JP2011243327A - Manufacturing method of separator and solid polymer fuel cell using separator manufactured by manufacturing method thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a manufacturing method of an inexpensive separator for a solid polymer fuel cell low in electric resistance and excellent in corrosion resistance.SOLUTION: A manufacturing method of a separator for a solid polymer fuel cell includes: a first step of processing a austenitic stainless steel; a second step of heating the austenitic stainless steel, which is processed in the first step, in a fluorine gas atmosphere; a third step of carburizing of the austenitic stainless steel, which is treated in the second step, at a temperature of 400-680°C; and a fourth step of acid-cleaning the austenitic stainless steel carburized in the third step.

Description

  The present invention relates to a method for producing a separator used in a polymer electrolyte fuel cell and a polymer electrolyte fuel cell using a separator produced by the method.

Fuel cells that extract electricity by electrochemically reacting hydrogen and oxygen are technologies that can greatly reduce carbon dioxide (CO ₂ ) emissions and are more efficient than conventional internal combustion engines. In addition, it is characterized in that it is high in quietness and emits less NO _x , SO _x, PM, etc., which cause air pollution.

  For this reason, fuel cells have been energetically researched and developed internationally as clean energy conversion devices. To date, phosphoric acid fuel cells, molten carbonate fuel cells, and solid oxide fuel cells have been developed. Fuel cells have been developed.

  Under such circumstances, in recent years, a polymer electrolyte fuel cell has attracted attention as a fuel cell suitable for small-scale power generation for automobiles and households. This solid polymer fuel cell has attracted attention because the use of a solid polymer electrolyte membrane with further improved performance dramatically improves the output density of the cell, resulting in high efficiency. This is because in addition to the characteristics of the battery, miniaturization and low-temperature operation are possible.

  The polymer electrolyte fuel cell obtains required power by connecting several tens to several hundreds of unit cells in series. The unit cell includes a solid polymer electrolyte membrane, an anode side gas diffusion electrode, a cathode side gas diffusion electrode, an anode side separator, and a cathode side separator. The anode side gas diffusion electrode and the cathode side gas diffusion electrode are arranged on both sides of the solid polymer electrolyte membrane. The anode side separator is disposed in contact with the anode side gas diffusion electrode, and the cathode side separator is disposed in contact with the cathode side gas diffusion electrode.

  Such an anode-side separator and cathode-side separator not only serve as a current collector for electrically connecting adjacent unit cells, but also function as an outer wall structural member of the unit cell. Respectively function as a passage for supplying the gas to the anode side gas diffusion electrode or the cathode side gas diffusion electrode.

  Therefore, the anode side separator and the cathode side separator are required to have mechanical strength, electrical conductivity, and corrosion resistance against a corrosive environment where the polymer electrolyte fuel cell is placed.

  Conventionally, a separator made of stainless steel has been used for the purpose of improving productivity. However, although the corrosion resistance is improved by forming a passive film on the surface of stainless steel, the electrical resistance is lowered.

  Therefore, conventionally, a separator made of stainless steel whose surface is plated with gold in order to reduce electric resistance is known (Patent Document 1). In addition, a separator made of stainless steel having a conductive carbide metal or boride metal deposited on the surface is known (Patent Document 2). Furthermore, a separator made of a metal member having a conductive carbon film formed on the surface is known (Patent Document 3). The conductive carbon film is formed by ECR (Electron Cyclotron Resonance) sputtering.

  On the other hand, for the purpose of improving corrosion resistance, a separator made of a ferritic stainless alloy whose surface is coated with titanium or a titanium alloy is known (Patent Document 4).

JP-A-10-228914 JP 2001-32056 A JP 2008-144245 A JP 2005-2411 A

  However, since the separator disclosed in Patent Document 1 is manufactured by plating gold on the surface of stainless steel, there is a problem that it is expensive.

  In addition, the separator disclosed in Patent Document 2 is produced by depositing carbide-based metal or boride-based metal on the surface of stainless steel, and thus has a problem of low corrosion resistance.

  Furthermore, in patent document 3, since a conductive carbon film is formed by ECR sputtering, there exists a problem that a separator becomes expensive.

  Furthermore, in patent document 4, it is necessary to form the coating layer which consists of a material different from stainless steel on the surface of stainless steel, and there exists a problem that a separator becomes expensive.

