JP7697402B2 - fuel cell - Google Patents

Description

This disclosure relates to fuel cells.

Patent Document 1 discloses a structure in which an adhesive and a cover sheet are arranged to bridge the support frame and the membrane electrode assembly, and a gas diffusion layer is laminated on the cover sheet. Patent Document 2 discloses a dummy resin member having a stepped surface.

JP 2021-144854 A JP 2020-145026 A

With conventional technology, when the cover sheet was placed, there was a problem in that the membrane electrode assembly or the cover sheet itself would tear. This tear could lead to a leak of the reactant gas.

In view of the above problems, the present disclosure aims to provide a fuel cell that can suppress the occurrence of damage to the membrane electrode assembly and the gas diffusion layer during bonding between the support and the membrane electrode assembly.

After extensive research, the inventors came up with the idea that a space occurs at the tip of the cover sheet on the membrane electrode assembly side due to the thickness of the cover sheet, and that this space is the cause of damage to the membrane electrode assembly and gas diffusion layer. They then developed the technology of the present disclosure by taking specific measures to solve this problem. Specifically, they are as follows.

The present application discloses a fuel cell comprising a membrane electrode assembly including a first catalyst layer, a second catalyst layer, and an electrolyte membrane disposed between the first catalyst layer and the second catalyst layer, a first gas diffusion layer laminated on the first catalyst layer with at least a portion of its outer circumferential edge extending beyond the outer circumferential edge of the membrane electrode assembly, a second gas diffusion layer laminated on the second catalyst layer, a support disposed around the membrane electrode assembly, and a cover sheet disposed to bridge the support and at least one of the electrolyte membrane and the first catalyst layer, the cover sheet being configured such that the tip portion on the side that will become at least one of the electrolyte membrane and the first catalyst layer is thinner than the other portions of the cover sheet.

The tip may be configured to have a sloping surface that becomes thinner toward the tip.

According to the present disclosure, it is possible to reduce the space caused by the thickness of the cover sheet without thinning the cover sheet (without reducing the strength of the cover sheet), thereby suppressing the occurrence of tears (breakage) of the membrane electrode assembly or the cover sheet itself.

FIG. 1 is a plan view of a power generating unit cell 10. As shown in FIG. FIG. 2 is a cross-sectional view of the power generating section 11, illustrating its layer structure. FIG. 3 is a cross-sectional view of the outer peripheral portion 21, illustrating its layer structure. FIG. 4 is an enlarged view of a portion of FIG. FIG. 5 is an enlarged view of a portion of FIG. FIG. 6 is a diagram for explaining another embodiment. FIG. 7 is a diagram for explaining another embodiment. FIG. 8 is a diagram for explaining another embodiment. FIG. 9 is a diagram illustrating the fuel cell 30. As shown in FIG.

1 to 3 are diagrams illustrating a power generation unit cell 10 according to one embodiment. The power generation unit cell 10 is a unit element for generating electricity by supplying hydrogen and oxygen (air), and a plurality of such power generation unit cells 10 are stacked to form a fuel cell.
FIG. 1 is a plan view of a power generating unit cell 10, FIG. 2 is a diagram illustrating the layer structure in a power generating section 11 of the power generating unit cell 10, and FIG. 3 is a diagram illustrating the layer structure in an outer circumferential section 21 of the power generating unit cell 10.

