JP5192908B2 - Titanium substrate for fuel cell separator, fuel cell separator, and fuel cell separator manufacturing method - Google Patents

Description

  The present invention relates to a titanium substrate for a fuel cell separator used for a separator of a fuel cell, a fuel cell separator using the titanium substrate, and a method for producing the fuel cell separator.

  Unlike a primary battery such as a dry battery or a secondary battery such as a lead storage battery, a fuel cell can continuously extract electric power by continuously supplying a fuel such as hydrogen and an oxidant such as oxygen. Therefore, the fuel cell is expected to be an energy source that covers various uses and scales because it has high power generation efficiency, is not significantly affected by the size of the system, and has little noise and vibration. Specifically, the fuel cell includes a polymer electrolyte fuel cell (PEFC), an alkaline electrolyte fuel cell (AFC), a phosphoric acid fuel cell (PAFC), a molten carbonate fuel cell (MCFC), a solid fuel cell. It has been developed as an oxide fuel cell (SOFC), biofuel cell, and the like.

  A solid polymer fuel cell will be described as an example of a fuel cell. The solid polymer fuel cell includes an anode electrode on both sides of a solid polymer film that is an electrolyte, and a catalyst layer serving as a cathode electrode, A gas diffusion layer is provided on the outside, and a separator (or bipolar plate) having a fuel gas flow path formed on the outside is provided.

  Solid polymer fuel cells are being developed mainly for fuel cell vehicles, home cogeneration systems, mobile phones and personal computers. To increase output, it is necessary to increase the number of fuel cell stacks. . Therefore, it is desired to reduce the size and weight of the separator used in the polymer electrolyte fuel cell. In addition, the separator used in the polymer electrolyte fuel cell not only functions as a gas flow path but also serves as a current extractor. Therefore, an interface phenomenon occurs between the contact resistance (electrode (catalyst layer) and the separator surface). Therefore, it is desired that the low contact resistance be maintained for a long time during use.

  In view of the above demand, conventionally, a metal substrate made of a metal plate such as an aluminum alloy, stainless steel, nickel alloy, or titanium alloy is used for the separator in consideration of workability and strength. For example, when a pure titanium plate is used, the thickness of the metal substrate (metal plate) per separator is set to 0.3 mm or less.

Patent Documents 1 to 3 describe a fuel cell separator having the following configuration. Patent Document 1 describes a fuel cell separator using stainless steel as a base material and gold-plated on the surface thereof. Patent Document 2 describes a fuel cell separator in which a noble metal or a noble metal alloy is adhered after a stainless steel or titanium material is used as a base material and the oxide film on the surface thereof is removed. Further, Patent Document 3 describes a fuel cell separator in which a titanium base material is used as a base material and an oxide film on the surface thereof is removed, and then island-shaped gold plating portions of 1 to 100 nm are scattered. .
JP-A-10-228914 JP 2001-6713 A JP 2006-97088 A

  However, metal substrates made of metal plates such as aluminum alloy, stainless steel, nickel alloy, and titanium alloy are exposed to severe environments such as high temperature, high pressure, and strong acidity when used as fuel cell separators. There is a tendency that the contact resistance is remarkably increased by an oxide film or the like formed on the surface. Therefore, separators using these metal substrates cannot maintain the contact resistance for a long time even if the contact resistance at the beginning of use is low, and the contact resistance increases with time, resulting in a current loss of the fuel cell. I was there. Further, due to corrosion, the solid polymer electrolyte membrane has been deteriorated by metal ions eluted from the metal substrate.

  Also, in the base materials described in Patent Documents 1 to 3, it is possible to reduce the contact resistance at the beginning of use, but when exposed to a harsh environment, the gold plating layer on the surface of the base material is peeled off. As a result, the contact resistance is increased, which may cause a current loss of the fuel cell. Further, the gold plating layer or the like is peeled off to cause corrosion, and there is a possibility that the solid polymer electrolyte membrane is deteriorated by metal ions eluted from the base material.

  Under such circumstances, the present inventor, while researching a base material for producing a thin plate separator, applied a noble metal film made of noble metal such as gold on the surface of a titanium plate made of pure titanium or titanium alloy. A titanium substrate for a fuel cell separator capable of maintaining a low contact resistance for a long period of time even when used in a severe environment by forming and heat-treating it under conditions of, for example, 300 to 800 ° C. is found. It came to.

