Conductive fiber sheet, gas diffusion electrode, and moisture control sheet

Abstract

To provide a conductive fiber sheet, a gas diffusion electrode, and a moisture control sheet, capable of suppressing a decrease in conductivity.SOLUTION: A conductive fiber sheet 1 includes a first conductive fiber 2, a conductive particulate body 3 provided on a surface of the first conductive fiber 2, and a second conductive fiber 4. Each of the first conductive fiber 2, the conductive particulate body 3, and the second conductive fiber 4 contains an organic resin and a conductive particle, and the ratio of the mass of the organic resin, which is contained in the second conductive fiber 4, in the mass of the second conductive fiber 4 is greater than the ratio of the organic resin, which is contained in the first conductive fiber 2, in the mass of the first conductive fiber 2.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] This disclosure relates to conductive fiber sheets, gas diffusion electrodes, and moisture management sheets. [Background technology]

[0002] Conductive fiber sheets possessing conductivity and porosity are known. Conductive fiber sheets are being considered for use as gas diffusion electrodes for fuel cells, moisture control sheets for fuel cells, electrodes for electric double-layer capacitors, or electrodes for lithium-ion secondary batteries. As such a conductive fiber sheet, Patent Document 1 describes a conductive fiber sheet that, in addition to conductive fibers, contains conductive granular material consisting of organic resin and conductive particles on the surface of the conductive fibers. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2016-169450 [Overview of the Initiative] [Problems that the invention aims to solve]

[0004] In the conductive fiber sheet described in Patent Document 1, conductive granular material that contributes to the conductivity of the conductive fiber sheet may fall off. For example, when force is applied to the conductive fiber sheet during handling or during process passing, the conductive fiber sheet may break or deform unintentionally. In such cases, it is thought that conductive particles may fall off. As a result, the conductivity of the conductive fiber sheet may decrease.

[0005] This disclosure describes a conductive fiber sheet, a gas diffusion electrode, and a moisture management sheet that can suppress the decrease in conductivity. [Means for solving the problem]

[0006] A conductive fiber sheet relating to one aspect of this disclosure comprises a first conductive fiber, conductive granular material provided on the surface of the first conductive fiber, and a second conductive fiber. Each of the first conductive fiber, the conductive granular material, and the second conductive fiber contains an organic resin and conductive particles. The ratio of the mass of the organic resin contained in the second conductive fiber to the mass of the second conductive fiber is greater than the ratio of the mass of the organic resin contained in the first conductive fiber to the mass of the first conductive fiber.

[0007] In conductive fibers containing organic resin and conductive particles, fracture and other damage are more likely to occur at the interface between the organic resin and the conductive particles, so the strength of the conductive fibers may decrease as the content of conductive particles increases. In the conductive fiber sheet described above, the ratio of the mass of organic resin contained in the second conductive fiber to the mass of the second conductive fiber is greater than the ratio of the mass of organic resin contained in the first conductive fiber to the mass of the first conductive fiber, so the second conductive fiber is stronger than the first conductive fiber. For this reason, the strength (rigidity) of the conductive fiber sheet can be increased compared to a conductive fiber sheet consisting of the first conductive fiber and conductive granular material provided on the surface of the first conductive fiber. Consequently, fracture and deformation of the conductive fiber sheet can be suppressed, and the possibility of conductive particles falling off the conductive fiber sheet can be reduced. As a result, it is possible to suppress the decrease in conductivity of the conductive fiber sheet.

[0008] In some embodiments, the first conductive fibers may contain the same organic resin as the organic resin contained in the conductive granules. In this case, the adhesion between the first conductive fibers and the conductive granules becomes stronger. Therefore, the possibility of the conductive granules falling off is reduced, making it possible to suppress a decrease in the conductivity of the conductive fiber sheet.

[0009] In some embodiments, the composition of the first conductive fibers may be the same as that of the conductive granules. In this case, the first conductive fibers and the conductive granules can be manufactured using the same material. Therefore, the manufacturing of conductive fiber sheets can be simplified.

[0010] In some embodiments, the conductive fiber sheet may further comprise an electrode catalyst for a fuel cell supported on the conductive fiber sheet. In this case, the catalyst can react efficiently with reactants such as oxygen or hydrogen, and the electrons generated by the reaction can move efficiently through the conductive fiber sheet with minimal influence from electrical resistance. As a result, it is possible to realize a fuel cell with excellent power generation performance and low internal resistance.

[0011] A gas diffusion electrode relating to another aspect of this disclosure is a gas diffusion electrode for an electrochemical element, comprising the conductive fiber sheet described above. Because this gas diffusion electrode is equipped with a conductive fiber sheet, the decrease in conductivity in the conductive fiber sheet can be suppressed. Therefore, the resistance loss in the gas diffusion electrode can be reduced.

[0012] A moisture management sheet relating to yet another aspect of this disclosure is a moisture management sheet for an electrochemical element, comprising the conductive fiber sheet described above. Because the conductive fiber sheet has excellent strength (rigidity), the thickness and basis weight of the conductive fiber sheet can be reduced. Therefore, a moisture management sheet for an electrochemical element can be provided that suppresses the decrease in conductivity with a thin conductive fiber sheet, and also has low electrical resistance and excellent drainage performance. [Effects of the Invention]

[0013] According to this disclosure, the decrease in conductivity can be suppressed. [Brief explanation of the drawing]

[0014] [Figure 1] Figure 1 is a schematic diagram showing an enlarged view of a conductive fiber sheet according to one embodiment. [Figure 2] Figure 2 is a schematic diagram showing an enlarged view of the conductive fiber sheet relating to the comparative example. [Modes for carrying out the invention]

[0015] Hereinafter, embodiments of the present disclosure will be described in detail while referring to the accompanying drawings. In this specification, a numerical range indicated by using "~" indicates a range including the numerical values described before and after "~" as the minimum value and the maximum value, respectively. The individually described upper limit value and lower limit value can be arbitrarily combined.

[0016] <Conductive fiber sheet> Referring to FIG. 1, the configuration of the conductive fiber sheet according to an embodiment will be described. FIG. 1 is a schematic configuration diagram showing an enlarged view of the conductive fiber sheet according to an embodiment. The conductive fiber sheet 1 shown in FIG. 1 is a fiber sheet having conductivity and porosity, and is used, for example, as a gas diffusion electrode for an electrochemical element or a moisture management sheet for an electrochemical element. The conductive fiber sheet 1 includes a first conductive fiber 2, a conductive granular body 3 provided on the surface of the first conductive fiber 2, and a second conductive fiber 4. In the conductive fiber sheet 1, the first conductive fiber 2 provided with the conductive granular body 3 on its surface and the second conductive fiber 4 may be mixed. The conductive fiber sheet 1 may be configured by laminating a fiber layer including the first conductive fiber 2 and the conductive granular body 3 and a fiber layer including the second conductive fiber 4.