The power generating section 11 is a section that contributes to power generation, for example, in the area surrounded by a dotted line in Fig. 1, and is formed by stacking a plurality of layers, as shown in Fig. 2, which shows the layer structure of the power generating section 11 (part of the A-A cross section).
In the power generation section 11 of the power generation unit cell 10, one side of the electrolyte membrane 12 is a cathode (oxygen supply side) and the other side is an anode (hydrogen supply side). The cathode has a cathode catalyst layer 13 (first catalyst layer), a cathode gas diffusion layer 14 (first gas diffusion layer), and a cathode separator 15 (first separator) laminated in this order from the electrolyte membrane 12 side. On the other hand, the anode has an anode catalyst layer 16 (second catalyst layer), an anode gas diffusion layer 17 (second gas diffusion layer), and an anode separator 18 (second separator) laminated in this order from the electrolyte membrane 12 side. The laminate of the electrolyte membrane 12, the cathode catalyst layer 13, and the anode catalyst layer 16 may be called a membrane electrode assembly. The thickness of the membrane electrode assembly is typically about 0.4 mm, and the thickness of the power generation unit cell 10 in the power generation section 11 is typically about 1.3 mm.
Each layer may be constructed as known in the art, for example as follows:

The electrolyte membrane 12 is a solid polymer thin film that exhibits good proton conductivity in a wet state. For example, it is made of a fluorine-based ion exchange membrane, and for example, a carbon-fluorine-based polymer can be used, specifically, a perfluoroalkylsulfonic acid-based polymer (Nafion (registered trademark)) can be used.
The thickness of the electrolyte membrane 12 is not particularly limited, but is 100 μm or less, preferably 50 μm or less, and more preferably 10 μm or less.

1.1b. Cathode catalyst layer The cathode catalyst layer 13 is a layer containing a catalyst metal in a form in which the catalyst metal is supported on a carrier. For example, the catalyst metal may be Pt, Pd, Rh, or an alloy containing these. The carrier may be a carbon carrier, more specifically, carbon particles made of glassy carbon, carbon black, activated carbon, coke, natural graphite, artificial graphite, or the like.

1.1c. Anode catalyst layer The anode catalyst layer 16 is also a layer containing a catalyst metal in the form of the catalyst metal being supported on a carrier, similar to the cathode catalyst layer 13. For example, the catalyst metal may be Pt, Pd, Rh, or an alloy containing these. The carrier may be a carbon carrier, more specifically, carbon particles made of glassy carbon, carbon black, activated carbon, coke, natural graphite, artificial graphite, or the like.

In this embodiment, the cathode gas diffusion layer 14 is a layer made of, for example, a porous material having electrical conductivity. More specific examples include carbon porous materials (carbon paper, carbon cloth, glassy carbon, etc.), metal porous materials (metal mesh, foamed metal), etc.
The cathode gas diffusion layer 14 may be provided with a microporous layer (MPL) which is a thin coating film applied to the cathode catalyst layer 13 side. The MPL has water repellency or hydrophilicity as necessary and functions to adjust moisture. MPLs are typically made mainly of a water repellent resin such as polytetrafluoroethylene (PTFE) and a conductive material such as carbon black.

The anode gas diffusion layer 17 is a layer made of, for example, a porous material having electrical conductivity. More specific examples include carbon porous materials (carbon paper, carbon cloth, glassy carbon, etc.), metal porous materials (metal mesh, metal foam), etc.

1.1f. Cathode separator The cathode separator 15 is a member that supplies a reactant gas (air in this embodiment) to the cathode gas diffusion layer 14, and has a plurality of grooves 15a on the surface facing the cathode gas diffusion layer 14, and these grooves function as reactant gas flow paths. The shape of the grooves is not particularly limited as long as it can appropriately supply the reactant gas to the cathode gas diffusion layer 14, and examples of the grooves include a serpentine type in which a plate-shaped member is formed into a corrugated shape as in this embodiment. In this case, the plate thickness is typically 0.1 mm to 0.2 mm, and the height of the irregularities is typically about 0.5 mm.
In the case of the serpentine type, a groove 15b is formed between adjacent grooves 15a on the opposite side of the cathode separator 15, and functions as a cooling water flow path.

1, the cathode separator 15 is provided with an air inlet hole Ain, a cooling water inlet hole Win, and a hydrogen outlet hole Hout at one end of the grooves 15a and 15b in the direction in which the grooves 15a and 15b extend, and with an _air outlet hole _Aout , a cooling water outlet hole _Wout , and a hydrogen inlet hole Hin at the other end of the grooves _15a and _15b in the direction in which the grooves 15a and 15b extend. _Here , the groove 15a communicates with the air inlet hole _Ain and the air outlet hole _Aout , and the groove 15b communicates with the cooling water inlet hole _Win and the cooling water outlet hole _Wout .

