Fuel cell and method for manufacturing the same

Abstract

To provide a fuel cell and a method for manufacturing the same that do not use adhesive to bond an electrode layer and a gas diffusion layer.SOLUTION: A fuel cell (1) having an electrode layer (3) and a gas diffusion layer (5) joined to the electrode layer (3), and the electrode layer (3) contains an ionomer (41), and the gas diffusion layer (5) has ionomer particles (42) on at least a portion of the surface facing the electrode layer (3), the ionomer particles (42) are the same as the ionomer (41) contained in the electrode layer (3), and the ionomer particles (42) are spray-applied.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a fuel cell and a method for manufacturing a fuel cell. [Background technology]

[0002] Conventionally, fuel cells have been used that have a structure in which a membrane electrode assembly (MEA) is formed by sandwiching an electrolyte membrane between a pair of electrode layers on both sides, and is further sandwiched between gas diffusion layers (GDLs) and a pair of separators that form flow paths for oxygen gas (air), hydrogen gas, or generated liquid water. Poor bonding between the electrode layers and the GDLs can cause liquid water generated during power generation to accumulate between the electrode layers and the GDLs, potentially resulting in unstable power generation. For this reason, in conventional fuel cells 20, as shown in FIG. 6 , the electrode layers 3 and the gas diffusion layers 5 that sandwich the electrolyte membrane 2 on both sides are typically bonded via adhesive layers 21 and gaskets 22.

[0003] However, in a structure in which the electrode layer and the gas diffusion layer are bonded via an adhesive layer, there is a problem that when the adhesive layer interposed between the electrode layer and the gas diffusion layer thermally expands during the process of thermocompression bonding the separator and the support frame, the membrane electrode assembly deforms and breaks due to the expansion of the adhesive layer. Therefore, to solve the problem of thermal expansion, a method has been proposed in which, rather than directly bonding the electrode layer and the gas diffusion layer to the gasket, the electrode layer and the gas diffusion layer are bonded via a membrane-like member that acts to alleviate the transmission of stress from the gasket to the membrane electrode assembly (see Patent Document 1). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 2023-139564 Summary of the Invention [Problem to be solved by the invention]

[0005] However, in the fuel cell of Patent Document 1, it is necessary to use an adhesive and a new membrane member to bond the electrode layer and the gas diffusion layer. The need for a process using the adhesive and membrane member increases the equipment cost and man-hours, and it is also necessary to select an adhesive and material that do not adversely affect the membrane electrode assembly.

[0006] An object of the present invention is to provide a fuel cell and a method for manufacturing the fuel cell that do not use adhesive to bond the electrode layer and the gas diffusion layer. [Means for solving the problem]

[0007] (1) A fuel cell of the present invention (e.g., fuel cell 1 described below) is a fuel cell having an electrode layer (e.g., electrode layer 3 described below) and a gas diffusion layer (e.g., gas diffusion layer 5 described below) joined to the electrode layer, wherein the electrode layer contains an ionomer (e.g., ionomer 41 described below), and the gas diffusion layer has ionomer particles (e.g., ionomer particles 42 described below) on at least a portion of the surface facing the electrode layer.

[0008] The fuel cell includes an electrode layer and a gas diffusion layer bonded to the electrode layer, the electrode layer containing an ionomer. Meanwhile, the gas diffusion layer has ionomer particles on at least a portion of the surface corresponding to the electrode layer. Ionomer is a synthetic resin formed by agglomerating polymers using the cohesive force of metal ions, and can be bonded by softening the ionomer particles together through thermocompression bonding. The bonding between the electrode layer and the gas diffusion layer having the ionomer layer is strong due to the anchoring effect of the ionomer. Furthermore, the presence of ionomer particles on at least a portion of the surface of the gas diffusion layer allows gas from the gas diffusion layer to pass through to the electrode layer without being obstructed.

[0009] (2) In the fuel cell, the ionomer contained in the ionomer particles is the same as the ionomer contained in the electrode layer.

