fuel cells

Abstract

To provide a fuel cell capable of suppressing the occurrence of damage to a membrane electrode junction and a gas diffusion layer even if a cover sheet is arranged upon bonding a support to the membrane electrode junction.SOLUTION: A fuel cell includes a membrane electrode junction including a first catalyst layer, a second catalyst layer, and an electrolyte membrane, a first gas diffusion layer, a second gas diffusion layer, a support arranged around the membrane electrode junction, and a cover sheet arranged to bridge between the support and at least one of the electrolyte membrane and the first catalyst layer. A space having a distance LA (mm) is formed between an end surface of the support and an end surface of the membrane electrode junction. When the elastic modulus of the cover sheet is denoted as E (MPa) and the thickness is denoted as t (mm), E>0.048×LA4 / t3 is satisfied. In the first gas diffusion layer, a reduction ratio of a gap in at least a portion of an area in which a cover sheet is arranged to a gap in an area in which no cover sheet is arranged is 5% or more and 25% or less.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present disclosure relates to fuel cells. [Background technology]

[0002] Patent Document 1 discloses a structure in which an adhesive and a cover sheet are arranged so as to bridge a support frame and a membrane electrode assembly, and a gas diffusion layer is laminated on the cover sheet. Patent Document 2 discloses that the thickness of the plate-like member is configured so that the compressibility of the contact portion of the gas diffusion layer that comes into contact with the separator becomes a predetermined value. Patent Document 3 discloses that the Young's modulus of the material forming the protrusion is lower than the Young's modulus of the material forming the support frame body. Patent Document 4 discloses that the frame has a Young's modulus of 1 GPa or more. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent Publication No. 2021-144854 [Patent Document 2] Japanese Patent Application Laid-Open No. 2006-216294 [Patent Document 3] Japanese Patent Application Laid-Open No. 2016-170960 [Patent Document 4] Japanese Patent Application Publication No. 2019-16586 Summary of the Invention [Problem to be solved by the invention]

[0004] In conventional technology, when a cover sheet is placed, problems such as tears or poor sealing can occur in the membrane electrode assembly, gas diffusion layer, or cover sheet itself, which can lead to leakage of reactant gases.

[0005] In view of the above problems, the present disclosure aims to provide a fuel cell that can suppress damage to the membrane electrode assembly and gas diffusion layer even when a cover sheet is placed at the joint between the support and the membrane electrode assembly. [Means for solving the problem]

[0006] The present application relates to 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 peripheral edge extending beyond the outer peripheral 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 so as to bridge the support and at least one of the electrolyte membrane and the first catalyst layer, wherein a distance L is provided between an end face of the support and an end face of the membrane electrode assembly. A The cover sheet has a space of (mm), and when the modulus of elasticity is E (MPa) and the thickness is t (mm), E>0.048×L A 4 / t 3 and the first gas diffusion layer has a void reduction rate of at least a portion of the area where the cover sheet is placed, relative to the voids in the area where the cover sheet is not placed, of 5% to 25%.

[0007] The present application also provides a method for manufacturing 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; and a membrane electrode assembly having a distance L between end faces of the membrane electrode assembly. A a support disposed around the membrane electrode assembly with a space of (mm) between the support and at least one of the electrolyte membrane and the first catalyst layer, the support having an elastic modulus of E (MPa) and a thickness of t (mm), E>0.048×L A 4 / t 3 a cover sheet that satisfies the above formula, a first gas diffusion layer is disposed on the cover sheet and the membrane electrode assembly, and the first gas diffusion layer is pressed so that the reduction rate of voids in at least a portion of the area where the cover sheet is disposed relative to voids in an area where the cover sheet is not disposed is 5% to 25%. [Effects of the Invention]

