JP2008078148A - Fuel cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fuel cell capable of suppressing the changes in the fastening load of a stack, even if the environmental temperature of the fuel cell is changed. <P>SOLUTION: In the fuel cell 10 in which a stack 23 constituted by arranging a terminal 20, an insulator 21, and an end plate 22 at both ends in the stacking direction of a module 19, comprising a stack of a membrane-electrode assembly and a separator 18, is fastened with a tension plate 24 that extends in the stacking direction on the outside of the stack 23, the coefficient of linear expansion α<SB>s</SB>in the stacking direction of the stack 23 and the coefficient of linear expansion α<SB>c</SB>in the stacking direction of the tension plate 24 are set identical or substantially identical thereto. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a fuel cell, and more particularly to a fuel cell in which a fastening load of a fuel cell stack is substantially constant regardless of changes in environmental temperature.

The solid polymer electrolyte fuel cell is arranged on the other side of the electrolyte membrane, which is an electrolyte membrane made of an ion exchange membrane, an electrode (anode, fuel electrode) made of a catalyst layer and a diffusion layer arranged on one side of the electrolyte membrane, and the electrolyte membrane. Membrane-Electrode Assembly (MEA) consisting of an electrode (cathode, air electrode) consisting of a catalyst layer and a diffusion layer, and fuel gas (hydrogen) and oxidizing gas (oxygen, usually air) at the anode and cathode Separators that form fluid passages for supplying gas, and a stack constituted by arranging terminals, insulators, and end plates at both ends in the stacking direction of a module group composed of a stack of these MEAs and separators. It is composed of one that is fastened by a fastening member (tie rod, tension plate, etc.) that extends in the laminate lamination direction on the outside.
In the solid polymer electrolyte fuel cell, a reaction for converting hydrogen into hydrogen ions and electrons is performed on the anode side, the hydrogen ions move through the electrolyte membrane 11 to the cathode side, and oxygen, hydrogen ions and electrons (on the cathode side). The reaction of generating water from the electrons generated at the anode of the adjacent MEA passes through the separator).
Anode side: H ₂ → 2H ⁺ + 2e ⁻
Cathode side: 2H ⁺ + 2e ⁻ + (1/2) O ₂ → H ₂ O
Since heat is generated in the water generation reaction at the cathode, a flow path through which a cooling medium (usually cooling water) flows is formed between the separators for each MEA or for each MEA. It is cooling. The environmental temperature of the fuel cell changes between the ambient temperature when the operation is stopped (for example, 20 ° C.) and the coolant temperature during the operation (about 80 ° C.). In addition, in order for the above-described chemoelectric reaction to be performed normally, it is desirable that the stack tightening load does not fluctuate greatly.For this reason, conventionally, a spring mechanism is inserted between the end plate and the insulator, The change in load due to the difference in thermal expansion is reduced.
However, if a spring mechanism is not inserted between the end plate and the insulator in the conventional fuel cell, the fastening load of the fuel cell stack greatly changes as the environmental temperature changes. When the fastening load changes, the fuel cell output decreases or, in the worst case, gas (hydrogen, air) leak occurs.
Further, when a spring mechanism is inserted between the end plate and the insulator to reduce the change in the fastening load, the dimension in the stacking direction of the fuel cell stack increases, resulting in a space problem when mounted on the vehicle.
In order to suppress the above problems, a microfilm of Japanese Utility Model Application No. 56-127957 (Japanese Utility Model Application Publication No. 58-034362 ), Japanese Patent Application Laid-Open No. 58-014472, Japanese Utility Model Application No. 02-106290 (Japanese Utility Model Application Publication No. 04-066353). microfilm, JP 58-119171 and JP No.), the selected structure and / or material of the fastening member appropriately, the combined thermal expansion coefficient of the fastening member to the coefficient of thermal expansion of the stack (total) A fuel cell is disclosed.
Microfilm of Japanese Utility Model No. 56-127957 (Japanese Utility Model Publication No. 58-034362) JP 58-014472 A Microfilm of Japanese Utility Model Application No. 02-106290 (Japanese Utility Model Application Publication No. 04-066353) JP 58-119171 A

An object of the present invention, be varied environmental temperature of the fuel cell, in each part of the stack (at least metal contacts) is to provide a fuel cell capable of suppressing the change in the fastening load of the fuel cell stack.