[0010] When the ionomer contained in the ionomer particles is the same as the ionomer contained in the electrode layer, a stronger anchor effect is exerted, enabling a strong bond between the electrode layer and the gas diffusion layer.

[0011] (3) The ionomer particles of the fuel cell are spray-coated ionomer particles.

[0012] The ionomer particles in the gas diffusion layer are adhered by spraying the ionomer onto the surface of the gas diffusion layer facing the electrode layer. This allows the ionomer particles to be adhered only to at least a portion of the surface of the substrate arranged on the side of the gas diffusion layer facing the electrode layer. In other words, this prevents the ionomer from penetrating into the porous gas diffusion layer 5, allowing the ionomer to be disposed only on the surface layer of the gas diffusion layer, thereby reducing the amount of ionomer used.

[0013] (4) This method for manufacturing a fuel cell includes an electrode layer and a gas diffusion layer bonded to the electrode layer, and includes a coating step of applying an ionomer to a surface of the gas diffusion layer facing the electrode layer, and a bonding step of bonding the electrode layer and the gas diffusion layer such that the surface of the gas diffusion layer coated with the ionomer faces the electrode layer.

[0014] The fuel cell is manufactured by a manufacturing method including a coating step of coating an ionomer on the surface of the gas diffusion layer facing the electrode layer, and a bonding step of bonding the electrode layer and the gas diffusion layer so that the ionomer-coated surface of the gas diffusion layer faces the electrode layer. This bonds the electrode layer containing the ionomer to the ionomer particles adhered to the gas diffusion layer, and the anchor effect of the ionomer enables a strong bond between the electrode layer and the gas diffusion layer.

[0015] (5) In the application step of the fuel cell manufacturing method, the ionomer is spray-applied onto the surface of the gas diffusion layer facing the electrode layer.

[0016] The application step of spraying the ionomer onto the surface of the gas diffusion layer facing the electrode layer allows the ionomer particles to adhere only to at least a portion of the surface of the substrate arranged on the side of the gas diffusion layer facing the electrode layer. In other words, this prevents the ionomer from penetrating into the porous gas diffusion layer 5, allowing the ionomer to be disposed only on the surface layer of the gas diffusion layer, thereby reducing the amount of ionomer used. [Effects of the Invention]

[0017] According to the present invention, by including ionomer particles on at least a portion of the surface of the gas diffusion layer corresponding to the electrode layer, the electrode layer and the gas diffusion layer can be firmly bonded together, and a fuel cell can be provided in which no adhesive is used to bond the electrode layer and the gas diffusion layer, thereby reducing the cost of using adhesives and preventing liquid water from accumulating between the electrode layer and the gas diffusion layer. [Brief explanation of the drawings]

[0018] [Figure 1] FIG. 2 is a cross-sectional view of a membrane electrode assembly according to the present embodiment. [Figure 2] FIG. 1 is a schematic diagram showing how an ionomer is applied to a gas diffusion layer by spraying. [Figure 3] FIG. 1 is a schematic diagram showing a state in which an ionomer is applied to a gas diffusion layer using a slot die coater. [Figure 4] FIG. 2 is a cross-sectional view showing a bonding state between an electrode layer and a gas diffusion layer according to an example. [Figure 5] 1 is a graph showing the relationship between the amount of ionomer impregnation and peel strength according to an example. [Figure 6] FIG. 1 is a cross-sectional view showing a state in which an electrode layer and a gas diffusion layer are joined via a conventional adhesive and a gasket. DETAILED DESCRIPTION OF THE INVENTION

[0019] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will now be described in detail with reference to the accompanying drawings. First, the configuration of a fuel cell 1 will be described.

[0020] As shown in Fig. 1, the fuel cell 1 is a polymer electrolyte fuel cell that includes a membrane electrode assembly (MEA) 10, a gas diffusion layer (GDL) 5, and a separator (not shown). Polymer electrolyte fuel cells have the advantages of low operating temperatures, short start-up times, and compact construction, and are therefore used in fields such as power sources for automobiles.

