Method for manufacturing gas diffusion electrode substrate

Abstract

The present invention aims to provide a method for producing a gas diffusion electrode substrate that reduces manufacturing costs while exhibiting high electrical conductivity and chemical resistance. The present invention provides a method for producing a gas diffusion electrode substrate in which a microporous layer is formed on a conductive porous body formed by bonding carbon fibers together via a cured binder resin. The method comprises the following steps: a binder resin impregnation step in which a binder resin composition is impregnated into the carbon fiber structure to form a prepreg; a coating step in which a microporous layer coating liquid is applied to the surface of the prepreg; and a heat treatment step in which the prepreg, having undergone the coating step, is heat-treated at a temperature of 200°C or higher. The binder resin composition is a liquid composition comprising a binder resin and carbon powder, and the binder resin is a thermosetting resin. No heat treatment of the prepreg at a temperature of 200°C or higher occurs between the binder resin impregnation step and the heat treatment step.

Description

Technical Field

[0001] The present invention relates to a method for producing a gas diffusion electrode substrate suitable for use in a fuel cell, particularly a solid polymer fuel cell electrode. Background Art

[0002] In recent years, global environmental concerns have led to growing expectations for energy sources that do not emit carbon dioxide. In particular, fuel cells using hydrogen as fuel have attracted significant attention. A fuel cell is a power generation device that generates electromotive force through the electrochemical reaction between the two electrodes, which generates fuel gas containing hydrogen and oxidizing gas containing oxygen, supplied to the cathode.

[0003] Among fuel cells, polymer electrolyte fuel cells are particularly versatile. Polymer electrolyte fuel cells are typically constructed by stacking a diaphragm, a gas diffusion electrode substrate, a catalyst layer, an electrolyte membrane, a catalyst layer, a gas diffusion electrode substrate, and a diaphragm in this order. Specifically, conductive porous materials such as carbon felt, carbon paper, and carbon cloth containing carbon fibers are used as the gas diffusion electrode substrate.

[0004] Because conductive porous materials are required to have elasticity sufficient to absorb dimensional changes in the thickness direction of the electrolyte membrane, carbon fibers are often bonded together using an adhesive. Resin carbides, which provide high conductivity, are widely used as such adhesives. However, obtaining resin carbides requires heat treatment of the porous material in an inert atmosphere at temperatures above 1000°C after applying the resin.

[0005] In addition, the gas diffusion electrode substrate described above has a coarse mesh of fibers, so when water vapor condenses, large water droplets are generated, and the water droplets adhere to the electrode surface, which easily causes overflow that hinders the supply of gas to the electrode. Therefore, a microporous layer (MPL) composed of conductive particles such as carbon fiber powder is sometimes provided on the conductive porous body. MPL is usually formed by applying a coating liquid (hereinafter referred to as MPL coating liquid) composed of carbon powder and fluororesin particles as its binder and a surfactant dispersed in water to the surface of the conductive porous body, and drying and sintering.

[0006] Because, in order to produce a gas diffusion electrode substrate having an MPL, a heat treatment for firing the resin carbide and a heat treatment for sintering the MPL coating liquid to form the MPL are generally required. However, this requires multiple large heating furnaces, which increases the production cost.

[0007] Therefore, Patent Document 1 attempts to reduce costs by mixing carbon powders such as carbon black and graphite in a porous body and setting the heat treatment temperature to a low temperature. Patent Document 2 attempts to ensure electrical conductivity and chemical resistance by including split fibers having fibril portions in a porous body, while omitting the heating step for forming resin carbide.

[0008] Prior art literature

[0009] Patent Literature

[0010] Patent Document 1: International Publication No. 2001 / 022509

[0011] Patent Document 2: Japanese Patent Application Laid-Open No. 2004-363018. Summary of the Invention

[0012] Problems to be solved by the invention

[0013] Patent Document 1 states that carbon fibers can be bonded together through relatively low-temperature heat treatment. However, to improve the chemical resistance of the adhesive, the heat treatment temperature for the porous body is preferably 400°C or higher, more preferably 450°C or higher. Heat treatment of the MPL at this temperature range thermally decomposes the water repellent contained in the MPL. Therefore, the use of the MPL requires a second heat treatment, limiting cost reduction.

