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

Abstract

Provided is a carbon fiber sheet having excellent performance suitable as a constituent member of a gas diffusion layer in a fuel cell. One embodiment of the present disclosure is a carbon fiber sheet characterized by containing a carbon fiber, conductive particles, an organic fiber, and a binder resin, the binder resin containing an olefin resin, a composite containing the conductive particles, the organic fibers, and the binder resin is affixed to a portion of a mesh structure formed by the carbon fibers.

Description

Technical Field

[0001] The present invention relates to a carbon fiber sheet, a gas diffusion layer for a fuel cell and a membrane electrode complex. Background Art

[0002] Fuel cells are gaining widespread popularity as a power source for automobiles and other applications. Fuel cells typically use an electrode component consisting of a catalyst layer and a gas diffusion layer in contact with the catalyst layer. This porous gas diffusion layer serves as an electrode substrate, homogenizes the gas reaching the catalyst layer, and facilitates the removal of excess water within the system. Improving the performance of the gas diffusion layer is crucial for fuel cell performance. Therefore, extensive research is underway to improve the performance of the gas diffusion layer.

[0003] In addition to being porous, the gas diffusion layer also requires electrical conductivity and strength, so carbon fiber sheets are sometimes used as components of the gas diffusion layer. For example, Patent Document 1 discloses a method in which carbon fibers are bonded with an adhesive and each 200 m 2 A carbon fiber sheet having a conductive material dust emission rate of 200,000 or less per area is used for the gas diffusion layer.

[0004] Prior art literature Patent Literature Patent Document 1: Japanese Patent Application Publication No. 2018-085332 Summary of the Invention Problems to be solved by the invention However, even when such a carbon fiber sheet is used, it is difficult to obtain sufficient performance as a constituent member of a gas diffusion layer in a fuel cell.

[0005] Therefore, an object of the present invention is to provide a carbon fiber sheet having excellent performance that is suitable as a constituent member of a gas diffusion layer in a fuel cell.

[0006] Means used to solve problems The present inventors have discovered that the above-mentioned problems can be solved by forming a carbon fiber sheet having a specific structure, and have thus completed the present invention.

[0007] A first aspect of the present invention is a carbon fiber sheet characterized in that: Contains carbon fibers, conductive particles, organic fibers and binder resin. The binder resin contains an olefin resin, A composite containing the conductive particles, the organic fibers, and the binder resin is fixed to a portion of the mesh structure formed by the carbon fibers.

[0008] The organic fibers are preferably fibrillated fibers.

[0009] The average fiber length of the carbon fibers is preferably 5 to 10 mm.

[0010] The average particle size of the conductive particles is preferably 10 to 500 μm.

[0011] The conductive particles are preferably scaly.

[0012] The density of the carbon fiber sheet is preferably 0.4 to 0.8 g / cm 3 .

[0013] Preferably, the carbon fiber sheet does not contain a fluorine-based resin, or the carbon fiber sheet contains the fluorine-based resin, and the content of the fluorine-based resin is 10% by mass or less when the entire carbon fiber sheet is taken as 100% by mass.

[0014] A second aspect of the present invention is a gas diffusion layer for a fuel cell, characterized in that: A microporous layer is laminated on the surface of the carbon fiber sheet.

[0015] The microporous layer preferably contains scaly conductive particles and an olefin-based resin.

[0016] A third aspect of the present invention is a membrane electrode assembly, The invention comprises an electrolyte membrane formed of a solid polymer electrolyte, a fuel electrode laminated on one surface of the electrolyte membrane, and an air electrode laminated on the other surface of the electrolyte membrane. The fuel electrode includes a first catalyst layer in contact with the electrolyte membrane and a first gas diffusion layer stacked on the first catalyst layer. The air electrode includes a second catalyst layer in contact with the electrolyte membrane and a second gas diffusion layer stacked on the second catalyst layer. At least one of the first gas diffusion layer and the second gas diffusion layer is the fuel cell gas diffusion layer.

[0017] Effects of the Invention According to the present invention, there is provided a carbon fiber sheet having excellent performance that is suitable as a constituent member of a gas diffusion layer in a fuel cell. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 This is a schematic diagram of a carbon fiber sheet disclosed herein.