[0021] The membrane electrode assembly 10 is sandwiched on both sides by separators (not shown) to form a fuel cell 1. The fuel cell 1 can be used alone, or multiple fuel cells 1 can be stacked together. The membrane electrode assembly 10 has an electrolyte membrane 2 and electrode layers 3 that sandwich the electrolyte membrane 2 on both sides. An anode catalyst layer 31 as the electrode layer 3 is provided on the upper side of the electrolyte membrane 2, and a cathode catalyst layer 32 as the electrode layer 3 is provided on the lower side of the electrolyte membrane 2. Gas diffusion layers 5 are provided on both sides of the membrane electrode assembly 10, and the electrode layers 3 and gas diffusion layers 5 are bonded together via ionomer particles 42.

[0022] Next, the components of the fuel cell 1 of this embodiment will be described in detail with reference to the drawings.

[0023] [Electrolyte membrane 2] The electrolyte membrane 2 in the fuel cell 1 of this embodiment is not limited, and various electrolyte membranes 2 can be used. For example, the proton-conductive resin for the electrolyte membrane 2 can be, but is not limited to, an aromatic polymer compound in which a sulfonic acid group is introduced into a hydrocarbon polymer such as an aromatic polyarylene ether ketone or an aromatic polyarylene ether sulfone.

[0024] [Electrode layer 3] As shown in FIG. 1, the electrode layer 3 includes an anode catalyst layer 31 and a cathode catalyst layer 32. The electrode layer 3 includes carbon particles (catalyst particles) 6 carrying a catalyst metal 7, and an ionomer 41, which is a polymer electrolyte. The carbon particles 6 may be carbon black, but other carbon compounds such as graphite, carbon fiber, activated carbon, or pulverized products thereof, carbon nanofiber, carbon nanotubes, carbon nitride, carbon sulfide, and carbon phosphide may also be used. The catalyst metal 7 may be platinum, ruthenium, iridium, rhodium, palladium, osnium, tungsten, lead, iron, chromium, cobalt, nickel, manganese, vanadium, molybdenum, gallium, aluminum, or other metals, either alone or in combination.

[0025] The ionomer 41 serves to bond the carbon particles 6 together and to act as a proton conductor produced by a chemical reaction. Commonly used ionomers include perfluorocarbon sulfonic acid polymers such as Nafion (registered trademark), which are also widely used as electrolyte materials. However, sulfonated plastic electrolytes such as sulfonated polyether ketone, sulfonated polyether sulfone, sulfonated polyether ether sulfone, sulfonated polysulfone, sulfonated polysulfide, and sulfonated polyphenylene, as well as sulfoalkylated plastic electrolytes such as sulfoalkylated polyether ether ketone, sulfoalkylated polyether sulfone, sulfoalkylated polyether ether sulfone, sulfoalkylated polysulfone, sulfoalkylated polysulfide, and sulfoalkylated polyphenylene, can also be used.

[0026] [Gas diffusion layer 5] The gas diffusion layers 5 are laminated on both sides of the membrane electrode assembly 10 and serve to uniformly distribute the reaction gases and transmit the generated electrical energy. The gas diffusion layer 5 is formed by laminating a substrate 8 and a porous layer. The substrate 8 can be made of conductive carbon particles, carbon paper, carbon cloth, or the like. As described above, ionomer particles 42 are adhered to the surface of the gas diffusion layer 5 facing the electrode layer 3. As shown in FIG. 1 , the ionomer 41 contained in the electrode layer 3 and the ionomer particles 42 adhered to the gas diffusion layer 5 exert a bonding effect, thereby reliably bonding the electrode layer 3 and the gas diffusion layer 5.

[0027] [Ionomer particles 42] The ionomer particles 42 are particles of an ionomer that are applied to and adhered to the surface of the substrate 8 of the gas diffusion layer 5. The ionomer used in the ionomer particles 42 can be any of the ionomers listed in the description of the ionomers used in the electrode layer 3. Preferably, the ionomer particles 42 and the ionomer 41 used in the electrode layer 3 are the same.

