Separator, and manufacturing method thereof

Abstract

To provide a fuel cell separator with sufficient corrosion resistance and low contact resistance, and a manufacturing method of the separator at a low cost.SOLUTION: A disclosed separator is a stainless steel fuel cell separator that has a coolant contact surface that comes into contact with coolant and a gas contact surface that comes into contact with gas. The coolant contact surface has a conductive passive film, and the gas contact surface has a corrosion-resistant metal intermediate layer on the substrate and a conductive layer on the corrosion-resistant metal intermediate layer. The manufacturing method is also provided.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a separator and a method for manufacturing the same, and more particularly to a separator for a fuel cell and a method for manufacturing the same. [Background technology]

[0002] A fuel cell has a stack structure in which a predetermined number of unit cells are stacked, each of which generates electromotive force through a reaction between a fuel gas (hydrogen) and an oxidant gas (oxygen). Each unit cell has a membrane electrode assembly (MEA) with anode and cathode electrode layers (catalyst layers and gas diffusion layers) on both sides of an electrolyte membrane, and separators arranged on both sides of the MEA.

[0003] The fuel cell separator functions to electrically connect the unit cells in series and also to act as a partition wall that isolates the fuel gas, oxidant gas, and coolant from each other.

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

[0005] For example, Patent Document 1 discloses a fuel cell separator characterized by having a base layer formed from a separator substrate, a metal layer formed on the base layer and continuous with the surface of the base layer, and a metal nitride layer formed on the metal layer.

[0006] Patent Document 2 discloses a stainless steel material for separators of polymer electrolyte fuel cells, comprising 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 comprising a non-metallic conductive material, and a conductive material provided so as to penetrate the oxide film and electrically connect to the stainless steel base material and the conductive layer, wherein the non-metallic conductive material provided on the surface of the oxide film comprises graphite carbon, and when comparing the peak intensities of diffraction lines from atomic planes obtained by wide-angle X-ray diffraction measurement of the graphite carbon crystals, the ratio of the peak intensity of the diffraction line from the (110) atomic plane to the peak intensity of the diffraction line from the (004) atomic plane is less than 0.1.

[0007] Patent Document 3 discloses a method for manufacturing a carbon fiber reinforced concrete substrate, which includes a metal substrate, a corrosion-resistant metal intermediate layer formed on the metal substrate, and a carbon layer formed on the corrosion-resistant metal intermediate layer, and in which the D-band peak intensity (I D ) and G-band peak intensity (I G ) intensity ratio (I D / I G ) is 0.70 or more and less than 0.95. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Japanese Patent Application Laid-Open No. 2010-86897 [Patent Document 2] Japanese Patent Application Laid-Open No. 2010-140886 [Patent Document 3] Japanese Patent Publication No. 2022-45138 Summary of the Invention [Problem to be solved by the invention]

[0009] Fuel cell separators (hereafter simply referred to as "separators") also play a role in passing the generated current to adjacent cells. Therefore, the substrate that makes up the separator must have high electrical conductivity and sufficient corrosion resistance to maintain this high electrical conductivity for long periods of time, even in the high-temperature, acidic atmosphere inside the fuel cell. Here, high electrical conductivity means low contact resistance. Furthermore, contact resistance refers to the voltage drop that occurs between the electrode and the separator surface due to interfacial phenomena.

[0010] For this reason, pure titanium or titanium alloys, which have excellent electrical conductivity and corrosion resistance, are often used as the substrate for the separator, which is one of the major factors that increase the cost of producing separators.

[0011] Therefore, in order to reduce costs, attempts have been made to produce separators that are conductive and corrosion-resistant by using an inexpensive substrate such as stainless steel as the substrate and forming a layer that imparts conductivity and corrosion resistance on the surface of the substrate.

[0012] The layer that imparts electrical conductivity and corrosion resistance to the stainless steel is formed by, for example, physical vapor deposition (PVD) processing.

[0013] However, such PVD treatment requires processing in a vacuum and multiple steps for film formation. Furthermore, in the prior art, such PVD treatment is performed on both the separator surface that comes into contact with a coolant (e.g., cooling water) (coolant contact surface) and the separator surface that comes into contact with a supply gas (fuel gas and / or oxidant gas) (gas contact surface), which may result in excessive performance in some parts of the separator.

[0014] Therefore, an object of the present invention is to provide a fuel cell separator having sufficient corrosion resistance and low contact resistance, and a method for producing such a separator at low cost. [Means for solving the problem]

[0015] The inventors have considered various means for solving the above-mentioned problems, and as a result have found that by stacking two stainless steel substrates with a coating (conductive passivation coating) formed on their surfaces so that the coolant contact surfaces face inward, and then using PVD treatment to form a corrosion-resistant metal intermediate layer as an intermediate layer on the substrates on the exposed gas contact surfaces, and then forming a conductive layer as an upper layer on the corrosion-resistant metal intermediate layer, it is possible to simultaneously manufacture two fuel cell separators with sufficient corrosion resistance and low contact resistance, i.e., high conductivity, according to each contact surface, and have completed the present invention.

