Cooler component for fuel cell

Abstract

To provide a cooler component for fuel cells to be placed on a separator surface with high durability and low contact resistance.SOLUTION: The present invention relates to a cooler component for fuel cells comprising an aluminum substrate, a copper plating layer with an average thickness of 1.0 μm to 3.0 μm formed on the aluminum substrate, and a tin plating layer with an average thickness of 1.5 μm to 4.0 μm formed on the copper plating layer.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a cooler member for a fuel cell, and more particularly to a cooler member for a fuel cell that is disposed between separators for the fuel cell. [Background technology]

[0002] A fuel cell has a stack structure in which a predetermined number of unit cells are stacked, each of which generates electromotive force through a reaction between a fuel gas (hydrogen) and an oxidant gas (oxygen). Each unit cell has a membrane electrode assembly (MEA) with anode and cathode electrode layers (catalyst layers and gas diffusion layers) on both sides of an electrolyte membrane, and separators arranged on both sides of the MEA.

[0003] The separator functions to electrically connect the unit cells in series and also to act as a partition wall to isolate the fuel gas, oxidant gas, and coolant from each other.

[0004] Various studies have been conducted on such separators.

[0005] For example, Patent Document 1 discloses a fuel cell separator comprising a substrate made of pure aluminum or an aluminum alloy and a plating layer formed on the substrate, wherein the plating layer comprises a copper layer formed on the substrate side and a tin layer formed on the copper layer, the tin layer being formed as the outermost layer, the copper layer having a thickness of 0.10 μm or more, and the value obtained by dividing the thickness of the tin layer by the thickness of the copper layer being 0.1 to 50.

[0006] Patent Document 2 discloses a fuel cell separator comprising a substrate made of pure aluminum or an aluminum alloy, a copper layer formed on the substrate, a tin layer formed on the copper layer, and a metal layer formed on the tin layer and made of one or more metals selected from the group consisting of titanium, vanadium, chromium, zirconium, niobium, molybdenum, hafnium, tantalum, and tungsten, or an alloy based on such metals, wherein the thickness of the metal layer is 0.5 to 100 nm. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Laid-Open No. 2011-071080 [Patent Document 2] Japanese Patent Application Laid-Open No. 2011-198573 Summary of the Invention [Problem to be solved by the invention]

[0008] Fuel cells generate high heat of reaction and heat resulting from resistance during operation, and this heat must be cooled. Fuel cell cooling methods can be broadly divided into air-cooled and water-cooled. In order to simplify the configuration and reduce size, air-cooled fuel cells are desirable, as they can use part of the air, which is also the fuel cell's raw material, as a cooling medium. In such air-cooled fuel cells, the parts that come into contact with the cooling medium, such as the separator surface, must be made of metal with good thermal conductivity.

[0009] On the other hand, fuel cell separators also play a role in passing the generated current to adjacent cells, so the substrate that makes up the separator must have high conductivity and conductive durability to maintain that high conductivity for long periods of time, even in the high-temperature, acidic atmosphere inside the fuel cell. Here, high conductivity and conductive durability mean low contact resistance. Contact resistance refers to the voltage drop that occurs between the electrode and the separator surface due to interfacial phenomena.

[0010] Therefore, an object of the present invention is to provide a fuel cell cooler member that has high durability and low contact resistance and is to be disposed on the surface of a separator. [Means for solving the problem]

[0011] Aluminum metal, which has good thermal conductivity, is commonly used as a cooler material. However, because aluminum metal forms a passive film on its surface, it is not possible to obtain the high electrical conductivity (low contact resistance) required for a cooler material for a fuel cell.

[0012] To address this issue, surface treatments such as plating with gold or silver could be considered to impart conductivity to aluminum metal, but these metals are more expensive than other metals, reducing the cost competitiveness of parts.

[0013] Furthermore, condensation occurs in the cooler component during use. If condensation adheres to the surface treatment film, it is possible that corrosion of the aluminum base material will occur from defects in the surface treatment film, resulting in a loss of electrical conductivity.

