Gas diffusion layer, membrane electrode assembly, fuel cell, and method for manufacturing gas diffusion layer

Abstract

Provided are a gas diffusion layer, a membrane electrode assembly, a fuel cell, and a method for producing a gas diffusion layer. A gas diffusion layer having excellent mechanical strength is provided. The gas diffusion layer includes electrically conductive particles and a fluororesin, and the fluororesin contains first fibers having a first average fiber diameter and second fibers having a second average fiber diameter that is different from the first average fiber diameter.

Description

Technical Field

[0001] This disclosure relates to a gas diffusion layer, a membrane electrode assembly, a fuel cell, and a method for manufacturing the gas diffusion layer. Background Technology

[0002] The gas diffusion layer possesses both permeability and gas diffusion properties, making it suitable for applications such as fuel cells. In a polymeric electrolyte fuel cell, which serves as an example of a fuel cell, one side of a hydrogen ion-conducting polymeric electrolyte membrane is exposed to a fuel gas such as hydrogen, while the other side is exposed to oxygen. Water is synthesized through a chemical reaction mediated by the electrolyte membrane, and the energy generated during this reaction is extracted electrically.

[0003] A single cell of a polymeric electrolyte fuel cell has a membrane electrode assembly (hereinafter referred to as "MEA") and a pair of conductive spacers disposed on both sides of the MEA. The MEA has a hydrogen ion-conducting polymeric electrolyte membrane and a pair of electrode layers sandwiching the electrolyte membrane. The pair of electrode layers has a catalyst layer and a gas diffusion layer. The catalyst layer is formed on both sides of the polymeric electrolyte membrane and is mainly composed of carbon powder supporting a platinum group catalyst. The gas diffusion layer is formed on the catalyst layer and has the functions of current collection, gas permeability, and hydrophobicity.

[0004] In a MEA (Metal-Oxide-Anatomical), the gas diffusion layer uniformly supplies gas from the spacers to the catalyst layer. Furthermore, the gas diffusion layer also functions as a conductive path for electrons between the catalyst layer and the spacers. Therefore, conductive porous materials are sometimes used for the gas diffusion layer in MEAs.

[0005] Furthermore, for the gas diffusion layer in the MEA, it is required to rapidly remove excess water generated by the battery reaction using the catalyst layer, allowing it to escape from the MEA system. High hydrophobicity is also required to prevent the pores of the gas diffusion layer from being blocked by the generated water. Therefore, the following gas diffusion layer is typically used: a conductive porous component is hydrophobically treated with a fluoropolymer or similar material, and a hydrophobic layer composed primarily of carbon powder and hydrophobic resins such as fluoropolymers is further formed on the side of the conductive substrate in contact with the catalyst layer.

[0006] Patent document 1 discloses a gas diffusion layer composed of a porous component mainly composed of conductive particles and polymer resin.

[0007] Existing technical documents

[0008] Patent documents

[0009] Patent Document 1: Japanese Patent No. 4938133 Summary of the Invention

[0010] The problem that the invention aims to solve

[0011] However, the gas diffusion layer in Patent Document 1 has weak mechanical strength, and it may rupture due to the pressure of gas or water. Therefore, there is a need to improve the mechanical strength of the gas diffusion layer.

[0012] The purpose of this disclosure is to provide a gas diffusion layer with excellent mechanical strength.

[0013] Methods for solving problems

[0014] The gas diffusion layer disclosed herein comprises conductive particles and a fluororesin, wherein the fluororesin contains a first fiber having a first average fiber diameter and a second fiber having a second average fiber diameter different from the first average fiber diameter.

[0015] The membrane electrode assembly disclosed herein comprises the aforementioned gas diffusion layer, a pair of electrodes, and an electrolyte membrane.

[0016] The fuel cell disclosed herein has the aforementioned gas diffusion layer and current collector.

[0017] The method for manufacturing the gas diffusion layer disclosed herein includes:

[0018] The step of mixing conductive particles, a first fluororesin having a first average particle size, and a second fluororesin having a second average particle size different from the first average particle size.

[0019] The step of calendering the above-mentioned compound to fiberize the first fluororesin and the second fluororesin.

[0020] The effects of the invention

[0021] According to this disclosure, a gas diffusion layer with excellent mechanical strength, a membrane electrode assembly using the gas diffusion layer, and a fuel cell can be provided. Attached Figure Description

[0022] Figure 1 This is a schematic diagram showing the structure of the polymer electrolyte fuel cell stack according to Embodiment 1 of this disclosure.

[0023] Figure 2 This is a schematic cross-sectional view showing the configuration of a polymer electrolyte type fuel cell unit according to an embodiment of the present disclosure.

[0024] Figure 3A This is a schematic diagram of the gas diffusion layer according to Embodiment 1 of this disclosure.

[0025] Figure 3B This is a partially enlarged schematic diagram of the cross-section of the gas diffusion layer according to Embodiment 1 of this disclosure.

