JP2003331884A - Fuel cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fuel cell capable of changing the cross section of a gas passage according to a request from the outside of the cell, and of forcibly changing the cross section of the passage independently of the environment in the cell, in improving durability of the fuel cell by closing a gas passage in OC (open circuit). <P>SOLUTION: (1) In this fuel cell, the cross sections of the gas passages 27 and 28 in a cell surface are variable, and the cross sections of the gas passages are varied according to a fuel cell load. (2) In OC, the gas passages 27 and 28 are completely closed. (3) Each gas passage is composed of a fixed part 18a, and a movable part 18b formed separately from the fixed part and movable with respect to the fixed part, and the gas passages 27 and 28 are changed between a state without a passage and a state with the passage by moving the moving part 18b. (4) The gas passages 27 and 28 are brought into the state without a passage in OC, and into the state with the passage enabling the variation of the passage cross section in outputting power. (5) For the gas passages 27 and 28, the passage cross section is fully opened when the demand output is small, and intermediately opened when the demand output is large. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fuel cell, and more particularly to a fuel cell having a variable gas channel cross-sectional area.

[0002]

2. Description of the Related Art As shown in FIGS. 3 and 4, a solid polymer electrolyte fuel cell 10 includes a membrane-electrode assembly (ME).
A: Membrane-Electrode Assembly) and a separator. The membrane-electrode assembly includes an electrode (anode, fuel electrode) 14 including an electrolyte membrane 11 made of an ion exchange membrane and a catalyst layer 12 arranged on one surface of the electrolyte membrane.
And an electrode (cathode, air electrode) 17 composed of a catalyst layer 15 arranged on the other surface of the electrolyte membrane. Gas flow channels 27, 28 (fuel gas flow channel 27, oxidizing gas flow channel 28) for supplying fuel gas (hydrogen) and oxidizing gas (oxygen, usually air) to the anode 14 and the cathode 17 in the separator 18 and A coolant flow path 26 for flowing a coolant (normally, cooling water) is formed. Diffusion layers 13 and 16 are provided between the membrane-electrode assembly and the separator 18 on the anode side and the cathode side, respectively. Membrane
A cell is constructed by stacking the electrode assembly and the separator 18, and a module is constructed from at least one cell, and the modules are laminated to form a cell laminated body, and the terminal 20 and the insulator 2 are provided at both ends of the cell laminated body in the cell laminating direction.
1, the end plates 22 are arranged, the cell stack is tightened in the cell stacking direction, and a fastening member (for example, the tension plate 2) extending outside the cell stack in the cell stacking direction is provided.
4), fix with bolts and nuts 25, and stack 23
Make up. On the anode side of each cell, a reaction is carried out to convert hydrogen into hydrogen ions (protons) and electrons, and the hydrogen ions move to the cathode side in the electrolyte membrane, and on the cathode side, oxygen, hydrogen ions and electrons (adjacent MEA Electrons generated at the anode of (1) come through the separator, or electrons generated at the anode of the cell at one end of the cell stacking direction come to the cathode of the cell at the other end through an external circuit) to generate water. Anode side: H ₂ → 2H ⁺ + 2e ⁻ Cathode side: 2H ⁺ + 2e ⁻ + (1/2) O ₂ → H ₂ O Hydrogen ions move in the electrolyte membrane and the electrolyte membrane is required to carry out the power generation reaction. It is necessary to be properly moistened, and the fuel gas and the oxidizing gas are humidified and supplied to the cell.
However, the conventional fuel cell has a problem of durability in OC (open circuit, that is, no electric load). That is, at OC, at a current of 0 (in an automobile, in an idle state), the flow velocity becomes 0, the water does not stick out, and the water content becomes high, and the hydrogen cross leak is proportional to the water content (membrane from anode to cathode The amount of hydrogen that leaks through a very small amount increases), cross-leaked hydrogen reacts with oxygen flowing through the oxidizing gas flow path on the cathode side, the electrode on the cathode side generates heat, and there is no water produced on the cathode side. The phenomenon of causing a significant increase in temperature may occur in a chain and holes may be formed in the film, which may cause a problem in durability. As a countermeasure, it is possible to dry the membrane at the time of OC, consume hydrogen as electric power in order to prevent cross-leakage of hydrogen in the anode, and cut hydrogen as close to the anode electrode as possible.
In the present invention, it was decided to develop a method of suppressing gas supply to the electrode at the time of OC (method of closing gas passage). Regarding the variable gas channel cross-sectional area, Japanese Patent Laid-Open No. 2000-3
No. 06591 is provided with a valve for varying the flow passage cross-sectional area in the cell plane of the fuel cell in order to enable uniform gas distribution (thus, a subject different from the subject of the present invention) Accordingly, a bimetal valve or the like that can change the flow passage cross-sectional area) is disclosed.

