JP2010086897A - Fuel cell separator, and method of manufacturing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fuel cell separator which is low in contact resistance generated between the separator and an electrode, superior in corrosion resistance, and low in cost. <P>SOLUTION: The fuel cell separator 1 has a base layer 3 formed by a separator base material, a metal layer 4 which is formed on this base layer 3 and installed successively on the base layer 3 surface, and a metal nitride layer 5 formed on this metal layer 4. This fuel cell separator 1 is obtained by forming the metal layer 4 on a surface of the separator base material, and next by forming the metal nitride layer 5 on this metal layer 4 by physical vapor growth method. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a fuel cell separator and a method for manufacturing the fuel cell separator.

  In the fuel cell, in order to reduce the contact resistance of the separator to be used and increase the durability, a fuel cell in which a nitride layer is directly provided on the surface of the separator has been proposed.

For example, a fuel cell separator in which a conductive ceramic layer is formed on the surface of a stainless steel plate has been proposed (see Patent Document 1). In addition, a fuel cell separator has been proposed in which two or more different types of metal nitride layers are formed on the surface of a separator substrate (see Patent Document 2).
JP 2003-123783 A JP 2001-236967 A

  However, since the nitride has a characteristic of being hard, the nitride layer cannot be thickened. For this reason, film defects such as pinholes are likely to occur in the nitride layer, and there is a problem that the corrosion resistance cannot be maintained by long-term use. For this reason, the base material is limited to stainless steel and titanium having excellent corrosion resistance, and inexpensive aluminum or the like cannot be used.

  Further, there is a large difference in material hardness between the stainless steel and the nitride layer. For this reason, the adhesion of the nitride layer formed on the substrate surface to the substrate is poor, and there is a problem that the nitride layer is peeled off by long-term use and the durability is poor.

  Further, in order to reduce the mass productivity and cost of the separator, it is indispensable to perform the process of forming the separator shape after the surface treatment with the roll material. However, since the elongation of the nitride is small, there is a problem that the nitride layer is cracked by molding with a press or the like, the base material is exposed, and the ion elution amount increases. As described above, since the order of operations is limited to the order of surface treatment after press molding, there is a problem that productivity is poor and cost is high.

  The present invention has been made to solve the above problems, and a fuel cell separator according to the present invention includes a base layer formed by a separator base material and a base layer formed on the base layer and continuously provided on the base layer surface. And a metal nitride layer formed on the metal layer.

  The method for producing a fuel cell separator according to the present invention is characterized in that a metal layer is formed on the surface of a separator substrate, and then a metal nitride layer is formed on the metal layer by physical vapor deposition. .

  According to the present invention, it is possible to provide a fuel cell separator that has low contact resistance, excellent corrosion resistance, and low manufacturing costs.

  Further, according to the present invention, as described above, it is possible to manufacture a fuel cell separator that has low contact resistance, excellent corrosion resistance, and low cost.

  Hereinafter, the fuel cell separator and the method for producing the fuel cell separator according to the present invention will be described with reference to an example applied to a polymer electrolyte fuel cell.

  FIG. 1 is a plan view of a fuel cell separator 1 according to an embodiment of the present invention. FIG. 2 is an enlarged view of a main part of the fuel cell separator 1. A plurality of fuel cell separators 1 are alternately stacked with a single cell serving as a basic unit for generating electric power by an electrochemical reaction to constitute a fuel cell stack. The fuel cell stack is mounted on a fuel cell electric vehicle as a power source, for example.

  Each single cell forms a membrane electrode assembly by forming a gas diffusion layer having an oxidizer electrode and a gas diffusion layer having a fuel electrode on both sides of a solid polymer electrolyte membrane, and a fuel electrode on both sides of the membrane electrode assembly. The battery separator 1 is disposed and a gas flow path is defined inside the fuel cell separator 1. As the polymer electrolyte membrane, a perfluorocarbon polymer membrane having a sulfonic acid group (Nafion 1128 (registered trademark), DuPont) or the like can be used. After the single cell and the fuel cell separator 1 are stacked, end flanges are arranged at both ends, and the outer peripheral portion is fastened with fastening bolts to constitute a fuel cell stack. The fuel cell stack is supplied with a hydrogen supply line for supplying a fuel gas containing hydrogen such as hydrogen gas to each single cell, an air supply line for supplying air as an oxidant gas, and cooling water. A cooling water supply line is provided.