  However, in the manufacture of a titanium base material for a fuel cell separator, the titanium plate is manufactured by cold rolling using a lubricating oil, and has a thickness of 0.3 mm or less, for example. Since the lubricating oil contains carbon, depending on the manufacturing conditions (rolling conditions), carbon is mechanochemically bonded to the surface of the titanium plate to form a large amount of titanium carbide, and the carbon concentration of the titanium plate surface layer May be higher.

  Usually, titanium plates are inevitably oxidized when they come into contact with the atmosphere, and an oxide film having excellent acid resistance mainly composed of titanium oxide is formed. And since titanium carbide is inferior in acid resistance compared with a titanium oxide, when many such titanium carbides are formed, formation of an oxide film will be inhibited and the function which an oxide film performs will be lost.

  And when a titanium plate with a large amount of titanium carbide is used to form a noble metal film on the surface of the titanium plate and, for example, heat treatment is performed at 300 to 800 ° C. to produce a fuel cell separator, noble metal An oxide film having an oxygen-deficient titanium oxide crystallized under the film (which will be described in detail later) is not formed. Further, since the oxide film is not formed, aggregation is likely to occur in the conductive noble metal film, and the noble metal film is scattered in an island shape.

  When such a fuel cell separator is exposed to a high temperature, high pressure, and strong acid atmosphere, the titanium plate constituting the fuel cell separator is corroded and oxidized (hereinafter referred to as corrosion) in proportion to the exposure time. A thick oxide film is formed on the surface of the plate, increasing the contact resistance of the fuel cell separator. This is because, even if a noble metal film having high corrosion resistance and excellent conductivity is formed on a titanium plate, if the thickness of the noble metal film is not increased, corrosion proceeds from the pinhole of the noble metal film, and the corrosion etc. This is because the titanium plate under the noble metal film also moves to the noble metal film interface. On the other hand, when the thickness of the noble metal film is increased, the cost is increased. That is, a fuel cell separator using a titanium plate having a high surface layer carbon concentration (relatively high titanium carbide formation ratio) has a problem that a low contact resistance cannot be maintained for a long time.

  The present invention has been made in view of the above problems, and its object is to provide a titanium substrate for a fuel cell separator that can maintain a low contact resistance for a long period of time even when a titanium plate having a high surface carbon concentration is used. Another object of the present invention is to provide a fuel cell separator using the substrate and a method for producing the fuel cell separator.

  In order to solve the above-mentioned problems, a titanium substrate for a fuel cell separator according to the present invention is a titanium substrate for a fuel cell separator used for a fuel cell separator having a noble metal film, and is an X-ray photoelectron from the surface to a predetermined depth. A titanium plate made of pure titanium or a titanium alloy having a binding energy of 280 to 284 eV measured by spectroscopic analysis having a concentration of 5 atomic% or more, and formed on the surface of the titanium plate, selected from titanium and zirconium It comprises a metal film having a film thickness of 15 to 500 nm made of one or more metals and an oxide film made of the metal oxide and formed on the surface of the metal film.

  According to the said structure, it consists of the metal film which consists of 1 or more types of metals chosen from the titanium and zirconium of the predetermined film thickness formed in the surface of a titanium plate, and the metal oxide formed in the surface of a metal film. By providing the oxide film, the metal film and the oxide film serve as a protective film, and the surface of the titanium plate having a high carbon concentration and low acid resistance can be isolated from the surrounding environment. As a result, the acid resistance of the titanium base material is improved.

  In addition, even when a noble metal film is formed on the surface of the titanium base material during production of the fuel cell separator, an oxide film is formed between the titanium plate having a high carbon concentration and the noble metal film. There is almost no carbon having a binding energy of 280 to 284 eV on the surface, and the noble metal film does not aggregate. As a result, even when the fuel cell separator is used in a high temperature, high pressure, strong acid atmosphere, the conductive noble metal film is not peeled off, so that corrosion or the like does not progress on the titanium plate surface. As a result, the contact resistance of the fuel cell separator can be kept low. Further, when the fuel cell separator is manufactured, oxygen in the oxide film diffuses into the titanium plate and oxygen-deficient titanium oxide is formed in the oxide film, so that the conductivity of the oxide film is improved. As a result, the contact resistance of the fuel cell separator can be kept low. Furthermore, since the oxide film blocks hydrogen entering through the noble metal film, hydrogen embrittlement of the titanium plate can be suppressed.

  Moreover, the fuel cell separator according to the present invention is formed on the surface of the titanium base material for a fuel cell separator according to claim 1 and the titanium base material for the fuel cell separator, and is one or more selected from gold and platinum. And a noble metal film having a thickness of 5 to 200 nm made of a noble metal.

