JP2007095318A - Anti-corrosion member, separator for fuel cell, and fuel cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an anti-corrosion member which has an anti-corrosion property even if a usage of precious metal is smaller than in a conventional one, and provide a separator for a fuel cell as well as a fuel cell using the above anti-corrosion member. <P>SOLUTION: The anti-corrosion member is composed of a passivating metal or an alloy 10 and precious metal 12 electrically connected with a conductive member 14 in-between. A ratio of a surface area of the precious metal 12 to a total area of the metal or the alloy 10 and the precious metal 12 is desirable to be 5% or more. A separator for a fuel cell is composed of the above anti-corrosion member and a fuel cell is composed of the above separator for a fuel cell. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a corrosion-resistant member, a fuel cell separator, and a fuel cell.

  In recent years, applications that require corrosion-resistant members such as stainless steel have been expanded. For example, in the field of fuel cells, a corrosion-resistant member may be used as a material for a separator that is interposed between single cells in which a fuel electrode, an electrolyte, and an air electrode are stacked in this order.

  The separator has a function of separating the fuel gas supplied to the fuel electrode of the single cell and the oxidant gas supplied to the air electrode and electrically connecting the single cells.

  Therefore, the separator needs to have strength as a structural member and be excellent in gas tightness, electrical conductivity, etc., but since the separator is exposed to a high-temperature oxidizing atmosphere during power generation of the fuel cell, it is further corrosion resistant. It is necessary to be excellent.

  In a polymer electrolyte fuel cell (PEFC) using a solid polymer electrolyte having a strong acid group such as a sulfonic acid group as an electrolyte, the separator is exposed to a strong acidic atmosphere such as a sulfuric acid environment.

  However, in such an environment, the corrosion resistance of stainless steel alone is not sufficient. Therefore, when stainless steel is used alone as the separator material, the stainless steel corrodes, and the electrical resistance of the corroded portion increases, or the electrolyte deteriorates due to ions eluted from the stainless steel and the ion conductivity decreases. As a result, there has been a problem that the battery performance deteriorates.

  In order to improve this kind of problem, for example, Patent Document 1 discloses that a corrosion-resistant member obtained by applying gold plating to the surface of a stainless steel plate is used as a separator material.

  Patent Document 2 discloses that a corrosion-resistant member obtained by cladding gold on the surface of a stainless steel plate is used as a separator material.

JP-A-10-228914 JP 2005-100813 A

  However, both the conventional corrosion-resistant members described above have the following problems.

  That is, the conventional corrosion-resistant member has a surface covered with gold, such as a stainless steel plate, regardless of the method.

  Since noble metals such as gold are very expensive, the material cost increases if the amount used is large. In particular, a fuel cell has many relatively expensive components, and its high material cost is one of the factors that hinder the spread of fuel cells. Therefore, it is desired that a corrosion-resistant member used in a fuel cell separator or the like reduce the amount of noble metal such as gold as much as possible while maintaining corrosion resistance.

  By the way, to reduce the amount of noble metal used, it is conceivable to reduce the thickness of the noble metal. However, it is extremely difficult to apply a thin precious metal on an industrial scale. In addition, as the thickness of the noble metal is reduced, problems such as difficulty in securing the adhesion of the noble metal and difficulty in reliably ensuring the film quality occur.

  In particular, in the fuel cell separator described above, in recent years, the thickness of the noble metal has become extremely thin at 100 nm or less. For this reason, the above problem occurs remarkably.

  Further, in a corrosion-resistant member in which a noble metal is plated on a surface such as a stainless steel plate, a large number of pinholes are usually formed on the plated surface. Therefore, the base material component is likely to elute through this pinhole. To avoid this, if a high-corrosion-resistant metal or alloy is used as the base material, plating becomes abruptly difficult due to the passive film formed on the surface of the base material, and plating is performed unless the passive film is removed. Inconveniences such as being unable to do so also occur.

  Therefore, the problem to be solved by the present invention is to provide a corrosion-resistant member having corrosion resistance even if the amount of noble metal used is less than that of the prior art.

  Another object is to provide a fuel cell separator and a fuel cell using the corrosion-resistant member.

  In order to solve the above problems, the gist of the corrosion-resistant member according to the present invention is that a metal or alloy to be passivated and a noble metal are electrically connected via a conductive member.

  Here, as the noble metal, it is preferable to use gold, platinum, or an alloy containing at least one of these.

  The ratio of the surface area of the noble metal to the total surface area of the metal or alloy and the noble metal is preferably 5% or more.

  On the other hand, the fuel cell separator according to the present invention uses the above corrosion-resistant member.

