Electrode substrate, and polymer electrolyte fuel cell equipped with said electrode substrate.

Abstract

To provide an electrode substrate with lower electrical resistance. [Solution] The electrode substrate comprises a nonwoven fabric, and the nonwoven fabric contains conductive fibers as constituent fibers, which include at least one organic resin containing carbon nanotubes and other conductive particles.

Description

[Technical Field]

[0001] The present invention relates to an electrode substrate and a polymer electrolyte fuel cell equipped with the electrode substrate. [Background technology]

[0002] Fuel cells are devices that directly convert chemical energy into electrical energy, and due to their efficiency and environmental considerations, much research and development is underway. The gas diffusion layer (GDL), which is part of the fuel cell, plays an important role in promoting the uniform supply of fuel and oxidizer gases to the catalyst layer where they react, and also in managing the water produced. Such gas diffusion layers are composed of electrode substrates, and these electrode substrates mainly consist of substrates such as carbon paper and carbon cloth, as well as substrates with a microporous layer (MPL).

[0003] As an electrode substrate that can also be used in such gas diffusion layers, the present applicant is also developing an electrode substrate, and in Patent Document 1, proposes "a substrate for a gas diffusion electrode comprising a nonwoven fabric containing conductive fibers that contain conductive particles at least inside an organic resin." [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] International Publication No. 2014 / 010715 [Overview of the project] [Problems that the invention aims to solve]

[0005] However, the electrode substrate described in Patent Document 1 had high electrical resistance and did not exhibit sufficient performance. Patent Document 1 discloses that carbon black, carbon nanotubes, carbon nanofibers, etc., can be used as the conductive particles. However, Patent Document 1 does not disclose or suggest the knowledge of combining and incorporating multiple types of conductive particles at least inside the organic resin, nor does it disclose the optimal blending ratio in such cases. Therefore, the object of the present invention is to provide an electrode substrate with lower electrical resistance. [Means for solving the problem]

[0006] The present invention [1] An electrode substrate comprising a nonwoven fabric, wherein the nonwoven fabric comprises conductive fibers as constituent fibers, which contain carbon nanotubes and other conductive particles at least within an organic resin, [2] The electrode substrate of [1] wherein the percentage of the mass of the carbon nanotubes in relation to the sum of the masses of the carbon nanotubes and the other conductive particles is greater than 0.0% by mass and 3.5% by mass or less. A polymer electrolyte fuel cell comprising an electrode substrate of [3][1] or [2], Regarding. [Effects of the Invention]

[0007] According to the electrode substrate [1] of the present invention, the conductive fibers constituting the nonwoven fabric contain at least carbon nanotubes and other conductive particles as conductive particles, thus providing an electrode substrate with low electrical resistance. As will be clear from the examples described later, the electrical resistance of the electrode substrate [1] of the present invention is lower compared to those containing only carbon black as a conductive component, or those containing both carbon black and carbon nanofibers.

[0008] According to the electrode substrate of [2], which is one preferred embodiment of the present invention, an electrode substrate with excellent handling properties can be provided.

[0009] The polymer electrolyte fuel cell according to [3] of the present invention, which comprises the electrode substrates described in [1] or [2] above, has low internal resistance and is therefore highly efficient in generating electricity. [Modes for carrying out the invention]

[0010] (Electrode substrate of the present invention) The electrode substrate of the present invention comprises a nonwoven fabric containing conductive fibers as constituent fibers, which contain carbon nanotubes and other conductive particles at least within an organic resin. Because the conductive fibers of this nonwoven fabric are flexible due to the inclusion of the organic resin, the risk of the conductive fibers damaging the solid polymer film and causing a short circuit is reduced.

[0011] The organic resin constituting these conductive fibers may be either a hydrophobic or hydrophilic organic resin, and is not particularly limited to any one type. The former, a hydrophobic organic resin, is preferable as it exhibits excellent water repellency and excellent drainage properties as an electrode substrate, even without impregnation with hydrophobic resins such as fluororesins. On the other hand, if the electrode substrate is a hydrophilic organic resin, it is preferable because the electrode substrate can retain moisture. Therefore, in a polymer electrolyte fuel cell using this electrode substrate as the gas diffusion layer, the polymer film can be kept moist, and a polymer electrolyte fuel cell capable of generating sufficient power can be manufactured. In particular, if it consists solely of a hydrophilic organic resin, it can retain moisture and keep the polymer film moist even in low-humidity environments, thus enabling the manufacture of a polymer electrolyte fuel cell capable of generating sufficient power.