[0017] (First conductive fiber) The first conductive fiber 2 is a fiber having conductivity. The first conductive fiber 2 includes an organic resin and conductive particles.

[0018] The conductive particles are particles having conductivity. Examples of the conductive particles include carbon-based particles, metal particles, and metal oxide particles. Examples of the carbon-based particles include carbon black, carbon nanotubes, and carbon nanofibers. From the viewpoints of improving chemical resistance, conductivity, and dispersibility, carbon-based particles, particularly carbon black, may be used as the conductive particles.

[0019] The shape of the conductive particles is not particularly limited. Examples of conductive particle shapes include spherical (approximately spherical and perfectly spherical), fibrous, needle-shaped (e.g., tetrapod-shaped), plate-shaped, polyhedral, feather-shaped, and amorphous. The conductive particles may be hollow or solid. The particle size of the conductive particles is not particularly limited. The average particle size of the conductive particles may be 5 nm to 200 nm or 10 nm to 1000 nm.

[0020] "Average particle size" basically refers to the average particle size determined by a particle size analyzer using dynamic light scattering. For example, in cases where measurement by dynamic light scattering is difficult, such as with particles that form aggregates or structures like carbon black, the average particle size represents the arithmetic mean of the diameters of 50 particles captured in an electron microscope image of the particle. In this case, if the particle shape is not circular in the electron microscope image, the diameter of a circle with the same area as the particle in the image is considered to be the diameter of the particle.

[0021] The first conductive fiber 2 may contain two or more types of conductive particles that differ in at least one of the material and average particle size.

[0022] The first conductive fiber 2 has excellent flexibility, and the conductive particles are bonded to each other via an organic resin to prevent them from falling off.

[0023] The organic resin is a resin capable of bonding conductive particles together, and may be a hydrophobic organic resin, a hydrophilic organic resin, or a mixture or composite resin of these resins. When the conductive fiber sheet 1 is used as a substrate for a gas diffusion electrode, if the organic resin contained in the first conductive fiber 2 is a hydrophobic organic resin, it exhibits excellent water permeability without impregnation with a hydrophobic resin such as a fluorine-based resin, and exhibits excellent drainage and gas diffusion properties. If the organic resin contained in the first conductive fiber 2 is a hydrophilic organic resin, moisture can be retained. Therefore, since the solid polymer film is kept moist even under low humidity conditions, a solid polymer fuel cell capable of exhibiting sufficient power generation performance can be manufactured.

[0024] A "hydrophobic organic resin" is an organic resin with a contact angle of 90° or more with water. Examples of hydrophobic organic resins include fluororesins, polyolefin resins, and polyester resins. Examples of fluororesins include polytetrafluoroethylene (PTFE), polychlorotrifluoroethylene (PCTFE), polyvinylidene fluoride (PVDF), polyvinyl fluoride (PVF), perfluoroalkoxy fluororesins (PFA), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), ethylene-tetrafluoroethylene copolymer (ETFE), ethylene-chlorotrifluoroethylene copolymer (ECTFE), vinylidene fluoride-tetrafluoroethylene-hexafluoropropylene copolymer (THV), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP), and copolymers of various monomers that constitute the aforementioned resins. Examples of polyolefin resins include polyethylene (PE), polypropylene (PP), polymethylpentene, and copolymers of various monomers that constitute the aforementioned resins. Examples of polyester resins include polyethylene terephthalate (PET), polytrimethylene terephthalate (PTT), polybutylene terephthalate (PBT), polyethylene naphthalate (PEN), and polybutylene naphthalate (PBN). These hydrophobic organic resins may be used individually, or two or more hydrophobic organic resins may be mixed or compounded. From the viewpoint of improving heat resistance, chemical resistance, and hydrophobicity, fluororesins may be used as hydrophobic organic resins. In particular, ternary fluororesins such as vinylidene fluoride-tetrafluoroethylene-hexafluoropropylene copolymer may be used to achieve excellent water repellency. The molecular weight of the fluororesin can be appropriately selected. For example, fluororesins with a molecular weight of 600,000 to 1,500,000 may be used.

[0025] A "hydrophilic organic resin" is an organic resin with a contact angle with water of less than 90°. Examples of hydrophilic organic resins include cellulose (e.g., rayon), polyamide resins, acrylic resins, resins having hydrophilic groups, polyacrylonitrile, acrylic oxide, polyvinyl alcohol resins, and polyethylene glycol resins. Examples of polyamide resins include nylon 6 and nylon 66. Examples of acrylic resins include polyacrylic acid and polymethacrylic acid. Examples of hydrophilic groups include amide groups, carboxyl groups, hydroxyl groups, amino groups, and sulfonic acid groups. Examples of resins having such hydrophilic groups include hydrophilic polyurethane and polyvinylpyrrolidone. These hydrophilic organic resins may be used individually, or two or more hydrophilic organic resins may be mixed or compounded for use. From the viewpoint of improving heat resistance, polyacrylonitrile may be used as the hydrophilic organic resin. Polyacrylonitrile is less likely to lose thickness even when the solid polymer film swells, and can maintain the voids of the conductive fiber sheet 1. Therefore, when the conductive fiber sheet 1 is used as a substrate for a gas diffusion electrode, polyacrylonitrile may be used as the organic resin.

[0026] At least one of the hydrophobic organic resin and the hydrophilic organic resin may be a thermosetting resin, and in addition to the thermosetting resin, a curing accelerator may also be included.

[0027] Examples of "thermosetting resins" include phenolic resins, epoxy resins, thermosetting polyimide resins, melamine resins, unsaturated polyester resins, and diallyl phthalate resins. Among these, phenolic resins and epoxy resins have excellent heat resistance and acid resistance, so the rigidity of the first conductive fiber 2 can be increased by heat treatment. The organic resin may consist of one type of thermosetting resin, or it may be composed of a mixture or composite of two or more types of thermosetting resins, or it may be composed of a mixture or composite of one or more types of thermosetting resins and one or more types of thermoplastic hydrophobic organic resins or thermoplastic hydrophilic organic resins.

[0028] The mass ratio of organic resin to conductive particles in the first conductive fiber 2 is not particularly limited. If the amount of conductive particles is less than 10% by mass, the conductivity tends to be insufficient. If the amount of conductive particles is more than 95% by mass, sufficient flexibility tends not to be obtained. Therefore, from the viewpoint of excellent conductivity and flexibility, the mass ratio of organic resin to conductive particles in the first conductive fiber 2 may be 10:90 to 90:10, 20:80 to 80:20, 30:70 to 70:30, or 30:70 to 60:40.