[0014] On the other hand, in Patent Document 2, although the cost is reduced by not including heat treatment, the electrical conductivity is low and the performance of the fuel cell is degraded.

[0015] An object of the present invention is to provide a method for producing a gas diffusion electrode substrate having high electrical conductivity and chemical resistance while reducing production costs.

[0016] Means for solving problems

[0017] The present invention for solving the above-mentioned problems is a method for manufacturing a gas diffusion electrode substrate, wherein a microporous layer is formed on a conductive porous body in which carbon fibers are bonded to each other by a cured product of an adhesive resin, and the method comprises the following steps in sequence: an adhesive resin impregnation step, in which an adhesive resin composition is impregnated into a carbon fiber structure to obtain a prepreg; a coating step, in which a microporous layer coating liquid is coated on the surface of the prepreg; and a heat treatment step, in which the prepreg after the coating step is heat-treated at a temperature above 200°C, wherein the adhesive resin composition is a liquid composition comprising a thermosetting resin and carbon powder, and there is no step of heat-treating the prepreg at a temperature above 200°C between the adhesive resin impregnation step and the heat treatment step.

[0018] Effects of the Invention

[0019] By using the method for producing a gas diffusion electrode substrate of the present invention, it is possible to obtain a gas diffusion electrode substrate having excellent electrical conductivity and chemical resistance while suppressing production costs. DETAILED DESCRIPTION

[0020] [Conductive porous body]

[0021] In the present invention, "gas diffusion electrode substrate" refers to a carbon fiber structure having a certain shape such as a paper body made of carbon fiber (as described later, for example, a carbon fiber paper body in a state where it is bonded only by an organic polymer such as polyvinyl alcohol, etc.), which is then impregnated with an adhesive resin to form a prepreg, and the carbon fibers are bonded to each other by curing the adhesive resin, thereby forming a microporous layer on the surface of the substrate.

[0022] The conductive porous body (hereinafter sometimes referred to as a "porous body") in the present invention is a porous structure having a sheet-like form due to the bonding of carbon fibers. Examples of such porous bodies include carbon fiber papermaking, carbon fiber fabrics, and carbon fiber nonwoven fabrics. As long as the carbon fibers are bonded together, porous bodies in which gaps or cracks are formed between the cured binder resin and the carbon fibers are also included.

[0023] As a conductive porous material, carbon fiber paper is preferred due to its excellent elasticity, which allows it to absorb dimensional changes in the electrolyte membrane perpendicular to the surface. It should be noted that the term "carbon fiber paper" herein refers to a sheet-like substrate in which carbon fibers are randomly dispersed in a two-dimensional plane.

[0024] Carbon fiber papermaking can be produced by either the wet papermaking method, where carbon fibers are dispersed in a liquid, or the dry papermaking method, where carbon fibers are dispersed in air. The wet papermaking method is preferred due to its superior productivity. To improve the conductivity and drainage properties of the gas diffusion electrode substrate, carbon fiber papermaking can be made by mixing carbon powder or organic fibers. Furthermore, to enhance form retention and handling, organic polymers such as polyvinyl alcohol, polyvinyl acetate, polyacrylonitrile, and cellulose can be used as binders.

[0025] Examples of the carbon fibers constituting the porous body include polyacrylonitrile (PAN)-based, pitch-based, and rayon-based carbon fibers. Among these, PAN-based carbon fibers and pitch-based carbon fibers are preferably used due to their excellent mechanical strength.