[0019] Figure 2 This is a schematic diagram of the membrane electrode assembly disclosed in the present invention.

[0020] Figure 3 This is a SEM photograph of the surface of the carbon fiber sheet of this example. DETAILED DESCRIPTION

[0021] Hereinafter, when an upper limit value and a lower limit value are described separately, a numerical range combining an arbitrary upper limit value and an arbitrary lower limit value is substantially disclosed.

[0022] Hereinafter, unless otherwise specified, various measurements were performed with the ambient temperature being room temperature (23° C.).

[0023] Hereinafter, the carbon fiber sheet of the present disclosure, the gas diffusion layer for a fuel cell using the carbon fiber sheet of the present disclosure, and the membrane electrode assembly having the gas diffusion layer for a fuel cell will be described.

[0024] <<<Carbon fiber sheet>>> <<Ingredients>> The carbon fiber sheet disclosed herein contains carbon fibers, conductive particles, organic fibers, and a binder resin.

[0025] The carbon fiber sheet disclosed herein is formed by attaching a composite material containing conductive particles, organic fibers, and a binder resin to a portion of the mesh structure formed by the carbon fibers. In other words, the carbon fiber sheet is formed by attaching organic fibers, conductive particles, and a binder resin to (or around) the intertwining points where the carbon fibers intertwine. This structure, in which the specific composite material containing the conductive material is attached to the intertwining points of the carbon fiber sheet, improves strength while reducing electrical resistance.

[0026] Carbon fiber Carbon fibers constitute the main skeleton of the base material of the carbon fiber sheet and function as a conductive path or as a base for other components.

[0027] The average fiber length of the carbon fibers is preferably 1 mm or longer, 3 mm or longer, or 5 mm or longer, and preferably 100 mm or shorter, 50 mm or shorter, or 10 mm or shorter. The average fiber length of the carbon fibers is such that the fibers are sufficiently intertwined with one another and a mesh structure that serves as a foothold for other components is appropriately formed. Furthermore, since a uniform sheet is formed, a carbon fiber sheet having excellent electrical conductivity and strength can be obtained.

[0028] The average fiber length of the carbon fibers was calculated as the average value of the fiber diameters of 50 carbon fibers constituting the carbon fiber sheet measured using an optical microscope.

[0029] When the entire carbon fiber sheet is taken as 100 mass%, the carbon fiber content is preferably 10-50 mass%, 15-45 mass%, or 20-40 mass%. Adjusting the carbon fiber content to this range can improve the conductivity, strength, flexibility, etc. of the carbon fiber sheet.

[0030] Organic Fiber The organic fibers are preferably fibrillated fibers.

[0031] Organic fibers can be natural or synthetic.

[0032] Natural fibers include wood fibers such as MP (Mechanical pulp), CP (Chemical pulp), GP (Groundwood pulp), RGP (Refiner groundwood), CGP (Chemical groundwood), SP (Sulphite pulp), AP (Soda pulp), KP (Kraft pulp), and SCP (Semichemical pulp) made from coniferous and broadleaved trees, as well as fibers such as cotton, straw, bamboo, esparto grass, bagasse, linters, Manila hemp, flax, hemp, jute, and kansai.

[0033] Examples of synthetic fibers include olefin resin fibers such as polyethylene fibers and polypropylene fibers, polyacetal, polyimide, PBO (poly(p-phenylenebenzobisoxazole)), fluororesins such as PTFE (polytetrafluoroethylene), styrene and copolymers thereof, and acrylic acid esters and copolymers thereof.

[0034] These fibers are preferably fibrillated fibers. In addition, the fibrillation of fibers herein means that the fibers are subjected to a fibrillation process (a process of raising the fibers).

[0035] The method of fibrillating the fibers is not particularly limited, and the fibers can be fibrillated using a beater such as an SDR (Single Disc Refiner), a DDR (Double Disc Refiner), or a beater.

[0036] The fiber beating degree of the organic fiber as freeness (according to Canadian Standard Freeness, ie, JISP 8121) is preferably 300 CSF or less, 250 CSF or less, 200 CSF or less, or 150 CSF or less.