  Details of the fuel cell separator 1 shown in FIGS. The fuel cell separator 1 is obtained by surface-treating the surface portion 3a of the separator base material, and is formed on the base layer 3 that is an untreated layer of the base material formed by the separator base material, and on the base layer 3. It has a metal layer 4 provided continuously on the surface of the base layer 3 and a metal nitride layer 5 formed on the metal layer 4. The metal layer 4 is densely formed so as to cover the entire surface portion 3a of the base material, and the metal nitride layer 5 is formed on the metal layer 4 by physical vapor deposition. The lower surface 4 a of the metal layer 4 is in contact with the surface portion 3 a of the separator substrate, that is, the base layer 3, and the upper surface 4 b of the metal layer 4 is in contact with the lower surface 5 a of the metal nitride layer 5. The fuel cell separator 1 is formed with a groove-like flow path 2 of fuel or oxidant having a rectangular cross section by press molding. A flat plate portion defined by the flow channel 2 and the flow channel 2 is provided between the flow channel 2 and the flow channel 2, and the metal nitride layer 5 extends along the outer surface of the flow channel 2 and the flat plate portion. To do. The flat plate portion contacts the gas diffusion layer on the adjacent solid polymer membrane when the fuel cell separators 1 and the single cells are alternately stacked, and defines a fuel gas flow path between the flat plate portion and the gas diffusion layer. .

  In the fuel cell separator 1 according to the embodiment of the present invention, the metal nitride layer 5 is sandwiched between the base layer 3 and the metal nitride layer 5 so that a pinhole is formed in the metal nitride layer 5. Even if it exists, since the metal layer 4 shows corrosion resistance, the corrosion resistance of the fuel cell separator 1 is maintained. As described above, in the case of a single layer film of metal nitride, it is difficult to produce a coating without pinholes, so that the corrosion resistance deteriorates after long-term use. On the other hand, since the fuel cell separator 1 according to the embodiment of the present invention has the metal layer 4, this point can be solved. In addition, since the metal has a better elongation than the nitride, even if the outermost metal nitride layer 5 is cracked, the metal layer 4 is not cracked and the base layer 3 is not exposed. For this reason, the ion elution amount from the base layer 3 is kept low, and the durability is good.

  Moreover, by having the metal layer 4, it is not limited to the stainless steel and titanium which were excellent in corrosion resistance as a material of a base material, but cheap aluminum etc. can be used. For this reason, cost reduction can be achieved. When an aluminum material is used as the base material, the weight of the fuel cell can be reduced because aluminum is lightweight. Furthermore, since the metal nitride layer 5 having a low contact resistance is provided on the surface, a fuel cell separator having a low contact resistance can be provided. In addition, since the metal layer 4 between the base layer 3 and the metal nitride layer 5 improves the adhesion between the base layer 3 and the metal nitride layer 5, the metal nitride layer 5 is not easily peeled off over a long period of use. , Durability is improved.

  In the fuel cell separator 1 according to the embodiment of the present invention, the metal layer 4 is formed on the surface of the separator substrate, and then the metal nitride layer 5 is formed on the metal layer 4 by physical vapor deposition (PVD). Is obtained. When this method is used, the process of forming the roll material after the surface treatment is established, so that the mass productivity is good and the cost is low. Thus, according to the present invention, as described above, it is possible to manufacture a fuel cell separator that has low contact resistance, excellent corrosion resistance, and low cost.