[0026] The average diameter of the carbon fibers constituting the porous body (hereinafter referred to as "carbon fiber diameter") is preferably in the range of 3 to 20 μm, more preferably in the range of 5 to 10 μm. When the carbon fiber diameter is 3 μm or more, more preferably 5 μm or more, the diameter of the pores becomes larger and the drainage property is improved, making it easy to suppress overflow. On the other hand, when the carbon fiber diameter is 20 μm or less, more preferably 10 μm or less, the thickness unevenness becomes smaller, making it easy to control within the thickness range of the preferred porous body described later. Here, as for the carbon fiber diameter, the carbon fibers can be magnified 1000 times using a microscope such as a scanning electron microscope to take a picture, and 30 different single fibers are randomly selected to measure their diameters to find the average value.

[0027] In addition, the average length of the carbon fibers constituting the porous body (hereinafter referred to as "carbon fiber length") is preferably in the range of 3 to 20 mm, more preferably in the range of 5 to 15 mm. When the carbon fiber length is 3 mm or more, more preferably 5 mm or more, it is easy to make a porous body with excellent mechanical strength, electrical conductivity and thermal conductivity. On the other hand, when the carbon fiber length is 20 mm or less, more preferably 15 mm or less, the dispersion of the carbon fibers is excellent, and a homogeneous porous body is easy to obtain. Carbon fibers having such a carbon fiber length can be obtained by a method such as cutting continuous carbon fibers into the desired length. As for the carbon fiber length, the carbon fibers are magnified 50 times and photographed using a microscope such as a scanning electron microscope, 30 different single fibers are randomly selected, their lengths are measured, and the average value is calculated.

[0028] [Binder resin impregnation step]

[0029] The method for producing a gas diffusion electrode substrate of the present invention comprises a binder resin impregnation step of impregnating the carbon fiber structure described above with a binder resin composition to obtain a prepreg. In the present invention, the binder resin composition is a liquid composition containing a thermosetting resin and carbon powder.

[0030] As the thermosetting resin, phenolic resin, epoxy resin, melamine resin, furan resin, etc. can be used, and preferably, a mixture of a thermoplastic resin and these thermosetting resins is used.

[0031] As carbon powder, graphites such as flaky graphite, scaly graphite, earthy graphite, artificial graphite, expanded graphite and flake graphite can be used. In addition, nano-carbon materials such as carbon blacks such as furnace black, acetylene black, lamp black and thermal black, carbon nanotubes, carbon nanofibers can be particularly preferably used. Nano-carbon materials easily form conductive paths in a small amount and can obtain the effect of reducing conductive resistance with an addition amount less than that of graphite larger than particle size.

[0032] The binder resin composition is preferably a liquid composition in which the binder resin and carbon powder are dispersed in a solvent. When dispersing the binder resin and carbon powder in the solvent, applying strong shear after adding the binder resin and carbon powder to the solvent improves the dispersibility of the carbon powder and allows the carbon powder to be uniformly attached to the carbon fiber structure. For example, applying strong shear can be achieved by stirring the mixture at a speed of 3000 rpm or higher for 10 minutes or longer using a homogenizer.

[0033] Methods for impregnating a carbon fiber structure with an adhesive resin composition include a method of impregnating the carbon fiber structure with a liquid adhesive resin composition comprising carbon powder and an adhesive resin and a solvent added thereto; a method of coating the carbon fiber structure with the adhesive resin composition; and the like. Among these, the method of impregnating the carbon fiber structure with a liquid adhesive resin composition is particularly preferred due to its excellent productivity.

[0034] When impregnating the carbon fiber structure with the binder resin composition, it is preferably impregnated so that the binder resin content is 10 to 400 parts by mass, more preferably 20 to 300 parts by mass, per 100 parts by mass of the carbon fibers in the prepreg. When the binder resin content is 10 parts by mass or greater, more preferably 20 parts by mass or greater, per 100 parts by mass of the carbon fibers in the prepreg, the porous body can contain uncarbonized resin while also attaching an amount of carbon powder sufficient to achieve high electrical conductivity. On the other hand, when the binder resin content is 400 parts by mass or less, more preferably 300 parts by mass or less, per 100 parts by mass of the carbon fibers in the prepreg, the electrical conductivity of the porous body can be maintained while achieving excellent gas diffusion properties.