[0003]

In order to improve durability during OC in a conventional fuel cell, a structure (a bimetal valve of Japanese Patent Laid-Open No. 2000-306591) that reduces the cross-sectional area of the flow path in the cell plane is adopted, and the OC is improved. Even if the gas supply to the electrodes is sometimes suppressed, the following problems occur. In the conventional structure, since the flow passage cross-sectional area is changed according to the environment inside the cell (for example, temperature), the flow passage cross-sectional area is changed according to the request (for example, load) from the outside of the cell independently of the environment inside the cell. I can't. Further, the flow passage cross-sectional area becomes a value determined by the environment (for example, temperature) inside the cell, and the flow passage cross-sectional area cannot be forcibly changed independently of the environment inside the cell. In the structure in which the bimetal valve is provided at one place in the flow passage, even if the flow passage is closed by the valve, the valve cannot be pressed against the diffusion layer over the entire flow passage groove, so contact between the diffusion layer and the separator over the entire flow passage groove. I can not take the area,
The electron passage cross-sectional area of the separator does not increase, and heat conduction with the separator does not improve even if the gas passage is blocked. An object of the present invention is to improve the durability of a fuel cell by closing the gas passage at the time of OC, the passage cross-sectional area can be changed according to a request from the outside of the cell, and the passage cross-sectional area can be changed to the environment in the cell. To provide a fuel cell that can be forced to change independently. Another object of the present invention is to
When the gas flow path is closed at the time of OC to improve the fuel cell durability, the flow path cross-sectional area can be changed according to the demand from the outside of the cell, and the flow path cross-sectional area is forced independently of the environment inside the cell. It is an object of the present invention to provide a fuel cell that can be changed to the above and can improve the thermal conductivity with the separator when the gas flow path is closed at the time of OC.

[0004]

The present invention which achieves the above object is as follows. (1) A fuel cell in which the cross-sectional area of the gas flow passage in the cell plane is variable, and the cross-sectional area of the gas flow passage is changed according to the fuel cell load. (2) The fuel cell according to (1), wherein the gas flow path is fully closed during OC. (3) A fuel cell having a gas flow path formed on a cell surface, wherein the gas flow path is composed of a fixed part and a movable part that is a part separate from the fixed part and is movable with respect to the fixed part. A fuel cell in which the gas flow path is changed between a flow path-less state and a flow path-present state by moving the movable part. (4) The fuel cell according to (3), wherein the gas flow passage is flowless when OC, and has a flow passage whose flow passage cross-sectional area is variable when output. (5) When there is a flow path at the time of output, the gas flow path is
The fuel cell according to (4), wherein the flow passage cross-sectional area is fully opened when the required output is low, and the flow passage cross-sectional area is opened when the required output is high.

In the fuel cell of the above (1), since the cross sectional area of the gas flow passage in the cell surface is variable, it is possible to close the flow passage cross sectional area at the time of OC. At that time, since the gas flow passage cross-sectional area is changed according to the load (an example of a request from the outside), it is not changed according to the environment inside the cell.
It can be forcibly changed independently of the environment inside the cell, and the control response can be improved. In the fuel cell of the above (2), by closing the flow passage cross-sectional area at the time of OC, hydrogen cross-leak can be prevented and the durability at OC can be improved. In the fuel cell of the above (3), since the gas flow path is composed of the fixed part and the movable part and the movable part can be moved to make the flow path less, the flow path can be closed at the time of OC to close the flow path. it can. Further, by moving the movable portion in response to a request from outside the cell, the flow passage cross-sectional area can be forcibly changed independently of the environment inside the cell, and the control response can be improved. In addition, since the movable part can be moved so as to have no flow passage, the whole movable part can be pressed against the diffusion layer as a flow passage is not present at the time of OC, and the thermal conductivity of the separator when the gas flow passage is closed at the time of OC can be improved. Can be improved. In the fuel cell of the above (4), by cutting off the supply of hydrogen at the time of OC with no flow passage, it is possible to prevent cross-leakage of hydrogen and improve durability at OC. In the fuel cell of the above (5), in the presence of the flow passage at the time of output, the gas flow passage is fully opened when the required output is low, and is opened midway when the required output is high. When the required output is low, the pressure loss can be reduced to improve the fuel consumption, and when the required output is high, the flow velocity can be increased and the generated water can be blown off to increase the fuel cell output. As a result, at the time of output, it is possible to achieve both high fuel efficiency and high output depending on the required output.

