131] Input gas: Ar

[0132] Gas flow rate: 250sccm

[0133] Bias: PLS

[0134] Voltage value: -20V

[0135] Frequency: 40kHz

[0136] Off time in frequency: 5μS

[0137] C cathode output: 60kW / A / V

[0138] Revolution speed: 4rpm

[0139] During the etching and film formation, the stainless steel substrate was rotated appropriately to form a titanium layer and a carbon layer on both sides.

[0140] <Example 1>

[0141] The step of (i) providing a conductive passivation film on a substrate to prepare a conductive substrate will be described.

[0142] (A) Step of injecting fluorine into the passivation film

[0143] First, a stainless steel substrate (SUS304, 0.1 mm thick) with a flow path pattern formed on it was prepared as a substrate. The prepared substrate was immersed in acetone, ultrasonically cleaned, and then heated in air at 300°C for 5 minutes. Then, it was immersed in a 5% by mass HF aqueous solution at 30°C for 1 minute, rinsed with distilled water, and dried with cold air (25°C).

[0144] (B) Step of Implanting Lithium into the Passivation Film

[0145] Then, at 1 kmol / m 3 In LiOH aqueous solution, 1A / dm 2 , 1 minute of cathode electrolysis treatment, distilled water washing and cold air (25 ° C) drying were performed.

[0146] (C) Step of dissolving iron in the passivation film

[0147] Then, the sample was immersed in a 5% by mass HF aqueous solution at 30° C. for 10 seconds, and then washed with distilled water and dried with cold air (25° C.).

[0148] The step (ii) of overlapping two conductive substrates will be described.

[0149] Two conductive substrates with conductive passivation films on both sides obtained in step (i) are placed on a frame (clamp) in such a way that the gas contact surface of each conductive substrate that contacts the gas is exposed and the coolant contact surface that contacts the coolant faces inward.

[0150] The step (iii) of performing PVD treatment on the exposed gas contact surfaces of the two conductive substrates to form a corrosion-resistant metal intermediate layer and a conductive layer (carbon layer) will be described.

[0151] The two conductive substrates stacked in step (ii) were subjected to PVD treatment on their exposed gas contact surfaces, forming a corrosion-resistant metal intermediate layer on the substrates and a carbon layer on the corrosion-resistant metal intermediate layer. The PVD treatment conditions for forming the corrosion-resistant metal intermediate layer and the carbon layer on the gas contact surfaces of the conductive substrates were the same as those in Reference Example 1.

[0152] II. Evaluation of separators

[0153] Contact resistance measurement

[0154] The contact resistance between the comparative example 1 (a separator without PVD treatment and only pressed), the reference example 1 (a separator having a titanium layer and a carbon layer on both the coolant contact surface and the gas contact surface), and the example 1 (a separator having a conductive passivation film on the coolant contact surface and a titanium layer and a carbon layer on the gas contact surface) and the GDL (manufactured by Toray Industries, Ltd.) was measured. Note that the load pressure was set to 1.0 MPa. Then, each separator was immersed in an FCC solution (ethylene glycol: water = 50:50) and left at 85°C for 1000 hours (durability test). Next, for each sample after the durability test, the contact resistance between the sample and the GDL (manufactured by Toray Industries, Ltd.) was measured in the same manner as above.

[0155] TOF-SIMS in-depth analysis

[0156] The coolant contact surface of the separator of Example 1 was subjected to TOF-SIMS depth analysis.

[0157] XPS analysis

[0158] XPS analysis was performed on the coolant contact surface of the separator of Example 1. The measurement conditions of the XPS analysis were as described above.

[0159] GD-OES in-depth analysis

[0160] GD-OES depth analysis was performed on the coolant contact surface of the separators of Example 1 and Comparative Example 1. The measurement conditions of the GD-OES depth analysis were as described above.

[0161] TEM-EDX elemental mapping analysis

[0162] TEM-EDX element mapping analysis was performed on the coolant contact surface of the separator of Example 1.

