JP2002075399A - Separator for solid polymer electrolyte fuel cell - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a low-cost, highly durable, and highly anti-corrosive metal separator for solid polymer electrolyte fuel cell by forming an additive element concentrated layer on the surface of an iron based alloy containing an anti-corro sive element, oxidizing it, and forming an anti-corrosive layer. SOLUTION: This metal separator with improve anti-corrosivity is so formed that the surface of a base metal 1 composed of the iron-based alloy containing at least one kind out of chromium, nickel, titanium, niobium, aluminum and silicon is etched to form the concentration layer 2 having concentrated additive element concentration in the vicinity of the surface. The formation of the additive element concentrated layer can bring out higher anti-corrosivity than the original anti-corrosivity of the base metal with less quantity of the additive element.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a fuel cell separator, and more particularly to a separator material suitable for a solid polymer electrolyte type fuel cell.

[0002]

2. Description of the Related Art Among various types of fuel cells, a solid polymer electrolyte fuel cell has a membrane solid electrolyte composed of a polymer sandwiched between carbon electrodes carrying a catalyst such as platinum.
Further, this is a structure in which a flow path for the hydrogen gas and the oxidizing gas (oxygen or air) of the fuel is formed, and a pair of separators having a current collecting action sandwich the fuel gas. This is called a single cell, and a fuel cell stack is formed by stacking a plurality of these single cells.

Conventionally, artificial graphite or the like having excellent corrosion resistance has been used as a separator. However, recently, from the viewpoint of cost reduction, a method using a metal as a separator material has been developed.

However, when a practical metal such as iron-based or nickel-based or aluminum is adopted as the metal material,
As the operation time of the battery elapses, protons generated at the electrode interface corrode the separator.

Furthermore, metal ions generated by corrosion are fixed to ion exchange groups of the electrolyte membrane, which block the passage of protons, so that the membrane resistance increases and the battery performance may deteriorate.

Although a metal separator can be expected as a method of reducing cost, it is necessary to suppress corrosion in order to use a metal. Many metal surface treatment methods have been invented to prevent this. However, in the surface treatment method described here, since the separator also has a function as a current collector, it is necessary to maintain conductivity even after the surface treatment.

The technique described in Japanese Patent Application Laid-Open No. 05-182679 is a method of coating a metal having corrosion resistance and conductivity on a substrate metal having poor corrosion resistance. The technique described in JP-A-08-222237 is a method for improving corrosion resistance by coating an electrically conductive material on the front and back surfaces of a metal material.

In particular, as an example using plating, see Japanese Patent Application Laid-Open No.
00-036309, JP-A-2000-10045
2, JP-A-2000-106197, JP-A-10-228914, JP-A-11-126621
JP, JP-A-11-126622, JP-A-11-126622
162478.

For the same purpose, carbon or carbon paint is applied to improve corrosion resistance.
JP-A-310471, JP-A-07-272731, JP-A-10-255823, JP-A-10-2
No. 55823, Japanese Unexamined Patent Publication No. 11-12018,
JP-A-11-144744, JP-A-11-345
618 and JP-A-11-345618.

When the surface coating material is an oxide conductor,
JP-A-07-153470, JP-A-07-201
340, JP-A-07-296827, and JP-A-11-273693.

In addition, as examples of coating with ceramics and the like, see JP-A-08-203544 and JP-A-10-
JP-A-0745527, JP-A-11-126620, JP-A-11-162479, and JP-A-11-2
No. 60382, JP-A-11-260383 and the like, and JP-A-11-12 coated with a resin or the like.
9396, and Japanese Patent Application Laid-Open No. 11-268075.

Each of the inventions described in these publications is an invention for protecting a metal substrate from corrosion.

[0013]

The above-mentioned various metal surface treatments may not have sufficient corrosion resistance and durability.
There is a sufficient method when it is used for an object such as a fuel cell for an automobile that has a substantial operating time of less than 5000 hours until its life, but for a relatively long time such as a distributed power source,
Continuously used fuel cells require tens of thousands of hours of durability.

[0014] In addition, considering that cost reduction is indispensable for the spread of fuel cells, a low-cost substrate material and a low-cost surface treatment method can provide tens of thousands of hours of durability. It is necessary to develop a separator having the same.