[0006]

BEST MODE FOR CARRYING OUT THE INVENTION The fuel cell of the present invention is shown in FIG.
~ It demonstrates with reference to FIG. The general configuration of the conventional fuel cell of FIGS. 3 and 4 is also applied to the fuel cell of the present invention, except that the separator 18 is composed of a fixed portion and a movable portion movable with respect to the fixed portion in the present invention. . The fuel cell of the present invention is a solid polymer electrolyte fuel cell 10. The fuel cell 10
Is mounted in, for example, a fuel cell vehicle. However, it may be used for other than automobiles.

As shown in FIGS. 1, 3, and 4, the solid polymer electrolyte fuel cell 10 is composed of a laminate of a membrane-electrode assembly (MEA: Membrane-Electrode Assembly) and a separator 18. The membrane-electrode assembly is
An electrode (anode, anode, composed of an electrolyte membrane 11 made of an ion exchange membrane and a catalyst layer 12 arranged on one surface of the electrolyte membrane)
A fuel electrode) 14 and an electrode (cathode, air electrode) 17 including a catalyst layer 15 disposed on the other surface of the electrolyte membrane 11. The separator 18 has gas passages 27 and 28 for supplying a fuel gas (hydrogen) and an oxidizing gas (oxygen, usually air) to the anode and cathode, or a refrigerant passage 26 for flowing a refrigerant. Diffusion layers 13 and 16 are provided between the membrane-electrode assembly and the separator 18 on the anode side and the cathode side, respectively. FIG. 1 shows one MEA and a part of the separator 18 on both sides of the stack 23 (one channel of each of the gas channels 27 and 28 and its channel bottom wall and channel sidewall portion). There is.

In the fuel cell of the present invention, as shown in FIG. 1, the gas flow path 2 in the cell surface (in the power generation region of the cell)
The flow passage cross-sectional areas of Nos. 7 and 28 (fuel gas flow passage 27, oxidizing gas flow passage 28) are variable, and the gas flow passage cross-sectional area is changed according to the demand outside the cell, for example, the fuel cell load. .
The gas flow path whose flow path cross-sectional area is variable is the fuel gas flow path 2
7 and the oxidizing gas flow path 28 are both desirable,
Since only one of the fuel gas flow path 27 and the oxidizing gas flow path 28 is effective in improving the OC durability, only one of the fuel gas flow path 27 and the oxidizing gas flow path 28 may be used. The following description will be made on the fuel gas flow path 27 and the oxidizing gas flow path 2.
Take both cases of 8 as an example. When the gas flow passage cross-sectional area is changed, as shown in FIG.
8 is fully closed.

The fuel cell of the present invention, as shown in FIG.
It has gas flow paths 27 and 28 (fuel gas flow path 27, oxidizing gas flow path 28) formed on the cell surface.
7 and 28 are a fixed portion 18a and a fixed portion 18a, respectively.
A movable part 18b which is a separate component from the fixed part 18a and is movable.
It consists of The fixed portion 18a and the movable portion 18b are
Each of them constitutes a part of the separator 18. By moving the movable portion 18b, the gas flow paths 27 and 28 are changed between a flow path-less state and a flow path-present state. Movable part 18
b is moved in response to a request outside the cell, for example, a fuel cell load, and the movable portion 18b is moved to change the gas flow passage cross-sectional area.

The movable portion 18b is moved in the depth direction of the flow channel grooves of the gas flow channels 27 and 28. That is, the fixed portion 18a constitutes the rib of the separator, the movable portion 18b constitutes the valley bottom between the ribs, and the movable portion 18b can be moved, so that the movable valley bottom is formed between the fixed ribs. It is moved in the direction toward and away from the diffusion layers 13 and 16 (direction in which the depth of the channel groove becomes deeper or shallower).
The movement of the movable portion 18b may be accompanied by the movement of the gas passages 27, 28 in the passage longitudinal direction, but when accompanied by the movement in the passage longitudinal direction, the diffusion layers 13, 16 are rubbed near the passageless state. Therefore, it is better that there is no movement in the longitudinal direction of the flow path. Movable part 18b
Is not locally provided in one place of the gas flow paths 27 and 28 as in the conventional bimetal valve, but is provided in the gas flow path 2
It is provided long in the longitudinal direction of 7, 28. Therefore, in the flow pathless state, the movable portion 18b is pressed against the diffusion layers 13 and 16 over the entire length of the movable portion 18b.

