FUEL CELL SEPARATOR AND FUEL CELL DEVICE

Abstract

Method for manufacturing a fuel cell separator (3) including a stainless steel substrate (31), comprising: Forming a tin oxide film (32) on a surface of the stainless steel substrate (31); and Binding of phosphoric acid or phosphate to at least one defect section (33) in the tin oxide film (32), the binding comprising: Contacting the stainless steel substrate (31) on which the tin oxide film (32) is formed with a solution containing phosphoric acid or phosphate; and Drying of the stainless steel substrate (31) after contact.

Description

Technical area

[0001] The present disclosure relates to a fuel cell separator and a fuel cell device using the same. State of the art

[0002] A fuel cell of a solid polymer fuel cell device includes a membrane electrode assembly (MEA) comprising an ion-permeable electrolyte membrane, an anode-side catalyst layer (electrode layer), and a cathode-side catalyst layer (electrode layer). The electrolyte membrane is sandwiched between the anode-side catalyst layer and the cathode-side catalyst layer. The membrane electrode assembly has gas diffusion layers (GDL) formed on both sides to supply fuel gas or oxidant gas and collect electricity generated by an electrochemical reaction. The membrane electrode assembly has both sides on which the GDLs are arranged and is referred to as a membrane electrode and gas diffusion layer assembly (MEGA), and the MEGA is sandwiched by a pair of separators.Here, the MEGA serves as a power generation unit of the fuel cell device, and when the gas diffusion layer is not present or arranged, the membrane electrode assembly serves as the power generation unit of the fuel cell device.

[0003] For example, JP H08-185870 A proposes the following separator as a fuel cell separator. This separator comprises a cermet substrate body made of a refractory metal containing chromium and ceramic, and a protective film of metal oxide coated such that a surface of the substrate body opposite the cathode gas does not contact the cathode gas. JP H08-185870 A further exemplifies tin oxide as an example of this metal oxide.

[0004] Furthermore, DE 10 2005 059 614 A1 and DE 10 2006 029 473 A1 disclose a coating material for protecting metals and its manufacturing method, and a fuel cell and its manufacturing method from the prior art, respectively. ReferencePatent literature Patent Literature 1: JP H08-185870 A Patent literature 2: DE 10 2005 059 614 A1 Patent literature 3: DE 10 2006 029 473 A1 Summary of the inventionTechnical problem

[0005] In the fuel cell separator according to JP H08-185870 A, it is believed that reducing the diffusion of chromium into a cathode with the metal oxide protective film ensures a reduction in the deterioration of power generation performance of a fuel cell device. Furthermore, since tin oxide has a comparatively high conductivity property, tin oxide is believed to ensure a reduction in contact resistance. However, forming a tin oxide film on a substrate as the metal oxide protective film may generate a defect portion (such as a recessed portion where the tin oxide film is not formed) in the tin oxide film. For the defect portion in the tin oxide film, there is a possibility of corrosion occurring in a corrosive environment due to exposure to a stainless steel substrate, etc.

[0006] Specifically, the fluoride ion derived from a solid electrolyte membrane (e.g., a perfluorosulfonic acid-based polymer) or the like, in contact with the defect portion, forms a complex with a metal such as iron contained in the stainless steel substrate, thereby dissolving the metal in the substrate. Dissolution of the metal such as Fe causes pitting corrosion. Furthermore, an oxide (insulating property) of the dissolved metal binds to a surface of the tin oxide film, resulting in deterioration of the conductivity of the separator. Furthermore, dissolution of the metal such as Fe generates hydrogen peroxide with metal ions such as Fe ions, which act as a catalyst (Fenton reaction), possibly causing decomposition or dissolution of the solid electrolyte membrane. The decomposition or dissolution of the solid electrolyte membrane obviously deteriorates the power generation performance of the fuel cell device.