[0008] According to the present disclosure, even if a cover sheet is disposed when joining the support and the membrane electrode assembly, damage to the membrane electrode assembly and the gas diffusion layer can be suppressed. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 1 is a plan view of a power generating unit cell 10. As shown in FIG. [Figure 2] FIG. 2 is a cross-sectional view of the power generating section 11, illustrating its layer structure. [Figure 3] FIG. 3 is a cross-sectional view of the outer peripheral portion 21, illustrating its layer structure. [Figure 4] FIG. 4 is an enlarged view of a part of FIG. [Figure 5] FIG. 5 is a diagram explaining the test method. [Figure 6] FIG. 6 is a diagram illustrating the test results. [Figure 7] FIG. 7 is a diagram illustrating another embodiment. [Figure 8] FIG. 8 is a diagram illustrating another embodiment. [Figure 9] FIG. 9 is a diagram illustrating the fuel cell 40. As shown in FIG. [Figure 10] FIG. 10 is a diagram illustrating a part of the process for manufacturing a fuel cell. DETAILED DESCRIPTION OF THE INVENTION

[0010] 1. Power generation unit cell 1 to 3 show diagrams illustrating one embodiment of a power generating unit cell 10. The power generating unit cell 10 is a unit element for generating electricity by supplying hydrogen and oxygen (air), and a plurality of such power generating unit cells 10 are stacked to form a fuel cell. FIG. 1 is a plan view of the power generating unit cell 10, FIG. 2 is a diagram illustrating the layer structure of the power generating section 11 of the power generating unit cell 10, and FIG. 3 is a diagram illustrating the layer structure of the outer peripheral section 21 of the power generating unit cell 10.

[0011] 1.1.Power Generation Unit The power generation section 11 is a section that contributes to power generation, for example, the section surrounded by a dotted line in FIG. 1, and is formed by laminating multiple layers, as shown in FIG. 2, which shows the layer structure of the power generation section 11 (part of the AA 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) stacked 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) stacked in this order from the electrolyte membrane 12 side. The stack of the electrolyte membrane 12, cathode catalyst layer 13, and anode catalyst layer 16 is sometimes referred to as 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. The layers are, for example, as follows:

[0012] 1.1.1. Electrolyte membrane 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, such as a perfluoroalkylsulfonic acid-based polymer (Nafion (registered trademark)), can be used. The thickness of the electrolyte membrane 12 is not particularly limited, but is 200 μm or less, preferably 100 μm or less, and more preferably 50 μm or less.

[0013] 1.1.2. Cathode catalyst layer The cathode catalyst layer 13 is a layer containing a catalyst metal supported on a carrier. Examples of the catalyst metal include Pt, Pd, Rh, and alloys containing these. Examples of the carrier include carbon carriers, more specifically, carbon particles made of glassy carbon, carbon black, activated carbon, coke, natural graphite, artificial graphite, etc.

[0014] 1.1.3. Anode catalyst layer Like the cathode catalyst layer 13, the anode catalyst layer 16 is a layer containing a catalyst metal supported on a carrier. Examples of the catalyst metal include Pt, Pd, Rh, and alloys containing these. Examples of the carrier include carbon carriers, more specifically, carbon particles made of glassy carbon, carbon black, activated carbon, coke, natural graphite, artificial graphite, etc.

[0015] 1.1.4. Cathode gas diffusion layer In this embodiment, the cathode gas diffusion layer 14 is a layer made of, for example, a conductive porous material. More specific examples include porous carbon materials (carbon paper, carbon cloth, glassy carbon, etc.) and porous metal materials (metal mesh, metal foam). The cathode gas diffusion layer 14 may be provided with an MPL (microporous layer) as needed. The MPL is a thin coating applied to the cathode catalyst layer 13 side of the cathode gas diffusion layer 14. The MPL has water repellency or hydrophilicity as needed, allowing it to regulate moisture. It also serves to prevent fluff generated in the carbon porous body from piercing the electrolyte membrane. MPLs are typically made primarily of a water-repellent resin such as polytetrafluoroethylene (PTFE) and a conductive material such as carbon black.

