Conductive fiber sheet, gas diffusion layer for fuel cell, and membrane electrode assembly

Abstract

Provided is a conductive fiber sheet that exhibits excellent conductivity without carbonization treatment and is suitable for use as a constituent member of a gas diffusion layer in a fuel cell. One aspect of the present disclosure is a conductive fiber sheet. The conductive fiber sheet comprises an inorganic component containing conductive fibers and conductive particles, and an organic component. The conductive fiber sheet satisfies the following conditions i) and ii). i) The porosity of the conductive fiber sheet, as measured by a prescribed measurement method, is 25-60%. ii) Among the pores forming the voids of the conductive fiber sheet, as measured by a prescribed measurement method, the ratio (specific pore ratio) of pores having a diameter of 10-30 μm is 50 volume% or more.

Description

Conductive fiber sheet, gas diffusion layer for fuel cell, and membrane electrode composite

[0001] The present invention relates to a conductive fiber sheet, a gas diffusion layer for fuel cells, and a membrane electrode composite.

[0002] Fuel cells are widely used as power sources for automobiles and other applications. Fuel cells typically utilize electrode components that include a catalyst layer and a gas diffusion layer in contact with the catalyst layer. This gas diffusion layer is a porous layer that serves as an electrode substrate, homogenizes the gas reaching the catalyst layer, and promotes the discharge of excess moisture within the system. Improving the performance of the gas diffusion layer is therefore crucial for improving fuel cell performance. Consequently, much research has been conducted to enhance the performance of the gas diffusion layer.

[0003] Gas diffusion layers are typically formed using conductive fiber sheets. For example, Patent Document 1 discloses a method for forming a gas diffusion layer, which includes steps such as impregnating a carbon fiber sheet with a resin component and carbonizing it as needed to obtain a porous electrode substrate, performing a predetermined process on the porous electrode substrate, and then applying a coating layer containing a water repellent or conductive material after the porous electrode substrate has undergone a predetermined treatment.

[0004] Japanese Patent Publication No. 2018-85332

[0005] In conventional gas diffusion layers, conductive pathways are typically formed by carbonizing a conductive fiber sheet impregnated with a resin component (e.g., phenolic resin). Therefore, without carbonization, it was difficult to obtain sufficient conductivity. On the other hand, carbonization resulted in a rigid structure in the gas diffusion layer, making it susceptible to bending and potentially damaging it when incorporated into a battery.

[0006] Therefore, the present invention aims to provide a conductive fiber sheet that exhibits excellent conductivity without carbonization treatment and is suitable for use as a component of the gas diffusion layer in fuel cells.

[0007] The inventors have discovered that the above problems can be solved by a conductive fiber sheet having a specific configuration, and have completed the present invention. That is, the present invention is as follows.

[0008] One embodiment of the present invention is a conductive fiber sheet comprising an inorganic component containing conductive fibers and conductive particles, and an organic component. The conductive fiber sheet satisfies the following conditions i) and ii). i) The porosity of the conductive fiber sheet is 25 to 60% when measured by the measurement method described below. ii) The proportion of pores with a diameter of 10 μm or more and 30 μm or less (specific pore ratio) in the pores forming the voids of the conductive fiber sheet is 50 volume% or more when measured by the measurement method described below. (Measurement method) A 1 cm × 1 cm conductive fiber sheet is used as the measurement sample. The measurement sample is measured using an X-ray CT scanner (manufactured by BRUKER) with a resolution of 0.98 μm / pixel. The porosity is calculated using the Basic Value in 3D analysis (3D analysis) with analysis software (product name: CTAn, manufactured by BRUKER). Using the same analysis software, the relative abundance of each pore size is calculated, and for all pores, the proportion of pores with a diameter of 10 μm or more and 30 μm or less that occupy the void (specific pore ratio, volume %) is determined. The analysis range is a cylindrical shape of φ2 mm × 500 μm. Two analyses are performed on each measurement sample, and the average values ​​are calculated as the porosity and specific pore ratio.

[0009] The organic component preferably includes one or more selected from the group consisting of polyolefins, silicones, and non-fluorinated water-repellent resins.

[0010] When measured using the measurement method described below, the variation in the mass loss rate of the conductive fiber sheet is preferably 0.15 or less in terms of the coefficient of variation. (Measurement method) A conductive fiber sheet with a width of 25 cm and a length of 5 cm is used as the measurement sample (N=5). The measurement sample is left to dry in a constant temperature bath at 130°C for 10 minutes, and the mass of the measurement sample (X) after drying is measured. The measurement sample after drying is heated in an electric heating furnace at 450°C for 120 minutes, left in a desiccator for 10 minutes, and the mass of the measurement sample (Y) after heating is measured. The mass loss rate is calculated as [100 × (X - Y) / X]. The mass loss rate is measured 5 times, the average value and standard deviation of the mass loss rate are calculated, and the coefficient of variation of the mass loss rate is calculated as [standard deviation of mass loss rate / average value of mass loss rate].

