JP2003142120A - Fuel cell - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fuel cell capable of suppressing corrosion of a separator having a metallic surface. SOLUTION: (1) In this fuel cell 10, passages 31, 32 to discharge at least a part of reaction gas are formed in diffusion layers 13, 15 in contact with the separator 18 having a metallic surface. (2) In this fuel cell, the passages 31, 32 capable of discharging at least a part of the reaction gas directly to the outside of the separator surface without passing through gas passages 26, 27 are formed in the diffusion layers 13, 15 in contact with the separator 18 having the metallic surface. (3) In this fuel cell 10, conductive water repellent layers 33, 34 are formed in a part brought into contact with the diffusion layers 13, 15 of the separator 18.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a fuel cell,
Particularly, it relates to a flow path structure of a solid polymer electrolyte fuel cell.

[0002]

2. Description of the Related Art A solid polymer electrolyte fuel cell has a membrane-electrode assembly (MEA).
y) and one or more cells each including a diffusion layer and a separator are stacked to form a module, and the modules are stacked. The MEA is composed of an electrolyte membrane composed of an ion exchange membrane, an electrode (anode) composed of a catalyst layer arranged on one surface of the electrolyte membrane, and an electrode (cathode) composed of a catalyst layer arranged on the other surface of the electrolyte membrane. A diffusion layer is usually provided between the MEA and the separator. Fuel gas (hydrogen) is added to the anode of the separator that sandwiches the MEA and diffusion layer.
A fuel gas flow path for supplying oxygen and an oxidizing gas flow path for supplying an oxidizing gas (oxygen, usually air) to the cathode are formed. Further, in order to cool the fuel cell, the separator is provided with a refrigerant (cooling water) for each cell or for each plurality of cells.
A flow path is formed. The separator constitutes a passage for electrons between adjacent cells. Terminals (electrode plates), insulators, and end plates are arranged at both ends of the cell stack in the cell stack direction, the cell stack is fastened in the cell stack direction, and fastening members extending in the cell stack direction outside the cell stack (for example, Tension plate) and bolts to form a stack. In a solid polymer electrolyte fuel cell, hydrogen is converted into hydrogen ions and electrons on the anode side, the hydrogen ions move to the cathode side in the electrolyte membrane, and on the cathode side, oxygen, hydrogen ions and electrons (adjacent The electrons generated at the MEA anode come through the separator, or the electrons generated at the anode of the cell at one end of the cell stack come to the cathode of the cell at the other end of the cell stack through an external circuit to generate water. The reaction is carried out. Anode side: H ₂ → 2H ⁺ + 2e ⁻ Cathode side: 2H ⁺ + 2e ⁻ + (1/2) O ₂ → H ₂ O In conventional polymer electrolyte fuel cells, the thickness of each cell is thin to reduce size and weight. Therefore, a metal separator made of a metal such as stainless steel, aluminum, nickel, niobium, or tantalum may be used instead of the separator fired or molded with carbon. Further, in order to improve the corrosion resistance, there may be used one that has been subjected to surface treatment such as plating or sputtering with a noble metal such as gold or silver. Further, Japanese Patent Laid-Open No. 2001-76740A discloses a metal separator in which a conductive water-repellent layer is formed to improve the corrosion resistance of the metal separator.

[0003]

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention
At least a separator made of metal on the surface (a metal-plated separator may be a separator having only a metal surface) may have a ME
When hydrofluoric acid eluted from A or sulfuric acid contained in the reformed gas is exposed to acidic water for a long time, there is a problem that corrosion is likely to occur. In particular, the portion of the separator that is in contact with the portion where moisture is likely to stay and is difficult to dry, for example, the portion of the diffusion layer that is pressed by the ribs between the grooves of the separator is likely to be corroded. Japanese Patent Laid-Open No. 2001-
Even if a conductive water-repellent layer is formed on the surface of the metal separator like 76740A, the corrosion of the separator cannot be sufficiently suppressed. An object of the present invention is to provide a fuel cell capable of suppressing corrosion of a separator having a metal surface.