[0007] Therefore, the present disclosure provides a fuel cell separator having low contact resistance due to a tin oxide film and having excellent corrosion resistance. Solution to the problem

[0008] Aspects of the embodiment are as follows. (1) A method for manufacturing a fuel cell separator including a stainless steel substrate comprises: forming a tin oxide film on a surface of the stainless steel substrate; and bonding phosphoric acid or phosphate to at least one defect portion in the tin oxide film, wherein the bonding comprises: bringing the stainless steel substrate on which the tin oxide film is formed into contact with a solution containing the phosphoric acid or phosphate; and drying the stainless steel substrate after the contact. (2) In the process for producing a fuel cell separator according to (1), the phosphate is an inorganic phosphate. (3) In the process for producing a fuel cell separator according to (2), the inorganic phosphate is orthophosphate. (4) The method for manufacturing a fuel cell separator according to any one of (1) to (3) further comprises: removing a passive film present on the surface of the stainless steel substrate under a vacuum condition prior to forming. The forming includes forming the tin oxide film while maintaining the vacuum condition. (5) A fuel cell separator manufactured by the method according to any one of (1) to (4), wherein the fuel cell separator comprises a stainless steel substrate and a tin oxide film. The tin oxide film is formed on a surface of the stainless steel substrate. Phosphoric acid or phosphate bonds to a defect portion in the tin oxide film. (6) A fuel cell device comprises the fuel cell separator according to (5). (7) The fuel cell device according to (6) further comprises a solid electrolyte membrane. (8) In the fuel cell device according to (7), the solid electrolyte membrane contains a fluorine-based electrolyte resin. Advantageous effects of the invention

[0009] The present disclosure makes it possible to provide a fuel cell separator having low contact resistance due to a tin oxide film and having excellent corrosion resistance. Short description of the drawing Fig. 1A is a schematic cross-sectional view describing a flow chart of corrosion generation in a defect portion on a tin oxide film; Fig. Fig. 1B is a schematic cross-sectional view showing the flow diagram of corrosion generation in the defect portion on the tin oxide film continuously from Fig. 1A describes; Fig. Figure 1C is a schematic cross-sectional view showing the flow diagram of corrosion generation in the defect portion on the tin oxide film of Fig. 1B describes continuously; Fig. 2A is a schematic cross-sectional view describing a reason why corrosion resistance of a separator is improved by a manufacturing method according to an embodiment; Fig. Fig. 2B is a schematic cross-sectional view describing the reason why the corrosion resistance of the separator is improved by the manufacturing method according to the embodiment of Fig. 2A is continuously improved; Fig. Fig. 2C is a schematic cross-sectional view describing the reason why the corrosion resistance of the separator is improved by the manufacturing method according to the embodiment of Fig. 2B is continuously improved; Fig. 3 is a cross-sectional view of a main part of a fuel cell stack including fuel cell separators according to the embodiment; Fig. 4 is an enlarged cross-sectional view near a surface of the fuel cell separator according to the embodiment; Fig. 5 is a graph showing results of a contact resistance test on test pieces E1 and C1 prepared in Example 1 and Comparative Example 1; Fig. 6 is a graph showing the results of a corrosion resistance test in strong acid solutions containing fluoride ions on the test pieces E1 and C1 prepared in Example 1 and Comparative Example 1, respectively, and a SUS447 plate of a stainless steel substrate (test piece C2); and Fig. Figure 7 is a graph showing the results of the corrosion resistance test on the SUS447 plate of the stainless steel substrate in etchants containing various test substances. Description of the embodiments

[0010] The formation of a tin oxide film on a substrate may generate a defect portion in the tin oxide film. The defect portion includes, for example, a recessed portion where the tin oxide film is not formed, or a recessed portion with an insufficient film thickness for protection. There may be a case where many defect portions occur depending on the materials and conditions used for the formation of the tin oxide film. The defect portion in the tin oxide film has a possibility of causing corrosion in a corrosive environment due to exposure of a stainless steel substrate and the like. The following describes this occurrence of corrosion with reference to Fig. 1A to Fig. 1C. In Fig. 1A, a defect portion 33 occurs in a region of a tin oxide film 32 formed on a stainless steel substrate 31. Next, as shown in Fig. 1B, the fluoride ion derived from a solid electrolyte membrane (e.g., perfluorosulfonic acid-based polymer) or the like, which is in contact with the defect portion, forms a complex with a metal such as Fe contained in the stainless steel substrate, thereby dissolving the metal in the substrate. As shown in Fig. As shown in Figure 1C, the dissolution of metals such as Fe causes pitting corrosion. Furthermore, the oxide (insulating property) of the dissolved metal binds to the surface of the tin oxide film, leading to a deterioration in the conductivity of the separator. Furthermore, the dissolution of metals such as Fe generates hydrogen peroxide with metal ions such as Fe ions, which act as a catalyst (Fenton reaction), potentially causing the decomposition of the solid electrolyte membrane. The decomposition of the solid electrolyte membrane obviously deteriorates the power generation performance of the fuel cell device.