The present invention for achieving the above object is as follows.
(1) membrane - electrode assembly and the stacking direction at both ends in the terminal module comprising a stack of the separators, insulators, a stack constructed by arranging the end plates, and fastening by the fastening member extending in front Symbol module stacking direction Fuel In batteries,
The stack includes an electrode portion, the periphery of the electrode portion includes a region having multiple sealing material comprising an adhesive or a bead,
In each section including a region having a plurality of electrode portions and the sealing material of the stack, and the linear expansion coefficient of the module stacking direction of the stack, or the linear expansion coefficient of the module stacking direction of the fastening member the same or nearly the same A fuel cell characterized in that
(2) In the electrode part, the membrane-electrode assembly is sandwiched between the separators via the diffusion layer ,
In the electrode portions, the electrolyte membrane, the diffusion layer, the material of the electrode portions constituting member including a separator thickness, by selecting at least one of thickness ratio, the module stack of said stack in said electrode portion The fuel cell according to (1) , wherein the linear expansion coefficient in the direction and the linear expansion coefficient in the module stacking direction of the fastening member are the same or substantially the same.
(3) a region having a plurality of the sealing material comprises a sizing unit including a plurality of sealing material by the adhesive, and a sealing portion including a plurality of sealing material by the sealing member and the bead with an adhesive material, the sizing unit, the separator The electrolyte membrane, adhesive, and insulating beads are sandwiched between them, and in the seal portion, the electrolyte membrane, adhesive, and insulating beads are sandwiched between separators, and the beads are sandwiched between separators through which a cooling medium flows ,
In the above sizing portion, the material of the adhesive insulating bead, thickness, grain size of the ferrite beads, by selecting the thickness ratio of the adhesive and the separator over data, the in the region where there is a plurality of sealing material the linear expansion coefficient of the stacking direction, wherein a linear expansion coefficient of the laminate direction same bite others were approximately the same (1) or (2) the fuel cell according of the fastening member of the stack.

(1) - in fuel cells (3) (at least the electrode portion) was side in each part of the stack, since the linear expansion coefficient of the stack and the outer clamping member and the same or substantially the same, the environmental temperature Is changed at each part of the stack (at least at the electrode part), the stack and the fastening member expand by the same amount, and there is no change in the fastening load or even a change in the fastening load is small. As a result, the output of the fuel cell is substantially constant at each part of the stack (at least at the electrode part) , and no leakage of reaction gas (hydrogen, air) occurs.

Below, the fuel cell of this invention is demonstrated with reference to FIGS. 1-3.
The fuel cell of the present invention is a solid polymer electrolyte fuel cell 10. The fuel cell 10 of the present invention is mounted on, for example, a fuel cell vehicle. However, it may be used other than an automobile.
As shown in FIGS. 1 and 2, the solid polymer electrolyte fuel cell 10 includes an electrolyte membrane 11 made of an ion exchange membrane, and an electrode 14 made up of a catalyst layer 12 and a diffusion layer 13 disposed on one surface of the electrolyte membrane 11. A membrane-electrode assembly (MEA) composed of (anode, fuel electrode) and an electrode (cathode, air electrode) composed of a catalyst layer 15 and a diffusion layer 16 disposed on the other surface of the electrolyte membrane 11; Separators 18 forming fluid passages for supplying fuel gas (hydrogen) and oxidizing gas (oxygen, usually air) to the electrodes 14 and 17 are alternately arranged to form a module 19 (for example, a two-cell module). create, at opposite ends in the stacking direction of the laminate formed by laminating the module 1 9 (modules), the terminal 20, the insulator 21, by placing the end plate 22 structure The stack 23, and outwardly fastening member extending stack stacking direction of the stack 23 (tension plate, tie rods, through bolt, etc.) consists of those clamped in the stacking direction at 24.