[0026] Figure 4AThis is a schematic diagram of the gas diffusion layer according to Embodiment 1 of this disclosure.

[0027] Figure 4B This is a partially enlarged schematic diagram of the cross-section of the gas diffusion layer according to Embodiment 1 of this disclosure.

[0028] Figure 5A This is a schematic diagram of the gas diffusion layer according to Embodiment 1 of this disclosure.

[0029] Figure 5B This is a partially enlarged schematic diagram of the cross-section of the gas diffusion layer according to Embodiment 1 of this disclosure.

[0030] Figure 6 This is a flowchart illustrating a method for manufacturing a gas diffusion layer according to Embodiment 1 of this disclosure.

[0031] Figure 7 Table 1 shows the conditions and evaluation results of the raw materials used in Examples 1-8 and Comparative Examples 1-4.

[0032] Explanation of reference numerals in the attached figures

[0033] 100: Fuel Cell

[0034] 1: Polymer electrolyte membrane

[0035] 2: Catalyst layer

[0036] 2a: Anode catalyst layer

[0037] 2b: Cathode catalyst layer

[0038] 3: Gas diffusion layer

[0039] 3a: Anode-side gas diffusion layer

[0040] 3b: Gas diffusion layer for cathode

[0041] 4: Spacer

[0042] 4a: Anode-side spacer

[0043] 4b: Cathode-side spacer

[0044] 5: Fluid flow path

[0045] 6: Ribs

[0046] 10: Battery Unit

[0047] 11: Current collector

[0048] 12: Insulation board

[0049] 13: End plate

[0050] 20: Membrane electrode assembly

[0051] 30: Porous structure

[0052] 31: Conductive particles

[0053] 32: Fluoropolymer

[0054] 32-f1: First fiber

[0055] 32-f2: Second fiber

[0056] 32-p: Fluoropolymer particles

[0057] 33: Conductive fibers Detailed Implementation

[0058] The gas diffusion layer of the first method comprises conductive particles and fluoropolymer.

[0059] The aforementioned fluororesin contains a first fiber having a first average fiber diameter and a second fiber having a second average fiber diameter different from the aforementioned first average fiber diameter.

[0060] Regarding the gas diffusion layer of the second method, based on the first method described above, the average fiber diameter can be 10 nm or more and 100 nm or less.

[0061] The second average fiber diameter mentioned above is 0.5 μm or more and 50 μm or less.

[0062] Regarding the gas diffusion layer of the third method, based on the first or second method described above, the proportion of the second fiber relative to the total fluororesin can be 10% by mass or more and 90% by mass or less.

[0063] Regarding the gas diffusion layer of the fourth type, it may further include conductive fibers based on any of the first to third types mentioned above.

[0064] Regarding the gas diffusion layer of the fifth method, based on any of the methods 1 to 4 above, the fluororesin may contain particulate fluororesin.

[0065] Regarding the gas diffusion layer of the sixth method, based on the fifth method described above, the average particle size of the particulate fluororesin can be 0.1 μm or more and 10 μm or less.

[0066] Regarding the gas diffusion layer of the seventh method, based on the fifth or sixth method described above, the proportion of the particulate fluororesin to the total fluororesin can be more than 1% by mass and less than 50% by mass.

[0067] Regarding the gas diffusion layer of the eighth embodiment, based on any of the embodiments of the first to seventh embodiments, the gas diffusion layer may have a porous component composed of the conductive particles and the fluororesin.

[0068] Regarding the gas diffusion layer of the ninth type, based on any of the types 1 to 8 described above, the tensile breaking strength of the gas diffusion layer can be 0.20 N / mm. 2 above.

[0069] Regarding the gas diffusion layer of the 10th embodiment, based on any of the 1st to 9th embodiments described above, the gas diffusion layer may be a self-supporting membrane supported by the conductive particles and the fluororesin described above.

[0070] Regarding the gas diffusion layer of the 11th embodiment, based on any of the 1st to 10th embodiments described above, the fluoropolymer may contain PTFE (polytetrafluoroethylene).

[0071] The membrane electrode assembly of the 12th type comprises:

[0072] Gas diffusion layer of any of the above-mentioned types 1 to 11;

[0073] A pair of electrodes; and

[0074] Electrolyte membrane.

[0075] The fuel cell of the 13th type has the following characteristics:

[0076] Gas diffusion layer of any of the above-mentioned types 1 to 11; and

[0077] Current collector.

[0078] The method for manufacturing the gas diffusion layer in the 14th manner includes:

[0079] The step of mixing conductive particles, a first fluororesin having a first average particle size, and a second fluororesin having a second average particle size different from the first average particle size; and

[0080] The step of calendering the above-mentioned compound to fiberize the first fluororesin and the second fluororesin.