[0012] This "hydrophobic organic resin" refers to an organic resin with a contact angle of 90° or more with water. Examples include fluororesins such as polytetrafluoroethylene (PTFE), polychlorotrifluoroethylene (PCTFE), polyvinylidene fluoride resins (polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-tetrafluoroethylene-hexafluoropropylene copolymer, and mixed resins thereof), polyvinyl fluoride (PVF), perfluoroalkoxy fluororesins (PFA), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), ethylene-tetrafluoroethylene copolymer (ETFE), ethylene-chlorotrifluoroethylene copolymer (ECTFE), and copolymers of various monomers that constitute the above resins, polyolefin resins such as polyethylene (PE) and polypropylene (PP), and polyester resins such as polyethylene terephthalate (PET) and polyethylene naphthalate (PEN). Furthermore, these resins can be used individually or in mixtures of two or more types. Among these, fluororesins are particularly suitable for use due to their strong heat resistance, chemical resistance, and hydrophobicity. Polyvinylidene fluoride resins are even more preferable due to their excellent processability and mechanical properties.

[0013] On the other hand, "hydrophilic organic resins" are organic resins with a contact angle with water of less than 90°. Examples include cellulose (e.g., rayon), polyamide resins (e.g., nylon 6, nylon 66), polyacrylonitrile, acrylic oxide, polyvinyl alcohol resins, acrylic resins (e.g., polyacrylic acid, polymethacrylic acid), and resins having hydrophilic groups (amide groups, carboxyl groups, hydroxyl groups, amino groups, sulfonic acid groups, etc.) (e.g., hydrophilic polyurethane, polyvinylpyrrolidone, acrylonitrile copolymer, polybenzimidazole, polyethersulfone, polyimide, etc.). These resins can be used individually or in mixtures of two or more. Among these, polyacrylonitrile is preferred because it has excellent heat resistance and is less likely to collapse due to swelling of the solid polymer film. In the conductive fibers of the present invention, a hydrophobic organic resin and a hydrophilic organic resin may also be mixed or composited. When the conductive fibers contain a hydrophobic organic resin and a hydrophilic organic resin, the electrode base material can exhibit both of the effects described above, which is preferable. The contact angle can be measured as follows. A membrane sample with a smooth surface made of a resin to be measured, or a sample with a smooth surface coated with the resin to be measured (such as a glass plate coated with the resin to be measured) is prepared. Then, using a contact angle measuring device (model DM500, manufactured by Kyowa Interface Science Co., Ltd.), 3 µL of a droplet of pure water (equivalent to secondary distilled water after distillation and ion exchange, temperature: 25°C) is dropped onto the surface of the sample. 15 seconds after dropping, the contact angle is obtained by measuring the angle formed by the dropped droplet relative to the sample surface.

[0014] The conductive fibers according to the present invention contain carbon nanotubes, which are one type of conductive particles, in at least the interior of the organic resin, and other conductive particles having conductivity other than the carbon nanotubes (hereinafter, the carbon nanotubes and the other conductive particles may be collectively referred to as conductive particles), so that an electrode base material excellent in electron mobility and low in electrical resistance can be formed. That is, in conductive fibers having conductive particles only on the outer surface of the organic resin, the organic resin component acts as a resistance component, resulting in poor conductivity. However, in the present invention, since conductive particles are contained inside the organic resin, the conductive fibers according to the present invention are excellent in conductivity. From the viewpoint of conductivity, it is preferable that the conductive particles are exposed from the organic resin. The phrase "contains carbon nanotubes and other conductive particles in the interior" does not only mean a state where the conductive particles are completely embedded in the organic resin, but also means a state where part of the conductive particles are exposed from the organic resin. Such conductive fibers containing conductive particles in at least the interior of the organic resin can be produced, for example, by spinning a spinning solution containing an organic resin and conductive particles.