[0029] In the first conductive fiber 2, it is sufficient that the organic resin adheres to the conductive particles, and the positional relationship between the conductive particles and the organic resin in the first conductive fiber 2 is not particularly limited. If conductive particles are present only on the outer surface of the first conductive fiber 2, the resin component inside the first conductive fiber 2 becomes a resistive component, and the conductivity tends to be poor. Therefore, conductive particles may be present inside the first conductive fiber 2. To improve the conductivity between the first conductive fibers 2, the conductive particles may be exposed on the outer surface of the first conductive fiber 2. A first conductive fiber 2 in which conductive particles are present inside and conductive particles are exposed on the outer surface can be manufactured, for example, by spinning a spinning solution containing an organic resin and conductive particles.

[0030] The average fiber diameter of the first conductive fiber 2 is not particularly limited. If the average fiber diameter of the first conductive fiber 2 is greater than 10 μm, there are fewer contact points between the first conductive fibers 2, and conductivity tends to be insufficient. If the average fiber diameter of the first conductive fiber 2 is less than 10 nm, the handling of the conductive fiber sheet 1 tends to be poor. From these viewpoints, the average fiber diameter of the first conductive fiber 2 may be, for example, 10 nm to 10 μm, 100 nm to 1 μm, or 300 nm to 500 nm. The average fiber diameter of the first conductive fiber 2 may be 5 times or more the average particle size of the conductive particles so that conductive particles do not easily fall off.

[0031] Here, "average fiber diameter" refers to the arithmetic mean of the fiber diameters of 40 fibers. "Fiber diameter" is the length (thickness) of the fiber in the direction perpendicular to the length direction, measured based on a microscope image. If conductive particles are exposed on the entire outer surface of the first conductive fiber 2, the fiber diameter of the first conductive fiber 2 is the thickness of the first conductive fiber 2 including the conductive particles. If conductive particles are exposed on only a part of the outer surface of the first conductive fiber 2, the fiber diameter of the first conductive fiber 2 is the thickness (diameter) of the part where the conductive particles are not exposed.

[0032] From the viewpoint of having excellent conductivity, the first conductive fiber 2 may be a continuous fiber having a continuous length without a specific length, rather than a long fiber or short fiber having a specific length. Such a continuous first conductive fiber 2 can be manufactured, for example, by electrospinning or spunbonding.

[0033] (Conductive granules) The conductive granular material 3 is a conductive granular material. The conductive granular material 3 is a separate component from the first conductive fiber 2 and the second conductive fiber 4, and is provided on the surface of the first conductive fiber 2. The manner in which the conductive granular material 3 is provided on the surface of the first conductive fiber 2 can be adjusted as appropriate. For example, the first conductive fiber 2 and the conductive granular material 3 may be integrated at the point where the surface of the first conductive fiber 2 and the surface of the conductive granular material 3 are in contact. The conductive granular material 3 and the second conductive fiber 4 do not have to be integrated. The conductive granular material 3 contains an organic resin and conductive particles.

[0034] The average particle size of the conductive granules 3 is not particularly limited. The average particle size of the conductive granules 3 may be 50 nm to 50 μm, 100 nm to 10 μm, or 1 μm to 5 μm. The average particle size of the conductive granules 3 may be larger than the average fiber diameter of the first conductive fiber 2, as this makes it easier to provide a conductive fiber sheet 1 with high conductivity.

[0035] The conductive particles contained in the conductive granular material 3 are the same conductive particles that may be contained in the first conductive fiber 2 described above. The conductive particles contained in the conductive granular material 3 may be the same as or different from the conductive particles contained in the first conductive fiber 2. For example, the conductive particles contained in the conductive granular material 3 may differ from the conductive particles contained in the first conductive fiber 2 in at least one respect of material and average particle size.

[0036] The organic resin used in the conductive granular material 3 is the same organic resin that may be used in the first conductive fiber 2 described above. The organic resin in the conductive granular material 3 may be the same as or different from the organic resin in the first conductive fiber 2.

[0037] The composition of the conductive granules 3 may be the same as that of the first conductive fibers 2. In this case, the first conductive fibers 2 and the conductive granules 3 can be manufactured using the same material. The composition of the conductive granules 3 may be different from that of the first conductive fibers 2.

[0038] (Second conductive fiber) The second conductive fiber 4 contains an organic resin and conductive particles.

[0039] The conductive particles included in the second conductive fiber 4 are the same conductive particles that may be included in the first conductive fiber 2 as described above. The conductive particles included in the second conductive fiber 4 may be the same as or different from the conductive particles included in the first conductive fiber 2. For example, the conductive particles included in the second conductive fiber 4 may differ from the conductive particles included in the first conductive fiber 2 in at least one respect of material and average particle size. Similarly, the conductive particles included in the second conductive fiber 4 may be the same as or different from the conductive particles included in the conductive granular material 3.

[0040] The organic resin used in the second conductive fiber 4 is the same organic resin that may be used in the first conductive fiber 2 as described above. The organic resin in the second conductive fiber 4 may be the same as or different from the organic resin in the first conductive fiber 2. Similarly, the organic resin in the second conductive fiber 4 may be the same as or different from the organic resin in the conductive granular material 3.

[0041] The ratio (mass%) of the mass of the second conductive fiber 4 to the mass of the second conductive fiber 4 is greater than the ratio (mass%) of the mass of the first conductive fiber 2 to the mass of the first conductive fiber 2. The mass ratio of organic resin to conductive particles in the second conductive fiber 4 may be 10:90 to 90:10, 20:80 to 80:20, 30:70 to 70:30, or 40:60 to 60:40.

[0042] From the viewpoint of further improving the rigidity of the conductive fiber sheet 1, the average fiber diameter of the second conductive fiber 4 may be larger than the average fiber diameter of the first conductive fiber 2. The average fiber diameter of the second conductive fiber 4 may be, for example, 10 nm to 10 μm, 500 nm to 3 μm, or 700 nm to 1 μm. From the viewpoint of excellent conductivity, the second conductive fiber 4 may be a continuous fiber.

[0043] The first conductive fiber 2, conductive granular material 3, and second conductive fiber 4 may also contain non-conductive materials other than conductive particles, such as inorganic particles, ion exchange resin powder, and plant seeds. Examples of inorganic particles include manganese dioxide, iron oxide, copper oxide, nickel oxide, cobalt oxide, zinc oxide, titanium-containing oxide, zeolite, catalyst-supported ceramics, and silica.

[0044] The conductive fibers constituting the conductive fiber sheet 1 may be bonded to each other in any way. The conductive fibers may be bonded to each other, for example, by entanglement, bonding by plasticization of the organic resin with a solvent, bonding by fusion of the organic resin with heat, or a combination of these methods.