[0011] Therefore, the embodiment provides a method for manufacturing a fuel cell separator including a stainless steel substrate, which comprises a forming step of forming a tin oxide film on a surface of the stainless steel substrate and a bonding step of bonding phosphoric acid or phosphate to at least one defect portion in the tin oxide film.

[0012] In the embodiment, first, after the tin oxide film is formed on the surface of the stainless steel substrate, the phosphoric acid or phosphate is bonded to at least the defect portion in the tin oxide film. Bonding the phosphoric acid or phosphate to the defect portion in the tin oxide film enables an improvement in corrosion resistance. The following describes with reference to Fig. 2A to Fig. 2C a reason why corrosion resistance is improved by binding the phosphoric acid or phosphate. In Fig. 2A, the defect portion 33 occurs in a region of the tin oxide film 32 formed on the stainless steel substrate 31. Next, as shown in Fig. 2B, the fluoride ion in contact with the defect portion forms a complex ([Fe 2+ (F - )6] 4- ). The complex reacts with the phosphoric acid or phosphate (for example, trisodium phosphate) bound to the substrate surface and forms a film 34 (for example, Fe(PO)4) of iron phosphate or the like. Consequently, the protective film 34 is formed at least at the defect portion, thereby improving corrosion resistance. Note that the theory described above is based on a conjecture and therefore the conjecture does not limit the embodiment. While Fig. 2C illustrates a configuration in which the protective film 34 is formed in the defect portion 33 on the stainless steel substrate 31, the protective film 34 may be formed on the tin oxide film 32.

[0013] In this specification, the binding of phosphoric acid or phosphate means the presence of phosphoric acid or phosphate on the surface of the substrate or tin oxide film in any form, including the case where the phosphoric acid or phosphate itself is physically adsorbed onto the surface of the substrate or tin oxide film and the case where the phosphoric acid or phosphate binds to the surface in the form of dissociated ions. The phosphoric acid or phosphate, or their ions, may form a chemical bond with a functional group present on the surface of the substrate or tin oxide film.

[0014] The following describes the embodiment in detail. [Educational step]

[0015] The method for manufacturing the fuel cell separator according to the embodiment includes the forming step of forming the tin oxide film on the surface of the stainless steel substrate.

[0016] In the embodiment, the tin oxide film only needs to be disposed on at least a portion of the surface of the stainless steel substrate. Meanwhile, in some embodiments, since corrosion resistance is particularly required in portions that contact a gas diffusion layer and the separator, the tin oxide film is formed on at least the portion of the surface of the stainless steel substrate that is in contact with the gas diffusion layer.

[0017] A method for forming the tin oxide film on the stainless steel substrate is not particularly limited. For example, the film can be formed by the physical vapor deposition method (PVD) using, for example, sputtering, vacuum deposition, ionization deposition, or ion plating. For example, the tin oxide film can be formed on the surface of the stainless steel substrate by sputtering using plasma, targeting a sintered body obtained by sintering a raw material containing tin oxide particles, and the like. In the embodiment, there may be a case where the defect portion occurs depending on the materials used and conditions for forming the tin oxide film. For example, a large amount of impurities contained in the material is likely to generate the defect portion.

[0018] To form the tin oxide film by sputtering, sputtering can be performed under an oxygen gas atmosphere, an inert gas atmosphere, or a vacuum atmosphere (under a pressureless atmosphere) during the formation of the tin oxide film. Specifically, in some embodiments, the tin oxide film is formed under the inert gas atmosphere or the vacuum atmosphere (under the pressureless atmosphere).

[0019] In some embodiments, the tin oxide film has a film thickness in a range of 10 to 300 nm. A tin oxide film having a film thickness of 10 nm or more can effectively develop the effect provided by the tin oxide film. A tin oxide film having a film thickness of 300 nm or less can reduce the residual stress of the tin oxide film and effectively reduce the peeling of the tin oxide film from the stainless steel substrate.

