Cooler components for fuel cells

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, specifically, a cooler member for a fuel cell disposed between separators for a fuel cell.

Background Art

[0002] A fuel cell has a stack structure in which a predetermined number of single cells that generate electric power by the reaction of a fuel gas (hydrogen) and an oxidant gas (oxygen) are stacked. A single cell includes a membrane electrode assembly having anode and cathode electrode layers (catalyst layer and gas diffusion layer) on both sides of an electrolyte membrane, and separators disposed on both sides of the membrane electrode assembly, respectively.

[0003] The separator has a function of electrically connecting single cells in series and a function as a partition wall that blocks fuel gas, oxidant gas, and cooling water from each other.

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

[0005] For example, Patent Document 1 discloses a fuel cell separator including a substrate made of pure aluminum or an aluminum alloy and a plating layer formed on the substrate, the plating layer including a copper layer formed on the substrate side and a tin layer formed on the copper layer, the tin layer being formed on the outermost layer, the thickness of the copper layer being 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, which is 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 Publication No. 2011-071080 [Patent Document 2] Japanese Patent Publication No. 2011-198573 [Overview of the project] [Problems that the invention aims to solve]

[0008] Fuel cells generate high levels of heat during operation due to reaction heat and resistance, requiring cooling. There are two main types of fuel cell cooling methods: air cooling and water cooling. To simplify the configuration and miniaturize the device, air cooling, which allows the use of a portion of the air (a raw material for the fuel cell) as a cooling medium, is preferable. In such air-cooled fuel cells, it is necessary to use a metal with good thermal conductivity for the parts that come into contact with the cooling medium, such as the separator surface.

[0009] On the other hand, since fuel cell separators also play a role in passing the generated current to adjacent cells, the substrates that make up the separators are required to have high conductivity and conductivity durability to maintain that high conductivity for a long period of time even in the high temperature and acidic atmosphere inside the fuel cell cells. Here, high conductivity and conductivity 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, the object of the present invention is to provide a fuel cell cooler component for placement on a separator surface that has high durability and low contact resistance. [Means for solving the problem]

[0011] Aluminum metal, which has good thermal conductivity, is commonly used as a cooler component. However, because the surface of aluminum metal forms a passive film, it cannot obtain the high conductivity (low contact resistance) required for fuel cell cooler components as described above.

[0012] In response to this, surface treatments such as plating with gold or silver can be considered to impart conductivity to aluminum metal. However, these metals are more expensive than other metals, reducing the price competitiveness of the parts.

[0013] Furthermore, condensation water is generated in the cooler component during use. If this condensation water adheres to the surface treatment film, it is possible that the aluminum base material may corrode starting from defects in the surface treatment film, potentially impairing its conductivity.

[0014] Therefore, the inventors have investigated various means to solve the above problem and have found that in a cooler member using an aluminum substrate as the base material, a 1.0 μm to 3.0 μm undercoat copper plating is applied to the aluminum substrate, and then a 1.5 μm to 4.0 μm surface tin plating is applied on the undercoat copper plating layer, resulting in a cooler member with a contact resistance of 14 mΩ·cm. 2 We discovered that it is possible to manufacture a cooler component that achieves both conductivity and durability by reducing the material density to less than [amount missing], thus completing the present invention.

[0015] In other words, the gist of this invention is as follows: (1) Aluminum substrate and A copper plating layer with an average thickness of 1.0 μm to 3.0 μm formed on an aluminum substrate, A tin plating layer with an average film thickness of 1.5 μm to 4.0 μm formed on a copper plating layer and A cooler member for a fuel cell.

Effect of the Invention

[0016] According to the present invention, there is provided a cooler member for a fuel cell for arranging on the surface of a separator, which has high durability and low contact resistance.

Brief Description of the Drawings

[0017] [Figure 1] It is a schematic diagram showing an example of the basic structure of a contact resistance measuring device. [Figure 2] It is a graph showing the relationship between the film thickness of the copper plating layer, the film 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] It 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.