[0037] When the entire carbon fiber sheet is taken as 100 mass%, the content of organic fibers is preferably 1 to 20 mass%, 3 to 18 mass%, or 5 to 15 mass%. Adjusting the content of organic fibers to such a range can improve the conductivity, strength, and flexibility of the carbon fiber sheet.

[0038] In the carbon fiber sheet, the content of the organic fibers relative to the content of the carbon fibers (organic fibers / carbon fibers) is preferably 0.1 to 0.7, 0.1 to 0.6, or 0.2 to 0.5.

[0039] <Conductive particles> The average particle size of the conductive particles is preferably 1 to 500 μm, 10 to 500 μm, or 15 to 200 μm. Setting the average particle size of the conductive particles within this range improves the conductivity of the carbon fiber sheet while improving air permeability and preventing particle shedding.

[0040] The average particle size of the conductive particles is calculated as the average value of the particle sizes (maximum diameters) of 50 conductive particles contained in the carbon fiber sheet measured using an optical microscope.

[0041] The conductive particles may have any shape such as spherical, plate-like, linear, flake-like, or scaly. However, from the viewpoint of improving conductivity, the conductive particles are preferably scaly.

[0042] The conductive particles are not particularly limited as long as they have conductivity, and examples thereof include metal materials such as gold, silver, copper, nickel, tin, lead, zinc, bismuth, and alloys thereof, and carbon materials such as carbon black, graphite, carbon nanotubes, and fullerenes.

[0043] When the entire carbon fiber sheet is 100 mass %, the content of the conductive particles is preferably 10-50 mass %, 10-60 mass %, or 30-50 mass %. By setting the content of the conductive particles within this range, the conductivity and strength of the carbon fiber sheet can be improved.

[0044] In the carbon fiber sheet, the content of the conductive particles relative to the content of the carbon fibers (conductive particles / carbon fibers) is preferably 0.5 to 1.7, 0.8 to 1.6, or 1.0 to 1.5.

[0045] <Binder resin> The binder resin preferably contains an olefin-based resin. The binder resin in the present disclosure is a component generally used as a binder, and is a component different from the above-mentioned organic fiber.

[0046] Examples of the olefin-based resin include polyethylene, polypropylene, and cycloolefin polymer (COP resin).

[0047] By using such a resin as a binder component of the carbon fiber sheet, the water repellency, flexibility, strength, etc. of the carbon fiber sheet can be improved.

[0048] The binder resin content is preferably 5-30% or 10-25% by mass based on 100% by mass of the entire carbon fiber sheet. The binder resin content within this range can improve the conductivity, strength, and other properties of the carbon fiber sheet.

[0049] In the carbon fiber sheet, the content of the binder resin relative to the carbon fiber content (binder resin / carbon fiber) is preferably 0.3 to 1.2, 0.4 to 1.1, or 0.5 to 1.0.

[0050] In the carbon fiber sheet, the total content of the conductive particles, organic fibers, and binder resin relative to the carbon fiber content ((conductive particles+organic fibers+binder resin) / carbon fibers) is preferably 1.5 to 3.0, 1.8 to 2.8, or 2.0 to 2.5.

[0051] <Other ingredients> The carbon fiber sheet may contain other components as long as they do not impair the effects of the present invention. Examples of these other components include surfactants, dispersants, thickeners, defoamers, paper strengthening agents, inorganic binders, organic binders other than olefin resins, and inorganic fibers other than carbon fibers. When the total mass of the carbon fiber sheet is taken as 100%, these components are preferably 10% by mass or less, 5% by mass or less, 3% by mass or less, or 1% by mass or less.

[0052] The carbon fiber sheet preferably contains no fluorine-based resin, or preferably has a fluorine-based resin content of 10% by mass or less, based on 100% by mass of the entire carbon fiber sheet. Furthermore, the fluorine-based resin content, based on 100% by mass of the entire carbon fiber sheet, is preferably 5% by mass or less, 3% by mass or less, or 1% by mass or less. Because the carbon fiber sheet disclosed herein readily exhibits sufficient water repellency even without containing a fluorine-based resin (or even with a trace amount of fluorine-based resin), performance and productivity can be easily improved by optimizing the material.

