JP4100473B2 - Metal separator for fuel cell and manufacturing method thereof - Google Patents

Description

  The present invention relates to a metal separator for a polymer electrolyte fuel cell and a method for manufacturing the same, and in particular, by preventing peeling of a gold coating layer from a material plate, preventing a decrease in contact resistance of the separator, The present invention relates to a technology for developing a fuel cell that maintains high power generation efficiency over a long period of time.

  In the polymer electrolyte fuel cell, a laminated body in which separators are laminated on both sides of a plate-like electrode is one unit, and a plurality of units are laminated to constitute a fuel cell stack. The electrode has a three-layer structure in which an electrolyte layer made of an ion exchange resin or the like is sandwiched between a pair of gas diffusion electrode plates (a positive electrode plate and a negative electrode plate). The separator is formed with a gas passage through which a gas flows between the gas diffusion electrode plate. In such a fuel cell, for example, an electrochemical reaction is induced by causing an oxidizing gas such as oxygen or air to flow through a gas passage facing the gas diffusion electrode plate on the negative electrode side, thereby generating electricity.

  By the way, as the material of the separator, there are a gas-impermeable graphite material obtained by impregnating a fired isotropic graphite with a resin such as phenol, and an amorphous carbon material obtained by firing a component shape with a resin such as phenol. Can be mentioned. In addition, graphite-based materials such as composite molding materials made of resin and graphite, and highly corrosion-resistant metal materials such as stainless steel or titanium alloys are also used. Furthermore, metal-based materials such as metal materials whose surfaces are coated with noble metal-based plating such as gold or platinum are also used.

  In the separator using such various materials, for example, it is disposed on both sides of a fuel cell module including a positive electrode, a negative electrode, and an electrolyte interposed between the positive and negative electrodes, and a groove for gas circulation is formed. There has been proposed a fuel cell metal separator in which a noble metal composite plating film in which fluororesin or fluorinated graphite particles are co-deposited is formed on the surface of the groove (see Patent Document 1). The separator plate is provided with a plurality of parallel and straight gas flow passage grooves on the surface of the metal plate on which the noble metal film is formed, and a heat-resistant and acid-resistant plastic frame for fixing the periphery of the separator plate. A separator for a polymer electrolyte fuel cell has been proposed in which a gas flow passage tube, a guide groove, and the like are formed in the plastic frame (see Patent Document 2). Both of the separators described in Patent Documents 1 and 2 are obtained by coating the surface of a metal material plate with gold plating.

JP 2000-36309 A (abstract) JP 2003-223905 A (abstract)

  However, in the separators described in Patent Documents 1 and 2, during power generation of the fuel cell, the adhesion of the gold coating layer to the material plate decreases, thereby increasing the contact resistance of the separator, and high power generation efficiency. There was a problem that it could not be maintained for a long time.

  The present invention has been made to solve the above-described problems of the prior art, and prevents peeling of the gold coating layer from the material plate during power generation of the fuel cell, thereby reducing the contact resistance of the separator. An object of the present invention is to provide a metal separator for a fuel cell and a method for producing the same.

The inventors of the present invention diligently researched a means for preventing peeling of the gold coating layer from the material plate during power generation of the fuel cell. As a result, in the normal separator obtained by the techniques described in Patent Documents 1 and 2 above, it is noted that a sufficient anchor effect is not obtained between the conductive inclusion and the gold coating layer. It was confirmed that this is the cause. Therefore, when the average roughness Ra of the surface of the material plate before gold plating is set to 0.4 μm or more in order to improve the anchor effect, there is a sufficient anchor effect between the conductive inclusion and the gold coating layer. The knowledge that it was obtained was obtained. This is because when gold particles adhere to the surface of the roughened material plate, the conductive inclusions and gold are intertwined in a complicated manner while ensuring a sufficient contact area. In addition, when such an excellent anchor effect is obtained, the present inventors improve the adhesion between the conductive inclusion and the gold, and prevent the gold coating layer from being peeled off from the material plate. I was sure that. On the other hand, when the above-mentioned average roughness Ra exceeds 5.2 μm, the inventors can improve the adhesion by securing a sufficient contact area between the conductive inclusion and gold. Since the amount of the conductive inclusions protruding from the material plate is large, the substantial contact area between the separator and the carbon paper as the diffusion layer is small, and it has been found that the battery performance may be deteriorated. Furthermore, the present inventors have confirmed that, for example, it is preferable that the surface of stainless steel is subjected to a thermal cutting treatment with ferric chloride as a roughening means for the material plate. In addition, when Cr ₂ B, TiN, ZrN, CrN, TiC, TaC, CrC, or the like is used as the conductive inclusion, sufficient anchor effect suitable between gold by performing the above-described cutting processing It was also confirmed that

The metal separator for a fuel cell according to the present invention is made based on the above knowledge, and in the metal separator for a fuel cell provided with an austenitic stainless steel plate having corrosion resistance, the surface of the austenitic stainless steel plate is subjected to cutting. On the conductive inclusion protruding from the surface of the austenitic stainless steel sheet after the treatment, the conductive inclusion protrudes from the surface and the average roughness Ra of the surface is 0.4 to 5.2 μm. It is characterized by forming a gold coating layer.

