JP2003123801A - Polymer electrolyte stacked fuel cell - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent voltage drop caused by contact resistance on the cooling surface between separator plates in a polymer electrolyte stacked fuel cell. SOLUTION: The polymer electrolyte stacked fuel cell has a conductive sheet gasket 30, preferably containing conductive carbon between contact faces of separator plates 10A, 20A equipped with channels 16, 26 of cooling water for constituting a cooling part.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fuel cell useful as a power generator for a consumer cogeneration system or a mobile body, and more particularly to a polymer electrolyte type laminated fuel cell using a polymer electrolyte.

[0002]

2. Description of the Related Art A fuel cell using a polymer electrolyte membrane generates electric power and heat at the same time by electrochemically reacting a fuel gas containing hydrogen with an oxidant gas containing oxygen such as air. Let This fuel cell is basically
It is composed of a polymer electrolyte membrane that selectively transports hydrogen ions, and a pair of electrodes formed on both sides of the polymer electrolyte membrane, that is, an anode and a cathode. The electrodes are
Usually, the main component is a carbon powder carrying a platinum group metal catalyst, a catalyst layer formed on the surface of the polymer electrolyte membrane, and formed on the outer surface of this catalyst layer, which has both air permeability and electron conductivity. The diffusion layer is made of carbon fiber. Gaskets are arranged around the electrodes with a polymer electrolyte membrane sandwiched therebetween so that the fuel gas and the oxidant gas supplied to the electrodes do not leak outside and the two kinds of gases do not mix with each other. This gasket is often assembled in advance by thermal bonding with the diffusion layer, the electrode and the polymer electrolyte membrane, and this is called MEA (electrolyte membrane-electrode assembly).

In order to mechanically fix the MEA to the outside of the MEA, electrically connect adjacent MEAs to each other in series, supply a reaction gas to the electrode surface, and carry away a generated gas and a surplus gas. A conductive separator plate having a gas flow path is arranged. As a material of the separator plate, a carbon plate is often used from the viewpoint of conductivity and chemical stability. The processing method is generally by mechanically processing a sliced carbon plate such as milling and blasting. In recent years, from the viewpoint of cost, studies have been conducted to manufacture a separator plate by using a carbon powder mixed with a small amount of resin as a material and by a molding technique such as press molding or injection molding.

Since the fuel cell generates heat during operation, it is necessary to cool it with cooling water or the like in order to maintain the cell in a good temperature state. Therefore, usually, a cooling water flow path is provided for every 1 to 3 cells. It is common that these MEAs, separator plates, and cooling units are alternately stacked to stack 10 to 200 cells, the stacked body is sandwiched between end plates via a collector plate and an insulating plate, and fixed from both ends with fastening bolts. It is a structure of various laminated batteries. Therefore, the general form of this laminated battery is as shown in FIG.
The anode-side separator plate 10 and the cathode-side separator plate 20 each having a cooling water flow path on the back surface allow M
This is a configuration in which unit cells sandwiching the EA5 are stacked. Here, the cooling unit is provided for each cell. However, in a laminated battery having a structure having a cooling unit for each of a plurality of cells, one surface is an anode-side separator plate and the other surface is a cathode-side separator plate. The separator plate will be inserted between the MEAs.

In order to prevent the leakage of the cooling water to the outside of the cell and the gas into the manifold hole and the leakage of the gas to the outside of the cell on the surface of the separator plate having the cooling water passage,
A sealing mechanism is required. Generally, as shown in FIG. 2, a separator plate is provided with a seal groove, and the seal groove is provided with an O
Sealing is performed by a method of fitting a ring and laminating, or filling a seal groove with a sealant or a liquid gasket and laminating.

[0006]

Although there are some problems depending on the processing method, the surface of the separator plate always has surface roughness. This affects the contact resistance between cells in the laminated battery, which is reflected in the voltage loss of the laminated battery. ME
For the diffusion layer of A, carbon cloth or carbon paper made of woven or paper-made carbon fibers is generally used.
Since these have sufficient flexibility to absorb the surface roughness of the separator plate, the contact resistance between the separator plate and the MEA is very low, usually several mΩ / cm ² or less.
However, in the laminated structure shown in FIG. 4, since the separator plates having almost no flexibility come into direct contact with each other on the surface having the flow path of the cooling water, microscopically, as shown in FIG. It is in a contact state, and there is a problem that the contact resistance is as large as several tens mΩ / cm ² . This problem becomes more serious in the case of a molded separator plate having unevenness in thickness and warpage in addition to surface roughness.