  Accordingly, the present invention has been made to solve such a problem, and an object of the present invention is to provide an inexpensive separator manufacturing method for a polymer electrolyte fuel cell having low electrical resistance and excellent corrosion resistance. It is to be.

  Another object of the present invention is to provide a polymer electrolyte fuel cell including an inexpensive separator having a low electric resistance and excellent corrosion resistance without using a noble metal.

  According to this invention, a separator manufacturing method is a separator manufacturing method used for a polymer electrolyte fuel cell, which includes a first step of processing austenitic stainless steel, and an austenite processed by the first step. A second step of treating the stainless steel in a heated state in a fluorine gas atmosphere, a third step of carburizing the austenitic stainless steel treated in the second step at a temperature of 400 to 680 ° C., and a third step And a fourth step of cleaning the austenitic stainless steel carburized by the acid.

  According to the invention, the polymer electrolyte fuel cell includes the separator manufactured by the manufacturing method described in claim 1.

  According to the method for manufacturing a separator according to the embodiment of the present invention, a separator is manufactured by sequentially performing processing of an austenitic stainless steel, fluorination treatment, carburization treatment, and cleaning with an acid. As a result, a carburized hardened layer is formed on the surface of the austenitic stainless steel, and a layer containing fluorine is formed on the outermost surface of the austenitic stainless steel. The manufactured separator has excellent corrosion resistance and low contact resistance almost equal to that of the carbon separator. Moreover, the manufactured separator is not manufactured through the process of forming the coating layer which consists of another material on the surface of the austenitic stainless steel which is a base material.

  Therefore, a polymer electrolyte fuel cell separator having excellent corrosion resistance and low contact resistance can be provided at low cost.

  Moreover, according to the embodiment of the present invention, a polymer electrolyte fuel cell is manufactured using an inexpensive separator having excellent corrosion resistance and low contact resistance.

  Accordingly, it is possible to provide a polymer electrolyte fuel cell including an inexpensive separator having excellent corrosion resistance and low contact resistance.

It is a flowchart which shows the manufacturing method of the separator by embodiment of this invention. It is the schematic of the processing apparatus which performs the process in step S2, S3 shown in FIG. It is a figure which shows the measurement result of the X-ray photoelectron spectroscopy of the austenitic stainless steel after various processes. It is a figure which shows the relationship between the voltage and current density of austenitic stainless steel. It is a figure which shows the measurement result of an anodic polarization curve. It is sectional drawing of the polymer electrolyte fuel cell provided with the separator manufactured by the manufacturing method shown in FIG. It is a figure which shows the output characteristic of a polymer electrolyte fuel cell. It is a figure which shows the impedance plot of a polymer electrolyte fuel cell.

  Embodiments of the present invention will be described in detail with reference to the drawings. In the drawings, the same or corresponding parts are denoted by the same reference numerals and description thereof will not be repeated.

  FIG. 1 is a flowchart showing a separator manufacturing method according to an embodiment of the present invention. Referring to FIG. 1, when the manufacture of the separator is started, austenitic stainless steel is processed (step S1). In this case, the austenitic stainless steel is processed by, for example, cutting or pressing. By this processing, a flow path for flowing hydrogen gas or air (or oxygen gas) is formed, and a separator is manufactured.

  Then, the processed austenitic stainless steel is treated in a heated state in a fluorine gas atmosphere (step S2).

  Thereafter, the austenitic stainless steel treated in the fluorine gas atmosphere is carburized at a temperature of 400 to 680 ° C. (step S3).

  Subsequently, the austenitic stainless steel after the carburizing treatment is washed with an acid (step S4). Thereby, a separator is manufactured.

  In the embodiment of the present invention, the austenitic stainless steel is SUS316, SUS316L, SUS317, 5-6% by weight molybdenum containing 1-3% by weight molybdenum, and 0.1-0. Stainless steel containing 4 wt% nitrogen (N), 22-25 wt% nickel (Ni), and molybdenum free, 13-25 wt% chromium (Cr), and 8-22 wt% Ni SUS304, SUS310, etc. including these.

  FIG. 2 is a schematic diagram of a processing apparatus that performs the processes in steps S2 and S3 shown in FIG. Referring to FIG. 2, the processing apparatus 100 includes a muffle furnace 1, a vacuum pump 13, an exhaust gas processing apparatus 14, cylinders 15 and 16, a flow meter 17, and a valve 18. The muffle furnace 1 includes an outer shell 2, a heater 3, an inner container 4, a gas introduction pipe 5, an exhaust pipe 6, a motor 7, a fan 8, and a car 11. The car 11 is made of wire mesh.