[0004]

The present invention which achieves the above object is as follows. (1) A fuel cell in which a passage for discharging at least a part of a reaction gas is formed in a diffusion layer whose surface is in contact with a separator made of metal. (2) A fuel cell in which a passage is formed in a diffusion layer whose surface is in contact with a separator made of metal so that at least a part of the reaction gas can be directly discharged to the outside of the separator without passing through the gas flow path of the separator. (3) The fuel cell according to (1) or (2), wherein a conductive water repellent layer is formed on a contact portion of the separator with the diffusion layer.

In the fuel cells of the above (1) and (2), since gas flows in the diffusion layer in contact with the separator, water does not stay therein, and the surface in contact with it is made of a metal separator (metal plated, only the surface is made of metal). It may be a separator). In the fuel cell of (3) above, since the conductive water repellent layer is formed at the contact portion of the separator with the diffusion layer,
The separator surface is less likely to get wet with water, and the corrosion of the separator having a metal surface can be suppressed.

[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. 1 shows a configuration applicable to any of the embodiments of the present invention, FIG. 2 shows a first embodiment of the present invention, FIG. 3 shows a second embodiment of the present invention, FIG. 5 shows Example 3 of the present invention. Components that are common or similar across all embodiments of the invention are labeled with the same reference numerals across all embodiments of the invention. First, components common or similar (but not necessarily essential) to all embodiments of the invention are
This will be described with reference to FIGS. 1 and 4. The fuel cell of the present invention is a solid polymer electrolyte fuel cell 10. The solid polymer electrolyte fuel cell 10 is mounted in, for example, a fuel cell vehicle. However, it may be used for other than automobiles.

The solid polymer electrolyte fuel cell 10 has a membrane
MEA (Membrane-Electrode Assembly)
A module 16 is formed by stacking one or more layers of cells 16 each composed of a bly) and a separator 18, and the modules 17 are laminated. The MEA is composed of an electrolyte membrane 11 made of an ion exchange membrane, an electrode 12 (anode) made of a catalyst layer arranged on one surface of the electrolyte membrane 11, and an electrode 14 (cathode made of a catalyst layer arranged on the other surface of the electrolyte membrane 11). ) And. Diffusion layers 13 and 15 are usually provided between the MEA and the separator 18. Terminals (electrode plates) 20, insulators 21, and end plates 22 are arranged at both ends of the cell stack 19 in the cell stacking direction.
Are fastened in the cell stacking direction, and fixed with a fastening member (for example, a tension plate 24) extending in the cell stacking direction outside the cell stack 19 with bolts 25.
Is formed.

A fuel gas passage 26 for supplying a fuel gas (hydrogen) to the anode 12 is provided in the anode side of the pair of separators sandwiching the MEA and the diffusion layers 13 and 15.
Is formed, and an oxidizing gas flow path 27 for supplying an oxidizing gas (oxygen, usually air) to the cathode 14 is formed in the cathode side separator. Further, in order to cool the fuel cell, the separator 18 is provided with a coolant passage 28 through which a coolant (cooling water) flows, for each cell or for each plurality of cells. For example, in FIG. 2, one cell 1
Configure modules 17 from 6 and 1 for each module 17
One refrigerant channel 28 is provided. Separator 18
Separates the cooling water from the fuel gas and oxidizing gas,
Alternatively, the fuel gas and the oxidizing gas are divided. In the illustrated example, a separator for partitioning the fuel gas and the refrigerant of one cell and a separator for partitioning the oxidizing gas and the refrigerant of the adjacent cells are overlapped with their refrigerant channels aligned. The separator 18 also forms an electrical passage through which electrons flow from the anodes of adjacent cells to the cathodes.