[0011] The ratio of the total mass of the conductive fibers and conductive particles to the mass of the organic component in the conductive fiber sheet is preferably 1.0 to 3.0. The average fiber length of the conductive fibers is preferably 3 to 9 mm. The conductive fibers preferably include carbon fibers. At least a portion of the conductive particles is preferably carbon black. The degree of graphitization of the carbon black is preferably 1.00 or higher. The organic component includes organic fibers, and at least a portion of the organic fibers has fibrilized fibril regions, and the inorganic component is preferably held within the fibril regions.

[0012] Another embodiment of the present invention is a gas diffusion layer for a fuel cell, wherein a microporous layer is laminated on the surface of the conductive fiber sheet.

[0013] A further embodiment of the present invention is a membrane electrode composite comprising an electrolyte membrane formed of a solid polymer electrolyte, a fuel electrode laminated on one side of the electrolyte membrane, and an air electrode laminated on the other side of the electrolyte membrane, wherein the fuel electrode comprises a first catalyst layer in contact with the electrolyte membrane and a first gas diffusion layer laminated on the first catalyst layer, and the air electrode comprises a second catalyst layer in contact with the electrolyte membrane and a second gas diffusion layer laminated on the second catalyst layer, and at least one of the first gas diffusion layer and the second gas diffusion layer is the fuel cell gas diffusion layer.

[0014] According to the present invention, a conductive fiber sheet is provided that exhibits excellent conductivity without carbonization treatment and is suitable for use as a component of the gas diffusion layer in a fuel cell.

[0015] Figure 1 is a conceptual diagram of a gas diffusion layer for a fuel cell according to this disclosure. Figure 2 is a conceptual diagram of a membrane electrode composite according to this disclosure.

[0016] In the following, if the upper and lower limits are listed separately, it shall be assumed that a numerical range is substantially disclosed by combining any upper and lower limit.

[0017] In the following, unless otherwise specified, all measurements will be conducted at room temperature (23°C).

[0018] The composition, structure / properties, manufacturing method, and applications / usage methods of the conductive fiber sheet relating to this disclosure will be described below, but the present invention is not limited to the following.

[0019] <<Composition>> The conductive fiber sheet according to this disclosure contains conductive fibers and conductive particles as inorganic components, and further contains organic components. The conductive fiber sheet according to this disclosure may also contain other components. The following describes each component.

[0020] Conductive fibers are conductive materials that can generally be considered fibrous and can constitute the sheet framework of a conductive fiber sheet. Preferably, the conductive fibers are conductive materials with a fiber length (average fiber length) of 0.5 mm or more and an aspect ratio of 15.0 or more.

[0021] <Conductive Fibers> Conductive fibers are preferably metal fibers (fibers composed of metal or alloy) or carbon fibers, and more preferably carbon fibers. Using carbon fibers as conductive fibers makes it easier to form conductive fiber sheets with excellent durability, conductivity, flexibility, etc. Examples of metals or alloys that make up metal fibers include stainless steel, aluminum, copper, lead, nickel, etc.

[0022] The average fiber length of the conductive fibers is not particularly limited. Preferably, the average fiber length of the conductive fibers is 0.5 mm or more, 0.8 mm or more, 1 mm or more, or 3 mm or more, and preferably 100 mm or less, 50 mm or less, 15 mm or less, or 9 mm or less. By setting the average fiber length of the conductive fibers within this range, the electrical properties of the conductive fiber sheet can be improved, and a uniform conductive fiber sheet with good form can be produced, making it easier to form a conductive fiber sheet with excellent strength.

[0023] The average fiber length and average fiber diameter of the conductive fibers were calculated by measuring the fiber length and fiber diameter of 50 carbon fibers constituting the conductive fiber sheet using visual inspection or an optical microscope, and then averaging these values.

[0024] The conductive fiber content, based on the total amount of the conductive fiber sheet, is preferably 10% by mass or more, 15% by mass or more, or 20% by mass or more, and also preferably 60% by mass or less, 50% by mass or less, or 40% by mass or less.

[0025] <Conductive Particles> Conductive particles are not particularly limited as long as they are conductive. Furthermore, the shape of the conductive particles is not particularly limited. Examples of conductive particle shapes include spherical, plate-shaped, linear, flake-shaped, and flaky shapes.

[0026] Examples of materials for conductive particles include metallic materials such as gold, silver, copper, nickel, tin, lead, zinc, bismuth, and alloys thereof, as well as carbon-based materials such as carbon black, graphite, carbon nanotubes, and fullerenes.

[0027] It is preferable that the conductive particles contain carbon black (at least a portion of the conductive particles are carbon black). By including carbon black as conductive particles, the electrical resistance in the thickness direction of the conductive fiber sheet can be reduced, while the specific surface area of ​​the conductive fiber sheet can be improved, thereby improving water repellency.

[0028] The average particle size of the conductive particles is preferably 1 μm or more, 3 μm or more, or 8 μm or more, and also preferably 100 μm or less, 50 μm or less, or 20 μm or less. The average particle size of the conductive particles is calculated by measuring the particle diameters of 50 conductive particles constituting the conductive fiber sheet using an optical microscope or electron microscope and taking the average value. The aspect ratio of the conductive particles is not particularly limited, but is preferably less than 5.0 or less than 3.0.

[0029] When conductive particles contain carbon black, the degree of graphitization of the carbon black is preferably 0.90 or higher, or 1.00 or higher. By using carbon black with a degree of graphitization within this range, the aforementioned effects can be further enhanced. The degree of graphitization is measured based on the following measurement method.