A stainless steel product 10 made of austenitic stainless steel is placed in a car 11 of a muffle furnace 1, a cylinder 16 is connected to a flow path, and a fluorine-based gas such as NF _{3 is} passed through a flow meter 17, a valve 18 and a gas introduction pipe 5. It introduce | transduces in the muffle furnace 1, The stainless steel product 10 is fluorinated while heating.

  Thereafter, the fluorine-based gas introduced into the muffle furnace 1 is exhausted from the exhaust pipe 6 by the vacuum pump 13, and the fluorine-based gas is detoxified in the exhaust gas treatment device 14 and released to the outside.

Next, the cylinder 15 is connected to the flow path, and a carburizing gas composed of H ₂ gas, CO gas, and CO ₂ gas is introduced into the muffle furnace 1 through the flow meter 17, the valve 18, and the gas introduction pipe 5. Carburizing treatment is performed.

  Thereafter, the gas is discharged to the outside via the exhaust pipe 6 and the exhaust gas treatment device 14. By this series of operations, fluorination treatment and carburization treatment are performed.

  By performing such a fluorination treatment and a carburizing treatment, a diffusion penetration layer (carburization hardening layer) of “carbon” is uniformly formed on the surface of the austenitic stainless steel. This carburized hardened layer is in a state in which a large amount of carbon atoms are dissolved in the austenite phase, which is the matrix phase, causing lattice distortion, and the hardness is significantly improved compared to the matrix, and more than that of the matrix. Demonstrate the corrosion resistance.

  Details of the fluorination treatment and the carburization treatment will be described. A SUS316 plate piece, which is a typical austenitic stainless steel, was used as a sample, and SUS316 was placed in the muffle furnace 1 of the processing apparatus 100 shown in FIG. 2 to perform fluorination treatment and carburization treatment.

More specifically, SUS316 is fluorinated at 350 ° C. for 20 minutes in a fluorine-based gas atmosphere of NF ₃ + N ₂ (NF ₃ : 10 vol%, N ₂ : 90 vol%). Then, after exhausting the fluorine-based gas from the muffle furnace 1, a mixed gas composed of CO + CO ₂ + H ₂ which is a carburizing gas (CO: 38 vol% + CO ₂ : 2 vol% + H ₂ : 60 vol%) is used in the muffle furnace 1. It was introduced into the inside and kept at 450 ° C. for 18 hours to perform carburizing treatment.

  As a result of subjecting the carburized SUS316 to the salt spray test of JIS 2371, no rusting occurred even after 480 hours. Moreover, the carburized hardened layer formed by the carburizing treatment was not etched even by the Birla reagent (acidic picric alcohol solution) used for the corrosion resistance test of the stainless steel structure.

  As a result of investigating by changing the kind of austenitic stainless steel and the temperature of carburizing treatment, it was found that the temperature of carburizing treatment is suitably 680 ° C. or less. It has been confirmed that when the temperature of the carburizing treatment exceeds 680 ° C., the core portion of the austenitic stainless steel is extremely easily softened and the corrosion resistance of the carburized hardened layer is significantly reduced. Therefore, from the viewpoint of corrosion resistance, the temperature of the carburizing treatment is preferably 680 ° C. or less, more preferably 500 ° C. or less, and even more preferably 400 to 500 ° C.

  As a result, in the embodiment of the present invention, as shown in step S2 of FIG. 1, carburization of austenitic stainless steel is performed at a temperature of 400 to 680 ° C.

Further, the acid cleaning shown in step S3 of FIG. 1 is performed under the following conditions. Austenitic stainless steel is immersed in a solution composed of 5 volume% HF + 25 volume% HNO ₃ at room temperature for 20 minutes to clean the austenitic stainless steel after carburizing treatment.

  In addition, you may perform the washing | cleaning by an acid in the state heated at 50 degreeC. As the acid used for washing, various acids such as hydrofluoric acid, nitric acid, hydrochloric acid and sulfuric acid are used. And these acids may be used independently and may be used as liquid mixture, such as nitric acid + hydrofluoric acid, nitric acid + hydrochloric acid, and sulfuric acid + nitric acid. Further, electrolytic treatment using an electrolytic solution such as nitric acid and sulfuric acid may be performed.