[0045] In order to effectively utilize the voids in the conductive fiber sheet 1, the conductive fiber sheet 1 may have a porosity of 20% or more, 30% or more, or 50% or more. The upper limit of the porosity is not particularly limited, but may be 99% or less from the viewpoint of morphological stability. The porosity P (unit: %) is calculated by the formula (1) using the filling rate Fr n (unit: %) of N components constituting the conductive fiber sheet 1. N is an integer of 2 or more, and n is an integer from 1 to N. The components constituting the conductive fiber sheet 1 include, for example, conductive particles and an organic resin.

[0046]

Number

[0047] Here, the filling rate Fr n (unit: %) of the n-th component is calculated by the formula (2) using the basis weight M (unit: g / cm 2 ) of the conductive fiber sheet 1, the thickness T (unit: cm) of the conductive fiber sheet 1, the mass ratio Pr n of the n-th component in the conductive fiber sheet 1, and the specific gravity SG n (unit: g / cm 3 ) of the n-th component.

[0048]

Number

[0049] The basis weight of the conductive fiber sheet 1 is not particularly limited. From the viewpoints that the conductive fiber sheet 1 has a certain amount of conductive fibers and is excellent in conductivity, and also from the viewpoints of handling property and productivity, the basis weight of the conductive fiber sheet 1 may be 0.1 g / m 2 to 200 g / m 2 , may be 0.3 g / m 2 to 100 g / m 2 , or may be 0.5 g / m 2 to 50 g / m 2The thickness of the conductive fiber sheet 1 is not particularly limited. For example, the thickness of the conductive fiber sheet 1 may be 1 μm to 1000 μm, 5 μm to 500 μm, 10 μm to 400 μm, or 10 μm to 300 μm.

[0050] "Balance" is calculated by considering the mass of a 10cm square conductive fiber sheet as 1m 2 This refers to the value converted from size to mass. "Thickness" is the value measured using a thickness gauge (Mitutoyo Corporation: Code No. 547-401: Measuring force 3.5N or less).

[0051] <Method for manufacturing conductive fiber sheets> As an example, a method for manufacturing a conductive fiber sheet 1 by electrospinning will be described.

[0052] First, a spinning solution for forming the first conductive fiber 2 and conductive granules 3 (hereinafter referred to as the "first spinning solution") and a spinning solution for forming the second conductive fiber 4 (hereinafter referred to as the "second spinning solution") are prepared. The first and second spinning solutions each contain an organic resin, conductive particles, and a dispersion medium. The mass percentage of the organic resin in the first spinning solution is adjusted so that the first conductive fiber 2 and conductive granules 3 are obtained in the first electrostatic spinning described later. The mass percentage of the organic resin required to obtain the first conductive fiber 2 and conductive granules 3 differs depending on the composition of the spinning solution and the spinning conditions. Therefore, the mass percentage of the organic resin in the first spinning solution is set considering the composition of the spinning solution and the spinning conditions.

[0053] The percentage (mass%) of the mass of the organic resin relative to the mass of the first spinning solution can be adjusted as appropriate. To facilitate the realization of a conductive fiber sheet 1 having conductive granular material 3 provided on the surface of the first conductive fiber 2, the mass% in the first spinning solution may be 0.1% to 10.0%, 0.3% to 5.0%, 0.5% to 3.0%, or 0.8% to 1.6%.

[0054] The percentage (mass%) of the mass of conductive particles relative to the mass of the first spinning solution can be adjusted as appropriate. Since it is easy to realize a conductive fiber sheet 1 having conductive granular bodies 3 provided on the surface of the first conductive fiber 2, the mass% in the first spinning solution may be 3% to 20%, 5% to 10%, or 6.4% to 7.2%.

[0055] The solvent constituting the first spinning solution can be any solvent capable of dissolving organic resins and can be selected as appropriate. Since it is easy to realize a conductive fiber sheet 1 having conductive granular material 3 provided on the surface of the first conductive fiber 2, N,N-dimethylacetamide, N-methyl-2-pyrrolidone, or N,N-dimethylformamide may be used as the solvent constituting the first spinning solution.

[0056] Similarly, the mass percentage of organic resin in the second spinning solution is adjusted so that the second conductive fiber 4 is obtained in the second electrospinning process described later. The mass percentage of organic resin required to obtain the second conductive fiber 4 varies depending on the composition of the spinning solution and the spinning conditions. Therefore, the mass percentage of organic resin in the second spinning solution is set considering the composition of the spinning solution and the spinning conditions. The mass percentage of organic resin in the second spinning solution is greater than the mass percentage of organic resin in the first spinning solution.

[0057] The percentage (mass%) of the mass of the organic resin relative to the mass of the second spinning solution can be adjusted as appropriate. Since it is easy to realize a conductive fiber sheet 1 having the second conductive fiber 4, the mass% in the second spinning solution may be 2.5% to 6.5%, 3.0% to 6.0%, 3.5% to 5.5%, or 4.0% to 5.0%.

[0058] The percentage (mass%) of the mass of conductive particles relative to the mass of the second spinning solution can be adjusted as appropriate. To facilitate the realization of a conductive fiber sheet 1 having the second conductive fibers 4, the mass% in the second spinning solution may be 4.8% to 20%, 6.0% to 15.0%, or 7.2% to 11.2%.

[0059] The solvent constituting the second spinning solution can be any solvent capable of dissolving organic resins and can be selected as appropriate. Since it facilitates the realization of a conductive fiber sheet 1 having the second conductive fiber 4, N,N-dimethylacetamide, N-methyl-2-pyrrolidone, or N,N-dimethylformamide may be used as the solvent constituting the second spinning solution.

[0060] Then, the first spinning solution and the second spinning solution are filled into syringes with different nozzles.

[0061] Next, a process of electrospinning (first electrospinning) using the first spinning solution is carried out. In this process, the first spinning solution is discharged from a nozzle and accumulated on the counter electrode. As a result, a conductive fiber web is formed on the counter electrode, which includes the first conductive fiber 2 and conductive granular material 3 fixed to the surface of the first conductive fiber 2. Since the first conductive fiber 2 and the conductive granular material 3 are formed from the same spinning solution (first spinning solution), they have the same composition.

[0062] In the first electrospinning process, the voltage applied to the first spinning solution discharged from the nozzle (in other words, the voltage difference between the first spinning solution and the collector (counter electrode)) can be adjusted as appropriate. Since it is easy to realize a conductive fiber sheet 1 having conductive granular material 3 provided on the surface of the first conductive fiber 2, a voltage of 1kV to 20kV may be applied, a voltage of 4kV to 16kV may be applied, or a voltage of 8kV to 12kV may be applied.

[0063] The amount of the first spinning solution discharged from the nozzle can be adjusted as appropriate. Since it is easy to realize a conductive fiber sheet 1 having conductive granular material 3 provided on the surface of the first conductive fiber 2, the amount of the first spinning solution discharged from the nozzle may be 0.1 g / hour to 10 g / hour, 0.5 g / hour to 5 g / hour, or 1 g / hour to 2 g / hour.