  According to the said structure, the contact resistance of a separator becomes low with the electroconductivity of a noble metal film by providing the noble metal film of the predetermined film thickness which consists of 1 or more types of noble metals chosen from gold | metal | money and platinum. In addition, since the oxide film formed on the surface of the titanium base material is not exposed to the atmosphere (acid atmosphere) due to the formation of the noble metal film, the oxygen-deficient titanium oxide in the oxide film is exposed to the atmosphere (acid atmosphere). Is suppressed from being supplied with oxygen. As a result, since the conductivity of the oxide film is not impaired, the contact resistance of the fuel cell separator can be kept low. Further, since the noble metal film is composed of one or more kinds of noble metals selected from gold and platinum, the noble metal film does not corrode (gold, platinum or an alloy thereof is eluted) under the use environment of the fuel cell.

  The method for producing a fuel cell separator according to the present invention comprises pure titanium or a titanium alloy having a carbon concentration having a binding energy of 280 to 284 eV, measured by X-ray photoelectron spectroscopy from the surface to a predetermined depth, of 5 atomic% or more. A metal film forming step of forming a metal film made of one or more metals selected from titanium and zirconium on the surface of the titanium plate having a film thickness of 15 to 500 nm; and a surface of the metal film from the metal oxide. Forming an oxide film to form a titanium substrate for a fuel cell separator, and the surface of the oxide film of the fuel cell separator substrate is made of one or more precious metals selected from gold and platinum A noble metal film forming step of forming a noble metal film with a film thickness of 5 to 200 nm; and the fuel cell separator on which the noble metal film is formed. The use of titanium substrate, characterized in that it comprises a heat treatment step of heat-treating at 300 to 600 ° C..

  According to the above procedure, the metal film forming step of forming a metal film made of one or more metals selected from titanium and zirconium on the surface of the titanium plate with a predetermined film thickness, and the surface of the metal film is made of a metal oxide. By including the oxide film forming step for forming the oxide film, the surface of the titanium plate having a high carbon concentration is covered with the metal film and the oxide film, and the surface of the titanium base material is almost free of carbon. As a result, even when a noble metal film made of one or more kinds of noble metals selected from gold and platinum is formed on the surface of the titanium base material, no aggregation occurs in the noble metal film. The subsequent heat treatment forms oxygen-deficient titanium oxide in the oxide film and improves the conductivity of the oxide film, thereby reducing the contact resistance of the fuel cell separator.

  According to the titanium base material for a fuel cell separator according to the present invention, contact resistance can be kept low by using a titanium plate having a high carbon concentration in the surface layer by forming a metal film and an oxide film on the surface of the titanium plate. . Thereby, when this titanium substrate is used for a fuel cell separator, the contact resistance of the separator can be kept low for a long time.

  Moreover, according to the fuel cell separator according to the present invention, a low contact resistance can be maintained for a long time by providing a noble metal film on the surface of the titanium substrate having the above-described configuration.

  Furthermore, according to the method of manufacturing a fuel cell separator according to the present invention, a fuel capable of maintaining a low contact resistance for a long time by including a metal film forming process, an oxide film forming process, a noble metal film forming process, and a heat treatment process. A battery separator can be manufactured.

  A titanium substrate for a fuel cell separator, a fuel cell separator, and a method for producing the fuel cell separator according to the present invention will be described with reference to the drawings. Here, FIG. 1A is a cross-sectional view showing the structure of a titanium substrate for a fuel cell separator, FIG. 1B is a cross-sectional view showing the structure of the fuel cell separator, and FIG. 2 is a process flow showing a method for manufacturing the fuel cell separator. It is.

<Titanium substrate for fuel cell separator>
As shown in FIG. 1 (a), a titanium substrate for a fuel cell separator (hereinafter referred to as a titanium substrate) 1 includes a titanium plate 2, a metal film 3 formed on the surface of the titanium plate 2, and a metal film. 3 and the oxide film 4 formed on the surface. In the present invention, the term “surface” is used to include both one side and both sides.

(Titanium plate)
The titanium plate 2 is made of pure titanium or a titanium alloy, and the plate thickness is preferably 0.05 to 0.3 mm in order to make the fuel cell separator (fuel cell) used light and compact. Such a thin titanium plate is manufactured by cold rolling using a lubricating oil, etc., and carbon contained in the lubricating oil is mechanochemically bonded to the surface of the titanium plate 2 to form titanium carbide. Therefore, the region from the surface to a predetermined depth, that is, the carbon concentration in the surface layer is increased. Specifically, the carbon concentration is 5 atomic% or more. Here, the predetermined depth is about 100 to 200 nm.