  FIG. 3 is a diagram showing measurement results of X-ray photoelectron spectroscopy of austenitic stainless steel after various treatments.

  (A) of FIG. 3 is a measurement result of the X-ray photoelectron spectroscopy of the austenitic stainless steel which performed the process of step S2-S4 shown in FIG. Moreover, (b) of FIG. 3 is the measurement result of the X-ray photoelectron spectroscopy of the austenitic stainless steel which performed the surface polishing process after the process of step S1-S3 shown in FIG. Further, (c) of FIG. 3 is a measurement result of X-ray photoelectron spectroscopy of the austenitic stainless steel subjected to the processing of only step S1 shown in FIG.

  The surface polishing treatment was performed by spraying fine alumina powder for about 1 to 2 minutes under an air pressure of 0.5 MPa. Further, the time shown in FIG. 3 is an etching time by Ar ions.

  Referring to FIG. 3, in the austenitic stainless steel subjected to fluorination treatment, carburization treatment and pickling, a peak due to fluorine was observed around 685.5 eV in the range of the etching time up to 60 s ((a )reference). This is considered to be because the fluorine used in the fluorination treatment shown in step S2 of FIG. 1 remains.

  On the other hand, in the austenitic stainless steel subjected to fluorination treatment, carburization treatment, pickling and polishing treatment, no peak due to fluorine was observed (see FIG. 3B). This is considered to be because the layer containing fluorine was removed by the polishing treatment.

  Further, in the austenitic stainless steel subjected to only the fluorination treatment, a peak (peak near 688 eV) caused by fluorine continues to be observed even after etching for 500 seconds or more (see (c) of FIG. 3). Therefore, it is considered that an austenitic stainless steel that has undergone only fluorination treatment has a much thicker film than austenitic stainless steel that has undergone fluorination treatment, carburization treatment, and pickling.

  Thus, it was found that the austenitic stainless steel subjected to fluorination treatment, carburization treatment and pickling has a fluorine-containing layer on the surface layer.

  FIG. 4 is a diagram showing the relationship between voltage and current density of austenitic stainless steel. In FIG. 4, the vertical axis represents voltage, and the horizontal axis represents current density. Moreover, the straight line group k1 shows the relationship between the voltage and current density of raw austenitic stainless steel. Furthermore, the straight line group k2 shows the relationship between the voltage and current density of austenitic stainless steel that has undergone only fluorination treatment. Furthermore, the straight line group k3 (triangle) shows the relationship between the voltage and current density of the austenitic stainless steel subjected to the fluorination treatment and the carburization treatment. Furthermore, the straight line group k4 (except for the triangle) shows the relationship between the voltage and current density of austenitic stainless steel subjected to fluorination treatment, carburization treatment and pickling. Furthermore, the straight line group k5 shows the relationship between the voltage and current density of austenitic stainless steel subjected to fluorination treatment, carburization treatment, pickling and surface polishing.

The relationship between voltage and current density shown in FIG. 4 was measured by the following method using a four-terminal method. A carbon paper (EC-TP1-060T) used for MEA (Membrane Electrode Assembly) of a fuel cell is brought into contact with one side of austenitic stainless steel, and a pressure of about 1 MPa is applied to the austenitic stainless steel, and ± 1 [A / cm ² The current density was scanned at a scanning speed of 0.2 [A / cm ² / s] in the current density range, and the relationship between voltage and current density was measured.

Referring to FIG. 4, raw austenitic stainless steel has a contact resistance of about 41 mΩ · cm ² (see straight line group k1).

Moreover, the austenitic stainless steel which performed only the fluorination process has a high contact resistance of about 0.9 ohm * cm < ² > (refer linear source k2).

Furthermore, the austenitic stainless steel subjected to the fluorination treatment and the carburization treatment has a contact resistance of about 3 mΩ · cm ² (see the straight line group k3).

Furthermore, the austenitic stainless steel subjected to the fluorination treatment, the carburization treatment and the pickling has a contact resistance of about 3 mΩ · cm ² (see the straight line group k4).

Further, the austenitic stainless steel subjected to fluorination treatment, carburization treatment, pickling and surface polishing has a contact resistance of about 90 mΩ · cm ² (see the straight line group k5).

In addition, although not shown in FIG. 4, as a result of performing the same measurement on the carbon separator, the contact resistance was ² mΩ · cm ² .