[0016] That is, the gist of the present invention is as follows. (1) A stainless steel separator for a fuel cell having a coolant contact surface that comes into contact with the coolant and a gas contact surface that comes into contact with the gas, wherein the coolant contact surface has a conductive passivation coating, 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 (1), wherein the Cr / Fe ratio (atomic %) in the conductive passive film analyzed by surface X-ray photoelectron spectroscopy (XPS) is 2 or more, the F concentration in the conductive passive film analyzed by surface X-ray photoelectron spectroscopy (XPS) is 0.1 atomic % or more, and the Li concentration in the conductive passive 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, comprising: (i) a step of preparing a conductive substrate by applying a conductive passivation film to a stainless steel substrate; (ii) a step of stacking two or more conductive substrates obtained in step (i) so that the entire gas contact surface of each conductive substrate that will come into contact with gas is exposed; and (iii) a step of performing PVD treatment on the exposed gas contact surfaces of the two or more conductive substrates stacked in step (ii) to form a corrosion-resistant metal intermediate layer on the substrate and a conductive layer on the corrosion-resistant metal intermediate layer. (4) The method according to (3), wherein the step (i) comprises: (A) a step of injecting fluorine into the passive film; (B) a step of injecting lithium into the passive film; and (C) a step of dissolving iron in the passive film. [Effects of the Invention]

[0017] The present invention provides a fuel cell separator having sufficient corrosion resistance and low contact resistance, and a method for producing the separator at low cost. [Brief explanation of the drawings]

[0018] [Figure 1] 1 is a schematic cross-sectional view comparing a cell including an embodiment of a fuel cell separator of the present invention with a cell including a conventional fuel cell separator. [Figure 2] 1A is a schematic diagram comparing an embodiment of the method for producing a fuel cell separator of the present invention with a conventional method for producing a fuel cell separator (B). [Figure 3] 1A to 1C are schematic diagrams illustrating in more detail one embodiment of the method for producing a fuel cell separator of the present invention. [Figure 4] 1 is a graph showing the results of contact resistance in Comparative Example 1, Reference Example 1, and Example 1. [Figure 5] 1 is a graph showing the results of XPS analysis of the coolant contact surface of Example 1. [Figure 6] 1 is a graph showing the results of TOF-SIMS depth analysis of the coolant contact surface of Example 1. [Figure 7] 1 is a graph showing the results of GD-OES depth analysis of the coolant contact surfaces of Example 1 and Comparative Example 1. [Figure 8] 1 is a graph showing the results of TEM-EDX elemental mapping analysis of the coolant contact surface of Example 1. DETAILED DESCRIPTION OF THE INVENTION

[0019] Preferred embodiments of the present invention will now be described in detail. In this specification, the features of the present invention will be described with reference to the drawings as appropriate. In the drawings, the dimensions and shapes of each part are exaggerated for clarity and do not accurately depict the actual dimensions and shapes. Therefore, the technical scope of the present invention is not limited to the dimensions and shapes of each part shown in these drawings. The separator and its manufacturing method of the present invention are not limited to the following embodiments, and can be embodied in various forms incorporating modifications and improvements that can be made by those skilled in the art without departing from the spirit of the present invention.

[0020] The present invention relates to a stainless steel separator for a fuel cell having a coolant contact surface that comes into contact with a coolant and a gas contact surface that comes into contact with a gas, the coolant contact surface and the gas contact surface having a specific coating or layer.

[0021] In the present invention, the substrate of the separator is not limited to stainless steel. Examples of stainless steel include austenitic, ferritic, martensitic, austenitic-ferritic (two-phase), and precipitation-hardened stainless steels, such as SUS301, SUS304, SUS304L, SUS316, SUS316L, SUS430, SUS430J1L, SUS434, SUS444, SUS447, and SUS631. Surface finishes include bright annealed (BA), pickled (2D), pickled and lightly rolled (2B), and temper-rolled.

[0022] By selecting stainless steel as the substrate for the separator, raw material costs can be reduced.

[0023] The thickness of the substrate is not limited, but is usually 0.05 mm to 0.2 mm, and in one embodiment, 0.08 mm to 0.12 mm.

[0024] By setting the thickness of the substrate within the above range, raw material costs can be reduced.

[0025] The coolant contact surface of the separator of the present invention, which comes into contact with the coolant, has a conductive passivation film. Note that the "coolant contact surface" means the surface of the separator that comes into contact with the coolant, and the surface of the substrate that comes into contact with the coolant when it is made into a separator as a product.