[0014] Therefore, the present inventors have investigated various means for solving the above problems, and have found that in a cooler member using an aluminum substrate as the base material, by applying a 1.0 μm to 3.0 μm undercoat copper plating layer on the aluminum substrate and then applying a 1.5 μm to 4.0 μm top layer tin plating layer on the undercoat copper plating layer, the contact resistance of the obtained cooler member is 14 mΩ cm 2 The inventors have found that it is possible to manufacture a cooler member having both electrical conductivity and durability, with a working life of less than 1000 sq. m, and have completed the present invention.

[0015] That is, the gist of the present invention is as follows. (1) an aluminum substrate; a copper plating layer having an average film thickness of 1.0 μm to 3.0 μm formed on an aluminum substrate; A tin plating layer having an average thickness of 1.5 μm to 4.0 μm formed on the copper plating layer. A fuel cell cooler member comprising: [Effects of the Invention]

[0016] The present invention provides a fuel cell cooler member for placement on a separator surface, which has high durability and low contact resistance. [Brief explanation of the drawings]

[0017] [Figure 1] FIG. 1 is a schematic diagram showing an example of the basic structure of a contact resistance measuring device. [Figure 2] 1 is a graph showing the relationship between the thickness of the copper plating layer and the thickness of the tin plating layer and the contact resistance after a high-temperature immersion test in Examples 1 to 7 and Comparative Examples 1 to 4. [Figure 3] 1 is a graph showing the relationship between the arithmetic mean height (Sa) as the surface roughness after a high-temperature immersion test and the contact resistance in Examples 1 to 7 and Comparative Examples 1 to 4. DETAILED DESCRIPTION OF THE INVENTION

[0018] Preferred embodiments of the present invention will now be described in detail. In this specification, the features of the present invention will be described with reference to the drawings as appropriate. In the drawings, the dimensions and shapes of each part are exaggerated for clarity and do not accurately depict the actual dimensions and shapes. Therefore, the technical scope of the present invention is not limited to the dimensions and shapes of each part shown in these drawings. Note that the fuel cell cooling member of the present invention is not limited to the following embodiments, and can be embodied in various forms including modifications and improvements that can be made by those skilled in the art without departing from the gist of the present invention.

[0019] The fuel cell cooler member of the present invention is a component of the fuel cell and is disposed on the surface of a separator, which is a portion that comes into contact with a cooling medium, for example, between two separators. The separators are disposed on both sides of a membrane electrode assembly (electrolyte membrane, anode and cathode electrode layers disposed on both sides of the electrolyte membrane).

[0020] The substrate of the fuel cell cooler member of the present invention is an aluminum substrate, which may be made of aluminum metal alone or an alloy of aluminum metal and another metal (aluminum alloy).

[0021] The average thickness of the aluminum substrate is usually 0.09 mm to 0.11 mm.

[0022] Here, in the present invention, the "average thickness" or "average film thickness" can be calculated by observing an object, such as an aluminum substrate or a plating layer, using an optical microscope or a scanning electron microscope (SEM), measuring the thickness or film thickness of any 10 or more portions, and calculating the average value of the thickness or film thickness.

[0023] The average thickness of the copper (Cu) plating layer formed as the undercoat plating layer on the aluminum substrate is 1.0 μm to 3.0 μm.

[0024] The copper plating layer having the above average thickness can ensure rust prevention, plating adhesion, and whisker resistance.

[0025] The average thickness of the tin (Sn) plating layer formed as a surface plating layer on the copper plating layer is 1.5 μm to 4.0 μm.

[0026] The tin plating layer having the above average thickness can ensure electrical conductivity and rust prevention.

[0027] The fuel cell cooler member of the present invention typically has a resistance of 14 mΩ·cm 2 The contact resistance after the durability test is less than

[0028] Furthermore, in the fuel cell cooler member of the present invention, the arithmetic mean height (Sa) as the surface roughness after the durability test is usually 0.43 μm or less.

[0029] Here, the durability test refers to a high temperature immersion test in the following examples.