[0015] In this invention, carbon nanotubes refer to fibrous hollow carbon materials in which graphite sheets, i.e., carbon atom planes with a graphite structure or graphene sheets, are closed into a tubular shape. The fiber diameter is on the nanometer scale, and the wall structure has a graphite structure. In carbon nanotubes, the length of the fiber (length in the long side direction) perpendicular to the fiber diameter (fiber diameter, length in the short side direction) is less than 50 nm. Furthermore, the aspect ratio between the length in the long side direction and the length in the short side direction is greater than 3. Among carbon nanotubes having such structures, those with a wall structure enclosed in a tube shape by a single graphite sheet are called single-walled carbon nanotubes (SWCNTs), while those with a structure in which multiple graphite sheets are each enclosed in a tube shape and nested together are called multi-walled carbon nanotubes (nested multi-walled carbon nanotubes or MWCNTs). Carbon nanotubes also include fibrous hollow carbon material called carbon nanohorns, which have one end closed to form a cone shape. In this invention, these carbon nanotubes may be used individually or in combination. In particular, single-walled carbon nanotubes are preferred as carbon nanotubes because they have a fine fiber diameter and excellent conductivity and flexibility.

[0016] There are no particular limitations on the type of other conductive particles having conductivity other than carbon nanotubes contained in the conductive fibers (hereinafter may be abbreviated as other conductive particles), and examples thereof include graphite particles, charcoal black particles, carbon black particles, carbon nanofibers, metal particles, and metal oxide particles. Graphite particles, charcoal black particles, carbon black particles, metal particles, and metal oxide particles all have a spherical particle shape in which the aspect ratio of the average primary particle diameter in the longest direction (long side direction) of the particle shown in an electron micrograph to the length in the short side direction orthogonal to the long side direction is 3 or less, so they are conductive particles having a structure different from that of carbon nanotubes. In addition, carbon nanofibers have a fiber diameter of 50 nm or more, so they are conductive particles having a structure different from that of carbon nanotubes. This "fiber diameter" means the fiber diameter of the measurement object measured based on a micrograph such as an electron micrograph. Among these, carbon black particles are suitably used from the viewpoints of chemical resistance, conductivity, and dispersibility. There are no particular limitations on the particle diameter of the suitable carbon black particles, but carbon black particles having an average primary particle diameter of 5 nm to 200 nm, more preferably 10 nm to 100 nm can be used. It is preferable that the average primary particle diameter of the other conductive particles is smaller than the fiber diameter of the conductive fibers constituting the nonwoven fabric included in the electrode substrate, so that the particles are less likely to fall off and easily form a fiber morphology. This "average primary particle diameter" means the arithmetic average value of the longest diameter of each of 40 measurement objects, measured based on a micrograph such as an electron micrograph.

[0017] The mass ratio of conductive particles to organic resin contained in such conductive fibers (i.e., the ratio of the total mass of carbon nanotubes and other conductive particles having conductivity other than said carbon nanotubes to the mass of the organic resin) is not particularly limited, but is preferably 10-90:90-10, more preferably 20-80:80-20, even more preferably 30-70:70-30, and still more preferably 40-60:60-40. This is because if the amount of conductive particles falls below 10 mass%, conductivity tends to be insufficient, while if the amount of conductive particles exceeds 90 mass%, fiber formation tends to decrease.

[0018] The percentage of carbon nanotubes in relation to the total mass of conductive particles (i.e., the total mass of carbon nanotubes and other conductive particles having conductivity other than said carbon nanotubes) is greater than 0.0 mass%, but to obtain an electrode substrate that is more conductive and has lower electrical resistance, this percentage is preferably 0.5 mass% or more, more preferably 0.8 mass% or more, more preferably 1.0 mass% or more, more preferably 1.5 mass% or more, more preferably 2.0 mass% or more, more preferably 2.5 mass% or more, more preferably 3.0 mass% or more, and most preferably 3.5 mass% or more. On the other hand, the upper limit of this percentage can be adjusted as appropriate, but to obtain an electrode substrate with excellent handling properties, it is preferably 10 mass% or less, more preferably 5 mass% or less, and most preferably 3.5 mass% or less.

[0019] The average fiber diameter of the conductive fibers in this invention is not particularly limited, but it is preferably 10 nm to 10 μm. If the average fiber diameter exceeds 10 μm, there are fewer contact points between the conductive fibers on the electrode substrate, and conductivity tends to be insufficient. On the other hand, if it is less than 10 nm, it tends to be difficult to contain conductive particles inside the conductive fibers.