  The gist of the fuel cell according to the present invention is that the fuel cell separator is used.

  The corrosion-resistant member according to the present invention is formed by electrically connecting a passivating metal or alloy and a noble metal via a conductive member. Therefore, unlike the conventional corrosion resistant member, it is not necessary to cover the surface of the metal or alloy with the noble metal, so that the amount of the noble metal used can be greatly reduced and the cost can be reduced.

  Further, in general, in the case of a single metal or alloy, even if the potential is in the active state region and corrosion occurs, the corrosion-resistant member according to the present invention is such that the metal or alloy is noble metal via the conductive member. And the potential of the metal or alloy shifts from the active state region to the passive state region. Thereby, even if the corrosion-resistant member which concerns on this invention exists in a strong acidic atmosphere, passivation of a metal or an alloy is accelerated | stimulated and can exhibit the outstanding corrosion resistance.

  Further, according to the corrosion-resistant member according to the present invention, for example, a metal or alloy pre-plated with a noble metal is processed to produce a part, or a part obtained by processing a metal or an alloy is later plated with a noble metal. It becomes unnecessary to do. Therefore, it is possible to simplify the manufacturing process of the corrosion resistant member itself or a part using the same.

  At this time, when gold, platinum or an alloy containing one or more of these is used as the noble metal, the effect of promoting the passivation of the metal or alloy is particularly high, and therefore the corrosion resistance is further improved.

  Further, when the ratio of the surface area of the noble metal to the total surface area of the metal or alloy and the noble metal is 5% or more, the corrosion amount of the metal or alloy can be extremely reduced.

On the other hand, since the fuel cell separator according to the present invention uses the corrosion-resistant member,
In addition to being excellent in strength, gas tightness and electrical conductivity as a structural member, it has high corrosion resistance and is low in cost.

  Further, since the metal or alloy and the noble metal are connected by the conductive member, it is easy to manufacture the fuel cell stack.

  Further, according to the fuel cell of the present invention, since the fuel cell separator is used, an increase in electrical resistance due to the corrosion of the separator and an electrolyte deterioration due to eluted ions are unlikely to occur. Therefore, it is easy to maintain battery performance.

  Hereinafter, the corrosion-resistant member, the fuel cell separator, and the fuel cell according to this embodiment will be described in detail. In the following, the corrosion-resistant member according to this embodiment is referred to as “this corrosion-resistant member”, the fuel cell separator according to this embodiment is referred to as “this separator”, and the fuel cell according to this embodiment is referred to as “this fuel cell”. Sometimes.

1. This corrosion-resistant member This corrosion-resistant member is formed by electrically connecting a metal or alloy and a noble metal via a conductive member.

  In the present corrosion resistant member, the metal or alloy used is a passive material. Specific examples of the passivated metal or alloy include Fe, Fe-base alloy, Ni, Ni-base alloy, Ti, Ti-base alloy, Al, Al-base alloy, and the like.

  Of these, an Fe-based alloy is preferable from the viewpoint of excellent corrosion resistance, workability, cost, and the like. Most preferred is stainless steel.

  Further, the form of the metal or alloy may be any form such as a plate, a rod, or a lump.

  In the present corrosion resistant member, specific examples of the noble metal include simple metals such as Au, Ag, Pt, Pd, Ru, Rh, Os, and Ir, and alloys containing at least one of these. be able to. These may be used alone or in combination of two or more.

  Among these, gold, platinum, or an alloy containing at least one or more of these is preferable from the viewpoint that the effect of promoting passivation of the metal or alloy is particularly high.

  Further, the form of the noble metal may be any form such as a plate, a rod, or a lump, and the noble metal may be plated or clad on another base material.

  In the present corrosion resistant member, the conductive member is for electrically connecting the metal or alloy and the noble metal.

  As a material of the conductive member, any material may be used as long as it is conductive and can withstand a power generation environment or a use atmosphere of the fuel cell described later. Preferable examples include noble metals such as Au, Ag, Pt, Pd, Ru, Rh, Os and Ir, elements such as Cu and Co, and alloys containing at least one of these.

  Among these, a noble metal or an alloy containing at least one kind of these noble metals is preferable. This is because the conductive member is also often exposed to a corrosive environment, and therefore it is advantageous to use a material having excellent corrosion resistance.

  Further, the conductive member may have any form such as a wire, a bar, or a plate as long as the metal or alloy and the noble metal can be electrically connected.

  Of these forms, the linear form is preferred because of its excellent flexibility and excellent freedom of electrical connection.