[0026] Here, the conductive passive film refers to a film in which fluorine and lithium are injected into the passive film normally formed on the surface of the stainless steel substrate, and the Cr ratio is further increased to impart electrical conductivity and corrosion resistance to the passive film.

[0027] The Cr / Fe ratio (atomic %) in the conductive passive film, as analyzed by surface X-ray photoelectron spectroscopy (XPS), is usually at least 2, and in one embodiment, at least 2.5. As described above, the film properties can be improved by increasing the Cr ratio and decreasing the Fe ratio on the surface of the conductive passive film, so there is no upper limit to the Cr / Fe ratio.

[0028] The F concentration in the conductive passive film analyzed by surface X-ray photoelectron spectroscopy (XPS) is typically 0.1 atomic % or higher, and in one embodiment, 1.0 atomic % or higher. There is no upper limit to the F concentration. The F concentration is typically 20 atomic % or lower. The concentrations of various elements in the conductive passive film (Cr / Fe ratio (atomic %), F concentration, etc.) by XPS can be measured using the following measurement conditions: X-ray photoelectron spectrometer: PHI5000 VersaProbe II (manufactured by ULVAC-PHI Corporation), X-ray source: Al-Kα (1486.6 eV), X-ray source conditions: 15 kV (25 W), shift correction: C1s C-C, C-H bond energy is 284.8 eV, beam diameter: 100 μm Φ, measurement range: approximately 200 μm × 1000 μm.

[0029] The Li concentration in the conductive passive film analyzed by glow discharge optical emission spectroscopy (GD-OES) is typically 0.05 atomic % or more, and in one embodiment, 0.1 atomic % or more. There is no upper limit to the Li concentration. The Li concentration is typically 5 atomic % or less. The Li concentration in the conductive passive film analyzed by GD-OES can be measured under the following measurement conditions: glow discharge optical emission spectroscopy: GD-Profiler2 (manufactured by HORIBA, Ltd.), discharge gas: Ar gas, gas pressure: 600 Pa, electrode: 4 mm electrode.

[0030] The implantation of Li and F, which act as electron carriers, into the passive film improves the electrical conductivity of the passive film, significantly improving the contact electrical resistance of conventional passive films. Furthermore, modifying the passive film to a composition primarily composed of Cr oxide and Cr hydroxide improves corrosion resistance, and the film remains intact even when left in the atmosphere for long periods of time, preventing or suppressing the deterioration of the surface contact electrical resistance over time.

[0031] The thickness of the conductive passivation film is not limited. The average thickness of the conductive passivation film 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, for example, by cross-sectional TEM observation.

[0032] By ensuring that the thickness of the conductive passivation film is within the above range, sufficient conductivity and corrosion resistance can be ensured for the coolant contact surface.

[0033] The gas contact surface of the separator of the present invention, which comes into contact with 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. Note that the "gas contact surface" refers to the surface of the separator that comes into contact with gas, and the surface of the substrate that comes into contact with gas when the separator is made into a finished separator.

[0034] The corrosion-resistant metal intermediate layer is a layer for imparting corrosion resistance to the separator, and is not limited to any particular material, and may be, for example, a titanium layer.

[0035] The separator of the present invention has a corrosion-resistant metal intermediate layer, thereby ensuring the corrosion resistance of the separator.

[0036] The conductive layer is a layer for imparting electrical conductivity to the separator, and is not limited to a specific material, and may be, for example, a carbon layer.

[0037] By providing the separator of the present invention with a conductive layer, low contact resistance of the separator can be ensured.

[0038] FIG. 1 shows a schematic cross-sectional view comparing one embodiment of a fuel cell separator of the present invention with a conventional fuel cell separator. In FIG. 1, "FCC" stands for Fuel Cell Stack Coolant, which refers to a fuel cell coolant, "AN separator" refers to an anode separator, "CA separator" refers to a cathode separator, and "MEGA sheet assembly" refers to a membrane electrode gas diffusion layer assembly sheet assembly. The AN separator and CA separator are made of the same material, including the surface treatment layer. However, the AN separator and CA separator have different flow channel geometries suited to their fuel cell characteristics. Because the flow channel geometries are not essential to the present invention, for simplicity, the AN separator and CA separator are depicted in Figure 1 and other drawings as if they have the same structure.

[0039] As shown in Figure 1, in the fuel cell separator of the present invention, a conductive passivation film is formed on the coolant contact surface that comes into contact with the coolant, and a surface treatment layer is formed on the gas contact surface that comes into contact with the gas. In conventional fuel cell separators, surface treatment layers are formed on both the coolant contact surface and the gas contact surface. Since the surface treatment layer usually comprises a corrosion-resistant metal intermediate layer and a conductive layer, conventional fuel cell separators that have surface treatment layers formed on both sides are expensive and have excessive performance for the coolant contact surface.

[0040] The present invention further relates to a method for producing the fuel cell separator of the present invention.