An object of the present invention is to provide corrosion resistance by increasing the concentration of additional elements on a metal surface by using means for etching the surface of an iron-based alloy. Further, it is to oxidize, nitride, carbonize or borate to strengthen the acid resistance of the passivation film on the surface and to provide more corrosion resistance.

[0016]

In order to solve the above-mentioned problems, in the present invention, an iron-based alloy is used for a separator of a solid polymer electrolyte fuel cell, and a concentrated layer of an additive element is formed on the surface of the separator. Thereby, a separator and a solid polymer electrolyte fuel cell having improved corrosion resistance can be obtained. Hereinafter, some aspects of the means will be described.

As a first embodiment, in a separator which plays a role of forming a flow path of a fuel gas and an oxidizing gas (oxygen or air) and collecting current in a solid polymer electrolyte fuel cell, the separator is made of an iron-based alloy. I do. After processing this alloy into the shape of a separator, it is etched. This selectively dissolves iron near the separator surface, increases the concentration of the added element on the surface, and is expected to improve corrosion resistance.

As a second aspect, in a separator that plays a role of forming a flow path of a fuel gas and an oxidizing gas of a solid polymer electrolyte fuel cell and performing a current collecting function, the separator is an iron-based alloy, The oxide film is formed of an oxide film, a hydroxide film, and an oxyhydroxide film formed by the additive element, and the concentration of the additive element on the metal side of the interface between the film and the metal is a mixing ratio of iron and the additive element. Use a higher concentration.

In a third embodiment, the separator is further formed with an inorganic film on the surface of the separator by at least one of oxidation, nitridation, carbonization and boration. This increases the thickness of the barrier separating the environment and the material, thereby further improving the corrosion resistance.

As a fourth embodiment, an additional element for converting an oxide film formed on the alloy into an impurity semiconductor is added to the iron-based alloy. As a result, an oxide film having electron conductivity is obtained, so that corrosion resistance and conductivity can be maintained.

As a fifth aspect, the outermost surface of the fuel cell separator is coated with a coating layer having electron conductivity to protect the base metal layer of the separator from corrosion.

In a sixth aspect, the iron-based alloy adds at least one element of chromium, nickel, aluminum, titanium, zirconium, niobium, tungsten, and silicon.

According to a seventh aspect, the composition of the alloy is at least one element of 12 wt% or more of chromium and 2 to 5 wt% of titanium or 2 to 5 wt% of aluminum, or a combination of the above elements. Iron-based alloy.

Hereinafter, the operation of the present invention will be described. A fuel cell is a battery that uses an electromotive force generated between the electrodes in which a hydrogen gas and an oxidizing gas (oxygen or air) are oxidized and reduced by separate electrodes, respectively.

Here, the electrode on the hydrogen gas side is called a hydrogen electrode, and the electrode on the oxidant gas side is called an oxygen electrode. These electrodes are generally made of a catalytic metal such as platinum having a low hydrogen overvoltage and a low oxygen overvoltage. In a solid polymer electrolyte fuel cell, the hydrogen electrode and the oxygen electrode
What carries fine particles of platinum on carbon is used.

Both electrodes are sandwiched by a polymer membrane made of an ion exchange resin having no ion conductivity but having ion conductivity. There is a feature of a solid polymer electrolyte fuel cell in that a solid polymer is used for the ion conductive portion.

The separator has a role of a flow path for hydrogen gas and oxygen gas and a function of flowing current generated by a battery reaction. Conventionally, a graphite-based material has been used for the separator, but it is advantageous to use a metal in view of cost.

On the other hand, practical metals have a disadvantage that they are easily corroded. When hydrogen molecules as fuel are oxidized, they become protons. At the interface where the separator and the electrode are in contact, the proton concentration is considered to be extremely high, and there is a concern that the hydrogen-producing type corrosion reaction proceeds and the separator corrodes.

The disadvantages of metals are not only that they corrode, but also that metal ions, which are corrosion products, migrate to the polymer electrolyte membrane and are trapped by ion exchange groups. The easiness of ion exchange in the ion exchange resin is represented by a selectivity coefficient. The larger the ion radius and the higher the ionic valence, the stronger the tendency to bind to the exchange group of the ion exchange resin.