[0028] As in the examples described below, the ionomer particles 42 are adhered by applying an ionomer to the surface of the gas diffusion layer 5 facing the electrode layer 3. If the ionomer particles 42 are applied without any gaps and form a layer, the gas from the gas diffusion layer 5 is prevented from passing through to the electrode layer 3, and therefore it is desirable that the ionomer particles 42 be adhered to at least a portion of the surface of the gas diffusion layer 5. For this reason, in a preferred embodiment, the ionomer particles 42 are adhered to the substrate 8 by spray application, as shown in FIG.

[0029] This allows the ionomer particles 42 to be adhered only to at least a portion of the surface of the substrate 8 arranged on the side of the gas diffusion layer 5 facing the electrode layer 3, thereby having the effect of allowing the gas from the gas diffusion layer 5 to permeate into the electrode layer 3. In addition, since the penetration of the ionomer into the porous gas diffusion layer 5 can be suppressed and the ionomer can be applied only to the surface layer of the gas diffusion layer 5, the amount of ionomer used can be reduced.

[0030] Furthermore, the surface of the electrode layer 3 containing the ionomer 41 and the ionomer particles 42 are softened by thermocompression bonding and are thereby bonded to each other. As a result, when bonding the electrode layer 3 to the gas diffusion layer 5 containing the ionomer particles 42, a strong bond can be achieved due to the anchor effect of the ionomer. Note that the anchor effect in the present invention refers to a state in which ionomers softened by heat are firmly bonded to each other, resulting in an adhesive effect.

[0031] <Example> Next, the present embodiment will be described in more detail based on examples, but the present embodiment is not limited to these examples.

[0032] [Test method] The electrode layer 3 and the gas diffusion layer 5 were securely bonded via the ionomer particles 42, and then a test was conducted in which the peel strength when the two layers were peeled off was measured using a force gauge. Specifically, as shown in FIG. 3 , a slot die coater 9 was used to evenly coat one side of the gas diffusion layer 5 with an ionomer solution and a dispersion solvent, and the ionomer particles 42 were then adhered to the surface of the substrate 8 of the gas diffusion layer 5. At this time, care was taken to ensure that the ionomer particles 42 were coated without any gaps and were not layered on the gas diffusion layer 5. The ionomer particles 42 used here may be the same as the ionomer 41 described above. Furthermore, the dispersion solvent used may be water or an alcohol-based solvent such as ethanol or 1-propanol, but any alcohol-based solvent capable of dispersing the ionomer solution may be used.

[0033] Next, as shown in FIG. 4 , the electrode layer 3 and the gas diffusion layer 5 are laminated with the surface of the gas diffusion layer 5 to which the ionomer particles 42 are bonded facing the upper surface of the electrode layer 3 placed on the cushioning material C. Next, the laminated gas diffusion layer 5 and electrode layer 3 are heat-pressed from above using a thermal surface plate H. The temperature of the thermal surface plate H is 148°C, which ensures that the gas diffusion layer 5 and the electrode layer 3 are securely bonded together by the anchor effect of the ionomer. While this bonding method was used in the examples, when actually mass-producing gas diffusion layers 5 and electrode layers 3, a roll-to-roll (RTR) production system may be used to efficiently bond the gas diffusion layer 5 and the electrode layer 3.

[0034] In the process of adhering the ionomer particles 42 to the gas diffusion layer 5, the amount of ionomer impregnated into the gas diffusion layer 5 was gradually changed, and the peel strength for each impregnation amount was compared. Figure 5 shows the results of the peel strength measurement experiment. Figure 4 shows that when the amount of ionomer impregnated in the gas diffusion layer 5 reached approximately 0.16 mg / cm2, the peel strength exceeded 0 N / inch, and thereafter the peel strength increased in direct proportion to the amount of ionomer impregnated.