[0020] This "average fiber diameter" refers to the arithmetic mean of the individual fiber diameters at 40 points on the object being measured, and the "fiber diameter" is a value measured based on microscopic images such as electron microscope images at 1000 to 10000x magnification. If the object is composed only of conductive fibers with exposed conductive particles, it refers to the diameter including the exposed conductive particles. If the object does not contain conductive fibers with exposed conductive particles, or if it contains conductive fibers with exposed conductive particles but also includes portions where the conductive particles are not exposed, it refers to the diameter of the portion where the conductive particles are not exposed.

[0021] In the present invention, the conductive fibers are preferably continuous fibers to ensure excellent electron mobility. Furthermore, in a polymer electrolyte fuel cell using an electrode substrate made of continuous conductive fibers as the gas diffusion layer, the reduced number of ends of the conductive fibers makes it less likely to damage the polymer electrolyte film, which is preferable. Such continuous conductive fibers can be manufactured by the manufacturing method described later.

[0022] The mass content of conductive fibers in the nonwoven fabric constituting the electrode substrate of the present invention is preferably 10% by mass or more, more preferably 50% by mass or more, even more preferably 70% by mass or more, and even more preferably 90% by mass or more, in order to ensure excellent electron mobility, and it is most preferable that the substrate is composed solely of conductive fibers. In addition, other constituent fibers besides conductive fibers may include, for example, fibers composed of hydrophobic organic resins or fibers composed of hydrophilic organic resins.

[0023] The electrode substrate of the present invention preferably has a surface resistivity Rs (unit: Ω / sq) of 2000 Ω / sq or less, more preferably 1500 Ω / sq or less, and most preferably 1000 Ω / sq or less, so that it has excellent conductivity. Here, the smaller this value, the more conductive the electrode substrate subjected to measurement is in the direction of its main surface and the lower its electrical resistance. The surface resistivity is measured using the method described in JIS K7194:1994 "Test Method for Resistivity of Conductive Plastics by Four-Probe Method," and this is defined as the surface resistivity (Ω / sq). The apparatus used is a Loresta-GX MCP-T700 (probe: PSP probe) manufactured by Mitsubishi Chemical Analytec.

[0024] Furthermore, the volume resistivity (unit: Ωcm), which indicates the resistance per unit volume of the electrode substrate of the present invention, is preferably 8 Ωcm or less, more preferably 5 Ωcm or less, even more preferably 3 Ωcm or less, and most preferably 1 Ωcm or less. Here, the smaller this value, the more conductive and low the electrical resistance of the electrode substrate subjected to measurement. The volume resistivity is calculated by multiplying the surface resistivity Rs by the thickness of the electrode substrate (in cm).

[0025] The nonwoven fabric constituting the electrode substrate of the present invention may be bonded using an adhesive to maintain its shape, but it is preferable that its shape be maintained by bonding the organic resin constituting the conductive fibers in order to achieve excellent conductivity. Examples of this preferred bonding of the organic resin include entanglement of fibers, bonding by plasticization with a solvent, bonding by thermal fusion, and compression by pressing.

[0026] The basis weight of the nonwoven fabric constituting the electrode substrate of the present invention is not particularly limited, but from the viewpoint of ease of handling and productivity, and from the viewpoint of having good drainage and gas diffusion properties when the electrode substrate is used as a gas diffusion layer in a polymer electrolyte fuel cell, 0.5 to 200 g / m² is recommended. 2 Preferably, it is 0.5 to 100 g / m 2 It is more preferable that the density be 0.5 to 50 g / m 2 It is even more preferable that it is as follows. The thickness is also not particularly limited, but is preferably 1 to 1000 μm, more preferably 3 to 500 μm, more preferably 5 to 300 μm, and even more preferably 10 to 100 μm.