Since austenitic stainless steel was carried out only fluorination treatment is particularly thick film from the measurement results of X-ray photoelectron spectroscopy (see FIG. 3 (c)), a large contact resistance of about 0.9Ω · cm ^2, the coating Corresponds to the thick.

  Carburizing treatment subsequent to fluorination treatment reduces the thickness of the coating, resulting in lower contact resistance. In order to reduce the contact resistance, it is important to perform a carburizing process after the fluorination process.

  As described above, the austenitic stainless steel subjected to the fluorination treatment, the carburizing treatment, and the pickling has a low contact resistance substantially equal to that of the carbon separator. As described above, this is considered to be because a layer containing fluorine exists on the outermost surface of the austenitic stainless steel that has been subjected to fluorination treatment, carburization treatment, and pickling.

  Therefore, it has been found that an austenitic stainless steel having low contact resistance can be obtained by subjecting the austenitic stainless steel to fluorination treatment, carburizing treatment and pickling.

  FIG. 5 is a diagram showing the measurement results of the anodic polarization curve. In FIG. 5, the vertical axis represents the current density, and the horizontal axis represents the potential with respect to the reference electrode. A curve k6 shows an anodic polarization curve of austenitic stainless steel that has been subjected to fluorination treatment and carburization treatment. Further, a curve k7 shows an anodic polarization curve of austenitic stainless steel subjected to fluorination treatment, carburization treatment and pickling. Further, a curve k8 shows an anodic polarization curve of austenitic stainless steel subjected to fluorination treatment, carburization treatment, pickling and surface polishing. Furthermore, the curve k9 shows the anodic polarization curve of raw austenitic stainless steel. Further, a curve k10 shows an anodic polarization curve of austenitic stainless steel that has been subjected only to the fluorination treatment.

  The anodic polarization curve shown in FIG. 5 is obtained when the reference electrode made of Ag / AgCl, the counter electrode made of platinum, and each austenitic stainless steel are immersed in an electrolyte solution made of 1N sulfuric acid aqueous solution, and then 24 hours have passed. The measurement was performed at room temperature and a sweep rate of 20 mV / s with the natural potential as the sweep start potential.

  Referring to FIG. 5, a relatively flat region up to around 0.9 V is called a passive state region. The current observed in this passive region is called the passive state maintaining current, and is used to repair the amount reduced by the chemical dissolution of the passive film. The smaller the passive state maintaining current, the slower the chemical dissolution and the higher the corrosion resistance.

  Further, in FIG. 5, the region on the right side of the vicinity of 1V is referred to as the overpassive region. In this overpassive region, the passive film is oxidized and dissolved. It is desirable that the rise of the current value in this overpassive region is on the high potential side.

  The austenitic stainless steel (curve k6) subjected to the fluorination treatment and the carburizing treatment has a larger passive state maintaining current than the austenitic stainless steel (curve k7) subjected to the fluorination treatment, carburization treatment and pickling. In addition, austenitic stainless steel (curve k10) subjected to only fluorination treatment also has a passive state maintaining current larger than austenitic stainless steel (curve k7) subjected to fluorination treatment, carburization treatment and pickling.

  However, austenitic stainless steel (curve k6) shows a response close to that of austenitic stainless steel (curve k7) in the second and subsequent potential scans. Therefore, it is considered that the austenitic stainless steel (curve k6) does not have a large passive state maintaining current but a current due to oxidation removal of the surface product generated during the fluorination treatment and the carburizing treatment. Pickling is considered to be effective in removing easily oxidizable substances generated on the surface.

  The austenitic stainless steel (curve k8) subjected to fluorination treatment, carburizing treatment, pickling and surface polishing has a lower passive state maintaining current than the austenitic stainless steel (curve k7). This is because the surface of the austenitic stainless steel (curve k7) is relatively rough, whereas the surface of the austenitic stainless steel (curve k8) is smoothed by the polishing finish, so the austenitic stainless steel (curve k8). ) The actual surface area per unit area is smaller than that of austenitic stainless steel (curve k7), and the current density per actual surface area is the same for austenitic stainless steel (curve k7) and austenitic stainless steel (curve k8). This is because the apparent current per unit area of the austenitic stainless steel (curve k8), that is, the current density, is smaller than that of the austenitic stainless steel (curve k7).

