JP2003123781A - Solid polymer electrolyte fuel cell separator and method for producing the same - Google Patents

Abstract

(57) [Problem] To provide a separator for a solid polymer electrolyte fuel cell having particularly high corrosion resistance and good conductivity among stainless steel separators. SOLUTION: A solid polymer electrolyte fuel cell separator is provided with a general corrosion resistance GI = [Cr%] + 3.6 [Ni%].
It is configured by coating a surface of a stainless steel having +4.7 [Mo%] + 11.5 [Cu%] of 90 or more with a conductive compound such as metal nitride or metal-dispersed diamond-like carbon. When forming a film, ion bombing is performed as a pretreatment on the surface of the high corrosion-resistant stainless steel, and then a conductive compound is coated by ion plating. And, in the coated part, high corrosion resistance and good conductivity are secured by this surface film, and in the uncoated part (the part with a defect such as pinhole),
High corrosion resistance is ensured by the passive film of stainless steel itself.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a separator used in a fuel cell, and more particularly to a solid polymer electrolyte type fuel cell separator and a method for producing the same.

[0002]

2. Description of the Related Art In recent years, solid polymer electrolyte fuel cells generally have the advantages of high power generation efficiency and no emission of SOx and NOx. Therefore, they are spotlighted as small-scale fuel cells for homes and automobiles. Therefore, they are expected to be used for stationary power generation and automobile power generation, respectively. Conventionally, this type of solid polymer electrolyte fuel cell generally has a structure described below.

In the solid polymer electrolyte fuel cell, the solid polymer electrolyte membrane has a thickness of about 50 μm, and electrodes are bonded to both surfaces of the electrolyte membrane. The electrode is basically made of a platinum porous material, but platinum fine particles are attached to carbon black fine particles and a small amount of Teflon (registered trademark)
It is mixed with a polymer such as fine particles and thinly coated on carbon fiber paper to form a two-layer structure of a porous graphite body and carbon fiber paper. Then, a single cell of the solid polymer electrolyte fuel cell has a structure in which the graphite porous body side of this electrode is superposed on both surfaces of the electrolyte membrane and thermocompression-bonded to be integrated.
A single unit is formed by disposing graphite separators on the carbon fiber paper side of the electrode. Thus, fuel cells are typically used as a stack of units.

Conventionally, in solid polymer electrolyte fuel cells, since a fuel gas and an oxidizing gas respectively flow on both sides of an electrode, a grooved separator made by grooving graphite is usually used as the separator. ing. The graphite grooved separator sandwiches both sides of the electrode as a flow channel substrate and forms flow channels on both sides of the electrode so that the fuel gas and the oxidizing gas are not mixed. The graphite grooved separator serves as a partition of each cell to prevent the fuel gas and the oxidizing gas from being mixed in this way, and also serves as a passage for an electric current generated in each cell.

However, since the graphite separator is fragile in terms of material, there is a problem that impact resistance is insufficient particularly when it is used in a fuel cell for automobiles. Moreover, there is a problem in that the groove processing of graphite requires an additional processing cost such as a cutting process, and the fuel cell cost increases accordingly.

Therefore, in place of such a graphite separator, a metal separator has been proposed recently. If the separator is made of metal, it will not only have high impact resistance, but it does not need to be cut and can be formed by pressing, so the processing cost will be low and the volume efficiency will be good. This is because there is an advantage that it can be made compact.

[0007]

By the way, in the solid polymer electrolyte fuel cell, the solid polymer electrolyte membrane originally has the same main chain as Teflon and has a structure having a sulfone group at the terminal. Is ionized, and the proton exhibits ionic conductivity. Therefore, the solid polymer electrolyte membrane exhibits acidity, and the electrodes and the separator are required to have corrosion resistance against acid. Especially as a separator,
When a metal material having low corrosion resistance is used, the eluted metal ions react with the electrolyte membrane, impairing the ion conductivity of the membrane, resulting in a decrease in power generation capacity. Therefore, the metal separator must first have high corrosion resistance.