[0027] In the present invention, "mass per unit area" refers to a value obtained by measuring the mass of a measurement object such as an electrode substrate and converting it to the mass per 1 m 2 of the main surface, which is the surface with the largest area; "thickness" refers to the length of the shortest distance between both main surfaces of a measurement object such as an electrode substrate, measured using a thickness gauge (manufactured by Mitutoyo Corporation, Code No. 547-401, measuring force: 3.5 N or less). Further, the density (unit: g / cm 3 ) of the nonwoven fabric constituting the electrode substrate of the present invention can be appropriately adjusted. The density is preferably 0.1 g / cm 3 or more, more preferably 0.2 g / cm 3 or more, still more preferably 0.3 g / cm 3 or more, still more preferably 0.4 g / cm 3 or more, still more preferably 0.5 g / cm 3 or more, still more preferably 0.6 g / cm 3 or more, and most preferably 0.6 g / cm or more. The upper limit can be adjusted as appropriate, but is preferably less than 1.0 g / cm 3 and more preferably 0.9 g / cm 3 or less. In the present invention, the "density" can be calculated by dividing the mass per unit area by the thickness.

[0028] When the electrode substrate is used as a gas diffusion layer for a polymer electrolyte fuel cell, the nonwoven fabric constituting the electrode substrate of the present invention preferably has a porosity of 20% or more, more preferably 30% or more, still more preferably 40% or more, still more preferably 50% or more, and most preferably 60% or more, from the viewpoint of excellent drainage performance and gas diffusivity. The upper limit of the porosity is not particularly limited, but is 99% or less from the viewpoint of morphological stability. In addition, the porosity P (unit: %) refers to a value obtained from the following formula. P=100-(Fr1+Fr2+··+Frn) Here, Frn represents the filling rate (unit: %) of component n constituting the nonwoven fabric, and refers to a value obtained from the following formula. Frn=(M×Prn / T×SGn)×100 Here, M is the basis weight of the nonwoven fabric (unit: g / cm²). 2 ), T is the thickness of the nonwoven fabric (cm), Prn is the mass ratio of component n (e.g., organic resin, conductive particles) in the nonwoven fabric, and SGn is the specific gravity of component n (unit: g / cm³). 3 These each mean the following:

[0029] Furthermore, the surface and / or voids of the nonwoven fabric may contain fluororesin and / or other conductive particles. The inclusion of the former, fluororesin, can increase the supply or discharge of fuel gas and moisture generated internally, while the inclusion of the latter, other conductive particles, can increase conductivity. As this fluorine-based resin, for example, the resin mentioned above as a hydrophobic organic resin can be used. Furthermore, as another conductive particle, it can be appropriately selected and used from the conductive particles mentioned above.

[0030] The nonwoven fabrics described above can be used as electrode substrates as they are. However, nonwoven fabrics that have undergone surface treatments such as water-repellent treatment or hydrophilic treatment to achieve the desired physical properties may also be used as electrode substrates. Furthermore, depending on the application and manner of use, nonwoven fabrics that have undergone various secondary processes, such as punching out the fabric to achieve the desired shape or pressing to adjust various physical properties such as thickness and surface smoothness, may also be used as electrode substrates.

[0031] (Method for manufacturing electrode substrate of the present invention) The electrode substrate of the present invention can be manufactured, for example, as follows.

[0032] First, conductive fibers are formed by spinning using a spinning solution that mixes an organic resin, a solvent for the organic resin, and conductive particles. These conductive fibers are then directly collected and accumulated to form a fiber web. If the fiber web itself is sufficiently entangled to be strong enough to be handled, it can be used as a nonwoven fabric as is. Alternatively, to impart or improve its strength, it can be bonded by methods such as plasticization with a solvent, thermal fusion, bonding with an adhesive, or compression by pressing to form a nonwoven fabric. It is preferable that the fibers constituting the fiber web formed by directly collecting and accumulating conductive fibers are continuous long fibers.

[0033] Examples of methods for forming the fiber web include electrospinning, spunbonding, meltblowing, or a method disclosed in Japanese Patent Publication No. 2009-287138, in which gas is discharged parallel to the spinning solution discharged from a liquid discharge unit, and a shear force is applied to the spinning solution in a single linear direction to form fibers. Among these, electrospinning or the method disclosed in Japanese Patent Publication No. 2009-287138 is preferable because it is possible to spin conductive fibers with a small fiber diameter, thereby enabling the production of a thin nonwoven fabric, and as a result, an electrode substrate with excellent conductivity can be realized. Furthermore, when mixing conductive particles into a solution obtained by dissolving an organic resin in a solvent, such as in the electrospinning method or the method disclosed in Japanese Patent Publication No. 2009-287138, it is preferable to use a solvent that does not easily volatilize during spinning, and then remove the spinning solvent by solvent replacement after forming a fiber web or nonwoven fabric. This makes it easier for the conductive fibers to become plastically bonded to each other, resulting in the production of a highly conductive nonwoven fabric, and also allows for the realization of an electrode substrate with excellent conductivity due to its dense structure.