  Since the austenitic stainless steel (curve k7) and the austenitic stainless steel (curve k8) are relatively close to the behavior of the standard austenitic stainless steel (curve k9), the carburizing treatment is performed at a potential of up to 1 V under the above-described experimental conditions. If it is in the range, it is considered that the corrosion resistance of the substrate is not adversely affected.

  As described above, it has been found that the austenitic stainless steel subjected to fluorination treatment, carburization treatment and pickling has excellent corrosion resistance and low contact resistance. In this austenitic stainless steel, a coating layer made of a different material is not formed on the surface.

  Therefore, by manufacturing the separator using the manufacturing method shown in FIG. 1, an inexpensive separator having excellent corrosion resistance and low contact resistance can be provided.

  And as shown in FIG. 1, after performing a fluorination process, a carburizing process, and pickling, it is important to manufacture a separator, without surface-polishing. If the surface polishing is not performed, the fluorine-containing layer is not removed (see FIG. 3), and the separator has low contact resistance (see FIG. 4) and excellent corrosion resistance (see FIG. 5).

  6 is a cross-sectional view of a polymer electrolyte fuel cell including a separator manufactured by the manufacturing method shown in FIG. Referring to FIG. 6, the solid polymer fuel cell 200 includes a solid polymer electrolyte membrane 110, gas diffusion electrodes 120 and 130, separators 140 and 150, and gaskets 160 and 170.

  The gas diffusion electrode 120 carries a catalyst 180 on one main surface thereof, and is disposed on one side of the solid polymer electrolyte membrane 110 so that the catalyst 180 is in contact with one surface of the solid polymer electrolyte membrane 110. The gas diffusion electrode 130 carries a catalyst 190 on one main surface thereof, and is disposed on the other side of the solid polymer electrolyte membrane 110 so that the catalyst 190 is in contact with the other surface of the solid polymer electrolyte membrane 110.

  The separator 140 is manufactured by the manufacturing method shown in FIG. 1 and is disposed so as to be in contact with one main surface of the gas diffusion electrode 120 (one main surface opposite to the one main surface on which the catalyst 180 is supported). The separator 150 is manufactured by the manufacturing method shown in FIG. 1 and is disposed so as to be in contact with one main surface of the gas diffusion electrode 130 (one main surface opposite to the one main surface on which the catalyst 190 is supported).

  The gasket 160 is provided between the outer periphery of the solid polymer electrolyte membrane 110 and the outer periphery of the separator 140, and maintains the airtightness to connect the outer periphery of the separator 140 to the outer periphery of the solid polymer electrolyte membrane 110. . The gasket 170 is provided between the outer periphery of the solid polymer electrolyte membrane 110 and the outer periphery of the separator 150, and maintains the airtightness to connect the outer periphery of the separator 150 to the outer periphery of the solid polymer electrolyte membrane 110. .

  The solid polymer electrolyte membrane 110 is made of, for example, a fluorine ion exchange membrane. Each of the gas diffusion electrodes 120 and 130 is made of a porous body having gas permeability and conductivity. Each of the catalysts 180 and 190 is made of platinum (Pt) or a platinum alloy (Pt—Ru). Each of the gaskets 160 and 170 is made of any one of fluororesin, Viton rubber, silicon rubber, ethylene propylene rubber, and the like. More specifically, the fluororesin is, for example, polytetrafluoroethylene (PTFE), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA), or the like. It is.

The solid polymer electrolyte membrane 110 allows only the hydrogen ions H ⁺ out of the electrons e ⁻ and hydrogen ions H ⁺ separated by the catalyst 180 to pass to the catalyst 190 side. The gas diffusion electrode 120 diffuses the hydrogen gas supplied from the separator 140 into the catalyst 180. The catalyst 180 separates the hydrogen gas supplied to the gas diffusion electrode 120 into electrons e ⁻ and hydrogen ions H ⁺ .

The gas diffusion electrode 130 diffuses air (or oxygen) supplied from the separator 150 into the catalyst 190. The catalyst 190 reacts the hydrogen ions H ⁺ supplied from the solid polymer electrolyte membrane 110 with the electrons e ⁻ supplied from the gas diffusion electrode 130 and air (or oxygen) to generate water.

  The separator 140 has a gas supply groove 140 </ b> A having a concavo-convex structure on one main surface in contact with the gas diffusion electrode 120. The separator 140 supplies hydrogen gas to the gas diffusion electrode 120 via the gas supply groove 140A.