Modes for Carrying Out the Invention

[0018] Hereinafter, preferred embodiments of the present invention will 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 cooler member for a fuel cell of the present invention is not limited to the following embodiments, and can be implemented in various forms with modifications and improvements that can be made by those skilled in the art without departing from the gist of the present invention.

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

[0020] The base material of the cooler member for a fuel cell of the present invention is an aluminum substrate. The aluminum substrate may be composed of only aluminum metal or an alloy of aluminum metal and other metals (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, for example, 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 obtaining the average value of the thickness or film thickness.

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

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

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

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

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

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

[0029] Here, the durability test is shown in the high-temperature immersion test in the following example.

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

[0031] The fuel cell cooler component of the present invention can be placed between fuel cell cells (single cells) in an air-cooled fuel cell. A fuel cell cell consists of a membrane electrode assembly and two separators arranged on both sides of it. The fuel cell cooler component of the present invention makes it possible to maintain the cooling efficiency of the fuel cell while ensuring the conductivity and corrosion resistance required for the fuel cell. [Examples]

[0032] The following describes some embodiments of the present invention, but the present invention is not intended to be limited to those shown in these embodiments.

[0033] Cooler components for fuel cells (Examples 1-7 and Comparative Examples 1-4) were formed by forming copper plating layers as undercoat plating layers with varying average film thicknesses on an aluminum substrate, and then forming tin plating layers as surface plating layers on top of the copper plating layers with varying average film thicknesses.

[0034] For each of the cooler components obtained in Examples 1-7 and Comparative Examples 1-4, the contact resistance 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℃ • Time: 100 hours ·method: 1. Place the condenser components into the container and add 500 ml of distilled water. 2. The container was covered and placed in a constant temperature bath (80°C). 3. The container was removed after 100 hours. 4. The cooler components were dried and the contact resistance was measured.

[0036] (Contact resistance measurement) ·Device: Contact resistance was measured using a DC resistance measuring instrument (or a constant current application device and DC voltmeter as shown in Figure 1). (1) Figure 1 shows an example of the basic structure of a contact resistance measuring device. (2) The contact resistance value was measured using the four-terminal method. (3) A current terminal was connected to the current electrode. A voltage measuring terminal (clip) was connected to one end of the cooler component (test piece) and the separator. (4) The jig is designed to be able to apply a load to the test specimen, and the load is designed to allow the surface pressure of the test specimen to be set arbitrarily.

[0037] ·Measurement method: (a) The test specimen and separator were set up so that they extended beyond the current electrode contact area on all sides, and the test specimen was placed on top of the separator so that it was in contact with the cooling water surface side of the separator. (b) The upper and lower current electrodes were brought into contact so that their contact surfaces did not shift, and a pressure of 0.8 MPa (accuracy ±2%) was applied. (c) Voltage measuring terminals (clips) were connected to the test specimen and separator. An arbitrary current was passed through the current electrodes in the translayer direction. (d) After applying surface pressure, the resistance value was measured between 10 and 30 seconds. (e) Contact resistance [mΩ·cm] is the value obtained by multiplying the resistance by the contact area (≈ area of ​​current electrode contact). 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 adjusting 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 It was found that it could be done in less than [amount missing].

[0041] Furthermore, Figure 3 shows the relationship between the arithmetic mean height (Sa) as surface roughness after the high-temperature immersion test and the contact resistance. From Figure 3, it can be seen that the cooler component with an Sa of 0.43 μm or less after the high-temperature immersion test has a contact resistance of 14 mΩ·cm. 2 It was found to have a contact resistance of less than 100% after high-temperature immersion testing.

Claims

[Claim 1] A cooler member disposed between separators in an air-cooled fuel cell, Aluminum substrate and A copper plating layer with an average thickness of 1.0 μm to 3.0 μm formed on an aluminum substrate, A tin plating layer with an average thickness of 1.5 μm to 4.0 μm is formed on the copper plating layer. The cooler member comprising the above-mentioned features.

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