Such carbon has a binding energy of 280 to 284 eV. The carbon concentration is measured by X-ray photoelectron spectroscopy. For example, X-ray source: monochromatic Al-Kα, X-ray output: 43.7 W, X-ray beam diameter: 200 μm, photoelectron extraction angle: 45 °, Ar ⁺ sputtering rate: about 4.6 nm / min in terms of SiO ₂ Under the measurement conditions, X-ray photoelectron spectroscopy is performed to measure the composition of the four elements of Ti, O, C, and N on the surface layer (region from the surface to about 100 to 200 nm), and thereby the C concentration (atomic%) ). In general, X-ray photoelectron spectroscopy can measure only a few nm in depth. Therefore, when measuring to a depth of 100 nm or 200 nm, it is better to measure the surface while performing Ar ⁺ sputtering.

(Metal film)
The metal film 3 is formed on the surface of the titanium plate 2 and is composed of one or more metals selected from titanium and zirconium (titanium, zirconium, or alloys thereof). As a result, the surface of the titanium plate 2 with poor acid resistance and high carbon concentration (having titanium carbide) is shielded from high temperature, high pressure, and strong acid atmosphere, and the titanium oxide has better acid resistance than titanium carbide described later. And / or oxide film 4 composed of zirconium oxide is formed.

  The film thickness of the metal film 3 is 15 to 500 nm. If the film thickness is less than 15 nm, there are many pinholes in the metal film 3, so that oxygen enters from the pinholes, corrodes the titanium plate 2, and the contact resistance of the titanium substrate 1 increases. Moreover, even if the film thickness exceeds 500 nm, there is no change in the action of blocking the titanium plate 2 from the high temperature, high pressure, strong acid atmosphere and the action of forming the oxide film, but instead of the titanium plate 2 (metal film 3). Productivity decreases. Moreover, although the film thickness of the metal film 3 is dependent also on the surface roughness of the titanium plate 2, 20-300 nm is preferable and 30-200 nm is the most preferable.

(Oxide film)
The oxide film 4 is formed on the surface of the metal film 3, constitutes the surface of the titanium substrate 1, and is made of an oxide of a metal constituting the metal film 3. Since the oxide film 4 is made of a metal oxide (titanium oxide and / or zirconium oxide) constituting the metal film 3, the surface of the titanium plate 2 made of titanium carbide has better acid resistance than titanium carbide. Since it can be covered with a film of oxide (titanium oxide and / or zirconium oxide), the acid resistance of the titanium substrate 1 is improved. Moreover, the oxide (titanium oxide and / or zirconium oxide) constituting the oxide film reduces the contact resistance of the titanium substrate 1 for the following reason.

  When a noble metal film is formed on the surface of the oxide film 4 at the time of manufacturing a fuel cell separator 11 (see FIG. 1B), which will be described later, and heat treatment is performed at a temperature of 300 to 600 ° C., the oxide film 4 The oxygen therein diffuses into the metal film 3 and the titanium plate 2 to form oxygen-deficient titanium oxide and / or zirconium oxide. Since this oxygen-deficient metal oxide functions as an n-type semiconductor, the contact resistance of the titanium substrate 1 (fuel cell separator 11) is reduced.

  Further, when the fuel cell separator 11 is used in a high temperature, high pressure, strong acid atmosphere, the noble metal film 12 formed on the surface of the oxide film 4 allows hydrogen to pass through, so that hydrogen diffuses the noble metal film 12 and titanium. It penetrates into the substrate 1. Therefore, the titanium plate 2 may cause hydrogen embrittlement. However, when the oxide film 4 exists between the noble metal film 12 and the titanium plate 2, the oxide film serves as a barrier layer and suppresses the entry of hydrogen, so that the titanium plate 2 is less likely to be hydrogen embrittled.

  The film thickness of the oxide film 4 is preferably 3 nm or more. When the film thickness is less than 3 nm, the barrier property of the oxide film 4 becomes insufficient, hydrogen enters, and the titanium plate 2 is liable to be hydrogen embrittled.

<Fuel cell separator>
As shown in FIG. 1B, a fuel cell separator (hereinafter referred to as a separator) 11 includes a titanium substrate 1 and a noble metal film 12 formed on the surface of the titanium substrate 1. In the present invention, the term “surface” is used to include both one side and both sides. Here, since the titanium substrate 1 is as described above, the description thereof is omitted.