[0020] In some embodiments, the tin oxide film contains antimony (Sb). The inclusion of antimony enables the conversion of the tin oxide film into a semiconductor. Specifically, in some embodiments, the tin oxide film is tin oxide containing antimony in a concentration of 0.2 to 10 atomic %. In such a tin oxide film, tetravalent tin is substituted with pentavalent antimony at the positions of the tetravalent tin in a crystal lattice of the tin oxide. This increases a carrier concentration in the tin oxide film and improves the conductivity of the tin oxide film. Accordingly, the contact resistance of the separator in which the tin oxide film is formed can be reduced, and consequently, the internal resistance of the fuel cell stack can be reduced.An antimony content of 0.2 atomic% or more enables a sufficient increase in the carrier concentration brought about by substitution with antimony; thus, the conductivity of the tin oxide film can be effectively improved. An antimony content of 10 atomic% or less enables the reduction of inhibition or suppression of carrier movement due to an excessive amount of antimony. In some embodiments, the tin oxide film is tin oxide containing antimony in a concentration of 0.5 to 10 atomic%.

[0021] When measuring tin oxide containing antimony in a concentration of 0.2 to 10 atomic% by an X-ray diffraction method using CuKα radiation, a diffraction peak of a (110) plane of tetravalent tin oxide is detected or determined at approximately a Bragg angle of 2θ = 26.6° (specifically, in a range of 26.6°±0.5°). In some embodiments, by the X-ray diffraction method using CuKα radiation, a half-width W of the diffraction peak of the (110) plane of tin oxide in the tin oxide film at approximately 2θ = 26.6° may be 1° or less. The half-width W is a width of the diffraction peak with a value that is half of the maximum value P (P / 2) of the diffraction intensity of the diffraction peak. In the embodiment which satisfies the condition that the half width of the diffraction peak is 1° or less, a crystal property orThe crystalline nature of the tin oxide, which forms the tin oxide film, allows for improved conductivity. Consequently, the contact resistance of the separator can be further reduced. A half-width of the diffraction peak of the (1 10) plane of the tin oxide of 0.5° or less enables a further reduction in the contact resistance of the separator.

[0022] Furthermore, in some embodiments, the tin oxide film contains oxygen-deficient tin oxide and in some embodiments contains SnO 2-X(0.1 ≤ X ≤ 0.4) is oxygen-deficient tin oxide. Oxygen-deficient tin oxide increases the carrier concentration in the tin oxide film, which improves the conductivity of the tin oxide film. Consequently, the contact resistance of the separator decreases, ensuring a reduction in the internal resistance of the fuel cell stack. Note that oxygen-deficient tin oxide is a tin oxide in which oxygen is partially absent, similar to the tetragonal crystal structure of SnO2.

[0023] The oxygen-deficient tin oxide satisfying the above-described range of X can be obtained, for example, by adjusting a partial pressure of the oxygen gas in film formation and / or an applied voltage in sputtering.

[0024] The tin oxide film may contain at least one other metal in addition to tin. The other metal includes, for example, bismuth or tellurium. The content of the other metal can be adjusted appropriately, taking into account conductivity, corrosion resistance, and similar specifications.

[0025] The concentration of a metallic element in the stainless steel substrate can be measured by composition analysis using, for example, an X-ray photoelectron spectroscopy (XPS) apparatus.

[0026] In some embodiments, a removal step of removing a passive film present on the surface of the stainless steel substrate under a vacuum condition is included prior to the formation step. Furthermore, the formation step forms the tin oxide film under the vacuum condition in the removal step, which is included in some embodiments. The formation of the tin oxide film with the removed passive film present on the surface of the stainless steel substrate enables a further effective improvement of the conductivity property. [Binding process]

[0027] The embodiment includes the bonding step of bonding the phosphoric acid or the phosphate to at least the defect portion in the tin oxide film after the forming step.