[0081] Regarding the manufacturing method of the gas diffusion layer in the 15th embodiment, based on the 14th embodiment described above, the first embodiment may have an average particle size of 0.1 μm or more and 0.5 μm or less.

[0082] The second average particle size mentioned above is greater than 1 μm and less than 1000 μm.

[0083] Hereinafter, the gas diffusion layer, membrane electrode assembly, fuel cell, and method for manufacturing the gas diffusion layer according to embodiments of the present disclosure will be described with reference to the accompanying drawings. It should be noted that substantially identical components are labeled with the same reference numerals in the drawings.

[0084] (Implementation Method 1)

[0085] use Figure 1 The basic configuration of the fuel cell 100 according to Embodiment 1 of this disclosure will be described. Figure 1 This is a schematic diagram showing the configuration of the fuel cell (hereinafter also referred to as a "polymer electrolyte type fuel cell stack") 100 according to Embodiment 1. It should be noted that Embodiment 1 is not limited to polymer electrolyte type fuel cells and can be applied to various types of fuel cells.

[0086] <Fuel Cells>

[0087] like Figure 1 As shown, the fuel cell 100 is formed by stacking one or more battery cells 10 as basic units, and using current collectors 11, insulating plates 12 and end plates 13 arranged on both sides of the stacked battery cells 10 to compress and fasten them under a specified load.

[0088] The current collector 11 is formed of an airtight conductive material. For example, copper or brass is used for the current collector 11. A current extraction terminal (not shown) is provided on the current collector 11, from which current is extracted during power generation.

[0089] The insulating board 12 is formed of an insulating material such as resin. For example, fluorinated resin or PPS resin is used for the insulating board 12.

[0090] The end plate 13 secures and holds the stacked battery cell 10, current collector 11, and insulating plate 12 with a specified load by a pressurizing means (not shown). The end plate 13 is made of a high-rigidity metal material such as steel.

[0091] <Battery Unit>

[0092] Figure 2 This is a schematic cross-sectional view showing the configuration of the battery cell 10. In the battery cell 10, the membrane electrode assembly (hereinafter also referred to as MEA) 20 is held by an anode-side spacer 4a and a cathode-side spacer 4b. Hereinafter, the anode-side spacer 4a and the cathode-side spacer 4b will be referred to together as spacer 4. Other components will also be described in the same way when multiple components are described together.

[0093] A fluid flow path 5 is formed in the spacer 4. A fluid flow path 5 for fuel gas is formed in the anode-side spacer 4a. A fluid flow path 5 for oxidant gas is formed in the cathode-side spacer 4b. The spacer 4 can be made of carbon-based or metallic materials.

[0094] The fluid flow path 5 is a groove formed in the spacer 4. Ribs 6 are provided around the fluid flow path 5.

[0095] <Membrane Electrode Assembly: MEA>

[0096] The membrane electrode assembly (MEA) 20 has a polymer electrolyte membrane 1, a catalyst layer 2, and a gas diffusion layer 3. An anode catalyst layer 2a and a cathode catalyst layer 2b (collectively referred to as catalyst layer 2) are formed on both sides of the polymer electrolyte membrane 1, which selectively transports hydrogen ions. An anode-side gas diffusion layer 3a and a cathode-side gas diffusion layer 3b (collectively referred to as gas diffusion layer 3) are respectively disposed on its outer side.

[0097] The polymeric electrolyte membrane 1 can be, for example, a perfluorocarbon sulfonic acid polymer, but there are no particular limitations as long as it has proton conductivity.

[0098] Catalyst layer 2 can be a layer containing a polymer electrolyte and a carbon material supported on catalyst particles such as platinum.

[0099] <Gas Diffusion Layer>

[0100] Next, use Figure 3A and Figure 3B The structure of the gas diffusion layer 3 in Embodiment 1 of this disclosure will be described in detail.

[0101] Figure 3A This is a schematic diagram of the porous structure 30 that constitutes the gas diffusion layer 3. Figure 3B This is an enlarged schematic diagram showing a portion of the porous structure 30 constituting the gas diffusion layer 3. The porous structure 30 includes conductive particles 31 and fluororesin 32. That is, the gas diffusion layer 3 includes conductive particles 31 and fluororesin 32. In this embodiment 1, as... Figure 3A As shown, the gas diffusion layer 3 is composed of a porous structure 30. It should be noted that the gas diffusion layer 3 is preferably a self-standing membrane supported by conductive particles 31 and fluororesin 32.

[0102] <Conductive particles>

[0103] Examples of conductive particles 31 include carbon materials such as carbon black, graphite, and activated carbon. Conductive particles 31 preferably contain carbon black with high conductivity and a fine primary particle size. Examples of carbon black used in conductive particles 31 include acetylene black, Ketjen black, furnace black, and Balkan. Conductive particles 31 are particularly preferably composed of either acetylene black with low impurity content or Ketjen black with a large specific surface area and high conductivity.