(Precious metal film)
The noble metal film 12 is formed on the surface of the titanium substrate 1 and is made of one or more kinds of noble metals (gold, platinum or alloys thereof) selected from gold and platinum. Thereby, the contact resistance of the separator 11 becomes low. Further, since the noble metal film 12 is composed of a noble metal, the noble metal is not eluted even when the separator 11 is used in a high temperature, high pressure, and strong acid atmosphere, so that no corrosion or the like occurs in the noble metal film 12. .

  The noble metal film 12 has a thickness of 5 to 200 nm. When the film thickness is less than 5 nm, when the separator 11 is used in a high temperature, high pressure, strong acid atmosphere, the noble metal film 12 is agglomerated and the noble metal film 12 is peeled off, and the titanium substrate 1 is corroded. Will occur. Further, since oxygen is supplied from the atmosphere side to the oxygen-deficient metal oxide in the oxide film, the conductivity of the oxide film is lowered. As a result, the contact resistance of the separator 11 is increased. Further, even if the film thickness exceeds 200 nm, the rate of decrease in contact resistance does not change, and instead the productivity of the separator 11 (noble metal film 12) decreases.

<Method for producing fuel cell separator>
As shown in FIG. 3, the fuel cell separator manufacturing method includes a metal film forming step S1, an oxide film forming step S2, a noble metal film forming step S3, and a heat treatment step S4. Hereinafter, each step will be described.

(Metal film forming step: S1)
In the metal film forming step S1, the concentration of carbon having a binding energy of 280 to 284 eV measured by X-ray photoelectron spectroscopy analysis from the surface to a predetermined depth, that is, pure titanium or titanium having a surface layer carbon concentration of 5 atomic% or more This is a step of forming a metal film made of one or more metals selected from titanium and zirconium (titanium, zirconium or alloys thereof) with a film thickness of 15 to 500 nm on the surface of a titanium plate made of an alloy.

  The PVD method can be used as a method for forming (depositing) the metal film. In order to form a highly dense metal film, an ion plating method or a sputtering method is preferable. If a metal film having a predetermined thickness can be formed, the method is not limited to the PVD method, and for example, a CVD method may be used. Note that the PVD method is preferably performed with a low oxygen partial pressure in the deposition chamber.

(Oxide film forming step: S2)
The oxide film forming step S2 is a step of forming an oxide film made of an oxide of the metal constituting the metal film on the surface of the metal film formed in the previous step S1 to form a titanium substrate for a fuel cell separator. is there. And the formation (film formation) method of the oxide film is formed by oxidizing the surface of the metal film by exposing the surface of the metal film formed in the previous step S1 to the atmosphere or immersing it in an acidic aqueous solution. (Film formation). Preferably, it is performed by introducing oxygen or air into the film forming chamber used in the previous step S1.

(Precious metal film forming step: S3)
The noble metal film forming step S3 is made of one or more kinds of noble metals (gold, platinum or alloys thereof) selected from gold and platinum on the surface of the oxide film of the titanium base material for a fuel cell separator manufactured in the previous step S2. This is a step of forming a noble metal film with a film thickness of 5 to 200 nm. A PVD method can be used as a method for forming (depositing) the noble metal film. In order to form a highly dense noble metal film, an ion plating method or a sputtering method is preferable. As long as a noble metal film having a predetermined thickness can be formed, the method is not limited to the PVD method, and for example, a CVD method may be used.

(Heat treatment step: S4)
The heat treatment step S4 is a step of heat-treating the fuel cell separator base material on which the noble metal film is formed at 300 to 600 ° C. to obtain a fuel cell separator. Then, after the precious metal film is formed, when heat treatment is performed at 300 to 600 ° C., as described above, oxygen in the oxide film diffuses and oxygen-deficient metal oxide (titanium oxide and / or zirconium oxide). And the conductivity of the oxide film is improved. When the heat treatment temperature is less than 300 ° C., the diffusion of oxygen is slow, the oxygen-deficient metal oxide is not formed, and the conductivity of the oxide film is not improved. On the other hand, when the heat treatment temperature exceeds 600 ° C., the diffusion of oxygen is too fast and the oxide film disappears, so that the effect of preventing hydrogen absorption is lost.

  The heat treatment atmosphere is preferably 1.33 Pa or less and more preferably 0.133 Pa or less because the durability of the noble metal film is higher when the oxygen partial pressure is lower. However, since gold, platinum or an alloy thereof constituting the noble metal film is not oxidized, it may be heat-treated in the atmosphere.