The outer peripheral portion of the cell is composed of a resin frame body (hollow out). The fuel gas supply manifold 29a, the fuel gas discharge manifold 29b,
An oxidizing gas supply manifold 30a, an oxidizing gas discharge manifold 30b, a refrigerant supply manifold, and a refrigerant discharge manifold are formed. Fuel gas supply manifold 2
9a and the fuel gas discharge manifold 29b communicate with the fuel gas flow path 26, and the oxidizing gas supply manifold 30
a, the oxidizing gas exhaust manifold 30b is the oxidizing gas flow path 2
7, the refrigerant supply manifold and the refrigerant discharge manifold communicate with the refrigerant manifold 28.

The separator 18 is a separator whose surface is made of metal. The separator 18 is a metal plate (for example,
A metal separator made of an inexpensive metal plate such as stainless steel or aluminum), or another metal plating (other than gold or silver, etc.) on the surface of the metal plate (for example, an inexpensive metal plate such as stainless steel or aluminum) is relatively inexpensive A metal separator that has been plated with various metals, or the surface of a resin plate that has been made conductive by mixing carbon plates or conductive particles (for example, carbon particles) with metal plating (other than gold or silver, etc. The metal-made separator is the only surface that has been plated with an inexpensive metal. The fluid passages 26, 27, 28 formed in the separator 18 are formed by a group of a plurality of grooves formed in the separator 18 by press molding or the like, or a large number of convex portions formed in the separator 18 by press molding or the like. Or a combination of the spaces between the plurality of grooves and the protrusions.

The electrodes 12 and 14 are composed of catalyst (for example, platinum Pt) particles, carbon particles, and an electrolyte. The diffusion layers 13 and 15 are made of, for example, a layer in which carbon particles or carbon fibers are crossed or paper-shaped with a binder (carbonized or non-carbonized), and have breathability and conductivity.
Diffusion layers 13, 15 whose surface is in contact with a metallic separator
Is a passage 31 for discharging at least a part of the reaction gas,
32. The passages 31 and 32 include a passage 31 formed in the diffusion layer 13 and a passage 32 formed in the diffusion layer 15. That is, in the diffusion layers 13 and 15 whose surfaces are in contact with the separator made of metal, at least a part of the reaction gas can be directly discharged to the outside of the separator surface without passing through the gas passages 26 and 27 of the separator. Are formed.

The diffusion layer 13 (which may be inside or on the surface of the diffusion layer 13) which is in contact with the anode 12 has substantially the separator 1.
A passage 31 formed in parallel with 8 is formed. The passages 31 are preferably formed of a large number of gas outflow holes formed in parallel or in a grid pattern with a fine pitch, or are formed of a sparse layer of a diffusion layer having a multi-layered structure in which layers of different sparseness are stacked. The passage 31 is the fuel gas exhaust manifold 2
It communicates with 9b. Therefore, the fuel gas flow passage 26 directly communicates with the fuel gas discharge manifold 29b, and the fuel gas discharge manifold 29b via the passage 31.
Is in communication with. The passage 31 may communicate with the fuel gas supply manifold 29a.

Similarly, the diffusion layer 15 in contact with the cathode 14
A passage 32 formed substantially parallel to the separator 18 is formed in the diffusion layer 15 (inside or on the surface of the diffusion layer 15). The passages 32 are preferably formed of a large number of gas outflow holes formed in parallel or in a grid pattern with a fine pitch, or are preferably formed of a sparse layer of a diffusion layer having a multi-layered structure in which layers of different sparseness are stacked. The passage 32 communicates with the oxidizing gas exhaust manifold 30b. Therefore, the oxidizing gas flow passage 27 directly communicates with the oxidizing gas exhaust manifold 30b and also communicates with the oxidizing gas exhaust manifold 30b through the passage 32. The passage 32 may communicate with the oxidizing gas supply manifold 30a.