[0163] III. Evaluation results of separators

[0164] Contact resistance measurement results

[0165] exist Figure 4 The contact resistance results of Comparative Example 1, Reference Example 1, and Example 1 are shown in FIG. Figure 4 It can be seen that Example 1 shows a very low resistance of 5 mΩ·cm, which is equivalent to that of Reference Example 1, before and after the durability test. 2 Contact resistance below 3mΩ·cm 2 The following contact resistance.

[0166] Results of XPS analysis, GD-OES, TOF-SIMS depth analysis, and TEM-EDX elemental mapping analysis

[0167] exist Figure 5 The results of XPS analysis of the coolant contact surface of Example 1 are shown in FIG. 6A to 6D The results of TOF-SIMS depth analysis of the coolant contact surface of Example 1 are shown in FIG. Figure 7 The results of GD-OES depth analysis of the coolant contact surface of Example 1 are shown in FIG. Figure 8 The results of TEM-EDX element mapping analysis of the coolant contact surface of Example 1 are shown in FIG. Figure 5 It can be seen that in the coolant contact surface of Example 1, there is a peak of bond energy derived from fluoride between 682eV and 688eV. 6A to 6D It can be seen that in the coolant contact surface of Example 1, Li, F, and Cr are detected in the short sputtering time, that is, near the surface of the coolant contact surface. Figure 7 It can be seen that Li was detected in a shallow range of 0 to 0.002 μm in the coolant contact surface of Example 1. In addition, Li was not detected in the coolant contact surface of Comparative Example 1. Figure 8 It can be seen that the Cr ratio of the oxide layer is high in the coolant contact surface of Example 1. Figures 5 to 8 It is found that in the separator of Example 1, a conductive passivation film in which F, Li, and Cr contributing to the conductivity of the coolant contact surface are formed on the coolant contact surface.

[0168] From the above, it can be seen that even if there is no film-forming related corrosion-resistant metal intermediate layer and conductive layer on the coolant contact surface in the partition, by making it a conductive passivation film with better productivity than this layer, the obtained partition can maintain a sufficiently low contact resistance after the durability test.

Claims

1. A fuel cell separator made of stainless steel, characterized in that: include: a coolant contact surface configured to interface with the coolant; and The gas contact surface is formed in a manner that it is in contact with the gas, The coolant contact surface has a conductive passivation film, and the gas contact surface has a corrosion-resistant metal intermediate layer on a substrate and a conductive layer on the corrosion-resistant metal intermediate layer.

2. The separator according to claim 1, characterized in that The Cr / Fe ratio in the conductive passivation film, which is related to atomic % by surface X-ray photoelectron spectroscopy XPS analysis, is 2 or more. The F concentration in the conductive passivation film analyzed by surface X-ray photoelectron spectroscopy XPS is 0.1 atomic % or more, and The Li concentration in the conductive passivation film analyzed by glow discharge optical emission spectroscopy (GD-OES) is 0.05 atomic % or more.

3. A method for manufacturing a separator for a fuel cell, characterized in that: include: (i) providing a conductive passivation film on a stainless steel substrate to prepare a conductive substrate; (ii) overlapping two or more conductive substrates obtained by the above preparation so that the gas contact surface of each of the two or more conductive substrates is entirely exposed and the entire gas contact surface is in contact with the gas; and (iii) Physical vapor deposition (PVD) treatment is performed on the gas contact surfaces of the two or more conductive substrates overlapped by the overlap to form a corrosion-resistant metal intermediate layer on the substrate and a conductive layer on the corrosion-resistant metal intermediate layer, and the gas contact surfaces of the two or more conductive substrates are exposed.

4. The method according to claim 3, characterized in that The preparation comprises: (A) injecting fluorine into the passivation film; (B) injecting lithium into the passivation film; and (C) dissolving iron in the passivation film.

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