[0030] (Measurement Method) Using a laser Raman spectrophotometer, measure the peak intensities of the G-band derived from the graphite structure and the D-band derived from graphite defects from the Raman spectrum, and define the ratio thereof (D / G) as the degree of graphitization (R value).

[0031] The content of conductive particles based on the total mass of the conductive fiber sheet is preferably 10% by mass or more, 15% by mass or more, or 20% by mass or more, and is preferably 70% by mass or less, 60% by mass or less, or 50% by mass or less.

[0032] In the conductive fiber sheet, the ratio of the content of conductive particles to the content of conductive fibers (conductive particles / conductive fibers) is preferably 0.2 or more, 0.4 or more, or 0.6 or more, and is preferably 5.0 or less, 2.5 or less, or 1.5 or less.

[0033] <Organic Component> The organic component may be a fibrous organic component (organic fiber), a non-fibrous organic component, or may include both.

[0034] The organic fiber may be a synthetic fiber or a natural fiber. Examples of materials constituting synthetic fibers include olefin resins such as polyethylene, polypropylene and cycloolefin polymer (COP resin), acrylic resins, fluorine resins, polyimide resins, polyamide resins such as aramid, and polyester resins.

[0035] The organic fiber is preferably a fibrillated fiber. When fibrillated organic fibers are used, inorganic components such as conductive particles are easily retained in the conductive fiber sheet. In other words, by using fibrillated organic fibers, a fibril region (a region where fine fluffing is present) is formed as a part of the organic fibers, and conductive particles and the like can be retained in this fibril region. As a result, a conductive fiber sheet having excellent performance can be formed.

[0036] Note that the fibrillation of fibers described herein refers to subjecting fibers to fibrillation treatment (treatment to fluff the fibers).

[0037] The method for fibrillating the fibers is not particularly limited, but it can be carried out using beating machines such as SDRs, DDRs, and beaters.

[0038] In organic fibers, the degree of beating is preferably 400 CSF or less, 200 CSF or less, or 100 CSF or less, as measured by the water filtration rate (according to JIS P 8121, the Canadian standard for water filtration rate). By setting the degree of beating within this range, inorganic components such as conductive particles are more easily retained within the conductive fiber sheet.

[0039] When the organic component includes organic fibers, the organic fiber content relative to the total amount of organic components is preferably 1% by mass or more, 2% by mass or more, 5% by mass or more, or 10% by mass or more, and also preferably 50% by mass or less, 45% by mass or less, or 40% by mass or less.

[0040] The organic components other than the aforementioned organic fibers are not particularly limited, but are preferably components that can provide water repellency. More specifically, the organic components (e.g., non-fibrous organic components) preferably contain one or more selected from polyolefins, silicones, and non-fluorinated water-repellent resins, and preferably contain polyolefins. By including such organic components, the water repellency, flexibility, strength, etc. of the resulting conductive fiber sheet can be improved. The non-fluorinated water-repellent resin is a non-fluorinated resin component (e.g., bismaleimide resin) to which a water-repellent component has been added.

[0041] In a conductive fiber sheet, the ratio of the total mass of conductive fibers and conductive particles to the mass of organic components is preferably 0.5 or more, 0.8 or more, or 1.0 or more, and also preferably 4.0 or less, 3.5 or less, or 3.0 or less. By setting the ratio of organic components to predetermined inorganic components within these ranges, it is easier to form a conductive fiber sheet with excellent electrical properties, water repellency, and strength.

[0042] From another perspective, the content of organic components in the conductive fiber sheet is preferably 20% by mass or more, 25% by mass or more, or 30% by mass or more, and also preferably 60% by mass or less, 55% by mass or less, or 50% by mass or less.

[0043] <Other ingredients> Other ingredients include surfactants, dispersants, thickeners, defoamers, flocculants, and inorganic binders.

[0044] The content of other components is 30% by mass or less, 20% by mass or less, 10% by mass or less, 5% by mass or less, or 3% by mass or less, when the entire conductive fiber sheet is considered to be 100% by mass.

[0045] <<Structure / Physical Properties>> <Porrosion and Specific Pore Ratio> The conductive fiber sheet according to this disclosure preferably satisfies the following conditions i) and ii). i) The porosity of the conductive fiber sheet, when measured by the measurement method described below, is 25 to 60%. ii) The proportion of pores with a diameter of 10 μm or more and 30 μm or less (specific pore ratio), when measured by the measurement method described below, is 50 volume% or more.

[0046] (Measurement Method) A 1 cm x 1 cm conductive fiber sheet is used as the measurement sample. The measurement sample is measured using an X-ray CT scanner (manufactured by BRUKER) at a resolution of 0.98 μm / pixel. The porosity is calculated using the Basic Value in 3D analysis (3D analysis) with analysis software (product name: CTAn, manufactured by BRUKER). The relative abundance of each pore size is calculated using the same analysis software, and the percentage of the void occupied by pores with a diameter of 10 μm or more and 30 μm or less (specific pore ratio, volume %) is determined for all pores. The analysis range is a cylindrical shape of φ2 mm x 500 μm. Two analyses are performed for each measurement sample, and the average values ​​are calculated as the porosity and specific pore ratio.