[0028] Bonding the phosphoric acid or phosphate to the defect portion can be performed by a general method in which the stainless steel substrate on which the tin oxide film is formed is brought into contact with a solution (water solution) containing the phosphoric acid or phosphate, and then the stainless steel substrate is dried, thereby performing the bonding. Specifically, the method includes a method of immersing the stainless steel substrate on which the tin oxide film is formed in the solution containing the phosphoric acid or phosphate, a method of spraying the solution containing the phosphoric acid or phosphate onto the stainless steel substrate on which the tin oxide film is formed, and similar methods. The phosphoric acid or phosphate in the solution has a concentration of 0.005 to 0.2 M in some embodiments, and 0.01 to 0.1 M in some embodiments.A concentration of 0.005 M or more increases the amount of bound phosphoric acid or phosphate, ensuring effective improvement in corrosion resistance. A concentration of 0.2 M or less prevents excessively high pH of the solution and allows for a reduction in the dissolution of tin oxide. A contact period or contact time with the solution can be appropriately adjusted by considering, for example, the concentration of phosphoric acid or phosphate. Although a solvent is not particularly limited, water, for example, can be used. The pH of the solution is not particularly limited and is, for example, 3 to 9.

[0029] In some embodiments, the phosphate is inorganic phosphate. Specific examples of the inorganic phosphate include trisodium phosphate (Na3PO4), tripotassium phosphate (K3PO4), disodium hydrogen phosphate (Na2HPO4), sodium dihydrogen phosphate (NaH2PO4), dipotassium hydrogen phosphate (K2HPO4), potassium dihydrogen phosphate (KH2PO4), and the like. These inorganic salts may have a hydrate structure. One type of phosphate may be used alone, or multiple types of phosphates may be used together or in combination. The phosphoric acid and the phosphate may be used together or in combination.

[0030] After the formation step, the bonding step may be performed in an environment where the passive film is not formed on the defect portion in the tin oxide film. For example, after performing the removal step of removing the passive film present on the surface of the stainless steel substrate while maintaining the vacuum condition, the tin oxide film formation step is performed under the vacuum condition maintained in the removal step. The bonding step is performed under an inert gas environment without moving the stainless steel substrate on which the tin oxide film is formed into an environment where the passive film is formed. For example, nitrogen and argon can be used as the inert gas. In some embodiments, the solution containing the phosphoric acid or phosphate is purged with the inert gas (for example, nitrogen or argon) to reduce dissolved oxygen.

[0031] The following describes a configuration of a fuel cell device according to the embodiment with reference to the drawing. The following describes the case of applying the fuel cell separator according to the embodiment to fuel cell devices mounted on a fuel cell vehicle or the like as an example. However, the embodiment is not limited by the example.

[0032] Fig. 3 is a cross-sectional view of a main part of a fuel cell stack (fuel cell device) 10. As shown in Fig. As shown in Figure 3, a plurality of cells (individual cells) 1 are stacked in the fuel cell stack 10 as a basic unit. Each of the cells 1 is a solid polymer fuel cell device that generates an electromotive force through an electrochemical reaction between an oxidant gas (e.g., air) and a fuel gas (e.g., hydrogen). The cell 1 includes a MEGA 2 and separators (fuel cell separators) 3 that contact the MEGA 2 to separate the MEGA 2. In the embodiment, the MEGA 2 is sandwiched by the pair of separators 3 and 3.

[0033] The MEGA 2 is manufactured by integrating a membrane electrode assembly (MEA) 4 and gas diffusion layers 7 and 7 disposed on both sides of the membrane electrode assembly 4. The membrane electrode assembly 4 includes an electrolyte membrane 5 and a pair of electrodes 6 and 6 bonded such that the electrolyte membrane 5 is sandwiched between the pair of electrodes 6 and 6. The electrolyte membrane 5 includes a proton-conductive ion exchange membrane formed from a solid polymer material. The electrode 6 is formed, for example, from a porous carbon material supporting a catalyst such as platinum. The electrode 6 disposed on one side of the electrolyte membrane 5 becomes an anode, and the electrode 6 on the other side becomes a cathode.The gas diffusion layer 7 is formed of a conductive member having gas permeability, which comprises a porous carbon body such as a carbon paper or a carbon cloth, or a porous metal body such as a metal net or a porous metal.

[0034] The MEGA 2 is a power generation unit of a fuel cell device 10. The separator 3 is in contact with the gas diffusion layer 7 of the MEGA 2. When the gas diffusion layer 7 is missing, the membrane electrode assembly 4 serves as the power generation unit, and in this case, the separator 3 is in contact with the membrane electrode assembly 4. Accordingly, the power generation unit of the fuel cell device 10 includes the membrane electrode assembly 4 and is in contact with the separator 3.