That is, the ion-exchange group has the property of binding more strongly to the metal ion than to the proton. Therefore, the path through which the protons should originally pass is blocked by the metal ions, and the proton conductivity is reduced. As a result, the electric resistance of the film increases with the progress of corrosion, and there is a possibility that current cannot pass.

As described above, in order to use a metal as a separator, it is essential to suppress corrosion.
Noble metals typified by platinum and the like have excellent acid resistance in a non-oxidizing environment, but conventional practical metal materials such as stainless steel have poor acid resistance.

Usually, there are excellent metallic materials such as high nickel-high chromium stainless steel and nickel-based chromium-molybdenum alloy as practical materials for sulfuric acid resistance and hydrochloric acid resistance, but they are accompanied by some ion elution. . Furthermore, in the case of a fuel cell, it must be noted that the separator is used in a polarized state because the separator is in electrical contact with the electrode.

[0033] Stainless steels, especially high chromium-high nickel steels, have significantly poorer corrosion resistance in the overpassivation region, and in some cases worse than passivated carbon steel. This is because nickel and chromium contained in this alloy
This is because they are eluted as ions in a potential range relatively lower than the potential of the oxygen generation reaction.

That is, there is a disadvantage that the ion elution amount in the actual working potential range is extremely large. As described above, nickel (divalent or trivalent) ions and chromium (hexavalent as chromic acid) ions both have a large ionic radius and valence, so that it is expected that the proton blocking effect in the membrane will increase.

A similar phenomenon is concerned on the hydrogen electrode side. Since the potential region on the hydrogen electrode side exactly matches the active region of stainless steel, the amount of metal ions eluted is large. However, depending on the type of steel, the active maximum current density may be smaller than the transpassive current density, so that the influence of active dissolution may be reduced.

Although the problems of practical alloys have been described above using stainless steel as an example, nickel-base-chromium-molybdenum alloys, which have much higher acid resistance than stainless steel, show the same tendency. On the other hand, titanium, zirconium, and niobium are completely corrosion resistant in a sulfuric acid aqueous solution having a pH of about 1.

However, the price of titanium is about an order of magnitude higher than SUS304, which is the most common stainless steel, and the price of nickel-base-chromium-molybdenum alloy is about twice that of titanium. Therefore, it is difficult to select these materials.

Considering the cost, it is important to focus on the steel material. In the present invention, the corrosion resistance of the separator is improved by characteristically performing the surface treatment of the iron-based alloy.

In the first embodiment described above, for example, an iron-based alloy containing at least one of additional elements such as titanium, niobium, zirconium, aluminum, chromium, nickel, and silicon having excellent sulfuric acid resistance is used. .

Among these additional elements, chromium is an element capable of improving the corrosion resistance of iron, and when it contains 12 wt% or more, the corrosion resistance is remarkably improved. In the case of titanium, niobium, zirconium or aluminum, increasing the amount of addition to about 10 wt% can be expected to improve corrosion resistance, but in exchange for this, it becomes hard and brittle, and the workability becomes extremely poor. The practical addition amount varies depending on the element, but approximately 3 wt.
%.

Since the corrosion resistance cannot be expected to be improved with the added amount as it is, the surface of the steel containing several wt% of the above-mentioned element is gently treated by etching means such as chemical etching or electrolytic polishing.

As a result, iron having poor corrosion resistance is preferentially dissolved, and as a result, a layer in which the additive element is concentrated on the surface is formed. This makes it possible to improve corrosion resistance with a small amount of expensive element added.

As another additive element, nickel is
It has an important function for forming austenite having excellent machinability. By adding an appropriate amount, an austenite phase can be obtained.

Although silicon does not directly contribute to corrosion resistance, as described in the following embodiment, when forming an anti-corrosion oxide film by oxidizing an alloy, the growth of an oxide film mainly composed of iron-chromium is suppressed, and It has a function to help excellent film formation.

In the second embodiment, in the iron-based alloy to which the additive element is added as described in the first embodiment, a concentrated layer of the additive element is formed near the surface. Since the additive element having excellent corrosion resistance is concentrated on the surface, an oxide film (passive film) formed on the alloy surface is formed of any of the oxide, hydroxide, and oxyhydroxide formed by the additive element, or Formed in combination, it can provide even more corrosion resistance.