[0007]

The present invention solves the above-mentioned problems by laminating a conductive sheet gasket between separator plates having cooling water flow paths. That is, the present invention is a hydrogen ion conductive polymer electrolyte membrane, a pair of electrodes sandwiching the hydrogen ion conductive polymer electrolyte membrane, an anode side separator plate having a flow path for supplying a fuel gas to one of the electrodes, A cathode side separator plate having a flow path for supplying an oxidant gas to the other of the electrodes,
And a polymer electrolyte laminated fuel cell comprising a cooling unit including a cooling water channel formed on the contact surface between the anode side separator plate and the cathode side separator plate,
A conductive sheet gasket is interposed between the separator plates forming the cooling part. The conductive sheet gasket is preferably a sheet containing conductive carbon, particularly a graphite sheet. Among them, an expanded graphite sheet having excellent conductivity and elasticity is suitable.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION The polymer electrolyte laminated fuel cell of the present invention will be described in comparison with a conventional example. As shown in FIGS. 7 to 9, the anode side separator plate 10 includes a pair of fuel gas manifold holes 11 and an oxidant manifold hole 1.
2 and a cooling water manifold hole 13, a fuel gas passage 15 connecting the pair of manifold holes 11 to each other on the surface facing the anode, and a pair of cooling water manifold holes 13 on the back surface. It has the flow path 16 of the cooling water which connects. Reference numeral 14 is a hole for passing a bolt for fastening the cell. On the other hand, the cathode side separator plate 20 is shown in FIGS.
2, a pair of fuel gas manifold holes 2
1, a manifold hole 22 for oxidant, and a manifold hole 23 for cooling water, and a channel 25 for the oxidant gas that connects the pair of manifold holes 22 to the surface facing the cathode.
And a flow path 26 for cooling water that connects the pair of cooling water manifold holes 23 to each other. Reference numeral 14 is a hole for passing a bolt for fastening the cell.

As shown in FIG. 2, the MEA 5 comprises a polymer electrolyte membrane 3, an anode 1 and a cathode 2 sandwiching the membrane,
And a gasket 4 that covers the peripheral portion of the electrolyte membrane. Manifold holes for fuel gas, oxidant gas, and cooling water, which are common to the separator plates 10 and 20, are provided in the gasket portion.
In the figure, the oxidant gas manifold hole 6 is shown. This MEA 5 is connected to the separator plates 10 and 20 described above.
A unit cell is formed by sandwiching it with. When such unit cells are stacked, the joint between the surfaces of the two separator plates having the cooling water channels (hereinafter referred to as water cooling surfaces) becomes as shown in FIG. 6, and the contact resistance increases.

Therefore, conventionally, in order to prevent the leakage of the cooling water out of the cell and the gas to the manifold hole, and the leakage of the gas out of the cell, the following sealing mechanism has been provided. On the water-cooled surface of the separator plate 10, as shown in FIG. 9, seal grooves 17 and 18 surrounding the fuel gas manifold hole 11 and the oxidant gas manifold hole 12, respectively, and the cooling water manifold hole 13 and the cooling water are provided. A seal groove 19 that surrounds the flow path 16 is provided. Similarly, on the water-cooled surface of the separator plate 20, as shown in FIG. 12, seal grooves 27 and 28 surrounding the fuel gas manifold hole 21 and the oxidant gas manifold hole 22, respectively, and the cooling water manifold hole 23 and A seal groove 29 that surrounds the cooling water passage 26 is provided. Then, in a portion where the water cooling surfaces of the separator plates 10 and 20 are in contact with each other, a sealing groove that surrounds the fuel gas manifold hole and the oxidant gas manifold hole, and a cooling water manifold hole and a cooling water flow path are enclosed. Fit an O-ring in each seal groove. FIGS. 4 and 5 show an O-ring 38 that fits in the oxidant manifold hole and an O-ring 39 that fits in the seal groove that surrounds the portion where the cooling water flows. Here, the seal groove is provided in both separator plates 10 and 20, but the seal groove may be provided only in one separator plate.

The present invention provides a fuel cell, which can be assembled more simply, instead of the above-described sealing mechanism including the sealing groove and the O-ring. That is, in a laminated fuel cell including a cooling unit including a cooling water flow path formed on the contact surface between the anode side separator plate and the cathode side separator plate which are adjacent to each other, the conductive property is provided between the separator plates forming the cooling unit. Insert the sheet gasket of. In the embodiment shown here, except that the seal grooves 17, 18 and 19 described above are eliminated, the anode side separator plate 10A which is exactly the same as the separator plate 10 and the seal grooves 27, 28 and 29 are eliminated. The same cathode side separator plate 20A as the separator plate 20 is used. Then, a conductive sheet gasket 30 is interposed between the water-cooled surfaces of the separator plates 10 and 20. The gasket 30 is provided with a pair of fuel gas manifold holes, oxidant manifold holes, and cooling water manifold holes common to the separator plates 10A and 20A. Figure 1
In 2 and 2, the manifold hole 32 for the oxidant is shown.