The material constituting the cathode separator 15 may be any material that can be used as a separator for a power generation unit cell, and may be a gas-impermeable conductive material. Examples of such materials include dense carbon made by compressing carbon to make it gas-impermeable, and press-molded metal plates.

1.1g. Anode separator The anode separator 18 is a member that supplies a reactant gas (hydrogen) to the anode gas diffusion layer 17, and has a plurality of grooves 18a on the surface facing the anode gas diffusion layer 17, and these grooves function as reactant gas flow paths. The shape of the grooves is not particularly limited as long as it can appropriately supply the reactant gas to the anode gas diffusion layer 17, and an example of the groove shape is a serpentine type as in this embodiment. In this case, the plate thickness is typically 0.1 mm to 0.2 mm, and the height of the irregularities is typically about 0.4 mm.
In the case of the serpentine type, a groove 18b is formed between adjacent grooves 18a on the opposite side of the anode separator 18, and functions as a cooling water flow path.

1, the anode separator 18 is provided with an air inlet hole A _{in, a cooling water inlet hole W in, and a hydrogen outlet hole H out at one end of the grooves 18a and 18b in the direction in which the grooves 18a and 18b extend, and with an air outlet hole A out ,} a cooling water outlet hole W _out , _and a hydrogen inlet hole H _in at the other end of the grooves 18a and _18b in the direction in which the grooves 18a and 18b extend. Here, the groove 18a communicates with the hydrogen inlet hole H _in and the hydrogen outlet hole H _out , and the groove 18b communicates with the cooling water inlet hole W _in and the cooling water outlet hole W _out .

The material constituting the anode separator 18 may be any material that can be used as a separator for a power generation unit cell, and may be a gas-impermeable conductive material. Examples of such materials include dense carbon made by compressing carbon to make it gas-impermeable, and press-molded metal plates.

1.1h. Power Generation by Power Generation Section As is well known, power generation is performed by the power generation unit cell 10 described above as follows.
Hydrogen supplied from the hydrogen inlet hole H _in to the groove 18a of the anode separator 18 passes through the anode gas diffusion layer 17 and is decomposed into protons (H ⁺ ) and electrons (e ^- ) in the anode catalyst layer 16. The protons pass through the electrolyte membrane 12, and the electrons pass through conductive wires connected to the outside, each reaching the cathode catalyst layer 13. The remaining hydrogen is discharged from the hydrogen outlet hole H _out .
Oxygen (air) is supplied to the cathode catalyst layer 13 from the air inlet hole A _in through the grooves 15a of the cathode separator 15 and the cathode gas diffusion layer 14, and water (H ₂ O) is generated from protons, electrons, and oxygen in the cathode catalyst layer 13. The generated water and the remaining air pass through the cathode gas diffusion layer 14 to reach the grooves 15a of the cathode separator 15 and are discharged from the air outlet hole A _out .
In the power generating unit cell 10, the flow of electrons passing through the conductive wire connecting the anode catalyst layer 16 to the outside is utilized as an electric current.

Furthermore, by arranging the anode separator 18 of one power generating unit cell 10 so as to overlap the cathode separator 15 of the other power generating unit cell 10 adjacent to each other, a cooling water flow path is formed by the groove 15b of the cathode separator 15 and the groove 18b of the anode separator 18. Cooling water is supplied to this cooling water flow path from a cooling water inlet hole W _in , the supplied cooling water cools the power generating unit cells 10, and is discharged from a cooling water outlet hole W _out .

The peripheral portion 21 is the outer periphery of the power generation unit cell 10 outside the power generation portion 11 surrounded by a dotted line in FIG. 1, and is formed by stacking a plurality of layers as shown in the layer structure (cross section B-B) of the peripheral portion 21 in FIG.