[0035] The separator 3 is a plate-shaped element that uses a metal with excellent conductivity, gas impermeability, and similar properties as a substrate. The separator 3 has one surface adjacent to the gas diffusion layer 7 of the MEGA 2 and the other surface adjacent to an adjacent separator 3.

[0036] Each of the separators 3 is formed in a waveform. The shape of the separator 3, the waveform, forms an isosceles trapezoid, and an upper portion of the waveform is flat. This upper portion has both ends forming equal angles to provide a square or angular shape. That is, each of the separators 3 presents an approximately identical shape regardless of whether viewed from the front or back. The upper portions of the separator 3 are in surface contact with one gas diffusion layer 7 of the MEGA 2, and the upper portions of the separator 3 are in surface contact with the other gas diffusion layer 7 of the MEGA 2.

[0037] A gas flow channel 21, defined between the gas diffusion layer 7 on one side of one electrode (namely, the anode) 6 and the separator 3, is a flow passage through which fuel gas flows. A gas flow channel 22, defined between the gas diffusion layer 7 on one side of the other electrode (namely, the cathode) 6 and the separator 3, is a flow passage through which an oxidant gas flows. When the fuel gas is supplied to the gas flow channel 21 on a side opposite to the gas flow channel 22 via the cell 1, and the oxidant gas is supplied to the gas flow channel 22, an electrochemical reaction occurs in the cell 1 to generate an electromotive force.

[0038] Further, one cell 1 and another cell 1 adjacent to one cell 1 are arranged such that the electrode 6 as the anode and the electrode 6 as the cathode face each other. The upper portions on a back surface of the separator 3 arranged along the electrode 6 as the anode of one cell 1 are in surface contact with the upper portions on the back surface of the separator 3 arranged along the electrode 6 as a cathode of another cell 1. Water as a coolant for cooling the cells 1 flows through a space 23 defined between the separators 3 and 3, which are in surface contact between the adjacent two cells 1.

[0039] As in Fig. As shown in Figure 4, the separator 3 includes the stainless steel substrate 31. A material of the stainless steel substrate includes stainless steel. Furthermore, the tin oxide films 32 are coated or deposited on both surfaces (i.e., the surface on the side in contact with the gas diffusion layer 7 and the surface on the side in contact with the adjacent separator 3) of the separator 3.

[0040] In the embodiment, the phosphoric acid or phosphate is bonded to at least the defect portion in the tin oxide film. As described above, the phosphoric acid or phosphate bonded to the defect portion in the tin oxide film enables the corrosion resistance of the separator to be improved. For example, dissolving the phosphoric acid or phosphate present on the separator surface with a solvent such as water and examining the resulting solution ensures confirmation of the presence / absence of phosphoric acid or phosphate.

[0041] As described above, in the fuel cell device, the fluoride ion is likely to be generated from the fluorine-based electrolyte resin such as the perfluorosulfonic acid-based polymer. Therefore, the solid electrolyte membrane containing the fluorine-based electrolyte resin used in the fuel cell device makes the fuel cell separator of the embodiment particularly effective. Examples of the fluorine-based electrolyte resin include a perfluorosulfonic acid-based polymer and the like, and in particular, for example, Nafion (product name, manufactured by DuPont), Flemion (product name, manufactured by AGC Inc.), and Aciplex (product name, manufactured by Asahi Kasei Corporation) can be included. Among these substances, Nafion (product name, manufactured by DuPont) is usable in some embodiments due to its excellent proton conductivity properties. [Examples]

[0042] The following examples describe the embodiment. Note that the following examples do not limit the embodiment. [Example 1]

[0043] A test piece corresponding to the separator was manufactured according to a method described below. First, a 0.1 mm thick SUS447 plate was prepared as the stainless steel substrate of the separator. Next, the stainless steel substrate was mounted or installed inside a vacuum vessel. Argon gas was introduced into the vacuum vessel under a vacuum condition, a voltage was applied to generate argon ions, and an oxide film on a surface of the stainless steel substrate was removed with these argon ions.