A unit cell is formed by sandwiching the MEA 5 with the separator plates 10A and 20A. A sheet gasket sandwiched between the water-cooled surfaces of the separator plates 10A and 20A is inserted between the unit cells. The laminated battery thus assembled is shown in FIG. MEA5
Includes a pair of fuel gas manifold holes common to the separator plates 10A and 20A, an oxidant manifold hole,
And a manifold hole for cooling water. 1 and 2
In, the oxidant manifold hole 6 is shown. Here, the cooling unit is provided for each cell. However, in a laminated battery having a structure having a cooling unit for each of a plurality of cells, one surface is an anode-side separator plate and the other surface is a cathode-side separator plate. The separator plate will be inserted between the MEAs.

[0013]

EXAMPLES Examples of the present invention will be described below. Example 1 Separator plate X: size 120 × 120 mm, thickness 4 m
The anode-side separator plate 10 and the cathode-side separator plate 20 having the structure described in the embodiment were manufactured by milling using a double-sided polished glass plate of m (manufactured by Tokai Carbon Co., Ltd.). Separator plate 1
The zero gas flow path 15 was provided with three grooves having a width of 2 mm and a depth of 0.4 in parallel with a pitch of 4 mm. Separator plate 20
In the gas flow path 25, 5 grooves having a width of 2 mm and a depth of 0.6 were provided in parallel with a pitch of 4 mm. The cooling water flow paths 16 and 26 are formed with grooves having a width of 2 mm and a depth of 0.4 mm at a pitch of 4.
Three of them were provided in parallel in mm. Also, the seal grooves 17-1
9 and 27 to 29 had a width of 2 mm and a depth of 0.2 mm. The average surface roughness of the separator plate was 5.2 μm.

Separator plate Y: The entire water-cooled surface of the separator plate X was sandblasted to raise the average surface roughness to 19.3 μm. The contact area (area excluding manifold holes, bolt holes, and flow path portions) on the water-cooled surface of the separator plate is about 100 cm ² .

With respect to the above two kinds of separator plates, resistance measurement experiments were conducted in the following two kinds of experimental sections. (Experimental section A) Silicone sealant (manufactured by Shin-Etsu Chemical Co., Ltd.) was filled in the seal groove on the water cooling surface of the separator plate, and the water cooling surfaces of the anode side separator plate and the cathode side separator plate were pasted together under a stress of 1 Mpa. Measure total resistance with. (Experimental section B) Graphite sheet gasket (Nikafilm 0.2 m manufactured by Nippon Carbon Co., Ltd.) is attached to the water-cooled surface of the separator plate.
(m thickness), and the total resistance is measured under a stress of 1 Mpa.

Considering the contact area of the separator plate (area excluding the manifold, bolt holes, and flow passages), 1
Converted into resistance value per cm ² , the following results were obtained.

[0017]

[Table 1]

Since the separator plate X and the separator plate Y are made of the same material and have the same bulk resistance, the difference between the separator plate X and the separator plate Y in each of the above experimental sections is the difference between them. This is the difference in contact resistance between the surfaces. As is clear from the above experimental results, the structure of the present invention is effective even when the surface is sufficiently smooth, but is particularly effective in reducing the contact resistance when the surface roughness is large. This is a great advantage when using inexpensive molded separator plates.

Example 2 Next, a battery was actually assembled according to the following procedure, the battery was operated under the operating conditions described later, and a test for measuring the battery voltage was conducted.

MEA preparation method; specific surface area 800 m ² / g,
Platinum was supported on Ketjen Black EC (Furness Black manufactured by Ketjen Black International Co., Ltd.) having a DBP oil absorption of 360 ml / 100 g at a weight ratio of 1: 1. To 10 g of this catalyst powder, 35 g of water and 59 g of an alcohol dispersion liquid of hydrogen ion conductive polymer electrolyte (9% FSS manufactured by Asahi Glass Co., Ltd.) were mixed and dispersed using an ultrasonic stirrer to form a catalyst layer ink. It was made. This catalyst ink was applied to a polypropylene film (Trephan 50-2500 manufactured by Toray Industries, Inc.) and dried to form a catalyst layer. The obtained catalyst layer was cut into a size of 58 × 58 mm, and the polymer electrolyte membrane (Napon manufactured by Dupont) was cut.
on 117, 50 μm thick) on both sides under conditions of temperature 135 ° C. and pressure 32 kgf / cm ² and thickness 10 on both sides.
A μm catalyst layer was formed.