Conductive water-repellent layers 33, 3 are provided on the contact surface of the separator 18 with at least one of the diffusion layers 13, 15.
4 (the conductive water-repellent layer 33 is formed on the contact surface with the diffusion layer 13 and the conductive water-repellent layer 34 is formed on the contact surface with the diffusion layer 15). However, formation of the conductive water repellent layers 33 and 34 is not essential. Conductive water repellent layer 3
When forming 3, 34 on the contact surface of the separator 18 with the diffusion layers 13, 15, it may be applied and formed by a roller. The diffusion layer 1 of the separator 18 is formed by coating and forming with a roller.
The conductive water-repellent layers 33 and 34 can be formed only on the contact surfaces with the electrodes 3 and 15 (without forming on the surfaces of the gas flow paths 27 and 28, only on the contact surfaces with the diffusion layers). Conductive water repellent layers 33, 34
For example, apply and dry a mixture of carbon powder and carbon fibers to give conductivity to a water-repellent resin (for example, polytetrafluoroethylene, but not limited to polytetrafluoroethylene). Is formed by.

The operation of common or similar components across all embodiments of the invention will now be described. The fuel gas flows into the fuel gas passage 26 from the fuel gas supply manifold 29a, and a part of the fuel gas passes through the passage 3 from the fuel gas passage 26.
1 to the fuel gas discharge manifold 29b,
The rest is from the fuel gas passage 26 (without passing through the passage 31)
It directly flows out to the fuel gas discharge manifold 29b. Similarly, the oxidizing gas flows from the oxidizing gas supply manifold 30a into the oxidizing gas flow passage 27, a part of the oxidizing gas flows out of the oxidizing gas flow passage 27 through the passage 32 to the oxidizing gas discharge manifold 30b, and the rest flows into the oxidizing gas flow. It directly flows out of the passage 27 (without passing through the passage 32) to the oxidizing gas exhaust manifold 30b.

Since the fuel gas (and the water vapor) flows through the passage 31 formed in the diffusion layer 13, the fuel gas (and water vapor) flows from the separator 18 to M.
On the EA side, the flow of gas prevents the acidic gas or liquid having a high concentration of pH (pH is substantially lower than 3) from staying in the vicinity of the separator, and is pushed by the rib portion of the separator of the diffusion layer 13. Since the vicinity of the exposed portion is dried, it is possible to prevent or suppress the separator 18 from being corroded by being exposed to acidic water for a long time. The surface of the separator 18 that does not come into contact with the diffusion layer 13 of the fuel gas flow path 26 is relatively easy to dry due to the fuel gas flow of the fuel gas flow path 26, so corrosion problems do not occur easily. On the other hand, the diffusion layer 13 of the separator 18
Although the contact portion with is a portion that is easily corroded, the durability of the separator 18 and the fuel cell is improved because the portion is less likely to be corroded.

Similarly, since the oxidizing gas (and water vapor) flows through the passage 32 formed in the diffusion layer 15, the separator 1
The gas flows from 8 to the MEA side so that an acidic gas or liquid having a high concentration of pH (a pH of a level lower than 3) does not stay near the separator, and the rib portion of the separator of the diffusion layer 15 is prevented. Since the vicinity of the portion pressed by is dried, it is possible to prevent or suppress the separator 18 from being corroded by being exposed to acidic water for a long time. The surface of the separator 18 that does not come into contact with the diffusion layer 15 of the oxidizing gas passage 27 is the oxidizing gas passage 2
The fuel gas flow of No. 7 makes it relatively easy to dry, so that a corrosion problem is unlikely to occur. On the other hand, the contact portion of the separator 18 with the diffusion layer 15 was a portion that was easily corroded,
Since the portion is less likely to corrode, the durability of the separator 18 and the fuel cell is improved.

As a result, the material forming the separator 18 may be an inexpensive metal such as stainless steel or aluminum (or an aluminum alloy may be used), and it is not necessary to perform surface treatment such as plating or surface treatment such as plating. In the case of performing, it is not necessary to use a precious metal such as gold for the plating material, and it is possible to significantly reduce the cost. Further, the separator 18 can be composed of a metal separator, and in the case of a carbon separator, it must be thick (for example, 3 mm) to prevent cracking.
Thin by using a metal separator (approx. 1 mm with irregularities in the flow path, metal plate itself is about 0.2 mm, for example)
Therefore, the dimension of the fuel cell stack 23 in the stacking direction can be greatly reduced, and the weight can be reduced, which greatly contributes to easy mounting in a vehicle, improvement in fuel consumption, and the like.