Next, in the first place, the separator not only prevents the fuel gas and the oxidizing gas from mixing with each other by forming the boundary between the cells as described above, but also serves as a passage for the electric current generated in each cell. Therefore, it is necessary to have sufficient conductivity.

Therefore, stainless steel separators have hitherto attracted attention as metal separators that are highly likely to satisfy the requirements of high corrosion resistance and good conductivity.

However, stainless steel is known to have excellent corrosion resistance, and the corrosion resistance is maintained by the passivation film formed on the surface, while the passivation film is insulating. Yes, impedes conductivity. Therefore, conventionally, when providing a separator made of stainless steel, from the viewpoint of ensuring the function of the separator, while the corrosion resistance is secured by the passivation film on the surface, the conductivity is hindered by the passivation film. There is a problem that it is necessary to eliminate the harmful effects.

Therefore, an object of the present invention is to solve the above-mentioned conventional problems, and to provide a separator for a solid polymer electrolyte fuel cell, which has particularly high corrosion resistance and good conductivity among the stainless steel separators. Especially.

[0012]

Means for Solving the Problems As a result of intensive studies, the inventors of the present invention have found that as a means for solving the above-mentioned technical problems, first, by subjecting stainless steel to a surface treatment such as ion plating, We have found a structure that forms a film of a conductive compound having both high corrosion resistance and good conductivity. In the present invention, the term “coating” simply refers to a coating layer formed on the surface of the underlying stainless steel by surface treatment such as ion plating unless otherwise specified.

Further, in stainless steel, since the passivation film is mainly composed of a hydroxide such as chromium, which is a contained component, the higher the content of chromium and molybdenum, the higher the corrosion resistance of the surface passivation film. On the other hand, it is known that a film formed by ion plating or the like inevitably has a defective portion such as a pinhole while being maintained. These defects are caused by various factors such as dust adhering during the film formation process and fine cracks caused by the grain boundaries of the film. It is not possible to make a film without parts. If there are defects such as pinholes, no matter how excellent the corrosion resistance of the coating itself is, the underlying metal ions will elute from the pinholes without coating, which react with the electrolyte membrane to cause electrolyte membrane As a result, the ionic conductivity of is impaired. Therefore, we focused on the fact that the underlying stainless steel requires that at least the underlying metal ions do not elute even if defects such as pinholes occur in the film. It was found that the required high corrosion resistance stainless steel was used, and the present invention having the following constitution was completed.

That is, the solid polymer electrolyte fuel cell separator of the present invention is [Cr%] +
It is characterized in that the surface of stainless steel having a general corrosion resistance coefficient of 3.6 [Ni%] + 4.7 [Mo%] + 11.5 [Cu%] of 90 or more is coated with a conductive compound. . If the surface of the stainless steel is coated with a conductive compound in this way, the coated portion does not have a passivation film between the film and the underlying metal, and thus good conductivity is ensured, while also regarding corrosion resistance, The coated portion has a high corrosion resistance secured by the corrosion resistance of the coating itself, and the non-coated portion (the portion having a defective portion such as a pinhole) is secured by the passivation coating of the high corrosion resistant stainless steel itself which is the base. As a result, a solid polymer electrolyte fuel cell separator having both high corrosion resistance and good conductivity is provided, and the object of the present invention is achieved.

In the solid polymer electrolyte fuel cell separator of the present invention, the conductive compound may be any one having both high corrosion resistance and good conductivity. For example, metal nitrides such as chromium nitride and titanium nitride. Is preferred.

In the present invention, the conductive compound is also preferably metal-dispersed diamond-like carbon, which is a substance in which a metal is dispersed in diamond-like carbon to impart conductivity. This is because the film of the metal-dispersed diamond-like carbon has excellent acid resistance, but conductivity is imparted to the diamond-like carbon, which is an insulator, by adding a metal.