1.2a. Structure of the Outer Periphery As can be seen from FIG. 3, in this embodiment, at least a part of the outer periphery 21 has the following structure.
The electrolyte membrane 12, anode catalyst layer 16, and anode gas diffusion layer 17 are stacked so that their end faces are generally at the same position, and the end face of the cathode catalyst layer 13 is stacked so that it is recessed (set back) from the end face of the electrolyte membrane 12. Furthermore, the end face of the cathode gas diffusion layer 14 is at a position that protrudes (advances) from the end face of the electrolyte membrane 12, and extends to a position that overlaps with the support 23 when viewed from the top of the power generation unit cell 10 (viewed from the direction of FIG. 1, line of sight in the direction indicated by arrow L in FIG. 3). The support 23 will be described later.

The cathode separator 15 and the anode separator 18 are arranged in the outer peripheral portion 21 so as to sandwich the above-mentioned layers therebetween, similar to the electrode portion 11. The end faces of the cathode separator 15 and the anode separator 18 extend so as to protrude beyond the end faces of the membrane electrode assembly, the cathode gas diffusion layer 14, and the anode gas diffusion layer 17, and a support 23 is arranged between the card separator 15 and the anode separator 18 at the extended portion. In addition, since the cathode separator 15 and the anode separator 18 do not require a flow path in the outer peripheral portion 21, the grooves 15a and the grooves 18a are not formed (however, as can be seen from FIG. 3, this does not prevent grooves from being formed in some parts).

A cover sheet 22 is arranged to span the end of the surface of the support 23 facing the cathode side and the end of the surface of the membrane electrode assembly facing the cathode side. The cover sheet 22 will be described later.

1.2b. Support The support 23 described above functions as a sealing member that seals the gap between the cathode separator 15 and the anode separator 18 at the outer periphery 21 of the power generating unit cell 10 .
The support 23 comprises a base material 23a and adhesive layers 23b disposed on both sides of the base material 23a (the surface facing the cathode side and the surface facing the anode side). The adhesive layers 23b are adhered to the cathode separator 15 and the anode separator 18 to seal the inside of the power generation section 11. Therefore, the gap between the cathode separator 15 and the anode separator 18 is curved so as to change depending on the layer sandwiched between them, and as can be seen from Figure 3, in the area where only the support 23 is disposed, the gap is narrowed in part, and the support 23 is sandwiched and fixed between the cathode separator 15 and the anode separator 18.

The base material 23a is made of a thermoplastic resin material that is electrically insulating and airtight and has a relatively high melting point. Such materials include crystalline polymers, more specifically, engineering plastics. Examples of engineering plastics include polyethylene naphthalate resin (PEN) and polyethylene terephthalate resin (PET).
The thickness of the base material 23a is not particularly limited, but is preferably 0.05 mm or more and 0.25 mm or less.

The adhesive layer 23b may be any known material that has adhesive properties when bonded. For example, it may be a modified polyolefin in which a functional group (maleic anhydride, epoxy, etc.) is introduced into the polyolefin to impart adhesive properties.

As can be seen from FIG. 3, such a support 23 is arranged so that its end faces face the end faces of the membrane electrode assembly and the anode gas diffusion layer 17 with a gap S therebetween, and extends toward the opposite side of the power generation section 11. This gap S makes it possible to absorb dimensional changes due to linear expansion of the support 23 and the membrane electrode assembly, etc., and to suppress the occurrence of damage due to expansion and contraction.

1.2c. Cover sheet As described above, the cover sheet 22 is disposed so as to span the end of the surface of the support 23 facing the cathode side and the end of the surface of the membrane electrode assembly facing the cathode side. Fig. 4 shows an enlarged view of the area in Fig. 3 where the cover sheet 22 is disposed.