  The separator 150 has a gas supply groove 150 </ b> A having a concavo-convex structure on one main surface in contact with the gas diffusion electrode 130. The separator 150 supplies air (or oxygen) to the gas diffusion electrode 130 via the gas supply groove 150A.

An operation of generating power by the polymer electrolyte fuel cell 100 will be described. When hydrogen is supplied to the gas diffusion electrode 120 via the gas supply groove 140A of the separator 140, the gas diffusion electrode 120 diffuses hydrogen gas into the catalyst 180, and the catalyst 180 converts hydrogen into hydrogen ions H ⁺ and electrons e. ^- is separated into a.

Then, the solid polymer electrolyte membrane 110 transmits only the hydrogen ions H ⁺ out of the hydrogen ions H ⁺ and electrons e ⁻ separated by the catalyst 180 and supplies them to the catalyst 190. On the other hand, the electrons e ⁻ move from the catalyst 180 to the separator 140 via the gas diffusion electrode 120 and flow from the separator 140 to the separator 150 via an external load (not shown). Then, the separator 150 supplies the electron e ⁻ to the gas diffusion electrode 130.

Air (or oxygen) is supplied to the gas diffusion electrode 130 via the gas supply groove 150 </ b> A of the separator 150. The gas diffusion electrode 130 diffuses air (or oxygen) into the catalyst 190 and supplies electrons e ⁻ to the catalyst 190.

Then, the hydrogen ions H ⁺ , air (or oxygen), and electrons e ⁻ react with the help of the catalyst 190 to become water.

  In this way, the polymer electrolyte fuel cell 200 generates electricity.

  FIG. 7 is a graph showing output characteristics of the polymer electrolyte fuel cell. In FIG. 7, the vertical axis represents cell voltage, and the horizontal axis represents current density and current.

  The black triangles indicate the output characteristics of a polymer electrolyte fuel cell using a separator made of austenitic stainless steel subjected to fluorination treatment, carburization treatment, pickling and surface polishing.

  Further, white circles indicate the output characteristics of a polymer electrolyte fuel cell using a separator made of austenitic stainless steel that has been fluorinated, carburized, and pickled.

  Further, the black squares indicate the output characteristics of the polymer electrolyte fuel cell using the carbon separator.

  Furthermore, the white rhombus shows the output characteristics of a polymer electrolyte fuel cell using a separator made of austenitic stainless steel subjected to only fluorination treatment.

  The output characteristics shown in FIG. 7 are output characteristics during power generation at a dew point of 65 ° C. and an operating temperature of 70 ° C.

  Referring to FIG. 7, the cell voltage of a polymer electrolyte fuel cell (for comparison) using a separator made of austenitic stainless steel subjected to fluorination treatment, carburization treatment, pickling and surface polishing is increased in current density. Abruptly decreases with this (see black triangle).

  In addition, the output characteristics of the polymer electrolyte fuel cell (for comparison) using a separator made of austenitic stainless steel subjected to only fluorination treatment is very low (see white rhombus).

  On the other hand, the cell voltage of the polymer electrolyte fuel cell 200 using a separator made of austenitic stainless steel subjected to fluorination treatment, carburization treatment, and pickling gradually decreases as the current density increases (see white circles). ). The cell voltage of the polymer electrolyte fuel cell 200 is higher than the cell voltage of the polymer electrolyte fuel cell (for comparison) at each current density. The difference from the cell voltage of the type fuel cell (for comparison) increases as the current density increases. Further, the cell voltage of the polymer electrolyte fuel cell 200 is substantially equal to the cell voltage of the polymer electrolyte fuel cell using the carbon separator (see white circles and black squares).

  Therefore, it was found that the polymer electrolyte fuel cell 200 has higher output characteristics than the polymer electrolyte fuel cell (for comparison) and is equivalent to the polymer electrolyte fuel cell using the carbon separator.

  FIG. 8 is a diagram showing an impedance plot of the polymer electrolyte fuel cell. In FIG. 8, the vertical axis and the horizontal axis represent impedance. A curve k11 shows an impedance plot of the polymer electrolyte fuel cell 200. Curves k12 and k14 show impedance plots of the polymer electrolyte fuel cell (for comparison). A curve k13 shows an impedance plot of a polymer electrolyte fuel cell using a carbon separator.

The impedance plot shown in FIG. 8 is an impedance plot during power generation at a current density of 0.08 [A / cm ² ].