[0030] The fuel cell cooler member of the present invention can be produced by a method known in the art, except that the average thickness of the copper plating layer and the tin plating layer is within the above-mentioned range. Examples of methods for forming each plating layer include electroplating, displacement plating, and electroless plating.

[0031] The fuel cell cooler member of the present invention can be disposed between fuel cell cells (single cells) in an air-cooled fuel cell. The fuel cell cell is composed of a membrane electrode assembly and two separators disposed on both sides of the assembly. The fuel cell cooler member of the present invention can ensure the electrical conductivity and rust prevention required for the fuel cell while maintaining the cooling efficiency of the fuel cell. [Example]

[0032] Hereinafter, several examples of the present invention will be described, but it is not intended that the present invention be limited to those shown in these examples.

[0033] A copper plating layer having various average film thicknesses was formed on an aluminum substrate as a base plating layer, and then a tin plating layer having various average film thicknesses was formed on the copper plating layer as a surface plating layer to form fuel cell cooler components (Examples 1 to 7 and Comparative Examples 1 to 4).

[0034] The contact resistance of each of the obtained cooler members of Examples 1 to 7 and Comparative Examples 1 to 4 was measured before and after a high-temperature immersion test as a durability test.

[0035] (High temperature immersion test) ·Solution: Pure water (pH6.0) ·Temperature: 80℃ Duration: 100 hours ·method: 1. The cooling element was placed in a container and 500 ml of pure water was added. 2. The container was covered with a lid and placed in a thermostatic bath (80°C). 3. After 100 hours, the container was removed. 4. The cooler components were dried and the contact resistance was measured.

[0036] (Contact resistance measurement) ·Device: The contact resistance was measured using a DC resistance measuring device (or a constant current application device and a voltmeter DC device as shown in FIG. 1). (1) Figure 1 shows an example of the basic structure of a contact resistance measuring device. (2) The contact resistance was measured using the four-terminal method. (3) A current terminal was connected to the current electrode, and a voltage measurement terminal (clip) was connected to one end of the cooler member (test piece) and one end of the separator. (4) The jig was designed so that a load could be applied to the test piece, and the load could be set to any desired surface pressure on the test piece.

[0037] ·Measurement method: (a) The test piece and the separator were placed one on top of the other so that they protruded from the current electrode contact area on all sides and the cooling water surface of the separator was in contact with the test piece. (b) The contact surfaces of the upper and lower current electrodes were brought into contact with each other without any misalignment, and a pressure of 0.8 MPa (with an accuracy of ±2%) was applied. (c) Voltage measurement terminals (clips) were connected to the test piece and separator, and an arbitrary current was passed through the current electrode in the translaminar direction. (d) After applying the surface pressure, the resistance value was measured for 10 to 30 seconds. (e) The resistance value multiplied by the contact area (≒ current electrode contact area) is the contact resistance [mΩ cm 2 ].

[0038] The results are shown in Table 1 and Figure 2.

[0039] [Table 1]

[0040] From Table 1 and Figure 2, by adjusting the average thickness of the copper plating layer formed on the aluminum substrate to 1.0 μm to 3.0 μm and the average thickness of the tin plating layer formed on the copper plating layer to 1.5 μm to 4.0 μm, the contact resistance after the high-temperature immersion test was reduced to 14 mΩ cm. 2 I found that I could do less than that.

[0041] Furthermore, Figure 3 shows the relationship between the arithmetic mean height (Sa) as the surface roughness after the high-temperature immersion test and the contact resistance. Figure 3 shows that cooler components with an Sa of 0.43 μm or less after the high-temperature immersion test have a contact resistance of 14 mΩ cm 2 It was found that the contact resistance after the high temperature immersion test was less than 1000kJ / cm2.

Claims

[Claim 1] An aluminum substrate; a copper plating layer having an average thickness of 1.0 μm to 3.0 μm formed on an aluminum substrate; a tin plating layer having an average thickness of 1.5 μm to 4.0 μm formed on the copper plating layer; A fuel cell cooler member comprising:

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