Subsequently, polytetrafluoroethylene (PTFE) fine powder (manufactured by Daikin Industries, Ltd.) and acetylene black (on one surface of the gas diffusion layer substrate (TGPH120 manufactured by Toray Industries, Inc.) made of carbon fibers ( Denki Kagaku Kogyo Co., Ltd.) applied an aqueous dispersion liquid in a weight ratio of 1: 4 and baked at 350 ° C. for 20 minutes to give a thickness of 40 μm.
The water-repellent layer was formed, and this was die-cut into a size of 59 × 59 mm. Next, a thickness 320 having a three-layer structure of ethylene-propylene-diene terpolymer blend (EPDM) / polyethylene terephthalate (PET) / silicone.
A sheet-shaped gasket material of μm was punched out to prepare two MEA gaskets having a manifold hole, a bolt hole, and an electrode exposed surface (60 × 60 mm). The water-repellent electrode having the water-repellent layer formed on the exposed surface of the catalyst layer is positioned so that the water-repellent layer is in contact with the catalyst layer, a MEA gasket is provided around the water-repellent electrode, and the polymer electrolyte membrane has an EPDM surface. It was positioned so that it touched. Then, these are collectively subjected to hot press bonding (130 ° C., 1.5 MPa) and M
EA was formed.

Using the MEA and the separator plate described above, fastening was performed under two fastening modes of the experimental section A and the experimental section B with a fastening load of 600 kgf, a 40-cell laminated battery was assembled, and the battery voltage was measured. The operating conditions are as follows. Cell temperature is 75 ° C, fuel gas is pure hydrogen humidified to dew point 70 ° C, oxidant gas is air humidified to dew point 70 ° C, fuel utilization rate is 80%, air utilization rate is 40%, current density is 0.7A / It was cm ² .

[0023]

[Table 2]

As is clear from the above results, according to the present invention, even when the surface roughness of the separator plate is rough, no voltage drop is observed on the water-cooled surface, and stable electrical connection can be maintained. Met.

[0025]

According to the present invention, it is possible to provide a high performance polymer electrolyte type laminated fuel cell which suppresses voltage drop due to contact resistance on the water-cooled surface of the separator plate.

[Brief description of drawings]

FIG. 1 is a vertical cross-sectional view of a main part of a polymer electrolyte layered fuel cell according to an example of the present invention.

FIG. 2 is a sectional view of an essential part of the assembling process.

FIG. 3 is an enlarged cross-sectional view of a joint between water-cooled surfaces of a separator plate.

FIG. 4 is a vertical cross-sectional view of a main part of a conventional laminated battery.

FIG. 5 is a cross-sectional view of an essential part of the assembling process.

FIG. 6 is an enlarged cross-sectional view of a joint between water-cooled surfaces of a separator plate.

FIG. 7 is a front view of an anode-side separator plate.

8 is a sectional view taken along the line VIII-VIII ′ of FIG. 7.

FIG. 9 is a rear view of the separator plate.

FIG. 10 is a front view of a cathode side separator plate.

11 is a sectional view taken along line XI-VII ′ of FIG.

FIG. 12 is a rear view of the separator plate.

[Explanation of symbols]

1 anode 2 cathode 3 Polymer electrolyte membrane 4 gasket 5 MEA 10 Anode side separator plate 15 Fuel gas flow path 16, 26 Cooling water flow path 20 Cathode side separator plate 25 Oxidant gas flow path 30 sheet gasket

Continued front page    (72) Inventor Hiroki Kusakabe             1006 Kadoma, Kadoma-shi, Osaka Matsushita Electric             Sangyo Co., Ltd. (72) Inventor Hideo Ohara             1006 Kadoma, Kadoma-shi, Osaka Matsushita Electric             Sangyo Co., Ltd. (72) Inventor Nobuhiro Hase             1006 Kadoma, Kadoma-shi, Osaka Matsushita Electric             Sangyo Co., Ltd. (72) Inventor Tatsuto Yamazaki             1006 Kadoma, Kadoma-shi, Osaka Matsushita Electric             Sangyo Co., Ltd. (72) Inventor Shinsuke Takeguchi             1006 Kadoma, Kadoma-shi, Osaka Matsushita Electric             Sangyo Co., Ltd. F-term (reference) 5H026 AA06 CC03 CC08 CX05 EE05

Claims (2)

[Claims] 1. A hydrogen ion conductive polymer electrolyte membrane, a pair of electrodes sandwiching the hydrogen ion conductive polymer electrolyte membrane, an anode side separator plate having a flow path for supplying a fuel gas to one of the electrodes, the electrode A cathode side separator plate having a flow path for supplying an oxidant gas to the other side, and a cooling section including a flow path of cooling water formed on a contact surface between the adjacent anode side separator plate and cathode side separator plate, A polymer electrolyte type laminated fuel cell, wherein a conductive sheet gasket is interposed between the separator plates constituting the cooling part. 2. The polymer electrolyte type laminated fuel cell according to claim 1, wherein the conductive sheet gasket is a sheet containing conductive carbon.