[0047] By setting the pores and void ratio of the conductive fiber sheet within this range, the voids formed in the conductive fiber sheet become appropriate, ensuring sufficient conductive fibers and conductive particles within the sheet while maintaining excellent flexibility, thereby improving the electrical properties of the conductive fiber sheet. Furthermore, it facilitates the removal of water when applied as a gas diffusion layer.

[0048] The porosity and void ratio of conductive fiber sheets can be adjusted by changing the proportions of conductive fibers, conductive particles, and organic components (organic fibers and non-fibrous organic components). More specifically, increasing the proportion of conductive fibers and organic fibers tends to improve the void ratio. Additionally, increasing the fiber length of conductive fibers and organic fibers also tends to improve the void ratio.

[0049] <Variation in Mass Loss Rate> The conductive fiber sheet according to this disclosure preferably has a coefficient of variation of 0.25 or less, 0.20 or less, or 0.15 or less when measured by the measurement method described below.

[0050] (Measurement Method) Conductive fiber sheets measuring 25 cm wide x 5 cm long are used as measurement samples (N=5). The measurement samples are left to dry in a constant temperature bath at 130°C for 10 minutes, and the mass of the measurement sample after drying (X) is measured. The measurement samples after drying are heated in an electric furnace at 450°C for 120 minutes, left in a desiccator for 10 minutes, and the mass of the measurement sample after heating (Y) is measured. The mass loss rate is calculated as [100 × (X - Y) / X]. The mass loss rate is measured five times, and the mean and standard deviation of the mass loss rate are calculated, and the coefficient of variation of the mass loss rate is calculated as [standard deviation of mass loss rate / mean of mass loss rate].

[0051] The variation in the mass loss rate within this range allows for the formation of conductive fiber sheets with excellent electrical properties and water repellency.

[0052] <Thickness> The thickness of the conductive fiber sheet is preferably 50 μm or more, 75 μm or more, or 100 μm or more, and preferably 1000 μm or less, 500 μm or less, or 250 μm or less. A 25 cm square conductive fiber sheet is used as the measurement sample, and eight points around the measurement sample are measured with a micrometer, and the average value is taken as the thickness.

[0053] <Basis Weight> The basis weight of the conductive fiber sheet is 10 g / m². ２ Above, 20g / m ２ Above, or 40 g / m² ２ Preferably, it should be 120 g / m² or more. ２ Below, 100g / m２ or 80 g / m ２ It is preferably not more than the above value. A 25 cm square conductive fiber sheet is used as a measurement sample. After drying the measurement sample at 130°C for 10 minutes, the mass is measured, and the basis weight is obtained by dividing the mass of the measurement sample by the area of the measurement sample (25 cm × 25 cm).

[0054] <Density> The density of the conductive fiber sheet is 0.20 g / cm ３ or more, 0.30 g / cm ３ , or 0.35 g / cm ３ or more, and preferably 0.70 g / cm ３ or less, 0.60 g / cm ３ or less, or 0.55 g / cm ３ or less. The density is calculated from the aforementioned thickness and basis weight of the conductive fiber sheet.

[0055] <<Manufacturing Method>> Hereinafter, an example of a method for manufacturing the conductive fiber sheet according to the present disclosure will be described.

[0056] The conductive fiber sheet according to the present disclosure can be manufactured by wet papermaking. More specifically, the conductive fiber sheet according to the present disclosure can be obtained by performing a raw material preparation step, a papermaking step, and a drying step. Each step will be described below.

[0057] <Raw Material Preparation Step> Each raw material (carbon fibers, conductive particles, organic components, other components, liquid medium, etc.) is uniformly dispersed to prepare a raw material slurry. The carbon fibers, conductive particles, organic components, and other components are as described above.

[0058] The liquid medium is usually water. The liquid medium may be a liquid medium other than water that can be used for papermaking (for example, an aqueous medium such as alcohol), or a mixture of water and a liquid medium other than water. The solid content concentration in the raw material slurry may be appropriately set in consideration of manufacturing ease, manufacturing cost, etc., and is not particularly limited.

[0059] <Papermaking Step> The raw material slurry is subjected to papermaking using a known paper machine to form a moisture-containing fiber sheet (wet sheet).

[0060] The paper machines used in the papermaking process are not particularly limited and can be any paper machines applicable to general papermaking techniques. Examples of paper machines include long-wire paper machines, short-wire paper machines, cylinder paper machines, inclined paper machines, twin-wire paper machines, and combination paper machines which combine the same or different types of paper machines from among these.

[0061] Here, by controlling the average diameter of the conductive fibers used during the papermaking process and the stirring conditions during slurry supply, variations in concentration and pressure are eliminated, and structural variations in the conductive fiber sheet are reduced.

[0062] <Drying Process> The moisture contained in the wet sheet is dried to form a conductive fiber sheet.

[0063] The drying equipment used in the drying process is not particularly limited and can be any equipment that is generally used for drying conductive fiber sheets. Examples of drying equipment include Yankee dryers, rotary dryers, hand dryers, air dryers, cylinder dryers, suction drum dryers, and infrared dryers.