The diffusion layers 13 and 15 of the separator 18 are also
When the conductive water-repellent layers 33 and 34 are formed in contact with the separator 18, even if the acidic water stays in the diffusion layers 13 and 15, the conductive water-repellent layers 33 and 34 repel the water, so that the separator 18 Becomes less susceptible to the effects of acid water and corrosion, and the separator 18
And the durability of the fuel cell is improved. In addition, since an inexpensive material can be used as the material of the metal separator, the cost can be reduced, and the operation and effects of reducing the size and weight of the fuel cell stack 23 by adopting the metal separator and improving the mountability on the vehicle can be obtained. To be

According to the present invention, the passages 3 are formed in the diffusion layers 13 and 15.
1, 32 (only one of the passages 31, 32 may be formed, or the passages 31, 32 may be formed).
32 may be formed), and the conductive water-repellent layer 3 is formed on the contact portion of the separator 18 with the diffusion layers 13 and 15.
Forming 3, 34 may be a configuration in which only one is adopted, or a configuration in which both are combined.

Next, the structure peculiar to each embodiment of the present invention,
The operation will be described. In Example 1 of the present invention, as shown in FIG. 2, the separator 18 is a metal separator, and no conductive water repellent layer is formed on the metal separator. The surface of the metal separator may or may not be plated. However, even if the plating treatment is performed, the cost of precious metal plating does not increase, so it is not necessary. A passage 31 is formed in the diffusion layer 13, and a passage 32 is formed in the diffusion layer 15. Diffusion layers 13, 1
The passages 31 and 32 of No. 5 are composed of a large number of holes formed in the diffusion layers 13 and 15 and extending substantially parallel to the separator. The method of forming the passages 31 and 32 is such that each diffusion layer is made up of a plurality of diffusion layers and a groove-like passage is formed on the surface of one of the diffusion layers, and another layer is laminated on top of it. The holes can be easily formed inside the diffusion layer. The operation and effect of the first embodiment of the present invention is the same as the operation of the passages 31 and 32 among the operations common to all the embodiments of the present invention.

In Example 2 of the present invention, as shown in FIG. 3, the separator 18 is a metal separator, and no conductive water repellent layer is formed on the metal separator. The surface of the metal separator may or may not be plated. However, even if the plating treatment is performed, the cost of precious metal plating does not increase, so it is not necessary. A passage 31 is formed in the diffusion layer 13, and a passage 32 is formed in the diffusion layer 15. Diffusion layers 13 and 15
The passages 31 and 32 are composed of sparse layers formed inside or on the surfaces of the diffusion layers 13 and 15. In the method of forming the passages 31 and 32, each diffusion layer is a diffusion layer formed by laminating a plurality of layers having different sparseness and denseness, and the sparse layer of the passages 31 and 32 is formed.
Used as 32. In the example of FIG. 3, the diffusion layers 13 and 15 are
Shows a configuration in which a sparse one layer is sandwiched between two dense layers, but the configuration is not limited to this, and, for example,
The sparse layer and the dense layer may have a two-layer structure, and the sparse layer may be adhered to the separator. The functions and effects of the second embodiment of the present invention are the same as those of all the embodiments of the present invention.
Is the same as the action by.