[0041] The method for producing a fuel cell separator of the present invention includes (i) a conductive passivation film forming step for preparing a conductive substrate, (ii) a step for stacking two or more conductive substrates, and (iii) a surface treatment step for forming a corrosion-resistant metal intermediate layer and a conductive layer on the exposed gas-contact surfaces of the two or more conductive substrates. Here, the conductive substrate refers to stainless steel having a conductive passivation film.

[0042] The step (i) includes the steps of (A) injecting fluorine into the passive film, (B) injecting lithium into the passive film, and (C) dissolving iron from the passive film.

[0043] In the step (i), the substrate used is as described above.

[0044] The thickness of the substrate is not limited, but is usually 0.05 mm to 0.2 mm, and in one embodiment, 0.08 mm to 0.12 mm.

[0045] By setting the thickness of the substrate within the above range, raw material costs can be reduced.

[0046] As the substrate, a substrate that has been pressed into the final shape of the separator in advance can be used.

[0047] 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.

[0048] In step (A), methods for injecting fluorine into the passive film include immersing the stainless steel in an aqueous solution containing fluoride ions (chemical treatment) or electrolytic treatment (electrochemical treatment).

[0049] The fluoride ion source used for fluorine implantation is not limited to hydrofluoric acid or any fluorine compound that dissolves in water to generate fluoride ions, and any compound can be used. Examples include alkali metal fluorides (e.g., sodium fluoride, potassium fluoride, etc.), ammonium fluoride, antimony trifluoride, copper fluoride, sodium hydrogen difluoride, potassium hydrogen difluoride, etc. In one embodiment, the fluoride ion source is an alkali metal fluoride, such as sodium fluoride or potassium fluoride.

[0050] To electrochemically inject fluoride, stainless steel is subjected to direct current or pulse electrolysis (polarity is anode and cathode) in an aqueous hydrogen fluoride solution or an acidic aqueous solution prepared by adding nitric acid, sulfuric acid, phosphoric acid, or the like to the fluoride ion source. The pH of the treatment solution is usually 0 to 3, and in one embodiment, 0 to 2. The fluoride concentration is usually 0.001 kmol / m 3 The aqueous solution does not need to be heated, and can be used at, for example, typically 10°C to 30°C, and in one embodiment, room temperature (e.g., 20°C). The DC or pulse electrolysis conditions are 0.001 A / dm (both anode and cathode). 2 ~50A / dm 2 , 0.1 A / dm in one embodiment 2 ~10A / dm 2 The electrolysis time is usually 5 to 600 seconds, and in one embodiment, 10 to 180 seconds.

[0051] Chemical fluorine implantation involves immersion in a solution of hydrofluoric acid or the fluoride ion source with an oxidizing agent added. The fluoride concentration is typically 0.001 kmol / m -3 ~A wide range of saturation concentrations can be achieved.

[0052] Examples of oxidizing agents include nitric acid, potassium permanganate, and hydrogen peroxide. The concentration of the oxidizing agent is usually 0.1 kmol / m 3 ~10 kmol / m 3 , in one embodiment 1 kmol / m 3 ~5kmol / m 3The 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.

[0053] In step (B), methods for injecting lithium into the passive film include immersing the stainless steel in an aqueous or non-aqueous solution containing lithium ions (chemical treatment), or electrolytic treatment (electrochemical treatment).

[0054] The lithium ion source for lithium injection can be any lithium compound that dissolves in water or a non-aqueous solvent to generate lithium ions, and any compound can be used. For example, oxygen compounds include lithium hydroxide and lithium oxide, halides include lithium chloride, lithium bromide, and lithium iodide, and oxygen acid salts include lithium nitrate and lithium sulfate. Non-aqueous solvents include ethanol, methanol, dimethyl ether, diethyl ether, and methyl ethyl ether. A mixture of water and a water-miscible non-aqueous solvent may also be used.

[0055] The concentration of the lithium compound in the aqueous or non-aqueous solution containing the lithium ion source is usually 0.1 kmol / m 3 The solution temperature can be in a wide range from 10°C to 30°C, and in one embodiment, room temperature (for example, 20°C). In the case of immersion treatment, the treatment time is usually 10 seconds to 10 minutes, and in one embodiment, about 30 seconds to 5 minutes. In the case of direct current or pulse electrolysis (polarity is anode and cathode), the direct current or pulse electrolysis density is 0.001 A / dm (for both anode and cathode). 2 ~10A / dm 2 , 0.1 A / dm in one embodiment 2 ~5A / dm 2 The electrolysis time is usually 10 seconds to 10 minutes, and in one embodiment, about 20 seconds to 5 minutes.

[0056] An effective method for implanting fluoride ions and lithium ions into the passive film is to repeatedly perform the above-described steps (A) and (B). The order of steps (A) and (B) is not critical. In one embodiment, step (A) is performed first, and then step (B) is performed.