[0016] The thickness of the cathode gas diffusion layer 14 in the power generation section 11 is preferably 50 μm or more and 250 μm or less. If this thickness exceeds 250 μm, the electronic resistance will be high, and if it is thinner than 50 μm, the flexibility of the cathode gas diffusion layer will be insufficient, and a uniform surface pressure may not be obtained in the power generation section. More specifically, a surface pressure of 0.2 MPa or more and 2 MPa or less is applied to the power generation section, utilizing the springiness (elasticity) of the cathode gas diffusion layer 14 to maintain a constant surface pressure in the power generation section. Furthermore, as will be described later, the thickness of the cathode gas diffusion layer at the portion that overlaps the cover sheet in a plan view is reduced to within a range of 5 μm to 50 μm to reduce voids (void reduction rate of 5% to 25%) and to reduce space B, so the cathode gas diffusion layer needs to have a certain thickness.

[0017] 1.1.5. Anode gas diffusion layer The anode gas diffusion layer 17 is a layer made of, for example, a conductive porous material. More specific examples include porous carbon materials (carbon paper, carbon cloth, glassy carbon, etc.) and porous metal materials (metal mesh, metal foam).

[0018] The thickness of the anode gas diffusion layer 17 in the power generation section 11 is preferably 50 μm or more and 250 μm or less. If this thickness exceeds 250 μm, the electronic resistance will be high, and if it is thinner than 50 μm, the flexibility of the anode gas diffusion layer will be insufficient, and uniform surface pressure may not be obtained in the power generation section. More specifically, a surface pressure of 0.2 MPa or more and 2 MPa or less is applied to the power generation section, utilizing the springiness (elasticity) of the anode gas diffusion layer 14 to maintain a constant surface pressure in the power generation section. Furthermore, as will be described later, the thickness of the anode gas diffusion layer at the portion that overlaps the cover sheet in plan view may be reduced to a thickness of 5 μm or more and 50 μm or less to reduce voids (void reduction rate of 5% or more and 25% or less) and reduce space B, so the anode gas diffusion layer needs to have a certain thickness.

[0019] 1.1.6. 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, which 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 include a plate-shaped member 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. Between adjacent grooves 15a, grooves 15b are formed on the opposite side of the cathode separator 15, and function as cooling water flow paths.

[0020] As can be seen from FIG. 1, the cathode separator 15 has an air inlet hole A at a position extending outward from the power generating section 11 and at one end of the grooves 15a and 15b in the extending direction. in , cooling water inlet hole W in , hydrogen outlet hole H out At the other end of the groove 15a and the groove 15b in the extending direction, an air outlet hole A out , cooling water outlet hole W out , hydrogen inlet hole H in Here, the groove 15a is the air inlet hole A in , air outlet hole A out The groove 15b is connected to the cooling water inlet hole W in , cooling water outlet hole W out It is connected to.

[0021] 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 a press-molded metal plate.

[0022] 1.1.7. 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, which 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. The plate thickness is typically 0.1 mm to 0.2 mm, and the height of the irregularities is typically about 0.4 mm. Between adjacent grooves 18a, grooves 18b are formed on the opposite side of the anode separator 18, and these function as cooling water flow paths.

[0023] As can be seen from FIG. 1, the anode separator 18 has an air inlet hole A at a position extending outward from the power generation section 11 and at one end of the grooves 18a and 18b in the extending direction. in , cooling water inlet hole W in , hydrogen outlet hole H out At the other end of the groove 18a and the groove 18b in the extending direction, an air outlet hole A is provided. out , cooling water outlet hole W out , hydrogen inlet hole H in Here, the groove 18a is provided with a hydrogen inlet hole H in , hydrogen outlet hole H out The groove 18b is connected to the cooling water inlet hole W in , cooling water outlet hole W out It is connected to.

[0024] 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 a press-molded metal plate.