Further, in the present invention, when a film of a conductive compound is formed on the surface of stainless steel, the above-mentioned highly corrosion resistant stainless steel having a general corrosion resistance of 90 or more is used as a base metal, and ions are formed on the surface of the stainless steel. It is preferable to perform bomber ring as a pretreatment and then coat the conductive compound by ion plating.

[0018]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be described in detail.

The solid polymer electrolyte fuel cell separator of the present invention has a structure in which highly corrosion-resistant stainless steel is used as a base metal, and the surface of the stainless steel is coated with a conductive compound.

That is, the present invention forms a film of a conductive compound having both high corrosion resistance and good conductivity by subjecting the surface of high corrosion resistance stainless steel to surface treatment by the ion plating described later. The conductive compound has both high corrosion resistance and good conductivity, for example, chromium nitride,
It is preferably a metal nitride such as titanium nitride. Further, as the film of such a conductive compound, as a pretreatment of the nitride film coating, a metal coating, for example, a film having a two-layer structure of metal chromium and chromium nitride, or a film of metal titanium and titanium nitride is used. Having a two-layer structure is effective in further increasing the corrosion resistance.

The conductive compound film of the present invention is effective even if it is coated with metal-dispersed diamond-like carbon. Examples of the film of the metal-dispersed diamond-like carbon include a tungsten carbide film in which metallic tungsten is dispersed, a tantalum carbide film in which metallic tantalum is dispersed, and the like. Diamond-like carbon such as tungsten carbide and tantalum carbide has excellent acid resistance, but since it is an insulator, conductivity is imparted by adding a metal.

The thickness of the coating on the underlying stainless steel is not limited, but from the viewpoint of ensuring corrosion resistance, it is 2 to 3 μm.
The above is desirable.

Here, the results of a study of what kind of stainless steel is particularly effective as the base metal as the high corrosion resistant stainless steel used in the present invention will be described. The present inventors have found that for stainless steels having various component compositions, 10
The corrosion weight loss was measured at 80 ° C. in% sulfuric acid and 20% sulfuric acid. When this result was arranged for the general corrosion resistance (hereinafter referred to as "GI"), a clear correlation was observed between GI and the corrosion weight loss as shown in FIG. Here, GI is GI = [Cr%] + 3.
It is an index obtained by 6 [Ni%] + 4.7 [Mo%] + 11.5 [Cu%]. From this relationship, it was found that if GI is 90 or more, sufficient corrosion resistance can be obtained.

Therefore, in the solid polymer electrolyte fuel cell separator of the present invention, when expressed in mass% as a base metal, [Cr%] + 3.6 [Ni%] + 4.7 [Mo%] + 1
A highly corrosion resistant stainless steel having a general corrosion resistance of 1.5 [Cu%] of 90 or more is selected, and the surface of the stainless steel is coated with the conductive compound.

Stainless steels having a GI of 90 or more include, for example, JIS steel types such as SUS317 and SUS310S, and other commercial steel types include NTK30AC (C ≦ 0.07, Cr: 19.00 to 21.00, Ni:
32.00 ~ 38.00, Mo: 2.00 ~ 3.00, Cu: 3.00 ~ 4.00, Nb:
8xC% ~ 10xC%), NTK30A (C ≤ 0.020, Cr: 19.00 ~ 21.0
0, Ni: 28.00 to 30.00, Mo: 2.00 to 3.00, Cu: 3.00 to 4.0
0, Mn: 2.50 ~ 3.50), NTK22A (C ≤ 0.020, Cr: 19.00 ~
21.00, Ni: 21.00-23.00, Mo: 1.75-2.75, Cu: 1.75
~ 2.75, Mn: 2.50 ~ 3.50) etc. However, the present invention is not limited to the steel types listed above as the high corrosion-resistant stainless steel of the base.

Next, a method for forming a film of a conductive compound by subjecting the high corrosion-resistant stainless steel as a base to a surface treatment will be described.