Further, the method for producing a fuel cell metal separator according to the present invention is a method for suitably producing the fuel cell metal separator, wherein the surface of the austenitic stainless steel plate is subjected to a cutting process by performing a cutting process. The conductive inclusions are projected from the surface so that the average roughness Ra of the surface is 0.4 to 5.2 μm , the surface of the austenitic stainless steel plate is passivated, and then the conductive property is not applied. A gold coating layer is formed by directly performing gold plating on the inclusions.

In the present invention, the average roughness Ra of the surface of the austenitic stainless steel plate before gold plating is 0.4 to 5.2 μm, and the reasons for this limitation are as follows. That is, when the surface roughness Ra is less than 0.4 μm, the amount of conductive inclusions protruding from the austenitic stainless steel sheet is small, so that gold particles adhere to the roughened austenitic stainless steel sheet surface. In addition, a sufficient contact area between the conductive inclusion and gold cannot be secured, and these cannot be entangled in a complicated manner. For this reason, a sufficient anchor effect cannot be obtained, and peeling of the gold coating layer from the austenitic stainless steel sheet during power generation cannot be prevented. On the other hand, when the surface roughness Ra exceeds 5.2 μm, a sufficient contact area between the conductive inclusion and gold can be secured, and these can be intertwined in a complicated manner. However, since the amount of the conductive inclusion protruding from the austenitic stainless steel sheet is large, the substantial contact area between the separator and the carbon paper as the diffusion layer is small, which may lead to a decrease in battery performance. Therefore, according to the present invention, by optimizing the average roughness Ra of the surface of the austenitic stainless steel plate before gold plating, the conductive inclusions and the gold coating layer are brought about without causing deterioration in battery performance. A sufficient anchoring effect can be obtained between the two, preventing peeling of the gold coating layer from the austenitic stainless steel plate during power generation of the fuel cell, and in turn preventing a decrease in the contact resistance of the separator. be able to. Therefore, the fuel cell using the separator of the present invention can maintain high power generation efficiency for a long time.

Hereinafter, a preferred embodiment of the present invention will be described.
When producing the fuel cell metallic separator of the present invention, first, the surface of the stainless steel blank is subjected to a cutting process using ferric chloride, and the average roughness Ra of the surface of the blank is determined. Adjust to 0.4 to 5.2 μm. Next, the surface of the base plate from which the conductive inclusions protrude is subjected to passivation treatment, and gold plating is directly applied to the conductive inclusions without applying a base treatment to cover the conductive inclusions with gold. Form a layer. In addition, in the place mentioned above, although the cutting process is used for roughening of a raw material board, roughening is not restricted to this, For example, other roughening processes, such as blasting, are also employable. it can.

  1 (a) to 1 (c) are main part conceptual views showing states after gold plating of various metal separators for fuel cells, in which the average roughness Ra of the surface of the material plate before gold plating is varied. . FIG. 1A is a conceptual diagram of a main part of a metal separator for a fuel cell according to the present invention. According to the figure, the average roughness Ra of the surface of the material plate before gold plating is 0.4-5. Since the protrusion amount of the conductive inclusions from the material plate is within an appropriate range because it is 2 μm, excellent adhesion due to a sufficient contact area between the conductive inclusions and gold can be secured. Therefore, it is possible to prevent the gold covering layer from being peeled off from the material plate during power generation of the fuel cell.

  On the other hand, FIG. 1B shows that the average roughness Ra of the surface of the material plate before gold plating is less than 0.4 μm, so that when gold particles adhere to the roughened material plate surface, A sufficient contact area between the sexual inclusions and gold cannot be ensured, and these cannot be intertwined in a complicated manner. For this reason, a sufficient anchor effect cannot be obtained, and peeling of the gold coating layer from the material plate cannot be prevented during power generation. Further, FIG. 1 (c) shows that the average roughness Ra of the surface of the material plate before gold plating exceeds 5.2, so that the amount of conductive inclusions protruding from the material plate is large, and the diffusion with the separator Since the substantial contact area with the carbon paper as the layer is reduced, the battery performance may be deteriorated.

Next, examples of the present invention will be described.
A. Production of separator [Comparative Example 1]
An austenitic stainless steel plate having the components shown in Table 1 was rolled to a thickness of 0.2 mm, and a 100 mm × 100 mm square thin plate was cut out from the rolled steel. Next, this thin plate was press-molded to obtain a separator plate as shown in FIG. This material plate has a power generation part with a concave-convex cross section at the center and a flat edge around the power generation part. Further, in this material plate, B in the component is precipitated in the metal structure as M ₂ B and MB type borides and M ₂₃ (C, B) ₆ type borides, and these borides are separated into the separator. It is a conductive inclusion that forms a conductive path on the surface.