[0035] When graphite is used as the carbon powder, the graphite and the binder resin in the binder resin composition are preferably mixed so that the graphite is 150 to 400 parts by mass relative to 100 parts by mass of the binder resin, and more preferably so that the graphite is 170 to 350 parts by mass.

[0036] When the prepreg contains 150 parts by mass or more (more preferably 170 parts by mass or more) of graphite relative to 100 parts by mass of the binder resin, excellent electrical conductivity is achieved. By coating the graphite with the binder resin, a porous body with excellent chemical resistance can be obtained. On the other hand, when the graphite content is 400 parts by mass or less, more preferably 350 parts by mass or less, the graphite adheres uniformly to the carbon fiber structure during impregnation, and the porous body exhibits excellent gas diffusion properties. Chemical resistance refers to the resistance to degradation of the adhesive properties and decrease in electrical conductivity caused by oxidative degradation of the resin, even with repeated power generation.

[0037] In particular, when nanocarbon material is used as carbon powder, excellent conductivity can be obtained with a small amount of addition compared to the case of using ordinary graphite. Therefore, it is preferred to mix the nanocarbon material and the binder resin in the binder resin composition in a manner such that the nanocarbon material becomes 30 to 200 parts by mass relative to 100 parts by mass of the binder resin, and it is more preferred to mix the nanocarbon material and the binder resin in the binder resin composition in a manner such that the nanocarbon material becomes 50 to 100 parts by mass.

[0038] When the amount of nanocarbon material is 30 parts by mass or more, more preferably 50 parts by mass or more, relative to 100 parts by mass of the binder resin, a porous body can be obtained that achieves both electrical conductivity and chemical resistance. On the other hand, when the amount of nanocarbon material is 200 parts by mass or less, more preferably 100 parts by mass, relative to 100 parts by mass of the binder resin, the nanocarbon material is uniformly attached to the carbon fiber structure during impregnation, resulting in excellent gas diffusion properties in the porous body.

[0039] The thickness of the porous body is preferably 50 to 230 μm, more preferably 70 to 180 μm. By making the thickness of the porous body 230 μm or less, more preferably 180 μm or less, the diffusivity of the gas is easily improved, and the generated water is also easily discharged. Furthermore, the size of the fuel cell as a whole is also easily reduced. On the other hand, by making the thickness of the porous body 50 μm or more, more preferably 70 μm or more, the gas diffusion in the in-plane direction inside the porous body can be efficiently carried out, and the power generation performance is easily improved. It should be noted that the thickness of the porous body is obtained by the following method. The porous body is placed on a smooth platform, and the height difference between the case where the measured object is present and the case where the measured object is not present is measured under a pressure of 0.15 MPa. Samples are taken at 10 different locations, and the average of the measured values ​​of the height difference is taken as the thickness.

[0040] [Water repellent applying step]

[0041] The method for manufacturing a gas diffusion electrode substrate of the present invention may include a water repellent imparting step of imparting a water repellent containing a fluororesin to the prepreg before the coating step described later. As the fluororesin contained in the water repellent, one or more resins selected from polytetrafluoroethylene (PTFE), tetrafluoroethylene hexafluoropropylene copolymer (FEP), perfluoroalkoxy fluororesin (PFA), ethylene tetrafluoroethylene copolymer (ETFE), polyvinylidene fluoride (PVDF), and polyvinyl fluoride (PVF) can be used. Among them, PTFE or FEP that exhibits strong water repellency is preferred. When the water repellent containing a fluororesin is imparted to the prepreg, the amount of the fluororesin contained in the prepreg is not particularly limited, but it is appropriate to be 1% by mass or more and 10% by mass or less relative to the mass of the entire prepreg. By being 1% by mass or more, sufficient water repellency can be exerted; by being 10% by mass or less, it is possible to easily ensure pores that serve as diffusion paths or drainage paths for gas while exhibiting water repellency.