[0025] 1.1.8. Power Generation by the Power Generation Unit As is well known, the power generation unit cell 10 described above generates power as follows. Hydrogen inlet hole H inThe hydrogen supplied from the anode separator 18 to the grooves 18a passes through the anode gas diffusion layer 17 and is converted into protons (H + ) and electrons (e - The protons pass through the electrolyte membrane 12, and the electrons pass through the conductive wires connected to the outside, and each reaches the cathode catalyst layer 13. The remaining hydrogen is discharged through the hydrogen outlet hole H out is emitted from The cathode catalyst layer 13 has an air inlet hole A in Oxygen (air) is supplied from the cathode catalyst layer 13 through the grooves 15a of the cathode separator 15 and the cathode gas diffusion layer 14, and water (H2O) is generated from the 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 and reach the grooves 15a of the cathode separator 15, and then exit the air outlet hole A. out is emitted from In the power generating unit cell 10, the flow of electrons through the conductive wire connecting from the anode catalyst layer 16 to the outside is utilized as an electric current.

[0026] In addition, the cathode separator 15 of one power generating unit cell 10 is arranged to overlap with the anode separator 18 of the other power generating unit cell 10 adjacent to the cathode separator 15 of the other power generating unit cell 10, so that 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. A cooling water inlet hole W in The cooling water is supplied from the cooling water outlet W out is emitted from

[0027] 1.2.Outer periphery The outer peripheral portion 21 is the outer peripheral portion 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 laminating a plurality of layers, as shown in Fig. 3, which shows the layer structure (part of the B-B cross section) of the outer peripheral portion 21. Fig. 4 shows an enlarged view of a part of Fig. 3.

[0028] 1.2.1. Basic structure of the outer periphery As can be seen from FIGS. 3 and 4, in this embodiment, at least a part of the outer peripheral portion 21 has the following configuration. The electrolyte membrane 12, anode catalyst layer 16, and anode gas diffusion layer 17 are stacked so that their end faces are generally in 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 positioned protruding (advanced) from the end face of the electrolyte membrane 12, and extends to a position overlapping the support 23 in a plan view 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.

[0029] The cathode separator 15 and the anode separator 18 are also arranged in the outer peripheral portion 21 to sandwich the above-mentioned layers therebetween, similar to the power generation 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 cathode separator 15 and the anode separator 18 at the extended portions. In the outer peripheral portion 21, neither the cathode separator 15 nor the anode separator 18 requires a flow path, and therefore no grooves 15a or grooves 18a are formed therein (however, as can be seen from FIG. 3 , this does not prevent grooves from being formed in part of the outer peripheral portion).

[0030] A cover sheet 22 is disposed so as to span the edge of the surface of the support 23 facing the cathode side and the edge of the surface of the membrane electrode assembly facing the cathode side. The cover sheet 22 will be described later.

[0031] 1.2.2.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 includes a base material 23a and adhesive layers 23b disposed on both surfaces 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, thereby sealing the inside of the power generation section 11. Therefore, the distance 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 Figures 3 and 4, the distance is narrowed in part in the area where only the support 23 is disposed, and the support 23 is sandwiched and fixed between the cathode separator 15 and the anode separator 18.

[0032] The substrate 23a is formed from any electrically insulating and airtight material. Examples of such materials include crystalline polymers, more specifically, engineering plastics. Examples of engineering plastics include polyethylene naphthalate resin (PEN), polyethylene terephthalate resin (PET), polyphenyl ether (PPE), polyphenylsulfone (PPSU), polysulfone (PSU), polyethersulfone (PSU), polyetheretherketone (PEEK), polyimide (PI), polyetherimide (PEI), polyamideimide (PAI), polyphenylsulfide (PPS), syndiotactic polystyrene (SPS), nylon resins, and the like. 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.

[0033] The adhesive layer 23b may be made of any known material as long as it has adhesive properties when adhered. Examples of adhesive materials used for the adhesive layer include polyolefin polymers containing maleic acid and maleic anhydride. More specifically, Admer (registered trademark, Mitsui Chemicals, Inc.) is one example.