[0064] The drying temperature is not particularly limited and can be 100 to 300°C, for example.

[0065] The drying time is not particularly limited and can be adjusted so that the moisture content in the wet sheet is sufficiently low.

[0066] <<Applications>> The conductive fiber sheet according to this disclosure can be used for various applications. The conductive fiber sheet according to this disclosure is preferably used as a material constituting an electrode material. The conductive fiber sheet according to this disclosure can also be used in electrolytic devices, etc., but is particularly preferably used for gas diffusion layers in fuel cells. That is, the conductive fiber sheet according to this disclosure is preferably used as a conductive fiber sheet for forming a gas diffusion layer in a fuel cell. In particular, the conductive fiber sheet according to this disclosure can have sufficient electrical properties even in its unfired state. Furthermore, by applying it to the gas diffusion layer in a fuel cell in its unfired state, flexibility is maintained, resulting in less damage when incorporated into a battery. The conductive fiber sheet according to this disclosure is preferably used, for example, as a component of a membrane electrode composite that constitutes a fuel cell. In other words, the technology according to this disclosure may be provided as a fuel cell or fuel cell stack comprising a membrane electrode composite including a conductive fiber sheet. This fuel cell or fuel cell stack may be incorporated into an automobile as a power source.

[0067] Next, a specific example of a gas diffusion layer for a fuel cell including a conductive fiber sheet according to this disclosure will be described.

[0068] <Gas Diffusion Layer A for Fuel Cells> As shown in Figure 1, the gas diffusion layer A for fuel cells according to this disclosure is a laminate having a conductive fiber sheet A1 and a microporous layer A2 laminated on the surface of the conductive fiber sheet.

[0069] The conductive fiber sheet A1 has the function of uniformly diffusing the gas introduced into the gas diffusion layer 1 and stabilizing the gas reaction (catalytic reaction) in fuel cells and the like.

[0070] The specific composition of the conductive fiber sheet A1 is as described above, so we will omit further explanation.

[0071] The microporous layer A2 is a layer formed from a porous material and serves to discharge water or water vapor, which are by-products generated by reactions within the fuel cell.

[0072] While conventionally known materials may be used as the microporous layer A2, it is preferable that it be a mixture of a binder resin and conductive particles.

[0073] The binder resin and conductive particles can be those described in the section on conductive fiber sheets.

[0074] The binder resin is preferably an olefin-based resin. Furthermore, the conductive particles are preferably carbon black. Using these components makes it easier to form a fuel cell gas diffusion layer with excellent strength and conductivity.

[0075] When the entire microporous layer A2 is considered to be 100% by mass, the binder resin content is preferably 10 to 50% by mass, 15 to 45% by mass, or 20 to 40% by mass.

[0076] When the entire microporous layer A2 is considered to be 100% by mass, the content of conductive particles is preferably 50 to 90% by mass, 55 to 85% by mass, or 60 to 80% by mass.

[0077] A laminate comprising a conductive fiber sheet A1 and a microporous layer A2 can be manufactured, for example, by the following method.

[0078] A conductive fiber sheet A1 is manufactured according to the method described above. Next, a slurry is prepared in which conductive particles and a binder resin are uniformly dispersed in an organic solvent. The organic solvent is not particularly limited as long as it can dissolve the binder resin. The amount of organic solvent may be adjusted as appropriate so that the viscosity is such that the coating method described later can be easily carried out. Next, the slurry containing the conductive particles and the binder resin is coated onto the conductive fiber sheet A1. The coating method may include, for example, a method using a coating machine such as a dam, lip, die, or bar. The amount of slurry coated (coating thickness) may be adjusted as appropriate so that the desired thickness is achieved after drying. The conductive fiber sheet A1 coated with the slurry is heated to dry the organic solvent contained in the slurry and form a microporous layer A2.

[0079] As described above, a laminate having a conductive fiber sheet A1 and a microporous layer A2 laminated on the conductive fiber sheet A1 can be manufactured.

[0080] Furthermore, the drying process for the conductive fiber sheet A1 and the drying process for the microporous layer A2 may be carried out simultaneously by applying the slurry for forming the microporous layer A2 to the conductive fiber sheet A1 while it is still containing moisture (or in the state of a wet sheet, which is a precursor to the conductive fiber sheet A1) before the drying process is completed in the manufacturing method of the conductive fiber sheet A1, and then carrying out the drying process.

[0081] The thickness of the microporous layer A2 is not particularly limited, but is, for example, 5 to 50 μm.

[0082] Next, a membrane electrode composite including a gas diffusion layer A (or conductive fiber sheet A1) for fuel cells according to this disclosure will be described.

[0083] <Membrane electrode composite 100> As shown in Figure 2, the membrane electrode composite 100 according to the present disclosure comprises at least an electrolyte membrane 30 formed of a solid polymer electrolyte, a fuel electrode 10 laminated on one main surface of the electrolyte membrane 30, and an air electrode 20 laminated on the other main surface of the electrolyte membrane 30 (the main surface opposite to the main surface on which the fuel electrode 10 is laminated).

[0084] The fuel electrode 10 comprises a first catalyst layer 11 in contact with the electrolyte membrane 30 and a first gas diffusion layer 12 laminated on the first catalyst layer 11.