  Further, the conductive member may be in contact with the metal or alloy and the noble metal, or may be joined to at least one by welding or the like. It can be appropriately selected in consideration of the form of the conductive member.

  Here, in the corrosion resistant member, the ratio of the surface area of the noble metal to the total surface area of the metal or alloy and the noble metal (hereinafter referred to as “the surface area ratio of the noble metal”) is 5% or more, preferably 7% or more. More preferably, it is 10% or more.

  When the surface area ratio of the noble metal is less than 5%, it becomes difficult to passivate the metal or alloy, and the corrosion amount of the metal or alloy tends to increase rapidly.

  On the other hand, even if the surface area ratio of the noble metal is excessively increased, the effect of suppressing the corrosion amount of the metal or alloy is saturated and only the amount of noble metal used is increased. Accordingly, the upper limit of the surface area ratio of the noble metal is not particularly limited, but generally, it is 50% or less, preferably 40% or less, more preferably 25% or less in consideration of cost and the like. It is good to do.

  In calculating the surface area ratio of the noble metal, when the metal or alloy and the noble metal are in the form of a plate and the area of the end face is extremely small compared to the area of the plane part, The surface area ratio of the noble metal may be calculated by excluding the area of the end face.

  Moreover, as an electrical connection form of the metal or alloy, the noble metal, and the conductive member in the corrosion resistant member, for example, the connection form shown in FIG. 1 can be exemplified.

  That is, in this corrosion-resistant member, as shown in FIG. 1A, it is desirable that the metal or alloy 10 and the noble metal 12 are connected by the conductive member 14 in a one-to-one relationship. Moreover, as shown in FIG.1 (b), the some metal or alloy 10,10 ... and the single noble metal 12 may be connected by the electroconductive member 14,14 .... Further, as shown in FIG. 1C, a single metal or alloy 10 and a plurality of noble metals 12, 12,... May be connected by conductive members 14, 14.

  Moreover, this corrosion-resistant member may be coated with an anti-corrosion paint or the like, if necessary, on the surface of the metal or alloy from the viewpoint of enhancing the corrosion resistance.

  Although the present corrosion-resistant member has been described above, the application field of the corrosion-resistant member is not particularly limited, and can be used as a material for products, parts, and the like that require low cost and corrosion resistance.

  In particular, it can be suitably used as a fuel cell separator material that requires low cost and excellent corrosion resistance. Hereinafter, this case will be described.

2. This separator, this fuel cell This separator uses the above-mentioned corrosion-resistant member. That is, the separator is specifically manufactured by, for example, pressing a metal or alloy portion of the corrosion-resistant member and appropriately forming uneven gas flow paths, gas introduction holes, gas outlet holes, and the like. Is.

  At this time, the separator is formed by first pressing the metal or alloy of the corrosion-resistant member to form a gas flow path, and then electrically connecting the metal or alloy portion and the noble metal through the conductive member. Or a metal channel or an alloy and a noble metal are electrically connected in advance through a conductive member, and then the metal or alloy portion is pressed to form a gas flow path or the like. It may be formed to manufacture this separator.

  In the present separator, the shape of the gas flow path, the thickness of the separator, and the like can adopt various generally known shapes and thicknesses, and are not particularly limited.

  In addition, this separator can be applied to any type of fuel cell as long as it can generate power in a temperature range in which a metal separator can be used.

  Specific examples of the fuel cell include a polymer electrolyte fuel cell, a phosphoric acid fuel cell, a solid oxide fuel cell, and a molten carbonate fuel cell.

  Among these, it can be suitably used for a polymer electrolyte fuel cell that is often exposed to a strongly acidic atmosphere such as a sulfuric acid environment.

  On the other hand, the present fuel cell has a configuration in which a plurality of single cells in which a fuel electrode, an electrolyte, and an air electrode are stacked in this order are stacked via the separator.

  The configuration of the single cell differs depending on the type of the fuel cell, and a configuration generally known in the art can be adopted as appropriate.

  In the fuel cell, a plurality of separators are used. One or two or more noble metals may be connected to each of the separators via a conductive member. Alternatively, all of the separators may be connected to one noble metal via a conductive member. Alternatively, these separators may be divided into several group units, and all of the separators in each group may be connected to one noble metal via a conductive member.

  Preferably, the latter two connection modes are selected. This is because the electrical connection between the conductive member and the noble metal after manufacturing the stack is relatively simple, and thus the productivity of the fuel cell is excellent.

  In addition, a conductive paint or the like may be applied to the surface of the metal or alloy forming the separator as necessary.