[0034] As can be seen from FIGS. 3 and 4, the end faces of such a support 23 are spaced apart from the end faces of the membrane electrode assembly and the anode gas diffusion layer 17 by a distance L. AThe support 23 and the membrane electrode assembly 11 are disposed opposite each other with a space A therebetween, and extend in the direction opposite to the power generation section 11. This space A can absorb dimensional changes due to linear expansion of the support 23, the membrane electrode assembly, etc., and can suppress breakage due to expansion and contraction. More specifically, the space A is defined by a distance L in the direction in which the support 23 faces the membrane electrode assembly and the anode gas diffusion layer 17. A It is preferable that the distance L is 0.01 mm or more and 2 mm or less. A If the distance L is less than 0.01 mm, it becomes difficult to absorb the dimensional change of the support. A If the distance exceeds 2 mm, the pressure difference between the space A and the cathode gas diffusion layer 14 may cause deformation or damage to the support 23, resulting in a decrease in sealing performance.

[0035] 1.2.3.Cover Sheet As described above, the cover sheet 22 is disposed so as to span the edge of the surface of the support 23 facing the cathode side and the edge of the surface of the membrane electrode assembly facing the cathode side.

[0036] 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, covering at least one surface end of the electrolyte membrane 12 and the cathode catalyst layer 13 (in this embodiment, the cover sheet is arranged so as to cover the surface ends of both 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.

[0037] The cover sheet 22 is made of a material that is impermeable to the reactant gases of the fuel cell. Examples of materials that can be used as the material that is impermeable to the reactant gases include film-like materials made of resins such as polypropylene, polyphenylene sulfide, polyethylene naphthalate, nylon, and ethylene-vinyl alcohol copolymer. In particular, from the viewpoints of hydrolysis resistance and adhesion to the electrolyte membrane, nylon 11, nylon 12, nylon 9T, and ethylene-vinyl alcohol may be used. Furthermore, additives having amide groups, epoxy groups, hydroxyl groups, etc. may be added to improve adhesion to the electrolyte membrane 12.

[0038] The cover sheet 22 is adhered to the support 23 at the portion where it overlaps with the support 23 by an 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 cover sheet 22 by providing an adhesive layer on the cover sheet 22 as needed. However, when nylon is used as the cover sheet 22, the cover sheet and the membrane electrode assembly can be adhered by thermocompression bonding, so that an adhesive layer may not be necessary.

[0039] When one end of the cover sheet 22 is placed between the cathode gas diffusion layer and the membrane electrode assembly, a space (space B) is generated at the location indicated by B in Figures 3 and 4 due to the thickness of the cover sheet 22. Space B tends to become larger as the cover sheet 22 becomes thicker.

[0040] 1.2.4. Damage prevention As a result of intensive research by the inventors, it was discovered that when a cover sheet is placed, the cover sheet or the anode gas diffusion layer is damaged (torn) due to the above-mentioned space A and space B, resulting in poor sealing. In response to this, the inventors came to the following conclusion.

[0041] The space A is necessary as a space to absorb dimensional changes due to thermal expansion of the support 23 and other parts. On the other hand, space B is a space that is inevitably generated by the arrangement of the cover sheet as described above, and if it is too large, there is a risk of damage to the cover sheet, the membrane electrode assembly, and the gas diffusion layer. Since this damage could lead to reactant gas leakage, it is preferable to make space B as small as possible. To address this, it is effective to make the cover sheet 22 thinner in order to reduce space B. However, making the cover sheet 22 thinner reduces the rigidity of the cover sheet 22, making it more susceptible to deformation due to the pressure difference between space A and the cathode gas diffusion layer 14 across the cover sheet 22, raising concerns about damage. On the other hand, if the rigidity of the cover sheet 22 is increased too much, for example by adjusting the material of the cover sheet 22, the cover sheet 22 becomes less likely to deform, reducing the sealing performance (the material needs to have a certain degree of flexibility to maintain sealing performance). Therefore, the inventors have come to the conclusion that the problem can be solved by a structure that reduces the space B while suppressing damage to the cover sheet 22 due to the pressure difference, and further ensures sealing properties. This will be specifically described below.