[0053] Conventionally known carbon fiber sheets are generally obtained by a production method in which a carbon fiber sheet is formed, then immersed in a phenol material to carbonize the carbon fiber sheet, and then immersed in a fluorine-based resin material and fired.

[0054] Preferred embodiments of the carbon fiber sheet disclosed herein are as follows.

[0055] The carbon fiber sheet contains carbon fibers, conductive particles, organic fibers, and a binder resin.

[0056] The binder resin preferably contains an olefin-based resin.

[0057] When the entire carbon fiber sheet is taken as 100% by mass, the content of the carbon fibers is preferably 10 to 50% by mass.

[0058] When the entire carbon fiber sheet is taken as 100% by mass, the content of the organic fiber is preferably 1 to 20% by mass.

[0059] When the entire carbon fiber sheet is taken as 100% by mass, the content of the conductive particles is preferably 10 to 60% by mass.

[0060] When the entire carbon fiber sheet is taken as 100% by mass, the content of the binder resin is preferably 5 to 30% by mass.

[0061] When the entire carbon fiber sheet is taken as 100 mass %, the content of the fluorine-based resin is preferably 10 mass % or less (including 0 mass %).

[0062] In the carbon fiber sheet, the content of the organic fibers relative to the content of the carbon fibers (organic fibers / carbon fibers) is preferably 0.1 to 0.7.

[0063] In the carbon fiber sheet, the content of the conductive particles relative to the content of the carbon fibers (conductive particles / carbon fibers) is preferably 0.5 to 1.7.

[0064] In the carbon fiber sheet, the content of the binder resin relative to the content of the carbon fibers (binder resin / carbon fibers) is preferably 0.3 to 1.2.

[0065] Such a carbon fiber sheet is formed to exhibit excellent performance in terms of conductivity, flexibility, strength, etc.

[0066] <<Structure / Physical Properties>> The density of the carbon fiber sheet is preferably 0.1 to 1.5 g / cm 3 , 0.2~1.0g / cm 3 or 0.4~0.8g / cm 3 By setting the density of the carbon fiber sheet within such a range, it is possible to form a sheet having excellent electrical conductivity while ensuring the air permeability of the sheet.

[0067] The density of the carbon fiber sheet is calculated based on the mass and thickness of the carbon fiber sheet.

[0068] The thickness of the carbon fiber sheet is not particularly limited, but is preferably 10 to 1000 μm or 100 to 400 μm.

[0069] <<<Manufacturing method>>> An example of a method for producing a carbon fiber sheet is described below.

[0070] A carbon fiber sheet can be obtained by performing a raw material preparation step, a papermaking step, and a drying step. Each step will be described below.

[0071] <<Raw material preparation process>> The raw materials (carbon fibers, conductive particles, organic fibers, binder resin, etc.) are uniformly dispersed to prepare a raw material slurry.

[0072] <<Papermaking Process>> The raw material slurry is made into paper using a known papermaking machine to form a fiber sheet containing water (wet sheet).

[0073] As the papermaking machine used in the papermaking process, any papermaking machine suitable for general papermaking technology can be applied without particular limitation. Examples thereof include fourdrinier papermaking machines, short-wire papermaking machines, cylinder papermaking machines, inclined papermaking machines, twin-wire papermaking machines, and combination papermaking machines in which the same or different types of papermaking machines are combined.

[0074] <<Drying process>> The water contained in the wet sheet is dried to form a carbon fiber sheet.

[0075] As the drying apparatus used in the drying step, any apparatus suitable for drying carbon fiber sheets can be applied without particular limitation, and examples thereof include a Yankee dryer, a rotary dryer, a manual dryer, an air dryer, a cylinder dryer, a suction drum dryer, and an infrared dryer.

[0076] The drying temperature is not particularly limited and may be 100°C to 200°C.

[0077] The drying time may be extended until the water retention in the wet sheet reaches a predetermined range (eg, less than 1% by mass of the total sheet).