Hereinafter, the present invention will be described more specifically with reference to examples.
1. Corrosion test <1>
SUS316L (plate thickness of 0.1 mm) and gold (plate thickness of 0.1 mm) were electrically connected via a platinum wire to produce corrosion-resistant members according to Examples 1 to 4. At this time, the ratio of the surface area of gold to the total surface area of SUS316L and gold (= surface area of gold / (surface area of SUS316L + surface area of gold) × 100) is 5% (Example 1) and 9% (implementation), respectively. Example 2), 17% (Example 3), 50% (Example 4).

  On the other hand, SUS316L (plate thickness: 0.1 mm) alone was used as the corrosion-resistant member according to Comparative Example 1. Further, a SUS316L (plate thickness of 0.1 mm) with the entire surface plated with gold (thickness: 40 nm) (no sealing) was used as the corrosion-resistant member according to Comparative Example 2. The surface areas of gold in Comparative Examples 1 and 2 are 0% and 100%, respectively.

  Table 1 schematically shows the corrosion-resistant members according to Examples and Comparative Examples. In Table 1, points in the corrosion-resistant member according to Comparative Example 2 schematically show pinholes. Moreover, the surface area ratio of each gold | metal | money is the value computed not including the surface area of the end surface of each board | plate material.

  Next, a sulfuric acid corrosion test was performed on the corrosion resistant members according to these examples and comparative examples, and the ion elution amount was measured.

  That is, the corrosion-resistant members according to Examples and Comparative Examples were immersed and held in a boiling sulfuric acid solution (sulfuric acid concentration 1 wt%) for 168 hours, and the amount of ions eluted from each corrosion-resistant member was measured. At this time, the number of samples was n = 2. In addition, the ion elution amount was measured by an emission analysis method using ICPV-1000 (manufactured by Shimadzu Corporation) and using plasma as a light source.

  The result is shown in FIG. According to FIG. 2, the corrosion resistant member according to Examples 1 to 4 in which SUS316L and gold are electrically connected via a platinum wire as compared with the corrosion resistant member according to Comparative Example 1 which is a single SUS316L is ion-eluting. It can be seen that the amount is small and the corrosion resistance is excellent. In particular, it has been confirmed that the amount of ion elution is extremely reduced when the surface area ratio of gold exceeds 5%.

  Moreover, although the corrosion-resistant member which concerns on Examples 1-4 compared with the corrosion-resistant member which concerns on the comparative example 2 which gave the gold plating to the whole surface of SUS316L, in the sulfuric acid environment, although there is little usage-amount of gold | metal | money. It turns out that it has corrosion resistance equivalent to the corrosion-resistant member which concerns on the comparative example 2.

  From the above results, it was confirmed that according to the corrosion-resistant members according to Examples 1 to 4, it was possible to reduce the amount of gold used and to ensure sufficient corrosion resistance.

  This is because in the corrosion-resistant member according to Examples 1 to 4, since SUS316L is electrically connected to gold via a platinum wire, the potential of SUS316L is shifted from the active state region to the passive state region, It is presumed that this was because the passivation of SUS316L was promoted even in a sulfuric acid environment.

2. Corrosion test <2>
Next, each alloy plate (plate thickness 0.2 mm) shown in Table 2 and each noble metal simple substance or noble metal alloy (plate thickness 0.2 mm) were electrically connected through a platinum wire, and Examples 5 to 11 were used. A corrosion-resistant member according to the above was produced. At this time, the ratio of the surface area of each noble metal simple substance or noble metal alloy to the total surface area of each alloy plate and each noble metal simple substance or noble metal alloy was 25%.

  In addition, about the corrosion-resistant member which concerns on Example 10, the carbon type electrically conductive coating material was apply | coated (application | coating thickness of 10 micrometers) on the surface of the alloy (SUS316L).

  The carbon-based conductive paint imparts high corrosion resistance to the metal or alloy portion on which the separator is formed, for example, when a separator for a fuel cell is produced using the corrosion-resistant member according to the present invention. This is for reducing the contact resistance with the electrode portion. Here, the object is to confirm that there is no problem even if a carbon-based conductive paint is applied to the corrosion-resistant member according to the present invention.

  On the other hand, about the comparative example, the alloy single shown in Table 2 was made into the corrosion-resistant member which concerns on Comparative Examples 3-6. In addition, about the corrosion-resistant member which concerns on the comparative example 4, the carbon type electrically conductive coating material was apply | coated similarly to the corrosion-resistant member which concerns on Example 10. FIG.