[0064] The spinning distance in the first electrospinning process can be adjusted as appropriate. The spinning distance is the distance from the spinning solution discharge portion (nozzle tip) to the collector (counter electrode). Since it is easy to realize a conductive fiber sheet 1 having conductive granular material 3 provided on the surface of the first conductive fiber 2, the spinning distance in the first electrospinning process may be 4 cm to 20 cm, 6 cm to 16 cm, or 8 cm to 12 cm.

[0065] Furthermore, a process of electrospinning using a second spinning solution (second electrospinning) is carried out. In this process, the second spinning solution is discharged from a nozzle and accumulated on the counter electrode. As a result, a conductive fiber web containing second conductive fibers 4 is formed on the counter electrode. Conductive granular material 3 is not formed on the surface of this second conductive fiber 4.

[0066] In the second electrospinning process, the voltage applied to the second spinning solution discharged from the nozzle (in other words, the voltage difference between the second spinning solution and the collector (counter electrode)) can be adjusted as appropriate. Since it is easy to realize a conductive fiber sheet 1 having the second conductive fiber 4, a voltage of 1kV to 20kV may be applied, a voltage of 4kV to 16kV may be applied, or a voltage of 8kV to 12kV may be applied.

[0067] The amount of the second spinning solution discharged from the nozzle can be adjusted as appropriate. To facilitate the realization of a conductive fiber sheet 1 having the second conductive fibers 4, the amount of the second spinning solution discharged from the nozzle may be 0.1 g / hour to 10 g / hour, 0.5 g / hour to 5 g / hour, or 1 g / hour to 2 g / hour.

[0068] The spinning distance in the second electrospinning process can be adjusted as appropriate. Since it is easy to realize a conductive fiber sheet 1 having the second conductive fiber 4, the spinning distance in the second electrospinning process may be 4 cm to 20 cm, 6 cm to 16 cm, or 8 cm to 12 cm.

[0069] The temperature and humidity of the spinning space can be adjusted as appropriate. To facilitate the realization of the conductive fiber sheet 1, the temperature of the spinning space may be 10°C to 40°C, 18°C ​​to 33°C, or 23°C to 28°C. The humidity of the spinning space may be 5%RH to 60%RH, 10%RH to 50%RH, or 20%RH to 40%RH.

[0070] Furthermore, the second electrospinning may be performed after the first electrospinning, the first and second electrospinning may be performed alternately, or the second electrospinning may be performed in parallel with the first electrospinning.

[0071] Next, a process is carried out to remove the dispersion medium from the conductive fiber web. Through this process, the conductive fiber sheet 1 is manufactured.

[0072] Furthermore, the strength of the entanglement (amount of overlap) between the molecular chains of the organic resin contained in the spinning solution can determine whether a conductive fiber web containing first conductive fibers 2 and conductive granular material 3 fixed to the surface of the first conductive fibers 2, or a conductive fiber web containing second conductive fibers 4, is formed. For example, if the concentration of organic resin in the spinning solution is high, the entanglement between the molecular chains becomes stronger, making it easier for second conductive fibers 4 with a thicker fiber diameter to form. On the other hand, if the concentration of organic resin in the spinning solution is low, the entanglement between the molecular chains becomes weaker, making it easier for first conductive fibers 2 with a thinner fiber diameter to form, and for conductive granular material 3 to form on their surface.

[0073] <Effects of conductive fiber sheets> Next, the effects of the conductive fiber sheet 1 according to this embodiment will be explained with further reference to Figure 2. Figure 2 is a schematic diagram showing an enlarged view of a conductive fiber sheet according to a comparative example. The conductive fiber sheet 100 shown in Figure 2 differs from the conductive fiber sheet 1 mainly in that it does not include the second conductive fiber 4. In other words, the conductive fiber sheet 100 is composed of a first conductive fiber 2 and conductive granular material 3 provided on the surface of the first conductive fiber 2.

[0074] In conductive fibers containing organic resin and conductive particles, fractures and other damage are more likely to occur at the interface between the organic resin and the conductive particles, so the strength of the conductive fibers may decrease as the content of conductive particles increases. In conductive fiber sheet 1, the ratio of the mass of organic resin contained in the second conductive fiber 4 to the mass of the second conductive fiber 4 is greater than the ratio of the mass of organic resin contained in the first conductive fiber 2 to the mass of the first conductive fiber 2, so the second conductive fiber 4 is stronger than the first conductive fiber 2. Therefore, the strength (rigidity) of conductive fiber sheet 1 can be increased compared to conductive fiber sheet 100. Consequently, the possibility of damage (fracture) or unintended deformation of conductive fiber sheet 1 during handling and process passage is reduced, and the possibility of conductive particles falling off conductive fiber sheet 1 can be reduced. As a result, it is possible to suppress the decrease in conductivity of conductive fiber sheet 1. In other words, it is possible to reduce the electrical resistance of conductive fiber sheet 1. Since the possibility of conductive particles falling off is reduced, it is also possible to increase the amount of conductive particles contained in conductive fiber sheet 1.

[0075] Since the conductive fiber sheet 1 has rigidity, it can be made easier to handle and further reduce the defect rate in the process.

[0076] The first conductive fiber 2 may contain the same organic resin as the organic resin contained in the conductive granular material 3. In this case, the adhesion between the first conductive fiber 2 and the conductive granular material 3 becomes stronger. Therefore, the possibility of the conductive granular material 3 falling off is reduced, making it possible to further suppress the decrease in conductivity of the conductive fiber sheet 1. By strengthening the adhesion between the first conductive fiber 2 and the conductive granular material 3, the contact resistance between the first conductive fiber 2 and the conductive granular material 3 can be reduced. Therefore, electricity can pass between the first conductive fiber 2 and the conductive granular material 3 with low resistance, making it possible to reduce the electrical resistance of the conductive fiber sheet 1.

[0077] The composition of the first conductive fiber 2 may be the same as that of the conductive granular material 3. In this case, the first conductive fiber 2 and the conductive granular material 3 can be manufactured using the same material. Therefore, the manufacturing of the conductive fiber sheet 1 can be simplified.

[0078] The average fiber diameter of the second conductive fiber 4 may be larger than the average fiber diameter of the first conductive fiber 2. In this case, the strength of the second conductive fiber 4 will be further increased. Therefore, the strength (rigidity) of the conductive fiber sheet 1 can be further increased, and the possibility of conductive particles falling off the conductive fiber sheet 1 can be further reduced. As a result, it becomes possible to further suppress the decrease in conductivity of the conductive fiber sheet 1.