In the present invention, the above-mentioned highly corrosion resistant stainless steel having a GI of 90 or more is used as a base metal, and the surface of the stainless steel is preferably subjected to ion bombarding as a pretreatment, and then metal nitriding is performed by ion plating. Or a conductive compound such as metal-dispersed diamond-like carbon.

In the ion plating process, in order to improve the film adhesion, an ion bomber ring process is performed before the process. The ion bombarding process cleans the surface by accelerating argon ions etc. to collide with the surface of the object to be treated and removes the impurities and oxide film on the surface, and the film formed by the subsequent coating process and the substrate. It improves the adhesion to metal. By this ion bombarding treatment, the passivation film existing on the surface of stainless steel is removed in advance. Therefore, if ion bombarding is performed as a pretreatment before the ion plating treatment,
In the coated portion where the coating is formed, there is no passivation coating between the coating and the underlying metal, and as a result, the conductivity of the stainless steel itself and the coating is ensured. With respect to the corrosion resistance, the high corrosion resistance of this coating portion is ensured by the corrosion resistance of the film itself.

On the other hand, defects (uncoated portions) such as pinholes in which a film is not formed expose the underlying stainless steel directly to the outside, but the passive film of the stainless steel has a moisture and oxygen content in the atmosphere. Corrosion resistance is also ensured because it is formed naturally by contact with. By the above film forming method, a solid polymer electrolyte fuel cell separator having both high corrosion resistance and good conductivity is produced, and the object of the present invention is achieved.

The method for forming a film is not particularly limited to the above method as long as it can achieve the object of the present invention, that is, a method for forming a film having both high corrosion resistance and good conductivity on the surface of stainless steel. Although not a thing, ion plating is one of the best methods. Further, as a pretreatment, a more preferable result can be obtained by adopting a configuration including a step of previously removing the non-conductive coating of stainless steel called ion bomber ring.

[0031]

EXAMPLES Next, the present invention will be explained in more detail and specifically based on the following examples, but it goes without saying that the present invention is not limited to these examples.

(1) Preparation of Sample A stainless steel plate (thickness: 0.2 mm, steel type: NTK30AC) was coated with chromium nitride using a multi-arc ion plating device. In that case, first, as a pretreatment, while applying an argon gas of 5 to 10 × 10 ⁻² Pa, a voltage of 400 V was applied to perform ion bomber ring. Then, using chromium for the electrodes, nitrogen gas was flown into the chamber so as to have a pressure of 0.5 Pa, an arc was generated at the electrodes and the chamber wall surface at a voltage of 200 V and a current of 80 A, and the sample plate was rotated while nitriding Chrome 5μ
m coated (hereinafter referred to as "CrN coating material").

Using the same apparatus as above, the above stainless steel plate was subjected to ion bombarding, followed by coating with metallic chromium of 2 μm in an argon gas atmosphere, and then forming a chromium nitride layer of 3 μm in a nitrogen atmosphere (hereinafter referred to as “Cr / Cr
N film material ").

Using a magnetron sputtering device,
After ion bombarding the stainless steel plate described above, a tungsten target was used to form a film in which metallic tungsten was dispersed in tungsten carbide in a mixed gas of argon and acetylene (hereinafter referred to as "W-DLC film material"). .

(2) Evaluation of characteristics The above-mentioned CrN coating material, Cr / CrN coating material and W-DLC coating material were evaluated for conductivity and corrosion resistance as follows.

The electrical conductivity was evaluated by measuring the contact electric resistance of the film with a contact electric resistance measuring device [Yamazaki SQ meter manufactured by Yamazaki Seiki Laboratory Co., Ltd.]. A graphite electrode was brought into contact with the surface of the sample at a contact pressure of 20 kg / cm ² , and the contact electric resistance when scanning for 10 mm was measured. As a result, the CrN coating material 0.
355Ω, Cr / CrN coating material 0.285Ω, W-DLC coating material 0.593Ω, these are pure stainless steel 13
The value is sufficiently smaller than 4.66Ω and is a value close to 0.158Ω of pure gold.