In the third embodiment of the present invention, as shown in FIG. 4, the separator 18 is a metal separator, and conductive water repellent layers 33 and 34 are formed on the contact surface of the metal separator with the diffusion layers 13 and 15. Has been done. The surface of the metal separator may or may not be plated. However, even if the plating treatment is performed, the cost of precious metal plating does not increase, so it is not necessary. A passage 31 is formed in the diffusion layer 13, and a passage 32 is formed in the diffusion layer 15. The passages 31 of the diffusion layers 13, 15;
Reference numeral 32 denotes a passage formed of a large number of holes formed inside the diffusion layers 13 and 15, or the diffusion layers 13 and 1 in which dense and dense layers are stacked.
5 is composed of a sparse layer formed on the inside or the surface thereof. The function and effect of the third embodiment of the present invention are the same as those of all the embodiments of the present invention, and both the function of the passages 31 and 32 and the function of the conductive water-repellent layers 33 and 34 can be obtained. To be

In Example 4 of the present invention, as shown in FIG. 5, the separator 18 is a metal separator, and conductive water repellent layers 33 and 34 are formed on the contact surface of the metal separator with the diffusion layers 13 and 15. Has been done. The surface of the metal separator may or may not be plated. However, even if the plating treatment is performed, the cost of precious metal plating does not increase, so it is not necessary. Passages 31 and 32 are not formed in the diffusion layers 13 and 15. The operation and effect of the fourth embodiment of the present invention is the same as the operation of the conductive water-repellent layers 33 and 34 among the operations common to all the embodiments of the present invention.

[0025]

According to the fuel cell of the first and second aspects, since the reaction gas can flow in the diffusion layer in contact with the separator, moisture does not stay in the diffusion layer portion in contact with the separator, and the diffusion layer portion is in contact with the diffusion layer portion. The corrosion of the separator whose surface is made of metal can be suppressed. According to the fuel cell of claim 3, since the conductive water-repellent layer is formed in the contact portion of the separator with the diffusion layer, the separator surface is hard to be wet with water, and the corrosion of the separator having a metal surface can be suppressed. .

[Brief description of drawings]

FIG. 1 is an overall schematic view of a fuel cell of the present invention.

FIG. 2 shows the fuel cell of Example 1 of the present invention (for 3 cells, 3
It is a partial expanded sectional view (for a module).

FIG. 3 shows a fuel cell of Example 2 of the present invention (for one cell, 1
It is a partial expanded sectional view (for a module).

FIG. 4 shows a fuel cell of Example 3 of the present invention (for one cell, 1
It is a partial expanded sectional view (for a module).

FIG. 5 shows a fuel cell of Example 4 of the present invention (for 3 cells, 3
It is a partial expanded sectional view (for a module).

[Explanation of symbols]

10 (Solid Polymer Electrolyte Type) Fuel Cell 11 Electrolyte Membrane 12 Catalyst Layer, Electrode (Anode) 13 Diffusion Layer 14 Catalyst Layer, Electrode (Cathode) 15 Diffusion Layer 16 Cell 17 Module 18 Separator 19 Cell Stack 20 Terminal 21 Insulator 22 End plate 23 Stack 24 Tension plate 25 Bolt 26 Fuel gas flow path (hydrogen flow path) 27 Oxidizing gas flow path (air flow path) 28 Refrigerant flow path (cooling water flow path when the refrigerant is water) 29a Fuel gas supply manifold 29b Fuel gas exhaust manifold 30a Oxidizing gas supply manifold 30b Oxidizing gas exhaust manifold 31 Passage (passage formed in diffusion layer 13) 32 Passage (passage formed in diffusion layer 15) 33 Conductive water repellent layer (with diffusion layer 13) What is formed on the contact surface) 34 Conductive water-repellent layer (diffusion layer 1) Those formed in the contact surface between)

Claims (3)

[Claims] 1. A fuel cell in which a passage for discharging at least a part of a reaction gas is formed in a diffusion layer whose surface is in contact with a separator made of metal. 2. A fuel cell in which a passage is formed in a diffusion layer, the surface of which is in contact with a separator made of metal, so that at least a part of the reaction gas can be directly discharged to the outside of the separator without passing through the gas passage of the separator. 3. The fuel cell according to claim 1, wherein a conductive water repellent layer is formed on a contact portion of the separator with the diffusion layer.