  The metal layer 4 is formed by physical vapor deposition or plating the surface portion 3a of the separator substrate. Any method can be used as long as it is a method for forming a metal layer on the surface of a substrate. For example, electroplating and vapor deposition are mentioned. Among vapor deposition, PVD which is one of vacuum plating can be used. In film formation by PVD, first, the surface is sputter cleaned with argon in order to remove the oxide film from the surface of the separator substrate. Next, nitrogen gas is introduced together with argon to form a metal layer. When PVD is used, a metal layer can be easily formed on the surface of the separator substrate.

  As for the base material which forms the base layer 3, metal base materials, such as stainless steel material, titanium material, and aluminum material, are mentioned, for example. Since these metal materials are light, it is possible to reduce the weight of the fuel cell, and thus to reduce the weight and energy of the fuel cell vehicle. Moreover, these materials are easy to form a metal layer by surface treatment. As the stainless steel material, any of martensite, ferrite, austenite, austenite / ferrite, and precipitation hardening can be used depending on the application. As the titanium material, both pure titanium and a titanium alloy can be used, and as the aluminum material, both pure aluminum and an aluminum alloy can be used.

  The metal layer 4 preferably contains chromium. Since chromium has good corrosion resistance, when the metal layer 4 contains chromium, the amount of ions eluted from the fuel cell separator 1 is reduced. Moreover, since chromium is located in the middle of the hardness of the base material and the metal nitride when a stainless steel material, a titanium material, or an aluminum material is used as the base material, the base layer 3 is further added when the metal layer 4 contains chromium. And the metal nitride layer 5 are improved, and the durability is improved because the film does not peel off even when used for a long time. Further, since chromium has a better elongation than metal nitride, even if the outermost metal nitride is cracked, the chromium layer is not cracked, and the base layer 3 is not exposed because the chromium layer has few pinholes. Therefore, the ion elution amount from the fuel cell separator 1 is kept low, and the durability is improved.

  The metal nitride layer 5 preferably contains chromium nitride. Since chromium nitride has a low resistance, the conductivity of the fuel cell separator is improved. Further, since chromium nitride has good corrosion resistance, the amount of ion elution is reduced.

  The metal nitride layer 5 is formed on the metal layer 4 by PVD after forming the metal layer 4 on the surface of the separator substrate as described above. In this case, since chromium has a high sputter rate, the productivity is good and the cost is low. Also, since PVD can be coated with few defects such as pinholes, a metal nitride layer having good conductivity and corrosion resistance can be obtained. .

  As described above, according to the fuel cell separator and the method for manufacturing the fuel cell separator according to the embodiment of the present invention, a fuel cell separator having low contact resistance, excellent corrosion resistance, and low manufacturing cost can be obtained. In addition, the fuel cell stack to which the fuel cell separator according to the embodiment of the present invention is applied has excellent power generation performance. By mounting this fuel cell stack on a vehicle such as an automobile, the fuel consumption of the fuel cell vehicle is improved. Can do. Further, the present invention can be applied not only to fuel cell vehicles but also to aircraft and other engines that require electrical energy, and stationary fuel cells.

  Next, Examples 1 to 3 and Comparative Examples 1 to 3 will be described. Each example was for examining the effectiveness of the fuel cell separator according to the present invention, and each sample was prepared by treating the raw material under different conditions, and is limited to the illustrated example. is not.

<Preparation of sample>
In each example and comparative example, a JIS standard SUS316L vacuum annealed material (thickness 0.1 mm) was used as a base material. After degreasing and cleaning, the substrate surface was coated. The coating includes a step of sputter cleaning with argon gas, a step of forming a metal layer under an argon gas atmosphere (0.1 Pa to 10 Pa), a temperature of 200 ° C. and a bias voltage of 200 V, and a mixed gas atmosphere of argon and nitrogen (0. 1 Pa to 10 Pa), a temperature of 200 ° C., and a bias voltage of 200 V, including three steps of forming a metal nitride layer.

In Examples 1, 2, and 3, as shown in Table 1, the nitrogen partial pressure during coating was set in the range of 0.02 Pa to 1.00 Pa, respectively. Further, only the metal layer of Comparative Example 1 and the metal nitride layer of Comparative Example 2 were configured. In Comparative Example 6, the coating was not performed and the stainless steel substrate was used as it was.