[0042] When the water repellent is applied as described above, water repellency treatment is performed using a water repellent treatment liquid in which a water repellent containing a fluororesin is dispersed. Examples of methods for water repellency treatment include a method of immersing the prepreg in the water repellent treatment liquid; and a method of applying the water repellent treatment liquid to the prepreg by die coating or the like. From the perspective of uniformly distributing the fluororesin in the porous body in a direction perpendicular to the surface, the method of immersing the prepreg in the water repellent treatment liquid is preferred. After the water repellency treatment, a heating and drying step may be performed. In this case, in the present invention, a heat treatment at a temperature of 200°C or higher may also be performed as described later.

[0043] [Coating process]

[0044] The method for producing a gas diffusion electrode substrate of the present invention then includes a coating step of applying an MPL coating liquid to the surface of the obtained prepreg. As described above, the MPL coating liquid is a coating liquid obtained by dispersing carbon powder, a water repellent, and, if necessary, a dispersing aid such as a surfactant in water.

[0045] Examples of the carbon powder contained in the MPL coating liquid include graphites such as flake graphite, scaly graphite, earthy graphite, artificial graphite, expanded graphite, and flake graphite; carbon blacks such as furnace black, acetylene black, lamp black, and thermal black; carbon nanotubes; and carbon nanofibers. Among them, carbon black is preferably used.

[0046] As the water repellent contained in the MPL coating liquid, fluororesins such as polytetrafluoroethylene (PTFE), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), and tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA) are preferably used.

[0047] As the dispersing aid, a nonionic surfactant is preferably used.

[0048] The MPL coating liquid may be applied to the surface of the prepreg by screen printing, rotary screen printing, spray coating, gravure printing, die coating, rod coating, and doctor blade coating.

[0049] [Heat treatment process]

[0050] The manufacturing method of the present invention further includes a heat treatment step, in which the prepreg, coated with the MPL coating liquid in the coating step, is heat treated at a temperature of 200°C or higher. Heating at 200°C or higher melts the water repellent contained in the MPL coating liquid, sintering the MPL coating liquid and transforming it into MPL. The heating temperature in the heat treatment step is preferably 200-400°C, more preferably 300-400°C.

[0051] The MPL after the heat treatment step usually becomes a porous layer with an average pore size of 0.01 μm to 1 μm. The weight per unit area of ​​the MPL is not particularly limited, but is preferably 5 to 50 g / m2 after the heat treatment. 2 In the range of 10 to 30 g / m 2 The unit area weight of MPL is 5g / m 2 More than 10 g / m 2 When the above is achieved, the surface of one side of the porous body can be covered by MPL, which can further promote the reverse diffusion of generated water and further inhibit the drying of the electrolyte membrane. In addition, the unit area weight of MPL is 50g / m 2 Below, more preferably 30g / m 2 When the pressure is less than 500 MPa, the drainage performance is further improved and the overflow can be further suppressed.

[0052] [Drying process]

[0053] If necessary, before the heat treatment step, a drying step may be provided in which the prepreg after the coating step is dried at a temperature of 80 to 180° C. in order to volatilize water in the MPL coating liquid.

[0054] Among them, in the manufacturing method of the present invention, there is no step of substantially heat-treating the prepreg at a temperature of 200°C or above between the binder resin impregnation step and the heat treatment step. In the conventional method for manufacturing a gas diffusion electrode substrate, in order to make the binder resin conductive and chemical-resistant, a step of carbonizing the binder resin by heat-treating it at 1000°C or above in an inert atmosphere is provided before applying the MPL coating liquid. In the manufacturing method of the present invention, since the heat treatment step before applying the MPL coating liquid is omitted, the binder resin that does not have conductivity remains in the porous body. However, as a binder resin composition, by containing a certain amount of highly conductive carbon powder, conductivity and chemical resistance can be ensured even if a heat treatment is performed once after applying the MPL coating liquid.