[0057] In step (C), a method for preferentially dissolving iron from the passive film includes immersion in an aqueous solution containing fluoride ions. It is effective to perform a heat treatment in air or an inert gas atmosphere such as nitrogen gas or Ar gas before this treatment. This is thought to be because Fe, concentrated in the outermost layer of the passive film by the heat treatment, easily forms a complex with fluoride ions and is then dissolved from the passive film by the subsequent immersion treatment in an aqueous solution containing fluoride ions. By preferentially dissolving Fe from the passive film, the film is modified to a composition mainly composed of Cr oxide and Cr hydroxide.

[0058] To dissolve the iron in the passive film, the stainless steel may be immersed in an aqueous solution containing fluoride ions. Examples of the aqueous solution include hydrofluoric acid and an aqueous solution obtained by adding an acid to the fluoride ion source. The pH is usually 0 to 3, and in one embodiment, 0 to 2. The fluoride concentration is usually 0.001 kmol / m 3 Acids for adjusting pH include nitric acid, sulfuric acid, and phosphoric acid. The concentration is usually 0.01 kmol / m 3 ~10 kmol / m 3 , in one embodiment 0.1 kmol / m 3 ~5kmol / m 3 The 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.

[0059] Furthermore, in order to efficiently dissolve iron from the passive film, it is desirable 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 usually 100°C to 600°C, and in one embodiment, 140°C to 500°C, and the treatment time is usually 1 second to 30 minutes, and in one embodiment, 10 seconds to 20 minutes.

[0060] This heat treatment forms an iron-concentrated layer on the outermost surface of the passive film, and subsequent immersion in an aqueous solution containing fluoride ions causes the Fe and fluoride ions to easily form complexes that dissolve into the solution. This treatment results in a passive film with a composition primarily composed of Cr, which improves corrosion resistance and prevents film deterioration even when left in the atmosphere for long periods of time, thereby minimizing the deterioration of the surface contact electrical resistance over time.

[0061] As described above, by injecting Li and F, which act as electron carriers, into the passive film, the electrical conductivity of the passive film is improved, and the contact electrical resistance of the conventionally formed passive film can be significantly improved. Furthermore, by modifying the passive film to a composition mainly composed of Cr oxides and hydroxides, corrosion resistance is improved, and the film does not change even when left in the atmosphere for a long time, preventing or suppressing the deterioration of the surface contact electrical resistance over time.

[0062] For a method of forming a conductive passivation film on the surface of stainless steel, see, for example, Japanese Patent Application Laid-Open No. 2008-277146.

[0063] The step (i) may be performed on both sides of the substrate, or only on the surface of the substrate that comes into contact with the coolant.

[0064] In step (ii), two or more conductive substrates obtained in step (i) are stacked together so that one of the two surfaces of each conductive substrate, i.e., the gas contact surface, is exposed, while the coolant contact surface is not exposed.

[0065] The method for stacking two or more conductive substrates is not limited as long as the entire gas-contacting surfaces of the two or more conductive substrates can be surface-treated in step (iii), which will be described in detail below. For example, two conductive substrates can be stacked with their coolant-contacting surfaces facing inward, optionally secured in place with a frame (jig), and stacked so that the entire gas-contacting surface of each substrate is exposed. For example, two or more conductive substrates can be stacked by sandwiching a plate-like or film-like material between the two or more conductive substrates and attaching them to both sides of the material with their gas-contacting surfaces exposed. Since the coolant-contacting surfaces are not exposed, they are not surface-treated in step (iii). However, if necessary, masking may be applied to all or part of the coolant-contacting surfaces to prevent damage to the conductive passivation film.

[0066] In step (ii), two or more conductive substrates are stacked on top of each other, and in step (iii), the surface treatment can be performed simultaneously on only the entire gas-contact surfaces of the conductive substrates, which particularly require corrosion resistance and conductivity.

[0067] In the surface treatment step (iii), a surface treatment, i.e., a PVD treatment, is performed on the gas-contact surfaces of the two or more conductive substrates exposed in step (ii), to form a corrosion-resistant metal intermediate layer and a conductive layer on the corrosion-resistant metal intermediate layer on the substrates.

[0068] The method for forming the corrosion-resistant metal intermediate layer on the substrate and the conductive layer on the corrosion-resistant metal intermediate layer can be any method known in the art, and is not limited thereto.

[0069] For example, when forming a corrosion-resistant metal intermediate layer on a substrate, an etching process is first performed to remove the passivation film on the substrate, and then a metal layer as the intermediate layer is formed by a PVD method as an intermediate layer film formation process. The corrosion-resistant metal intermediate layer is not limited as long as it can impart corrosion resistance to the separator. Examples of the corrosion-resistant metal intermediate layer include a titanium layer.

[0070] PVD methods for forming the metal layer include, but are not limited to, vacuum deposition, sputtering, ion plating, and the like.