  Subsequently, the above-described sulfuric acid corrosion test was performed on the corrosion resistant members according to the examples and comparative examples, except that the sulfuric acid concentration was 0.1 wt%, and the corrosion amount was measured.

  Table 2 shows the configurations of the corrosion-resistant members according to Examples and Comparative Examples and the results of the sulfuric acid corrosion test.

  According to Table 2, the corrosion resistance member according to Comparative Examples 3 to 5 has a corrosion amount of 20 mg, and the corrosion resistance member according to Comparative Example 6 has a corrosion amount of over 2 mg, indicating that the corrosion resistance is inferior.

  On the other hand, the corrosion resistance members according to Examples 5 to 11 using alloys having various components, noble metals, and noble metal alloys have an corrosion amount of less than 0.1 mg and have excellent corrosion resistance. I was able to confirm.

3. Next, a SUS316L plate (plate thickness of 0.1 mm) is pressed to form a gas flow path and the like, and an end portion of the SUS316L plate and a metal plate (plate thickness of 0.02 mm) are formed. The separator which concerns on Example 12 was produced electrically connected with the platinum wire.

  At this time, the surface area ratio of gold was 9%. The platinum wire and each plate material were connected by spot welding. In addition, the gas flow path of the separator was 2 mm in pitch, 1 mm in width, and 0.5 mm in depth.

  On the other hand, in the production of the separator according to Example 12, after the press working, the surface of the SUS316L plate was plated with 1 μm of Ni (base plating), and then 2 μm of gold was plated. A separator according to Comparative Example 7 was produced in the same manner except that the wires were not electrically connected.

  Further, in the production of the separator according to Example 12, the SUS316L after the press working was used as it was, and the end of the SUS316L plate and the metal plate were not electrically connected with a platinum wire. The separator according to FIG.

  Next, the separator according to Example 12 or Comparative Examples 7 and 8 and the membrane electrode assembly (MEA) were laminated to produce each polymer electrolyte fuel cell (PEFC).

  Next, a power generation test was performed for each PEFC for 200 hours, and the amount of metal ions present in each MEA was measured. At this time, the amount of metal ions was measured in the same manner as described above.

In the power generation test, current density: 0.3 A / cm ² , fuel gas: hydrogen (flow rate 0.5 L / min), oxidant gas: air (flow rate 2.0 L / min), humidification temperature: fuel electrode 70 ° C. The air electrode was 70 ° C., and the single cell temperature was 70 ° C. Table 3 shows the results.

According to Table 3, the PEFC using the separators according to Comparative Examples 7 and 8 in which the end portion of the SUS316L plate in which the gas flow path and the like are formed and the metal plate are not electrically connected with the platinum wire is included in the MEA. The total metal element concentration exceeded 10 g / 10 cm ² . Therefore, it can be said that the separators according to Comparative Examples 7 and 8 are inferior in corrosion resistance.

On the other hand, the PEFC using the separator according to Example 12 in which the end of the SUS316L plate in which the gas flow path or the like is formed and the metal plate are electrically connected with a platinum wire has a total metal element concentration in the MEA of 0. It was very small, less than 1 μg / 10 cm ² . Therefore, it can be said that the separator according to Example 12 is excellent in corrosion resistance.

  From the above results, it can be seen that the separator according to Example 12 has high corrosion resistance. In addition, it was confirmed that PEFCs using this were not easily subject to increase in electrical resistance due to corrosion of the separator or deterioration of electrolyte due to eluted ions, and it was easy to maintain battery performance.

  The corrosion-resistant member, the fuel cell separator, and the fuel cell according to the present invention have been described above. However, the present invention can be variously modified without departing from the spirit of the present invention.

It is the figure which showed typically an example of the electrical connection form of the metal or alloy, noble metal, and electroconductive member in the corrosion-resistant member which concerns on this invention. It is the figure which showed the relationship between the surface area ratio of the gold | metal | money of the corrosion-resistant member which concerns on an Example, and the amount of ion elution in a corrosion test <1>.

Explanation of symbols

10 Metal or alloy 12 Precious metal 14 Conductive member

Claims (5)

  A corrosion-resistant member, wherein a metal or alloy to be passivated and a noble metal are electrically connected via a conductive member.   The corrosion-resistant member according to claim 1, wherein the noble metal is gold, platinum, or an alloy containing at least one of these.   The corrosion-resistant member according to claim 1 or 2, wherein a ratio of a surface area of the noble metal to a total surface area of the metal or alloy and the noble metal is 5% or more.   A fuel cell separator using the corrosion-resistant member according to any one of claims 1 to 3.   A fuel cell using the fuel cell separator according to claim 4.

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