[0042] (1) Relationship between the elastic modulus and thickness of the cover sheet When the thickness of the cover sheet is t (mm) and the modulus of elasticity of the cover sheet is E (MPa), the cover sheet 22 is configured so that the following formula (1) holds. E>0.048 L A 4 / t 3 …(1) Here, L A As described above, (mm) is the distance in the space A in the direction in which the end face of the support 23 faces the end faces of the membrane electrode assembly and the anode gas diffusion layer 17 (see FIG. 4). By satisfying formula (1), the cover sheet 22 can be made to have a predetermined flexibility and rigidity, which makes it possible to suppress damage caused by the pressure difference resulting from space A and maintain sealing properties.

[0043] As can be seen from FIG. 4, the relationship between the space A and the cover sheet 22 is a distance L AThe load can be considered as a uniformly distributed load supported on both ends (the load is a surface pressure acting on the cover sheet 22 based on a pressure difference). Therefore, the formula (2) expressing the deflection δ can be applied. δ=(5·w·L) / (384·E·I) …(2) Here, w is the load (surface pressure), L is L A , I is the section modulus when the thickness of the cover sheet is t (I=t 3 / 12) Formula (1) was obtained by applying the example A2, which is the result of the test below, to formula (2).

[0044] A part of the test is shown below. Figure 5 shows an exploded perspective view to explain the test. A cover sheet 32 ​​was sandwiched between foam rubber 31 with 1 mm x 3 mm slits cut into a stainless steel substrate 30 so that pressure was applied to an area 1 mm wide x 3 mm long. A fatigue test was performed on this cover sheet 32, in which pressure was repeatedly applied and removed from the slit side of the foam rubber 31 at a gauge pressure of 0.07 MPa and a temperature of 120°C. The cover sheets used and the results (the number of repetitions before leakage occurred) are shown in Table 1.

[0045] [Table 1]

[0046] The range (hatched area) of formula (1) and the positions of test examples A1, A2, and B1 to B6 are shown in a graph in Figure 6. In Figure 6, the horizontal axis represents the elastic modulus, and the vertical axis represents the thickness of the cover sheet. As can be seen from Table 1 and Figure 6, A1 and A2, which do not satisfy formula (1), leaked after a small number of cycles, whereas B1 to B6, which satisfy formula (1), did not show any leaks even after more than 300,000 cycles.

[0047] (2) Crushing the gas diffusion layer The reduction rate of the voids of the gas diffusion layer in the portion (portion C) where the cover sheet is placed, shown as C in Figures 3 and 4, relative to the voids of the gas diffusion layer in the power generation section 11 (portion where no cover sheet is placed) is 5% to 25%. By compressing and arranging the first gas diffusion layer so as to reduce its thickness in the portion where the cover sheet is placed in this way, it is possible to reduce space B and maintain the sealing properties of the cover sheet. Here, region C refers to the region of the first gas diffusion layer (cathode gas diffusion layer) 14 that overlaps the cover sheet 22 within a range of 60 μm from the leading end of the cover sheet 22 on the membrane electrode assembly side in a plan view of the power generation unit cell 10.

[0048] As described above, the cathode gas diffusion layer 14 and the anode gas diffusion layer 17 (sometimes simply referred to as gas diffusion layers when there is no need to distinguish between them) have gaps through which gas can pass in order to supply gas to the power generation section 11. These gaps are unnecessary in the outer peripheral section 21 where the cover sheet 22 is disposed, so it is possible to eliminate the gaps. However, if the gap reduction rate is less than 5%, the effect of reducing the space B is reduced, and if the gap reduction rate exceeds 25%, the gas diffusion layer becomes too thin and there is a risk of buckling.

[0049] In this embodiment, only the cathode gas diffusion layer 14 is crushed, but this is not limiting, and both the cathode gas diffusion layer 14 and the anode gas diffusion layer 17 may be crushed. When both the cathode gas diffusion layer 14 and the anode gas diffusion layer 17 are crushed, the periphery of space B takes on a shape as shown in FIG. Even when both gas diffusion layers are crushed, the reduction rate of the voids in each gas diffusion layer is 5% or more and 25% or less.