[0044] Next, tin oxide particles and antimony oxide particles were mixed and sintered to produce a sintered body as a target, and the sintered body was placed in a vacuum vessel. Targeting this sintered body formed a tin oxide film on the surface of the stainless steel substrate by sputtering. Specifically, the stainless steel substrate was first placed in a position facing the target, and the vacuum vessel was evacuated to place the vacuum vessel under a vacuum (zero pressure) atmosphere. Next, argon gas was introduced into the vacuum vessel as a sputtering gas, and while the stainless steel substrate was heated to 450°C, a voltage was applied to cause the argon ions to collide with the target, thereby depositing the target material onto the stainless steel substrate.A bias voltage was applied between the target and the stainless steel substrate. Thus, a Sb-doped tin oxide film with a thickness of 100 nm was formed on the surface of the stainless steel substrate. The antimony content of the tin oxide film, measured using an X-ray spectrometer, was 3.0 atomic%.

[0045] Next, the stainless steel substrate on which the tin oxide film was formed was immersed in a 0.1 M trisodium phosphate solution at room temperature for 30 seconds and then dried to obtain a test piece E1 as the separator. [Comparison example 1]

[0046] A test piece C1 was prepared in a similar manner to Example 1, except that the immersion process using the trisodium phosphate solution was not carried out. <kontaktwiderstandstest>

[0047] The corrosion resistance test was performed on the respective test pieces E1 and C1 prepared in Example 1 and Comparative Example 1 in strongly acidic solutions containing fluoride ions, and their contact resistances were measured using the following method. Carbon papers (TGP-H120, TORAY INDUSTRIES, INC., thickness: 0.5 mm), which correspond to diffusion layers of the power generation units in fuel cell devices, were placed on the surfaces of the tin oxide films on the respective test pieces. Gold-plated copper plates were stacked on the carbon papers, and thus the carbon papers were sandwiched between the test pieces and the copper plates.To measure the contact resistances of the tin oxide films alone with the carbon papers, the gold-plated copper plates were also brought into contact with the other surfaces (the surfaces on which the films were not formed) of the test pieces to avoid generating contact resistances between these elements. Next, pressures with a constant load (0.98 MPa) were applied to the surfaces of the test pieces with a measuring tool. In this state, a current was flowed from a power supply while adjusting using an ammeter so that the currents flowing through the test pieces became constant. The voltages applied to the test pieces were measured by a voltmeter, and the contact resistances of the tin oxide films with the carbon papers of the test pieces were calculated. Fig. 5 presents the results.

[0048] As in Fig. 5, after a corrosion period of 60 minutes, the contact resistance of the test piece E1 to which the immersion process with the trisodium phosphate solution was carried out had a value of approximately half of the contact resistance of the test piece C1 without the immersion process, and a deterioration rate of the contact resistance of the test piece E1 was reduced to approximately 1 / 3 of a deterioration rate of the contact resistance of the test piece C1. <Korrosionsbeständigkeitstest in einer Fluoridionen enthaltenden stark sauren Lösung>

[0049] The corrosion resistance test in the strongly acidic solution containing the fluoride ion was carried out on the test pieces E1 and C1 prepared in Example 1 and Comparative Example 1, respectively, and the SUS447 plate of the stainless steel substrate (test piece C2) by the following method, and their corrosion resistances were examined using a general anode polarization test (three-pole method). First, NaF was added to sulfuric acid (pH 2) to prepare a strongly acidic solution containing fluoride ions. Subsequently, the inside of a container was filled with this strongly acidic solution, and the test pieces, a reference electrode (Ag / AgCl electrodes) and a counter electrode (Pt electrode), which were electrically connected to each other, were arranged. Next, an electric potential in this solution was changed from a natural immersion electric potential to a positive side.to positive at a constant scanning rate (20 to 40 mV / minute), and the anode polarization test was performed. The sulfuric acid solution was maintained at 80 °C during this test, and air was further introduced into the solution via a bubble tube located in the container. Fig. Figure 6 shows a relationship between the electric potential and a current density measured in this anode polarization test. The horizontal axis or X-axis indicates the electric potential relative to the reference electrode, and the vertical axis or Y-axis indicates the current density.