  Further, the heat treatment time t (min) is (420−T) / 40 ≦ t ≦ 2/3 · exp {(806.4−T) / when 300 ≦ T ≦ 600, assuming that the heat treatment temperature is T (° C.). 109.2} and t ≧ 0.5. When the heat treatment time is shorter than the above range, the oxygen-deficient metal oxide is not easily formed, and the conductivity of the oxide film tends to be insufficiently improved. On the other hand, if the above range is exceeded, the oxide film may disappear. Specifically, when the heat treatment temperature is 400 ° C., the heat treatment time is preferably 0.5 to 27.6 minutes.

Next, examples of the present invention will be described.
<Examples 1-7>
Seven types of titanium plates (No. 1-7, plate thickness 0.15 mm) manufactured under the conditions shown in Table 1 were prepared using JIS H 4600 standard titanium material and cut into a size of 20 × 50 mm. And ultrasonically cleaned in acetone. And the carbon (C) density | concentration (atomic%) of each titanium plate surface layer was measured as follows. The results are shown in Table 1.

The measurement of the C concentration on the surface layer of the titanium plate was performed by X-ray photoelectron spectroscopic analysis using a fully automatic traveling X-ray photoelectron spectroscopic analyzer (Quantera SXM manufactured by Physical Electronics). The measurement conditions of X-ray photoelectron spectroscopy are as follows. As for the C concentration of the titanium plate surface layer, the composition of the depth from the surface to the depth of 100 nm was analyzed for the four elements of Ti, O, C, and N, and the maximum value of the C concentration analysis value was determined as the C concentration of the titanium plate surface layer. Concentration (atomic%) was used.
(Measurement conditions for X-ray photoelectron spectroscopy)
X-ray source: Monochromatic Al-Kα
X-ray output: 43.7W
X-ray beam diameter: 200 μm
Photoelectron extraction angle: 45 °
Ar ⁺ sputtering rate: about 4.6 nm / min in terms of SiO ₂

  Next, a metal film is formed on the surface of each titanium plate (No. 1 to 7) by sputtering using titanium (Ti), zirconium (Zr), and an alloy of titanium and zirconium (Ti-Zr alloy) as a target material. Membrane was performed.

First, a titanium plate was individually attached to a substrate stand in a chamber of a magnetron sputtering apparatus, and one of Ti, Zr, and Ti—Zr alloy target materials was attached to an electrode in the chamber. Thereafter, the inside of the chamber was evacuated to a vacuum of 0.00133 Pa (1 × 10 ⁻⁵ Torr) or less. And Ar gas was introduce | transduced in the chamber and it adjusted so that a pressure might be set to 0.266 Pa (2 * 10 < ^-3 > Torr). Then, sputtering of the target material was performed by applying DC (direct current voltage) to the electrode to which the target material was attached to excite Ar gas and generating Ar plasma. Other target materials were also sputtered by the same method as described above to form a metal film made of Ti, Zr, Ti—Zr alloy on the surface of the titanium plate.

  The chamber was opened to the atmosphere, and an oxide film was formed (film formation) on the surface of the metal film. Then, the titanium plate was turned over, and the same metal film and oxide film were formed on the other surface of the titanium plate in the same manner as described above to obtain a titanium substrate for a fuel cell separator. The film types and film thicknesses of the metal film and oxide film are shown in Table 2.

  Next, the target material is replaced with gold (Au), and sputtering is performed in the same manner as described above to form a noble metal film made of Au with a film thickness of 10 nm on both surfaces of the titanium base material for the fuel cell separator (film formation). did. And after putting the titanium base material for fuel cell separators in which the noble metal film was formed into a vacuum heat treatment furnace, exhausting the pressure in the furnace to 0.0133 Pa or less, and heating at 400 ° C. for 5 minutes, Manufactured.

<Reference example>
A titanium plate (No. 8) was prepared by pickling the titanium plate (No. 5) to remove carbon on the surface layer and setting the C concentration of the surface layer of the titanium plate to 3 atomic%. A titanium film for a fuel cell separator was formed without forming (depositing) a metal film or an oxide film on the surface of the titanium plate (No. 8). In the same manner as in Example 6, a noble metal film made of Au was formed (film formation) on both surfaces of the titanium base material for the fuel cell separator, followed by heat treatment to produce a fuel cell separator.

<Comparative Example 1>
A fuel cell separator was manufactured in the same manner as in Example 6 except that a metal film and an oxide film were not formed (film formation) on both surfaces of the titanium plate (No. 5).
<Comparative example 2>
A fuel cell separator was produced in the same manner as in Example 6 except that the thickness of the metal film made of Ti was 5 nm outside the scope of the claims.