[0055] Example

[0056] <Evaluation of Conductive Resistance>

[0057] The conductive resistance in the direction perpendicular to the surface of the gas diffusion electrode substrate is calculated as follows: the gas diffusion electrode substrate is cut into 30 mm × 30 mm pieces, clamped between two gold-plated plates and subjected to a uniform surface pressure of 1.0 MPa. A current of 1.0 A is applied, and the resistance at this time is measured and multiplied by the area of ​​the substrate.

[0058] <Evaluation of Power Generation Performance of Solid Polymer Fuel Cells>

[0059] A catalyst solution was prepared by sequentially adding 1.00 g of platinum-supported carbon (manufactured by Tanaka Kikinzoku Kogyo Co., Ltd., platinum loading: 50 mass %), 1.00 g of purified water, 8.00 g of a "Nafion (registered trademark)" solution (5.0 mass % "Nafion (registered trademark)" manufactured by Aldrich Co., Ltd.), and 18.00 g of isopropyl alcohol (manufactured by Nakalai Tesque Co., Ltd.).

[0060] Next, the catalyst solution was applied by spraying onto a "Naflon (registered trademark)" PTFE tape "TOMBO (registered trademark)" No. 9001 (manufactured by NICHIAS Co., Ltd.) cut into 5 cm × 5 cm, and dried at room temperature to prepare a platinum content of 0.3 mg / cm 2 A PTFE sheet with a catalyst layer was then prepared. Next, a solid polymer electrolyte membrane, "Nafion (registered trademark)" NRE-211CS (manufactured by DuPont), cut into 8 cm x 8 cm pieces, was sandwiched between two PTFE sheets with catalyst layers. The membrane was pressed at 130°C for 5 minutes while applying pressure to 5 MPa using a flatbed press to transfer the catalyst layer to the solid polymer electrolyte membrane. After pressing, the PTFE sheets were peeled off to produce a solid polymer electrolyte membrane with a catalyst layer.

[0061] Next, a solid polymer electrolyte membrane with a catalyst layer was sandwiched between two gas diffusion electrode substrates cut into 5 cm x 5 cm pieces. The membrane electrode assembly was then pressed at 130°C for 5 minutes while applying a pressure of 3 MPa using a flatbed press. The gas diffusion electrode substrates were positioned so that the surface with the microporous layer was in contact with the catalyst layer.

[0062] The resulting membrane electrode assembly was installed in a fuel cell evaluation cell, and the voltage was measured as the current density varied. A serpentine-type diaphragm with a single flow path and a groove width, groove depth, and rib width of 1.0 mm was used as the diaphragm. Evaluations were conducted while supplying unpressurized hydrogen to the anode side and unpressurized air to the cathode side.

[0063] The battery was humidified by a humidifier tank with both hydrogen and air set to 70°C. The humidity at this time was 100%. The utilization rates of hydrogen and oxygen in the air were 70 mol% and 40 mol%, respectively. The battery temperature was 70°C. The measured current density was 1.5 A / cm 2 The output voltage is used as an indicator of power generation performance.

[0064] (Example 1)

[0065] Toray Industries, Inc. polyacrylonitrile carbon fibers were cut into 12 mm lengths, dispersed in water for papermaking, and then immersed in a 10% by mass aqueous dispersion of polyvinyl alcohol and dried to obtain carbon fibers having a unit area weight of approximately 20 g / m 2 The long carbon fiber paper body (carbon fiber structure) is wound into a roll.