[0078] <<<Application>>> The carbon fiber sheet disclosed herein can be used for various purposes. The carbon fiber sheet disclosed herein can be preferably used as a material constituting an electrode material. The carbon fiber sheet disclosed herein can also be used in electrolysis devices, etc., but is particularly preferably used in a gas diffusion layer for a fuel cell. That is, the carbon fiber sheet disclosed herein can be preferably used as a carbon fiber sheet for forming a gas diffusion layer in a fuel cell. For example, the carbon fiber sheet disclosed herein can be preferably used as a component constituting a membrane electrode assembly of a fuel cell. In other words, the technology disclosed herein can also be provided as a fuel cell or a fuel cell stack having a membrane electrode assembly including a carbon fiber sheet. The fuel cell or fuel cell stack can be installed in an automobile as a power source.

[0079] Next, a specific example of a fuel cell gas diffusion layer including the carbon fiber sheet of the present disclosure will be described.

[0080] <<<<Gas Diffusion Layer A for Fuel Cell>>>> like Figure 1 As shown, the gas diffusion layer A for a fuel cell of the present disclosure is a laminate having a carbon fiber sheet A1 and a microporous layer A2 laminated on the surface of the carbon fiber sheet.

[0081] The carbon fiber sheet A1 has a function of uniformly diffusing the gas introduced into the gas diffusion layer 1 and stabilizing the reaction (catalytic reaction) of the gas in a fuel cell or the like.

[0082] The specific structure of the carbon fiber sheet A1 is as described above, and therefore its description is omitted.

[0083] The microporous layer A2 is a layer formed of a porous material and has a function of discharging water or water vapor, which are by-products generated by the reaction within the fuel cell.

[0084] As the microporous layer A2, a conventionally known microporous layer can be used, and a mixture of a binder resin and conductive particles is preferred.

[0085] As the olefin-based resin and the conductive particles, those described in the carbon fiber sheet A1 can be used.

[0086] The binder resin is preferably an olefin resin. Furthermore, the conductive particles are preferably flaky. By using the same binder resin and / or conductive particles as those used to form the carbon fiber sheet A1, the binder resin and / or conductive particles constituting the microporous layer A2 can provide a fuel cell gas diffusion layer having excellent strength and conductivity.

[0087] When the entire microporous layer A2 is taken as 100 mass %, the content of the binder resin is preferably 50 to 90 mass %, 55 to 85 mass %, or 60 to 80 mass %.

[0088] When the entire microporous layer A2 is taken as 100 mass %, the content of the conductive particles is preferably 10 to 50 mass %, 15 to 45 mass %, or 20 to 40 mass %.

[0089] The laminate including the carbon fiber sheet A1 and the microporous layer A2 can be produced, for example, by the following method.

[0090] The carbon fiber sheet A1 was manufactured according to the above method.

[0091] Next, a slurry is prepared by uniformly dispersing the conductive particles and the binder resin in an organic solvent. The organic solvent is not particularly limited as long as it can dissolve the binder resin. The amount of organic solvent is appropriately adjusted to achieve a viscosity that facilitates the coating method described below.

[0092] Next, a slurry containing conductive particles and a binder resin is applied to the carbon fiber sheet A1. Examples of coating methods include methods using a coater such as a dam coater, lip coater, die coater, or bar coater. The amount of slurry applied (coating thickness) can be appropriately adjusted to achieve the desired thickness after drying.

[0093] The carbon fiber sheet A1 coated with the slurry is heated to dry the organic solvent contained in the slurry, thereby forming a microporous layer A2.

[0094] As described above, a laminate including the carbon fiber sheet A1 and the microporous layer A2 laminated on the carbon fiber sheet A1 can be produced.

[0095] Furthermore, by applying the slurry for forming the microporous layer A2 and performing the drying step in a state containing moisture (or in a wet sheet state, which is a precursor of the carbon fiber sheet A1) before the drying step in the method for manufacturing the carbon fiber sheet A1 is completed, the drying steps of the carbon fiber sheet A1 and the microporous layer A2 can be performed simultaneously.

[0096] The thickness of the microporous layer A2 is not particularly limited, but is preferably 10 to 100 μm.