[0104] Fluororesin

[0105] like Figure 3B As shown, the fluororesin 32 contains fluororesin fibers with different average fiber diameters, such as fluororesin fibers with fine diameters (hereinafter also referred to as "first fibers") 32-f1 and fluororesin fibers with coarse diameters (hereinafter also referred to as "second fibers") 32-f2. Because the fluororesin 32 contains fluororesin fibers with different average fiber diameters, such as the fine first fibers 32-f1 and the coarse second fibers 32-f2, the gas diffusion layer 3 exhibits excellent mechanical strength. This is believed to be because the fine first fibers 32-f1 bind the conductive particles 31 together, preventing the conductive particles 31 from detaching from the porous structure 30, and the coarse second fibers 32-f2 contribute to improving the strength of the porous structure 30 itself.

[0106] Examples of materials for the fluororesin 32 include PTFE (polytetrafluoroethylene). PTFE has the property of becoming fibrous when shear force is applied. During the mixing and dispersion process and the sheeting process in the manufacture of the gas diffusion layer 3, PTFE, as a material, becomes fibrous by applying shear force. At this time, the PTFE dispersion with a small particle size becomes the first fiber 32-f1 with a fine fiber diameter, and the PTFE powder with a large particle size becomes the second fiber 32-f2 with a coarse fiber diameter. Thus, by using PTFE, the first fiber 32-f1 and the second fiber 32-f2 can be easily formed inside the gas diffusion layer 3 (porous structure 30). However, the material for the fluororesin 32 is not limited to PTFE; any fluororesin capable of forming the first and second fibers can be used. It should be noted that the first fiber 32-f1 and the second fiber 32-f2 can be the same type of fluororesin or different types of fluororesin. From the viewpoint of facilitating the manufacture of the gas diffusion layer 3, the first fiber 32-f1 and the second fiber 32-f2 are preferably made of the same type of fluororesin. Furthermore, the first fiber 32-f1 can be made of only one type of fluororesin, or it can be made of a combination of two or more different fluororesins. Similarly, the second fiber 32-f2 can be made of only one type of fluororesin, or it can be made of a combination of two or more different fluororesins.

[0107] The average fiber diameter (first average fiber diameter) of the first fiber 32-f1 is preferably 10 nm or more and 100 nm or less. By making the first average fiber diameter 10 nm or more, the adhesion between the conductive particles 31 becomes stronger, and the detachment of the conductive particles 31 is less likely to occur. In addition, by making the first average fiber diameter 100 nm or less, the first fiber can better bond the conductive particles 31, and therefore the detachment of the bonded conductive particles is less likely to occur.

[0108] The average fiber diameter of the second fiber (second average fiber diameter) is preferably 0.5 μm or more and 50 μm or less. By making the second average fiber diameter 0.5 μm or more, the strength of the gas diffusion layer 3 can be improved more sufficiently. In addition, by making the second average fiber diameter 50 μm or less, it is easy to ensure the number of fibers contained in the gas diffusion layer 3, and the strength of the gas diffusion layer can be improved more efficiently.

[0109] <Content of conductive particles and fluoropolymers in the gas diffusion layer>

[0110] The proportion of conductive particles 31 relative to the overall gas diffusion layer 3 is preferably 60% by mass or more and 95% by mass or less. By making the proportion of conductive particles 31 60% by mass or more, the conductive particles 31 can be sufficiently present in the gas diffusion layer 3, which can further improve the conductivity of the gas diffusion layer 3. In addition, by making the proportion of conductive particles 31 95% by mass or less, the conductive particles 31 can be sufficiently bonded by the fluororesin 32, and the strength of the gas diffusion layer 3 can be further improved by the fluororesin 32.

[0111] The proportion of fluororesin 32 relative to the overall gas diffusion layer 3 is preferably 5% by mass or more and 40% by mass or less. By making the proportion of fluororesin 32 5% by mass or more, the bonding function of the conductive particles 31 is further improved, and the strength of the gas diffusion layer 3 is further improved. In addition, by making the proportion of fluororesin 32 40% by mass or less, the conductive particles 31 are sufficiently present in the gas diffusion layer 3, so the conductivity of the gas diffusion layer 3 is less likely to decrease.

[0112] The proportion of the second fiber 32-f2 relative to the total fluororesin 32 is preferably 10% by mass or more and 90% by mass or less. By making the proportion of fluororesin fibers 32-f2 with a large average fiber diameter in the fluororesin 32 10% by mass or more, the strength of the gas diffusion layer 3 can be further improved. In addition, by making the proportion of fluororesin 32-f2 with a large average fiber diameter 90% by mass or less, the conductive particles 31 can be fully bonded to each other, so the conductive particles 31 are not easy to fall off, and the durability of the gas diffusion layer 3 is further improved.