[0066] A dispersion (adhesive resin composition) containing phenol resin, flaky graphite (average particle size 5 μm), and methanol was prepared in a mass ratio of 2:7:91. The carbon fiber structure, cut into 10 cm x 10 cm pieces, was immersed in the dispersion, pulled up, and squeezed with a roller to remove excess liquid. The carbon fiber structure was then dried at 100°C for 10 minutes. After drying, the phenol resin was attached in a ratio of 50 parts by mass to 100 parts by mass of the carbon fiber and 350 parts by mass of the flaky graphite was attached to 100 parts by mass of the phenol resin to obtain a prepreg.

[0067] Next, the prepreg was subjected to a heat and pressure treatment at 180°C for 5 minutes while being pressurized using a flatbed press. It should be noted that during the pressurization, a spacer was placed on the flatbed press to adjust the spacing between the upper and lower pressing panels so that the thickness after heat treatment became 130 μm. The prepreg was then impregnated with a fluororesin by immersing it in an aqueous dispersion of PTFE resin ("Polyflon (registered trademark)" PTFE Dispersion D-210C (manufactured by Daikin Industries, Ltd.)). After being impregnated in the aqueous PTFE dispersion, the prepreg was pulled up and dried, with 5 parts by mass of PTFE attached to 100 parts by mass of the prepreg.

[0068] Finally, an MPL coating solution containing carbon black, PTFE, and a surfactant, TRITON (registered trademark) X-100 (manufactured by Nacalai Tesque Co., Ltd.), at a mass ratio of 3:1:6, was applied to one side of the prepreg after the water repellent treatment. The solution was then heat treated at 380°C for 10 minutes to obtain a prepreg having a surface roughness of approximately 20 g / m2. 2 A gas diffusion electrode substrate having a microporous layer.

[0069] (Example 2)

[0070] A carbon fiber structure was impregnated in an adhesive resin composition in which phenol resin, flaky graphite, and methanol were mixed in a mass ratio of 2:3:95, with the phenol resin being 50 parts by mass relative to 100 parts by mass of the carbon fiber and the flaky graphite being 154 parts by mass relative to 100 parts by mass of the phenol resin. A gas diffusion electrode substrate was obtained in the same manner as in Example 1, except that the mixture was impregnated in an adhesive resin composition in which the phenol resin was 50 parts by mass relative to 100 parts by mass of the carbon fiber and the flaky graphite was 154 parts by mass relative to 100 parts by mass of the phenol resin.

[0071] (Example 3)

[0072] Acetylene black "Denka Black (registered trademark)" (manufactured by Denka Co., Ltd.) was used instead of flaky graphite, and the carbon fiber structure was impregnated in an adhesive resin composition in which phenol resin, acetylene black, and methanol were mixed in a mass ratio of 2:2:96. The impregnation was performed in a manner such that the phenol resin became 50 parts by mass with respect to 100 parts by mass of the carbon fiber and the acetylene black became 83 parts by mass with respect to 100 parts by mass of the phenol resin. Except for this, a gas diffusion electrode substrate was obtained in the same manner as in Example 1.

[0073] (Example 4)

[0074] Furnace black "KETJENBLACK (registered trademark)" (manufactured by Lion Specialty Chemicals Co., Ltd.) was used instead of flaky graphite, and the carbon fiber structure was impregnated in an adhesive resin composition in which phenol resin, furnace black, and methanol were mixed in a mass ratio of 2:2:96. The impregnation was performed in a manner such that the phenol resin became 50 parts by mass relative to 100 parts by mass of the carbon fiber and the furnace black became 83 parts by mass relative to 100 parts by mass of the phenol resin. Except for this, a gas diffusion electrode substrate was obtained in the same manner as in Example 1.

[0075] (Example 5)

[0076] Linear carbon vapor-grown carbon fibers (carbon nanotubes) "VGCF (registered trademark)" (manufactured by Showa Denko K.K.) were used instead of flaky graphite, and the carbon fiber structure was impregnated in an adhesive resin composition in which phenol resin, carbon nanotubes, and methanol were mixed in a mass ratio of 2:2:96. The impregnation was performed in such a manner that the phenol resin accounted for 50 parts by mass relative to 100 parts by mass of the carbon fibers and the carbon nanotubes accounted for 83 parts by mass relative to 100 parts by mass of the phenol resin. Except for this, a gas diffusion electrode substrate was obtained in the same manner as in Example 1.