[0071] For example, the titanium layer can be formed by sputtering, which facilitates mass production control.

[0072] For the sputtering method, for example, the bias voltage to the substrate, the initial vacuum level in the device chamber, the cleaning conditions for the metal substrate surface (e.g., the conditions for argon bombardment treatment), the conditions for the plasma generation gas, the film formation time, the film formation temperature, and the like can be conditions known in the art (see, for example, WO 2015 / 068776).

[0073] The thickness of the corrosion-resistant metal intermediate layer is not limited, but is usually 50 nm to 1000 nm, and in one embodiment, 50 nm to 300 nm, in average thickness. The average thickness of the corrosion-resistant metal intermediate layer can be measured, for example, by cross-sectional TEM observation.

[0074] By setting the upper limit of the thickness of the corrosion-resistant metal intermediate layer as described above, it is possible to obtain the effect of reducing the amount of corrosion-resistant metal used, and to prevent the film stress caused by forming the corrosion-resistant metal intermediate layer from becoming too large, thereby suppressing the occurrence of cracks in the corrosion-resistant metal intermediate layer, deformation of the substrate on which the corrosion-resistant metal intermediate layer is laminated, etc. By setting the lower limit of the thickness of the corrosion-resistant metal intermediate layer as described above, it is possible to ensure sufficient corrosion resistance.

[0075] Subsequently, in the conductive layer forming step, a conductive layer is formed on the corrosion-resistant metal intermediate layer by a PVD method.

[0076] The conductive layer is not limited as long as it has conductivity and can reduce the contact resistance of the separator. Examples of the conductive layer include a carbon layer.

[0077] PVD methods for forming the conductive layer include, but are not limited to, vacuum deposition, sputtering, ion plating, and the like.

[0078] For example, the carbon layer can be formed by sputtering, the details of which are the same as those of the corrosion-resistant metal intermediate layer.

[0079] For example, the carbon layer can be formed by using an ion plating method.

[0080] An example of the ion plating method is the arc ion plating (AIP) method.

[0081] For the arc ion plating method, for example, the bias voltage, the initial degree of vacuum in the chamber of the device, the cleaning conditions of the metal substrate surface (e.g., the conditions of the argon bombardment treatment), the conditions of the plasma generating gas, the film formation time, the film formation temperature, and the like can be conditions known in the technical field (see, for example, JP 2008-204876 A).

[0082] The thickness of the conductive layer is not limited, but is usually 5 nm to 500 nm, and in one embodiment, 30 nm to 150 nm, in average thickness. The average thickness of the conductive layer can be measured, for example, by cross-sectional TEM observation.

[0083] By setting the thickness of the conductive layer within the above range, low contact resistance of the separator, that is, high conductivity, can be ensured.

[0084] The manufacturing method of the present invention makes it possible to simultaneously manufacture two or more separators that have the corrosion resistance and conductivity required for the coolant contact surface, as well as the sufficient corrosion resistance provided by the corrosion-resistant metal intermediate layer and the low contact resistance provided by the conductive layer required for the gas contact surface, thereby significantly reducing manufacturing costs and improving manufacturing efficiency.

[0085] Figure 2 shows a schematic diagram comparing one embodiment (A) of the fuel cell separator manufacturing method of the present invention with a conventional fuel cell separator manufacturing method (B). Figure 2 illustrates the following: In the manufacturing method (A) of the present invention, a stainless steel (SUS substrate) having a conductive passivation film on its surface is used. The conductive passivation film sufficiently ensures corrosion resistance and conductivity at the coolant-contact surface. In other words, no additional surface treatment is required on the coolant-contact surface. Therefore, a surface treatment layer with superior corrosion resistance and conductivity need only be formed on the gas-contact surface. Thus, in the surface treatment process of the present invention, two SUS substrates with conductive passivation films are stacked with their coolant-contact surfaces facing each other and their gas-contact surfaces exposed, thereby simultaneously treating the gas-contact surfaces of two separators. In contrast, in the conventional manufacturing method (B), the surface treatment is performed on both sides of the SUS substrate, so only one separator can be produced with a single surface treatment.

[0086] FIG. 3 shows a more detailed example of one embodiment of the manufacturing method for a fuel cell separator of the present invention. (A) is a diagram specifically illustrating the surface treatment process in a conventional manufacturing method. In the surface treatment process, (1) a passivation film on the surface of a SUS substrate is removed by an etching process, (2) a corrosion-resistant metal intermediate layer is formed by an intermediate layer deposition process, and (3) a conductive layer is formed by a conductive layer deposition process. (B) is a diagram specifically illustrating the features of the present invention, and is a schematic diagram showing how two SUS substrates with conductive passivation films are stacked on top of each other with their coolant-contacting surfaces facing each other and their gas-contacting surfaces exposed, and then placed in a frame (jig). (C) is a diagram comparing the method of the present invention with a conventional method. Therefore, in the present invention, the conventional surface treatment process shown in (A) of FIG. 3 is replaced by a manufacturing method in which two or more SUS substrates are placed as shown in (B). In other words, the present invention replaces the conventional manufacturing method in which a film is formed on both the coolant-contacting surface and the gas-contacting surface, with a manufacturing method in which a film is formed only on the gas-contacting surface (one side). By forming the film on only one side, it is now possible to load twice as many separators onto the rack (cart) during film formation, which doubles the efficiency of the film formation process on the separator, as shown in Figure 3C.