[0079] The second conductive fiber 4 may contain the same organic resin as the first conductive fiber 2. In this case, the first conductive fiber 2 and the second conductive fiber 4 can be firmly in contact or fixed together, thereby reducing the contact resistance between the first conductive fiber 2 and the second conductive fiber 4. Consequently, electricity can pass between the first conductive fiber 2 and the second conductive fiber 4 with low resistance, thus reducing the electrical resistance of the conductive fiber sheet 1.

[0080] The organic resin contained in the first conductive fiber 2, conductive granular material 3, and second conductive fiber 4 may be a fluororesin. In this case, a conductive fiber sheet 1 with excellent water repellency can be realized. For example, when the conductive fiber sheet 1 is used in a gas diffusion electrode for an electrochemical element, it is possible to suppress blockage of the gas flow path by water generated in the gas diffusion electrode, thereby preventing impairment of the diffusibility of the supplied gas.

[0081] The conductive fiber sheet relating to this disclosure is not limited to the embodiments described above.

[0082] Since the conductive fiber sheet 1 has a low electrical resistance, it can be used in applications requiring conductivity. For example, the conductive fiber sheet 1 may be used as a substrate for gas diffusion electrodes in fuel cells, a substrate for moisture management sheets in fuel cells, an electrode in an electric double-layer capacitor, or an electrode in a lithium-ion secondary battery.

[0083] The case in which the conductive fiber sheet 1 is used as a substrate for a gas diffusion electrode of an electrochemical element will be described. In this case, the gas diffusion electrode includes the conductive fiber sheet 1. The gas diffusion electrode has the same structure as a conventional gas diffusion electrode, except that the conductive fiber sheet 1 is used as the substrate for the gas diffusion electrode.

[0084] Since the conductive fiber sheet 1 is porous, when nothing is filled into the voids of the substrate for the gas diffusion electrode (conductive fiber sheet 1), it has excellent drainage properties in the thickness direction and surface direction of the substrate for the gas diffusion electrode (conductive fiber sheet 1), as well as excellent diffusion properties of the supplied gas.

[0085] The conductive fiber sheet 1 may contain at least one of a fluororesin and carbon in the voids of the conductive fiber sheet 1. The inclusion of a fluororesin makes it easier for liquid water to be pushed out, thereby improving the drainage properties of the conductive fiber sheet 1. The inclusion of carbon can further enhance the conductivity of the conductive fiber sheet 1.

[0086] Examples of fluoropolymers include polytetrafluoroethylene (PTFE), polychlorotrifluoroethylene (PCTFE), polyvinylidene fluoride (PVDF), polyvinyl fluoride (PVF), perfluoroalkoxy fluoropolymer (PFA), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), ethylene-tetrafluoroethylene copolymer (ETFE), ethylene-chlorotrifluoroethylene copolymer (ECTFE), vinylidene fluoride-tetrafluoroethylene-hexafluoropropylene copolymer, and copolymers of various monomers that can constitute the above organic resins.

[0087] Examples of carbon include carbon black, carbon nanotubes, and carbon nanofibers.

[0088] The gas diffusion electrode may further include an electrode catalyst for a fuel cell supported on a conductive fiber sheet 1. As such an electrode catalyst, one or more catalysts selected from the group consisting of platinum, platinum alloys, palladium, palladium alloys, titanium, manganese, magnesium, lanthanum, cerium, vanadium, zirconium, iridium, rhodium, ruthenium, gold, nickel-lanthanum alloys, and titanium-iron alloys are supported on the conductive fiber sheet 1. In this case, the catalyst can react efficiently with reactants such as oxygen or hydrogen, and the electrons generated by the reaction can move efficiently through the conductive fiber sheet 1 with minimal influence from electrical resistance. As a result, a fuel cell with excellent power generation performance and low internal resistance can be realized.

[0089] Furthermore, the gas diffusion electrode may contain not only a catalyst but also an electron conductor and a proton conductor. As the electron conductor, conductive particles similar to those used in carbon black may be used. The catalyst may be supported on this electron conductor (conductive particle). As the proton conductor, an ion exchange resin may be used.

[0090] Such gas diffusion electrodes can be manufactured, for example, by the following method. First, a catalyst is added to a solvent and mixed, then an ion exchange resin solution is added and the mixture is homogeneously mixed by ultrasonic dispersion or the like to obtain a catalyst dispersion suspension. As the solvent, a single solvent or a mixed solvent consisting of ethyl alcohol, propyl alcohol, butyl alcohol, and ethylene glycol dimethyl ether can be used. As the catalyst, for example, carbon powder supported with a catalyst such as platinum can be used. Then, the above catalyst dispersion suspension is coated or sprayed onto the conductive fiber sheet 1 as described above, and the gas diffusion electrode is manufactured by drying it.

[0091] Since the gas diffusion electrode includes a conductive fiber sheet 1, the decrease in conductivity in the conductive fiber sheet 1 can be suppressed. Therefore, resistance loss in the gas diffusion electrode can be reduced, making it possible to manufacture a solid polymer fuel cell that can exhibit sufficient power generation performance. Because the conductive fiber sheet 1 has a certain degree of rigidity, swelling and shrinkage of the solid polymer membrane are suppressed, thus reducing the possibility of cracks occurring in the solid polymer membrane. Furthermore, since the gas diffusion electrode is less likely to collapse even when the solid polymer membrane swells, the void can be maintained, and gas diffusion can be maintained.

[0092] In a gas diffusion electrode, electron conduction occurs not only through contact between catalysts, but also through the formation of electron conduction pathways by the first conductive fiber 2, conductive granules 3, and second conductive fiber 4. As a result, there is less catalyst isolated from the electron conduction pathways. Therefore, the utilization efficiency of the catalyst can be improved, and the amount of catalyst required can be reduced.

[0093] The above-mentioned gas diffusion electrode may be used in a membrane-electrode assembly. The membrane-electrode assembly has the same configuration as a conventional membrane-electrode assembly, except for the gas diffusion electrode. For example, as the solid polymer membrane, a perfluorocarbon sulfonic acid resin membrane, a sulfonated aromatic hydrocarbon resin membrane, or an alkyl sulfonated aromatic hydrocarbon resin membrane can be used. For example, a membrane-electrode assembly can be manufactured by sandwiching a solid polymer membrane between the catalyst-supported surfaces of a pair of gas diffusion electrodes and joining them by hot pressing.

[0094] The method for manufacturing the membrane-electrode assembly is not limited to this. For example, a catalyst layer is formed by coating the catalyst dispersion suspension onto a support. After transferring this catalyst layer to a solid polymer film, a conductive fiber sheet 1 is laminated so as to be in contact with the catalyst layer, and the membrane-electrode assembly is manufactured by heat pressing these together.