[0113] <Conductive Fibers>

[0114] The gas diffusion layer 3 preferably further comprises conductive fibers 33. That is, the porous structure 30 constituting the gas diffusion layer 3 preferably further comprises conductive fibers 33. Figure 4A A schematic diagram showing a porous structure 30 containing conductive fibers 33. Figure 4B Indicates will Figure 4A A magnified schematic diagram of a portion of the porous structure 30. By including conductive fibers 33 in the gas diffusion layer 3, the conductivity of the gas diffusion layer 3 can be improved, as can the gas diffusion properties, and the mechanical strength of the gas diffusion layer 3 can be further improved.

[0115] In the case where the porous structure 30 contains conductive fibers 33, such as Figure 4B As shown, the first fiber 32-f1 and the second fiber 32-f2 function not only as adhesives to bond the conductive particles 31 together, but also as adhesives to bond the conductive fibers 33 together. Therefore, even when the gas diffusion layer 3 contains conductive fibers 33, the strength of the gas diffusion layer 3 can be improved by the first fiber 32-f1 and the second fiber 32-f2. Furthermore, the conductive fibers 33 are also fibrous, thus contributing to the improvement of the mechanical strength of the gas diffusion layer 3.

[0116] The material of conductive fiber 33 is not particularly limited; for example, fibers such as carbon nanotubes can be used.

[0117] The average fiber diameter of the conductive fiber 33 is preferably 50 nm or more and 300 nm or less. By making the average fiber diameter of the conductive fiber 33 50 nm or more, the conductivity of the gas diffusion layer 3 can be improved more effectively, and the mechanical strength of the gas diffusion layer 3 can be further improved. In addition, by making the average fiber diameter of the conductive fiber 33 300 nm or less, the diameter will not become too large, so the pore volume in the porous structure 30 can be sufficiently ensured, and the gas diffusion of the gas diffusion layer 3 can be further improved.

[0118] The average fiber length of the conductive fiber 33 is preferably 1 μm or more and 50 μm or less. By making the average fiber length of the conductive fiber 33 1 μm or more, the conductivity of the gas diffusion layer 3 can be improved more effectively, and the mechanical strength of the gas diffusion layer 3 can be further improved. In addition, by making the average fiber length of the conductive fiber 33 50 μm or less, the fiber does not become too long, so the pore volume in the porous structure 30 can be sufficiently ensured, and the gas diffusivity of the gas diffusion layer 3 can be further improved.

[0119] <Concepts involving conductive fibers: Content of conductive particles, conductive fibers, and fluoropolymers in the gas diffusion layer>

[0120] When the gas diffusion layer 3 includes conductive fibers 33, the proportion of conductive particles 31 relative to the total gas diffusion layer 3 is preferably 5% by mass or more. By making the proportion of conductive particles 31 5% by mass or more, sufficient conductive particles 31 are present in the gas diffusion layer 3, which can further improve the conductivity of the gas diffusion layer 3.

[0121] When the gas diffusion layer 3 includes conductive fibers 33, the proportion of conductive fibers 33 relative to the total gas diffusion layer 3 is preferably 90% by mass or less. By making the proportion of conductive fibers 33 90% by mass or less, the conductive fibers 33 can be bonded better using fluororesin 32, thereby further improving the mechanical strength of the gas diffusion layer 3.

[0122] When the gas diffusion layer 3 includes conductive fibers 33, the proportion of fluororesin 32 relative to the total gas diffusion layer 3 is preferably 5% by mass or more and 40% by mass or less. By making the proportion of fluororesin 32 5% by mass or more, the conductive particles 31 and the conductive fibers 33 can be bonded to each other better, and the strength of the gas diffusion layer 3 can be further improved. In addition, by making the proportion of fluororesin 32 40% by mass or less, the ratio of conductive particles 31 to conductive fibers 33 in the gas diffusion layer 3 can be sufficiently ensured, so the gas diffusion layer 3 can have better conductivity. It should be noted that the proportion of the second fiber 32-f2 relative to the total fluororesin 32 is preferably 10% by mass or more and 90% by mass or less.

[0123] <Fluoropolymer Particles>

[0124] The gas diffusion layer 3 preferably further comprises particulate fluororesin (hereinafter also referred to as "fluororesin particles") 32-p. That is, the porous structure 30 constituting the gas diffusion layer 3 preferably further comprises particulate fluororesin 32-p. In other words, the fluororesin 32 preferably contains particulate fluororesin 32-p in addition to the first fiber 32-f1 and the second fiber 32-f2. Figure 5A A schematic diagram showing a porous structure 30 containing fluoropolymer particles 32-p. Figure 5B Indicates will Figure 5A A magnified schematic diagram of a portion of the porous structure 30. It should be noted that... Figure 5A and Figure 5BThe diagram shows a porous structure 30 comprising conductive particles 31, first fibers 32-f1, second fibers 32-f2, conductive fibers 33, and fluoropolymer particles 32-p, but is not limited thereto. For example, the porous structure 30 may also comprise conductive particles 31, first fibers 32-f1, second fibers 32-f2, and fluoropolymer particles 32-p, but without the conductive fibers 33.