  Next, when the surface of the fuel cell separator (Examples 1 to 7, Reference Example, Comparative Examples 1 and 2) was observed with an FE-SEM (acceleration voltage 20 keV, magnification 10,000 times), Examples 1 to 7 and Reference Example In Comparative Example 2, almost no pinholes were observed in the noble metal (Au) film. On the other hand, in Comparative Example 1, agglomeration of Au was observed in the noble metal film, and many pinholes were observed.

Further, when the cross section of the fuel cell separator was observed by TEM, in Examples 1, 3, 5, 6, Reference Example, and Comparative Example 2, an oxide film made of titanium oxide (TiO ₂ ) was recognized immediately below the noble metal film. In Examples 2, 4, and 8, an oxide film made of zirconium oxide (ZrO ₂ ) is recognized immediately under the noble metal film, and in Example 7, titanium oxide (TiO ₂ ) and zirconium oxide are directly under the noble metal film. An oxide film composed of (ZrO ₂ ) was observed. On the other hand, in Comparative Example 1, no oxide film was observed immediately below the noble metal film.

  Next, the contact resistance of the fuel cell separators (Examples 1 to 7, Reference Examples, Comparative Examples 1 and 2) was measured using the contact resistance measuring device 30 shown in FIG. FIG. 3 is a diagram schematically showing the configuration of the contact resistance measuring device.

(Contact resistance measurement procedure)
As shown in FIG. 3, each fuel cell separator 11 is sandwiched between carbon cloth C and C on both sides, and the outside is pressurized with 98 N (10 kgf) using copper electrodes 31 and 31 having a contact area of 1 cm ² . Electricity of 7.4 mA was applied using the direct current power source 32, the voltage applied between the carbon cloths C and C was measured with the voltmeter 33, and the contact resistance was calculated. The contact resistance before heat treatment was measured and calculated in the same manner. The results are shown in Table 2.

These fuel cell separators were immersed in an aqueous sulfuric acid solution (pH 2) at 80 ° C. for 1000 hours, and the contact resistance of each fuel cell separator was measured in the same manner as described above. In addition, the contact resistance after immersion was 10 mΩ · cm ² or less. The results are shown in Table 2.

From the results of Table 2, Examples 1-7, the contact resistance by heat treatment is reduced from 11~14mΩ · cm ² to 4~5mΩ · cm ^2, showed good contact resistance. Moreover, it was confirmed that Examples 1-7 can maintain 10 mohm * cm < ² > or less whose contact resistance is an acceptance | permission reference | standard after immersion in sulfuric acid aqueous solution.

On the other hand, Comparative Example 1 showed low contact resistance without heat treatment, but the carbon concentration of the titanium plate was as high as 33 atomic%, and no metal film or oxide film was formed on the surface of the titanium plate. A lot of pinholes were formed in the noble metal film. As a result, under the immersion in sulfuric acid aqueous solution, the corrosion of the titanium plate progressed through the pinhole, and the contact resistance increased greatly. In Comparative Example 2, a decrease in contact resistance was observed due to heat treatment. However, since the metal film was too thin, many pinholes were formed in the metal film. As a result, under immersion in a sulfuric acid aqueous solution, corrosion of the titanium plate proceeds through the pinhole, and the contact resistance is 10 mΩ. cm ² was exceeded.

Incidentally, reference examples, the contact resistance by heat treatment is reduced from 11mΩ · cm ² to 5 m [Omega · cm ^2, after sulfuric acid aqueous solution immersion, maintained a low contact resistance. However, productivity is not good because the titanium plate needs to be cleaned.

  In this way, even if the carbon concentration of the surface layer of the titanium plate is high, if a noble metal film is formed after forming a metal film and an oxide film on the surface of the titanium plate and then heat-treated, stable and low contact resistance can be obtained. It was confirmed that it can be obtained.

<Examples 9 to 13>
Using the titanium plate (No. 3) in Table 1, a metal film made of Ti was formed on the surface thereof by the same sputtering method as in Example 3, and then the chamber was opened to the atmosphere to form an oxide film made of TiO _2. Was formed into a titanium substrate for a fuel cell separator. The metal film and oxide film were formed on both sides of the titanium plate. The film types and film thicknesses of the metal film and oxide film are shown in Table 3. Various kinds of precious metal films made of gold (Au), platinum (Pt), and an alloy of gold and platinum (Au—Pt alloy) are formed on the surface of the titanium base material for the fuel cell separator by the same sputtering method as in Example 3. After forming a film with a thickness and exhausting the pressure in the furnace to 0.00013 Pa or less using a heat treatment furnace, the fuel cell separator was manufactured by heating at 500 ° C. for 2 minutes. Table 3 shows the film type and film thickness of the noble metal film.