[0050] As in Fig. As shown in Figure 6, the test piece E1, which was subjected to the immersion process with the trisodium phosphate solution, showed the highest corrosion resistance. [Reference example]

[0051] To investigate whether substances other than trisodium phosphate have a corrosion-reducing effect, various test substances were added to the etchant (a strongly acidic solution containing fluoride ions), and the corrosion resistance test was conducted on the SUS447 plate. Trisodium phosphate, sodium metasilicate (Na2O3Si), sodium tungstate (Na2WO4), or sodium molybdate (Na2MoO4) were used as the added test substances. The concentration of each added substance was 1 mM. Specifically, the test was conducted using the following method. <Korrosionsbeständigkeitstest in einer Ätzmittel enthaltenden Testsubstanz>

[0052] The corrosion resistance test in a strong acid solution containing the test substance and fluoride ion was conducted on a SUS447 plate of a stainless steel substrate using the following procedure. First, NaF and the test substance (trisodium phosphate, sodium metasilicate, sodium tungstate, or sodium molybdate) were added at 1 mM to sulfuric acid (pH 2) to prepare a strong acid solution containing fluoride ions. Next, a container was filled with this strong acid solution, and the stainless steel substrate, reference electrodes (Ag / AgCl electrodes), and counter electrodes (Pt electrodes), which were electrically connected to each other, were placed. Next, the electric potential in this solution was changed from a natural immersion electric potential to a positive side.to positive at a constant scan rate (20 to 40 mV / minute), and the anode polarization test was performed. The sulfuric acid solution was maintained at 80 °C during this test, and air was further introduced into the solution via a bubble tube located in the container. Fig. Figure 7 shows a relationship between the electric potential and a current density measured in this anode polarization test. The horizontal axis or X-axis indicates the electric potential relative to the reference electrode, and the vertical axis or Y-axis indicates the current density.

[0053] If another test substance also provides the corrosion-reducing effect of the stainless steel substrate, similar to the trisodium phosphate in the test system, it is assumed that a corrosion current will be reduced to the same extent as the trisodium phosphate. However, compared to the trisodium phosphate, as shown in Fig. 7, the corrosion currents of the other test substances (sodium metasilicate, sodium tungstate, and sodium molybdate) are large.

[0054] While the embodiment has been described in detail, the specific arrangement is not limited to the embodiment. List of reference symbols 1 cell 2 MEGA (power generation unit) 3 Separator (fuel cell separator) 4 membrane electrode assembly (MEA) 6 Electrode 7 Gas diffusion layer 10 fuel cell stacks (fuel cell device) 21 Gas flow channel 22 Gas flow channel 31 stainless steel substrate 32 Tin oxide film 33 Defect section 34 Film (protective film)< / kontaktwiderstandstest>

Claims

[1] A method for producing a fuel cell separator (3) including a stainless steel substrate (31), comprising: Forming a tin oxide film (32) on a surface of the stainless steel substrate (31); and Bonding phosphoric acid or phosphate to at least one defect portion (33) in the tin oxide film (32), wherein the bonding comprises: contacting the stainless steel substrate (31) on which the tin oxide film (32) is formed with a solution containing the phosphoric acid or the phosphate; and Drying the stainless steel substrate (31) after contact. [2] A method for producing a fuel cell separator (3) according to claim 1, wherein the phosphate is an inorganic phosphate. [3] A method for producing a fuel cell separator (3) according to claim 2, wherein the inorganic phosphate is orthophosphate. [4] A method for producing a fuel cell separator (3) according to any one of claims 1 to 3, further comprising: Removing a passive film present on the surface of the stainless steel substrate (31) under a vacuum condition prior to forming, wherein the forming comprises forming the tin oxide film (32) while maintaining the vacuum condition. [5] Fuel cell separator (3) manufactured according to the method according to one of claims 1 to 4, wherein the fuel cell separator (3) comprises: a stainless steel substrate (31) and; a tin oxide film (32) formed on a surface of the stainless steel substrate (31), wherein phosphoric acid or phosphate binds to a defect portion (33) in the tin oxide film (32). [6] A fuel cell device (10) comprising the fuel cell separator (3) according to claim 5. [7] The fuel cell device (10) according to claim 6, further comprising a solid electrolyte membrane. [8] The fuel cell device (10) according to claim 7, wherein the solid electrolyte membrane contains a fluorine-based electrolyte resin.

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