[0125] When the gas diffusion layer 3 contains fluoropolymer particles 32-p, in addition to the first fiber 32-f1 that bonds the conductive particles 31 to each other and the conductive fibers 33 to each other to prevent them from falling off, and the second fiber 32-f2 that increases strength, the gas diffusion layer 3 also has particulate fluoropolymer 32-p remaining in particle form. Compared with the fibrous fluoropolymers 32-f1 and 32-f2, it has high hydrophobicity near the particles, so the fluoropolymer particles 32-p can prevent water from being trapped in the pores inside the gas diffusion layer 3 and thus hindering gas permeation.

[0126] The material of the fluororesin particles 32-p is not particularly limited; it can be the same type of fluororesin as either or both of the first fiber 32-f1 and the second fiber 32-f2, or a different type of fluororesin. From the viewpoint of facilitating the manufacture of the gas diffusion layer 3, the first fiber 32-f1, the second fiber 32-f2, and the fluororesin particles 32-p are preferably of the same type of fluororesin. It should be noted that, as the fluororesin particles 32-p, only one type of fluororesin can be used, or two or more different fluororesins can be used in combination.

[0127] The average particle size of the fluoropolymer particles 32-p is preferably 0.1 μm or more and 10 μm or less. Furthermore, both the minor and major axes of the fluoropolymer particles 32-p are preferably within the range of 0.1 μm or more and 10 μm or less. By making the average particle size of the fluoropolymer particles 32-p 0.1 μm or more, manufacturing becomes easier. Additionally, by making the average particle size of the fluoropolymer particles 32-p 10 μm or less, conductivity is less likely to decrease, thus improving the conductivity of the gas diffusion layer 3.

[0128] The proportion of particulate fluororesin 32-p relative to the total fluororesin 32 is preferably 1% by mass or more and 50% by mass or less. By making the proportion of fluororesin particles 32-p 1% by mass or more, the hydrophobicity in the gas diffusion layer 3 can be significantly improved, thus preventing a decrease in air permeability due to water retention. In addition, by making the proportion of fluororesin particles 32-p 50% by mass or less, the first fiber 32-f1 and the second fiber 32-f2 are sufficiently present in the gas diffusion layer 3, which allows for better adhesion between conductive particles 31 and conductive fibers 33, and improves the mechanical strength of the gas diffusion layer 3.

[0129] The tensile breaking strength of the gas diffusion layer 3 is preferably 0.20 N / mm. 2 The above is the result. The tensile breaking strength of the gas diffusion layer 3 is set to 0.20 N / mm. 2 In summary, the gas diffusion layer 3 is less prone to fracture during the swelling and contraction of the polymer electrolyte membrane 1, the pressure of the gas, and the drainage of generated water, thus further improving the durability of MEA20. This tensile strength can be achieved by including the first fiber 32-f1 and the second fiber 32-f2 in the gas diffusion layer 3.

[0130] <Method for Manufacturing Gas Diffusion Layer>

[0131] Next, a method for manufacturing the gas diffusion layer 3 according to Embodiment 1 of this disclosure will be described. The method for manufacturing the gas diffusion layer 3 according to Embodiment 1 of this disclosure includes: a step of mixing conductive particles 31, a first fluororesin having a first average particle size, and a second fluororesin having a second average particle size different from the first average particle size; and a step of calendering the mixed compound to fiberize the first fluororesin and the second fluororesin. The first fluororesin is fiberized to form first fibers 32-f1. The second fluororesin is fiberized to form second fibers 32-f2. Thus, a gas diffusion layer 3 comprising first fibers 32-f1 and second fibers 32-f2 with different average fiber diameters can be obtained.

[0132] Reference Figure 6 The manufacturing method of the gas diffusion layer 3 in Embodiment 1 is described in detail. Figure 6 This is a flowchart of the manufacturing method of the gas diffusion layer 3. It should be noted that the manufacturing method of the gas diffusion layer 3 disclosed herein is not limited to... Figure 6 The flowcharts and manufacturing methods described below may be modified without departing from the spirit of this disclosure.

[0133] (1) In step S1, conductive particles 31, first fluororesin, second fluororesin, surfactant, and dispersing solvent are mixed. First, conductive particles 31 such as carbon materials, conductive fibers 32 such as carbon nanotubes as needed, surfactant, and dispersing solvent are added and stirred and mixed. Then, first fluororesin and second fluororesin are added and stirred and mixed again to obtain a mixture.

[0134] Any material can be used as the first fluoropolymer. For example, a dispersion of fluoropolymer can be used. In this embodiment, a PTFE dispersion is used.

[0135] The average particle size of the first fluororesin (hereinafter also referred to as the first average particle size) is preferably 0.1 μm or more and 0.5 μm or less. In this case, the first fluororesin is fiberized into first fibers 32-f1 with fine fiber diameter in the calendering process described later.