  The linear expansion coefficient of the fastening member 24 in the stacked body stacking direction and the linear expansion coefficient of the stack 23 (end plate 22 + insulator 21 + terminal 20 + module 19) in the stacked body stacking direction are the same or substantially the same. Here, “substantially the same” means that even if there is a difference in coefficient of linear expansion, the change in the stack fastening load due to the difference in coefficient of linear expansion is caused by the difference in coefficient of linear expansion when the conventional spring mechanism is arranged at the end of the stack. It shall be within the same range as the change in the stack fastening load.

  Here, the linear expansion coefficient of the module 19 group has the respective linear expansion coefficients of the electrode portion 19a, the sizing portion 19b, and the seal portion 19c, but the linear expansion coefficient of the fastening member 24 should be substantially the same. The linear expansion coefficient of the electrode portion 19a in the stacking direction of the laminate, and preferably the linear expansion coefficient in the stacking direction of each of the sizing portion 19b and the seal portion 19c is substantially the same as the linear expansion coefficient of the fastening member 24. The In the fixed dimension portion 19b, the electrolyte membrane 11, the adhesive 25, and the insulating beads 26 are sandwiched between the separators 18, and in the seal portion 19c, the electrolyte membrane 11, the adhesive 25, and the insulating beads 26 are sandwiched between the separators 18, A bead 27 as a sealing material is sandwiched between separators through which the cooling medium flows.

In the above, the linear expansion coefficient in the stacking direction of the stack is
Σ (linear expansion coefficient of each layer × thickness of the layer) / Σ (thickness of each layer)
Is required.
Table 1 shows the material of each component of the fuel cell and its linear expansion coefficient.

  Normally, the separator 18 is carbon, and the linear expansion coefficient of the fastening member 24 (usually metal) is larger. For this reason, the material of the member between the separators 18 is made of a material having a larger linear expansion coefficient than carbon. The linear expansion coefficient of the entire stack 23 can be made close to the linear expansion coefficient of the fastening member 24. Then, by changing the material, thickness, thickness ratio (for example, the thickness ratio of the separator and the diffusion layer) of each component of the fuel cell, etc., the linear expansion coefficient of the fastening member 24 in the stacking direction and the stack 23 The linear expansion coefficient in the stacking direction of the electrode body 19a can be substantially matched.

The rough calculation is as follows. For example, if the fastening member 24 is made of SUS304 and the separator 18 is made of carbon, the end plate 22 of the stack 23 is made of SUS304, and the terminal 20 is made of gold plating of copper. It becomes almost the same as the linear expansion coefficient of the member 24, and it is sufficient to match the linear expansion coefficient except for the portion. The thickness of the electrolyte membrane 11 in which the thin layers of the catalyst layers (C + Pt) 12 and 15 are formed on both surfaces is 30 μm, the thickness of the diffusion layers (carbon cloth) 13 and 16 is 150 μm, and the thickness of the separator 18 is Assuming that tμm is almost the same as the linear expansion coefficient per unit cell,
300 × 96 + 30 × 46 + t × 6 = (t + 330) × 14.8
t = 2875 μm
Thus, when the thickness of the separator 18 is about 2.9 mm, the linear expansion coefficient of the fastening member 24 in the stacked body stacking direction and the linear expansion coefficient of the electrode portion 19a of the stack 23 in the stacked body stacking direction are substantially the same. . However, in practice, the linear expansion coefficient is matched between the total length of the stack 23 and the total length of the fastening member 24.

  The linear expansion coefficient can be adjusted in accordance with the fixed dimension portion 19b and the seal portion 19c. In the case of the sizing portion 19b, it can be adjusted by selecting the material, thickness, particle size, and thickness ratio of the adhesive 25 and insulating beads 26 (for example, the thickness ratio of the adhesive 25 and the separator 18). . In the case of the seal part 19c, it can match | combine by selecting the material of the bead 27, thickness, and thickness ratio (for example, thickness ratio of the bead 27 and the separator 18). Usually, the thickness of the adhesive layer is about 100 μm, the diameter of the insulating beads 26 is about 50 μm, and the height of the beads 27 is about 500 μm.