[0095] Since the membrane-electrode assembly includes the aforementioned gas diffusion electrode, electrical resistance can be reduced, and a solid polymer fuel cell capable of exhibiting sufficient power generation performance can be manufactured.

[0096] A polymer electrolyte fuel cell includes a gas diffusion electrode. Aside from the presence of the aforementioned gas diffusion electrode, the fuel cell has the same configuration as a conventional fuel cell. For example, a cell unit is fabricated by sandwiching the aforementioned membrane-electrode assembly between a pair of bipolar plates, and a fuel cell is manufactured by stacking and fixing multiple cell units. Because the fuel cell includes the aforementioned gas diffusion electrode, its electrical resistance can be reduced, allowing it to exhibit sufficient power generation performance.

[0097] A bipolar plate only needs to have high conductivity, be impermeable to gas, and have a channel that can supply gas to a gas diffusion electrode. Examples of bipolar plates include carbon molding materials, carbon-resin composite materials, and metallic materials.

[0098] The conductive fiber sheet 1 may be used as a substrate for a moisture management sheet for an electrochemical element. In this case, the moisture management sheet includes the conductive fiber sheet 1. Because the conductive fiber sheet 1 has excellent strength (rigidity), its thickness and basis weight can be reduced. Therefore, a thin conductive fiber sheet 1 can suppress the decrease in conductivity, and a moisture management sheet for an electrochemical element can be provided that has low electrical resistance and excellent drainage performance. [Examples]

[0099] The following describes the results of evaluation tests using the examples and comparative examples related to this disclosure in more detail. However, this disclosure is not limited to these examples.

[0100] Spinning solutions S1 to S3 having the following compositions were prepared.

[0101] (Spinning solution S1) • Organic resin: polyvinylidene fluoride-tetrafluoroethylene-hexafluoropropylene copolymer • Conductive particles: A dispersion in which conductive particles, carbon black (CB), are dispersed in N-methyl-2-pyrrolidone [solid content concentration 22% by mass, average particle size 280 nm]. • Dispersion medium: Dimethylformamide The total solid content of the spinning solution S1, including both organic resin and conductive particles, was 8% by mass. The mass ratio of organic resin to conductive particles in the spinning solution S1 was set to 20:80.

[0102] (Spinning solution S2) • Organic resin: polyvinylidene fluoride-tetrafluoroethylene-hexafluoropropylene copolymer • Conductive particles: A dispersion in which conductive particles, carbon black (CB), are dispersed in N-methyl-2-pyrrolidone [solid content concentration 22% by mass, average particle size 280 nm]. • Dispersion medium: Dimethylformamide The total solid content of the spinning solution S2, including both organic resin and conductive particles, was 12% by mass. The mass ratio of organic resin to conductive particles in the spinning solution S2 was set to 40:60.

[0103] (Spinning solution S3) • Organic resin: polyvinylidene fluoride-tetrafluoroethylene-hexafluoropropylene copolymer • Conductive particles: A dispersion in which conductive particles, carbon black (CB), are dispersed in N-methyl-2-pyrrolidone [solid content concentration 22% by mass, average particle size 280 nm]. • Dispersion medium: Dimethylformamide The total solid content of the spinning solution S3, including both organic resin and conductive particles, was 8% by mass. The mass ratio of organic resin to conductive particles in the spinning solution S3 was set to 10:90.

[0104] (Electrospinning conditions) Details of nozzle A (hereinafter simply referred to as "nozzle") on the syringe: The shape of the spinning fluid discharge portion is a metal nozzle with an inner diameter of 0.2 mm. Voltage applied to nozzle A (voltage applied to the spinning solution discharged from nozzle A): 9kV Distance from the spinning fluid discharge point in nozzle A to the grounded stainless steel rotating drum (collector): 10 cm Details of Nozzle B: A metal nozzle with a circular shape for the spinning fluid discharge portion, with an inner diameter of 0.25 mm. Voltage applied to nozzle B (voltage applied to the spinning solution discharged from nozzle B): 9kV Distance from the spinning fluid discharge point in nozzle B to the grounded stainless steel rotating drum (collector): 10 cm Spinning environment temperature: 25℃ Humidity in the spinning space: 20%RH

[0105] (Comparative Example 1) Electrospinning was performed by discharging spinning solution S1 from nozzle A at a discharge rate of 2.0 g / hour and accumulating on a stainless steel rotating drum, which served as a grounded counter electrode. Electrospinning formed a conductive fiber web on the entire surface of the rotating drum, consisting solely of first conductive fibers, which were continuous fibers mixed with organic resin and conductive particles in a mass ratio of 20:80. In this conductive fiber web, conductive granular material with the same composition as the first conductive fibers was adhered to the surface of the first conductive fibers. The dispersion medium was then removed from the conductive fiber web, and a conductive fiber sheet was prepared on the entire surface of the rotating drum. The basis weight of the conductive fiber sheet on the rotating drum was 7 g / m². 2 This was the calculated result.

[0106] (Example 1) Electrospinning was performed by discharging spinning solution S1 from nozzle A at a discharge rate of 2.0 g / hour, and simultaneously discharging spinning solution S2 from nozzle B at a discharge rate of 2.0 g / hour, with spinning solution S1 and spinning solution S2 accumulating on a stainless steel rotating drum, which served as a grounded counter electrode. The spinning time was such that the amount of yarn on the rotating drum was 7 g / m². 2The spinning conditions were set to be short so that a conductive fiber sheet could be prepared. Other spinning conditions were set to be the same as in Comparative Example 1. By electrospinning, a conductive fiber web was formed on the entire surface of the rotating drum, in which first conductive fibers, which are continuous fibers in which organic resin and conductive particles are mixed in a mass ratio of 20:80, and second conductive fibers, which are continuous fibers in which organic resin and conductive particles are mixed in a mass ratio of 40:60, were mixed. In this conductive fiber web, conductive granular material with the same composition as the first conductive fibers was fixed to the surface of the first conductive fibers. On the other hand, conductive granular material with the same composition as the second conductive fibers was not fixed to the surface of the second conductive fibers. The average fiber diameter of the second conductive fibers was larger than the average fiber diameter of the first conductive fibers. Then, the dispersion medium was removed from the conductive fiber web, and a conductive fiber sheet was prepared on the entire surface of the rotating drum.

[0107] (Comparative Example 2) Electrospinning was performed by discharging spinning solution S3 from nozzle A at a discharge rate of 2.0 g / hour and accumulating on a stainless steel rotating drum, which served as a grounded counter electrode. The spinning conditions were set to be the same as in Comparative Example 1. By electrospinning, a conductive fiber web was formed on the entire surface of the rotating drum, consisting only of first conductive fibers, which are continuous fibers mixed with organic resin and conductive particles in a mass ratio of 10:90. In this conductive fiber web, conductive granular material with the same composition as the first conductive fibers was fixed to the surface of the first conductive fibers. Then, the dispersion medium was removed from the conductive fiber web, and a conductive fiber sheet was prepared on the entire surface of the rotating drum. The basis weight of the conductive fiber sheet on the rotating drum was 16 g / m². 2 This was the calculated result.