[0136] Any material can be used as the second fluoropolymer. For example, fluoropolymer powder can be used. In this embodiment, fine PTFE powder is used.

[0137] The average particle size of the second fluororesin (hereinafter also referred to as the second average particle size) is preferably 1 μm or more and 1000 μm or less. In this case, the second fluororesin is fiberized into second fibers 32-f2 with a coarse fiber diameter in the calendering process described later.

[0138] In the mixing of materials in step S1, a planetary mixer, a rotary mixer, a kneader, a roller mill, etc., can be used, for example. In step S1, which is a mixing process, the conductive particles 31, conductive fibers 33, surfactants and dispersing solvents are first mixed and dispersed, and then the first fluororesin and the second fluororesin are added and stirred, thereby forming a state in which the fluororesin 32 is uniformly dispersed in the mixture.

[0139] (2) In step S2, the compound is calendered and stretched into sheets. For example, a rolling mill can be used for calendering in step S2. For example, a pressure of 0.001 ton / cm to 4 ton / cm is used as the calendering condition, and calendering is performed once or multiple times, thereby applying shear force to the first and second fluororesins and causing them to become fibrous. At this time, as described above, the fluororesin dispersion with a small average particle size becomes the first fiber 32-f1 with a fine fiber diameter, and the fluororesin powder with a large average particle size becomes the second fiber 32-f2 with a coarse fiber diameter. Thus, fluororesin fibers 32-f1 with a fine fiber diameter and fluororesin fibers 32-f2 with a coarse fiber diameter are formed inside the gas diffusion layer 3 (porous structure 30). Furthermore, by adjusting the pressure and number of calendering cycles, a portion of the first fluororesin in the fluororesin dispersion is not fibrous and remains as fluororesin particles 32-p.

[0140] (3) In step S3, the compound stretched into sheet form is fired to remove surfactant and dispersing solvent from the compound.

[0141] In the firing process of step S3, an IR furnace or a hot air drying furnace can be used, for example. The firing temperature is set to be higher than the temperature at which the surfactant decomposes but lower than the temperature at which the fluoropolymer 32 melts. The reason is as follows: If the firing temperature is lower than the temperature at which the surfactant decomposes, the surfactant remains inside the gas diffusion layer 3, causing the interior of the gas diffusion layer 3 to become hydrophilic, whereby water is easily trapped, and thus the permeability of the gas diffusion layer 3 may decrease. On the other hand, if the firing temperature is higher than the melting point of the fluoropolymer 32, the fluoropolymer 32 melts, and thus the strength of the gas diffusion layer 3 may decrease. Specifically, for example, when using PTFE as the fluoropolymer 32, the firing temperature is preferably 280°C or higher and 340°C or lower.

[0142] (4) In step S4, the sheet-like compound from which the surfactant and dispersing solvent have been removed is re-calendered using a roller press to adjust the thickness. This allows the gas diffusion layer 3 of the embodiments of this disclosure to be manufactured.

[0143] In the recalendering process of step S4, a rolling mill can be used, for example. For example, by performing recalendering once or multiple times under rolling conditions with a pressure of 0.01 ton / cm or more to 4 ton / cm or less, the thickness and porosity of the gas diffusion layer 3 can be adjusted.

[0144] This disclosure is not limited to the above-described embodiments and can be implemented in various other ways.

[0145]

Example

[0146] The embodiments of this disclosure will now be described. The following materials are used, and the following methods are employed for each evaluation.

[0147] [Conductive Particles 31] Acetylene Black (hereinafter referred to as AB) (manufactured by Electrochemical Industry, DENKA BLACK powder), Ketjen Black (hereinafter referred to as KB) (Lion ECP300).

[0148] [Conductive Fiber 33] VGCF (Showa Denko, VGCF-H)

[0149] [Fluoropolymer Dispersion] PTFE dispersion (manufactured by DAIKIN), average particle size 0.25μm

[0150] [Fluoropolymer Powder] PTFE fine powder (manufactured by DAIKIN), average particle size 550μm

[0151] (Manufacturing of the gas diffusion layer in the examples and comparative examples)

[0152] The gas diffusion layers of Examples 1-8 and Comparative Examples 1-4 were manufactured as follows. First, conductive particles, conductive fibers, surfactants, and dispersing solvents were mixed in proportions shown in the raw material column of Table 1 and kneaded using a planetary mixer. Next, fluoropolymer dispersion (first fluoropolymer) and fluoropolymer powder (second fluoropolymer) were added to the kneaded mixture in proportions shown in the raw material column of Table 1, and the mixture was further kneaded using a planetary mixer. Next, the mixture was calendered 5 times at 0.1 ton / cm using a rolling mill. Then, the calendered sheet was placed in an IR furnace and fired at 300°C for 0.5 hours. The fired sheet was then recalendered 3 times at 1 ton / cm using a rolling mill to obtain a gas diffusion layer with a thickness of 100 μm.