The cover sheet 22 is arranged so that one end is the surface end on the cathode side of the support 23, and the other end is on the membrane electrode assembly side to cover at least one surface end of the electrolyte membrane 12 and the cathode catalyst layer 13 (in this embodiment, the cover sheet is arranged to cover both surface ends of the electrolyte membrane 12 and the cathode catalyst layer 13). This allows the cathode and anode to be appropriately separated at the outer periphery 21. Therefore, the cover sheet 22 is arranged between the membrane electrode assembly and the cathode gas diffusion layer 14 at the end on the membrane electrode assembly side.

The cover sheet 22 is made of a material that is impermeable to the reaction gas of the fuel cell. Examples of materials that can be used as materials that are impermeable to the reaction gas include film-like materials made of resins such as polypropylene, polyphenylene sulfide, polyethylene naphthalate, nylon, and ethylene vinyl alcohol copolymer. In particular, from the standpoint of hydrolysis resistance and adhesion to the electrolyte membrane, examples of such materials include nylon 11, nylon 12, nylon 9T, and ethylene vinyl alcohol. In order to increase adhesion to the electrolyte membrane 12, additives having amide groups, epoxy groups, hydroxyl groups, etc. may be added.

The cover sheet 22 is adhered to the support 23 at the portion where it overlaps with the support 23 by the adhesive layer 23b of the support 23. On the other hand, the cover sheet 22 is adhered to the membrane electrode assembly at the portion where it overlaps with the membrane electrode assembly by providing an adhesive layer on the cover sheet 22 as necessary. However, if nylon is used as the cover sheet 22, the cover sheet and the membrane electrode assembly can be adhered by thermocompression bonding, so no adhesive layer is required.

The cover sheet 22 has a tip portion 22a at the end facing the membrane electrode assembly, which is configured to be thinner than the other portions. Figure 5 shows an enlarged view of the tip portion 22a, which is the portion indicated by V in Figure 4.

As can be seen from Figure 5, in this embodiment, the tip 22a has an inclined surface 22b that becomes thinner toward the tip, and this inclined surface 22b has a concave curved shape. This allows the tip 22a to reduce the size of the space A, making it possible to solve the problem. Details will be explained later.

Here, the thickness of the cover sheet 22 is not particularly limited, and it is preferable that the thickness be 60 μm or less at the tip of the tip portion 22a, and that the portion other than the tip portion 22a be thicker than 60 μm. By making the portion other than the tip portion 22a thicker than 60 μm, the strength of the cover sheet 22 can be increased, and it is possible to suppress the occurrence of defects such as tearing. In addition, by making the tip portion 22a 60 μm or less, the size of the space A can be reduced more reliably.

2. Effects, etc. When one end of the cover sheet is placed between the cathode gas diffusion layer and the membrane electrode assembly, a space is generated at the portion indicated by A in Figure 5 due to the thickness of the cover sheet. This space tends to become larger as the cover sheet becomes thicker. The inventors have discovered that the larger this space A is, the more likely it is that it will cause damage to the membrane electrode assembly and the cathode gas diffusion layer.
On the other hand, the cover sheet needs to have a certain thickness for sealing as described above, and therefore the space A tends to be large.
In contrast, according to the present disclosure, the tip portion 22a acts to fill at least a portion of the space A, thereby reducing the size of the space A, thereby reducing the possibility of damage to the membrane electrode assembly or the cathode gas diffusion layer and suppressing leakage of reactant gas due to damage.

3. Other Embodiments Other embodiment examples regarding the outer periphery will be described below.
3.1. Other embodiment example 1
Fig. 6 is a diagram illustrating another example of the configuration of the outer periphery. Fig. 6 is a diagram viewed from the same perspective as Fig. 4. In the example of Fig. 6, the end face of the cathode catalyst layer 13 is also positioned at the same position as the end face of the electrolyte membrane 12. In this case, the cover sheet 22 is not laminated to the electrolyte membrane 12, but is laminated to the cathode catalyst layer 13.
Even in this form, the same effects as those described above can be obtained.