<Comparative Example 3>
A fuel cell separator was produced in the same manner as in Example 9, except that the thickness of the noble metal film was 3 nm outside the scope of the claims.
<Comparative example 4>
A fuel cell separator was produced in the same manner as in Example 11 except that the thickness of the noble metal film was 2 nm outside the scope of the claims.

Next, when the surface of the fuel cell separator (Examples 9 to 13 and Comparative Examples 3 to 4) was observed with an FE-SEM (acceleration voltage 20 keV, magnification 10,000 times), Examples 9 to 13 and Comparative Examples 3 to 4 were used. , Almost no pinholes were observed in the noble metal (Au, Pt or Au—Pt alloy) film. Moreover, when the fuel cell separator was cross-sectionally observed by TEM, in Examples 9 to 13 and Comparative Examples 3 to 4, an oxide film made of titanium oxide (TiO ₂ ) was recognized immediately below the noble metal film.

  Further, the contact resistances of the fuel cell separators (Examples 9 to 13 and Comparative Examples 3 to 4) were measured and calculated using the contact resistance measuring device 30 shown in FIG. The contact resistance before heat treatment and after immersion in a sulfuric acid aqueous solution was measured and calculated in the same manner. The results are shown in Table 3.

From the results of Table 3, Examples 9-13, contact resistance by heat treatment is reduced from 10~13mΩ · cm ² to 4~5mΩ · cm ^2, showed good contact resistance. Moreover, it was confirmed that Examples 9-13 can maintain 10 mohm * cm < ² > or less whose contact resistance is an acceptance | permission reference | standard after immersion in sulfuric acid aqueous solution.

  On the other hand, in Comparative Examples 3 and 4, since the film thickness of the noble metal film was too thin, agglomeration of Au or Pt occurred in the noble metal film and the noble metal film was peeled off under sulfuric acid immersion, and titanium for fuel cell separator Corrosion progressed on the substrate. Moreover, since oxygen was supplied from the sulfuric acid aqueous solution side to the oxygen-deficient titanium oxide in the oxide film, the conductivity of the oxide film was lowered. As a result, the contact resistance of the fuel cell separator increased.

(A) Sectional drawing which shows the structure of the titanium base material for fuel cell separators which concerns on this invention, (b) is sectional drawing which shows the structure of a fuel cell separator. It is a process flow which shows the manufacturing method of the fuel cell separator which concerns on this invention. It is a figure which shows typically the structure of a contact resistance measuring apparatus.

Explanation of symbols

1 Titanium substrate for fuel cell separator (titanium substrate)
2 Titanium plate 3 Metal film 4 Oxide film 11 Fuel cell separator (separator)
12 Noble metal film S1 Metal film formation process S2 Oxide film formation process S3 Noble metal film formation process S4 Heat treatment process

Claims (3)

A titanium base material for a fuel cell separator used for a fuel cell separator provided with a noble metal coating,
A titanium plate made of pure titanium or a titanium alloy having a carbon concentration of 280 to 284 eV measured by X-ray photoelectron spectroscopy from the surface to a predetermined depth of 5 atomic% or more;
A metal film having a film thickness of 15 to 500 nm formed on the surface of the titanium plate and made of one or more metals selected from titanium and zirconium;
A titanium base material for a fuel cell separator, comprising: an oxide film formed on the surface of the metal film and made of an oxide of the metal. A titanium substrate for a fuel cell separator according to claim 1;
A fuel cell separator, comprising: a noble metal film having a thickness of 5 to 200 nm formed on a surface of the titanium base material for the fuel cell separator and made of one or more kinds of noble metals selected from gold and platinum. Selected from titanium and zirconium on the surface of a titanium plate made of pure titanium or a titanium alloy having a carbon concentration of 280 to 284 eV measured by X-ray photoelectron spectroscopy from the surface to a predetermined depth and having a bond energy of 5 atomic% or more A metal film forming step of forming a metal film composed of one or more kinds of metals having a film thickness of 15 to 500 nm;
On the surface of the metal film, an oxide film forming step of forming an oxide film made of the metal oxide to form a titanium substrate for a fuel cell separator;
A noble metal film forming step of forming a noble metal film made of one or more kinds of noble metals selected from gold and platinum on the surface of the oxide film of the titanium base material for the fuel cell separator with a film thickness of 5 to 200 nm;
And a heat treatment step of heat-treating the titanium base material for a fuel cell separator on which the noble metal film is formed at 300 to 600 ° C.

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