JP7614791B2 - Fuel Cell Stack - Google Patents

Description

An embodiment of the present invention relates to a fuel cell stack.

A fuel cell system is a power generation system that directly converts the bond energy between hydrogen in the fuel electrode gas and oxygen in the air electrode gas (air) into electricity, and has high power generation efficiency and excellent environmental friendliness. Fuel cell systems generally include a fuel cell stack, a reformer, a control unit, and other devices. A fuel cell stack includes a fuel cell cell in which an electrolyte membrane is interposed between the fuel electrode and the air electrode, and multiple fuel cell cells are stacked. In the fuel cell stack, fuel electrode gas containing hydrogen produced in the reformer is supplied to the fuel electrode, and air is supplied to the air electrode (oxidizer electrode), causing an electrochemical reaction and generating electricity.

In a polymer electrolyte fuel cell stack, fuel cells using a polymer electrolyte membrane with proton conductivity and separators are stacked alternately in the stacking direction. The separators are provided with a fuel electrode gas flow path through which the fuel electrode gas supplied to the fuel electrode flows, and an air electrode gas flow path through which the air electrode gas supplied to the air electrode flows.

The proton resistance of the polymer electrolyte membrane is inversely proportional to the water content of the polymer electrolyte membrane. Therefore, in order to reduce the proton resistance and increase the power generation performance, it is necessary to humidify the polymer electrolyte membrane and increase the water content. There are two known methods of humidifying the polymer electrolyte membrane: external humidification and internal humidification. In the external humidification method, steam is supplied to the fuel electrode gas or air electrode gas. In the internal humidification method, liquid water is supplied through a separator.

To maintain the temperature of the fuel cell within an appropriate range, it is necessary to cool the fuel cell whose temperature has risen due to the heat generated by the fuel cell reaction. To achieve this, cooling water is circulated to cool the fuel cell stack. In cogeneration systems that use the heat of reaction along with the electricity obtained by power generation, hot water is obtained using heat recovered through heat exchange from the cooling water. A cooling water flow path for the cooling water is formed, for example, between the fuel electrode gas separator and the air electrode gas separator. By forming a cooling water groove on the back surface of one of the separators and bonding them together, cooling water can be circulated between the separators of both poles.

In addition to the above, cooling using a latent heat cooling method is also known. In the latent heat cooling method, a conductive porous plate with micropores is used as a separator, and a water flow path is provided in the fuel cell. Water is then supplied to the fuel cell through the conductive porous plate, thereby humidifying and cooling by the latent heat of vaporization of water. In the latent heat cooling method, the pressure of the fuel electrode gas and the air electrode gas is made higher than the pressure of the cooling water. This allows the generated water and condensed moisture to be removed from the conductive porous plate, and humidification and cooling are achieved over the entire reaction surface of the fuel cell.

If water flow paths were to be installed in all fuel cell cells, two separators would be required for each fuel cell, increasing costs. For this reason, methods have been proposed that eliminate the need for water flow paths by supplying cooling water from the side of the conductive porous plate that serves as the separator.

Special Publication No. 11-508726 Patent No. 4738979 JP 2017-188224 A JP 2017-188226 A JP 2014-102969 A

However, in the past, water supplied from the side of the conductive porous plate would evaporate into the air electrode gas, causing the conductive porous plate to dry out locally, making it difficult to adequately humidify and cool the plate. When this happens, the locally dried conductive porous plate loses its ability to isolate the fuel electrode gas and the air electrode gas, and there is a risk that the fuel electrode gas and the air electrode gas will mix.

The problem that this invention aims to solve is to provide a fuel cell stack that can adequately perform humidification and cooling.

The fuel cell stack of the embodiment includes a laminate in which fuel cell units and separators are alternately laminated in a stacking direction. The fuel cell units have a polymer electrolyte membrane interposed between a fuel electrode and an air electrode. The separator includes a fuel electrode side separator part in which a fuel electrode gas flow passage through which a fuel electrode gas supplied to the fuel electrode flows, and an air electrode side separator part in which an air electrode gas flow passage through which an air electrode gas supplied to the air electrode flows. The fuel electrode side separator part is made of a porous plate, and the air electrode side separator part is made of a dense plate that is less permeable to gas than the porous plate. The stacking direction is a horizontal direction perpendicular to the vertical direction, and the laminate is configured so that water is introduced from above to below in the vertical direction.

FIG. 1 is a perspective view showing a schematic overall configuration of a fuel cell stack 1 according to a first embodiment. FIG. 2 is a cross-sectional view that typically shows a detailed configuration of the stack 10 in the fuel cell stack 1 according to the first embodiment. FIG. 3 is a perspective view showing a schematic overall configuration of a fuel cell stack 1b according to the second embodiment.