This is formed of three layers: a metal base material / a concentrated layer / an oxide film (passive film) layer, and the concentration of the additive element in the concentrated layer is higher than the concentration calculated from the mixing ratio of iron and the additive element. It is achieved by doing.

In the third embodiment, the metal material of the first and second embodiments is subjected to oxidation, nitridation, carbonization or boride treatment. Since a thick inorganic coating layer is formed on the surface by any of these treatments, a barrier separating the metal base material and the environment is strengthened, and more corrosion resistance can be imparted.

The film on the new surface, such as immediately after polishing, does not have a thickness of several atomic layers, but the film can be grown to the order of microns by the above-mentioned treatment. As a result, the function of preventing corrosive ions from reaching the metal base material is increased.
When nitrides or carbides are formed, many of them have excellent electron conductivity, so that they can also wait for an excellent current collecting function.

In the fourth embodiment, an element capable of forming an impurity semiconductor is added to the iron-based alloy in order to improve the electron conductivity of the film formed in the first and second embodiments. For example, when an iron-titanium alloy is oxidized, a film mainly composed of titanium dioxide is formed on the surface of the alloy. However, since this film is a semiconductor, it may have poor electron conductivity.

When, for example, niobium is added to the alloy, a composite oxide film of titanium oxide-niobium oxide is formed,
It is considered that it becomes an n-type impurity semiconductor. Thereby, electron conductivity can be increased.

In a fifth embodiment, the metal described in the first to fourth embodiments is further covered with a coating layer having electron conductivity.
Even if an oxide film layer is formed, a uniform film is not always formed, and a weak portion may be partially formed.

In other words, pinholes or cracks may be present, and there is a possibility that these portions may become corrosion starting points. However, by covering the whole with a coating layer having electron conductivity, the current collector can be used. Without losing the function of
Since the coating covers the weak part of the film and the pinhole part,
Further improvement in corrosion resistance can be expected.

In a sixth aspect, the iron-based alloy in the first and second aspects is such that chromium, nickel, aluminum,
It is composed of at least one element of titanium, zirconium, niobium and silicon. These elements are more excellent in sulfuric acid resistance than iron, and the corrosion resistance is improved by adding these elements. Further, since the surface is etched to form a concentrated layer of the additional element, the corrosion resistance can be improved.

In the seventh embodiment, when iron contains 12% by weight or more of chromium, the corrosion resistance can be remarkably improved. Further, either 2-5 wt% of titanium or 2-5 wt% of aluminum, or both are added to this alloy.

Titanium is a metal having excellent sulfuric acid resistance. Since aluminum is an amphoteric metal, it is generally not corrosion-resistant to acids and alkalis. However, in sulfuric acid, the corrosion rate is lower than that of iron, and as in the third embodiment, the alumina film grows by oxidizing the surface. The corrosion resistance can be further improved.

In addition, unavoidable impurity elements such as carbon, phosphorus, sulfur, and oxygen affect corrosion resistance and mechanical properties. However, unlike the other types of fuel cells, the solid polymer electrolyte fuel cell has a low temperature. (Approximately 80 ° C.) and no special strength is required, so it is not specified here.

[0057]

Embodiments of the present invention will be described below. First, an example of the first aspect will be described in detail.

First, a substrate material is manufactured. As raw materials for the substrate material, chromium having a purity of 99.9% to 99.99% was 12 wt%, titanium was 3 wt%, and niobium was 0.0.
3 wt% of each metal with the balance being iron is arc melted in an argon atmosphere to produce an alloy. This is subjected to a homogenizing heat treatment,
After hot rolling and cold rolling, the plate is made 2 mm thick and homogenized again to obtain a substrate alloy.

After that, the separator is subjected to machining for forming a fuel gas flow path to form a separator having a flow path having a rectangular cross section.
In addition, any method other than press molding, injection molding, casting, or any other method that can form a flow path may be employed.