[0108] (Example 2) Electrospinning was performed by discharging spinning solution S3 from nozzle A at a discharge rate of 2.0 g / hour, and simultaneously discharging spinning solution S2 from nozzle B at a discharge rate of 2.0 g / hour, with spinning solution S3 and spinning solution S2 accumulating on a stainless steel rotating drum, which served as a grounded counter electrode. The spinning time was 16 g / m² on the rotating drum. 2The spinning conditions were set to be long enough to prepare a conductive fiber sheet. Other spinning conditions were set to be the same as in Example 1, Comparative Example 1, and Comparative Example 2. By electrospinning, a conductive fiber web was formed on the entire surface of the rotating drum, in which first conductive fibers, which are continuous fibers in which organic resin and conductive particles are mixed in a mass ratio of 10:90, and second conductive fibers, which are continuous fibers in which organic resin and conductive particles are mixed in a mass ratio of 40:60, were mixed. In this conductive fiber web, conductive granular material with the same composition as the first conductive fibers was fixed to the surface of the first conductive fibers. On the other hand, conductive granular material with the same composition as the second conductive fibers was not fixed to the surface of the second conductive fibers. The average fiber diameter of the second conductive fibers was larger than the average fiber diameter of the first conductive fibers. Then, the dispersion medium was removed from the conductive fiber web, and a conductive fiber sheet was prepared on the entire surface of the rotating drum.

[0109] <Evaluation Method> The conductive fiber sheets of the examples and comparative examples were evaluated by the following method.

[0110] (Strength evaluation method) An attempt was made to peel a conductive fiber sheet from a rotating drum. If the conductive fiber sheet was peeled from the rotating drum without cracking or fracturing, and a single conductive fiber sheet was obtained, the strength evaluation was set to "OK". On the other hand, if cracking or fracturing occurred, and the conductive fiber sheet could not be peeled from the rotating drum, and a single conductive fiber sheet could not be obtained, the strength evaluation was set to "NG".

[0111] Conductive fiber sheets rated "OK" are considered to be highly rigid, easy to handle, and have a low defect rate in the process. Even when force is applied to the conductive fiber sheet, the conductive fibers that make up the sheet are unlikely to break, thus reducing the possibility of conductive granular material falling off. Conductive fiber sheets rated "NG" are considered to be less rigid, difficult to handle, and have a high defect rate in the process. When force is applied to the conductive fiber sheet, the conductive fibers that make up the sheet are likely to break, thus making it likely that conductive granular material will fall off.

[0112] (Method for evaluating resistance in liquid) A conductive fiber sheet was immersed in a 33 v / v% alcohol aqueous solution (color: transparent) filled in a beaker, and the beaker was gently shaken. The conductive fiber sheet was then removed from the alcohol aqueous solution. The resistance evaluation was performed by visually observing the alcohol aqueous solution after the conductive fiber sheet was removed. If the color of the alcohol aqueous solution was perceived to remain transparent, the resistance evaluation was set to "OK," and if the color of the alcohol aqueous solution was perceived to have changed to gray, the resistance evaluation was set to "NG."

[0113] Conductive fiber sheets rated "OK" are considered to be conductive fiber sheets in which conductive granular material containing black conductive particles does not easily fall off. Conductive fiber sheets rated "NG" are considered to be conductive fiber sheets in which conductive granular material containing black conductive particles easily falls off.

[0114] (Method for measuring electrical resistance) A test specimen, obtained by cutting a conductive fiber sheet to a size of φ25 mm, was sandwiched on both sides between gold-plated metal plates, and a pressure of 2 MPa was applied in the direction of the stacking of the metal plates. In this state, the resistance value (mΩ) of the test specimen was measured using a low-resistance measuring device (HIOKI E.E. CORPORATION, model: RM3545), and furthermore, the measured resistance value was multiplied by the area of ​​the test specimen (4.9 cm²). 2 By multiplying by ), the electrical resistance value (mΩ·cm) can be calculated. 2 The result was calculated.

[0115] (Method for measuring contact angle) The contact angle was measured using a dynamic contact angle measuring device (manufactured by Kyowa Interface Science Co., Ltd., model: DM500). Specifically, a droplet of pure water was dropped onto the surface of a test piece taken from a conductive fiber sheet, and 15 seconds after dropping, the angle that the dropped droplet made with respect to the surface of the test piece was measured. A larger contact angle indicates a more water-repellent conductive fiber sheet.

[0116] Table 1 shows the evaluation results and measurement results for each. In Comparative Example 1, since a conductive fiber sheet could not be obtained on its own, resistance evaluation was not performed, and thickness, electrical resistance, and contact angle were not measured.

[0117] [Table 1]

[0118] As shown in Table 1, the conductive fiber sheets of Comparative Example 1 and Comparative Example 2 failed the strength evaluation. Therefore, it is considered that the conductive granular material is prone to falling off in the conductive fiber sheets of Comparative Example 1 and Comparative Example 2. On the other hand, the conductive fiber sheets of Example 1 and Example 2 passed both the strength evaluation and the resistance evaluation. Therefore, it is considered that the conductive granular material is less likely to fall off in the conductive fiber sheets of Example 1 and Example 2. [Explanation of symbols]

[0119] 1...Conductive fiber sheet, 2...First conductive fiber, 3...Conductive granular material, 4...Second conductive fiber.

Claims

1. First conductive fiber, A conductive granular material provided on the surface of the first conductive fiber, Second conductive fiber, Equipped with, Each of the first conductive fiber, the conductive granular body, and the second conductive fiber comprises an organic resin and conductive particles. A conductive fiber sheet in which the ratio of the mass of the second conductive fiber to the mass of the second conductive fiber is greater than the ratio of the mass of the first conductive fiber to the mass of the first conductive fiber.

2. The conductive fiber sheet according to claim 1, wherein the first conductive fiber contains the same organic resin as the organic resin contained in the conductive granular material.

3. The conductive fiber sheet according to claim 2, wherein the composition of the first conductive fiber is the same as the composition of the conductive granular material.

4. The conductive fiber sheet according to any one of claims 1 to 3, further comprising an electrode catalyst for a fuel cell supported on the conductive fiber sheet.

5. A gas diffusion electrode for an electrochemical element, A gas diffusion electrode comprising the conductive fiber sheet described in claim 4.

6. A moisture management sheet for electrochemical elements, A moisture control sheet comprising a conductive fiber sheet according to any one of claims 1 to 3.

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