The corrosion resistance was evaluated by immersing it in 5% sulfuric acid at 80 ° C. for 148 hours and measuring the amount of elution on the coating surface. Elution amount, CrN coating material is ^{0.25mg / m 2 / h, Cr} / CrN coating material is ^{0.22mg / m 2 / h, W} -DLC film material is 0.38mg / ^{m 2} / h,
And a small value.

Next, after pressing the groove-shaped structure using the above-mentioned three types of film-formed stainless steel plates, it was incorporated into a single cell fuel cell as a separator and a power generation test was conducted. When the polymer electrolyte membrane and the electrode integrated with each other were sandwiched between the separators and an oxidizing gas and a hydrogen gas were supplied to both ends, an initial voltage of 0.7 V was obtained. In addition, 500
An output of about 0.67 V was obtained in each case even after continuous operation for an hour. This is a voltage drop of only 5%.

[0039]

According to the present invention configured as described above, the following remarkable effects can be obtained.

According to the invention described in claim 1, the solid polymer electrolyte fuel cell separator is provided with a general corrosion resistance G
I = [Cr%] + 3.6 [Ni%] + 4.7 [Mo%] + 1
Since the surface of stainless steel having 1.5 [Cu%] of 90 or more is coated with a conductive compound,
As a result of the absence of a passivation film between the film and the underlying metal in the coated part, good conductivity is assured, while also in terms of corrosion resistance, the coated part has a high corrosion resistance due to the corrosion resistance of the film itself. The coated part (the part with defects such as pinholes) is secured by the passivation film of the high corrosion-resistant stainless steel itself, which is the base, and as a result, it is a solid polymer with both high corrosion resistance and good conductivity that have never been seen before. It is possible to provide a separator for an electrolyte fuel cell.

In addition, since it is a stainless steel separator in the first place, it does not have the brittleness of conventional graphite separators due to its material, and can be widely used for fuel cells for automobiles that require impact resistance. You can Further, it is not necessary to perform cutting work for groove processing for the flow path, and it can be easily and inexpensively formed by press work, and as a result, a low cost fuel cell can be provided, and Since the volume efficiency is good, it can be made compact.

According to the invention described in claims 2 and 3,
By using a metal nitride and a metal-dispersed diamond-like carbon as the conductive compound that coats the surface of each stainless steel, it is possible to more effectively secure high corrosion resistance and good conductivity for the coated portion. .

According to the fourth aspect of the present invention, the surface of the high corrosion resistant stainless steel having the above general corrosion resistance of 90 or more is subjected to ion bomber ring pretreatment, and then ion plating is performed to form a conductive compound. By coating the stainless steel, the passivation film existing on the surface of the stainless steel is removed in advance, the adhesion between the film and the underlying metal is improved, and a film having both high corrosion resistance and good conductivity is formed on the stainless steel. It can be effectively formed on the steel surface.

[Brief description of drawings]

FIG. 1 is a chart showing a relationship between a general corrosion resistance coefficient and a corrosion weight loss under a predetermined condition in stainless steel having various component compositions.

Claims (4)

[Claims] 1. When expressed in mass%, [Cr%] + 3.6 [Ni
%] + 4.7 [Mo%] + 11.5 [Cu%] stainless steel having a general corrosion resistance of 90 or more, which is obtained by coating a conductive compound on the surface of the solid polymer electrolyte. Type fuel cell separator. 2. The solid polymer electrolyte fuel cell separator according to claim 1, wherein the conductive compound is a metal nitride. 3. The solid polymer electrolyte fuel cell separator according to claim 1, wherein the conductive compound is metal-dispersed diamond-like carbon. 4. The stainless steel is used as a base metal, the surface of the stainless steel is subjected to ion bombarding as a pretreatment, and then the conductive compound is coated by ion plating. The method for producing the solid polymer electrolyte fuel cell separator according to claim 1, 2, or 3.