Next, passivation treatment was performed on both surfaces of the material plate to form a strong oxide film on the surface of the material plate. The passivation treatment was performed by degreasing and washing the material plate with acetone for 10 minutes and then immersing in a 50 wt% nitric acid bath maintained at 50 ° C. for 10 minutes. After the passivation treatment, washing with normal temperature water was performed twice for 10 minutes, followed by drying. Next, gold plating was performed on both surfaces of the material plate. Gold plating was performed by dipping for 10 minutes in a plating bath of gold cyanide (3 g / L) maintained at 30 ° C. and having a current density set to 1 A / dm ² . After gold plating, washing with normal temperature water for 10 minutes was performed twice to obtain a separator of Comparative Example 1. In the separator of Comparative Example 1, the average roughness Ra of the surface of the material plate before gold plating was 0.2 μm.

[Invention Examples 1 to 5 and Comparative Example 2]
After carrying out the passivation treatment, washing, and drying employed in Comparative Example 1 above, subjecting the surface to an average roughness Ra of 0.4 to 7.3 μm by subjecting it to a cutting with ferric chloride. After adjusting, the said gold plating and water washing were performed, and each separator of this invention 1-5 and the comparative example 2 was obtained.

B. Measurement of initial contact resistance for each comparative example and each inventive example The initial contact resistance at a contact surface pressure of 10 kg / cm ² and 25 ° C. was measured. These results are shown in Table 2 and FIG.

  According to Table 2 and FIG. 3, the separators (Invention Examples 1 to 5) that were subjected to the cutting treatment before gold plating were compared to the separators (Comparative Example 1) that were subjected to the gold plating treatment without performing the cutting treatment. It can be seen that the contact resistance is excellent. This is because by roughening the surface of the material plate, the substantial contact area with the carbon paper as the diffusion layer is large. On the other hand, the separator (Comparative Example 2) having an average roughness of 7.3 shows a higher contact resistance value than the respective inventive examples. This is because the amount of conductive inclusions protruding from the material plate is too large, so that the substantial contact area with the carbon paper as the diffusion layer is small.

C. Measurement of contact resistance after energization for Comparative Example and Example of the Invention After conducting energization at 75 ° C. for 4 hours, the test was allowed to stand at 25 ° C. for 1 hour for 250 cycles, and a durability test for 1250 hours in total. The contact resistance was measured at 25 ° C. with a contact pressure of 10 kg / cm ² . The results are also shown in Table 2 and FIG.

  According to Table 2 and FIG. 3, about the separator (comparative example 1) which has not performed the cutting process, it turns out that the contact resistance after durability rises remarkably. On the other hand, it can be seen that almost no increase in contact resistance is observed for the separators (Invention Examples 1 to 5 and Comparative Example 2) subjected to the thermal cutting treatment. This is because the surface of the surface is roughened by performing a cutting process, so that the contact area between the conductive inclusion and the gold can be sufficiently secured, and these are intricately entangled and closely adhered to each other. This is because peeling of the layer is prevented.

  The metal separator for a fuel cell according to the present invention can prevent peeling of the gold coating layer from the material plate during power generation of the fuel cell, and thus can prevent a decrease in the contact resistance of the separator. It can be used as various power sources that are required to maintain efficiency over a long period of time, and in particular, can be used in a wide range of fields such as the automobile industry, electrical equipment industry, and communication industry.

It is a principal part conceptual diagram of various metal separators for fuel cells, (a) shows the case where the average roughness Ra of the surface of the raw material board before heat processing is appropriate, (b) shows that said Ra is less than 0.4 micrometer. (C) shows the case where the Ra exceeds 5.2 μm. It is a photograph of the material board of the separator manufactured by each comparative example and each example of the present invention. It is a graph which shows the relationship between the initial contact resistance and contact resistance after electricity supply about each comparative example and each example of this invention, and average roughness Ra of the surface of a raw material board.

Claims (2)

In a metal separator for a fuel cell comprising an austenitic stainless steel plate having corrosion resistance, the surface of the austenitic stainless steel plate is subjected to a cutting process so that conductive inclusions protrude from the surface, and the average roughness Ra of the surface is A metal separator for a fuel cell, characterized in that a gold coating layer is formed on conductive inclusions having a thickness of 0.4 to 5.2 μm and protruding from the surface of the austenitic stainless steel plate . By performing scarfing process on the surface of austenitic stainless steel, it is protruded conductive inclusions from the surface by the average roughness Ra of the surface and 0.4～5.2Myuemu, the surface of the austenitic stainless steel A method for producing a metallic separator for a fuel cell, comprising performing a passivation treatment and then performing gold plating directly on the conductive inclusions without performing a base treatment to form a gold coating layer.

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