[0035] However, if the amount of ionomer impregnated in the gas diffusion layer 5 is too large, the gas diffusion layer 5 and the electrode layer 3 are less likely to peel off, but this causes a problem of a decrease in the power generation performance of the fuel cell 1. In the examples, the amount of ionomer impregnation at which the power generation performance does not decrease is 0.24 mg / cm. 2 This value is the optimum value for the amount of ionomer impregnation in the examples. However, in a fuel cell, the porosity varies depending on the configuration of the substrate 8 and porous layer used in the gas diffusion layer, and the degree of penetration of the ionomer solution varies depending on the porosity state of the gas diffusion layer. Therefore, the optimum value for the amount of ionomer impregnation in the gas diffusion layer 5 according to this embodiment is not limited to this value. The optimum value for the amount of ionomer impregnation in the gas diffusion layer 5 is calculated by taking into account the peel strength between the gas diffusion layer 5 and the electrode layer 3 and the power generation performance of the fuel cell 1.

[0036] It is also desirable that the ionomer particles 42 are uniformly applied and adhered only to the surface of the substrate 8 without the ionomer penetrating into the gas diffusion layer 5. Therefore, in a more preferred embodiment, the ionomer is applied to the surface of the gas diffusion layer 5 facing the electrode layer 3 by spray coating as shown in FIG. 2 , rather than the application method of the ionomer using the slot die coater 9 used in the examples.

[0037] According to this embodiment, the following effects are achieved.

[0038] The fuel cell 1 according to this embodiment has an electrode layer 3 and a gas diffusion layer 5, with an ionomer applied to the surface of the gas diffusion layer 5 facing the electrode layer 3, and ionomer particles 42 adhered to the surface of the substrate 8.

[0039] As a result, the ionomer 41 contained in the electrode layer 3 and the ionomer particles 42 adhered to the surface of the gas diffusion layer 5 exert an anchoring effect, reliably bonding the electrode layer 3 and the gas diffusion layer 5 together. This eliminates the need for a separate step of using an adhesive or a step of connecting the electrode layer 3 and the gas diffusion layer 5 via a gasket, thereby reducing the number of steps required to produce the fuel cell 1. The number of steps required to prepare an adhesive that does not adversely affect the electrodes and membranes is reduced, and the present invention directly bonds the electrode layer 3 and the gas diffusion layer 5, preventing generated liquid water from accumulating between the electrode layer 3 and the gas diffusion layer 5. Preventing excess liquid water from accumulating between the membrane electrode assembly 10 and the gas diffusion layer 5 improves the power generation performance of the fuel cell 1.

[0040] Although the preferred embodiments of the present invention have been described above, the present invention is not limited to the above embodiments and can be modified as appropriate within the scope of the present invention. [Explanation of symbols]

[0041] 1 fuel cell, 3 electrode layer, 5 gas diffusion layer, 41 ionomer, 42 ionomer particles

Claims

1. A fuel cell having an electrode layer and a gas diffusion layer joined to the electrode layer, the electrode layer comprises an ionomer; The gas diffusion layer has ionomer particles on at least a portion of a surface facing the electrode layer.

2. 2. The fuel cell according to claim 1, wherein the ionomer contained in the ionomer particles is the same as the ionomer contained in the electrode layer.

3. 3. The fuel cell according to claim 1, wherein the ionomer particles are a spray coating of ionomer.

4. A method for manufacturing a fuel cell having an electrode layer and a gas diffusion layer joined to the electrode layer, comprising the steps of: a coating step of coating an ionomer on a surface of the gas diffusion layer facing the electrode layer; a bonding step of bonding the electrode layer and the gas diffusion layer so that the surface of the gas diffusion layer to which the ionomer is applied faces the electrode layer.

5. The method for manufacturing a fuel cell according to claim 4 , wherein the coating step comprises spraying the ionomer onto the surface of the gas diffusion layer facing the electrode layer.

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