[0050] Some of the tests (Tests D and E) conducted to confirm that the space B can be reduced by crushing the gas diffusion layer at the portion C are shown below. In Tests D and E, a membrane electrode assembly was used, with a 10 μm thick perfluoro-based electrolyte membrane as the electrolyte membrane, a 10 μm thick platinum-supported carbon as the cathode catalyst layer, and a 5 μm thick platinum-supported carbon as the anode catalyst layer. Nylon 12 (with 10% Admer (registered trademark) added) was used as the cover sheet (thickness is shown in Table 2). The thicknesses and porosity reduction rates of the cathode and anode gas diffusion layers are shown in Table 2.

[0051] [Test D] Each gas diffusion layer is 3 cm long and 1 cm wide. A cover sheet 1.5 cm long and 1 cm wide is sandwiched between two gas diffusion layers. The size of the space B when a surface pressure of 0.6 MPa is applied (L in Figure 4) B ) and the amount of crushing of the gas diffusion layer were observed and measured using a microscope. The results are shown in Table 2. Here, the thickness of the gas diffusion layer in the area where the cover sheet was not placed is t H , the thickness of the gas diffusion layer at site C is t C As the void reduction rate R S was calculated using the following formula: R S (%)=(t H -t C ) / t H ×100(%)

[0052] [Test E] Each gas diffusion layer is 3 cm long and 1 cm wide. A cover sheet 1.5 cm long and 1 cm wide is sandwiched between two gas diffusion layers. The size of the space B when a surface pressure of 0.1 MPa is applied (L in Figure 4) B ) and the amount of crushing of the gas diffusion layer was observed and measured using a microscope. S The calculation method was the same as in Test D. The results are shown in Table 2.

[0053] [Table 2]

[0054] As can be seen from Table 2, the dimensions of space B are reduced by compressing the gas diffusion layer so that the void reduction rate in region C is 5% or more. This reduces the stress on the electrolyte membrane, improving the sealing performance of the cover sheet.

[0055] 1.2.5. Other Forms Fig. 8 shows another example of the configuration of the outer periphery. Fig. 8 is a view from the same perspective as Fig. 4. In the example of Fig. 8, the end face of the cathode catalyst layer 13 is 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 configuration, the same effect as above can be achieved if the relationship between the elastic modulus and thickness of the cover sheet and the reduction in the porosity of the cathode catalyst layer and the anode catalyst layer in the portion where the cover sheet overlaps the cathode catalyst layer 13 in a plan view (region C) satisfy the above-mentioned predetermined ranges.

[0056] 2. Effects etc. As described above, when a cover sheet is placed, damage (tears) of the cover sheet or poor sealing may occur due to the above-mentioned spaces A and B. However, by adjusting the elastic modulus and thickness of the cover sheet to the above-mentioned specified relationship and by compressing the gas diffusion layer where the cover sheet is placed so that the porosity falls within the above-mentioned specified range, the effects of spaces A and B can be reduced, 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.

[0057] 3.Fuel cell The fuel cell 40 is a member formed by stacking a plurality of (approximately 50 to 400) power generating unit cells 10 described above, and collects current from the plurality of power generating unit cells 10. An outline of the configuration is shown in Fig. 9. The fuel cell 40 includes a stack case 41, end plates 42, a plurality of power generating unit cells 10, current collecting plates 44, and a biasing member 45.

[0058] The stack case 41 is a housing that houses a plurality of stacked power generating unit cells 10, current collector plates 44, and biasing members 45. In this embodiment, the stack case 41 is a rectangular cylinder with one open end and the other closed end, and a plate-like piece protrudes along the edge of the opening to the opposite side of the opening, forming a flange 41a.

[0059] The end plate 42 is a plate-shaped member that closes the opening of the stack case 41. The end plate 42 is fixed to the stack case 41 with bolts, nuts, etc. at the portion where it overlaps with the flange 41a of the stack case 41 so as to cover the stack case 41.

[0060] The power generating unit cell 10 is as described above. A plurality of such power generating unit cells 10 are stacked. At this time, the anode separator 18 of one power generating unit cell 10 overlaps with the cathode separator 15 of the adjacent power generating unit cell 10. The grooves 15b of the cathode separator 15 and the grooves 18b of the anode separator 18 overlap to form a cooling water flow path.