[0097] The tensile strength of the fuel cell gas diffusion layer A is preferably not less than 15 N. The tensile strength is a value measured using a tensile tester in accordance with JIS P8113.

[0098] The surface resistivity of the fuel cell gas diffusion layer A (microporous layer side) is preferably 2.0 Ω / □ or less or 1.4 Ω / □ or less.

[0099] The surface resistivity of the fuel cell gas diffusion layer A (microporous layer side) was obtained by preparing a 30 mm square test piece, measuring the IV characteristics, and calculating the resistance value.

[0100] Next, a membrane electrode assembly including the fuel cell gas diffusion layer A (or carbon fiber sheet A1) of the present disclosure will be described.

[0101] <<<<Membrane Electrode Assembly 100>>>> like Figure 2 As shown, the membrane electrode assembly 100 disclosed in the present invention has at least an electrolyte membrane 30 formed of a solid polymer electrolyte, a fuel electrode 10 stacked on one main surface of the electrolyte membrane 30, and an air electrode 20 stacked on the other main surface of the electrolyte membrane 30 (the main surface opposite to the main surface on which the fuel electrode 10 is stacked).

[0102] The fuel electrode 10 includes a first catalyst layer 11 in contact with the electrolyte membrane 30 and a first gas diffusion layer 12 stacked on the first catalyst layer 11 .

[0103] The air electrode 20 includes a second catalyst layer 21 in contact with the electrolyte membrane 30 and a second gas diffusion layer 22 stacked on the second catalyst layer 21 .

[0104] Preferably, at least one of the first gas diffusion layer 12 and the second gas diffusion layer 22 is formed from the fuel cell gas diffusion layer A disclosed herein (a gas diffusion layer comprising the carbon fiber sheet A1 and the microporous layer A2 disclosed herein). Alternatively, both the first gas diffusion layer 12 and the second gas diffusion layer 22 may be formed from the fuel cell gas diffusion layer A disclosed herein. When a gas diffusion layer other than the fuel cell gas diffusion layer A disclosed herein is used, a conventionally known gas diffusion layer (a gas diffusion layer composed of a conductive porous material) may be used.

[0105] In this example, both the first gas diffusion layer 12 and the second gas diffusion layer 22 are the fuel cell gas diffusion layer A disclosed herein. Figure 2 As shown, the first gas diffusion layer 12 is laminated so that the microporous layer A2 side is in contact with the electrolyte membrane 30. Similarly, the second gas diffusion layer 22 is laminated so that the microporous layer A2 side is in contact with the electrolyte membrane 30.

[0106] The first catalyst layer 11 and the second catalyst layer 21 can be conventionally known catalyst layers.

[0107] The catalyst layer is preferably a porous layer composed of a catalyst, and more preferably a porous layer formed of a granular catalyst substance.

[0108] Examples of the catalyst include metal materials such as platinum, palladium, ruthenium, iridium, rhodium, osmium, iron, lead, copper, chromium, cobalt, nickel, manganese, vanadium, molybdenum, gallium, and aluminum. The catalyst may also be an alloy or oxide of these metal materials.

[0109] Furthermore, the catalyst substance is preferably catalyst particles on which a carbon material is supported.

[0110] Examples of the carbon material include carbon black, graphite, carbon nanotubes, and fullerene.

[0111] The shape and particle size of the catalyst substance, the porosity of the catalyst layer (the filling rate of the catalyst substance or the porosity of the catalyst layer), and the like can be freely changed as appropriate depending on the conditions of use and the like.

[0112] The electrolyte membrane 30 is not particularly limited, and examples thereof include solid polymer electrolyte membranes such as fluorine-based electrolyte membranes and hydrocarbon-based electrolyte membranes.

[0113] The electrolyte membrane 30 may be an oxygen ion conductor or a hydrogen ion conductor.

[0114] In addition, if Figure 2 As shown, the membrane electrode assembly 100 is preferably formed on the opposite side of the fuel electrode 10 to the side on which the electrolyte membrane 30 is stacked ( Figure 2In the embodiment, the carbon fiber sheet A1 side of the fuel electrode 10 further includes a first separator 41. In addition, the membrane electrode assembly 100 preferably has a first separator 41 on the opposite side of the surface of the air electrode 20 on which the electrolyte membrane 30 is laminated. Figure 2 In the embodiment, the air electrode 20 (on the carbon fiber sheet A1 side) further includes a second separator 42.