3.2. Other embodiment example 2
Fig. 7 is a diagram for explaining another example of the shape of the outer periphery. Fig. 7 is a diagram seen from the same perspective as Fig. 5. In the example of Fig. 7, the tip portion 22a is tapered in a stepped manner compared to the other portions.
Even in this form, the same effects as those described above can be obtained.

3.3. Other embodiment example 3
Fig. 8 is a diagram for explaining another example of the configuration of the outer periphery. Fig. 8 is a diagram seen from the same perspective as Fig. 5. In the example of Fig. 8, the tip portion 22a has a linear inclined surface 22d.
Even in this form, the same effects as those described above can be obtained.

4. Fuel Cell The fuel cell 30 is a member in which a plurality of (approximately 50 to 400) power generating unit cells 10 described above are stacked, and collects current from the plurality of power generating unit cells 10. An outline of the configuration is shown in Figure 9. The fuel cell 30 includes a stack case 31, end plates 32, the plurality of power generating unit cells 10, current collector plates 34, and biasing members 35.

The stack case 31 is a housing that houses multiple stacked power generating unit cells 10, current collector plates 34, and biasing members 35 inside. In this embodiment, the stack case 31 is a rectangular cylinder with one end open and the other end closed, and a plate-like piece protrudes along the edge of the opening on the opposite side to the opening, forming a flange 31a.

The end plate 32 is a plate-shaped member that closes the opening of the stack case 31. The end plate 32 is fixed to the stack case 31 with bolts, nuts, etc. so that the overlapping portion with the flange 31a of the stack case 31 covers the stack case 31.

The power generation unit cell 10 is as described above. A plurality of such power generation unit cells 10 are stacked. At this time, the anode separator 18 of the adjacent power generation unit cell 10 is arranged so as to overlap with the cathode separator 15 of one power generation unit cell 10. The groove 15b of the cathode separator 15 and the groove 18b of the anode separator 18 overlap to form a cooling water flow path.

The current collector 34 is a member that collects current from the stacked power generation unit cells 10. Therefore, the current collector 34 is disposed at each end of the stack of power generation unit cells 10, one of which is a positive electrode and the other is a negative electrode. A terminal (not shown) is connected to this current collector 34, and it is configured so that it can be electrically connected to the outside.

The biasing member 35 is fitted inside the stack case 31 and applies a pressing force to the stack of power generating unit cells 10 in the stacking direction. An example of the biasing member is a disc spring.

5. Others In the above description, the components on the cathode side are referred to as the "first" and the components on the anode side are referred to as the "second", but the same effects can be obtained by replacing the components on the cathode side with the "second" and the anode side with the "first".

REFERENCE SIGNS LIST 10 power generation unit cell 11 power generation section 12 electrolyte membrane 13 cathode catalyst layer 14 cathode gas diffusion layer 15 cathode separator 16 anode catalyst layer 17 anode gas diffusion layer 18 anode separator 21 outer periphery 22 cover sheet 22a tip portion 23 support 23a substrate 23b adhesive layer 30 fuel cell

Claims (2)

a membrane electrode assembly including a first catalyst layer, a second catalyst layer, and an electrolyte membrane disposed between the first catalyst layer and the second catalyst layer;
a first gas diffusion layer that is laminated on the first catalyst layer and has at least a portion of an outer circumferential edge that extends beyond the outer circumferential edge of the membrane electrode assembly;
a second gas diffusion layer laminated on the second catalyst layer;
A support disposed around the membrane electrode assembly;
a cover sheet disposed so as to bridge the support and at least one of the electrolyte membrane and the first catalyst layer;
the cover sheet is configured so that a tip portion on a side that will become at least one of the electrolyte membrane and the first catalyst layer is thinner than other portions of the cover sheet.
fuel cell. The fuel cell according to claim 1, wherein the tip portion has an inclined surface that becomes thinner toward the tip.

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