First Embodiment
[A] Overall configuration of fuel cell stack 1 Fig. 1 is a perspective view showing a schematic overall configuration of a fuel cell stack 1 according to a first embodiment. In Fig. 1, the y-axis is aligned along the vertical direction, the z-axis is aligned along a first horizontal direction, and the x-axis is aligned along a second horizontal direction perpendicular to the first horizontal direction.

As shown in FIG. 1, the fuel cell stack 1 includes a stack 10, a first water manifold 21, a second water manifold 22, a first fuel electrode gas manifold 31, a second fuel electrode gas manifold 32, a first air electrode gas manifold 41, and a second air electrode gas manifold 42.

In FIG. 1, for ease of understanding, gaps are shown between the laminate 10 and each of the manifolds 21, 22, 31, 32, 41, and 42, but in reality, each of the manifolds 21, 22, 31, 32, 41, and 42 is attached so that it is in contact with the laminate 10.

Each part that makes up the fuel cell stack 1 will be explained in turn.

[A-1] Laminate 10
1, in the fuel cell stack 1, a stack 10 includes a plurality of fuel cells 11 and a plurality of separators 12. In the stack 10, the fuel cells 11 and the separators 12 are stacked alternately in the stacking direction.

In this embodiment, the stacking direction is along a first horizontal direction (z) perpendicular to the vertical direction (y). The stack 10 is interposed between a pair of fastening plates 15 in the stacking direction, and the pair of fastening plates 15 is fastened using a fastening member (not shown) such as a tie rod or a band.

The detailed configuration of the laminate 10 will be described later.

[A-2] First water manifold 21
The first water manifold 21 is installed above the laminate 10. In other words, the first water manifold 21 is disposed so as to face the upper surface of the laminate 10 that is located on the upper side of a horizontal plane (xz plane) along the stacking direction.

The first water manifold 21 is provided with a water inlet pipe section 211. The first water manifold 21 is configured so that water flows into the inside from the water inlet pipe section 211 and the flowed-in water is supplied to the laminate 10. Here, the first water manifold 21 supplies water to the upper surface of the laminate 10 from an opening (not shown) formed on the lower surface. The water is supplied to cool the laminate 10 and to humidify the laminate 10.

[A-3] Second water manifold 22
The second water manifold 22 is installed below the laminate 10. That is, the second water manifold 22 is disposed so as to face the lower surface of the laminate 10 that is located on the lower side of the horizontal plane (xz plane) along the stacking direction.

The second water manifold 22 is provided with a water outlet pipe section 221. The second water manifold 22 is configured so that water that has passed through the laminate 10 flows into the inside and is discharged to the outside from the water outlet pipe section 221. Here, the second water manifold 22 allows water to flow from the underside of the laminate 10 into an opening (not shown) formed on the upper surface, and flows out via the water outlet pipe section 221.

[A-4] First fuel electrode gas manifold 31
The first fuel electrode gas manifold 31 is disposed above the stack 10 so as to be aligned with the first water manifold 21. That is, like the first water manifold 21, the first fuel electrode gas manifold 31 is disposed so as to face the upper surface of the stack 10 that is located on the upper side of the horizontal plane (xz plane) along the stacking direction.

The first fuel electrode gas manifold 31 is provided with a fuel electrode gas inlet pipe section 311. The first fuel electrode gas manifold 31 is configured so that fuel electrode gas flows into the inside from the fuel electrode gas inlet pipe section 311 and the flowed-in fuel electrode gas is supplied to the stack 10. Here, the first fuel electrode gas manifold 31 supplies fuel electrode gas to the upper surface of the stack 10 from an opening (not shown) formed on the lower surface. The fuel electrode gas contains hydrogen (fuel) and is supplied as a reactant for the power generation reaction in the stack 10.

[A-5] Second fuel electrode gas manifold 32
The second fuel electrode gas manifold 32 is disposed below the stack 10 so as to be aligned with the second water manifold 22. That is, like the second water manifold 22, the second fuel electrode gas manifold 32 is disposed so as to face the lower surface of the stack 10 that is located on the lower side of the horizontal plane (xz plane) along the stacking direction.

The second fuel electrode gas manifold 32 is provided with a fuel electrode gas outlet piping section 321. The second fuel electrode gas manifold 32 is configured so that fuel electrode gas that has passed through the stack 10 without being consumed in the electrochemical reaction in the stack 10 flows into the inside and is discharged to the outside from the fuel electrode gas outlet piping section 321. Here, the second fuel electrode gas manifold 32 is configured so that fuel electrode gas flows from the bottom surface of the stack 10 into an opening (not shown) formed on the top surface, and flows out via the fuel electrode gas outlet piping section 321.