[0087] The fuel cell separator produced according to the present invention is a component of a fuel cell (single cell) and is arranged on both sides of a membrane electrode assembly (electrolyte membrane, anode and cathode electrode layers arranged on both sides of the electrolyte membrane).

[0088] The fuel cell separator produced according to the present invention is bonded to fuel cell components known in the art, such as a membrane electrode assembly and a seal member, for example, with an adhesive to produce a fuel cell.

[0089] A fuel cell manufactured using the fuel cell separator manufactured according to the present invention can be used in various electrochemical devices such as polymer electrolyte fuel cells. [Example]

[0090] Hereinafter, several examples of the present invention will be described, but it is not intended that the present invention be limited to those shown in these examples.

[0091] I. Separator manufacturing <Comparative Example 1> A stainless steel substrate with a flow channel shape was prepared by press-molding a 0.1 mm thick stainless steel plate as the separator of Comparative Example 1. The stainless steel material was SUS304-BA.

[0092] <Reference example 1> The separator of Reference Example 1 was produced by the method described in Example 1 of JP-A No. 2022-45138. Specifically, the method is as follows.

[0093] A stainless steel substrate (SUS304, 0.1 mm thick) with a flow path formed thereon was prepared as the substrate. A corrosion-resistant metal intermediate layer and a carbon layer were then formed on both sides of the stainless steel substrate using a PVD deposition system (Hauzer, FC1200). Specifically, the stainless steel substrate was first placed in the reactor chamber of the system, and the reactor chamber was evacuated and heated using an internal heater. Next, the pure Ti cathode target used for sputtering was etched (cleaned) with Ar gas plasma. The stainless steel substrate was also etched with Ar gas plasma to remove the passivation layer present on its surface. Next, a titanium layer was formed by unbalanced magnetron sputtering (UBMS) using the pure Ti cathode target described above. The deposition conditions for the titanium layer were set as follows:

[0094] Target film thickness: 250nm Processing temperature: 150℃ Vacuum level: 2E-03mbar Input gas: Ar Gas flow rate: 250sccm Bias voltage: PLS Voltage: -75V Frequency: 40kHz Off time during frequency: 5µS Ti cathode output: 8kW / A / V UBM coil current: 2A Orbital speed: 3 rpm

[0095] Next, a carbon layer was formed by arc ion plating (AIP) using a high-purity ta-C raw material under the following conditions:

[0096] Target film thickness: 50nm Processing temperature: 180℃ Vacuum level: 2E-03mbar Input gas: Ar Gas flow rate: 250sccm Bias voltage: PLS Voltage value: -20V Frequency: 40kHz Off time during frequency: 5µS C cathode output: 60kW / A / V Orbital speed: 4 rpm

[0097] During the etching and film formation, the stainless steel substrate was rotated as needed to form a titanium layer and a carbon layer on both sides. Through the above steps, a separator of Reference Example 1 was obtained.

[0098] Example 1 (i) A step of providing a conductive passivation film on a substrate to prepare a conductive substrate. (A) A step of injecting fluorine into the passive film First, a stainless steel substrate (SUS304, thickness 0.1 mm) with a flow path formed was prepared as the substrate. The prepared substrate was immersed in acetone and subjected to ultrasonic cleaning, and then heated in air at 300°C for 5 minutes. Next, the substrate was immersed in a 5% by mass HF aqueous solution at 30°C for 1 minute, followed by washing with distilled water and drying with cold air (25°C). (B) A step of injecting lithium into the passive film Next, 1 kmol / m 3 In LiOH solution, 1 A / dm 2 The substrate was subjected to cathodic electrolysis for 1 minute, washed with distilled water, and dried with cold air (25°C). (C) A step of dissolving iron from the passive film Thereafter, the substrate was again subjected to an immersion treatment in a 5 mass % HF aqueous solution at 30°C for 10 seconds, followed by washing with distilled water and drying with cold air (25°C).

[0099] (ii) A process of overlapping two conductive substrates The two conductive substrates obtained in step (i), each having a conductive passivation film applied to both sides, were stacked together with their coolant contact surfaces facing inward, so that the gas contact surfaces of each conductive substrate that would come into contact with the gas were exposed, and the substrates were placed in a frame (jig).