Next, the substrate on which the flow channel has been formed is chemically etched. In the chemical etching method, a 30% aqueous nitric acid solution is heated to 50 ° C., and the substrate is immersed in the aqueous solution for about one hour.
This preferentially dissolves iron at the surface,
A surface layer in which chromium, titanium, and niobium as added elements are concentrated can be formed.

The chemical etching method described here is only an example, and the type of chemical used, the temperature, and the immersion time can be changed depending on the composition of the alloy. For example, steel containing no chromium is severely corroded when immersed in the above-mentioned nitric acid solution, which has an adverse effect. Therefore, it is necessary to select mild conditions.

Dipping in a solution having a weak acidity with an inorganic acid or an organic acid, adding a salt such as potassium thiocyanate, which easily forms complex ions with iron, may be carried out in an explosive aqueous sodium chloride solution. There are many methods such as immersion to corrode only the iron and finally removing the corrosion products with hydrochloric acid or the like.

On the other hand, in the case of high chromium and high nickel steels, stricter chemical etching conditions can be used to shorten the processing time. Although the chemical etching is employed here, a method using electrolytic polishing may be used. In any case, if it is a method that preferentially dissolves iron on the surface,
Either method may be used.

Since the surface of the chemically etched surface has a higher additive element concentration than that of the mother phase, the corrosion resistance is improved. FIG. 2 shows the polarization curves of the as-alloy state (A) and the chemically etched state (B) measured in a sulfuric acid aqueous solution (0.05 MH2 SO4) at 30 ° C. and pH 1.24.

The substrate (B) that has been chemically etched has a lower current density as a whole, as compared with the state of the alloy as it is (A), which is approximately 1/3 to 1/2. The fact that the current density is reduced by the chemical etching means that the corrosion resistance is improved.

As another example, steel (silicon steel sheet) containing 3 wt% of silicon was immersed in a 10 wt% aqueous sodium chloride solution at 30 ° C. for 24 hours, and then the corrosion products on the surface were dissolved with dilute hydrochloric acid. FIG. 3 shows the results measured under the same conditions as the polarization curve described above.

In FIG. 3, the material subjected to the surface treatment (B) has a slightly lower current density than that of the untreated material (A), which is approximately １ ／. Actually, the current density is extremely large, whether treated or untreated, so it is difficult to use it as an actual separator material.However, even with steel that has no corrosion resistance, the improvement in corrosion resistance due to chemical etching treatment is not possible. It is possible.

Next, an embodiment of the second aspect will be described. As an example, as shown in the first embodiment, 12 wt% of chromium, 3 wt% of titanium, and 0.03 w of niobium.
The following description is based on an alloy containing t% and the remainder being iron.

FIG. 1 is a diagram schematically showing a cross section of the separator material of the present invention. The base material 1 is composed of 12 wt% of chromium, 3 wt% of titanium, and 0.03 w of niobium.
In the vicinity of the base material surface, a concentrated layer 2 of titanium, chromium, and niobium with reduced iron is formed. In addition, a passivation film layer 3 of an ultra-thin film of the order of nm is formed on the surface thereof, which is composed of oxides of these additional elements.

However, depending on the method of oxidation treatment and its conditions, it is not always limited to oxides alone, but may be hydroxides, oxyhydroxides or metal salts. The dynamic film layer 3 may be used.

In the concentrated layer 2, additional elements having excellent corrosion resistance are concentrated, and the passivation film layer 3 containing these additional elements as main components is formed. However, the corrosion resistance can be improved.

Next, an embodiment of the third aspect of the present invention will be described. The material described here is chromium 12wt
%, Titanium is 3 wt%, niobium is 0.03 wt%, and the remainder is an iron alloy. After the groove processing, it is the same as the first embodiment until it is chemically etched in a nitric acid aqueous solution.

This alloy is heated to 300 ° C.
In an electric furnace heated for 24 hours. As a result, an oxide film on the surface of the substrate metal grows, and a film on the order of μm is formed. The component of this film is mainly an oxide composed of titanium and iron contained in the alloy.

Since the film contains titanium dioxide, which is an oxide of titanium, the film has excellent acid resistance, and the ability to protect the base material by oxidation treatment is improved. FIG. 2C is a polarization curve of the oxidized alloy. The autothermal potential is higher than that of the untreated (A), and the active dissolution zone and the transpassive zone have disappeared. As described above, the current density can be reduced as a whole by the oxidation treatment, which contributes to the improvement of corrosion resistance.