[0077] (Example 6)

[0078] Acetylene black "Denka Black (registered trademark)" (manufactured by Denka Co., Ltd.) was used instead of flaky graphite, and the carbon fiber structure was impregnated in an adhesive resin composition in which phenol resin, acetylene black, and methanol were mixed in a mass ratio of 3:1:96. The impregnation was performed in a manner such that the phenol resin became 50 parts by mass with respect to 100 parts by mass of the carbon fiber and the acetylene black became 36 parts by mass with respect to 100 parts by mass of the phenol resin. Except for this, a gas diffusion electrode substrate was obtained in the same manner as in Example 1.

[0079] (Comparative Example 1)

[0080] A gas diffusion electrode substrate was obtained in the same manner as in Example 1 except that the carbon fiber structure was impregnated with a binder resin composition in which phenol resin and methanol were mixed in a mass ratio of 7:93 and the phenol resin was impregnated in an amount of 50 parts by mass relative to 100 parts by mass of the carbon fibers.

[0081] Table 1 shows the evaluation results of the electrical resistance and power generation performance (output voltage) of the gas diffusion electrode substrates produced in each of the Examples and Comparative Examples.

[0082] [Table 1]

[0083]

Claims

1. A method for producing a gas diffusion electrode substrate, comprising forming a microporous layer on a conductive porous body in which carbon fibers are bonded to each other using a cured product of a binder resin. The manufacturing method comprises the following steps in sequence: An adhesive resin impregnation step of impregnating the carbon fiber structure with an adhesive resin composition to obtain a prepreg; a coating step of coating a microporous layer coating liquid on the surface of the prepreg; The heat treatment step is to heat treat the prepreg after the coating step at a temperature above 200°C. The average length of the single carbon fibers is in the range of 3 to 20 mm, and the binder resin composition is a liquid composition comprising a binder resin and carbon powder. The binder resin is a thermosetting resin, There is no step of heat-treating the prepreg at a temperature of 200° C. or higher between the binder resin impregnation step and the heat treatment step.

2. The method for producing a gas diffusion electrode substrate according to claim 1, wherein: In the binder resin impregnation step, the binder resin composition is impregnated into the carbon fiber structure so that the binder resin content is 10 to 400 parts by mass relative to 100 parts by mass of the carbon fibers in the prepreg.

3. The method for producing a gas diffusion electrode substrate according to claim 1 or 2, wherein: The carbon fiber structure is a carbon fiber papermaking body.

4. The method for producing a gas diffusion electrode substrate according to any one of claims 1 to 3, wherein: The carbon powder is graphite.

5. The method for producing a gas diffusion electrode substrate according to claim 4, wherein: In the binder resin composition, the amount of graphite is 150 to 400 parts by mass based on 100 parts by mass of the binder resin.

6. The method for producing a gas diffusion electrode substrate according to any one of claims 1 to 3, wherein: The carbon powder is a nanocarbon material selected from carbon black, carbon nanotubes or carbon nanofibers.

7. The method for producing a gas diffusion electrode substrate according to claim 6, wherein: In the binder resin composition, the nanocarbon material is contained in an amount of 30 to 200 parts by mass based on 100 parts by mass of the binder resin. 8 . The method for producing a gas diffusion electrode substrate according to claim 1 , further comprising a water-repellent-applying step of applying a water-repellent containing a fluororesin to the prepreg before the coating step. 9 . The method for producing a gas diffusion electrode substrate according to claim 1 , further comprising a drying step of drying the prepreg after the coating step at a temperature of 80 to 180° C. before the heat treatment step.

10. The method for producing a gas diffusion electrode substrate according to any one of claims 1 to 9, wherein: The heat treatment temperature in the heat treatment step is 200-400°C.

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