[0034] Alternatively, conductive fibers may be wound as continuous fibers, then cut to a desired fiber length to form short fibers, and then a fiber web may be formed by a known dry or wet method. These short fibers may then be bonded together by entanglement, plasticization with a solvent, thermal fusion, adhesive bonding, or compression by pressing to form a nonwoven fabric.

[0035] A polymer electrolyte fuel cell can be prepared by using the electrode substrate of the present invention as a gas diffusion layer. The gas diffusion layer may be formed by laminating a substrate such as carbon paper or carbon cloth on the main surface of the electrode substrate according to the present invention, or the electrode substrate according to the present invention may be used as a gas diffusion layer (in this case, referred to as a self-supporting MPL) without using such a substrate. Furthermore, the gas diffusion layer can be used by laminating it so that the catalyst layer of the solid polymer electrolyte membrane is in contact with the main surface of the gas diffusion layer. Alternatively, the gas diffusion layer, which has a catalyst layer on its main surface, can be used by laminating it so that it is in contact with the solid polymer electrolyte membrane. The electrode substrate according to the present invention makes it possible to manufacture a polymer electrolyte fuel cell that is less prone to short circuits and has excellent power generation performance. Furthermore, in a gas diffusion layer employing the electrode substrate according to the present invention, electron conduction is not only carried out by contact between catalysts supported on the conductive fiber surface, but electron conduction paths are also formed by the conductive fibers, resulting in fewer catalysts isolated from the electron conduction paths. Furthermore, because the electrode substrate is made of a nonwoven fabric with excellent liquid permeability and breathability, it has superior drainage and gas diffusion properties, allowing for a sufficiently stable supply of gas to the three-phase interface (the reaction field where gas, catalyst, and electrolyte resin meet). For these reasons, the catalyst can be utilized efficiently, resulting in a reduction in the amount of catalyst required.

[0036] A gas diffusion layer employing the electrode substrate according to the present invention can have the same structure as a conventional gas diffusion layer, except that it comprises the electrode substrate according to the present invention. For example, examples of catalysts include platinum, platinum alloys, palladium, palladium alloys, titanium, manganese, magnesium, lanthanum, vanadium, zirconium, iridium, rhodium, ruthenium, cerium, gold, nickel-lanthanum alloys, titanium-iron alloys, and one or more catalysts selected from these can be supported. Furthermore, it is preferable that the material also contains an electron conductor and a proton conductor in addition to the catalyst. As the electron conductor, conductive particles similar to other conductive particles contained in conductive fibers such as carbon black particles are preferred, and the catalyst may be supported on these other conductive particles. As the proton conductor, an ion exchange resin is preferred.

[0037] A gas diffusion layer comprising a catalyst layer employing the electrode substrate according to the present invention can be manufactured, for example, by the following method. First, a catalyst (for example, carbon powder supported with a catalyst such as platinum) is added to a single or mixed solvent consisting of ethyl alcohol, propyl alcohol, butyl alcohol, ethylene glycol dimethyl ether, etc., and mixed. Then, an ion exchange resin solution is added and the mixture is uniformly mixed by ultrasonic dispersion or the like to obtain a catalyst dispersion suspension. Then, the catalyst dispersion suspension is coated or sprayed onto the electrode substrate according to the present invention, and dried to produce a gas diffusion layer having a catalyst layer on its main surface.