The above structural conditions are, for example, the fixed portion 18
a is formed by forming parallel holes in a flat plate, and the movable portion 18b is formed on one surface of the flat plate with a large number of parallel comb-shaped flow path bottom walls protruding in a direction orthogonal to the flat plate. And the comb teeth of the movable portion 18b are fixed to the fixed portion 18a.
Gas flow paths 27 and 28 are formed by inserting the side surfaces of the parallel holes into the side surfaces of the parallel holes to form the bottom surfaces of the flow paths with the comb teeth. This is achieved by a structure that moves in the thickness direction to change the depth of the flow path. However, the flow channel structure is not limited to this structure.

As shown in FIG. 2, each gas flow path 27, 28
The flow of the movable part 18b is controlled so that the flow path is not present at the time of OC, and the flow path having the variable flow passage cross-sectional area is provided at the time of output. Further, in the presence of the flow passage at the time of output, the gas flow passages 27 and 28 have the flow passage cross-sectional area fully opened when the required output is low as shown in A of FIG. As described above, when the required output is high (when the load is high), the movement of the movable portion 18b is controlled so that the flow passage cross-sectional area is opened midway (opening between the full open and the flow passageless closed). To be done. The movement of the movable part 18b is controlled by a signal from a control device outside the cell, and is provided in an operating device of the movable part 18b (for example, provided on a side part of the stack 23, which is then provided to the movable part 18b of the cell).
Connected to)). It is desirable to control the movement of the movable portion 18b in all cells of the stack 23 at the same time.

Next, the operation of the fuel cell of the present invention will be described. In the above fuel cell 10, since the flow passage cross-sectional areas of the gas flow passages 27 and 28 in the cell plane are variable, the gas flow passages 27 and 28 are closed at the time of OC (the flow passage cross-sectional areas of the gas flow passages 27 and 28). Can be set to 0). At that time, the gas flow passage cross-sectional area is changed according to the load (an example from the outside), so it is not changed according to the environment inside the cell as in the past, so it is forced independently of the environment inside the cell. And can be controlled proactively on demand,
The control response can be improved.

Further, since the flow passage cross-sectional area is closed at the time of OC, the supply of hydrogen can be cut over the entire length of the fuel gas flow passage 27 at the time of OC, hydrogen cross leak can be prevented, and OC
When endurance can be improved. Further, if the flow path cross-sectional area on the cathode side is closed, even if a very small amount of hydrogen cross- leaks to the cathode side, the reaction between hydrogen and oxygen on the oxygen side and the resulting heat generation and damage to the membrane 11 may occur. It can be suppressed, and the durability at OC can be improved.
On the other hand, when the supply flow rate of hydrogen is stopped by the conventional bi-vetal valve, the cross leak of hydrogen remaining in the fuel gas flow path 27 is always generated, so that it is possible to effectively reduce O.
Durability at C cannot be improved.

In the fuel cell 10 of the present invention, the gas flow path is composed of the fixed part 18a and the movable part 18b, and the movable part 18b can be moved to make the flow path less. Can be blocked. Further, since the movable part 18b is moved in response to a request from the outside of the cell, it is not uniquely operated according to the environmental conditions inside the cell unlike the conventional bimetal valve. It can be forcibly changed to an arbitrary value independently of the environment, and the control response can be improved.

Further, since the movable portion 18b can be moved so that the gas flow passages 27 and 28 are flow passageless, the OC
Sometimes the entire movable part 18b is made into a diffusion layer 13, 1 without a flow path.
6 can be pressed against the separator 1
8 is the entire surface, including the rib portion and the groove portion,
By being pressed against the diffusion layers 13 and 16, the electron passage of the separator 18 is increased when the gas flow path is closed at the time of OC, and the thermal conductivity and conductivity with the separator 18 can be improved. With the conventional bimetal valve method, although the flow rate of the supplied gas can be reduced, the flow path is still in the groove state, and the separator cannot contact the diffusion layer at that part, so stop the gas supply without any effort. However, the flow path cannot be effectively used for the electronic passage of the separator. On the other hand, in the present invention, when the flow path is not used, the portion that was the flow path groove when there is output can be effectively used as the electronic passage of the separator 18 by filling it with the movable portion 18b. Further, in the bimetal method, the contact pressure of the bimetal with respect to the diffusion layer does not become large, so the contact resistance becomes large and it cannot be effectively used as an electron passage.

In the fuel cell 10 having the movable portion 18b, the movable portion 18b is operated to cut off the supply of hydrogen and oxygen without a flow passage at the time of OC, thereby preventing the cross leak of hydrogen and causing the cross leak. It is possible to prevent the reaction between hydrogen and oxygen that have been trapped, suppress heat generation, prevent damage to the film 11, and improve durability during OC. In contrast,
When the flow rate of hydrogen supply is stopped by the conventional bi-vetal valve, cross-leakage of hydrogen remaining in the fuel gas flow path 27 is inevitably generated, so that the OC durability cannot be effectively improved.