The oxidation treatment method in this embodiment employs a method of heating in air, but is not limited to this. As long as it is a technique capable of growing a film on the base material surface, a method such as steam heating, oxygen gas heating, ozone treatment, hot water immersion, salt bath, or electrochemical anodic oxidation may be selected.

In addition to the oxidation treatment described above, nitriding treatment of the surface layer by ion nitriding or gas nitriding, or carbonizing treatment by ion carburizing, salt bath carburizing, salt bath carbonitriding, or gas boronization Boration treatment by a method or the like may be selected.

In particular, in the above materials, since titanium is concentrated on the surface, when this is nitrided, TiN is generated,
A surface layer having both acid resistance and electron conductivity can be formed.
Note that the above-described materials are examples, and the present invention is not particularly limited to these materials.

The film layers described in the first to third embodiments are composed of metal oxides or the like, and thus may have poor electron conductivity. If the electric resistance increases, the energy taken out of the fuel cell is lost, so it is necessary to keep the electric resistance as low as possible. In order to improve this,
In the embodiment, the additional element is added so that the film formed on the surface of the alloy shown in the first embodiment to the third embodiment has the property of an n-type semiconductor.

For example, the chromium described above is replaced with 1
2wt%, titanium 3wt%, niobium 0.03wt
%, With the balance being iron, the passivation film layer 3 after the formation of the concentrated layer 2 by the method described in the first embodiment, or a further oxidation treatment as described in the second embodiment. The composition of the film layer on which is grown is titanium oxide as a main component, but since titanium oxide is inferior in electron conductivity as it is, it is necessary to improve this.

Niobium contained in the alloy forms a composite oxide with titanium oxide and imparts properties as an n-type semiconductor, so that the electric resistance of the coating layer can be reduced. In this example, niobium is exemplified as an additive element for forming an n-type semiconductor, but is not particularly limited to niobium, and may be any element that imparts properties as an impurity semiconductor.

If the oxide film on the surface is a silicon oxide, aluminum, phosphorus or the like may be added.
However, from the viewpoint of corrosion, since the p-type semiconductor is easily dissolved by anodic polarization, it is preferable to use an n-type semiconductor.

The metal materials shown in the first and second embodiments are formed by forming a concentrated layer of an additional element in order to improve the corrosion resistance. In the third embodiment, the metal material is used to further improve the corrosion resistance. , The passivation film is forcibly grown by oxidizing the metal material of the first and second aspects to form a thick oxide film layer, or by nitriding, carbonizing or boring, and These compound layers are formed with the concentrated additive element.

However, when a non-uniform film layer is formed, a thin portion of the film, a pinhole, or a crack may occur, and the metal layer immediately below this portion may be preferentially corroded. . In order to prevent this, an electrically conductive coating layer was provided on the outermost layer. FIG. 4 shows a schematic view of the step structure.

In FIG. 4, the matrix 1 contains chromium of 12 watts.
An enriched layer 2 of an additional element is formed in the vicinity of the surface by chemical etching with an alloy containing t%, titanium at 3 wt%, niobium at 0.03 wt%, and the remainder iron. Then, an oxide layer 4 of the additive element on which a passivation film has been grown by oxidation treatment is formed on the surface.

The above is the same as the method described in the embodiment of FIG. In this example, furthermore, gold having excellent corrosion resistance was applied to this surface by electrochemical plating to provide a plating layer 5. Since the plated gold fills cracks and pinholes 6, it protects weak portions of the film and suppresses the progress of local corrosion.

Here, the corrosion resistance was improved by gold plating. However, a coating using a polymer containing a conductive filler such as carbon as a binder, as well as dry plating typified by sputtering, ion plating, CPD, PVD, etc. May form a metal film or a ceramics film.

Further, a method such as thermal spraying, salt bath nitridation, salt bath oxidation, etc. may be used. Does not matter.

Next, an embodiment in the sixth mode will be described. FIG. 5 shows polarization curves of various pure metals in a 0.05 M sulfuric acid aqueous solution at 30 ° C. When the iron is polarized, the current density sharply increases from the spontaneous potential, and continues active dissolution in any potential range.