[0085] The air electrode 20 comprises a second catalyst layer 21 in contact with the electrolyte membrane 30 and a second gas diffusion layer 22 laminated on the second catalyst layer 21.

[0086] Preferably, at least one of the first gas diffusion layer 12 and the second gas diffusion layer 22 is made of the fuel cell gas diffusion layer A according to this disclosure (a gas diffusion layer including a conductive fiber sheet A1 and a microporous layer A2 according to this disclosure). Alternatively, both the first gas diffusion layer 12 and the second gas diffusion layer 22 may be made of the fuel cell gas diffusion layer A according to this disclosure. If the gas diffusion layer is to be a gas diffusion layer other than the fuel cell gas diffusion layer A according to this disclosure, a conventionally known gas diffusion layer (a gas diffusion layer made of a conductive porous material) can be used.

[0087] In this example, both the first gas diffusion layer 12 and the second gas diffusion layer 22 are gas diffusion layers A for fuel cells according to the present disclosure. In this case, as shown in Figure 2, the first gas diffusion layer 12 is laminated such that the microporous layer A2 side is in contact with the first catalyst layer. Similarly, the second gas diffusion layer 22 is laminated such that the microporous layer A2 side is in contact with the second catalyst layer.

[0088] The first catalyst layer 11 and the second catalyst layer 21 can be conventionally known catalyst layers.

[0089] The catalyst layer is preferably a porous layer composed of a catalyst, and more preferably a porous layer formed of granular catalyst material.

[0090] Examples of catalytic materials include metallic materials such as platinum, palladium, ruthenium, iridium, rhodium, osmium, iron, lead, copper, chromium, cobalt, nickel, manganese, vanadium, molybdenum, gallium, and aluminum. The catalytic material may also be an alloy or oxide of these materials.

[0091] Furthermore, the catalyst material is preferably catalyst particles on which a carbon material is supported.

[0092] Examples of carbon materials include carbon black, graphite, carbon nanotubes, and fullerenes.

[0093] The shape and particle size of the catalyst material, as well as the porosity of the catalyst layer (the packing density of the catalyst material or the porosity of the catalyst layer), can be freely modified as appropriate according to the usage conditions.

[0094] The electrolyte membrane 30 is not particularly limited, but examples include solid polymer electrolyte membranes such as fluorine-based electrolyte membranes and hydrocarbon-based electrolyte membranes.

[0095] The electrolyte membrane 30 may be an oxygen ion conductor or a hydrogen ion conductor.

[0096] Furthermore, as shown in Figure 2, it is preferable that the membrane electrode composite 100 has a first separator 41 on the opposite side of the fuel electrode 10 from the side on which the electrolyte membrane 30 is laminated (in Figure 2, the side of the fuel electrode 10 on the conductive fiber sheet A1). Furthermore, it is preferable that the membrane electrode composite 100 has a second separator 42 on the opposite side of the air electrode 20 from the side on which the electrolyte membrane 30 is laminated (in Figure 2, the side of the air electrode 20 on the conductive fiber sheet A1).

[0097] The first separator 41 and the second separator 42 can be conventionally known separators.

[0098] The first separator 41 is a flat plate-shaped member. Although not shown in the figure, the main surface of the first separator 41 facing the fuel electrode 10 is provided with multiple grooves. These grooves serve as flow paths that can guide gas (hydrogen-containing gas) into the membrane electrode composite 100.

[0099] Similarly, the second separator 42 is a flat plate-shaped member. Although not shown in the figures, the main surface of the second separator 42 facing the air electrode 20 is provided with multiple grooves. These grooves serve as flow channels that can guide gas (oxygen-containing gas) into the membrane electrode composite 100.

[0100] Furthermore, the first separator 41 and the second separator 42 serve to shield the entire membrane electrode complex 100.

[0101] In a fuel cell using the membrane electrode composite 100 shown in Figure 2, the reaction occurs as follows: Hydrogen is guided to the first gas diffusion layer 12 through grooves provided in the first separator 41. The hydrogen introduced into the first gas diffusion layer 12 is homogenized in the planar direction and reaches the first catalyst layer 11. Similarly, oxygen is introduced into the second gas diffusion layer 22 through grooves provided in the second separator 42. The oxygen introduced into the second gas diffusion layer 22 is homogenized in the planar direction and reaches the second catalyst layer 21. When the electrolyte membrane 30 is a hydrogen ion conductor, hydrogen ions and electrons are generated from hydrogen in the first catalyst layer 11. The generated hydrogen ions pass through the electrolyte membrane 30 to the second catalyst layer 21, where the hydrogen ions, oxygen, and electrons react to produce water. This water is discharged to the outside, for example, by passing through the microporous layer A2 in contact with the second catalyst layer 21. When the electrolyte membrane 30 is an oxygen ion conductor, oxygen ions are generated from oxygen and electrons in the second catalyst layer 21. The generated oxygen ions pass through the electrolyte membrane 30 to the first catalyst layer 11, where hydrogen and oxygen ions react to produce water and electrons. This water is then discharged to the outside, for example, by passing through the microporous layer A2 in contact with the first catalyst layer 11.