[0038] A membrane-electrode assembly, which is a composite of the gas diffusion layer and a solid polymer electrolyte membrane, can be used to produce a solid polymer fuel cell that is less prone to short circuits and has excellent power generation performance. A membrane-electrode assembly equipped with the electrode substrate according to the present invention can have the same structure as a conventional membrane-electrode assembly, except that it is equipped with the electrode substrate according to the present invention. Such a membrane-electrode assembly can be manufactured, for example, by sandwiching a solid polymer electrolyte membrane between a pair of gas diffusion layers, or between the catalyst-supporting surfaces of the gas diffusion layer according to the present invention provided on one of them, and joining them by hot pressing. Alternatively, it can also be manufactured by coating a catalyst dispersion suspension as described above onto a support to form a catalyst layer, transferring this catalyst layer to a solid polymer electrolyte membrane, then laminating the gas diffusion layer as described above onto the catalyst layer, and then hot pressing. As the solid polymer electrolyte membrane, for example, perfluorocarbon sulfonic acid-based resin membranes, sulfonated aromatic hydrocarbon-based resin membranes, alkyl sulfonated aromatic hydrocarbon-based resin membranes, etc., can be used.

[0039] Furthermore, a polymer electrolyte fuel cell has a structure in which multiple cell units are stacked, each consisting of a membrane-electrode assembly sandwiched between a pair of bipolar plates, as described above. For example, multiple cell units can be stacked and fixed in place for manufacturing. The bipolar plates are not particularly limited, as long as they have high conductivity, are impermeable to gas, and have channels that can supply gas to the gas diffusion layer. For example, carbon molding materials, carbon-resin composite materials, and metal materials can be used. [Examples]

[0040] The present invention will be specifically described below with reference to examples, but these examples are not intended to limit the scope of the present invention.

[0041] <Preparation of spinning solution> Spinning solutions A1 to A3, having the formulations listed in Table 1, were prepared by mixing N,N-dimethylformamide and N-methylpyrrolidone with polyvinylidene fluoride resin and conductive particles. Next, N,N-dimethylformamide and N-methylpyrrolidone were mixed with polyvinylidene fluoride resin, polyacrylonitrile, and conductive particles to prepare spinning solutions B1 to B3 having the formulations shown in Table 1. In the table, CNT refers to single-walled carbon nanotubes (fiber diameter: less than 10 nm, aspect ratio: greater than 15), CB refers to carbon black particles (average primary particle diameter: 40 nm, aspect ratio: 3 or less), and CNF refers to carbon nanofibers (fiber diameter: several hundred nm). Additionally, configurations that are not present are marked with a "-" in the table.

[0042] [Table 1]

[0043] <Fabrication of electrode substrates> (Example 1) The aforementioned spinning solution A1 was subjected to electrospinning to produce conductive fibers, which were then directly accumulated on a stainless steel drum serving as the counter electrode to create a nonwoven fabric (average fiber diameter: 800 nm) consisting solely of continuous conductive fibers. The electrospinning conditions were as follows. Electrode: Metal nozzle (inner diameter: 0.33 mm) and stainless steel drum Discharge amount: 1g / hour Distance between nozzle tip and stainless steel drum: 10cm Applied voltage: Voltage in the range of 10kV-20kV at which spinning is stable. Temperature / Humidity: 25℃ / 40%RH Furthermore, on the surface of the conductive fibers constituting the nonwoven fabric prepared in this manner, a portion of the conductive particles was exposed, and the conductive fibers were bonded together during assembly. The nonwoven fabric prepared in this manner was used as the electrode substrate. Subsequently, the electrode substrate was successfully removed from the stainless steel drum without damage, resulting in an electrode substrate with excellent handling properties.

[0044] (Comparative Example 1) A nonwoven fabric consisting only of continuous conductive fibers was prepared on a stainless steel drum in the same manner as in Example 1, except that spinning solution A2 was used instead of spinning solution A1. Furthermore, on the surface of the conductive fibers constituting the nonwoven fabric prepared in this manner, a portion of the conductive particles was exposed, and the conductive fibers were bonded together during assembly. The nonwoven fabric prepared in this manner was used as the electrode substrate. Subsequently, the electrode substrate was successfully removed from the stainless steel drum without damage, resulting in an electrode substrate with excellent handling properties.

[0045] (Comparative Example 2) A nonwoven fabric consisting only of continuous conductive fibers was prepared on a stainless steel drum in the same manner as in Example 1, except that spinning solution A3 was used instead of spinning solution A1. Furthermore, on the surface of the conductive fibers constituting the nonwoven fabric prepared in this manner, a portion of the conductive particles was exposed, and the conductive fibers were bonded together during assembly. The nonwoven fabric prepared in this manner was used as the electrode substrate. Subsequently, the electrode substrate was successfully removed from the stainless steel drum without damage, resulting in an electrode substrate with excellent handling properties.