Aluminum also exhibits the same behavior, but the current density is about two orders of magnitude lower than iron. On the other hand, nickel and chromium actively dissolve, but passivate medium potential and are corrosion resistant. Titanium, niobium, and zirconium do not actively dissolve, are passivated in any potential range, and exhibit excellent corrosion resistance.

Therefore, by adding these elements to iron, an improvement in corrosion resistance can be obtained. Further, in the present invention, since the surface is etched to form a concentrated layer of the additional element on the surface, the corrosion resistance can be further improved.

As described above, if iron is used as it is, it cannot maintain passivity in an acidic environment.
Corrodes indefinitely. However, it was stated that the corrosion resistance of the iron alloy can be improved by adding an acid-resistant element.

The corrosion resistance is remarkably improved only by containing 12% by weight or more of chromium. Aluminum, titanium, niobium and the like are also corrosion-resistant metals, but since these metals do not form a solid solution with respect to iron, the upper limit that can be added naturally arises.

[0093] Even if the addition amount is less than the amount of the solid solution, the workability specific to the metal may be lost due to hardening or brittleness. Therefore, the amount that can be added practically is determined. For titanium and niobium, around 3 wt% is a practical upper limit. With such a small addition amount, great improvement in corrosion resistance cannot be expected.

Therefore, in order to improve the corrosion resistance with a small amount of addition, the present invention uses the disadvantage that iron is easily corroded, and etches the surface in a relatively mild environment to remove the iron on the outermost surface. Was preferentially dissolved to concentrate the corrosion-resistant additive element, thereby improving the corrosion resistance.

In the seventh aspect, chromium is contained in an amount of 12 wt% or more, and is composed of at least one element of 2 to 5 wt% of titanium or 2 to 5 wt% of aluminum, or a combination of these elements. I chose an iron-based alloy.

The corrosion resistance of this alloy itself is SUS403, SUS405, SUS41 specified by JIS.
It has the same corrosion resistance as 13Cr stainless steel such as 0, but the corrosion resistance increases when oxidized through chemical etching.

According to this method, the corrosion resistance can be improved with a small amount of expensive elements added. There are advantages in terms.

[0098]

According to the present invention, in a fuel cell separator, corrosion resistance is imparted by a concentrated layer in which the concentration of an additive element is increased on a metal surface by using a means for etching the surface of an iron-based alloy. It can be oxidized, nitrided, carbonized or borated to strengthen the acid resistance of the passive film on the surface.

Therefore, a fuel cell separator and a solid polymer electrolyte fuel cell having corrosion resistance further improved than the corrosion resistance inherent in the base material can be obtained with a small amount of added elements.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view of a separator material according to a second embodiment of the present invention.

FIG. 2 is a polarization curve showing the function of the present invention, showing a state of an alloy as measured in an aqueous sulfuric acid solution (A), a state of chemically etched state (B), and a state of oxidation treatment (C).

FIG. 3 is a polarization curve showing the effect of the present invention after chemically etching steel containing 3 wt% of silicon.

FIG. 4 is a schematic sectional view of a separator having an outermost layer having an electrically conductive coating layer formed thereon.

FIG. 5 is a polarization curve diagram of various pure metals in a sulfuric acid aqueous solution.

[Explanation of symbols]