[0115] Conventionally known diaphragms can be used as the first diaphragm 41 and the second diaphragm 42 .

[0116] The first separator 41 is a flat plate-shaped member. Although not shown, a plurality of grooves are provided on the main surface of the first separator 41 facing the fuel electrode 10 . These grooves serve as flow paths for guiding gas (hydrogen-containing gas) into the membrane electrode assembly 100 .

[0117] Similarly, the second diaphragm 42 is a flat plate-shaped member. Although not shown, a plurality of grooves are provided on the main surface of the second diaphragm 42 facing the air electrode 20. These grooves serve as flow paths for guiding gas (oxygen-containing gas) into the membrane electrode assembly 100.

[0118] In addition, the first separator 41 and the second separator 42 have a function of shielding the entire membrane electrode assembly 100 .

[0119] According to the use Figure 2 The fuel cell of the membrane electrode assembly 100 shown reacts as follows.

[0120] The hydrogen is introduced into the first gas diffusion layer 12 via the grooves provided in the first separator 41. The hydrogen introduced into the first gas diffusion layer 12 is uniformed in the surface direction and reaches the first catalyst layer 11.

[0121] Likewise, oxygen is introduced into the second gas diffusion layer 22 via the grooves provided in the second separator 42. The oxygen introduced into the second gas diffusion layer 22 is uniformed in the surface direction and reaches the second catalyst layer 21.

[0122] When the electrolyte membrane 30 is a hydrogen ion conductor, hydrogen ions and electrons are generated from hydrogen in the first catalyst layer 11. The generated hydrogen ions pass through the electrolyte membrane 30 and reach the second catalyst layer 21. In the second catalyst layer 21, the hydrogen ions, oxygen, and electrons react to generate water. This water passes through the microporous layer A2 in contact with the second catalyst layer 21 and is discharged to the outside.

[0123] When the electrolyte membrane 30 is an oxygen ion conductor, oxygen ions are generated from oxygen and electrons in the second catalyst layer 21. The generated oxygen ions pass through the electrolyte membrane 30 and reach the first catalyst layer 11. In the first catalyst layer 11, hydrogen and oxygen ions react to generate water and electrons. This water, for example, passes through the microporous layer A2 in contact with the first catalyst layer 11 and is discharged to the outside.

[0124] When the membrane electrode assembly 100 of the present disclosure is assembled into a fuel cell, the fuel cell may further include other components such as a current collector, a gas supply device, a cooling device, an outer shell, etc. Alternatively, a plurality of membrane electrode assemblies 100 may be stacked to form a cell stack.

[0125] [Example] Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited to the following.

[0126] <<Example 1>> <Carbon Fiber Sheet Production> Carbon fibers, conductive particles, organic fibers, and a binder resin were mixed so that the contents of the components in the obtained carbon fiber sheet were at the ratios shown in Table 1 to prepare a raw material slurry.

[0127] A papermaking sheet was obtained from the raw material slurry using an inclined papermaking machine.

[0128] The paper sheet was dried using a Yankee dryer to obtain a carbon fiber sheet of Example 1. The density of the obtained carbon fiber sheet is shown in Table 1.

[0129] <Manufacturing of Carbon Fiber Sheet / Microporous Layer Laminate> The conductive particles and the binder resin were mixed to prepare a slurry for the microporous layer so that the contents of the components in the obtained microporous layer were the ratios shown in Table 1. Toluene was used as the organic solvent.

[0130] The microporous layer slurry was applied to the carbon fiber sheet using toluene, and then the organic solvent in the microporous layer slurry was dried to obtain a laminate in which the microporous layer was laminated on the carbon fiber sheet.

[0131] <<Examples 2-20, Comparative Examples 1-4>> Laminated bodies of Examples 2 to 20 and Comparative Examples 1 to 4 were obtained in the same manner as in Example 1 except that the raw materials used were changed to those shown in Tables 1 and 2.