[0102] When the membrane electrode composite 100 according to this disclosure is incorporated into a fuel cell, the fuel cell may further include other components such as a current collector, a gas supply device, a cooling device, and an outer casing. Furthermore, a cell stack may be formed by stacking multiple membrane electrode composites 100.

[0103] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to the following.

[0104] <<Example 1>> Conductive fibers, conductive particles, and organic components were mixed and water was added to prepare a raw material slurry so that the content of each component in the resulting conductive fiber sheet would be in the proportions shown in Table 1.

[0105] Using an inclined paper machine, paper sheets were formed from raw material slurry so that the thickness, basis weight, and density of the resulting conductive fiber sheets were as shown in Table 1.

[0106] The papermaking sheet was dried using a Yankee dryer to obtain the conductive fiber sheet according to Example 1.

[0107] <<Example 2-28, Comparative Example 1-3>> Conductive fiber sheets according to Example 2-28 and Comparative Example 1-3 were obtained in the same manner as in Example 1, except that the raw materials used were changed to those shown in Table 1-3.

[0108] In the production of the conductive fiber sheets in each example and comparative example, either condition (A) or condition (B) below was adopted as the condition for preparing the raw material slurry. The stirring conditions adopted in each example and comparative example are shown in Table 1-3. (A) After adding 1% by mass of dispersant to the conductive fibers, the mixture is stirred at 3000 rpm in a homogenizer. (B) After adding 1% by mass of dispersant to the conductive fibers, the mixture is stirred at 500 to 1000 rpm in a homogenizer.

[0109] We confirmed that by using fibrillated fibers, a structure can be obtained in which inorganic components (such as conductive particles) are retained within the fibril region of the organic fiber.

[0110] <<Measurement / Evaluation>> For each example and comparative example of conductive fiber sheet, the porosity, specific pore ratio, and mass loss rate were measured based on the method described above. The measurement results are shown in Table 1-3.

[0111] <Resistance to wrapping> The resistance to wrapping was evaluated for the conductive fiber sheets of each example and comparative example based on the following measurement method and evaluation criteria. The evaluation results are shown in Table 1-3.

[0112] (Measurement Method) A measurement sample measuring 15 mm in width and 110 mm in length was prepared. A cylinder of φ15 mm and a cylinder of φ25 mm were prepared, and the measurement sample was wrapped around the cylinder. A sample was deemed acceptable if there was no lifting when the measurement sample was wrapped around the cylinder and no defects (bends, cracks, breaks, etc.) occurred in the measurement sample. A sample was deemed unacceptable if lifting occurred and / or defects occurred in the measurement sample, and was evaluated based on the following criteria.

[0113] (Evaluation Criteria) A: Passes for the φ15mm cylinder. B: Fails for the φ15mm cylinder, but passes for the φ25mm cylinder. C: Fails for both the φ15mm and φ25mm cylinders.

[0114] For reference, a conventional fired product was evaluated for its resistance to wrapping, and it received a rating of C.

[0115] <Conductivity (Inter-cell Resistance)> The conductivity of the conductive fiber sheets for each example and comparative example was evaluated based on the following measurement method and evaluation criteria. The evaluation results are shown in Table 1-3.

[0116] (Measurement Method) Prepare a 20 mm square measurement sample. Clamp the measurement sample between electrode plates, tighten with a bolt to a torque of 1 Nm, and measure the resistance value at a measurement frequency of 10 kHz using an LCR meter ZM2376 (manufactured by NF Circuit Design Block Co., Ltd.). Measure the resistance value for four measurement samples and perform an evaluation based on the average value.

[0117] (Evaluation Criteria) A: Less than 1.50 mΩ B: 1.50 mΩ or more and less than 2.00 mΩ C: 2.00 mΩ or more and less than 3.00 mΩ D: 3.00 mΩ or more

[0118] <Water Repellency (Gas Adsorption Characteristics)> The water repellency of the conductive fiber sheets in each example and comparative example was evaluated based on the following measurement method and evaluation criteria. The evaluation results are shown in Table 1-3.

[0119] (Measurement Method) Nitrogen adsorption and water vapor adsorption measurements of the sample are performed using a gas adsorption apparatus. BET method analysis is performed on each adsorption isotherm to calculate the specific surface area value. The specific surface area value obtained from the water vapor adsorption measurement is divided by the specific surface area value obtained from the nitrogen adsorption measurement [BET(H ２ O) / BET(N ２ The following criteria are used to calculate and evaluate the following:

[0120] (Evaluation criteria) A: [BET(H ２ O) / BET(N ２ ) ] is 0.6 or less B: [BET(H ２ O) / BET(N ２) ] is greater than 0.6 and less than or equal to 1.0 C: [BET(H ２ O) / BET(N ２ )] is greater than 1.0 and less than or equal to 1.5 D: [BET(H ２ O) / BET(N ２ ) ] is greater than 1.5

[0121] <Voltage Test> Conductive fiber sheets for each example and comparative example were evaluated by voltage testing based on the following measurement method and evaluation criteria. The evaluation results are shown in Table 1-3.

[0122] (Measurement Method) Prepare a 1 cm square measurement sample. For the measurement sample, perform an I-V measurement test under the following conditions: cell temperature: 80°C, dew point: 80°C (100% Rh), gas / stoichiometric gas utilization rate: 50%, and obtain a reading of 1.5 A / cm². ２ Measure the voltage value at that time.