 1 Base material 2 Concentrated layer 3 Passive film layer 4 Oxide layer 5 Plating layer 6 Pinhole

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Yukio Saito 7-1-1, Omikacho, Hitachi City, Ibaraki Prefecture Inside the Hitachi Research Laboratory, Hitachi, Ltd. (72) Inventor Takefumi Yamaga 7-1, Omikamachi, Hitachi City, Ibaraki Prefecture No. 1 Inside Hitachi, Ltd.Hitachi Research Laboratories (72) Inventor Kazue Kawano 7-1-1, Omika-cho, Hitachi City, Ibaraki Prefecture Inside Hitachi, Ltd. Hitachi Research Laboratory Co., Ltd. (72) Inventor Kazuhisa Higashiyama, Hitachi City, Ibaraki 7-1-1, Machimachi, Hitachi Research Laboratory, Hitachi, Ltd. (72) Inventor Masanori Yoshikawa 7-1-1, Omikamachi, Hitachi City, Ibaraki Prefecture, Hitachi, Ltd. Hitachi Research Laboratory, Hitachi, Ltd. (72) Inventor, Masahiko Arai Ibaraki 7-1-1, Omika-cho, Hitachi City, Japan Inside Hitachi Research Laboratory, Hitachi Ltd. (72) Inventor Hiroyuki Doi Hitachi City, Ibaraki Prefecture 7-1-1, Omikacho Hitachi Research Laboratory, Hitachi, Ltd. (72) Inventor Yasuto Aono 7-1-1, Omikamachi, Hitachi City, Ibaraki Pref. Hitachi, Ltd. Hitachi Research Laboratory, Ltd. (72) Inventor Kamo Tomoichi 7-1-1, Omika-cho, Hitachi City, Ibaraki Prefecture Within Hitachi Research Laboratory, Hitachi, Ltd. (72) Inventor Toshihiro Uehara 2107-2, Yasugi-cho, Yasugi-shi, Shimane Hitachi Metals Research Laboratory, Metallurgy (72) Inventor Yoshitaka Chiba Hitachi Metals Co., Ltd., 1-2-1, Shibaura, Minato-ku, Tokyo (72) Inventor Ken Ichihashi 2107-2, Yasugi-cho, Yasugi City, Shimane Prefecture Hitachi Metals Co., Ltd. Yasugi Plant (72) Inventor Takehiro Ohno 2107 Yasugi-cho, Yasugi-shi, Shimane Prefecture Inside Hitachi Metals Co., Ltd. Yasugi Factory (72) Inventor Hideo Murata 2107-2 Yasugi-cho, Yasugi-shi, Shimane Prefecture Hitachi Metals Co., Ltd. Metallurgy Research Laboratory F-term (reference) 5H026 AA06 BB10 CC03 EE08 EE11 EE12 HH05

Claims (9)

[Claims] 1. A separator for a solid polymer electrolyte fuel cell, wherein a concentrated layer having an increased concentration of the additive element is formed on a surface layer by etching a surface of an iron-based alloy containing the additive element. 2. A separator formed of an alloy having a current collecting function while forming a flow path for a fuel gas and an oxidizing gas of a solid polymer electrolyte fuel cell, wherein the alloy is an iron-based alloy containing an additional element. A separator for a solid polymer electrolyte fuel cell, wherein the separator is made of an alloy, and the concentration of the additive element near the surface is increased by etching the surface of the alloy. 3. A separator formed of an alloy having a current collecting function while forming a flow path for a fuel gas and an oxidizing gas of a solid polymer electrolyte fuel cell, wherein the alloy is an iron-based separator containing an additional element. An oxide film formed of an alloy, wherein the oxide film on the surface of the alloy is a compound of the additive element;
The additive element concentration on the metal side between the oxide film and the metal interface of the alloy, which is composed of one or more of a hydroxide and an oxyhydroxide, is higher than the mixing ratio of the additive element and iron. A separator for a solid polymer electrolyte fuel cell, wherein the separator has a concentration. 4. The solid polymer according to claim 1, wherein the surface of the alloy is oxidized, nitrided, carbonized or borated to form an inorganic film on the surface. Electrolyte type fuel cell separator. 5. The solid according to claim 1, wherein the additive element is such that an oxide film formed on the surface of the alloy becomes an impurity semiconductor. Polymer electrolyte fuel cell separator. 6. The solid polymer electrolyte fuel cell according to claim 1, wherein the outermost surface of the alloy is coated with a coating layer having electron conductivity. For separator. 7. The separator according to claim 1, wherein the iron-based alloy is added with at least one element of chromium, nickel, aluminum, titanium, zirconium, niobium, and silicon. A solid polymer electrolyte fuel cell separator. 8. The separator according to claim 1, wherein the iron-based alloy contains chromium in an amount of 12 wt% or more, and one of titanium 2-5 wt% and aluminum 2-5 wt%. A separator for a solid polymer electrolyte fuel cell, comprising one or both of them. 9. A solid polymer electrolyte fuel cell comprising the solid polymer electrolyte fuel cell separator according to claim 1. Description: