JP4314696B2 - Polymer electrolyte fuel cell stack - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a fuel cell stack using a polymer electrolyte used for a portable power source, a power source for an electric vehicle, a domestic cogeneration system, and the like, and more particularly to a fastening method thereof.
[0002]
[Prior art]
A fuel cell using a polymer electrolyte generates electric power and heat simultaneously by electrochemically reacting a fuel gas containing hydrogen and a fuel gas containing oxygen such as air. . In the structure, first, a catalytic reaction layer composed mainly of carbon powder carrying a platinum-based metal catalyst is formed on both surfaces of a polymer electrolyte membrane that selectively transports hydrogen ions. Next, a diffusion layer having both fuel gas permeability and electronic conductivity is formed on the outer surface of the catalytic reaction layer, and the diffusion layer and the catalytic reaction layer are combined to form an electrode.
[0003]
Next, a gas seal material or a gasket is disposed around the electrode with a polymer electrolyte membrane interposed so that the fuel gas to be supplied leaks outside or the two kinds of fuel gases are not mixed with each other. This sealing material or gasket is integrated with an electrode and a polymer electrolyte membrane and assembled in advance, and this is called an MEA (electrode electrolyte membrane assembly). On the outside of the MEA, a conductive separator plate for mechanically fixing the MEA and electrically connecting adjacent MEAs to each other in series is disposed. In the portion of the separator plate that contacts the MEA, a reaction gas is supplied to the electrode surface, and a gas flow path for carrying away the generated gas and surplus gas is formed. The gas flow path can be provided separately from the separator plate, but a system in which a groove is provided on the surface of the separator to form a gas flow path is common.
[0004]
In order to supply the fuel gas to the groove, a pipe jig for branching the pipe for supplying the fuel gas to the number of separators to be used and directly connecting the branch destination to the separator-like groove is required. This jig is called a manifold, and the type that connects directly from the fuel gas supply pipe as described above is called an external manifold. There is a type of this manifold called an internal manifold with a simplified structure. The internal manifold is a separator plate in which a gas flow path is formed with a through hole, a gas flow outlet / outlet is passed to this hole, and fuel gas is directly supplied from this hole.
[0005]
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 battery at a good temperature. Usually, a cooling unit that allows cooling water to flow every 1 to 3 cells is inserted between the separator and the separator. However, a cooling water channel is often provided on the back surface of the separator to form a cooling unit. These MEAs, separators and cooling units are alternately stacked, and after stacking 10 to 200 cells, it is generally sandwiched between end plates via current collector plates and insulating plates, and fixed from both ends with fastening bolts. This is a structure of a laminated battery.
[0006]
In polymer electrolyte fuel cells, when a single cell is stacked, a constant surface pressure is applied to the polymer electrolyte membrane and the electrode to reduce the cell impedance and smoothly promote the hydrogen / oxygen redox reaction. There is a need. At this time, it is important to apply a uniform surface pressure to the surface of the MEA. If there is a variation in the MEA pressurization, the reaction occurs intensively in the strong pressurization part, and the current concentrates in that part. At this time, since the polarization of the battery concentrates on the portion, the temperature may increase greatly locally, the electrode may deteriorate, or the polymer electrolyte membrane may be damaged.
[0007]
Under such circumstances, the conventional fastening method of the polymer electrolyte fuel cell is the fastening plate in which end plates are arranged at both ends in the stacking direction of the battery stack, and four or more bolts having the same diameter are arranged. Was pressurized. In addition, a method in which the fastening plate is divided into two parts has been proposed in order to make the fastening strain uniform.
[0008]
[Problems to be solved by the invention]
When the end plate is pressed with a fastening plate on which four or more bolts of the same diameter are arranged, the pressed state of the end plate varies in the surface direction. The reason is that the plane is uniquely limited by three points, but if there are four points, two planes are generated. This is why the four-legged desk rattles. When four bolts are completely tightened at the same pressure, there will naturally be no variation, but it is difficult to tighten the polymer fuel cell stack with several tens of cells stacked at the same pressure. .
[0009]
Further, when such a battery stack is used as a power source of an electric vehicle, the battery stack is subjected to strong vibrations due to the traveling of the vehicle. In that case, the in-plane variation of the pressurization is further promoted, which causes deterioration of battery characteristics.
[0010]
In addition, with the conventional fastening method, the number of parts for fastening increases, and the number of work steps in assembling the fuel cell increases, and the strain on the battery increases, so that each time assembly is performed. These are obstacles to practical use due to non-uniform surface pressure applied to the electrodes.
[0011]
In addition, when the battery is operated for a long time in a state in which the fastening part receives an extremely excessive force, the part is expected to deteriorate, and there is a problem that it is questioned in terms of safety such as occurrence of fuel gas leakage.
[0012]
[Means for Solving the Problems]
In order to solve the above problems, a polymer electrolyte fuel cell stack according to the present invention includes a hydrogen ion conductive polymer electrolyte membrane, a pair of electrodes disposed on both sides of the hydrogen ion conductive polymer electrolyte membrane, and the electrodes A polymer electrolyte fuel cell stack in which a plurality of unit cells each having a pair of conductive separators having a gas flow path for supplying and discharging fuel gas to one side and supplying and discharging oxidant gas to the other side are stacked. And
A pair of end plates disposed at both ends in the stacking direction of the battery stack;
A band-shaped fastening frame that pressurize the pair of end plates in the stacking direction of the cell stack,
Three bolts arranged on the belt-like fastening frame and arranged on one side of the pair of end plates ;
The diameter of the three bolts arranged on the belt-like fastening frame is made larger as it is closer to the center of one surface of the pair of end plates.
[0014]
In addition, it is effective to have a plurality of the belt-like fastening frames on which the three bolts are arranged .
[0015]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to the drawings.
[0016]
The point of the present invention is that the number of parts and work processes required for fastening can be reduced while tightening the fuel cell with three different diameter fastening bolts that define the surface while taking strain on the entire surface of the battery. It has been found a method of always maintaining a uniform surface pressure.
[0017]
【Example】
Embodiments suitable for the present invention will be specifically described with reference to the drawings.
[0018]
Example 1
First, a fuel cell fastening structure, which is a point of the present invention, will be described with reference to FIGS. 1, 2, and 3. FIG. 1 is an external view showing a tightening structure, and FIG. 2 is a cross-sectional view thereof. In FIG. 1, reference numeral 11 denotes a stacked portion of unit cells. End plates 12 are arranged above and below the stacked portion 11 of the unit cells. A current collector 13 is electrically connected to the output terminal 14. Although not particularly shown, the unit cell stack 11 and the end plate 12 are electrically insulated by an insulating means. The end plate 12 and the laminated portion 11 of the unit cells are fastened by a fastening plate 14 and a fastening member 15. That is, in FIG. 2, the left and right periphery of the end plate and unit cell stack are covered with the fastening member 15, and the fastening bolts 16 and 17 from the top and the disc spring 22 from the bottom are pressed against the end plate 12. Then, the stacked portion 11 of the unit cell is tightened. However, since the position of the fastening bolt 17 is in the central portion in the plane direction of the battery as compared with the position of the fastening bolt 16, it must be tightened with a larger force in order to pressurize the battery uniformly in the plane direction. . Therefore, the fastening bolt 16 having a diameter of 10 mm was used, and the fastening bolt 17 having a diameter of 16 mm was used. The outline of the attachment position of the bolt 16 and the bolt 17 on the fastening plate 14 is shown in FIG.
[0019]
Hereinafter, a method for manufacturing a fuel cell will be described.
[0020]
The electrode catalyst was a carbon fine powder (VXC72, manufactured by Cabot, USA, primary particle size: 30 nm, specific surface area: 254 m ² / g) supported by 25% by weight of platinum particles having an average particle size of about 30 mm. A dispersion solution in which perfluorocarbonsulfonic acid powder, which is a hydrogen ion conductive polymer electrolyte, was dispersed in ethyl alcohol was mixed with a solution in which this catalyst powder was dispersed in isopropanol to prepare a catalyst paste.
[0021]
On the other hand, the carbon paper used as the porous substrate of the electrode was subjected to water repellent treatment. After impregnating a carbon non-woven fabric (manufactured by Toray Industries, Inc., TGP-H-120) having a thickness of 360 μm into a polytetrafluoroethylene-containing aqueous dispersion (manufactured by Daikin Industries, Neoflon ND1), this is dried and dried at 400 ° C. for 30 minutes. Water repellency was given by heating for a minute.
[0022]
A catalyst layer was formed on the carbon nonwoven fabric by applying the above-described catalyst paste using a clean printing method. The catalyst layer thus prepared and the carbon nonwoven fabric were combined to form an electrode. The amount of platinum is 0.5 mg / cm ² contained in the electrode, the amount of perfluorocarbon sulfonic acid was adjusted to be 1.2 mg / cm ^2.
[0023]
Next, the catalyst layer is in contact with the side of the electrolyte membrane on both sides of the proton conductive polymer electrolyte membrane (Nafion 112 manufactured by DuPont, USA) whose outer size is 5 mm larger than the above electrode. Thus, it joined by hot press, and this was set as the electrode electrolyte membrane assembly (MEA).
[0024]
This MEA was sandwiched between separator plates to form a unit cell. The separator plate was prepared by using a carbon plate obtained by cold press-molding a carbon powder material and impregnating and curing a phenolic resin to improve the gas sealing property, and then forming a gas flow path by cutting. . The size of the separator is 10 cm × 20 cm, the thickness is 4 mm, the groove is a recess having a width of 2 mm and a depth of 1.5 mm, and gas flows through this part. Moreover, the rib part between gas flow paths is a convex part of width 1mm. Also, a manifold hole for oxidant gas, a manifold hole for fuel gas, and a manifold hole for cooling water were formed in the separator. A gas seal portion was formed around the gas flow passage and the manifold hole with a conductive gas sealant in which conductive carbon was dispersed in polyisobutylene.
[0025]
The fuel cell circulation side on the surface of the conductive separator and the oxidant gas circulation side on the back surface of the conductive separator were joined to both surfaces of the MEA produced as described above to form a unit cell A. Moreover, the fuel gas distribution side of the surface of the conductive separator and the cooling water distribution side of the back surface of the conductive separator were joined to both surfaces of the MEA to form a unit cell B.
[0026]
Next, the unit cells A and the unit cells B were alternately stacked one by one, and a total of 50 cells were stacked to obtain a stacked portion of the unit battery.
[0027]
End plates are arranged on the top and bottom of the laminate, and the fastening structure described in FIGS. In other words, the fastening bolts 16 and 17 and the disc spring 22 are used to provide a fastening force via the fastening member 12, and the fastening pressure during assembly is 13 kgf / cm ² . When the pressure distribution of the separator plate was examined using pressure sensitive paper, it was confirmed that the pressure distribution was uniform over the entire surface.
[0028]
(Comparative Example 1)
In Example 1, the laminated battery part was fastened with three bolts, but this part was fastened with four bolts as a comparative example. The outline of the bolt attachment position on the fastening plate is shown in FIG. In the comparative example, a bolt having a diameter of 16 mm was used. Except for this, the batteries were the same as those prepared in Example 1.
[0029]
(Characteristic evaluation)
The characteristics of the batteries prepared in Example 1 and Comparative Example 1 were evaluated under the following conditions. Pure hydrogen gas was supplied to the fuel electrode and air was supplied to the air electrode. The fuel gas utilization rate (Uf) was 70%, and the air utilization rate (Uo) was 20%. The humidification of the gas was performed by passing the fuel gas through a humidified bubbler at 85 ° C and air at 65-70 ° C. The battery temperature was maintained at 75 ° C. by adjusting the cooling water temperature and flow rate. The drive current was 0.5 A / cm ² per MEA area.
[0030]
FIG. 4 shows the characteristics of the battery of the example of the present invention and the battery of the comparative example. In FIG. 4, the vertical axis represents the output voltage of the fuel cell divided by the number of stacked unit cells, and the horizontal axis represents the operation time. From the results shown in FIG. 4, it was confirmed that the battery of the present invention was excellent in long-term reliability as compared with the battery of the comparative example.
[0031]
【The invention's effect】
According to the present invention, as a method of fastening the fuel cell stack, instead of the conventional four-point support, the MEA can be given uniform surface pressure without giving extra strain to the MEA. Contribute to realization. This effect becomes more prominent when this battery stack is applied to an electric vehicle. In addition, cost reduction during mass production can be achieved by reducing the number of parts and work processes.
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram showing the appearance of a polymer electrolyte fuel cell stack according to an embodiment of the present invention. FIG. 2 is a configuration showing a cross section of the polymer electrolyte fuel cell stack according to an embodiment of the present invention. Schematic diagram [Fig. 3] Schematic diagram of bolt mounting positions of a polymer electrolyte fuel cell stack according to an embodiment of the present invention [Fig. 4] Graph showing characteristics of the battery of the embodiment of the present invention and the battery of the comparative example [ Explanation of symbols]
11 Unit Battery Stack 12 End Plate 13 Current Collector Plate 14 Fastening Plate 15 Fastening Member 16, 17 Fastening Bolt 18 Output Terminal 22 Disc Spring

Claims (2)

A hydrogen ion conductive polymer electrolyte membrane, a pair of electrodes arranged on both sides of the hydrogen ion conductive polymer electrolyte membrane, and supply and discharge of fuel gas to one of the electrodes and supply and discharge of oxidant gas to the other A polymer electrolyte fuel cell stack in which a plurality of unit cells each having a pair of conductive separators having gas flow paths are stacked,
A pair of end plates disposed at both ends in the stacking direction of the battery stack;
A band-shaped fastening frame that pressurize the pair of end plates in the stacking direction of the cell stack,
Three bolts arranged on the belt-like fastening frame and arranged on one side of the pair of end plates ;
A polymer electrolyte fuel cell stack, characterized in that the diameters of the three bolts arranged in the belt-like fastening frame are larger as they are closer to the center of one surface of the pair of end plates. 2. The polymer electrolyte fuel cell stack according to claim 1, comprising a plurality of the belt-like fastening frames on which the three bolts are arranged .

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