[0153] (Evaluation Test)

[0154] In Examples 1-8 and Comparative Examples 1-4, the average fiber diameter of the finer PTFE fibers (first fiber) 32-f1 in the cross-section of the gas diffusion layer, the average fiber diameter of the coarser PTFE fibers (second fiber) 32-f2 in the cross-section of the gas diffusion layer, the average particle size of the PTFE particles (fluoropolymer particles) 32-p in the cross-section of the gas diffusion layer, the tensile breaking strength of the gas diffusion layer, and the contact angle of the gas diffusion layer were measured. The conditions and evaluation results of the raw materials in Examples 1-8 and Comparative Examples 1-4 are shown below. Figure 7 Table 1.

[0155] The average fiber diameters of fibers 32-f1 (first fiber) and 32-f2 (second fiber) were determined using the following method. First, the gas diffusion layer was cut, the cross-section was ground using ion milling, and then a cross-sectional photograph was taken using SEM or an optical microscope. Next, the fiber diameters of fibers 32-f1 and 32-f2 were measured in the cross-sectional photographs, and the average value based on the numerical average was calculated.

[0156] Regarding the average particle size of fluoropolymer particles 32-p, the particle size of the fluoropolymer particles was measured in the cross-sectional photographs taken using the above method, and the average value based on the number average was calculated.

[0157] Regarding tensile breaking strength, the gas diffusion layer was punched into dumbbell-shaped test pieces (dumbbell-shaped No. 4) as specified in JISK 6251 using a Thomson die, and the tensile breaking strength was determined using a tensile compression testing machine (Imada Seisakusho SVZ-200NB type).

[0158] Regarding the contact angle, the static contact angle relative to pure water was measured using a portable contact angle meter (MATSUBO PG-X).

[0159] like Figure 7 As shown in Table 1, it can be confirmed that the gas diffusion layers of Examples 1 to 8, which contain both the first fiber 32-f1 and the second fiber 32-f2, have a higher tensile breaking strength than the gas diffusion layers of Comparative Examples 1 to 4, which do not contain the second fiber.

[0160] It should be noted that this disclosure includes situations where any of the above-described various implementation methods and / or embodiments are appropriately combined, which can achieve the effects of each implementation method and / or embodiment.

[0161] Industrial availability

[0162] The gas diffusion layer disclosed herein is particularly useful as a component used in fuel cells and can be applied to applications such as residential combined heat and power systems, automotive fuel cells, mobile fuel cells, and backup fuel cells.

Claims

1. A gas diffusion layer comprising conductive particles, a first fiber made of fluororesin having a first average fiber diameter, and a second fiber made of fluororesin having a second average fiber diameter larger than the first average fiber diameter. in, The first average fiber diameter is 10 nm or more and 100 nm or less, and the second average fiber diameter is 5 μm or more and 50 μm or less. The first fiber, with its fine diameter, binds the conductive particles together. The tensile breaking strength of the gas diffusion layer is 0.20 N / mm. 2 above.

2. The gas diffusion layer according to claim 1, wherein, The proportion of the second fiber relative to the total fluororesin is more than 10% by mass and less than 90% by mass.

3. The gas diffusion layer according to claim 1, further comprising conductive fibers.

4. The gas diffusion layer according to claim 1, wherein, The fluororesin contains particulate fluororesin.

5. The gas diffusion layer according to claim 4, wherein, The average particle size of the fluoropolymer is greater than 0.1 μm and less than 10 μm.

6. The gas diffusion layer according to claim 4, wherein, The proportion of the particulate fluororesin relative to the total fluororesin is more than 1% by mass and less than 50% by mass.

7. The gas diffusion layer according to any one of claims 1 to 6, wherein, The gas diffusion layer has a porous structure formed by the conductive particles and the fluororesin.

8. The gas diffusion layer according to any one of claims 1 to 6, wherein the gas diffusion layer is a self-supporting membrane supported by the conductive particles and the fluororesin.

9. The gas diffusion layer according to any one of claims 1 to 6, wherein, The fluororesin contains PTFE, i.e., polytetrafluoroethylene.

10. A membrane electrode assembly comprising: Gas diffusion layer according to any one of claims 1 to 9; A pair of electrodes; and Electrolyte membrane.

11. A fuel cell, comprising: The gas diffusion layer according to any one of claims 1 to 9; and Current collector.

12. A method for manufacturing the gas diffusion layer according to claim 1, comprising: The step of mixing conductive particles, a first fluororesin having a first average particle size, and a second fluororesin having a second average particle size that is coarser than the first average particle size. as well as The step of calendering the compound obtained by the compounding process to fiberize the first fluororesin and the second fluororesin is as follows: The first average particle size is greater than 0.1 μm and less than 0.5 μm, and the second average particle size is greater than 1 μm and less than 1000 μm.

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