[0061] The current collector 44 is a member that collects current from the stacked power generating unit cells 10. Therefore, the current collector 44 is disposed at each end of the stack of power generating unit cells 10, with one serving as a positive electrode and the other as a negative electrode. Terminals (not shown) are connected to the current collector 44, allowing electrical connection to the outside.

[0062] The biasing member 45 is housed inside the stack case 41 and applies a pressing force in the stacking direction to the stack of power generating unit cells 10. An example of the biasing member is a disc spring.

[0063] In addition, the fuel cell generates heat during operation, so it is desirable to operate it at a higher temperature. Specifically, it is preferable that it can be operated at a temperature up to 140°C, but since some perfluoro-based electrolyte membranes used soften at around 120°C, it is more preferable to operate it at 120°C or less.

[0064] 4. Fuel Cell Fabrication The fuel cell of the present disclosure can be manufactured, for example, by the following steps.

[0065] First, as shown in FIG. 10 , a membrane electrode assembly including a cathode catalyst layer 13, an anode catalyst layer 16, and an electrolyte membrane 12 disposed between the cathode catalyst layer 13 and the anode catalyst layer 16 is placed on an anode separator 18, and a support 23 is placed around the membrane electrode assembly, forming a space A between the support 22 and the end face of the membrane electrode assembly, and a cover sheet 22 whose relationship between elastic modulus and thickness satisfies the above formula (1) is placed between the support 22 and at least one of the electrolyte membrane 12 and the cathode catalyst layer 13.

[0066] Next, the cathode gas diffusion layer 14 is placed on the cover sheet 22 and pressed against the voids of the gas diffusion layer in the power generation section so that the void reduction rate at the above-mentioned region C is 5% to 25%. Here, it is preferable to obtain the relationship between the pressing force and the void reduction rate in advance so that it is not necessary to measure the void reduction rate each time.

[0067] Then, the cathode separator 15 is laminated on the cathode gas diffusion layer 14 and pressed to form the power generation unit cells 10, and the various components are arranged as shown in FIG.

[0068] 5.Other In the above explanation, each component on the cathode side has been referred to as the "first" and each component on the anode side as the "second," but the reverse is also possible, and the same effect can be achieved by replacing the cathode side with the "second" and the anode side with the "first." [Explanation of symbols]

[0069] 10 Power generating unit cells 11 Power Generation Department 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 23 Support 23a Base material 23b Adhesive layer 40 Fuel Cell

Claims

1. 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, the first gas diffusion layer having at least a portion of its outer periphery extending beyond the outer periphery 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 distance L between the end surface of the support and the end surface of the membrane electrode assembly is Ａ A space having a length of 1 / 4 in. (mm) is formed, When the longitudinal elastic modulus of the cover sheet is E (MPa) and the thickness is t (mm), the L Ａ , the E and the t are used as an equation to compare only their numerical values. E>0.048×L Ａ ４ / t ３ holds, and The longitudinal elastic modulus is 137 MPa or more and 160 MPa or less, and the thickness is 0.04 mm or more and 0.1 mm or less, the first gas diffusion layer has a void reduction rate of at least a portion of a region where the cover sheet is disposed relative to a void in a region where the cover sheet is not disposed, of 5% to 25%. fuel cell.

2. A method for manufacturing 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; and a distance L between the end surface of the membrane electrode assembly. Ａ When the longitudinal elastic modulus is E (MPa) and the thickness is t (mm), the L Ａ , the E and the t are used as an equation to compare only their numerical values. E>0.048×L Ａ ４ / t ３ holds, and The longitudinal elastic modulus is 137 MPa or more and 160 MPa or less, and the thickness is 0.04 mm or more and 0.1 mm or less. Place the cover sheet a first gas diffusion layer is disposed on the cover sheet and the membrane electrode assembly, and the first gas diffusion layer is pressed so that a reduction rate of voids in at least a portion of a region where the cover sheet is disposed relative to voids in a region where the cover sheet is not disposed is 5% to 25%. A method for manufacturing a fuel cell.

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