[0046] (Example 2) The electrode substrate peeled from the stainless steel drum prepared in Example 1 was subjected to a press, and a pressure of 2 MPa was applied between its two main surfaces at a heating temperature of 30°C. In this way, an electrode substrate with reduced thickness was obtained.

[0047] Table 2 summarizes the various physical properties of the electrode substrates prepared in Comparative Examples 1-2 and Examples 1-2.

[0048] [Table 2]

[0049] A comparison of electrode substrates prepared in Comparative Example 1 (containing only carbon black particles as conductive particles) and Comparative Example 2 (containing carbon black particles and carbon nanofibers as conductive particles) with an electrode substrate prepared in Example 1, which is one aspect of the present invention (containing carbon nanotubes and carbon black particles as conductive particles) revealed that including carbon nanotubes as conductive particles resulted in a significant decrease in the surface resistivity Rs (and volume resistivity) of the electrode substrate. In particular, despite the fact that the mass percentage of conductive particles contained in the electrode substrate was lower than that of the electrode substrates prepared in Comparative Examples 1 and 2, the electrode substrate prepared in Example 1 exhibited high conductivity and low electrical resistance. Furthermore, when comparing Comparative Example 2, which also contains conductive particles with a fibrous shape (carbon nanofibers, carbon nanotubes), with Example 1, the electrode substrate prepared in Example 1 exhibited high conductivity and low electrical resistance despite the small mass percentage of conductive particles contained in the electrode substrate. From these results, it was found that electrode substrates equipped with nonwoven fabric containing conductive fibers that include carbon nanotubes and other conductive particles exhibit high conductivity and low electrical resistance.

[0050] Furthermore, the electrode substrate prepared in Example 2, which had a higher fiber density due to its reduced thickness, was more electrically conductive and had lower electrical resistance than the electrode substrate prepared in Example 1.

[0051] (Examples 3-5) Nonwoven fabrics consisting solely of continuous conductive fibers were prepared on a stainless steel drum in the same manner as in Example 1, except that spinning solution B1 (Example 3), spinning solution B2 (Example 4), and spinning solution B3 (Example 5) were used instead of spinning solution A1. Furthermore, on the surface of the conductive fibers constituting each nonwoven fabric prepared in this manner, a portion of the conductive particles was exposed, and the conductive fibers were bonded together during assembly. The nonwoven fabrics prepared in this manner were each used as electrode substrates. Subsequently, the electrode substrate was successfully removed from the stainless steel drum without damage, resulting in an electrode substrate with excellent handling properties.

[0052] (Example 6) Except for increasing the spinning time, a nonwoven fabric consisting only of continuous conductive fibers was prepared on a stainless steel drum in the same manner as in Example 5. Furthermore, on the surface of the conductive fibers constituting the nonwoven fabric prepared in this manner, a portion of the conductive particles was exposed, and the conductive fibers were bonded together during assembly. The nonwoven fabric prepared in this manner was used as the electrode substrate. Subsequently, the electrode substrate was successfully removed from the stainless steel drum without causing any damage.

[0053] The physical properties of the electrode substrates prepared in Examples 3 to 6 are summarized in Table 3.

[0054] [Table 3]

[0055] Since the electrode substrate according to the above-described embodiment is highly conductive and has low electrical resistance, by incorporating this electrode substrate, it is possible to provide a polymer electrolyte fuel cell with low internal resistance and high power generation efficiency. [Industrial applicability]

[0056] The electrode substrate of the present invention can be used, for example, as a substrate for a gas diffusion electrode for a fuel cell, as an electrode for an electric double-layer capacitor, or as an electrode for a lithium-ion secondary battery.

Claims

1. An electrode substrate comprising a nonwoven fabric, The nonwoven fabric contains conductive fibers as constituent fibers, which include at least one organic resin containing carbon nanotubes and other conductive particles. Electrode base material.

2. The percentage of the mass of the carbon nanotube in relation to the sum of the masses of the carbon nanotube and the other conductive particles is greater than 0.0% by mass and less than or equal to 3.5% by mass. The electrode substrate according to claim 1.

3. A polymer electrolyte fuel cell comprising the electrode substrate described in claim 1 or 2.

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