Further, at the time of output of the fuel cell 10 (state with flow passage), as shown in FIG. 2, the gas flow passage is fully opened when the required output is low, and when the required output is high. Since the cross-sectional area of the flow path is medium open, pressure loss can be reduced to improve fuel efficiency when the required output is low, and when the required output is high, the flow velocity is increased and the generated water is blown away, and the output in the downstream region of the oxidizing gas is increased. The density can be improved and the fuel cell output can be increased (however, the pressure loss becomes large at middle opening and the fuel consumption is lower than at full opening). As a result, at the time of output, it is possible to achieve both high fuel efficiency and high output depending on the required output. On the other hand, in the conventional bimetal valve system, the valve opening is uniquely determined according to the temperature, and it is not possible to obtain the fuel consumption or output according to the required output, so that it is possible to improve the fuel consumption like the present invention. It is not possible to achieve both high output and high output.

[0019]

According to the fuel cell of the first aspect, since the cross sectional area of the gas flow passage in the cell surface is variable, it is possible to close the flow passage cross sectional area at the time of OC. At that time, since the gas flow passage cross-sectional area is changed according to the load (required output), the gas flow passage cross-sectional area can be forcibly changed independently of the internal environment of the cell, and the control response can be improved. . According to the fuel cell of the second aspect, by closing the flow passage cross-sectional area at the time of OC, hydrogen cross-leak can be prevented and the durability of the fuel cell at the time of OC can be improved. According to the fuel cell of the third aspect, the gas passage is composed of the fixed portion and the movable portion, and the movable portion can be moved so as to eliminate the passage.
At times, the flow passage can be closed without using the flow passage. Further, by moving the movable portion in response to a request from outside the cell, the flow passage cross-sectional area can be forcibly changed independently of the environment inside the cell, and the control response can be improved. Further, since the movable part can be moved so as to have no flow passage, the whole movable part can be pressed against the diffusion layer as a flow passage is not present at the time of OC, and the heat conduction with the separator when the gas flow passage is closed at the time of OC. It is possible to improve the sex. Claim 4
According to the fuel cell of No. 3, the cross-leakage of hydrogen can be prevented by cutting off the supply of hydrogen at OC without a flow path.
The durability at OC can be improved. According to the fuel cell of claim 5, in the presence of the flow passage at the time of output, the gas flow passage is
When the required output is low, the flow passage cross-sectional area is fully opened, and when the required output is high, the flow passage cross-sectional area is opened midway.When the required output is low, it is possible to reduce pressure loss and improve fuel efficiency. When it is high, the flow velocity can be increased to blow off the produced water to increase the fuel cell output. As a result, at the time of output, both improvement in fuel consumption and high output can be achieved.

[Brief description of drawings]

FIG. 1 is an enlarged sectional view of a part of a fuel cell of the present invention.

FIG. 2 is a voltage / current density graph of the fuel cell of the present invention.

FIG. 3 is an overall front view of a general fuel cell (applicable to the present invention except for a gas flow path portion).

4 is a partially enlarged cross-sectional view of the fuel cell of FIG.

[Explanation of symbols]

10 (Polymer electrolyte type) fuel cell 11 Electrolyte membrane 12 Catalyst layer 13 Diffusion layer 14 electrodes (anode, fuel electrode) 15 Catalyst layer 16 diffusion layer 17 electrodes (cathode, air electrode) 18 separator 18a fixed part 18b movable part 19 modules 20 terminals 21 insulator 22 End plate 23 stack 24 Fastening member (tension plate) 25 volts 26 Refrigerant flow path (cooling water flow path) 27 Fuel gas flow path 28 Oxidizing gas flow path

Claims (5)

[Claims] 1. A fuel cell in which the cross-sectional area of the gas flow passage in the cell plane is variable and the cross-sectional area of the gas flow passage is changed according to the fuel cell load. 2. The fuel cell according to claim 1, wherein the gas flow path is fully closed during OC. 3. A fuel cell having a gas flow path formed on a cell surface, wherein the gas flow path is a movable part movable from the fixed part and a part separate from the fixed part. Configure and
A fuel cell in which the gas flow path is changed between a flow path-less state and a flow path-present state by moving the movable portion. 4. The fuel cell according to claim 3, wherein the gas flow passage has no flow passage at OC and has a flow passage having a variable flow passage cross-sectional area at output. 5. The gas flow passage having a flow passage at the time of output, the gas flow passage is fully opened when the required output is low, and is opened midway when the required output is high. Fuel cell.