Next, the operation of the fuel cell in which the linear expansion coefficients are combined as described above will be described.
3, the linear expansion coefficient of the stack 23 alpha _s, when expressed the linear expansion coefficient of the fastening member 24 in alpha _c, the magnitude of alpha _s and alpha _c, how fastening load of the stack due to the environmental temperature Shows how it will change. Here, the environmental temperature varies from the outside air temperature (−30 ° C. to 30 ° C.) to the fuel cell operating temperature (about 80 ° C.), and repeatedly varies depending on the cycle of operation stop to operation.
When the separator 18 of the stack 23 is carbon and the fastening member 24 is a metal (for example, stainless steel) (conventionally belongs to this case), since α _s <α _c , the proper tightening load is set at room temperature. In the fuel cell, the fastening load is reduced at the fuel cell operating temperature due to the difference in thermal expansion between the stack 23 and the fastening member 24, and the output of the fuel cell is lowered due to a decrease in the contact load between the separator 18 and the electrode surface (diffusion layer). In the worst case, gas leakage may occur.
On the other hand, when α _s > α _c , the fuel cell output is expected to decrease when the fuel cell is not sufficiently warmed, such as when starting up in a cold region.
In addition, the tightening load increases excessively during normal operation, and there is a risk that the separator may cause internal damage such as buckling of the diffusion layer (in the case of paper) and film breakage.

On the other hand, in the case of the present invention, α _s = α _c , or α _s and α _c are almost the same, so that when the environmental temperature changes, the stack 23 and the fastening member 24 thermally expand and contract by the same amount. Therefore, the fastening load of the fuel cell does not change. As a result, the fuel cell that is initially fastened with an appropriate load maintains the fastening load, and does not cause a decrease in fuel cell output or gas leakage caused by a change in the fastening load. The thermal expansion and contraction is more desirable in consideration of the increase in size due to the swelling of the film.
Therefore, it is possible to remove the spring mechanism arranged between the end plate and the insulator for reducing the fastening load fluctuation, which has been necessary in the past (however, the spring mechanism may be arranged). When it is removed, the stack length can be reduced by the amount occupied by the spring mechanism, which is advantageous for mounting on a vehicle, and also reduces the weight of the mechanism and the cost.

According to the fuel cell of the present invention, the linear expansion coefficients of the stack and the outer fastening member are the same or substantially the same in each part of the middle stack (at least in the electrode part) . At each part of the stack (at least at the electrode part), the stack and the fastening member expand by the same amount, and there is no change in fastening load, or even if there is a change in fastening load. As a result, the output of the fuel cell is substantially constant at each part of the stack (at least at the electrode part) , and no leakage of reaction gas (hydrogen, air) occurs.

It is a partially expanded sectional view of the fuel cell of the Example of this invention. 1 is an overall cross-sectional view of a fuel cell according to an embodiment of the present invention. It is a graph which shows the relationship between environmental temperature and fastening load of the fuel cell of this invention Example, and a conventional fuel cell.

Explanation of symbols

10 (solid polymer electrolyte type) fuel cell 11 electrolyte membrane 12 catalyst layer 13 diffusion layer 14 electrode (anode, fuel electrode)
15 Catalyst layer 16 Diffusion layer 17 Electrode (cathode, air electrode)
18 linear expansion coefficient of the separator 19 modules 19a electrode portion 19b sizing portion 19c seal portion 20 Terminal 21 insulator 22 end plate 23 stack 24 fastening member 25 coefficient of linear expansion of the adhesive 26 insulating beads 27 bead alpha _s stack alpha _c fastening member

Claims (1)

  In a fuel cell in which a stack composed of terminals, insulators, and end plates arranged at both ends in a stacking direction of a module composed of a laminate of a membrane-electrode assembly and a separator is fastened by a fastening member extending in the stacking direction outside the stack. The fuel cell characterized in that the linear expansion coefficient of the stack in the stacking direction and the linear expansion coefficient of the fastening member in the stacking direction are the same or substantially the same.

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