[A-6] First air electrode gas manifold 41
The first air electrode gas manifold 41 is disposed so as to face a side surface (left side surface) located on one side (the left side in FIG. 1 ) of vertical surfaces (yz surfaces) along the stacking direction of the stack 10 .

The first air electrode gas manifold 41 is provided with an air electrode gas inlet pipe section 411. The first air electrode gas manifold 41 is configured so that air electrode gas flows into the inside from the air electrode gas inlet pipe section 411 and the air electrode gas that flows in is supplied to the stack 10. Here, the first air electrode gas manifold 41 supplies air electrode gas to the side of the stack 10 from an opening (not shown) formed on the side. The air electrode gas is air containing oxygen (oxidant), and is supplied as a reactant for the power generation reaction in the stack 10, similar to the fuel electrode gas.

[A-7] Second air electrode gas manifold 42
The second air electrode gas manifold 42 is disposed so as to face the other side surface (right side surface) (the right side surface in FIG. 1 ) of the vertical surfaces (yz surfaces) along the stacking direction of the stack 10 .

The second air electrode gas manifold 42 is provided with an air electrode gas outlet piping section 421. The second air electrode gas manifold 42 is configured so that the air electrode gas that has passed through the stack 10 without being consumed in the electrochemical reaction in the stack 10 flows into the inside and is discharged to the outside from the air electrode gas outlet piping section 421. Here, the second air electrode gas manifold 42 is configured so that the air electrode gas flows from the bottom surface of the stack 10 into an opening (not shown) formed on the top surface and flows out through the air electrode gas outlet piping section 421.

[B] Detailed Configuration of Stack 10 Fig. 2 is a cross-sectional view showing a schematic detailed configuration of stack 10 in fuel cell stack 1 according to the first embodiment. Fig. 2 shows a part of a cross section corresponding to a horizontal plane (xz plane) in Fig. 1.

The detailed structure of the laminate 10 is described with reference to Figure 2.

As already explained, the stack 10 is constructed by stacking fuel cells 11 and separators 12 alternately in the stacking direction z.

[B-1] Fuel cell 11
In the laminate 10, the fuel cell 11 includes a polymer electrolyte membrane 110, an anode 111, and a cathode 112. The fuel cell 11 is a membrane/electrode assembly in which the polymer electrolyte membrane 110 is interposed between the anode 111 and the cathode 112.

The polymer electrolyte membrane 110 is made of, for example, a fluorine-based polymer material having sulfonic acid groups. The fuel electrode 111 and the air electrode 112 are made of, for example, a platinum catalyst supported on a carbon black carrier.

[B-2] Separator 12
In the laminate 10, the separator 12 includes a fuel electrode side separator part 121 and an air electrode side separator part 122, and is made of a conductive material. Here, the separator 12 is an assembly in which the fuel electrode side separator part 121 and the air electrode side separator part 122 are laminated.

[B-2-1] Fuel electrode side separator part 121
In the separator 12, the fuel electrode side separator portion 121 has a fuel electrode gas flow passage F121 formed therein.

The fuel electrode gas flow passage F121 is formed along the vertical direction (y-axis direction), and fuel electrode gas flows through it to be supplied to the fuel electrode 111 of the fuel cell 11. There are multiple fuel electrode gas flow passages F121, and the multiple fuel electrode gas flow passages F121 are spaced apart in the second horizontal direction (x-axis direction).

The fuel electrode gas flow path F121 is formed on the surface of the fuel electrode side separator part 121 on the fuel electrode 111 side of the fuel cell 11 that supplies the fuel electrode gas. For example, the fuel electrode side separator part 121 constituting the separator 12 shown in the center in FIG. 2 has the fuel electrode gas flow path F121 formed so as to supply the fuel electrode gas to the fuel electrode 111 of one of the two adjacent fuel cell cells 11 shown in FIG. 2 (the upper one in FIG. 2).

The fuel electrode gas flows into the fuel electrode gas flow path F121 from the first fuel electrode gas manifold 31 (see FIG. 1) located vertically above the stack 10. After passing through the fuel electrode gas flow path F121, the fuel electrode gas flows out to the second fuel electrode gas manifold 32 (see FIG. 1) located vertically below the stack 10.

In this embodiment, the fuel electrode side separator section 121 is made of a porous plate. For example, the porous plate is made of a plate made of solidified carbon particles and phenolic resin, and is press molded with a pressure that leaves an appropriate amount of pores during molding.