[0123] (Evaluation Criteria) A: Voltage value of 0.60V or higher B: Voltage value of 0.45V or higher but less than 0.60V C: Voltage value of 0.30V or higher but less than 0.45V D: Voltage value less than 0.30V

[0124] <Overall Evaluation> For each evaluation item of conductivity, water repellency, and voltage test, points were assigned as follows: A: 3 points, B: 2 points, C: 1 point, D: 0 points. The total score was used for the overall evaluation.

[0125]

[0126]

[0127]

[0128] According to the present invention, a conductive fiber sheet with excellent conductivity and other properties can be obtained. Such a conductive fiber sheet is preferably applicable as a component of a fuel cell, including a fuel cell separator. Cross-reference of related applications

[0129] This application claims priority over Japanese Patent Application No. 2025-054424, filed with the Japan Patent Office on 27 March 2025, all of which disclosures are incorporated herein by reference in their entirety.

[0130] A1 Gas diffusion layer for fuel cell A1 Conductive fiber sheet A2 Microporous layer 10 Fuel electrode 11 First catalyst layer 12 First gas diffusion layer 20 Air electrode 21 Second catalyst layer 22 Second gas diffusion layer 30 Electrolyte membrane 41 First separator 42 Second separator 100 Membrane electrode composite

Claims

1. A conductive fiber sheet containing an inorganic component including conductive fibers and conductive particles, and an organic component, satisfying the following conditions i) and ii). i) The porosity of the conductive fiber sheet is 25-60% when measured by the following measurement method. ii) The proportion of pores with a diameter of 10 μm or more and 30 μm or less (specific pore ratio) in the pores forming the voids of the conductive fiber sheet is 50 volume% or more when measured by the following measurement method. (Measurement method) A 1 cm x 1 cm conductive fiber sheet is used as the measurement sample. The measurement sample is measured using an X-ray CT scanner (manufactured by BRUKER) with a resolution of 0.98 μm / pixel. The porosity is calculated using the Basic Value in 3D analysis (3D analysis) with analysis software (product name: CTAn, manufactured by BRUKER). Using the same analysis software, the relative abundance of each pore size is calculated, and for all pores, the proportion of pores with a diameter of 10 μm or more and 30 μm or less that occupy the void (specific pore ratio, volume %) is determined. The analysis range is a cylindrical shape of φ2 mm × 500 μm. Two analyses are performed on each measurement sample, and the average values ​​are calculated as the porosity and specific pore ratio.

2. The conductive fiber sheet according to claim 1, wherein the organic component comprises one or more selected from the group consisting of polyolefins, silicones, and non-fluorine water-repellent resins.

3. The conductive fiber sheet according to claim 1, wherein the variation in the mass loss rate of the conductive fiber sheet when measured by the measurement method described below is 0.15 or less in terms of coefficient of variation. (Measurement method) A conductive fiber sheet with a width of 25 cm and a length of 5 cm is used as the measurement sample (N=5). The measurement sample is left to dry in a constant temperature bath at 130°C for 10 minutes, and the mass of the measurement sample after drying (X) is measured. The measurement sample after drying is heated in an electric heating furnace at 450°C for 120 minutes, left in a desiccator for 10 minutes, and the mass of the measurement sample after heating (Y) is measured. The mass loss rate is calculated as [100 × (X - Y) / X]. The mass loss rate is measured 5 times, the average value and standard deviation of the mass loss rate are calculated, and the coefficient of variation of the mass loss rate is calculated as [standard deviation of mass loss rate / average value of mass loss rate].

4. The conductive fiber sheet according to claim 1, wherein the ratio of the total mass of the conductive fibers and conductive particles to the mass of the organic component in the conductive fiber sheet is 1.0 to 3.

0.

5. The conductive fiber sheet according to claim 1, wherein the average fiber length of the conductive fibers is 3 to 9 mm.

6. The conductive fiber sheet according to claim 1, wherein the conductive fibers include carbon fibers.

7. The conductive fiber sheet according to claim 1, wherein at least a portion of the conductive particles is carbon black.

8. The conductive fiber sheet according to claim 7, wherein the degree of graphitization of the carbon black is 1.00 or higher.

9. The conductive fiber sheet according to claim 1, wherein the organic component includes organic fibers, the organic fibers having fibrilized fibril regions in which at least a portion is fibrilized, and the inorganic component is held within the fibril regions.

10. A gas diffusion layer for a fuel cell, wherein a microporous layer is laminated on the surface of the conductive fiber sheet according to claim 1.

11. A membrane electrode composite comprising an electrolyte membrane formed of a solid polymer electrolyte, a fuel electrode laminated on one side of the electrolyte membrane, and an air electrode laminated on the other side of the electrolyte membrane, wherein the fuel electrode comprises a first catalyst layer in contact with the electrolyte membrane and a first gas diffusion layer laminated on the first catalyst layer, and the air electrode comprises a second catalyst layer in contact with the electrolyte membrane and a second gas diffusion layer laminated on the second catalyst layer, wherein at least one of the first gas diffusion layer and the second gas diffusion layer is the gas diffusion layer for fuel cell according to claim 10.

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