  Referring to FIG. 8, Rs1 of the polymer electrolyte fuel cell 200 is 5.9 mΩ (see curve k11), and Rs2 of the polymer electrolyte fuel cell (for comparison) is 48 mΩ (see curve k12). ), Rs4 of the polymer electrolyte fuel cell (for comparison) is 93 mΩ (see curve k14), and Rs3 of the polymer electrolyte fuel cell using the carbon separator is 5.0 mΩ (curve k13). reference).

  Rs1 to Rs3 reflect the contact resistance of the separator. Further, Rs4 of the polymer electrolyte fuel cell using a separator made of austenitic stainless steel subjected to only fluorination treatment reflects a high contact resistance. Therefore, the contact resistance of the polymer electrolyte fuel cell 200 is smaller than the contact resistance of the polymer electrolyte fuel cell (for comparison), and is almost equal to the contact resistance of the polymer electrolyte fuel cell using the carbon separator. .

  As a result, it was demonstrated that a separator made of austenitic stainless steel subjected to fluorination treatment, carburization treatment and pickling has a low contact resistance in a device called a polymer electrolyte fuel cell.

  As described above, the austenitic stainless steel subjected to fluorination treatment, carburization treatment and pickling has a carburized hardened layer on the surface side and a layer containing fluorine on the outermost surface. As a result, a separator made of austenitic stainless steel subjected to fluorination treatment, carburization treatment and pickling has excellent corrosion resistance and low contact resistance. The polymer electrolyte fuel cell 200 is almost equivalent to a polymer electrolyte fuel cell using a carbon separator due to the low contact resistance of a separator made of austenitic stainless steel subjected to fluorination treatment, carburization treatment and pickling. Has output characteristics. The polymer electrolyte fuel cell 200 has high reliability due to the excellent corrosion resistance of the separator made of austenitic stainless steel subjected to fluorination treatment, carburization treatment and pickling.

  Therefore, by using the manufacturing method shown in FIG. 1, a separator for a polymer electrolyte fuel cell having low electrical resistance and excellent corrosion resistance can be provided at low cost.

  Further, as described above, in order to produce an austenitic stainless steel suitable for a separator of a polymer electrolyte fuel cell, fluorination treatment, carburization treatment and pickling are performed, and surface polishing after pickling is not performed. is important.

  This is because if the surface polishing is performed, the output characteristics of the polymer electrolyte fuel cell are lowered (see the black triangle in FIG. 7), and Rs is increased to 48 mΩ.

  Moreover, it is because only the fluorination treatment causes the output characteristics of the polymer electrolyte fuel cell to be extremely deteriorated (see the white rhombus in FIG. 7), and Rs becomes as large as 93 mΩ.

  The inventors of the present application have found that an austenitic stainless steel suitable for a separator of a polymer electrolyte fuel cell is manufactured by performing fluorination treatment, carburization treatment, and pickling.

  The embodiment disclosed this time should be considered as illustrative in all points and not restrictive. The scope of the present invention is shown not by the above description of the embodiments but by the scope of claims for patent, and is intended to include meanings equivalent to the scope of claims for patent and all modifications within the scope.

  The present invention is applied to a method for producing a separator for a polymer electrolyte fuel cell. The present invention is also applied to a polymer electrolyte fuel cell having a separator.

  1 Muffle furnace, 2 outer shell, 3 heater, 4 inner vessel, 5 gas introduction pipe, 6 exhaust pipe, 7 motor, 8 fan, 10 stainless steel product, 11 cage, 13 vacuum pump, 14 exhaust gas treatment device, 15, 16 cylinder , 17 flow meter, 18 valve, 100 processing device, 110 solid polymer electrolyte membrane, 120, 130 gas diffusion electrode, 140, 150 separator, 140A, 150A gas supply groove, 160, 170 gasket, 180, 190 catalyst, 200 solid Polymer fuel cell.

Claims (2)

A method for producing a separator used in a polymer electrolyte fuel cell,
A first step of processing austenitic stainless steel;
A second step of treating the austenitic stainless steel processed by the first step in a heated state in a fluorine gas atmosphere;
A third step of carburizing the austenitic stainless steel treated in the second step at a temperature of 400 to 680 ° C .;
A separator manufacturing method comprising: a fourth step of washing the austenitic stainless steel carburized in the third step with an acid.   A polymer electrolyte fuel cell comprising a separator produced by the production method according to claim 1.

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