[B-2-2] Air electrode side separator part 122
In the separator 12, the air electrode side separator part 122 has an air electrode gas flow passage F122 formed therein.

The air electrode gas flow passage F122 is formed along a second horizontal direction (x-axis direction) perpendicular to a first horizontal direction (z-axis direction) along the stacking direction, and the air electrode gas supplied to the air electrode 112 of the fuel cell 11 flows through the air electrode gas flow passage F122. Although not shown in the figure, there are multiple air electrode gas flow passages F122, and the multiple air electrode gas flow passages F122 are provided at intervals in the first horizontal direction (y-axis direction).

The air electrode gas flow path F122 is formed on the surface of the air electrode side separator part 122 that faces the air electrode 112 of the fuel cell 11 to which the air electrode gas is supplied. For example, the air electrode side separator part 122 that constitutes the separator 12 shown in the center in FIG. 2 has the air electrode gas flow path F122 formed so as to supply the air electrode gas to the air electrode 112 of the other (lower in FIG. 2) of the two adjacent fuel cell cells 11 shown in FIG. 2.

The air electrode gas flows into the air electrode gas flow path F122 from a first air electrode gas manifold 41 (see FIG. 1) located on one side of the stack 10 in the second horizontal direction (x-axis direction). After passing through the air electrode gas flow path F122, the air electrode gas flows out to a second air electrode gas manifold 42 (see FIG. 1) located on one side of the stack 10 in the second horizontal direction (x-axis direction).

In this embodiment, the air electrode side separator section 122 is made of a dense plate that is less permeable to gas than the porous plate that constitutes the fuel electrode side separator section 121. For example, the dense plate is made of carbon particles and phenolic resin, just like the porous separator. However, by pressing at high pressure during molding, a dense structure without air holes and with reduced gas permeation is obtained.

[C] Functions and Effects The functions and effects of the fuel cell stack 1 of this embodiment will be described.

When generating electricity in the fuel cell stack 1 of this embodiment, as described above, anode gas is supplied to the anode 111, and cathode gas is supplied to the cathode 112. The anode gas contains, for example, hydrogen (H ₂ ) at a ratio of 80 volume % to 100 volume %. The cathode gas is, for example, air and contains oxygen (O ₂ ) at a ratio of about 21 volume %.

Then, a power generation reaction occurs between the fuel electrode gas supplied to the fuel electrode 111 and the air electrode gas supplied to the air electrode 112, generating power in the fuel cell 11. Specifically, at the fuel electrode 111, hydrogen (H ₂ ) contained in the fuel electrode gas is decomposed into protons (H ⁺ ) and electrons (e ⁻ ). The decomposed protons (H ⁺ ) move to the air electrode 112 via the polymer electrolyte membrane 110. At the air electrode 112, oxygen (O ² ) contained in the air, which is the air electrode gas, reacts with the protons (H ⁺ ) and electrons (e ⁻ ) (4H ⁺ +O ₂ +4e ⁻ →2H ₂ O). As a result, water (H ₂ O) is produced as a product.

To improve the power generation performance of the fuel cell 11, it is necessary to reduce the proton resistance of the polymer electrolyte membrane 110 by increasing the water content of the polymer electrolyte membrane 110. In addition, since the temperature of the fuel cell 11 rises due to heat generated by the power generation reaction, it is necessary to maintain the temperature of the fuel cell 11 within an appropriate range.

For this reason, in this embodiment, water is introduced from above to below the laminate 10 in the vertical direction (y-axis). Specifically, water is introduced into the laminate 10 from a first water manifold 21 (see FIG. 1) located above the laminate 10. Then, the water that passes through the laminate 10 is discharged into a second water manifold 22 located below the laminate 10.

As described above, in the stack 10 of this embodiment, the separator 12 includes the fuel electrode side separator part 121 made of a porous plate and the air electrode side separator part 122 made of a dense plate. Water introduced into the stack 10 from the first water manifold 21 (see FIG. 1) permeates into the fuel electrode side separator part 121 made of a porous plate rather than into the air electrode side separator part 122 made of a dense plate. For this reason, in this embodiment, the water content of the polymer electrolyte membrane 110 is increased and the fuel cell 11 is cooled mainly by the water that has permeated into the fuel electrode side separator part 121.

In this embodiment, the air electrode side separator part 122 is made of a dense plate, so there is almost no penetration of water introduced into the laminate 10. This makes it possible to prevent the water introduced into the laminate 10 from drying out. As a result, in this embodiment, it is possible to efficiently both improve the water content of the polymer electrolyte membrane 110 and cool the fuel cell 11.