  After measuring the contact resistance of the obtained sample, a corrosion test was performed and the contact resistance was measured again.

<Measurement of contact resistance value>
A sample was cut into a size of 30 mm × 30 mm from the vicinity of the center of the obtained sample, and the contact resistance of this sample was measured. As a measuring device, a pressure load contact electric resistance measuring device TRS-2000SS type manufactured by ULVAC-RIKO Inc. was used. As shown in FIG. 3, carbon papers 13a and 13b are interposed between the electrodes 11a and 11b and the sample 12 to form an electrode 11a / carbon paper 13a / sample 12 / carbon paper 13b / electrode 11b. An ammeter, a voltmeter, and a DC power source were connected to this assembly. The average value of the electrical resistance when a current of 1 A / cm ² was passed at a measurement surface pressure of 1.0 MPa was determined as the contact resistance value. The carbon paper is a carbon paper coated with a platinum catalyst supported by carbon black (carbon paper TGP-H-090 manufactured by Toray Industries, Inc., thickness 0.26 mm, bulk density 0.49 g / cm ³ , volume resistivity 0 in the thickness direction). .07Ω · cm ² ) was used. As the electrode, a Cu electrode having a diameter of φ10 was used.

<Corrosion test>
The sample was cut out to a size of 30 mm × 30 mm and then immersed in a sulfuric acid aqueous solution of pH 4 at a temperature of 80 ° C. for 70 hours.

<Result>
Regarding the results obtained in Examples 1 to 3 and Comparative Examples 1 to 3, Table 2 shows the contact resistance before and after the corrosion test.

  As shown in Comparative Example 3, when the substrate surface treatment was not performed, the contact resistance was high both before and after the corrosion test because there was an oxide film on the substrate surface. As shown in Examples 1 to 3, in the case of a multilayer structure in which a metal layer and a metal nitride layer were formed on the surface of a substrate, the contact resistance was kept low even after corrosion. On the other hand, in the case of the metal nitride single layer of Comparative Example 1, the resistance before corrosion was equivalent to the multilayer structure of Examples 1 to 3, but the metal nitride layer had defects such as pinholes. Due to the large number of structures, oxygen entered the metal nitride layer during the corrosion test, and the contact resistance after corrosion increased. In the case of the single metal layer of Comparative Example 2, an oxide film was formed on the surface of the metal layer, so that the contact resistance was high both before and after corrosion.

  From the above, the samples obtained in Examples 1 to 3 can be kept low in contact resistance before and after the corrosion test, and are excellent in corrosion resistance. Moreover, the surface treatment process is easy for the samples obtained in Examples 1 to 3. Thus, it has been found that the separator according to the embodiment of the present invention has both low contact resistance and corrosion resistance at the same time, and can be obtained at low cost. It was shown that by using this separator, the output of the fuel cell can be maintained in a high state and the durability is improved.

It is a top view which shows the fuel cell separator which concerns on embodiment of this invention. It is an enlarged view of the principal part of the fuel cell separator which concerns on embodiment of this invention. It is a schematic diagram explaining the apparatus used for the measurement of the contact resistance of the sample obtained in each Example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Fuel cell separator 2 ... Flow path 3 ... Base layer 3a ... Surface part 4 ... Metal layer 4a ... Lower surface 4b ... Upper surface 5 ... Metal nitride layer 5a ... Lower surface

Claims (5)

A base layer formed by a separator substrate;
A metal layer formed on the base layer and continuously provided on the surface of the base layer;
And a metal nitride layer formed on the metal layer.   The fuel cell separator according to claim 1, wherein the metal nitride layer includes chromium nitride.   The fuel cell separator according to claim 1, wherein the metal layer contains chromium. Forming a metal layer on the surface of the separator substrate,
Next, a method of manufacturing a fuel cell separator, comprising forming a metal nitride layer on the metal layer by physical vapor deposition.   The method of manufacturing a fuel cell separator according to claim 4, wherein the metal layer is formed by physical vapor deposition or plating.

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