[0132] <<Evaluation>> The conductivity, tensile strength, and flexibility of the laminated bodies of each example and comparative example were evaluated. The evaluation results are shown in Tables 1 and 2.

[0133] Conductivity The surface resistivity was measured according to the above method, and a value of less than 1.4 Ω / □ was evaluated as “◯”, a value of 1.4 Ω / □ or more and less than 2.0 Ω / □ was evaluated as “Δ”, and a value of 2.0 Ω / □ or more was evaluated as “×”.

[0134] Tensile strength The tensile strength was measured according to the above method, and a tensile strength (N / 15 mm) of 15 N or more was evaluated as “0”, and a tensile strength of less than 15 N was evaluated as “×”.

[0135] <Softness> The flexibility was evaluated according to the following method and evaluation criteria.

[0136] Flexibility is measured according to JIS 8115-2001. Prepare a test piece 15 mm wide and 110 mm long and set it on the MIT testing machine. Set the test load to 0.5 kgf and align the plunger with the test piece. Mount the test piece vertically on a jig with a 0.38 mm R angle and begin measurement. Count the number of reciprocating bends until fracture occurs.

[0137] When the number of bending times was 10 or more, it was evaluated as “∘”; when it was 5 or more and less than 10 times, it was evaluated as “Δ”; and when it was less than 5 times, it was evaluated as “×”.

[0138] [Table 1]

[0139] [Table 2]

[0140] Figure 3 The SEM photograph of the surface of the carbon fiber sheet of Example 1 is shown. Figure 3 As shown, the carbon fiber sheets of each example, including Example 1, were confirmed to have a composite material containing conductive particles, organic fibers, and a binder resin fixed to a portion of the mesh structure formed by the carbon fibers. The carbon fiber sheets of each example exhibited excellent electrical conductivity, flexibility, and strength. Furthermore, since the carbon fiber sheets of each example also had sufficient water repellency, they were found to possess excellent performance as components of gas diffusion layers in fuel cells.

Claims

1. A carbon fiber sheet, characterized in that: Contains carbon fibers, conductive particles, organic fibers and binder resin. The binder resin contains an olefin resin, A composite containing the conductive particles, the organic fibers, and the binder resin is fixed to a portion of the mesh structure formed by the carbon fibers.

2. The carbon fiber sheet according to claim 1, wherein The organic fibers are fibrillated fibers.

3. The carbon fiber sheet according to claim 1 or 2, wherein: The average fiber length of the carbon fibers is 5 to 10 mm.

4. The carbon fiber sheet according to claim 1 or 2, wherein The conductive particles have an average particle size of 10 to 500 μm.

5. The carbon fiber sheet according to claim 1 or 2, wherein The conductive particles are scaly.

6. The carbon fiber sheet according to claim 1 or 2, wherein: The density of the carbon fiber sheet is 0.4-0.8 g / cm 3 .

7. The carbon fiber sheet according to claim 1 or 2, wherein: The carbon fiber sheet does not contain a fluorine-based resin, or contains the fluorine-based resin, and the content of the fluorine-based resin is 10% by mass or less when the entire carbon fiber sheet is taken as 100% by mass.

8. A gas diffusion layer for a fuel cell, wherein: A microporous layer is laminated on the surface of the carbon fiber sheet according to claim 1 or 2.

9. The gas diffusion layer for a fuel cell according to claim 8, wherein: The microporous layer contains scaly conductive particles and an olefin-based resin.

10. A membrane electrode assembly, wherein: The invention comprises an electrolyte membrane formed of a solid polymer electrolyte, a fuel electrode laminated on one surface of the electrolyte membrane, and an air electrode laminated on the other surface of the electrolyte membrane. The fuel electrode includes a first catalyst layer in contact with the electrolyte membrane and a first gas diffusion layer stacked on the first catalyst layer. The air electrode includes a second catalyst layer in contact with the electrolyte membrane and a second gas diffusion layer stacked on the second catalyst layer. At least one of the first gas diffusion layer and the second gas diffusion layer is the fuel cell gas diffusion layer according to claim 8 .

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