In particular, in this embodiment, the stacking direction of the stack 10 is a horizontal direction perpendicular to the vertical direction, and water is introduced into the stack 10 from above to below in the vertical direction. In other words, in the stack 10, water flows from above to below due to its own weight. Therefore, in this embodiment, it is possible to improve the water content of the polymer electrolyte membrane 110 and cool the fuel cell 11 with a simple configuration.

[D] Modifications In the above embodiment, the separator 12 is described as being configured with the fuel electrode side separator part 121 being made of a porous plate and the air electrode side separator part 122 being made of a dense plate, but this is not limited thereto. The fuel electrode side separator part 121 may be configured of a dense plate and the air electrode side separator part 122 may be configured of a porous plate. In other words, it is sufficient that one of the fuel electrode side separator part 121 and the air electrode side separator part 122 is configured of a porous plate and the other is configured of a dense plate.

However, as exemplified in the above embodiment, it is preferable that the separator 12 is configured such that the fuel electrode side separator part 121 is made of a porous plate and the air electrode side separator part 122 is made of a dense plate. In the above embodiment, the fuel electrode gas contains, for example, hydrogen (H ₂ ) at a ratio of 80 volume % to 100 volume %. And, the air electrode gas is, for example, air and contains oxygen (O ₂ ) at a ratio of about 21 volume %. That is, the ratio of the component (oxygen component) contained as a reactant in the air electrode gas (about 21 volume %) is smaller than the ratio of the component (hydrogen component) contained as a reactant in the fuel electrode gas (80 volume % to 100 volume %). Therefore, in order to efficiently proceed with the power generation reaction, it is necessary to increase the supply amount of the air electrode gas more than the supply amount of the fuel electrode gas, so that the air electrode side separator part 122 is more likely to dry than the fuel electrode side separator part 121. However, in this embodiment, the air electrode side separator part 122 is made of a dense plate that is less permeable to gas than a porous plate, so drying due to the air electrode gas can be effectively prevented.

Second Embodiment
[A] Configuration FIG. 3 is a perspective view that shows a schematic overall configuration of a fuel cell stack 1b according to the second embodiment.

As shown in FIG. 3, unlike the first embodiment (see FIG. 1), the fuel cell stack 1b of this embodiment does not have a first air electrode gas manifold 41 and a second air electrode gas manifold 42. In this embodiment, an air supply unit 60 is provided. Except for this point and related points, this embodiment is similar to the first embodiment. Therefore, explanations of overlapping points will be omitted as appropriate.

The air supply unit 60 is configured to cool the laminate 10 using air as a cooling medium. Here, as shown in FIG. 3, the air supply unit 60 includes a cooling fan 61 and a tubular portion 62, and supplies air as a cooling medium from the cooling fan 61 to the laminate 10 through the inside of the tubular portion 62. The tubular portion 62 is configured so that the inside expands as it moves from the cooling fan 61 toward the laminate 10.

The air supplied from the air supply unit 60 to the stack 10 functions as an air electrode gas and also as a cooling medium.

[B] Function and Effects As described above, in this embodiment, the air supply unit 60 uses air as a cooling medium to cool the stack body 10. Therefore, in this embodiment, the stack body 10 can be cooled efficiently.

＜Other＞
Although some embodiments of the present invention have been described, these embodiments are presented as examples and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their modifications are included in the scope and spirit of the invention, and are included in the scope of the invention and its equivalents described in the claims.

1: fuel cell stack, 10: laminate, 11: fuel cell, 12: separator, 21: first water manifold, 22: second water manifold, 31: first fuel electrode gas manifold, 32: second fuel electrode gas manifold, 41: first air electrode gas manifold, 42: second air electrode gas manifold, 110: polymer electrolyte membrane, 111: fuel electrode, 112: air electrode.

Claims (1)

A fuel cell stack including a stack of fuel cells and separators stacked alternately in a stacking direction,
The fuel cell has a polymer electrolyte membrane interposed between a fuel electrode and an air electrode,
The separator is
a fuel electrode side separator portion having a fuel electrode gas flow passage formed therein through which a fuel electrode gas to be supplied to the fuel electrode flows;
an air electrode-side separator portion having an air electrode gas flow path through which an air electrode gas to be supplied to the air electrode flows;
The fuel electrode side separator portion is composed of a porous plate,
the air electrode side separator portion is made of a dense plate which is less permeable to gas than the porous plate ,
The stacking direction is a horizontal direction perpendicular to a vertical direction,
The laminate is configured so that water is introduced from above to below in the vertical direction.
Fuel cell stack.

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