[0100] (iii) A process 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). For the two conductive substrates overlapped in the step of (ii), PVD treatment was performed on each exposed gas contact surface to form a corrosion-resistant metal intermediate layer on the substrate and a carbon layer on the corrosion-resistant metal intermediate layer. The conditions of the PVD treatment for forming the corrosion-resistant metal intermediate layer and the carbon layer on the gas contact surface of the conductive substrate were the same as those in Reference Example 1.

[0101] II. Evaluation of the separator <Measurement of contact resistance> For Comparative Example 1 (separator with only pressing without PVD treatment), Reference Example 1 (separator having titanium layers and carbon layers on both the coolant contact surface and the gas contact surface), and Example 1 (separator having a conductive passive film on the coolant contact surface and titanium layers and carbon layers on the gas contact surface), the contact resistance with GDL (manufactured by Toray Industries, Inc.) was measured. 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 (endurance test). Subsequently, for each sample after the endurance test, the contact resistance with GDL (manufactured by Toray Industries, Inc.) was measured as described above.

[0102] [[ID=,13]]<TOF-SIMS depth analysis> TOF-SIMS depth analysis was performed on the coolant contact surface of the separator of Example 1.

[0103] <XPS analysis> XPS analysis was performed on the coolant contact surface of the separator of Example 1. The measurement conditions of the XPS analysis were the same as those described above.

[0104] <GD-OES depth analysis> GD-OES depth analysis was performed on the coolant contact surfaces of the separators of Example 1 and Comparative Example 1. The measurement conditions of the GD-OES depth analysis were the same as those described above.

[0105] <TEM-EDX elemental mapping analysis><" TEM-EDX elemental mapping analysis was performed on the coolant contact surface of the separator of Example 1.

[0106] III. Evaluation Results of the Separator <Contact Resistance Measurement Results> Figure 4 shows the contact resistance results of Comparative Example 1, Reference Example 1, and Example 1. From Figure 4, it can be seen that Example 1 has a very low contact resistance of 5 mΩ·cm, equivalent to that of Reference Example 1, before and after the durability test. 2 The following contact resistance, especially 3 mΩ·cm 2 It was found that the following contact resistance was shown.

[0107] <Results of XPS Analysis, GD-OES, TOF-SIMS Depth Analysis, and TEM-EDX Elemental Mapping Analysis> Figure 5 shows the results of XPS analysis of the coolant contact surface of Example 1, Figure 6 shows the results of TOF-SIMS depth analysis of the coolant contact surface of Example 1, Figure 7 shows the results of GD-OES depth analysis of the coolant contact surface of Example 1, and Figure 8 shows the results of TEM-EDX elemental mapping analysis of the coolant contact surface of Example 1. From Figure 5, it was found that there is a peak derived from the binding energy of fluoride between 682 eV and 688 eV on the coolant contact surface of Example 1. From Figure 6, it was found that Li, F, and Cr are detected in the coolant contact surface of Example 1 at a short sputtering time, that is, near the surface. From Figure 7, it was found that Li was detected in a shallow range of 0 to 0.0μm in depth on the coolant contact surface of Example 1. Also, Li was not detected on the coolant contact surface of Comparative Example 1. From Figure 8, it was found that the ratio of Cr in the oxide layer is high on the coolant contact surface of Example 1. Therefore, from Figures 5 to 8, it was found that on the separator of Example 1, a conductive passive film in which F, Li, and Cr, which contribute to the conductivity of the coolant contact surface, are present is formed on the coolant contact surface.

[0108] From the above, it was found that for the separator obtained by forming a conductive passive film with better productivity than the conventional corrosion-resistant metal intermediate layer and conductive layer on the coolant contact surface of the separator, a sufficiently low contact resistance can be maintained even after the durability test.

Claims

1. A stainless steel fuel cell separator having a coolant contact surface that contacts a coolant and a gas contact surface that contacts a gas, the coolant contact surface has a conductive passivation coating; the gas contact surface has a corrosion-resistant metal intermediate layer on the substrate and a conductive layer on the corrosion-resistant metal intermediate layer; Separator.

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

3. (i) providing a conductive passivation coating on a stainless steel substrate to prepare a conductive substrate; (ii) a step of stacking the two or more conductive substrates obtained in step (i) so that the entire gas contact surface of each conductive substrate that will come into contact with the gas is exposed; (iii) performing a PVD treatment on the exposed gas-contact surfaces of the two or more conductive substrates stacked in step (ii) to form a corrosion-resistant metal intermediate layer on the substrate and a conductive layer on the corrosion-resistant metal intermediate layer; A method for manufacturing a separator for a fuel cell, comprising:

4. 4. The method according to claim 3, wherein step (i) comprises the steps of: (A) injecting fluorine into the passive film; (B) injecting lithium into the passive film; and (C) dissolving iron in the passive film.

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